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gsha1sum
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Print or check SHA1 (160-bit) checksums. With no FILE, or when FILE is -, read standard input. -b, --binary read in binary mode -c, --check read checksums from the FILEs and check them --tag create a BSD-style checksum -t, --text read in text mode (default) -z, --zero end each output line with NUL, not newline, and disable file name escaping The following five options are useful only when verifying checksums: --ignore-missing don't fail or report status for missing files --quiet don't print OK for each successfully verified file --status don't output anything, status code shows success --strict exit non-zero for improperly formatted checksum lines -w, --warn warn about improperly formatted checksum lines --help display this help and exit --version output version information and exit The sums are computed as described in FIPS-180-1. When checking, the input should be a former output of this program. The default mode is to print a line with: checksum, a space, a character indicating input mode ('*' for binary, ' ' for text or where binary is insignificant), and name for each FILE. Note: There is no difference between binary mode and text mode on GNU systems. BUGS Do not use the SHA-1 algorithm for security related purposes. Instead, use an SHA-2 algorithm, implemented in the programs sha224sum(1), sha256sum(1), sha384sum(1), sha512sum(1), or the BLAKE2 algorithm, implemented in b2sum(1) AUTHOR Written by Ulrich Drepper, Scott Miller, and David Madore. REPORTING BUGS GNU coreutils online help: <https://www.gnu.org/software/coreutils/> Report any translation bugs to <https://translationproject.org/team/> COPYRIGHT Copyright © 2023 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. SEE ALSO cksum(1) Full documentation <https://www.gnu.org/software/coreutils/sha1sum> or available locally via: info '(coreutils) sha1sum invocation' GNU coreutils 9.3 April 2023 SHA1SUM(1)
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sha1sum - compute and check SHA1 message digest
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sha1sum [OPTION]... [FILE]...
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ambiguous_words
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fc-pattern
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argon2
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my_print_defaults
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my_print_defaults displays the options that are present in option groups of option files. The output indicates what options are used by programs that read the specified option groups. For example, the mysqlcheck program reads the [mysqlcheck] and [client] option groups. To see what options are present in those groups in the standard option files, invoke my_print_defaults like this: $> my_print_defaults mysqlcheck client --user=myusername --password=password --host=localhost The output consists of options, one per line, in the form that they would be specified on the command line. my_print_defaults supports the following options. • --help, -? Display a help message and exit. • --config-file=file_name, --defaults-file=file_name, -c file_name Read only the given option file. • --debug=debug_options, -# debug_options Write a debugging log. A typical debug_options string is d:t:o,file_name. The default is d:t:o,/tmp/my_print_defaults.trace. • --defaults-extra-file=file_name, --extra-file=file_name, -e file_name Read this option file after the global option file but (on Unix) before the user option file. For additional information about this and other option-file options, see Section 4.2.2.3, “Command-Line Options that Affect Option-File Handling”. • --defaults-group-suffix=suffix, -g suffix In addition to the groups named on the command line, read groups that have the given suffix. For additional information about this and other option-file options, see Section 4.2.2.3, “Command-Line Options that Affect Option-File Handling”. • --login-path=name, -l name Read options from the named login path in the .mylogin.cnf login path file. A “login path” is an option group containing options that specify which MySQL server to connect to and which account to authenticate as. To create or modify a login path file, use the mysql_config_editor utility. See mysql_config_editor(1). For additional information about this and other option-file options, see Section 4.2.2.3, “Command-Line Options that Affect Option-File Handling”. • --no-login-paths Skips reading options from the login path file. See --login-path for related information. For additional information about this and other option-file options, see Section 4.2.2.3, “Command-Line Options that Affect Option-File Handling”. • --no-defaults, -n Return an empty string. For additional information about this and other option-file options, see Section 4.2.2.3, “Command-Line Options that Affect Option-File Handling”. • --show, -s my_print_defaults masks passwords by default. Use this option to display passwords as cleartext. • --verbose, -v Verbose mode. Print more information about what the program does. • --version, -V Display version information and exit. COPYRIGHT Copyright © 1997, 2023, Oracle and/or its affiliates. This documentation is free software; you can redistribute it and/or modify it only under the terms of the GNU General Public License as published by the Free Software Foundation; version 2 of the License. This documentation is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with the program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA or see http://www.gnu.org/licenses/. SEE ALSO For more information, please refer to the MySQL Reference Manual, which may already be installed locally and which is also available online at http://dev.mysql.com/doc/. AUTHOR Oracle Corporation (http://dev.mysql.com/). MySQL 8.3 11/23/2023 MY_PRINT_DEFAULTS(1)
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my_print_defaults - display options from option files
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my_print_defaults [options] option_group ...
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identify-cli
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lstmeval
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coverage3
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mysqlrouter_keyring
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yt-dlp
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yt-dlp is a feature-rich command-line audio/video downloader with support for thousands of sites. The project is a fork of youtube-dl (https://github.com/ytdl-org/youtube-dl) based on the now inactive youtube-dlc (https://github.com/blackjack4494/yt-dlc).
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yt-dlp - A feature-rich command-line audio/video downloader
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yt-dlp [OPTIONS] URL [URL...]
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General Options: -h, --help Print this help text and exit --version Print program version and exit -U, --update Update this program to the latest version --no-update Do not check for updates (default) --update-to [CHANNEL]@[TAG] Upgrade/downgrade to a specific version. CHANNEL can be a repository as well. CHANNEL and TAG default to "stable" and "latest" respectively if omitted; See "UPDATE" for details. Supported channels: stable, nightly, master -i, --ignore-errors Ignore download and postprocessing errors. The download will be considered successful even if the postprocessing fails --no-abort-on-error Continue with next video on download errors; e.g. to skip unavailable videos in a playlist (default) --abort-on-error Abort downloading of further videos if an error occurs (Alias: --no-ignore-errors) --dump-user-agent Display the current user-agent and exit --list-extractors List all supported extractors and exit --extractor-descriptions Output descriptions of all supported extractors and exit --use-extractors NAMES Extractor names to use separated by commas. You can also use regexes, "all", "default" and "end" (end URL matching); e.g. --ies "holodex.*,end,youtube". Prefix the name with a "-" to exclude it, e.g. --ies default,-generic. Use --list-extractors for a list of extractor names. (Alias: --ies) --default-search PREFIX Use this prefix for unqualified URLs. E.g. "gvsearch2:python" downloads two videos from google videos for the search term "python". Use the value "auto" to let yt-dlp guess ("auto_warning" to emit a warning when guessing). "error" just throws an error. The default value "fixup_error" repairs broken URLs, but emits an error if this is not possible instead of searching --ignore-config Don't load any more configuration files except those given to --config-locations. For backward compatibility, if this option is found inside the system configuration file, the user configuration is not loaded. (Alias: --no-config) --no-config-locations Do not load any custom configuration files (default). When given inside a configuration file, ignore all previous --config- locations defined in the current file --config-locations PATH Location of the main configuration file; either the path to the config or its containing directory ("-" for stdin). Can be used multiple times and inside other configuration files --flat-playlist Do not extract the videos of a playlist, only list them --no-flat-playlist Fully extract the videos of a playlist (default) --live-from-start Download livestreams from the start. Currently only supported for YouTube (Experimental) --no-live-from-start Download livestreams from the current time (default) --wait-for-video MIN[-MAX] Wait for scheduled streams to become available. Pass the minimum number of seconds (or range) to wait between retries --no-wait-for-video Do not wait for scheduled streams (default) --mark-watched Mark videos watched (even with --simulate) --no-mark-watched Do not mark videos watched (default) --color [STREAM:]POLICY Whether to emit color codes in output, optionally prefixed by the STREAM (stdout or stderr) to apply the setting to. Can be one of "always", "auto" (default), "never", or "no_color" (use non color terminal sequences). Use "auto-tty" or "no_color-tty" to decide based on terminal support only. Can be used multiple times --compat-options OPTS Options that can help keep compatibility with youtube-dl or youtube-dlc configurations by reverting some of the changes made in yt-dlp. See "Differences in default behavior" for details --alias ALIASES OPTIONS Create aliases for an option string. Unless an alias starts with a dash "-", it is prefixed with "--". Arguments are parsed according to the Python string formatting mini-language. E.g. --alias get-audio,-X "-S=aext:{0},abr -x --audio-format {0}" creates options "--get-audio" and "-X" that takes an argument (ARG0) and expands to "-S=aext:ARG0,abr -x --audio-format ARG0". All defined aliases are listed in the --help output. Alias options can trigger more aliases; so be careful to avoid defining recursive options. As a safety measure, each alias may be triggered a maximum of 100 times. This option can be used multiple times Network Options: --proxy URL Use the specified HTTP/HTTPS/SOCKS proxy. To enable SOCKS proxy, specify a proper scheme, e.g. socks5://user:pass@127.0.0.1:1080/. Pass in an empty string (--proxy "") for direct connection --socket-timeout SECONDS Time to wait before giving up, in seconds --source-address IP Client-side IP address to bind to --impersonate CLIENT[:OS] Client to impersonate for requests. E.g. chrome, chrome-110, chrome:windows-10. Pass --impersonate="" to impersonate any client. Note that forcing impersonation for all requests may have a detrimental impact on download speed and stability --list-impersonate-targets List available clients to impersonate. -4, --force-ipv4 Make all connections via IPv4 -6, --force-ipv6 Make all connections via IPv6 --enable-file-urls Enable file:// URLs. This is disabled by default for security reasons. Geo-restriction: --geo-verification-proxy URL Use this proxy to verify the IP address for some geo-restricted sites. The default proxy specified by --proxy (or none, if the option is not present) is used for the actual downloading --xff VALUE How to fake X-Forwarded-For HTTP header to try bypassing geographic restriction. One of "default" (only when known to be useful), "never", an IP block in CIDR notation, or a two-letter ISO 3166-2 country code Video Selection: -I, --playlist-items ITEM_SPEC Comma separated playlist_index of the items to download. You can specify a range using "[START]:[STOP][:STEP]". For backward compatibility, START-STOP is also supported. Use negative indices to count from the right and negative STEP to download in reverse order. E.g. "-I 1:3,7,-5::2" used on a playlist of size 15 will download the items at index 1,2,3,7,11,13,15 --min-filesize SIZE Abort download if filesize is smaller than SIZE, e.g. 50k or 44.6M --max-filesize SIZE Abort download if filesize is larger than SIZE, e.g. 50k or 44.6M --date DATE Download only videos uploaded on this date. The date can be "YYYYMMDD" or in the format [now|today|yesterday][-N[day|week|month|year]]. E.g. "--date today-2weeks" downloads only videos uploaded on the same day two weeks ago --datebefore DATE Download only videos uploaded on or before this date. The date formats accepted is the same as --date --dateafter DATE Download only videos uploaded on or after this date. The date formats accepted is the same as --date --match-filters FILTER Generic video filter. Any "OUTPUT TEMPLATE" field can be compared with a number or a string using the operators defined in "Filtering Formats". You can also simply specify a field to match if the field is present, use "!field" to check if the field is not present, and "&" to check multiple conditions. Use a "" to escape "&" or quotes if needed. If used multiple times, the filter matches if at least one of the conditions is met. E.g. --match-filter !is_live --match-filter "like_count>?100 & description~='(?i)& dogs" matches only videos that are not live OR those that have a like count more than 100 (or the like field is not available) and also has a description that contains the phrase "cats & dogs" (caseless). Use "--match-filter -" to interactively ask whether to download each video --no-match-filters Do not use any --match-filter (default) --break-match-filters FILTER Same as "--match-filters" but stops the download process when a video is rejected --no-break-match-filters Do not use any --break-match-filters (default) --no-playlist Download only the video, if the URL refers to a video and a playlist --yes-playlist Download the playlist, if the URL refers to a video and a playlist --age-limit YEARS Download only videos suitable for the given age --download-archive FILE Download only videos not listed in the archive file. Record the IDs of all downloaded videos in it --no-download-archive Do not use archive file (default) --max-downloads NUMBER Abort after downloading NUMBER files --break-on-existing Stop the download process when encountering a file that is in the archive --no-break-on-existing Do not stop the download process when encountering a file that is in the archive (default) --break-per-input Alters --max-downloads, --break-on-existing, --break-match- filter, and autonumber to reset per input URL --no-break-per-input --break-on-existing and similar options terminates the entire download queue --skip-playlist-after-errors N Number of allowed failures until the rest of the playlist is skipped Download Options: -N, --concurrent-fragments N Number of fragments of a dash/hlsnative video that should be downloaded concurrently (default is 1) -r, --limit-rate RATE Maximum download rate in bytes per second, e.g. 50K or 4.2M --throttled-rate RATE Minimum download rate in bytes per second below which throttling is assumed and the video data is re-extracted, e.g. 100K -R, --retries RETRIES Number of retries (default is 10), or "infinite" --file-access-retries RETRIES Number of times to retry on file access error (default is 3), or "infinite" --fragment-retries RETRIES Number of retries for a fragment (default is 10), or "infinite" (DASH, hlsnative and ISM) --retry-sleep [TYPE:]EXPR Time to sleep between retries in seconds (optionally) prefixed by the type of retry (http (default), fragment, file_access, extractor) to apply the sleep to. EXPR can be a number, linear=START[:END[:STEP=1]] or exp=START[:END[:BASE=2]]. This option can be used multiple times to set the sleep for the different retry types, e.g. --retry-sleep linear=1::2 --retry- sleep fragment:exp=1:20 --skip-unavailable-fragments Skip unavailable fragments for DASH, hlsnative and ISM downloads (default) (Alias: --no-abort-on-unavailable-fragments) --abort-on-unavailable-fragments Abort download if a fragment is unavailable (Alias: --no-skip- unavailable-fragments) --keep-fragments Keep downloaded fragments on disk after downloading is finished --no-keep-fragments Delete downloaded fragments after downloading is finished (default) --buffer-size SIZE Size of download buffer, e.g. 1024 or 16K (default is 1024) --resize-buffer The buffer size is automatically resized from an initial value of --buffer-size (default) --no-resize-buffer Do not automatically adjust the buffer size --http-chunk-size SIZE Size of a chunk for chunk-based HTTP downloading, e.g. 10485760 or 10M (default is disabled). May be useful for bypassing bandwidth throttling imposed by a webserver (experimental) --playlist-random Download playlist videos in random order --lazy-playlist Process entries in the playlist as they are received. This disables n_entries, --playlist-random and --playlist-reverse --no-lazy-playlist Process videos in the playlist only after the entire playlist is parsed (default) --xattr-set-filesize Set file xattribute ytdl.filesize with expected file size --hls-use-mpegts Use the mpegts container for HLS videos; allowing some players to play the video while downloading, and reducing the chance of file corruption if download is interrupted. This is enabled by default for live streams --no-hls-use-mpegts Do not use the mpegts container for HLS videos. This is default when not downloading live streams --download-sections REGEX Download only chapters that match the regular expression. A "*" prefix denotes time-range instead of chapter. Negative timestamps are calculated from the end. "*from-url" can be used to download between the "start_time" and "end_time" extracted from the URL. Needs ffmpeg. This option can be used multiple times to download multiple sections, e.g. --download-sections "*10:15-inf" --download-sections "intro" --downloader [PROTO:]NAME Name or path of the external downloader to use (optionally) prefixed by the protocols (http, ftp, m3u8, dash, rstp, rtmp, mms) to use it for. Currently supports native, aria2c, avconv, axel, curl, ffmpeg, httpie, wget. You can use this option multiple times to set different downloaders for different protocols. E.g. --downloader aria2c --downloader "dash,m3u8:native" will use aria2c for http/ftp downloads, and the native downloader for dash/m3u8 downloads (Alias: --external-downloader) --downloader-args NAME:ARGS Give these arguments to the external downloader. Specify the downloader name and the arguments separated by a colon ":". For ffmpeg, arguments can be passed to different positions using the same syntax as --postprocessor-args. You can use this option multiple times to give different arguments to different downloaders (Alias: --external-downloader-args) Filesystem Options: -a, --batch-file FILE File containing URLs to download ("-" for stdin), one URL per line. Lines starting with "#", ";" or "]" are considered as comments and ignored --no-batch-file Do not read URLs from batch file (default) -P, --paths [TYPES:]PATH The paths where the files should be downloaded. Specify the type of file and the path separated by a colon ":". All the same TYPES as --output are supported. Additionally, you can also provide "home" (default) and "temp" paths. All intermediary files are first downloaded to the temp path and then the final files are moved over to the home path after download is finished. This option is ignored if --output is an absolute path -o, --output [TYPES:]TEMPLATE Output filename template; see "OUTPUT TEMPLATE" for details --output-na-placeholder TEXT Placeholder for unavailable fields in --output (default: "NA") --restrict-filenames Restrict filenames to only ASCII characters, and avoid "&" and spaces in filenames --no-restrict-filenames Allow Unicode characters, "&" and spaces in filenames (default) --windows-filenames Force filenames to be Windows-compatible --no-windows-filenames Make filenames Windows-compatible only if using Windows (default) --trim-filenames LENGTH Limit the filename length (excluding extension) to the specified number of characters -w, --no-overwrites Do not overwrite any files --force-overwrites Overwrite all video and metadata files. This option includes --no-continue --no-force-overwrites Do not overwrite the video, but overwrite related files (default) -c, --continue Resume partially downloaded files/fragments (default) --no-continue Do not resume partially downloaded fragments. If the file is not fragmented, restart download of the entire file --part Use .part files instead of writing directly into output file (default) --no-part Do not use .part files - write directly into output file --mtime Use the Last-modified header to set the file modification time (default) --no-mtime Do not use the Last-modified header to set the file modification time --write-description Write video description to a .description file --no-write-description Do not write video description (default) --write-info-json Write video metadata to a .info.json file (this may contain personal information) --no-write-info-json Do not write video metadata (default) --write-playlist-metafiles Write playlist metadata in addition to the video metadata when using --write-info-json, --write-description etc. (default) --no-write-playlist-metafiles Do not write playlist metadata when using --write-info-json, --write-description etc. --clean-info-json Remove some internal metadata such as filenames from the infojson (default) --no-clean-info-json Write all fields to the infojson --write-comments Retrieve video comments to be placed in the infojson. The comments are fetched even without this option if the extraction is known to be quick (Alias: --get-comments) --no-write-comments Do not retrieve video comments unless the extraction is known to be quick (Alias: --no-get-comments) --load-info-json FILE JSON file containing the video information (created with the "--write-info-json" option) --cookies FILE Netscape formatted file to read cookies from and dump cookie jar in --no-cookies Do not read/dump cookies from/to file (default) --cookies-from-browser BROWSER[+KEYRING][:PROFILE][::CONTAINER] The name of the browser to load cookies from. Currently supported browsers are: brave, chrome, chromium, edge, firefox, opera, safari, vivaldi, whale. Optionally, the KEYRING used for decrypting Chromium cookies on Linux, the name/path of the PROFILE to load cookies from, and the CONTAINER name (if Firefox) ("none" for no container) can be given with their respective separators. By default, all containers of the most recently accessed profile are used. Currently supported keyrings are: basictext, gnomekeyring, kwallet, kwallet5, kwallet6 --no-cookies-from-browser Do not load cookies from browser (default) --cache-dir DIR Location in the filesystem where yt-dlp can store some downloaded information (such as client ids and signatures) permanently. By default ${XDG_CACHE_HOME}/yt-dlp --no-cache-dir Disable filesystem caching --rm-cache-dir Delete all filesystem cache files Thumbnail Options: --write-thumbnail Write thumbnail image to disk --no-write-thumbnail Do not write thumbnail image to disk (default) --write-all-thumbnails Write all thumbnail image formats to disk --list-thumbnails List available thumbnails of each video. Simulate unless --no- simulate is used Internet Shortcut Options: --write-link Write an internet shortcut file, depending on the current platform (.url, .webloc or .desktop). The URL may be cached by the OS --write-url-link Write a .url Windows internet shortcut. The OS caches the URL based on the file path --write-webloc-link Write a .webloc macOS internet shortcut --write-desktop-link Write a .desktop Linux internet shortcut Verbosity and Simulation Options: -q, --quiet Activate quiet mode. If used with --verbose, print the log to stderr --no-quiet Deactivate quiet mode. (Default) --no-warnings Ignore warnings -s, --simulate Do not download the video and do not write anything to disk --no-simulate Download the video even if printing/listing options are used --ignore-no-formats-error Ignore "No video formats" error. Useful for extracting metadata even if the videos are not actually available for download (experimental) --no-ignore-no-formats-error Throw error when no downloadable video formats are found (default) --skip-download Do not download the video but write all related files (Alias: --no-download) -O, --print [WHEN:]TEMPLATE Field name or output template to print to screen, optionally prefixed with when to print it, separated by a ":". Supported values of "WHEN" are the same as that of --use-postprocessor (default: video). Implies --quiet. Implies --simulate unless --no-simulate or later stages of WHEN are used. This option can be used multiple times --print-to-file [WHEN:]TEMPLATE FILE Append given template to the file. The values of WHEN and TEMPLATE are same as that of --print. FILE uses the same syntax as the output template. This option can be used multiple times -j, --dump-json Quiet, but print JSON information for each video. Simulate unless --no-simulate is used. See "OUTPUT TEMPLATE" for a description of available keys -J, --dump-single-json Quiet, but print JSON information for each url or infojson passed. Simulate unless --no-simulate is used. If the URL refers to a playlist, the whole playlist information is dumped in a single line --force-write-archive Force download archive entries to be written as far as no errors occur, even if -s or another simulation option is used (Alias: --force-download-archive) --newline Output progress bar as new lines --no-progress Do not print progress bar --progress Show progress bar, even if in quiet mode --console-title Display progress in console titlebar --progress-template [TYPES:]TEMPLATE Template for progress outputs, optionally prefixed with one of "download:" (default), "download-title:" (the console title), "postprocess:", or "postprocess-title:". The video's fields are accessible under the "info" key and the progress attributes are accessible under "progress" key. E.g. --console-title --progress-template "download- title:%(info.id)s-%(progress.eta)s" --progress-delta SECONDS Time between progress output (default: 0) -v, --verbose Print various debugging information --dump-pages Print downloaded pages encoded using base64 to debug problems (very verbose) --write-pages Write downloaded intermediary pages to files in the current directory to debug problems --print-traffic Display sent and read HTTP traffic Workarounds: --encoding ENCODING Force the specified encoding (experimental) --legacy-server-connect Explicitly allow HTTPS connection to servers that do not support RFC 5746 secure renegotiation --no-check-certificates Suppress HTTPS certificate validation --prefer-insecure Use an unencrypted connection to retrieve information about the video (Currently supported only for YouTube) --add-headers FIELD:VALUE Specify a custom HTTP header and its value, separated by a colon ":". You can use this option multiple times --bidi-workaround Work around terminals that lack bidirectional text support. Requires bidiv or fribidi executable in PATH --sleep-requests SECONDS Number of seconds to sleep between requests during data extraction --sleep-interval SECONDS Number of seconds to sleep before each download. This is the minimum time to sleep when used along with --max-sleep-interval (Alias: --min-sleep-interval) --max-sleep-interval SECONDS Maximum number of seconds to sleep. Can only be used along with --min-sleep-interval --sleep-subtitles SECONDS Number of seconds to sleep before each subtitle download Video Format Options: -f, --format FORMAT Video format code, see "FORMAT SELECTION" for more details -S, --format-sort SORTORDER Sort the formats by the fields given, see "Sorting Formats" for more details --format-sort-force Force user specified sort order to have precedence over all fields, see "Sorting Formats" for more details (Alias: --S- force) --no-format-sort-force Some fields have precedence over the user specified sort order (default) --video-multistreams Allow multiple video streams to be merged into a single file --no-video-multistreams Only one video stream is downloaded for each output file (default) --audio-multistreams Allow multiple audio streams to be merged into a single file --no-audio-multistreams Only one audio stream is downloaded for each output file (default) --prefer-free-formats Prefer video formats with free containers over non-free ones of same quality. Use with "-S ext" to strictly prefer free containers irrespective of quality --no-prefer-free-formats Don't give any special preference to free containers (default) --check-formats Make sure formats are selected only from those that are actually downloadable --check-all-formats Check all formats for whether they are actually downloadable --no-check-formats Do not check that the formats are actually downloadable -F, --list-formats List available formats of each video. Simulate unless --no- simulate is used --merge-output-format FORMAT Containers that may be used when merging formats, separated by "/", e.g. "mp4/mkv". Ignored if no merge is required. (currently supported: avi, flv, mkv, mov, mp4, webm) Subtitle Options: --write-subs Write subtitle file --no-write-subs Do not write subtitle file (default) --write-auto-subs Write automatically generated subtitle file (Alias: --write- automatic-subs) --no-write-auto-subs Do not write auto-generated subtitles (default) (Alias: --no- write-automatic-subs) --list-subs List available subtitles of each video. Simulate unless --no- simulate is used --sub-format FORMAT Subtitle format; accepts formats preference, e.g. "srt" or "ass/srt/best" --sub-langs LANGS Languages of the subtitles to download (can be regex) or "all" separated by commas, e.g. --sub-langs "en.*,ja". You can prefix the language code with a "-" to exclude it from the requested languages, e.g. --sub-langs all,-live_chat. Use --list-subs for a list of available language tags Authentication Options: -u, --username USERNAME Login with this account ID -p, --password PASSWORD Account password. If this option is left out, yt-dlp will ask interactively -2, --twofactor TWOFACTOR Two-factor authentication code -n, --netrc Use .netrc authentication data --netrc-location PATH Location of .netrc authentication data; either the path or its containing directory. Defaults to ~/.netrc --netrc-cmd NETRC_CMD Command to execute to get the credentials for an extractor. --video-password PASSWORD Video-specific password --ap-mso MSO Adobe Pass multiple-system operator (TV provider) identifier, use --ap-list-mso for a list of available MSOs --ap-username USERNAME Multiple-system operator account login --ap-password PASSWORD Multiple-system operator account password. If this option is left out, yt-dlp will ask interactively --ap-list-mso List all supported multiple-system operators --client-certificate CERTFILE Path to client certificate file in PEM format. May include the private key --client-certificate-key KEYFILE Path to private key file for client certificate --client-certificate-password PASSWORD Password for client certificate private key, if encrypted. If not provided, and the key is encrypted, yt-dlp will ask interactively Post-Processing Options: -x, --extract-audio Convert video files to audio-only files (requires ffmpeg and ffprobe) --audio-format FORMAT Format to convert the audio to when -x is used. (currently supported: best (default), aac, alac, flac, m4a, mp3, opus, vorbis, wav). You can specify multiple rules using similar syntax as --remux-video --audio-quality QUALITY Specify ffmpeg audio quality to use when converting the audio with -x. Insert a value between 0 (best) and 10 (worst) for VBR or a specific bitrate like 128K (default 5) --remux-video FORMAT Remux the video into another container if necessary (currently supported: avi, flv, gif, mkv, mov, mp4, webm, aac, aiff, alac, flac, m4a, mka, mp3, ogg, opus, vorbis, wav). If target container does not support the video/audio codec, remuxing will fail. You can specify multiple rules; e.g. "aac>m4a/mov>mp4/mkv" will remux aac to m4a, mov to mp4 and anything else to mkv --recode-video FORMAT Re-encode the video into another format if necessary. The syntax and supported formats are the same as --remux-video --postprocessor-args NAME:ARGS Give these arguments to the postprocessors. Specify the postprocessor/executable name and the arguments separated by a colon ":" to give the argument to the specified postprocessor/executable. Supported PP are: Merger, ModifyChapters, SplitChapters, ExtractAudio, VideoRemuxer, VideoConvertor, Metadata, EmbedSubtitle, EmbedThumbnail, SubtitlesConvertor, ThumbnailsConvertor, FixupStretched, FixupM4a, FixupM3u8, FixupTimestamp and FixupDuration. The supported executables are: AtomicParsley, FFmpeg and FFprobe. You can also specify "PP+EXE:ARGS" to give the arguments to the specified executable only when being used by the specified postprocessor. Additionally, for ffmpeg/ffprobe, "_i"/"_o" can be appended to the prefix optionally followed by a number to pass the argument before the specified input/output file, e.g. --ppa "Merger+ffmpeg_i1:-v quiet". You can use this option multiple times to give different arguments to different postprocessors. (Alias: --ppa) -k, --keep-video Keep the intermediate video file on disk after post-processing --no-keep-video Delete the intermediate video file after post-processing (default) --post-overwrites Overwrite post-processed files (default) --no-post-overwrites Do not overwrite post-processed files --embed-subs Embed subtitles in the video (only for mp4, webm and mkv videos) --no-embed-subs Do not embed subtitles (default) --embed-thumbnail Embed thumbnail in the video as cover art --no-embed-thumbnail Do not embed thumbnail (default) --embed-metadata Embed metadata to the video file. Also embeds chapters/infojson if present unless --no-embed-chapters/--no-embed-info-json are used (Alias: --add-metadata) --no-embed-metadata Do not add metadata to file (default) (Alias: --no-add-metadata) --embed-chapters Add chapter markers to the video file (Alias: --add-chapters) --no-embed-chapters Do not add chapter markers (default) (Alias: --no-add-chapters) --embed-info-json Embed the infojson as an attachment to mkv/mka video files --no-embed-info-json Do not embed the infojson as an attachment to the video file --parse-metadata [WHEN:]FROM:TO Parse additional metadata like title/artist from other fields; see "MODIFYING METADATA" for details. Supported values of "WHEN" are the same as that of --use-postprocessor (default: pre_process) --replace-in-metadata [WHEN:]FIELDS REGEX REPLACE Replace text in a metadata field using the given regex. This option can be used multiple times. Supported values of "WHEN" are the same as that of --use-postprocessor (default: pre_process) --xattrs Write metadata to the video file's xattrs (using dublin core and xdg standards) --concat-playlist POLICY Concatenate videos in a playlist. One of "never", "always", or "multi_video" (default; only when the videos form a single show). All the video files must have same codecs and number of streams to be concatable. The "pl_video:" prefix can be used with "--paths" and "--output" to set the output filename for the concatenated files. See "OUTPUT TEMPLATE" for details --fixup POLICY Automatically correct known faults of the file. One of never (do nothing), warn (only emit a warning), detect_or_warn (the default; fix file if we can, warn otherwise), force (try fixing even if file already exists) --ffmpeg-location PATH Location of the ffmpeg binary; either the path to the binary or its containing directory --exec [WHEN:]CMD Execute a command, optionally prefixed with when to execute it, separated by a ":". Supported values of "WHEN" are the same as that of --use-postprocessor (default: after_move). Same syntax as the output template can be used to pass any field as arguments to the command. If no fields are passed, %(filepath,_filename|)q is appended to the end of the command. This option can be used multiple times --no-exec Remove any previously defined --exec --convert-subs FORMAT Convert the subtitles to another format (currently supported: ass, lrc, srt, vtt) (Alias: --convert-subtitles) --convert-thumbnails FORMAT Convert the thumbnails to another format (currently supported: jpg, png, webp). You can specify multiple rules using similar syntax as --remux-video --split-chapters Split video into multiple files based on internal chapters. The "chapter:" prefix can be used with "--paths" and "--output" to set the output filename for the split files. See "OUTPUT TEMPLATE" for details --no-split-chapters Do not split video based on chapters (default) --remove-chapters REGEX Remove chapters whose title matches the given regular expression. The syntax is the same as --download-sections. This option can be used multiple times --no-remove-chapters Do not remove any chapters from the file (default) --force-keyframes-at-cuts Force keyframes at cuts when downloading/splitting/removing sections. This is slow due to needing a re-encode, but the resulting video may have fewer artifacts around the cuts --no-force-keyframes-at-cuts Do not force keyframes around the chapters when cutting/splitting (default) --use-postprocessor NAME[:ARGS] The (case sensitive) name of plugin postprocessors to be enabled, and (optionally) arguments to be passed to it, separated by a colon ":". ARGS are a semicolon ";" delimited list of NAME=VALUE. The "when" argument determines when the postprocessor is invoked. It can be one of "pre_process" (after video extraction), "after_filter" (after video passes filter), "video" (after --format; before --print/--output), "before_dl" (before each video download), "post_process" (after each video download; default), "after_move" (after moving video file to its final locations), "after_video" (after downloading and processing all formats of a video), or "playlist" (at end of playlist). This option can be used multiple times to add different postprocessors SponsorBlock Options: Make chapter entries for, or remove various segments (sponsor, introductions, etc.) from downloaded YouTube videos using the SponsorBlock API (https://sponsor.ajay.app) --sponsorblock-mark CATS SponsorBlock categories to create chapters for, separated by commas. Available categories are sponsor, intro, outro, selfpromo, preview, filler, interaction, music_offtopic, poi_highlight, chapter, all and default (=all). You can prefix the category with a "-" to exclude it. See [1] for description of the categories. E.g. --sponsorblock-mark all,-preview [1] https://wiki.sponsor.ajay.app/w/Segment_Categories --sponsorblock-remove CATS SponsorBlock categories to be removed from the video file, separated by commas. If a category is present in both mark and remove, remove takes precedence. The syntax and available categories are the same as for --sponsorblock-mark except that "default" refers to "all,-filler" and poi_highlight, chapter are not available --sponsorblock-chapter-title TEMPLATE An output template for the title of the SponsorBlock chapters created by --sponsorblock-mark. The only available fields are start_time, end_time, category, categories, name, category_names. Defaults to "[SponsorBlock]: %(category_names)l" --no-sponsorblock Disable both --sponsorblock-mark and --sponsorblock-remove --sponsorblock-api URL SponsorBlock API location, defaults to https://sponsor.ajay.app Extractor Options: --extractor-retries RETRIES Number of retries for known extractor errors (default is 3), or "infinite" --allow-dynamic-mpd Process dynamic DASH manifests (default) (Alias: --no-ignore- dynamic-mpd) --ignore-dynamic-mpd Do not process dynamic DASH manifests (Alias: --no-allow- dynamic-mpd) --hls-split-discontinuity Split HLS playlists to different formats at discontinuities such as ad breaks --no-hls-split-discontinuity Do not split HLS playlists to different formats at discontinuities such as ad breaks (default) --extractor-args IE_KEY:ARGS Pass ARGS arguments to the IE_KEY extractor. See "EXTRACTOR ARGUMENTS" for details. You can use this option multiple times to give arguments for different extractors CONFIGURATION You can configure yt-dlp by placing any supported command line option to a configuration file. The configuration is loaded from the following locations: 1. Main Configuration: • The file given to --config-location 2. Portable Configuration: (Recommended for portable installations) • If using a binary, yt-dlp.conf in the same directory as the binary • If running from source-code, yt-dlp.conf in the parent directory of yt_dlp 3. Home Configuration: • yt-dlp.conf in the home path given to -P • If -P is not given, the current directory is searched 4. User Configuration: • ${XDG_CONFIG_HOME}/yt-dlp.conf • ${XDG_CONFIG_HOME}/yt-dlp/config (recommended on Linux/macOS) • ${XDG_CONFIG_HOME}/yt-dlp/config.txt • ${APPDATA}/yt-dlp.conf • ${APPDATA}/yt-dlp/config (recommended on Windows) • ${APPDATA}/yt-dlp/config.txt • ~/yt-dlp.conf • ~/yt-dlp.conf.txt • ~/.yt-dlp/config • ~/.yt-dlp/config.txt See also: Notes about environment variables 5. System Configuration: • /etc/yt-dlp.conf • /etc/yt-dlp/config • /etc/yt-dlp/config.txt E.g. with the following configuration file, yt-dlp will always extract the audio, not copy the mtime, use a proxy and save all videos under YouTube directory in your home directory: # Lines starting with # are comments # Always extract audio -x # Do not copy the mtime --no-mtime # Use this proxy --proxy 127.0.0.1:3128 # Save all videos under YouTube directory in your home directory -o ~/YouTube/%(title)s.%(ext)s Note: Options in configuration file are just the same options aka switches used in regular command line calls; thus there must be no whitespace after - or --, e.g. -o or --proxy but not - o or -- proxy. They must also be quoted when necessary, as if it were a UNIX shell. You can use --ignore-config if you want to disable all configuration files for a particular yt-dlp run. If --ignore-config is found inside any configuration file, no further configuration will be loaded. For example, having the option in the portable configuration file prevents loading of home, user, and system configurations. Additionally, (for backward compatibility) if --ignore-config is found inside the system configuration file, the user configuration is not loaded. Configuration file encoding The configuration files are decoded according to the UTF BOM if present, and in the encoding from system locale otherwise. If you want your file to be decoded differently, add # coding: ENCODING to the beginning of the file (e.g. # coding: shift-jis). There must be no characters before that, even spaces or BOM. Authentication with netrc You may also want to configure automatic credentials storage for extractors that support authentication (by providing login and password with --username and --password) in order not to pass credentials as command line arguments on every yt-dlp execution and prevent tracking plain text passwords in the shell command history. You can achieve this using a .netrc file (https://stackoverflow.com/tags/.netrc/info) on a per-extractor basis. For that, you will need to create a .netrc file in --netrc-location and restrict permissions to read/write by only you: touch ${HOME}/.netrc chmod a-rwx,u+rw ${HOME}/.netrc After that, you can add credentials for an extractor in the following format, where extractor is the name of the extractor in lowercase: machine <extractor> login <username> password <password> E.g. machine youtube login myaccount@gmail.com password my_youtube_password machine twitch login my_twitch_account_name password my_twitch_password To activate authentication with the .netrc file you should pass --netrc to yt-dlp or place it in the configuration file. The default location of the .netrc file is ~ (see below). As an alternative to using the .netrc file, which has the disadvantage of keeping your passwords in a plain text file, you can configure a custom shell command to provide the credentials for an extractor. This is done by providing the --netrc-cmd parameter, it shall output the credentials in the netrc format and return 0 on success, other values will be treated as an error. {} in the command will be replaced by the name of the extractor to make it possible to select the credentials for the right extractor. E.g. To use an encrypted .netrc file stored as .authinfo.gpg yt-dlp --netrc-cmd 'gpg --decrypt ~/.authinfo.gpg' https://www.youtube.com/watch?v=BaW_jenozKc Notes about environment variables • Environment variables are normally specified as ${VARIABLE}/$VARIABLE on UNIX and %VARIABLE% on Windows; but is always shown as ${VARIABLE} in this documentation • yt-dlp also allow using UNIX-style variables on Windows for path-like options; e.g. --output, --config-location • If unset, ${XDG_CONFIG_HOME} defaults to ~/.config and ${XDG_CACHE_HOME} to ~/.cache • On Windows, ~ points to ${HOME} if present; or, ${USERPROFILE} or ${HOMEDRIVE}${HOMEPATH} otherwise • On Windows, ${USERPROFILE} generally points to C:\Users\<user name> and ${APPDATA} to ${USERPROFILE}\AppData\Roaming OUTPUT TEMPLATE The -o option is used to indicate a template for the output file names while -P option is used to specify the path each type of file should be saved to. The simplest usage of -o is not to set any template arguments when downloading a single file, like in yt-dlp -o funny_video.flv "https://some/video" (hard-coding file extension like this is not recommended and could break some post-processing). It may however also contain special sequences that will be replaced when downloading each video. The special sequences may be formatted according to Python string formatting operations (https://docs.python.org/3/library/stdtypes.html#printf-style-string- formatting), e.g. %(NAME)s or %(NAME)05d. To clarify, that is a percent symbol followed by a name in parentheses, followed by formatting operations. The field names themselves (the part inside the parenthesis) can also have some special formatting: 1. Object traversal: The dictionaries and lists available in metadata can be traversed by using a dot . separator; e.g. %(tags.0)s, %(subtitles.en.-1.ext)s. You can do Python slicing with colon :; E.g. %(id.3:7)s, %(id.6:2:-1)s, %(formats.:.format_id)s. Curly braces {} can be used to build dictionaries with only specific keys; e.g. %(formats.:.{format_id,height})#j. An empty field name %()s refers to the entire infodict; e.g. %(.{id,title})s. Note that all the fields that become available using this method are not listed below. Use -j to see such fields 2. Arithmetic: Simple arithmetic can be done on numeric fields using +, - and *. E.g. %(playlist_index+10)03d, %(n_entries+1-playlist_index)d 3. Date/time Formatting: Date/time fields can be formatted according to strftime formatting (https://docs.python.org/3/library/datetime.html#strftime-and- strptime-format-codes) by specifying it separated from the field name using a >. E.g. %(duration>%H-%M-%S)s, %(upload_date>%Y-%m-%d)s, %(epoch-3600>%H-%M-%S)s 4. Alternatives: Alternate fields can be specified separated with a ,. E.g. %(release_date>%Y,upload_date>%Y|Unknown)s 5. Replacement: A replacement value can be specified using a & separator according to the str.format mini-language (https://docs.python.org/3/library/string.html#format-specification- mini-language). If the field is not empty, this replacement value will be used instead of the actual field content. This is done after alternate fields are considered; thus the replacement is used if any of the alternative fields is not empty. E.g. %(chapters&has chapters|no chapters)s, %(title&TITLE={:>20}|NO TITLE)s 6. Default: A literal default value can be specified for when the field is empty using a | separator. This overrides --output-na-placeholder. E.g. %(uploader|Unknown)s 7. More Conversions: In addition to the normal format types diouxXeEfFgGcrs, yt-dlp additionally supports converting to B = Bytes, j = json (flag # for pretty-printing, + for Unicode), h = HTML escaping, l = a comma separated list (flag # for \n newline-separated), q = a string quoted for the terminal (flag # to split a list into different arguments), D = add Decimal suffixes (e.g. 10M) (flag # to use 1024 as factor), and S = Sanitize as filename (flag # for restricted) 8. Unicode normalization: The format type U can be used for NFC Unicode normalization (https://docs.python.org/3/library/unicodedata.html#unicodedata.normalize). The alternate form flag (#) changes the normalization to NFD and the conversion flag + can be used for NFKC/NFKD compatibility equivalence normalization. E.g. %(title)+.100U is NFKC To summarize, the general syntax for a field is: %(name[.keys][addition][>strf][,alternate][&replacement][|default])[flags][width][.precision][length]type Additionally, you can set different output templates for the various metadata files separately from the general output template by specifying the type of file followed by the template separated by a colon :. The different file types supported are subtitle, thumbnail, description, annotation (deprecated), infojson, link, pl_thumbnail, pl_description, pl_infojson, chapter, pl_video. E.g. -o "%(title)s.%(ext)s" -o "thumbnail:%(title)s\%(title)s.%(ext)s" will put the thumbnails in a folder with the same name as the video. If any of the templates is empty, that type of file will not be written. E.g. --write-thumbnail -o "thumbnail:" will write thumbnails only for playlists and not for video. Note: Due to post-processing (i.e. merging etc.), the actual output filename might differ. Use --print after_move:filepath to get the name after all post-processing is complete. The available fields are: • id (string): Video identifier • title (string): Video title • fulltitle (string): Video title ignoring live timestamp and generic title • ext (string): Video filename extension • alt_title (string): A secondary title of the video • description (string): The description of the video • display_id (string): An alternative identifier for the video • uploader (string): Full name of the video uploader • uploader_id (string): Nickname or id of the video uploader • uploader_url (string): URL to the video uploader's profile • license (string): License name the video is licensed under • creators (list): The creators of the video • creator (string): The creators of the video; comma-separated • timestamp (numeric): UNIX timestamp of the moment the video became available • upload_date (string): Video upload date in UTC (YYYYMMDD) • release_timestamp (numeric): UNIX timestamp of the moment the video was released • release_date (string): The date (YYYYMMDD) when the video was released in UTC • release_year (numeric): Year (YYYY) when the video or album was released • modified_timestamp (numeric): UNIX timestamp of the moment the video was last modified • modified_date (string): The date (YYYYMMDD) when the video was last modified in UTC • channel (string): Full name of the channel the video is uploaded on • channel_id (string): Id of the channel • channel_url (string): URL of the channel • channel_follower_count (numeric): Number of followers of the channel • channel_is_verified (boolean): Whether the channel is verified on the platform • location (string): Physical location where the video was filmed • duration (numeric): Length of the video in seconds • duration_string (string): Length of the video (HH:mm:ss) • view_count (numeric): How many users have watched the video on the platform • concurrent_view_count (numeric): How many users are currently watching the video on the platform. • like_count (numeric): Number of positive ratings of the video • dislike_count (numeric): Number of negative ratings of the video • repost_count (numeric): Number of reposts of the video • average_rating (numeric): Average rating give by users, the scale used depends on the webpage • comment_count (numeric): Number of comments on the video (For some extractors, comments are only downloaded at the end, and so this field cannot be used) • age_limit (numeric): Age restriction for the video (years) • live_status (string): One of "not_live", "is_live", "is_upcoming", "was_live", "post_live" (was live, but VOD is not yet processed) • is_live (boolean): Whether this video is a live stream or a fixed- length video • was_live (boolean): Whether this video was originally a live stream • playable_in_embed (string): Whether this video is allowed to play in embedded players on other sites • availability (string): Whether the video is "private", "premium_only", "subscriber_only", "needs_auth", "unlisted" or "public" • media_type (string): The type of media as classified by the site, e.g. "episode", "clip", "trailer" • start_time (numeric): Time in seconds where the reproduction should start, as specified in the URL • end_time (numeric): Time in seconds where the reproduction should end, as specified in the URL • extractor (string): Name of the extractor • extractor_key (string): Key name of the extractor • epoch (numeric): Unix epoch of when the information extraction was completed • autonumber (numeric): Number that will be increased with each download, starting at --autonumber-start, padded with leading zeros to 5 digits • video_autonumber (numeric): Number that will be increased with each video • n_entries (numeric): Total number of extracted items in the playlist • playlist_id (string): Identifier of the playlist that contains the video • playlist_title (string): Name of the playlist that contains the video • playlist (string): playlist_title if available or else playlist_id • playlist_count (numeric): Total number of items in the playlist. May not be known if entire playlist is not extracted • playlist_index (numeric): Index of the video in the playlist padded with leading zeros according the final index • playlist_autonumber (numeric): Position of the video in the playlist download queue padded with leading zeros according to the total length of the playlist • playlist_uploader (string): Full name of the playlist uploader • playlist_uploader_id (string): Nickname or id of the playlist uploader • playlist_channel (string): Display name of the channel that uploaded the playlist • playlist_channel_id (string): Identifier of the channel that uploaded the playlist • webpage_url (string): A URL to the video webpage which, if given to yt-dlp, should yield the same result again • webpage_url_basename (string): The basename of the webpage URL • webpage_url_domain (string): The domain of the webpage URL • original_url (string): The URL given by the user (or same as webpage_url for playlist entries) • categories (list): List of categories the video belongs to • tags (list): List of tags assigned to the video • cast (list): List of cast members All the fields in Filtering Formats can also be used Available for the video that belongs to some logical chapter or section: • chapter (string): Name or title of the chapter the video belongs to • chapter_number (numeric): Number of the chapter the video belongs to • chapter_id (string): Id of the chapter the video belongs to Available for the video that is an episode of some series or program: • series (string): Title of the series or program the video episode belongs to • series_id (string): Id of the series or program the video episode belongs to • season (string): Title of the season the video episode belongs to • season_number (numeric): Number of the season the video episode belongs to • season_id (string): Id of the season the video episode belongs to • episode (string): Title of the video episode • episode_number (numeric): Number of the video episode within a season • episode_id (string): Id of the video episode Available for the media that is a track or a part of a music album: • track (string): Title of the track • track_number (numeric): Number of the track within an album or a disc • track_id (string): Id of the track • artists (list): Artist(s) of the track • artist (string): Artist(s) of the track; comma-separated • genres (list): Genre(s) of the track • genre (string): Genre(s) of the track; comma-separated • composers (list): Composer(s) of the piece • composer (string): Composer(s) of the piece; comma-separated • album (string): Title of the album the track belongs to • album_type (string): Type of the album • album_artists (list): All artists appeared on the album • album_artist (string): All artists appeared on the album; comma- separated • disc_number (numeric): Number of the disc or other physical medium the track belongs to Available only when using --download-sections and for chapter: prefix when using --split-chapters for videos with internal chapters: • section_title (string): Title of the chapter • section_number (numeric): Number of the chapter within the file • section_start (numeric): Start time of the chapter in seconds • section_end (numeric): End time of the chapter in seconds Available only when used in --print: • urls (string): The URLs of all requested formats, one in each line • filename (string): Name of the video file. Note that the actual filename may differ • formats_table (table): The video format table as printed by --list-formats • thumbnails_table (table): The thumbnail format table as printed by --list-thumbnails • subtitles_table (table): The subtitle format table as printed by --list-subs • automatic_captions_table (table): The automatic subtitle format table as printed by --list-subs Available only after the video is downloaded (post_process/after_move): • filepath: Actual path of downloaded video file Available only in --sponsorblock-chapter-title: • start_time (numeric): Start time of the chapter in seconds • end_time (numeric): End time of the chapter in seconds • categories (list): The SponsorBlock categories (https://wiki.sponsor.ajay.app/w/Types#Category) the chapter belongs to • category (string): The smallest SponsorBlock category the chapter belongs to • category_names (list): Friendly names of the categories • name (string): Friendly name of the smallest category • type (string): The SponsorBlock action type (https://wiki.sponsor.ajay.app/w/Types#Action_Type) of the chapter Each aforementioned sequence when referenced in an output template will be replaced by the actual value corresponding to the sequence name. E.g. for -o %(title)s-%(id)s.%(ext)s and an mp4 video with title yt-dlp test video and id BaW_jenozKc, this will result in a yt-dlp test video-BaW_jenozKc.mp4 file created in the current directory. Note: Some of the sequences are not guaranteed to be present, since they depend on the metadata obtained by a particular extractor. Such sequences will be replaced with placeholder value provided with --output-na-placeholder (NA by default). Tip: Look at the -j output to identify which fields are available for the particular URL For numeric sequences you can use numeric related formatting (https://docs.python.org/3/library/stdtypes.html#printf-style-string- formatting); e.g. %(view_count)05d will result in a string with view count padded with zeros up to 5 characters, like in 00042. Output templates can also contain arbitrary hierarchical path, e.g. -o "%(playlist)s/%(playlist_index)s - %(title)s.%(ext)s" which will result in downloading each video in a directory corresponding to this path template. Any missing directory will be automatically created for you. To use percent literals in an output template use %%. To output to stdout use -o -. The current default template is %(title)s [%(id)s].%(ext)s. In some cases, you don't want special characters such as 中, spaces, or &, such as when transferring the downloaded filename to a Windows system or the filename through an 8bit-unsafe channel. In these cases, add the --restrict-filenames flag to get a shorter title. Output template examples $ yt-dlp --print filename -o "test video.%(ext)s" BaW_jenozKc test video.webm # Literal name with correct extension $ yt-dlp --print filename -o "%(title)s.%(ext)s" BaW_jenozKc youtube-dl test video ''_ä↭𝕐.webm # All kinds of weird characters $ yt-dlp --print filename -o "%(title)s.%(ext)s" BaW_jenozKc --restrict-filenames youtube-dl_test_video_.webm # Restricted file name # Download YouTube playlist videos in separate directory indexed by video order in a playlist $ yt-dlp -o "%(playlist)s/%(playlist_index)s - %(title)s.%(ext)s" "https://www.youtube.com/playlist?list=PLwiyx1dc3P2JR9N8gQaQN_BCvlSlap7re" # Download YouTube playlist videos in separate directories according to their uploaded year $ yt-dlp -o "%(upload_date>%Y)s/%(title)s.%(ext)s" "https://www.youtube.com/playlist?list=PLwiyx1dc3P2JR9N8gQaQN_BCvlSlap7re" # Prefix playlist index with " - " separator, but only if it is available $ yt-dlp -o "%(playlist_index&{} - |)s%(title)s.%(ext)s" BaW_jenozKc "https://www.youtube.com/user/TheLinuxFoundation/playlists" # Download all playlists of YouTube channel/user keeping each playlist in separate directory: $ yt-dlp -o "%(uploader)s/%(playlist)s/%(playlist_index)s - %(title)s.%(ext)s" "https://www.youtube.com/user/TheLinuxFoundation/playlists" # Download Udemy course keeping each chapter in separate directory under MyVideos directory in your home $ yt-dlp -u user -p password -P "~/MyVideos" -o "%(playlist)s/%(chapter_number)s - %(chapter)s/%(title)s.%(ext)s" "https://www.udemy.com/java-tutorial" # Download entire series season keeping each series and each season in separate directory under C:/MyVideos $ yt-dlp -P "C:/MyVideos" -o "%(series)s/%(season_number)s - %(season)s/%(episode_number)s - %(episode)s.%(ext)s" "https://videomore.ru/kino_v_detalayah/5_sezon/367617" # Download video as "C:\MyVideos\uploader\title.ext", subtitles as "C:\MyVideos\subs\uploader\title.ext" # and put all temporary files in "C:\MyVideos\tmp" $ yt-dlp -P "C:/MyVideos" -P "temp:tmp" -P "subtitle:subs" -o "%(uploader)s/%(title)s.%(ext)s" BaW_jenoz --write-subs # Download video as "C:\MyVideos\uploader\title.ext" and subtitles as "C:\MyVideos\uploader\subs\title.ext" $ yt-dlp -P "C:/MyVideos" -o "%(uploader)s/%(title)s.%(ext)s" -o "subtitle:%(uploader)s/subs/%(title)s.%(ext)s" BaW_jenozKc --write-subs # Stream the video being downloaded to stdout $ yt-dlp -o - BaW_jenozKc FORMAT SELECTION By default, yt-dlp tries to download the best available quality if you don't pass any options. This is generally equivalent to using -f bestvideo*+bestaudio/best. However, if multiple audiostreams is enabled (--audio-multistreams), the default format changes to -f bestvideo+bestaudio/best. Similarly, if ffmpeg is unavailable, or if you use yt-dlp to stream to stdout (-o -), the default becomes -f best/bestvideo+bestaudio. Deprecation warning: Latest versions of yt-dlp can stream multiple formats to the stdout simultaneously using ffmpeg. So, in future versions, the default for this will be set to -f bv*+ba/b similar to normal downloads. If you want to preserve the -f b/bv+ba setting, it is recommended to explicitly specify it in the configuration options. The general syntax for format selection is -f FORMAT (or --format FORMAT) where FORMAT is a selector expression, i.e. an expression that describes format or formats you would like to download. The simplest case is requesting a specific format; e.g. with -f 22 you can download the format with format code equal to 22. You can get the list of available format codes for particular video using --list-formats or -F. Note that these format codes are extractor specific. You can also use a file extension (currently 3gp, aac, flv, m4a, mp3, mp4, ogg, wav, webm are supported) to download the best quality format of a particular file extension served as a single file, e.g. -f webm will download the best quality format with the webm extension served as a single file. You can use -f - to interactively provide the format selector for each video You can also use special names to select particular edge case formats: • all: Select all formats separately • mergeall: Select and merge all formats (Must be used with --audio-multistreams, --video-multistreams or both) • b*, best*: Select the best quality format that contains either a video or an audio or both (i.e.; vcodec!=none or acodec!=none) • b, best: Select the best quality format that contains both video and audio. Equivalent to best*[vcodec!=none][acodec!=none] • bv, bestvideo: Select the best quality video-only format. Equivalent to best*[acodec=none] • bv*, bestvideo*: Select the best quality format that contains video. It may also contain audio. Equivalent to best*[vcodec!=none] • ba, bestaudio: Select the best quality audio-only format. Equivalent to best*[vcodec=none] • ba*, bestaudio*: Select the best quality format that contains audio. It may also contain video. Equivalent to best*[acodec!=none] (Do not use! (https://github.com/yt-dlp/yt- dlp/issues/979#issuecomment-919629354)) • w*, worst*: Select the worst quality format that contains either a video or an audio • w, worst: Select the worst quality format that contains both video and audio. Equivalent to worst*[vcodec!=none][acodec!=none] • wv, worstvideo: Select the worst quality video-only format. Equivalent to worst*[acodec=none] • wv*, worstvideo*: Select the worst quality format that contains video. It may also contain audio. Equivalent to worst*[vcodec!=none] • wa, worstaudio: Select the worst quality audio-only format. Equivalent to worst*[vcodec=none] • wa*, worstaudio*: Select the worst quality format that contains audio. It may also contain video. Equivalent to worst*[acodec!=none] For example, to download the worst quality video-only format you can use -f worstvideo. It is, however, recommended not to use worst and related options. When your format selector is worst, the format which is worst in all respects is selected. Most of the time, what you actually want is the video with the smallest filesize instead. So it is generally better to use -S +size or more rigorously, -S +size,+br,+res,+fps instead of -f worst. See Sorting Formats for more details. You can select the n'th best format of a type by using best<type>.<n>. For example, best.2 will select the 2nd best combined format. Similarly, bv*.3 will select the 3rd best format that contains a video stream. If you want to download multiple videos, and they don't have the same formats available, you can specify the order of preference using slashes. Note that formats on the left hand side are preferred; e.g. -f 22/17/18 will download format 22 if it's available, otherwise it will download format 17 if it's available, otherwise it will download format 18 if it's available, otherwise it will complain that no suitable formats are available for download. If you want to download several formats of the same video use a comma as a separator, e.g. -f 22,17,18 will download all these three formats, of course if they are available. Or a more sophisticated example combined with the precedence feature: -f 136/137/mp4/bestvideo,140/m4a/bestaudio. You can merge the video and audio of multiple formats into a single file using -f <format1>+<format2>+... (requires ffmpeg installed); e.g. -f bestvideo+bestaudio will download the best video-only format, the best audio-only format and mux them together with ffmpeg. Deprecation warning: Since the below described behavior is complex and counter-intuitive, this will be removed and multistreams will be enabled by default in the future. A new operator will be instead added to limit formats to single audio/video Unless --video-multistreams is used, all formats with a video stream except the first one are ignored. Similarly, unless --audio-multistreams is used, all formats with an audio stream except the first one are ignored. E.g. -f bestvideo+best+bestaudio --video-multistreams --audio-multistreams will download and merge all 3 given formats. The resulting file will have 2 video streams and 2 audio streams. But -f bestvideo+best+bestaudio --no-video-multistreams will download and merge only bestvideo and bestaudio. best is ignored since another format containing a video stream (bestvideo) has already been selected. The order of the formats is therefore important. -f best+bestaudio --no-audio-multistreams will download only best while -f bestaudio+best --no-audio-multistreams will ignore best and download only bestaudio. Filtering Formats You can also filter the video formats by putting a condition in brackets, as in -f "best[height=720]" (or -f "[filesize>10M]" since filters without a selector are interpreted as best). The following numeric meta fields can be used with comparisons <, <=, >, >=, = (equals), != (not equals): • filesize: The number of bytes, if known in advance • filesize_approx: An estimate for the number of bytes • width: Width of the video, if known • height: Height of the video, if known • aspect_ratio: Aspect ratio of the video, if known • tbr: Average bitrate of audio and video in kbps • abr: Average audio bitrate in kbps • vbr: Average video bitrate in kbps • asr: Audio sampling rate in Hertz • fps: Frame rate • audio_channels: The number of audio channels • stretched_ratio: width:height of the video's pixels, if not square Also filtering work for comparisons = (equals), ^= (starts with), $= (ends with), *= (contains), ~= (matches regex) and following string meta fields: • url: Video URL • ext: File extension • acodec: Name of the audio codec in use • vcodec: Name of the video codec in use • container: Name of the container format • protocol: The protocol that will be used for the actual download, lower-case (http, https, rtsp, rtmp, rtmpe, mms, f4m, ism, http_dash_segments, m3u8, or m3u8_native) • language: Language code • dynamic_range: The dynamic range of the video • format_id: A short description of the format • format: A human-readable description of the format • format_note: Additional info about the format • resolution: Textual description of width and height Any string comparison may be prefixed with negation ! in order to produce an opposite comparison, e.g. !*= (does not contain). The comparand of a string comparison needs to be quoted with either double or single quotes if it contains spaces or special characters other than ._-. Note: None of the aforementioned meta fields are guaranteed to be present since this solely depends on the metadata obtained by the particular extractor, i.e. the metadata offered by the website. Any other field made available by the extractor can also be used for filtering. Formats for which the value is not known are excluded unless you put a question mark (?) after the operator. You can combine format filters, so -f "bv[height<=?720][tbr>500]" selects up to 720p videos (or videos where the height is not known) with a bitrate of at least 500 kbps. You can also use the filters with all to download all formats that satisfy the filter, e.g. -f "all[vcodec=none]" selects all audio-only formats. Format selectors can also be grouped using parentheses; e.g. -f "(mp4,webm)[height<480]" will download the best pre-merged mp4 and webm formats with a height lower than 480. Sorting Formats You can change the criteria for being considered the best by using -S (--format-sort). The general format for this is --format-sort field1,field2.... The available fields are: • hasvid: Gives priority to formats that have a video stream • hasaud: Gives priority to formats that have an audio stream • ie_pref: The format preference • lang: The language preference • quality: The quality of the format • source: The preference of the source • proto: Protocol used for download (https/ftps > http/ftp > m3u8_native/m3u8 > http_dash_segments> websocket_frag > mms/rtsp > f4f/f4m) • vcodec: Video Codec (av01 > vp9.2 > vp9 > h265 > h264 > vp8 > h263 > theora > other) • acodec: Audio Codec (flac/alac > wav/aiff > opus > vorbis > aac > mp4a > mp3 > ac4 > eac3 > ac3 > dts > other) • codec: Equivalent to vcodec,acodec • vext: Video Extension (mp4 > mov > webm > flv > other). If --prefer-free-formats is used, webm is preferred. • aext: Audio Extension (m4a > aac > mp3 > ogg > opus > webm > other). If --prefer-free-formats is used, the order changes to ogg > opus > webm > mp3 > m4a > aac • ext: Equivalent to vext,aext • filesize: Exact filesize, if known in advance • fs_approx: Approximate filesize • size: Exact filesize if available, otherwise approximate filesize • height: Height of video • width: Width of video • res: Video resolution, calculated as the smallest dimension. • fps: Framerate of video • hdr: The dynamic range of the video (DV > HDR12 > HDR10+ > HDR10 > HLG > SDR) • channels: The number of audio channels • tbr: Total average bitrate in kbps • vbr: Average video bitrate in kbps • abr: Average audio bitrate in kbps • br: Average bitrate in kbps, tbr/vbr/abr • asr: Audio sample rate in Hz Deprecation warning: Many of these fields have (currently undocumented) aliases, that may be removed in a future version. It is recommended to use only the documented field names. All fields, unless specified otherwise, are sorted in descending order. To reverse this, prefix the field with a +. E.g. +res prefers format with the smallest resolution. Additionally, you can suffix a preferred value for the fields, separated by a :. E.g. res:720 prefers larger videos, but no larger than 720p and the smallest video if there are no videos less than 720p. For codec and ext, you can provide two preferred values, the first for video and the second for audio. E.g. +codec:avc:m4a (equivalent to +vcodec:avc,+acodec:m4a) sets the video codec preference to h264 > h265 > vp9 > vp9.2 > av01 > vp8 > h263 > theora and audio codec preference to mp4a > aac > vorbis > opus > mp3 > ac3 > dts. You can also make the sorting prefer the nearest values to the provided by using ~ as the delimiter. E.g. filesize~1G prefers the format with filesize closest to 1 GiB. The fields hasvid and ie_pref are always given highest priority in sorting, irrespective of the user-defined order. This behavior can be changed by using --format-sort-force. Apart from these, the default order used is: lang,quality,res,fps,hdr:12,vcodec:vp9.2,channels,acodec,size,br,asr,proto,ext,hasaud,source,id. The extractors may override this default order, but they cannot override the user-provided order. Note that the default has vcodec:vp9.2; i.e. av1 is not preferred. Similarly, the default for hdr is hdr:12; i.e. Dolby Vision is not preferred. These choices are made since DV and AV1 formats are not yet fully compatible with most devices. This may be changed in the future as more devices become capable of smoothly playing back these formats. If your format selector is worst, the last item is selected after sorting. This means it will select the format that is worst in all respects. Most of the time, what you actually want is the video with the smallest filesize instead. So it is generally better to use -f best -S +size,+br,+res,+fps. Tip: You can use the -v -F to see how the formats have been sorted (worst to best). Format Selection examples # Download and merge the best video-only format and the best audio-only format, # or download the best combined format if video-only format is not available $ yt-dlp -f "bv+ba/b" # Download best format that contains video, # and if it doesn't already have an audio stream, merge it with best audio-only format $ yt-dlp -f "bv*+ba/b" # Same as above $ yt-dlp # Download the best video-only format and the best audio-only format without merging them # For this case, an output template should be used since # by default, bestvideo and bestaudio will have the same file name. $ yt-dlp -f "bv,ba" -o "%(title)s.f%(format_id)s.%(ext)s" # Download and merge the best format that has a video stream, # and all audio-only formats into one file $ yt-dlp -f "bv*+mergeall[vcodec=none]" --audio-multistreams # Download and merge the best format that has a video stream, # and the best 2 audio-only formats into one file $ yt-dlp -f "bv*+ba+ba.2" --audio-multistreams # The following examples show the old method (without -S) of format selection # and how to use -S to achieve a similar but (generally) better result # Download the worst video available (old method) $ yt-dlp -f "wv*+wa/w" # Download the best video available but with the smallest resolution $ yt-dlp -S "+res" # Download the smallest video available $ yt-dlp -S "+size,+br" # Download the best mp4 video available, or the best video if no mp4 available $ yt-dlp -f "bv*[ext=mp4]+ba[ext=m4a]/b[ext=mp4] / bv*+ba/b" # Download the best video with the best extension # (For video, mp4 > mov > webm > flv. For audio, m4a > aac > mp3 ...) $ yt-dlp -S "ext" # Download the best video available but no better than 480p, # or the worst video if there is no video under 480p $ yt-dlp -f "bv*[height<=480]+ba/b[height<=480] / wv*+ba/w" # Download the best video available with the largest height but no better than 480p, # or the best video with the smallest resolution if there is no video under 480p $ yt-dlp -S "height:480" # Download the best video available with the largest resolution but no better than 480p, # or the best video with the smallest resolution if there is no video under 480p # Resolution is determined by using the smallest dimension. # So this works correctly for vertical videos as well $ yt-dlp -S "res:480" # Download the best video (that also has audio) but no bigger than 50 MB, # or the worst video (that also has audio) if there is no video under 50 MB $ yt-dlp -f "b[filesize<50M] / w" # Download largest video (that also has audio) but no bigger than 50 MB, # or the smallest video (that also has audio) if there is no video under 50 MB $ yt-dlp -f "b" -S "filesize:50M" # Download best video (that also has audio) that is closest in size to 50 MB $ yt-dlp -f "b" -S "filesize~50M" # Download best video available via direct link over HTTP/HTTPS protocol, # or the best video available via any protocol if there is no such video $ yt-dlp -f "(bv*+ba/b)[protocol^=http][protocol!*=dash] / (bv*+ba/b)" # Download best video available via the best protocol # (https/ftps > http/ftp > m3u8_native > m3u8 > http_dash_segments ...) $ yt-dlp -S "proto" # Download the best video with either h264 or h265 codec, # or the best video if there is no such video $ yt-dlp -f "(bv*[vcodec~='^((he|a)vc|h26[45])']+ba) / (bv*+ba/b)" # Download the best video with best codec no better than h264, # or the best video with worst codec if there is no such video $ yt-dlp -S "codec:h264" # Download the best video with worst codec no worse than h264, # or the best video with best codec if there is no such video $ yt-dlp -S "+codec:h264" # More complex examples # Download the best video no better than 720p preferring framerate greater than 30, # or the worst video (still preferring framerate greater than 30) if there is no such video $ yt-dlp -f "((bv*[fps>30]/bv*)[height<=720]/(wv*[fps>30]/wv*)) + ba / (b[fps>30]/b)[height<=720]/(w[fps>30]/w)" # Download the video with the largest resolution no better than 720p, # or the video with the smallest resolution available if there is no such video, # preferring larger framerate for formats with the same resolution $ yt-dlp -S "res:720,fps" # Download the video with smallest resolution no worse than 480p, # or the video with the largest resolution available if there is no such video, # preferring better codec and then larger total bitrate for the same resolution $ yt-dlp -S "+res:480,codec,br" MODIFYING METADATA The metadata obtained by the extractors can be modified by using --parse-metadata and --replace-in-metadata --replace-in-metadata FIELDS REGEX REPLACE is used to replace text in any metadata field using Python regular expression (https://docs.python.org/3/library/re.html#regular-expression-syntax). Backreferences (https://docs.python.org/3/library/re.html?highlight=backreferences#re.sub) can be used in the replace string for advanced use. The general syntax of --parse-metadata FROM:TO is to give the name of a field or an output template to extract data from, and the format to interpret it as, separated by a colon :. Either a Python regular expression (https://docs.python.org/3/library/re.html#regular- expression-syntax) with named capture groups, a single field name, or a similar syntax to the output template (only %(field)s formatting is supported) can be used for TO. The option can be used multiple times to parse and modify various fields. Note that these options preserve their relative order, allowing replacements to be made in parsed fields and viceversa. Also, any field thus created can be used in the output template and will also affect the media file's metadata added when using --embed-metadata. This option also has a few special uses: • You can download an additional URL based on the metadata of the currently downloaded video. To do this, set the field additional_urls to the URL that you want to download. E.g. --parse-metadata "description:(?P<additional_urls>https?://www\.vimeo\.com/\d+)" will download the first vimeo video found in the description • You can use this to change the metadata that is embedded in the media file. To do this, set the value of the corresponding field with a meta_ prefix. For example, any value you set to meta_description field will be added to the description field in the file - you can use this to set a different "description" and "synopsis". To modify the metadata of individual streams, use the meta<n>_ prefix (e.g. meta1_language). Any value set to the meta_ field will overwrite all default values. Note: Metadata modification happens before format selection, post- extraction and other post-processing operations. Some fields may be added or changed during these steps, overriding your changes. For reference, these are the fields yt-dlp adds by default to the file metadata: Metadata fields From ──────────────────────────────────────────────────── title track or title date upload_date description, synopsis description purl, comment webpage_url track track_number artist artist, artists, creator, creators, uploader or uploader_id composer composer or composers genre genre or genres album album album_artist album_artist or album_artists disc disc_number show series season_number season_number episode_id episode or episode_id episode_sort episode_number language of each stream the format's language Note: The file format may not support some of these fields Modifying metadata examples # Interpret the title as "Artist - Title" $ yt-dlp --parse-metadata "title:%(artist)s - %(title)s" # Regex example $ yt-dlp --parse-metadata "description:Artist - (?P<artist>.+)" # Set title as "Series name S01E05" $ yt-dlp --parse-metadata "%(series)s S%(season_number)02dE%(episode_number)02d:%(title)s" # Prioritize uploader as the "artist" field in video metadata $ yt-dlp --parse-metadata "%(uploader|)s:%(meta_artist)s" --embed-metadata # Set "comment" field in video metadata using description instead of webpage_url, # handling multiple lines correctly $ yt-dlp --parse-metadata "description:(?s)(?P<meta_comment>.+)" --embed-metadata # Do not set any "synopsis" in the video metadata $ yt-dlp --parse-metadata ":(?P<meta_synopsis>)" # Remove "formats" field from the infojson by setting it to an empty string $ yt-dlp --parse-metadata "video::(?P<formats>)" --write-info-json # Replace all spaces and "_" in title and uploader with a `-` $ yt-dlp --replace-in-metadata "title,uploader" "[ _]" "-" EXTRACTOR ARGUMENTS Some extractors accept additional arguments which can be passed using --extractor-args KEY:ARGS. ARGS is a ; (semicolon) separated string of ARG=VAL1,VAL2. E.g. --extractor-args "youtube:player-client=android_embedded,web;formats=incomplete" --extractor-args "funimation:version=uncut" Note: In CLI, ARG can use - instead of _; e.g. youtube:player-client" becomes youtube:player_client" The following extractors use this feature: youtube • lang: Prefer translated metadata (title, description etc) of this language code (case-sensitive). By default, the video primary language metadata is preferred, with a fallback to en translated. See youtube.py (https://github.com/yt-dlp/yt- dlp/blob/c26f9b991a0681fd3ea548d535919cec1fbbd430/yt_dlp/extractor/youtube.py#L381-L390) for list of supported content language codes • skip: One or more of hls, dash or translated_subs to skip extraction of the m3u8 manifests, dash manifests and auto-translated subtitles (https://github.com/yt-dlp/yt- dlp/issues/4090#issuecomment-1158102032) respectively • player_client: Clients to extract video data from. The main clients are web, ios and android, with variants _music, _embedded, _embedscreen, _creator (e.g. web_embedded); and mediaconnect, mweb, mweb_embedscreen and tv_embedded (agegate bypass) with no variants. By default, ios,web is used, but tv_embedded and creator variants are added as required for age-gated videos. Similarly, the music variants are added for music.youtube.com urls. The android clients will always be given lowest priority since their formats are broken. You can use all to use all the clients, and default for the default clients. • player_skip: Skip some network requests that are generally needed for robust extraction. One or more of configs (skip client configs), webpage (skip initial webpage), js (skip js player). While these options can help reduce the number of requests needed or avoid some rate-limiting, they could cause some issues. See #860 (https://github.com/yt-dlp/yt-dlp/pull/860) for more details • player_params: YouTube player parameters to use for player requests. Will overwrite any default ones set by yt-dlp. • comment_sort: top or new (default) - choose comment sorting mode (on YouTube's side) • max_comments: Limit the amount of comments to gather. Comma- separated list of integers representing max-comments,max-parents,max-replies,max-replies-per-thread. Default is all,all,all,all • E.g. all,all,1000,10 will get a maximum of 1000 replies total, with up to 10 replies per thread. 1000,all,100 will get a maximum of 1000 comments, with a maximum of 100 replies total • formats: Change the types of formats to return. dashy (convert HTTP to DASH), duplicate (identical content but different URLs or protocol; includes dashy), incomplete (cannot be downloaded completely - live dash and post-live m3u8) • innertube_host: Innertube API host to use for all API requests; e.g. studio.youtube.com, youtubei.googleapis.com. Note that cookies exported from one subdomain will not work on others • innertube_key: Innertube API key to use for all API requests • raise_incomplete_data: Incomplete Data Received raises an error instead of reporting a warning youtubetab (YouTube playlists, channels, feeds, etc.) • skip: One or more of webpage (skip initial webpage download), authcheck (allow the download of playlists requiring authentication when no initial webpage is downloaded. This may cause unwanted behavior, see #1122 (https://github.com/yt-dlp/yt-dlp/pull/1122) for more details) • approximate_date: Extract approximate upload_date and timestamp in flat-playlist. This may cause date-based filters to be slightly off generic • fragment_query: Passthrough any query in mpd/m3u8 manifest URLs to their fragments if no value is provided, or else apply the query string given as fragment_query=VALUE. Note that if the stream has an HLS AES-128 key, then the query parameters will be passed to the key URI as well, unless the key_query extractor-arg is passed, or unless an external key URI is provided via the hls_key extractor-arg. Does not apply to ffmpeg • variant_query: Passthrough the master m3u8 URL query to its variant playlist URLs if no value is provided, or else apply the query string given as variant_query=VALUE • key_query: Passthrough the master m3u8 URL query to its HLS AES-128 decryption key URI if no value is provided, or else apply the query string given as key_query=VALUE. Note that this will have no effect if the key URI is provided via the hls_key extractor-arg. Does not apply to ffmpeg • hls_key: An HLS AES-128 key URI or key (as hex), and optionally the IV (as hex), in the form of (URI|KEY)[,IV]; e.g. generic:hls_key=ABCDEF1234567980,0xFEDCBA0987654321. Passing any of these values will force usage of the native HLS downloader and override the corresponding values found in the m3u8 playlist • is_live: Bypass live HLS detection and manually set live_status - a value of false will set not_live, any other value (or no value) will set is_live funimation • language: Audio languages to extract, e.g. funimation:language=english,japanese • version: The video version to extract - uncut or simulcast crunchyrollbeta (Crunchyroll) • hardsub: One or more hardsub versions to extract (in order of preference), or all (default: None = no hardsubs will be extracted), e.g. crunchyrollbeta:hardsub=en-US,de-DE vikichannel • video_types: Types of videos to download - one or more of episodes, movies, clips, trailers niconico • segment_duration: Segment duration in milliseconds for HLS-DMC formats. Use it at your own risk since this feature may result in your account termination. youtubewebarchive • check_all: Try to check more at the cost of more requests. One or more of thumbnails, captures gamejolt • comment_sort: hot (default), you (cookies needed), top, new - choose comment sorting mode (on GameJolt's side) hotstar • res: resolution to ignore - one or more of sd, hd, fhd • vcodec: vcodec to ignore - one or more of h264, h265, dvh265 • dr: dynamic range to ignore - one or more of sdr, hdr10, dv niconicochannelplus • max_comments: Maximum number of comments to extract - default is 120 tiktok • api_hostname: Hostname to use for mobile API calls, e.g. api22-normal-c-alisg.tiktokv.com • app_name: Default app name to use with mobile API calls, e.g. trill • app_version: Default app version to use with mobile API calls - should be set along with manifest_app_version, e.g. 34.1.2 • manifest_app_version: Default numeric app version to use with mobile API calls, e.g. 2023401020 • aid: Default app ID to use with mobile API calls, e.g. 1180 • app_info: Enable mobile API extraction with one or more app info strings in the format of <iid>/[app_name]/[app_version]/[manifest_app_version]/[aid], where iid is the unique app install ID. iid is the only required value; all other values and their / separators can be omitted, e.g. tiktok:app_info=1234567890123456789 or tiktok:app_info=123,456/trill///1180,789//34.0.1/340001 • device_id: Enable mobile API extraction with a genuine device ID to be used with mobile API calls. Default is a random 19-digit string rokfinchannel • tab: Which tab to download - one of new, top, videos, podcasts, streams, stacks twitter • api: Select one of graphql (default), legacy or syndication as the API for tweet extraction. Has no effect if logged in stacommu, wrestleuniverse • device_id: UUID value assigned by the website and used to enforce device limits for paid livestream content. Can be found in browser local storage twitch • client_id: Client ID value to be sent with GraphQL requests, e.g. twitch:client_id=kimne78kx3ncx6brgo4mv6wki5h1ko nhkradirulive (NHK ら • area: Which regional variation to extract. Valid areas are: sapporo, sendai, tokyo, nagoya, osaka, hiroshima, matsuyama, fukuoka. Defaults to tokyo nflplusreplay • type: Type(s) of game replays to extract. Valid types are: full_game, full_game_spanish, condensed_game and all_22. You can use all to extract all available replay types, which is the default jiocinema • refresh_token: The refreshToken UUID from browser local storage can be passed to extend the life of your login session when logging in with token as username and the accessToken from browser local storage as password jiosaavn • bitrate: Audio bitrates to request. One or more of 16, 32, 64, 128, 320. Default is 128,320 afreecatvlive • cdn: One or more CDN IDs to use with the API call for stream URLs, e.g. gcp_cdn, gs_cdn_pc_app, gs_cdn_mobile_web, gs_cdn_pc_web soundcloud • formats: Formats to request from the API. Requested values should be in the format of {protocol}_{extension} (omitting the bitrate), e.g. hls_opus,http_aac. The * character functions as a wildcard, e.g. *_mp3, and can be passed by itself to request all formats. Known protocols include http, hls and hls-aes; known extensions include aac, opus and mp3. Original download formats are always extracted. Default is http_aac,hls_aac,http_opus,hls_opus,http_mp3,hls_mp3 orfon (orf:on) • prefer_segments_playlist: Prefer a playlist of program segments instead of a single complete video when available. If individual segments are desired, use --concat-playlist never --extractor-args "orfon:prefer_segments_playlist" bilibili • prefer_multi_flv: Prefer extracting flv formats over mp4 for older videos that still provide legacy formats digitalconcerthall • prefer_combined_hls: Prefer extracting combined/pre-merged video and audio HLS formats. This will exclude 4K/HEVC video and lossless/FLAC audio formats, which are only available as split video/audio HLS formats Note: These options may be changed/removed in the future without concern for backward compatibility INSTALLATION You can install yt-dlp using the binaries, pip (https://pypi.org/project/yt-dlp) or one using a third-party package manager. See the wiki (https://github.com/yt-dlp/yt- dlp/wiki/Installation) for detailed instructions Note: The manpages, shell completion (autocomplete) files etc. are available inside the source tarball (https://github.com/yt-dlp/yt- dlp/releases/latest/download/yt-dlp.tar.gz) UPDATE You can use yt-dlp -U to update if you are using the release binaries If you installed with pip (https://github.com/yt-dlp/yt- dlp/wiki/Installation#with-pip), simply re-run the same command that was used to install the program For other third-party package managers, see the wiki (https://github.com/yt-dlp/yt-dlp/wiki/Installation#third-party- package-managers) or refer to their documentation There are currently three release channels for binaries: stable, nightly and master. • stable is the default channel, and many of its changes have been tested by users of the nightly and master channels. • The nightly channel has releases scheduled to build every day around midnight UTC, for a snapshot of the project's new patches and changes. This is the recommended channel for regular users of yt- dlp. The nightly releases are available from yt-dlp/yt-dlp-nightly- builds (https://github.com/yt-dlp/yt-dlp-nightly-builds/releases) or as development releases of the yt-dlp PyPI package (which can be installed with pip's --pre flag). • The master channel features releases that are built after each push to the master branch, and these will have the very latest fixes and additions, but may also be more prone to regressions. They are available from yt-dlp/yt-dlp-master-builds (https://github.com/yt- dlp/yt-dlp-master-builds/releases). When using --update/-U, a release binary will only update to its current channel. --update-to CHANNEL can be used to switch to a different channel when a newer version is available. --update-to [CHANNEL@]TAG can also be used to upgrade or downgrade to specific tags from a channel. You may also use --update-to <repository> (<owner>/<repository>) to update to a channel on a completely different repository. Be careful with what repository you are updating to though, there is no verification done for binaries from different repositories. Example usage: • yt-dlp --update-to master switch to the master channel and update to its latest release • yt-dlp --update-to stable@2023.07.06 upgrade/downgrade to release to stable channel tag 2023.07.06 • yt-dlp --update-to 2023.10.07 upgrade/downgrade to tag 2023.10.07 if it exists on the current channel • yt-dlp --update-to example/yt-dlp@2023.09.24 upgrade/downgrade to the release from the example/yt-dlp repository, tag 2023.09.24 Important: Any user experiencing an issue with the stable release should install or update to the nightly release before submitting a bug report: # To update to nightly from stable executable/binary: yt-dlp --update-to nightly # To install nightly with pip: python3 -m pip install -U --pre "yt-dlp[default]" DEPENDENCIES Python versions 3.8+ (CPython and PyPy) are supported. Other versions and implementations may or may not work correctly. While all the other dependencies are optional, ffmpeg and ffprobe are highly recommended Strongly recommended • ffmpeg and ffprobe (https://www.ffmpeg.org) - Required for merging separate video and audio files, as well as for various post- processing tasks. License depends on the build (https://www.ffmpeg.org/legal.html) There are bugs in ffmpeg that cause various issues when used alongside yt-dlp. Since ffmpeg is such an important dependency, we provide custom builds (https://github.com/yt-dlp/FFmpeg- Builds#ffmpeg-static-auto-builds) with patches for some of these issues at yt-dlp/FFmpeg-Builds (https://github.com/yt-dlp/FFmpeg- Builds). See the readme (https://github.com/yt-dlp/FFmpeg- Builds#patches-applied) for details on the specific issues solved by these builds Important: What you need is ffmpeg binary, NOT the Python package of the same name (https://pypi.org/project/ffmpeg) Networking • certifi (https://github.com/certifi/python-certifi)* - Provides Mozilla's root certificate bundle. Licensed under MPLv2 (https://github.com/certifi/python-certifi/blob/master/LICENSE) • brotli (https://github.com/google/brotli)* or brotlicffi (https://github.com/python-hyper/brotlicffi) - Brotli (https://en.wikipedia.org/wiki/Brotli) content encoding support. Both licensed under MIT 1 (https://github.com/google/brotli/blob/master/LICENSE) 2 (https://github.com/python-hyper/brotlicffi/blob/master/LICENSE) • websockets (https://github.com/aaugustin/websockets)* - For downloading over websocket. Licensed under BSD-3-Clause (https://github.com/aaugustin/websockets/blob/main/LICENSE) • requests (https://github.com/psf/requests)* - HTTP library. For HTTPS proxy and persistent connections support. Licensed under Apache-2.0 (https://github.com/psf/requests/blob/main/LICENSE) Impersonation The following provide support for impersonating browser requests. This may be required for some sites that employ TLS fingerprinting. • curl_cffi (https://github.com/yifeikong/curl_cffi) (recommended) - Python binding for curl-impersonate (https://github.com/lwthiker/curl-impersonate). Provides impersonation targets for Chrome, Edge and Safari. Licensed under MIT (https://github.com/yifeikong/curl_cffi/blob/main/LICENSE) • Can be installed with the curl-cffi group, e.g. pip install "yt-dlp[default,curl-cffi]" • Currently included in yt-dlp.exe, yt-dlp_linux and yt-dlp_macos builds Metadata • mutagen (https://github.com/quodlibet/mutagen)* - For --embed-thumbnail in certain formats. Licensed under GPLv2+ (https://github.com/quodlibet/mutagen/blob/master/COPYING) • AtomicParsley (https://github.com/wez/atomicparsley) - For --embed-thumbnail in mp4/m4a files when mutagen/ffmpeg cannot. Licensed under GPLv2+ (https://github.com/wez/atomicparsley/blob/master/COPYING) • xattr (https://github.com/xattr/xattr), pyxattr (https://github.com/iustin/pyxattr) or setfattr (http://savannah.nongnu.org/projects/attr) - For writing xattr metadata (--xattr) on Mac and BSD. Licensed under MIT (https://github.com/xattr/xattr/blob/master/LICENSE.txt), LGPL2.1 (https://github.com/iustin/pyxattr/blob/master/COPYING) and GPLv2+ (http://git.savannah.nongnu.org/cgit/attr.git/tree/doc/COPYING) respectively Misc • pycryptodomex (https://github.com/Legrandin/pycryptodome)* - For decrypting AES-128 HLS streams and various other data. Licensed under BSD-2-Clause (https://github.com/Legrandin/pycryptodome/blob/master/LICENSE.rst) • phantomjs (https://github.com/ariya/phantomjs) - Used in extractors where javascript needs to be run. Licensed under BSD-3-Clause (https://github.com/ariya/phantomjs/blob/master/LICENSE.BSD) • secretstorage (https://github.com/mitya57/secretstorage)* - For --cookies-from-browser to access the Gnome keyring while decrypting cookies of Chromium-based browsers on Linux. Licensed under BSD-3-Clause (https://github.com/mitya57/secretstorage/blob/master/LICENSE) • Any external downloader that you want to use with --downloader Deprecated • avconv and avprobe (https://www.libav.org) - Now deprecated alternative to ffmpeg. License depends on the build (https://libav.org/legal) • sponskrub (https://github.com/faissaloo/SponSkrub) - For using the now deprecated sponskrub options. Licensed under GPLv3+ (https://github.com/faissaloo/SponSkrub/blob/master/LICENCE.md) • rtmpdump (http://rtmpdump.mplayerhq.hu) - For downloading rtmp streams. ffmpeg can be used instead with --downloader ffmpeg. Licensed under GPLv2+ (http://rtmpdump.mplayerhq.hu) • mplayer (http://mplayerhq.hu/design7/info.html) or mpv (https://mpv.io) - For downloading rstp/mms streams. ffmpeg can be used instead with --downloader ffmpeg. Licensed under GPLv2+ (https://github.com/mpv-player/mpv/blob/master/Copyright) To use or redistribute the dependencies, you must agree to their respective licensing terms. The standalone release binaries are built with the Python interpreter and the packages marked with * included. If you do not have the necessary dependencies for a task you are attempting, yt-dlp will warn you. All the currently available dependencies are visible at the top of the --verbose output COMPILE Standalone PyInstaller Builds To build the standalone executable, you must have Python and pyinstaller (plus any of yt-dlp's optional dependencies if needed). The executable will be built for the same CPU architecture as the Python used. You can run the following commands: python3 devscripts/install_deps.py --include pyinstaller python3 devscripts/make_lazy_extractors.py python3 -m bundle.pyinstaller On some systems, you may need to use py or python instead of python3. python -m bundle.pyinstaller accepts any arguments that can be passed to pyinstaller, such as --onefile/-F or --onedir/-D, which is further documented here (https://pyinstaller.org/en/stable/usage.html#what-to- generate). Note: Pyinstaller versions below 4.4 do not support (https://github.com/pyinstaller/pyinstaller#requirements-and-tested- platforms) Python installed from the Windows store without using a virtual environment. Important: Running pyinstaller directly instead of using python -m bundle.pyinstaller is not officially supported. This may or may not work correctly. Platform-independent Binary (UNIX) You will need the build tools python (3.8+), zip, make (GNU), pandoc* and pytest*. After installing these, simply run make. You can also run make yt-dlp instead to compile only the binary without updating any of the additional files. (The build tools marked with * are not needed for this) Standalone Py2Exe Builds (Windows) While we provide the option to build with py2exe (https://www.py2exe.org), it is recommended to build using PyInstaller instead since the py2exe builds cannot contain pycryptodomex/certifi/requests and need VC++14 on the target computer to run. If you wish to build it anyway, install Python (if it is not already installed) and you can run the following commands: py devscripts/install_deps.py --include py2exe py devscripts/make_lazy_extractors.py py -m bundle.py2exe Related scripts • devscripts/install_deps.py - Install dependencies for yt-dlp. • devscripts/update-version.py - Update the version number based on the current date. • devscripts/set-variant.py - Set the build variant of the executable. • devscripts/make_changelog.py - Create a markdown changelog using short commit messages and update CONTRIBUTORS file. • devscripts/make_lazy_extractors.py - Create lazy extractors. Running this before building the binaries (any variant) will improve their startup performance. Set the environment variable YTDLP_NO_LAZY_EXTRACTORS=1 if you wish to forcefully disable lazy extractor loading. Note: See their --help for more info. Forking the project If you fork the project on GitHub, you can run your fork's build workflow to automatically build the selected version(s) as artifacts. Alternatively, you can run the release workflow or enable the nightly workflow to create full (pre-)releases. PLUGINS Note that all plugins are imported even if not invoked, and that there are no checks performed on plugin code. Use plugins at your own risk and only if you trust the code! Plugins can be of <type>s extractor or postprocessor. - Extractor plugins do not need to be enabled from the CLI and are automatically invoked when the input URL is suitable for it. - Extractor plugins take priority over built-in extractors. - Postprocessor plugins can be invoked using --use-postprocessor NAME. Plugins are loaded from the namespace packages yt_dlp_plugins.extractor and yt_dlp_plugins.postprocessor. In other words, the file structure on the disk looks something like: yt_dlp_plugins/ extractor/ myplugin.py postprocessor/ myplugin.py yt-dlp looks for these yt_dlp_plugins namespace folders in many locations (see below) and loads in plugins from all of them. See the wiki for some known plugins (https://github.com/yt-dlp/yt- dlp/wiki/Plugins) Installing Plugins Plugins can be installed using various methods and locations. 1. Configuration directories: Plugin packages (containing a yt_dlp_plugins namespace folder) can be dropped into the following standard configuration locations: • User Plugins • ${XDG_CONFIG_HOME}/yt-dlp/plugins/<package name>/yt_dlp_plugins/ (recommended on Linux/macOS) • ${XDG_CONFIG_HOME}/yt-dlp-plugins/<package name>/yt_dlp_plugins/ • ${APPDATA}/yt-dlp/plugins/<package name>/yt_dlp_plugins/ (recommended on Windows) • ${APPDATA}/yt-dlp-plugins/<package name>/yt_dlp_plugins/ • ~/.yt-dlp/plugins/<package name>/yt_dlp_plugins/ • ~/yt-dlp-plugins/<package name>/yt_dlp_plugins/ • System Plugins • /etc/yt-dlp/plugins/<package name>/yt_dlp_plugins/ • /etc/yt-dlp-plugins/<package name>/yt_dlp_plugins/ 2. Executable location: Plugin packages can similarly be installed in a yt-dlp-plugins directory under the executable location (recommended for portable installations): • Binary: where <root-dir>/yt-dlp.exe, <root-dir>/yt-dlp-plugins/<package name>/yt_dlp_plugins/ • Source: where <root-dir>/yt_dlp/__main__.py, <root-dir>/yt-dlp-plugins/<package name>/yt_dlp_plugins/ 3. pip and other locations in PYTHONPATH • Plugin packages can be installed and managed using pip. See yt- dlp-sample-plugins (https://github.com/yt-dlp/yt-dlp-sample- plugins) for an example. • Note: plugin files between plugin packages installed with pip must have unique filenames. • Any path in PYTHONPATH is searched in for the yt_dlp_plugins namespace folder. • Note: This does not apply for Pyinstaller/py2exe builds. .zip, .egg and .whl archives containing a yt_dlp_plugins namespace folder in their root are also supported as plugin packages. • e.g. ${XDG_CONFIG_HOME}/yt-dlp/plugins/mypluginpkg.zip where mypluginpkg.zip contains yt_dlp_plugins/<type>/myplugin.py Run yt-dlp with --verbose to check if the plugin has been loaded. Developing Plugins See the yt-dlp-sample-plugins (https://github.com/yt-dlp/yt-dlp-sample- plugins) repo for a template plugin package and the Plugin Development (https://github.com/yt-dlp/yt-dlp/wiki/Plugin-Development) section of the wiki for a plugin development guide. All public classes with a name ending in IE/PP are imported from each file for extractors and postprocessors respectively. This respects underscore prefix (e.g. _MyBasePluginIE is private) and __all__. Modules can similarly be excluded by prefixing the module name with an underscore (e.g. _myplugin.py). To replace an existing extractor with a subclass of one, set the plugin_name class keyword argument (e.g. class MyPluginIE(ABuiltInIE, plugin_name='myplugin') will replace ABuiltInIE with MyPluginIE). Since the extractor replaces the parent, you should exclude the subclass extractor from being imported separately by making it private using one of the methods described above. If you are a plugin author, add yt-dlp-plugins (https://github.com/topics/yt-dlp-plugins) as a topic to your repository for discoverability. See the Developer Instructions (https://github.com/yt-dlp/yt- dlp/blob/master/CONTRIBUTING.md#developer-instructions) on how to write and test an extractor. EMBEDDING YT-DLP yt-dlp makes the best effort to be a good command-line program, and thus should be callable from any programming language. Your program should avoid parsing the normal stdout since they may change in future versions. Instead, they should use options such as -J, --print, --progress-template, --exec etc to create console output that you can reliably reproduce and parse. From a Python program, you can embed yt-dlp in a more powerful fashion, like this: from yt_dlp import YoutubeDL URLS = ['https://www.youtube.com/watch?v=BaW_jenozKc'] with YoutubeDL() as ydl: ydl.download(URLS) Most likely, you'll want to use various options. For a list of options available, have a look at yt_dlp/YoutubeDL.py or help(yt_dlp.YoutubeDL) in a Python shell. If you are already familiar with the CLI, you can use devscripts/cli_to_api.py (https://github.com/yt-dlp/yt-dlp/blob/master/devscripts/cli_to_api.py) to translate any CLI switches to YoutubeDL params. Tip: If you are porting your code from youtube-dl to yt-dlp, one important point to look out for is that we do not guarantee the return value of YoutubeDL.extract_info to be json serializable, or even be a dictionary. It will be dictionary-like, but if you want to ensure it is a serializable dictionary, pass it through YoutubeDL.sanitize_info as shown in the example below Embedding examples Extracting information import json import yt_dlp URL = 'https://www.youtube.com/watch?v=BaW_jenozKc' # ℹ️ See help(yt_dlp.YoutubeDL) for a list of available options and public functions ydl_opts = {} with yt_dlp.YoutubeDL(ydl_opts) as ydl: info = ydl.extract_info(URL, download=False) # ℹ️ ydl.sanitize_info makes the info json-serializable print(json.dumps(ydl.sanitize_info(info))) Download using an info-json import yt_dlp INFO_FILE = 'path/to/video.info.json' with yt_dlp.YoutubeDL() as ydl: error_code = ydl.download_with_info_file(INFO_FILE) print('Some videos failed to download' if error_code else 'All videos successfully downloaded') Extract audio import yt_dlp URLS = ['https://www.youtube.com/watch?v=BaW_jenozKc'] ydl_opts = { 'format': 'm4a/bestaudio/best', # ℹ️ See help(yt_dlp.postprocessor) for a list of available Postprocessors and their arguments 'postprocessors': [{ # Extract audio using ffmpeg 'key': 'FFmpegExtractAudio', 'preferredcodec': 'm4a', }] } with yt_dlp.YoutubeDL(ydl_opts) as ydl: error_code = ydl.download(URLS) Filter videos import yt_dlp URLS = ['https://www.youtube.com/watch?v=BaW_jenozKc'] def longer_than_a_minute(info, *, incomplete): """Download only videos longer than a minute (or with unknown duration)""" duration = info.get('duration') if duration and duration < 60: return 'The video is too short' ydl_opts = { 'match_filter': longer_than_a_minute, } with yt_dlp.YoutubeDL(ydl_opts) as ydl: error_code = ydl.download(URLS) Adding logger and progress hook import yt_dlp URLS = ['https://www.youtube.com/watch?v=BaW_jenozKc'] class MyLogger: def debug(self, msg): # For compatibility with youtube-dl, both debug and info are passed into debug # You can distinguish them by the prefix '[debug] ' if msg.startswith('[debug] '): pass else: self.info(msg) def info(self, msg): pass def warning(self, msg): pass def error(self, msg): print(msg) # ℹ️ See "progress_hooks" in help(yt_dlp.YoutubeDL) def my_hook(d): if d['status'] == 'finished': print('Done downloading, now post-processing ...') ydl_opts = { 'logger': MyLogger(), 'progress_hooks': [my_hook], } with yt_dlp.YoutubeDL(ydl_opts) as ydl: ydl.download(URLS) Add a custom PostProcessor import yt_dlp URLS = ['https://www.youtube.com/watch?v=BaW_jenozKc'] # ℹ️ See help(yt_dlp.postprocessor.PostProcessor) class MyCustomPP(yt_dlp.postprocessor.PostProcessor): def run(self, info): self.to_screen('Doing stuff') return [], info with yt_dlp.YoutubeDL() as ydl: # ℹ️ "when" can take any value in yt_dlp.utils.POSTPROCESS_WHEN ydl.add_post_processor(MyCustomPP(), when='pre_process') ydl.download(URLS) Use a custom format selector import yt_dlp URLS = ['https://www.youtube.com/watch?v=BaW_jenozKc'] def format_selector(ctx): """ Select the best video and the best audio that won't result in an mkv. NOTE: This is just an example and does not handle all cases """ # formats are already sorted worst to best formats = ctx.get('formats')[::-1] # acodec='none' means there is no audio best_video = next(f for f in formats if f['vcodec'] != 'none' and f['acodec'] == 'none') # find compatible audio extension audio_ext = {'mp4': 'm4a', 'webm': 'webm'}[best_video['ext']] # vcodec='none' means there is no video best_audio = next(f for f in formats if ( f['acodec'] != 'none' and f['vcodec'] == 'none' and f['ext'] == audio_ext)) # These are the minimum required fields for a merged format yield { 'format_id': f'{best_video["format_id"]}+{best_audio["format_id"]}', 'ext': best_video['ext'], 'requested_formats': [best_video, best_audio], # Must be + separated list of protocols 'protocol': f'{best_video["protocol"]}+{best_audio["protocol"]}' } ydl_opts = { 'format': format_selector, } with yt_dlp.YoutubeDL(ydl_opts) as ydl: ydl.download(URLS) CHANGES FROM YOUTUBE-DL New features • Forked from yt-dlc@f9401f2 (https://github.com/blackjack4494/yt- dlc/commit/f9401f2a91987068139c5f757b12fc711d4c0cee) and merged with youtube-dl@a08f2b7 (https://github.com/ytdl-org/youtube- dl/commit/a08f2b7e4567cdc50c0614ee0a4ffdff49b8b6e6) (exceptions (https://github.com/yt-dlp/yt-dlp/issues/21)) • SponsorBlock Integration: You can mark/remove sponsor sections in YouTube videos by utilizing the SponsorBlock (https://sponsor.ajay.app) API • Format Sorting: The default format sorting options have been changed so that higher resolution and better codecs will be now preferred instead of simply using larger bitrate. Furthermore, you can now specify the sort order using -S. This allows for much easier format selection than what is possible by simply using --format (examples) • Merged with animelover1984/youtube-dl: You get most of the features and improvements from animelover1984/youtube-dl (https://github.com/animelover1984/youtube-dl) including --write-comments, BiliBiliSearch, BilibiliChannel, Embedding thumbnail in mp4/ogg/opus, playlist infojson etc. Note that NicoNico livestreams are not available. See #31 (https://github.com/yt- dlp/yt-dlp/pull/31) for details. • YouTube improvements: • Supports Clips, Stories (ytstories:<channel UCID>), Search (including filters)*, YouTube Music Search, Channel-specific search, Search prefixes (ytsearch:, ytsearchdate:)*, Mixes, and Feeds (:ytfav, :ytwatchlater, :ytsubs, :ythistory, :ytrec, :ytnotif) • Fix for n-sig based throttling (https://github.com/ytdl- org/youtube-dl/issues/29326) * • Supports some (but not all) age-gated content without cookies • Download livestreams from the start using --live-from-start (experimental) • Channel URLs download all uploads of the channel, including shorts and live • Cookies from browser: Cookies can be automatically extracted from all major web browsers using --cookies-from-browser BROWSER[+KEYRING][:PROFILE][::CONTAINER] • Download time range: Videos can be downloaded partially based on either timestamps or chapters using --download-sections • Split video by chapters: Videos can be split into multiple files based on chapters using --split-chapters • Multi-threaded fragment downloads: Download multiple fragments of m3u8/mpd videos in parallel. Use --concurrent-fragments (-N) option to set the number of threads used • Aria2c with HLS/DASH: You can use aria2c as the external downloader for DASH(mpd) and HLS(m3u8) formats • New and fixed extractors: Many new extractors have been added and a lot of existing ones have been fixed. See the changelog or the list of supported sites • New MSOs: Philo, Spectrum, SlingTV, Cablevision, RCN etc. • Subtitle extraction from manifests: Subtitles can be extracted from streaming media manifests. See commit/be6202f (https://github.com/yt-dlp/yt- dlp/commit/be6202f12b97858b9d716e608394b51065d0419f) for details • Multiple paths and output templates: You can give different output templates and download paths for different types of files. You can also set a temporary path where intermediary files are downloaded to using --paths (-P) • Portable Configuration: Configuration files are automatically loaded from the home and root directories. See CONFIGURATION for details • Output template improvements: Output templates can now have date-time formatting, numeric offsets, object traversal etc. See output template for details. Even more advanced operations can also be done with the help of --parse-metadata and --replace-in-metadata • Other new options: Many new options have been added such as --alias, --print, --concat-playlist, --wait-for-video, --retry-sleep, --sleep-requests, --convert-thumbnails, --force-download-archive, --force-overwrites, --break-match-filter etc • Improvements: Regex and other operators in --format/--match-filter, multiple --postprocessor-args and --downloader-args, faster archive checking, more format selection options, merge multi-video/audio, multiple --config-locations, --exec at different stages, etc • Plugins: Extractors and PostProcessors can be loaded from an external file. See plugins for details • Self updater: The releases can be updated using yt-dlp -U, and downgraded using --update-to if required • Automated builds: Nightly/master builds can be used with --update-to nightly and --update-to master See changelog or commits (https://github.com/yt-dlp/yt-dlp/commits) for the full list of changes Features marked with a * have been back-ported to youtube-dl Differences in default behavior Some of yt-dlp's default options are different from that of youtube-dl and youtube-dlc: • yt-dlp supports only Python 3.8+, and may remove support for more versions as they become EOL (https://devguide.python.org/versions/#python-release-cycle); while youtube-dl still supports Python 2.6+ and 3.2+ (https://github.com/ytdl-org/youtube- dl/issues/30568#issue-1118238743) • The options --auto-number (-A), --title (-t) and --literal (-l), no longer work. See removed options for details • avconv is not supported as an alternative to ffmpeg • yt-dlp stores config files in slightly different locations to youtube-dl. See CONFIGURATION for a list of correct locations • The default output template is %(title)s [%(id)s].%(ext)s. There is no real reason for this change. This was changed before yt-dlp was ever made public and now there are no plans to change it back to %(title)s-%(id)s.%(ext)s. Instead, you may use --compat-options filename • The default format sorting is different from youtube-dl and prefers higher resolution and better codecs rather than higher bitrates. You can use the --format-sort option to change this to any order you prefer, or use --compat-options format-sort to use youtube-dl's sorting order • The default format selector is bv*+ba/b. This means that if a combined video + audio format that is better than the best video-only format is found, the former will be preferred. Use -f bv+ba/b or --compat-options format-spec to revert this • Unlike youtube-dlc, yt-dlp does not allow merging multiple audio/video streams into one file by default (since this conflicts with the use of -f bv*+ba). If needed, this feature must be enabled using --audio-multistreams and --video-multistreams. You can also use --compat-options multistreams to enable both • --no-abort-on-error is enabled by default. Use --abort-on-error or --compat-options abort-on-error to abort on errors instead • When writing metadata files such as thumbnails, description or infojson, the same information (if available) is also written for playlists. Use --no-write-playlist-metafiles or --compat-options no-playlist-metafiles to not write these files • --add-metadata attaches the infojson to mkv files in addition to writing the metadata when used with --write-info-json. Use --no-embed-info-json or --compat-options no-attach-info-json to revert this • Some metadata are embedded into different fields when using --add-metadata as compared to youtube-dl. Most notably, comment field contains the webpage_url and synopsis contains the description. You can use --parse-metadata to modify this to your liking or use --compat-options embed-metadata to revert this • playlist_index behaves differently when used with options like --playlist-reverse and --playlist-items. See #302 (https://github.com/yt-dlp/yt-dlp/issues/302) for details. You can use --compat-options playlist-index if you want to keep the earlier behavior • The output of -F is listed in a new format. Use --compat-options list-formats to revert this • Live chats (if available) are considered as subtitles. Use --sub-langs all,-live_chat to download all subtitles except live chat. You can also use --compat-options no-live-chat to prevent any live chat/danmaku from downloading • YouTube channel URLs download all uploads of the channel. To download only the videos in a specific tab, pass the tab's URL. If the channel does not show the requested tab, an error will be raised. Also, /live URLs raise an error if there are no live videos instead of silently downloading the entire channel. You may use --compat-options no-youtube-channel-redirect to revert all these redirections • Unavailable videos are also listed for YouTube playlists. Use --compat-options no-youtube-unavailable-videos to remove this • The upload dates extracted from YouTube are in UTC when available (https://github.com/yt-dlp/yt- dlp/blob/89e4d86171c7b7c997c77d4714542e0383bf0db0/yt_dlp/extractor/youtube.py#L3898-L3900). Use --compat-options no-youtube-prefer-utc-upload-date to prefer the non-UTC upload date. • If ffmpeg is used as the downloader, the downloading and merging of formats happen in a single step when possible. Use --compat-options no-direct-merge to revert this • Thumbnail embedding in mp4 is done with mutagen if possible. Use --compat-options embed-thumbnail-atomicparsley to force the use of AtomicParsley instead • Some internal metadata such as filenames are removed by default from the infojson. Use --no-clean-infojson or --compat-options no-clean-infojson to revert this • When --embed-subs and --write-subs are used together, the subtitles are written to disk and also embedded in the media file. You can use just --embed-subs to embed the subs and automatically delete the separate file. See #630 (comment) (https://github.com/yt-dlp/yt- dlp/issues/630#issuecomment-893659460) for more info. --compat-options no-keep-subs can be used to revert this • certifi will be used for SSL root certificates, if installed. If you want to use system certificates (e.g. self-signed), use --compat-options no-certifi • yt-dlp's sanitization of invalid characters in filenames is different/smarter than in youtube-dl. You can use --compat-options filename-sanitization to revert to youtube-dl's behavior • [STRIKEOUT:yt-dlp tries to parse the external downloader outputs into the standard progress output if possible (Currently implemented: aria2c (https://github.com/yt-dlp/yt-dlp/issues/5931)). You can use --compat-options no-external-downloader-progress to get the downloader output as-is] • yt-dlp versions between 2021.09.01 and 2023.01.02 applies --match-filter to nested playlists. This was an unintentional side- effect of 8f18ac (https://github.com/yt-dlp/yt- dlp/commit/8f18aca8717bb0dd49054555af8d386e5eda3a88) and is fixed in d7b460 (https://github.com/yt-dlp/yt- dlp/commit/d7b460d0e5fc710950582baed2e3fc616ed98a80). Use --compat-options playlist-match-filter to revert this • yt-dlp versions between 2021.11.10 and 2023.06.21 estimated filesize_approx values for fragmented/manifest formats. This was added for convenience in f2fe69 (https://github.com/yt-dlp/yt- dlp/commit/f2fe69c7b0d208bdb1f6292b4ae92bc1e1a7444a), but was reverted in 0dff8e (https://github.com/yt-dlp/yt- dlp/commit/0dff8e4d1e6e9fb938f4256ea9af7d81f42fd54f) due to the potentially extreme inaccuracy of the estimated values. Use --compat-options manifest-filesize-approx to keep extracting the estimated values • yt-dlp uses modern http client backends such as requests. Use --compat-options prefer-legacy-http-handler to prefer the legacy http handler (urllib) to be used for standard http requests. • The sub-modules swfinterp, casefold are removed. • Passing --simulate (or calling extract_info with download=False) no longer alters the default format selection. See #9843 (https://github.com/yt-dlp/yt-dlp/issues/9843) for details. For ease of use, a few more compat options are available: • --compat-options all: Use all compat options (Do NOT use this!) • --compat-options youtube-dl: Same as --compat-options all,-multistreams,-playlist-match-filter,-manifest-filesize-approx,-allow-unsafe-ext • --compat-options youtube-dlc: Same as --compat-options all,-no-live-chat,-no-youtube-channel-redirect,-playlist-match-filter,-manifest-filesize-approx,-allow-unsafe-ext • --compat-options 2021: Same as --compat-options 2022,no-certifi,filename-sanitization,no-youtube-prefer-utc-upload-date • --compat-options 2022: Same as --compat-options 2023,playlist-match-filter,no-external-downloader-progress,prefer-legacy-http-handler,manifest-filesize-approx • --compat-options 2023: Currently does nothing. Use this to enable all future compat options The following compat options restore vulnerable behavior from before security patches: • --compat-options allow-unsafe-ext: Allow files with any extension (including unsafe ones) to be downloaded (GHSA-79w7-vh3h-8g4j (https://github.com/yt-dlp/yt- dlp/security/advisories/GHSA-79w7-vh3h-8g4j)) :warning: Only use if a valid file download is rejected because its extension is detected as uncommon This option can enable remote code execution! Consider opening an issue (https://github.com/yt-dlp/yt-dlp/issues/new/choose) instead! Deprecated options These are all the deprecated options and the current alternative to achieve the same effect Almost redundant options While these options are almost the same as their new counterparts, there are some differences that prevents them being redundant -j, --dump-json --print "%()j" -F, --list-formats --print formats_table --list-thumbnails --print thumbnails_table --print playlist:thumbnails_table --list-subs --print automatic_captions_table --print subtitles_table Redundant options While these options are redundant, they are still expected to be used due to their ease of use --get-description --print description --get-duration --print duration_string --get-filename --print filename --get-format --print format --get-id --print id --get-thumbnail --print thumbnail -e, --get-title --print title -g, --get-url --print urls --match-title REGEX --match-filter "title ~= (?i)REGEX" --reject-title REGEX --match-filter "title !~= (?i)REGEX" --min-views COUNT --match-filter "view_count >=? COUNT" --max-views COUNT --match-filter "view_count <=? COUNT" --break-on-reject Use --break-match-filter --user-agent UA --add-header "User-Agent:UA" --referer URL --add-header "Referer:URL" --playlist-start NUMBER -I NUMBER: --playlist-end NUMBER -I :NUMBER --playlist-reverse -I ::-1 --no-playlist-reverse Default --no-colors --color no_color Not recommended While these options still work, their use is not recommended since there are other alternatives to achieve the same --force-generic-extractor --ies generic,default --exec-before-download CMD --exec "before_dl:CMD" --no-exec-before-download --no-exec --all-formats -f all --all-subs --sub-langs all --write-subs --print-json -j --no-simulate --autonumber-size NUMBER Use string formatting, e.g. %(autonumber)03d --autonumber-start NUMBER Use internal field formatting like %(autonumber+NUMBER)s --id -o "%(id)s.%(ext)s" --metadata-from-title FORMAT --parse-metadata "%(title)s:FORMAT" --hls-prefer-native --downloader "m3u8:native" --hls-prefer-ffmpeg --downloader "m3u8:ffmpeg" --list-formats-old --compat-options list-formats (Alias: --no-list-formats-as-table) --list-formats-as-table --compat-options -list-formats [Default] (Alias: --no-list-formats-old) --youtube-skip-dash-manifest --extractor-args "youtube:skip=dash" (Alias: --no-youtube-include-dash-manifest) --youtube-skip-hls-manifest --extractor-args "youtube:skip=hls" (Alias: --no-youtube-include-hls-manifest) --youtube-include-dash-manifest Default (Alias: --no-youtube-skip-dash-manifest) --youtube-include-hls-manifest Default (Alias: --no-youtube-skip-hls-manifest) --geo-bypass --xff "default" --no-geo-bypass --xff "never" --geo-bypass-country CODE --xff CODE --geo-bypass-ip-block IP_BLOCK --xff IP_BLOCK Developer options These options are not intended to be used by the end-user --test Download only part of video for testing extractors --load-pages Load pages dumped by --write-pages --youtube-print-sig-code For testing youtube signatures --allow-unplayable-formats List unplayable formats also --no-allow-unplayable-formats Default Old aliases These are aliases that are no longer documented for various reasons --avconv-location --ffmpeg-location --clean-infojson --clean-info-json --cn-verification-proxy URL --geo-verification-proxy URL --dump-headers --print-traffic --dump-intermediate-pages --dump-pages --force-write-download-archive --force-write-archive --load-info --load-info-json --no-clean-infojson --no-clean-info-json --no-split-tracks --no-split-chapters --no-write-srt --no-write-subs --prefer-unsecure --prefer-insecure --rate-limit RATE --limit-rate RATE --split-tracks --split-chapters --srt-lang LANGS --sub-langs LANGS --trim-file-names LENGTH --trim-filenames LENGTH --write-srt --write-subs --yes-overwrites --force-overwrites Sponskrub Options Support for SponSkrub (https://github.com/faissaloo/SponSkrub) has been deprecated in favor of the --sponsorblock options --sponskrub --sponsorblock-mark all --no-sponskrub --no-sponsorblock --sponskrub-cut --sponsorblock-remove all --no-sponskrub-cut --sponsorblock-remove -all --sponskrub-force Not applicable --no-sponskrub-force Not applicable --sponskrub-location Not applicable --sponskrub-args Not applicable No longer supported These options may no longer work as intended --prefer-avconv avconv is not officially supported by yt-dlp (Alias: --no-prefer-ffmpeg) --prefer-ffmpeg Default (Alias: --no-prefer-avconv) -C, --call-home Not implemented --no-call-home Default --include-ads No longer supported --no-include-ads Default --write-annotations No supported site has annotations now --no-write-annotations Default --compat-options seperate-video-versions No longer needed --compat-options no-youtube-prefer-utc-upload-date No longer supported Removed These options were deprecated since 2014 and have now been entirely removed -A, --auto-number -o "%(autonumber)s-%(id)s.%(ext)s" -t, -l, --title, --literal -o "%(title)s-%(id)s.%(ext)s" CONTRIBUTING See CONTRIBUTING.md for instructions on Opening an Issue and Contributing code to the project WIKI See the Wiki (https://github.com/yt-dlp/yt-dlp/wiki) for more information yt-dlp(1)
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pidproxy
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mackup
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rtmpdump
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rtmpdump is a tool for dumping media content streamed over RTMP. rtmpdump makes a connection to the specified RTMP server and plays the media specified by the given url. The url should be of the form rtmp[t][e]://hostname[:port][/app[/playpath]] Plain rtmp, as well as tunneled and encrypted sessions are supported.
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rtmpdump - RTMP streaming media client
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rtmpdump -r_url [-n_hostname] [-c_port] [-l_protocol] [-S_host:port] [-a_app] [-t_tcUrl] [-p_pageUrl] [-s_swfUrl] [-f_flashVer] [-u_auth] [-C_conndata] [-y_playpath] [-Y] [-v] [-d_subscription] [-e] [-k_skip] [-A_start] [-B_stop] [-b_buffer] [-m_timeout] [-T_key] [-j_JSON] [-w_swfHash] [-x_swfSize] [-W_swfUrl] [-X_swfAge] [-o_output] [-#] [-q] [-V] [-z] rtmpdump -h
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Network Parameters These options define how to connect to the media server. --rtmp -r url URL of the server and media content. --host -n hostname Overrides the hostname in the RTMP URL. --port -c port Overrides the port number in the RTMP URL. --protocol -l number Overrides the protocol in the RTMP URL. 0 = rtmp 1 = rtmpt 2 = rtmpe 3 = rtmpte 4 = rtmps 5 = rtmpts --socks -S host:port Use the specified SOCKS4 proxy. Connection Parameters These options define the content of the RTMP Connect request packet. If correct values are not provided, the media server will reject the connection attempt. --app -a app Name of application to connect to on the RTMP server. Overrides the app in the RTMP URL. Sometimes the rtmpdump URL parser cannot determine the app name automatically, so it must be given explicitly using this option. --tcUrl -t url URL of the target stream. Defaults to rtmp[e]://host[:port]/app/playpath. --pageUrl -p url URL of the web page in which the media was embedded. By default no value will be sent. --swfUrl -s url URL of the SWF player for the media. By default no value will be sent. --flashVer -f version Version of the Flash plugin used to run the SWF player. The default is "LNX 10,0,32,18". --auth -u string An authentication string to be appended to the Connect message. Using this option will append a Boolean TRUE and then the specified string. This option is only used by some particular servers and is deprecated. The more general --conn option should be used instead. --conn -C type:data Append arbitrary AMF data to the Connect message. The type must be B for Boolean, N for number, S for string, O for object, or Z for null. For Booleans the data must be either 0 or 1 for FALSE or TRUE, respectively. Likewise for Objects the data must be 0 or 1 to end or begin an object, respectively. Data items in subobjects may be named, by prefixing the type with 'N' and specifying the name before the value, e.g. NB:myFlag:1. This option may be used multiple times to construct arbitrary AMF sequences. E.g. -C B:1 -C S:authMe -C O:1 -C NN:code:1.23 -C NS:flag:ok -C O:0 Session Parameters These options take effect after the Connect request has succeeded. --playpath -y path Overrides the playpath parsed from the RTMP URL. Sometimes the rtmpdump URL parser cannot determine the correct playpath automatically, so it must be given explicitly using this option. --playlist -Y Issue a set_playlist command before sending the play command. The playlist will just contain the current playpath. --live -v Specify that the media is a live stream. No resuming or seeking in live streams is possible. --subscribe -d stream Name of live stream to subscribe to. Defaults to playpath. --realtime -R Download approximately in realtime, without attempting to speed up via Pause/Unpause commands ("the BUFX hack"). Useful for servers that jump backwards in time at the Unpause command. Resuming and seeking in realtime streams is still possible. --resume -e Resume an incomplete RTMP download. --skip -k num Skip num keyframes when looking for the last keyframe from which to resume. This may be useful if a regular attempt to resume fails. The default is 0. --start -A num Start at num seconds into the stream. Not valid for live streams. --stop -B num Stop at num seconds into the stream. --buffer -b num Set buffer time to num milliseconds. The default is 36000000. --timeout -m num Timeout the session after num seconds without receiving any data from the server. The default is 120. Security Parameters These options handle additional authentication requests from the server. --token -T key Key for SecureToken response, used if the server requires SecureToken authentication. --jtv -j JSON JSON token used by legacy Justin.tv servers. Invokes NetStream.Authenticate.UsherToken --swfhash -w hexstring SHA256 hash of the decompressed SWF file. This option may be needed if the server uses SWF Verification, but see the --swfVfy option below. The hash is 32 bytes, and must be given in hexadecimal. The --swfsize option must always be used with this option. --swfsize -x num Size of the decompressed SWF file. This option may be needed if the server uses SWF Verification, but see the --swfVfy option below. The --swfhash option must always be used with this option. --swfVfy -W url URL of the SWF player for this media. This option replaces all three of the --swfUrl, --swfhash, and --swfsize options. When this option is used, the SWF player is retrieved from the specified URL and the hash and size are computed automatically. Also the information is cached in a .swfinfo file in the user's home directory, so that it doesn't need to be retrieved and recalculated every time rtmpdump is run. The .swfinfo file records the URL, the time it was fetched, the modification timestamp of the SWF file, its size, and its hash. By default, the cached info will be used for 30 days before re-checking. --swfAge -X days Specify how many days to use the cached SWF info before re- checking. Use 0 to always check the SWF URL. Note that if the check shows that the SWF file has the same modification timestamp as before, it will not be retrieved again. Miscellaneous --flv -o output Specify the output file name. If the name is - or is omitted, the stream is written to stdout. --hashes -# Display streaming progress with a hash mark for each 1% of progress, instead of a byte counter. --quiet -q Suppress all command output. --verbose -V Verbose command output. --debug -z Debug level output. Extremely verbose, including hex dumps of all packet data. --help -h Print a summary of command options. EXIT STATUS 0 Successful program execution. 1 Unrecoverable error. 2 Incomplete transfer, resuming may get further. ENVIRONMENT HOME The value of $HOME is used as the location for the .swfinfo file. FILES $HOME/.swfinfo Cache of SWF Verification information SEE ALSO rtmpgw(8) AUTHORS Andrej Stepanchuk, Howard Chu, The Flvstreamer Team <http://rtmpdump.mplayerhq.hu> RTMPDump v2.4 2012-07-24 RTMPDUMP(1)
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g++-13
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When you invoke GCC, it normally does preprocessing, compilation, assembly and linking. The "overall options" allow you to stop this process at an intermediate stage. For example, the -c option says not to run the linker. Then the output consists of object files output by the assembler. Other options are passed on to one or more stages of processing. Some options control the preprocessor and others the compiler itself. Yet other options control the assembler and linker; most of these are not documented here, since you rarely need to use any of them. Most of the command-line options that you can use with GCC are useful for C programs; when an option is only useful with another language (usually C++), the explanation says so explicitly. If the description for a particular option does not mention a source language, you can use that option with all supported languages. The usual way to run GCC is to run the executable called gcc, or machine-gcc when cross-compiling, or machine-gcc-version to run a specific version of GCC. When you compile C++ programs, you should invoke GCC as g++ instead. The gcc program accepts options and file names as operands. Many options have multi-letter names; therefore multiple single-letter options may not be grouped: -dv is very different from -d -v. You can mix options and other arguments. For the most part, the order you use doesn't matter. Order does matter when you use several options of the same kind; for example, if you specify -L more than once, the directories are searched in the order specified. Also, the placement of the -l option is significant. Many options have long names starting with -f or with -W---for example, -fmove-loop-invariants, -Wformat and so on. Most of these have both positive and negative forms; the negative form of -ffoo is -fno-foo. This manual documents only one of these two forms, whichever one is not the default. Some options take one or more arguments typically separated either by a space or by the equals sign (=) from the option name. Unless documented otherwise, an argument can be either numeric or a string. Numeric arguments must typically be small unsigned decimal or hexadecimal integers. Hexadecimal arguments must begin with the 0x prefix. Arguments to options that specify a size threshold of some sort may be arbitrarily large decimal or hexadecimal integers followed by a byte size suffix designating a multiple of bytes such as "kB" and "KiB" for kilobyte and kibibyte, respectively, "MB" and "MiB" for megabyte and mebibyte, "GB" and "GiB" for gigabyte and gigibyte, and so on. Such arguments are designated by byte-size in the following text. Refer to the NIST, IEC, and other relevant national and international standards for the full listing and explanation of the binary and decimal byte size prefixes.
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gcc - GNU project C and C++ compiler
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gcc [-c|-S|-E] [-std=standard] [-g] [-pg] [-Olevel] [-Wwarn...] [-Wpedantic] [-Idir...] [-Ldir...] [-Dmacro[=defn]...] [-Umacro] [-foption...] [-mmachine-option...] [-o outfile] [@file] infile... Only the most useful options are listed here; see below for the remainder. g++ accepts mostly the same options as gcc.
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Option Summary Here is a summary of all the options, grouped by type. Explanations are in the following sections. Overall Options -c -S -E -o file -dumpbase dumpbase -dumpbase-ext auxdropsuf -dumpdir dumppfx -x language -v -### --help[=class[,...]] --target-help --version -pass-exit-codes -pipe -specs=file -wrapper @file -ffile-prefix-map=old=new -fcanon-prefix-map -fplugin=file -fplugin-arg-name=arg -fdump-ada-spec[-slim] -fada-spec-parent=unit -fdump-go-spec=file C Language Options -ansi -std=standard -aux-info filename -fno-asm -fno-builtin -fno-builtin-function -fcond-mismatch -ffreestanding -fgimple -fgnu-tm -fgnu89-inline -fhosted -flax-vector-conversions -fms-extensions -foffload=arg -foffload-options=arg -fopenacc -fopenacc-dim=geom -fopenmp -fopenmp-simd -fopenmp-target-simd-clone[=device-type] -fpermitted-flt-eval-methods=standard -fplan9-extensions -fsigned-bitfields -funsigned-bitfields -fsigned-char -funsigned-char -fstrict-flex-arrays[=n] -fsso-struct=endianness C++ Language Options -fabi-version=n -fno-access-control -faligned-new=n -fargs-in-order=n -fchar8_t -fcheck-new -fconstexpr-depth=n -fconstexpr-cache-depth=n -fconstexpr-loop-limit=n -fconstexpr-ops-limit=n -fno-elide-constructors -fno-enforce-eh-specs -fno-gnu-keywords -fno-implicit-templates -fno-implicit-inline-templates -fno-implement-inlines -fmodule-header[=kind] -fmodule-only -fmodules-ts -fmodule-implicit-inline -fno-module-lazy -fmodule-mapper=specification -fmodule-version-ignore -fms-extensions -fnew-inheriting-ctors -fnew-ttp-matching -fno-nonansi-builtins -fnothrow-opt -fno-operator-names -fno-optional-diags -fpermissive -fno-pretty-templates -fno-rtti -fsized-deallocation -ftemplate-backtrace-limit=n -ftemplate-depth=n -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ -fvisibility-inlines-hidden -fvisibility-ms-compat -fext-numeric-literals -flang-info-include-translate[=header] -flang-info-include-translate-not -flang-info-module-cmi[=module] -stdlib=libstdc++,libc++ -Wabi-tag -Wcatch-value -Wcatch-value=n -Wno-class-conversion -Wclass-memaccess -Wcomma-subscript -Wconditionally-supported -Wno-conversion-null -Wctad-maybe-unsupported -Wctor-dtor-privacy -Wdangling-reference -Wno-delete-incomplete -Wdelete-non-virtual-dtor -Wno-deprecated-array-compare -Wdeprecated-copy -Wdeprecated-copy-dtor -Wno-deprecated-enum-enum-conversion -Wno-deprecated-enum-float-conversion -Weffc++ -Wno-exceptions -Wextra-semi -Wno-inaccessible-base -Wno-inherited-variadic-ctor -Wno-init-list-lifetime -Winvalid-constexpr -Winvalid-imported-macros -Wno-invalid-offsetof -Wno-literal-suffix -Wmismatched-new-delete -Wmismatched-tags -Wmultiple-inheritance -Wnamespaces -Wnarrowing -Wnoexcept -Wnoexcept-type -Wnon-virtual-dtor -Wpessimizing-move -Wno-placement-new -Wplacement-new=n -Wrange-loop-construct -Wredundant-move -Wredundant-tags -Wreorder -Wregister -Wstrict-null-sentinel -Wno-subobject-linkage -Wtemplates -Wno-non-template-friend -Wold-style-cast -Woverloaded-virtual -Wno-pmf-conversions -Wself-move -Wsign-promo -Wsized-deallocation -Wsuggest-final-methods -Wsuggest-final-types -Wsuggest-override -Wno-terminate -Wuseless-cast -Wno-vexing-parse -Wvirtual-inheritance -Wno-virtual-move-assign -Wvolatile -Wzero-as-null-pointer-constant Objective-C and Objective-C++ Language Options -fconstant-string-class=class-name -fgnu-runtime -fnext-runtime -fno-nil-receivers -fobjc-abi-version=n -fobjc-call-cxx-cdtors -fobjc-direct-dispatch -fobjc-exceptions -fobjc-gc -fobjc-nilcheck -fobjc-std=objc1 -fno-local-ivars -fivar-visibility=[public|protected|private|package] -freplace-objc-classes -fzero-link -gen-decls -Wassign-intercept -Wno-property-assign-default -Wno-protocol -Wobjc-root-class -Wselector -Wstrict-selector-match -Wundeclared-selector Diagnostic Message Formatting Options -fmessage-length=n -fdiagnostics-plain-output -fdiagnostics-show-location=[once|every-line] -fdiagnostics-color=[auto|never|always] -fdiagnostics-urls=[auto|never|always] -fdiagnostics-format=[text|sarif-stderr|sarif-file|json|json- stderr|json-file] -fno-diagnostics-show-option -fno-diagnostics-show-caret -fno-diagnostics-show-labels -fno-diagnostics-show-line-numbers -fno-diagnostics-show-cwe -fno-diagnostics-show-rule -fdiagnostics-minimum-margin-width=width -fdiagnostics-parseable-fixits -fdiagnostics-generate-patch -fdiagnostics-show-template-tree -fno-elide-type -fdiagnostics-path-format=[none|separate-events|inline-events] -fdiagnostics-show-path-depths -fno-show-column -fdiagnostics-column-unit=[display|byte] -fdiagnostics-column-origin=origin -fdiagnostics-escape-format=[unicode|bytes] Warning Options -fsyntax-only -fmax-errors=n -Wpedantic -pedantic-errors -w -Wextra -Wall -Wabi=n -Waddress -Wno-address-of-packed-member -Waggregate-return -Walloc-size-larger-than=byte-size -Walloc-zero -Walloca -Walloca-larger-than=byte-size -Wno-aggressive-loop-optimizations -Warith-conversion -Warray-bounds -Warray-bounds=n -Warray-compare -Wno-attributes -Wattribute-alias=n -Wno-attribute-alias -Wno-attribute-warning -Wbidi-chars=[none|unpaired|any|ucn] -Wbool-compare -Wbool-operation -Wno-builtin-declaration-mismatch -Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat -Wc11-c2x-compat -Wc++-compat -Wc++11-compat -Wc++14-compat -Wc++17-compat -Wc++20-compat -Wno-c++11-extensions -Wno-c++14-extensions -Wno-c++17-extensions -Wno-c++20-extensions -Wno-c++23-extensions -Wcast-align -Wcast-align=strict -Wcast-function-type -Wcast-qual -Wchar-subscripts -Wclobbered -Wcomment -Wno-complain-wrong-lang -Wconversion -Wno-coverage-mismatch -Wno-cpp -Wdangling-else -Wdangling-pointer -Wdangling-pointer=n -Wdate-time -Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init -Wdisabled-optimization -Wno-discarded-array-qualifiers -Wno-discarded-qualifiers -Wno-div-by-zero -Wdouble-promotion -Wduplicated-branches -Wduplicated-cond -Wempty-body -Wno-endif-labels -Wenum-compare -Wenum-conversion -Wenum-int-mismatch -Werror -Werror=* -Wexpansion-to-defined -Wfatal-errors -Wfloat-conversion -Wfloat-equal -Wformat -Wformat=2 -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral -Wformat-overflow=n -Wformat-security -Wformat-signedness -Wformat-truncation=n -Wformat-y2k -Wframe-address -Wframe-larger-than=byte-size -Wno-free-nonheap-object -Wno-if-not-aligned -Wno-ignored-attributes -Wignored-qualifiers -Wno-incompatible-pointer-types -Wimplicit -Wimplicit-fallthrough -Wimplicit-fallthrough=n -Wno-implicit-function-declaration -Wno-implicit-int -Winfinite-recursion -Winit-self -Winline -Wno-int-conversion -Wint-in-bool-context -Wno-int-to-pointer-cast -Wno-invalid-memory-model -Winvalid-pch -Winvalid-utf8 -Wno-unicode -Wjump-misses-init -Wlarger-than=byte-size -Wlogical-not-parentheses -Wlogical-op -Wlong-long -Wno-lto-type-mismatch -Wmain -Wmaybe-uninitialized -Wmemset-elt-size -Wmemset-transposed-args -Wmisleading-indentation -Wmissing-attributes -Wmissing-braces -Wmissing-field-initializers -Wmissing-format-attribute -Wmissing-include-dirs -Wmissing-noreturn -Wno-missing-profile -Wno-multichar -Wmultistatement-macros -Wnonnull -Wnonnull-compare -Wnormalized=[none|id|nfc|nfkc] -Wnull-dereference -Wno-odr -Wopenacc-parallelism -Wopenmp-simd -Wno-overflow -Woverlength-strings -Wno-override-init-side-effects -Wpacked -Wno-packed-bitfield-compat -Wpacked-not-aligned -Wpadded -Wparentheses -Wno-pedantic-ms-format -Wpointer-arith -Wno-pointer-compare -Wno-pointer-to-int-cast -Wno-pragmas -Wno-prio-ctor-dtor -Wredundant-decls -Wrestrict -Wno-return-local-addr -Wreturn-type -Wno-scalar-storage-order -Wsequence-point -Wshadow -Wshadow=global -Wshadow=local -Wshadow=compatible-local -Wno-shadow-ivar -Wno-shift-count-negative -Wno-shift-count-overflow -Wshift-negative-value -Wno-shift-overflow -Wshift-overflow=n -Wsign-compare -Wsign-conversion -Wno-sizeof-array-argument -Wsizeof-array-div -Wsizeof-pointer-div -Wsizeof-pointer-memaccess -Wstack-protector -Wstack-usage=byte-size -Wstrict-aliasing -Wstrict-aliasing=n -Wstrict-overflow -Wstrict-overflow=n -Wstring-compare -Wno-stringop-overflow -Wno-stringop-overread -Wno-stringop-truncation -Wstrict-flex-arrays -Wsuggest-attribute=[pure|const|noreturn|format|malloc] -Wswitch -Wno-switch-bool -Wswitch-default -Wswitch-enum -Wno-switch-outside-range -Wno-switch-unreachable -Wsync-nand -Wsystem-headers -Wtautological-compare -Wtrampolines -Wtrigraphs -Wtrivial-auto-var-init -Wtsan -Wtype-limits -Wundef -Wuninitialized -Wunknown-pragmas -Wunsuffixed-float-constants -Wunused -Wunused-but-set-parameter -Wunused-but-set-variable -Wunused-const-variable -Wunused-const-variable=n -Wunused-function -Wunused-label -Wunused-local-typedefs -Wunused-macros -Wunused-parameter -Wno-unused-result -Wunused-value -Wunused-variable -Wno-varargs -Wvariadic-macros -Wvector-operation-performance -Wvla -Wvla-larger-than=byte-size -Wno-vla-larger-than -Wvolatile-register-var -Wwrite-strings -Wxor-used-as-pow -Wzero-length-bounds Static Analyzer Options -fanalyzer -fanalyzer-call-summaries -fanalyzer-checker=name -fno-analyzer-feasibility -fanalyzer-fine-grained -fno-analyzer-state-merge -fno-analyzer-state-purge -fno-analyzer-suppress-followups -fanalyzer-transitivity -fno-analyzer-undo-inlining -fanalyzer-verbose-edges -fanalyzer-verbose-state-changes -fanalyzer-verbosity=level -fdump-analyzer -fdump-analyzer-callgraph -fdump-analyzer-exploded-graph -fdump-analyzer-exploded-nodes -fdump-analyzer-exploded-nodes-2 -fdump-analyzer-exploded-nodes-3 -fdump-analyzer-exploded-paths -fdump-analyzer-feasibility -fdump-analyzer-json -fdump-analyzer-state-purge -fdump-analyzer-stderr -fdump-analyzer-supergraph -fdump-analyzer-untracked -Wno-analyzer-double-fclose -Wno-analyzer-double-free -Wno-analyzer-exposure-through-output-file -Wno-analyzer-exposure-through-uninit-copy -Wno-analyzer-fd-access-mode-mismatch -Wno-analyzer-fd-double-close -Wno-analyzer-fd-leak -Wno-analyzer-fd-phase-mismatch -Wno-analyzer-fd-type-mismatch -Wno-analyzer-fd-use-after-close -Wno-analyzer-fd-use-without-check -Wno-analyzer-file-leak -Wno-analyzer-free-of-non-heap -Wno-analyzer-imprecise-fp-arithmetic -Wno-analyzer-infinite-recursion -Wno-analyzer-jump-through-null -Wno-analyzer-malloc-leak -Wno-analyzer-mismatching-deallocation -Wno-analyzer-null-argument -Wno-analyzer-null-dereference -Wno-analyzer-out-of-bounds -Wno-analyzer-possible-null-argument -Wno-analyzer-possible-null-dereference -Wno-analyzer-putenv-of-auto-var -Wno-analyzer-shift-count-negative -Wno-analyzer-shift-count-overflow -Wno-analyzer-stale-setjmp-buffer -Wno-analyzer-tainted-allocation-size -Wno-analyzer-tainted-assertion -Wno-analyzer-tainted-array-index -Wno-analyzer-tainted-divisor -Wno-analyzer-tainted-offset -Wno-analyzer-tainted-size -Wanalyzer-too-complex -Wno-analyzer-unsafe-call-within-signal-handler -Wno-analyzer-use-after-free -Wno-analyzer-use-of-pointer-in-stale-stack-frame -Wno-analyzer-use-of-uninitialized-value -Wno-analyzer-va-arg-type-mismatch -Wno-analyzer-va-list-exhausted -Wno-analyzer-va-list-leak -Wno-analyzer-va-list-use-after-va-end -Wno-analyzer-write-to-const -Wno-analyzer-write-to-string-literal C and Objective-C-only Warning Options -Wbad-function-cast -Wmissing-declarations -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs -Wold-style-declaration -Wold-style-definition -Wstrict-prototypes -Wtraditional -Wtraditional-conversion -Wdeclaration-after-statement -Wpointer-sign Debugging Options -g -glevel -gdwarf -gdwarf-version -gbtf -gctf -gctflevel -ggdb -grecord-gcc-switches -gno-record-gcc-switches -gstrict-dwarf -gno-strict-dwarf -gas-loc-support -gno-as-loc-support -gas-locview-support -gno-as-locview-support -gcolumn-info -gno-column-info -gdwarf32 -gdwarf64 -gstatement-frontiers -gno-statement-frontiers -gvariable-location-views -gno-variable-location-views -ginternal-reset-location-views -gno-internal-reset-location-views -ginline-points -gno-inline-points -gvms -gz[=type] -gsplit-dwarf -gdescribe-dies -gno-describe-dies -fdebug-prefix-map=old=new -fdebug-types-section -fno-eliminate-unused-debug-types -femit-struct-debug-baseonly -femit-struct-debug-reduced -femit-struct-debug-detailed[=spec-list] -fno-eliminate-unused-debug-symbols -femit-class-debug-always -fno-merge-debug-strings -fno-dwarf2-cfi-asm -fvar-tracking -fvar-tracking-assignments Optimization Options -faggressive-loop-optimizations -falign-functions[=n[:m:[n2[:m2]]]] -falign-jumps[=n[:m:[n2[:m2]]]] -falign-labels[=n[:m:[n2[:m2]]]] -falign-loops[=n[:m:[n2[:m2]]]] -fno-allocation-dce -fallow-store-data-races -fassociative-math -fauto-profile -fauto-profile[=path] -fauto-inc-dec -fbranch-probabilities -fcaller-saves -fcombine-stack-adjustments -fconserve-stack -fcompare-elim -fcprop-registers -fcrossjumping -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range -fdata-sections -fdce -fdelayed-branch -fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively -fdevirtualize-at-ltrans -fdse -fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects -ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=style -ffinite-loops -fforward-propagate -ffp-contract=style -ffunction-sections -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity -fgcse-sm -fhoist-adjacent-loads -fif-conversion -fif-conversion2 -findirect-inlining -finline-functions -finline-functions-called-once -finline-limit=n -finline-small-functions -fipa-modref -fipa-cp -fipa-cp-clone -fipa-bit-cp -fipa-vrp -fipa-pta -fipa-profile -fipa-pure-const -fipa-reference -fipa-reference-addressable -fipa-stack-alignment -fipa-icf -fira-algorithm=algorithm -flive-patching=level -fira-region=region -fira-hoist-pressure -fira-loop-pressure -fno-ira-share-save-slots -fno-ira-share-spill-slots -fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute -fivopts -fkeep-inline-functions -fkeep-static-functions -fkeep-static-consts -flimit-function-alignment -flive-range-shrinkage -floop-block -floop-interchange -floop-strip-mine -floop-unroll-and-jam -floop-nest-optimize -floop-parallelize-all -flra-remat -flto -flto-compression-level -flto-partition=alg -fmerge-all-constants -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fmove-loop-stores -fno-branch-count-reg -fno-defer-pop -fno-fp-int-builtin-inexact -fno-function-cse -fno-guess-branch-probability -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 -fno-printf-return-value -fno-sched-interblock -fno-sched-spec -fno-signed-zeros -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss -fomit-frame-pointer -foptimize-sibling-calls -fpartial-inlining -fpeel-loops -fpredictive-commoning -fprefetch-loop-arrays -fprofile-correction -fprofile-use -fprofile-use=path -fprofile-partial-training -fprofile-values -fprofile-reorder-functions -freciprocal-math -free -frename-registers -freorder-blocks -freorder-blocks-algorithm=algorithm -freorder-blocks-and-partition -freorder-functions -frerun-cse-after-loop -freschedule-modulo-scheduled-loops -frounding-math -fsave-optimization-record -fsched2-use-superblocks -fsched-pressure -fsched-spec-load -fsched-spec-load-dangerous -fsched-stalled-insns-dep[=n] -fsched-stalled-insns[=n] -fsched-group-heuristic -fsched-critical-path-heuristic -fsched-spec-insn-heuristic -fsched-rank-heuristic -fsched-last-insn-heuristic -fsched-dep-count-heuristic -fschedule-fusion -fschedule-insns -fschedule-insns2 -fsection-anchors -fselective-scheduling -fselective-scheduling2 -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops -fsemantic-interposition -fshrink-wrap -fshrink-wrap-separate -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-loops -fsplit-paths -fsplit-wide-types -fsplit-wide-types-early -fssa-backprop -fssa-phiopt -fstdarg-opt -fstore-merging -fstrict-aliasing -fipa-strict-aliasing -fthread-jumps -ftracer -ftree-bit-ccp -ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-coalesce-vars -ftree-copy-prop -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre -fcode-hoisting -ftree-loop-if-convert -ftree-loop-im -ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize -ftree-loop-vectorize -ftree-parallelize-loops=n -ftree-pre -ftree-partial-pre -ftree-pta -ftree-reassoc -ftree-scev-cprop -ftree-sink -ftree-slsr -ftree-sra -ftree-switch-conversion -ftree-tail-merge -ftree-ter -ftree-vectorize -ftree-vrp -ftrivial-auto-var-init -funconstrained-commons -funit-at-a-time -funroll-all-loops -funroll-loops -funsafe-math-optimizations -funswitch-loops -fipa-ra -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb -fwhole-program -fwpa -fuse-linker-plugin -fzero-call-used-regs --param name=value -O -O0 -O1 -O2 -O3 -Os -Ofast -Og -Oz Program Instrumentation Options -p -pg -fprofile-arcs --coverage -ftest-coverage -fprofile-abs-path -fprofile-dir=path -fprofile-generate -fprofile-generate=path -fprofile-info-section -fprofile-info-section=name -fprofile-note=path -fprofile-prefix-path=path -fprofile-update=method -fprofile-filter-files=regex -fprofile-exclude-files=regex -fprofile-reproducible=[multithreaded|parallel-runs|serial] -fsanitize=style -fsanitize-recover -fsanitize-recover=style -fsanitize-trap -fsanitize-trap=style -fasan-shadow-offset=number -fsanitize-sections=s1,s2,... -fsanitize-undefined-trap-on-error -fbounds-check -fcf-protection=[full|branch|return|none|check] -fharden-compares -fharden-conditional-branches -fstack-protector -fstack-protector-all -fstack-protector-strong -fstack-protector-explicit -fstack-check -fstack-limit-register=reg -fstack-limit-symbol=sym -fno-stack-limit -fsplit-stack -fvtable-verify=[std|preinit|none] -fvtv-counts -fvtv-debug -finstrument-functions -finstrument-functions-once -finstrument-functions-exclude-function-list=sym,sym,... -finstrument-functions-exclude-file-list=file,file,... -fprofile-prefix-map=old=new Preprocessor Options -Aquestion=answer -A-question[=answer] -C -CC -Dmacro[=defn] -dD -dI -dM -dN -dU -fdebug-cpp -fdirectives-only -fdollars-in-identifiers -fexec-charset=charset -fextended-identifiers -finput-charset=charset -flarge-source-files -fmacro-prefix-map=old=new -fmax-include-depth=depth -fno-canonical-system-headers -fpch-deps -fpch-preprocess -fpreprocessed -ftabstop=width -ftrack-macro-expansion -fwide-exec-charset=charset -fworking-directory -H -imacros file -include file -M -MD -MF -MG -MM -MMD -MP -MQ -MT -Mno-modules -no-integrated-cpp -P -pthread -remap -traditional -traditional-cpp -trigraphs -Umacro -undef -Wp,option -Xpreprocessor option Assembler Options -Wa,option -Xassembler option Linker Options object-file-name -fuse-ld=linker -llibrary -nostartfiles -nodefaultlibs -nolibc -nostdlib -nostdlib++ -e entry --entry=entry -pie -pthread -r -rdynamic -s -static -static-pie -static-libgcc -static-libstdc++ -static-libasan -static-libtsan -static-liblsan -static-libubsan -shared -shared-libgcc -symbolic -T script -Wl,option -Xlinker option -u symbol -z keyword Directory Options -Bprefix -Idir -I- -idirafter dir -imacros file -imultilib dir -iplugindir=dir -iprefix file -iquote dir -isysroot dir -isystem dir -iwithprefix dir -iwithprefixbefore dir -Ldir -no-canonical-prefixes --no-sysroot-suffix -nostdinc -nostdinc++ --sysroot=dir Code Generation Options -fcall-saved-reg -fcall-used-reg -ffixed-reg -fexceptions -fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables -fasynchronous-unwind-tables -fno-gnu-unique -finhibit-size-directive -fcommon -fno-ident -fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt -fno-jump-tables -fno-bit-tests -frecord-gcc-switches -freg-struct-return -fshort-enums -fshort-wchar -fverbose-asm -fpack-struct[=n] -fleading-underscore -ftls-model=model -fstack-reuse=reuse_level -fstack-use-cumulative-args -ftrampolines -foff-stack-trampolines -ftrapv -fwrapv -fvisibility=[default|internal|hidden|protected] -fstrict-volatile-bitfields -fsync-libcalls Developer Options -dletters -dumpspecs -dumpmachine -dumpversion -dumpfullversion -fcallgraph-info[=su,da] -fchecking -fchecking=n -fdbg-cnt-list -fdbg-cnt=counter-value-list -fdisable-ipa-pass_name -fdisable-rtl-pass_name -fdisable-rtl-pass-name=range-list -fdisable-tree-pass_name -fdisable-tree-pass-name=range-list -fdump-debug -fdump-earlydebug -fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links -fdump-final-insns[=file] -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline -fdump-lang-all -fdump-lang-switch -fdump-lang-switch-options -fdump-lang-switch-options=filename -fdump-passes -fdump-rtl-pass -fdump-rtl-pass=filename -fdump-statistics -fdump-tree-all -fdump-tree-switch -fdump-tree-switch-options -fdump-tree-switch-options=filename -fcompare-debug[=opts] -fcompare-debug-second -fenable-kind-pass -fenable-kind-pass=range- list -fira-verbose=n -flto-report -flto-report-wpa -fmem-report-wpa -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fopt-info -fopt-info-options[=file] -fmultiflags -fprofile-report -frandom-seed=string -fsched-verbose=n -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose -fstats -fstack-usage -ftime-report -ftime-report-details -fvar-tracking-assignments-toggle -gtoggle -print-file-name=library -print-libgcc-file-name -print-multi-directory -print-multi-lib -print-multi-os-directory -print-prog-name=program -print-search-dirs -Q -print-sysroot -print-sysroot-headers-suffix -save-temps -save-temps=cwd -save-temps=obj -time[=file] Machine-Dependent Options AArch64 Options -mabi=name -mbig-endian -mlittle-endian -mgeneral-regs-only -mcmodel=tiny -mcmodel=small -mcmodel=large -mstrict-align -mno-strict-align -momit-leaf-frame-pointer -mtls-dialect=desc -mtls-dialect=traditional -mtls-size=size -mfix-cortex-a53-835769 -mfix-cortex-a53-843419 -mlow-precision-recip-sqrt -mlow-precision-sqrt -mlow-precision-div -mpc-relative-literal-loads -msign-return-address=scope -mbranch-protection=none|standard|pac- ret[+leaf +b-key]|bti -mharden-sls=opts -march=name -mcpu=name -mtune=name -moverride=string -mverbose-cost-dump -mstack-protector-guard=guard -mstack-protector-guard-reg=sysreg -mstack-protector-guard-offset=offset -mtrack-speculation -moutline-atomics Adapteva Epiphany Options -mhalf-reg-file -mprefer-short-insn-regs -mbranch-cost=num -mcmove -mnops=num -msoft-cmpsf -msplit-lohi -mpost-inc -mpost-modify -mstack-offset=num -mround-nearest -mlong-calls -mshort-calls -msmall16 -mfp-mode=mode -mvect-double -max-vect-align=num -msplit-vecmove-early -m1reg-reg AMD GCN Options -march=gpu -mtune=gpu -mstack-size=bytes ARC Options -mbarrel-shifter -mjli-always -mcpu=cpu -mA6 -mARC600 -mA7 -mARC700 -mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr -mea -mno-mpy -mmul32x16 -mmul64 -matomic -mnorm -mspfp -mspfp-compact -mspfp-fast -msimd -msoft-float -mswap -mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc -mswape -mtelephony -mxy -misize -mannotate-align -marclinux -marclinux_prof -mlong-calls -mmedium-calls -msdata -mirq-ctrl-saved -mrgf-banked-regs -mlpc-width=width -G num -mvolatile-cache -mtp-regno=regno -malign-call -mauto-modify-reg -mbbit-peephole -mno-brcc -mcase-vector-pcrel -mcompact-casesi -mno-cond-exec -mearly-cbranchsi -mexpand-adddi -mindexed-loads -mlra -mlra-priority-none -mlra-priority-compact -mlra-priority-noncompact -mmillicode -mmixed-code -mq-class -mRcq -mRcw -msize-level=level -mtune=cpu -mmultcost=num -mcode-density-frame -munalign-prob-threshold=probability -mmpy-option=multo -mdiv-rem -mcode-density -mll64 -mfpu=fpu -mrf16 -mbranch-index ARM Options -mapcs-frame -mno-apcs-frame -mabi=name -mapcs-stack-check -mno-apcs-stack-check -mapcs-reentrant -mno-apcs-reentrant -mgeneral-regs-only -msched-prolog -mno-sched-prolog -mlittle-endian -mbig-endian -mbe8 -mbe32 -mfloat-abi=name -mfp16-format=name -mthumb-interwork -mno-thumb-interwork -mcpu=name -march=name -mfpu=name -mtune=name -mprint-tune-info -mstructure-size-boundary=n -mabort-on-noreturn -mlong-calls -mno-long-calls -msingle-pic-base -mno-single-pic-base -mpic-register=reg -mnop-fun-dllimport -mpoke-function-name -mthumb -marm -mflip-thumb -mtpcs-frame -mtpcs-leaf-frame -mcaller-super-interworking -mcallee-super-interworking -mtp=name -mtls-dialect=dialect -mword-relocations -mfix-cortex-m3-ldrd -mfix-cortex-a57-aes-1742098 -mfix-cortex-a72-aes-1655431 -munaligned-access -mneon-for-64bits -mslow-flash-data -masm-syntax-unified -mrestrict-it -mverbose-cost-dump -mpure-code -mcmse -mfix-cmse-cve-2021-35465 -mstack-protector-guard=guard -mstack-protector-guard-offset=offset -mfdpic -mbranch-protection=none|standard|pac-ret[+leaf] [+bti]|bti[+pac- ret[+leaf]] AVR Options -mmcu=mcu -mabsdata -maccumulate-args -mbranch-cost=cost -mcall-prologues -mgas-isr-prologues -mint8 -mdouble=bits -mlong-double=bits -mn_flash=size -mno-interrupts -mmain-is-OS_task -mrelax -mrmw -mstrict-X -mtiny-stack -mfract-convert-truncate -mshort-calls -nodevicelib -nodevicespecs -Waddr-space-convert -Wmisspelled-isr Blackfin Options -mcpu=cpu[-sirevision] -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library -mno-id-shared-library -mshared-library-id=n -mleaf-id-shared-library -mno-leaf-id-shared-library -msep-data -mno-sep-data -mlong-calls -mno-long-calls -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram -micplb C6X Options -mbig-endian -mlittle-endian -march=cpu -msim -msdata=sdata-type CRIS Options -mcpu=cpu -march=cpu -mtune=cpu -mmax-stack-frame=n -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects -mstack-align -mdata-align -mconst-align -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -melf -maout -sim -sim2 -mmul-bug-workaround -mno-mul-bug-workaround C-SKY Options -march=arch -mcpu=cpu -mbig-endian -EB -mlittle-endian -EL -mhard-float -msoft-float -mfpu=fpu -mdouble-float -mfdivdu -mfloat-abi=name -melrw -mistack -mmp -mcp -mcache -msecurity -mtrust -mdsp -medsp -mvdsp -mdiv -msmart -mhigh-registers -manchor -mpushpop -mmultiple-stld -mconstpool -mstack-size -mccrt -mbranch-cost=n -mcse-cc -msched-prolog -msim Darwin Options -all_load -allowable_client -arch -arch_errors_fatal -arch_only -bind_at_load -bundle -bundle_loader -client_name -compatibility_version -current_version -dead_strip -dependency-file -dylib_file -dylinker_install_name -dynamic -dynamiclib -exported_symbols_list -filelist -flat_namespace -force_cpusubtype_ALL -force_flat_namespace -headerpad_max_install_names -iframework -image_base -init -install_name -keep_private_externs -multi_module -multiply_defined -multiply_defined_unused -noall_load -no_dead_strip_inits_and_terms -nofixprebinding -nomultidefs -noprebind -noseglinkedit -pagezero_size -prebind -prebind_all_twolevel_modules -private_bundle -read_only_relocs -sectalign -sectobjectsymbols -whyload -seg1addr -sectcreate -sectobjectsymbols -sectorder -segaddr -segs_read_only_addr -segs_read_write_addr -seg_addr_table -seg_addr_table_filename -seglinkedit -segprot -segs_read_only_addr -segs_read_write_addr -single_module -static -sub_library -sub_umbrella -twolevel_namespace -umbrella -undefined -unexported_symbols_list -weak_reference_mismatches -whatsloaded -F -gused -gfull -mmacosx-version-min=version -mkernel -mone-byte-bool DEC Alpha Options -mno-fp-regs -msoft-float -mieee -mieee-with-inexact -mieee-conformant -mfp-trap-mode=mode -mfp-rounding-mode=mode -mtrap-precision=mode -mbuild-constants -mcpu=cpu-type -mtune=cpu-type -mbwx -mmax -mfix -mcix -mfloat-vax -mfloat-ieee -mexplicit-relocs -msmall-data -mlarge-data -msmall-text -mlarge-text -mmemory-latency=time eBPF Options -mbig-endian -mlittle-endian -mkernel=version -mframe-limit=bytes -mxbpf -mco-re -mno-co-re -mjmpext -mjmp32 -malu32 -mcpu=version FR30 Options -msmall-model -mno-lsim FT32 Options -msim -mlra -mnodiv -mft32b -mcompress -mnopm FRV Options -mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 -mhard-float -msoft-float -malloc-cc -mfixed-cc -mdword -mno-dword -mdouble -mno-double -mmedia -mno-media -mmuladd -mno-muladd -mfdpic -minline-plt -mgprel-ro -multilib-library-pic -mlinked-fp -mlong-calls -malign-labels -mlibrary-pic -macc-4 -macc-8 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move -moptimize-membar -mno-optimize-membar -mscc -mno-scc -mcond-exec -mno-cond-exec -mvliw-branch -mno-vliw-branch -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec -mno-nested-cond-exec -mtomcat-stats -mTLS -mtls -mcpu=cpu GNU/Linux Options -mglibc -muclibc -mmusl -mbionic -mandroid -tno-android-cc -tno-android-ld H8/300 Options -mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300 HPPA Options -march=architecture-type -matomic-libcalls -mbig-switch -mcaller-copies -mdisable-fpregs -mdisable-indexing -mordered -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld -mfixed-range=register-range -mcoherent-ldcw -mjump-in-delay -mlinker-opt -mlong-calls -mlong-load-store -mno-atomic-libcalls -mno-disable-fpregs -mno-disable-indexing -mno-fast-indirect-calls -mno-gas -mno-jump-in-delay -mno-long-load-store -mno-portable-runtime -mno-soft-float -mno-space-regs -msoft-float -mpa-risc-1-0 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime -mschedule=cpu-type -mspace-regs -msoft-mult -msio -mwsio -munix=unix-std -nolibdld -static -threads IA-64 Options -mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic -mvolatile-asm-stop -mregister-names -msdata -mno-sdata -mconstant-gp -mauto-pic -mfused-madd -minline-float-divide-min-latency -minline-float-divide-max-throughput -mno-inline-float-divide -minline-int-divide-min-latency -minline-int-divide-max-throughput -mno-inline-int-divide -minline-sqrt-min-latency -minline-sqrt-max-throughput -mno-inline-sqrt -mdwarf2-asm -mearly-stop-bits -mfixed-range=register-range -mtls-size=tls-size -mtune=cpu-type -milp32 -mlp64 -msched-br-data-spec -msched-ar-data-spec -msched-control-spec -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec -msched-spec-ldc -msched-spec-control-ldc -msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns -msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path -msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost -msched-max-memory-insns-hard-limit -msched-max-memory-insns=max- insns LM32 Options -mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled -msign-extend-enabled -muser-enabled LoongArch Options -march=cpu-type -mtune=cpu-type -mabi=base-abi- type -mfpu=fpu-type -msoft-float -msingle-float -mdouble-float -mbranch-cost=n -mcheck-zero-division -mno-check-zero-division -mcond-move-int -mno-cond-move-int -mcond-move-float -mno-cond-move-float -memcpy -mno-memcpy -mstrict-align -mno-strict-align -mmax-inline-memcpy-size=n -mexplicit-relocs -mno-explicit-relocs -mdirect-extern-access -mno-direct-extern-access -mcmodel=code-model M32R/D Options -m32r2 -m32rx -m32r -mdebug -malign-loops -mno-align-loops -missue-rate=number -mbranch-cost=number -mmodel=code-size-model-type -msdata=sdata-type -mno-flush-func -mflush-func=name -mno-flush-trap -mflush-trap=number -G num M32C Options -mcpu=cpu -msim -memregs=number M680x0 Options -march=arch -mcpu=cpu -mtune=tune -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort -mno-short -mhard-float -m68881 -msoft-float -mpcrel -malign-int -mstrict-align -msep-data -mno-sep-data -mshared-library-id=n -mid-shared-library -mno-id-shared-library -mxgot -mno-xgot -mlong-jump-table-offsets MCore Options -mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields -m4byte-functions -mno-4byte-functions -mcallgraph-data -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment MicroBlaze Options -msoft-float -mhard-float -msmall-divides -mcpu=cpu -mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift -mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss -mxl-multiply-high -mxl-float-convert -mxl-float-sqrt -mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-app-model -mpic-data-is-text-relative MIPS Options -EL -EB -march=arch -mtune=arch -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips32r3 -mips32r5 -mips32r6 -mips64 -mips64r2 -mips64r3 -mips64r5 -mips64r6 -mips16 -mno-mips16 -mflip-mips16 -minterlink-compressed -mno-interlink-compressed -minterlink-mips16 -mno-interlink-mips16 -mabi=abi -mabicalls -mno-abicalls -mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot -mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float -mno-float -msingle-float -mdouble-float -modd-spreg -mno-odd-spreg -mabs=mode -mnan=encoding -mdsp -mno-dsp -mdspr2 -mno-dspr2 -mmcu -mmno-mcu -meva -mno-eva -mvirt -mno-virt -mxpa -mno-xpa -mcrc -mno-crc -mginv -mno-ginv -mmicromips -mno-micromips -mmsa -mno-msa -mloongson-mmi -mno-loongson-mmi -mloongson-ext -mno-loongson-ext -mloongson-ext2 -mno-loongson-ext2 -mfpu=fpu- type -msmartmips -mno-smartmips -mpaired-single -mno-paired-single -mdmx -mno-mdmx -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc -mlong64 -mlong32 -msym32 -mno-sym32 -Gnum -mlocal-sdata -mno-local-sdata -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt -membedded-data -mno-embedded-data -muninit-const-in-rodata -mno-uninit-const-in-rodata -mcode-readable=setting -msplit-addresses -mno-split-addresses -mexplicit-relocs -mno-explicit-relocs -mcheck-zero-division -mno-check-zero-division -mdivide-traps -mdivide-breaks -mload-store-pairs -mno-load-store-pairs -munaligned-access -mno-unaligned-access -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls -mmad -mno-mad -mimadd -mno-imadd -mfused-madd -mno-fused-madd -nocpp -mfix-24k -mno-fix-24k -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 -mfix-r5900 -mno-fix-r5900 -mfix-r10000 -mno-fix-r10000 -mfix-rm7000 -mno-fix-rm7000 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 -mflush-func=func -mno-flush-func -mbranch-cost=num -mbranch-likely -mno-branch-likely -mcompact-branches=policy -mfp-exceptions -mno-fp-exceptions -mvr4130-align -mno-vr4130-align -msynci -mno-synci -mlxc1-sxc1 -mno-lxc1-sxc1 -mmadd4 -mno-madd4 -mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address -mframe-header-opt -mno-frame-header-opt MMIX Options -mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols -melf -mbranch-predict -mno-branch-predict -mbase-addresses -mno-base-addresses -msingle-exit -mno-single-exit MN10300 Options -mmult-bug -mno-mult-bug -mno-am33 -mam33 -mam33-2 -mam34 -mtune=cpu-type -mreturn-pointer-on-d0 -mno-crt0 -mrelax -mliw -msetlb Moxie Options -meb -mel -mmul.x -mno-crt0 MSP430 Options -msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax -mwarn-mcu -mcode-region= -mdata-region= -msilicon-errata= -msilicon-errata-warn= -mhwmult= -minrt -mtiny-printf -mmax-inline-shift= NDS32 Options -mbig-endian -mlittle-endian -mreduced-regs -mfull-regs -mcmov -mno-cmov -mext-perf -mno-ext-perf -mext-perf2 -mno-ext-perf2 -mext-string -mno-ext-string -mv3push -mno-v3push -m16bit -mno-16bit -misr-vector-size=num -mcache-block-size=num -march=arch -mcmodel=code-model -mctor-dtor -mrelax Nios II Options -G num -mgpopt=option -mgpopt -mno-gpopt -mgprel-sec=regexp -mr0rel-sec=regexp -mel -meb -mno-bypass-cache -mbypass-cache -mno-cache-volatile -mcache-volatile -mno-fast-sw-div -mfast-sw-div -mhw-mul -mno-hw-mul -mhw-mulx -mno-hw-mulx -mno-hw-div -mhw-div -mcustom-insn=N -mno-custom-insn -mcustom-fpu-cfg=name -mhal -msmallc -msys-crt0=name -msys-lib=name -march=arch -mbmx -mno-bmx -mcdx -mno-cdx Nvidia PTX Options -m64 -mmainkernel -moptimize OpenRISC Options -mboard=name -mnewlib -mhard-mul -mhard-div -msoft-mul -msoft-div -msoft-float -mhard-float -mdouble-float -munordered-float -mcmov -mror -mrori -msext -msfimm -mshftimm -mcmodel=code-model PDP-11 Options -mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 -mint32 -mno-int16 -mint16 -mno-int32 -msplit -munix-asm -mdec-asm -mgnu-asm -mlra PowerPC Options See RS/6000 and PowerPC Options. PRU Options -mmcu=mcu -minrt -mno-relax -mloop -mabi=variant RISC-V Options -mbranch-cost=N-instruction -mplt -mno-plt -mabi=ABI-string -mfdiv -mno-fdiv -mdiv -mno-div -misa-spec=ISA- spec-string -march=ISA-string -mtune=processor-string -mpreferred-stack-boundary=num -msmall-data-limit=N-bytes -msave-restore -mno-save-restore -mshorten-memrefs -mno-shorten-memrefs -mstrict-align -mno-strict-align -mcmodel=medlow -mcmodel=medany -mexplicit-relocs -mno-explicit-relocs -mrelax -mno-relax -mriscv-attribute -mno-riscv-attribute -malign-data=type -mbig-endian -mlittle-endian -mstack-protector-guard=guard -mstack-protector-guard-reg=reg -mstack-protector-guard-offset=offset -mcsr-check -mno-csr-check -minline-atomics -mno-inline-atomics RL78 Options -msim -mmul=none -mmul=g13 -mmul=g14 -mallregs -mcpu=g10 -mcpu=g13 -mcpu=g14 -mg10 -mg13 -mg14 -m64bit-doubles -m32bit-doubles -msave-mduc-in-interrupts RS/6000 and PowerPC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model -mpowerpc64 -maltivec -mno-altivec -mpowerpc-gpopt -mno-powerpc-gpopt -mpowerpc-gfxopt -mno-powerpc-gfxopt -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd -mfprnd -mno-fprnd -mcmpb -mno-cmpb -mhard-dfp -mno-hard-dfp -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc -m64 -m32 -mxl-compat -mno-xl-compat -mpe -malign-power -malign-natural -msoft-float -mhard-float -mmultiple -mno-multiple -mupdate -mno-update -mavoid-indexed-addresses -mno-avoid-indexed-addresses -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align -mstrict-align -mno-strict-align -mrelocatable -mno-relocatable -mrelocatable-lib -mno-relocatable-lib -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian -mdynamic-no-pic -mswdiv -msingle-pic-base -mprioritize-restricted-insns=priority -msched-costly-dep=dependence_type -minsert-sched-nops=scheme -mcall-aixdesc -mcall-eabi -mcall-freebsd -mcall-linux -mcall-netbsd -mcall-openbsd -mcall-sysv -mcall-sysv-eabi -mcall-sysv-noeabi -mtraceback=traceback_type -maix-struct-return -msvr4-struct-return -mabi=abi-type -msecure-plt -mbss-plt -mlongcall -mno-longcall -mpltseq -mno-pltseq -mblock-move-inline-limit=num -mblock-compare-inline-limit=num -mblock-compare-inline-loop-limit=num -mno-block-ops-unaligned-vsx -mstring-compare-inline-limit=num -misel -mno-isel -mvrsave -mno-vrsave -mmulhw -mno-mulhw -mdlmzb -mno-dlmzb -mprototype -mno-prototype -msim -mmvme -mads -myellowknife -memb -msdata -msdata=opt -mreadonly-in-sdata -mvxworks -G num -mrecip -mrecip=opt -mno-recip -mrecip-precision -mno-recip-precision -mveclibabi=type -mfriz -mno-friz -mpointers-to-nested-functions -mno-pointers-to-nested-functions -msave-toc-indirect -mno-save-toc-indirect -mpower8-fusion -mno-mpower8-fusion -mpower8-vector -mno-power8-vector -mcrypto -mno-crypto -mhtm -mno-htm -mquad-memory -mno-quad-memory -mquad-memory-atomic -mno-quad-memory-atomic -mcompat-align-parm -mno-compat-align-parm -mfloat128 -mno-float128 -mfloat128-hardware -mno-float128-hardware -mgnu-attribute -mno-gnu-attribute -mstack-protector-guard=guard -mstack-protector-guard-reg=reg -mstack-protector-guard-offset=offset -mprefixed -mno-prefixed -mpcrel -mno-pcrel -mmma -mno-mmma -mrop-protect -mno-rop-protect -mprivileged -mno-privileged RX Options -m64bit-doubles -m32bit-doubles -fpu -nofpu -mcpu= -mbig-endian-data -mlittle-endian-data -msmall-data -msim -mno-sim -mas100-syntax -mno-as100-syntax -mrelax -mmax-constant-size= -mint-register= -mpid -mallow-string-insns -mno-allow-string-insns -mjsr -mno-warn-multiple-fast-interrupts -msave-acc-in-interrupts S/390 and zSeries Options -mtune=cpu-type -march=cpu-type -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp -mlong-double-64 -mlong-double-128 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack -msmall-exec -mno-small-exec -mmvcle -mno-mvcle -m64 -m31 -mdebug -mno-debug -mesa -mzarch -mhtm -mvx -mzvector -mtpf-trace -mno-tpf-trace -mtpf-trace-skip -mno-tpf-trace-skip -mfused-madd -mno-fused-madd -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard -mhotpatch=halfwords,halfwords SH Options -m1 -m2 -m2e -m2a-nofpu -m2a-single-only -m2a-single -m2a -m3 -m3e -m4-nofpu -m4-single-only -m4-single -m4 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al -mb -ml -mdalign -mrelax -mbigtable -mfmovd -mrenesas -mno-renesas -mnomacsave -mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct -mprefergot -musermode -multcost=number -mdiv=strategy -mdivsi3_libfunc=name -mfixed-range=register-range -maccumulate-outgoing-args -matomic-model=atomic-model -mbranch-cost=num -mzdcbranch -mno-zdcbranch -mcbranch-force-delay-slot -mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra -mpretend-cmove -mtas Solaris 2 Options -mclear-hwcap -mno-clear-hwcap -mimpure-text -mno-impure-text -pthreads SPARC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model -mmemory-model=mem-model -m32 -m64 -mapp-regs -mno-app-regs -mfaster-structs -mno-faster-structs -mflat -mno-flat -mfpu -mno-fpu -mhard-float -msoft-float -mhard-quad-float -msoft-quad-float -mstack-bias -mno-stack-bias -mstd-struct-return -mno-std-struct-return -munaligned-doubles -mno-unaligned-doubles -muser-mode -mno-user-mode -mv8plus -mno-v8plus -mvis -mno-vis -mvis2 -mno-vis2 -mvis3 -mno-vis3 -mvis4 -mno-vis4 -mvis4b -mno-vis4b -mcbcond -mno-cbcond -mfmaf -mno-fmaf -mfsmuld -mno-fsmuld -mpopc -mno-popc -msubxc -mno-subxc -mfix-at697f -mfix-ut699 -mfix-ut700 -mfix-gr712rc -mlra -mno-lra System V Options -Qy -Qn -YP,paths -Ym,dir V850 Options -mlong-calls -mno-long-calls -mep -mno-ep -mprolog-function -mno-prolog-function -mspace -mtda=n -msda=n -mzda=n -mapp-regs -mno-app-regs -mdisable-callt -mno-disable-callt -mv850e2v3 -mv850e2 -mv850e1 -mv850es -mv850e -mv850 -mv850e3v5 -mloop -mrelax -mlong-jumps -msoft-float -mhard-float -mgcc-abi -mrh850-abi -mbig-switch VAX Options -mg -mgnu -munix -mlra Visium Options -mdebug -msim -mfpu -mno-fpu -mhard-float -msoft-float -mcpu=cpu-type -mtune=cpu-type -msv-mode -muser-mode VMS Options -mvms-return-codes -mdebug-main=prefix -mmalloc64 -mpointer-size=size VxWorks Options -mrtp -non-static -Bstatic -Bdynamic -Xbind-lazy -Xbind-now x86 Options -mtune=cpu-type -march=cpu-type -mtune-ctrl=feature- list -mdump-tune-features -mno-default -mfpmath=unit -masm=dialect -mno-fancy-math-387 -mno-fp-ret-in-387 -m80387 -mhard-float -msoft-float -mno-wide-multiply -mrtd -malign-double -mpreferred-stack-boundary=num -mincoming-stack-boundary=num -mcld -mcx16 -msahf -mmovbe -mcrc32 -mmwait -mrecip -mrecip=opt -mvzeroupper -mprefer-avx128 -mprefer-vector-width=opt -mmove-max=bits -mstore-max=bits -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx -mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -mavx512vl -mavx512bw -mavx512dq -mavx512ifma -mavx512vbmi -msha -maes -mpclmul -mfsgsbase -mrdrnd -mf16c -mfma -mpconfig -mwbnoinvd -mptwrite -mprefetchwt1 -mclflushopt -mclwb -mxsavec -mxsaves -msse4a -m3dnow -m3dnowa -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -madx -mlzcnt -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mhle -mlwp -mmwaitx -mclzero -mpku -mthreads -mgfni -mvaes -mwaitpkg -mshstk -mmanual-endbr -mcet-switch -mforce-indirect-call -mavx512vbmi2 -mavx512bf16 -menqcmd -mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b -mavx512vpopcntdq -mavx5124fmaps -mavx512vnni -mavx5124vnniw -mprfchw -mrdpid -mrdseed -msgx -mavx512vp2intersect -mserialize -mtsxldtrk -mamx-tile -mamx-int8 -mamx-bf16 -muintr -mhreset -mavxvnni -mavx512fp16 -mavxifma -mavxvnniint8 -mavxneconvert -mcmpccxadd -mamx-fp16 -mprefetchi -mraoint -mamx-complex -mcldemote -mms-bitfields -mno-align-stringops -minline-all-stringops -minline-stringops-dynamically -mstringop-strategy=alg -mkl -mwidekl -mmemcpy-strategy=strategy -mmemset-strategy=strategy -mpush-args -maccumulate-outgoing-args -m128bit-long-double -m96bit-long-double -mlong-double-64 -mlong-double-80 -mlong-double-128 -mregparm=num -msseregparm -mveclibabi=type -mvect8-ret-in-mem -mpc32 -mpc64 -mpc80 -mdaz-ftz -mstackrealign -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs -mcmodel=code-model -mabi=name -maddress-mode=mode -m32 -m64 -mx32 -m16 -miamcu -mlarge-data-threshold=num -msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv -minstrument-return=type -mfentry-name=name -mfentry-section=name -mavx256-split-unaligned-load -mavx256-split-unaligned-store -malign-data=type -mstack-protector-guard=guard -mstack-protector-guard-reg=reg -mstack-protector-guard-offset=offset -mstack-protector-guard-symbol=symbol -mgeneral-regs-only -mcall-ms2sysv-xlogues -mrelax-cmpxchg-loop -mindirect-branch=choice -mfunction-return=choice -mindirect-branch-register -mharden-sls=choice -mindirect-branch-cs-prefix -mneeded -mno-direct-extern-access -munroll-only-small-loops -mlam=choice x86 Windows Options -mconsole -mcygwin -mno-cygwin -mdll -mnop-fun-dllimport -mthread -municode -mwin32 -mwindows -fno-set-stack-executable Xstormy16 Options -msim Xtensa Options -mconst16 -mno-const16 -mfused-madd -mno-fused-madd -mforce-no-pic -mserialize-volatile -mno-serialize-volatile -mtext-section-literals -mno-text-section-literals -mauto-litpools -mno-auto-litpools -mtarget-align -mno-target-align -mlongcalls -mno-longcalls -mabi=abi-type -mextra-l32r-costs=cycles zSeries Options See S/390 and zSeries Options. Options Controlling the Kind of Output Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. GCC is capable of preprocessing and compiling several files either into several assembler input files, or into one assembler input file; then each assembler input file produces an object file, and linking combines all the object files (those newly compiled, and those specified as input) into an executable file. For any given input file, the file name suffix determines what kind of compilation is done: file.c C source code that must be preprocessed. file.i C source code that should not be preprocessed. file.ii C++ source code that should not be preprocessed. file.m Objective-C source code. Note that you must link with the libobjc library to make an Objective-C program work. file.mi Objective-C source code that should not be preprocessed. file.mm file.M Objective-C++ source code. Note that you must link with the libobjc library to make an Objective-C++ program work. Note that .M refers to a literal capital M. file.mii Objective-C++ source code that should not be preprocessed. file.h C, C++, Objective-C or Objective-C++ header file to be turned into a precompiled header (default), or C, C++ header file to be turned into an Ada spec (via the -fdump-ada-spec switch). file.cc file.cp file.cxx file.cpp file.CPP file.c++ file.C C++ source code that must be preprocessed. Note that in .cxx, the last two letters must both be literally x. Likewise, .C refers to a literal capital C. file.mm file.M Objective-C++ source code that must be preprocessed. file.mii Objective-C++ source code that should not be preprocessed. file.hh file.H file.hp file.hxx file.hpp file.HPP file.h++ file.tcc C++ header file to be turned into a precompiled header or Ada spec. file.f file.for file.ftn Fixed form Fortran source code that should not be preprocessed. file.F file.FOR file.fpp file.FPP file.FTN Fixed form Fortran source code that must be preprocessed (with the traditional preprocessor). file.f90 file.f95 file.f03 file.f08 Free form Fortran source code that should not be preprocessed. file.F90 file.F95 file.F03 file.F08 Free form Fortran source code that must be preprocessed (with the traditional preprocessor). file.go Go source code. file.d D source code. file.di D interface file. file.dd D documentation code (Ddoc). file.ads Ada source code file that contains a library unit declaration (a declaration of a package, subprogram, or generic, or a generic instantiation), or a library unit renaming declaration (a package, generic, or subprogram renaming declaration). Such files are also called specs. file.adb Ada source code file containing a library unit body (a subprogram or package body). Such files are also called bodies. file.s Assembler code. file.S file.sx Assembler code that must be preprocessed. other An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way. You can specify the input language explicitly with the -x option: -x language Specify explicitly the language for the following input files (rather than letting the compiler choose a default based on the file name suffix). This option applies to all following input files until the next -x option. Possible values for language are: c c-header cpp-output c++ c++-header c++-system-header c++-user-header c++-cpp-output objective-c objective-c-header objective-c-cpp-output objective-c++ objective-c++-header objective-c++-cpp-output assembler assembler-with-cpp ada d f77 f77-cpp-input f95 f95-cpp-input go -x none Turn off any specification of a language, so that subsequent files are handled according to their file name suffixes (as they are if -x has not been used at all). If you only want some of the stages of compilation, you can use -x (or filename suffixes) to tell gcc where to start, and one of the options -c, -S, or -E to say where gcc is to stop. Note that some combinations (for example, -x cpp-output -E) instruct gcc to do nothing at all. -c Compile or assemble the source files, but do not link. The linking stage simply is not done. The ultimate output is in the form of an object file for each source file. By default, the object file name for a source file is made by replacing the suffix .c, .i, .s, etc., with .o. Unrecognized input files, not requiring compilation or assembly, are ignored. -S Stop after the stage of compilation proper; do not assemble. The output is in the form of an assembler code file for each non- assembler input file specified. By default, the assembler file name for a source file is made by replacing the suffix .c, .i, etc., with .s. Input files that don't require compilation are ignored. -E Stop after the preprocessing stage; do not run the compiler proper. The output is in the form of preprocessed source code, which is sent to the standard output. Input files that don't require preprocessing are ignored. -o file Place the primary output in file file. This applies to whatever sort of output is being produced, whether it be an executable file, an object file, an assembler file or preprocessed C code. If -o is not specified, the default is to put an executable file in a.out, the object file for source.suffix in source.o, its assembler file in source.s, a precompiled header file in source.suffix.gch, and all preprocessed C source on standard output. Though -o names only the primary output, it also affects the naming of auxiliary and dump outputs. See the examples below. Unless overridden, both auxiliary outputs and dump outputs are placed in the same directory as the primary output. In auxiliary outputs, the suffix of the input file is replaced with that of the auxiliary output file type; in dump outputs, the suffix of the dump file is appended to the input file suffix. In compilation commands, the base name of both auxiliary and dump outputs is that of the primary output; in compile and link commands, the primary output name, minus the executable suffix, is combined with the input file name. If both share the same base name, disregarding the suffix, the result of the combination is that base name, otherwise, they are concatenated, separated by a dash. gcc -c foo.c ... will use foo.o as the primary output, and place aux outputs and dumps next to it, e.g., aux file foo.dwo for -gsplit-dwarf, and dump file foo.c.???r.final for -fdump-rtl-final. If a non-linker output file is explicitly specified, aux and dump files by default take the same base name: gcc -c foo.c -o dir/foobar.o ... will name aux outputs dir/foobar.* and dump outputs dir/foobar.c.*. A linker output will instead prefix aux and dump outputs: gcc foo.c bar.c -o dir/foobar ... will generally name aux outputs dir/foobar-foo.* and dir/foobar-bar.*, and dump outputs dir/foobar-foo.c.* and dir/foobar-bar.c.*. The one exception to the above is when the executable shares the base name with the single input: gcc foo.c -o dir/foo ... in which case aux outputs are named dir/foo.* and dump outputs named dir/foo.c.*. The location and the names of auxiliary and dump outputs can be adjusted by the options -dumpbase, -dumpbase-ext, -dumpdir, -save-temps=cwd, and -save-temps=obj. -dumpbase dumpbase This option sets the base name for auxiliary and dump output files. It does not affect the name of the primary output file. Intermediate outputs, when preserved, are not regarded as primary outputs, but as auxiliary outputs: gcc -save-temps -S foo.c saves the (no longer) temporary preprocessed file in foo.i, and then compiles to the (implied) output file foo.s, whereas: gcc -save-temps -dumpbase save-foo -c foo.c preprocesses to in save-foo.i, compiles to save-foo.s (now an intermediate, thus auxiliary output), and then assembles to the (implied) output file foo.o. Absent this option, dump and aux files take their names from the input file, or from the (non-linker) output file, if one is explicitly specified: dump output files (e.g. those requested by -fdump-* options) with the input name suffix, and aux output files (those requested by other non-dump options, e.g. "-save-temps", "-gsplit-dwarf", "-fcallgraph-info") without it. Similar suffix differentiation of dump and aux outputs can be attained for explicitly-given -dumpbase basename.suf by also specifying -dumpbase-ext .suf. If dumpbase is explicitly specified with any directory component, any dumppfx specification (e.g. -dumpdir or -save-temps=*) is ignored, and instead of appending to it, dumpbase fully overrides it: gcc foo.c -c -o dir/foo.o -dumpbase alt/foo \ -dumpdir pfx- -save-temps=cwd ... creates auxiliary and dump outputs named alt/foo.*, disregarding dir/ in -o, the ./ prefix implied by -save-temps=cwd, and pfx- in -dumpdir. When -dumpbase is specified in a command that compiles multiple inputs, or that compiles and then links, it may be combined with dumppfx, as specified under -dumpdir. Then, each input file is compiled using the combined dumppfx, and default values for dumpbase and auxdropsuf are computed for each input file: gcc foo.c bar.c -c -dumpbase main ... creates foo.o and bar.o as primary outputs, and avoids overwriting the auxiliary and dump outputs by using the dumpbase as a prefix, creating auxiliary and dump outputs named main-foo.* and main-bar.*. An empty string specified as dumpbase avoids the influence of the output basename in the naming of auxiliary and dump outputs during compilation, computing default values : gcc -c foo.c -o dir/foobar.o -dumpbase " ... will name aux outputs dir/foo.* and dump outputs dir/foo.c.*. Note how their basenames are taken from the input name, but the directory still defaults to that of the output. The empty-string dumpbase does not prevent the use of the output basename for outputs during linking: gcc foo.c bar.c -o dir/foobar -dumpbase " -flto ... The compilation of the source files will name auxiliary outputs dir/foo.* and dir/bar.*, and dump outputs dir/foo.c.* and dir/bar.c.*. LTO recompilation during linking will use dir/foobar. as the prefix for dumps and auxiliary files. -dumpbase-ext auxdropsuf When forming the name of an auxiliary (but not a dump) output file, drop trailing auxdropsuf from dumpbase before appending any suffixes. If not specified, this option defaults to the suffix of a default dumpbase, i.e., the suffix of the input file when -dumpbase is not present in the command line, or dumpbase is combined with dumppfx. gcc foo.c -c -o dir/foo.o -dumpbase x-foo.c -dumpbase-ext .c ... creates dir/foo.o as the main output, and generates auxiliary outputs in dir/x-foo.*, taking the location of the primary output, and dropping the .c suffix from the dumpbase. Dump outputs retain the suffix: dir/x-foo.c.*. This option is disregarded if it does not match the suffix of a specified dumpbase, except as an alternative to the executable suffix when appending the linker output base name to dumppfx, as specified below: gcc foo.c bar.c -o main.out -dumpbase-ext .out ... creates main.out as the primary output, and avoids overwriting the auxiliary and dump outputs by using the executable name minus auxdropsuf as a prefix, creating auxiliary outputs named main-foo.* and main-bar.* and dump outputs named main-foo.c.* and main-bar.c.*. -dumpdir dumppfx When forming the name of an auxiliary or dump output file, use dumppfx as a prefix: gcc -dumpdir pfx- -c foo.c ... creates foo.o as the primary output, and auxiliary outputs named pfx-foo.*, combining the given dumppfx with the default dumpbase derived from the default primary output, derived in turn from the input name. Dump outputs also take the input name suffix: pfx-foo.c.*. If dumppfx is to be used as a directory name, it must end with a directory separator: gcc -dumpdir dir/ -c foo.c -o obj/bar.o ... creates obj/bar.o as the primary output, and auxiliary outputs named dir/bar.*, combining the given dumppfx with the default dumpbase derived from the primary output name. Dump outputs also take the input name suffix: dir/bar.c.*. It defaults to the location of the output file, unless the output file is a special file like "/dev/null". Options -save-temps=cwd and -save-temps=obj override this default, just like an explicit -dumpdir option. In case multiple such options are given, the last one prevails: gcc -dumpdir pfx- -c foo.c -save-temps=obj ... outputs foo.o, with auxiliary outputs named foo.* because -save-temps=* overrides the dumppfx given by the earlier -dumpdir option. It does not matter that =obj is the default for -save-temps, nor that the output directory is implicitly the current directory. Dump outputs are named foo.c.*. When compiling from multiple input files, if -dumpbase is specified, dumpbase, minus a auxdropsuf suffix, and a dash are appended to (or override, if containing any directory components) an explicit or defaulted dumppfx, so that each of the multiple compilations gets differently-named aux and dump outputs. gcc foo.c bar.c -c -dumpdir dir/pfx- -dumpbase main ... outputs auxiliary dumps to dir/pfx-main-foo.* and dir/pfx-main-bar.*, appending dumpbase- to dumppfx. Dump outputs retain the input file suffix: dir/pfx-main-foo.c.* and dir/pfx-main-bar.c.*, respectively. Contrast with the single-input compilation: gcc foo.c -c -dumpdir dir/pfx- -dumpbase main ... that, applying -dumpbase to a single source, does not compute and append a separate dumpbase per input file. Its auxiliary and dump outputs go in dir/pfx-main.*. When compiling and then linking from multiple input files, a defaulted or explicitly specified dumppfx also undergoes the dumpbase- transformation above (e.g. the compilation of foo.c and bar.c above, but without -c). If neither -dumpdir nor -dumpbase are given, the linker output base name, minus auxdropsuf, if specified, or the executable suffix otherwise, plus a dash is appended to the default dumppfx instead. Note, however, that unlike earlier cases of linking: gcc foo.c bar.c -dumpdir dir/pfx- -o main ... does not append the output name main to dumppfx, because -dumpdir is explicitly specified. The goal is that the explicitly-specified dumppfx may contain the specified output name as part of the prefix, if desired; only an explicitly-specified -dumpbase would be combined with it, in order to avoid simply discarding a meaningful option. When compiling and then linking from a single input file, the linker output base name will only be appended to the default dumppfx as above if it does not share the base name with the single input file name. This has been covered in single-input linking cases above, but not with an explicit -dumpdir that inhibits the combination, even if overridden by -save-temps=*: gcc foo.c -dumpdir alt/pfx- -o dir/main.exe -save-temps=cwd ... Auxiliary outputs are named foo.*, and dump outputs foo.c.*, in the current working directory as ultimately requested by -save-temps=cwd. Summing it all up for an intuitive though slightly imprecise data flow: the primary output name is broken into a directory part and a basename part; dumppfx is set to the former, unless overridden by -dumpdir or -save-temps=*, and dumpbase is set to the latter, unless overriden by -dumpbase. If there are multiple inputs or linking, this dumpbase may be combined with dumppfx and taken from each input file. Auxiliary output names for each input are formed by combining dumppfx, dumpbase minus suffix, and the auxiliary output suffix; dump output names are only different in that the suffix from dumpbase is retained. When it comes to auxiliary and dump outputs created during LTO recompilation, a combination of dumppfx and dumpbase, as given or as derived from the linker output name but not from inputs, even in cases in which this combination would not otherwise be used as such, is passed down with a trailing period replacing the compiler- added dash, if any, as a -dumpdir option to lto-wrapper; being involved in linking, this program does not normally get any -dumpbase and -dumpbase-ext, and it ignores them. When running sub-compilers, lto-wrapper appends LTO stage names to the received dumppfx, ensures it contains a directory component so that it overrides any -dumpdir, and passes that as -dumpbase to sub-compilers. -v Print (on standard error output) the commands executed to run the stages of compilation. Also print the version number of the compiler driver program and of the preprocessor and the compiler proper. -### Like -v except the commands are not executed and arguments are quoted unless they contain only alphanumeric characters or "./-_". This is useful for shell scripts to capture the driver-generated command lines. --help Print (on the standard output) a description of the command-line options understood by gcc. If the -v option is also specified then --help is also passed on to the various processes invoked by gcc, so that they can display the command-line options they accept. If the -Wextra option has also been specified (prior to the --help option), then command-line options that have no documentation associated with them are also displayed. --target-help Print (on the standard output) a description of target-specific command-line options for each tool. For some targets extra target- specific information may also be printed. --help={class|[^]qualifier}[,...] Print (on the standard output) a description of the command-line options understood by the compiler that fit into all specified classes and qualifiers. These are the supported classes: optimizers Display all of the optimization options supported by the compiler. warnings Display all of the options controlling warning messages produced by the compiler. target Display target-specific options. Unlike the --target-help option however, target-specific options of the linker and assembler are not displayed. This is because those tools do not currently support the extended --help= syntax. params Display the values recognized by the --param option. language Display the options supported for language, where language is the name of one of the languages supported in this version of GCC. If an option is supported by all languages, one needs to select common class. common Display the options that are common to all languages. These are the supported qualifiers: undocumented Display only those options that are undocumented. joined Display options taking an argument that appears after an equal sign in the same continuous piece of text, such as: --help=target. separate Display options taking an argument that appears as a separate word following the original option, such as: -o output-file. Thus for example to display all the undocumented target-specific switches supported by the compiler, use: --help=target,undocumented The sense of a qualifier can be inverted by prefixing it with the ^ character, so for example to display all binary warning options (i.e., ones that are either on or off and that do not take an argument) that have a description, use: --help=warnings,^joined,^undocumented The argument to --help= should not consist solely of inverted qualifiers. Combining several classes is possible, although this usually restricts the output so much that there is nothing to display. One case where it does work, however, is when one of the classes is target. For example, to display all the target-specific optimization options, use: --help=target,optimizers The --help= option can be repeated on the command line. Each successive use displays its requested class of options, skipping those that have already been displayed. If --help is also specified anywhere on the command line then this takes precedence over any --help= option. If the -Q option appears on the command line before the --help= option, then the descriptive text displayed by --help= is changed. Instead of describing the displayed options, an indication is given as to whether the option is enabled, disabled or set to a specific value (assuming that the compiler knows this at the point where the --help= option is used). Here is a truncated example from the ARM port of gcc: % gcc -Q -mabi=2 --help=target -c The following options are target specific: -mabi= 2 -mabort-on-noreturn [disabled] -mapcs [disabled] The output is sensitive to the effects of previous command-line options, so for example it is possible to find out which optimizations are enabled at -O2 by using: -Q -O2 --help=optimizers Alternatively you can discover which binary optimizations are enabled by -O3 by using: gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts diff /tmp/O2-opts /tmp/O3-opts | grep enabled --version Display the version number and copyrights of the invoked GCC. -pass-exit-codes Normally the gcc program exits with the code of 1 if any phase of the compiler returns a non-success return code. If you specify -pass-exit-codes, the gcc program instead returns with the numerically highest error produced by any phase returning an error indication. The C, C++, and Fortran front ends return 4 if an internal compiler error is encountered. -pipe Use pipes rather than temporary files for communication between the various stages of compilation. This fails to work on some systems where the assembler is unable to read from a pipe; but the GNU assembler has no trouble. -specs=file Process file after the compiler reads in the standard specs file, in order to override the defaults which the gcc driver program uses when determining what switches to pass to cc1, cc1plus, as, ld, etc. More than one -specs=file can be specified on the command line, and they are processed in order, from left to right. -wrapper Invoke all subcommands under a wrapper program. The name of the wrapper program and its parameters are passed as a comma separated list. gcc -c t.c -wrapper gdb,--args This invokes all subprograms of gcc under gdb --args, thus the invocation of cc1 is gdb --args cc1 .... -ffile-prefix-map=old=new When compiling files residing in directory old, record any references to them in the result of the compilation as if the files resided in directory new instead. Specifying this option is equivalent to specifying all the individual -f*-prefix-map options. This can be used to make reproducible builds that are location independent. Directories referenced by directives are not affected by these options. See also -fmacro-prefix-map, -fdebug-prefix-map, -fprofile-prefix-map and -fcanon-prefix-map. -fcanon-prefix-map For the -f*-prefix-map options normally comparison of old prefix against the filename that would be normally referenced in the result of the compilation is done using textual comparison of the prefixes, or ignoring character case for case insensitive filesystems and considering slashes and backslashes as equal on DOS based filesystems. The -fcanon-prefix-map causes such comparisons to be done on canonicalized paths of old and the referenced filename. -fplugin=name.so Load the plugin code in file name.so, assumed to be a shared object to be dlopen'd by the compiler. The base name of the shared object file is used to identify the plugin for the purposes of argument parsing (See -fplugin-arg-name-key=value below). Each plugin should define the callback functions specified in the Plugins API. -fplugin-arg-name-key=value Define an argument called key with a value of value for the plugin called name. -fdump-ada-spec[-slim] For C and C++ source and include files, generate corresponding Ada specs. -fada-spec-parent=unit In conjunction with -fdump-ada-spec[-slim] above, generate Ada specs as child units of parent unit. -fdump-go-spec=file For input files in any language, generate corresponding Go declarations in file. This generates Go "const", "type", "var", and "func" declarations which may be a useful way to start writing a Go interface to code written in some other language. @file Read command-line options from file. The options read are inserted in place of the original @file option. If file does not exist, or cannot be read, then the option will be treated literally, and not removed. Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional @file options; any such options will be processed recursively. Compiling C++ Programs C++ source files conventionally use one of the suffixes .C, .cc, .cpp, .CPP, .c++, .cp, or .cxx; C++ header files often use .hh, .hpp, .H, or (for shared template code) .tcc; and preprocessed C++ files use the suffix .ii. GCC recognizes files with these names and compiles them as C++ programs even if you call the compiler the same way as for compiling C programs (usually with the name gcc). However, the use of gcc does not add the C++ library. g++ is a program that calls GCC and automatically specifies linking against the C++ library. It treats .c, .h and .i files as C++ source files instead of C source files unless -x is used. This program is also useful when precompiling a C header file with a .h extension for use in C++ compilations. On many systems, g++ is also installed with the name c++. When you compile C++ programs, you may specify many of the same command-line options that you use for compiling programs in any language; or command-line options meaningful for C and related languages; or options that are meaningful only for C++ programs. Options Controlling C Dialect The following options control the dialect of C (or languages derived from C, such as C++, Objective-C and Objective-C++) that the compiler accepts: -ansi In C mode, this is equivalent to -std=c90. In C++ mode, it is equivalent to -std=c++98. This turns off certain features of GCC that are incompatible with ISO C90 (when compiling C code), or of standard C++ (when compiling C++ code), such as the "asm" and "typeof" keywords, and predefined macros such as "unix" and "vax" that identify the type of system you are using. It also enables the undesirable and rarely used ISO trigraph feature. For the C compiler, it disables recognition of C++ style // comments as well as the "inline" keyword. The alternate keywords "__asm__", "__extension__", "__inline__" and "__typeof__" continue to work despite -ansi. You would not want to use them in an ISO C program, of course, but it is useful to put them in header files that might be included in compilations done with -ansi. Alternate predefined macros such as "__unix__" and "__vax__" are also available, with or without -ansi. The -ansi option does not cause non-ISO programs to be rejected gratuitously. For that, -Wpedantic is required in addition to -ansi. The macro "__STRICT_ANSI__" is predefined when the -ansi option is used. Some header files may notice this macro and refrain from declaring certain functions or defining certain macros that the ISO standard doesn't call for; this is to avoid interfering with any programs that might use these names for other things. Functions that are normally built in but do not have semantics defined by ISO C (such as "alloca" and "ffs") are not built-in functions when -ansi is used. -std= Determine the language standard. This option is currently only supported when compiling C or C++. The compiler can accept several base standards, such as c90 or c++98, and GNU dialects of those standards, such as gnu90 or gnu++98. When a base standard is specified, the compiler accepts all programs following that standard plus those using GNU extensions that do not contradict it. For example, -std=c90 turns off certain features of GCC that are incompatible with ISO C90, such as the "asm" and "typeof" keywords, but not other GNU extensions that do not have a meaning in ISO C90, such as omitting the middle term of a "?:" expression. On the other hand, when a GNU dialect of a standard is specified, all features supported by the compiler are enabled, even when those features change the meaning of the base standard. As a result, some strict-conforming programs may be rejected. The particular standard is used by -Wpedantic to identify which features are GNU extensions given that version of the standard. For example -std=gnu90 -Wpedantic warns about C++ style // comments, while -std=gnu99 -Wpedantic does not. A value for this option must be provided; possible values are c90 c89 iso9899:1990 Support all ISO C90 programs (certain GNU extensions that conflict with ISO C90 are disabled). Same as -ansi for C code. iso9899:199409 ISO C90 as modified in amendment 1. c99 c9x iso9899:1999 iso9899:199x ISO C99. This standard is substantially completely supported, modulo bugs and floating-point issues (mainly but not entirely relating to optional C99 features from Annexes F and G). See <https://gcc.gnu.org/c99status.html> for more information. The names c9x and iso9899:199x are deprecated. c11 c1x iso9899:2011 ISO C11, the 2011 revision of the ISO C standard. This standard is substantially completely supported, modulo bugs, floating-point issues (mainly but not entirely relating to optional C11 features from Annexes F and G) and the optional Annexes K (Bounds-checking interfaces) and L (Analyzability). The name c1x is deprecated. c17 c18 iso9899:2017 iso9899:2018 ISO C17, the 2017 revision of the ISO C standard (published in 2018). This standard is same as C11 except for corrections of defects (all of which are also applied with -std=c11) and a new value of "__STDC_VERSION__", and so is supported to the same extent as C11. c2x The next version of the ISO C standard, still under development. The support for this version is experimental and incomplete. gnu90 gnu89 GNU dialect of ISO C90 (including some C99 features). gnu99 gnu9x GNU dialect of ISO C99. The name gnu9x is deprecated. gnu11 gnu1x GNU dialect of ISO C11. The name gnu1x is deprecated. gnu17 gnu18 GNU dialect of ISO C17. This is the default for C code. gnu2x The next version of the ISO C standard, still under development, plus GNU extensions. The support for this version is experimental and incomplete. c++98 c++03 The 1998 ISO C++ standard plus the 2003 technical corrigendum and some additional defect reports. Same as -ansi for C++ code. gnu++98 gnu++03 GNU dialect of -std=c++98. c++11 c++0x The 2011 ISO C++ standard plus amendments. The name c++0x is deprecated. gnu++11 gnu++0x GNU dialect of -std=c++11. The name gnu++0x is deprecated. c++14 c++1y The 2014 ISO C++ standard plus amendments. The name c++1y is deprecated. gnu++14 gnu++1y GNU dialect of -std=c++14. The name gnu++1y is deprecated. c++17 c++1z The 2017 ISO C++ standard plus amendments. The name c++1z is deprecated. gnu++17 gnu++1z GNU dialect of -std=c++17. This is the default for C++ code. The name gnu++1z is deprecated. c++20 c++2a The 2020 ISO C++ standard plus amendments. Support is experimental, and could change in incompatible ways in future releases. The name c++2a is deprecated. gnu++20 gnu++2a GNU dialect of -std=c++20. Support is experimental, and could change in incompatible ways in future releases. The name gnu++2a is deprecated. c++2b c++23 The next revision of the ISO C++ standard, planned for 2023. Support is highly experimental, and will almost certainly change in incompatible ways in future releases. gnu++2b gnu++23 GNU dialect of -std=c++2b. Support is highly experimental, and will almost certainly change in incompatible ways in future releases. -aux-info filename Output to the given filename prototyped declarations for all functions declared and/or defined in a translation unit, including those in header files. This option is silently ignored in any language other than C. Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (I, N for new or O for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition (C or F, respectively, in the following character). In the case of function definitions, a K&R-style list of arguments followed by their declarations is also provided, inside comments, after the declaration. -fno-asm Do not recognize "asm", "inline" or "typeof" as a keyword, so that code can use these words as identifiers. You can use the keywords "__asm__", "__inline__" and "__typeof__" instead. In C, -ansi implies -fno-asm. In C++, "inline" is a standard keyword and is not affected by this switch. You may want to use the -fno-gnu-keywords flag instead, which disables "typeof" but not "asm" and "inline". In C99 mode (-std=c99 or -std=gnu99), this switch only affects the "asm" and "typeof" keywords, since "inline" is a standard keyword in ISO C99. In C2X mode (-std=c2x or -std=gnu2x), this switch only affects the "asm" keyword, since "typeof" is a standard keyword in ISO C2X. -fno-builtin -fno-builtin-function Don't recognize built-in functions that do not begin with __builtin_ as prefix. GCC normally generates special code to handle certain built-in functions more efficiently; for instance, calls to "alloca" may become single instructions which adjust the stack directly, and calls to "memcpy" may become inline copy loops. The resulting code is often both smaller and faster, but since the function calls no longer appear as such, you cannot set a breakpoint on those calls, nor can you change the behavior of the functions by linking with a different library. In addition, when a function is recognized as a built-in function, GCC may use information about that function to warn about problems with calls to that function, or to generate more efficient code, even if the resulting code still contains calls to that function. For example, warnings are given with -Wformat for bad calls to "printf" when "printf" is built in and "strlen" is known not to modify global memory. With the -fno-builtin-function option only the built-in function function is disabled. function must not begin with __builtin_. If a function is named that is not built-in in this version of GCC, this option is ignored. There is no corresponding -fbuiltin-function option; if you wish to enable built-in functions selectively when using -fno-builtin or -ffreestanding, you may define macros such as: #define abs(n) __builtin_abs ((n)) #define strcpy(d, s) __builtin_strcpy ((d), (s)) -fcond-mismatch Allow conditional expressions with mismatched types in the second and third arguments. The value of such an expression is void. This option is not supported for C++. -ffreestanding Assert that compilation targets a freestanding environment. This implies -fno-builtin. A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at "main". The most obvious example is an OS kernel. This is equivalent to -fno-hosted. -fgimple Enable parsing of function definitions marked with "__GIMPLE". This is an experimental feature that allows unit testing of GIMPLE passes. -fgnu-tm When the option -fgnu-tm is specified, the compiler generates code for the Linux variant of Intel's current Transactional Memory ABI specification document (Revision 1.1, May 6 2009). This is an experimental feature whose interface may change in future versions of GCC, as the official specification changes. Please note that not all architectures are supported for this feature. For more information on GCC's support for transactional memory, Note that the transactional memory feature is not supported with non-call exceptions (-fnon-call-exceptions). -fgnu89-inline The option -fgnu89-inline tells GCC to use the traditional GNU semantics for "inline" functions when in C99 mode. Using this option is roughly equivalent to adding the "gnu_inline" function attribute to all inline functions. The option -fno-gnu89-inline explicitly tells GCC to use the C99 semantics for "inline" when in C99 or gnu99 mode (i.e., it specifies the default behavior). This option is not supported in -std=c90 or -std=gnu90 mode. The preprocessor macros "__GNUC_GNU_INLINE__" and "__GNUC_STDC_INLINE__" may be used to check which semantics are in effect for "inline" functions. -fhosted Assert that compilation targets a hosted environment. This implies -fbuiltin. A hosted environment is one in which the entire standard library is available, and in which "main" has a return type of "int". Examples are nearly everything except a kernel. This is equivalent to -fno-freestanding. -flax-vector-conversions Allow implicit conversions between vectors with differing numbers of elements and/or incompatible element types. This option should not be used for new code. -fms-extensions Accept some non-standard constructs used in Microsoft header files. In C++ code, this allows member names in structures to be similar to previous types declarations. typedef int UOW; struct ABC { UOW UOW; }; Some cases of unnamed fields in structures and unions are only accepted with this option. Note that this option is off for all targets except for x86 targets using ms-abi. -foffload=disable -foffload=default -foffload=target-list Specify for which OpenMP and OpenACC offload targets code should be generated. The default behavior, equivalent to -foffload=default, is to generate code for all supported offload targets. The -foffload=disable form generates code only for the host fallback, while -foffload=target-list generates code only for the specified comma-separated list of offload targets. Offload targets are specified in GCC's internal target-triplet format. You can run the compiler with -v to show the list of configured offload targets under "OFFLOAD_TARGET_NAMES". -foffload-options=options -foffload-options=target-triplet-list=options With -foffload-options=options, GCC passes the specified options to the compilers for all enabled offloading targets. You can specify options that apply only to a specific target or targets by using the -foffload-options=target-list=options form. The target-list is a comma-separated list in the same format as for the -foffload= option. Typical command lines are -foffload-options=-lgfortran -foffload-options=-lm -foffload-options="-lgfortran -lm" -foffload-options=nvptx-none=-latomic -foffload-options=amdgcn-amdhsa=-march=gfx906 -foffload-options=-lm -fopenacc Enable handling of OpenACC directives "#pragma acc" in C/C++ and "!$acc" in Fortran. When -fopenacc is specified, the compiler generates accelerated code according to the OpenACC Application Programming Interface v2.6 <https://www.openacc.org>. This option implies -pthread, and thus is only supported on targets that have support for -pthread. -fopenacc-dim=geom Specify default compute dimensions for parallel offload regions that do not explicitly specify. The geom value is a triple of ':'-separated sizes, in order 'gang', 'worker' and, 'vector'. A size can be omitted, to use a target-specific default value. -fopenmp Enable handling of OpenMP directives "#pragma omp" in C/C++, "[[omp::directive(...)]]" and "[[omp::sequence(...)]]" in C++ and "!$omp" in Fortran. When -fopenmp is specified, the compiler generates parallel code according to the OpenMP Application Program Interface v4.5 <https://www.openmp.org>. This option implies -pthread, and thus is only supported on targets that have support for -pthread. -fopenmp implies -fopenmp-simd. -fopenmp-simd Enable handling of OpenMP's "simd", "declare simd", "declare reduction", "assume", "ordered", "scan", "loop" directives and combined or composite directives with "simd" as constituent with "#pragma omp" in C/C++, "[[omp::directive(...)]]" and "[[omp::sequence(...)]]" in C++ and "!$omp" in Fortran. Other OpenMP directives are ignored. -fopenmp-target-simd-clone -fopenmp-target-simd-clone=device-type In addition to generating SIMD clones for functions marked with the "declare simd" directive, GCC also generates clones for functions marked with the OpenMP "declare target" directive that are suitable for vectorization when this option is in effect. The device-type may be one of "none", "host", "nohost", and "any", which correspond to keywords for the "device_type" clause of the "declare target" directive; clones are generated for the intersection of devices specified. -fopenmp-target-simd-clone is equivalent to -fopenmp-target-simd-clone=any and -fno-openmp-target-simd-clone is equivalent to -fopenmp-target-simd-clone=none. At -O2 and higher (but not -Os or -Og) this optimization defaults to -fopenmp-target-simd-clone=nohost; otherwise it is disabled by default. -fpermitted-flt-eval-methods=style ISO/IEC TS 18661-3 defines new permissible values for "FLT_EVAL_METHOD" that indicate that operations and constants with a semantic type that is an interchange or extended format should be evaluated to the precision and range of that type. These new values are a superset of those permitted under C99/C11, which does not specify the meaning of other positive values of "FLT_EVAL_METHOD". As such, code conforming to C11 may not have been written expecting the possibility of the new values. -fpermitted-flt-eval-methods specifies whether the compiler should allow only the values of "FLT_EVAL_METHOD" specified in C99/C11, or the extended set of values specified in ISO/IEC TS 18661-3. style is either "c11" or "ts-18661-3" as appropriate. The default when in a standards compliant mode (-std=c11 or similar) is -fpermitted-flt-eval-methods=c11. The default when in a GNU dialect (-std=gnu11 or similar) is -fpermitted-flt-eval-methods=ts-18661-3. -fplan9-extensions Accept some non-standard constructs used in Plan 9 code. This enables -fms-extensions, permits passing pointers to structures with anonymous fields to functions that expect pointers to elements of the type of the field, and permits referring to anonymous fields declared using a typedef. This is only supported for C, not C++. -fsigned-bitfields -funsigned-bitfields -fno-signed-bitfields -fno-unsigned-bitfields These options control whether a bit-field is signed or unsigned, when the declaration does not use either "signed" or "unsigned". By default, such a bit-field is signed, because this is consistent: the basic integer types such as "int" are signed types. -fsigned-char Let the type "char" be signed, like "signed char". Note that this is equivalent to -fno-unsigned-char, which is the negative form of -funsigned-char. Likewise, the option -fno-signed-char is equivalent to -funsigned-char. -funsigned-char Let the type "char" be unsigned, like "unsigned char". Each kind of machine has a default for what "char" should be. It is either like "unsigned char" by default or like "signed char" by default. Ideally, a portable program should always use "signed char" or "unsigned char" when it depends on the signedness of an object. But many programs have been written to use plain "char" and expect it to be signed, or expect it to be unsigned, depending on the machines they were written for. This option, and its inverse, let you make such a program work with the opposite default. The type "char" is always a distinct type from each of "signed char" or "unsigned char", even though its behavior is always just like one of those two. -fstrict-flex-arrays Control when to treat the trailing array of a structure as a flexible array member for the purpose of accessing the elements of such an array. The positive form is equivalent to -fstrict-flex-arrays=3, which is the strictest. A trailing array is treated as a flexible array member only when it is declared as a flexible array member per C99 standard onwards. The negative form is equivalent to -fstrict-flex-arrays=0, which is the least strict. All trailing arrays of structures are treated as flexible array members. -fstrict-flex-arrays=level Control when to treat the trailing array of a structure as a flexible array member for the purpose of accessing the elements of such an array. The value of level controls the level of strictness. The possible values of level are the same as for the "strict_flex_array" attribute. You can control this behavior for a specific trailing array field of a structure by using the variable attribute "strict_flex_array" attribute. -fsso-struct=endianness Set the default scalar storage order of structures and unions to the specified endianness. The accepted values are big-endian, little-endian and native for the native endianness of the target (the default). This option is not supported for C++. Warning: the -fsso-struct switch causes GCC to generate code that is not binary compatible with code generated without it if the specified endianness is not the native endianness of the target. Options Controlling C++ Dialect This section describes the command-line options that are only meaningful for C++ programs. You can also use most of the GNU compiler options regardless of what language your program is in. For example, you might compile a file firstClass.C like this: g++ -g -fstrict-enums -O -c firstClass.C In this example, only -fstrict-enums is an option meant only for C++ programs; you can use the other options with any language supported by GCC. Some options for compiling C programs, such as -std, are also relevant for C++ programs. Here is a list of options that are only for compiling C++ programs: -fabi-version=n Use version n of the C++ ABI. The default is version 0. Version 0 refers to the version conforming most closely to the C++ ABI specification. Therefore, the ABI obtained using version 0 will change in different versions of G++ as ABI bugs are fixed. Version 1 is the version of the C++ ABI that first appeared in G++ 3.2. Version 2 is the version of the C++ ABI that first appeared in G++ 3.4, and was the default through G++ 4.9. Version 3 corrects an error in mangling a constant address as a template argument. Version 4, which first appeared in G++ 4.5, implements a standard mangling for vector types. Version 5, which first appeared in G++ 4.6, corrects the mangling of attribute const/volatile on function pointer types, decltype of a plain decl, and use of a function parameter in the declaration of another parameter. Version 6, which first appeared in G++ 4.7, corrects the promotion behavior of C++11 scoped enums and the mangling of template argument packs, const/static_cast, prefix ++ and --, and a class scope function used as a template argument. Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a builtin type and corrects the mangling of lambdas in default argument scope. Version 8, which first appeared in G++ 4.9, corrects the substitution behavior of function types with function-cv- qualifiers. Version 9, which first appeared in G++ 5.2, corrects the alignment of "nullptr_t". Version 10, which first appeared in G++ 6.1, adds mangling of attributes that affect type identity, such as ia32 calling convention attributes (e.g. stdcall). Version 11, which first appeared in G++ 7, corrects the mangling of sizeof... expressions and operator names. For multiple entities with the same name within a function, that are declared in different scopes, the mangling now changes starting with the twelfth occurrence. It also implies -fnew-inheriting-ctors. Version 12, which first appeared in G++ 8, corrects the calling conventions for empty classes on the x86_64 target and for classes with only deleted copy/move constructors. It accidentally changes the calling convention for classes with a deleted copy constructor and a trivial move constructor. Version 13, which first appeared in G++ 8.2, fixes the accidental change in version 12. Version 14, which first appeared in G++ 10, corrects the mangling of the nullptr expression. Version 15, which first appeared in G++ 10.3, corrects G++ 10 ABI tag regression. Version 16, which first appeared in G++ 11, changes the mangling of "__alignof__" to be distinct from that of "alignof", and dependent operator names. Version 17, which first appeared in G++ 12, fixes layout of classes that inherit from aggregate classes with default member initializers in C++14 and up. Version 18, which first appeard in G++ 13, fixes manglings of lambdas that have additional context. See also -Wabi. -fabi-compat-version=n On targets that support strong aliases, G++ works around mangling changes by creating an alias with the correct mangled name when defining a symbol with an incorrect mangled name. This switch specifies which ABI version to use for the alias. With -fabi-version=0 (the default), this defaults to 13 (GCC 8.2 compatibility). If another ABI version is explicitly selected, this defaults to 0. For compatibility with GCC versions 3.2 through 4.9, use -fabi-compat-version=2. If this option is not provided but -Wabi=n is, that version is used for compatibility aliases. If this option is provided along with -Wabi (without the version), the version from this option is used for the warning. -fno-access-control Turn off all access checking. This switch is mainly useful for working around bugs in the access control code. -faligned-new Enable support for C++17 "new" of types that require more alignment than "void* ::operator new(std::size_t)" provides. A numeric argument such as "-faligned-new=32" can be used to specify how much alignment (in bytes) is provided by that function, but few users will need to override the default of "alignof(std::max_align_t)". This flag is enabled by default for -std=c++17. -fchar8_t -fno-char8_t Enable support for "char8_t" as adopted for C++20. This includes the addition of a new "char8_t" fundamental type, changes to the types of UTF-8 string and character literals, new signatures for user-defined literals, associated standard library updates, and new "__cpp_char8_t" and "__cpp_lib_char8_t" feature test macros. This option enables functions to be overloaded for ordinary and UTF-8 strings: int f(const char *); // #1 int f(const char8_t *); // #2 int v1 = f("text"); // Calls #1 int v2 = f(u8"text"); // Calls #2 and introduces new signatures for user-defined literals: int operator""_udl1(char8_t); int v3 = u8'x'_udl1; int operator""_udl2(const char8_t*, std::size_t); int v4 = u8"text"_udl2; template<typename T, T...> int operator""_udl3(); int v5 = u8"text"_udl3; The change to the types of UTF-8 string and character literals introduces incompatibilities with ISO C++11 and later standards. For example, the following code is well-formed under ISO C++11, but is ill-formed when -fchar8_t is specified. const char *cp = u8"xx";// error: invalid conversion from // `const char8_t*' to `const char*' int f(const char*); auto v = f(u8"xx"); // error: invalid conversion from // `const char8_t*' to `const char*' std::string s{u8"xx"}; // error: no matching function for call to // `std::basic_string<char>::basic_string()' using namespace std::literals; s = u8"xx"s; // error: conversion from // `basic_string<char8_t>' to non-scalar // type `basic_string<char>' requested -fcheck-new Check that the pointer returned by "operator new" is non-null before attempting to modify the storage allocated. This check is normally unnecessary because the C++ standard specifies that "operator new" only returns 0 if it is declared "throw()", in which case the compiler always checks the return value even without this option. In all other cases, when "operator new" has a non-empty exception specification, memory exhaustion is signalled by throwing "std::bad_alloc". See also new (nothrow). -fconcepts -fconcepts-ts Enable support for the C++ Concepts feature for constraining template arguments. With -std=c++20 and above, Concepts are part of the language standard, so -fconcepts defaults to on. Some constructs that were allowed by the earlier C++ Extensions for Concepts Technical Specification, ISO 19217 (2015), but didn't make it into the standard, can additionally be enabled by -fconcepts-ts. -fconstexpr-depth=n Set the maximum nested evaluation depth for C++11 constexpr functions to n. A limit is needed to detect endless recursion during constant expression evaluation. The minimum specified by the standard is 512. -fconstexpr-cache-depth=n Set the maximum level of nested evaluation depth for C++11 constexpr functions that will be cached to n. This is a heuristic that trades off compilation speed (when the cache avoids repeated calculations) against memory consumption (when the cache grows very large from highly recursive evaluations). The default is 8. Very few users are likely to want to adjust it, but if your code does heavy constexpr calculations you might want to experiment to find which value works best for you. -fconstexpr-fp-except Annex F of the C standard specifies that IEC559 floating point exceptions encountered at compile time should not stop compilation. C++ compilers have historically not followed this guidance, instead treating floating point division by zero as non-constant even though it has a well defined value. This flag tells the compiler to give Annex F priority over other rules saying that a particular operation is undefined. constexpr float inf = 1./0.; // OK with -fconstexpr-fp-except -fconstexpr-loop-limit=n Set the maximum number of iterations for a loop in C++14 constexpr functions to n. A limit is needed to detect infinite loops during constant expression evaluation. The default is 262144 (1<<18). -fconstexpr-ops-limit=n Set the maximum number of operations during a single constexpr evaluation. Even when number of iterations of a single loop is limited with the above limit, if there are several nested loops and each of them has many iterations but still smaller than the above limit, or if in a body of some loop or even outside of a loop too many expressions need to be evaluated, the resulting constexpr evaluation might take too long. The default is 33554432 (1<<25). -fcontracts Enable experimental support for the C++ Contracts feature, as briefly added to and then removed from the C++20 working paper (N4820). The implementation also includes proposed enhancements from papers P1290, P1332, and P1429. This functionality is intended mostly for those interested in experimentation towards refining the feature to get it into shape for a future C++ standard. On violation of a checked contract, the violation handler is called. Users can replace the violation handler by defining void handle_contract_violation (const std::experimental::contract_violation&); There are different sets of additional flags that can be used together to specify which contracts will be checked and how, for N4820 contracts, P1332 contracts, or P1429 contracts; these sets cannot be used together. -fcontract-mode=[on|off] Control whether any contracts have any semantics at all. Defaults to on. -fcontract-assumption-mode=[on|off] [N4820] Control whether contracts with level axiom should have the assume semantic. Defaults to on. -fcontract-build-level=[off|default|audit] [N4820] Specify which level of contracts to generate checks for. Defaults to default. -fcontract-continuation-mode=[on|off] [N4820] Control whether to allow the program to continue executing after a contract violation. That is, do checked contracts have the maybe semantic described below rather than the never semantic. Defaults to off. -fcontract-role=<name>:<default>,<audit>,<axiom> [P1332] Specify the concrete semantics for each contract level of a particular contract role. -fcontract-semantic=[default|audit|axiom]:<semantic> [P1429] Specify the concrete semantic for a particular contract level. -fcontract-strict-declarations=[on|off] Control whether to reject adding contracts to a function after its first declaration. Defaults to off. The possible concrete semantics for that can be specified with -fcontract-role or -fcontract-semantic are: "ignore" This contract has no effect. "assume" This contract is treated like C++23 "[[assume]]". "check_never_continue" "never" "abort" This contract is checked. If it fails, the violation handler is called. If the handler returns, "std::terminate" is called. "check_maybe_continue" "maybe" This contract is checked. If it fails, the violation handler is called. If the handler returns, execution continues normally. -fcoroutines Enable support for the C++ coroutines extension (experimental). -fno-elide-constructors The C++ standard allows an implementation to omit creating a temporary that is only used to initialize another object of the same type. Specifying this option disables that optimization, and forces G++ to call the copy constructor in all cases. This option also causes G++ to call trivial member functions which otherwise would be expanded inline. In C++17, the compiler is required to omit these temporaries, but this option still affects trivial member functions. -fno-enforce-eh-specs Don't generate code to check for violation of exception specifications at run time. This option violates the C++ standard, but may be useful for reducing code size in production builds, much like defining "NDEBUG". This does not give user code permission to throw exceptions in violation of the exception specifications; the compiler still optimizes based on the specifications, so throwing an unexpected exception results in undefined behavior at run time. -fextern-tls-init -fno-extern-tls-init The C++11 and OpenMP standards allow "thread_local" and "threadprivate" variables to have dynamic (runtime) initialization. To support this, any use of such a variable goes through a wrapper function that performs any necessary initialization. When the use and definition of the variable are in the same translation unit, this overhead can be optimized away, but when the use is in a different translation unit there is significant overhead even if the variable doesn't actually need dynamic initialization. If the programmer can be sure that no use of the variable in a non- defining TU needs to trigger dynamic initialization (either because the variable is statically initialized, or a use of the variable in the defining TU will be executed before any uses in another TU), they can avoid this overhead with the -fno-extern-tls-init option. On targets that support symbol aliases, the default is -fextern-tls-init. On targets that do not support symbol aliases, the default is -fno-extern-tls-init. -ffold-simple-inlines -fno-fold-simple-inlines Permit the C++ frontend to fold calls to "std::move", "std::forward", "std::addressof" and "std::as_const". In contrast to inlining, this means no debug information will be generated for such calls. Since these functions are rarely interesting to debug, this flag is enabled by default unless -fno-inline is active. -fno-gnu-keywords Do not recognize "typeof" as a keyword, so that code can use this word as an identifier. You can use the keyword "__typeof__" instead. This option is implied by the strict ISO C++ dialects: -ansi, -std=c++98, -std=c++11, etc. -fimplicit-constexpr Make inline functions implicitly constexpr, if they satisfy the requirements for a constexpr function. This option can be used in C++14 mode or later. This can result in initialization changing from dynamic to static and other optimizations. -fno-implicit-templates Never emit code for non-inline templates that are instantiated implicitly (i.e. by use); only emit code for explicit instantiations. If you use this option, you must take care to structure your code to include all the necessary explicit instantiations to avoid getting undefined symbols at link time. -fno-implicit-inline-templates Don't emit code for implicit instantiations of inline templates, either. The default is to handle inlines differently so that compiles with and without optimization need the same set of explicit instantiations. -fno-implement-inlines To save space, do not emit out-of-line copies of inline functions controlled by "#pragma implementation". This causes linker errors if these functions are not inlined everywhere they are called. -fmodules-ts -fno-modules-ts Enable support for C++20 modules. The -fno-modules-ts is usually not needed, as that is the default. Even though this is a C++20 feature, it is not currently implicitly enabled by selecting that standard version. -fmodule-header -fmodule-header=user -fmodule-header=system Compile a header file to create an importable header unit. -fmodule-implicit-inline Member functions defined in their class definitions are not implicitly inline for modular code. This is different to traditional C++ behavior, for good reasons. However, it may result in a difficulty during code porting. This option makes such function definitions implicitly inline. It does however generate an ABI incompatibility, so you must use it everywhere or nowhere. (Such definitions outside of a named module remain implicitly inline, regardless.) -fno-module-lazy Disable lazy module importing and module mapper creation. -fmodule-mapper=[hostname]:port[?ident] -fmodule-mapper=|program[?ident] args... -fmodule-mapper==socket[?ident] -fmodule-mapper=<>[inout][?ident] -fmodule-mapper=<in>out[?ident] -fmodule-mapper=file[?ident] An oracle to query for module name to filename mappings. If unspecified the CXX_MODULE_MAPPER environment variable is used, and if that is unset, an in-process default is provided. -fmodule-only Only emit the Compiled Module Interface, inhibiting any object file. -fms-extensions Disable Wpedantic warnings about constructs used in MFC, such as implicit int and getting a pointer to member function via non- standard syntax. -fnew-inheriting-ctors Enable the P0136 adjustment to the semantics of C++11 constructor inheritance. This is part of C++17 but also considered to be a Defect Report against C++11 and C++14. This flag is enabled by default unless -fabi-version=10 or lower is specified. -fnew-ttp-matching Enable the P0522 resolution to Core issue 150, template template parameters and default arguments: this allows a template with default template arguments as an argument for a template template parameter with fewer template parameters. This flag is enabled by default for -std=c++17. -fno-nonansi-builtins Disable built-in declarations of functions that are not mandated by ANSI/ISO C. These include "ffs", "alloca", "_exit", "index", "bzero", "conjf", and other related functions. -fnothrow-opt Treat a "throw()" exception specification as if it were a "noexcept" specification to reduce or eliminate the text size overhead relative to a function with no exception specification. If the function has local variables of types with non-trivial destructors, the exception specification actually makes the function smaller because the EH cleanups for those variables can be optimized away. The semantic effect is that an exception thrown out of a function with such an exception specification results in a call to "terminate" rather than "unexpected". -fno-operator-names Do not treat the operator name keywords "and", "bitand", "bitor", "compl", "not", "or" and "xor" as synonyms as keywords. -fno-optional-diags Disable diagnostics that the standard says a compiler does not need to issue. Currently, the only such diagnostic issued by G++ is the one for a name having multiple meanings within a class. -fpermissive Downgrade some diagnostics about nonconformant code from errors to warnings. Thus, using -fpermissive allows some nonconforming code to compile. -fno-pretty-templates When an error message refers to a specialization of a function template, the compiler normally prints the signature of the template followed by the template arguments and any typedefs or typenames in the signature (e.g. "void f(T) [with T = int]" rather than "void f(int)") so that it's clear which template is involved. When an error message refers to a specialization of a class template, the compiler omits any template arguments that match the default template arguments for that template. If either of these behaviors make it harder to understand the error message rather than easier, you can use -fno-pretty-templates to disable them. -fno-rtti Disable generation of information about every class with virtual functions for use by the C++ run-time type identification features ("dynamic_cast" and "typeid"). If you don't use those parts of the language, you can save some space by using this flag. Note that exception handling uses the same information, but G++ generates it as needed. The "dynamic_cast" operator can still be used for casts that do not require run-time type information, i.e. casts to "void *" or to unambiguous base classes. Mixing code compiled with -frtti with that compiled with -fno-rtti may not work. For example, programs may fail to link if a class compiled with -fno-rtti is used as a base for a class compiled with -frtti. -fsized-deallocation Enable the built-in global declarations void operator delete (void *, std::size_t) noexcept; void operator delete[] (void *, std::size_t) noexcept; as introduced in C++14. This is useful for user-defined replacement deallocation functions that, for example, use the size of the object to make deallocation faster. Enabled by default under -std=c++14 and above. The flag -Wsized-deallocation warns about places that might want to add a definition. -fstrict-enums Allow the compiler to optimize using the assumption that a value of enumerated type can only be one of the values of the enumeration (as defined in the C++ standard; basically, a value that can be represented in the minimum number of bits needed to represent all the enumerators). This assumption may not be valid if the program uses a cast to convert an arbitrary integer value to the enumerated type. -fstrong-eval-order Evaluate member access, array subscripting, and shift expressions in left-to-right order, and evaluate assignment in right-to-left order, as adopted for C++17. Enabled by default with -std=c++17. -fstrong-eval-order=some enables just the ordering of member access and shift expressions, and is the default without -std=c++17. -ftemplate-backtrace-limit=n Set the maximum number of template instantiation notes for a single warning or error to n. The default value is 10. -ftemplate-depth=n Set the maximum instantiation depth for template classes to n. A limit on the template instantiation depth is needed to detect endless recursions during template class instantiation. ANSI/ISO C++ conforming programs must not rely on a maximum depth greater than 17 (changed to 1024 in C++11). The default value is 900, as the compiler can run out of stack space before hitting 1024 in some situations. -fno-threadsafe-statics Do not emit the extra code to use the routines specified in the C++ ABI for thread-safe initialization of local statics. You can use this option to reduce code size slightly in code that doesn't need to be thread-safe. -fuse-cxa-atexit Register destructors for objects with static storage duration with the "__cxa_atexit" function rather than the "atexit" function. This option is required for fully standards-compliant handling of static destructors, but only works if your C library supports "__cxa_atexit". -fno-use-cxa-get-exception-ptr Don't use the "__cxa_get_exception_ptr" runtime routine. This causes "std::uncaught_exception" to be incorrect, but is necessary if the runtime routine is not available. -fvisibility-inlines-hidden This switch declares that the user does not attempt to compare pointers to inline functions or methods where the addresses of the two functions are taken in different shared objects. The effect of this is that GCC may, effectively, mark inline methods with "__attribute__ ((visibility ("hidden")))" so that they do not appear in the export table of a DSO and do not require a PLT indirection when used within the DSO. Enabling this option can have a dramatic effect on load and link times of a DSO as it massively reduces the size of the dynamic export table when the library makes heavy use of templates. The behavior of this switch is not quite the same as marking the methods as hidden directly, because it does not affect static variables local to the function or cause the compiler to deduce that the function is defined in only one shared object. You may mark a method as having a visibility explicitly to negate the effect of the switch for that method. For example, if you do want to compare pointers to a particular inline method, you might mark it as having default visibility. Marking the enclosing class with explicit visibility has no effect. Explicitly instantiated inline methods are unaffected by this option as their linkage might otherwise cross a shared library boundary. -fvisibility-ms-compat This flag attempts to use visibility settings to make GCC's C++ linkage model compatible with that of Microsoft Visual Studio. The flag makes these changes to GCC's linkage model: 1. It sets the default visibility to "hidden", like -fvisibility=hidden. 2. Types, but not their members, are not hidden by default. 3. The One Definition Rule is relaxed for types without explicit visibility specifications that are defined in more than one shared object: those declarations are permitted if they are permitted when this option is not used. In new code it is better to use -fvisibility=hidden and export those classes that are intended to be externally visible. Unfortunately it is possible for code to rely, perhaps accidentally, on the Visual Studio behavior. Among the consequences of these changes are that static data members of the same type with the same name but defined in different shared objects are different, so changing one does not change the other; and that pointers to function members defined in different shared objects may not compare equal. When this flag is given, it is a violation of the ODR to define types with the same name differently. -fno-weak Do not use weak symbol support, even if it is provided by the linker. By default, G++ uses weak symbols if they are available. This option exists only for testing, and should not be used by end- users; it results in inferior code and has no benefits. This option may be removed in a future release of G++. -fext-numeric-literals (C++ and Objective-C++ only) Accept imaginary, fixed-point, or machine-defined literal number suffixes as GNU extensions. When this option is turned off these suffixes are treated as C++11 user-defined literal numeric suffixes. This is on by default for all pre-C++11 dialects and all GNU dialects: -std=c++98, -std=gnu++98, -std=gnu++11, -std=gnu++14. This option is off by default for ISO C++11 onwards (-std=c++11, ...). -nostdinc++ Do not search for header files in the standard directories specific to C++, but do still search the other standard directories. (This option is used when building the C++ library.) -flang-info-include-translate -flang-info-include-translate-not -flang-info-include-translate=header Inform of include translation events. The first will note accepted include translations, the second will note declined include translations. The header form will inform of include translations relating to that specific header. If header is of the form "user" or "<system>" it will be resolved to a specific user or system header using the include path. -flang-info-module-cmi -flang-info-module-cmi=module Inform of Compiled Module Interface pathnames. The first will note all read CMI pathnames. The module form will not reading a specific module's CMI. module may be a named module or a header- unit (the latter indicated by either being a pathname containing directory separators or enclosed in "<>" or ""). -stdlib=libstdc++,libc++ When G++ is configured to support this option, it allows specification of alternate C++ runtime libraries. Two options are available: libstdc++ (the default, native C++ runtime for G++) and libc++ which is the C++ runtime installed on some operating systems (e.g. Darwin versions from Darwin11 onwards). The option switches G++ to use the headers from the specified library and to emit "-lstdc++" or "-lc++" respectively, when a C++ runtime is required for linking. In addition, these warning options have meanings only for C++ programs: -Wabi-tag (C++ and Objective-C++ only) Warn when a type with an ABI tag is used in a context that does not have that ABI tag. See C++ Attributes for more information about ABI tags. -Wcomma-subscript (C++ and Objective-C++ only) Warn about uses of a comma expression within a subscripting expression. This usage was deprecated in C++20 and is going to be removed in C++23. However, a comma expression wrapped in "( )" is not deprecated. Example: void f(int *a, int b, int c) { a[b,c]; // deprecated in C++20, invalid in C++23 a[(b,c)]; // OK } In C++23 it is valid to have comma separated expressions in a subscript when an overloaded subscript operator is found and supports the right number and types of arguments. G++ will accept the formerly valid syntax for code that is not valid in C++23 but used to be valid but deprecated in C++20 with a pedantic warning that can be disabled with -Wno-comma-subscript. Enabled by default with -std=c++20 unless -Wno-deprecated, and with -std=c++23 regardless of -Wno-deprecated. -Wctad-maybe-unsupported (C++ and Objective-C++ only) Warn when performing class template argument deduction (CTAD) on a type with no explicitly written deduction guides. This warning will point out cases where CTAD succeeded only because the compiler synthesized the implicit deduction guides, which might not be what the programmer intended. Certain style guides allow CTAD only on types that specifically "opt-in"; i.e., on types that are designed to support CTAD. This warning can be suppressed with the following pattern: struct allow_ctad_t; // any name works template <typename T> struct S { S(T) { } }; // Guide with incomplete parameter type will never be considered. S(allow_ctad_t) -> S<void>; -Wctor-dtor-privacy (C++ and Objective-C++ only) Warn when a class seems unusable because all the constructors or destructors in that class are private, and it has neither friends nor public static member functions. Also warn if there are no non- private methods, and there's at least one private member function that isn't a constructor or destructor. -Wdangling-reference (C++ and Objective-C++ only) Warn when a reference is bound to a temporary whose lifetime has ended. For example: int n = 1; const int& r = std::max(n - 1, n + 1); // r is dangling In the example above, two temporaries are created, one for each argument, and a reference to one of the temporaries is returned. However, both temporaries are destroyed at the end of the full expression, so the reference "r" is dangling. This warning also detects dangling references in member initializer lists: const int& f(const int& i) { return i; } struct S { const int &r; // r is dangling S() : r(f(10)) { } }; Member functions are checked as well, but only their object argument: struct S { const S& self () { return *this; } }; const S& s = S().self(); // s is dangling Certain functions are safe in this respect, for example "std::use_facet": they take and return a reference, but they don't return one of its arguments, which can fool the warning. Such functions can be excluded from the warning by wrapping them in a "#pragma": #pragma GCC diagnostic push #pragma GCC diagnostic ignored "-Wdangling-reference" const T& foo (const T&) { ... } #pragma GCC diagnostic pop -Wdangling-reference also warns about code like auto p = std::minmax(1, 2); where "std::minmax" returns "std::pair<const int&, const int&>", and both references dangle after the end of the full expression that contains the call to "std::minmax". This warning is enabled by -Wextra. -Wdelete-non-virtual-dtor (C++ and Objective-C++ only) Warn when "delete" is used to destroy an instance of a class that has virtual functions and non-virtual destructor. It is unsafe to delete an instance of a derived class through a pointer to a base class if the base class does not have a virtual destructor. This warning is enabled by -Wall. -Wdeprecated-copy (C++ and Objective-C++ only) Warn that the implicit declaration of a copy constructor or copy assignment operator is deprecated if the class has a user-provided copy constructor or copy assignment operator, in C++11 and up. This warning is enabled by -Wextra. With -Wdeprecated-copy-dtor, also deprecate if the class has a user-provided destructor. -Wno-deprecated-enum-enum-conversion (C++ and Objective-C++ only) Disable the warning about the case when the usual arithmetic conversions are applied on operands where one is of enumeration type and the other is of a different enumeration type. This conversion was deprecated in C++20. For example: enum E1 { e }; enum E2 { f }; int k = f - e; -Wdeprecated-enum-enum-conversion is enabled by default with -std=c++20. In pre-C++20 dialects, this warning can be enabled by -Wenum-conversion. -Wno-deprecated-enum-float-conversion (C++ and Objective-C++ only) Disable the warning about the case when the usual arithmetic conversions are applied on operands where one is of enumeration type and the other is of a floating-point type. This conversion was deprecated in C++20. For example: enum E1 { e }; enum E2 { f }; bool b = e <= 3.7; -Wdeprecated-enum-float-conversion is enabled by default with -std=c++20. In pre-C++20 dialects, this warning can be enabled by -Wenum-conversion. -Wno-init-list-lifetime (C++ and Objective-C++ only) Do not warn about uses of "std::initializer_list" that are likely to result in dangling pointers. Since the underlying array for an "initializer_list" is handled like a normal C++ temporary object, it is easy to inadvertently keep a pointer to the array past the end of the array's lifetime. For example: * If a function returns a temporary "initializer_list", or a local "initializer_list" variable, the array's lifetime ends at the end of the return statement, so the value returned has a dangling pointer. * If a new-expression creates an "initializer_list", the array only lives until the end of the enclosing full-expression, so the "initializer_list" in the heap has a dangling pointer. * When an "initializer_list" variable is assigned from a brace- enclosed initializer list, the temporary array created for the right side of the assignment only lives until the end of the full-expression, so at the next statement the "initializer_list" variable has a dangling pointer. // li's initial underlying array lives as long as li std::initializer_list<int> li = { 1,2,3 }; // assignment changes li to point to a temporary array li = { 4, 5 }; // now the temporary is gone and li has a dangling pointer int i = li.begin()[0] // undefined behavior * When a list constructor stores the "begin" pointer from the "initializer_list" argument, this doesn't extend the lifetime of the array, so if a class variable is constructed from a temporary "initializer_list", the pointer is left dangling by the end of the variable declaration statement. -Winvalid-constexpr Warn when a function never produces a constant expression. In C++20 and earlier, for every "constexpr" function and function template, there must be at least one set of function arguments in at least one instantiation such that an invocation of the function or constructor could be an evaluated subexpression of a core constant expression. C++23 removed this restriction, so it's possible to have a function or a function template marked "constexpr" for which no invocation satisfies the requirements of a core constant expression. This warning is enabled as a pedantic warning by default in C++20 and earlier. In C++23, -Winvalid-constexpr can be turned on, in which case it will be an ordinary warning. For example: void f (int& i); constexpr void g (int& i) { // Warns by default in C++20, in C++23 only with -Winvalid-constexpr. f(i); } -Winvalid-imported-macros Verify all imported macro definitions are valid at the end of compilation. This is not enabled by default, as it requires additional processing to determine. It may be useful when preparing sets of header-units to ensure consistent macros. -Wno-literal-suffix (C++ and Objective-C++ only) Do not warn when a string or character literal is followed by a ud- suffix which does not begin with an underscore. As a conforming extension, GCC treats such suffixes as separate preprocessing tokens in order to maintain backwards compatibility with code that uses formatting macros from "<inttypes.h>". For example: #define __STDC_FORMAT_MACROS #include <inttypes.h> #include <stdio.h> int main() { int64_t i64 = 123; printf("My int64: %" PRId64"\n", i64); } In this case, "PRId64" is treated as a separate preprocessing token. This option also controls warnings when a user-defined literal operator is declared with a literal suffix identifier that doesn't begin with an underscore. Literal suffix identifiers that don't begin with an underscore are reserved for future standardization. These warnings are enabled by default. -Wno-narrowing (C++ and Objective-C++ only) For C++11 and later standards, narrowing conversions are diagnosed by default, as required by the standard. A narrowing conversion from a constant produces an error, and a narrowing conversion from a non-constant produces a warning, but -Wno-narrowing suppresses the diagnostic. Note that this does not affect the meaning of well-formed code; narrowing conversions are still considered ill- formed in SFINAE contexts. With -Wnarrowing in C++98, warn when a narrowing conversion prohibited by C++11 occurs within { }, e.g. int i = { 2.2 }; // error: narrowing from double to int This flag is included in -Wall and -Wc++11-compat. -Wnoexcept (C++ and Objective-C++ only) Warn when a noexcept-expression evaluates to false because of a call to a function that does not have a non-throwing exception specification (i.e. "throw()" or "noexcept") but is known by the compiler to never throw an exception. -Wnoexcept-type (C++ and Objective-C++ only) Warn if the C++17 feature making "noexcept" part of a function type changes the mangled name of a symbol relative to C++14. Enabled by -Wabi and -Wc++17-compat. As an example: template <class T> void f(T t) { t(); }; void g() noexcept; void h() { f(g); } In C++14, "f" calls "f<void(*)()>", but in C++17 it calls "f<void(*)()noexcept>". -Wclass-memaccess (C++ and Objective-C++ only) Warn when the destination of a call to a raw memory function such as "memset" or "memcpy" is an object of class type, and when writing into such an object might bypass the class non-trivial or deleted constructor or copy assignment, violate const-correctness or encapsulation, or corrupt virtual table pointers. Modifying the representation of such objects may violate invariants maintained by member functions of the class. For example, the call to "memset" below is undefined because it modifies a non-trivial class object and is, therefore, diagnosed. The safe way to either initialize or clear the storage of objects of such types is by using the appropriate constructor or assignment operator, if one is available. std::string str = "abc"; memset (&str, 0, sizeof str); The -Wclass-memaccess option is enabled by -Wall. Explicitly casting the pointer to the class object to "void *" or to a type that can be safely accessed by the raw memory function suppresses the warning. -Wnon-virtual-dtor (C++ and Objective-C++ only) Warn when a class has virtual functions and an accessible non- virtual destructor itself or in an accessible polymorphic base class, in which case it is possible but unsafe to delete an instance of a derived class through a pointer to the class itself or base class. This warning is automatically enabled if -Weffc++ is specified. The -Wdelete-non-virtual-dtor option (enabled by -Wall) should be preferred because it warns about the unsafe cases without false positives. -Wregister (C++ and Objective-C++ only) Warn on uses of the "register" storage class specifier, except when it is part of the GNU Explicit Register Variables extension. The use of the "register" keyword as storage class specifier has been deprecated in C++11 and removed in C++17. Enabled by default with -std=c++17. -Wreorder (C++ and Objective-C++ only) Warn when the order of member initializers given in the code does not match the order in which they must be executed. For instance: struct A { int i; int j; A(): j (0), i (1) { } }; The compiler rearranges the member initializers for "i" and "j" to match the declaration order of the members, emitting a warning to that effect. This warning is enabled by -Wall. -Wno-pessimizing-move (C++ and Objective-C++ only) This warning warns when a call to "std::move" prevents copy elision. A typical scenario when copy elision can occur is when returning in a function with a class return type, when the expression being returned is the name of a non-volatile automatic object, and is not a function parameter, and has the same type as the function return type. struct T { ... }; T fn() { T t; ... return std::move (t); } But in this example, the "std::move" call prevents copy elision. This warning is enabled by -Wall. -Wno-redundant-move (C++ and Objective-C++ only) This warning warns about redundant calls to "std::move"; that is, when a move operation would have been performed even without the "std::move" call. This happens because the compiler is forced to treat the object as if it were an rvalue in certain situations such as returning a local variable, where copy elision isn't applicable. Consider: struct T { ... }; T fn(T t) { ... return std::move (t); } Here, the "std::move" call is redundant. Because G++ implements Core Issue 1579, another example is: struct T { // convertible to U ... }; struct U { ... }; U fn() { T t; ... return std::move (t); } In this example, copy elision isn't applicable because the type of the expression being returned and the function return type differ, yet G++ treats the return value as if it were designated by an rvalue. This warning is enabled by -Wextra. -Wrange-loop-construct (C++ and Objective-C++ only) This warning warns when a C++ range-based for-loop is creating an unnecessary copy. This can happen when the range declaration is not a reference, but probably should be. For example: struct S { char arr[128]; }; void fn () { S arr[5]; for (const auto x : arr) { ... } } It does not warn when the type being copied is a trivially-copyable type whose size is less than 64 bytes. This warning also warns when a loop variable in a range-based for- loop is initialized with a value of a different type resulting in a copy. For example: void fn() { int arr[10]; for (const double &x : arr) { ... } } In the example above, in every iteration of the loop a temporary value of type "double" is created and destroyed, to which the reference "const double &" is bound. This warning is enabled by -Wall. -Wredundant-tags (C++ and Objective-C++ only) Warn about redundant class-key and enum-key in references to class types and enumerated types in contexts where the key can be eliminated without causing an ambiguity. For example: struct foo; struct foo *p; // warn that keyword struct can be eliminated On the other hand, in this example there is no warning: struct foo; void foo (); // "hides" struct foo void bar (struct foo&); // no warning, keyword struct is necessary -Wno-subobject-linkage (C++ and Objective-C++ only) Do not warn if a class type has a base or a field whose type uses the anonymous namespace or depends on a type with no linkage. If a type A depends on a type B with no or internal linkage, defining it in multiple translation units would be an ODR violation because the meaning of B is different in each translation unit. If A only appears in a single translation unit, the best way to silence the warning is to give it internal linkage by putting it in an anonymous namespace as well. The compiler doesn't give this warning for types defined in the main .C file, as those are unlikely to have multiple definitions. -Wsubobject-linkage is enabled by default. -Weffc++ (C++ and Objective-C++ only) Warn about violations of the following style guidelines from Scott Meyers' Effective C++ series of books: * Define a copy constructor and an assignment operator for classes with dynamically-allocated memory. * Prefer initialization to assignment in constructors. * Have "operator=" return a reference to *this. * Don't try to return a reference when you must return an object. * Distinguish between prefix and postfix forms of increment and decrement operators. * Never overload "&&", "||", or ",". This option also enables -Wnon-virtual-dtor, which is also one of the effective C++ recommendations. However, the check is extended to warn about the lack of virtual destructor in accessible non- polymorphic bases classes too. When selecting this option, be aware that the standard library headers do not obey all of these guidelines; use grep -v to filter out those warnings. -Wno-exceptions (C++ and Objective-C++ only) Disable the warning about the case when an exception handler is shadowed by another handler, which can point out a wrong ordering of exception handlers. -Wstrict-null-sentinel (C++ and Objective-C++ only) Warn about the use of an uncasted "NULL" as sentinel. When compiling only with GCC this is a valid sentinel, as "NULL" is defined to "__null". Although it is a null pointer constant rather than a null pointer, it is guaranteed to be of the same size as a pointer. But this use is not portable across different compilers. -Wno-non-template-friend (C++ and Objective-C++ only) Disable warnings when non-template friend functions are declared within a template. In very old versions of GCC that predate implementation of the ISO standard, declarations such as friend int foo(int), where the name of the friend is an unqualified-id, could be interpreted as a particular specialization of a template function; the warning exists to diagnose compatibility problems, and is enabled by default. -Wold-style-cast (C++ and Objective-C++ only) Warn if an old-style (C-style) cast to a non-void type is used within a C++ program. The new-style casts ("dynamic_cast", "static_cast", "reinterpret_cast", and "const_cast") are less vulnerable to unintended effects and much easier to search for. -Woverloaded-virtual (C++ and Objective-C++ only) -Woverloaded-virtual=n Warn when a function declaration hides virtual functions from a base class. For example, in: struct A { virtual void f(); }; struct B: public A { void f(int); // does not override }; the "A" class version of "f" is hidden in "B", and code like: B* b; b->f(); fails to compile. In cases where the different signatures are not an accident, the simplest solution is to add a using-declaration to the derived class to un-hide the base function, e.g. add "using A::f;" to "B". The optional level suffix controls the behavior when all the declarations in the derived class override virtual functions in the base class, even if not all of the base functions are overridden: struct C { virtual void f(); virtual void f(int); }; struct D: public C { void f(int); // does override } This pattern is less likely to be a mistake; if D is only used virtually, the user might have decided that the base class semantics for some of the overloads are fine. At level 1, this case does not warn; at level 2, it does. -Woverloaded-virtual by itself selects level 2. Level 1 is included in -Wall. -Wno-pmf-conversions (C++ and Objective-C++ only) Disable the diagnostic for converting a bound pointer to member function to a plain pointer. -Wsign-promo (C++ and Objective-C++ only) Warn when overload resolution chooses a promotion from unsigned or enumerated type to a signed type, over a conversion to an unsigned type of the same size. Previous versions of G++ tried to preserve unsignedness, but the standard mandates the current behavior. -Wtemplates (C++ and Objective-C++ only) Warn when a primary template declaration is encountered. Some coding rules disallow templates, and this may be used to enforce that rule. The warning is inactive inside a system header file, such as the STL, so one can still use the STL. One may also instantiate or specialize templates. -Wmismatched-new-delete (C++ and Objective-C++ only) Warn for mismatches between calls to "operator new" or "operator delete" and the corresponding call to the allocation or deallocation function. This includes invocations of C++ "operator delete" with pointers returned from either mismatched forms of "operator new", or from other functions that allocate objects for which the "operator delete" isn't a suitable deallocator, as well as calls to other deallocation functions with pointers returned from "operator new" for which the deallocation function isn't suitable. For example, the "delete" expression in the function below is diagnosed because it doesn't match the array form of the "new" expression the pointer argument was returned from. Similarly, the call to "free" is also diagnosed. void f () { int *a = new int[n]; delete a; // warning: mismatch in array forms of expressions char *p = new char[n]; free (p); // warning: mismatch between new and free } The related option -Wmismatched-dealloc diagnoses mismatches involving allocation and deallocation functions other than "operator new" and "operator delete". -Wmismatched-new-delete is included in -Wall. -Wmismatched-tags (C++ and Objective-C++ only) Warn for declarations of structs, classes, and class templates and their specializations with a class-key that does not match either the definition or the first declaration if no definition is provided. For example, the declaration of "struct Object" in the argument list of "draw" triggers the warning. To avoid it, either remove the redundant class-key "struct" or replace it with "class" to match its definition. class Object { public: virtual ~Object () = 0; }; void draw (struct Object*); It is not wrong to declare a class with the class-key "struct" as the example above shows. The -Wmismatched-tags option is intended to help achieve a consistent style of class declarations. In code that is intended to be portable to Windows-based compilers the warning helps prevent unresolved references due to the difference in the mangling of symbols declared with different class-keys. The option can be used either on its own or in conjunction with -Wredundant-tags. -Wmultiple-inheritance (C++ and Objective-C++ only) Warn when a class is defined with multiple direct base classes. Some coding rules disallow multiple inheritance, and this may be used to enforce that rule. The warning is inactive inside a system header file, such as the STL, so one can still use the STL. One may also define classes that indirectly use multiple inheritance. -Wvirtual-inheritance Warn when a class is defined with a virtual direct base class. Some coding rules disallow multiple inheritance, and this may be used to enforce that rule. The warning is inactive inside a system header file, such as the STL, so one can still use the STL. One may also define classes that indirectly use virtual inheritance. -Wno-virtual-move-assign Suppress warnings about inheriting from a virtual base with a non- trivial C++11 move assignment operator. This is dangerous because if the virtual base is reachable along more than one path, it is moved multiple times, which can mean both objects end up in the moved-from state. If the move assignment operator is written to avoid moving from a moved-from object, this warning can be disabled. -Wnamespaces Warn when a namespace definition is opened. Some coding rules disallow namespaces, and this may be used to enforce that rule. The warning is inactive inside a system header file, such as the STL, so one can still use the STL. One may also use using directives and qualified names. -Wno-terminate (C++ and Objective-C++ only) Disable the warning about a throw-expression that will immediately result in a call to "terminate". -Wno-vexing-parse (C++ and Objective-C++ only) Warn about the most vexing parse syntactic ambiguity. This warns about the cases when a declaration looks like a variable definition, but the C++ language requires it to be interpreted as a function declaration. For instance: void f(double a) { int i(); // extern int i (void); int n(int(a)); // extern int n (int); } Another example: struct S { S(int); }; void f(double a) { S x(int(a)); // extern struct S x (int); S y(int()); // extern struct S y (int (*) (void)); S z(); // extern struct S z (void); } The warning will suggest options how to deal with such an ambiguity; e.g., it can suggest removing the parentheses or using braces instead. This warning is enabled by default. -Wno-class-conversion (C++ and Objective-C++ only) Do not warn when a conversion function converts an object to the same type, to a base class of that type, or to void; such a conversion function will never be called. -Wvolatile (C++ and Objective-C++ only) Warn about deprecated uses of the "volatile" qualifier. This includes postfix and prefix "++" and "--" expressions of "volatile"-qualified types, using simple assignments where the left operand is a "volatile"-qualified non-class type for their value, compound assignments where the left operand is a "volatile"-qualified non-class type, "volatile"-qualified function return type, "volatile"-qualified parameter type, and structured bindings of a "volatile"-qualified type. This usage was deprecated in C++20. Enabled by default with -std=c++20. -Wzero-as-null-pointer-constant (C++ and Objective-C++ only) Warn when a literal 0 is used as null pointer constant. This can be useful to facilitate the conversion to "nullptr" in C++11. -Waligned-new Warn about a new-expression of a type that requires greater alignment than the "alignof(std::max_align_t)" but uses an allocation function without an explicit alignment parameter. This option is enabled by -Wall. Normally this only warns about global allocation functions, but -Waligned-new=all also warns about class member allocation functions. -Wno-placement-new -Wplacement-new=n Warn about placement new expressions with undefined behavior, such as constructing an object in a buffer that is smaller than the type of the object. For example, the placement new expression below is diagnosed because it attempts to construct an array of 64 integers in a buffer only 64 bytes large. char buf [64]; new (buf) int[64]; This warning is enabled by default. -Wplacement-new=1 This is the default warning level of -Wplacement-new. At this level the warning is not issued for some strictly undefined constructs that GCC allows as extensions for compatibility with legacy code. For example, the following "new" expression is not diagnosed at this level even though it has undefined behavior according to the C++ standard because it writes past the end of the one-element array. struct S { int n, a[1]; }; S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]); new (s->a)int [32](); -Wplacement-new=2 At this level, in addition to diagnosing all the same constructs as at level 1, a diagnostic is also issued for placement new expressions that construct an object in the last member of structure whose type is an array of a single element and whose size is less than the size of the object being constructed. While the previous example would be diagnosed, the following construct makes use of the flexible member array extension to avoid the warning at level 2. struct S { int n, a[]; }; S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]); new (s->a)int [32](); -Wcatch-value -Wcatch-value=n (C++ and Objective-C++ only) Warn about catch handlers that do not catch via reference. With -Wcatch-value=1 (or -Wcatch-value for short) warn about polymorphic class types that are caught by value. With -Wcatch-value=2 warn about all class types that are caught by value. With -Wcatch-value=3 warn about all types that are not caught by reference. -Wcatch-value is enabled by -Wall. -Wconditionally-supported (C++ and Objective-C++ only) Warn for conditionally-supported (C++11 [intro.defs]) constructs. -Wno-delete-incomplete (C++ and Objective-C++ only) Do not warn when deleting a pointer to incomplete type, which may cause undefined behavior at runtime. This warning is enabled by default. -Wextra-semi (C++, Objective-C++ only) Warn about redundant semicolons after in-class function definitions. -Wno-inaccessible-base (C++, Objective-C++ only) This option controls warnings when a base class is inaccessible in a class derived from it due to ambiguity. The warning is enabled by default. Note that the warning for ambiguous virtual bases is enabled by the -Wextra option. struct A { int a; }; struct B : A { }; struct C : B, A { }; -Wno-inherited-variadic-ctor Suppress warnings about use of C++11 inheriting constructors when the base class inherited from has a C variadic constructor; the warning is on by default because the ellipsis is not inherited. -Wno-invalid-offsetof (C++ and Objective-C++ only) Suppress warnings from applying the "offsetof" macro to a non-POD type. According to the 2014 ISO C++ standard, applying "offsetof" to a non-standard-layout type is undefined. In existing C++ implementations, however, "offsetof" typically gives meaningful results. This flag is for users who are aware that they are writing nonportable code and who have deliberately chosen to ignore the warning about it. The restrictions on "offsetof" may be relaxed in a future version of the C++ standard. -Wsized-deallocation (C++ and Objective-C++ only) Warn about a definition of an unsized deallocation function void operator delete (void *) noexcept; void operator delete[] (void *) noexcept; without a definition of the corresponding sized deallocation function void operator delete (void *, std::size_t) noexcept; void operator delete[] (void *, std::size_t) noexcept; or vice versa. Enabled by -Wextra along with -fsized-deallocation. -Wsuggest-final-types Warn about types with virtual methods where code quality would be improved if the type were declared with the C++11 "final" specifier, or, if possible, declared in an anonymous namespace. This allows GCC to more aggressively devirtualize the polymorphic calls. This warning is more effective with link-time optimization, where the information about the class hierarchy graph is more complete. -Wsuggest-final-methods Warn about virtual methods where code quality would be improved if the method were declared with the C++11 "final" specifier, or, if possible, its type were declared in an anonymous namespace or with the "final" specifier. This warning is more effective with link- time optimization, where the information about the class hierarchy graph is more complete. It is recommended to first consider suggestions of -Wsuggest-final-types and then rebuild with new annotations. -Wsuggest-override Warn about overriding virtual functions that are not marked with the "override" keyword. -Wuse-after-free -Wuse-after-free=n Warn about uses of pointers to dynamically allocated objects that have been rendered indeterminate by a call to a deallocation function. The warning is enabled at all optimization levels but may yield different results with optimization than without. -Wuse-after-free=1 At level 1 the warning attempts to diagnose only unconditional uses of pointers made indeterminate by a deallocation call or a successful call to "realloc", regardless of whether or not the call resulted in an actual reallocatio of memory. This includes double-"free" calls as well as uses in arithmetic and relational expressions. Although undefined, uses of indeterminate pointers in equality (or inequality) expressions are not diagnosed at this level. -Wuse-after-free=2 At level 2, in addition to unconditional uses, the warning also diagnoses conditional uses of pointers made indeterminate by a deallocation call. As at level 2, uses in equality (or inequality) expressions are not diagnosed. For example, the second call to "free" in the following function is diagnosed at this level: struct A { int refcount; void *data; }; void release (struct A *p) { int refcount = --p->refcount; free (p); if (refcount == 0) free (p->data); // warning: p may be used after free } -Wuse-after-free=3 At level 3, the warning also diagnoses uses of indeterminate pointers in equality expressions. All uses of indeterminate pointers are undefined but equality tests sometimes appear after calls to "realloc" as an attempt to determine whether the call resulted in relocating the object to a different address. They are diagnosed at a separate level to aid legacy code gradually transition to safe alternatives. For example, the equality test in the function below is diagnosed at this level: void adjust_pointers (int**, int); void grow (int **p, int n) { int **q = (int**)realloc (p, n *= 2); if (q == p) return; adjust_pointers ((int**)q, n); } To avoid the warning at this level, store offsets into allocated memory instead of pointers. This approach obviates needing to adjust the stored pointers after reallocation. -Wuse-after-free=2 is included in -Wall. -Wuseless-cast (C++ and Objective-C++ only) Warn when an expression is cast to its own type. This warning does not occur when a class object is converted to a non-reference type as that is a way to create a temporary: struct S { }; void g (S&&); void f (S&& arg) { g (S(arg)); // make arg prvalue so that it can bind to S&& } -Wno-conversion-null (C++ and Objective-C++ only) Do not warn for conversions between "NULL" and non-pointer types. -Wconversion-null is enabled by default. Options Controlling Objective-C and Objective-C++ Dialects (NOTE: This manual does not describe the Objective-C and Objective-C++ languages themselves. This section describes the command-line options that are only meaningful for Objective-C and Objective-C++ programs. You can also use most of the language-independent GNU compiler options. For example, you might compile a file some_class.m like this: gcc -g -fgnu-runtime -O -c some_class.m In this example, -fgnu-runtime is an option meant only for Objective-C and Objective-C++ programs; you can use the other options with any language supported by GCC. Note that since Objective-C is an extension of the C language, Objective-C compilations may also use options specific to the C front- end (e.g., -Wtraditional). Similarly, Objective-C++ compilations may use C++-specific options (e.g., -Wabi). Here is a list of options that are only for compiling Objective-C and Objective-C++ programs: -fconstant-string-class=class-name Use class-name as the name of the class to instantiate for each literal string specified with the syntax "@"..."". The default class name is "NXConstantString" if the GNU runtime is being used, and "NSConstantString" if the NeXT runtime is being used (see below). On Darwin (macOS, MacOS X) platforms, the -fconstant-cfstrings option, if also present, overrides the -fconstant-string-class setting and cause "@"..."" literals to be laid out as constant CoreFoundation strings. Note that -fconstant-cfstrings is an alias for the target-specific -mconstant-cfstrings equivalent. -fgnu-runtime Generate object code compatible with the standard GNU Objective-C runtime. This is the default for most types of systems. -fnext-runtime Generate output compatible with the NeXT runtime. This is the default for NeXT-based systems, including Darwin and Mac OS X. The macro "__NEXT_RUNTIME__" is predefined if (and only if) this option is used. -fno-nil-receivers Assume that all Objective-C message dispatches ("[receiver message:arg]") in this translation unit ensure that the receiver is not "nil". This allows for more efficient entry points in the runtime to be used. This option is only available in conjunction with the NeXT runtime and ABI version 0 or 1. -fobjc-abi-version=n Use version n of the Objective-C ABI for the selected runtime. This option is currently supported only for the NeXT runtime. In that case, Version 0 is the traditional (32-bit) ABI without support for properties and other Objective-C 2.0 additions. Version 1 is the traditional (32-bit) ABI with support for properties and other Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If nothing is specified, the default is Version 0 on 32-bit target machines, and Version 2 on 64-bit target machines. -fobjc-call-cxx-cdtors For each Objective-C class, check if any of its instance variables is a C++ object with a non-trivial default constructor. If so, synthesize a special "- (id) .cxx_construct" instance method which runs non-trivial default constructors on any such instance variables, in order, and then return "self". Similarly, check if any instance variable is a C++ object with a non-trivial destructor, and if so, synthesize a special "- (void) .cxx_destruct" method which runs all such default destructors, in reverse order. The "- (id) .cxx_construct" and "- (void) .cxx_destruct" methods thusly generated only operate on instance variables declared in the current Objective-C class, and not those inherited from superclasses. It is the responsibility of the Objective-C runtime to invoke all such methods in an object's inheritance hierarchy. The "- (id) .cxx_construct" methods are invoked by the runtime immediately after a new object instance is allocated; the "- (void) .cxx_destruct" methods are invoked immediately before the runtime deallocates an object instance. As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has support for invoking the "- (id) .cxx_construct" and "- (void) .cxx_destruct" methods. -fobjc-direct-dispatch Allow fast jumps to the message dispatcher. On Darwin this is accomplished via the comm page. -fobjc-exceptions Enable syntactic support for structured exception handling in Objective-C, similar to what is offered by C++. This option is required to use the Objective-C keywords @try, @throw, @catch, @finally and @synchronized. This option is available with both the GNU runtime and the NeXT runtime (but not available in conjunction with the NeXT runtime on Mac OS X 10.2 and earlier). -fobjc-gc Enable garbage collection (GC) in Objective-C and Objective-C++ programs. This option is only available with the NeXT runtime; the GNU runtime has a different garbage collection implementation that does not require special compiler flags. -fobjc-nilcheck For the NeXT runtime with version 2 of the ABI, check for a nil receiver in method invocations before doing the actual method call. This is the default and can be disabled using -fno-objc-nilcheck. Class methods and super calls are never checked for nil in this way no matter what this flag is set to. Currently this flag does nothing when the GNU runtime, or an older version of the NeXT runtime ABI, is used. -fobjc-std=objc1 Conform to the language syntax of Objective-C 1.0, the language recognized by GCC 4.0. This only affects the Objective-C additions to the C/C++ language; it does not affect conformance to C/C++ standards, which is controlled by the separate C/C++ dialect option flags. When this option is used with the Objective-C or Objective-C++ compiler, any Objective-C syntax that is not recognized by GCC 4.0 is rejected. This is useful if you need to make sure that your Objective-C code can be compiled with older versions of GCC. -freplace-objc-classes Emit a special marker instructing ld(1) not to statically link in the resulting object file, and allow dyld(1) to load it in at run time instead. This is used in conjunction with the Fix-and- Continue debugging mode, where the object file in question may be recompiled and dynamically reloaded in the course of program execution, without the need to restart the program itself. Currently, Fix-and-Continue functionality is only available in conjunction with the NeXT runtime on Mac OS X 10.3 and later. -fzero-link When compiling for the NeXT runtime, the compiler ordinarily replaces calls to "objc_getClass("...")" (when the name of the class is known at compile time) with static class references that get initialized at load time, which improves run-time performance. Specifying the -fzero-link flag suppresses this behavior and causes calls to "objc_getClass("...")" to be retained. This is useful in Zero-Link debugging mode, since it allows for individual class implementations to be modified during program execution. The GNU runtime currently always retains calls to "objc_get_class("...")" regardless of command-line options. -fno-local-ivars By default instance variables in Objective-C can be accessed as if they were local variables from within the methods of the class they're declared in. This can lead to shadowing between instance variables and other variables declared either locally inside a class method or globally with the same name. Specifying the -fno-local-ivars flag disables this behavior thus avoiding variable shadowing issues. -fivar-visibility=[public|protected|private|package] Set the default instance variable visibility to the specified option so that instance variables declared outside the scope of any access modifier directives default to the specified visibility. -gen-decls Dump interface declarations for all classes seen in the source file to a file named sourcename.decl. -Wassign-intercept (Objective-C and Objective-C++ only) Warn whenever an Objective-C assignment is being intercepted by the garbage collector. -Wno-property-assign-default (Objective-C and Objective-C++ only) Do not warn if a property for an Objective-C object has no assign semantics specified. -Wno-protocol (Objective-C and Objective-C++ only) If a class is declared to implement a protocol, a warning is issued for every method in the protocol that is not implemented by the class. The default behavior is to issue a warning for every method not explicitly implemented in the class, even if a method implementation is inherited from the superclass. If you use the -Wno-protocol option, then methods inherited from the superclass are considered to be implemented, and no warning is issued for them. -Wobjc-root-class (Objective-C and Objective-C++ only) Warn if a class interface lacks a superclass. Most classes will inherit from "NSObject" (or "Object") for example. When declaring classes intended to be root classes, the warning can be suppressed by marking their interfaces with "__attribute__((objc_root_class))". -Wselector (Objective-C and Objective-C++ only) Warn if multiple methods of different types for the same selector are found during compilation. The check is performed on the list of methods in the final stage of compilation. Additionally, a check is performed for each selector appearing in a "@selector(...)" expression, and a corresponding method for that selector has been found during compilation. Because these checks scan the method table only at the end of compilation, these warnings are not produced if the final stage of compilation is not reached, for example because an error is found during compilation, or because the -fsyntax-only option is being used. -Wstrict-selector-match (Objective-C and Objective-C++ only) Warn if multiple methods with differing argument and/or return types are found for a given selector when attempting to send a message using this selector to a receiver of type "id" or "Class". When this flag is off (which is the default behavior), the compiler omits such warnings if any differences found are confined to types that share the same size and alignment. -Wundeclared-selector (Objective-C and Objective-C++ only) Warn if a "@selector(...)" expression referring to an undeclared selector is found. A selector is considered undeclared if no method with that name has been declared before the "@selector(...)" expression, either explicitly in an @interface or @protocol declaration, or implicitly in an @implementation section. This option always performs its checks as soon as a "@selector(...)" expression is found, while -Wselector only performs its checks in the final stage of compilation. This also enforces the coding style convention that methods and selectors must be declared before being used. -print-objc-runtime-info Generate C header describing the largest structure that is passed by value, if any. Options to Control Diagnostic Messages Formatting Traditionally, diagnostic messages have been formatted irrespective of the output device's aspect (e.g. its width, ...). You can use the options described below to control the formatting algorithm for diagnostic messages, e.g. how many characters per line, how often source location information should be reported. Note that some language front ends may not honor these options. -fmessage-length=n Try to format error messages so that they fit on lines of about n characters. If n is zero, then no line-wrapping is done; each error message appears on a single line. This is the default for all front ends. Note - this option also affects the display of the #error and #warning pre-processor directives, and the deprecated function/type/variable attribute. It does not however affect the pragma GCC warning and pragma GCC error pragmas. -fdiagnostics-plain-output This option requests that diagnostic output look as plain as possible, which may be useful when running dejagnu or other utilities that need to parse diagnostics output and prefer that it remain more stable over time. -fdiagnostics-plain-output is currently equivalent to the following options: -fno-diagnostics-show-caret -fno-diagnostics-show-line-numbers -fdiagnostics-color=never -fdiagnostics-urls=never -fdiagnostics-path-format=separate-events In the future, if GCC changes the default appearance of its diagnostics, the corresponding option to disable the new behavior will be added to this list. -fdiagnostics-show-location=once Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit source location information once; that is, in case the message is too long to fit on a single physical line and has to be wrapped, the source location won't be emitted (as prefix) again, over and over, in subsequent continuation lines. This is the default behavior. -fdiagnostics-show-location=every-line Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit the same source location information (as prefix) for physical lines that result from the process of breaking a message which is too long to fit on a single line. -fdiagnostics-color[=WHEN] -fno-diagnostics-color Use color in diagnostics. WHEN is never, always, or auto. The default depends on how the compiler has been configured, it can be any of the above WHEN options or also never if GCC_COLORS environment variable isn't present in the environment, and auto otherwise. auto makes GCC use color only when the standard error is a terminal, and when not executing in an emacs shell. The forms -fdiagnostics-color and -fno-diagnostics-color are aliases for -fdiagnostics-color=always and -fdiagnostics-color=never, respectively. The colors are defined by the environment variable GCC_COLORS. Its value is a colon-separated list of capabilities and Select Graphic Rendition (SGR) substrings. SGR commands are interpreted by the terminal or terminal emulator. (See the section in the documentation of your text terminal for permitted values and their meanings as character attributes.) These substring values are integers in decimal representation and can be concatenated with semicolons. Common values to concatenate include 1 for bold, 4 for underline, 5 for blink, 7 for inverse, 39 for default foreground color, 30 to 37 for foreground colors, 90 to 97 for 16-color mode foreground colors, 38;5;0 to 38;5;255 for 88-color and 256-color modes foreground colors, 49 for default background color, 40 to 47 for background colors, 100 to 107 for 16-color mode background colors, and 48;5;0 to 48;5;255 for 88-color and 256-color modes background colors. The default GCC_COLORS is error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\ quote=01:path=01;36:fixit-insert=32:fixit-delete=31:\ diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\ type-diff=01;32:fnname=01;32:targs=35 where 01;31 is bold red, 01;35 is bold magenta, 01;36 is bold cyan, 32 is green, 34 is blue, 01 is bold, and 31 is red. Setting GCC_COLORS to the empty string disables colors. Supported capabilities are as follows. "error=" SGR substring for error: markers. "warning=" SGR substring for warning: markers. "note=" SGR substring for note: markers. "path=" SGR substring for colorizing paths of control-flow events as printed via -fdiagnostics-path-format=, such as the identifiers of individual events and lines indicating interprocedural calls and returns. "range1=" SGR substring for first additional range. "range2=" SGR substring for second additional range. "locus=" SGR substring for location information, file:line or file:line:column etc. "quote=" SGR substring for information printed within quotes. "fnname=" SGR substring for names of C++ functions. "targs=" SGR substring for C++ function template parameter bindings. "fixit-insert=" SGR substring for fix-it hints suggesting text to be inserted or replaced. "fixit-delete=" SGR substring for fix-it hints suggesting text to be deleted. "diff-filename=" SGR substring for filename headers within generated patches. "diff-hunk=" SGR substring for the starts of hunks within generated patches. "diff-delete=" SGR substring for deleted lines within generated patches. "diff-insert=" SGR substring for inserted lines within generated patches. "type-diff=" SGR substring for highlighting mismatching types within template arguments in the C++ frontend. -fdiagnostics-urls[=WHEN] Use escape sequences to embed URLs in diagnostics. For example, when -fdiagnostics-show-option emits text showing the command-line option controlling a diagnostic, embed a URL for documentation of that option. WHEN is never, always, or auto. auto makes GCC use URL escape sequences only when the standard error is a terminal, and when not executing in an emacs shell or any graphical terminal which is known to be incompatible with this feature, see below. The default depends on how the compiler has been configured. It can be any of the above WHEN options. GCC can also be configured (via the --with-diagnostics-urls=auto-if-env configure-time option) so that the default is affected by environment variables. Under such a configuration, GCC defaults to using auto if either GCC_URLS or TERM_URLS environment variables are present and non-empty in the environment of the compiler, or never if neither are. However, even with -fdiagnostics-urls=always the behavior is dependent on those environment variables: If GCC_URLS is set to empty or no, do not embed URLs in diagnostics. If set to st, URLs use ST escape sequences. If set to bel, the default, URLs use BEL escape sequences. Any other non-empty value enables the feature. If GCC_URLS is not set, use TERM_URLS as a fallback. Note: ST is an ANSI escape sequence, string terminator ESC \, BEL is an ASCII character, CTRL-G that usually sounds like a beep. At this time GCC tries to detect also a few terminals that are known to not implement the URL feature, and have bugs or at least had bugs in some versions that are still in use, where the URL escapes are likely to misbehave, i.e. print garbage on the screen. That list is currently xfce4-terminal, certain known to be buggy gnome-terminal versions, the linux console, and mingw. This check can be skipped with the -fdiagnostics-urls=always. -fno-diagnostics-show-option By default, each diagnostic emitted includes text indicating the command-line option that directly controls the diagnostic (if such an option is known to the diagnostic machinery). Specifying the -fno-diagnostics-show-option flag suppresses that behavior. -fno-diagnostics-show-caret By default, each diagnostic emitted includes the original source line and a caret ^ indicating the column. This option suppresses this information. The source line is truncated to n characters, if the -fmessage-length=n option is given. When the output is done to the terminal, the width is limited to the width given by the COLUMNS environment variable or, if not set, to the terminal width. -fno-diagnostics-show-labels By default, when printing source code (via -fdiagnostics-show-caret), diagnostics can label ranges of source code with pertinent information, such as the types of expressions: printf ("foo %s bar", long_i + long_j); ~^ ~~~~~~~~~~~~~~~ | | char * long int This option suppresses the printing of these labels (in the example above, the vertical bars and the "char *" and "long int" text). -fno-diagnostics-show-cwe Diagnostic messages can optionally have an associated CWE ("https://cwe.mitre.org/index.html") identifier. GCC itself only provides such metadata for some of the -fanalyzer diagnostics. GCC plugins may also provide diagnostics with such metadata. By default, if this information is present, it will be printed with the diagnostic. This option suppresses the printing of this metadata. -fno-diagnostics-show-rules Diagnostic messages can optionally have rules associated with them, such as from a coding standard, or a specification. GCC itself does not do this for any of its diagnostics, but plugins may do so. By default, if this information is present, it will be printed with the diagnostic. This option suppresses the printing of this metadata. -fno-diagnostics-show-line-numbers By default, when printing source code (via -fdiagnostics-show-caret), a left margin is printed, showing line numbers. This option suppresses this left margin. -fdiagnostics-minimum-margin-width=width This option controls the minimum width of the left margin printed by -fdiagnostics-show-line-numbers. It defaults to 6. -fdiagnostics-parseable-fixits Emit fix-it hints in a machine-parseable format, suitable for consumption by IDEs. For each fix-it, a line will be printed after the relevant diagnostic, starting with the string "fix-it:". For example: fix-it:"test.c":{45:3-45:21}:"gtk_widget_show_all" The location is expressed as a half-open range, expressed as a count of bytes, starting at byte 1 for the initial column. In the above example, bytes 3 through 20 of line 45 of "test.c" are to be replaced with the given string: 00000000011111111112222222222 12345678901234567890123456789 gtk_widget_showall (dlg); ^^^^^^^^^^^^^^^^^^ gtk_widget_show_all The filename and replacement string escape backslash as "\\", tab as "\t", newline as "\n", double quotes as "\"", non-printable characters as octal (e.g. vertical tab as "\013"). An empty replacement string indicates that the given range is to be removed. An empty range (e.g. "45:3-45:3") indicates that the string is to be inserted at the given position. -fdiagnostics-generate-patch Print fix-it hints to stderr in unified diff format, after any diagnostics are printed. For example: --- test.c +++ test.c @ -42,5 +42,5 @ void show_cb(GtkDialog *dlg) { - gtk_widget_showall(dlg); + gtk_widget_show_all(dlg); } The diff may or may not be colorized, following the same rules as for diagnostics (see -fdiagnostics-color). -fdiagnostics-show-template-tree In the C++ frontend, when printing diagnostics showing mismatching template types, such as: could not convert 'std::map<int, std::vector<double> >()' from 'map<[...],vector<double>>' to 'map<[...],vector<float>> the -fdiagnostics-show-template-tree flag enables printing a tree- like structure showing the common and differing parts of the types, such as: map< [...], vector< [double != float]>> The parts that differ are highlighted with color ("double" and "float" in this case). -fno-elide-type By default when the C++ frontend prints diagnostics showing mismatching template types, common parts of the types are printed as "[...]" to simplify the error message. For example: could not convert 'std::map<int, std::vector<double> >()' from 'map<[...],vector<double>>' to 'map<[...],vector<float>> Specifying the -fno-elide-type flag suppresses that behavior. This flag also affects the output of the -fdiagnostics-show-template-tree flag. -fdiagnostics-path-format=KIND Specify how to print paths of control-flow events for diagnostics that have such a path associated with them. KIND is none, separate-events, or inline-events, the default. none means to not print diagnostic paths. separate-events means to print a separate "note" diagnostic for each event within the diagnostic. For example: test.c:29:5: error: passing NULL as argument 1 to 'PyList_Append' which requires a non-NULL parameter test.c:25:10: note: (1) when 'PyList_New' fails, returning NULL test.c:27:3: note: (2) when 'i < count' test.c:29:5: note: (3) when calling 'PyList_Append', passing NULL from (1) as argument 1 inline-events means to print the events "inline" within the source code. This view attempts to consolidate the events into runs of sufficiently-close events, printing them as labelled ranges within the source. For example, the same events as above might be printed as: 'test': events 1-3 | | 25 | list = PyList_New(0); | | ^~~~~~~~~~~~~ | | | | | (1) when 'PyList_New' fails, returning NULL | 26 | | 27 | for (i = 0; i < count; i++) { | | ~~~ | | | | | (2) when 'i < count' | 28 | item = PyLong_FromLong(random()); | 29 | PyList_Append(list, item); | | ~~~~~~~~~~~~~~~~~~~~~~~~~ | | | | | (3) when calling 'PyList_Append', passing NULL from (1) as argument 1 | Interprocedural control flow is shown by grouping the events by stack frame, and using indentation to show how stack frames are nested, pushed, and popped. For example: 'test': events 1-2 | | 133 | { | | ^ | | | | | (1) entering 'test' | 134 | boxed_int *obj = make_boxed_int (i); | | ~~~~~~~~~~~~~~~~~~ | | | | | (2) calling 'make_boxed_int' | +--> 'make_boxed_int': events 3-4 | | 120 | { | | ^ | | | | | (3) entering 'make_boxed_int' | 121 | boxed_int *result = (boxed_int *)wrapped_malloc (sizeof (boxed_int)); | | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | | | | | (4) calling 'wrapped_malloc' | +--> 'wrapped_malloc': events 5-6 | | 7 | { | | ^ | | | | | (5) entering 'wrapped_malloc' | 8 | return malloc (size); | | ~~~~~~~~~~~~~ | | | | | (6) calling 'malloc' | <-------------+ | 'test': event 7 | | 138 | free_boxed_int (obj); | | ^~~~~~~~~~~~~~~~~~~~ | | | | | (7) calling 'free_boxed_int' | (etc) -fdiagnostics-show-path-depths This option provides additional information when printing control- flow paths associated with a diagnostic. If this is option is provided then the stack depth will be printed for each run of events within -fdiagnostics-path-format=inline-events. If provided with -fdiagnostics-path-format=separate-events, then the stack depth and function declaration will be appended when printing each event. This is intended for use by GCC developers and plugin developers when debugging diagnostics that report interprocedural control flow. -fno-show-column Do not print column numbers in diagnostics. This may be necessary if diagnostics are being scanned by a program that does not understand the column numbers, such as dejagnu. -fdiagnostics-column-unit=UNIT Select the units for the column number. This affects traditional diagnostics (in the absence of -fno-show-column), as well as JSON format diagnostics if requested. The default UNIT, display, considers the number of display columns occupied by each character. This may be larger than the number of bytes required to encode the character, in the case of tab characters, or it may be smaller, in the case of multibyte characters. For example, the character "GREEK SMALL LETTER PI (U+03C0)" occupies one display column, and its UTF-8 encoding requires two bytes; the character "SLIGHTLY SMILING FACE (U+1F642)" occupies two display columns, and its UTF-8 encoding requires four bytes. Setting UNIT to byte changes the column number to the raw byte count in all cases, as was traditionally output by GCC prior to version 11.1.0. -fdiagnostics-column-origin=ORIGIN Select the origin for column numbers, i.e. the column number assigned to the first column. The default value of 1 corresponds to traditional GCC behavior and to the GNU style guide. Some utilities may perform better with an origin of 0; any non-negative value may be specified. -fdiagnostics-escape-format=FORMAT When GCC prints pertinent source lines for a diagnostic it normally attempts to print the source bytes directly. However, some diagnostics relate to encoding issues in the source file, such as malformed UTF-8, or issues with Unicode normalization. These diagnostics are flagged so that GCC will escape bytes that are not printable ASCII when printing their pertinent source lines. This option controls how such bytes should be escaped. The default FORMAT, unicode displays Unicode characters that are not printable ASCII in the form <U+XXXX>, and bytes that do not correspond to a Unicode character validly-encoded in UTF-8-encoded will be displayed as hexadecimal in the form <XX>. For example, a source line containing the string before followed by the Unicode character U+03C0 ("GREEK SMALL LETTER PI", with UTF-8 encoding 0xCF 0x80) followed by the byte 0xBF (a stray UTF-8 trailing byte), followed by the string after will be printed for such a diagnostic as: before<U+03C0><BF>after Setting FORMAT to bytes will display all non-printable-ASCII bytes in the form <XX>, thus showing the underlying encoding of non-ASCII Unicode characters. For the example above, the following will be printed: before<CF><80><BF>after -fdiagnostics-format=FORMAT Select a different format for printing diagnostics. FORMAT is text, sarif-stderr, sarif-file, json, json-stderr, or json-file. The default is text. The sarif-stderr and sarif-file formats both emit diagnostics in SARIF Version 2.1.0 format, either to stderr, or to a file named source.sarif, respectively. The json format is a synonym for json-stderr. The json-stderr and json-file formats are identical, apart from where the JSON is emitted to - with the former, the JSON is emitted to stderr, whereas with json-file it is written to source.gcc.json. The emitted JSON consists of a top-level JSON array containing JSON objects representing the diagnostics. The JSON is emitted as one line, without formatting; the examples below have been formatted for clarity. Diagnostics can have child diagnostics. For example, this error and note: misleading-indentation.c:15:3: warning: this 'if' clause does not guard... [-Wmisleading-indentation] 15 | if (flag) | ^~ misleading-indentation.c:17:5: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if' 17 | y = 2; | ^ might be printed in JSON form (after formatting) like this: [ { "kind": "warning", "locations": [ { "caret": { "display-column": 3, "byte-column": 3, "column": 3, "file": "misleading-indentation.c", "line": 15 }, "finish": { "display-column": 4, "byte-column": 4, "column": 4, "file": "misleading-indentation.c", "line": 15 } } ], "message": "this \u2018if\u2019 clause does not guard...", "option": "-Wmisleading-indentation", "option_url": "https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wmisleading-indentation", "children": [ { "kind": "note", "locations": [ { "caret": { "display-column": 5, "byte-column": 5, "column": 5, "file": "misleading-indentation.c", "line": 17 } } ], "escape-source": false, "message": "...this statement, but the latter is ..." } ] "escape-source": false, "column-origin": 1, } ] where the "note" is a child of the "warning". A diagnostic has a "kind". If this is "warning", then there is an "option" key describing the command-line option controlling the warning. A diagnostic can contain zero or more locations. Each location has an optional "label" string and up to three positions within it: a "caret" position and optional "start" and "finish" positions. A position is described by a "file" name, a "line" number, and three numbers indicating a column position: * "display-column" counts display columns, accounting for tabs and multibyte characters. * "byte-column" counts raw bytes. * "column" is equal to one of the previous two, as dictated by the -fdiagnostics-column-unit option. All three columns are relative to the origin specified by -fdiagnostics-column-origin, which is typically equal to 1 but may be set, for instance, to 0 for compatibility with other utilities that number columns from 0. The column origin is recorded in the JSON output in the "column-origin" tag. In the remaining examples below, the extra column number outputs have been omitted for brevity. For example, this error: bad-binary-ops.c:64:23: error: invalid operands to binary + (have 'S' {aka 'struct s'} and 'T' {aka 'struct t'}) 64 | return callee_4a () + callee_4b (); | ~~~~~~~~~~~~ ^ ~~~~~~~~~~~~ | | | | | T {aka struct t} | S {aka struct s} has three locations. Its primary location is at the "+" token at column 23. It has two secondary locations, describing the left and right-hand sides of the expression, which have labels. It might be printed in JSON form as: { "children": [], "kind": "error", "locations": [ { "caret": { "column": 23, "file": "bad-binary-ops.c", "line": 64 } }, { "caret": { "column": 10, "file": "bad-binary-ops.c", "line": 64 }, "finish": { "column": 21, "file": "bad-binary-ops.c", "line": 64 }, "label": "S {aka struct s}" }, { "caret": { "column": 25, "file": "bad-binary-ops.c", "line": 64 }, "finish": { "column": 36, "file": "bad-binary-ops.c", "line": 64 }, "label": "T {aka struct t}" } ], "escape-source": false, "message": "invalid operands to binary + ..." } If a diagnostic contains fix-it hints, it has a "fixits" array, consisting of half-open intervals, similar to the output of -fdiagnostics-parseable-fixits. For example, this diagnostic with a replacement fix-it hint: demo.c:8:15: error: 'struct s' has no member named 'colour'; did you mean 'color'? 8 | return ptr->colour; | ^~~~~~ | color might be printed in JSON form as: { "children": [], "fixits": [ { "next": { "column": 21, "file": "demo.c", "line": 8 }, "start": { "column": 15, "file": "demo.c", "line": 8 }, "string": "color" } ], "kind": "error", "locations": [ { "caret": { "column": 15, "file": "demo.c", "line": 8 }, "finish": { "column": 20, "file": "demo.c", "line": 8 } } ], "escape-source": false, "message": "\u2018struct s\u2019 has no member named ..." } where the fix-it hint suggests replacing the text from "start" up to but not including "next" with "string"'s value. Deletions are expressed via an empty value for "string", insertions by having "start" equal "next". If the diagnostic has a path of control-flow events associated with it, it has a "path" array of objects representing the events. Each event object has a "description" string, a "location" object, along with a "function" string and a "depth" number for representing interprocedural paths. The "function" represents the current function at that event, and the "depth" represents the stack depth relative to some baseline: the higher, the more frames are within the stack. For example, the intraprocedural example shown for -fdiagnostics-path-format= might have this JSON for its path: "path": [ { "depth": 0, "description": "when 'PyList_New' fails, returning NULL", "function": "test", "location": { "column": 10, "file": "test.c", "line": 25 } }, { "depth": 0, "description": "when 'i < count'", "function": "test", "location": { "column": 3, "file": "test.c", "line": 27 } }, { "depth": 0, "description": "when calling 'PyList_Append', passing NULL from (1) as argument 1", "function": "test", "location": { "column": 5, "file": "test.c", "line": 29 } } ] Diagnostics have a boolean attribute "escape-source", hinting whether non-ASCII bytes should be escaped when printing the pertinent lines of source code ("true" for diagnostics involving source encoding issues). Options to Request or Suppress Warnings Warnings are diagnostic messages that report constructions that are not inherently erroneous but that are risky or suggest there may have been an error. The following language-independent options do not enable specific warnings but control the kinds of diagnostics produced by GCC. -fsyntax-only Check the code for syntax errors, but don't do anything beyond that. -fmax-errors=n Limits the maximum number of error messages to n, at which point GCC bails out rather than attempting to continue processing the source code. If n is 0 (the default), there is no limit on the number of error messages produced. If -Wfatal-errors is also specified, then -Wfatal-errors takes precedence over this option. -w Inhibit all warning messages. -Werror Make all warnings into errors. -Werror= Make the specified warning into an error. The specifier for a warning is appended; for example -Werror=switch turns the warnings controlled by -Wswitch into errors. This switch takes a negative form, to be used to negate -Werror for specific warnings; for example -Wno-error=switch makes -Wswitch warnings not be errors, even when -Werror is in effect. The warning message for each controllable warning includes the option that controls the warning. That option can then be used with -Werror= and -Wno-error= as described above. (Printing of the option in the warning message can be disabled using the -fno-diagnostics-show-option flag.) Note that specifying -Werror=foo automatically implies -Wfoo. However, -Wno-error=foo does not imply anything. -Wfatal-errors This option causes the compiler to abort compilation on the first error occurred rather than trying to keep going and printing further error messages. You can request many specific warnings with options beginning with -W, for example -Wimplicit to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning -Wno- to turn off warnings; for example, -Wno-implicit. This manual lists only one of the two forms, whichever is not the default. For further language-specific options also refer to C++ Dialect Options and Objective-C and Objective-C++ Dialect Options. Additional warnings can be produced by enabling the static analyzer; Some options, such as -Wall and -Wextra, turn on other options, such as -Wunused, which may turn on further options, such as -Wunused-value. The combined effect of positive and negative forms is that more specific options have priority over less specific ones, independently of their position in the command-line. For options of the same specificity, the last one takes effect. Options enabled or disabled via pragmas take effect as if they appeared at the end of the command-line. When an unrecognized warning option is requested (e.g., -Wunknown-warning), GCC emits a diagnostic stating that the option is not recognized. However, if the -Wno- form is used, the behavior is slightly different: no diagnostic is produced for -Wno-unknown-warning unless other diagnostics are being produced. This allows the use of new -Wno- options with old compilers, but if something goes wrong, the compiler warns that an unrecognized option is present. The effectiveness of some warnings depends on optimizations also being enabled. For example -Wsuggest-final-types is more effective with link- time optimization and some instances of other warnings may not be issued at all unless optimization is enabled. While optimization in general improves the efficacy of control and data flow sensitive warnings, in some cases it may also cause false positives. -Wpedantic -pedantic Issue all the warnings demanded by strict ISO C and ISO C++; reject all programs that use forbidden extensions, and some other programs that do not follow ISO C and ISO C++. For ISO C, follows the version of the ISO C standard specified by any -std option used. Valid ISO C and ISO C++ programs should compile properly with or without this option (though a rare few require -ansi or a -std option specifying the required version of ISO C). However, without this option, certain GNU extensions and traditional C and C++ features are supported as well. With this option, they are rejected. -Wpedantic does not cause warning messages for use of the alternate keywords whose names begin and end with __. This alternate format can also be used to disable warnings for non-ISO __intN types, i.e. __intN__. Pedantic warnings are also disabled in the expression that follows "__extension__". However, only system header files should use these escape routes; application programs should avoid them. Some users try to use -Wpedantic to check programs for strict ISO C conformance. They soon find that it does not do quite what they want: it finds some non-ISO practices, but not all---only those for which ISO C requires a diagnostic, and some others for which diagnostics have been added. A feature to report any failure to conform to ISO C might be useful in some instances, but would require considerable additional work and would be quite different from -Wpedantic. We don't have plans to support such a feature in the near future. Where the standard specified with -std represents a GNU extended dialect of C, such as gnu90 or gnu99, there is a corresponding base standard, the version of ISO C on which the GNU extended dialect is based. Warnings from -Wpedantic are given where they are required by the base standard. (It does not make sense for such warnings to be given only for features not in the specified GNU C dialect, since by definition the GNU dialects of C include all features the compiler supports with the given option, and there would be nothing to warn about.) -pedantic-errors Give an error whenever the base standard (see -Wpedantic) requires a diagnostic, in some cases where there is undefined behavior at compile-time and in some other cases that do not prevent compilation of programs that are valid according to the standard. This is not equivalent to -Werror=pedantic, since there are errors enabled by this option and not enabled by the latter and vice versa. -Wall This enables all the warnings about constructions that some users consider questionable, and that are easy to avoid (or modify to prevent the warning), even in conjunction with macros. This also enables some language-specific warnings described in C++ Dialect Options and Objective-C and Objective-C++ Dialect Options. -Wall turns on the following warning flags: -Waddress -Warray-bounds=1 (only with -O2) -Warray-compare -Warray-parameter=2 (C and Objective-C only) -Wbool-compare -Wbool-operation -Wc++11-compat -Wc++14-compat -Wcatch-value (C++ and Objective-C++ only) -Wchar-subscripts -Wcomment -Wdangling-pointer=2 -Wduplicate-decl-specifier (C and Objective-C only) -Wenum-compare (in C/ObjC; this is on by default in C++) -Wenum-int-mismatch (C and Objective-C only) -Wformat -Wformat-overflow -Wformat-truncation -Wint-in-bool-context -Wimplicit (C and Objective-C only) -Wimplicit-int (C and Objective-C only) -Wimplicit-function-declaration (C and Objective- C only) -Winit-self (only for C++) -Wlogical-not-parentheses -Wmain (only for C/ObjC and unless -ffreestanding) -Wmaybe-uninitialized -Wmemset-elt-size -Wmemset-transposed-args -Wmisleading-indentation (only for C/C++) -Wmismatched-dealloc -Wmismatched-new-delete (only for C/C++) -Wmissing-attributes -Wmissing-braces (only for C/ObjC) -Wmultistatement-macros -Wnarrowing (only for C++) -Wnonnull -Wnonnull-compare -Wopenmp-simd -Wparentheses -Wpessimizing-move (only for C++) -Wpointer-sign -Wrange-loop-construct (only for C++) -Wreorder -Wrestrict -Wreturn-type -Wself-move (only for C++) -Wsequence-point -Wsign-compare (only in C++) -Wsizeof-array-div -Wsizeof-pointer-div -Wsizeof-pointer-memaccess -Wstrict-aliasing -Wstrict-overflow=1 -Wswitch -Wtautological-compare -Wtrigraphs -Wuninitialized -Wunknown-pragmas -Wunused-function -Wunused-label -Wunused-value -Wunused-variable -Wuse-after-free=2 -Wvla-parameter (C and Objective-C only) -Wvolatile-register-var -Wzero-length-bounds Note that some warning flags are not implied by -Wall. Some of them warn about constructions that users generally do not consider questionable, but which occasionally you might wish to check for; others warn about constructions that are necessary or hard to avoid in some cases, and there is no simple way to modify the code to suppress the warning. Some of them are enabled by -Wextra but many of them must be enabled individually. -Wextra This enables some extra warning flags that are not enabled by -Wall. (This option used to be called -W. The older name is still supported, but the newer name is more descriptive.) -Wclobbered -Wcast-function-type -Wdangling-reference (C++ only) -Wdeprecated-copy (C++ only) -Wempty-body -Wenum-conversion (C only) -Wignored-qualifiers -Wimplicit-fallthrough=3 -Wmissing-field-initializers -Wmissing-parameter-type (C only) -Wold-style-declaration (C only) -Woverride-init -Wsign-compare (C only) -Wstring-compare -Wredundant-move (only for C++) -Wtype-limits -Wuninitialized -Wshift-negative-value (in C++11 to C++17 and in C99 and newer) -Wunused-parameter (only with -Wunused or -Wall) -Wunused-but-set-parameter (only with -Wunused or -Wall) The option -Wextra also prints warning messages for the following cases: * A pointer is compared against integer zero with "<", "<=", ">", or ">=". * (C++ only) An enumerator and a non-enumerator both appear in a conditional expression. * (C++ only) Ambiguous virtual bases. * (C++ only) Subscripting an array that has been declared "register". * (C++ only) Taking the address of a variable that has been declared "register". * (C++ only) A base class is not initialized in the copy constructor of a derived class. -Wabi (C, Objective-C, C++ and Objective-C++ only) Warn about code affected by ABI changes. This includes code that may not be compatible with the vendor-neutral C++ ABI as well as the psABI for the particular target. Since G++ now defaults to updating the ABI with each major release, normally -Wabi warns only about C++ ABI compatibility problems if there is a check added later in a release series for an ABI issue discovered since the initial release. -Wabi warns about more things if an older ABI version is selected (with -fabi-version=n). -Wabi can also be used with an explicit version number to warn about C++ ABI compatibility with a particular -fabi-version level, e.g. -Wabi=2 to warn about changes relative to -fabi-version=2. If an explicit version number is provided and -fabi-compat-version is not specified, the version number from this option is used for compatibility aliases. If no explicit version number is provided with this option, but -fabi-compat-version is specified, that version number is used for C++ ABI warnings. Although an effort has been made to warn about all such cases, there are probably some cases that are not warned about, even though G++ is generating incompatible code. There may also be cases where warnings are emitted even though the code that is generated is compatible. You should rewrite your code to avoid these warnings if you are concerned about the fact that code generated by G++ may not be binary compatible with code generated by other compilers. Known incompatibilities in -fabi-version=2 (which was the default from GCC 3.4 to 4.9) include: * A template with a non-type template parameter of reference type was mangled incorrectly: extern int N; template <int &> struct S {}; void n (S<N>) {2} This was fixed in -fabi-version=3. * SIMD vector types declared using "__attribute ((vector_size))" were mangled in a non-standard way that does not allow for overloading of functions taking vectors of different sizes. The mangling was changed in -fabi-version=4. * "__attribute ((const))" and "noreturn" were mangled as type qualifiers, and "decltype" of a plain declaration was folded away. These mangling issues were fixed in -fabi-version=5. * Scoped enumerators passed as arguments to a variadic function are promoted like unscoped enumerators, causing "va_arg" to complain. On most targets this does not actually affect the parameter passing ABI, as there is no way to pass an argument smaller than "int". Also, the ABI changed the mangling of template argument packs, "const_cast", "static_cast", prefix increment/decrement, and a class scope function used as a template argument. These issues were corrected in -fabi-version=6. * Lambdas in default argument scope were mangled incorrectly, and the ABI changed the mangling of "nullptr_t". These issues were corrected in -fabi-version=7. * When mangling a function type with function-cv-qualifiers, the un-qualified function type was incorrectly treated as a substitution candidate. This was fixed in -fabi-version=8, the default for GCC 5.1. * "decltype(nullptr)" incorrectly had an alignment of 1, leading to unaligned accesses. Note that this did not affect the ABI of a function with a "nullptr_t" parameter, as parameters have a minimum alignment. This was fixed in -fabi-version=9, the default for GCC 5.2. * Target-specific attributes that affect the identity of a type, such as ia32 calling conventions on a function type (stdcall, regparm, etc.), did not affect the mangled name, leading to name collisions when function pointers were used as template arguments. This was fixed in -fabi-version=10, the default for GCC 6.1. This option also enables warnings about psABI-related changes. The known psABI changes at this point include: * For SysV/x86-64, unions with "long double" members are passed in memory as specified in psABI. Prior to GCC 4.4, this was not the case. For example: union U { long double ld; int i; }; "union U" is now always passed in memory. -Wno-changes-meaning (C++ and Objective-C++ only) C++ requires that unqualified uses of a name within a class have the same meaning in the complete scope of the class, so declaring the name after using it is ill-formed: struct A; struct B1 { A a; typedef A A; }; // warning, 'A' changes meaning struct B2 { A a; struct A { }; }; // error, 'A' changes meaning By default, the B1 case is only a warning because the two declarations have the same type, while the B2 case is an error. Both diagnostics can be disabled with -Wno-changes-meaning. Alternately, the error case can be reduced to a warning with -Wno-error=changes-meaning or -fpermissive. Both diagnostics are also suppressed by -fms-extensions. -Wchar-subscripts Warn if an array subscript has type "char". This is a common cause of error, as programmers often forget that this type is signed on some machines. This warning is enabled by -Wall. -Wno-coverage-mismatch Warn if feedback profiles do not match when using the -fprofile-use option. If a source file is changed between compiling with -fprofile-generate and with -fprofile-use, the files with the profile feedback can fail to match the source file and GCC cannot use the profile feedback information. By default, this warning is enabled and is treated as an error. -Wno-coverage-mismatch can be used to disable the warning or -Wno-error=coverage-mismatch can be used to disable the error. Disabling the error for this warning can result in poorly optimized code and is useful only in the case of very minor changes such as bug fixes to an existing code-base. Completely disabling the warning is not recommended. -Wno-coverage-invalid-line-number Warn in case a function ends earlier than it begins due to an invalid linenum macros. The warning is emitted only with --coverage enabled. By default, this warning is enabled and is treated as an error. -Wno-coverage-invalid-line-number can be used to disable the warning or -Wno-error=coverage-invalid-line-number can be used to disable the error. -Wno-cpp (C, Objective-C, C++, Objective-C++ and Fortran only) Suppress warning messages emitted by "#warning" directives. -Wdouble-promotion (C, C++, Objective-C and Objective-C++ only) Give a warning when a value of type "float" is implicitly promoted to "double". CPUs with a 32-bit "single-precision" floating-point unit implement "float" in hardware, but emulate "double" in software. On such a machine, doing computations using "double" values is much more expensive because of the overhead required for software emulation. It is easy to accidentally do computations with "double" because floating-point literals are implicitly of type "double". For example, in: float area(float radius) { return 3.14159 * radius * radius; } the compiler performs the entire computation with "double" because the floating-point literal is a "double". -Wduplicate-decl-specifier (C and Objective-C only) Warn if a declaration has duplicate "const", "volatile", "restrict" or "_Atomic" specifier. This warning is enabled by -Wall. -Wformat -Wformat=n Check calls to "printf" and "scanf", etc., to make sure that the arguments supplied have types appropriate to the format string specified, and that the conversions specified in the format string make sense. This includes standard functions, and others specified by format attributes, in the "printf", "scanf", "strftime" and "strfmon" (an X/Open extension, not in the C standard) families (or other target-specific families). Which functions are checked without format attributes having been specified depends on the standard version selected, and such checks of functions without the attribute specified are disabled by -ffreestanding or -fno-builtin. The formats are checked against the format features supported by GNU libc version 2.2. These include all ISO C90 and C99 features, as well as features from the Single Unix Specification and some BSD and GNU extensions. Other library implementations may not support all these features; GCC does not support warning about features that go beyond a particular library's limitations. However, if -Wpedantic is used with -Wformat, warnings are given about format features not in the selected standard version (but not for "strfmon" formats, since those are not in any version of the C standard). -Wformat=1 -Wformat Option -Wformat is equivalent to -Wformat=1, and -Wno-format is equivalent to -Wformat=0. Since -Wformat also checks for null format arguments for several functions, -Wformat also implies -Wnonnull. Some aspects of this level of format checking can be disabled by the options: -Wno-format-contains-nul, -Wno-format-extra-args, and -Wno-format-zero-length. -Wformat is enabled by -Wall. -Wformat=2 Enable -Wformat plus additional format checks. Currently equivalent to -Wformat -Wformat-nonliteral -Wformat-security -Wformat-y2k. -Wno-format-contains-nul If -Wformat is specified, do not warn about format strings that contain NUL bytes. -Wno-format-extra-args If -Wformat is specified, do not warn about excess arguments to a "printf" or "scanf" format function. The C standard specifies that such arguments are ignored. Where the unused arguments lie between used arguments that are specified with $ operand number specifications, normally warnings are still given, since the implementation could not know what type to pass to "va_arg" to skip the unused arguments. However, in the case of "scanf" formats, this option suppresses the warning if the unused arguments are all pointers, since the Single Unix Specification says that such unused arguments are allowed. -Wformat-overflow -Wformat-overflow=level Warn about calls to formatted input/output functions such as "sprintf" and "vsprintf" that might overflow the destination buffer. When the exact number of bytes written by a format directive cannot be determined at compile-time it is estimated based on heuristics that depend on the level argument and on optimization. While enabling optimization will in most cases improve the accuracy of the warning, it may also result in false positives. -Wformat-overflow -Wformat-overflow=1 Level 1 of -Wformat-overflow enabled by -Wformat employs a conservative approach that warns only about calls that most likely overflow the buffer. At this level, numeric arguments to format directives with unknown values are assumed to have the value of one, and strings of unknown length to be empty. Numeric arguments that are known to be bounded to a subrange of their type, or string arguments whose output is bounded either by their directive's precision or by a finite set of string literals, are assumed to take on the value within the range that results in the most bytes on output. For example, the call to "sprintf" below is diagnosed because even with both a and b equal to zero, the terminating NUL character ('\0') appended by the function to the destination buffer will be written past its end. Increasing the size of the buffer by a single byte is sufficient to avoid the warning, though it may not be sufficient to avoid the overflow. void f (int a, int b) { char buf [13]; sprintf (buf, "a = %i, b = %i\n", a, b); } -Wformat-overflow=2 Level 2 warns also about calls that might overflow the destination buffer given an argument of sufficient length or magnitude. At level 2, unknown numeric arguments are assumed to have the minimum representable value for signed types with a precision greater than 1, and the maximum representable value otherwise. Unknown string arguments whose length cannot be assumed to be bounded either by the directive's precision, or by a finite set of string literals they may evaluate to, or the character array they may point to, are assumed to be 1 character long. At level 2, the call in the example above is again diagnosed, but this time because with a equal to a 32-bit "INT_MIN" the first %i directive will write some of its digits beyond the end of the destination buffer. To make the call safe regardless of the values of the two variables, the size of the destination buffer must be increased to at least 34 bytes. GCC includes the minimum size of the buffer in an informational note following the warning. An alternative to increasing the size of the destination buffer is to constrain the range of formatted values. The maximum length of string arguments can be bounded by specifying the precision in the format directive. When numeric arguments of format directives can be assumed to be bounded by less than the precision of their type, choosing an appropriate length modifier to the format specifier will reduce the required buffer size. For example, if a and b in the example above can be assumed to be within the precision of the "short int" type then using either the %hi format directive or casting the argument to "short" reduces the maximum required size of the buffer to 24 bytes. void f (int a, int b) { char buf [23]; sprintf (buf, "a = %hi, b = %i\n", a, (short)b); } -Wno-format-zero-length If -Wformat is specified, do not warn about zero-length formats. The C standard specifies that zero-length formats are allowed. -Wformat-nonliteral If -Wformat is specified, also warn if the format string is not a string literal and so cannot be checked, unless the format function takes its format arguments as a "va_list". -Wformat-security If -Wformat is specified, also warn about uses of format functions that represent possible security problems. At present, this warns about calls to "printf" and "scanf" functions where the format string is not a string literal and there are no format arguments, as in "printf (foo);". This may be a security hole if the format string came from untrusted input and contains %n. (This is currently a subset of what -Wformat-nonliteral warns about, but in future warnings may be added to -Wformat-security that are not included in -Wformat-nonliteral.) -Wformat-signedness If -Wformat is specified, also warn if the format string requires an unsigned argument and the argument is signed and vice versa. -Wformat-truncation -Wformat-truncation=level Warn about calls to formatted input/output functions such as "snprintf" and "vsnprintf" that might result in output truncation. When the exact number of bytes written by a format directive cannot be determined at compile-time it is estimated based on heuristics that depend on the level argument and on optimization. While enabling optimization will in most cases improve the accuracy of the warning, it may also result in false positives. Except as noted otherwise, the option uses the same logic -Wformat-overflow. -Wformat-truncation -Wformat-truncation=1 Level 1 of -Wformat-truncation enabled by -Wformat employs a conservative approach that warns only about calls to bounded functions whose return value is unused and that will most likely result in output truncation. -Wformat-truncation=2 Level 2 warns also about calls to bounded functions whose return value is used and that might result in truncation given an argument of sufficient length or magnitude. -Wformat-y2k If -Wformat is specified, also warn about "strftime" formats that may yield only a two-digit year. -Wnonnull Warn about passing a null pointer for arguments marked as requiring a non-null value by the "nonnull" function attribute. -Wnonnull is included in -Wall and -Wformat. It can be disabled with the -Wno-nonnull option. -Wnonnull-compare Warn when comparing an argument marked with the "nonnull" function attribute against null inside the function. -Wnonnull-compare is included in -Wall. It can be disabled with the -Wno-nonnull-compare option. -Wnull-dereference Warn if the compiler detects paths that trigger erroneous or undefined behavior due to dereferencing a null pointer. This option is only active when -fdelete-null-pointer-checks is active, which is enabled by optimizations in most targets. The precision of the warnings depends on the optimization options used. -Winfinite-recursion Warn about infinitely recursive calls. The warning is effective at all optimization levels but requires optimization in order to detect infinite recursion in calls between two or more functions. -Winfinite-recursion is included in -Wall. Compare with -Wanalyzer-infinite-recursion which provides a similar diagnostic, but is implemented in a different way (as part of -fanalyzer). -Winit-self (C, C++, Objective-C and Objective-C++ only) Warn about uninitialized variables that are initialized with themselves. Note this option can only be used with the -Wuninitialized option. For example, GCC warns about "i" being uninitialized in the following snippet only when -Winit-self has been specified: int f() { int i = i; return i; } This warning is enabled by -Wall in C++. -Wno-implicit-int (C and Objective-C only) This option controls warnings when a declaration does not specify a type. This warning is enabled by default in C99 and later dialects of C, and also by -Wall. -Wno-implicit-function-declaration (C and Objective-C only) This option controls warnings when a function is used before being declared. This warning is enabled by default in C99 and later dialects of C, and also by -Wall. The warning is made into an error by -pedantic-errors. -Wimplicit (C and Objective-C only) Same as -Wimplicit-int and -Wimplicit-function-declaration. This warning is enabled by -Wall. -Wimplicit-fallthrough -Wimplicit-fallthrough is the same as -Wimplicit-fallthrough=3 and -Wno-implicit-fallthrough is the same as -Wimplicit-fallthrough=0. -Wimplicit-fallthrough=n Warn when a switch case falls through. For example: switch (cond) { case 1: a = 1; break; case 2: a = 2; case 3: a = 3; break; } This warning does not warn when the last statement of a case cannot fall through, e.g. when there is a return statement or a call to function declared with the noreturn attribute. -Wimplicit-fallthrough= also takes into account control flow statements, such as ifs, and only warns when appropriate. E.g. switch (cond) { case 1: if (i > 3) { bar (5); break; } else if (i < 1) { bar (0); } else return; default: ... } Since there are occasions where a switch case fall through is desirable, GCC provides an attribute, "__attribute__ ((fallthrough))", that is to be used along with a null statement to suppress this warning that would normally occur: switch (cond) { case 1: bar (0); __attribute__ ((fallthrough)); default: ... } C++17 provides a standard way to suppress the -Wimplicit-fallthrough warning using "[[fallthrough]];" instead of the GNU attribute. In C++11 or C++14 users can use "[[gnu::fallthrough]];", which is a GNU extension. Instead of these attributes, it is also possible to add a fallthrough comment to silence the warning. The whole body of the C or C++ style comment should match the given regular expressions listed below. The option argument n specifies what kind of comments are accepted: *<-Wimplicit-fallthrough=0 disables the warning altogether.> *<-Wimplicit-fallthrough=1 matches ".*" regular> expression, any comment is used as fallthrough comment. *<-Wimplicit-fallthrough=2 case insensitively matches> ".*falls?[ \t-]*thr(ough|u).*" regular expression. *<-Wimplicit-fallthrough=3 case sensitively matches one of the> following regular expressions: *<"-fallthrough"> *<"@fallthrough@"> *<"lint -fallthrough[ \t]*"> *<"[ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?FALL(S | |-)?THR(OUGH|U)[ \t.!]*(-[^\n\r]*)?"> *<"[ \t.!]*(Else,? |Intentional(ly)? )?Fall((s | |-)[Tt]|t)hr(ough|u)[ \t.!]*(-[^\n\r]*)?"> *<"[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?fall(s | |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?"> *<-Wimplicit-fallthrough=4 case sensitively matches one of the> following regular expressions: *<"-fallthrough"> *<"@fallthrough@"> *<"lint -fallthrough[ \t]*"> *<"[ \t]*FALLTHR(OUGH|U)[ \t]*"> *<-Wimplicit-fallthrough=5 doesn't recognize any comments as> fallthrough comments, only attributes disable the warning. The comment needs to be followed after optional whitespace and other comments by "case" or "default" keywords or by a user label that precedes some "case" or "default" label. switch (cond) { case 1: bar (0); /* FALLTHRU */ default: ... } The -Wimplicit-fallthrough=3 warning is enabled by -Wextra. -Wno-if-not-aligned (C, C++, Objective-C and Objective-C++ only) Control if warnings triggered by the "warn_if_not_aligned" attribute should be issued. These warnings are enabled by default. -Wignored-qualifiers (C and C++ only) Warn if the return type of a function has a type qualifier such as "const". For ISO C such a type qualifier has no effect, since the value returned by a function is not an lvalue. For C++, the warning is only emitted for scalar types or "void". ISO C prohibits qualified "void" return types on function definitions, so such return types always receive a warning even without this option. This warning is also enabled by -Wextra. -Wno-ignored-attributes (C and C++ only) This option controls warnings when an attribute is ignored. This is different from the -Wattributes option in that it warns whenever the compiler decides to drop an attribute, not that the attribute is either unknown, used in a wrong place, etc. This warning is enabled by default. -Wmain Warn if the type of "main" is suspicious. "main" should be a function with external linkage, returning int, taking either zero arguments, two, or three arguments of appropriate types. This warning is enabled by default in C++ and is enabled by either -Wall or -Wpedantic. -Wmisleading-indentation (C and C++ only) Warn when the indentation of the code does not reflect the block structure. Specifically, a warning is issued for "if", "else", "while", and "for" clauses with a guarded statement that does not use braces, followed by an unguarded statement with the same indentation. In the following example, the call to "bar" is misleadingly indented as if it were guarded by the "if" conditional. if (some_condition ()) foo (); bar (); /* Gotcha: this is not guarded by the "if". */ In the case of mixed tabs and spaces, the warning uses the -ftabstop= option to determine if the statements line up (defaulting to 8). The warning is not issued for code involving multiline preprocessor logic such as the following example. if (flagA) foo (0); #if SOME_CONDITION_THAT_DOES_NOT_HOLD if (flagB) #endif foo (1); The warning is not issued after a "#line" directive, since this typically indicates autogenerated code, and no assumptions can be made about the layout of the file that the directive references. This warning is enabled by -Wall in C and C++. -Wmissing-attributes Warn when a declaration of a function is missing one or more attributes that a related function is declared with and whose absence may adversely affect the correctness or efficiency of generated code. For example, the warning is issued for declarations of aliases that use attributes to specify less restrictive requirements than those of their targets. This typically represents a potential optimization opportunity. By contrast, the -Wattribute-alias=2 option controls warnings issued when the alias is more restrictive than the target, which could lead to incorrect code generation. Attributes considered include "alloc_align", "alloc_size", "cold", "const", "hot", "leaf", "malloc", "nonnull", "noreturn", "nothrow", "pure", "returns_nonnull", and "returns_twice". In C++, the warning is issued when an explicit specialization of a primary template declared with attribute "alloc_align", "alloc_size", "assume_aligned", "format", "format_arg", "malloc", or "nonnull" is declared without it. Attributes "deprecated", "error", and "warning" suppress the warning.. You can use the "copy" attribute to apply the same set of attributes to a declaration as that on another declaration without explicitly enumerating the attributes. This attribute can be applied to declarations of functions, variables, or types. -Wmissing-attributes is enabled by -Wall. For example, since the declaration of the primary function template below makes use of both attribute "malloc" and "alloc_size" the declaration of the explicit specialization of the template is diagnosed because it is missing one of the attributes. template <class T> T* __attribute__ ((malloc, alloc_size (1))) allocate (size_t); template <> void* __attribute__ ((malloc)) // missing alloc_size allocate<void> (size_t); -Wmissing-braces Warn if an aggregate or union initializer is not fully bracketed. In the following example, the initializer for "a" is not fully bracketed, but that for "b" is fully bracketed. int a[2][2] = { 0, 1, 2, 3 }; int b[2][2] = { { 0, 1 }, { 2, 3 } }; This warning is enabled by -Wall. -Wmissing-include-dirs (C, C++, Objective-C, Objective-C++ and Fortran only) Warn if a user-supplied include directory does not exist. This option is disabled by default for C, C++, Objective-C and Objective-C++. For Fortran, it is partially enabled by default by warning for -I and -J, only. -Wno-missing-profile This option controls warnings if feedback profiles are missing when using the -fprofile-use option. This option diagnoses those cases where a new function or a new file is added between compiling with -fprofile-generate and with -fprofile-use, without regenerating the profiles. In these cases, the profile feedback data files do not contain any profile feedback information for the newly added function or file respectively. Also, in the case when profile count data (.gcda) files are removed, GCC cannot use any profile feedback information. In all these cases, warnings are issued to inform you that a profile generation step is due. Ignoring the warning can result in poorly optimized code. -Wno-missing-profile can be used to disable the warning, but this is not recommended and should be done only when non-existent profile data is justified. -Wmismatched-dealloc Warn for calls to deallocation functions with pointer arguments returned from from allocations functions for which the former isn't a suitable deallocator. A pair of functions can be associated as matching allocators and deallocators by use of attribute "malloc". Unless disabled by the -fno-builtin option the standard functions "calloc", "malloc", "realloc", and "free", as well as the corresponding forms of C++ "operator new" and "operator delete" are implicitly associated as matching allocators and deallocators. In the following example "mydealloc" is the deallocator for pointers returned from "myalloc". void mydealloc (void*); __attribute__ ((malloc (mydealloc, 1))) void* myalloc (size_t); void f (void) { void *p = myalloc (32); // ...use p... free (p); // warning: not a matching deallocator for myalloc mydealloc (p); // ok } In C++, the related option -Wmismatched-new-delete diagnoses mismatches involving either "operator new" or "operator delete". Option -Wmismatched-dealloc is included in -Wall. -Wmultistatement-macros Warn about unsafe multiple statement macros that appear to be guarded by a clause such as "if", "else", "for", "switch", or "while", in which only the first statement is actually guarded after the macro is expanded. For example: #define DOIT x++; y++ if (c) DOIT; will increment "y" unconditionally, not just when "c" holds. The can usually be fixed by wrapping the macro in a do-while loop: #define DOIT do { x++; y++; } while (0) if (c) DOIT; This warning is enabled by -Wall in C and C++. -Wparentheses Warn if parentheses are omitted in certain contexts, such as when there is an assignment in a context where a truth value is expected, or when operators are nested whose precedence people often get confused about. Also warn if a comparison like "x<=y<=z" appears; this is equivalent to "(x<=y ? 1 : 0) <= z", which is a different interpretation from that of ordinary mathematical notation. Also warn for dangerous uses of the GNU extension to "?:" with omitted middle operand. When the condition in the "?": operator is a boolean expression, the omitted value is always 1. Often programmers expect it to be a value computed inside the conditional expression instead. For C++ this also warns for some cases of unnecessary parentheses in declarations, which can indicate an attempt at a function call instead of a declaration: { // Declares a local variable called mymutex. std::unique_lock<std::mutex> (mymutex); // User meant std::unique_lock<std::mutex> lock (mymutex); } This warning is enabled by -Wall. -Wno-self-move (C++ and Objective-C++ only) This warning warns when a value is moved to itself with "std::move". Such a "std::move" typically has no effect. struct T { ... }; void fn() { T t; ... t = std::move (t); } This warning is enabled by -Wall. -Wsequence-point Warn about code that may have undefined semantics because of violations of sequence point rules in the C and C++ standards. The C and C++ standards define the order in which expressions in a C/C++ program are evaluated in terms of sequence points, which represent a partial ordering between the execution of parts of the program: those executed before the sequence point, and those executed after it. These occur after the evaluation of a full expression (one which is not part of a larger expression), after the evaluation of the first operand of a "&&", "||", "? :" or "," (comma) operator, before a function is called (but after the evaluation of its arguments and the expression denoting the called function), and in certain other places. Other than as expressed by the sequence point rules, the order of evaluation of subexpressions of an expression is not specified. All these rules describe only a partial order rather than a total order, since, for example, if two functions are called within one expression with no sequence point between them, the order in which the functions are called is not specified. However, the standards committee have ruled that function calls do not overlap. It is not specified when between sequence points modifications to the values of objects take effect. Programs whose behavior depends on this have undefined behavior; the C and C++ standards specify that "Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression. Furthermore, the prior value shall be read only to determine the value to be stored.". If a program breaks these rules, the results on any particular implementation are entirely unpredictable. Examples of code with undefined behavior are "a = a++;", "a[n] = b[n++]" and "a[i++] = i;". Some more complicated cases are not diagnosed by this option, and it may give an occasional false positive result, but in general it has been found fairly effective at detecting this sort of problem in programs. The C++17 standard will define the order of evaluation of operands in more cases: in particular it requires that the right-hand side of an assignment be evaluated before the left-hand side, so the above examples are no longer undefined. But this option will still warn about them, to help people avoid writing code that is undefined in C and earlier revisions of C++. The standard is worded confusingly, therefore there is some debate over the precise meaning of the sequence point rules in subtle cases. Links to discussions of the problem, including proposed formal definitions, may be found on the GCC readings page, at <https://gcc.gnu.org/readings.html>. This warning is enabled by -Wall for C and C++. -Wno-return-local-addr Do not warn about returning a pointer (or in C++, a reference) to a variable that goes out of scope after the function returns. -Wreturn-type Warn whenever a function is defined with a return type that defaults to "int". Also warn about any "return" statement with no return value in a function whose return type is not "void" (falling off the end of the function body is considered returning without a value). For C only, warn about a "return" statement with an expression in a function whose return type is "void", unless the expression type is also "void". As a GNU extension, the latter case is accepted without a warning unless -Wpedantic is used. Attempting to use the return value of a non-"void" function other than "main" that flows off the end by reaching the closing curly brace that terminates the function is undefined. Unlike in C, in C++, flowing off the end of a non-"void" function other than "main" results in undefined behavior even when the value of the function is not used. This warning is enabled by default in C++ and by -Wall otherwise. -Wno-shift-count-negative Controls warnings if a shift count is negative. This warning is enabled by default. -Wno-shift-count-overflow Controls warnings if a shift count is greater than or equal to the bit width of the type. This warning is enabled by default. -Wshift-negative-value Warn if left shifting a negative value. This warning is enabled by -Wextra in C99 (and newer) and C++11 to C++17 modes. -Wno-shift-overflow -Wshift-overflow=n These options control warnings about left shift overflows. -Wshift-overflow=1 This is the warning level of -Wshift-overflow and is enabled by default in C99 and C++11 modes (and newer). This warning level does not warn about left-shifting 1 into the sign bit. (However, in C, such an overflow is still rejected in contexts where an integer constant expression is required.) No warning is emitted in C++20 mode (and newer), as signed left shifts always wrap. -Wshift-overflow=2 This warning level also warns about left-shifting 1 into the sign bit, unless C++14 mode (or newer) is active. -Wswitch Warn whenever a "switch" statement has an index of enumerated type and lacks a "case" for one or more of the named codes of that enumeration. (The presence of a "default" label prevents this warning.) "case" labels outside the enumeration range also provoke warnings when this option is used (even if there is a "default" label). This warning is enabled by -Wall. -Wswitch-default Warn whenever a "switch" statement does not have a "default" case. -Wswitch-enum Warn whenever a "switch" statement has an index of enumerated type and lacks a "case" for one or more of the named codes of that enumeration. "case" labels outside the enumeration range also provoke warnings when this option is used. The only difference between -Wswitch and this option is that this option gives a warning about an omitted enumeration code even if there is a "default" label. -Wno-switch-bool Do not warn when a "switch" statement has an index of boolean type and the case values are outside the range of a boolean type. It is possible to suppress this warning by casting the controlling expression to a type other than "bool". For example: switch ((int) (a == 4)) { ... } This warning is enabled by default for C and C++ programs. -Wno-switch-outside-range This option controls warnings when a "switch" case has a value that is outside of its respective type range. This warning is enabled by default for C and C++ programs. -Wno-switch-unreachable Do not warn when a "switch" statement contains statements between the controlling expression and the first case label, which will never be executed. For example: switch (cond) { i = 15; ... case 5: ... } -Wswitch-unreachable does not warn if the statement between the controlling expression and the first case label is just a declaration: switch (cond) { int i; ... case 5: i = 5; ... } This warning is enabled by default for C and C++ programs. -Wsync-nand (C and C++ only) Warn when "__sync_fetch_and_nand" and "__sync_nand_and_fetch" built-in functions are used. These functions changed semantics in GCC 4.4. -Wtrivial-auto-var-init Warn when "-ftrivial-auto-var-init" cannot initialize the automatic variable. A common situation is an automatic variable that is declared between the controlling expression and the first case label of a "switch" statement. -Wunused-but-set-parameter Warn whenever a function parameter is assigned to, but otherwise unused (aside from its declaration). To suppress this warning use the "unused" attribute. This warning is also enabled by -Wunused together with -Wextra. -Wunused-but-set-variable Warn whenever a local variable is assigned to, but otherwise unused (aside from its declaration). This warning is enabled by -Wall. To suppress this warning use the "unused" attribute. This warning is also enabled by -Wunused, which is enabled by -Wall. -Wunused-function Warn whenever a static function is declared but not defined or a non-inline static function is unused. This warning is enabled by -Wall. -Wunused-label Warn whenever a label is declared but not used. This warning is enabled by -Wall. To suppress this warning use the "unused" attribute. -Wunused-local-typedefs (C, Objective-C, C++ and Objective-C++ only) Warn when a typedef locally defined in a function is not used. This warning is enabled by -Wall. -Wunused-parameter Warn whenever a function parameter is unused aside from its declaration. To suppress this warning use the "unused" attribute. -Wno-unused-result Do not warn if a caller of a function marked with attribute "warn_unused_result" does not use its return value. The default is -Wunused-result. -Wunused-variable Warn whenever a local or static variable is unused aside from its declaration. This option implies -Wunused-const-variable=1 for C, but not for C++. This warning is enabled by -Wall. To suppress this warning use the "unused" attribute. -Wunused-const-variable -Wunused-const-variable=n Warn whenever a constant static variable is unused aside from its declaration. -Wunused-const-variable=1 is enabled by -Wunused-variable for C, but not for C++. In C this declares variable storage, but in C++ this is not an error since const variables take the place of "#define"s. To suppress this warning use the "unused" attribute. -Wunused-const-variable=1 This is the warning level that is enabled by -Wunused-variable for C. It warns only about unused static const variables defined in the main compilation unit, but not about static const variables declared in any header included. -Wunused-const-variable=2 This warning level also warns for unused constant static variables in headers (excluding system headers). This is the warning level of -Wunused-const-variable and must be explicitly requested since in C++ this isn't an error and in C it might be harder to clean up all headers included. -Wunused-value Warn whenever a statement computes a result that is explicitly not used. To suppress this warning cast the unused expression to "void". This includes an expression-statement or the left-hand side of a comma expression that contains no side effects. For example, an expression such as "x[i,j]" causes a warning, while "x[(void)i,j]" does not. This warning is enabled by -Wall. -Wunused All the above -Wunused options combined. In order to get a warning about an unused function parameter, you must either specify -Wextra -Wunused (note that -Wall implies -Wunused), or separately specify -Wunused-parameter. -Wuninitialized Warn if an object with automatic or allocated storage duration is used without having been initialized. In C++, also warn if a non- static reference or non-static "const" member appears in a class without constructors. In addition, passing a pointer (or in C++, a reference) to an uninitialized object to a "const"-qualified argument of a built-in function known to read the object is also diagnosed by this warning. (-Wmaybe-uninitialized is issued for ordinary functions.) If you want to warn about code that uses the uninitialized value of the variable in its own initializer, use the -Winit-self option. These warnings occur for individual uninitialized elements of structure, union or array variables as well as for variables that are uninitialized as a whole. They do not occur for variables or elements declared "volatile". Because these warnings depend on optimization, the exact variables or elements for which there are warnings depend on the precise optimization options and version of GCC used. Note that there may be no warning about a variable that is used only to compute a value that itself is never used, because such computations may be deleted by data flow analysis before the warnings are printed. In C++, this warning also warns about using uninitialized objects in member-initializer-lists. For example, GCC warns about "b" being uninitialized in the following snippet: struct A { int a; int b; A() : a(b) { } }; -Wno-invalid-memory-model This option controls warnings for invocations of __atomic Builtins, __sync Builtins, and the C11 atomic generic functions with a memory consistency argument that is either invalid for the operation or outside the range of values of the "memory_order" enumeration. For example, since the "__atomic_store" and "__atomic_store_n" built- ins are only defined for the relaxed, release, and sequentially consistent memory orders the following code is diagnosed: void store (int *i) { __atomic_store_n (i, 0, memory_order_consume); } -Winvalid-memory-model is enabled by default. -Wmaybe-uninitialized For an object with automatic or allocated storage duration, if there exists a path from the function entry to a use of the object that is initialized, but there exist some other paths for which the object is not initialized, the compiler emits a warning if it cannot prove the uninitialized paths are not executed at run time. In addition, passing a pointer (or in C++, a reference) to an uninitialized object to a "const"-qualified function argument is also diagnosed by this warning. (-Wuninitialized is issued for built-in functions known to read the object.) Annotating the function with attribute "access (none)" indicates that the argument isn't used to access the object and avoids the warning. These warnings are only possible in optimizing compilation, because otherwise GCC does not keep track of the state of variables. These warnings are made optional because GCC may not be able to determine when the code is correct in spite of appearing to have an error. Here is one example of how this can happen: { int x; switch (y) { case 1: x = 1; break; case 2: x = 4; break; case 3: x = 5; } foo (x); } If the value of "y" is always 1, 2 or 3, then "x" is always initialized, but GCC doesn't know this. To suppress the warning, you need to provide a default case with assert(0) or similar code. This option also warns when a non-volatile automatic variable might be changed by a call to "longjmp". The compiler sees only the calls to "setjmp". It cannot know where "longjmp" will be called; in fact, a signal handler could call it at any point in the code. As a result, you may get a warning even when there is in fact no problem because "longjmp" cannot in fact be called at the place that would cause a problem. Some spurious warnings can be avoided if you declare all the functions you use that never return as "noreturn". This warning is enabled by -Wall or -Wextra. -Wunknown-pragmas Warn when a "#pragma" directive is encountered that is not understood by GCC. If this command-line option is used, warnings are even issued for unknown pragmas in system header files. This is not the case if the warnings are only enabled by the -Wall command-line option. -Wno-pragmas Do not warn about misuses of pragmas, such as incorrect parameters, invalid syntax, or conflicts between pragmas. See also -Wunknown-pragmas. -Wno-prio-ctor-dtor Do not warn if a priority from 0 to 100 is used for constructor or destructor. The use of constructor and destructor attributes allow you to assign a priority to the constructor/destructor to control its order of execution before "main" is called or after it returns. The priority values must be greater than 100 as the compiler reserves priority values between 0--100 for the implementation. -Wstrict-aliasing This option is only active when -fstrict-aliasing is active. It warns about code that might break the strict aliasing rules that the compiler is using for optimization. The warning does not catch all cases, but does attempt to catch the more common pitfalls. It is included in -Wall. It is equivalent to -Wstrict-aliasing=3 -Wstrict-aliasing=n This option is only active when -fstrict-aliasing is active. It warns about code that might break the strict aliasing rules that the compiler is using for optimization. Higher levels correspond to higher accuracy (fewer false positives). Higher levels also correspond to more effort, similar to the way -O works. -Wstrict-aliasing is equivalent to -Wstrict-aliasing=3. Level 1: Most aggressive, quick, least accurate. Possibly useful when higher levels do not warn but -fstrict-aliasing still breaks the code, as it has very few false negatives. However, it has many false positives. Warns for all pointer conversions between possibly incompatible types, even if never dereferenced. Runs in the front end only. Level 2: Aggressive, quick, not too precise. May still have many false positives (not as many as level 1 though), and few false negatives (but possibly more than level 1). Unlike level 1, it only warns when an address is taken. Warns about incomplete types. Runs in the front end only. Level 3 (default for -Wstrict-aliasing): Should have very few false positives and few false negatives. Slightly slower than levels 1 or 2 when optimization is enabled. Takes care of the common pun+dereference pattern in the front end: "*(int*)&some_float". If optimization is enabled, it also runs in the back end, where it deals with multiple statement cases using flow-sensitive points-to information. Only warns when the converted pointer is dereferenced. Does not warn about incomplete types. -Wstrict-overflow -Wstrict-overflow=n This option is only active when signed overflow is undefined. It warns about cases where the compiler optimizes based on the assumption that signed overflow does not occur. Note that it does not warn about all cases where the code might overflow: it only warns about cases where the compiler implements some optimization. Thus this warning depends on the optimization level. An optimization that assumes that signed overflow does not occur is perfectly safe if the values of the variables involved are such that overflow never does, in fact, occur. Therefore this warning can easily give a false positive: a warning about code that is not actually a problem. To help focus on important issues, several warning levels are defined. No warnings are issued for the use of undefined signed overflow when estimating how many iterations a loop requires, in particular when determining whether a loop will be executed at all. -Wstrict-overflow=1 Warn about cases that are both questionable and easy to avoid. For example the compiler simplifies "x + 1 > x" to 1. This level of -Wstrict-overflow is enabled by -Wall; higher levels are not, and must be explicitly requested. -Wstrict-overflow=2 Also warn about other cases where a comparison is simplified to a constant. For example: "abs (x) >= 0". This can only be simplified when signed integer overflow is undefined, because "abs (INT_MIN)" overflows to "INT_MIN", which is less than zero. -Wstrict-overflow (with no level) is the same as -Wstrict-overflow=2. -Wstrict-overflow=3 Also warn about other cases where a comparison is simplified. For example: "x + 1 > 1" is simplified to "x > 0". -Wstrict-overflow=4 Also warn about other simplifications not covered by the above cases. For example: "(x * 10) / 5" is simplified to "x * 2". -Wstrict-overflow=5 Also warn about cases where the compiler reduces the magnitude of a constant involved in a comparison. For example: "x + 2 > y" is simplified to "x + 1 >= y". This is reported only at the highest warning level because this simplification applies to many comparisons, so this warning level gives a very large number of false positives. -Wstring-compare Warn for calls to "strcmp" and "strncmp" whose result is determined to be either zero or non-zero in tests for such equality owing to the length of one argument being greater than the size of the array the other argument is stored in (or the bound in the case of "strncmp"). Such calls could be mistakes. For example, the call to "strcmp" below is diagnosed because its result is necessarily non-zero irrespective of the contents of the array "a". extern char a[4]; void f (char *d) { strcpy (d, "string"); ... if (0 == strcmp (a, d)) // cannot be true puts ("a and d are the same"); } -Wstring-compare is enabled by -Wextra. -Wno-stringop-overflow -Wstringop-overflow -Wstringop-overflow=type Warn for calls to string manipulation functions such as "memcpy" and "strcpy" that are determined to overflow the destination buffer. The optional argument is one greater than the type of Object Size Checking to perform to determine the size of the destination. The argument is meaningful only for functions that operate on character arrays but not for raw memory functions like "memcpy" which always make use of Object Size type-0. The option also warns for calls that specify a size in excess of the largest possible object or at most "SIZE_MAX / 2" bytes. The option produces the best results with optimization enabled but can detect a small subset of simple buffer overflows even without optimization in calls to the GCC built-in functions like "__builtin_memcpy" that correspond to the standard functions. In any case, the option warns about just a subset of buffer overflows detected by the corresponding overflow checking built-ins. For example, the option issues a warning for the "strcpy" call below because it copies at least 5 characters (the string "blue" including the terminating NUL) into the buffer of size 4. enum Color { blue, purple, yellow }; const char* f (enum Color clr) { static char buf [4]; const char *str; switch (clr) { case blue: str = "blue"; break; case purple: str = "purple"; break; case yellow: str = "yellow"; break; } return strcpy (buf, str); // warning here } Option -Wstringop-overflow=2 is enabled by default. -Wstringop-overflow -Wstringop-overflow=1 The -Wstringop-overflow=1 option uses type-zero Object Size Checking to determine the sizes of destination objects. At this setting the option does not warn for writes past the end of subobjects of larger objects accessed by pointers unless the size of the largest surrounding object is known. When the destination may be one of several objects it is assumed to be the largest one of them. On Linux systems, when optimization is enabled at this setting the option warns for the same code as when the "_FORTIFY_SOURCE" macro is defined to a non-zero value. -Wstringop-overflow=2 The -Wstringop-overflow=2 option uses type-one Object Size Checking to determine the sizes of destination objects. At this setting the option warns about overflows when writing to members of the largest complete objects whose exact size is known. However, it does not warn for excessive writes to the same members of unknown objects referenced by pointers since they may point to arrays containing unknown numbers of elements. This is the default setting of the option. -Wstringop-overflow=3 The -Wstringop-overflow=3 option uses type-two Object Size Checking to determine the sizes of destination objects. At this setting the option warns about overflowing the smallest object or data member. This is the most restrictive setting of the option that may result in warnings for safe code. -Wstringop-overflow=4 The -Wstringop-overflow=4 option uses type-three Object Size Checking to determine the sizes of destination objects. At this setting the option warns about overflowing any data members, and when the destination is one of several objects it uses the size of the largest of them to decide whether to issue a warning. Similarly to -Wstringop-overflow=3 this setting of the option may result in warnings for benign code. -Wno-stringop-overread Warn for calls to string manipulation functions such as "memchr", or "strcpy" that are determined to read past the end of the source sequence. Option -Wstringop-overread is enabled by default. -Wno-stringop-truncation Do not warn for calls to bounded string manipulation functions such as "strncat", "strncpy", and "stpncpy" that may either truncate the copied string or leave the destination unchanged. In the following example, the call to "strncat" specifies a bound that is less than the length of the source string. As a result, the copy of the source will be truncated and so the call is diagnosed. To avoid the warning use "bufsize - strlen (buf) - 1)" as the bound. void append (char *buf, size_t bufsize) { strncat (buf, ".txt", 3); } As another example, the following call to "strncpy" results in copying to "d" just the characters preceding the terminating NUL, without appending the NUL to the end. Assuming the result of "strncpy" is necessarily a NUL-terminated string is a common mistake, and so the call is diagnosed. To avoid the warning when the result is not expected to be NUL-terminated, call "memcpy" instead. void copy (char *d, const char *s) { strncpy (d, s, strlen (s)); } In the following example, the call to "strncpy" specifies the size of the destination buffer as the bound. If the length of the source string is equal to or greater than this size the result of the copy will not be NUL-terminated. Therefore, the call is also diagnosed. To avoid the warning, specify "sizeof buf - 1" as the bound and set the last element of the buffer to "NUL". void copy (const char *s) { char buf[80]; strncpy (buf, s, sizeof buf); ... } In situations where a character array is intended to store a sequence of bytes with no terminating "NUL" such an array may be annotated with attribute "nonstring" to avoid this warning. Such arrays, however, are not suitable arguments to functions that expect "NUL"-terminated strings. To help detect accidental misuses of such arrays GCC issues warnings unless it can prove that the use is safe. -Wstrict-flex-arrays Warn about inproper usages of flexible array members according to the level of the "strict_flex_array (level)" attribute attached to the trailing array field of a structure if it's available, otherwise according to the level of the option -fstrict-flex-arrays=level. This option is effective only when level is bigger than 0. Otherwise, it will be ignored with a warning. when level=1, warnings will be issued for a trailing array reference of a structure that have 2 or more elements if the trailing array is referenced as a flexible array member. when level=2, in addition to level=1, additional warnings will be issued for a trailing one-element array reference of a structure if the array is referenced as a flexible array member. when level=3, in addition to level=2, additional warnings will be issued for a trailing zero-length array reference of a structure if the array is referenced as a flexible array member. -Wsuggest-attribute=[pure|const|noreturn|format|cold|malloc] Warn for cases where adding an attribute may be beneficial. The attributes currently supported are listed below. -Wsuggest-attribute=pure -Wsuggest-attribute=const -Wsuggest-attribute=noreturn -Wmissing-noreturn -Wsuggest-attribute=malloc Warn about functions that might be candidates for attributes "pure", "const" or "noreturn" or "malloc". The compiler only warns for functions visible in other compilation units or (in the case of "pure" and "const") if it cannot prove that the function returns normally. A function returns normally if it doesn't contain an infinite loop or return abnormally by throwing, calling "abort" or trapping. This analysis requires option -fipa-pure-const, which is enabled by default at -O and higher. Higher optimization levels improve the accuracy of the analysis. -Wsuggest-attribute=format -Wmissing-format-attribute Warn about function pointers that might be candidates for "format" attributes. Note these are only possible candidates, not absolute ones. GCC guesses that function pointers with "format" attributes that are used in assignment, initialization, parameter passing or return statements should have a corresponding "format" attribute in the resulting type. I.e. the left-hand side of the assignment or initialization, the type of the parameter variable, or the return type of the containing function respectively should also have a "format" attribute to avoid the warning. GCC also warns about function definitions that might be candidates for "format" attributes. Again, these are only possible candidates. GCC guesses that "format" attributes might be appropriate for any function that calls a function like "vprintf" or "vscanf", but this might not always be the case, and some functions for which "format" attributes are appropriate may not be detected. -Wsuggest-attribute=cold Warn about functions that might be candidates for "cold" attribute. This is based on static detection and generally only warns about functions which always leads to a call to another "cold" function such as wrappers of C++ "throw" or fatal error reporting functions leading to "abort". -Walloc-zero Warn about calls to allocation functions decorated with attribute "alloc_size" that specify zero bytes, including those to the built- in forms of the functions "aligned_alloc", "alloca", "calloc", "malloc", and "realloc". Because the behavior of these functions when called with a zero size differs among implementations (and in the case of "realloc" has been deprecated) relying on it may result in subtle portability bugs and should be avoided. -Walloc-size-larger-than=byte-size Warn about calls to functions decorated with attribute "alloc_size" that attempt to allocate objects larger than the specified number of bytes, or where the result of the size computation in an integer type with infinite precision would exceed the value of PTRDIFF_MAX on the target. -Walloc-size-larger-than=PTRDIFF_MAX is enabled by default. Warnings controlled by the option can be disabled either by specifying byte-size of SIZE_MAX or more or by -Wno-alloc-size-larger-than. -Wno-alloc-size-larger-than Disable -Walloc-size-larger-than= warnings. The option is equivalent to -Walloc-size-larger-than=SIZE_MAX or larger. -Walloca This option warns on all uses of "alloca" in the source. -Walloca-larger-than=byte-size This option warns on calls to "alloca" with an integer argument whose value is either zero, or that is not bounded by a controlling predicate that limits its value to at most byte-size. It also warns for calls to "alloca" where the bound value is unknown. Arguments of non-integer types are considered unbounded even if they appear to be constrained to the expected range. For example, a bounded case of "alloca" could be: void func (size_t n) { void *p; if (n <= 1000) p = alloca (n); else p = malloc (n); f (p); } In the above example, passing "-Walloca-larger-than=1000" would not issue a warning because the call to "alloca" is known to be at most 1000 bytes. However, if "-Walloca-larger-than=500" were passed, the compiler would emit a warning. Unbounded uses, on the other hand, are uses of "alloca" with no controlling predicate constraining its integer argument. For example: void func () { void *p = alloca (n); f (p); } If "-Walloca-larger-than=500" were passed, the above would trigger a warning, but this time because of the lack of bounds checking. Note, that even seemingly correct code involving signed integers could cause a warning: void func (signed int n) { if (n < 500) { p = alloca (n); f (p); } } In the above example, n could be negative, causing a larger than expected argument to be implicitly cast into the "alloca" call. This option also warns when "alloca" is used in a loop. -Walloca-larger-than=PTRDIFF_MAX is enabled by default but is usually only effective when -ftree-vrp is active (default for -O2 and above). See also -Wvla-larger-than=byte-size. -Wno-alloca-larger-than Disable -Walloca-larger-than= warnings. The option is equivalent to -Walloca-larger-than=SIZE_MAX or larger. -Warith-conversion Do warn about implicit conversions from arithmetic operations even when conversion of the operands to the same type cannot change their values. This affects warnings from -Wconversion, -Wfloat-conversion, and -Wsign-conversion. void f (char c, int i) { c = c + i; // warns with B<-Wconversion> c = c + 1; // only warns with B<-Warith-conversion> } -Warray-bounds -Warray-bounds=n Warn about out of bounds subscripts or offsets into arrays. This warning is enabled by -Wall. It is more effective when -ftree-vrp is active (the default for -O2 and above) but a subset of instances are issued even without optimization. By default, the trailing array of a structure will be treated as a flexible array member by -Warray-bounds or -Warray-bounds=n if it is declared as either a flexible array member per C99 standard onwards ([]), a GCC zero-length array extension ([0]), or an one- element array ([1]). As a result, out of bounds subscripts or offsets into zero-length arrays or one-element arrays are not warned by default. You can add the option -fstrict-flex-arrays or -fstrict-flex-arrays=level to control how this option treat trailing array of a structure as a flexible array member: when level<=1, no change to the default behavior. when level=2, additional warnings will be issued for out of bounds subscripts or offsets into one-element arrays; when level=3, in addition to level=2, additional warnings will be issued for out of bounds subscripts or offsets into zero-length arrays. -Warray-bounds=1 This is the default warning level of -Warray-bounds and is enabled by -Wall; higher levels are not, and must be explicitly requested. -Warray-bounds=2 This warning level also warns about the intermediate results of pointer arithmetic that may yield out of bounds values. This warning level may give a larger number of false positives and is deactivated by default. -Warray-compare Warn about equality and relational comparisons between two operands of array type. This comparison was deprecated in C++20. For example: int arr1[5]; int arr2[5]; bool same = arr1 == arr2; -Warray-compare is enabled by -Wall. -Warray-parameter -Warray-parameter=n Warn about redeclarations of functions involving arguments of array or pointer types of inconsistent kinds or forms, and enable the detection of out-of-bounds accesses to such parameters by warnings such as -Warray-bounds. If the first function declaration uses the array form the bound specified in the array is assumed to be the minimum number of elements expected to be provided in calls to the function and the maximum number of elements accessed by it. Failing to provide arguments of sufficient size or accessing more than the maximum number of elements may be diagnosed by warnings such as -Warray-bounds. At level 1 the warning diagnoses inconsistencies involving array parameters declared using the "T[static N]" form. For example, the warning triggers for the following redeclarations because the first one allows an array of any size to be passed to "f" while the second one with the keyword "static" specifies that the array argument must have at least four elements. void f (int[static 4]); void f (int[]); // warning (inconsistent array form) void g (void) { int *p = (int *)malloc (4); f (p); // warning (array too small) ... } At level 2 the warning also triggers for redeclarations involving any other inconsistency in array or pointer argument forms denoting array sizes. Pointers and arrays of unspecified bound are considered equivalent and do not trigger a warning. void g (int*); void g (int[]); // no warning void g (int[8]); // warning (inconsistent array bound) -Warray-parameter=2 is included in -Wall. The -Wvla-parameter option triggers warnings for similar inconsistencies involving Variable Length Array arguments. -Wattribute-alias=n -Wno-attribute-alias Warn about declarations using the "alias" and similar attributes whose target is incompatible with the type of the alias. -Wattribute-alias=1 The default warning level of the -Wattribute-alias option diagnoses incompatibilities between the type of the alias declaration and that of its target. Such incompatibilities are typically indicative of bugs. -Wattribute-alias=2 At this level -Wattribute-alias also diagnoses cases where the attributes of the alias declaration are more restrictive than the attributes applied to its target. These mismatches can potentially result in incorrect code generation. In other cases they may be benign and could be resolved simply by adding the missing attribute to the target. For comparison, see the -Wmissing-attributes option, which controls diagnostics when the alias declaration is less restrictive than the target, rather than more restrictive. Attributes considered include "alloc_align", "alloc_size", "cold", "const", "hot", "leaf", "malloc", "nonnull", "noreturn", "nothrow", "pure", "returns_nonnull", and "returns_twice". -Wattribute-alias is equivalent to -Wattribute-alias=1. This is the default. You can disable these warnings with either -Wno-attribute-alias or -Wattribute-alias=0. -Wbidi-chars=[none|unpaired|any|ucn] Warn about possibly misleading UTF-8 bidirectional control characters in comments, string literals, character constants, and identifiers. Such characters can change left-to-right writing direction into right-to-left (and vice versa), which can cause confusion between the logical order and visual order. This may be dangerous; for instance, it may seem that a piece of code is not commented out, whereas it in fact is. There are three levels of warning supported by GCC. The default is -Wbidi-chars=unpaired, which warns about improperly terminated bidi contexts. -Wbidi-chars=none turns the warning off. -Wbidi-chars=any warns about any use of bidirectional control characters. By default, this warning does not warn about UCNs. It is, however, possible to turn on such checking by using -Wbidi-chars=unpaired,ucn or -Wbidi-chars=any,ucn. Using -Wbidi-chars=ucn is valid, and is equivalent to -Wbidi-chars=unpaired,ucn, if no previous -Wbidi-chars=any was specified. -Wbool-compare Warn about boolean expression compared with an integer value different from "true"/"false". For instance, the following comparison is always false: int n = 5; ... if ((n > 1) == 2) { ... } This warning is enabled by -Wall. -Wbool-operation Warn about suspicious operations on expressions of a boolean type. For instance, bitwise negation of a boolean is very likely a bug in the program. For C, this warning also warns about incrementing or decrementing a boolean, which rarely makes sense. (In C++, decrementing a boolean is always invalid. Incrementing a boolean is invalid in C++17, and deprecated otherwise.) This warning is enabled by -Wall. -Wduplicated-branches Warn when an if-else has identical branches. This warning detects cases like if (p != NULL) return 0; else return 0; It doesn't warn when both branches contain just a null statement. This warning also warn for conditional operators: int i = x ? *p : *p; -Wduplicated-cond Warn about duplicated conditions in an if-else-if chain. For instance, warn for the following code: if (p->q != NULL) { ... } else if (p->q != NULL) { ... } -Wframe-address Warn when the __builtin_frame_address or __builtin_return_address is called with an argument greater than 0. Such calls may return indeterminate values or crash the program. The warning is included in -Wall. -Wno-discarded-qualifiers (C and Objective-C only) Do not warn if type qualifiers on pointers are being discarded. Typically, the compiler warns if a "const char *" variable is passed to a function that takes a "char *" parameter. This option can be used to suppress such a warning. -Wno-discarded-array-qualifiers (C and Objective-C only) Do not warn if type qualifiers on arrays which are pointer targets are being discarded. Typically, the compiler warns if a "const int (*)[]" variable is passed to a function that takes a "int (*)[]" parameter. This option can be used to suppress such a warning. -Wno-incompatible-pointer-types (C and Objective-C only) Do not warn when there is a conversion between pointers that have incompatible types. This warning is for cases not covered by -Wno-pointer-sign, which warns for pointer argument passing or assignment with different signedness. -Wno-int-conversion (C and Objective-C only) Do not warn about incompatible integer to pointer and pointer to integer conversions. This warning is about implicit conversions; for explicit conversions the warnings -Wno-int-to-pointer-cast and -Wno-pointer-to-int-cast may be used. -Wzero-length-bounds Warn about accesses to elements of zero-length array members that might overlap other members of the same object. Declaring interior zero-length arrays is discouraged because accesses to them are undefined. For example, the first two stores in function "bad" are diagnosed because the array elements overlap the subsequent members "b" and "c". The third store is diagnosed by -Warray-bounds because it is beyond the bounds of the enclosing object. struct X { int a[0]; int b, c; }; struct X x; void bad (void) { x.a[0] = 0; // -Wzero-length-bounds x.a[1] = 1; // -Wzero-length-bounds x.a[2] = 2; // -Warray-bounds } Option -Wzero-length-bounds is enabled by -Warray-bounds. -Wno-div-by-zero Do not warn about compile-time integer division by zero. Floating- point division by zero is not warned about, as it can be a legitimate way of obtaining infinities and NaNs. -Wsystem-headers Print warning messages for constructs found in system header files. Warnings from system headers are normally suppressed, on the assumption that they usually do not indicate real problems and would only make the compiler output harder to read. Using this command-line option tells GCC to emit warnings from system headers as if they occurred in user code. However, note that using -Wall in conjunction with this option does not warn about unknown pragmas in system headers---for that, -Wunknown-pragmas must also be used. -Wtautological-compare Warn if a self-comparison always evaluates to true or false. This warning detects various mistakes such as: int i = 1; ... if (i > i) { ... } This warning also warns about bitwise comparisons that always evaluate to true or false, for instance: if ((a & 16) == 10) { ... } will always be false. This warning is enabled by -Wall. -Wtrampolines Warn about trampolines generated for pointers to nested functions. A trampoline is a small piece of data or code that is created at run time on the stack when the address of a nested function is taken, and is used to call the nested function indirectly. For some targets, it is made up of data only and thus requires no special treatment. But, for most targets, it is made up of code and thus requires the stack to be made executable in order for the program to work properly. -Wfloat-equal Warn if floating-point values are used in equality comparisons. The idea behind this is that sometimes it is convenient (for the programmer) to consider floating-point values as approximations to infinitely precise real numbers. If you are doing this, then you need to compute (by analyzing the code, or in some other way) the maximum or likely maximum error that the computation introduces, and allow for it when performing comparisons (and when producing output, but that's a different problem). In particular, instead of testing for equality, you should check to see whether the two values have ranges that overlap; and this is done with the relational operators, so equality comparisons are probably mistaken. -Wtraditional (C and Objective-C only) Warn about certain constructs that behave differently in traditional and ISO C. Also warn about ISO C constructs that have no traditional C equivalent, and/or problematic constructs that should be avoided. * Macro parameters that appear within string literals in the macro body. In traditional C macro replacement takes place within string literals, but in ISO C it does not. * In traditional C, some preprocessor directives did not exist. Traditional preprocessors only considered a line to be a directive if the # appeared in column 1 on the line. Therefore -Wtraditional warns about directives that traditional C understands but ignores because the # does not appear as the first character on the line. It also suggests you hide directives like "#pragma" not understood by traditional C by indenting them. Some traditional implementations do not recognize "#elif", so this option suggests avoiding it altogether. * A function-like macro that appears without arguments. * The unary plus operator. * The U integer constant suffix, or the F or L floating-point constant suffixes. (Traditional C does support the L suffix on integer constants.) Note, these suffixes appear in macros defined in the system headers of most modern systems, e.g. the _MIN/_MAX macros in "<limits.h>". Use of these macros in user code might normally lead to spurious warnings, however GCC's integrated preprocessor has enough context to avoid warning in these cases. * A function declared external in one block and then used after the end of the block. * A "switch" statement has an operand of type "long". * A non-"static" function declaration follows a "static" one. This construct is not accepted by some traditional C compilers. * The ISO type of an integer constant has a different width or signedness from its traditional type. This warning is only issued if the base of the constant is ten. I.e. hexadecimal or octal values, which typically represent bit patterns, are not warned about. * Usage of ISO string concatenation is detected. * Initialization of automatic aggregates. * Identifier conflicts with labels. Traditional C lacks a separate namespace for labels. * Initialization of unions. If the initializer is zero, the warning is omitted. This is done under the assumption that the zero initializer in user code appears conditioned on e.g. "__STDC__" to avoid missing initializer warnings and relies on default initialization to zero in the traditional C case. * Conversions by prototypes between fixed/floating-point values and vice versa. The absence of these prototypes when compiling with traditional C causes serious problems. This is a subset of the possible conversion warnings; for the full set use -Wtraditional-conversion. * Use of ISO C style function definitions. This warning intentionally is not issued for prototype declarations or variadic functions because these ISO C features appear in your code when using libiberty's traditional C compatibility macros, "PARAMS" and "VPARAMS". This warning is also bypassed for nested functions because that feature is already a GCC extension and thus not relevant to traditional C compatibility. -Wtraditional-conversion (C and Objective-C only) Warn if a prototype causes a type conversion that is different from what would happen to the same argument in the absence of a prototype. This includes conversions of fixed point to floating and vice versa, and conversions changing the width or signedness of a fixed-point argument except when the same as the default promotion. -Wdeclaration-after-statement (C and Objective-C only) Warn when a declaration is found after a statement in a block. This construct, known from C++, was introduced with ISO C99 and is by default allowed in GCC. It is not supported by ISO C90. -Wshadow Warn whenever a local variable or type declaration shadows another variable, parameter, type, class member (in C++), or instance variable (in Objective-C) or whenever a built-in function is shadowed. Note that in C++, the compiler warns if a local variable shadows an explicit typedef, but not if it shadows a struct/class/enum. If this warning is enabled, it includes also all instances of local shadowing. This means that -Wno-shadow=local and -Wno-shadow=compatible-local are ignored when -Wshadow is used. Same as -Wshadow=global. -Wno-shadow-ivar (Objective-C only) Do not warn whenever a local variable shadows an instance variable in an Objective-C method. -Wshadow=global Warn for any shadowing. Same as -Wshadow. -Wshadow=local Warn when a local variable shadows another local variable or parameter. -Wshadow=compatible-local Warn when a local variable shadows another local variable or parameter whose type is compatible with that of the shadowing variable. In C++, type compatibility here means the type of the shadowing variable can be converted to that of the shadowed variable. The creation of this flag (in addition to -Wshadow=local) is based on the idea that when a local variable shadows another one of incompatible type, it is most likely intentional, not a bug or typo, as shown in the following example: for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i) { for (int i = 0; i < N; ++i) { ... } ... } Since the two variable "i" in the example above have incompatible types, enabling only -Wshadow=compatible-local does not emit a warning. Because their types are incompatible, if a programmer accidentally uses one in place of the other, type checking is expected to catch that and emit an error or warning. Use of this flag instead of -Wshadow=local can possibly reduce the number of warnings triggered by intentional shadowing. Note that this also means that shadowing "const char *i" by "char *i" does not emit a warning. This warning is also enabled by -Wshadow=local. -Wlarger-than=byte-size Warn whenever an object is defined whose size exceeds byte-size. -Wlarger-than=PTRDIFF_MAX is enabled by default. Warnings controlled by the option can be disabled either by specifying byte- size of SIZE_MAX or more or by -Wno-larger-than. Also warn for calls to bounded functions such as "memchr" or "strnlen" that specify a bound greater than the largest possible object, which is PTRDIFF_MAX bytes by default. These warnings can only be disabled by -Wno-larger-than. -Wno-larger-than Disable -Wlarger-than= warnings. The option is equivalent to -Wlarger-than=SIZE_MAX or larger. -Wframe-larger-than=byte-size Warn if the size of a function frame exceeds byte-size. The computation done to determine the stack frame size is approximate and not conservative. The actual requirements may be somewhat greater than byte-size even if you do not get a warning. In addition, any space allocated via "alloca", variable-length arrays, or related constructs is not included by the compiler when determining whether or not to issue a warning. -Wframe-larger-than=PTRDIFF_MAX is enabled by default. Warnings controlled by the option can be disabled either by specifying byte- size of SIZE_MAX or more or by -Wno-frame-larger-than. -Wno-frame-larger-than Disable -Wframe-larger-than= warnings. The option is equivalent to -Wframe-larger-than=SIZE_MAX or larger. -Wfree-nonheap-object Warn when attempting to deallocate an object that was either not allocated on the heap, or by using a pointer that was not returned from a prior call to the corresponding allocation function. For example, because the call to "stpcpy" returns a pointer to the terminating nul character and not to the beginning of the object, the call to "free" below is diagnosed. void f (char *p) { p = stpcpy (p, "abc"); // ... free (p); // warning } -Wfree-nonheap-object is included in -Wall. -Wstack-usage=byte-size Warn if the stack usage of a function might exceed byte-size. The computation done to determine the stack usage is conservative. Any space allocated via "alloca", variable-length arrays, or related constructs is included by the compiler when determining whether or not to issue a warning. The message is in keeping with the output of -fstack-usage. * If the stack usage is fully static but exceeds the specified amount, it's: warning: stack usage is 1120 bytes * If the stack usage is (partly) dynamic but bounded, it's: warning: stack usage might be 1648 bytes * If the stack usage is (partly) dynamic and not bounded, it's: warning: stack usage might be unbounded -Wstack-usage=PTRDIFF_MAX is enabled by default. Warnings controlled by the option can be disabled either by specifying byte- size of SIZE_MAX or more or by -Wno-stack-usage. -Wno-stack-usage Disable -Wstack-usage= warnings. The option is equivalent to -Wstack-usage=SIZE_MAX or larger. -Wunsafe-loop-optimizations Warn if the loop cannot be optimized because the compiler cannot assume anything on the bounds of the loop indices. With -funsafe-loop-optimizations warn if the compiler makes such assumptions. -Wno-pedantic-ms-format (MinGW targets only) When used in combination with -Wformat and -pedantic without GNU extensions, this option disables the warnings about non-ISO "printf" / "scanf" format width specifiers "I32", "I64", and "I" used on Windows targets, which depend on the MS runtime. -Wpointer-arith Warn about anything that depends on the "size of" a function type or of "void". GNU C assigns these types a size of 1, for convenience in calculations with "void *" pointers and pointers to functions. In C++, warn also when an arithmetic operation involves "NULL". This warning is also enabled by -Wpedantic. -Wno-pointer-compare Do not warn if a pointer is compared with a zero character constant. This usually means that the pointer was meant to be dereferenced. For example: const char *p = foo (); if (p == '\0') return 42; Note that the code above is invalid in C++11. This warning is enabled by default. -Wtsan Warn about unsupported features in ThreadSanitizer. ThreadSanitizer does not support "std::atomic_thread_fence" and can report false positives. This warning is enabled by default. -Wtype-limits Warn if a comparison is always true or always false due to the limited range of the data type, but do not warn for constant expressions. For example, warn if an unsigned variable is compared against zero with "<" or ">=". This warning is also enabled by -Wextra. -Wabsolute-value (C and Objective-C only) Warn for calls to standard functions that compute the absolute value of an argument when a more appropriate standard function is available. For example, calling "abs(3.14)" triggers the warning because the appropriate function to call to compute the absolute value of a double argument is "fabs". The option also triggers warnings when the argument in a call to such a function has an unsigned type. This warning can be suppressed with an explicit type cast and it is also enabled by -Wextra. -Wcomment -Wcomments Warn whenever a comment-start sequence /* appears in a /* comment, or whenever a backslash-newline appears in a // comment. This warning is enabled by -Wall. -Wtrigraphs Warn if any trigraphs are encountered that might change the meaning of the program. Trigraphs within comments are not warned about, except those that would form escaped newlines. This option is implied by -Wall. If -Wall is not given, this option is still enabled unless trigraphs are enabled. To get trigraph conversion without warnings, but get the other -Wall warnings, use -trigraphs -Wall -Wno-trigraphs. -Wundef Warn if an undefined identifier is evaluated in an "#if" directive. Such identifiers are replaced with zero. -Wexpansion-to-defined Warn whenever defined is encountered in the expansion of a macro (including the case where the macro is expanded by an #if directive). Such usage is not portable. This warning is also enabled by -Wpedantic and -Wextra. -Wunused-macros Warn about macros defined in the main file that are unused. A macro is used if it is expanded or tested for existence at least once. The preprocessor also warns if the macro has not been used at the time it is redefined or undefined. Built-in macros, macros defined on the command line, and macros defined in include files are not warned about. Note: If a macro is actually used, but only used in skipped conditional blocks, then the preprocessor reports it as unused. To avoid the warning in such a case, you might improve the scope of the macro's definition by, for example, moving it into the first skipped block. Alternatively, you could provide a dummy use with something like: #if defined the_macro_causing_the_warning #endif -Wno-endif-labels Do not warn whenever an "#else" or an "#endif" are followed by text. This sometimes happens in older programs with code of the form #if FOO ... #else FOO ... #endif FOO The second and third "FOO" should be in comments. This warning is on by default. -Wbad-function-cast (C and Objective-C only) Warn when a function call is cast to a non-matching type. For example, warn if a call to a function returning an integer type is cast to a pointer type. -Wc90-c99-compat (C and Objective-C only) Warn about features not present in ISO C90, but present in ISO C99. For instance, warn about use of variable length arrays, "long long" type, "bool" type, compound literals, designated initializers, and so on. This option is independent of the standards mode. Warnings are disabled in the expression that follows "__extension__". -Wc99-c11-compat (C and Objective-C only) Warn about features not present in ISO C99, but present in ISO C11. For instance, warn about use of anonymous structures and unions, "_Atomic" type qualifier, "_Thread_local" storage-class specifier, "_Alignas" specifier, "Alignof" operator, "_Generic" keyword, and so on. This option is independent of the standards mode. Warnings are disabled in the expression that follows "__extension__". -Wc11-c2x-compat (C and Objective-C only) Warn about features not present in ISO C11, but present in ISO C2X. For instance, warn about omitting the string in "_Static_assert", use of [[]] syntax for attributes, use of decimal floating-point types, and so on. This option is independent of the standards mode. Warnings are disabled in the expression that follows "__extension__". -Wc++-compat (C and Objective-C only) Warn about ISO C constructs that are outside of the common subset of ISO C and ISO C++, e.g. request for implicit conversion from "void *" to a pointer to non-"void" type. -Wc++11-compat (C++ and Objective-C++ only) Warn about C++ constructs whose meaning differs between ISO C++ 1998 and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords in ISO C++ 2011. This warning turns on -Wnarrowing and is enabled by -Wall. -Wc++14-compat (C++ and Objective-C++ only) Warn about C++ constructs whose meaning differs between ISO C++ 2011 and ISO C++ 2014. This warning is enabled by -Wall. -Wc++17-compat (C++ and Objective-C++ only) Warn about C++ constructs whose meaning differs between ISO C++ 2014 and ISO C++ 2017. This warning is enabled by -Wall. -Wc++20-compat (C++ and Objective-C++ only) Warn about C++ constructs whose meaning differs between ISO C++ 2017 and ISO C++ 2020. This warning is enabled by -Wall. -Wno-c++11-extensions (C++ and Objective-C++ only) Do not warn about C++11 constructs in code being compiled using an older C++ standard. Even without this option, some C++11 constructs will only be diagnosed if -Wpedantic is used. -Wno-c++14-extensions (C++ and Objective-C++ only) Do not warn about C++14 constructs in code being compiled using an older C++ standard. Even without this option, some C++14 constructs will only be diagnosed if -Wpedantic is used. -Wno-c++17-extensions (C++ and Objective-C++ only) Do not warn about C++17 constructs in code being compiled using an older C++ standard. Even without this option, some C++17 constructs will only be diagnosed if -Wpedantic is used. -Wno-c++20-extensions (C++ and Objective-C++ only) Do not warn about C++20 constructs in code being compiled using an older C++ standard. Even without this option, some C++20 constructs will only be diagnosed if -Wpedantic is used. -Wno-c++23-extensions (C++ and Objective-C++ only) Do not warn about C++23 constructs in code being compiled using an older C++ standard. Even without this option, some C++23 constructs will only be diagnosed if -Wpedantic is used. -Wcast-qual Warn whenever a pointer is cast so as to remove a type qualifier from the target type. For example, warn if a "const char *" is cast to an ordinary "char *". Also warn when making a cast that introduces a type qualifier in an unsafe way. For example, casting "char **" to "const char **" is unsafe, as in this example: /* p is char ** value. */ const char **q = (const char **) p; /* Assignment of readonly string to const char * is OK. */ *q = "string"; /* Now char** pointer points to read-only memory. */ **p = 'b'; -Wcast-align Warn whenever a pointer is cast such that the required alignment of the target is increased. For example, warn if a "char *" is cast to an "int *" on machines where integers can only be accessed at two- or four-byte boundaries. -Wcast-align=strict Warn whenever a pointer is cast such that the required alignment of the target is increased. For example, warn if a "char *" is cast to an "int *" regardless of the target machine. -Wcast-function-type Warn when a function pointer is cast to an incompatible function pointer. In a cast involving function types with a variable argument list only the types of initial arguments that are provided are considered. Any parameter of pointer-type matches any other pointer-type. Any benign differences in integral types are ignored, like "int" vs. "long" on ILP32 targets. Likewise type qualifiers are ignored. The function type "void (*) (void)" is special and matches everything, which can be used to suppress this warning. In a cast involving pointer to member types this warning warns whenever the type cast is changing the pointer to member type. This warning is enabled by -Wextra. -Wwrite-strings When compiling C, give string constants the type "const char[length]" so that copying the address of one into a non-"const" "char *" pointer produces a warning. These warnings help you find at compile time code that can try to write into a string constant, but only if you have been very careful about using "const" in declarations and prototypes. Otherwise, it is just a nuisance. This is why we did not make -Wall request these warnings. When compiling C++, warn about the deprecated conversion from string literals to "char *". This warning is enabled by default for C++ programs. -Wclobbered Warn for variables that might be changed by "longjmp" or "vfork". This warning is also enabled by -Wextra. -Wno-complain-wrong-lang By default, language front ends complain when a command-line option is valid, but not applicable to that front end. This may be disabled with -Wno-complain-wrong-lang, which is mostly useful when invoking a single compiler driver for multiple source files written in different languages, for example: $ g++ -fno-rtti a.cc b.f90 The driver g++ invokes the C++ front end to compile a.cc and the Fortran front end to compile b.f90. The latter front end diagnoses f951: Warning: command-line option '-fno-rtti' is valid for C++/D/ObjC++ but not for Fortran, which may be disabled with -Wno-complain-wrong-lang. -Wconversion Warn for implicit conversions that may alter a value. This includes conversions between real and integer, like "abs (x)" when "x" is "double"; conversions between signed and unsigned, like "unsigned ui = -1"; and conversions to smaller types, like "sqrtf (M_PI)". Do not warn for explicit casts like "abs ((int) x)" and "ui = (unsigned) -1", or if the value is not changed by the conversion like in "abs (2.0)". Warnings about conversions between signed and unsigned integers can be disabled by using -Wno-sign-conversion. For C++, also warn for confusing overload resolution for user- defined conversions; and conversions that never use a type conversion operator: conversions to "void", the same type, a base class or a reference to them. Warnings about conversions between signed and unsigned integers are disabled by default in C++ unless -Wsign-conversion is explicitly enabled. Warnings about conversion from arithmetic on a small type back to that type are only given with -Warith-conversion. -Wdangling-else Warn about constructions where there may be confusion to which "if" statement an "else" branch belongs. Here is an example of such a case: { if (a) if (b) foo (); else bar (); } In C/C++, every "else" branch belongs to the innermost possible "if" statement, which in this example is "if (b)". This is often not what the programmer expected, as illustrated in the above example by indentation the programmer chose. When there is the potential for this confusion, GCC issues a warning when this flag is specified. To eliminate the warning, add explicit braces around the innermost "if" statement so there is no way the "else" can belong to the enclosing "if". The resulting code looks like this: { if (a) { if (b) foo (); else bar (); } } This warning is enabled by -Wparentheses. -Wdangling-pointer -Wdangling-pointer=n Warn about uses of pointers (or C++ references) to objects with automatic storage duration after their lifetime has ended. This includes local variables declared in nested blocks, compound literals and other unnamed temporary objects. In addition, warn about storing the address of such objects in escaped pointers. The warning is enabled at all optimization levels but may yield different results with optimization than without. -Wdangling-pointer=1 At level 1 the warning diagnoses only unconditional uses of dangling pointers. For example int f (int c1, int c2, x) { char *p = strchr ((char[]){ c1, c2 }, c3); // warning: dangling pointer to a compound literal return p ? *p : 'x'; } In the following function the store of the address of the local variable "x" in the escaped pointer *p also triggers the warning. void g (int **p) { int x = 7; // warning: storing the address of a local variable in *p *p = &x; } -Wdangling-pointer=2 At level 2, in addition to unconditional uses the warning also diagnoses conditional uses of dangling pointers. For example, because the array a in the following function is out of scope when the pointer s that was set to point is used, the warning triggers at this level. void f (char *s) { if (!s) { char a[12] = "tmpname"; s = a; } // warning: dangling pointer to a may be used strcat (s, ".tmp"); ... } -Wdangling-pointer=2 is included in -Wall. -Wdate-time Warn when macros "__TIME__", "__DATE__" or "__TIMESTAMP__" are encountered as they might prevent bit-wise-identical reproducible compilations. -Wempty-body Warn if an empty body occurs in an "if", "else" or "do while" statement. This warning is also enabled by -Wextra. -Wno-endif-labels Do not warn about stray tokens after "#else" and "#endif". -Wenum-compare Warn about a comparison between values of different enumerated types. In C++ enumerated type mismatches in conditional expressions are also diagnosed and the warning is enabled by default. In C this warning is enabled by -Wall. -Wenum-conversion Warn when a value of enumerated type is implicitly converted to a different enumerated type. This warning is enabled by -Wextra in C. -Wenum-int-mismatch (C and Objective-C only) Warn about mismatches between an enumerated type and an integer type in declarations. For example: enum E { l = -1, z = 0, g = 1 }; int foo(void); enum E foo(void); In C, an enumerated type is compatible with "char", a signed integer type, or an unsigned integer type. However, since the choice of the underlying type of an enumerated type is implementation-defined, such mismatches may cause portability issues. In C++, such mismatches are an error. In C, this warning is enabled by -Wall and -Wc++-compat. -Wjump-misses-init (C, Objective-C only) Warn if a "goto" statement or a "switch" statement jumps forward across the initialization of a variable, or jumps backward to a label after the variable has been initialized. This only warns about variables that are initialized when they are declared. This warning is only supported for C and Objective-C; in C++ this sort of branch is an error in any case. -Wjump-misses-init is included in -Wc++-compat. It can be disabled with the -Wno-jump-misses-init option. -Wsign-compare Warn when a comparison between signed and unsigned values could produce an incorrect result when the signed value is converted to unsigned. In C++, this warning is also enabled by -Wall. In C, it is also enabled by -Wextra. -Wsign-conversion Warn for implicit conversions that may change the sign of an integer value, like assigning a signed integer expression to an unsigned integer variable. An explicit cast silences the warning. In C, this option is enabled also by -Wconversion. -Wfloat-conversion Warn for implicit conversions that reduce the precision of a real value. This includes conversions from real to integer, and from higher precision real to lower precision real values. This option is also enabled by -Wconversion. -Wno-scalar-storage-order Do not warn on suspicious constructs involving reverse scalar storage order. -Wsizeof-array-div Warn about divisions of two sizeof operators when the first one is applied to an array and the divisor does not equal the size of the array element. In such a case, the computation will not yield the number of elements in the array, which is likely what the user intended. This warning warns e.g. about int fn () { int arr[10]; return sizeof (arr) / sizeof (short); } This warning is enabled by -Wall. -Wsizeof-pointer-div Warn for suspicious divisions of two sizeof expressions that divide the pointer size by the element size, which is the usual way to compute the array size but won't work out correctly with pointers. This warning warns e.g. about "sizeof (ptr) / sizeof (ptr[0])" if "ptr" is not an array, but a pointer. This warning is enabled by -Wall. -Wsizeof-pointer-memaccess Warn for suspicious length parameters to certain string and memory built-in functions if the argument uses "sizeof". This warning triggers for example for "memset (ptr, 0, sizeof (ptr));" if "ptr" is not an array, but a pointer, and suggests a possible fix, or about "memcpy (&foo, ptr, sizeof (&foo));". -Wsizeof-pointer-memaccess also warns about calls to bounded string copy functions like "strncat" or "strncpy" that specify as the bound a "sizeof" expression of the source array. For example, in the following function the call to "strncat" specifies the size of the source string as the bound. That is almost certainly a mistake and so the call is diagnosed. void make_file (const char *name) { char path[PATH_MAX]; strncpy (path, name, sizeof path - 1); strncat (path, ".text", sizeof ".text"); ... } The -Wsizeof-pointer-memaccess option is enabled by -Wall. -Wno-sizeof-array-argument Do not warn when the "sizeof" operator is applied to a parameter that is declared as an array in a function definition. This warning is enabled by default for C and C++ programs. -Wmemset-elt-size Warn for suspicious calls to the "memset" built-in function, if the first argument references an array, and the third argument is a number equal to the number of elements, but not equal to the size of the array in memory. This indicates that the user has omitted a multiplication by the element size. This warning is enabled by -Wall. -Wmemset-transposed-args Warn for suspicious calls to the "memset" built-in function where the second argument is not zero and the third argument is zero. For example, the call "memset (buf, sizeof buf, 0)" is diagnosed because "memset (buf, 0, sizeof buf)" was meant instead. The diagnostic is only emitted if the third argument is a literal zero. Otherwise, if it is an expression that is folded to zero, or a cast of zero to some type, it is far less likely that the arguments have been mistakenly transposed and no warning is emitted. This warning is enabled by -Wall. -Waddress Warn about suspicious uses of address expressions. These include comparing the address of a function or a declared object to the null pointer constant such as in void f (void); void g (void) { if (!f) // warning: expression evaluates to false abort (); } comparisons of a pointer to a string literal, such as in void f (const char *x) { if (x == "abc") // warning: expression evaluates to false puts ("equal"); } and tests of the results of pointer addition or subtraction for equality to null, such as in void f (const int *p, int i) { return p + i == NULL; } Such uses typically indicate a programmer error: the address of most functions and objects necessarily evaluates to true (the exception are weak symbols), so their use in a conditional might indicate missing parentheses in a function call or a missing dereference in an array expression. The subset of the warning for object pointers can be suppressed by casting the pointer operand to an integer type such as "intptr_t" or "uintptr_t". Comparisons against string literals result in unspecified behavior and are not portable, and suggest the intent was to call "strcmp". The warning is suppressed if the suspicious expression is the result of macro expansion. -Waddress warning is enabled by -Wall. -Wno-address-of-packed-member Do not warn when the address of packed member of struct or union is taken, which usually results in an unaligned pointer value. This is enabled by default. -Wlogical-op Warn about suspicious uses of logical operators in expressions. This includes using logical operators in contexts where a bit-wise operator is likely to be expected. Also warns when the operands of a logical operator are the same: extern int a; if (a < 0 && a < 0) { ... } -Wlogical-not-parentheses Warn about logical not used on the left hand side operand of a comparison. This option does not warn if the right operand is considered to be a boolean expression. Its purpose is to detect suspicious code like the following: int a; ... if (!a > 1) { ... } It is possible to suppress the warning by wrapping the LHS into parentheses: if ((!a) > 1) { ... } This warning is enabled by -Wall. -Waggregate-return Warn if any functions that return structures or unions are defined or called. (In languages where you can return an array, this also elicits a warning.) -Wno-aggressive-loop-optimizations Warn if in a loop with constant number of iterations the compiler detects undefined behavior in some statement during one or more of the iterations. -Wno-attributes Do not warn if an unexpected "__attribute__" is used, such as unrecognized attributes, function attributes applied to variables, etc. This does not stop errors for incorrect use of supported attributes. Additionally, using -Wno-attributes=, it is possible to suppress warnings about unknown scoped attributes (in C++11 and C2X). For example, -Wno-attributes=vendor::attr disables warning about the following declaration: [[vendor::attr]] void f(); It is also possible to disable warning about all attributes in a namespace using -Wno-attributes=vendor:: which prevents warning about both of these declarations: [[vendor::safe]] void f(); [[vendor::unsafe]] void f2(); Note that -Wno-attributes= does not imply -Wno-attributes. -Wno-builtin-declaration-mismatch Warn if a built-in function is declared with an incompatible signature or as a non-function, or when a built-in function declared with a type that does not include a prototype is called with arguments whose promoted types do not match those expected by the function. When -Wextra is specified, also warn when a built-in function that takes arguments is declared without a prototype. The -Wbuiltin-declaration-mismatch warning is enabled by default. To avoid the warning include the appropriate header to bring the prototypes of built-in functions into scope. For example, the call to "memset" below is diagnosed by the warning because the function expects a value of type "size_t" as its argument but the type of 32 is "int". With -Wextra, the declaration of the function is diagnosed as well. extern void* memset (); void f (void *d) { memset (d, '\0', 32); } -Wno-builtin-macro-redefined Do not warn if certain built-in macros are redefined. This suppresses warnings for redefinition of "__TIMESTAMP__", "__TIME__", "__DATE__", "__FILE__", and "__BASE_FILE__". -Wstrict-prototypes (C and Objective-C only) Warn if a function is declared or defined without specifying the argument types. (An old-style function definition is permitted without a warning if preceded by a declaration that specifies the argument types.) -Wold-style-declaration (C and Objective-C only) Warn for obsolescent usages, according to the C Standard, in a declaration. For example, warn if storage-class specifiers like "static" are not the first things in a declaration. This warning is also enabled by -Wextra. -Wold-style-definition (C and Objective-C only) Warn if an old-style function definition is used. A warning is given even if there is a previous prototype. A definition using () is not considered an old-style definition in C2X mode, because it is equivalent to (void) in that case, but is considered an old- style definition for older standards. -Wmissing-parameter-type (C and Objective-C only) A function parameter is declared without a type specifier in K&R-style functions: void foo(bar) { } This warning is also enabled by -Wextra. -Wmissing-prototypes (C and Objective-C only) Warn if a global function is defined without a previous prototype declaration. This warning is issued even if the definition itself provides a prototype. Use this option to detect global functions that do not have a matching prototype declaration in a header file. This option is not valid for C++ because all function declarations provide prototypes and a non-matching declaration declares an overload rather than conflict with an earlier declaration. Use -Wmissing-declarations to detect missing declarations in C++. -Wmissing-declarations Warn if a global function is defined without a previous declaration. Do so even if the definition itself provides a prototype. Use this option to detect global functions that are not declared in header files. In C, no warnings are issued for functions with previous non-prototype declarations; use -Wmissing-prototypes to detect missing prototypes. In C++, no warnings are issued for function templates, or for inline functions, or for functions in anonymous namespaces. -Wmissing-field-initializers Warn if a structure's initializer has some fields missing. For example, the following code causes such a warning, because "x.h" is implicitly zero: struct s { int f, g, h; }; struct s x = { 3, 4 }; This option does not warn about designated initializers, so the following modification does not trigger a warning: struct s { int f, g, h; }; struct s x = { .f = 3, .g = 4 }; In C this option does not warn about the universal zero initializer { 0 }: struct s { int f, g, h; }; struct s x = { 0 }; Likewise, in C++ this option does not warn about the empty { } initializer, for example: struct s { int f, g, h; }; s x = { }; This warning is included in -Wextra. To get other -Wextra warnings without this one, use -Wextra -Wno-missing-field-initializers. -Wno-missing-requires By default, the compiler warns about a concept-id appearing as a C++20 simple-requirement: bool satisfied = requires { C<T> }; Here satisfied will be true if C<T> is a valid expression, which it is for all T. Presumably the user meant to write bool satisfied = requires { requires C<T> }; so satisfied is only true if concept C is satisfied for type T. This warning can be disabled with -Wno-missing-requires. -Wno-missing-template-keyword The member access tokens ., -> and :: must be followed by the "template" keyword if the parent object is dependent and the member being named is a template. template <class X> void DoStuff (X x) { x.template DoSomeOtherStuff<X>(); // Good. x.DoMoreStuff<X>(); // Warning, x is dependent. } In rare cases it is possible to get false positives. To silence this, wrap the expression in parentheses. For example, the following is treated as a template, even where m and N are integers: void NotATemplate (my_class t) { int N = 5; bool test = t.m < N > (0); // Treated as a template. test = (t.m < N) > (0); // Same meaning, but not treated as a template. } This warning can be disabled with -Wno-missing-template-keyword. -Wno-multichar Do not warn if a multicharacter constant ('FOOF') is used. Usually they indicate a typo in the user's code, as they have implementation-defined values, and should not be used in portable code. -Wnormalized=[none|id|nfc|nfkc] In ISO C and ISO C++, two identifiers are different if they are different sequences of characters. However, sometimes when characters outside the basic ASCII character set are used, you can have two different character sequences that look the same. To avoid confusion, the ISO 10646 standard sets out some normalization rules which when applied ensure that two sequences that look the same are turned into the same sequence. GCC can warn you if you are using identifiers that have not been normalized; this option controls that warning. There are four levels of warning supported by GCC. The default is -Wnormalized=nfc, which warns about any identifier that is not in the ISO 10646 "C" normalized form, NFC. NFC is the recommended form for most uses. It is equivalent to -Wnormalized. Unfortunately, there are some characters allowed in identifiers by ISO C and ISO C++ that, when turned into NFC, are not allowed in identifiers. That is, there's no way to use these symbols in portable ISO C or C++ and have all your identifiers in NFC. -Wnormalized=id suppresses the warning for these characters. It is hoped that future versions of the standards involved will correct this, which is why this option is not the default. You can switch the warning off for all characters by writing -Wnormalized=none or -Wno-normalized. You should only do this if you are using some other normalization scheme (like "D"), because otherwise you can easily create bugs that are literally impossible to see. Some characters in ISO 10646 have distinct meanings but look identical in some fonts or display methodologies, especially once formatting has been applied. For instance "\u207F", "SUPERSCRIPT LATIN SMALL LETTER N", displays just like a regular "n" that has been placed in a superscript. ISO 10646 defines the NFKC normalization scheme to convert all these into a standard form as well, and GCC warns if your code is not in NFKC if you use -Wnormalized=nfkc. This warning is comparable to warning about every identifier that contains the letter O because it might be confused with the digit 0, and so is not the default, but may be useful as a local coding convention if the programming environment cannot be fixed to display these characters distinctly. -Wno-attribute-warning Do not warn about usage of functions declared with "warning" attribute. By default, this warning is enabled. -Wno-attribute-warning can be used to disable the warning or -Wno-error=attribute-warning can be used to disable the error when compiled with -Werror flag. -Wno-deprecated Do not warn about usage of deprecated features. -Wno-deprecated-declarations Do not warn about uses of functions, variables, and types marked as deprecated by using the "deprecated" attribute. -Wno-overflow Do not warn about compile-time overflow in constant expressions. -Wno-odr Warn about One Definition Rule violations during link-time optimization. Enabled by default. -Wopenacc-parallelism Warn about potentially suboptimal choices related to OpenACC parallelism. -Wopenmp-simd Warn if the vectorizer cost model overrides the OpenMP simd directive set by user. The -fsimd-cost-model=unlimited option can be used to relax the cost model. -Woverride-init (C and Objective-C only) Warn if an initialized field without side effects is overridden when using designated initializers. This warning is included in -Wextra. To get other -Wextra warnings without this one, use -Wextra -Wno-override-init. -Wno-override-init-side-effects (C and Objective-C only) Do not warn if an initialized field with side effects is overridden when using designated initializers. This warning is enabled by default. -Wpacked Warn if a structure is given the packed attribute, but the packed attribute has no effect on the layout or size of the structure. Such structures may be mis-aligned for little benefit. For instance, in this code, the variable "f.x" in "struct bar" is misaligned even though "struct bar" does not itself have the packed attribute: struct foo { int x; char a, b, c, d; } __attribute__((packed)); struct bar { char z; struct foo f; }; -Wnopacked-bitfield-compat The 4.1, 4.2 and 4.3 series of GCC ignore the "packed" attribute on bit-fields of type "char". This was fixed in GCC 4.4 but the change can lead to differences in the structure layout. GCC informs you when the offset of such a field has changed in GCC 4.4. For example there is no longer a 4-bit padding between field "a" and "b" in this structure: struct foo { char a:4; char b:8; } __attribute__ ((packed)); This warning is enabled by default. Use -Wno-packed-bitfield-compat to disable this warning. -Wpacked-not-aligned (C, C++, Objective-C and Objective-C++ only) Warn if a structure field with explicitly specified alignment in a packed struct or union is misaligned. For example, a warning will be issued on "struct S", like, "warning: alignment 1 of 'struct S' is less than 8", in this code: struct __attribute__ ((aligned (8))) S8 { char a[8]; }; struct __attribute__ ((packed)) S { struct S8 s8; }; This warning is enabled by -Wall. -Wpadded Warn if padding is included in a structure, either to align an element of the structure or to align the whole structure. Sometimes when this happens it is possible to rearrange the fields of the structure to reduce the padding and so make the structure smaller. -Wredundant-decls Warn if anything is declared more than once in the same scope, even in cases where multiple declaration is valid and changes nothing. -Wrestrict Warn when an object referenced by a "restrict"-qualified parameter (or, in C++, a "__restrict"-qualified parameter) is aliased by another argument, or when copies between such objects overlap. For example, the call to the "strcpy" function below attempts to truncate the string by replacing its initial characters with the last four. However, because the call writes the terminating NUL into "a[4]", the copies overlap and the call is diagnosed. void foo (void) { char a[] = "abcd1234"; strcpy (a, a + 4); ... } The -Wrestrict option detects some instances of simple overlap even without optimization but works best at -O2 and above. It is included in -Wall. -Wnested-externs (C and Objective-C only) Warn if an "extern" declaration is encountered within a function. -Winline Warn if a function that is declared as inline cannot be inlined. Even with this option, the compiler does not warn about failures to inline functions declared in system headers. The compiler uses a variety of heuristics to determine whether or not to inline a function. For example, the compiler takes into account the size of the function being inlined and the amount of inlining that has already been done in the current function. Therefore, seemingly insignificant changes in the source program can cause the warnings produced by -Winline to appear or disappear. -Winterference-size Warn about use of C++17 "std::hardware_destructive_interference_size" without specifying its value with --param destructive-interference-size. Also warn about questionable values for that option. This variable is intended to be used for controlling class layout, to avoid false sharing in concurrent code: struct independent_fields { alignas(std::hardware_destructive_interference_size) std::atomic<int> one; alignas(std::hardware_destructive_interference_size) std::atomic<int> two; }; Here one and two are intended to be far enough apart that stores to one won't require accesses to the other to reload the cache line. By default, --param destructive-interference-size and --param constructive-interference-size are set based on the current -mtune option, typically to the L1 cache line size for the particular target CPU, sometimes to a range if tuning for a generic target. So all translation units that depend on ABI compatibility for the use of these variables must be compiled with the same -mtune (or -mcpu). If ABI stability is important, such as if the use is in a header for a library, you should probably not use the hardware interference size variables at all. Alternatively, you can force a particular value with --param. If you are confident that your use of the variable does not affect ABI outside a single build of your project, you can turn off the warning with -Wno-interference-size. -Wint-in-bool-context Warn for suspicious use of integer values where boolean values are expected, such as conditional expressions (?:) using non-boolean integer constants in boolean context, like "if (a <= b ? 2 : 3)". Or left shifting of signed integers in boolean context, like "for (a = 0; 1 << a; a++);". Likewise for all kinds of multiplications regardless of the data type. This warning is enabled by -Wall. -Wno-int-to-pointer-cast Suppress warnings from casts to pointer type of an integer of a different size. In C++, casting to a pointer type of smaller size is an error. Wint-to-pointer-cast is enabled by default. -Wno-pointer-to-int-cast (C and Objective-C only) Suppress warnings from casts from a pointer to an integer type of a different size. -Winvalid-pch Warn if a precompiled header is found in the search path but cannot be used. -Winvalid-utf8 Warn if an invalid UTF-8 character is found. This warning is on by default for C++23 if -finput-charset=UTF-8 is used and turned into error with -pedantic-errors. -Wno-unicode Don't diagnose invalid forms of delimited or named escape sequences which are treated as separate tokens. Wunicode is enabled by default. -Wlong-long Warn if "long long" type is used. This is enabled by either -Wpedantic or -Wtraditional in ISO C90 and C++98 modes. To inhibit the warning messages, use -Wno-long-long. -Wvariadic-macros Warn if variadic macros are used in ISO C90 mode, or if the GNU alternate syntax is used in ISO C99 mode. This is enabled by either -Wpedantic or -Wtraditional. To inhibit the warning messages, use -Wno-variadic-macros. -Wno-varargs Do not warn upon questionable usage of the macros used to handle variable arguments like "va_start". These warnings are enabled by default. -Wvector-operation-performance Warn if vector operation is not implemented via SIMD capabilities of the architecture. Mainly useful for the performance tuning. Vector operation can be implemented "piecewise", which means that the scalar operation is performed on every vector element; "in parallel", which means that the vector operation is implemented using scalars of wider type, which normally is more performance efficient; and "as a single scalar", which means that vector fits into a scalar type. -Wvla Warn if a variable-length array is used in the code. -Wno-vla prevents the -Wpedantic warning of the variable-length array. -Wvla-larger-than=byte-size If this option is used, the compiler warns for declarations of variable-length arrays whose size is either unbounded, or bounded by an argument that allows the array size to exceed byte-size bytes. This is similar to how -Walloca-larger-than=byte-size works, but with variable-length arrays. Note that GCC may optimize small variable-length arrays of a known value into plain arrays, so this warning may not get triggered for such arrays. -Wvla-larger-than=PTRDIFF_MAX is enabled by default but is typically only effective when -ftree-vrp is active (default for -O2 and above). See also -Walloca-larger-than=byte-size. -Wno-vla-larger-than Disable -Wvla-larger-than= warnings. The option is equivalent to -Wvla-larger-than=SIZE_MAX or larger. -Wvla-parameter Warn about redeclarations of functions involving arguments of Variable Length Array types of inconsistent kinds or forms, and enable the detection of out-of-bounds accesses to such parameters by warnings such as -Warray-bounds. If the first function declaration uses the VLA form the bound specified in the array is assumed to be the minimum number of elements expected to be provided in calls to the function and the maximum number of elements accessed by it. Failing to provide arguments of sufficient size or accessing more than the maximum number of elements may be diagnosed. For example, the warning triggers for the following redeclarations because the first one allows an array of any size to be passed to "f" while the second one specifies that the array argument must have at least "n" elements. In addition, calling "f" with the associated VLA bound parameter in excess of the actual VLA bound triggers a warning as well. void f (int n, int[n]); // warning: argument 2 previously declared as a VLA void f (int, int[]); void g (int n) { if (n > 4) return; int a[n]; // warning: access to a by f may be out of bounds f (sizeof a, a); ... } -Wvla-parameter is included in -Wall. The -Warray-parameter option triggers warnings for similar problems involving ordinary array arguments. -Wvolatile-register-var Warn if a register variable is declared volatile. The volatile modifier does not inhibit all optimizations that may eliminate reads and/or writes to register variables. This warning is enabled by -Wall. -Wxor-used-as-pow (C, C++, Objective-C and Objective-C++ only) Warn about uses of "^", the exclusive or operator, where it appears the user meant exponentiation. Specifically, the warning occurs when the left-hand side is the decimal constant 2 or 10 and the right-hand side is also a decimal constant. In C and C++, "^" means exclusive or, whereas in some other languages (e.g. TeX and some versions of BASIC) it means exponentiation. This warning is enabled by default. It can be silenced by converting one of the operands to hexadecimal. -Wdisabled-optimization Warn if a requested optimization pass is disabled. This warning does not generally indicate that there is anything wrong with your code; it merely indicates that GCC's optimizers are unable to handle the code effectively. Often, the problem is that your code is too big or too complex; GCC refuses to optimize programs when the optimization itself is likely to take inordinate amounts of time. -Wpointer-sign (C and Objective-C only) Warn for pointer argument passing or assignment with different signedness. This option is only supported for C and Objective-C. It is implied by -Wall and by -Wpedantic, which can be disabled with -Wno-pointer-sign. -Wstack-protector This option is only active when -fstack-protector is active. It warns about functions that are not protected against stack smashing. -Woverlength-strings Warn about string constants that are longer than the "minimum maximum" length specified in the C standard. Modern compilers generally allow string constants that are much longer than the standard's minimum limit, but very portable programs should avoid using longer strings. The limit applies after string constant concatenation, and does not count the trailing NUL. In C90, the limit was 509 characters; in C99, it was raised to 4095. C++98 does not specify a normative minimum maximum, so we do not diagnose overlength strings in C++. This option is implied by -Wpedantic, and can be disabled with -Wno-overlength-strings. -Wunsuffixed-float-constants (C and Objective-C only) Issue a warning for any floating constant that does not have a suffix. When used together with -Wsystem-headers it warns about such constants in system header files. This can be useful when preparing code to use with the "FLOAT_CONST_DECIMAL64" pragma from the decimal floating-point extension to C99. -Wno-lto-type-mismatch During the link-time optimization, do not warn about type mismatches in global declarations from different compilation units. Requires -flto to be enabled. Enabled by default. -Wno-designated-init (C and Objective-C only) Suppress warnings when a positional initializer is used to initialize a structure that has been marked with the "designated_init" attribute. Options That Control Static Analysis -fanalyzer This option enables an static analysis of program flow which looks for "interesting" interprocedural paths through the code, and issues warnings for problems found on them. This analysis is much more expensive than other GCC warnings. In technical terms, it performs coverage-guided symbolic execution of the code being compiled. It is neither sound nor complete: it can have false positives and false negatives. It is a bug-finding tool, rather than a tool for proving program correctness. The analyzer is only suitable for use on C code in this release. Enabling this option effectively enables the following warnings: -Wanalyzer-allocation-size -Wanalyzer-deref-before-check -Wanalyzer-double-fclose -Wanalyzer-double-free -Wanalyzer-exposure-through-output-file -Wanalyzer-exposure-through-uninit-copy -Wanalyzer-fd-access-mode-mismatch -Wanalyzer-fd-double-close -Wanalyzer-fd-leak -Wanalyzer-fd-phase-mismatch -Wanalyzer-fd-type-mismatch -Wanalyzer-fd-use-after-close -Wanalyzer-fd-use-without-check -Wanalyzer-file-leak -Wanalyzer-free-of-non-heap -Wanalyzer-imprecise-fp-arithmetic -Wanalyzer-infinite-recursion -Wanalyzer-jump-through-null -Wanalyzer-malloc-leak -Wanalyzer-mismatching-deallocation -Wanalyzer-null-argument -Wanalyzer-null-dereference -Wanalyzer-out-of-bounds -Wanalyzer-possible-null-argument -Wanalyzer-possible-null-dereference -Wanalyzer-putenv-of-auto-var -Wanalyzer-shift-count-negative -Wanalyzer-shift-count-overflow -Wanalyzer-stale-setjmp-buffer -Wanalyzer-unsafe-call-within-signal-handler -Wanalyzer-use-after-free -Wanalyzer-use-of-pointer-in-stale-stack-frame -Wanalyzer-use-of-uninitialized-value -Wanalyzer-va-arg-type-mismatch -Wanalyzer-va-list-exhausted -Wanalyzer-va-list-leak -Wanalyzer-va-list-use-after-va-end -Wanalyzer-write-to-const -Wanalyzer-write-to-string-literal This option is only available if GCC was configured with analyzer support enabled. -Wanalyzer-too-complex If -fanalyzer is enabled, the analyzer uses various heuristics to attempt to explore the control flow and data flow in the program, but these can be defeated by sufficiently complicated code. By default, the analysis silently stops if the code is too complicated for the analyzer to fully explore and it reaches an internal limit. The -Wanalyzer-too-complex option warns if this occurs. -Wno-analyzer-allocation-size This warning requires -fanalyzer, which enables it; to disable it, use -Wno-analyzer-allocation-size. This diagnostic warns for paths through the code in which a pointer to a buffer is assigned to point at a buffer with a size that is not a multiple of "sizeof (*pointer)". See CWE-131: Incorrect Calculation of Buffer Size ("https://cwe.mitre.org/data/definitions/131.html"). -Wno-analyzer-deref-before-check This warning requires -fanalyzer, which enables it; use -Wno-analyzer-deref-before-check to disable it. This diagnostic warns for paths through the code in which a pointer is checked for "NULL" *after* it has already been dereferenced, suggesting that the pointer could have been NULL. Such cases suggest that the check for NULL is either redundant, or that it needs to be moved to before the pointer is dereferenced. This diagnostic also considers values passed to a function argument marked with "__attribute__((nonnull))" as requiring a non-NULL value, and thus will complain if such values are checked for "NULL" after returning from such a function call. This diagnostic is unlikely to be reported when any level of optimization is enabled, as GCC's optimization logic will typically consider such checks for NULL as being redundant, and optimize them away before the analyzer "sees" them. Hence optimization should be disabled when attempting to trigger this diagnostic. -Wno-analyzer-double-fclose This warning requires -fanalyzer, which enables it; use -Wno-analyzer-double-fclose to disable it. This diagnostic warns for paths through the code in which a "FILE *" can have "fclose" called on it more than once. See CWE-1341: Multiple Releases of Same Resource or Handle ("https://cwe.mitre.org/data/definitions/1341.html"). -Wno-analyzer-double-free This warning requires -fanalyzer, which enables it; use -Wno-analyzer-double-free to disable it. This diagnostic warns for paths through the code in which a pointer can have a deallocator called on it more than once, either "free", or a deallocator referenced by attribute "malloc". See CWE-415: Double Free ("https://cwe.mitre.org/data/definitions/415.html"). -Wno-analyzer-exposure-through-output-file This warning requires -fanalyzer, which enables it; use -Wno-analyzer-exposure-through-output-file to disable it. This diagnostic warns for paths through the code in which a security-sensitive value is written to an output file (such as writing a password to a log file). See CWE-532: Information Exposure Through Log Files ("https://cwe.mitre.org/data/definitions/532.html"). -Wanalyzer-exposure-through-uninit-copy This warning requires both -fanalyzer and the use of a plugin to specify a function that copies across a "trust boundary". Use -Wno-analyzer-exposure-through-uninit-copy to disable it. This diagnostic warns for "infoleaks" - paths through the code in which uninitialized values are copied across a security boundary (such as code within an OS kernel that copies a partially- initialized struct on the stack to user space). See CWE-200: Exposure of Sensitive Information to an Unauthorized Actor ("https://cwe.mitre.org/data/definitions/200.html"). -Wno-analyzer-fd-access-mode-mismatch This warning requires -fanalyzer, which enables it; use -Wno-analyzer-fd-access-mode-mismatch to disable it. This diagnostic warns for paths through code in which a "read" on a write-only file descriptor is attempted, or vice versa. This diagnostic also warns for code paths in a which a function with attribute "fd_arg_read (N)" is called with a file descriptor opened with "O_WRONLY" at referenced argument "N" or a function with attribute "fd_arg_write (N)" is called with a file descriptor opened with "O_RDONLY" at referenced argument N. -Wno-analyzer-fd-double-close This warning requires -fanalyzer, which enables it; use -Wno-analyzer-fd-double-close to disable it. This diagnostic warns for paths through code in which a file descriptor can be closed more than once. See CWE-1341: Multiple Releases of Same Resource or Handle ("https://cwe.mitre.org/data/definitions/1341.html"). -Wno-analyzer-fd-leak This warning requires -fanalyzer, which enables it; use -Wno-analyzer-fd-leak to disable it. This diagnostic warns for paths through code in which an open file descriptor is leaked. See CWE-775: Missing Release of File Descriptor or Handle after Effective Lifetime ("https://cwe.mitre.org/data/definitions/775.html"). -Wno-analyzer-fd-phase-mismatch This warning requires -fanalyzer, which enables it; use -Wno-analyzer-fd-phase-mismatch to disable it. This diagnostic warns for paths through code in which an operation is attempted in the wrong phase of a file descriptor's lifetime. For example, it will warn on attempts to call "accept" on a stream socket that has not yet had "listen" successfully called on it. See CWE-666: Operation on Resource in Wrong Phase of Lifetime ("https://cwe.mitre.org/data/definitions/666.html"). -Wno-analyzer-fd-type-mismatch This warning requires -fanalyzer, which enables it; use -Wno-analyzer-fd-type-mismatch to disable it. This diagnostic warns for paths through code in which an operation is attempted on the wrong type of file descriptor. For example, it will warn on attempts to use socket operations on a file descriptor obtained via "open", or when attempting to use a stream socket operation on a datagram socket. -Wno-analyzer-fd-use-after-close This warning requires -fanalyzer, which enables it; use -Wno-analyzer-fd-use-after-close to disable it. This diagnostic warns for paths through code in which a read or write is called on a closed file descriptor. This diagnostic also warns for paths through code in which a function with attribute "fd_arg (N)" or "fd_arg_read (N)" or "fd_arg_write (N)" is called with a closed file descriptor at referenced argument "N". -Wno-analyzer-fd-use-without-check This warning requires -fanalyzer, which enables it; use -Wno-analyzer-fd-use-without-check to disable it. This diagnostic warns for paths through code in which a file descriptor is used without being checked for validity. This diagnostic also warns for paths through code in which a function with attribute "fd_arg (N)" or "fd_arg_read (N)" or "fd_arg_write (N)" is called with a file descriptor, at referenced argument "N", without being checked for validity. -Wno-analyzer-file-leak This warning requires -fanalyzer, which enables it; use -Wno-analyzer-file-leak to disable it. This diagnostic warns for paths through the code in which a "<stdio.h>" "FILE *" stream object is leaked. See CWE-775: Missing Release of File Descriptor or Handle after Effective Lifetime ("https://cwe.mitre.org/data/definitions/775.html"). -Wno-analyzer-free-of-non-heap This warning requires -fanalyzer, which enables it; use -Wno-analyzer-free-of-non-heap to disable it. This diagnostic warns for paths through the code in which "free" is called on a non-heap pointer (e.g. an on-stack buffer, or a global). See CWE-590: Free of Memory not on the Heap ("https://cwe.mitre.org/data/definitions/590.html"). -Wno-analyzer-imprecise-fp-arithmetic This warning requires -fanalyzer, which enables it; use -Wno-analyzer-imprecise-fp-arithmetic to disable it. This diagnostic warns for paths through the code in which floating- point arithmetic is used in locations where precise computation is needed. This diagnostic only warns on use of floating-point operands inside the calculation of an allocation size at the moment. -Wno-analyzer-infinite-recursion This warning requires -fanalyzer, which enables it; use -Wno-analyzer-infinite-recursion to disable it. This diagnostics warns for paths through the code which appear to lead to infinite recursion. Specifically, when the analyzer "sees" a recursive call, it will compare the state of memory at the entry to the new frame with that at the entry to the previous frame of that function on the stack. The warning is issued if nothing in memory appears to be changing; any changes observed to parameters or globals are assumed to lead to termination of the recursion and thus suppress the warning. This diagnostic is likely to miss cases of infinite recursion that are convered to iteration by the optimizer before the analyzer "sees" them. Hence optimization should be disabled when attempting to trigger this diagnostic. Compare with -Winfinite-recursion, which provides a similar diagnostic, but is implemented in a different way. -Wno-analyzer-jump-through-null This warning requires -fanalyzer, which enables it; use -Wno-analyzer-jump-through-null to disable it. This diagnostic warns for paths through the code in which a "NULL" function pointer is called. -Wno-analyzer-malloc-leak This warning requires -fanalyzer, which enables it; use -Wno-analyzer-malloc-leak to disable it. This diagnostic warns for paths through the code in which a pointer allocated via an allocator is leaked: either "malloc", or a function marked with attribute "malloc". See CWE-401: Missing Release of Memory after Effective Lifetime ("https://cwe.mitre.org/data/definitions/401.html"). -Wno-analyzer-mismatching-deallocation This warning requires -fanalyzer, which enables it; use -Wno-analyzer-mismatching-deallocation to disable it. This diagnostic warns for paths through the code in which the wrong deallocation function is called on a pointer value, based on which function was used to allocate the pointer value. The diagnostic will warn about mismatches between "free", scalar "delete" and vector "delete[]", and those marked as allocator/deallocator pairs using attribute "malloc". See CWE-762: Mismatched Memory Management Routines ("https://cwe.mitre.org/data/definitions/762.html"). -Wno-analyzer-out-of-bounds This warning requires -fanalyzer, which enables it; use -Wno-analyzer-out-of-bounds to disable it. This diagnostic warns for paths through the code in which a buffer is definitely read or written out-of-bounds. The diagnostic applies for cases where the analyzer is able to determine a constant offset and for accesses past the end of a buffer, also a constant capacity. Further, the diagnostic does limited checking for accesses past the end when the offset as well as the capacity is symbolic. See CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer ("https://cwe.mitre.org/data/definitions/119.html"). -Wno-analyzer-possible-null-argument This warning requires -fanalyzer, which enables it; use -Wno-analyzer-possible-null-argument to disable it. This diagnostic warns for paths through the code in which a possibly-NULL value is passed to a function argument marked with "__attribute__((nonnull))" as requiring a non-NULL value. See CWE-690: Unchecked Return Value to NULL Pointer Dereference ("https://cwe.mitre.org/data/definitions/690.html"). -Wno-analyzer-possible-null-dereference This warning requires -fanalyzer, which enables it; use -Wno-analyzer-possible-null-dereference to disable it. This diagnostic warns for paths through the code in which a possibly-NULL value is dereferenced. See CWE-690: Unchecked Return Value to NULL Pointer Dereference ("https://cwe.mitre.org/data/definitions/690.html"). -Wno-analyzer-null-argument This warning requires -fanalyzer, which enables it; use -Wno-analyzer-null-argument to disable it. This diagnostic warns for paths through the code in which a value known to be NULL is passed to a function argument marked with "__attribute__((nonnull))" as requiring a non-NULL value. See CWE-476: NULL Pointer Dereference ("https://cwe.mitre.org/data/definitions/476.html"). -Wno-analyzer-null-dereference This warning requires -fanalyzer, which enables it; use -Wno-analyzer-null-dereference to disable it. This diagnostic warns for paths through the code in which a value known to be NULL is dereferenced. See CWE-476: NULL Pointer Dereference ("https://cwe.mitre.org/data/definitions/476.html"). -Wno-analyzer-putenv-of-auto-var This warning requires -fanalyzer, which enables it; use -Wno-analyzer-putenv-of-auto-var to disable it. This diagnostic warns for paths through the code in which a call to "putenv" is passed a pointer to an automatic variable or an on- stack buffer. See POS34-C. Do not call putenv() with a pointer to an automatic variable as the argument ("https://wiki.sei.cmu.edu/confluence/x/6NYxBQ"). -Wno-analyzer-shift-count-negative This warning requires -fanalyzer, which enables it; use -Wno-analyzer-shift-count-negative to disable it. This diagnostic warns for paths through the code in which a shift is attempted with a negative count. It is analogous to the -Wshift-count-negative diagnostic implemented in the C/C++ front ends, but is implemented based on analyzing interprocedural paths, rather than merely parsing the syntax tree. However, the analyzer does not prioritize detection of such paths, so false negatives are more likely relative to other warnings. -Wno-analyzer-shift-count-overflow This warning requires -fanalyzer, which enables it; use -Wno-analyzer-shift-count-overflow to disable it. This diagnostic warns for paths through the code in which a shift is attempted with a count greater than or equal to the precision of the operand's type. It is analogous to the -Wshift-count-overflow diagnostic implemented in the C/C++ front ends, but is implemented based on analyzing interprocedural paths, rather than merely parsing the syntax tree. However, the analyzer does not prioritize detection of such paths, so false negatives are more likely relative to other warnings. -Wno-analyzer-stale-setjmp-buffer This warning requires -fanalyzer, which enables it; use -Wno-analyzer-stale-setjmp-buffer to disable it. This diagnostic warns for paths through the code in which "longjmp" is called to rewind to a "jmp_buf" relating to a "setjmp" call in a function that has returned. When "setjmp" is called on a "jmp_buf" to record a rewind location, it records the stack frame. The stack frame becomes invalid when the function containing the "setjmp" call returns. Attempting to rewind to it via "longjmp" would reference a stack frame that no longer exists, and likely lead to a crash (or worse). -Wno-analyzer-tainted-allocation-size This warning requires both -fanalyzer and -fanalyzer-checker=taint to enable it; use -Wno-analyzer-tainted-allocation-size to disable it. This diagnostic warns for paths through the code in which a value that could be under an attacker's control is used as the size of an allocation without being sanitized, so that an attacker could inject an excessively large allocation and potentially cause a denial of service attack. See CWE-789: Memory Allocation with Excessive Size Value ("https://cwe.mitre.org/data/definitions/789.html"). -Wno-analyzer-tainted-assertion This warning requires both -fanalyzer and -fanalyzer-checker=taint to enable it; use -Wno-analyzer-tainted-assertion to disable it. This diagnostic warns for paths through the code in which a value that could be under an attacker's control is used as part of a condition without being first sanitized, and that condition guards a call to a function marked with attribute "noreturn" (such as the function "__builtin_unreachable"). Such functions typically indicate abnormal termination of the program, such as for assertion failure handlers. For example: assert (some_tainted_value < SOME_LIMIT); In such cases: * when assertion-checking is enabled: an attacker could trigger a denial of service by injecting an assertion failure * when assertion-checking is disabled, such as by defining "NDEBUG", an attacker could inject data that subverts the process, since it presumably violates a precondition that is being assumed by the code. Note that when assertion-checking is disabled, the assertions are typically removed by the preprocessor before the analyzer has a chance to "see" them, so this diagnostic can only generate warnings on builds in which assertion-checking is enabled. For the purpose of this warning, any function marked with attribute "noreturn" is considered as a possible assertion failure handler, including "__builtin_unreachable". Note that these functions are sometimes removed by the optimizer before the analyzer "sees" them. Hence optimization should be disabled when attempting to trigger this diagnostic. See CWE-617: Reachable Assertion ("https://cwe.mitre.org/data/definitions/617.html"). The warning can also report problematic constructions such as switch (some_tainted_value) { case 0: /* [...etc; various valid cases omitted...] */ break; default: __builtin_unreachable (); /* BUG: attacker can trigger this */ } despite the above not being an assertion failure, strictly speaking. -Wno-analyzer-tainted-array-index This warning requires both -fanalyzer and -fanalyzer-checker=taint to enable it; use -Wno-analyzer-tainted-array-index to disable it. This diagnostic warns for paths through the code in which a value that could be under an attacker's control is used as the index of an array access without being sanitized, so that an attacker could inject an out-of-bounds access. See CWE-129: Improper Validation of Array Index ("https://cwe.mitre.org/data/definitions/129.html"). -Wno-analyzer-tainted-divisor This warning requires both -fanalyzer and -fanalyzer-checker=taint to enable it; use -Wno-analyzer-tainted-divisor to disable it. This diagnostic warns for paths through the code in which a value that could be under an attacker's control is used as the divisor in a division or modulus operation without being sanitized, so that an attacker could inject a division-by-zero. See CWE-369: Divide By Zero ("https://cwe.mitre.org/data/definitions/369.html"). -Wno-analyzer-tainted-offset This warning requires both -fanalyzer and -fanalyzer-checker=taint to enable it; use -Wno-analyzer-tainted-offset to disable it. This diagnostic warns for paths through the code in which a value that could be under an attacker's control is used as a pointer offset without being sanitized, so that an attacker could inject an out-of-bounds access. See CWE-823: Use of Out-of-range Pointer Offset ("https://cwe.mitre.org/data/definitions/823.html"). -Wno-analyzer-tainted-size This warning requires both -fanalyzer and -fanalyzer-checker=taint to enable it; use -Wno-analyzer-tainted-size to disable it. This diagnostic warns for paths through the code in which a value that could be under an attacker's control is used as the size of an operation such as "memset" without being sanitized, so that an attacker could inject an out-of-bounds access. See CWE-129: Improper Validation of Array Index ("https://cwe.mitre.org/data/definitions/129.html"). -Wno-analyzer-unsafe-call-within-signal-handler This warning requires -fanalyzer, which enables it; use -Wno-analyzer-unsafe-call-within-signal-handler to disable it. This diagnostic warns for paths through the code in which a function known to be async-signal-unsafe (such as "fprintf") is called from a signal handler. See CWE-479: Signal Handler Use of a Non-reentrant Function ("https://cwe.mitre.org/data/definitions/479.html"). -Wno-analyzer-use-after-free This warning requires -fanalyzer, which enables it; use -Wno-analyzer-use-after-free to disable it. This diagnostic warns for paths through the code in which a pointer is used after a deallocator is called on it: either "free", or a deallocator referenced by attribute "malloc". See CWE-416: Use After Free ("https://cwe.mitre.org/data/definitions/416.html"). -Wno-analyzer-use-of-pointer-in-stale-stack-frame This warning requires -fanalyzer, which enables it; use -Wno-analyzer-use-of-pointer-in-stale-stack-frame to disable it. This diagnostic warns for paths through the code in which a pointer is dereferenced that points to a variable in a stale stack frame. -Wno-analyzer-va-arg-type-mismatch This warning requires -fanalyzer, which enables it; use -Wno-analyzer-va-arg-type-mismatch to disable it. This diagnostic warns for interprocedural paths through the code for which the analyzer detects an attempt to use "va_arg" to extract a value passed to a variadic call, but uses a type that does not match that of the expression passed to the call. See CWE-686: Function Call With Incorrect Argument Type ("https://cwe.mitre.org/data/definitions/686.html"). -Wno-analyzer-va-list-exhausted This warning requires -fanalyzer, which enables it; use -Wno-analyzer-va-list-exhausted to disable it. This diagnostic warns for interprocedural paths through the code for which the analyzer detects an attempt to use "va_arg" to access the next value passed to a variadic call, but all of the values in the "va_list" have already been consumed. See CWE-685: Function Call With Incorrect Number of Arguments ("https://cwe.mitre.org/data/definitions/685.html"). -Wno-analyzer-va-list-leak This warning requires -fanalyzer, which enables it; use -Wno-analyzer-va-list-leak to disable it. This diagnostic warns for interprocedural paths through the code for which the analyzer detects that "va_start" or "va_copy" has been called on a "va_list" without a corresponding call to "va_end". -Wno-analyzer-va-list-use-after-va-end This warning requires -fanalyzer, which enables it; use -Wno-analyzer-va-list-use-after-va-end to disable it. This diagnostic warns for interprocedural paths through the code for which the analyzer detects an attempt to use a "va_list" after "va_end" has been called on it. "va_list". -Wno-analyzer-write-to-const This warning requires -fanalyzer, which enables it; use -Wno-analyzer-write-to-const to disable it. This diagnostic warns for paths through the code in which the analyzer detects an attempt to write through a pointer to a "const" object. However, the analyzer does not prioritize detection of such paths, so false negatives are more likely relative to other warnings. -Wno-analyzer-write-to-string-literal This warning requires -fanalyzer, which enables it; use -Wno-analyzer-write-to-string-literal to disable it. This diagnostic warns for paths through the code in which the analyzer detects an attempt to write through a pointer to a string literal. However, the analyzer does not prioritize detection of such paths, so false negatives are more likely relative to other warnings. -Wno-analyzer-use-of-uninitialized-value This warning requires -fanalyzer, which enables it; use -Wno-analyzer-use-of-uninitialized-value to disable it. This diagnostic warns for paths through the code in which an uninitialized value is used. See CWE-457: Use of Uninitialized Variable ("https://cwe.mitre.org/data/definitions/457.html"). The analyzer has hardcoded knowledge about the behavior of the following memory-management functions: *<"alloca"> *<The built-in functions "__builtin_alloc",> "__builtin_alloc_with_align", @item "__builtin_calloc", "__builtin_free", "__builtin_malloc", "__builtin_memcpy", "__builtin_memcpy_chk", "__builtin_memset", "__builtin_memset_chk", "__builtin_realloc", "__builtin_stack_restore", and "__builtin_stack_save" *<"calloc"> *<"free"> *<"malloc"> *<"memset"> *<"operator delete"> *<"operator delete []"> *<"operator new"> *<"operator new []"> *<"realloc"> *<"strdup"> *<"strndup"> of the following functions for working with file descriptors: *<"open"> *<"close"> *<"creat"> *<"dup", "dup2" and "dup3"> *<"isatty"> *<"pipe", and "pipe2"> *<"read"> *<"write"> *<"socket", "bind", "listen", "accept", and "connect"> of the following functions for working with "<stdio.h>" streams: *<The built-in functions "__builtin_fprintf",> "__builtin_fprintf_unlocked", "__builtin_fputc", "__builtin_fputc_unlocked", "__builtin_fputs", "__builtin_fputs_unlocked", "__builtin_fwrite", "__builtin_fwrite_unlocked", "__builtin_printf", "__builtin_printf_unlocked", "__builtin_putc", "__builtin_putchar", "__builtin_putchar_unlocked", "__builtin_putc_unlocked", "__builtin_puts", "__builtin_puts_unlocked", "__builtin_vfprintf", and "__builtin_vprintf" *<"fopen"> *<"fclose"> *<"ferror"> *<"fgets"> *<"fgets_unlocked"> *<"fileno"> *<"fread"> *<"getc"> *<"getchar"> *<"fprintf"> *<"printf"> *<"fwrite"> and of the following functions: *<The built-in functions "__builtin_expect",> "__builtin_expect_with_probability", "__builtin_strchr", "__builtin_strcpy", "__builtin_strcpy_chk", "__builtin_strlen", "__builtin_va_copy", and "__builtin_va_start" *<The GNU extensions "error" and "error_at_line"> *<"getpass"> *<"longjmp"> *<"putenv"> *<"setjmp"> *<"siglongjmp"> *<"signal"> *<"sigsetjmp"> *<"strchr"> *<"strlen"> In addition, various functions with an "__analyzer_" prefix have special meaning to the analyzer, described in the GCC Internals manual. Pertinent parameters for controlling the exploration are: *<--param analyzer-bb-explosion-factor=value> *<--param analyzer-max-enodes-per-program-point=value> *<--param analyzer-max-recursion-depth=value> *<--param analyzer-min-snodes-for-call-summary=value> The following options control the analyzer. -fanalyzer-call-summaries Simplify interprocedural analysis by computing the effect of certain calls, rather than exploring all paths through the function from callsite to each possible return. If enabled, call summaries are only used for functions with more than one call site, and that are sufficiently complicated (as per --param analyzer-min-snodes-for-call-summary=value). -fanalyzer-checker=name Restrict the analyzer to run just the named checker, and enable it. Some checkers are disabled by default (even with -fanalyzer), such as the "taint" checker that implements -Wanalyzer-tainted-array-index, and this option is required to enable them. Note: currently, -fanalyzer-checker=taint disables the following warnings from -fanalyzer: -Wanalyzer-deref-before-check -Wanalyzer-double-fclose -Wanalyzer-double-free -Wanalyzer-exposure-through-output-file -Wanalyzer-fd-access-mode-mismatch -Wanalyzer-fd-double-close -Wanalyzer-fd-leak -Wanalyzer-fd-use-after-close -Wanalyzer-fd-use-without-check -Wanalyzer-file-leak -Wanalyzer-free-of-non-heap -Wanalyzer-malloc-leak -Wanalyzer-mismatching-deallocation -Wanalyzer-null-argument -Wanalyzer-null-dereference -Wanalyzer-possible-null-argument -Wanalyzer-possible-null-dereference -Wanalyzer-unsafe-call-within-signal-handler -Wanalyzer-use-after-free -Wanalyzer-va-list-leak -Wanalyzer-va-list-use-after-va-end -fno-analyzer-feasibility This option is intended for analyzer developers. By default the analyzer verifies that there is a feasible control flow path for each diagnostic it emits: that the conditions that hold are not mutually exclusive. Diagnostics for which no feasible path can be found are rejected. This filtering can be suppressed with -fno-analyzer-feasibility, for debugging issues in this code. -fanalyzer-fine-grained This option is intended for analyzer developers. Internally the analyzer builds an "exploded graph" that combines control flow graphs with data flow information. By default, an edge in this graph can contain the effects of a run of multiple statements within a basic block. With -fanalyzer-fine-grained, each statement gets its own edge. -fanalyzer-show-duplicate-count This option is intended for analyzer developers: if multiple diagnostics have been detected as being duplicates of each other, it emits a note when reporting the best diagnostic, giving the number of additional diagnostics that were suppressed by the deduplication logic. -fno-analyzer-state-merge This option is intended for analyzer developers. By default the analyzer attempts to simplify analysis by merging sufficiently similar states at each program point as it builds its "exploded graph". With -fno-analyzer-state-merge this merging can be suppressed, for debugging state-handling issues. -fno-analyzer-state-purge This option is intended for analyzer developers. By default the analyzer attempts to simplify analysis by purging aspects of state at a program point that appear to no longer be relevant e.g. the values of locals that aren't accessed later in the function and which aren't relevant to leak analysis. With -fno-analyzer-state-purge this purging of state can be suppressed, for debugging state-handling issues. -fno-analyzer-suppress-followups This option is intended for analyzer developers. By default the analyzer will stop exploring an execution path after encountering certain diagnostics, in order to avoid potentially issuing a cascade of follow-up diagnostics. The diagnostics that terminate analysis along a path are: *<-Wanalyzer-null-argument> *<-Wanalyzer-null-dereference> *<-Wanalyzer-use-after-free> *<-Wanalyzer-use-of-pointer-in-stale-stack-frame> *<-Wanalyzer-use-of-uninitialized-value> With -fno-analyzer-suppress-followups the analyzer will continue to explore such paths even after such diagnostics, which may be helpful for debugging issues in the analyzer, or for microbenchmarks for detecting undefined behavior. -fanalyzer-transitivity This option enables transitivity of constraints within the analyzer. -fno-analyzer-undo-inlining This option is intended for analyzer developers. -fanalyzer runs relatively late compared to other code analysis tools, and some optimizations have already been applied to the code. In particular function inlining may have occurred, leading to the interprocedural execution paths emitted by the analyzer containing function frames that don't correspond to those in the original source code. By default the analyzer attempts to reconstruct the original function frames, and to emit events showing the inlined calls. With -fno-analyzer-undo-inlining this attempt to reconstruct the original frame information can be be disabled, which may be of help when debugging issues in the analyzer. -fanalyzer-verbose-edges This option is intended for analyzer developers. It enables more verbose, lower-level detail in the descriptions of control flow within diagnostic paths. -fanalyzer-verbose-state-changes This option is intended for analyzer developers. It enables more verbose, lower-level detail in the descriptions of events relating to state machines within diagnostic paths. -fanalyzer-verbosity=level This option controls the complexity of the control flow paths that are emitted for analyzer diagnostics. The level can be one of: 0 At this level, interprocedural call and return events are displayed, along with the most pertinent state-change events relating to a diagnostic. For example, for a double-"free" diagnostic, both calls to "free" will be shown. 1 As per the previous level, but also show events for the entry to each function. 2 As per the previous level, but also show events relating to control flow that are significant to triggering the issue (e.g. "true path taken" at a conditional). This level is the default. 3 As per the previous level, but show all control flow events, not just significant ones. 4 This level is intended for analyzer developers; it adds various other events intended for debugging the analyzer. -fdump-analyzer Dump internal details about what the analyzer is doing to file.analyzer.txt. -fdump-analyzer-stderr overrides this option. -fdump-analyzer-stderr Dump internal details about what the analyzer is doing to stderr. This option overrides -fdump-analyzer. -fdump-analyzer-callgraph Dump a representation of the call graph suitable for viewing with GraphViz to file.callgraph.dot. -fdump-analyzer-exploded-graph Dump a representation of the "exploded graph" suitable for viewing with GraphViz to file.eg.dot. Nodes are color-coded based on state-machine states to emphasize state changes. -fdump-analyzer-exploded-nodes Emit diagnostics showing where nodes in the "exploded graph" are in relation to the program source. -fdump-analyzer-exploded-nodes-2 Dump a textual representation of the "exploded graph" to file.eg.txt. -fdump-analyzer-exploded-nodes-3 Dump a textual representation of the "exploded graph" to one dump file per node, to file.eg-id.txt. This is typically a large number of dump files. -fdump-analyzer-exploded-paths Dump a textual representation of the "exploded path" for each diagnostic to file.idx.kind.epath.txt. -fdump-analyzer-feasibility Dump internal details about the analyzer's search for feasible paths. The details are written in a form suitable for viewing with GraphViz to filenames of the form file.*.fg.dot, file.*.tg.dot, and file.*.fpath.txt. -fdump-analyzer-json Dump a compressed JSON representation of analyzer internals to file.analyzer.json.gz. The precise format is subject to change. -fdump-analyzer-state-purge As per -fdump-analyzer-supergraph, dump a representation of the "supergraph" suitable for viewing with GraphViz, but annotate the graph with information on what state will be purged at each node. The graph is written to file.state-purge.dot. -fdump-analyzer-supergraph Dump representations of the "supergraph" suitable for viewing with GraphViz to file.supergraph.dot and to file.supergraph-eg.dot. These show all of the control flow graphs in the program, with interprocedural edges for calls and returns. The second dump contains annotations showing nodes in the "exploded graph" and diagnostics associated with them. -fdump-analyzer-untracked Emit custom warnings with internal details intended for analyzer developers. Options for Debugging Your Program To tell GCC to emit extra information for use by a debugger, in almost all cases you need only to add -g to your other options. Some debug formats can co-exist (like DWARF with CTF) when each of them is enabled explicitly by adding the respective command line option to your other options. GCC allows you to use -g with -O. The shortcuts taken by optimized code may occasionally be surprising: some variables you declared may not exist at all; flow of control may briefly move where you did not expect it; some statements may not be executed because they compute constant results or their values are already at hand; some statements may execute in different places because they have been moved out of loops. Nevertheless it is possible to debug optimized output. This makes it reasonable to use the optimizer for programs that might have bugs. If you are not using some other optimization option, consider using -Og with -g. With no -O option at all, some compiler passes that collect information useful for debugging do not run at all, so that -Og may result in a better debugging experience. -g Produce debugging information in the operating system's native format (stabs, COFF, XCOFF, or DWARF). GDB can work with this debugging information. On most systems that use stabs format, -g enables use of extra debugging information that only GDB can use; this extra information makes debugging work better in GDB but probably makes other debuggers crash or refuse to read the program. If you want to control for certain whether to generate the extra information, use -gvms (see below). -ggdb Produce debugging information for use by GDB. This means to use the most expressive format available (DWARF, stabs, or the native format if neither of those are supported), including GDB extensions if at all possible. -gdwarf -gdwarf-version Produce debugging information in DWARF format (if that is supported). The value of version may be either 2, 3, 4 or 5; the default version for most targets is 5 (with the exception of VxWorks, TPF and Darwin/Mac OS X, which default to version 2, and AIX, which defaults to version 4). Note that with DWARF Version 2, some ports require and always use some non-conflicting DWARF 3 extensions in the unwind tables. Version 4 may require GDB 7.0 and -fvar-tracking-assignments for maximum benefit. Version 5 requires GDB 8.0 or higher. GCC no longer supports DWARF Version 1, which is substantially different than Version 2 and later. For historical reasons, some other DWARF-related options such as -fno-dwarf2-cfi-asm) retain a reference to DWARF Version 2 in their names, but apply to all currently-supported versions of DWARF. -gbtf Request BTF debug information. BTF is the default debugging format for the eBPF target. On other targets, like x86, BTF debug information can be generated along with DWARF debug information when both of the debug formats are enabled explicitly via their respective command line options. -gctf -gctflevel Request CTF debug information and use level to specify how much CTF debug information should be produced. If -gctf is specified without a value for level, the default level of CTF debug information is 2. CTF debug information can be generated along with DWARF debug information when both of the debug formats are enabled explicitly via their respective command line options. Level 0 produces no CTF debug information at all. Thus, -gctf0 negates -gctf. Level 1 produces CTF information for tracebacks only. This includes callsite information, but does not include type information. Level 2 produces type information for entities (functions, data objects etc.) at file-scope or global-scope only. -gvms Produce debugging information in Alpha/VMS debug format (if that is supported). This is the format used by DEBUG on Alpha/VMS systems. -glevel -ggdblevel -gvmslevel Request debugging information and also use level to specify how much information. The default level is 2. Level 0 produces no debug information at all. Thus, -g0 negates -g. Level 1 produces minimal information, enough for making backtraces in parts of the program that you don't plan to debug. This includes descriptions of functions and external variables, and line number tables, but no information about local variables. Level 3 includes extra information, such as all the macro definitions present in the program. Some debuggers support macro expansion when you use -g3. If you use multiple -g options, with or without level numbers, the last such option is the one that is effective. -gdwarf does not accept a concatenated debug level, to avoid confusion with -gdwarf-level. Instead use an additional -glevel option to change the debug level for DWARF. -fno-eliminate-unused-debug-symbols By default, no debug information is produced for symbols that are not actually used. Use this option if you want debug information for all symbols. -femit-class-debug-always Instead of emitting debugging information for a C++ class in only one object file, emit it in all object files using the class. This option should be used only with debuggers that are unable to handle the way GCC normally emits debugging information for classes because using this option increases the size of debugging information by as much as a factor of two. -fno-merge-debug-strings Direct the linker to not merge together strings in the debugging information that are identical in different object files. Merging is not supported by all assemblers or linkers. Merging decreases the size of the debug information in the output file at the cost of increasing link processing time. Merging is enabled by default. -fdebug-prefix-map=old=new When compiling files residing in directory old, record debugging information describing them as if the files resided in directory new instead. This can be used to replace a build-time path with an install-time path in the debug info. It can also be used to change an absolute path to a relative path by using . for new. This can give more reproducible builds, which are location independent, but may require an extra command to tell GDB where to find the source files. See also -ffile-prefix-map and -fcanon-prefix-map. -fvar-tracking Run variable tracking pass. It computes where variables are stored at each position in code. Better debugging information is then generated (if the debugging information format supports this information). It is enabled by default when compiling with optimization (-Os, -O, -O2, ...), debugging information (-g) and the debug info format supports it. -fvar-tracking-assignments Annotate assignments to user variables early in the compilation and attempt to carry the annotations over throughout the compilation all the way to the end, in an attempt to improve debug information while optimizing. Use of -gdwarf-4 is recommended along with it. It can be enabled even if var-tracking is disabled, in which case annotations are created and maintained, but discarded at the end. By default, this flag is enabled together with -fvar-tracking, except when selective scheduling is enabled. -gsplit-dwarf If DWARF debugging information is enabled, separate as much debugging information as possible into a separate output file with the extension .dwo. This option allows the build system to avoid linking files with debug information. To be useful, this option requires a debugger capable of reading .dwo files. -gdwarf32 -gdwarf64 If DWARF debugging information is enabled, the -gdwarf32 selects the 32-bit DWARF format and the -gdwarf64 selects the 64-bit DWARF format. The default is target specific, on most targets it is -gdwarf32 though. The 32-bit DWARF format is smaller, but can't support more than 2GiB of debug information in any of the DWARF debug information sections. The 64-bit DWARF format allows larger debug information and might not be well supported by all consumers yet. -gdescribe-dies Add description attributes to some DWARF DIEs that have no name attribute, such as artificial variables, external references and call site parameter DIEs. -gpubnames Generate DWARF ".debug_pubnames" and ".debug_pubtypes" sections. -ggnu-pubnames Generate ".debug_pubnames" and ".debug_pubtypes" sections in a format suitable for conversion into a GDB index. This option is only useful with a linker that can produce GDB index version 7. -fdebug-types-section When using DWARF Version 4 or higher, type DIEs can be put into their own ".debug_types" section instead of making them part of the ".debug_info" section. It is more efficient to put them in a separate comdat section since the linker can then remove duplicates. But not all DWARF consumers support ".debug_types" sections yet and on some objects ".debug_types" produces larger instead of smaller debugging information. -grecord-gcc-switches -gno-record-gcc-switches This switch causes the command-line options used to invoke the compiler that may affect code generation to be appended to the DW_AT_producer attribute in DWARF debugging information. The options are concatenated with spaces separating them from each other and from the compiler version. It is enabled by default. See also -frecord-gcc-switches for another way of storing compiler options into the object file. -gstrict-dwarf Disallow using extensions of later DWARF standard version than selected with -gdwarf-version. On most targets using non- conflicting DWARF extensions from later standard versions is allowed. -gno-strict-dwarf Allow using extensions of later DWARF standard version than selected with -gdwarf-version. -gas-loc-support Inform the compiler that the assembler supports ".loc" directives. It may then use them for the assembler to generate DWARF2+ line number tables. This is generally desirable, because assembler-generated line- number tables are a lot more compact than those the compiler can generate itself. This option will be enabled by default if, at GCC configure time, the assembler was found to support such directives. -gno-as-loc-support Force GCC to generate DWARF2+ line number tables internally, if DWARF2+ line number tables are to be generated. -gas-locview-support Inform the compiler that the assembler supports "view" assignment and reset assertion checking in ".loc" directives. This option will be enabled by default if, at GCC configure time, the assembler was found to support them. -gno-as-locview-support Force GCC to assign view numbers internally, if -gvariable-location-views are explicitly requested. -gcolumn-info -gno-column-info Emit location column information into DWARF debugging information, rather than just file and line. This option is enabled by default. -gstatement-frontiers -gno-statement-frontiers This option causes GCC to create markers in the internal representation at the beginning of statements, and to keep them roughly in place throughout compilation, using them to guide the output of "is_stmt" markers in the line number table. This is enabled by default when compiling with optimization (-Os, -O1, -O2, ...), and outputting DWARF 2 debug information at the normal level. -gvariable-location-views -gvariable-location-views=incompat5 -gno-variable-location-views Augment variable location lists with progressive view numbers implied from the line number table. This enables debug information consumers to inspect state at certain points of the program, even if no instructions associated with the corresponding source locations are present at that point. If the assembler lacks support for view numbers in line number tables, this will cause the compiler to emit the line number table, which generally makes them somewhat less compact. The augmented line number tables and location lists are fully backward-compatible, so they can be consumed by debug information consumers that are not aware of these augmentations, but they won't derive any benefit from them either. This is enabled by default when outputting DWARF 2 debug information at the normal level, as long as there is assembler support, -fvar-tracking-assignments is enabled and -gstrict-dwarf is not. When assembler support is not available, this may still be enabled, but it will force GCC to output internal line number tables, and if -ginternal-reset-location-views is not enabled, that will most certainly lead to silently mismatching location views. There is a proposed representation for view numbers that is not backward compatible with the location list format introduced in DWARF 5, that can be enabled with -gvariable-location-views=incompat5. This option may be removed in the future, is only provided as a reference implementation of the proposed representation. Debug information consumers are not expected to support this extended format, and they would be rendered unable to decode location lists using it. -ginternal-reset-location-views -gno-internal-reset-location-views Attempt to determine location views that can be omitted from location view lists. This requires the compiler to have very accurate insn length estimates, which isn't always the case, and it may cause incorrect view lists to be generated silently when using an assembler that does not support location view lists. The GNU assembler will flag any such error as a "view number mismatch". This is only enabled on ports that define a reliable estimation function. -ginline-points -gno-inline-points Generate extended debug information for inlined functions. Location view tracking markers are inserted at inlined entry points, so that address and view numbers can be computed and output in debug information. This can be enabled independently of location views, in which case the view numbers won't be output, but it can only be enabled along with statement frontiers, and it is only enabled by default if location views are enabled. -gz[=type] Produce compressed debug sections in DWARF format, if that is supported. If type is not given, the default type depends on the capabilities of the assembler and linker used. type may be one of none (don't compress debug sections), or zlib (use zlib compression in ELF gABI format). If the linker doesn't support writing compressed debug sections, the option is rejected. Otherwise, if the assembler does not support them, -gz is silently ignored when producing object files. -femit-struct-debug-baseonly Emit debug information for struct-like types only when the base name of the compilation source file matches the base name of file in which the struct is defined. This option substantially reduces the size of debugging information, but at significant potential loss in type information to the debugger. See -femit-struct-debug-reduced for a less aggressive option. See -femit-struct-debug-detailed for more detailed control. This option works only with DWARF debug output. -femit-struct-debug-reduced Emit debug information for struct-like types only when the base name of the compilation source file matches the base name of file in which the type is defined, unless the struct is a template or defined in a system header. This option significantly reduces the size of debugging information, with some potential loss in type information to the debugger. See -femit-struct-debug-baseonly for a more aggressive option. See -femit-struct-debug-detailed for more detailed control. This option works only with DWARF debug output. -femit-struct-debug-detailed[=spec-list] Specify the struct-like types for which the compiler generates debug information. The intent is to reduce duplicate struct debug information between different object files within the same program. This option is a detailed version of -femit-struct-debug-reduced and -femit-struct-debug-baseonly, which serves for most needs. A specification has the syntax[dir:|ind:][ord:|gen:](any|sys|base|none) The optional first word limits the specification to structs that are used directly (dir:) or used indirectly (ind:). A struct type is used directly when it is the type of a variable, member. Indirect uses arise through pointers to structs. That is, when use of an incomplete struct is valid, the use is indirect. An example is struct one direct; struct two * indirect;. The optional second word limits the specification to ordinary structs (ord:) or generic structs (gen:). Generic structs are a bit complicated to explain. For C++, these are non-explicit specializations of template classes, or non-template classes within the above. Other programming languages have generics, but -femit-struct-debug-detailed does not yet implement them. The third word specifies the source files for those structs for which the compiler should emit debug information. The values none and any have the normal meaning. The value base means that the base of name of the file in which the type declaration appears must match the base of the name of the main compilation file. In practice, this means that when compiling foo.c, debug information is generated for types declared in that file and foo.h, but not other header files. The value sys means those types satisfying base or declared in system or compiler headers. You may need to experiment to determine the best settings for your application. The default is -femit-struct-debug-detailed=all. This option works only with DWARF debug output. -fno-dwarf2-cfi-asm Emit DWARF unwind info as compiler generated ".eh_frame" section instead of using GAS ".cfi_*" directives. -fno-eliminate-unused-debug-types Normally, when producing DWARF output, GCC avoids producing debug symbol output for types that are nowhere used in the source file being compiled. Sometimes it is useful to have GCC emit debugging information for all types declared in a compilation unit, regardless of whether or not they are actually used in that compilation unit, for example if, in the debugger, you want to cast a value to a type that is not actually used in your program (but is declared). More often, however, this results in a significant amount of wasted space. Options That Control Optimization These options control various sorts of optimizations. Without any optimization option, the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the function and get exactly the results you expect from the source code. Turning on optimization flags makes the compiler attempt to improve the performance and/or code size at the expense of compilation time and possibly the ability to debug the program. The compiler performs optimization based on the knowledge it has of the program. Compiling multiple files at once to a single output file mode allows the compiler to use information gained from all of the files when compiling each of them. Not all optimizations are controlled directly by a flag. Only optimizations that have a flag are listed in this section. Most optimizations are completely disabled at -O0 or if an -O level is not set on the command line, even if individual optimization flags are specified. Similarly, -Og suppresses many optimization passes. Depending on the target and how GCC was configured, a slightly different set of optimizations may be enabled at each -O level than those listed here. You can invoke GCC with -Q --help=optimizers to find out the exact set of optimizations that are enabled at each level. -O -O1 Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function. With -O, the compiler tries to reduce code size and execution time, without performing any optimizations that take a great deal of compilation time. -O turns on the following optimization flags: -fauto-inc-dec -fbranch-count-reg -fcombine-stack-adjustments -fcompare-elim -fcprop-registers -fdce -fdefer-pop -fdelayed-branch -fdse -fforward-propagate -fguess-branch-probability -fif-conversion -fif-conversion2 -finline-functions-called-once -fipa-modref -fipa-profile -fipa-pure-const -fipa-reference -fipa-reference-addressable -fmerge-constants -fmove-loop-invariants -fmove-loop-stores -fomit-frame-pointer -freorder-blocks -fshrink-wrap -fshrink-wrap-separate -fsplit-wide-types -fssa-backprop -fssa-phiopt -ftree-bit-ccp -ftree-ccp -ftree-ch -ftree-coalesce-vars -ftree-copy-prop -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre -ftree-phiprop -ftree-pta -ftree-scev-cprop -ftree-sink -ftree-slsr -ftree-sra -ftree-ter -funit-at-a-time -O2 Optimize even more. GCC performs nearly all supported optimizations that do not involve a space-speed tradeoff. As compared to -O, this option increases both compilation time and the performance of the generated code. -O2 turns on all optimization flags specified by -O1. It also turns on the following optimization flags: -falign-functions -falign-jumps -falign-labels -falign-loops -fcaller-saves -fcode-hoisting -fcrossjumping -fcse-follow-jumps -fcse-skip-blocks -fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively -fexpensive-optimizations -ffinite-loops -fgcse -fgcse-lm -fhoist-adjacent-loads -finline-functions -finline-small-functions -findirect-inlining -fipa-bit-cp -fipa-cp -fipa-icf -fipa-ra -fipa-sra -fipa-vrp -fisolate-erroneous-paths-dereference -flra-remat -foptimize-sibling-calls -foptimize-strlen -fpartial-inlining -fpeephole2 -freorder-blocks-algorithm=stc -freorder-blocks-and-partition -freorder-functions -frerun-cse-after-loop -fschedule-insns -fschedule-insns2 -fsched-interblock -fsched-spec -fstore-merging -fstrict-aliasing -fthread-jumps -ftree-builtin-call-dce -ftree-loop-vectorize -ftree-pre -ftree-slp-vectorize -ftree-switch-conversion -ftree-tail-merge -ftree-vrp -fvect-cost-model=very-cheap Please note the warning under -fgcse about invoking -O2 on programs that use computed gotos. -O3 Optimize yet more. -O3 turns on all optimizations specified by -O2 and also turns on the following optimization flags: -fgcse-after-reload -fipa-cp-clone -floop-interchange -floop-unroll-and-jam -fpeel-loops -fpredictive-commoning -fsplit-loops -fsplit-paths -ftree-loop-distribution -ftree-partial-pre -funswitch-loops -fvect-cost-model=dynamic -fversion-loops-for-strides -O0 Reduce compilation time and make debugging produce the expected results. This is the default. -Os Optimize for size. -Os enables all -O2 optimizations except those that often increase code size: -falign-functions -falign-jumps -falign-labels -falign-loops -fprefetch-loop-arrays -freorder-blocks-algorithm=stc It also enables -finline-functions, causes the compiler to tune for code size rather than execution speed, and performs further optimizations designed to reduce code size. -Ofast Disregard strict standards compliance. -Ofast enables all -O3 optimizations. It also enables optimizations that are not valid for all standard-compliant programs. It turns on -ffast-math, -fallow-store-data-races and the Fortran-specific -fstack-arrays, unless -fmax-stack-var-size is specified, and -fno-protect-parens. It turns off -fsemantic-interposition. -Og Optimize debugging experience. -Og should be the optimization level of choice for the standard edit-compile-debug cycle, offering a reasonable level of optimization while maintaining fast compilation and a good debugging experience. It is a better choice than -O0 for producing debuggable code because some compiler passes that collect debug information are disabled at -O0. Like -O0, -Og completely disables a number of optimization passes so that individual options controlling them have no effect. Otherwise -Og enables all -O1 optimization flags except for those that may interfere with debugging: -fbranch-count-reg -fdelayed-branch -fdse -fif-conversion -fif-conversion2 -finline-functions-called-once -fmove-loop-invariants -fmove-loop-stores -fssa-phiopt -ftree-bit-ccp -ftree-dse -ftree-pta -ftree-sra -Oz Optimize aggressively for size rather than speed. This may increase the number of instructions executed if those instructions require fewer bytes to encode. -Oz behaves similarly to -Os including enabling most -O2 optimizations. If you use multiple -O options, with or without level numbers, the last such option is the one that is effective. Options of the form -fflag specify machine-independent flags. Most flags have both positive and negative forms; the negative form of -ffoo is -fno-foo. In the table below, only one of the forms is listed---the one you typically use. You can figure out the other form by either removing no- or adding it. The following options control specific optimizations. They are either activated by -O options or are related to ones that are. You can use the following flags in the rare cases when "fine-tuning" of optimizations to be performed is desired. -fno-defer-pop For machines that must pop arguments after a function call, always pop the arguments as soon as each function returns. At levels -O1 and higher, -fdefer-pop is the default; this allows the compiler to let arguments accumulate on the stack for several function calls and pop them all at once. -fforward-propagate Perform a forward propagation pass on RTL. The pass tries to combine two instructions and checks if the result can be simplified. If loop unrolling is active, two passes are performed and the second is scheduled after loop unrolling. This option is enabled by default at optimization levels -O1, -O2, -O3, -Os. -ffp-contract=style -ffp-contract=off disables floating-point expression contraction. -ffp-contract=fast enables floating-point expression contraction such as forming of fused multiply-add operations if the target has native support for them. -ffp-contract=on enables floating-point expression contraction if allowed by the language standard. This is currently not implemented and treated equal to -ffp-contract=off. The default is -ffp-contract=fast. -fomit-frame-pointer Omit the frame pointer in functions that don't need one. This avoids the instructions to save, set up and restore the frame pointer; on many targets it also makes an extra register available. On some targets this flag has no effect because the standard calling sequence always uses a frame pointer, so it cannot be omitted. Note that -fno-omit-frame-pointer doesn't guarantee the frame pointer is used in all functions. Several targets always omit the frame pointer in leaf functions. Enabled by default at -O1 and higher. -foptimize-sibling-calls Optimize sibling and tail recursive calls. Enabled at levels -O2, -O3, -Os. -foptimize-strlen Optimize various standard C string functions (e.g. "strlen", "strchr" or "strcpy") and their "_FORTIFY_SOURCE" counterparts into faster alternatives. Enabled at levels -O2, -O3. -fno-inline Do not expand any functions inline apart from those marked with the "always_inline" attribute. This is the default when not optimizing. Single functions can be exempted from inlining by marking them with the "noinline" attribute. -finline-small-functions Integrate functions into their callers when their body is smaller than expected function call code (so overall size of program gets smaller). The compiler heuristically decides which functions are simple enough to be worth integrating in this way. This inlining applies to all functions, even those not declared inline. Enabled at levels -O2, -O3, -Os. -findirect-inlining Inline also indirect calls that are discovered to be known at compile time thanks to previous inlining. This option has any effect only when inlining itself is turned on by the -finline-functions or -finline-small-functions options. Enabled at levels -O2, -O3, -Os. -finline-functions Consider all functions for inlining, even if they are not declared inline. The compiler heuristically decides which functions are worth integrating in this way. If all calls to a given function are integrated, and the function is declared "static", then the function is normally not output as assembler code in its own right. Enabled at levels -O2, -O3, -Os. Also enabled by -fprofile-use and -fauto-profile. -finline-functions-called-once Consider all "static" functions called once for inlining into their caller even if they are not marked "inline". If a call to a given function is integrated, then the function is not output as assembler code in its own right. Enabled at levels -O1, -O2, -O3 and -Os, but not -Og. -fearly-inlining Inline functions marked by "always_inline" and functions whose body seems smaller than the function call overhead early before doing -fprofile-generate instrumentation and real inlining pass. Doing so makes profiling significantly cheaper and usually inlining faster on programs having large chains of nested wrapper functions. Enabled by default. -fipa-sra Perform interprocedural scalar replacement of aggregates, removal of unused parameters and replacement of parameters passed by reference by parameters passed by value. Enabled at levels -O2, -O3 and -Os. -finline-limit=n By default, GCC limits the size of functions that can be inlined. This flag allows coarse control of this limit. n is the size of functions that can be inlined in number of pseudo instructions. Inlining is actually controlled by a number of parameters, which may be specified individually by using --param name=value. The -finline-limit=n option sets some of these parameters as follows: max-inline-insns-single is set to n/2. max-inline-insns-auto is set to n/2. See below for a documentation of the individual parameters controlling inlining and for the defaults of these parameters. Note: there may be no value to -finline-limit that results in default behavior. Note: pseudo instruction represents, in this particular context, an abstract measurement of function's size. In no way does it represent a count of assembly instructions and as such its exact meaning might change from one release to an another. -fno-keep-inline-dllexport This is a more fine-grained version of -fkeep-inline-functions, which applies only to functions that are declared using the "dllexport" attribute or declspec. -fkeep-inline-functions In C, emit "static" functions that are declared "inline" into the object file, even if the function has been inlined into all of its callers. This switch does not affect functions using the "extern inline" extension in GNU C90. In C++, emit any and all inline functions into the object file. -fkeep-static-functions Emit "static" functions into the object file, even if the function is never used. -fkeep-static-consts Emit variables declared "static const" when optimization isn't turned on, even if the variables aren't referenced. GCC enables this option by default. If you want to force the compiler to check if a variable is referenced, regardless of whether or not optimization is turned on, use the -fno-keep-static-consts option. -fmerge-constants Attempt to merge identical constants (string constants and floating-point constants) across compilation units. This option is the default for optimized compilation if the assembler and linker support it. Use -fno-merge-constants to inhibit this behavior. Enabled at levels -O1, -O2, -O3, -Os. -fmerge-all-constants Attempt to merge identical constants and identical variables. This option implies -fmerge-constants. In addition to -fmerge-constants this considers e.g. even constant initialized arrays or initialized constant variables with integral or floating- point types. Languages like C or C++ require each variable, including multiple instances of the same variable in recursive calls, to have distinct locations, so using this option results in non-conforming behavior. -fmodulo-sched Perform swing modulo scheduling immediately before the first scheduling pass. This pass looks at innermost loops and reorders their instructions by overlapping different iterations. -fmodulo-sched-allow-regmoves Perform more aggressive SMS-based modulo scheduling with register moves allowed. By setting this flag certain anti-dependences edges are deleted, which triggers the generation of reg-moves based on the life-range analysis. This option is effective only with -fmodulo-sched enabled. -fno-branch-count-reg Disable the optimization pass that scans for opportunities to use "decrement and branch" instructions on a count register instead of instruction sequences that decrement a register, compare it against zero, and then branch based upon the result. This option is only meaningful on architectures that support such instructions, which include x86, PowerPC, IA-64 and S/390. Note that the -fno-branch-count-reg option doesn't remove the decrement and branch instructions from the generated instruction stream introduced by other optimization passes. The default is -fbranch-count-reg at -O1 and higher, except for -Og. -fno-function-cse Do not put function addresses in registers; make each instruction that calls a constant function contain the function's address explicitly. This option results in less efficient code, but some strange hacks that alter the assembler output may be confused by the optimizations performed when this option is not used. The default is -ffunction-cse -fno-zero-initialized-in-bss If the target supports a BSS section, GCC by default puts variables that are initialized to zero into BSS. This can save space in the resulting code. This option turns off this behavior because some programs explicitly rely on variables going to the data section---e.g., so that the resulting executable can find the beginning of that section and/or make assumptions based on that. The default is -fzero-initialized-in-bss. -fthread-jumps Perform optimizations that check to see if a jump branches to a location where another comparison subsumed by the first is found. If so, the first branch is redirected to either the destination of the second branch or a point immediately following it, depending on whether the condition is known to be true or false. Enabled at levels -O1, -O2, -O3, -Os. -fsplit-wide-types When using a type that occupies multiple registers, such as "long long" on a 32-bit system, split the registers apart and allocate them independently. This normally generates better code for those types, but may make debugging more difficult. Enabled at levels -O1, -O2, -O3, -Os. -fsplit-wide-types-early Fully split wide types early, instead of very late. This option has no effect unless -fsplit-wide-types is turned on. This is the default on some targets. -fcse-follow-jumps In common subexpression elimination (CSE), scan through jump instructions when the target of the jump is not reached by any other path. For example, when CSE encounters an "if" statement with an "else" clause, CSE follows the jump when the condition tested is false. Enabled at levels -O2, -O3, -Os. -fcse-skip-blocks This is similar to -fcse-follow-jumps, but causes CSE to follow jumps that conditionally skip over blocks. When CSE encounters a simple "if" statement with no else clause, -fcse-skip-blocks causes CSE to follow the jump around the body of the "if". Enabled at levels -O2, -O3, -Os. -frerun-cse-after-loop Re-run common subexpression elimination after loop optimizations are performed. Enabled at levels -O2, -O3, -Os. -fgcse Perform a global common subexpression elimination pass. This pass also performs global constant and copy propagation. Note: When compiling a program using computed gotos, a GCC extension, you may get better run-time performance if you disable the global common subexpression elimination pass by adding -fno-gcse to the command line. Enabled at levels -O2, -O3, -Os. -fgcse-lm When -fgcse-lm is enabled, global common subexpression elimination attempts to move loads that are only killed by stores into themselves. This allows a loop containing a load/store sequence to be changed to a load outside the loop, and a copy/store within the loop. Enabled by default when -fgcse is enabled. -fgcse-sm When -fgcse-sm is enabled, a store motion pass is run after global common subexpression elimination. This pass attempts to move stores out of loops. When used in conjunction with -fgcse-lm, loops containing a load/store sequence can be changed to a load before the loop and a store after the loop. Not enabled at any optimization level. -fgcse-las When -fgcse-las is enabled, the global common subexpression elimination pass eliminates redundant loads that come after stores to the same memory location (both partial and full redundancies). Not enabled at any optimization level. -fgcse-after-reload When -fgcse-after-reload is enabled, a redundant load elimination pass is performed after reload. The purpose of this pass is to clean up redundant spilling. Enabled by -O3, -fprofile-use and -fauto-profile. -faggressive-loop-optimizations This option tells the loop optimizer to use language constraints to derive bounds for the number of iterations of a loop. This assumes that loop code does not invoke undefined behavior by for example causing signed integer overflows or out-of-bound array accesses. The bounds for the number of iterations of a loop are used to guide loop unrolling and peeling and loop exit test optimizations. This option is enabled by default. -funconstrained-commons This option tells the compiler that variables declared in common blocks (e.g. Fortran) may later be overridden with longer trailing arrays. This prevents certain optimizations that depend on knowing the array bounds. -fcrossjumping Perform cross-jumping transformation. This transformation unifies equivalent code and saves code size. The resulting code may or may not perform better than without cross-jumping. Enabled at levels -O2, -O3, -Os. -fauto-inc-dec Combine increments or decrements of addresses with memory accesses. This pass is always skipped on architectures that do not have instructions to support this. Enabled by default at -O1 and higher on architectures that support this. -fdce Perform dead code elimination (DCE) on RTL. Enabled by default at -O1 and higher. -fdse Perform dead store elimination (DSE) on RTL. Enabled by default at -O1 and higher. -fif-conversion Attempt to transform conditional jumps into branch-less equivalents. This includes use of conditional moves, min, max, set flags and abs instructions, and some tricks doable by standard arithmetics. The use of conditional execution on chips where it is available is controlled by -fif-conversion2. Enabled at levels -O1, -O2, -O3, -Os, but not with -Og. -fif-conversion2 Use conditional execution (where available) to transform conditional jumps into branch-less equivalents. Enabled at levels -O1, -O2, -O3, -Os, but not with -Og. -fdeclone-ctor-dtor The C++ ABI requires multiple entry points for constructors and destructors: one for a base subobject, one for a complete object, and one for a virtual destructor that calls operator delete afterwards. For a hierarchy with virtual bases, the base and complete variants are clones, which means two copies of the function. With this option, the base and complete variants are changed to be thunks that call a common implementation. Enabled by -Os. -fdelete-null-pointer-checks Assume that programs cannot safely dereference null pointers, and that no code or data element resides at address zero. This option enables simple constant folding optimizations at all optimization levels. In addition, other optimization passes in GCC use this flag to control global dataflow analyses that eliminate useless checks for null pointers; these assume that a memory access to address zero always results in a trap, so that if a pointer is checked after it has already been dereferenced, it cannot be null. Note however that in some environments this assumption is not true. Use -fno-delete-null-pointer-checks to disable this optimization for programs that depend on that behavior. This option is enabled by default on most targets. On Nios II ELF, it defaults to off. On AVR and MSP430, this option is completely disabled. Passes that use the dataflow information are enabled independently at different optimization levels. -fdevirtualize Attempt to convert calls to virtual functions to direct calls. This is done both within a procedure and interprocedurally as part of indirect inlining (-findirect-inlining) and interprocedural constant propagation (-fipa-cp). Enabled at levels -O2, -O3, -Os. -fdevirtualize-speculatively Attempt to convert calls to virtual functions to speculative direct calls. Based on the analysis of the type inheritance graph, determine for a given call the set of likely targets. If the set is small, preferably of size 1, change the call into a conditional deciding between direct and indirect calls. The speculative calls enable more optimizations, such as inlining. When they seem useless after further optimization, they are converted back into original form. -fdevirtualize-at-ltrans Stream extra information needed for aggressive devirtualization when running the link-time optimizer in local transformation mode. This option enables more devirtualization but significantly increases the size of streamed data. For this reason it is disabled by default. -fexpensive-optimizations Perform a number of minor optimizations that are relatively expensive. Enabled at levels -O2, -O3, -Os. -free Attempt to remove redundant extension instructions. This is especially helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit registers after writing to their lower 32-bit half. Enabled for Alpha, AArch64 and x86 at levels -O2, -O3, -Os. -fno-lifetime-dse In C++ the value of an object is only affected by changes within its lifetime: when the constructor begins, the object has an indeterminate value, and any changes during the lifetime of the object are dead when the object is destroyed. Normally dead store elimination will take advantage of this; if your code relies on the value of the object storage persisting beyond the lifetime of the object, you can use this flag to disable this optimization. To preserve stores before the constructor starts (e.g. because your operator new clears the object storage) but still treat the object as dead after the destructor, you can use -flifetime-dse=1. The default behavior can be explicitly selected with -flifetime-dse=2. -flifetime-dse=0 is equivalent to -fno-lifetime-dse. -flive-range-shrinkage Attempt to decrease register pressure through register live range shrinkage. This is helpful for fast processors with small or moderate size register sets. -fira-algorithm=algorithm Use the specified coloring algorithm for the integrated register allocator. The algorithm argument can be priority, which specifies Chow's priority coloring, or CB, which specifies Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented for all architectures, but for those targets that do support it, it is the default because it generates better code. -fira-region=region Use specified regions for the integrated register allocator. The region argument should be one of the following: all Use all loops as register allocation regions. This can give the best results for machines with a small and/or irregular register set. mixed Use all loops except for loops with small register pressure as the regions. This value usually gives the best results in most cases and for most architectures, and is enabled by default when compiling with optimization for speed (-O, -O2, ...). one Use all functions as a single region. This typically results in the smallest code size, and is enabled by default for -Os or -O0. -fira-hoist-pressure Use IRA to evaluate register pressure in the code hoisting pass for decisions to hoist expressions. This option usually results in smaller code, but it can slow the compiler down. This option is enabled at level -Os for all targets. -fira-loop-pressure Use IRA to evaluate register pressure in loops for decisions to move loop invariants. This option usually results in generation of faster and smaller code on machines with large register files (>= 32 registers), but it can slow the compiler down. This option is enabled at level -O3 for some targets. -fno-ira-share-save-slots Disable sharing of stack slots used for saving call-used hard registers living through a call. Each hard register gets a separate stack slot, and as a result function stack frames are larger. -fno-ira-share-spill-slots Disable sharing of stack slots allocated for pseudo-registers. Each pseudo-register that does not get a hard register gets a separate stack slot, and as a result function stack frames are larger. -flra-remat Enable CFG-sensitive rematerialization in LRA. Instead of loading values of spilled pseudos, LRA tries to rematerialize (recalculate) values if it is profitable. Enabled at levels -O2, -O3, -Os. -fdelayed-branch If supported for the target machine, attempt to reorder instructions to exploit instruction slots available after delayed branch instructions. Enabled at levels -O1, -O2, -O3, -Os, but not at -Og. -fschedule-insns If supported for the target machine, attempt to reorder instructions to eliminate execution stalls due to required data being unavailable. This helps machines that have slow floating point or memory load instructions by allowing other instructions to be issued until the result of the load or floating-point instruction is required. Enabled at levels -O2, -O3. -fschedule-insns2 Similar to -fschedule-insns, but requests an additional pass of instruction scheduling after register allocation has been done. This is especially useful on machines with a relatively small number of registers and where memory load instructions take more than one cycle. Enabled at levels -O2, -O3, -Os. -fno-sched-interblock Disable instruction scheduling across basic blocks, which is normally enabled when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher. -fno-sched-spec Disable speculative motion of non-load instructions, which is normally enabled when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher. -fsched-pressure Enable register pressure sensitive insn scheduling before register allocation. This only makes sense when scheduling before register allocation is enabled, i.e. with -fschedule-insns or at -O2 or higher. Usage of this option can improve the generated code and decrease its size by preventing register pressure increase above the number of available hard registers and subsequent spills in register allocation. -fsched-spec-load Allow speculative motion of some load instructions. This only makes sense when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher. -fsched-spec-load-dangerous Allow speculative motion of more load instructions. This only makes sense when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher. -fsched-stalled-insns -fsched-stalled-insns=n Define how many insns (if any) can be moved prematurely from the queue of stalled insns into the ready list during the second scheduling pass. -fno-sched-stalled-insns means that no insns are moved prematurely, -fsched-stalled-insns=0 means there is no limit on how many queued insns can be moved prematurely. -fsched-stalled-insns without a value is equivalent to -fsched-stalled-insns=1. -fsched-stalled-insns-dep -fsched-stalled-insns-dep=n Define how many insn groups (cycles) are examined for a dependency on a stalled insn that is a candidate for premature removal from the queue of stalled insns. This has an effect only during the second scheduling pass, and only if -fsched-stalled-insns is used. -fno-sched-stalled-insns-dep is equivalent to -fsched-stalled-insns-dep=0. -fsched-stalled-insns-dep without a value is equivalent to -fsched-stalled-insns-dep=1. -fsched2-use-superblocks When scheduling after register allocation, use superblock scheduling. This allows motion across basic block boundaries, resulting in faster schedules. This option is experimental, as not all machine descriptions used by GCC model the CPU closely enough to avoid unreliable results from the algorithm. This only makes sense when scheduling after register allocation, i.e. with -fschedule-insns2 or at -O2 or higher. -fsched-group-heuristic Enable the group heuristic in the scheduler. This heuristic favors the instruction that belongs to a schedule group. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. -fsched-critical-path-heuristic Enable the critical-path heuristic in the scheduler. This heuristic favors instructions on the critical path. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. -fsched-spec-insn-heuristic Enable the speculative instruction heuristic in the scheduler. This heuristic favors speculative instructions with greater dependency weakness. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. -fsched-rank-heuristic Enable the rank heuristic in the scheduler. This heuristic favors the instruction belonging to a basic block with greater size or frequency. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. -fsched-last-insn-heuristic Enable the last-instruction heuristic in the scheduler. This heuristic favors the instruction that is less dependent on the last instruction scheduled. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. -fsched-dep-count-heuristic Enable the dependent-count heuristic in the scheduler. This heuristic favors the instruction that has more instructions depending on it. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. -freschedule-modulo-scheduled-loops Modulo scheduling is performed before traditional scheduling. If a loop is modulo scheduled, later scheduling passes may change its schedule. Use this option to control that behavior. -fselective-scheduling Schedule instructions using selective scheduling algorithm. Selective scheduling runs instead of the first scheduler pass. -fselective-scheduling2 Schedule instructions using selective scheduling algorithm. Selective scheduling runs instead of the second scheduler pass. -fsel-sched-pipelining Enable software pipelining of innermost loops during selective scheduling. This option has no effect unless one of -fselective-scheduling or -fselective-scheduling2 is turned on. -fsel-sched-pipelining-outer-loops When pipelining loops during selective scheduling, also pipeline outer loops. This option has no effect unless -fsel-sched-pipelining is turned on. -fsemantic-interposition Some object formats, like ELF, allow interposing of symbols by the dynamic linker. This means that for symbols exported from the DSO, the compiler cannot perform interprocedural propagation, inlining and other optimizations in anticipation that the function or variable in question may change. While this feature is useful, for example, to rewrite memory allocation functions by a debugging implementation, it is expensive in the terms of code quality. With -fno-semantic-interposition the compiler assumes that if interposition happens for functions the overwriting function will have precisely the same semantics (and side effects). Similarly if interposition happens for variables, the constructor of the variable will be the same. The flag has no effect for functions explicitly declared inline (where it is never allowed for interposition to change semantics) and for symbols explicitly declared weak. -fshrink-wrap Emit function prologues only before parts of the function that need it, rather than at the top of the function. This flag is enabled by default at -O and higher. -fshrink-wrap-separate Shrink-wrap separate parts of the prologue and epilogue separately, so that those parts are only executed when needed. This option is on by default, but has no effect unless -fshrink-wrap is also turned on and the target supports this. -fcaller-saves Enable allocation of values to registers that are clobbered by function calls, by emitting extra instructions to save and restore the registers around such calls. Such allocation is done only when it seems to result in better code. This option is always enabled by default on certain machines, usually those which have no call-preserved registers to use instead. Enabled at levels -O2, -O3, -Os. -fcombine-stack-adjustments Tracks stack adjustments (pushes and pops) and stack memory references and then tries to find ways to combine them. Enabled by default at -O1 and higher. -fipa-ra Use caller save registers for allocation if those registers are not used by any called function. In that case it is not necessary to save and restore them around calls. This is only possible if called functions are part of same compilation unit as current function and they are compiled before it. Enabled at levels -O2, -O3, -Os, however the option is disabled if generated code will be instrumented for profiling (-p, or -pg) or if callee's register usage cannot be known exactly (this happens on targets that do not expose prologues and epilogues in RTL). -fconserve-stack Attempt to minimize stack usage. The compiler attempts to use less stack space, even if that makes the program slower. This option implies setting the large-stack-frame parameter to 100 and the large-stack-frame-growth parameter to 400. -ftree-reassoc Perform reassociation on trees. This flag is enabled by default at -O1 and higher. -fcode-hoisting Perform code hoisting. Code hoisting tries to move the evaluation of expressions executed on all paths to the function exit as early as possible. This is especially useful as a code size optimization, but it often helps for code speed as well. This flag is enabled by default at -O2 and higher. -ftree-pre Perform partial redundancy elimination (PRE) on trees. This flag is enabled by default at -O2 and -O3. -ftree-partial-pre Make partial redundancy elimination (PRE) more aggressive. This flag is enabled by default at -O3. -ftree-forwprop Perform forward propagation on trees. This flag is enabled by default at -O1 and higher. -ftree-fre Perform full redundancy elimination (FRE) on trees. The difference between FRE and PRE is that FRE only considers expressions that are computed on all paths leading to the redundant computation. This analysis is faster than PRE, though it exposes fewer redundancies. This flag is enabled by default at -O1 and higher. -ftree-phiprop Perform hoisting of loads from conditional pointers on trees. This pass is enabled by default at -O1 and higher. -fhoist-adjacent-loads Speculatively hoist loads from both branches of an if-then-else if the loads are from adjacent locations in the same structure and the target architecture has a conditional move instruction. This flag is enabled by default at -O2 and higher. -ftree-copy-prop Perform copy propagation on trees. This pass eliminates unnecessary copy operations. This flag is enabled by default at -O1 and higher. -fipa-pure-const Discover which functions are pure or constant. Enabled by default at -O1 and higher. -fipa-reference Discover which static variables do not escape the compilation unit. Enabled by default at -O1 and higher. -fipa-reference-addressable Discover read-only, write-only and non-addressable static variables. Enabled by default at -O1 and higher. -fipa-stack-alignment Reduce stack alignment on call sites if possible. Enabled by default. -fipa-pta Perform interprocedural pointer analysis and interprocedural modification and reference analysis. This option can cause excessive memory and compile-time usage on large compilation units. It is not enabled by default at any optimization level. -fipa-profile Perform interprocedural profile propagation. The functions called only from cold functions are marked as cold. Also functions executed once (such as "cold", "noreturn", static constructors or destructors) are identified. Cold functions and loop less parts of functions executed once are then optimized for size. Enabled by default at -O1 and higher. -fipa-modref Perform interprocedural mod/ref analysis. This optimization analyzes the side effects of functions (memory locations that are modified or referenced) and enables better optimization across the function call boundary. This flag is enabled by default at -O1 and higher. -fipa-cp Perform interprocedural constant propagation. This optimization analyzes the program to determine when values passed to functions are constants and then optimizes accordingly. This optimization can substantially increase performance if the application has constants passed to functions. This flag is enabled by default at -O2, -Os and -O3. It is also enabled by -fprofile-use and -fauto-profile. -fipa-cp-clone Perform function cloning to make interprocedural constant propagation stronger. When enabled, interprocedural constant propagation performs function cloning when externally visible function can be called with constant arguments. Because this optimization can create multiple copies of functions, it may significantly increase code size (see --param ipa-cp-unit-growth=value). This flag is enabled by default at -O3. It is also enabled by -fprofile-use and -fauto-profile. -fipa-bit-cp When enabled, perform interprocedural bitwise constant propagation. This flag is enabled by default at -O2 and by -fprofile-use and -fauto-profile. It requires that -fipa-cp is enabled. -fipa-vrp When enabled, perform interprocedural propagation of value ranges. This flag is enabled by default at -O2. It requires that -fipa-cp is enabled. -fipa-icf Perform Identical Code Folding for functions and read-only variables. The optimization reduces code size and may disturb unwind stacks by replacing a function by equivalent one with a different name. The optimization works more effectively with link- time optimization enabled. Although the behavior is similar to the Gold Linker's ICF optimization, GCC ICF works on different levels and thus the optimizations are not same - there are equivalences that are found only by GCC and equivalences found only by Gold. This flag is enabled by default at -O2 and -Os. -flive-patching=level Control GCC's optimizations to produce output suitable for live- patching. If the compiler's optimization uses a function's body or information extracted from its body to optimize/change another function, the latter is called an impacted function of the former. If a function is patched, its impacted functions should be patched too. The impacted functions are determined by the compiler's interprocedural optimizations. For example, a caller is impacted when inlining a function into its caller, cloning a function and changing its caller to call this new clone, or extracting a function's pureness/constness information to optimize its direct or indirect callers, etc. Usually, the more IPA optimizations enabled, the larger the number of impacted functions for each function. In order to control the number of impacted functions and more easily compute the list of impacted function, IPA optimizations can be partially enabled at two different levels. The level argument should be one of the following: inline-clone Only enable inlining and cloning optimizations, which includes inlining, cloning, interprocedural scalar replacement of aggregates and partial inlining. As a result, when patching a function, all its callers and its clones' callers are impacted, therefore need to be patched as well. -flive-patching=inline-clone disables the following optimization flags: -fwhole-program -fipa-pta -fipa-reference -fipa-ra -fipa-icf -fipa-icf-functions -fipa-icf-variables -fipa-bit-cp -fipa-vrp -fipa-pure-const -fipa-reference-addressable -fipa-stack-alignment -fipa-modref inline-only-static Only enable inlining of static functions. As a result, when patching a static function, all its callers are impacted and so need to be patched as well. In addition to all the flags that -flive-patching=inline-clone disables, -flive-patching=inline-only-static disables the following additional optimization flags: -fipa-cp-clone -fipa-sra -fpartial-inlining -fipa-cp When -flive-patching is specified without any value, the default value is inline-clone. This flag is disabled by default. Note that -flive-patching is not supported with link-time optimization (-flto). -fisolate-erroneous-paths-dereference Detect paths that trigger erroneous or undefined behavior due to dereferencing a null pointer. Isolate those paths from the main control flow and turn the statement with erroneous or undefined behavior into a trap. This flag is enabled by default at -O2 and higher and depends on -fdelete-null-pointer-checks also being enabled. -fisolate-erroneous-paths-attribute Detect paths that trigger erroneous or undefined behavior due to a null value being used in a way forbidden by a "returns_nonnull" or "nonnull" attribute. Isolate those paths from the main control flow and turn the statement with erroneous or undefined behavior into a trap. This is not currently enabled, but may be enabled by -O2 in the future. -ftree-sink Perform forward store motion on trees. This flag is enabled by default at -O1 and higher. -ftree-bit-ccp Perform sparse conditional bit constant propagation on trees and propagate pointer alignment information. This pass only operates on local scalar variables and is enabled by default at -O1 and higher, except for -Og. It requires that -ftree-ccp is enabled. -ftree-ccp Perform sparse conditional constant propagation (CCP) on trees. This pass only operates on local scalar variables and is enabled by default at -O1 and higher. -fssa-backprop Propagate information about uses of a value up the definition chain in order to simplify the definitions. For example, this pass strips sign operations if the sign of a value never matters. The flag is enabled by default at -O1 and higher. -fssa-phiopt Perform pattern matching on SSA PHI nodes to optimize conditional code. This pass is enabled by default at -O1 and higher, except for -Og. -ftree-switch-conversion Perform conversion of simple initializations in a switch to initializations from a scalar array. This flag is enabled by default at -O2 and higher. -ftree-tail-merge Look for identical code sequences. When found, replace one with a jump to the other. This optimization is known as tail merging or cross jumping. This flag is enabled by default at -O2 and higher. The compilation time in this pass can be limited using max-tail- merge-comparisons parameter and max-tail-merge-iterations parameter. -ftree-dce Perform dead code elimination (DCE) on trees. This flag is enabled by default at -O1 and higher. -ftree-builtin-call-dce Perform conditional dead code elimination (DCE) for calls to built- in functions that may set "errno" but are otherwise free of side effects. This flag is enabled by default at -O2 and higher if -Os is not also specified. -ffinite-loops Assume that a loop with an exit will eventually take the exit and not loop indefinitely. This allows the compiler to remove loops that otherwise have no side-effects, not considering eventual endless looping as such. This option is enabled by default at -O2 for C++ with -std=c++11 or higher. -ftree-dominator-opts Perform a variety of simple scalar cleanups (constant/copy propagation, redundancy elimination, range propagation and expression simplification) based on a dominator tree traversal. This also performs jump threading (to reduce jumps to jumps). This flag is enabled by default at -O1 and higher. -ftree-dse Perform dead store elimination (DSE) on trees. A dead store is a store into a memory location that is later overwritten by another store without any intervening loads. In this case the earlier store can be deleted. This flag is enabled by default at -O1 and higher. -ftree-ch Perform loop header copying on trees. This is beneficial since it increases effectiveness of code motion optimizations. It also saves one jump. This flag is enabled by default at -O1 and higher. It is not enabled for -Os, since it usually increases code size. -ftree-loop-optimize Perform loop optimizations on trees. This flag is enabled by default at -O1 and higher. -ftree-loop-linear -floop-strip-mine -floop-block Perform loop nest optimizations. Same as -floop-nest-optimize. To use this code transformation, GCC has to be configured with --with-isl to enable the Graphite loop transformation infrastructure. -fgraphite-identity Enable the identity transformation for graphite. For every SCoP we generate the polyhedral representation and transform it back to gimple. Using -fgraphite-identity we can check the costs or benefits of the GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations are also performed by the code generator isl, like index splitting and dead code elimination in loops. -floop-nest-optimize Enable the isl based loop nest optimizer. This is a generic loop nest optimizer based on the Pluto optimization algorithms. It calculates a loop structure optimized for data-locality and parallelism. This option is experimental. -floop-parallelize-all Use the Graphite data dependence analysis to identify loops that can be parallelized. Parallelize all the loops that can be analyzed to not contain loop carried dependences without checking that it is profitable to parallelize the loops. -ftree-coalesce-vars While transforming the program out of the SSA representation, attempt to reduce copying by coalescing versions of different user- defined variables, instead of just compiler temporaries. This may severely limit the ability to debug an optimized program compiled with -fno-var-tracking-assignments. In the negated form, this flag prevents SSA coalescing of user variables. This option is enabled by default if optimization is enabled, and it does very little otherwise. -ftree-loop-if-convert Attempt to transform conditional jumps in the innermost loops to branch-less equivalents. The intent is to remove control-flow from the innermost loops in order to improve the ability of the vectorization pass to handle these loops. This is enabled by default if vectorization is enabled. -ftree-loop-distribution Perform loop distribution. This flag can improve cache performance on big loop bodies and allow further loop optimizations, like parallelization or vectorization, to take place. For example, the loop DO I = 1, N A(I) = B(I) + C D(I) = E(I) * F ENDDO is transformed to DO I = 1, N A(I) = B(I) + C ENDDO DO I = 1, N D(I) = E(I) * F ENDDO This flag is enabled by default at -O3. It is also enabled by -fprofile-use and -fauto-profile. -ftree-loop-distribute-patterns Perform loop distribution of patterns that can be code generated with calls to a library. This flag is enabled by default at -O2 and higher, and by -fprofile-use and -fauto-profile. This pass distributes the initialization loops and generates a call to memset zero. For example, the loop DO I = 1, N A(I) = 0 B(I) = A(I) + I ENDDO is transformed to DO I = 1, N A(I) = 0 ENDDO DO I = 1, N B(I) = A(I) + I ENDDO and the initialization loop is transformed into a call to memset zero. This flag is enabled by default at -O3. It is also enabled by -fprofile-use and -fauto-profile. -floop-interchange Perform loop interchange outside of graphite. This flag can improve cache performance on loop nest and allow further loop optimizations, like vectorization, to take place. For example, the loop for (int i = 0; i < N; i++) for (int j = 0; j < N; j++) for (int k = 0; k < N; k++) c[i][j] = c[i][j] + a[i][k]*b[k][j]; is transformed to for (int i = 0; i < N; i++) for (int k = 0; k < N; k++) for (int j = 0; j < N; j++) c[i][j] = c[i][j] + a[i][k]*b[k][j]; This flag is enabled by default at -O3. It is also enabled by -fprofile-use and -fauto-profile. -floop-unroll-and-jam Apply unroll and jam transformations on feasible loops. In a loop nest this unrolls the outer loop by some factor and fuses the resulting multiple inner loops. This flag is enabled by default at -O3. It is also enabled by -fprofile-use and -fauto-profile. -ftree-loop-im Perform loop invariant motion on trees. This pass moves only invariants that are hard to handle at RTL level (function calls, operations that expand to nontrivial sequences of insns). With -funswitch-loops it also moves operands of conditions that are invariant out of the loop, so that we can use just trivial invariantness analysis in loop unswitching. The pass also includes store motion. -ftree-loop-ivcanon Create a canonical counter for number of iterations in loops for which determining number of iterations requires complicated analysis. Later optimizations then may determine the number easily. Useful especially in connection with unrolling. -ftree-scev-cprop Perform final value replacement. If a variable is modified in a loop in such a way that its value when exiting the loop can be determined using only its initial value and the number of loop iterations, replace uses of the final value by such a computation, provided it is sufficiently cheap. This reduces data dependencies and may allow further simplifications. Enabled by default at -O1 and higher. -fivopts Perform induction variable optimizations (strength reduction, induction variable merging and induction variable elimination) on trees. -ftree-parallelize-loops=n Parallelize loops, i.e., split their iteration space to run in n threads. This is only possible for loops whose iterations are independent and can be arbitrarily reordered. The optimization is only profitable on multiprocessor machines, for loops that are CPU- intensive, rather than constrained e.g. by memory bandwidth. This option implies -pthread, and thus is only supported on targets that have support for -pthread. -ftree-pta Perform function-local points-to analysis on trees. This flag is enabled by default at -O1 and higher, except for -Og. -ftree-sra Perform scalar replacement of aggregates. This pass replaces structure references with scalars to prevent committing structures to memory too early. This flag is enabled by default at -O1 and higher, except for -Og. -fstore-merging Perform merging of narrow stores to consecutive memory addresses. This pass merges contiguous stores of immediate values narrower than a word into fewer wider stores to reduce the number of instructions. This is enabled by default at -O2 and higher as well as -Os. -ftree-ter Perform temporary expression replacement during the SSA->normal phase. Single use/single def temporaries are replaced at their use location with their defining expression. This results in non- GIMPLE code, but gives the expanders much more complex trees to work on resulting in better RTL generation. This is enabled by default at -O1 and higher. -ftree-slsr Perform straight-line strength reduction on trees. This recognizes related expressions involving multiplications and replaces them by less expensive calculations when possible. This is enabled by default at -O1 and higher. -ftree-vectorize Perform vectorization on trees. This flag enables -ftree-loop-vectorize and -ftree-slp-vectorize if not explicitly specified. -ftree-loop-vectorize Perform loop vectorization on trees. This flag is enabled by default at -O2 and by -ftree-vectorize, -fprofile-use, and -fauto-profile. -ftree-slp-vectorize Perform basic block vectorization on trees. This flag is enabled by default at -O2 and by -ftree-vectorize, -fprofile-use, and -fauto-profile. -ftrivial-auto-var-init=choice Initialize automatic variables with either a pattern or with zeroes to increase the security and predictability of a program by preventing uninitialized memory disclosure and use. GCC still considers an automatic variable that doesn't have an explicit initializer as uninitialized, -Wuninitialized and -Wanalyzer-use-of-uninitialized-value will still report warning messages on such automatic variables and the compiler will perform optimization as if the variable were uninitialized. With this option, GCC will also initialize any padding of automatic variables that have structure or union types to zeroes. However, the current implementation cannot initialize automatic variables that are declared between the controlling expression and the first case of a "switch" statement. Using -Wtrivial-auto-var-init to report all such cases. The three values of choice are: * uninitialized doesn't initialize any automatic variables. This is C and C++'s default. * pattern Initialize automatic variables with values which will likely transform logic bugs into crashes down the line, are easily recognized in a crash dump and without being values that programmers can rely on for useful program semantics. The current value is byte-repeatable pattern with byte "0xFE". The values used for pattern initialization might be changed in the future. * zero Initialize automatic variables with zeroes. The default is uninitialized. You can control this behavior for a specific variable by using the variable attribute "uninitialized". -fvect-cost-model=model Alter the cost model used for vectorization. The model argument should be one of unlimited, dynamic, cheap or very-cheap. With the unlimited model the vectorized code-path is assumed to be profitable while with the dynamic model a runtime check guards the vectorized code-path to enable it only for iteration counts that will likely execute faster than when executing the original scalar loop. The cheap model disables vectorization of loops where doing so would be cost prohibitive for example due to required runtime checks for data dependence or alignment but otherwise is equal to the dynamic model. The very-cheap model only allows vectorization if the vector code would entirely replace the scalar code that is being vectorized. For example, if each iteration of a vectorized loop would only be able to handle exactly four iterations of the scalar loop, the very-cheap model would only allow vectorization if the scalar iteration count is known to be a multiple of four. The default cost model depends on other optimization flags and is either dynamic or cheap. -fsimd-cost-model=model Alter the cost model used for vectorization of loops marked with the OpenMP simd directive. The model argument should be one of unlimited, dynamic, cheap. All values of model have the same meaning as described in -fvect-cost-model and by default a cost model defined with -fvect-cost-model is used. -ftree-vrp Perform Value Range Propagation on trees. This is similar to the constant propagation pass, but instead of values, ranges of values are propagated. This allows the optimizers to remove unnecessary range checks like array bound checks and null pointer checks. This is enabled by default at -O2 and higher. Null pointer check elimination is only done if -fdelete-null-pointer-checks is enabled. -fsplit-paths Split paths leading to loop backedges. This can improve dead code elimination and common subexpression elimination. This is enabled by default at -O3 and above. -fsplit-ivs-in-unroller Enables expression of values of induction variables in later iterations of the unrolled loop using the value in the first iteration. This breaks long dependency chains, thus improving efficiency of the scheduling passes. A combination of -fweb and CSE is often sufficient to obtain the same effect. However, that is not reliable in cases where the loop body is more complicated than a single basic block. It also does not work at all on some architectures due to restrictions in the CSE pass. This optimization is enabled by default. -fvariable-expansion-in-unroller With this option, the compiler creates multiple copies of some local variables when unrolling a loop, which can result in superior code. This optimization is enabled by default for PowerPC targets, but disabled by default otherwise. -fpartial-inlining Inline parts of functions. This option has any effect only when inlining itself is turned on by the -finline-functions or -finline-small-functions options. Enabled at levels -O2, -O3, -Os. -fpredictive-commoning Perform predictive commoning optimization, i.e., reusing computations (especially memory loads and stores) performed in previous iterations of loops. This option is enabled at level -O3. It is also enabled by -fprofile-use and -fauto-profile. -fprefetch-loop-arrays If supported by the target machine, generate instructions to prefetch memory to improve the performance of loops that access large arrays. This option may generate better or worse code; results are highly dependent on the structure of loops within the source code. Disabled at level -Os. -fno-printf-return-value Do not substitute constants for known return value of formatted output functions such as "sprintf", "snprintf", "vsprintf", and "vsnprintf" (but not "printf" of "fprintf"). This transformation allows GCC to optimize or even eliminate branches based on the known return value of these functions called with arguments that are either constant, or whose values are known to be in a range that makes determining the exact return value possible. For example, when -fprintf-return-value is in effect, both the branch and the body of the "if" statement (but not the call to "snprint") can be optimized away when "i" is a 32-bit or smaller integer because the return value is guaranteed to be at most 8. char buf[9]; if (snprintf (buf, "%08x", i) >= sizeof buf) ... The -fprintf-return-value option relies on other optimizations and yields best results with -O2 and above. It works in tandem with the -Wformat-overflow and -Wformat-truncation options. The -fprintf-return-value option is enabled by default. -fno-peephole -fno-peephole2 Disable any machine-specific peephole optimizations. The difference between -fno-peephole and -fno-peephole2 is in how they are implemented in the compiler; some targets use one, some use the other, a few use both. -fpeephole is enabled by default. -fpeephole2 enabled at levels -O2, -O3, -Os. -fno-guess-branch-probability Do not guess branch probabilities using heuristics. GCC uses heuristics to guess branch probabilities if they are not provided by profiling feedback (-fprofile-arcs). These heuristics are based on the control flow graph. If some branch probabilities are specified by "__builtin_expect", then the heuristics are used to guess branch probabilities for the rest of the control flow graph, taking the "__builtin_expect" info into account. The interactions between the heuristics and "__builtin_expect" can be complex, and in some cases, it may be useful to disable the heuristics so that the effects of "__builtin_expect" are easier to understand. It is also possible to specify expected probability of the expression with "__builtin_expect_with_probability" built-in function. The default is -fguess-branch-probability at levels -O, -O2, -O3, -Os. -freorder-blocks Reorder basic blocks in the compiled function in order to reduce number of taken branches and improve code locality. Enabled at levels -O1, -O2, -O3, -Os. -freorder-blocks-algorithm=algorithm Use the specified algorithm for basic block reordering. The algorithm argument can be simple, which does not increase code size (except sometimes due to secondary effects like alignment), or stc, the "software trace cache" algorithm, which tries to put all often executed code together, minimizing the number of branches executed by making extra copies of code. The default is simple at levels -O1, -Os, and stc at levels -O2, -O3. -freorder-blocks-and-partition In addition to reordering basic blocks in the compiled function, in order to reduce number of taken branches, partitions hot and cold basic blocks into separate sections of the assembly and .o files, to improve paging and cache locality performance. This optimization is automatically turned off in the presence of exception handling or unwind tables (on targets using setjump/longjump or target specific scheme), for linkonce sections, for functions with a user-defined section attribute and on any architecture that does not support named sections. When -fsplit-stack is used this option is not enabled by default (to avoid linker errors), but may be enabled explicitly (if using a working linker). Enabled for x86 at levels -O2, -O3, -Os. -freorder-functions Reorder functions in the object file in order to improve code locality. This is implemented by using special subsections ".text.hot" for most frequently executed functions and ".text.unlikely" for unlikely executed functions. Reordering is done by the linker so object file format must support named sections and linker must place them in a reasonable way. This option isn't effective unless you either provide profile feedback (see -fprofile-arcs for details) or manually annotate functions with "hot" or "cold" attributes. Enabled at levels -O2, -O3, -Os. -fstrict-aliasing Allow the compiler to assume the strictest aliasing rules applicable to the language being compiled. For C (and C++), this activates optimizations based on the type of expressions. In particular, an object of one type is assumed never to reside at the same address as an object of a different type, unless the types are almost the same. For example, an "unsigned int" can alias an "int", but not a "void*" or a "double". A character type may alias any other type. Pay special attention to code like this: union a_union { int i; double d; }; int f() { union a_union t; t.d = 3.0; return t.i; } The practice of reading from a different union member than the one most recently written to (called "type-punning") is common. Even with -fstrict-aliasing, type-punning is allowed, provided the memory is accessed through the union type. So, the code above works as expected. However, this code might not: int f() { union a_union t; int* ip; t.d = 3.0; ip = &t.i; return *ip; } Similarly, access by taking the address, casting the resulting pointer and dereferencing the result has undefined behavior, even if the cast uses a union type, e.g.: int f() { double d = 3.0; return ((union a_union *) &d)->i; } The -fstrict-aliasing option is enabled at levels -O2, -O3, -Os. -fipa-strict-aliasing Controls whether rules of -fstrict-aliasing are applied across function boundaries. Note that if multiple functions gets inlined into a single function the memory accesses are no longer considered to be crossing a function boundary. The -fipa-strict-aliasing option is enabled by default and is effective only in combination with -fstrict-aliasing. -falign-functions -falign-functions=n -falign-functions=n:m -falign-functions=n:m:n2 -falign-functions=n:m:n2:m2 Align the start of functions to the next power-of-two greater than or equal to n, skipping up to m-1 bytes. This ensures that at least the first m bytes of the function can be fetched by the CPU without crossing an n-byte alignment boundary. If m is not specified, it defaults to n. Examples: -falign-functions=32 aligns functions to the next 32-byte boundary, -falign-functions=24 aligns to the next 32-byte boundary only if this can be done by skipping 23 bytes or less, -falign-functions=32:7 aligns to the next 32-byte boundary only if this can be done by skipping 6 bytes or less. The second pair of n2:m2 values allows you to specify a secondary alignment: -falign-functions=64:7:32:3 aligns to the next 64-byte boundary if this can be done by skipping 6 bytes or less, otherwise aligns to the next 32-byte boundary if this can be done by skipping 2 bytes or less. If m2 is not specified, it defaults to n2. Some assemblers only support this flag when n is a power of two; in that case, it is rounded up. -fno-align-functions and -falign-functions=1 are equivalent and mean that functions are not aligned. If n is not specified or is zero, use a machine-dependent default. The maximum allowed n option value is 65536. Enabled at levels -O2, -O3. -flimit-function-alignment If this option is enabled, the compiler tries to avoid unnecessarily overaligning functions. It attempts to instruct the assembler to align by the amount specified by -falign-functions, but not to skip more bytes than the size of the function. -falign-labels -falign-labels=n -falign-labels=n:m -falign-labels=n:m:n2 -falign-labels=n:m:n2:m2 Align all branch targets to a power-of-two boundary. Parameters of this option are analogous to the -falign-functions option. -fno-align-labels and -falign-labels=1 are equivalent and mean that labels are not aligned. If -falign-loops or -falign-jumps are applicable and are greater than this value, then their values are used instead. If n is not specified or is zero, use a machine-dependent default which is very likely to be 1, meaning no alignment. The maximum allowed n option value is 65536. Enabled at levels -O2, -O3. -falign-loops -falign-loops=n -falign-loops=n:m -falign-loops=n:m:n2 -falign-loops=n:m:n2:m2 Align loops to a power-of-two boundary. If the loops are executed many times, this makes up for any execution of the dummy padding instructions. If -falign-labels is greater than this value, then its value is used instead. Parameters of this option are analogous to the -falign-functions option. -fno-align-loops and -falign-loops=1 are equivalent and mean that loops are not aligned. The maximum allowed n option value is 65536. If n is not specified or is zero, use a machine-dependent default. Enabled at levels -O2, -O3. -falign-jumps -falign-jumps=n -falign-jumps=n:m -falign-jumps=n:m:n2 -falign-jumps=n:m:n2:m2 Align branch targets to a power-of-two boundary, for branch targets where the targets can only be reached by jumping. In this case, no dummy operations need be executed. If -falign-labels is greater than this value, then its value is used instead. Parameters of this option are analogous to the -falign-functions option. -fno-align-jumps and -falign-jumps=1 are equivalent and mean that loops are not aligned. If n is not specified or is zero, use a machine-dependent default. The maximum allowed n option value is 65536. Enabled at levels -O2, -O3. -fno-allocation-dce Do not remove unused C++ allocations in dead code elimination. -fallow-store-data-races Allow the compiler to perform optimizations that may introduce new data races on stores, without proving that the variable cannot be concurrently accessed by other threads. Does not affect optimization of local data. It is safe to use this option if it is known that global data will not be accessed by multiple threads. Examples of optimizations enabled by -fallow-store-data-races include hoisting or if-conversions that may cause a value that was already in memory to be re-written with that same value. Such re- writing is safe in a single threaded context but may be unsafe in a multi-threaded context. Note that on some processors, if- conversions may be required in order to enable vectorization. Enabled at level -Ofast. -funit-at-a-time This option is left for compatibility reasons. -funit-at-a-time has no effect, while -fno-unit-at-a-time implies -fno-toplevel-reorder and -fno-section-anchors. Enabled by default. -fno-toplevel-reorder Do not reorder top-level functions, variables, and "asm" statements. Output them in the same order that they appear in the input file. When this option is used, unreferenced static variables are not removed. This option is intended to support existing code that relies on a particular ordering. For new code, it is better to use attributes when possible. -ftoplevel-reorder is the default at -O1 and higher, and also at -O0 if -fsection-anchors is explicitly requested. Additionally -fno-toplevel-reorder implies -fno-section-anchors. -funreachable-traps With this option, the compiler turns calls to "__builtin_unreachable" into traps, instead of using them for optimization. This also affects any such calls implicitly generated by the compiler. This option has the same effect as -fsanitize=unreachable -fsanitize-trap=unreachable, but does not affect the values of those options. If -fsanitize=unreachable is enabled, that option takes priority over this one. This option is enabled by default at -O0 and -Og. -fweb Constructs webs as commonly used for register allocation purposes and assign each web individual pseudo register. This allows the register allocation pass to operate on pseudos directly, but also strengthens several other optimization passes, such as CSE, loop optimizer and trivial dead code remover. It can, however, make debugging impossible, since variables no longer stay in a "home register". Enabled by default with -funroll-loops. -fwhole-program Assume that the current compilation unit represents the whole program being compiled. All public functions and variables with the exception of "main" and those merged by attribute "externally_visible" become static functions and in effect are optimized more aggressively by interprocedural optimizers. With -flto this option has a limited use. In most cases the precise list of symbols used or exported from the binary is known the resolution info passed to the link-time optimizer by the linker plugin. It is still useful if no linker plugin is used or during incremental link step when final code is produced (with -flto -flinker-output=nolto-rel). -flto[=n] This option runs the standard link-time optimizer. When invoked with source code, it generates GIMPLE (one of GCC's internal representations) and writes it to special ELF sections in the object file. When the object files are linked together, all the function bodies are read from these ELF sections and instantiated as if they had been part of the same translation unit. To use the link-time optimizer, -flto and optimization options should be specified at compile time and during the final link. It is recommended that you compile all the files participating in the same link with the same options and also specify those options at link time. For example: gcc -c -O2 -flto foo.c gcc -c -O2 -flto bar.c gcc -o myprog -flto -O2 foo.o bar.o The first two invocations to GCC save a bytecode representation of GIMPLE into special ELF sections inside foo.o and bar.o. The final invocation reads the GIMPLE bytecode from foo.o and bar.o, merges the two files into a single internal image, and compiles the result as usual. Since both foo.o and bar.o are merged into a single image, this causes all the interprocedural analyses and optimizations in GCC to work across the two files as if they were a single one. This means, for example, that the inliner is able to inline functions in bar.o into functions in foo.o and vice-versa. Another (simpler) way to enable link-time optimization is: gcc -o myprog -flto -O2 foo.c bar.c The above generates bytecode for foo.c and bar.c, merges them together into a single GIMPLE representation and optimizes them as usual to produce myprog. The important thing to keep in mind is that to enable link-time optimizations you need to use the GCC driver to perform the link step. GCC automatically performs link-time optimization if any of the objects involved were compiled with the -flto command-line option. You can always override the automatic decision to do link- time optimization by passing -fno-lto to the link command. To make whole program optimization effective, it is necessary to make certain whole program assumptions. The compiler needs to know what functions and variables can be accessed by libraries and runtime outside of the link-time optimized unit. When supported by the linker, the linker plugin (see -fuse-linker-plugin) passes information to the compiler about used and externally visible symbols. When the linker plugin is not available, -fwhole-program should be used to allow the compiler to make these assumptions, which leads to more aggressive optimization decisions. When a file is compiled with -flto without -fuse-linker-plugin, the generated object file is larger than a regular object file because it contains GIMPLE bytecodes and the usual final code (see -ffat-lto-objects). This means that object files with LTO information can be linked as normal object files; if -fno-lto is passed to the linker, no interprocedural optimizations are applied. Note that when -fno-fat-lto-objects is enabled the compile stage is faster but you cannot perform a regular, non-LTO link on them. When producing the final binary, GCC only applies link-time optimizations to those files that contain bytecode. Therefore, you can mix and match object files and libraries with GIMPLE bytecodes and final object code. GCC automatically selects which files to optimize in LTO mode and which files to link without further processing. Generally, options specified at link time override those specified at compile time, although in some cases GCC attempts to infer link- time options from the settings used to compile the input files. If you do not specify an optimization level option -O at link time, then GCC uses the highest optimization level used when compiling the object files. Note that it is generally ineffective to specify an optimization level option only at link time and not at compile time, for two reasons. First, compiling without optimization suppresses compiler passes that gather information needed for effective optimization at link time. Second, some early optimization passes can be performed only at compile time and not at link time. There are some code generation flags preserved by GCC when generating bytecodes, as they need to be used during the final link. Currently, the following options and their settings are taken from the first object file that explicitly specifies them: -fcommon, -fexceptions, -fnon-call-exceptions, -fgnu-tm and all the -m target flags. The following options -fPIC, -fpic, -fpie and -fPIE are combined based on the following scheme: B<-fPIC> + B<-fpic> = B<-fpic> B<-fPIC> + B<-fno-pic> = B<-fno-pic> B<-fpic/-fPIC> + (no option) = (no option) B<-fPIC> + B<-fPIE> = B<-fPIE> B<-fpic> + B<-fPIE> = B<-fpie> B<-fPIC/-fpic> + B<-fpie> = B<-fpie> Certain ABI-changing flags are required to match in all compilation units, and trying to override this at link time with a conflicting value is ignored. This includes options such as -freg-struct-return and -fpcc-struct-return. Other options such as -ffp-contract, -fno-strict-overflow, -fwrapv, -fno-trapv or -fno-strict-aliasing are passed through to the link stage and merged conservatively for conflicting translation units. Specifically -fno-strict-overflow, -fwrapv and -fno-trapv take precedence; and for example -ffp-contract=off takes precedence over -ffp-contract=fast. You can override them at link time. Diagnostic options such as -Wstringop-overflow are passed through to the link stage and their setting matches that of the compile- step at function granularity. Note that this matters only for diagnostics emitted during optimization. Note that code transforms such as inlining can lead to warnings being enabled or disabled for regions if code not consistent with the setting at compile time. When you need to pass options to the assembler via -Wa or -Xassembler make sure to either compile such translation units with -fno-lto or consistently use the same assembler options on all translation units. You can alternatively also specify assembler options at LTO link time. To enable debug info generation you need to supply -g at compile time. If any of the input files at link time were built with debug info generation enabled the link will enable debug info generation as well. Any elaborate debug info settings like the dwarf level -gdwarf-5 need to be explicitly repeated at the linker command line and mixing different settings in different translation units is discouraged. If LTO encounters objects with C linkage declared with incompatible types in separate translation units to be linked together (undefined behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be issued. The behavior is still undefined at run time. Similar diagnostics may be raised for other languages. Another feature of LTO is that it is possible to apply interprocedural optimizations on files written in different languages: gcc -c -flto foo.c g++ -c -flto bar.cc gfortran -c -flto baz.f90 g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran Notice that the final link is done with g++ to get the C++ runtime libraries and -lgfortran is added to get the Fortran runtime libraries. In general, when mixing languages in LTO mode, you should use the same link command options as when mixing languages in a regular (non-LTO) compilation. If object files containing GIMPLE bytecode are stored in a library archive, say libfoo.a, it is possible to extract and use them in an LTO link if you are using a linker with plugin support. To create static libraries suitable for LTO, use gcc-ar and gcc-ranlib instead of ar and ranlib; to show the symbols of object files with GIMPLE bytecode, use gcc-nm. Those commands require that ar, ranlib and nm have been compiled with plugin support. At link time, use the flag -fuse-linker-plugin to ensure that the library participates in the LTO optimization process: gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo With the linker plugin enabled, the linker extracts the needed GIMPLE files from libfoo.a and passes them on to the running GCC to make them part of the aggregated GIMPLE image to be optimized. If you are not using a linker with plugin support and/or do not enable the linker plugin, then the objects inside libfoo.a are extracted and linked as usual, but they do not participate in the LTO optimization process. In order to make a static library suitable for both LTO optimization and usual linkage, compile its object files with -flto -ffat-lto-objects. Link-time optimizations do not require the presence of the whole program to operate. If the program does not require any symbols to be exported, it is possible to combine -flto and -fwhole-program to allow the interprocedural optimizers to use more aggressive assumptions which may lead to improved optimization opportunities. Use of -fwhole-program is not needed when linker plugin is active (see -fuse-linker-plugin). The current implementation of LTO makes no attempt to generate bytecode that is portable between different types of hosts. The bytecode files are versioned and there is a strict version check, so bytecode files generated in one version of GCC do not work with an older or newer version of GCC. Link-time optimization does not work well with generation of debugging information on systems other than those using a combination of ELF and DWARF. If you specify the optional n, the optimization and code generation done at link time is executed in parallel using n parallel jobs by utilizing an installed make program. The environment variable MAKE may be used to override the program used. You can also specify -flto=jobserver to use GNU make's job server mode to determine the number of parallel jobs. This is useful when the Makefile calling GCC is already executing in parallel. You must prepend a + to the command recipe in the parent Makefile for this to work. This option likely only works if MAKE is GNU make. Even without the option value, GCC tries to automatically detect a running GNU make's job server. Use -flto=auto to use GNU make's job server, if available, or otherwise fall back to autodetection of the number of CPU threads present in your system. -flto-partition=alg Specify the partitioning algorithm used by the link-time optimizer. The value is either 1to1 to specify a partitioning mirroring the original source files or balanced to specify partitioning into equally sized chunks (whenever possible) or max to create new partition for every symbol where possible. Specifying none as an algorithm disables partitioning and streaming completely. The default value is balanced. While 1to1 can be used as an workaround for various code ordering issues, the max partitioning is intended for internal testing only. The value one specifies that exactly one partition should be used while the value none bypasses partitioning and executes the link-time optimization step directly from the WPA phase. -flto-compression-level=n This option specifies the level of compression used for intermediate language written to LTO object files, and is only meaningful in conjunction with LTO mode (-flto). GCC currently supports two LTO compression algorithms. For zstd, valid values are 0 (no compression) to 19 (maximum compression), while zlib supports values from 0 to 9. Values outside this range are clamped to either minimum or maximum of the supported values. If the option is not given, a default balanced compression setting is used. -fuse-linker-plugin Enables the use of a linker plugin during link-time optimization. This option relies on plugin support in the linker, which is available in gold or in GNU ld 2.21 or newer. This option enables the extraction of object files with GIMPLE bytecode out of library archives. This improves the quality of optimization by exposing more code to the link-time optimizer. This information specifies what symbols can be accessed externally (by non-LTO object or during dynamic linking). Resulting code quality improvements on binaries (and shared libraries that use hidden visibility) are similar to -fwhole-program. See -flto for a description of the effect of this flag and how to use it. This option is enabled by default when LTO support in GCC is enabled and GCC was configured for use with a linker supporting plugins (GNU ld 2.21 or newer or gold). -ffat-lto-objects Fat LTO objects are object files that contain both the intermediate language and the object code. This makes them usable for both LTO linking and normal linking. This option is effective only when compiling with -flto and is ignored at link time. -fno-fat-lto-objects improves compilation time over plain LTO, but requires the complete toolchain to be aware of LTO. It requires a linker with linker plugin support for basic functionality. Additionally, nm, ar and ranlib need to support linker plugins to allow a full-featured build environment (capable of building static libraries etc). GCC provides the gcc-ar, gcc-nm, gcc-ranlib wrappers to pass the right options to these tools. With non fat LTO makefiles need to be modified to use them. Note that modern binutils provide plugin auto-load mechanism. Installing the linker plugin into $libdir/bfd-plugins has the same effect as usage of the command wrappers (gcc-ar, gcc-nm and gcc- ranlib). The default is -fno-fat-lto-objects on targets with linker plugin support. -fcompare-elim After register allocation and post-register allocation instruction splitting, identify arithmetic instructions that compute processor flags similar to a comparison operation based on that arithmetic. If possible, eliminate the explicit comparison operation. This pass only applies to certain targets that cannot explicitly represent the comparison operation before register allocation is complete. Enabled at levels -O1, -O2, -O3, -Os. -fcprop-registers After register allocation and post-register allocation instruction splitting, perform a copy-propagation pass to try to reduce scheduling dependencies and occasionally eliminate the copy. Enabled at levels -O1, -O2, -O3, -Os. -fprofile-correction Profiles collected using an instrumented binary for multi-threaded programs may be inconsistent due to missed counter updates. When this option is specified, GCC uses heuristics to correct or smooth out such inconsistencies. By default, GCC emits an error message when an inconsistent profile is detected. This option is enabled by -fauto-profile. -fprofile-partial-training With "-fprofile-use" all portions of programs not executed during train run are optimized agressively for size rather than speed. In some cases it is not practical to train all possible hot paths in the program. (For example, program may contain functions specific for a given hardware and trianing may not cover all hardware configurations program is run on.) With "-fprofile-partial-training" profile feedback will be ignored for all functions not executed during the train run leading them to be optimized as if they were compiled without profile feedback. This leads to better performance when train run is not representative but also leads to significantly bigger code. -fprofile-use -fprofile-use=path Enable profile feedback-directed optimizations, and the following optimizations, many of which are generally profitable only with profile feedback available: -fbranch-probabilities -fprofile-values -funroll-loops -fpeel-loops -ftracer -fvpt -finline-functions -fipa-cp -fipa-cp-clone -fipa-bit-cp -fpredictive-commoning -fsplit-loops -funswitch-loops -fgcse-after-reload -ftree-loop-vectorize -ftree-slp-vectorize -fvect-cost-model=dynamic -ftree-loop-distribute-patterns -fprofile-reorder-functions Before you can use this option, you must first generate profiling information. By default, GCC emits an error message if the feedback profiles do not match the source code. This error can be turned into a warning by using -Wno-error=coverage-mismatch. Note this may result in poorly optimized code. Additionally, by default, GCC also emits a warning message if the feedback profiles do not exist (see -Wmissing-profile). If path is specified, GCC looks at the path to find the profile feedback data files. See -fprofile-dir. -fauto-profile -fauto-profile=path Enable sampling-based feedback-directed optimizations, and the following optimizations, many of which are generally profitable only with profile feedback available: -fbranch-probabilities -fprofile-values -funroll-loops -fpeel-loops -ftracer -fvpt -finline-functions -fipa-cp -fipa-cp-clone -fipa-bit-cp -fpredictive-commoning -fsplit-loops -funswitch-loops -fgcse-after-reload -ftree-loop-vectorize -ftree-slp-vectorize -fvect-cost-model=dynamic -ftree-loop-distribute-patterns -fprofile-correction path is the name of a file containing AutoFDO profile information. If omitted, it defaults to fbdata.afdo in the current directory. Producing an AutoFDO profile data file requires running your program with the perf utility on a supported GNU/Linux target system. For more information, see <https://perf.wiki.kernel.org/>. E.g. perf record -e br_inst_retired:near_taken -b -o perf.data \ -- your_program Then use the create_gcov tool to convert the raw profile data to a format that can be used by GCC. You must also supply the unstripped binary for your program to this tool. See <https://github.com/google/autofdo>. E.g. create_gcov --binary=your_program.unstripped --profile=perf.data \ --gcov=profile.afdo The following options control compiler behavior regarding floating- point arithmetic. These options trade off between speed and correctness. All must be specifically enabled. -ffloat-store Do not store floating-point variables in registers, and inhibit other options that might change whether a floating-point value is taken from a register or memory. This option prevents undesirable excess precision on machines such as the 68000 where the floating registers (of the 68881) keep more precision than a "double" is supposed to have. Similarly for the x86 architecture. For most programs, the excess precision does only good, but a few programs rely on the precise definition of IEEE floating point. Use -ffloat-store for such programs, after modifying them to store all pertinent intermediate computations into variables. -fexcess-precision=style This option allows further control over excess precision on machines where floating-point operations occur in a format with more precision or range than the IEEE standard and interchange floating-point types. By default, -fexcess-precision=fast is in effect; this means that operations may be carried out in a wider precision than the types specified in the source if that would result in faster code, and it is unpredictable when rounding to the types specified in the source code takes place. When compiling C or C++, if -fexcess-precision=standard is specified then excess precision follows the rules specified in ISO C99 or C++; in particular, both casts and assignments cause values to be rounded to their semantic types (whereas -ffloat-store only affects assignments). This option is enabled by default for C or C++ if a strict conformance option such as -std=c99 or -std=c++17 is used. -ffast-math enables -fexcess-precision=fast by default regardless of whether a strict conformance option is used. -fexcess-precision=standard is not implemented for languages other than C or C++. On the x86, it has no effect if -mfpmath=sse or -mfpmath=sse+387 is specified; in the former case, IEEE semantics apply without excess precision, and in the latter, rounding is unpredictable. -ffast-math Sets the options -fno-math-errno, -funsafe-math-optimizations, -ffinite-math-only, -fno-rounding-math, -fno-signaling-nans, -fcx-limited-range and -fexcess-precision=fast. This option causes the preprocessor macro "__FAST_MATH__" to be defined. This option is not turned on by any -O option besides -Ofast since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. -fno-math-errno Do not set "errno" after calling math functions that are executed with a single instruction, e.g., "sqrt". A program that relies on IEEE exceptions for math error handling may want to use this flag for speed while maintaining IEEE arithmetic compatibility. This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. The default is -fmath-errno. On Darwin systems, the math library never sets "errno". There is therefore no reason for the compiler to consider the possibility that it might, and -fno-math-errno is the default. -funsafe-math-optimizations Allow optimizations for floating-point arithmetic that (a) assume that arguments and results are valid and (b) may violate IEEE or ANSI standards. When used at link time, it may include libraries or startup files that change the default FPU control word or other similar optimizations. This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. Enables -fno-signed-zeros, -fno-trapping-math, -fassociative-math and -freciprocal-math. The default is -fno-unsafe-math-optimizations. -fassociative-math Allow re-association of operands in series of floating-point operations. This violates the ISO C and C++ language standard by possibly changing computation result. NOTE: re-ordering may change the sign of zero as well as ignore NaNs and inhibit or create underflow or overflow (and thus cannot be used on code that relies on rounding behavior like "(x + 2**52) - 2**52". May also reorder floating-point comparisons and thus may not be used when ordered comparisons are required. This option requires that both -fno-signed-zeros and -fno-trapping-math be in effect. Moreover, it doesn't make much sense with -frounding-math. For Fortran the option is automatically enabled when both -fno-signed-zeros and -fno-trapping-math are in effect. The default is -fno-associative-math. -freciprocal-math Allow the reciprocal of a value to be used instead of dividing by the value if this enables optimizations. For example "x / y" can be replaced with "x * (1/y)", which is useful if "(1/y)" is subject to common subexpression elimination. Note that this loses precision and increases the number of flops operating on the value. The default is -fno-reciprocal-math. -ffinite-math-only Allow optimizations for floating-point arithmetic that assume that arguments and results are not NaNs or +-Infs. This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. The default is -fno-finite-math-only. -fno-signed-zeros Allow optimizations for floating-point arithmetic that ignore the signedness of zero. IEEE arithmetic specifies the behavior of distinct +0.0 and -0.0 values, which then prohibits simplification of expressions such as x+0.0 or 0.0*x (even with -ffinite-math-only). This option implies that the sign of a zero result isn't significant. The default is -fsigned-zeros. -fno-trapping-math Compile code assuming that floating-point operations cannot generate user-visible traps. These traps include division by zero, overflow, underflow, inexact result and invalid operation. This option requires that -fno-signaling-nans be in effect. Setting this option may allow faster code if one relies on "non-stop" IEEE arithmetic, for example. This option should never be turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. The default is -ftrapping-math. Future versions of GCC may provide finer control of this setting using C99's "FENV_ACCESS" pragma. This command-line option will be used along with -frounding-math to specify the default state for "FENV_ACCESS". -frounding-math Disable transformations and optimizations that assume default floating-point rounding behavior. This is round-to-zero for all floating point to integer conversions, and round-to-nearest for all other arithmetic truncations. This option should be specified for programs that change the FP rounding mode dynamically, or that may be executed with a non-default rounding mode. This option disables constant folding of floating-point expressions at compile time (which may be affected by rounding mode) and arithmetic transformations that are unsafe in the presence of sign-dependent rounding modes. The default is -fno-rounding-math. This option is experimental and does not currently guarantee to disable all GCC optimizations that are affected by rounding mode. Future versions of GCC may provide finer control of this setting using C99's "FENV_ACCESS" pragma. This command-line option will be used along with -ftrapping-math to specify the default state for "FENV_ACCESS". -fsignaling-nans Compile code assuming that IEEE signaling NaNs may generate user- visible traps during floating-point operations. Setting this option disables optimizations that may change the number of exceptions visible with signaling NaNs. This option implies -ftrapping-math. This option causes the preprocessor macro "__SUPPORT_SNAN__" to be defined. The default is -fno-signaling-nans. This option is experimental and does not currently guarantee to disable all GCC optimizations that affect signaling NaN behavior. -fno-fp-int-builtin-inexact Do not allow the built-in functions "ceil", "floor", "round" and "trunc", and their "float" and "long double" variants, to generate code that raises the "inexact" floating-point exception for noninteger arguments. ISO C99 and C11 allow these functions to raise the "inexact" exception, but ISO/IEC TS 18661-1:2014, the C bindings to IEEE 754-2008, as integrated into ISO C2X, does not allow these functions to do so. The default is -ffp-int-builtin-inexact, allowing the exception to be raised, unless C2X or a later C standard is selected. This option does nothing unless -ftrapping-math is in effect. Even if -fno-fp-int-builtin-inexact is used, if the functions generate a call to a library function then the "inexact" exception may be raised if the library implementation does not follow TS 18661. -fsingle-precision-constant Treat floating-point constants as single precision instead of implicitly converting them to double-precision constants. -fcx-limited-range When enabled, this option states that a range reduction step is not needed when performing complex division. Also, there is no checking whether the result of a complex multiplication or division is "NaN + I*NaN", with an attempt to rescue the situation in that case. The default is -fno-cx-limited-range, but is enabled by -ffast-math. This option controls the default setting of the ISO C99 "CX_LIMITED_RANGE" pragma. Nevertheless, the option applies to all languages. -fcx-fortran-rules Complex multiplication and division follow Fortran rules. Range reduction is done as part of complex division, but there is no checking whether the result of a complex multiplication or division is "NaN + I*NaN", with an attempt to rescue the situation in that case. The default is -fno-cx-fortran-rules. The following options control optimizations that may improve performance, but are not enabled by any -O options. This section includes experimental options that may produce broken code. -fbranch-probabilities After running a program compiled with -fprofile-arcs, you can compile it a second time using -fbranch-probabilities, to improve optimizations based on the number of times each branch was taken. When a program compiled with -fprofile-arcs exits, it saves arc execution counts to a file called sourcename.gcda for each source file. The information in this data file is very dependent on the structure of the generated code, so you must use the same source code and the same optimization options for both compilations. See details about the file naming in -fprofile-arcs. With -fbranch-probabilities, GCC puts a REG_BR_PROB note on each JUMP_INSN and CALL_INSN. These can be used to improve optimization. Currently, they are only used in one place: in reorg.cc, instead of guessing which path a branch is most likely to take, the REG_BR_PROB values are used to exactly determine which path is taken more often. Enabled by -fprofile-use and -fauto-profile. -fprofile-values If combined with -fprofile-arcs, it adds code so that some data about values of expressions in the program is gathered. With -fbranch-probabilities, it reads back the data gathered from profiling values of expressions for usage in optimizations. Enabled by -fprofile-generate, -fprofile-use, and -fauto-profile. -fprofile-reorder-functions Function reordering based on profile instrumentation collects first time of execution of a function and orders these functions in ascending order. Enabled with -fprofile-use. -fvpt If combined with -fprofile-arcs, this option instructs the compiler to add code to gather information about values of expressions. With -fbranch-probabilities, it reads back the data gathered and actually performs the optimizations based on them. Currently the optimizations include specialization of division operations using the knowledge about the value of the denominator. Enabled with -fprofile-use and -fauto-profile. -frename-registers Attempt to avoid false dependencies in scheduled code by making use of registers left over after register allocation. This optimization most benefits processors with lots of registers. Depending on the debug information format adopted by the target, however, it can make debugging impossible, since variables no longer stay in a "home register". Enabled by default with -funroll-loops. -fschedule-fusion Performs a target dependent pass over the instruction stream to schedule instructions of same type together because target machine can execute them more efficiently if they are adjacent to each other in the instruction flow. Enabled at levels -O2, -O3, -Os. -ftracer Perform tail duplication to enlarge superblock size. This transformation simplifies the control flow of the function allowing other optimizations to do a better job. Enabled by -fprofile-use and -fauto-profile. -funroll-loops Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop. -funroll-loops implies -frerun-cse-after-loop, -fweb and -frename-registers. It also turns on complete loop peeling (i.e. complete removal of loops with a small constant number of iterations). This option makes code larger, and may or may not make it run faster. Enabled by -fprofile-use and -fauto-profile. -funroll-all-loops Unroll all loops, even if their number of iterations is uncertain when the loop is entered. This usually makes programs run more slowly. -funroll-all-loops implies the same options as -funroll-loops. -fpeel-loops Peels loops for which there is enough information that they do not roll much (from profile feedback or static analysis). It also turns on complete loop peeling (i.e. complete removal of loops with small constant number of iterations). Enabled by -O3, -fprofile-use, and -fauto-profile. -fmove-loop-invariants Enables the loop invariant motion pass in the RTL loop optimizer. Enabled at level -O1 and higher, except for -Og. -fmove-loop-stores Enables the loop store motion pass in the GIMPLE loop optimizer. This moves invariant stores to after the end of the loop in exchange for carrying the stored value in a register across the iteration. Note for this option to have an effect -ftree-loop-im has to be enabled as well. Enabled at level -O1 and higher, except for -Og. -fsplit-loops Split a loop into two if it contains a condition that's always true for one side of the iteration space and false for the other. Enabled by -fprofile-use and -fauto-profile. -funswitch-loops Move branches with loop invariant conditions out of the loop, with duplicates of the loop on both branches (modified according to result of the condition). Enabled by -fprofile-use and -fauto-profile. -fversion-loops-for-strides If a loop iterates over an array with a variable stride, create another version of the loop that assumes the stride is always one. For example: for (int i = 0; i < n; ++i) x[i * stride] = ...; becomes: if (stride == 1) for (int i = 0; i < n; ++i) x[i] = ...; else for (int i = 0; i < n; ++i) x[i * stride] = ...; This is particularly useful for assumed-shape arrays in Fortran where (for example) it allows better vectorization assuming contiguous accesses. This flag is enabled by default at -O3. It is also enabled by -fprofile-use and -fauto-profile. -ffunction-sections -fdata-sections Place each function or data item into its own section in the output file if the target supports arbitrary sections. The name of the function or the name of the data item determines the section's name in the output file. Use these options on systems where the linker can perform optimizations to improve locality of reference in the instruction space. Most systems using the ELF object format have linkers with such optimizations. On AIX, the linker rearranges sections (CSECTs) based on the call graph. The performance impact varies. Together with a linker garbage collection (linker --gc-sections option) these options may lead to smaller statically-linked executables (after stripping). On ELF/DWARF systems these options do not degenerate the quality of the debug information. There could be issues with other object files/debug info formats. Only use these options when there are significant benefits from doing so. When you specify these options, the assembler and linker create larger object and executable files and are also slower. These options affect code generation. They prevent optimizations by the compiler and assembler using relative locations inside a translation unit since the locations are unknown until link time. An example of such an optimization is relaxing calls to short call instructions. -fstdarg-opt Optimize the prologue of variadic argument functions with respect to usage of those arguments. -fsection-anchors Try to reduce the number of symbolic address calculations by using shared "anchor" symbols to address nearby objects. This transformation can help to reduce the number of GOT entries and GOT accesses on some targets. For example, the implementation of the following function "foo": static int a, b, c; int foo (void) { return a + b + c; } usually calculates the addresses of all three variables, but if you compile it with -fsection-anchors, it accesses the variables from a common anchor point instead. The effect is similar to the following pseudocode (which isn't valid C): int foo (void) { register int *xr = &x; return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; } Not all targets support this option. -fzero-call-used-regs=choice Zero call-used registers at function return to increase program security by either mitigating Return-Oriented Programming (ROP) attacks or preventing information leakage through registers. The possible values of choice are the same as for the "zero_call_used_regs" attribute. The default is skip. You can control this behavior for a specific function by using the function attribute "zero_call_used_regs". --param name=value In some places, GCC uses various constants to control the amount of optimization that is done. For example, GCC does not inline functions that contain more than a certain number of instructions. You can control some of these constants on the command line using the --param option. The names of specific parameters, and the meaning of the values, are tied to the internals of the compiler, and are subject to change without notice in future releases. In order to get the minimal, maximal and default values of a parameter, use the --help=param -Q options. In each case, the value is an integer. The following choices of name are recognized for all targets: predictable-branch-outcome When branch is predicted to be taken with probability lower than this threshold (in percent), then it is considered well predictable. max-rtl-if-conversion-insns RTL if-conversion tries to remove conditional branches around a block and replace them with conditionally executed instructions. This parameter gives the maximum number of instructions in a block which should be considered for if- conversion. The compiler will also use other heuristics to decide whether if-conversion is likely to be profitable. max-rtl-if-conversion-predictable-cost RTL if-conversion will try to remove conditional branches around a block and replace them with conditionally executed instructions. These parameters give the maximum permissible cost for the sequence that would be generated by if-conversion depending on whether the branch is statically determined to be predictable or not. The units for this parameter are the same as those for the GCC internal seq_cost metric. The compiler will try to provide a reasonable default for this parameter using the BRANCH_COST target macro. max-crossjump-edges The maximum number of incoming edges to consider for cross- jumping. The algorithm used by -fcrossjumping is O(N^2) in the number of edges incoming to each block. Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in executable size. min-crossjump-insns The minimum number of instructions that must be matched at the end of two blocks before cross-jumping is performed on them. This value is ignored in the case where all instructions in the block being cross-jumped from are matched. max-grow-copy-bb-insns The maximum code size expansion factor when copying basic blocks instead of jumping. The expansion is relative to a jump instruction. max-goto-duplication-insns The maximum number of instructions to duplicate to a block that jumps to a computed goto. To avoid O(N^2) behavior in a number of passes, GCC factors computed gotos early in the compilation process, and unfactors them as late as possible. Only computed jumps at the end of a basic blocks with no more than max-goto- duplication-insns are unfactored. max-delay-slot-insn-search The maximum number of instructions to consider when looking for an instruction to fill a delay slot. If more than this arbitrary number of instructions are searched, the time savings from filling the delay slot are minimal, so stop searching. Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in execution time. max-delay-slot-live-search When trying to fill delay slots, the maximum number of instructions to consider when searching for a block with valid live register information. Increasing this arbitrarily chosen value means more aggressive optimization, increasing the compilation time. This parameter should be removed when the delay slot code is rewritten to maintain the control-flow graph. max-gcse-memory The approximate maximum amount of memory in "kB" that can be allocated in order to perform the global common subexpression elimination optimization. If more memory than specified is required, the optimization is not done. max-gcse-insertion-ratio If the ratio of expression insertions to deletions is larger than this value for any expression, then RTL PRE inserts or removes the expression and thus leaves partially redundant computations in the instruction stream. max-pending-list-length The maximum number of pending dependencies scheduling allows before flushing the current state and starting over. Large functions with few branches or calls can create excessively large lists which needlessly consume memory and resources. max-modulo-backtrack-attempts The maximum number of backtrack attempts the scheduler should make when modulo scheduling a loop. Larger values can exponentially increase compilation time. max-inline-functions-called-once-loop-depth Maximal loop depth of a call considered by inline heuristics that tries to inline all functions called once. max-inline-functions-called-once-insns Maximal estimated size of functions produced while inlining functions called once. max-inline-insns-single Several parameters control the tree inliner used in GCC. This number sets the maximum number of instructions (counted in GCC's internal representation) in a single function that the tree inliner considers for inlining. This only affects functions declared inline and methods implemented in a class declaration (C++). max-inline-insns-auto When you use -finline-functions (included in -O3), a lot of functions that would otherwise not be considered for inlining by the compiler are investigated. To those functions, a different (more restrictive) limit compared to functions declared inline can be applied (--param max-inline-insns-auto). max-inline-insns-small This is bound applied to calls which are considered relevant with -finline-small-functions. max-inline-insns-size This is bound applied to calls which are optimized for size. Small growth may be desirable to anticipate optimization oppurtunities exposed by inlining. uninlined-function-insns Number of instructions accounted by inliner for function overhead such as function prologue and epilogue. uninlined-function-time Extra time accounted by inliner for function overhead such as time needed to execute function prologue and epilogue. inline-heuristics-hint-percent The scale (in percents) applied to inline-insns-single, inline-insns-single-O2, inline-insns-auto when inline heuristics hints that inlining is very profitable (will enable later optimizations). uninlined-thunk-insns uninlined-thunk-time Same as --param uninlined-function-insns and --param uninlined- function-time but applied to function thunks. inline-min-speedup When estimated performance improvement of caller + callee runtime exceeds this threshold (in percent), the function can be inlined regardless of the limit on --param max-inline-insns- single and --param max-inline-insns-auto. large-function-insns The limit specifying really large functions. For functions larger than this limit after inlining, inlining is constrained by --param large-function-growth. This parameter is useful primarily to avoid extreme compilation time caused by non- linear algorithms used by the back end. large-function-growth Specifies maximal growth of large function caused by inlining in percents. For example, parameter value 100 limits large function growth to 2.0 times the original size. large-unit-insns The limit specifying large translation unit. Growth caused by inlining of units larger than this limit is limited by --param inline-unit-growth. For small units this might be too tight. For example, consider a unit consisting of function A that is inline and B that just calls A three times. If B is small relative to A, the growth of unit is 300\% and yet such inlining is very sane. For very large units consisting of small inlineable functions, however, the overall unit growth limit is needed to avoid exponential explosion of code size. Thus for smaller units, the size is increased to --param large- unit-insns before applying --param inline-unit-growth. lazy-modules Maximum number of concurrently open C++ module files when lazy loading. inline-unit-growth Specifies maximal overall growth of the compilation unit caused by inlining. For example, parameter value 20 limits unit growth to 1.2 times the original size. Cold functions (either marked cold via an attribute or by profile feedback) are not accounted into the unit size. ipa-cp-unit-growth Specifies maximal overall growth of the compilation unit caused by interprocedural constant propagation. For example, parameter value 10 limits unit growth to 1.1 times the original size. ipa-cp-large-unit-insns The size of translation unit that IPA-CP pass considers large. large-stack-frame The limit specifying large stack frames. While inlining the algorithm is trying to not grow past this limit too much. large-stack-frame-growth Specifies maximal growth of large stack frames caused by inlining in percents. For example, parameter value 1000 limits large stack frame growth to 11 times the original size. max-inline-insns-recursive max-inline-insns-recursive-auto Specifies the maximum number of instructions an out-of-line copy of a self-recursive inline function can grow into by performing recursive inlining. --param max-inline-insns-recursive applies to functions declared inline. For functions not declared inline, recursive inlining happens only when -finline-functions (included in -O3) is enabled; --param max-inline-insns-recursive-auto applies instead. max-inline-recursive-depth max-inline-recursive-depth-auto Specifies the maximum recursion depth used for recursive inlining. --param max-inline-recursive-depth applies to functions declared inline. For functions not declared inline, recursive inlining happens only when -finline-functions (included in -O3) is enabled; --param max-inline-recursive-depth-auto applies instead. min-inline-recursive-probability Recursive inlining is profitable only for function having deep recursion in average and can hurt for function having little recursion depth by increasing the prologue size or complexity of function body to other optimizers. When profile feedback is available (see -fprofile-generate) the actual recursion depth can be guessed from the probability that function recurses via a given call expression. This parameter limits inlining only to call expressions whose probability exceeds the given threshold (in percents). early-inlining-insns Specify growth that the early inliner can make. In effect it increases the amount of inlining for code having a large abstraction penalty. max-early-inliner-iterations Limit of iterations of the early inliner. This basically bounds the number of nested indirect calls the early inliner can resolve. Deeper chains are still handled by late inlining. comdat-sharing-probability Probability (in percent) that C++ inline function with comdat visibility are shared across multiple compilation units. modref-max-bases modref-max-refs modref-max-accesses Specifies the maximal number of base pointers, references and accesses stored for a single function by mod/ref analysis. modref-max-tests Specifies the maxmal number of tests alias oracle can perform to disambiguate memory locations using the mod/ref information. This parameter ought to be bigger than --param modref-max-bases and --param modref-max-refs. modref-max-depth Specifies the maximum depth of DFS walk used by modref escape analysis. Setting to 0 disables the analysis completely. modref-max-escape-points Specifies the maximum number of escape points tracked by modref per SSA-name. modref-max-adjustments Specifies the maximum number the access range is enlarged during modref dataflow analysis. profile-func-internal-id A parameter to control whether to use function internal id in profile database lookup. If the value is 0, the compiler uses an id that is based on function assembler name and filename, which makes old profile data more tolerant to source changes such as function reordering etc. min-vect-loop-bound The minimum number of iterations under which loops are not vectorized when -ftree-vectorize is used. The number of iterations after vectorization needs to be greater than the value specified by this option to allow vectorization. gcse-cost-distance-ratio Scaling factor in calculation of maximum distance an expression can be moved by GCSE optimizations. This is currently supported only in the code hoisting pass. The bigger the ratio, the more aggressive code hoisting is with simple expressions, i.e., the expressions that have cost less than gcse-unrestricted-cost. Specifying 0 disables hoisting of simple expressions. gcse-unrestricted-cost Cost, roughly measured as the cost of a single typical machine instruction, at which GCSE optimizations do not constrain the distance an expression can travel. This is currently supported only in the code hoisting pass. The lesser the cost, the more aggressive code hoisting is. Specifying 0 allows all expressions to travel unrestricted distances. max-hoist-depth The depth of search in the dominator tree for expressions to hoist. This is used to avoid quadratic behavior in hoisting algorithm. The value of 0 does not limit on the search, but may slow down compilation of huge functions. max-tail-merge-comparisons The maximum amount of similar bbs to compare a bb with. This is used to avoid quadratic behavior in tree tail merging. max-tail-merge-iterations The maximum amount of iterations of the pass over the function. This is used to limit compilation time in tree tail merging. store-merging-allow-unaligned Allow the store merging pass to introduce unaligned stores if it is legal to do so. max-stores-to-merge The maximum number of stores to attempt to merge into wider stores in the store merging pass. max-store-chains-to-track The maximum number of store chains to track at the same time in the attempt to merge them into wider stores in the store merging pass. max-stores-to-track The maximum number of stores to track at the same time in the attemt to to merge them into wider stores in the store merging pass. max-unrolled-insns The maximum number of instructions that a loop may have to be unrolled. If a loop is unrolled, this parameter also determines how many times the loop code is unrolled. max-average-unrolled-insns The maximum number of instructions biased by probabilities of their execution that a loop may have to be unrolled. If a loop is unrolled, this parameter also determines how many times the loop code is unrolled. max-unroll-times The maximum number of unrollings of a single loop. max-peeled-insns The maximum number of instructions that a loop may have to be peeled. If a loop is peeled, this parameter also determines how many times the loop code is peeled. max-peel-times The maximum number of peelings of a single loop. max-peel-branches The maximum number of branches on the hot path through the peeled sequence. max-completely-peeled-insns The maximum number of insns of a completely peeled loop. max-completely-peel-times The maximum number of iterations of a loop to be suitable for complete peeling. max-completely-peel-loop-nest-depth The maximum depth of a loop nest suitable for complete peeling. max-unswitch-insns The maximum number of insns of an unswitched loop. max-unswitch-depth The maximum depth of a loop nest to be unswitched. lim-expensive The minimum cost of an expensive expression in the loop invariant motion. min-loop-cond-split-prob When FDO profile information is available, min-loop-cond-split- prob specifies minimum threshold for probability of semi- invariant condition statement to trigger loop split. iv-consider-all-candidates-bound Bound on number of candidates for induction variables, below which all candidates are considered for each use in induction variable optimizations. If there are more candidates than this, only the most relevant ones are considered to avoid quadratic time complexity. iv-max-considered-uses The induction variable optimizations give up on loops that contain more induction variable uses. iv-always-prune-cand-set-bound If the number of candidates in the set is smaller than this value, always try to remove unnecessary ivs from the set when adding a new one. avg-loop-niter Average number of iterations of a loop. dse-max-object-size Maximum size (in bytes) of objects tracked bytewise by dead store elimination. Larger values may result in larger compilation times. dse-max-alias-queries-per-store Maximum number of queries into the alias oracle per store. Larger values result in larger compilation times and may result in more removed dead stores. scev-max-expr-size Bound on size of expressions used in the scalar evolutions analyzer. Large expressions slow the analyzer. scev-max-expr-complexity Bound on the complexity of the expressions in the scalar evolutions analyzer. Complex expressions slow the analyzer. max-tree-if-conversion-phi-args Maximum number of arguments in a PHI supported by TREE if conversion unless the loop is marked with simd pragma. vect-max-layout-candidates The maximum number of possible vector layouts (such as permutations) to consider when optimizing to-be-vectorized code. vect-max-version-for-alignment-checks The maximum number of run-time checks that can be performed when doing loop versioning for alignment in the vectorizer. vect-max-version-for-alias-checks The maximum number of run-time checks that can be performed when doing loop versioning for alias in the vectorizer. vect-max-peeling-for-alignment The maximum number of loop peels to enhance access alignment for vectorizer. Value -1 means no limit. max-iterations-to-track The maximum number of iterations of a loop the brute-force algorithm for analysis of the number of iterations of the loop tries to evaluate. hot-bb-count-fraction The denominator n of fraction 1/n of the maximal execution count of a basic block in the entire program that a basic block needs to at least have in order to be considered hot. The default is 10000, which means that a basic block is considered hot if its execution count is greater than 1/10000 of the maximal execution count. 0 means that it is never considered hot. Used in non-LTO mode. hot-bb-count-ws-permille The number of most executed permilles, ranging from 0 to 1000, of the profiled execution of the entire program to which the execution count of a basic block must be part of in order to be considered hot. The default is 990, which means that a basic block is considered hot if its execution count contributes to the upper 990 permilles, or 99.0%, of the profiled execution of the entire program. 0 means that it is never considered hot. Used in LTO mode. hot-bb-frequency-fraction The denominator n of fraction 1/n of the execution frequency of the entry block of a function that a basic block of this function needs to at least have in order to be considered hot. The default is 1000, which means that a basic block is considered hot in a function if it is executed more frequently than 1/1000 of the frequency of the entry block of the function. 0 means that it is never considered hot. unlikely-bb-count-fraction The denominator n of fraction 1/n of the number of profiled runs of the entire program below which the execution count of a basic block must be in order for the basic block to be considered unlikely executed. The default is 20, which means that a basic block is considered unlikely executed if it is executed in fewer than 1/20, or 5%, of the runs of the program. 0 means that it is always considered unlikely executed. max-predicted-iterations The maximum number of loop iterations we predict statically. This is useful in cases where a function contains a single loop with known bound and another loop with unknown bound. The known number of iterations is predicted correctly, while the unknown number of iterations average to roughly 10. This means that the loop without bounds appears artificially cold relative to the other one. builtin-expect-probability Control the probability of the expression having the specified value. This parameter takes a percentage (i.e. 0 ... 100) as input. builtin-string-cmp-inline-length The maximum length of a constant string for a builtin string cmp call eligible for inlining. align-threshold Select fraction of the maximal frequency of executions of a basic block in a function to align the basic block. align-loop-iterations A loop expected to iterate at least the selected number of iterations is aligned. tracer-dynamic-coverage tracer-dynamic-coverage-feedback This value is used to limit superblock formation once the given percentage of executed instructions is covered. This limits unnecessary code size expansion. The tracer-dynamic-coverage-feedback parameter is used only when profile feedback is available. The real profiles (as opposed to statically estimated ones) are much less balanced allowing the threshold to be larger value. tracer-max-code-growth Stop tail duplication once code growth has reached given percentage. This is a rather artificial limit, as most of the duplicates are eliminated later in cross jumping, so it may be set to much higher values than is the desired code growth. tracer-min-branch-ratio Stop reverse growth when the reverse probability of best edge is less than this threshold (in percent). tracer-min-branch-probability tracer-min-branch-probability-feedback Stop forward growth if the best edge has probability lower than this threshold. Similarly to tracer-dynamic-coverage two parameters are provided. tracer-min-branch-probability-feedback is used for compilation with profile feedback and tracer-min-branch- probability compilation without. The value for compilation with profile feedback needs to be more conservative (higher) in order to make tracer effective. stack-clash-protection-guard-size Specify the size of the operating system provided stack guard as 2 raised to num bytes. Higher values may reduce the number of explicit probes, but a value larger than the operating system provided guard will leave code vulnerable to stack clash style attacks. stack-clash-protection-probe-interval Stack clash protection involves probing stack space as it is allocated. This param controls the maximum distance between probes into the stack as 2 raised to num bytes. Higher values may reduce the number of explicit probes, but a value larger than the operating system provided guard will leave code vulnerable to stack clash style attacks. max-cse-path-length The maximum number of basic blocks on path that CSE considers. max-cse-insns The maximum number of instructions CSE processes before flushing. ggc-min-expand GCC uses a garbage collector to manage its own memory allocation. This parameter specifies the minimum percentage by which the garbage collector's heap should be allowed to expand between collections. Tuning this may improve compilation speed; it has no effect on code generation. The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when RAM >= 1GB. If "getrlimit" is available, the notion of "RAM" is the smallest of actual RAM and "RLIMIT_DATA" or "RLIMIT_AS". If GCC is not able to calculate RAM on a particular platform, the lower bound of 30% is used. Setting this parameter and ggc-min-heapsize to zero causes a full collection to occur at every opportunity. This is extremely slow, but can be useful for debugging. ggc-min-heapsize Minimum size of the garbage collector's heap before it begins bothering to collect garbage. The first collection occurs after the heap expands by ggc-min-expand% beyond ggc-min- heapsize. Again, tuning this may improve compilation speed, and has no effect on code generation. The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but with a lower bound of 4096 (four megabytes) and an upper bound of 131072 (128 megabytes). If GCC is not able to calculate RAM on a particular platform, the lower bound is used. Setting this parameter very large effectively disables garbage collection. Setting this parameter and ggc-min-expand to zero causes a full collection to occur at every opportunity. max-reload-search-insns The maximum number of instruction reload should look backward for equivalent register. Increasing values mean more aggressive optimization, making the compilation time increase with probably slightly better performance. max-cselib-memory-locations The maximum number of memory locations cselib should take into account. Increasing values mean more aggressive optimization, making the compilation time increase with probably slightly better performance. max-sched-ready-insns The maximum number of instructions ready to be issued the scheduler should consider at any given time during the first scheduling pass. Increasing values mean more thorough searches, making the compilation time increase with probably little benefit. max-sched-region-blocks The maximum number of blocks in a region to be considered for interblock scheduling. max-pipeline-region-blocks The maximum number of blocks in a region to be considered for pipelining in the selective scheduler. max-sched-region-insns The maximum number of insns in a region to be considered for interblock scheduling. max-pipeline-region-insns The maximum number of insns in a region to be considered for pipelining in the selective scheduler. min-spec-prob The minimum probability (in percents) of reaching a source block for interblock speculative scheduling. max-sched-extend-regions-iters The maximum number of iterations through CFG to extend regions. A value of 0 disables region extensions. max-sched-insn-conflict-delay The maximum conflict delay for an insn to be considered for speculative motion. sched-spec-prob-cutoff The minimal probability of speculation success (in percents), so that speculative insns are scheduled. sched-state-edge-prob-cutoff The minimum probability an edge must have for the scheduler to save its state across it. sched-mem-true-dep-cost Minimal distance (in CPU cycles) between store and load targeting same memory locations. selsched-max-lookahead The maximum size of the lookahead window of selective scheduling. It is a depth of search for available instructions. selsched-max-sched-times The maximum number of times that an instruction is scheduled during selective scheduling. This is the limit on the number of iterations through which the instruction may be pipelined. selsched-insns-to-rename The maximum number of best instructions in the ready list that are considered for renaming in the selective scheduler. sms-min-sc The minimum value of stage count that swing modulo scheduler generates. max-last-value-rtl The maximum size measured as number of RTLs that can be recorded in an expression in combiner for a pseudo register as last known value of that register. max-combine-insns The maximum number of instructions the RTL combiner tries to combine. integer-share-limit Small integer constants can use a shared data structure, reducing the compiler's memory usage and increasing its speed. This sets the maximum value of a shared integer constant. ssp-buffer-size The minimum size of buffers (i.e. arrays) that receive stack smashing protection when -fstack-protector is used. min-size-for-stack-sharing The minimum size of variables taking part in stack slot sharing when not optimizing. max-jump-thread-duplication-stmts Maximum number of statements allowed in a block that needs to be duplicated when threading jumps. max-jump-thread-paths The maximum number of paths to consider when searching for jump threading opportunities. When arriving at a block, incoming edges are only considered if the number of paths to be searched so far multiplied by the number of incoming edges does not exhaust the specified maximum number of paths to consider. max-fields-for-field-sensitive Maximum number of fields in a structure treated in a field sensitive manner during pointer analysis. prefetch-latency Estimate on average number of instructions that are executed before prefetch finishes. The distance prefetched ahead is proportional to this constant. Increasing this number may also lead to less streams being prefetched (see simultaneous- prefetches). simultaneous-prefetches Maximum number of prefetches that can run at the same time. l1-cache-line-size The size of cache line in L1 data cache, in bytes. l1-cache-size The size of L1 data cache, in kilobytes. l2-cache-size The size of L2 data cache, in kilobytes. prefetch-dynamic-strides Whether the loop array prefetch pass should issue software prefetch hints for strides that are non-constant. In some cases this may be beneficial, though the fact the stride is non-constant may make it hard to predict when there is clear benefit to issuing these hints. Set to 1 if the prefetch hints should be issued for non- constant strides. Set to 0 if prefetch hints should be issued only for strides that are known to be constant and below prefetch-minimum-stride. prefetch-minimum-stride Minimum constant stride, in bytes, to start using prefetch hints for. If the stride is less than this threshold, prefetch hints will not be issued. This setting is useful for processors that have hardware prefetchers, in which case there may be conflicts between the hardware prefetchers and the software prefetchers. If the hardware prefetchers have a maximum stride they can handle, it should be used here to improve the use of software prefetchers. A value of -1 means we don't have a threshold and therefore prefetch hints can be issued for any constant stride. This setting is only useful for strides that are known and constant. destructive-interference-size constructive-interference-size The values for the C++17 variables "std::hardware_destructive_interference_size" and "std::hardware_constructive_interference_size". The destructive interference size is the minimum recommended offset between two independent concurrently-accessed objects; the constructive interference size is the maximum recommended size of contiguous memory accessed together. Typically both will be the size of an L1 cache line for the target, in bytes. For a generic target covering a range of L1 cache line sizes, typically the constructive interference size will be the small end of the range and the destructive size will be the large end. The destructive interference size is intended to be used for layout, and thus has ABI impact. The default value is not expected to be stable, and on some targets varies with -mtune, so use of this variable in a context where ABI stability is important, such as the public interface of a library, is strongly discouraged; if it is used in that context, users can stabilize the value using this option. The constructive interference size is less sensitive, as it is typically only used in a static_assert to make sure that a type fits within a cache line. See also -Winterference-size. loop-interchange-max-num-stmts The maximum number of stmts in a loop to be interchanged. loop-interchange-stride-ratio The minimum ratio between stride of two loops for interchange to be profitable. min-insn-to-prefetch-ratio The minimum ratio between the number of instructions and the number of prefetches to enable prefetching in a loop. prefetch-min-insn-to-mem-ratio The minimum ratio between the number of instructions and the number of memory references to enable prefetching in a loop. use-canonical-types Whether the compiler should use the "canonical" type system. Should always be 1, which uses a more efficient internal mechanism for comparing types in C++ and Objective-C++. However, if bugs in the canonical type system are causing compilation failures, set this value to 0 to disable canonical types. switch-conversion-max-branch-ratio Switch initialization conversion refuses to create arrays that are bigger than switch-conversion-max-branch-ratio times the number of branches in the switch. max-partial-antic-length Maximum length of the partial antic set computed during the tree partial redundancy elimination optimization (-ftree-pre) when optimizing at -O3 and above. For some sorts of source code the enhanced partial redundancy elimination optimization can run away, consuming all of the memory available on the host machine. This parameter sets a limit on the length of the sets that are computed, which prevents the runaway behavior. Setting a value of 0 for this parameter allows an unlimited set length. rpo-vn-max-loop-depth Maximum loop depth that is value-numbered optimistically. When the limit hits the innermost rpo-vn-max-loop-depth loops and the outermost loop in the loop nest are value-numbered optimistically and the remaining ones not. sccvn-max-alias-queries-per-access Maximum number of alias-oracle queries we perform when looking for redundancies for loads and stores. If this limit is hit the search is aborted and the load or store is not considered redundant. The number of queries is algorithmically limited to the number of stores on all paths from the load to the function entry. ira-max-loops-num IRA uses regional register allocation by default. If a function contains more loops than the number given by this parameter, only at most the given number of the most frequently-executed loops form regions for regional register allocation. ira-max-conflict-table-size Although IRA uses a sophisticated algorithm to compress the conflict table, the table can still require excessive amounts of memory for huge functions. If the conflict table for a function could be more than the size in MB given by this parameter, the register allocator instead uses a faster, simpler, and lower-quality algorithm that does not require building a pseudo-register conflict table. ira-loop-reserved-regs IRA can be used to evaluate more accurate register pressure in loops for decisions to move loop invariants (see -O3). The number of available registers reserved for some other purposes is given by this parameter. Default of the parameter is the best found from numerous experiments. ira-consider-dup-in-all-alts Make IRA to consider matching constraint (duplicated operand number) heavily in all available alternatives for preferred register class. If it is set as zero, it means IRA only respects the matching constraint when it's in the only available alternative with an appropriate register class. Otherwise, it means IRA will check all available alternatives for preferred register class even if it has found some choice with an appropriate register class and respect the found qualified matching constraint. ira-simple-lra-insn-threshold Approximate function insn number in 1K units triggering simple local RA. lra-inheritance-ebb-probability-cutoff LRA tries to reuse values reloaded in registers in subsequent insns. This optimization is called inheritance. EBB is used as a region to do this optimization. The parameter defines a minimal fall-through edge probability in percentage used to add BB to inheritance EBB in LRA. The default value was chosen from numerous runs of SPEC2000 on x86-64. loop-invariant-max-bbs-in-loop Loop invariant motion can be very expensive, both in compilation time and in amount of needed compile-time memory, with very large loops. Loops with more basic blocks than this parameter won't have loop invariant motion optimization performed on them. loop-max-datarefs-for-datadeps Building data dependencies is expensive for very large loops. This parameter limits the number of data references in loops that are considered for data dependence analysis. These large loops are no handled by the optimizations using loop data dependencies. max-vartrack-size Sets a maximum number of hash table slots to use during variable tracking dataflow analysis of any function. If this limit is exceeded with variable tracking at assignments enabled, analysis for that function is retried without it, after removing all debug insns from the function. If the limit is exceeded even without debug insns, var tracking analysis is completely disabled for the function. Setting the parameter to zero makes it unlimited. max-vartrack-expr-depth Sets a maximum number of recursion levels when attempting to map variable names or debug temporaries to value expressions. This trades compilation time for more complete debug information. If this is set too low, value expressions that are available and could be represented in debug information may end up not being used; setting this higher may enable the compiler to find more complex debug expressions, but compile time and memory use may grow. max-debug-marker-count Sets a threshold on the number of debug markers (e.g. begin stmt markers) to avoid complexity explosion at inlining or expanding to RTL. If a function has more such gimple stmts than the set limit, such stmts will be dropped from the inlined copy of a function, and from its RTL expansion. min-nondebug-insn-uid Use uids starting at this parameter for nondebug insns. The range below the parameter is reserved exclusively for debug insns created by -fvar-tracking-assignments, but debug insns may get (non-overlapping) uids above it if the reserved range is exhausted. ipa-sra-deref-prob-threshold IPA-SRA replaces a pointer which is known not be NULL with one or more new parameters only when the probability (in percent, relative to function entry) of it being dereferenced is higher than this parameter. ipa-sra-ptr-growth-factor IPA-SRA replaces a pointer to an aggregate with one or more new parameters only when their cumulative size is less or equal to ipa-sra-ptr-growth-factor times the size of the original pointer parameter. ipa-sra-ptrwrap-growth-factor Additional maximum allowed growth of total size of new parameters that ipa-sra replaces a pointer to an aggregate with, if it points to a local variable that the caller only writes to and passes it as an argument to other functions. ipa-sra-max-replacements Maximum pieces of an aggregate that IPA-SRA tracks. As a consequence, it is also the maximum number of replacements of a formal parameter. sra-max-scalarization-size-Ospeed sra-max-scalarization-size-Osize The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA) aim to replace scalar parts of aggregates with uses of independent scalar variables. These parameters control the maximum size, in storage units, of aggregate which is considered for replacement when compiling for speed (sra-max- scalarization-size-Ospeed) or size (sra-max-scalarization-size- Osize) respectively. sra-max-propagations The maximum number of artificial accesses that Scalar Replacement of Aggregates (SRA) will track, per one local variable, in order to facilitate copy propagation. tm-max-aggregate-size When making copies of thread-local variables in a transaction, this parameter specifies the size in bytes after which variables are saved with the logging functions as opposed to save/restore code sequence pairs. This option only applies when using -fgnu-tm. graphite-max-nb-scop-params To avoid exponential effects in the Graphite loop transforms, the number of parameters in a Static Control Part (SCoP) is bounded. A value of zero can be used to lift the bound. A variable whose value is unknown at compilation time and defined outside a SCoP is a parameter of the SCoP. loop-block-tile-size Loop blocking or strip mining transforms, enabled with -floop-block or -floop-strip-mine, strip mine each loop in the loop nest by a given number of iterations. The strip length can be changed using the loop-block-tile-size parameter. ipa-jump-function-lookups Specifies number of statements visited during jump function offset discovery. ipa-cp-value-list-size IPA-CP attempts to track all possible values and types passed to a function's parameter in order to propagate them and perform devirtualization. ipa-cp-value-list-size is the maximum number of values and types it stores per one formal parameter of a function. ipa-cp-eval-threshold IPA-CP calculates its own score of cloning profitability heuristics and performs those cloning opportunities with scores that exceed ipa-cp-eval-threshold. ipa-cp-max-recursive-depth Maximum depth of recursive cloning for self-recursive function. ipa-cp-min-recursive-probability Recursive cloning only when the probability of call being executed exceeds the parameter. ipa-cp-profile-count-base When using -fprofile-use option, IPA-CP will consider the measured execution count of a call graph edge at this percentage position in their histogram as the basis for its heuristics calculation. ipa-cp-recursive-freq-factor The number of times interprocedural copy propagation expects recursive functions to call themselves. ipa-cp-recursion-penalty Percentage penalty the recursive functions will receive when they are evaluated for cloning. ipa-cp-single-call-penalty Percentage penalty functions containing a single call to another function will receive when they are evaluated for cloning. ipa-max-agg-items IPA-CP is also capable to propagate a number of scalar values passed in an aggregate. ipa-max-agg-items controls the maximum number of such values per one parameter. ipa-cp-loop-hint-bonus When IPA-CP determines that a cloning candidate would make the number of iterations of a loop known, it adds a bonus of ipa- cp-loop-hint-bonus to the profitability score of the candidate. ipa-max-loop-predicates The maximum number of different predicates IPA will use to describe when loops in a function have known properties. ipa-max-aa-steps During its analysis of function bodies, IPA-CP employs alias analysis in order to track values pointed to by function parameters. In order not spend too much time analyzing huge functions, it gives up and consider all memory clobbered after examining ipa-max-aa-steps statements modifying memory. ipa-max-switch-predicate-bounds Maximal number of boundary endpoints of case ranges of switch statement. For switch exceeding this limit, IPA-CP will not construct cloning cost predicate, which is used to estimate cloning benefit, for default case of the switch statement. ipa-max-param-expr-ops IPA-CP will analyze conditional statement that references some function parameter to estimate benefit for cloning upon certain constant value. But if number of operations in a parameter expression exceeds ipa-max-param-expr-ops, the expression is treated as complicated one, and is not handled by IPA analysis. lto-partitions Specify desired number of partitions produced during WHOPR compilation. The number of partitions should exceed the number of CPUs used for compilation. lto-min-partition Size of minimal partition for WHOPR (in estimated instructions). This prevents expenses of splitting very small programs into too many partitions. lto-max-partition Size of max partition for WHOPR (in estimated instructions). to provide an upper bound for individual size of partition. Meant to be used only with balanced partitioning. lto-max-streaming-parallelism Maximal number of parallel processes used for LTO streaming. cxx-max-namespaces-for-diagnostic-help The maximum number of namespaces to consult for suggestions when C++ name lookup fails for an identifier. sink-frequency-threshold The maximum relative execution frequency (in percents) of the target block relative to a statement's original block to allow statement sinking of a statement. Larger numbers result in more aggressive statement sinking. A small positive adjustment is applied for statements with memory operands as those are even more profitable so sink. max-stores-to-sink The maximum number of conditional store pairs that can be sunk. Set to 0 if either vectorization (-ftree-vectorize) or if- conversion (-ftree-loop-if-convert) is disabled. case-values-threshold The smallest number of different values for which it is best to use a jump-table instead of a tree of conditional branches. If the value is 0, use the default for the machine. jump-table-max-growth-ratio-for-size The maximum code size growth ratio when expanding into a jump table (in percent). The parameter is used when optimizing for size. jump-table-max-growth-ratio-for-speed The maximum code size growth ratio when expanding into a jump table (in percent). The parameter is used when optimizing for speed. tree-reassoc-width Set the maximum number of instructions executed in parallel in reassociated tree. This parameter overrides target dependent heuristics used by default if has non zero value. sched-pressure-algorithm Choose between the two available implementations of -fsched-pressure. Algorithm 1 is the original implementation and is the more likely to prevent instructions from being reordered. Algorithm 2 was designed to be a compromise between the relatively conservative approach taken by algorithm 1 and the rather aggressive approach taken by the default scheduler. It relies more heavily on having a regular register file and accurate register pressure classes. See haifa-sched.cc in the GCC sources for more details. The default choice depends on the target. max-slsr-cand-scan Set the maximum number of existing candidates that are considered when seeking a basis for a new straight-line strength reduction candidate. asan-globals Enable buffer overflow detection for global objects. This kind of protection is enabled by default if you are using -fsanitize=address option. To disable global objects protection use --param asan-globals=0. asan-stack Enable buffer overflow detection for stack objects. This kind of protection is enabled by default when using -fsanitize=address. To disable stack protection use --param asan-stack=0 option. asan-instrument-reads Enable buffer overflow detection for memory reads. This kind of protection is enabled by default when using -fsanitize=address. To disable memory reads protection use --param asan-instrument-reads=0. asan-instrument-writes Enable buffer overflow detection for memory writes. This kind of protection is enabled by default when using -fsanitize=address. To disable memory writes protection use --param asan-instrument-writes=0 option. asan-memintrin Enable detection for built-in functions. This kind of protection is enabled by default when using -fsanitize=address. To disable built-in functions protection use --param asan-memintrin=0. asan-use-after-return Enable detection of use-after-return. This kind of protection is enabled by default when using the -fsanitize=address option. To disable it use --param asan-use-after-return=0. Note: By default the check is disabled at run time. To enable it, add "detect_stack_use_after_return=1" to the environment variable ASAN_OPTIONS. asan-instrumentation-with-call-threshold If number of memory accesses in function being instrumented is greater or equal to this number, use callbacks instead of inline checks. E.g. to disable inline code use --param asan-instrumentation-with-call-threshold=0. asan-kernel-mem-intrinsic-prefix If nonzero, prefix calls to "memcpy", "memset" and "memmove" with __asan_ or __hwasan_ for -fsanitize=kernel-address or -fsanitize=kernel-hwaddress, respectively. hwasan-instrument-stack Enable hwasan instrumentation of statically sized stack- allocated variables. This kind of instrumentation is enabled by default when using -fsanitize=hwaddress and disabled by default when using -fsanitize=kernel-hwaddress. To disable stack instrumentation use --param hwasan-instrument-stack=0, and to enable it use --param hwasan-instrument-stack=1. hwasan-random-frame-tag When using stack instrumentation, decide tags for stack variables using a deterministic sequence beginning at a random tag for each frame. With this parameter unset tags are chosen using the same sequence but beginning from 1. This is enabled by default for -fsanitize=hwaddress and unavailable for -fsanitize=kernel-hwaddress. To disable it use --param hwasan-random-frame-tag=0. hwasan-instrument-allocas Enable hwasan instrumentation of dynamically sized stack- allocated variables. This kind of instrumentation is enabled by default when using -fsanitize=hwaddress and disabled by default when using -fsanitize=kernel-hwaddress. To disable instrumentation of such variables use --param hwasan-instrument-allocas=0, and to enable it use --param hwasan-instrument-allocas=1. hwasan-instrument-reads Enable hwasan checks on memory reads. Instrumentation of reads is enabled by default for both -fsanitize=hwaddress and -fsanitize=kernel-hwaddress. To disable checking memory reads use --param hwasan-instrument-reads=0. hwasan-instrument-writes Enable hwasan checks on memory writes. Instrumentation of writes is enabled by default for both -fsanitize=hwaddress and -fsanitize=kernel-hwaddress. To disable checking memory writes use --param hwasan-instrument-writes=0. hwasan-instrument-mem-intrinsics Enable hwasan instrumentation of builtin functions. Instrumentation of these builtin functions is enabled by default for both -fsanitize=hwaddress and -fsanitize=kernel-hwaddress. To disable instrumentation of builtin functions use --param hwasan-instrument-mem-intrinsics=0. use-after-scope-direct-emission-threshold If the size of a local variable in bytes is smaller or equal to this number, directly poison (or unpoison) shadow memory instead of using run-time callbacks. tsan-distinguish-volatile Emit special instrumentation for accesses to volatiles. tsan-instrument-func-entry-exit Emit instrumentation calls to __tsan_func_entry() and __tsan_func_exit(). max-fsm-thread-path-insns Maximum number of instructions to copy when duplicating blocks on a finite state automaton jump thread path. threader-debug threader-debug=[none|all] Enables verbose dumping of the threader solver. parloops-chunk-size Chunk size of omp schedule for loops parallelized by parloops. parloops-schedule Schedule type of omp schedule for loops parallelized by parloops (static, dynamic, guided, auto, runtime). parloops-min-per-thread The minimum number of iterations per thread of an innermost parallelized loop for which the parallelized variant is preferred over the single threaded one. Note that for a parallelized loop nest the minimum number of iterations of the outermost loop per thread is two. max-ssa-name-query-depth Maximum depth of recursion when querying properties of SSA names in things like fold routines. One level of recursion corresponds to following a use-def chain. max-speculative-devirt-maydefs The maximum number of may-defs we analyze when looking for a must-def specifying the dynamic type of an object that invokes a virtual call we may be able to devirtualize speculatively. evrp-sparse-threshold Maximum number of basic blocks before EVRP uses a sparse cache. ranger-debug Specifies the type of debug output to be issued for ranges. evrp-switch-limit Specifies the maximum number of switch cases before EVRP ignores a switch. unroll-jam-min-percent The minimum percentage of memory references that must be optimized away for the unroll-and-jam transformation to be considered profitable. unroll-jam-max-unroll The maximum number of times the outer loop should be unrolled by the unroll-and-jam transformation. max-rtl-if-conversion-unpredictable-cost Maximum permissible cost for the sequence that would be generated by the RTL if-conversion pass for a branch that is considered unpredictable. max-variable-expansions-in-unroller If -fvariable-expansion-in-unroller is used, the maximum number of times that an individual variable will be expanded during loop unrolling. partial-inlining-entry-probability Maximum probability of the entry BB of split region (in percent relative to entry BB of the function) to make partial inlining happen. max-tracked-strlens Maximum number of strings for which strlen optimization pass will track string lengths. gcse-after-reload-partial-fraction The threshold ratio for performing partial redundancy elimination after reload. gcse-after-reload-critical-fraction The threshold ratio of critical edges execution count that permit performing redundancy elimination after reload. max-loop-header-insns The maximum number of insns in loop header duplicated by the copy loop headers pass. vect-epilogues-nomask Enable loop epilogue vectorization using smaller vector size. vect-partial-vector-usage Controls when the loop vectorizer considers using partial vector loads and stores as an alternative to falling back to scalar code. 0 stops the vectorizer from ever using partial vector loads and stores. 1 allows partial vector loads and stores if vectorization removes the need for the code to iterate. 2 allows partial vector loads and stores in all loops. The parameter only has an effect on targets that support partial vector loads and stores. vect-inner-loop-cost-factor The maximum factor which the loop vectorizer applies to the cost of statements in an inner loop relative to the loop being vectorized. The factor applied is the maximum of the estimated number of iterations of the inner loop and this parameter. The default value of this parameter is 50. vect-induction-float Enable loop vectorization of floating point inductions. avoid-fma-max-bits Maximum number of bits for which we avoid creating FMAs. sms-loop-average-count-threshold A threshold on the average loop count considered by the swing modulo scheduler. sms-dfa-history The number of cycles the swing modulo scheduler considers when checking conflicts using DFA. graphite-allow-codegen-errors Whether codegen errors should be ICEs when -fchecking. sms-max-ii-factor A factor for tuning the upper bound that swing modulo scheduler uses for scheduling a loop. lra-max-considered-reload-pseudos The max number of reload pseudos which are considered during spilling a non-reload pseudo. max-pow-sqrt-depth Maximum depth of sqrt chains to use when synthesizing exponentiation by a real constant. max-dse-active-local-stores Maximum number of active local stores in RTL dead store elimination. asan-instrument-allocas Enable asan allocas/VLAs protection. max-iterations-computation-cost Bound on the cost of an expression to compute the number of iterations. max-isl-operations Maximum number of isl operations, 0 means unlimited. graphite-max-arrays-per-scop Maximum number of arrays per scop. max-vartrack-reverse-op-size Max. size of loc list for which reverse ops should be added. fsm-scale-path-stmts Scale factor to apply to the number of statements in a threading path crossing a loop backedge when comparing to --param=max-jump-thread-duplication-stmts. uninit-control-dep-attempts Maximum number of nested calls to search for control dependencies during uninitialized variable analysis. sched-autopref-queue-depth Hardware autoprefetcher scheduler model control flag. Number of lookahead cycles the model looks into; at ' ' only enable instruction sorting heuristic. loop-versioning-max-inner-insns The maximum number of instructions that an inner loop can have before the loop versioning pass considers it too big to copy. loop-versioning-max-outer-insns The maximum number of instructions that an outer loop can have before the loop versioning pass considers it too big to copy, discounting any instructions in inner loops that directly benefit from versioning. ssa-name-def-chain-limit The maximum number of SSA_NAME assignments to follow in determining a property of a variable such as its value. This limits the number of iterations or recursive calls GCC performs when optimizing certain statements or when determining their validity prior to issuing diagnostics. store-merging-max-size Maximum size of a single store merging region in bytes. hash-table-verification-limit The number of elements for which hash table verification is done for each searched element. max-find-base-term-values Maximum number of VALUEs handled during a single find_base_term call. analyzer-max-enodes-per-program-point The maximum number of exploded nodes per program point within the analyzer, before terminating analysis of that point. analyzer-max-constraints The maximum number of constraints per state. analyzer-min-snodes-for-call-summary The minimum number of supernodes within a function for the analyzer to consider summarizing its effects at call sites. analyzer-max-enodes-for-full-dump The maximum depth of exploded nodes that should appear in a dot dump before switching to a less verbose format. analyzer-max-recursion-depth The maximum number of times a callsite can appear in a call stack within the analyzer, before terminating analysis of a call that would recurse deeper. analyzer-max-svalue-depth The maximum depth of a symbolic value, before approximating the value as unknown. analyzer-max-infeasible-edges The maximum number of infeasible edges to reject before declaring a diagnostic as infeasible. gimple-fe-computed-hot-bb-threshold The number of executions of a basic block which is considered hot. The parameter is used only in GIMPLE FE. analyzer-bb-explosion-factor The maximum number of 'after supernode' exploded nodes within the analyzer per supernode, before terminating analysis. ranger-logical-depth Maximum depth of logical expression evaluation ranger will look through when evaluating outgoing edge ranges. ranger-recompute-depth Maximum depth of instruction chains to consider for recomputation in the outgoing range calculator. relation-block-limit Maximum number of relations the oracle will register in a basic block. min-pagesize Minimum page size for warning purposes. openacc-kernels Specify mode of OpenACC `kernels' constructs handling. With --param=openacc-kernels=decompose, OpenACC `kernels' constructs are decomposed into parts, a sequence of compute constructs, each then handled individually. This is work in progress. With --param=openacc-kernels=parloops, OpenACC `kernels' constructs are handled by the parloops pass, en bloc. This is the current default. openacc-privatization Control whether the -fopt-info-omp-note and applicable -fdump-tree-*-details options emit OpenACC privatization diagnostics. With --param=openacc-privatization=quiet, don't diagnose. This is the current default. With --param=openacc-privatization=noisy, do diagnose. The following choices of name are available on AArch64 targets: aarch64-sve-compare-costs When vectorizing for SVE, consider using "unpacked" vectors for smaller elements and use the cost model to pick the cheapest approach. Also use the cost model to choose between SVE and Advanced SIMD vectorization. Using unpacked vectors includes storing smaller elements in larger containers and accessing elements with extending loads and truncating stores. aarch64-float-recp-precision The number of Newton iterations for calculating the reciprocal for float type. The precision of division is proportional to this param when division approximation is enabled. The default value is 1. aarch64-double-recp-precision The number of Newton iterations for calculating the reciprocal for double type. The precision of division is propotional to this param when division approximation is enabled. The default value is 2. aarch64-autovec-preference Force an ISA selection strategy for auto-vectorization. Accepts values from 0 to 4, inclusive. 0 Use the default heuristics. 1 Use only Advanced SIMD for auto-vectorization. 2 Use only SVE for auto-vectorization. 3 Use both Advanced SIMD and SVE. Prefer Advanced SIMD when the costs are deemed equal. 4 Use both Advanced SIMD and SVE. Prefer SVE when the costs are deemed equal. The default value is 0. aarch64-loop-vect-issue-rate-niters The tuning for some AArch64 CPUs tries to take both latencies and issue rates into account when deciding whether a loop should be vectorized using SVE, vectorized using Advanced SIMD, or not vectorized at all. If this parameter is set to n, GCC will not use this heuristic for loops that are known to execute in fewer than n Advanced SIMD iterations. aarch64-vect-unroll-limit The vectorizer will use available tuning information to determine whether it would be beneficial to unroll the main vectorized loop and by how much. This parameter set's the upper bound of how much the vectorizer will unroll the main loop. The default value is four. The following choices of name are available on i386 and x86_64 targets: x86-stlf-window-ninsns Instructions number above which STFL stall penalty can be compensated. x86-stv-max-visits The maximum number of use and def visits when discovering a STV chain before the discovery is aborted. Program Instrumentation Options GCC supports a number of command-line options that control adding run- time instrumentation to the code it normally generates. For example, one purpose of instrumentation is collect profiling statistics for use in finding program hot spots, code coverage analysis, or profile-guided optimizations. Another class of program instrumentation is adding run- time checking to detect programming errors like invalid pointer dereferences or out-of-bounds array accesses, as well as deliberately hostile attacks such as stack smashing or C++ vtable hijacking. There is also a general hook which can be used to implement other forms of tracing or function-level instrumentation for debug or program analysis purposes. -p -pg Generate extra code to write profile information suitable for the analysis program prof (for -p) or gprof (for -pg). You must use this option when compiling the source files you want data about, and you must also use it when linking. You can use the function attribute "no_instrument_function" to suppress profiling of individual functions when compiling with these options. -fprofile-arcs Add code so that program flow arcs are instrumented. During execution the program records how many times each branch and call is executed and how many times it is taken or returns. On targets that support constructors with priority support, profiling properly handles constructors, destructors and C++ constructors (and destructors) of classes which are used as a type of a global variable. When the compiled program exits it saves this data to a file called auxname.gcda for each source file. The data may be used for profile-directed optimizations (-fbranch-probabilities), or for test coverage analysis (-ftest-coverage). Each object file's auxname is generated from the name of the output file, if explicitly specified and it is not the final executable, otherwise it is the basename of the source file. In both cases any suffix is removed (e.g. foo.gcda for input file dir/foo.c, or dir/foo.gcda for output file specified as -o dir/foo.o). Note that if a command line directly links source files, the corresponding .gcda files will be prefixed with the unsuffixed name of the output file. E.g. "gcc a.c b.c -o binary" would generate binary-a.gcda and binary-b.gcda files. --coverage This option is used to compile and link code instrumented for coverage analysis. The option is a synonym for -fprofile-arcs -ftest-coverage (when compiling) and -lgcov (when linking). See the documentation for those options for more details. * Compile the source files with -fprofile-arcs plus optimization and code generation options. For test coverage analysis, use the additional -ftest-coverage option. You do not need to profile every source file in a program. * Compile the source files additionally with -fprofile-abs-path to create absolute path names in the .gcno files. This allows gcov to find the correct sources in projects where compilations occur with different working directories. * Link your object files with -lgcov or -fprofile-arcs (the latter implies the former). * Run the program on a representative workload to generate the arc profile information. This may be repeated any number of times. You can run concurrent instances of your program, and provided that the file system supports locking, the data files will be correctly updated. Unless a strict ISO C dialect option is in effect, "fork" calls are detected and correctly handled without double counting. Moreover, an object file can be recompiled multiple times and the corresponding .gcda file merges as long as the source file and the compiler options are unchanged. * For profile-directed optimizations, compile the source files again with the same optimization and code generation options plus -fbranch-probabilities. * For test coverage analysis, use gcov to produce human readable information from the .gcno and .gcda files. Refer to the gcov documentation for further information. With -fprofile-arcs, for each function of your program GCC creates a program flow graph, then finds a spanning tree for the graph. Only arcs that are not on the spanning tree have to be instrumented: the compiler adds code to count the number of times that these arcs are executed. When an arc is the only exit or only entrance to a block, the instrumentation code can be added to the block; otherwise, a new basic block must be created to hold the instrumentation code. -ftest-coverage Produce a notes file that the gcov code-coverage utility can use to show program coverage. Each source file's note file is called auxname.gcno. Refer to the -fprofile-arcs option above for a description of auxname and instructions on how to generate test coverage data. Coverage data matches the source files more closely if you do not optimize. -fprofile-abs-path Automatically convert relative source file names to absolute path names in the .gcno files. This allows gcov to find the correct sources in projects where compilations occur with different working directories. -fprofile-dir=path Set the directory to search for the profile data files in to path. This option affects only the profile data generated by -fprofile-generate, -ftest-coverage, -fprofile-arcs and used by -fprofile-use and -fbranch-probabilities and its related options. Both absolute and relative paths can be used. By default, GCC uses the current directory as path, thus the profile data file appears in the same directory as the object file. In order to prevent the file name clashing, if the object file name is not an absolute path, we mangle the absolute path of the sourcename.gcda file and use it as the file name of a .gcda file. See details about the file naming in -fprofile-arcs. See similar option -fprofile-note. When an executable is run in a massive parallel environment, it is recommended to save profile to different folders. That can be done with variables in path that are exported during run-time: %p process ID. %q{VAR} value of environment variable VAR -fprofile-generate -fprofile-generate=path Enable options usually used for instrumenting application to produce profile useful for later recompilation with profile feedback based optimization. You must use -fprofile-generate both when compiling and when linking your program. The following options are enabled: -fprofile-arcs, -fprofile-values, -finline-functions, and -fipa-bit-cp. If path is specified, GCC looks at the path to find the profile feedback data files. See -fprofile-dir. To optimize the program based on the collected profile information, use -fprofile-use. -fprofile-info-section -fprofile-info-section=name Register the profile information in the specified section instead of using a constructor/destructor. The section name is name if it is specified, otherwise the section name defaults to ".gcov_info". A pointer to the profile information generated by -fprofile-arcs is placed in the specified section for each translation unit. This option disables the profile information registration through a constructor and it disables the profile information processing through a destructor. This option is not intended to be used in hosted environments such as GNU/Linux. It targets freestanding environments (for example embedded systems) with limited resources which do not support constructors/destructors or the C library file I/O. The linker could collect the input sections in a continuous memory block and define start and end symbols. A GNU linker script example which defines a linker output section follows: .gcov_info : { PROVIDE (__gcov_info_start = .); KEEP (*(.gcov_info)) PROVIDE (__gcov_info_end = .); } The program could dump the profiling information registered in this linker set for example like this: #include <gcov.h> #include <stdio.h> #include <stdlib.h> extern const struct gcov_info *const __gcov_info_start[]; extern const struct gcov_info *const __gcov_info_end[]; static void dump (const void *d, unsigned n, void *arg) { const unsigned char *c = d; for (unsigned i = 0; i < n; ++i) printf ("%02x", c[i]); } static void filename (const char *f, void *arg) { __gcov_filename_to_gcfn (f, dump, arg ); } static void * allocate (unsigned length, void *arg) { return malloc (length); } static void dump_gcov_info (void) { const struct gcov_info *const *info = __gcov_info_start; const struct gcov_info *const *end = __gcov_info_end; /* Obfuscate variable to prevent compiler optimizations. */ __asm__ ("" : "+r" (info)); while (info != end) { void *arg = NULL; __gcov_info_to_gcda (*info, filename, dump, allocate, arg); putchar ('\n'); ++info; } } int main (void) { dump_gcov_info (); return 0; } The merge-stream subcommand of gcov-tool may be used to deserialize the data stream generated by the "__gcov_filename_to_gcfn" and "__gcov_info_to_gcda" functions and merge the profile information into .gcda files on the host filesystem. -fprofile-note=path If path is specified, GCC saves .gcno file into path location. If you combine the option with multiple source files, the .gcno file will be overwritten. -fprofile-prefix-path=path This option can be used in combination with profile-generate=profile_dir and profile-use=profile_dir to inform GCC where is the base directory of built source tree. By default profile_dir will contain files with mangled absolute paths of all object files in the built project. This is not desirable when directory used to build the instrumented binary differs from the directory used to build the binary optimized with profile feedback because the profile data will not be found during the optimized build. In such setups -fprofile-prefix-path=path with path pointing to the base directory of the build can be used to strip the irrelevant part of the path and keep all file names relative to the main build directory. -fprofile-prefix-map=old=new When compiling files residing in directory old, record profiling information (with --coverage) describing them as if the files resided in directory new instead. See also -ffile-prefix-map and -fcanon-prefix-map. -fprofile-update=method Alter the update method for an application instrumented for profile feedback based optimization. The method argument should be one of single, atomic or prefer-atomic. The first one is useful for single-threaded applications, while the second one prevents profile corruption by emitting thread-safe code. Warning: When an application does not properly join all threads (or creates an detached thread), a profile file can be still corrupted. Using prefer-atomic would be transformed either to atomic, when supported by a target, or to single otherwise. The GCC driver automatically selects prefer-atomic when -pthread is present in the command line. -fprofile-filter-files=regex Instrument only functions from files whose name matches any of the regular expressions (separated by semi-colons). For example, -fprofile-filter-files=main\.c;module.*\.c will instrument only main.c and all C files starting with 'module'. -fprofile-exclude-files=regex Instrument only functions from files whose name does not match any of the regular expressions (separated by semi-colons). For example, -fprofile-exclude-files=/usr/.* will prevent instrumentation of all files that are located in the /usr/ folder. -fprofile-reproducible=[multithreaded|parallel-runs|serial] Control level of reproducibility of profile gathered by "-fprofile-generate". This makes it possible to rebuild program with same outcome which is useful, for example, for distribution packages. With -fprofile-reproducible=serial the profile gathered by -fprofile-generate is reproducible provided the trained program behaves the same at each invocation of the train run, it is not multi-threaded and profile data streaming is always done in the same order. Note that profile streaming happens at the end of program run but also before "fork" function is invoked. Note that it is quite common that execution counts of some part of programs depends, for example, on length of temporary file names or memory space randomization (that may affect hash-table collision rate). Such non-reproducible part of programs may be annotated by "no_instrument_function" function attribute. gcov-dump with -l can be used to dump gathered data and verify that they are indeed reproducible. With -fprofile-reproducible=parallel-runs collected profile stays reproducible regardless the order of streaming of the data into gcda files. This setting makes it possible to run multiple instances of instrumented program in parallel (such as with "make -j"). This reduces quality of gathered data, in particular of indirect call profiling. -fsanitize=address Enable AddressSanitizer, a fast memory error detector. Memory access instructions are instrumented to detect out-of-bounds and use-after-free bugs. The option enables -fsanitize-address-use-after-scope. See <https://github.com/google/sanitizers/wiki/AddressSanitizer> for more details. The run-time behavior can be influenced using the ASAN_OPTIONS environment variable. When set to "help=1", the available options are shown at startup of the instrumented program. See <https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags> for a list of supported options. The option cannot be combined with -fsanitize=thread or -fsanitize=hwaddress. Note that the only target -fsanitize=hwaddress is currently supported on is AArch64. To get more accurate stack traces, it is possible to use options such as -O0, -O1, or -Og (which, for instance, prevent most function inlining), -fno-optimize-sibling-calls (which prevents optimizing sibling and tail recursive calls; this option is implicit for -O0, -O1, or -Og), or -fno-ipa-icf (which disables Identical Code Folding for functions). Since multiple runs of the program may yield backtraces with different addresses due to ASLR (Address Space Layout Randomization), it may be desirable to turn ASLR off. On Linux, this can be achieved with setarch `uname -m` -R ./prog. -fsanitize=kernel-address Enable AddressSanitizer for Linux kernel. See <https://github.com/google/kernel-sanitizers> for more details. -fsanitize=hwaddress Enable Hardware-assisted AddressSanitizer, which uses a hardware ability to ignore the top byte of a pointer to allow the detection of memory errors with a low memory overhead. Memory access instructions are instrumented to detect out-of-bounds and use- after-free bugs. The option enables -fsanitize-address-use-after-scope. See <https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html> for more details. The run-time behavior can be influenced using the HWASAN_OPTIONS environment variable. When set to "help=1", the available options are shown at startup of the instrumented program. The option cannot be combined with -fsanitize=thread or -fsanitize=address, and is currently only available on AArch64. -fsanitize=kernel-hwaddress Enable Hardware-assisted AddressSanitizer for compilation of the Linux kernel. Similar to -fsanitize=kernel-address but using an alternate instrumentation method, and similar to -fsanitize=hwaddress but with instrumentation differences necessary for compiling the Linux kernel. These differences are to avoid hwasan library initialization calls and to account for the stack pointer having a different value in its top byte. Note: This option has different defaults to the -fsanitize=hwaddress. Instrumenting the stack and alloca calls are not on by default but are still possible by specifying the command- line options --param hwasan-instrument-stack=1 and --param hwasan-instrument-allocas=1 respectively. Using a random frame tag is not implemented for kernel instrumentation. -fsanitize=pointer-compare Instrument comparison operation (<, <=, >, >=) with pointer operands. The option must be combined with either -fsanitize=kernel-address or -fsanitize=address The option cannot be combined with -fsanitize=thread. Note: By default the check is disabled at run time. To enable it, add "detect_invalid_pointer_pairs=2" to the environment variable ASAN_OPTIONS. Using "detect_invalid_pointer_pairs=1" detects invalid operation only when both pointers are non-null. -fsanitize=pointer-subtract Instrument subtraction with pointer operands. The option must be combined with either -fsanitize=kernel-address or -fsanitize=address The option cannot be combined with -fsanitize=thread. Note: By default the check is disabled at run time. To enable it, add "detect_invalid_pointer_pairs=2" to the environment variable ASAN_OPTIONS. Using "detect_invalid_pointer_pairs=1" detects invalid operation only when both pointers are non-null. -fsanitize=shadow-call-stack Enable ShadowCallStack, a security enhancement mechanism used to protect programs against return address overwrites (e.g. stack buffer overflows.) It works by saving a function's return address to a separately allocated shadow call stack in the function prologue and restoring the return address from the shadow call stack in the function epilogue. Instrumentation only occurs in functions that need to save the return address to the stack. Currently it only supports the aarch64 platform. It is specifically designed for linux kernels that enable the CONFIG_SHADOW_CALL_STACK option. For the user space programs, runtime support is not currently provided in libc and libgcc. Users who want to use this feature in user space need to provide their own support for the runtime. It should be noted that this may cause the ABI rules to be broken. On aarch64, the instrumentation makes use of the platform register "x18". This generally means that any code that may run on the same thread as code compiled with ShadowCallStack must be compiled with the flag -ffixed-x18, otherwise functions compiled without -ffixed-x18 might clobber "x18" and so corrupt the shadow stack pointer. Also, because there is no userspace runtime support, code compiled with ShadowCallStack cannot use exception handling. Use -fno-exceptions to turn off exceptions. See <https://clang.llvm.org/docs/ShadowCallStack.html> for more details. -fsanitize=thread Enable ThreadSanitizer, a fast data race detector. Memory access instructions are instrumented to detect data race bugs. See <https://github.com/google/sanitizers/wiki#threadsanitizer> for more details. The run-time behavior can be influenced using the TSAN_OPTIONS environment variable; see <https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags> for a list of supported options. The option cannot be combined with -fsanitize=address, -fsanitize=leak. Note that sanitized atomic builtins cannot throw exceptions when operating on invalid memory addresses with non-call exceptions (-fnon-call-exceptions). -fsanitize=leak Enable LeakSanitizer, a memory leak detector. This option only matters for linking of executables. The executable is linked against a library that overrides "malloc" and other allocator functions. See <https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer> for more details. The run-time behavior can be influenced using the LSAN_OPTIONS environment variable. The option cannot be combined with -fsanitize=thread. -fsanitize=undefined Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector. Various computations are instrumented to detect undefined behavior at runtime. See <https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html> for more details. The run-time behavior can be influenced using the UBSAN_OPTIONS environment variable. Current suboptions are: -fsanitize=shift This option enables checking that the result of a shift operation is not undefined. Note that what exactly is considered undefined differs slightly between C and C++, as well as between ISO C90 and C99, etc. This option has two suboptions, -fsanitize=shift-base and -fsanitize=shift-exponent. -fsanitize=shift-exponent This option enables checking that the second argument of a shift operation is not negative and is smaller than the precision of the promoted first argument. -fsanitize=shift-base If the second argument of a shift operation is within range, check that the result of a shift operation is not undefined. Note that what exactly is considered undefined differs slightly between C and C++, as well as between ISO C90 and C99, etc. -fsanitize=integer-divide-by-zero Detect integer division by zero. -fsanitize=unreachable With this option, the compiler turns the "__builtin_unreachable" call into a diagnostics message call instead. When reaching the "__builtin_unreachable" call, the behavior is undefined. -fsanitize=vla-bound This option instructs the compiler to check that the size of a variable length array is positive. -fsanitize=null This option enables pointer checking. Particularly, the application built with this option turned on will issue an error message when it tries to dereference a NULL pointer, or if a reference (possibly an rvalue reference) is bound to a NULL pointer, or if a method is invoked on an object pointed by a NULL pointer. -fsanitize=return This option enables return statement checking. Programs built with this option turned on will issue an error message when the end of a non-void function is reached without actually returning a value. This option works in C++ only. -fsanitize=signed-integer-overflow This option enables signed integer overflow checking. We check that the result of "+", "*", and both unary and binary "-" does not overflow in the signed arithmetics. This also detects "INT_MIN / -1" signed division. Note, integer promotion rules must be taken into account. That is, the following is not an overflow: signed char a = SCHAR_MAX; a++; -fsanitize=bounds This option enables instrumentation of array bounds. Various out of bounds accesses are detected. Flexible array members, flexible array member-like arrays, and initializers of variables with static storage are not instrumented, with the exception of flexible array member-like arrays for which "-fstrict-flex-arrays" or "-fstrict-flex-arrays=" options or "strict_flex_array" attributes say they shouldn't be treated like flexible array member-like arrays. -fsanitize=bounds-strict This option enables strict instrumentation of array bounds. Most out of bounds accesses are detected, including flexible array member-like arrays. Initializers of variables with static storage are not instrumented. -fsanitize=alignment This option enables checking of alignment of pointers when they are dereferenced, or when a reference is bound to insufficiently aligned target, or when a method or constructor is invoked on insufficiently aligned object. -fsanitize=object-size This option enables instrumentation of memory references using the "__builtin_dynamic_object_size" function. Various out of bounds pointer accesses are detected. -fsanitize=float-divide-by-zero Detect floating-point division by zero. Unlike other similar options, -fsanitize=float-divide-by-zero is not enabled by -fsanitize=undefined, since floating-point division by zero can be a legitimate way of obtaining infinities and NaNs. -fsanitize=float-cast-overflow This option enables floating-point type to integer conversion checking. We check that the result of the conversion does not overflow. Unlike other similar options, -fsanitize=float-cast-overflow is not enabled by -fsanitize=undefined. This option does not work well with "FE_INVALID" exceptions enabled. -fsanitize=nonnull-attribute This option enables instrumentation of calls, checking whether null values are not passed to arguments marked as requiring a non-null value by the "nonnull" function attribute. -fsanitize=returns-nonnull-attribute This option enables instrumentation of return statements in functions marked with "returns_nonnull" function attribute, to detect returning of null values from such functions. -fsanitize=bool This option enables instrumentation of loads from bool. If a value other than 0/1 is loaded, a run-time error is issued. -fsanitize=enum This option enables instrumentation of loads from an enum type. If a value outside the range of values for the enum type is loaded, a run-time error is issued. -fsanitize=vptr This option enables instrumentation of C++ member function calls, member accesses and some conversions between pointers to base and derived classes, to verify the referenced object has the correct dynamic type. -fsanitize=pointer-overflow This option enables instrumentation of pointer arithmetics. If the pointer arithmetics overflows, a run-time error is issued. -fsanitize=builtin This option enables instrumentation of arguments to selected builtin functions. If an invalid value is passed to such arguments, a run-time error is issued. E.g. passing 0 as the argument to "__builtin_ctz" or "__builtin_clz" invokes undefined behavior and is diagnosed by this option. Note that sanitizers tend to increase the rate of false positive warnings, most notably those around -Wmaybe-uninitialized. We recommend against combining -Werror and [the use of] sanitizers. While -ftrapv causes traps for signed overflows to be emitted, -fsanitize=undefined gives a diagnostic message. This currently works only for the C family of languages. -fno-sanitize=all This option disables all previously enabled sanitizers. -fsanitize=all is not allowed, as some sanitizers cannot be used together. -fasan-shadow-offset=number This option forces GCC to use custom shadow offset in AddressSanitizer checks. It is useful for experimenting with different shadow memory layouts in Kernel AddressSanitizer. -fsanitize-sections=s1,s2,... Sanitize global variables in selected user-defined sections. si may contain wildcards. -fsanitize-recover[=opts] -fsanitize-recover= controls error recovery mode for sanitizers mentioned in comma-separated list of opts. Enabling this option for a sanitizer component causes it to attempt to continue running the program as if no error happened. This means multiple runtime errors can be reported in a single program run, and the exit code of the program may indicate success even when errors have been reported. The -fno-sanitize-recover= option can be used to alter this behavior: only the first detected error is reported and program then exits with a non-zero exit code. Currently this feature only works for -fsanitize=undefined (and its suboptions except for -fsanitize=unreachable and -fsanitize=return), -fsanitize=float-cast-overflow, -fsanitize=float-divide-by-zero, -fsanitize=bounds-strict, -fsanitize=kernel-address and -fsanitize=address. For these sanitizers error recovery is turned on by default, except -fsanitize=address, for which this feature is experimental. -fsanitize-recover=all and -fno-sanitize-recover=all is also accepted, the former enables recovery for all sanitizers that support it, the latter disables recovery for all sanitizers that support it. Even if a recovery mode is turned on the compiler side, it needs to be also enabled on the runtime library side, otherwise the failures are still fatal. The runtime library defaults to "halt_on_error=0" for ThreadSanitizer and UndefinedBehaviorSanitizer, while default value for AddressSanitizer is "halt_on_error=1". This can be overridden through setting the "halt_on_error" flag in the corresponding environment variable. Syntax without an explicit opts parameter is deprecated. It is equivalent to specifying an opts list of: undefined,float-cast-overflow,float-divide-by-zero,bounds-strict -fsanitize-address-use-after-scope Enable sanitization of local variables to detect use-after-scope bugs. The option sets -fstack-reuse to none. -fsanitize-trap[=opts] The -fsanitize-trap= option instructs the compiler to report for sanitizers mentioned in comma-separated list of opts undefined behavior using "__builtin_trap" rather than a "libubsan" library routine. If this option is enabled for certain sanitizer, it takes precedence over the -fsanitizer-recover= for that sanitizer, "__builtin_trap" will be emitted and be fatal regardless of whether recovery is enabled or disabled using -fsanitize-recover=. The advantage of this is that the "libubsan" library is not needed and is not linked in, so this is usable even in freestanding environments. Currently this feature works with -fsanitize=undefined (and its suboptions except for -fsanitize=vptr), -fsanitize=float-cast-overflow, -fsanitize=float-divide-by-zero and -fsanitize=bounds-strict. "-fsanitize-trap=all" can be also specified, which enables it for "undefined" suboptions, -fsanitize=float-cast-overflow, -fsanitize=float-divide-by-zero and -fsanitize=bounds-strict. If "-fsanitize-trap=undefined" or "-fsanitize-trap=all" is used and "-fsanitize=vptr" is enabled on the command line, the instrumentation is silently ignored as the instrumentation always needs "libubsan" support, -fsanitize-trap=vptr is not allowed. -fsanitize-undefined-trap-on-error The -fsanitize-undefined-trap-on-error option is deprecated equivalent of -fsanitize-trap=all. -fsanitize-coverage=trace-pc Enable coverage-guided fuzzing code instrumentation. Inserts a call to "__sanitizer_cov_trace_pc" into every basic block. -fsanitize-coverage=trace-cmp Enable dataflow guided fuzzing code instrumentation. Inserts a call to "__sanitizer_cov_trace_cmp1", "__sanitizer_cov_trace_cmp2", "__sanitizer_cov_trace_cmp4" or "__sanitizer_cov_trace_cmp8" for integral comparison with both operands variable or "__sanitizer_cov_trace_const_cmp1", "__sanitizer_cov_trace_const_cmp2", "__sanitizer_cov_trace_const_cmp4" or "__sanitizer_cov_trace_const_cmp8" for integral comparison with one operand constant, "__sanitizer_cov_trace_cmpf" or "__sanitizer_cov_trace_cmpd" for float or double comparisons and "__sanitizer_cov_trace_switch" for switch statements. -fcf-protection=[full|branch|return|none|check] Enable code instrumentation of control-flow transfers to increase program security by checking that target addresses of control-flow transfer instructions (such as indirect function call, function return, indirect jump) are valid. This prevents diverting the flow of control to an unexpected target. This is intended to protect against such threats as Return-oriented Programming (ROP), and similarly call/jmp-oriented programming (COP/JOP). The value "branch" tells the compiler to implement checking of validity of control-flow transfer at the point of indirect branch instructions, i.e. call/jmp instructions. The value "return" implements checking of validity at the point of returning from a function. The value "full" is an alias for specifying both "branch" and "return". The value "none" turns off instrumentation. The value "check" is used for the final link with link-time optimization (LTO). An error is issued if LTO object files are compiled with different -fcf-protection values. The value "check" is ignored at the compile time. The macro "__CET__" is defined when -fcf-protection is used. The first bit of "__CET__" is set to 1 for the value "branch" and the second bit of "__CET__" is set to 1 for the "return". You can also use the "nocf_check" attribute to identify which functions and calls should be skipped from instrumentation. Currently the x86 GNU/Linux target provides an implementation based on Intel Control-flow Enforcement Technology (CET) which works for i686 processor or newer. -fharden-compares For every logical test that survives gimple optimizations and is not the condition in a conditional branch (for example, conditions tested for conditional moves, or to store in boolean variables), emit extra code to compute and verify the reversed condition, and to call "__builtin_trap" if the results do not match. Use with -fharden-conditional-branches to cover all conditionals. -fharden-conditional-branches For every non-vectorized conditional branch that survives gimple optimizations, emit extra code to compute and verify the reversed condition, and to call "__builtin_trap" if the result is unexpected. Use with -fharden-compares to cover all conditionals. -fstack-protector Emit extra code to check for buffer overflows, such as stack smashing attacks. This is done by adding a guard variable to functions with vulnerable objects. This includes functions that call "alloca", and functions with buffers larger than or equal to 8 bytes. The guards are initialized when a function is entered and then checked when the function exits. If a guard check fails, an error message is printed and the program exits. Only variables that are actually allocated on the stack are considered, optimized away variables or variables allocated in registers don't count. -fstack-protector-all Like -fstack-protector except that all functions are protected. -fstack-protector-strong Like -fstack-protector but includes additional functions to be protected --- those that have local array definitions, or have references to local frame addresses. Only variables that are actually allocated on the stack are considered, optimized away variables or variables allocated in registers don't count. -fstack-protector-explicit Like -fstack-protector but only protects those functions which have the "stack_protect" attribute. -fstack-check Generate code to verify that you do not go beyond the boundary of the stack. You should specify this flag if you are running in an environment with multiple threads, but you only rarely need to specify it in a single-threaded environment since stack overflow is automatically detected on nearly all systems if there is only one stack. Note that this switch does not actually cause checking to be done; the operating system or the language runtime must do that. The switch causes generation of code to ensure that they see the stack being extended. You can additionally specify a string parameter: no means no checking, generic means force the use of old-style checking, specific means use the best checking method and is equivalent to bare -fstack-check. Old-style checking is a generic mechanism that requires no specific target support in the compiler but comes with the following drawbacks: 1. Modified allocation strategy for large objects: they are always allocated dynamically if their size exceeds a fixed threshold. Note this may change the semantics of some code. 2. Fixed limit on the size of the static frame of functions: when it is topped by a particular function, stack checking is not reliable and a warning is issued by the compiler. 3. Inefficiency: because of both the modified allocation strategy and the generic implementation, code performance is hampered. Note that old-style stack checking is also the fallback method for specific if no target support has been added in the compiler. -fstack-check= is designed for Ada's needs to detect infinite recursion and stack overflows. specific is an excellent choice when compiling Ada code. It is not generally sufficient to protect against stack-clash attacks. To protect against those you want -fstack-clash-protection. -fstack-clash-protection Generate code to prevent stack clash style attacks. When this option is enabled, the compiler will only allocate one page of stack space at a time and each page is accessed immediately after allocation. Thus, it prevents allocations from jumping over any stack guard page provided by the operating system. Most targets do not fully support stack clash protection. However, on those targets -fstack-clash-protection will protect dynamic stack allocations. -fstack-clash-protection may also provide limited protection for static stack allocations if the target supports -fstack-check=specific. -fstack-limit-register=reg -fstack-limit-symbol=sym -fno-stack-limit Generate code to ensure that the stack does not grow beyond a certain value, either the value of a register or the address of a symbol. If a larger stack is required, a signal is raised at run time. For most targets, the signal is raised before the stack overruns the boundary, so it is possible to catch the signal without taking special precautions. For instance, if the stack starts at absolute address 0x80000000 and grows downwards, you can use the flags -fstack-limit-symbol=__stack_limit and -Wl,--defsym,__stack_limit=0x7ffe0000 to enforce a stack limit of 128KB. Note that this may only work with the GNU linker. You can locally override stack limit checking by using the "no_stack_limit" function attribute. -fsplit-stack Generate code to automatically split the stack before it overflows. The resulting program has a discontiguous stack which can only overflow if the program is unable to allocate any more memory. This is most useful when running threaded programs, as it is no longer necessary to calculate a good stack size to use for each thread. This is currently only implemented for the x86 targets running GNU/Linux. When code compiled with -fsplit-stack calls code compiled without -fsplit-stack, there may not be much stack space available for the latter code to run. If compiling all code, including library code, with -fsplit-stack is not an option, then the linker can fix up these calls so that the code compiled without -fsplit-stack always has a large stack. Support for this is implemented in the gold linker in GNU binutils release 2.21 and later. -fvtable-verify=[std|preinit|none] This option is only available when compiling C++ code. It turns on (or off, if using -fvtable-verify=none) the security feature that verifies at run time, for every virtual call, that the vtable pointer through which the call is made is valid for the type of the object, and has not been corrupted or overwritten. If an invalid vtable pointer is detected at run time, an error is reported and execution of the program is immediately halted. This option causes run-time data structures to be built at program startup, which are used for verifying the vtable pointers. The options std and preinit control the timing of when these data structures are built. In both cases the data structures are built before execution reaches "main". Using -fvtable-verify=std causes the data structures to be built after shared libraries have been loaded and initialized. -fvtable-verify=preinit causes them to be built before shared libraries have been loaded and initialized. If this option appears multiple times in the command line with different values specified, none takes highest priority over both std and preinit; preinit takes priority over std. -fvtv-debug When used in conjunction with -fvtable-verify=std or -fvtable-verify=preinit, causes debug versions of the runtime functions for the vtable verification feature to be called. This flag also causes the compiler to log information about which vtable pointers it finds for each class. This information is written to a file named vtv_set_ptr_data.log in the directory named by the environment variable VTV_LOGS_DIR if that is defined or the current working directory otherwise. Note: This feature appends data to the log file. If you want a fresh log file, be sure to delete any existing one. -fvtv-counts This is a debugging flag. When used in conjunction with -fvtable-verify=std or -fvtable-verify=preinit, this causes the compiler to keep track of the total number of virtual calls it encounters and the number of verifications it inserts. It also counts the number of calls to certain run-time library functions that it inserts and logs this information for each compilation unit. The compiler writes this information to a file named vtv_count_data.log in the directory named by the environment variable VTV_LOGS_DIR if that is defined or the current working directory otherwise. It also counts the size of the vtable pointer sets for each class, and writes this information to vtv_class_set_sizes.log in the same directory. Note: This feature appends data to the log files. To get fresh log files, be sure to delete any existing ones. -finstrument-functions Generate instrumentation calls for entry and exit to functions. Just after function entry and just before function exit, the following profiling functions are called with the address of the current function and its call site. (On some platforms, "__builtin_return_address" does not work beyond the current function, so the call site information may not be available to the profiling functions otherwise.) void __cyg_profile_func_enter (void *this_fn, void *call_site); void __cyg_profile_func_exit (void *this_fn, void *call_site); The first argument is the address of the start of the current function, which may be looked up exactly in the symbol table. This instrumentation is also done for functions expanded inline in other functions. The profiling calls indicate where, conceptually, the inline function is entered and exited. This means that addressable versions of such functions must be available. If all your uses of a function are expanded inline, this may mean an additional expansion of code size. If you use "extern inline" in your C code, an addressable version of such functions must be provided. (This is normally the case anyway, but if you get lucky and the optimizer always expands the functions inline, you might have gotten away without providing static copies.) A function may be given the attribute "no_instrument_function", in which case this instrumentation is not done. This can be used, for example, for the profiling functions listed above, high-priority interrupt routines, and any functions from which the profiling functions cannot safely be called (perhaps signal handlers, if the profiling routines generate output or allocate memory). -finstrument-functions-once This is similar to -finstrument-functions, but the profiling functions are called only once per instrumented function, i.e. the first profiling function is called after the first entry into the instrumented function and the second profiling function is called before the exit corresponding to this first entry. The definition of "once" for the purpose of this option is a little vague because the implementation is not protected against data races. As a result, the implementation only guarantees that the profiling functions are called at least once per process and at most once per thread, but the calls are always paired, that is to say, if a thread calls the first function, then it will call the second function, unless it never reaches the exit of the instrumented function. -finstrument-functions-exclude-file-list=file,file,... Set the list of functions that are excluded from instrumentation (see the description of -finstrument-functions). If the file that contains a function definition matches with one of file, then that function is not instrumented. The match is done on substrings: if the file parameter is a substring of the file name, it is considered to be a match. For example: -finstrument-functions-exclude-file-list=/bits/stl,include/sys excludes any inline function defined in files whose pathnames contain /bits/stl or include/sys. If, for some reason, you want to include letter , in one of sym, write ,. For example, -finstrument-functions-exclude-file-list=',,tmp' (note the single quote surrounding the option). -finstrument-functions-exclude-function-list=sym,sym,... This is similar to -finstrument-functions-exclude-file-list, but this option sets the list of function names to be excluded from instrumentation. The function name to be matched is its user- visible name, such as "vector<int> blah(const vector<int> &)", not the internal mangled name (e.g., "_Z4blahRSt6vectorIiSaIiEE"). The match is done on substrings: if the sym parameter is a substring of the function name, it is considered to be a match. For C99 and C++ extended identifiers, the function name must be given in UTF-8, not using universal character names. -fpatchable-function-entry=N[,M] Generate N NOPs right at the beginning of each function, with the function entry point before the Mth NOP. If M is omitted, it defaults to 0 so the function entry points to the address just at the first NOP. The NOP instructions reserve extra space which can be used to patch in any desired instrumentation at run time, provided that the code segment is writable. The amount of space is controllable indirectly via the number of NOPs; the NOP instruction used corresponds to the instruction emitted by the internal GCC back-end interface "gen_nop". This behavior is target-specific and may also depend on the architecture variant and/or other compilation options. For run-time identification, the starting addresses of these areas, which correspond to their respective function entries minus M, are additionally collected in the "__patchable_function_entries" section of the resulting binary. Note that the value of "__attribute__ ((patchable_function_entry (N,M)))" takes precedence over command-line option -fpatchable-function-entry=N,M. This can be used to increase the area size or to remove it completely on a single function. If "N=0", no pad location is recorded. The NOP instructions are inserted at---and maybe before, depending on M---the function entry address, even before the prologue. On PowerPC with the ELFv2 ABI, for a function with dual entry points, the local entry point is this function entry address. The maximum value of N and M is 65535. On PowerPC with the ELFv2 ABI, for a function with dual entry points, the supported values for M are 0, 2, 6 and 14. Options Controlling the Preprocessor These options control the C preprocessor, which is run on each C source file before actual compilation. If you use the -E option, nothing is done except preprocessing. Some of these options make sense only together with -E because they cause the preprocessor output to be unsuitable for actual compilation. In addition to the options listed here, there are a number of options to control search paths for include files documented in Directory Options. Options to control preprocessor diagnostics are listed in Warning Options. -D name Predefine name as a macro, with definition 1. -D name=definition The contents of definition are tokenized and processed as if they appeared during translation phase three in a #define directive. In particular, the definition is truncated by embedded newline characters. If you are invoking the preprocessor from a shell or shell-like program you may need to use the shell's quoting syntax to protect characters such as spaces that have a meaning in the shell syntax. If you wish to define a function-like macro on the command line, write its argument list with surrounding parentheses before the equals sign (if any). Parentheses are meaningful to most shells, so you should quote the option. With sh and csh, -D'name(args...)=definition' works. -D and -U options are processed in the order they are given on the command line. All -imacros file and -include file options are processed after all -D and -U options. -U name Cancel any previous definition of name, either built in or provided with a -D option. -include file Process file as if "#include "file"" appeared as the first line of the primary source file. However, the first directory searched for file is the preprocessor's working directory instead of the directory containing the main source file. If not found there, it is searched for in the remainder of the "#include "..."" search chain as normal. If multiple -include options are given, the files are included in the order they appear on the command line. -imacros file Exactly like -include, except that any output produced by scanning file is thrown away. Macros it defines remain defined. This allows you to acquire all the macros from a header without also processing its declarations. All files specified by -imacros are processed before all files specified by -include. -undef Do not predefine any system-specific or GCC-specific macros. The standard predefined macros remain defined. -pthread Define additional macros required for using the POSIX threads library. You should use this option consistently for both compilation and linking. This option is supported on GNU/Linux targets, most other Unix derivatives, and also on x86 Cygwin and MinGW targets. -M Instead of outputting the result of preprocessing, output a rule suitable for make describing the dependencies of the main source file. The preprocessor outputs one make rule containing the object file name for that source file, a colon, and the names of all the included files, including those coming from -include or -imacros command-line options. Unless specified explicitly (with -MT or -MQ), the object file name consists of the name of the source file with any suffix replaced with object file suffix and with any leading directory parts removed. If there are many included files then the rule is split into several lines using \-newline. The rule has no commands. This option does not suppress the preprocessor's debug output, such as -dM. To avoid mixing such debug output with the dependency rules you should explicitly specify the dependency output file with -MF, or use an environment variable like DEPENDENCIES_OUTPUT. Debug output is still sent to the regular output stream as normal. Passing -M to the driver implies -E, and suppresses warnings with an implicit -w. -MM Like -M but do not mention header files that are found in system header directories, nor header files that are included, directly or indirectly, from such a header. This implies that the choice of angle brackets or double quotes in an #include directive does not in itself determine whether that header appears in -MM dependency output. -MF file When used with -M or -MM, specifies a file to write the dependencies to. If no -MF switch is given the preprocessor sends the rules to the same place it would send preprocessed output. When used with the driver options -MD or -MMD, -MF overrides the default dependency output file. If file is -, then the dependencies are written to stdout. -MG In conjunction with an option such as -M requesting dependency generation, -MG assumes missing header files are generated files and adds them to the dependency list without raising an error. The dependency filename is taken directly from the "#include" directive without prepending any path. -MG also suppresses preprocessed output, as a missing header file renders this useless. This feature is used in automatic updating of makefiles. -Mno-modules Disable dependency generation for compiled module interfaces. -MP This option instructs CPP to add a phony target for each dependency other than the main file, causing each to depend on nothing. These dummy rules work around errors make gives if you remove header files without updating the Makefile to match. This is typical output: test.o: test.c test.h test.h: -MT target Change the target of the rule emitted by dependency generation. By default CPP takes the name of the main input file, deletes any directory components and any file suffix such as .c, and appends the platform's usual object suffix. The result is the target. An -MT option sets the target to be exactly the string you specify. If you want multiple targets, you can specify them as a single argument to -MT, or use multiple -MT options. For example, -MT '$(objpfx)foo.o' might give $(objpfx)foo.o: foo.c -MQ target Same as -MT, but it quotes any characters which are special to Make. -MQ '$(objpfx)foo.o' gives $$(objpfx)foo.o: foo.c The default target is automatically quoted, as if it were given with -MQ. -MD -MD is equivalent to -M -MF file, except that -E is not implied. The driver determines file based on whether an -o option is given. If it is, the driver uses its argument but with a suffix of .d, otherwise it takes the name of the input file, removes any directory components and suffix, and applies a .d suffix. If -MD is used in conjunction with -E, any -o switch is understood to specify the dependency output file, but if used without -E, each -o is understood to specify a target object file. Since -E is not implied, -MD can be used to generate a dependency output file as a side effect of the compilation process. -MMD Like -MD except mention only user header files, not system header files. -fpreprocessed Indicate to the preprocessor that the input file has already been preprocessed. This suppresses things like macro expansion, trigraph conversion, escaped newline splicing, and processing of most directives. The preprocessor still recognizes and removes comments, so that you can pass a file preprocessed with -C to the compiler without problems. In this mode the integrated preprocessor is little more than a tokenizer for the front ends. -fpreprocessed is implicit if the input file has one of the extensions .i, .ii or .mi. These are the extensions that GCC uses for preprocessed files created by -save-temps. -fdirectives-only When preprocessing, handle directives, but do not expand macros. The option's behavior depends on the -E and -fpreprocessed options. With -E, preprocessing is limited to the handling of directives such as "#define", "#ifdef", and "#error". Other preprocessor operations, such as macro expansion and trigraph conversion are not performed. In addition, the -dD option is implicitly enabled. With -fpreprocessed, predefinition of command line and most builtin macros is disabled. Macros such as "__LINE__", which are contextually dependent, are handled normally. This enables compilation of files previously preprocessed with "-E -fdirectives-only". With both -E and -fpreprocessed, the rules for -fpreprocessed take precedence. This enables full preprocessing of files previously preprocessed with "-E -fdirectives-only". -fdollars-in-identifiers Accept $ in identifiers. -fextended-identifiers Accept universal character names and extended characters in identifiers. This option is enabled by default for C99 (and later C standard versions) and C++. -fno-canonical-system-headers When preprocessing, do not shorten system header paths with canonicalization. -fmax-include-depth=depth Set the maximum depth of the nested #include. The default is 200. -ftabstop=width Set the distance between tab stops. This helps the preprocessor report correct column numbers in warnings or errors, even if tabs appear on the line. If the value is less than 1 or greater than 100, the option is ignored. The default is 8. -ftrack-macro-expansion[=level] Track locations of tokens across macro expansions. This allows the compiler to emit diagnostic about the current macro expansion stack when a compilation error occurs in a macro expansion. Using this option makes the preprocessor and the compiler consume more memory. The level parameter can be used to choose the level of precision of token location tracking thus decreasing the memory consumption if necessary. Value 0 of level de-activates this option. Value 1 tracks tokens locations in a degraded mode for the sake of minimal memory overhead. In this mode all tokens resulting from the expansion of an argument of a function-like macro have the same location. Value 2 tracks tokens locations completely. This value is the most memory hungry. When this option is given no argument, the default parameter value is 2. Note that "-ftrack-macro-expansion=2" is activated by default. -fmacro-prefix-map=old=new When preprocessing files residing in directory old, expand the "__FILE__" and "__BASE_FILE__" macros as if the files resided in directory new instead. This can be used to change an absolute path to a relative path by using . for new which can result in more reproducible builds that are location independent. This option also affects "__builtin_FILE()" during compilation. See also -ffile-prefix-map and -fcanon-prefix-map. -fexec-charset=charset Set the execution character set, used for string and character constants. The default is UTF-8. charset can be any encoding supported by the system's "iconv" library routine. -fwide-exec-charset=charset Set the wide execution character set, used for wide string and character constants. The default is one of UTF-32BE, UTF-32LE, UTF-16BE, or UTF-16LE, whichever corresponds to the width of "wchar_t" and the big-endian or little-endian byte order being used for code generation. As with -fexec-charset, charset can be any encoding supported by the system's "iconv" library routine; however, you will have problems with encodings that do not fit exactly in "wchar_t". -finput-charset=charset Set the input character set, used for translation from the character set of the input file to the source character set used by GCC. If the locale does not specify, or GCC cannot get this information from the locale, the default is UTF-8. This can be overridden by either the locale or this command-line option. Currently the command-line option takes precedence if there's a conflict. charset can be any encoding supported by the system's "iconv" library routine. -fpch-deps When using precompiled headers, this flag causes the dependency- output flags to also list the files from the precompiled header's dependencies. If not specified, only the precompiled header are listed and not the files that were used to create it, because those files are not consulted when a precompiled header is used. -fpch-preprocess This option allows use of a precompiled header together with -E. It inserts a special "#pragma", "#pragma GCC pch_preprocess "filename"" in the output to mark the place where the precompiled header was found, and its filename. When -fpreprocessed is in use, GCC recognizes this "#pragma" and loads the PCH. This option is off by default, because the resulting preprocessed output is only really suitable as input to GCC. It is switched on by -save-temps. You should not write this "#pragma" in your own code, but it is safe to edit the filename if the PCH file is available in a different location. The filename may be absolute or it may be relative to GCC's current directory. -fworking-directory Enable generation of linemarkers in the preprocessor output that let the compiler know the current working directory at the time of preprocessing. When this option is enabled, the preprocessor emits, after the initial linemarker, a second linemarker with the current working directory followed by two slashes. GCC uses this directory, when it's present in the preprocessed input, as the directory emitted as the current working directory in some debugging information formats. This option is implicitly enabled if debugging information is enabled, but this can be inhibited with the negated form -fno-working-directory. If the -P flag is present in the command line, this option has no effect, since no "#line" directives are emitted whatsoever. -A predicate=answer Make an assertion with the predicate predicate and answer answer. This form is preferred to the older form -A predicate(answer), which is still supported, because it does not use shell special characters. -A -predicate=answer Cancel an assertion with the predicate predicate and answer answer. -C Do not discard comments. All comments are passed through to the output file, except for comments in processed directives, which are deleted along with the directive. You should be prepared for side effects when using -C; it causes the preprocessor to treat comments as tokens in their own right. For example, comments appearing at the start of what would be a directive line have the effect of turning that line into an ordinary source line, since the first token on the line is no longer a #. -CC Do not discard comments, including during macro expansion. This is like -C, except that comments contained within macros are also passed through to the output file where the macro is expanded. In addition to the side effects of the -C option, the -CC option causes all C++-style comments inside a macro to be converted to C-style comments. This is to prevent later use of that macro from inadvertently commenting out the remainder of the source line. The -CC option is generally used to support lint comments. -P Inhibit generation of linemarkers in the output from the preprocessor. This might be useful when running the preprocessor on something that is not C code, and will be sent to a program which might be confused by the linemarkers. -traditional -traditional-cpp Try to imitate the behavior of pre-standard C preprocessors, as opposed to ISO C preprocessors. See the GNU CPP manual for details. Note that GCC does not otherwise attempt to emulate a pre-standard C compiler, and these options are only supported with the -E switch, or when invoking CPP explicitly. -trigraphs Support ISO C trigraphs. These are three-character sequences, all starting with ??, that are defined by ISO C to stand for single characters. For example, ??/ stands for \, so '??/n' is a character constant for a newline. The nine trigraphs and their replacements are Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??- Replacement: [ ] { } # \ ^ | ~ By default, GCC ignores trigraphs, but in standard-conforming modes it converts them. See the -std and -ansi options. -remap Enable special code to work around file systems which only permit very short file names, such as MS-DOS. -H Print the name of each header file used, in addition to other normal activities. Each name is indented to show how deep in the #include stack it is. Precompiled header files are also printed, even if they are found to be invalid; an invalid precompiled header file is printed with ...x and a valid one with ...! . -dletters Says to make debugging dumps during compilation as specified by letters. The flags documented here are those relevant to the preprocessor. Other letters are interpreted by the compiler proper, or reserved for future versions of GCC, and so are silently ignored. If you specify letters whose behavior conflicts, the result is undefined. -dM Instead of the normal output, generate a list of #define directives for all the macros defined during the execution of the preprocessor, including predefined macros. This gives you a way of finding out what is predefined in your version of the preprocessor. Assuming you have no file foo.h, the command touch foo.h; cpp -dM foo.h shows all the predefined macros. If you use -dM without the -E option, -dM is interpreted as a synonym for -fdump-rtl-mach. -dD Like -dM except in two respects: it does not include the predefined macros, and it outputs both the #define directives and the result of preprocessing. Both kinds of output go to the standard output file. -dN Like -dD, but emit only the macro names, not their expansions. -dI Output #include directives in addition to the result of preprocessing. -dU Like -dD except that only macros that are expanded, or whose definedness is tested in preprocessor directives, are output; the output is delayed until the use or test of the macro; and #undef directives are also output for macros tested but undefined at the time. -fdebug-cpp This option is only useful for debugging GCC. When used from CPP or with -E, it dumps debugging information about location maps. Every token in the output is preceded by the dump of the map its location belongs to. When used from GCC without -E, this option has no effect. -Wp,option You can use -Wp,option to bypass the compiler driver and pass option directly through to the preprocessor. If option contains commas, it is split into multiple options at the commas. However, many options are modified, translated or interpreted by the compiler driver before being passed to the preprocessor, and -Wp forcibly bypasses this phase. The preprocessor's direct interface is undocumented and subject to change, so whenever possible you should avoid using -Wp and let the driver handle the options instead. -Xpreprocessor option Pass option as an option to the preprocessor. You can use this to supply system-specific preprocessor options that GCC does not recognize. If you want to pass an option that takes an argument, you must use -Xpreprocessor twice, once for the option and once for the argument. -no-integrated-cpp Perform preprocessing as a separate pass before compilation. By default, GCC performs preprocessing as an integrated part of input tokenization and parsing. If this option is provided, the appropriate language front end (cc1, cc1plus, or cc1obj for C, C++, and Objective-C, respectively) is instead invoked twice, once for preprocessing only and once for actual compilation of the preprocessed input. This option may be useful in conjunction with the -B or -wrapper options to specify an alternate preprocessor or perform additional processing of the program source between normal preprocessing and compilation. -flarge-source-files Adjust GCC to expect large source files, at the expense of slower compilation and higher memory usage. Specifically, GCC normally tracks both column numbers and line numbers within source files and it normally prints both of these numbers in diagnostics. However, once it has processed a certain number of source lines, it stops tracking column numbers and only tracks line numbers. This means that diagnostics for later lines do not include column numbers. It also means that options like -Wmisleading-indentation cease to work at that point, although the compiler prints a note if this happens. Passing -flarge-source-files significantly increases the number of source lines that GCC can process before it stops tracking columns. Passing Options to the Assembler You can pass options to the assembler. -Wa,option Pass option as an option to the assembler. If option contains commas, it is split into multiple options at the commas. -Xassembler option Pass option as an option to the assembler. You can use this to supply system-specific assembler options that GCC does not recognize. If you want to pass an option that takes an argument, you must use -Xassembler twice, once for the option and once for the argument. Options for Linking These options come into play when the compiler links object files into an executable output file. They are meaningless if the compiler is not doing a link step. object-file-name A file name that does not end in a special recognized suffix is considered to name an object file or library. (Object files are distinguished from libraries by the linker according to the file contents.) If linking is done, these object files are used as input to the linker. -c -S -E If any of these options is used, then the linker is not run, and object file names should not be used as arguments. -flinker-output=type This option controls code generation of the link-time optimizer. By default the linker output is automatically determined by the linker plugin. For debugging the compiler and if incremental linking with a non-LTO object file is desired, it may be useful to control the type manually. If type is exec, code generation produces a static binary. In this case -fpic and -fpie are both disabled. If type is dyn, code generation produces a shared library. In this case -fpic or -fPIC is preserved, but not enabled automatically. This allows to build shared libraries without position-independent code on architectures where this is possible, i.e. on x86. If type is pie, code generation produces an -fpie executable. This results in similar optimizations as exec except that -fpie is not disabled if specified at compilation time. If type is rel, the compiler assumes that incremental linking is done. The sections containing intermediate code for link-time optimization are merged, pre-optimized, and output to the resulting object file. In addition, if -ffat-lto-objects is specified, binary code is produced for future non-LTO linking. The object file produced by incremental linking is smaller than a static library produced from the same object files. At link time the result of incremental linking also loads faster than a static library assuming that the majority of objects in the library are used. Finally nolto-rel configures the compiler for incremental linking where code generation is forced, a final binary is produced, and the intermediate code for later link-time optimization is stripped. When multiple object files are linked together the resulting code is better optimized than with link-time optimizations disabled (for example, cross-module inlining happens), but most of benefits of whole program optimizations are lost. During the incremental link (by -r) the linker plugin defaults to rel. With current interfaces to GNU Binutils it is however not possible to incrementally link LTO objects and non-LTO objects into a single mixed object file. If any of object files in incremental link cannot be used for link-time optimization, the linker plugin issues a warning and uses nolto-rel. To maintain whole program optimization, it is recommended to link such objects into static library instead. Alternatively it is possible to use H.J. Lu's binutils with support for mixed objects. -fuse-ld=bfd Use the bfd linker instead of the default linker. -fuse-ld=gold Use the gold linker instead of the default linker. -fuse-ld=lld Use the LLVM lld linker instead of the default linker. -fuse-ld=mold Use the Modern Linker (mold) instead of the default linker. -llibrary -l library Search the library named library when linking. (The second alternative with the library as a separate argument is only for POSIX compliance and is not recommended.) The -l option is passed directly to the linker by GCC. Refer to your linker documentation for exact details. The general description below applies to the GNU linker. The linker searches a standard list of directories for the library. The directories searched include several standard system directories plus any that you specify with -L. Static libraries are archives of object files, and have file names like liblibrary.a. Some targets also support shared libraries, which typically have names like liblibrary.so. If both static and shared libraries are found, the linker gives preference to linking with the shared library unless the -static option is used. It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, foo.o -lz bar.o searches library z after file foo.o but before bar.o. If bar.o refers to functions in z, those functions may not be loaded. -lobjc You need this special case of the -l option in order to link an Objective-C or Objective-C++ program. -nostartfiles Do not use the standard system startup files when linking. The standard system libraries are used normally, unless -nostdlib, -nolibc, or -nodefaultlibs is used. -nodefaultlibs Do not use the standard system libraries when linking. Only the libraries you specify are passed to the linker, and options specifying linkage of the system libraries, such as -static-libgcc or -shared-libgcc, are ignored. The standard startup files are used normally, unless -nostartfiles is used. The compiler may generate calls to "memcmp", "memset", "memcpy" and "memmove". These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified. -nolibc Do not use the C library or system libraries tightly coupled with it when linking. Still link with the startup files, libgcc or toolchain provided language support libraries such as libgnat, libgfortran or libstdc++ unless options preventing their inclusion are used as well. This typically removes -lc from the link command line, as well as system libraries that normally go with it and become meaningless when absence of a C library is assumed, for example -lpthread or -lm in some configurations. This is intended for bare-board targets when there is indeed no C library available. -nostdlib Do not use the standard system startup files or libraries when linking. No startup files and only the libraries you specify are passed to the linker, and options specifying linkage of the system libraries, such as -static-libgcc or -shared-libgcc, are ignored. The compiler may generate calls to "memcmp", "memset", "memcpy" and "memmove". These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified. One of the standard libraries bypassed by -nostdlib and -nodefaultlibs is libgcc.a, a library of internal subroutines which GCC uses to overcome shortcomings of particular machines, or special needs for some languages. In most cases, you need libgcc.a even when you want to avoid other standard libraries. In other words, when you specify -nostdlib or -nodefaultlibs you should usually specify -lgcc as well. This ensures that you have no unresolved references to internal GCC library subroutines. (An example of such an internal subroutine is "__main", used to ensure C++ constructors are called.) -nostdlib++ Do not implicitly link with standard C++ libraries. -e entry --entry=entry Specify that the program entry point is entry. The argument is interpreted by the linker; the GNU linker accepts either a symbol name or an address. -pie Produce a dynamically linked position independent executable on targets that support it. For predictable results, you must also specify the same set of options used for compilation (-fpie, -fPIE, or model suboptions) when you specify this linker option. -no-pie Don't produce a dynamically linked position independent executable. -static-pie Produce a static position independent executable on targets that support it. A static position independent executable is similar to a static executable, but can be loaded at any address without a dynamic linker. For predictable results, you must also specify the same set of options used for compilation (-fpie, -fPIE, or model suboptions) when you specify this linker option. -pthread Link with the POSIX threads library. This option is supported on GNU/Linux targets, most other Unix derivatives, and also on x86 Cygwin and MinGW targets. On some targets this option also sets flags for the preprocessor, so it should be used consistently for both compilation and linking. -r Produce a relocatable object as output. This is also known as partial linking. -rdynamic Pass the flag -export-dynamic to the ELF linker, on targets that support it. This instructs the linker to add all symbols, not only used ones, to the dynamic symbol table. This option is needed for some uses of "dlopen" or to allow obtaining backtraces from within a program. -s Remove all symbol table and relocation information from the executable. -static On systems that support dynamic linking, this overrides -pie and prevents linking with the shared libraries. On other systems, this option has no effect. -shared Produce a shared object which can then be linked with other objects to form an executable. Not all systems support this option. For predictable results, you must also specify the same set of options used for compilation (-fpic, -fPIC, or model suboptions) when you specify this linker option.[1] -shared-libgcc -static-libgcc On systems that provide libgcc as a shared library, these options force the use of either the shared or static version, respectively. If no shared version of libgcc was built when the compiler was configured, these options have no effect. There are several situations in which an application should use the shared libgcc instead of the static version. The most common of these is when the application wishes to throw and catch exceptions across different shared libraries. In that case, each of the libraries as well as the application itself should use the shared libgcc. Therefore, the G++ driver automatically adds -shared-libgcc whenever you build a shared library or a main executable, because C++ programs typically use exceptions, so this is the right thing to do. If, instead, you use the GCC driver to create shared libraries, you may find that they are not always linked with the shared libgcc. If GCC finds, at its configuration time, that you have a non-GNU linker or a GNU linker that does not support option --eh-frame-hdr, it links the shared version of libgcc into shared libraries by default. Otherwise, it takes advantage of the linker and optimizes away the linking with the shared version of libgcc, linking with the static version of libgcc by default. This allows exceptions to propagate through such shared libraries, without incurring relocation costs at library load time. However, if a library or main executable is supposed to throw or catch exceptions, you must link it using the G++ driver, or using the option -shared-libgcc, such that it is linked with the shared libgcc. -static-libasan When the -fsanitize=address option is used to link a program, the GCC driver automatically links against libasan. If libasan is available as a shared library, and the -static option is not used, then this links against the shared version of libasan. The -static-libasan option directs the GCC driver to link libasan statically, without necessarily linking other libraries statically. -static-libtsan When the -fsanitize=thread option is used to link a program, the GCC driver automatically links against libtsan. If libtsan is available as a shared library, and the -static option is not used, then this links against the shared version of libtsan. The -static-libtsan option directs the GCC driver to link libtsan statically, without necessarily linking other libraries statically. -static-liblsan When the -fsanitize=leak option is used to link a program, the GCC driver automatically links against liblsan. If liblsan is available as a shared library, and the -static option is not used, then this links against the shared version of liblsan. The -static-liblsan option directs the GCC driver to link liblsan statically, without necessarily linking other libraries statically. -static-libubsan When the -fsanitize=undefined option is used to link a program, the GCC driver automatically links against libubsan. If libubsan is available as a shared library, and the -static option is not used, then this links against the shared version of libubsan. The -static-libubsan option directs the GCC driver to link libubsan statically, without necessarily linking other libraries statically. -static-libstdc++ When the g++ program is used to link a C++ program, it normally automatically links against libstdc++. If libstdc++ is available as a shared library, and the -static option is not used, then this links against the shared version of libstdc++. That is normally fine. However, it is sometimes useful to freeze the version of libstdc++ used by the program without going all the way to a fully static link. The -static-libstdc++ option directs the g++ driver to link libstdc++ statically, without necessarily linking other libraries statically. -symbolic Bind references to global symbols when building a shared object. Warn about any unresolved references (unless overridden by the link editor option -Xlinker -z -Xlinker defs). Only a few systems support this option. -T script Use script as the linker script. This option is supported by most systems using the GNU linker. On some targets, such as bare-board targets without an operating system, the -T option may be required when linking to avoid references to undefined symbols. -Xlinker option Pass option as an option to the linker. You can use this to supply system-specific linker options that GCC does not recognize. If you want to pass an option that takes a separate argument, you must use -Xlinker twice, once for the option and once for the argument. For example, to pass -assert definitions, you must write -Xlinker -assert -Xlinker definitions. It does not work to write -Xlinker "-assert definitions", because this passes the entire string as a single argument, which is not what the linker expects. When using the GNU linker, it is usually more convenient to pass arguments to linker options using the option=value syntax than as separate arguments. For example, you can specify -Xlinker -Map=output.map rather than -Xlinker -Map -Xlinker output.map. Other linkers may not support this syntax for command-line options. -Wl,option Pass option as an option to the linker. If option contains commas, it is split into multiple options at the commas. You can use this syntax to pass an argument to the option. For example, -Wl,-Map,output.map passes -Map output.map to the linker. When using the GNU linker, you can also get the same effect with -Wl,-Map=output.map. -u symbol Pretend the symbol symbol is undefined, to force linking of library modules to define it. You can use -u multiple times with different symbols to force loading of additional library modules. -z keyword -z is passed directly on to the linker along with the keyword keyword. See the section in the documentation of your linker for permitted values and their meanings. Options for Directory Search These options specify directories to search for header files, for libraries and for parts of the compiler: -I dir -iquote dir -isystem dir -idirafter dir Add the directory dir to the list of directories to be searched for header files during preprocessing. If dir begins with = or $SYSROOT, then the = or $SYSROOT is replaced by the sysroot prefix; see --sysroot and -isysroot. Directories specified with -iquote apply only to the quote form of the directive, "#include "file"". Directories specified with -I, -isystem, or -idirafter apply to lookup for both the "#include "file"" and "#include <file>" directives. You can specify any number or combination of these options on the command line to search for header files in several directories. The lookup order is as follows: 1. For the quote form of the include directive, the directory of the current file is searched first. 2. For the quote form of the include directive, the directories specified by -iquote options are searched in left-to-right order, as they appear on the command line. 3. Directories specified with -I options are scanned in left-to- right order. 4. Directories specified with -isystem options are scanned in left-to-right order. 5. Standard system directories are scanned. 6. Directories specified with -idirafter options are scanned in left-to-right order. You can use -I to override a system header file, substituting your own version, since these directories are searched before the standard system header file directories. However, you should not use this option to add directories that contain vendor-supplied system header files; use -isystem for that. The -isystem and -idirafter options also mark the directory as a system directory, so that it gets the same special treatment that is applied to the standard system directories. If a standard system include directory, or a directory specified with -isystem, is also specified with -I, the -I option is ignored. The directory is still searched but as a system directory at its normal position in the system include chain. This is to ensure that GCC's procedure to fix buggy system headers and the ordering for the "#include_next" directive are not inadvertently changed. If you really need to change the search order for system directories, use the -nostdinc and/or -isystem options. -I- Split the include path. This option has been deprecated. Please use -iquote instead for -I directories before the -I- and remove the -I- option. Any directories specified with -I options before -I- are searched only for headers requested with "#include "file""; they are not searched for "#include <file>". If additional directories are specified with -I options after the -I-, those directories are searched for all #include directives. In addition, -I- inhibits the use of the directory of the current file directory as the first search directory for "#include "file"". There is no way to override this effect of -I-. -iprefix prefix Specify prefix as the prefix for subsequent -iwithprefix options. If the prefix represents a directory, you should include the final /. -iwithprefix dir -iwithprefixbefore dir Append dir to the prefix specified previously with -iprefix, and add the resulting directory to the include search path. -iwithprefixbefore puts it in the same place -I would; -iwithprefix puts it where -idirafter would. -isysroot dir This option is like the --sysroot option, but applies only to header files (except for Darwin targets, where it applies to both header files and libraries). See the --sysroot option for more information. -imultilib dir Use dir as a subdirectory of the directory containing target- specific C++ headers. -nostdinc Do not search the standard system directories for header files. Only the directories explicitly specified with -I, -iquote, -isystem, and/or -idirafter options (and the directory of the current file, if appropriate) are searched. -nostdinc++ Do not search for header files in the C++-specific standard directories, but do still search the other standard directories. (This option is used when building the C++ library.) -iplugindir=dir Set the directory to search for plugins that are passed by -fplugin=name instead of -fplugin=path/name.so. This option is not meant to be used by the user, but only passed by the driver. -Ldir Add directory dir to the list of directories to be searched for -l. -Bprefix This option specifies where to find the executables, libraries, include files, and data files of the compiler itself. The compiler driver program runs one or more of the subprograms cpp, cc1, as and ld. It tries prefix as a prefix for each program it tries to run, both with and without machine/version/ for the corresponding target machine and compiler version. For each subprogram to be run, the compiler driver first tries the -B prefix, if any. If that name is not found, or if -B is not specified, the driver tries two standard prefixes, /usr/lib/gcc/ and /usr/local/lib/gcc/. If neither of those results in a file name that is found, the unmodified program name is searched for using the directories specified in your PATH environment variable. The compiler checks to see if the path provided by -B refers to a directory, and if necessary it adds a directory separator character at the end of the path. -B prefixes that effectively specify directory names also apply to libraries in the linker, because the compiler translates these options into -L options for the linker. They also apply to include files in the preprocessor, because the compiler translates these options into -isystem options for the preprocessor. In this case, the compiler appends include to the prefix. The runtime support file libgcc.a can also be searched for using the -B prefix, if needed. If it is not found there, the two standard prefixes above are tried, and that is all. The file is left out of the link if it is not found by those means. Another way to specify a prefix much like the -B prefix is to use the environment variable GCC_EXEC_PREFIX. As a special kludge, if the path provided by -B is [dir/]stageN/, where N is a number in the range 0 to 9, then it is replaced by [dir/]include. This is to help with boot-strapping the compiler. -no-canonical-prefixes Do not expand any symbolic links, resolve references to /../ or /./, or make the path absolute when generating a relative prefix. --sysroot=dir Use dir as the logical root directory for headers and libraries. For example, if the compiler normally searches for headers in /usr/include and libraries in /usr/lib, it instead searches dir/usr/include and dir/usr/lib. If you use both this option and the -isysroot option, then the --sysroot option applies to libraries, but the -isysroot option applies to header files. The GNU linker (beginning with version 2.16) has the necessary support for this option. If your linker does not support this option, the header file aspect of --sysroot still works, but the library aspect does not. --no-sysroot-suffix For some targets, a suffix is added to the root directory specified with --sysroot, depending on the other options used, so that headers may for example be found in dir/suffix/usr/include instead of dir/usr/include. This option disables the addition of such a suffix. Options for Code Generation Conventions These machine-independent options control the interface conventions used in code generation. Most of them have both positive and negative forms; the negative form of -ffoo is -fno-foo. In the table below, only one of the forms is listed---the one that is not the default. You can figure out the other form by either removing no- or adding it. -fstack-reuse=reuse-level This option controls stack space reuse for user declared local/auto variables and compiler generated temporaries. reuse_level can be all, named_vars, or none. all enables stack reuse for all local variables and temporaries, named_vars enables the reuse only for user defined local variables with names, and none disables stack reuse completely. The default value is all. The option is needed when the program extends the lifetime of a scoped local variable or a compiler generated temporary beyond the end point defined by the language. When a lifetime of a variable ends, and if the variable lives in memory, the optimizing compiler has the freedom to reuse its stack space with other temporaries or scoped local variables whose live range does not overlap with it. Legacy code extending local lifetime is likely to break with the stack reuse optimization. For example, int *p; { int local1; p = &local1; local1 = 10; .... } { int local2; local2 = 20; ... } if (*p == 10) // out of scope use of local1 { } Another example: struct A { A(int k) : i(k), j(k) { } int i; int j; }; A *ap; void foo(const A& ar) { ap = &ar; } void bar() { foo(A(10)); // temp object's lifetime ends when foo returns { A a(20); .... } ap->i+= 10; // ap references out of scope temp whose space // is reused with a. What is the value of ap->i? } The lifetime of a compiler generated temporary is well defined by the C++ standard. When a lifetime of a temporary ends, and if the temporary lives in memory, the optimizing compiler has the freedom to reuse its stack space with other temporaries or scoped local variables whose live range does not overlap with it. However some of the legacy code relies on the behavior of older compilers in which temporaries' stack space is not reused, the aggressive stack reuse can lead to runtime errors. This option is used to control the temporary stack reuse optimization. -fstack-use-cumulative-args This option instructs the compiler to use the "cumulative_args_t"-based stack layout target hooks, "TARGET_FUNCTION_ARG_BOUNDARY_CA" and "TARGET_FUNCTION_ARG_ROUND_BOUNDARY_CA". If a given target does not define these hooks, the default behaviour is to fallback to using the standard non-"_CA" variants instead. Certain targets (such as AArch64 Darwin) require using the more advanced "_CA"-based hooks: For these targets this option should be enabled by default. -ftrapv This option generates traps for signed overflow on addition, subtraction, multiplication operations. The options -ftrapv and -fwrapv override each other, so using -ftrapv -fwrapv on the command-line results in -fwrapv being effective. Note that only active options override, so using -ftrapv -fwrapv -fno-wrapv on the command-line results in -ftrapv being effective. -fwrapv This option instructs the compiler to assume that signed arithmetic overflow of addition, subtraction and multiplication wraps around using twos-complement representation. This flag enables some optimizations and disables others. The options -ftrapv and -fwrapv override each other, so using -ftrapv -fwrapv on the command-line results in -fwrapv being effective. Note that only active options override, so using -ftrapv -fwrapv -fno-wrapv on the command-line results in -ftrapv being effective. -fwrapv-pointer This option instructs the compiler to assume that pointer arithmetic overflow on addition and subtraction wraps around using twos-complement representation. This flag disables some optimizations which assume pointer overflow is invalid. -fstrict-overflow This option implies -fno-wrapv -fno-wrapv-pointer and when negated implies -fwrapv -fwrapv-pointer. -fexceptions Enable exception handling. Generates extra code needed to propagate exceptions. For some targets, this implies GCC generates frame unwind information for all functions, which can produce significant data size overhead, although it does not affect execution. If you do not specify this option, GCC enables it by default for languages like C++ that normally require exception handling, and disables it for languages like C that do not normally require it. However, you may need to enable this option when compiling C code that needs to interoperate properly with exception handlers written in C++. You may also wish to disable this option if you are compiling older C++ programs that don't use exception handling. -fnon-call-exceptions Generate code that allows trapping instructions to throw exceptions. Note that this requires platform-specific runtime support that does not exist everywhere. Moreover, it only allows trapping instructions to throw exceptions, i.e. memory references or floating-point instructions. It does not allow exceptions to be thrown from arbitrary signal handlers such as "SIGALRM". This enables -fexceptions. -foff-stack-trampolines Certain platforms (such as the Apple M1) do not permit an executable stack. Generate calls to "__builtin_nested_func_ptr_created" and "__builtin_nested_func_ptr_deleted" in order to allocate and deallocate trampoline space on the executable heap. Please note that these functions are implemented in libgcc, and will not be compiled in unless you provide --enable-off-stack-trampolines when building gcc. PLEASE NOTE: The trampolines are not guaranteed to be correctly deallocated if you "setjmp", instantiate nested functions, and then "longjmp" back to a state prior to having allocated those nested functions. -fdelete-dead-exceptions Consider that instructions that may throw exceptions but don't otherwise contribute to the execution of the program can be optimized away. This does not affect calls to functions except those with the "pure" or "const" attributes. This option is enabled by default for the Ada and C++ compilers, as permitted by the language specifications. Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels. -funwind-tables Similar to -fexceptions, except that it just generates any needed static data, but does not affect the generated code in any other way. You normally do not need to enable this option; instead, a language processor that needs this handling enables it on your behalf. -fasynchronous-unwind-tables Generate unwind table in DWARF format, if supported by target machine. The table is exact at each instruction boundary, so it can be used for stack unwinding from asynchronous events (such as debugger or garbage collector). -fno-gnu-unique On systems with recent GNU assembler and C library, the C++ compiler uses the "STB_GNU_UNIQUE" binding to make sure that definitions of template static data members and static local variables in inline functions are unique even in the presence of "RTLD_LOCAL"; this is necessary to avoid problems with a library used by two different "RTLD_LOCAL" plugins depending on a definition in one of them and therefore disagreeing with the other one about the binding of the symbol. But this causes "dlclose" to be ignored for affected DSOs; if your program relies on reinitialization of a DSO via "dlclose" and "dlopen", you can use -fno-gnu-unique. -fpcc-struct-return Return "short" "struct" and "union" values in memory like longer ones, rather than in registers. This convention is less efficient, but it has the advantage of allowing intercallability between GCC- compiled files and files compiled with other compilers, particularly the Portable C Compiler (pcc). The precise convention for returning structures in memory depends on the target configuration macros. Short structures and unions are those whose size and alignment match that of some integer type. Warning: code compiled with the -fpcc-struct-return switch is not binary compatible with code compiled with the -freg-struct-return switch. Use it to conform to a non-default application binary interface. -freg-struct-return Return "struct" and "union" values in registers when possible. This is more efficient for small structures than -fpcc-struct-return. If you specify neither -fpcc-struct-return nor -freg-struct-return, GCC defaults to whichever convention is standard for the target. If there is no standard convention, GCC defaults to -fpcc-struct-return, except on targets where GCC is the principal compiler. In those cases, we can choose the standard, and we chose the more efficient register return alternative. Warning: code compiled with the -freg-struct-return switch is not binary compatible with code compiled with the -fpcc-struct-return switch. Use it to conform to a non-default application binary interface. -fshort-enums Allocate to an "enum" type only as many bytes as it needs for the declared range of possible values. Specifically, the "enum" type is equivalent to the smallest integer type that has enough room. Warning: the -fshort-enums switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. -fshort-wchar Override the underlying type for "wchar_t" to be "short unsigned int" instead of the default for the target. This option is useful for building programs to run under WINE. Warning: the -fshort-wchar switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. -fcommon In C code, this option controls the placement of global variables defined without an initializer, known as tentative definitions in the C standard. Tentative definitions are distinct from declarations of a variable with the "extern" keyword, which do not allocate storage. The default is -fno-common, which specifies that the compiler places uninitialized global variables in the BSS section of the object file. This inhibits the merging of tentative definitions by the linker so you get a multiple-definition error if the same variable is accidentally defined in more than one compilation unit. The -fcommon places uninitialized global variables in a common block. This allows the linker to resolve all tentative definitions of the same variable in different compilation units to the same object, or to a non-tentative definition. This behavior is inconsistent with C++, and on many targets implies a speed and code size penalty on global variable references. It is mainly useful to enable legacy code to link without errors. -fno-ident Ignore the "#ident" directive. -finhibit-size-directive Don't output a ".size" assembler directive, or anything else that would cause trouble if the function is split in the middle, and the two halves are placed at locations far apart in memory. This option is used when compiling crtstuff.c; you should not need to use it for anything else. -fverbose-asm Put extra commentary information in the generated assembly code to make it more readable. This option is generally only of use to those who actually need to read the generated assembly code (perhaps while debugging the compiler itself). -fno-verbose-asm, the default, causes the extra information to be omitted and is useful when comparing two assembler files. The added comments include: * information on the compiler version and command-line options, * the source code lines associated with the assembly instructions, in the form FILENAME:LINENUMBER:CONTENT OF LINE, * hints on which high-level expressions correspond to the various assembly instruction operands. For example, given this C source file: int test (int n) { int i; int total = 0; for (i = 0; i < n; i++) total += i * i; return total; } compiling to (x86_64) assembly via -S and emitting the result direct to stdout via -o - gcc -S test.c -fverbose-asm -Os -o - gives output similar to this: .file "test.c" # GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu) [...snip...] # options passed: [...snip...] .text .globl test .type test, @function test: .LFB0: .cfi_startproc # test.c:4: int total = 0; xorl %eax, %eax # <retval> # test.c:6: for (i = 0; i < n; i++) xorl %edx, %edx # i .L2: # test.c:6: for (i = 0; i < n; i++) cmpl %edi, %edx # n, i jge .L5 #, # test.c:7: total += i * i; movl %edx, %ecx # i, tmp92 imull %edx, %ecx # i, tmp92 # test.c:6: for (i = 0; i < n; i++) incl %edx # i # test.c:7: total += i * i; addl %ecx, %eax # tmp92, <retval> jmp .L2 # .L5: # test.c:10: } ret .cfi_endproc .LFE0: .size test, .-test .ident "GCC: (GNU) 7.0.0 20160809 (experimental)" .section .note.GNU-stack,"",@progbits The comments are intended for humans rather than machines and hence the precise format of the comments is subject to change. -frecord-gcc-switches This switch causes the command line used to invoke the compiler to be recorded into the object file that is being created. This switch is only implemented on some targets and the exact format of the recording is target and binary file format dependent, but it usually takes the form of a section containing ASCII text. This switch is related to the -fverbose-asm switch, but that switch only records information in the assembler output file as comments, so it never reaches the object file. See also -grecord-gcc-switches for another way of storing compiler options into the object file. -fpic Generate position-independent code (PIC) suitable for use in a shared library, if supported for the target machine. Such code accesses all constant addresses through a global offset table (GOT). The dynamic loader resolves the GOT entries when the program starts (the dynamic loader is not part of GCC; it is part of the operating system). If the GOT size for the linked executable exceeds a machine-specific maximum size, you get an error message from the linker indicating that -fpic does not work; in that case, recompile with -fPIC instead. (These maximums are 8k on the SPARC, 28k on AArch64 and 32k on the m68k and RS/6000. The x86 has no such limit.) Position-independent code requires special support, and therefore works only on certain machines. For the x86, GCC supports PIC for System V but not for the Sun 386i. Code generated for the IBM RS/6000 is always position-independent. When this flag is set, the macros "__pic__" and "__PIC__" are defined to 1. -fPIC If supported for the target machine, emit position-independent code, suitable for dynamic linking and avoiding any limit on the size of the global offset table. This option makes a difference on AArch64, m68k, PowerPC and SPARC. Position-independent code requires special support, and therefore works only on certain machines. When this flag is set, the macros "__pic__" and "__PIC__" are defined to 2. -fpie -fPIE These options are similar to -fpic and -fPIC, but the generated position-independent code can be only linked into executables. Usually these options are used to compile code that will be linked using the -pie GCC option. -fpie and -fPIE both define the macros "__pie__" and "__PIE__". The macros have the value 1 for -fpie and 2 for -fPIE. -fno-plt Do not use the PLT for external function calls in position- independent code. Instead, load the callee address at call sites from the GOT and branch to it. This leads to more efficient code by eliminating PLT stubs and exposing GOT loads to optimizations. On architectures such as 32-bit x86 where PLT stubs expect the GOT pointer in a specific register, this gives more register allocation freedom to the compiler. Lazy binding requires use of the PLT; with -fno-plt all external symbols are resolved at load time. Alternatively, the function attribute "noplt" can be used to avoid calls through the PLT for specific external functions. In position-dependent code, a few targets also convert calls to functions that are marked to not use the PLT to use the GOT instead. -fno-jump-tables Do not use jump tables for switch statements even where it would be more efficient than other code generation strategies. This option is of use in conjunction with -fpic or -fPIC for building code that forms part of a dynamic linker and cannot reference the address of a jump table. On some targets, jump tables do not require a GOT and this option is not needed. -fno-bit-tests Do not use bit tests for switch statements even where it would be more efficient than other code generation strategies. -ffixed-reg Treat the register named reg as a fixed register; generated code should never refer to it (except perhaps as a stack pointer, frame pointer or in some other fixed role). reg must be the name of a register. The register names accepted are machine-specific and are defined in the "REGISTER_NAMES" macro in the machine description macro file. This flag does not have a negative form, because it specifies a three-way choice. -fcall-used-reg Treat the register named reg as an allocable register that is clobbered by function calls. It may be allocated for temporaries or variables that do not live across a call. Functions compiled this way do not save and restore the register reg. It is an error to use this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model produces disastrous results. This flag does not have a negative form, because it specifies a three-way choice. -fcall-saved-reg Treat the register named reg as an allocable register saved by functions. It may be allocated even for temporaries or variables that live across a call. Functions compiled this way save and restore the register reg if they use it. It is an error to use this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model produces disastrous results. A different sort of disaster results from the use of this flag for a register in which function values may be returned. This flag does not have a negative form, because it specifies a three-way choice. -fpack-struct[=n] Without a value specified, pack all structure members together without holes. When a value is specified (which must be a small power of two), pack structure members according to this value, representing the maximum alignment (that is, objects with default alignment requirements larger than this are output potentially unaligned at the next fitting location. Warning: the -fpack-struct switch causes GCC to generate code that is not binary compatible with code generated without that switch. Additionally, it makes the code suboptimal. Use it to conform to a non-default application binary interface. -fleading-underscore This option and its counterpart, -fno-leading-underscore, forcibly change the way C symbols are represented in the object file. One use is to help link with legacy assembly code. Warning: the -fleading-underscore switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. Not all targets provide complete support for this switch. -ftls-model=model Alter the thread-local storage model to be used. The model argument should be one of global-dynamic, local-dynamic, initial- exec or local-exec. Note that the choice is subject to optimization: the compiler may use a more efficient model for symbols not visible outside of the translation unit, or if -fpic is not given on the command line. The default without -fpic is initial-exec; with -fpic the default is global-dynamic. -ftrampolines For targets that normally need trampolines for nested functions, always generate them instead of using descriptors. Otherwise, for targets that do not need them, like for example HP-PA or IA-64, do nothing. A trampoline is a small piece of code that is created at run time on the stack when the address of a nested function is taken, and is used to call the nested function indirectly. Therefore, it requires the stack to be made executable in order for the program to work properly. -fno-trampolines is enabled by default on a language by language basis to let the compiler avoid generating them, if it computes that this is safe, and replace them with descriptors. Descriptors are made up of data only, but the generated code must be prepared to deal with them. As of this writing, -fno-trampolines is enabled by default only for Ada. Moreover, code compiled with -ftrampolines and code compiled with -fno-trampolines are not binary compatible if nested functions are present. This option must therefore be used on a program-wide basis and be manipulated with extreme care. For languages other than Ada, the "-ftrampolines" and "-fno-trampolines" options currently have no effect, and trampolines are always generated on platforms that need them for nested functions. -fvisibility=[default|internal|hidden|protected] Set the default ELF image symbol visibility to the specified option---all symbols are marked with this unless overridden within the code. Using this feature can very substantially improve linking and load times of shared object libraries, produce more optimized code, provide near-perfect API export and prevent symbol clashes. It is strongly recommended that you use this in any shared objects you distribute. Despite the nomenclature, default always means public; i.e., available to be linked against from outside the shared object. protected and internal are pretty useless in real-world usage so the only other commonly used option is hidden. The default if -fvisibility isn't specified is default, i.e., make every symbol public. A good explanation of the benefits offered by ensuring ELF symbols have the correct visibility is given by "How To Write Shared Libraries" by Ulrich Drepper (which can be found at <https://www.akkadia.org/drepper/>)---however a superior solution made possible by this option to marking things hidden when the default is public is to make the default hidden and mark things public. This is the norm with DLLs on Windows and with -fvisibility=hidden and "__attribute__ ((visibility("default")))" instead of "__declspec(dllexport)" you get almost identical semantics with identical syntax. This is a great boon to those working with cross-platform projects. For those adding visibility support to existing code, you may find "#pragma GCC visibility" of use. This works by you enclosing the declarations you wish to set visibility for with (for example) "#pragma GCC visibility push(hidden)" and "#pragma GCC visibility pop". Bear in mind that symbol visibility should be viewed as part of the API interface contract and thus all new code should always specify visibility when it is not the default; i.e., declarations only for use within the local DSO should always be marked explicitly as hidden as so to avoid PLT indirection overheads---making this abundantly clear also aids readability and self-documentation of the code. Note that due to ISO C++ specification requirements, "operator new" and "operator delete" must always be of default visibility. Be aware that headers from outside your project, in particular system headers and headers from any other library you use, may not be expecting to be compiled with visibility other than the default. You may need to explicitly say "#pragma GCC visibility push(default)" before including any such headers. "extern" declarations are not affected by -fvisibility, so a lot of code can be recompiled with -fvisibility=hidden with no modifications. However, this means that calls to "extern" functions with no explicit visibility use the PLT, so it is more effective to use "__attribute ((visibility))" and/or "#pragma GCC visibility" to tell the compiler which "extern" declarations should be treated as hidden. Note that -fvisibility does affect C++ vague linkage entities. This means that, for instance, an exception class that is be thrown between DSOs must be explicitly marked with default visibility so that the type_info nodes are unified between the DSOs. An overview of these techniques, their benefits and how to use them is at <https://gcc.gnu.org/wiki/Visibility>. -fstrict-volatile-bitfields This option should be used if accesses to volatile bit-fields (or other structure fields, although the compiler usually honors those types anyway) should use a single access of the width of the field's type, aligned to a natural alignment if possible. For example, targets with memory-mapped peripheral registers might require all such accesses to be 16 bits wide; with this flag you can declare all peripheral bit-fields as "unsigned short" (assuming short is 16 bits on these targets) to force GCC to use 16-bit accesses instead of, perhaps, a more efficient 32-bit access. If this option is disabled, the compiler uses the most efficient instruction. In the previous example, that might be a 32-bit load instruction, even though that accesses bytes that do not contain any portion of the bit-field, or memory-mapped registers unrelated to the one being updated. In some cases, such as when the "packed" attribute is applied to a structure field, it may not be possible to access the field with a single read or write that is correctly aligned for the target machine. In this case GCC falls back to generating multiple accesses rather than code that will fault or truncate the result at run time. Note: Due to restrictions of the C/C++11 memory model, write accesses are not allowed to touch non bit-field members. It is therefore recommended to define all bits of the field's type as bit-field members. The default value of this option is determined by the application binary interface for the target processor. -fsync-libcalls This option controls whether any out-of-line instance of the "__sync" family of functions may be used to implement the C++11 "__atomic" family of functions. The default value of this option is enabled, thus the only useful form of the option is -fno-sync-libcalls. This option is used in the implementation of the libatomic runtime library. GCC Developer Options This section describes command-line options that are primarily of interest to GCC developers, including options to support compiler testing and investigation of compiler bugs and compile-time performance problems. This includes options that produce debug dumps at various points in the compilation; that print statistics such as memory use and execution time; and that print information about GCC's configuration, such as where it searches for libraries. You should rarely need to use any of these options for ordinary compilation and linking tasks. Many developer options that cause GCC to dump output to a file take an optional =filename suffix. You can specify stdout or - to dump to standard output, and stderr for standard error. If =filename is omitted, a default dump file name is constructed by concatenating the base dump file name, a pass number, phase letter, and pass name. The base dump file name is the name of output file produced by the compiler if explicitly specified and not an executable; otherwise it is the source file name. The pass number is determined by the order passes are registered with the compiler's pass manager. This is generally the same as the order of execution, but passes registered by plugins, target-specific passes, or passes that are otherwise registered late are numbered higher than the pass named final, even if they are executed earlier. The phase letter is one of i (inter- procedural analysis), l (language-specific), r (RTL), or t (tree). The files are created in the directory of the output file. -fcallgraph-info -fcallgraph-info=MARKERS Makes the compiler output callgraph information for the program, on a per-object-file basis. The information is generated in the common VCG format. It can be decorated with additional, per-node and/or per-edge information, if a list of comma-separated markers is additionally specified. When the "su" marker is specified, the callgraph is decorated with stack usage information; it is equivalent to -fstack-usage. When the "da" marker is specified, the callgraph is decorated with information about dynamically allocated objects. When compiling with -flto, no callgraph information is output along with the object file. At LTO link time, -fcallgraph-info may generate multiple callgraph information files next to intermediate LTO output files. -dletters -fdump-rtl-pass -fdump-rtl-pass=filename Says to make debugging dumps during compilation at times specified by letters. This is used for debugging the RTL-based passes of the compiler. Some -dletters switches have different meaning when -E is used for preprocessing. Debug dumps can be enabled with a -fdump-rtl switch or some -d option letters. Here are the possible letters for use in pass and letters, and their meanings: -fdump-rtl-alignments Dump after branch alignments have been computed. -fdump-rtl-asmcons Dump after fixing rtl statements that have unsatisfied in/out constraints. -fdump-rtl-auto_inc_dec Dump after auto-inc-dec discovery. This pass is only run on architectures that have auto inc or auto dec instructions. -fdump-rtl-barriers Dump after cleaning up the barrier instructions. -fdump-rtl-bbpart Dump after partitioning hot and cold basic blocks. -fdump-rtl-bbro Dump after block reordering. -fdump-rtl-btl1 -fdump-rtl-btl2 -fdump-rtl-btl1 and -fdump-rtl-btl2 enable dumping after the two branch target load optimization passes. -fdump-rtl-bypass Dump after jump bypassing and control flow optimizations. -fdump-rtl-combine Dump after the RTL instruction combination pass. -fdump-rtl-compgotos Dump after duplicating the computed gotos. -fdump-rtl-ce1 -fdump-rtl-ce2 -fdump-rtl-ce3 -fdump-rtl-ce1, -fdump-rtl-ce2, and -fdump-rtl-ce3 enable dumping after the three if conversion passes. -fdump-rtl-cprop_hardreg Dump after hard register copy propagation. -fdump-rtl-csa Dump after combining stack adjustments. -fdump-rtl-cse1 -fdump-rtl-cse2 -fdump-rtl-cse1 and -fdump-rtl-cse2 enable dumping after the two common subexpression elimination passes. -fdump-rtl-dce Dump after the standalone dead code elimination passes. -fdump-rtl-dbr Dump after delayed branch scheduling. -fdump-rtl-dce1 -fdump-rtl-dce2 -fdump-rtl-dce1 and -fdump-rtl-dce2 enable dumping after the two dead store elimination passes. -fdump-rtl-eh Dump after finalization of EH handling code. -fdump-rtl-eh_ranges Dump after conversion of EH handling range regions. -fdump-rtl-expand Dump after RTL generation. -fdump-rtl-fwprop1 -fdump-rtl-fwprop2 -fdump-rtl-fwprop1 and -fdump-rtl-fwprop2 enable dumping after the two forward propagation passes. -fdump-rtl-gcse1 -fdump-rtl-gcse2 -fdump-rtl-gcse1 and -fdump-rtl-gcse2 enable dumping after global common subexpression elimination. -fdump-rtl-init-regs Dump after the initialization of the registers. -fdump-rtl-initvals Dump after the computation of the initial value sets. -fdump-rtl-into_cfglayout Dump after converting to cfglayout mode. -fdump-rtl-ira Dump after iterated register allocation. -fdump-rtl-jump Dump after the second jump optimization. -fdump-rtl-loop2 -fdump-rtl-loop2 enables dumping after the rtl loop optimization passes. -fdump-rtl-mach Dump after performing the machine dependent reorganization pass, if that pass exists. -fdump-rtl-mode_sw Dump after removing redundant mode switches. -fdump-rtl-rnreg Dump after register renumbering. -fdump-rtl-outof_cfglayout Dump after converting from cfglayout mode. -fdump-rtl-peephole2 Dump after the peephole pass. -fdump-rtl-postreload Dump after post-reload optimizations. -fdump-rtl-pro_and_epilogue Dump after generating the function prologues and epilogues. -fdump-rtl-sched1 -fdump-rtl-sched2 -fdump-rtl-sched1 and -fdump-rtl-sched2 enable dumping after the basic block scheduling passes. -fdump-rtl-ree Dump after sign/zero extension elimination. -fdump-rtl-seqabstr Dump after common sequence discovery. -fdump-rtl-shorten Dump after shortening branches. -fdump-rtl-sibling Dump after sibling call optimizations. -fdump-rtl-split1 -fdump-rtl-split2 -fdump-rtl-split3 -fdump-rtl-split4 -fdump-rtl-split5 These options enable dumping after five rounds of instruction splitting. -fdump-rtl-sms Dump after modulo scheduling. This pass is only run on some architectures. -fdump-rtl-stack Dump after conversion from GCC's "flat register file" registers to the x87's stack-like registers. This pass is only run on x86 variants. -fdump-rtl-subreg1 -fdump-rtl-subreg2 -fdump-rtl-subreg1 and -fdump-rtl-subreg2 enable dumping after the two subreg expansion passes. -fdump-rtl-unshare Dump after all rtl has been unshared. -fdump-rtl-vartrack Dump after variable tracking. -fdump-rtl-vregs Dump after converting virtual registers to hard registers. -fdump-rtl-web Dump after live range splitting. -fdump-rtl-regclass -fdump-rtl-subregs_of_mode_init -fdump-rtl-subregs_of_mode_finish -fdump-rtl-dfinit -fdump-rtl-dfinish These dumps are defined but always produce empty files. -da -fdump-rtl-all Produce all the dumps listed above. -dA Annotate the assembler output with miscellaneous debugging information. -dD Dump all macro definitions, at the end of preprocessing, in addition to normal output. -dH Produce a core dump whenever an error occurs. -dp Annotate the assembler output with a comment indicating which pattern and alternative is used. The length and cost of each instruction are also printed. -dP Dump the RTL in the assembler output as a comment before each instruction. Also turns on -dp annotation. -dx Just generate RTL for a function instead of compiling it. Usually used with -fdump-rtl-expand. -fdump-debug Dump debugging information generated during the debug generation phase. -fdump-earlydebug Dump debugging information generated during the early debug generation phase. -fdump-noaddr When doing debugging dumps, suppress address output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different compiler binaries and/or different text / bss / data / heap / stack / dso start locations. -freport-bug Collect and dump debug information into a temporary file if an internal compiler error (ICE) occurs. -fdump-unnumbered When doing debugging dumps, suppress instruction numbers and address output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different options, in particular with and without -g. -fdump-unnumbered-links When doing debugging dumps (see -d option above), suppress instruction numbers for the links to the previous and next instructions in a sequence. -fdump-ipa-switch -fdump-ipa-switch-options Control the dumping at various stages of inter-procedural analysis language tree to a file. The file name is generated by appending a switch specific suffix to the source file name, and the file is created in the same directory as the output file. The following dumps are possible: all Enables all inter-procedural analysis dumps. cgraph Dumps information about call-graph optimization, unused function removal, and inlining decisions. inline Dump after function inlining. Additionally, the options -optimized, -missed, -note, and -all can be provided, with the same meaning as for -fopt-info, defaulting to -optimized. For example, -fdump-ipa-inline-optimized-missed will emit information on callsites that were inlined, along with callsites that were not inlined. By default, the dump will contain messages about successful optimizations (equivalent to -optimized) together with low-level details about the analysis. -fdump-lang Dump language-specific information. The file name is made by appending .lang to the source file name. -fdump-lang-all -fdump-lang-switch -fdump-lang-switch-options -fdump-lang-switch-options=filename Control the dumping of language-specific information. The options and filename portions behave as described in the -fdump-tree option. The following switch values are accepted: all Enable all language-specific dumps. class Dump class hierarchy information. Virtual table information is emitted unless 'slim' is specified. This option is applicable to C++ only. module Dump module information. Options lineno (locations), graph (reachability), blocks (clusters), uid (serialization), alias (mergeable), asmname (Elrond), eh (mapper) & vops (macros) may provide additional information. This option is applicable to C++ only. raw Dump the raw internal tree data. This option is applicable to C++ only. -fdump-passes Print on stderr the list of optimization passes that are turned on and off by the current command-line options. -fdump-statistics-option Enable and control dumping of pass statistics in a separate file. The file name is generated by appending a suffix ending in .statistics to the source file name, and the file is created in the same directory as the output file. If the -option form is used, -stats causes counters to be summed over the whole compilation unit while -details dumps every event as the passes generate them. The default with no option is to sum counters for each function compiled. -fdump-tree-all -fdump-tree-switch -fdump-tree-switch-options -fdump-tree-switch-options=filename Control the dumping at various stages of processing the intermediate language tree to a file. If the -options form is used, options is a list of - separated options which control the details of the dump. Not all options are applicable to all dumps; those that are not meaningful are ignored. The following options are available address Print the address of each node. Usually this is not meaningful as it changes according to the environment and source file. Its primary use is for tying up a dump file with a debug environment. asmname If "DECL_ASSEMBLER_NAME" has been set for a given decl, use that in the dump instead of "DECL_NAME". Its primary use is ease of use working backward from mangled names in the assembly file. slim When dumping front-end intermediate representations, inhibit dumping of members of a scope or body of a function merely because that scope has been reached. Only dump such items when they are directly reachable by some other path. When dumping pretty-printed trees, this option inhibits dumping the bodies of control structures. When dumping RTL, print the RTL in slim (condensed) form instead of the default LISP-like representation. raw Print a raw representation of the tree. By default, trees are pretty-printed into a C-like representation. details Enable more detailed dumps (not honored by every dump option). Also include information from the optimization passes. stats Enable dumping various statistics about the pass (not honored by every dump option). blocks Enable showing basic block boundaries (disabled in raw dumps). graph For each of the other indicated dump files (-fdump-rtl-pass), dump a representation of the control flow graph suitable for viewing with GraphViz to file.passid.pass.dot. Each function in the file is pretty-printed as a subgraph, so that GraphViz can render them all in a single plot. This option currently only works for RTL dumps, and the RTL is always dumped in slim form. vops Enable showing virtual operands for every statement. lineno Enable showing line numbers for statements. uid Enable showing the unique ID ("DECL_UID") for each variable. verbose Enable showing the tree dump for each statement. eh Enable showing the EH region number holding each statement. scev Enable showing scalar evolution analysis details. optimized Enable showing optimization information (only available in certain passes). missed Enable showing missed optimization information (only available in certain passes). note Enable other detailed optimization information (only available in certain passes). all Turn on all options, except raw, slim, verbose and lineno. optall Turn on all optimization options, i.e., optimized, missed, and note. To determine what tree dumps are available or find the dump for a pass of interest follow the steps below. 1. Invoke GCC with -fdump-passes and in the stderr output look for a code that corresponds to the pass you are interested in. For example, the codes "tree-evrp", "tree-vrp1", and "tree-vrp2" correspond to the three Value Range Propagation passes. The number at the end distinguishes distinct invocations of the same pass. 2. To enable the creation of the dump file, append the pass code to the -fdump- option prefix and invoke GCC with it. For example, to enable the dump from the Early Value Range Propagation pass, invoke GCC with the -fdump-tree-evrp option. Optionally, you may specify the name of the dump file. If you don't specify one, GCC creates as described below. 3. Find the pass dump in a file whose name is composed of three components separated by a period: the name of the source file GCC was invoked to compile, a numeric suffix indicating the pass number followed by the letter t for tree passes (and the letter r for RTL passes), and finally the pass code. For example, the Early VRP pass dump might be in a file named myfile.c.038t.evrp in the current working directory. Note that the numeric codes are not stable and may change from one version of GCC to another. -fopt-info -fopt-info-options -fopt-info-options=filename Controls optimization dumps from various optimization passes. If the -options form is used, options is a list of - separated option keywords to select the dump details and optimizations. The options can be divided into three groups: 1. options describing what kinds of messages should be emitted, 2. options describing the verbosity of the dump, and 3. options describing which optimizations should be included. The options from each group can be freely mixed as they are non- overlapping. However, in case of any conflicts, the later options override the earlier options on the command line. The following options control which kinds of messages should be emitted: optimized Print information when an optimization is successfully applied. It is up to a pass to decide which information is relevant. For example, the vectorizer passes print the source location of loops which are successfully vectorized. missed Print information about missed optimizations. Individual passes control which information to include in the output. note Print verbose information about optimizations, such as certain transformations, more detailed messages about decisions etc. all Print detailed optimization information. This includes optimized, missed, and note. The following option controls the dump verbosity: internals By default, only "high-level" messages are emitted. This option enables additional, more detailed, messages, which are likely to only be of interest to GCC developers. One or more of the following option keywords can be used to describe a group of optimizations: ipa Enable dumps from all interprocedural optimizations. loop Enable dumps from all loop optimizations. inline Enable dumps from all inlining optimizations. omp Enable dumps from all OMP (Offloading and Multi Processing) optimizations. vec Enable dumps from all vectorization optimizations. optall Enable dumps from all optimizations. This is a superset of the optimization groups listed above. If options is omitted, it defaults to optimized-optall, which means to dump messages about successful optimizations from all the passes, omitting messages that are treated as "internals". If the filename is provided, then the dumps from all the applicable optimizations are concatenated into the filename. Otherwise the dump is output onto stderr. Though multiple -fopt-info options are accepted, only one of them can include a filename. If other filenames are provided then all but the first such option are ignored. Note that the output filename is overwritten in case of multiple translation units. If a combined output from multiple translation units is desired, stderr should be used instead. In the following example, the optimization info is output to stderr: gcc -O3 -fopt-info This example: gcc -O3 -fopt-info-missed=missed.all outputs missed optimization report from all the passes into missed.all, and this one: gcc -O2 -ftree-vectorize -fopt-info-vec-missed prints information about missed optimization opportunities from vectorization passes on stderr. Note that -fopt-info-vec-missed is equivalent to -fopt-info-missed-vec. The order of the optimization group names and message types listed after -fopt-info does not matter. As another example, gcc -O3 -fopt-info-inline-optimized-missed=inline.txt outputs information about missed optimizations as well as optimized locations from all the inlining passes into inline.txt. Finally, consider: gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt Here the two output filenames vec.miss and loop.opt are in conflict since only one output file is allowed. In this case, only the first option takes effect and the subsequent options are ignored. Thus only vec.miss is produced which contains dumps from the vectorizer about missed opportunities. -fsave-optimization-record Write a SRCFILE.opt-record.json.gz file detailing what optimizations were performed, for those optimizations that support -fopt-info. This option is experimental and the format of the data within the compressed JSON file is subject to change. It is roughly equivalent to a machine-readable version of -fopt-info-all, as a collection of messages with source file, line number and column number, with the following additional data for each message: * the execution count of the code being optimized, along with metadata about whether this was from actual profile data, or just an estimate, allowing consumers to prioritize messages by code hotness, * the function name of the code being optimized, where applicable, * the "inlining chain" for the code being optimized, so that when a function is inlined into several different places (which might themselves be inlined), the reader can distinguish between the copies, * objects identifying those parts of the message that refer to expressions, statements or symbol-table nodes, which of these categories they are, and, when available, their source code location, * the GCC pass that emitted the message, and * the location in GCC's own code from which the message was emitted Additionally, some messages are logically nested within other messages, reflecting implementation details of the optimization passes. -fsched-verbose=n On targets that use instruction scheduling, this option controls the amount of debugging output the scheduler prints to the dump files. For n greater than zero, -fsched-verbose outputs the same information as -fdump-rtl-sched1 and -fdump-rtl-sched2. For n greater than one, it also output basic block probabilities, detailed ready list information and unit/insn info. For n greater than two, it includes RTL at abort point, control-flow and regions info. And for n over four, -fsched-verbose also includes dependence info. -fenable-kind-pass -fdisable-kind-pass=range-list This is a set of options that are used to explicitly disable/enable optimization passes. These options are intended for use for debugging GCC. Compiler users should use regular options for enabling/disabling passes instead. -fdisable-ipa-pass Disable IPA pass pass. pass is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting from 1. -fdisable-rtl-pass -fdisable-rtl-pass=range-list Disable RTL pass pass. pass is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting from 1. range-list is a comma-separated list of function ranges or assembler names. Each range is a number pair separated by a colon. The range is inclusive in both ends. If the range is trivial, the number pair can be simplified as a single number. If the function's call graph node's uid falls within one of the specified ranges, the pass is disabled for that function. The uid is shown in the function header of a dump file, and the pass names can be dumped by using option -fdump-passes. -fdisable-tree-pass -fdisable-tree-pass=range-list Disable tree pass pass. See -fdisable-rtl for the description of option arguments. -fenable-ipa-pass Enable IPA pass pass. pass is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting from 1. -fenable-rtl-pass -fenable-rtl-pass=range-list Enable RTL pass pass. See -fdisable-rtl for option argument description and examples. -fenable-tree-pass -fenable-tree-pass=range-list Enable tree pass pass. See -fdisable-rtl for the description of option arguments. Here are some examples showing uses of these options. # disable ccp1 for all functions -fdisable-tree-ccp1 # disable complete unroll for function whose cgraph node uid is 1 -fenable-tree-cunroll=1 # disable gcse2 for functions at the following ranges [1,1], # [300,400], and [400,1000] # disable gcse2 for functions foo and foo2 -fdisable-rtl-gcse2=foo,foo2 # disable early inlining -fdisable-tree-einline # disable ipa inlining -fdisable-ipa-inline # enable tree full unroll -fenable-tree-unroll -fchecking -fchecking=n Enable internal consistency checking. The default depends on the compiler configuration. -fchecking=2 enables further internal consistency checking that might affect code generation. -frandom-seed=string This option provides a seed that GCC uses in place of random numbers in generating certain symbol names that have to be different in every compiled file. It is also used to place unique stamps in coverage data files and the object files that produce them. You can use the -frandom-seed option to produce reproducibly identical object files. The string can either be a number (decimal, octal or hex) or an arbitrary string (in which case it's converted to a number by computing CRC32). The string should be different for every file you compile. -save-temps Store the usual "temporary" intermediate files permanently; name them as auxiliary output files, as specified described under -dumpbase and -dumpdir. When used in combination with the -x command-line option, -save-temps is sensible enough to avoid overwriting an input source file with the same extension as an intermediate file. The corresponding intermediate file may be obtained by renaming the source file before using -save-temps. -save-temps=cwd Equivalent to -save-temps -dumpdir ./. -save-temps=obj Equivalent to -save-temps -dumpdir outdir/, where outdir/ is the directory of the output file specified after the -o option, including any directory separators. If the -o option is not used, the -save-temps=obj switch behaves like -save-temps=cwd. -time[=file] Report the CPU time taken by each subprocess in the compilation sequence. For C source files, this is the compiler proper and assembler (plus the linker if linking is done). Without the specification of an output file, the output looks like this: # cc1 0.12 0.01 # as 0.00 0.01 The first number on each line is the "user time", that is time spent executing the program itself. The second number is "system time", time spent executing operating system routines on behalf of the program. Both numbers are in seconds. With the specification of an output file, the output is appended to the named file, and it looks like this: 0.12 0.01 cc1 <options> 0.00 0.01 as <options> The "user time" and the "system time" are moved before the program name, and the options passed to the program are displayed, so that one can later tell what file was being compiled, and with which options. -fdump-final-insns[=file] Dump the final internal representation (RTL) to file. If the optional argument is omitted (or if file is "."), the name of the dump file is determined by appending ".gkd" to the dump base name, see -dumpbase. -fcompare-debug[=opts] If no error occurs during compilation, run the compiler a second time, adding opts and -fcompare-debug-second to the arguments passed to the second compilation. Dump the final internal representation in both compilations, and print an error if they differ. If the equal sign is omitted, the default -gtoggle is used. The environment variable GCC_COMPARE_DEBUG, if defined, non-empty and nonzero, implicitly enables -fcompare-debug. If GCC_COMPARE_DEBUG is defined to a string starting with a dash, then it is used for opts, otherwise the default -gtoggle is used. -fcompare-debug=, with the equal sign but without opts, is equivalent to -fno-compare-debug, which disables the dumping of the final representation and the second compilation, preventing even GCC_COMPARE_DEBUG from taking effect. To verify full coverage during -fcompare-debug testing, set GCC_COMPARE_DEBUG to say -fcompare-debug-not-overridden, which GCC rejects as an invalid option in any actual compilation (rather than preprocessing, assembly or linking). To get just a warning, setting GCC_COMPARE_DEBUG to -w%n-fcompare-debug not overridden will do. -fcompare-debug-second This option is implicitly passed to the compiler for the second compilation requested by -fcompare-debug, along with options to silence warnings, and omitting other options that would cause the compiler to produce output to files or to standard output as a side effect. Dump files and preserved temporary files are renamed so as to contain the ".gk" additional extension during the second compilation, to avoid overwriting those generated by the first. When this option is passed to the compiler driver, it causes the first compilation to be skipped, which makes it useful for little other than debugging the compiler proper. -gtoggle Turn off generation of debug info, if leaving out this option generates it, or turn it on at level 2 otherwise. The position of this argument in the command line does not matter; it takes effect after all other options are processed, and it does so only once, no matter how many times it is given. This is mainly intended to be used with -fcompare-debug. -fvar-tracking-assignments-toggle Toggle -fvar-tracking-assignments, in the same way that -gtoggle toggles -g. -Q Makes the compiler print out each function name as it is compiled, and print some statistics about each pass when it finishes. -ftime-report Makes the compiler print some statistics about the time consumed by each pass when it finishes. -ftime-report-details Record the time consumed by infrastructure parts separately for each pass. -fira-verbose=n Control the verbosity of the dump file for the integrated register allocator. The default value is 5. If the value n is greater or equal to 10, the dump output is sent to stderr using the same format as n minus 10. -flto-report Prints a report with internal details on the workings of the link- time optimizer. The contents of this report vary from version to version. It is meant to be useful to GCC developers when processing object files in LTO mode (via -flto). Disabled by default. -flto-report-wpa Like -flto-report, but only print for the WPA phase of link-time optimization. -fmem-report Makes the compiler print some statistics about permanent memory allocation when it finishes. -fmem-report-wpa Makes the compiler print some statistics about permanent memory allocation for the WPA phase only. -fpre-ipa-mem-report -fpost-ipa-mem-report Makes the compiler print some statistics about permanent memory allocation before or after interprocedural optimization. -fmultiflags This option enables multilib-aware "TFLAGS" to be used to build target libraries with options different from those the compiler is configured to use by default, through the use of specs Like "TFLAGS", this allows the target libraries to be built for portable baseline environments, while the compiler defaults to more demanding ones. That's useful because users can easily override the defaults the compiler is configured to use to build their own programs, if the defaults are not ideal for their target environment, whereas rebuilding the runtime libraries is usually not as easy or desirable. Unlike "TFLAGS", the use of specs enables different flags to be selected for different multilibs. The way to accomplish that is to build with make TFLAGS=-fmultiflags, after configuring --with-specs=%{fmultiflags:...}. This option is discarded by the driver once it's done processing driver self spec. It is also useful to check that "TFLAGS" are being used to build all target libraries, by configuring a non-bootstrap compiler --with-specs='%{!fmultiflags:%emissing TFLAGS}' and building the compiler and target libraries. -fprofile-report Makes the compiler print some statistics about consistency of the (estimated) profile and effect of individual passes. -fstack-usage Makes the compiler output stack usage information for the program, on a per-function basis. The filename for the dump is made by appending .su to the auxname. auxname is generated from the name of the output file, if explicitly specified and it is not an executable, otherwise it is the basename of the source file. An entry is made up of three fields: * The name of the function. * A number of bytes. * One or more qualifiers: "static", "dynamic", "bounded". The qualifier "static" means that the function manipulates the stack statically: a fixed number of bytes are allocated for the frame on function entry and released on function exit; no stack adjustments are otherwise made in the function. The second field is this fixed number of bytes. The qualifier "dynamic" means that the function manipulates the stack dynamically: in addition to the static allocation described above, stack adjustments are made in the body of the function, for example to push/pop arguments around function calls. If the qualifier "bounded" is also present, the amount of these adjustments is bounded at compile time and the second field is an upper bound of the total amount of stack used by the function. If it is not present, the amount of these adjustments is not bounded at compile time and the second field only represents the bounded part. -fstats Emit statistics about front-end processing at the end of the compilation. This option is supported only by the C++ front end, and the information is generally only useful to the G++ development team. -fdbg-cnt-list Print the name and the counter upper bound for all debug counters. -fdbg-cnt=counter-value-list Set the internal debug counter lower and upper bound. counter- value-list is a comma-separated list of name:lower_bound1-upper_bound1 [:lower_bound2-upper_bound2...] tuples which sets the name of the counter and list of closed intervals. The lower_bound is optional and is zero initialized if not set. For example, with -fdbg-cnt=dce:2-4:10-11,tail_call:10, "dbg_cnt(dce)" returns true only for second, third, fourth, tenth and eleventh invocation. For "dbg_cnt(tail_call)" true is returned for first 10 invocations. -print-file-name=library Print the full absolute name of the library file library that would be used when linking---and don't do anything else. With this option, GCC does not compile or link anything; it just prints the file name. -print-multi-directory Print the directory name corresponding to the multilib selected by any other switches present in the command line. This directory is supposed to exist in GCC_EXEC_PREFIX. -print-multi-lib Print the mapping from multilib directory names to compiler switches that enable them. The directory name is separated from the switches by ;, and each switch starts with an @ instead of the -, without spaces between multiple switches. This is supposed to ease shell processing. -print-multi-os-directory Print the path to OS libraries for the selected multilib, relative to some lib subdirectory. If OS libraries are present in the lib subdirectory and no multilibs are used, this is usually just ., if OS libraries are present in libsuffix sibling directories this prints e.g. ../lib64, ../lib or ../lib32, or if OS libraries are present in lib/subdir subdirectories it prints e.g. amd64, sparcv9 or ev6. -print-multiarch Print the path to OS libraries for the selected multiarch, relative to some lib subdirectory. -print-prog-name=program Like -print-file-name, but searches for a program such as cpp. -print-libgcc-file-name Same as -print-file-name=libgcc.a. This is useful when you use -nostdlib or -nodefaultlibs but you do want to link with libgcc.a. You can do: gcc -nostdlib <files>... `gcc -print-libgcc-file-name` -print-search-dirs Print the name of the configured installation directory and a list of program and library directories gcc searches---and don't do anything else. This is useful when gcc prints the error message installation problem, cannot exec cpp0: No such file or directory. To resolve this you either need to put cpp0 and the other compiler components where gcc expects to find them, or you can set the environment variable GCC_EXEC_PREFIX to the directory where you installed them. Don't forget the trailing /. -print-sysroot Print the target sysroot directory that is used during compilation. This is the target sysroot specified either at configure time or using the --sysroot option, possibly with an extra suffix that depends on compilation options. If no target sysroot is specified, the option prints nothing. -print-sysroot-headers-suffix Print the suffix added to the target sysroot when searching for headers, or give an error if the compiler is not configured with such a suffix---and don't do anything else. -dumpmachine Print the compiler's target machine (for example, i686-pc-linux-gnu)---and don't do anything else. -dumpversion Print the compiler version (for example, 3.0, 6.3.0 or 7)---and don't do anything else. This is the compiler version used in filesystem paths and specs. Depending on how the compiler has been configured it can be just a single number (major version), two numbers separated by a dot (major and minor version) or three numbers separated by dots (major, minor and patchlevel version). -dumpfullversion Print the full compiler version---and don't do anything else. The output is always three numbers separated by dots, major, minor and patchlevel version. -dumpspecs Print the compiler's built-in specs---and don't do anything else. (This is used when GCC itself is being built.) Machine-Dependent Options Each target machine supported by GCC can have its own options---for example, to allow you to compile for a particular processor variant or ABI, or to control optimizations specific to that machine. By convention, the names of machine-specific options start with -m. Some configurations of the compiler also support additional target- specific options, usually for compatibility with other compilers on the same platform. AArch64 Options These options are defined for AArch64 implementations: -mabi=name Generate code for the specified data model. Permissible values are ilp32 for SysV-like data model where int, long int and pointers are 32 bits, and lp64 for SysV-like data model where int is 32 bits, but long int and pointers are 64 bits. The default depends on the specific target configuration. Note that the LP64 and ILP32 ABIs are not link-compatible; you must compile your entire program with the same ABI, and link with a compatible set of libraries. -mbig-endian Generate big-endian code. This is the default when GCC is configured for an aarch64_be-*-* target. -mgeneral-regs-only Generate code which uses only the general-purpose registers. This will prevent the compiler from using floating-point and Advanced SIMD registers but will not impose any restrictions on the assembler. -mlittle-endian Generate little-endian code. This is the default when GCC is configured for an aarch64-*-* but not an aarch64_be-*-* target. -mcmodel=tiny Generate code for the tiny code model. The program and its statically defined symbols must be within 1MB of each other. Programs can be statically or dynamically linked. -mcmodel=small Generate code for the small code model. The program and its statically defined symbols must be within 4GB of each other. Programs can be statically or dynamically linked. This is the default code model. -mcmodel=large Generate code for the large code model. This makes no assumptions about addresses and sizes of sections. Programs can be statically linked only. The -mcmodel=large option is incompatible with -mabi=ilp32, -fpic and -fPIC. -mstrict-align -mno-strict-align Avoid or allow generating memory accesses that may not be aligned on a natural object boundary as described in the architecture specification. -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer Omit or keep the frame pointer in leaf functions. The former behavior is the default. -mstack-protector-guard=guard -mstack-protector-guard-reg=reg -mstack-protector-guard-offset=offset Generate stack protection code using canary at guard. Supported locations are global for a global canary or sysreg for a canary in an appropriate system register. With the latter choice the options -mstack-protector-guard-reg=reg and -mstack-protector-guard-offset=offset furthermore specify which system register to use as base register for reading the canary, and from what offset from that base register. There is no default register or offset as this is entirely for use within the Linux kernel. -mtls-dialect=desc Use TLS descriptors as the thread-local storage mechanism for dynamic accesses of TLS variables. This is the default. -mtls-dialect=traditional Use traditional TLS as the thread-local storage mechanism for dynamic accesses of TLS variables. -mtls-size=size Specify bit size of immediate TLS offsets. Valid values are 12, 24, 32, 48. This option requires binutils 2.26 or newer. -mfix-cortex-a53-835769 -mno-fix-cortex-a53-835769 Enable or disable the workaround for the ARM Cortex-A53 erratum number 835769. This involves inserting a NOP instruction between memory instructions and 64-bit integer multiply-accumulate instructions. -mfix-cortex-a53-843419 -mno-fix-cortex-a53-843419 Enable or disable the workaround for the ARM Cortex-A53 erratum number 843419. This erratum workaround is made at link time and this will only pass the corresponding flag to the linker. -mlow-precision-recip-sqrt -mno-low-precision-recip-sqrt Enable or disable the reciprocal square root approximation. This option only has an effect if -ffast-math or -funsafe-math-optimizations is used as well. Enabling this reduces precision of reciprocal square root results to about 16 bits for single precision and to 32 bits for double precision. -mlow-precision-sqrt -mno-low-precision-sqrt Enable or disable the square root approximation. This option only has an effect if -ffast-math or -funsafe-math-optimizations is used as well. Enabling this reduces precision of square root results to about 16 bits for single precision and to 32 bits for double precision. If enabled, it implies -mlow-precision-recip-sqrt. -mlow-precision-div -mno-low-precision-div Enable or disable the division approximation. This option only has an effect if -ffast-math or -funsafe-math-optimizations is used as well. Enabling this reduces precision of division results to about 16 bits for single precision and to 32 bits for double precision. -mtrack-speculation -mno-track-speculation Enable or disable generation of additional code to track speculative execution through conditional branches. The tracking state can then be used by the compiler when expanding calls to "__builtin_speculation_safe_copy" to permit a more efficient code sequence to be generated. -moutline-atomics -mno-outline-atomics Enable or disable calls to out-of-line helpers to implement atomic operations. These helpers will, at runtime, determine if the LSE instructions from ARMv8.1-A can be used; if not, they will use the load/store-exclusive instructions that are present in the base ARMv8.0 ISA. This option is only applicable when compiling for the base ARMv8.0 instruction set. If using a later revision, e.g. -march=armv8.1-a or -march=armv8-a+lse, the ARMv8.1-Atomics instructions will be used directly. The same applies when using -mcpu= when the selected cpu supports the lse feature. This option is on by default. -march=name Specify the name of the target architecture and, optionally, one or more feature modifiers. This option has the form -march=arch{+[no]feature}*. The table below summarizes the permissible values for arch and the features that they enable by default: arch value : Architecture : Includes by default armv8-a : Armv8-A : +fp, +simd armv8.1-a : Armv8.1-A : armv8-a, +crc, +lse, +rdma armv8.2-a : Armv8.2-A : armv8.1-a armv8.3-a : Armv8.3-A : armv8.2-a, +pauth armv8.4-a : Armv8.4-A : armv8.3-a, +flagm, +fp16fml, +dotprod armv8.5-a : Armv8.5-A : armv8.4-a, +sb, +ssbs, +predres armv8.6-a : Armv8.6-A : armv8.5-a, +bf16, +i8mm armv8.7-a : Armv8.7-A : armv8.6-a, +ls64 armv8.8-a : Armv8.8-a : armv8.7-a, +mops armv9-a : Armv9-A : armv8.5-a, +sve, +sve2 armv9.1-a : Armv9.1-A : armv9-a, +bf16, +i8mm armv9.2-a : Armv9.2-A : armv9.1-a, +ls64 armv9.3-a : Armv9.3-A : armv9.2-a, +mops armv8-r : Armv8-R : armv8-r The value native is available on native AArch64 GNU/Linux and causes the compiler to pick the architecture of the host system. This option has no effect if the compiler is unable to recognize the architecture of the host system, The permissible values for feature are listed in the sub-section on aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers. Where conflicting feature modifiers are specified, the right-most feature is used. GCC uses name to determine what kind of instructions it can emit when generating assembly code. If -march is specified without either of -mtune or -mcpu also being specified, the code is tuned to perform well across a range of target processors implementing the target architecture. -mtune=name Specify the name of the target processor for which GCC should tune the performance of the code. Permissible values for this option are: generic, cortex-a35, cortex-a53, cortex-a55, cortex-a57, cortex-a72, cortex-a73, cortex-a75, cortex-a76, cortex-a76ae, cortex-a77, cortex-a65, cortex-a65ae, cortex-a34, cortex-a78, cortex-a78ae, cortex-a78c, ares, exynos-m1, emag, falkor, neoverse-512tvb, neoverse-e1, neoverse-n1, neoverse-n2, neoverse-v1, neoverse-v2, qdf24xx, saphira, phecda, xgene1, vulcan, octeontx, octeontx81, octeontx83, octeontx2, octeontx2t98, octeontx2t96 octeontx2t93, octeontx2f95, octeontx2f95n, octeontx2f95mm, a64fx, thunderx, thunderxt88, thunderxt88p1, thunderxt81, tsv110, thunderxt83, thunderx2t99, thunderx3t110, zeus, cortex-a57.cortex-a53, cortex-a72.cortex-a53, cortex-a73.cortex-a35, cortex-a73.cortex-a53, cortex-a75.cortex-a55, cortex-a76.cortex-a55, cortex-r82, cortex-x1, cortex-x1c, cortex-x2, cortex-x3, cortex-a510, cortex-a710, cortex-a715, ampere1, ampere1a, and native. The values cortex-a57.cortex-a53, cortex-a72.cortex-a53, cortex-a73.cortex-a35, cortex-a73.cortex-a53, cortex-a75.cortex-a55, cortex-a76.cortex-a55 specify that GCC should tune for a big.LITTLE system. The value neoverse-512tvb specifies that GCC should tune for Neoverse cores that (a) implement SVE and (b) have a total vector bandwidth of 512 bits per cycle. In other words, the option tells GCC to tune for Neoverse cores that can execute 4 128-bit Advanced SIMD arithmetic instructions a cycle and that can execute an equivalent number of SVE arithmetic instructions per cycle (2 for 256-bit SVE, 4 for 128-bit SVE). This is more general than tuning for a specific core like Neoverse V1 but is more specific than the default tuning described below. Additionally on native AArch64 GNU/Linux systems the value native tunes performance to the host system. This option has no effect if the compiler is unable to recognize the processor of the host system. Where none of -mtune=, -mcpu= or -march= are specified, the code is tuned to perform well across a range of target processors. This option cannot be suffixed by feature modifiers. -mcpu=name Specify the name of the target processor, optionally suffixed by one or more feature modifiers. This option has the form -mcpu=cpu{+[no]feature}*, where the permissible values for cpu are the same as those available for -mtune. The permissible values for feature are documented in the sub-section on aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers. Where conflicting feature modifiers are specified, the right-most feature is used. GCC uses name to determine what kind of instructions it can emit when generating assembly code (as if by -march) and to determine the target processor for which to tune for performance (as if by -mtune). Where this option is used in conjunction with -march or -mtune, those options take precedence over the appropriate part of this option. -mcpu=neoverse-512tvb is special in that it does not refer to a specific core, but instead refers to all Neoverse cores that (a) implement SVE and (b) have a total vector bandwidth of 512 bits a cycle. Unless overridden by -march, -mcpu=neoverse-512tvb generates code that can run on a Neoverse V1 core, since Neoverse V1 is the first Neoverse core with these properties. Unless overridden by -mtune, -mcpu=neoverse-512tvb tunes code in the same way as for -mtune=neoverse-512tvb. -moverride=string Override tuning decisions made by the back-end in response to a -mtune= switch. The syntax, semantics, and accepted values for string in this option are not guaranteed to be consistent across releases. This option is only intended to be useful when developing GCC. -mverbose-cost-dump Enable verbose cost model dumping in the debug dump files. This option is provided for use in debugging the compiler. -mpc-relative-literal-loads -mno-pc-relative-literal-loads Enable or disable PC-relative literal loads. With this option literal pools are accessed using a single instruction and emitted after each function. This limits the maximum size of functions to 1MB. This is enabled by default for -mcmodel=tiny. -msign-return-address=scope Select the function scope on which return address signing will be applied. Permissible values are none, which disables return address signing, non-leaf, which enables pointer signing for functions which are not leaf functions, and all, which enables pointer signing for all functions. The default value is none. This option has been deprecated by -mbranch-protection. -mbranch-protection=none|standard|pac-ret[+leaf+b-key]|bti Select the branch protection features to use. none is the default and turns off all types of branch protection. standard turns on all types of branch protection features. If a feature has additional tuning options, then standard sets it to its standard level. pac-ret[+leaf] turns on return address signing to its standard level: signing functions that save the return address to memory (non-leaf functions will practically always do this) using the a-key. The optional argument leaf can be used to extend the signing to include leaf functions. The optional argument b-key can be used to sign the functions with the B-key instead of the A-key. bti turns on branch target identification mechanism. -mharden-sls=opts Enable compiler hardening against straight line speculation (SLS). opts is a comma-separated list of the following options: retbr blr In addition, -mharden-sls=all enables all SLS hardening while -mharden-sls=none disables all SLS hardening. -msve-vector-bits=bits Specify the number of bits in an SVE vector register. This option only has an effect when SVE is enabled. GCC supports two forms of SVE code generation: "vector-length agnostic" output that works with any size of vector register and "vector-length specific" output that allows GCC to make assumptions about the vector length when it is useful for optimization reasons. The possible values of bits are: scalable, 128, 256, 512, 1024 and 2048. Specifying scalable selects vector-length agnostic output. At present -msve-vector-bits=128 also generates vector-length agnostic output for big-endian targets. All other values generate vector-length specific code. The behavior of these values may change in future releases and no value except scalable should be relied on for producing code that is portable across different hardware SVE vector lengths. The default is -msve-vector-bits=scalable, which produces vector- length agnostic code. -march and -mcpu Feature Modifiers Feature modifiers used with -march and -mcpu can be any of the following and their inverses nofeature: crc Enable CRC extension. This is on by default for -march=armv8.1-a. crypto Enable Crypto extension. This also enables Advanced SIMD and floating-point instructions. fp Enable floating-point instructions. This is on by default for all possible values for options -march and -mcpu. simd Enable Advanced SIMD instructions. This also enables floating- point instructions. This is on by default for all possible values for options -march and -mcpu. sve Enable Scalable Vector Extension instructions. This also enables Advanced SIMD and floating-point instructions. lse Enable Large System Extension instructions. This is on by default for -march=armv8.1-a. rdma Enable Round Double Multiply Accumulate instructions. This is on by default for -march=armv8.1-a. fp16 Enable FP16 extension. This also enables floating-point instructions. fp16fml Enable FP16 fmla extension. This also enables FP16 extensions and floating-point instructions. This option is enabled by default for -march=armv8.4-a. Use of this option with architectures prior to Armv8.2-A is not supported. rcpc Enable the RCpc extension. This enables the use of the LDAPR instructions for load-acquire atomic semantics, and passes it on to the assembler, enabling inline asm statements to use instructions from the RCpc extension. dotprod Enable the Dot Product extension. This also enables Advanced SIMD instructions. aes Enable the Armv8-a aes and pmull crypto extension. This also enables Advanced SIMD instructions. sha2 Enable the Armv8-a sha2 crypto extension. This also enables Advanced SIMD instructions. sha3 Enable the sha512 and sha3 crypto extension. This also enables Advanced SIMD instructions. Use of this option with architectures prior to Armv8.2-A is not supported. sm4 Enable the sm3 and sm4 crypto extension. This also enables Advanced SIMD instructions. Use of this option with architectures prior to Armv8.2-A is not supported. profile Enable the Statistical Profiling extension. This option is only to enable the extension at the assembler level and does not affect code generation. rng Enable the Armv8.5-a Random Number instructions. This option is only to enable the extension at the assembler level and does not affect code generation. memtag Enable the Armv8.5-a Memory Tagging Extensions. Use of this option with architectures prior to Armv8.5-A is not supported. sb Enable the Armv8-a Speculation Barrier instruction. This option is only to enable the extension at the assembler level and does not affect code generation. This option is enabled by default for -march=armv8.5-a. ssbs Enable the Armv8-a Speculative Store Bypass Safe instruction. This option is only to enable the extension at the assembler level and does not affect code generation. This option is enabled by default for -march=armv8.5-a. predres Enable the Armv8-a Execution and Data Prediction Restriction instructions. This option is only to enable the extension at the assembler level and does not affect code generation. This option is enabled by default for -march=armv8.5-a. sve2 Enable the Armv8-a Scalable Vector Extension 2. This also enables SVE instructions. sve2-bitperm Enable SVE2 bitperm instructions. This also enables SVE2 instructions. sve2-sm4 Enable SVE2 sm4 instructions. This also enables SVE2 instructions. sve2-aes Enable SVE2 aes instructions. This also enables SVE2 instructions. sve2-sha3 Enable SVE2 sha3 instructions. This also enables SVE2 instructions. tme Enable the Transactional Memory Extension. i8mm Enable 8-bit Integer Matrix Multiply instructions. This also enables Advanced SIMD and floating-point instructions. This option is enabled by default for -march=armv8.6-a. Use of this option with architectures prior to Armv8.2-A is not supported. f32mm Enable 32-bit Floating point Matrix Multiply instructions. This also enables SVE instructions. Use of this option with architectures prior to Armv8.2-A is not supported. f64mm Enable 64-bit Floating point Matrix Multiply instructions. This also enables SVE instructions. Use of this option with architectures prior to Armv8.2-A is not supported. bf16 Enable brain half-precision floating-point instructions. This also enables Advanced SIMD and floating-point instructions. This option is enabled by default for -march=armv8.6-a. Use of this option with architectures prior to Armv8.2-A is not supported. ls64 Enable the 64-byte atomic load and store instructions for accelerators. This option is enabled by default for -march=armv8.7-a. mops Enable the instructions to accelerate memory operations like "memcpy", "memmove", "memset". This option is enabled by default for -march=armv8.8-a flagm Enable the Flag Manipulation instructions Extension. pauth Enable the Pointer Authentication Extension. cssc Enable the Common Short Sequence Compression instructions. Feature crypto implies aes, sha2, and simd, which implies fp. Conversely, nofp implies nosimd, which implies nocrypto, noaes and nosha2. Adapteva Epiphany Options These -m options are defined for Adapteva Epiphany: -mhalf-reg-file Don't allocate any register in the range "r32"..."r63". That allows code to run on hardware variants that lack these registers. -mprefer-short-insn-regs Preferentially allocate registers that allow short instruction generation. This can result in increased instruction count, so this may either reduce or increase overall code size. -mbranch-cost=num Set the cost of branches to roughly num "simple" instructions. This cost is only a heuristic and is not guaranteed to produce consistent results across releases. -mcmove Enable the generation of conditional moves. -mnops=num Emit num NOPs before every other generated instruction. -mno-soft-cmpsf For single-precision floating-point comparisons, emit an "fsub" instruction and test the flags. This is faster than a software comparison, but can get incorrect results in the presence of NaNs, or when two different small numbers are compared such that their difference is calculated as zero. The default is -msoft-cmpsf, which uses slower, but IEEE-compliant, software comparisons. -mstack-offset=num Set the offset between the top of the stack and the stack pointer. E.g., a value of 8 means that the eight bytes in the range "sp+0...sp+7" can be used by leaf functions without stack allocation. Values other than 8 or 16 are untested and unlikely to work. Note also that this option changes the ABI; compiling a program with a different stack offset than the libraries have been compiled with generally does not work. This option can be useful if you want to evaluate if a different stack offset would give you better code, but to actually use a different stack offset to build working programs, it is recommended to configure the toolchain with the appropriate --with-stack-offset=num option. -mno-round-nearest Make the scheduler assume that the rounding mode has been set to truncating. The default is -mround-nearest. -mlong-calls If not otherwise specified by an attribute, assume all calls might be beyond the offset range of the "b" / "bl" instructions, and therefore load the function address into a register before performing a (otherwise direct) call. This is the default. -mshort-calls If not otherwise specified by an attribute, assume all direct calls are in the range of the "b" / "bl" instructions, so use these instructions for direct calls. The default is -mlong-calls. -msmall16 Assume addresses can be loaded as 16-bit unsigned values. This does not apply to function addresses for which -mlong-calls semantics are in effect. -mfp-mode=mode Set the prevailing mode of the floating-point unit. This determines the floating-point mode that is provided and expected at function call and return time. Making this mode match the mode you predominantly need at function start can make your programs smaller and faster by avoiding unnecessary mode switches. mode can be set to one the following values: caller Any mode at function entry is valid, and retained or restored when the function returns, and when it calls other functions. This mode is useful for compiling libraries or other compilation units you might want to incorporate into different programs with different prevailing FPU modes, and the convenience of being able to use a single object file outweighs the size and speed overhead for any extra mode switching that might be needed, compared with what would be needed with a more specific choice of prevailing FPU mode. truncate This is the mode used for floating-point calculations with truncating (i.e. round towards zero) rounding mode. That includes conversion from floating point to integer. round-nearest This is the mode used for floating-point calculations with round-to-nearest-or-even rounding mode. int This is the mode used to perform integer calculations in the FPU, e.g. integer multiply, or integer multiply-and- accumulate. The default is -mfp-mode=caller -mno-split-lohi -mno-postinc -mno-postmodify Code generation tweaks that disable, respectively, splitting of 32-bit loads, generation of post-increment addresses, and generation of post-modify addresses. The defaults are msplit-lohi, -mpost-inc, and -mpost-modify. -mnovect-double Change the preferred SIMD mode to SImode. The default is -mvect-double, which uses DImode as preferred SIMD mode. -max-vect-align=num The maximum alignment for SIMD vector mode types. num may be 4 or 8. The default is 8. Note that this is an ABI change, even though many library function interfaces are unaffected if they don't use SIMD vector modes in places that affect size and/or alignment of relevant types. -msplit-vecmove-early Split vector moves into single word moves before reload. In theory this can give better register allocation, but so far the reverse seems to be generally the case. -m1reg-reg Specify a register to hold the constant -1, which makes loading small negative constants and certain bitmasks faster. Allowable values for reg are r43 and r63, which specify use of that register as a fixed register, and none, which means that no register is used for this purpose. The default is -m1reg-none. AMD GCN Options These options are defined specifically for the AMD GCN port. -march=gpu -mtune=gpu Set architecture type or tuning for gpu. Supported values for gpu are fiji Compile for GCN3 Fiji devices (gfx803). gfx900 Compile for GCN5 Vega 10 devices (gfx900). gfx906 Compile for GCN5 Vega 20 devices (gfx906). gfx908 Compile for CDNA1 Instinct MI100 series devices (gfx908). gfx90a Compile for CDNA2 Instinct MI200 series devices (gfx90a). -msram-ecc=on -msram-ecc=off -msram-ecc=any Compile binaries suitable for devices with the SRAM-ECC feature enabled, disabled, or either mode. This feature can be enabled per-process on some devices. The compiled code must match the device mode. The default is any, for devices that support it. -mstack-size=bytes Specify how many bytes of stack space will be requested for each GPU thread (wave-front). Beware that there may be many threads and limited memory available. The size of the stack allocation may also have an impact on run-time performance. The default is 32KB when using OpenACC or OpenMP, and 1MB otherwise. -mxnack Compile binaries suitable for devices with the XNACK feature enabled. Some devices always require XNACK and some allow the user to configure XNACK. The compiled code must match the device mode. The default is -mno-xnack. At present this option is a placeholder for support that is not yet implemented. ARC Options The following options control the architecture variant for which code is being compiled: -mbarrel-shifter Generate instructions supported by barrel shifter. This is the default unless -mcpu=ARC601 or -mcpu=ARCEM is in effect. -mjli-always Force to call a function using jli_s instruction. This option is valid only for ARCv2 architecture. -mcpu=cpu Set architecture type, register usage, and instruction scheduling parameters for cpu. There are also shortcut alias options available for backward compatibility and convenience. Supported values for cpu are arc600 Compile for ARC600. Aliases: -mA6, -mARC600. arc601 Compile for ARC601. Alias: -mARC601. arc700 Compile for ARC700. Aliases: -mA7, -mARC700. This is the default when configured with --with-cpu=arc700. arcem Compile for ARC EM. archs Compile for ARC HS. em Compile for ARC EM CPU with no hardware extensions. em4 Compile for ARC EM4 CPU. em4_dmips Compile for ARC EM4 DMIPS CPU. em4_fpus Compile for ARC EM4 DMIPS CPU with the single-precision floating-point extension. em4_fpuda Compile for ARC EM4 DMIPS CPU with single-precision floating- point and double assist instructions. hs Compile for ARC HS CPU with no hardware extensions except the atomic instructions. hs34 Compile for ARC HS34 CPU. hs38 Compile for ARC HS38 CPU. hs38_linux Compile for ARC HS38 CPU with all hardware extensions on. hs4x Compile for ARC HS4x CPU. hs4xd Compile for ARC HS4xD CPU. hs4x_rel31 Compile for ARC HS4x CPU release 3.10a. arc600_norm Compile for ARC 600 CPU with "norm" instructions enabled. arc600_mul32x16 Compile for ARC 600 CPU with "norm" and 32x16-bit multiply instructions enabled. arc600_mul64 Compile for ARC 600 CPU with "norm" and "mul64"-family instructions enabled. arc601_norm Compile for ARC 601 CPU with "norm" instructions enabled. arc601_mul32x16 Compile for ARC 601 CPU with "norm" and 32x16-bit multiply instructions enabled. arc601_mul64 Compile for ARC 601 CPU with "norm" and "mul64"-family instructions enabled. nps400 Compile for ARC 700 on NPS400 chip. em_mini Compile for ARC EM minimalist configuration featuring reduced register set. -mdpfp -mdpfp-compact Generate double-precision FPX instructions, tuned for the compact implementation. -mdpfp-fast Generate double-precision FPX instructions, tuned for the fast implementation. -mno-dpfp-lrsr Disable "lr" and "sr" instructions from using FPX extension aux registers. -mea Generate extended arithmetic instructions. Currently only "divaw", "adds", "subs", and "sat16" are supported. Only valid for -mcpu=ARC700. -mno-mpy Do not generate "mpy"-family instructions for ARC700. This option is deprecated. -mmul32x16 Generate 32x16-bit multiply and multiply-accumulate instructions. -mmul64 Generate "mul64" and "mulu64" instructions. Only valid for -mcpu=ARC600. -mnorm Generate "norm" instructions. This is the default if -mcpu=ARC700 is in effect. -mspfp -mspfp-compact Generate single-precision FPX instructions, tuned for the compact implementation. -mspfp-fast Generate single-precision FPX instructions, tuned for the fast implementation. -msimd Enable generation of ARC SIMD instructions via target-specific builtins. Only valid for -mcpu=ARC700. -msoft-float This option ignored; it is provided for compatibility purposes only. Software floating-point code is emitted by default, and this default can overridden by FPX options; -mspfp, -mspfp-compact, or -mspfp-fast for single precision, and -mdpfp, -mdpfp-compact, or -mdpfp-fast for double precision. -mswap Generate "swap" instructions. -matomic This enables use of the locked load/store conditional extension to implement atomic memory built-in functions. Not available for ARC 6xx or ARC EM cores. -mdiv-rem Enable "div" and "rem" instructions for ARCv2 cores. -mcode-density Enable code density instructions for ARC EM. This option is on by default for ARC HS. -mll64 Enable double load/store operations for ARC HS cores. -mtp-regno=regno Specify thread pointer register number. -mmpy-option=multo Compile ARCv2 code with a multiplier design option. You can specify the option using either a string or numeric value for multo. wlh1 is the default value. The recognized values are: 0 none No multiplier available. 1 w 16x16 multiplier, fully pipelined. The following instructions are enabled: "mpyw" and "mpyuw". 2 wlh1 32x32 multiplier, fully pipelined (1 stage). The following instructions are additionally enabled: "mpy", "mpyu", "mpym", "mpymu", and "mpy_s". 3 wlh2 32x32 multiplier, fully pipelined (2 stages). The following instructions are additionally enabled: "mpy", "mpyu", "mpym", "mpymu", and "mpy_s". 4 wlh3 Two 16x16 multipliers, blocking, sequential. The following instructions are additionally enabled: "mpy", "mpyu", "mpym", "mpymu", and "mpy_s". 5 wlh4 One 16x16 multiplier, blocking, sequential. The following instructions are additionally enabled: "mpy", "mpyu", "mpym", "mpymu", and "mpy_s". 6 wlh5 One 32x4 multiplier, blocking, sequential. The following instructions are additionally enabled: "mpy", "mpyu", "mpym", "mpymu", and "mpy_s". 7 plus_dmpy ARC HS SIMD support. 8 plus_macd ARC HS SIMD support. 9 plus_qmacw ARC HS SIMD support. This option is only available for ARCv2 cores. -mfpu=fpu Enables support for specific floating-point hardware extensions for ARCv2 cores. Supported values for fpu are: fpus Enables support for single-precision floating-point hardware extensions. fpud Enables support for double-precision floating-point hardware extensions. The single-precision floating-point extension is also enabled. Not available for ARC EM. fpuda Enables support for double-precision floating-point hardware extensions using double-precision assist instructions. The single-precision floating-point extension is also enabled. This option is only available for ARC EM. fpuda_div Enables support for double-precision floating-point hardware extensions using double-precision assist instructions. The single-precision floating-point, square-root, and divide extensions are also enabled. This option is only available for ARC EM. fpuda_fma Enables support for double-precision floating-point hardware extensions using double-precision assist instructions. The single-precision floating-point and fused multiply and add hardware extensions are also enabled. This option is only available for ARC EM. fpuda_all Enables support for double-precision floating-point hardware extensions using double-precision assist instructions. All single-precision floating-point hardware extensions are also enabled. This option is only available for ARC EM. fpus_div Enables support for single-precision floating-point, square- root and divide hardware extensions. fpud_div Enables support for double-precision floating-point, square- root and divide hardware extensions. This option includes option fpus_div. Not available for ARC EM. fpus_fma Enables support for single-precision floating-point and fused multiply and add hardware extensions. fpud_fma Enables support for double-precision floating-point and fused multiply and add hardware extensions. This option includes option fpus_fma. Not available for ARC EM. fpus_all Enables support for all single-precision floating-point hardware extensions. fpud_all Enables support for all single- and double-precision floating- point hardware extensions. Not available for ARC EM. -mirq-ctrl-saved=register-range, blink, lp_count Specifies general-purposes registers that the processor automatically saves/restores on interrupt entry and exit. register-range is specified as two registers separated by a dash. The register range always starts with "r0", the upper limit is "fp" register. blink and lp_count are optional. This option is only valid for ARC EM and ARC HS cores. -mrgf-banked-regs=number Specifies the number of registers replicated in second register bank on entry to fast interrupt. Fast interrupts are interrupts with the highest priority level P0. These interrupts save only PC and STATUS32 registers to avoid memory transactions during interrupt entry and exit sequences. Use this option when you are using fast interrupts in an ARC V2 family processor. Permitted values are 4, 8, 16, and 32. -mlpc-width=width Specify the width of the "lp_count" register. Valid values for width are 8, 16, 20, 24, 28 and 32 bits. The default width is fixed to 32 bits. If the width is less than 32, the compiler does not attempt to transform loops in your program to use the zero- delay loop mechanism unless it is known that the "lp_count" register can hold the required loop-counter value. Depending on the width specified, the compiler and run-time library might continue to use the loop mechanism for various needs. This option defines macro "__ARC_LPC_WIDTH__" with the value of width. -mrf16 This option instructs the compiler to generate code for a 16-entry register file. This option defines the "__ARC_RF16__" preprocessor macro. -mbranch-index Enable use of "bi" or "bih" instructions to implement jump tables. The following options are passed through to the assembler, and also define preprocessor macro symbols. -mdsp-packa Passed down to the assembler to enable the DSP Pack A extensions. Also sets the preprocessor symbol "__Xdsp_packa". This option is deprecated. -mdvbf Passed down to the assembler to enable the dual Viterbi butterfly extension. Also sets the preprocessor symbol "__Xdvbf". This option is deprecated. -mlock Passed down to the assembler to enable the locked load/store conditional extension. Also sets the preprocessor symbol "__Xlock". -mmac-d16 Passed down to the assembler. Also sets the preprocessor symbol "__Xxmac_d16". This option is deprecated. -mmac-24 Passed down to the assembler. Also sets the preprocessor symbol "__Xxmac_24". This option is deprecated. -mrtsc Passed down to the assembler to enable the 64-bit time-stamp counter extension instruction. Also sets the preprocessor symbol "__Xrtsc". This option is deprecated. -mswape Passed down to the assembler to enable the swap byte ordering extension instruction. Also sets the preprocessor symbol "__Xswape". -mtelephony Passed down to the assembler to enable dual- and single-operand instructions for telephony. Also sets the preprocessor symbol "__Xtelephony". This option is deprecated. -mxy Passed down to the assembler to enable the XY memory extension. Also sets the preprocessor symbol "__Xxy". The following options control how the assembly code is annotated: -misize Annotate assembler instructions with estimated addresses. -mannotate-align Explain what alignment considerations lead to the decision to make an instruction short or long. The following options are passed through to the linker: -marclinux Passed through to the linker, to specify use of the "arclinux" emulation. This option is enabled by default in tool chains built for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when profiling is not requested. -marclinux_prof Passed through to the linker, to specify use of the "arclinux_prof" emulation. This option is enabled by default in tool chains built for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when profiling is requested. The following options control the semantics of generated code: -mlong-calls Generate calls as register indirect calls, thus providing access to the full 32-bit address range. -mmedium-calls Don't use less than 25-bit addressing range for calls, which is the offset available for an unconditional branch-and-link instruction. Conditional execution of function calls is suppressed, to allow use of the 25-bit range, rather than the 21-bit range with conditional branch-and-link. This is the default for tool chains built for "arc-linux-uclibc" and "arceb-linux-uclibc" targets. -G num Put definitions of externally-visible data in a small data section if that data is no bigger than num bytes. The default value of num is 4 for any ARC configuration, or 8 when we have double load/store operations. -mno-sdata Do not generate sdata references. This is the default for tool chains built for "arc-linux-uclibc" and "arceb-linux-uclibc" targets. -mvolatile-cache Use ordinarily cached memory accesses for volatile references. This is the default. -mno-volatile-cache Enable cache bypass for volatile references. The following options fine tune code generation: -malign-call Does nothing. Preserved for backward compatibility. -mauto-modify-reg Enable the use of pre/post modify with register displacement. -mbbit-peephole Enable bbit peephole2. -mno-brcc This option disables a target-specific pass in arc_reorg to generate compare-and-branch ("brcc") instructions. It has no effect on generation of these instructions driven by the combiner pass. -mcase-vector-pcrel Use PC-relative switch case tables to enable case table shortening. This is the default for -Os. -mcompact-casesi Enable compact "casesi" pattern. This is the default for -Os, and only available for ARCv1 cores. This option is deprecated. -mno-cond-exec Disable the ARCompact-specific pass to generate conditional execution instructions. Due to delay slot scheduling and interactions between operand numbers, literal sizes, instruction lengths, and the support for conditional execution, the target-independent pass to generate conditional execution is often lacking, so the ARC port has kept a special pass around that tries to find more conditional execution generation opportunities after register allocation, branch shortening, and delay slot scheduling have been done. This pass generally, but not always, improves performance and code size, at the cost of extra compilation time, which is why there is an option to switch it off. If you have a problem with call instructions exceeding their allowable offset range because they are conditionalized, you should consider using -mmedium-calls instead. -mearly-cbranchsi Enable pre-reload use of the "cbranchsi" pattern. -mexpand-adddi Expand "adddi3" and "subdi3" at RTL generation time into "add.f", "adc" etc. This option is deprecated. -mindexed-loads Enable the use of indexed loads. This can be problematic because some optimizers then assume that indexed stores exist, which is not the case. -mlra Enable Local Register Allocation. This is still experimental for ARC, so by default the compiler uses standard reload (i.e. -mno-lra). -mlra-priority-none Don't indicate any priority for target registers. -mlra-priority-compact Indicate target register priority for r0..r3 / r12..r15. -mlra-priority-noncompact Reduce target register priority for r0..r3 / r12..r15. -mmillicode When optimizing for size (using -Os), prologues and epilogues that have to save or restore a large number of registers are often shortened by using call to a special function in libgcc; this is referred to as a millicode call. As these calls can pose performance issues, and/or cause linking issues when linking in a nonstandard way, this option is provided to turn on or off millicode call generation. -mcode-density-frame This option enable the compiler to emit "enter" and "leave" instructions. These instructions are only valid for CPUs with code-density feature. -mmixed-code Does nothing. Preserved for backward compatibility. -mq-class Ths option is deprecated. Enable q instruction alternatives. This is the default for -Os. -mRcq Does nothing. Preserved for backward compatibility. -mRcw Does nothing. Preserved for backward compatibility. -msize-level=level Fine-tune size optimization with regards to instruction lengths and alignment. The recognized values for level are: 0 No size optimization. This level is deprecated and treated like 1. 1 Short instructions are used opportunistically. 2 In addition, alignment of loops and of code after barriers are dropped. 3 In addition, optional data alignment is dropped, and the option Os is enabled. This defaults to 3 when -Os is in effect. Otherwise, the behavior when this is not set is equivalent to level 1. -mtune=cpu Set instruction scheduling parameters for cpu, overriding any implied by -mcpu=. Supported values for cpu are ARC600 Tune for ARC600 CPU. ARC601 Tune for ARC601 CPU. ARC700 Tune for ARC700 CPU with standard multiplier block. ARC700-xmac Tune for ARC700 CPU with XMAC block. ARC725D Tune for ARC725D CPU. ARC750D Tune for ARC750D CPU. core3 Tune for ARCv2 core3 type CPU. This option enable usage of "dbnz" instruction. release31a Tune for ARC4x release 3.10a. -mmultcost=num Cost to assume for a multiply instruction, with 4 being equal to a normal instruction. -munalign-prob-threshold=probability Does nothing. Preserved for backward compatibility. The following options are maintained for backward compatibility, but are now deprecated and will be removed in a future release: -margonaut Obsolete FPX. -mbig-endian -EB Compile code for big-endian targets. Use of these options is now deprecated. Big-endian code is supported by configuring GCC to build "arceb-elf32" and "arceb-linux-uclibc" targets, for which big endian is the default. -mlittle-endian -EL Compile code for little-endian targets. Use of these options is now deprecated. Little-endian code is supported by configuring GCC to build "arc-elf32" and "arc-linux-uclibc" targets, for which little endian is the default. -mbarrel_shifter Replaced by -mbarrel-shifter. -mdpfp_compact Replaced by -mdpfp-compact. -mdpfp_fast Replaced by -mdpfp-fast. -mdsp_packa Replaced by -mdsp-packa. -mEA Replaced by -mea. -mmac_24 Replaced by -mmac-24. -mmac_d16 Replaced by -mmac-d16. -mspfp_compact Replaced by -mspfp-compact. -mspfp_fast Replaced by -mspfp-fast. -mtune=cpu Values arc600, arc601, arc700 and arc700-xmac for cpu are replaced by ARC600, ARC601, ARC700 and ARC700-xmac respectively. -multcost=num Replaced by -mmultcost. ARM Options These -m options are defined for the ARM port: -mabi=name Generate code for the specified ABI. Permissible values are: apcs- gnu, atpcs, aapcs, aapcs-linux and iwmmxt. -mapcs-frame Generate a stack frame that is compliant with the ARM Procedure Call Standard for all functions, even if this is not strictly necessary for correct execution of the code. Specifying -fomit-frame-pointer with this option causes the stack frames not to be generated for leaf functions. The default is -mno-apcs-frame. This option is deprecated. -mapcs This is a synonym for -mapcs-frame and is deprecated. -mthumb-interwork Generate code that supports calling between the ARM and Thumb instruction sets. Without this option, on pre-v5 architectures, the two instruction sets cannot be reliably used inside one program. The default is -mno-thumb-interwork, since slightly larger code is generated when -mthumb-interwork is specified. In AAPCS configurations this option is meaningless. -mno-sched-prolog Prevent the reordering of instructions in the function prologue, or the merging of those instruction with the instructions in the function's body. This means that all functions start with a recognizable set of instructions (or in fact one of a choice from a small set of different function prologues), and this information can be used to locate the start of functions inside an executable piece of code. The default is -msched-prolog. -mfloat-abi=name Specifies which floating-point ABI to use. Permissible values are: soft, softfp and hard. Specifying soft causes GCC to generate output containing library calls for floating-point operations. softfp allows the generation of code using hardware floating-point instructions, but still uses the soft-float calling conventions. hard allows generation of floating-point instructions and uses FPU-specific calling conventions. The default depends on the specific target configuration. Note that the hard-float and soft-float ABIs are not link-compatible; you must compile your entire program with the same ABI, and link with a compatible set of libraries. -mgeneral-regs-only Generate code which uses only the general-purpose registers. This will prevent the compiler from using floating-point and Advanced SIMD registers but will not impose any restrictions on the assembler. -mlittle-endian Generate code for a processor running in little-endian mode. This is the default for all standard configurations. -mbig-endian Generate code for a processor running in big-endian mode; the default is to compile code for a little-endian processor. -mbe8 -mbe32 When linking a big-endian image select between BE8 and BE32 formats. The option has no effect for little-endian images and is ignored. The default is dependent on the selected target architecture. For ARMv6 and later architectures the default is BE8, for older architectures the default is BE32. BE32 format has been deprecated by ARM. -march=name[+extension...] This specifies the name of the target ARM architecture. GCC uses this name to determine what kind of instructions it can emit when generating assembly code. This option can be used in conjunction with or instead of the -mcpu= option. Permissible names are: armv4t, armv5t, armv5te, armv6, armv6j, armv6k, armv6kz, armv6t2, armv6z, armv6zk, armv7, armv7-a, armv7ve, armv8-a, armv8.1-a, armv8.2-a, armv8.3-a, armv8.4-a, armv8.5-a, armv8.6-a, armv9-a, armv7-r, armv8-r, armv6-m, armv6s-m, armv7-m, armv7e-m, armv8-m.base, armv8-m.main, armv8.1-m.main, armv9-a, iwmmxt and iwmmxt2. Additionally, the following architectures, which lack support for the Thumb execution state, are recognized but support is deprecated: armv4. Many of the architectures support extensions. These can be added by appending +extension to the architecture name. Extension options are processed in order and capabilities accumulate. An extension will also enable any necessary base extensions upon which it depends. For example, the +crypto extension will always enable the +simd extension. The exception to the additive construction is for extensions that are prefixed with +no...: these extensions disable the specified option and any other extensions that may depend on the presence of that extension. For example, -march=armv7-a+simd+nofp+vfpv4 is equivalent to writing -march=armv7-a+vfpv4 since the +simd option is entirely disabled by the +nofp option that follows it. Most extension names are generically named, but have an effect that is dependent upon the architecture to which it is applied. For example, the +simd option can be applied to both armv7-a and armv8-a architectures, but will enable the original ARMv7-A Advanced SIMD (Neon) extensions for armv7-a and the ARMv8-A variant for armv8-a. The table below lists the supported extensions for each architecture. Architectures not mentioned do not support any extensions. armv5te armv6 armv6j armv6k armv6kz armv6t2 armv6z armv6zk +fp The VFPv2 floating-point instructions. The extension +vfpv2 can be used as an alias for this extension. +nofp Disable the floating-point instructions. armv7 The common subset of the ARMv7-A, ARMv7-R and ARMv7-M architectures. +fp The VFPv3 floating-point instructions, with 16 double- precision registers. The extension +vfpv3-d16 can be used as an alias for this extension. Note that floating-point is not supported by the base ARMv7-M architecture, but is compatible with both the ARMv7-A and ARMv7-R architectures. +nofp Disable the floating-point instructions. armv7-a +mp The multiprocessing extension. +sec The security extension. +fp The VFPv3 floating-point instructions, with 16 double- precision registers. The extension +vfpv3-d16 can be used as an alias for this extension. +simd The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions. The extensions +neon and +neon-vfpv3 can be used as aliases for this extension. +vfpv3 The VFPv3 floating-point instructions, with 32 double- precision registers. +vfpv3-d16-fp16 The VFPv3 floating-point instructions, with 16 double- precision registers and the half-precision floating-point conversion operations. +vfpv3-fp16 The VFPv3 floating-point instructions, with 32 double- precision registers and the half-precision floating-point conversion operations. +vfpv4-d16 The VFPv4 floating-point instructions, with 16 double- precision registers. +vfpv4 The VFPv4 floating-point instructions, with 32 double- precision registers. +neon-fp16 The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions, with the half-precision floating-point conversion operations. +neon-vfpv4 The Advanced SIMD (Neon) v2 and the VFPv4 floating-point instructions. +nosimd Disable the Advanced SIMD instructions (does not disable floating point). +nofp Disable the floating-point and Advanced SIMD instructions. armv7ve The extended version of the ARMv7-A architecture with support for virtualization. +fp The VFPv4 floating-point instructions, with 16 double- precision registers. The extension +vfpv4-d16 can be used as an alias for this extension. +simd The Advanced SIMD (Neon) v2 and the VFPv4 floating-point instructions. The extension +neon-vfpv4 can be used as an alias for this extension. +vfpv3-d16 The VFPv3 floating-point instructions, with 16 double- precision registers. +vfpv3 The VFPv3 floating-point instructions, with 32 double- precision registers. +vfpv3-d16-fp16 The VFPv3 floating-point instructions, with 16 double- precision registers and the half-precision floating-point conversion operations. +vfpv3-fp16 The VFPv3 floating-point instructions, with 32 double- precision registers and the half-precision floating-point conversion operations. +vfpv4-d16 The VFPv4 floating-point instructions, with 16 double- precision registers. +vfpv4 The VFPv4 floating-point instructions, with 32 double- precision registers. +neon The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions. The extension +neon-vfpv3 can be used as an alias for this extension. +neon-fp16 The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions, with the half-precision floating-point conversion operations. +nosimd Disable the Advanced SIMD instructions (does not disable floating point). +nofp Disable the floating-point and Advanced SIMD instructions. armv8-a +crc The Cyclic Redundancy Check (CRC) instructions. +simd The ARMv8-A Advanced SIMD and floating-point instructions. +crypto The cryptographic instructions. +nocrypto Disable the cryptographic instructions. +nofp Disable the floating-point, Advanced SIMD and cryptographic instructions. +sb Speculation Barrier Instruction. +predres Execution and Data Prediction Restriction Instructions. armv8.1-a +simd The ARMv8.1-A Advanced SIMD and floating-point instructions. +crypto The cryptographic instructions. This also enables the Advanced SIMD and floating-point instructions. +nocrypto Disable the cryptographic instructions. +nofp Disable the floating-point, Advanced SIMD and cryptographic instructions. +sb Speculation Barrier Instruction. +predres Execution and Data Prediction Restriction Instructions. armv8.2-a armv8.3-a +fp16 The half-precision floating-point data processing instructions. This also enables the Advanced SIMD and floating-point instructions. +fp16fml The half-precision floating-point fmla extension. This also enables the half-precision floating-point extension and Advanced SIMD and floating-point instructions. +simd The ARMv8.1-A Advanced SIMD and floating-point instructions. +crypto The cryptographic instructions. This also enables the Advanced SIMD and floating-point instructions. +dotprod Enable the Dot Product extension. This also enables Advanced SIMD instructions. +nocrypto Disable the cryptographic extension. +nofp Disable the floating-point, Advanced SIMD and cryptographic instructions. +sb Speculation Barrier Instruction. +predres Execution and Data Prediction Restriction Instructions. +i8mm 8-bit Integer Matrix Multiply instructions. This also enables Advanced SIMD and floating-point instructions. +bf16 Brain half-precision floating-point instructions. This also enables Advanced SIMD and floating-point instructions. armv8.4-a +fp16 The half-precision floating-point data processing instructions. This also enables the Advanced SIMD and floating-point instructions as well as the Dot Product extension and the half-precision floating-point fmla extension. +simd The ARMv8.3-A Advanced SIMD and floating-point instructions as well as the Dot Product extension. +crypto The cryptographic instructions. This also enables the Advanced SIMD and floating-point instructions as well as the Dot Product extension. +nocrypto Disable the cryptographic extension. +nofp Disable the floating-point, Advanced SIMD and cryptographic instructions. +sb Speculation Barrier Instruction. +predres Execution and Data Prediction Restriction Instructions. +i8mm 8-bit Integer Matrix Multiply instructions. This also enables Advanced SIMD and floating-point instructions. +bf16 Brain half-precision floating-point instructions. This also enables Advanced SIMD and floating-point instructions. armv8.5-a +fp16 The half-precision floating-point data processing instructions. This also enables the Advanced SIMD and floating-point instructions as well as the Dot Product extension and the half-precision floating-point fmla extension. +simd The ARMv8.3-A Advanced SIMD and floating-point instructions as well as the Dot Product extension. +crypto The cryptographic instructions. This also enables the Advanced SIMD and floating-point instructions as well as the Dot Product extension. +nocrypto Disable the cryptographic extension. +nofp Disable the floating-point, Advanced SIMD and cryptographic instructions. +i8mm 8-bit Integer Matrix Multiply instructions. This also enables Advanced SIMD and floating-point instructions. +bf16 Brain half-precision floating-point instructions. This also enables Advanced SIMD and floating-point instructions. armv8.6-a +fp16 The half-precision floating-point data processing instructions. This also enables the Advanced SIMD and floating-point instructions as well as the Dot Product extension and the half-precision floating-point fmla extension. +simd The ARMv8.3-A Advanced SIMD and floating-point instructions as well as the Dot Product extension. +crypto The cryptographic instructions. This also enables the Advanced SIMD and floating-point instructions as well as the Dot Product extension. +nocrypto Disable the cryptographic extension. +nofp Disable the floating-point, Advanced SIMD and cryptographic instructions. +i8mm 8-bit Integer Matrix Multiply instructions. This also enables Advanced SIMD and floating-point instructions. +bf16 Brain half-precision floating-point instructions. This also enables Advanced SIMD and floating-point instructions. armv7-r +fp.sp The single-precision VFPv3 floating-point instructions. The extension +vfpv3xd can be used as an alias for this extension. +fp The VFPv3 floating-point instructions with 16 double- precision registers. The extension +vfpv3-d16 can be used as an alias for this extension. +vfpv3xd-d16-fp16 The single-precision VFPv3 floating-point instructions with 16 double-precision registers and the half-precision floating-point conversion operations. +vfpv3-d16-fp16 The VFPv3 floating-point instructions with 16 double- precision registers and the half-precision floating-point conversion operations. +nofp Disable the floating-point extension. +idiv The ARM-state integer division instructions. +noidiv Disable the ARM-state integer division extension. armv7e-m +fp The single-precision VFPv4 floating-point instructions. +fpv5 The single-precision FPv5 floating-point instructions. +fp.dp The single- and double-precision FPv5 floating-point instructions. +nofp Disable the floating-point extensions. armv8.1-m.main +dsp The DSP instructions. +mve The M-Profile Vector Extension (MVE) integer instructions. +mve.fp The M-Profile Vector Extension (MVE) integer and single precision floating-point instructions. +fp The single-precision floating-point instructions. +fp.dp The single- and double-precision floating-point instructions. +nofp Disable the floating-point extension. +cdecp0, +cdecp1, ... , +cdecp7 Enable the Custom Datapath Extension (CDE) on selected coprocessors according to the numbers given in the options in the range 0 to 7. +pacbti Enable the Pointer Authentication and Branch Target Identification Extension. armv8-m.main +dsp The DSP instructions. +nodsp Disable the DSP extension. +fp The single-precision floating-point instructions. +fp.dp The single- and double-precision floating-point instructions. +nofp Disable the floating-point extension. +cdecp0, +cdecp1, ... , +cdecp7 Enable the Custom Datapath Extension (CDE) on selected coprocessors according to the numbers given in the options in the range 0 to 7. armv8-r +crc The Cyclic Redundancy Check (CRC) instructions. +fp.sp The single-precision FPv5 floating-point instructions. +simd The ARMv8-A Advanced SIMD and floating-point instructions. +crypto The cryptographic instructions. +nocrypto Disable the cryptographic instructions. +nofp Disable the floating-point, Advanced SIMD and cryptographic instructions. -march=native causes the compiler to auto-detect the architecture of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect. -mtune=name This option specifies the name of the target ARM processor for which GCC should tune the performance of the code. For some ARM implementations better performance can be obtained by using this option. Permissible names are: arm7tdmi, arm7tdmi-s, arm710t, arm720t, arm740t, strongarm, strongarm110, strongarm1100, strongarm1110, arm8, arm810, arm9, arm9e, arm920, arm920t, arm922t, arm946e-s, arm966e-s, arm968e-s, arm926ej-s, arm940t, arm9tdmi, arm10tdmi, arm1020t, arm1026ej-s, arm10e, arm1020e, arm1022e, arm1136j-s, arm1136jf-s, mpcore, mpcorenovfp, arm1156t2-s, arm1156t2f-s, arm1176jz-s, arm1176jzf-s, generic-armv7-a, cortex-a5, cortex-a7, cortex-a8, cortex-a9, cortex-a12, cortex-a15, cortex-a17, cortex-a32, cortex-a35, cortex-a53, cortex-a55, cortex-a57, cortex-a72, cortex-a73, cortex-a75, cortex-a76, cortex-a76ae, cortex-a77, cortex-a78, cortex-a78ae, cortex-a78c, cortex-a710, ares, cortex-r4, cortex-r4f, cortex-r5, cortex-r7, cortex-r8, cortex-r52, cortex-r52plus, cortex-m0, cortex-m0plus, cortex-m1, cortex-m3, cortex-m4, cortex-m7, cortex-m23, cortex-m33, cortex-m35p, cortex-m55, cortex-m85, cortex-x1, cortex-x1c, cortex-m1.small-multiply, cortex-m0.small-multiply, cortex-m0plus.small-multiply, exynos-m1, marvell-pj4, neoverse-n1, neoverse-n2, neoverse-v1, xscale, iwmmxt, iwmmxt2, ep9312, fa526, fa626, fa606te, fa626te, fmp626, fa726te, star-mc1, xgene1. Additionally, this option can specify that GCC should tune the performance of the code for a big.LITTLE system. Permissible names are: cortex-a15.cortex-a7, cortex-a17.cortex-a7, cortex-a57.cortex-a53, cortex-a72.cortex-a53, cortex-a72.cortex-a35, cortex-a73.cortex-a53, cortex-a75.cortex-a55, cortex-a76.cortex-a55. -mtune=generic-arch specifies that GCC should tune the performance for a blend of processors within architecture arch. The aim is to generate code that run well on the current most popular processors, balancing between optimizations that benefit some CPUs in the range, and avoiding performance pitfalls of other CPUs. The effects of this option may change in future GCC versions as CPU models come and go. -mtune permits the same extension options as -mcpu, but the extension options do not affect the tuning of the generated code. -mtune=native causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto- detect is unsuccessful the option has no effect. -mcpu=name[+extension...] This specifies the name of the target ARM processor. GCC uses this name to derive the name of the target ARM architecture (as if specified by -march) and the ARM processor type for which to tune for performance (as if specified by -mtune). Where this option is used in conjunction with -march or -mtune, those options take precedence over the appropriate part of this option. Many of the supported CPUs implement optional architectural extensions. Where this is so the architectural extensions are normally enabled by default. If implementations that lack the extension exist, then the extension syntax can be used to disable those extensions that have been omitted. For floating-point and Advanced SIMD (Neon) instructions, the settings of the options -mfloat-abi and -mfpu must also be considered: floating-point and Advanced SIMD instructions will only be used if -mfloat-abi is not set to soft; and any setting of -mfpu other than auto will override the available floating-point and SIMD extension instructions. For example, cortex-a9 can be found in three major configurations: integer only, with just a floating-point unit or with floating- point and Advanced SIMD. The default is to enable all the instructions, but the extensions +nosimd and +nofp can be used to disable just the SIMD or both the SIMD and floating-point instructions respectively. Permissible names for this option are the same as those for -mtune. The following extension options are common to the listed CPUs: +nodsp Disable the DSP instructions on cortex-m33, cortex-m35p, cortex-m55 and cortex-m85. Also disable the M-Profile Vector Extension (MVE) integer and single precision floating-point instructions on cortex-m55 and cortex-m85. +nopacbti Disable the Pointer Authentication and Branch Target Identification Extension on cortex-m85. +nomve Disable the M-Profile Vector Extension (MVE) integer and single precision floating-point instructions on cortex-m55 and cortex-m85. +nomve.fp Disable the M-Profile Vector Extension (MVE) single precision floating-point instructions on cortex-m55 and cortex-m85. +cdecp0, +cdecp1, ... , +cdecp7 Enable the Custom Datapath Extension (CDE) on selected coprocessors according to the numbers given in the options in the range 0 to 7 on cortex-m55. +nofp Disables the floating-point instructions on arm9e, arm946e-s, arm966e-s, arm968e-s, arm10e, arm1020e, arm1022e, arm926ej-s, arm1026ej-s, cortex-r5, cortex-r7, cortex-r8, cortex-m4, cortex-m7, cortex-m33, cortex-m35p cortex-m4, cortex-m7, cortex-m33, cortex-m35p, cortex-m55 and cortex-m85. Disables the floating-point and SIMD instructions on generic-armv7-a, cortex-a5, cortex-a7, cortex-a8, cortex-a9, cortex-a12, cortex-a15, cortex-a17, cortex-a15.cortex-a7, cortex-a17.cortex-a7, cortex-a32, cortex-a35, cortex-a53 and cortex-a55. +nofp.dp Disables the double-precision component of the floating-point instructions on cortex-r5, cortex-r7, cortex-r8, cortex-r52, cortex-r52plus and cortex-m7. +nosimd Disables the SIMD (but not floating-point) instructions on generic-armv7-a, cortex-a5, cortex-a7 and cortex-a9. +crypto Enables the cryptographic instructions on cortex-a32, cortex-a35, cortex-a53, cortex-a55, cortex-a57, cortex-a72, cortex-a73, cortex-a75, exynos-m1, xgene1, cortex-a57.cortex-a53, cortex-a72.cortex-a53, cortex-a73.cortex-a35, cortex-a73.cortex-a53 and cortex-a75.cortex-a55. Additionally the generic-armv7-a pseudo target defaults to VFPv3 with 16 double-precision registers. It supports the following extension options: mp, sec, vfpv3-d16, vfpv3, vfpv3-d16-fp16, vfpv3-fp16, vfpv4-d16, vfpv4, neon, neon-vfpv3, neon-fp16, neon-vfpv4. The meanings are the same as for the extensions to -march=armv7-a. -mcpu=generic-arch is also permissible, and is equivalent to -march=arch -mtune=generic-arch. See -mtune for more information. -mcpu=native causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto- detect is unsuccessful the option has no effect. -mfpu=name This specifies what floating-point hardware (or hardware emulation) is available on the target. Permissible names are: auto, vfpv2, vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd, vfpv3xd-fp16, neon-vfpv3, neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16, neon-vfpv4, fpv5-d16, fpv5-sp-d16, fp-armv8, neon-fp-armv8 and crypto-neon-fp-armv8. Note that neon is an alias for neon-vfpv3 and vfp is an alias for vfpv2. The setting auto is the default and is special. It causes the compiler to select the floating-point and Advanced SIMD instructions based on the settings of -mcpu and -march. If the selected floating-point hardware includes the NEON extension (e.g. -mfpu=neon), note that floating-point operations are not generated by GCC's auto-vectorization pass unless -funsafe-math-optimizations is also specified. This is because NEON hardware does not fully implement the IEEE 754 standard for floating-point arithmetic (in particular denormal values are treated as zero), so the use of NEON instructions may lead to a loss of precision. You can also set the fpu name at function level by using the "target("fpu=")" function attributes or pragmas. -mfp16-format=name Specify the format of the "__fp16" half-precision floating-point type. Permissible names are none, ieee, and alternative; the default is none, in which case the "__fp16" type is not defined. -mstructure-size-boundary=n The sizes of all structures and unions are rounded up to a multiple of the number of bits set by this option. Permissible values are 8, 32 and 64. The default value varies for different toolchains. For the COFF targeted toolchain the default value is 8. A value of 64 is only allowed if the underlying ABI supports it. Specifying a larger number can produce faster, more efficient code, but can also increase the size of the program. Different values are potentially incompatible. Code compiled with one value cannot necessarily expect to work with code or libraries compiled with another value, if they exchange information using structures or unions. This option is deprecated. -mabort-on-noreturn Generate a call to the function "abort" at the end of a "noreturn" function. It is executed if the function tries to return. -mlong-calls -mno-long-calls Tells the compiler to perform function calls by first loading the address of the function into a register and then performing a subroutine call on this register. This switch is needed if the target function lies outside of the 64-megabyte addressing range of the offset-based version of subroutine call instruction. Even if this switch is enabled, not all function calls are turned into long calls. The heuristic is that static functions, functions that have the "short_call" attribute, functions that are inside the scope of a "#pragma no_long_calls" directive, and functions whose definitions have already been compiled within the current compilation unit are not turned into long calls. The exceptions to this rule are that weak function definitions, functions with the "long_call" attribute or the "section" attribute, and functions that are within the scope of a "#pragma long_calls" directive are always turned into long calls. This feature is not enabled by default. Specifying -mno-long-calls restores the default behavior, as does placing the function calls within the scope of a "#pragma long_calls_off" directive. Note these switches have no effect on how the compiler generates code to handle function calls via function pointers. -msingle-pic-base Treat the register used for PIC addressing as read-only, rather than loading it in the prologue for each function. The runtime system is responsible for initializing this register with an appropriate value before execution begins. -mpic-register=reg Specify the register to be used for PIC addressing. For standard PIC base case, the default is any suitable register determined by compiler. For single PIC base case, the default is R9 if target is EABI based or stack-checking is enabled, otherwise the default is R10. -mpic-data-is-text-relative Assume that the displacement between the text and data segments is fixed at static link time. This permits using PC-relative addressing operations to access data known to be in the data segment. For non-VxWorks RTP targets, this option is enabled by default. When disabled on such targets, it will enable -msingle-pic-base by default. -mpoke-function-name Write the name of each function into the text section, directly preceding the function prologue. The generated code is similar to this: t0 .ascii "arm_poke_function_name", 0 .align t1 .word 0xff000000 + (t1 - t0) arm_poke_function_name mov ip, sp stmfd sp!, {fp, ip, lr, pc} sub fp, ip, #4 When performing a stack backtrace, code can inspect the value of "pc" stored at "fp + 0". If the trace function then looks at location "pc - 12" and the top 8 bits are set, then we know that there is a function name embedded immediately preceding this location and has length "((pc[-3]) & 0xff000000)". -mthumb -marm Select between generating code that executes in ARM and Thumb states. The default for most configurations is to generate code that executes in ARM state, but the default can be changed by configuring GCC with the --with-mode=state configure option. You can also override the ARM and Thumb mode for each function by using the "target("thumb")" and "target("arm")" function attributes or pragmas. -mflip-thumb Switch ARM/Thumb modes on alternating functions. This option is provided for regression testing of mixed Thumb/ARM code generation, and is not intended for ordinary use in compiling code. -mtpcs-frame Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all non-leaf functions. (A leaf function is one that does not call any other functions.) The default is -mno-tpcs-frame. -mtpcs-leaf-frame Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all leaf functions. (A leaf function is one that does not call any other functions.) The default is -mno-apcs-leaf-frame. -mcallee-super-interworking Gives all externally visible functions in the file being compiled an ARM instruction set header which switches to Thumb mode before executing the rest of the function. This allows these functions to be called from non-interworking code. This option is not valid in AAPCS configurations because interworking is enabled by default. -mcaller-super-interworking Allows calls via function pointers (including virtual functions) to execute correctly regardless of whether the target code has been compiled for interworking or not. There is a small overhead in the cost of executing a function pointer if this option is enabled. This option is not valid in AAPCS configurations because interworking is enabled by default. -mtp=name Specify the access model for the thread local storage pointer. The valid models are soft, which generates calls to "__aeabi_read_tp", cp15, which fetches the thread pointer from "cp15" directly (supported in the arm6k architecture), and auto, which uses the best available method for the selected processor. The default setting is auto. -mtls-dialect=dialect Specify the dialect to use for accessing thread local storage. Two dialects are supported---gnu and gnu2. The gnu dialect selects the original GNU scheme for supporting local and global dynamic TLS models. The gnu2 dialect selects the GNU descriptor scheme, which provides better performance for shared libraries. The GNU descriptor scheme is compatible with the original scheme, but does require new assembler, linker and library support. Initial and local exec TLS models are unaffected by this option and always use the original scheme. -mword-relocations Only generate absolute relocations on word-sized values (i.e. R_ARM_ABS32). This is enabled by default on targets (uClinux, SymbianOS) where the runtime loader imposes this restriction, and when -fpic or -fPIC is specified. This option conflicts with -mslow-flash-data. -mfix-cortex-m3-ldrd Some Cortex-M3 cores can cause data corruption when "ldrd" instructions with overlapping destination and base registers are used. This option avoids generating these instructions. This option is enabled by default when -mcpu=cortex-m3 is specified. -mfix-cortex-a57-aes-1742098 -mno-fix-cortex-a57-aes-1742098 -mfix-cortex-a72-aes-1655431 -mno-fix-cortex-a72-aes-1655431 Enable (disable) mitigation for an erratum on Cortex-A57 and Cortex-A72 that affects the AES cryptographic instructions. This option is enabled by default when either -mcpu=cortex-a57 or -mcpu=cortex-a72 is specified. -munaligned-access -mno-unaligned-access Enables (or disables) reading and writing of 16- and 32- bit values from addresses that are not 16- or 32- bit aligned. By default unaligned access is disabled for all pre-ARMv6, all ARMv6-M and for ARMv8-M Baseline architectures, and enabled for all other architectures. If unaligned access is not enabled then words in packed data structures are accessed a byte at a time. The ARM attribute "Tag_CPU_unaligned_access" is set in the generated object file to either true or false, depending upon the setting of this option. If unaligned access is enabled then the preprocessor symbol "__ARM_FEATURE_UNALIGNED" is also defined. -mneon-for-64bits This option is deprecated and has no effect. -mslow-flash-data Assume loading data from flash is slower than fetching instruction. Therefore literal load is minimized for better performance. This option is only supported when compiling for ARMv7 M-profile and off by default. It conflicts with -mword-relocations. -masm-syntax-unified Assume inline assembler is using unified asm syntax. The default is currently off which implies divided syntax. This option has no impact on Thumb2. However, this may change in future releases of GCC. Divided syntax should be considered deprecated. -mrestrict-it Restricts generation of IT blocks to conform to the rules of ARMv8-A. IT blocks can only contain a single 16-bit instruction from a select set of instructions. This option is on by default for ARMv8-A Thumb mode. -mprint-tune-info Print CPU tuning information as comment in assembler file. This is an option used only for regression testing of the compiler and not intended for ordinary use in compiling code. This option is disabled by default. -mverbose-cost-dump Enable verbose cost model dumping in the debug dump files. This option is provided for use in debugging the compiler. -mpure-code Do not allow constant data to be placed in code sections. Additionally, when compiling for ELF object format give all text sections the ELF processor-specific section attribute "SHF_ARM_PURECODE". This option is only available when generating non-pic code for M-profile targets. -mcmse Generate secure code as per the "ARMv8-M Security Extensions: Requirements on Development Tools Engineering Specification", which can be found on <https://developer.arm.com/documentation/ecm0359818/latest/>. -mfix-cmse-cve-2021-35465 Mitigate against a potential security issue with the "VLLDM" instruction in some M-profile devices when using CMSE (CVE-2021-365465). This option is enabled by default when the option -mcpu= is used with "cortex-m33", "cortex-m35p", "cortex-m55", "cortex-m85" or "star-mc1". The option -mno-fix-cmse-cve-2021-35465 can be used to disable the mitigation. -mstack-protector-guard=guard -mstack-protector-guard-offset=offset Generate stack protection code using canary at guard. Supported locations are global for a global canary or tls for a canary accessible via the TLS register. The option -mstack-protector-guard-offset= is for use with -fstack-protector-guard=tls and not for use in user-land code. -mfdpic -mno-fdpic Select the FDPIC ABI, which uses 64-bit function descriptors to represent pointers to functions. When the compiler is configured for "arm-*-uclinuxfdpiceabi" targets, this option is on by default and implies -fPIE if none of the PIC/PIE-related options is provided. On other targets, it only enables the FDPIC-specific code generation features, and the user should explicitly provide the PIC/PIE-related options as needed. Note that static linking is not supported because it would still involve the dynamic linker when the program self-relocates. If such behavior is acceptable, use -static and -Wl,-dynamic-linker options. The opposite -mno-fdpic option is useful (and required) to build the Linux kernel using the same ("arm-*-uclinuxfdpiceabi") toolchain as the one used to build the userland programs. -mbranch-protection=none|standard|pac-ret[+leaf][+bti]|bti[+pac-ret[+leaf]] Enable branch protection features (armv8.1-m.main only). none generate code without branch protection or return address signing. standard[+leaf] generate code with all branch protection features enabled at their standard level. pac-ret[+leaf] generate code with return address signing set to its standard level, which is to sign all functions that save the return address to memory. leaf When return address signing is enabled, also sign leaf functions even if they do not write the return address to memory. +bti Add landing- pad instructions at the permitted targets of indirect branch instructions. If the +pacbti architecture extension is not enabled, then all branch protection and return address signing operations are constrained to use only the instructions defined in the architectural-NOP space. The generated code will remain backwards- compatible with earlier versions of the architecture, but the additional security can be enabled at run time on processors that support the PACBTI extension. Branch target enforcement using BTI can only be enabled at runtime if all code in the application has been compiled with at least -mbranch-protection=bti. Any setting other than none is supported only on armv8-m.main or later. The default is to generate code without branch protection or return address signing. AVR Options These options are defined for AVR implementations: -mmcu=mcu Specify Atmel AVR instruction set architectures (ISA) or MCU type. The default for this option is avr2. GCC supports the following AVR devices and ISAs: "avr2" "Classic" devices with up to 8 KiB of program memory. mcu = "attiny22", "attiny26", "at90s2313", "at90s2323", "at90s2333", "at90s2343", "at90s4414", "at90s4433", "at90s4434", "at90c8534", "at90s8515", "at90s8535". "avr25" "Classic" devices with up to 8 KiB of program memory and with the "MOVW" instruction. mcu = "attiny13", "attiny13a", "attiny24", "attiny24a", "attiny25", "attiny261", "attiny261a", "attiny2313", "attiny2313a", "attiny43u", "attiny44", "attiny44a", "attiny45", "attiny48", "attiny441", "attiny461", "attiny461a", "attiny4313", "attiny84", "attiny84a", "attiny85", "attiny87", "attiny88", "attiny828", "attiny841", "attiny861", "attiny861a", "ata5272", "ata6616c", "at86rf401". "avr3" "Classic" devices with 16 KiB up to 64 KiB of program memory. mcu = "at76c711", "at43usb355". "avr31" "Classic" devices with 128 KiB of program memory. mcu = "atmega103", "at43usb320". "avr35" "Classic" devices with 16 KiB up to 64 KiB of program memory and with the "MOVW" instruction. mcu = "attiny167", "attiny1634", "atmega8u2", "atmega16u2", "atmega32u2", "ata5505", "ata6617c", "ata664251", "at90usb82", "at90usb162". "avr4" "Enhanced" devices with up to 8 KiB of program memory. mcu = "atmega48", "atmega48a", "atmega48p", "atmega48pa", "atmega48pb", "atmega8", "atmega8a", "atmega8hva", "atmega88", "atmega88a", "atmega88p", "atmega88pa", "atmega88pb", "atmega8515", "atmega8535", "ata6285", "ata6286", "ata6289", "ata6612c", "at90pwm1", "at90pwm2", "at90pwm2b", "at90pwm3", "at90pwm3b", "at90pwm81". "avr5" "Enhanced" devices with 16 KiB up to 64 KiB of program memory. mcu = "atmega16", "atmega16a", "atmega16hva", "atmega16hva2", "atmega16hvb", "atmega16hvbrevb", "atmega16m1", "atmega16u4", "atmega161", "atmega162", "atmega163", "atmega164a", "atmega164p", "atmega164pa", "atmega165", "atmega165a", "atmega165p", "atmega165pa", "atmega168", "atmega168a", "atmega168p", "atmega168pa", "atmega168pb", "atmega169", "atmega169a", "atmega169p", "atmega169pa", "atmega32", "atmega32a", "atmega32c1", "atmega32hvb", "atmega32hvbrevb", "atmega32m1", "atmega32u4", "atmega32u6", "atmega323", "atmega324a", "atmega324p", "atmega324pa", "atmega324pb", "atmega325", "atmega325a", "atmega325p", "atmega325pa", "atmega328", "atmega328p", "atmega328pb", "atmega329", "atmega329a", "atmega329p", "atmega329pa", "atmega3250", "atmega3250a", "atmega3250p", "atmega3250pa", "atmega3290", "atmega3290a", "atmega3290p", "atmega3290pa", "atmega406", "atmega64", "atmega64a", "atmega64c1", "atmega64hve", "atmega64hve2", "atmega64m1", "atmega64rfr2", "atmega640", "atmega644", "atmega644a", "atmega644p", "atmega644pa", "atmega644rfr2", "atmega645", "atmega645a", "atmega645p", "atmega649", "atmega649a", "atmega649p", "atmega6450", "atmega6450a", "atmega6450p", "atmega6490", "atmega6490a", "atmega6490p", "ata5795", "ata5790", "ata5790n", "ata5791", "ata6613c", "ata6614q", "ata5782", "ata5831", "ata8210", "ata8510", "ata5702m322", "at90pwm161", "at90pwm216", "at90pwm316", "at90can32", "at90can64", "at90scr100", "at90usb646", "at90usb647", "at94k", "m3000". "avr51" "Enhanced" devices with 128 KiB of program memory. mcu = "atmega128", "atmega128a", "atmega128rfa1", "atmega128rfr2", "atmega1280", "atmega1281", "atmega1284", "atmega1284p", "atmega1284rfr2", "at90can128", "at90usb1286", "at90usb1287". "avr6" "Enhanced" devices with 3-byte PC, i.e. with more than 128 KiB of program memory. mcu = "atmega256rfr2", "atmega2560", "atmega2561", "atmega2564rfr2". "avrxmega2" "XMEGA" devices with more than 8 KiB and up to 64 KiB of program memory. mcu = "atxmega8e5", "atxmega16a4", "atxmega16a4u", "atxmega16c4", "atxmega16d4", "atxmega16e5", "atxmega32a4", "atxmega32a4u", "atxmega32c3", "atxmega32c4", "atxmega32d3", "atxmega32d4", "atxmega32e5", "avr64da28", "avr64da32", "avr64da48", "avr64da64", "avr64db28", "avr64db32", "avr64db48", "avr64db64". "avrxmega3" "XMEGA" devices with up to 64 KiB of combined program memory and RAM, and with program memory visible in the RAM address space. mcu = "attiny202", "attiny204", "attiny212", "attiny214", "attiny402", "attiny404", "attiny406", "attiny412", "attiny414", "attiny416", "attiny417", "attiny804", "attiny806", "attiny807", "attiny814", "attiny816", "attiny817", "attiny1604", "attiny1606", "attiny1607", "attiny1614", "attiny1616", "attiny1617", "attiny3214", "attiny3216", "attiny3217", "atmega808", "atmega809", "atmega1608", "atmega1609", "atmega3208", "atmega3209", "atmega4808", "atmega4809", "avr32da28", "avr32da32", "avr32da48", "avr32db28", "avr32db32", "avr32db48". "avrxmega4" "XMEGA" devices with more than 64 KiB and up to 128 KiB of program memory. mcu = "atxmega64a3", "atxmega64a3u", "atxmega64a4u", "atxmega64b1", "atxmega64b3", "atxmega64c3", "atxmega64d3", "atxmega64d4", "avr128da28", "avr128da32", "avr128da48", "avr128da64", "avr128db28", "avr128db32", "avr128db48", "avr128db64". "avrxmega5" "XMEGA" devices with more than 64 KiB and up to 128 KiB of program memory and more than 64 KiB of RAM. mcu = "atxmega64a1", "atxmega64a1u". "avrxmega6" "XMEGA" devices with more than 128 KiB of program memory. mcu = "atxmega128a3", "atxmega128a3u", "atxmega128b1", "atxmega128b3", "atxmega128c3", "atxmega128d3", "atxmega128d4", "atxmega192a3", "atxmega192a3u", "atxmega192c3", "atxmega192d3", "atxmega256a3", "atxmega256a3b", "atxmega256a3bu", "atxmega256a3u", "atxmega256c3", "atxmega256d3", "atxmega384c3", "atxmega384d3". "avrxmega7" "XMEGA" devices with more than 128 KiB of program memory and more than 64 KiB of RAM. mcu = "atxmega128a1", "atxmega128a1u", "atxmega128a4u". "avrtiny" "TINY" Tiny core devices with 512 B up to 4 KiB of program memory. mcu = "attiny4", "attiny5", "attiny9", "attiny10", "attiny20", "attiny40". "avr1" This ISA is implemented by the minimal AVR core and supported for assembler only. mcu = "attiny11", "attiny12", "attiny15", "attiny28", "at90s1200". -mabsdata Assume that all data in static storage can be accessed by LDS / STS instructions. This option has only an effect on reduced Tiny devices like ATtiny40. See also the "absdata" AVR Variable Attributes,variable attribute. -maccumulate-args Accumulate outgoing function arguments and acquire/release the needed stack space for outgoing function arguments once in function prologue/epilogue. Without this option, outgoing arguments are pushed before calling a function and popped afterwards. Popping the arguments after the function call can be expensive on AVR so that accumulating the stack space might lead to smaller executables because arguments need not be removed from the stack after such a function call. This option can lead to reduced code size for functions that perform several calls to functions that get their arguments on the stack like calls to printf-like functions. -mbranch-cost=cost Set the branch costs for conditional branch instructions to cost. Reasonable values for cost are small, non-negative integers. The default branch cost is 0. -mcall-prologues Functions prologues/epilogues are expanded as calls to appropriate subroutines. Code size is smaller. -mdouble=bits -mlong-double=bits Set the size (in bits) of the "double" or "long double" type, respectively. Possible values for bits are 32 and 64. Whether or not a specific value for bits is allowed depends on the "--with-double=" and "--with-long-double=" configure options ("https://gcc.gnu.org/install/configure.html#avr"), and the same applies for the default values of the options. -mgas-isr-prologues Interrupt service routines (ISRs) may use the "__gcc_isr" pseudo instruction supported by GNU Binutils. If this option is on, the feature can still be disabled for individual ISRs by means of the AVR Function Attributes,,"no_gccisr" function attribute. This feature is activated per default if optimization is on (but not with -Og, @pxref{Optimize Options}), and if GNU Binutils support PR21683 ("https://sourceware.org/PR21683"). -mint8 Assume "int" to be 8-bit integer. This affects the sizes of all types: a "char" is 1 byte, an "int" is 1 byte, a "long" is 2 bytes, and "long long" is 4 bytes. Please note that this option does not conform to the C standards, but it results in smaller code size. -mmain-is-OS_task Do not save registers in "main". The effect is the same like attaching attribute AVR Function Attributes,,"OS_task" to "main". It is activated per default if optimization is on. -mn-flash=num Assume that the flash memory has a size of num times 64 KiB. -mno-interrupts Generated code is not compatible with hardware interrupts. Code size is smaller. -mrelax Try to replace "CALL" resp. "JMP" instruction by the shorter "RCALL" resp. "RJMP" instruction if applicable. Setting -mrelax just adds the --mlink-relax option to the assembler's command line and the --relax option to the linker's command line. Jump relaxing is performed by the linker because jump offsets are not known before code is located. Therefore, the assembler code generated by the compiler is the same, but the instructions in the executable may differ from instructions in the assembler code. Relaxing must be turned on if linker stubs are needed, see the section on "EIND" and linker stubs below. -mrmw Assume that the device supports the Read-Modify-Write instructions "XCH", "LAC", "LAS" and "LAT". -mshort-calls Assume that "RJMP" and "RCALL" can target the whole program memory. This option is used internally for multilib selection. It is not an optimization option, and you don't need to set it by hand. -msp8 Treat the stack pointer register as an 8-bit register, i.e. assume the high byte of the stack pointer is zero. In general, you don't need to set this option by hand. This option is used internally by the compiler to select and build multilibs for architectures "avr2" and "avr25". These architectures mix devices with and without "SPH". For any setting other than -mmcu=avr2 or -mmcu=avr25 the compiler driver adds or removes this option from the compiler proper's command line, because the compiler then knows if the device or architecture has an 8-bit stack pointer and thus no "SPH" register or not. -mstrict-X Use address register "X" in a way proposed by the hardware. This means that "X" is only used in indirect, post-increment or pre- decrement addressing. Without this option, the "X" register may be used in the same way as "Y" or "Z" which then is emulated by additional instructions. For example, loading a value with "X+const" addressing with a small non-negative "const < 64" to a register Rn is performed as adiw r26, const ; X += const ld <Rn>, X ; <Rn> = *X sbiw r26, const ; X -= const -mtiny-stack Only change the lower 8 bits of the stack pointer. -mfract-convert-truncate Allow to use truncation instead of rounding towards zero for fractional fixed-point types. -nodevicelib Don't link against AVR-LibC's device specific library "lib<mcu>.a". -nodevicespecs Don't add -specs=device-specs/specs-mcu to the compiler driver's command line. The user takes responsibility for supplying the sub- processes like compiler proper, assembler and linker with appropriate command line options. This means that the user has to supply her private device specs file by means of -specs=path-to- specs-file. There is no more need for option -mmcu=mcu. This option can also serve as a replacement for the older way of specifying custom device-specs files that needed -B some-path to point to a directory which contains a folder named "device-specs" which contains a specs file named "specs-mcu", where mcu was specified by -mmcu=mcu. -Waddr-space-convert Warn about conversions between address spaces in the case where the resulting address space is not contained in the incoming address space. -Wmisspelled-isr Warn if the ISR is misspelled, i.e. without __vector prefix. Enabled by default. "EIND" and Devices with More Than 128 Ki Bytes of Flash Pointers in the implementation are 16 bits wide. The address of a function or label is represented as word address so that indirect jumps and calls can target any code address in the range of 64 Ki words. In order to facilitate indirect jump on devices with more than 128 Ki bytes of program memory space, there is a special function register called "EIND" that serves as most significant part of the target address when "EICALL" or "EIJMP" instructions are used. Indirect jumps and calls on these devices are handled as follows by the compiler and are subject to some limitations: * The compiler never sets "EIND". * The compiler uses "EIND" implicitly in "EICALL"/"EIJMP" instructions or might read "EIND" directly in order to emulate an indirect call/jump by means of a "RET" instruction. * The compiler assumes that "EIND" never changes during the startup code or during the application. In particular, "EIND" is not saved/restored in function or interrupt service routine prologue/epilogue. * For indirect calls to functions and computed goto, the linker generates stubs. Stubs are jump pads sometimes also called trampolines. Thus, the indirect call/jump jumps to such a stub. The stub contains a direct jump to the desired address. * Linker relaxation must be turned on so that the linker generates the stubs correctly in all situations. See the compiler option -mrelax and the linker option --relax. There are corner cases where the linker is supposed to generate stubs but aborts without relaxation and without a helpful error message. * The default linker script is arranged for code with "EIND = 0". If code is supposed to work for a setup with "EIND != 0", a custom linker script has to be used in order to place the sections whose name start with ".trampolines" into the segment where "EIND" points to. * The startup code from libgcc never sets "EIND". Notice that startup code is a blend of code from libgcc and AVR-LibC. For the impact of AVR-LibC on "EIND", see the AVR-LibC user manual ("https://www.nongnu.org/avr-libc/user-manual/"). * It is legitimate for user-specific startup code to set up "EIND" early, for example by means of initialization code located in section ".init3". Such code runs prior to general startup code that initializes RAM and calls constructors, but after the bit of startup code from AVR-LibC that sets "EIND" to the segment where the vector table is located. #include <avr/io.h> static void __attribute__((section(".init3"),naked,used,no_instrument_function)) init3_set_eind (void) { __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t" "out %i0,r24" :: "n" (&EIND) : "r24","memory"); } The "__trampolines_start" symbol is defined in the linker script. * Stubs are generated automatically by the linker if the following two conditions are met: -<The address of a label is taken by means of the "gs" modifier> (short for generate stubs) like so: LDI r24, lo8(gs(<func>)) LDI r25, hi8(gs(<func>)) -<The final location of that label is in a code segment> outside the segment where the stubs are located. * The compiler emits such "gs" modifiers for code labels in the following situations: -<Taking address of a function or code label.> -<Computed goto.> -<If prologue-save function is used, see -mcall-prologues> command-line option. -<Switch/case dispatch tables. If you do not want such dispatch> tables you can specify the -fno-jump-tables command-line option. -<C and C++ constructors/destructors called during startup/shutdown.> -<If the tools hit a "gs()" modifier explained above.> * Jumping to non-symbolic addresses like so is not supported: int main (void) { /* Call function at word address 0x2 */ return ((int(*)(void)) 0x2)(); } Instead, a stub has to be set up, i.e. the function has to be called through a symbol ("func_4" in the example): int main (void) { extern int func_4 (void); /* Call function at byte address 0x4 */ return func_4(); } and the application be linked with -Wl,--defsym,func_4=0x4. Alternatively, "func_4" can be defined in the linker script. Handling of the "RAMPD", "RAMPX", "RAMPY" and "RAMPZ" Special Function Registers Some AVR devices support memories larger than the 64 KiB range that can be accessed with 16-bit pointers. To access memory locations outside this 64 KiB range, the content of a "RAMP" register is used as high part of the address: The "X", "Y", "Z" address register is concatenated with the "RAMPX", "RAMPY", "RAMPZ" special function register, respectively, to get a wide address. Similarly, "RAMPD" is used together with direct addressing. * The startup code initializes the "RAMP" special function registers with zero. * If a AVR Named Address Spaces,named address space other than generic or "__flash" is used, then "RAMPZ" is set as needed before the operation. * If the device supports RAM larger than 64 KiB and the compiler needs to change "RAMPZ" to accomplish an operation, "RAMPZ" is reset to zero after the operation. * If the device comes with a specific "RAMP" register, the ISR prologue/epilogue saves/restores that SFR and initializes it with zero in case the ISR code might (implicitly) use it. * RAM larger than 64 KiB is not supported by GCC for AVR targets. If you use inline assembler to read from locations outside the 16-bit address range and change one of the "RAMP" registers, you must reset it to zero after the access. AVR Built-in Macros GCC defines several built-in macros so that the user code can test for the presence or absence of features. Almost any of the following built-in macros are deduced from device capabilities and thus triggered by the -mmcu= command-line option. For even more AVR-specific built-in macros see AVR Named Address Spaces and AVR Built-in Functions. "__AVR_ARCH__" Build-in macro that resolves to a decimal number that identifies the architecture and depends on the -mmcu=mcu option. Possible values are: 2, 25, 3, 31, 35, 4, 5, 51, 6 for mcu="avr2", "avr25", "avr3", "avr31", "avr35", "avr4", "avr5", "avr51", "avr6", respectively and 100, 102, 103, 104, 105, 106, 107 for mcu="avrtiny", "avrxmega2", "avrxmega3", "avrxmega4", "avrxmega5", "avrxmega6", "avrxmega7", respectively. If mcu specifies a device, this built-in macro is set accordingly. For example, with -mmcu=atmega8 the macro is defined to 4. "__AVR_Device__" Setting -mmcu=device defines this built-in macro which reflects the device's name. For example, -mmcu=atmega8 defines the built-in macro "__AVR_ATmega8__", -mmcu=attiny261a defines "__AVR_ATtiny261A__", etc. The built-in macros' names follow the scheme "__AVR_Device__" where Device is the device name as from the AVR user manual. The difference between Device in the built-in macro and device in -mmcu=device is that the latter is always lowercase. If device is not a device but only a core architecture like avr51, this macro is not defined. "__AVR_DEVICE_NAME__" Setting -mmcu=device defines this built-in macro to the device's name. For example, with -mmcu=atmega8 the macro is defined to "atmega8". If device is not a device but only a core architecture like avr51, this macro is not defined. "__AVR_XMEGA__" The device / architecture belongs to the XMEGA family of devices. "__AVR_HAVE_ELPM__" The device has the "ELPM" instruction. "__AVR_HAVE_ELPMX__" The device has the "ELPM Rn,Z" and "ELPM Rn,Z+" instructions. "__AVR_HAVE_MOVW__" The device has the "MOVW" instruction to perform 16-bit register- register moves. "__AVR_HAVE_LPMX__" The device has the "LPM Rn,Z" and "LPM Rn,Z+" instructions. "__AVR_HAVE_MUL__" The device has a hardware multiplier. "__AVR_HAVE_JMP_CALL__" The device has the "JMP" and "CALL" instructions. This is the case for devices with more than 8 KiB of program memory. "__AVR_HAVE_EIJMP_EICALL__" "__AVR_3_BYTE_PC__" The device has the "EIJMP" and "EICALL" instructions. This is the case for devices with more than 128 KiB of program memory. This also means that the program counter (PC) is 3 bytes wide. "__AVR_2_BYTE_PC__" The program counter (PC) is 2 bytes wide. This is the case for devices with up to 128 KiB of program memory. "__AVR_HAVE_8BIT_SP__" "__AVR_HAVE_16BIT_SP__" The stack pointer (SP) register is treated as 8-bit respectively 16-bit register by the compiler. The definition of these macros is affected by -mtiny-stack. "__AVR_HAVE_SPH__" "__AVR_SP8__" The device has the SPH (high part of stack pointer) special function register or has an 8-bit stack pointer, respectively. The definition of these macros is affected by -mmcu= and in the cases of -mmcu=avr2 and -mmcu=avr25 also by -msp8. "__AVR_HAVE_RAMPD__" "__AVR_HAVE_RAMPX__" "__AVR_HAVE_RAMPY__" "__AVR_HAVE_RAMPZ__" The device has the "RAMPD", "RAMPX", "RAMPY", "RAMPZ" special function register, respectively. "__NO_INTERRUPTS__" This macro reflects the -mno-interrupts command-line option. "__AVR_ERRATA_SKIP__" "__AVR_ERRATA_SKIP_JMP_CALL__" Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit instructions because of a hardware erratum. Skip instructions are "SBRS", "SBRC", "SBIS", "SBIC" and "CPSE". The second macro is only defined if "__AVR_HAVE_JMP_CALL__" is also set. "__AVR_ISA_RMW__" The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT). "__AVR_SFR_OFFSET__=offset" Instructions that can address I/O special function registers directly like "IN", "OUT", "SBI", etc. may use a different address as if addressed by an instruction to access RAM like "LD" or "STS". This offset depends on the device architecture and has to be subtracted from the RAM address in order to get the respective I/O address. "__AVR_SHORT_CALLS__" The -mshort-calls command line option is set. "__AVR_PM_BASE_ADDRESS__=addr" Some devices support reading from flash memory by means of "LD*" instructions. The flash memory is seen in the data address space at an offset of "__AVR_PM_BASE_ADDRESS__". If this macro is not defined, this feature is not available. If defined, the address space is linear and there is no need to put ".rodata" into RAM. This is handled by the default linker description file, and is currently available for "avrtiny" and "avrxmega3". Even more convenient, there is no need to use address spaces like "__flash" or features like attribute "progmem" and "pgm_read_*". "__WITH_AVRLIBC__" The compiler is configured to be used together with AVR-Libc. See the --with-avrlibc configure option. "__HAVE_DOUBLE_MULTILIB__" Defined if -mdouble= acts as a multilib option. "__HAVE_DOUBLE32__" "__HAVE_DOUBLE64__" Defined if the compiler supports 32-bit double resp. 64-bit double. The actual layout is specified by option -mdouble=. "__DEFAULT_DOUBLE__" The size in bits of "double" if -mdouble= is not set. To test the layout of "double" in a program, use the built-in macro "__SIZEOF_DOUBLE__". "__HAVE_LONG_DOUBLE32__" "__HAVE_LONG_DOUBLE64__" "__HAVE_LONG_DOUBLE_MULTILIB__" "__DEFAULT_LONG_DOUBLE__" Same as above, but for "long double" instead of "double". "__WITH_DOUBLE_COMPARISON__" Reflects the "--with-double-comparison={tristate|bool|libf7}" configure option ("https://gcc.gnu.org/install/configure.html#avr") and is defined to 2 or 3. "__WITH_LIBF7_LIBGCC__" "__WITH_LIBF7_MATH__" "__WITH_LIBF7_MATH_SYMBOLS__" Reflects the "--with-libf7={libgcc|math|math-symbols}" configure option ("https://gcc.gnu.org/install/configure.html#avr"). Blackfin Options -mcpu=cpu[-sirevision] Specifies the name of the target Blackfin processor. Currently, cpu can be one of bf512, bf514, bf516, bf518, bf522, bf523, bf524, bf525, bf526, bf527, bf531, bf532, bf533, bf534, bf536, bf537, bf538, bf539, bf542, bf544, bf547, bf548, bf549, bf542m, bf544m, bf547m, bf548m, bf549m, bf561, bf592. The optional sirevision specifies the silicon revision of the target Blackfin processor. Any workarounds available for the targeted silicon revision are enabled. If sirevision is none, no workarounds are enabled. If sirevision is any, all workarounds for the targeted processor are enabled. The "__SILICON_REVISION__" macro is defined to two hexadecimal digits representing the major and minor numbers in the silicon revision. If sirevision is none, the "__SILICON_REVISION__" is not defined. If sirevision is any, the "__SILICON_REVISION__" is defined to be 0xffff. If this optional sirevision is not used, GCC assumes the latest known silicon revision of the targeted Blackfin processor. GCC defines a preprocessor macro for the specified cpu. For the bfin-elf toolchain, this option causes the hardware BSP provided by libgloss to be linked in if -msim is not given. Without this option, bf532 is used as the processor by default. Note that support for bf561 is incomplete. For bf561, only the preprocessor macro is defined. -msim Specifies that the program will be run on the simulator. This causes the simulator BSP provided by libgloss to be linked in. This option has effect only for bfin-elf toolchain. Certain other options, such as -mid-shared-library and -mfdpic, imply -msim. -momit-leaf-frame-pointer Don't keep the frame pointer in a register for leaf functions. This avoids the instructions to save, set up and restore frame pointers and makes an extra register available in leaf functions. -mspecld-anomaly When enabled, the compiler ensures that the generated code does not contain speculative loads after jump instructions. If this option is used, "__WORKAROUND_SPECULATIVE_LOADS" is defined. -mno-specld-anomaly Don't generate extra code to prevent speculative loads from occurring. -mcsync-anomaly When enabled, the compiler ensures that the generated code does not contain CSYNC or SSYNC instructions too soon after conditional branches. If this option is used, "__WORKAROUND_SPECULATIVE_SYNCS" is defined. -mno-csync-anomaly Don't generate extra code to prevent CSYNC or SSYNC instructions from occurring too soon after a conditional branch. -mlow64k When enabled, the compiler is free to take advantage of the knowledge that the entire program fits into the low 64k of memory. -mno-low64k Assume that the program is arbitrarily large. This is the default. -mstack-check-l1 Do stack checking using information placed into L1 scratchpad memory by the uClinux kernel. -mid-shared-library Generate code that supports shared libraries via the library ID method. This allows for execute in place and shared libraries in an environment without virtual memory management. This option implies -fPIC. With a bfin-elf target, this option implies -msim. -mno-id-shared-library Generate code that doesn't assume ID-based shared libraries are being used. This is the default. -mleaf-id-shared-library Generate code that supports shared libraries via the library ID method, but assumes that this library or executable won't link against any other ID shared libraries. That allows the compiler to use faster code for jumps and calls. -mno-leaf-id-shared-library Do not assume that the code being compiled won't link against any ID shared libraries. Slower code is generated for jump and call insns. -mshared-library-id=n Specifies the identification number of the ID-based shared library being compiled. Specifying a value of 0 generates more compact code; specifying other values forces the allocation of that number to the current library but is no more space- or time-efficient than omitting this option. -msep-data Generate code that allows the data segment to be located in a different area of memory from the text segment. This allows for execute in place in an environment without virtual memory management by eliminating relocations against the text section. -mno-sep-data Generate code that assumes that the data segment follows the text segment. This is the default. -mlong-calls -mno-long-calls Tells the compiler to perform function calls by first loading the address of the function into a register and then performing a subroutine call on this register. This switch is needed if the target function lies outside of the 24-bit addressing range of the offset-based version of subroutine call instruction. This feature is not enabled by default. Specifying -mno-long-calls restores the default behavior. Note these switches have no effect on how the compiler generates code to handle function calls via function pointers. -mfast-fp Link with the fast floating-point library. This library relaxes some of the IEEE floating-point standard's rules for checking inputs against Not-a-Number (NAN), in the interest of performance. -minline-plt Enable inlining of PLT entries in function calls to functions that are not known to bind locally. It has no effect without -mfdpic. -mmulticore Build a standalone application for multicore Blackfin processors. This option causes proper start files and link scripts supporting multicore to be used, and defines the macro "__BFIN_MULTICORE". It can only be used with -mcpu=bf561[-sirevision]. This option can be used with -mcorea or -mcoreb, which selects the one-application-per-core programming model. Without -mcorea or -mcoreb, the single-application/dual-core programming model is used. In this model, the main function of Core B should be named as "coreb_main". If this option is not used, the single-core application programming model is used. -mcorea Build a standalone application for Core A of BF561 when using the one-application-per-core programming model. Proper start files and link scripts are used to support Core A, and the macro "__BFIN_COREA" is defined. This option can only be used in conjunction with -mmulticore. -mcoreb Build a standalone application for Core B of BF561 when using the one-application-per-core programming model. Proper start files and link scripts are used to support Core B, and the macro "__BFIN_COREB" is defined. When this option is used, "coreb_main" should be used instead of "main". This option can only be used in conjunction with -mmulticore. -msdram Build a standalone application for SDRAM. Proper start files and link scripts are used to put the application into SDRAM, and the macro "__BFIN_SDRAM" is defined. The loader should initialize SDRAM before loading the application. -micplb Assume that ICPLBs are enabled at run time. This has an effect on certain anomaly workarounds. For Linux targets, the default is to assume ICPLBs are enabled; for standalone applications the default is off. C6X Options -march=name This specifies the name of the target architecture. GCC uses this name to determine what kind of instructions it can emit when generating assembly code. Permissible names are: c62x, c64x, c64x+, c67x, c67x+, c674x. -mbig-endian Generate code for a big-endian target. -mlittle-endian Generate code for a little-endian target. This is the default. -msim Choose startup files and linker script suitable for the simulator. -msdata=default Put small global and static data in the ".neardata" section, which is pointed to by register "B14". Put small uninitialized global and static data in the ".bss" section, which is adjacent to the ".neardata" section. Put small read-only data into the ".rodata" section. The corresponding sections used for large pieces of data are ".fardata", ".far" and ".const". -msdata=all Put all data, not just small objects, into the sections reserved for small data, and use addressing relative to the "B14" register to access them. -msdata=none Make no use of the sections reserved for small data, and use absolute addresses to access all data. Put all initialized global and static data in the ".fardata" section, and all uninitialized data in the ".far" section. Put all constant data into the ".const" section. CRIS Options These options are defined specifically for the CRIS ports. -march=architecture-type -mcpu=architecture-type Generate code for the specified architecture. The choices for architecture-type are v3, v8 and v10 for respectively ETRAX 4, ETRAX 100, and ETRAX 100 LX. Default is v0. -mtune=architecture-type Tune to architecture-type everything applicable about the generated code, except for the ABI and the set of available instructions. The choices for architecture-type are the same as for -march=architecture-type. -mmax-stack-frame=n Warn when the stack frame of a function exceeds n bytes. -metrax4 -metrax100 The options -metrax4 and -metrax100 are synonyms for -march=v3 and -march=v8 respectively. -mmul-bug-workaround -mno-mul-bug-workaround Work around a bug in the "muls" and "mulu" instructions for CPU models where it applies. This option is disabled by default. -mpdebug Enable CRIS-specific verbose debug-related information in the assembly code. This option also has the effect of turning off the #NO_APP formatted-code indicator to the assembler at the beginning of the assembly file. -mcc-init Do not use condition-code results from previous instruction; always emit compare and test instructions before use of condition codes. -mno-side-effects Do not emit instructions with side effects in addressing modes other than post-increment. -mstack-align -mno-stack-align -mdata-align -mno-data-align -mconst-align -mno-const-align These options (no- options) arrange (eliminate arrangements) for the stack frame, individual data and constants to be aligned for the maximum single data access size for the chosen CPU model. The default is to arrange for 32-bit alignment. ABI details such as structure layout are not affected by these options. -m32-bit -m16-bit -m8-bit Similar to the stack- data- and const-align options above, these options arrange for stack frame, writable data and constants to all be 32-bit, 16-bit or 8-bit aligned. The default is 32-bit alignment. -mno-prologue-epilogue -mprologue-epilogue With -mno-prologue-epilogue, the normal function prologue and epilogue which set up the stack frame are omitted and no return instructions or return sequences are generated in the code. Use this option only together with visual inspection of the compiled code: no warnings or errors are generated when call-saved registers must be saved, or storage for local variables needs to be allocated. -melf Legacy no-op option. -sim This option arranges to link with input-output functions from a simulator library. Code, initialized data and zero-initialized data are allocated consecutively. -sim2 Like -sim, but pass linker options to locate initialized data at 0x40000000 and zero-initialized data at 0x80000000. C-SKY Options GCC supports these options when compiling for C-SKY V2 processors. -march=arch Specify the C-SKY target architecture. Valid values for arch are: ck801, ck802, ck803, ck807, and ck810. The default is ck810. -mcpu=cpu Specify the C-SKY target processor. Valid values for cpu are: ck801, ck801t, ck802, ck802t, ck802j, ck803, ck803h, ck803t, ck803ht, ck803f, ck803fh, ck803e, ck803eh, ck803et, ck803eht, ck803ef, ck803efh, ck803ft, ck803eft, ck803efht, ck803r1, ck803hr1, ck803tr1, ck803htr1, ck803fr1, ck803fhr1, ck803er1, ck803ehr1, ck803etr1, ck803ehtr1, ck803efr1, ck803efhr1, ck803ftr1, ck803eftr1, ck803efhtr1, ck803s, ck803st, ck803se, ck803sf, ck803sef, ck803seft, ck807e, ck807ef, ck807, ck807f, ck810e, ck810et, ck810ef, ck810eft, ck810, ck810v, ck810f, ck810t, ck810fv, ck810tv, ck810ft, and ck810ftv. -mbig-endian -EB -mlittle-endian -EL Select big- or little-endian code. The default is little-endian. -mfloat-abi=name Specifies which floating-point ABI to use. Permissible values are: soft, softfp and hard. Specifying soft causes GCC to generate output containing library calls for floating-point operations. softfp allows the generation of code using hardware floating-point instructions, but still uses the soft-float calling conventions. hard allows generation of floating-point instructions and uses FPU-specific calling conventions. The default depends on the specific target configuration. Note that the hard-float and soft-float ABIs are not link-compatible; you must compile your entire program with the same ABI, and link with a compatible set of libraries. -mhard-float -msoft-float Select hardware or software floating-point implementations. The default is soft float. -mdouble-float -mno-double-float When -mhard-float is in effect, enable generation of double- precision float instructions. This is the default except when compiling for CK803. -mfdivdu -mno-fdivdu When -mhard-float is in effect, enable generation of "frecipd", "fsqrtd", and "fdivd" instructions. This is the default except when compiling for CK803. -mfpu=fpu Select the floating-point processor. This option can only be used with -mhard-float. Values for fpu are fpv2_sf (equivalent to -mno-double-float -mno-fdivdu), fpv2 (-mdouble-float -mno-divdu), and fpv2_divd (-mdouble-float -mdivdu). -melrw -mno-elrw Enable the extended "lrw" instruction. This option defaults to on for CK801 and off otherwise. -mistack -mno-istack Enable interrupt stack instructions; the default is off. The -mistack option is required to handle the "interrupt" and "isr" function attributes. -mmp Enable multiprocessor instructions; the default is off. -mcp Enable coprocessor instructions; the default is off. -mcache Enable coprocessor instructions; the default is off. -msecurity Enable C-SKY security instructions; the default is off. -mtrust Enable C-SKY trust instructions; the default is off. -mdsp -medsp -mvdsp Enable C-SKY DSP, Enhanced DSP, or Vector DSP instructions, respectively. All of these options default to off. -mdiv -mno-div Generate divide instructions. Default is off. -msmart -mno-smart Generate code for Smart Mode, using only registers numbered 0-7 to allow use of 16-bit instructions. This option is ignored for CK801 where this is the required behavior, and it defaults to on for CK802. For other targets, the default is off. -mhigh-registers -mno-high-registers Generate code using the high registers numbered 16-31. This option is not supported on CK801, CK802, or CK803, and is enabled by default for other processors. -manchor -mno-anchor Generate code using global anchor symbol addresses. -mpushpop -mno-pushpop Generate code using "push" and "pop" instructions. This option defaults to on. -mmultiple-stld -mstm -mno-multiple-stld -mno-stm Generate code using "stm" and "ldm" instructions. This option isn't supported on CK801 but is enabled by default on other processors. -mconstpool -mno-constpool Create constant pools in the compiler instead of deferring it to the assembler. This option is the default and required for correct code generation on CK801 and CK802, and is optional on other processors. -mstack-size -mno-stack-size Emit ".stack_size" directives for each function in the assembly output. This option defaults to off. -mccrt -mno-ccrt Generate code for the C-SKY compiler runtime instead of libgcc. This option defaults to off. -mbranch-cost=n Set the branch costs to roughly "n" instructions. The default is 1. -msched-prolog -mno-sched-prolog Permit scheduling of function prologue and epilogue sequences. Using this option can result in code that is not compliant with the C-SKY V2 ABI prologue requirements and that cannot be debugged or backtraced. It is disabled by default. -msim Links the library libsemi.a which is in compatible with simulator. Applicable to ELF compiler only. Darwin Options These options are defined for all architectures running the Darwin operating system. FSF GCC on Darwin does not create "fat" object files; it creates an object file for the single architecture that GCC was built to target. Apple's GCC on Darwin does create "fat" files if multiple -arch options are used; it does so by running the compiler or linker multiple times and joining the results together with lipo. The subtype of the file created (like ppc7400 or ppc970 or i686) is determined by the flags that specify the ISA that GCC is targeting, like -mcpu or -march. The -force_cpusubtype_ALL option can be used to override this. The Darwin tools vary in their behavior when presented with an ISA mismatch. The assembler, as, only permits instructions to be used that are valid for the subtype of the file it is generating, so you cannot put 64-bit instructions in a ppc750 object file. The linker for shared libraries, /usr/bin/libtool, fails and prints an error if asked to create a shared library with a less restrictive subtype than its input files (for instance, trying to put a ppc970 object file in a ppc7400 library). The linker for executables, ld, quietly gives the executable the most restrictive subtype of any of its input files. -Fdir Add the framework directory dir to the head of the list of directories to be searched for header files. These directories are interleaved with those specified by -I options and are scanned in a left-to-right order. A framework directory is a directory with frameworks in it. A framework is a directory with a Headers and/or PrivateHeaders directory contained directly in it that ends in .framework. The name of a framework is the name of this directory excluding the .framework. Headers associated with the framework are found in one of those two directories, with Headers being searched first. A subframework is a framework directory that is in a framework's Frameworks directory. Includes of subframework headers can only appear in a header of a framework that contains the subframework, or in a sibling subframework header. Two subframeworks are siblings if they occur in the same framework. A subframework should not have the same name as a framework; a warning is issued if this is violated. Currently a subframework cannot have subframeworks; in the future, the mechanism may be extended to support this. The standard frameworks can be found in /System/Library/Frameworks and /Library/Frameworks. An example include looks like "#include <Framework/header.h>", where Framework denotes the name of the framework and header.h is found in the PrivateHeaders or Headers directory. -iframeworkdir Like -F except the directory is a treated as a system directory. The main difference between this -iframework and -F is that with -iframework the compiler does not warn about constructs contained within header files found via dir. This option is valid only for the C family of languages. -gused Emit debugging information for symbols that are used. For stabs debugging format, this enables -feliminate-unused-debug-symbols. This is by default ON. -gfull Emit debugging information for all symbols and types. -fconstant-cfstrings The -fconstant-cfstrings is an alias for -mconstant-cfstrings. -mconstant-cfstrings When the NeXT runtime is being used (the default on these systems), override any -fconstant-string-class setting and cause "@"..."" literals to be laid out as constant CoreFoundation strings. -mmacosx-version-min=version The earliest version of MacOS X that this executable will run on is version. Typical values supported for version include 12, 10.12, and 10.5.8. If the compiler was built to use the system's headers by default, then the default for this option is the system version on which the compiler is running, otherwise the default is to make choices that are compatible with as many systems and code bases as possible. -mkernel Enable kernel development mode. The -mkernel option sets -static, -fno-common, -fno-use-cxa-atexit, -fno-exceptions, -fno-non-call-exceptions, -fapple-kext, -fno-weak and -fno-rtti where applicable. This mode also sets -mno-altivec, -msoft-float, -fno-builtin and -mlong-branch for PowerPC targets. -mone-byte-bool Override the defaults for "bool" so that "sizeof(bool)==1". By default "sizeof(bool)" is 4 when compiling for Darwin/PowerPC and 1 when compiling for Darwin/x86, so this option has no effect on x86. Warning: The -mone-byte-bool switch causes GCC to generate code that is not binary compatible with code generated without that switch. Using this switch may require recompiling all other modules in a program, including system libraries. Use this switch to conform to a non-default data model. -mfix-and-continue -ffix-and-continue -findirect-data Generate code suitable for fast turnaround development, such as to allow GDB to dynamically load .o files into already-running programs. -findirect-data and -ffix-and-continue are provided for backwards compatibility. -all_load Loads all members of static archive libraries. See man ld(1) for more information. -arch_errors_fatal Cause the errors having to do with files that have the wrong architecture to be fatal. -bind_at_load Causes the output file to be marked such that the dynamic linker will bind all undefined references when the file is loaded or launched. -bundle Produce a Mach-o bundle format file. See man ld(1) for more information. -bundle_loader executable This option specifies the executable that will load the build output file being linked. See man ld(1) for more information. -dynamiclib When passed this option, GCC produces a dynamic library instead of an executable when linking, using the Darwin libtool command. -force_cpusubtype_ALL This causes GCC's output file to have the ALL subtype, instead of one controlled by the -mcpu or -march option. -allowable_client client_name -client_name -compatibility_version -current_version -dead_strip -dependency-file -dylib_file -dylinker_install_name -dynamic -exported_symbols_list -filelist -flat_namespace -force_flat_namespace -headerpad_max_install_names -image_base -init -install_name -keep_private_externs -multi_module -multiply_defined -multiply_defined_unused -noall_load -no_dead_strip_inits_and_terms -nofixprebinding -nomultidefs -noprebind -noseglinkedit -pagezero_size -prebind -prebind_all_twolevel_modules -private_bundle -read_only_relocs -sectalign -sectobjectsymbols -whyload -seg1addr -sectcreate -sectobjectsymbols -sectorder -segaddr -segs_read_only_addr -segs_read_write_addr -seg_addr_table -seg_addr_table_filename -seglinkedit -segprot -segs_read_only_addr -segs_read_write_addr -single_module -static -sub_library -sub_umbrella -twolevel_namespace -umbrella -undefined -unexported_symbols_list -weak_reference_mismatches -whatsloaded These options are passed to the Darwin linker. The Darwin linker man page describes them in detail. DEC Alpha Options These -m options are defined for the DEC Alpha implementations: -mno-soft-float -msoft-float Use (do not use) the hardware floating-point instructions for floating-point operations. When -msoft-float is specified, functions in libgcc.a are used to perform floating-point operations. Unless they are replaced by routines that emulate the floating-point operations, or compiled in such a way as to call such emulations routines, these routines issue floating-point operations. If you are compiling for an Alpha without floating- point operations, you must ensure that the library is built so as not to call them. Note that Alpha implementations without floating-point operations are required to have floating-point registers. -mfp-reg -mno-fp-regs Generate code that uses (does not use) the floating-point register set. -mno-fp-regs implies -msoft-float. If the floating-point register set is not used, floating-point operands are passed in integer registers as if they were integers and floating-point results are passed in $0 instead of $f0. This is a non-standard calling sequence, so any function with a floating-point argument or return value called by code compiled with -mno-fp-regs must also be compiled with that option. A typical use of this option is building a kernel that does not use, and hence need not save and restore, any floating-point registers. -mieee The Alpha architecture implements floating-point hardware optimized for maximum performance. It is mostly compliant with the IEEE floating-point standard. However, for full compliance, software assistance is required. This option generates code fully IEEE- compliant code except that the inexact-flag is not maintained (see below). If this option is turned on, the preprocessor macro "_IEEE_FP" is defined during compilation. The resulting code is less efficient but is able to correctly support denormalized numbers and exceptional IEEE values such as not-a-number and plus/minus infinity. Other Alpha compilers call this option -ieee_with_no_inexact. -mieee-with-inexact This is like -mieee except the generated code also maintains the IEEE inexact-flag. Turning on this option causes the generated code to implement fully-compliant IEEE math. In addition to "_IEEE_FP", "_IEEE_FP_EXACT" is defined as a preprocessor macro. On some Alpha implementations the resulting code may execute significantly slower than the code generated by default. Since there is very little code that depends on the inexact-flag, you should normally not specify this option. Other Alpha compilers call this option -ieee_with_inexact. -mfp-trap-mode=trap-mode This option controls what floating-point related traps are enabled. Other Alpha compilers call this option -fptm trap-mode. The trap mode can be set to one of four values: n This is the default (normal) setting. The only traps that are enabled are the ones that cannot be disabled in software (e.g., division by zero trap). u In addition to the traps enabled by n, underflow traps are enabled as well. su Like u, but the instructions are marked to be safe for software completion (see Alpha architecture manual for details). sui Like su, but inexact traps are enabled as well. -mfp-rounding-mode=rounding-mode Selects the IEEE rounding mode. Other Alpha compilers call this option -fprm rounding-mode. The rounding-mode can be one of: n Normal IEEE rounding mode. Floating-point numbers are rounded towards the nearest machine number or towards the even machine number in case of a tie. m Round towards minus infinity. c Chopped rounding mode. Floating-point numbers are rounded towards zero. d Dynamic rounding mode. A field in the floating-point control register (fpcr, see Alpha architecture reference manual) controls the rounding mode in effect. The C library initializes this register for rounding towards plus infinity. Thus, unless your program modifies the fpcr, d corresponds to round towards plus infinity. -mtrap-precision=trap-precision In the Alpha architecture, floating-point traps are imprecise. This means without software assistance it is impossible to recover from a floating trap and program execution normally needs to be terminated. GCC can generate code that can assist operating system trap handlers in determining the exact location that caused a floating-point trap. Depending on the requirements of an application, different levels of precisions can be selected: p Program precision. This option is the default and means a trap handler can only identify which program caused a floating-point exception. f Function precision. The trap handler can determine the function that caused a floating-point exception. i Instruction precision. The trap handler can determine the exact instruction that caused a floating-point exception. Other Alpha compilers provide the equivalent options called -scope_safe and -resumption_safe. -mieee-conformant This option marks the generated code as IEEE conformant. You must not use this option unless you also specify -mtrap-precision=i and either -mfp-trap-mode=su or -mfp-trap-mode=sui. Its only effect is to emit the line .eflag 48 in the function prologue of the generated assembly file. -mbuild-constants Normally GCC examines a 32- or 64-bit integer constant to see if it can construct it from smaller constants in two or three instructions. If it cannot, it outputs the constant as a literal and generates code to load it from the data segment at run time. Use this option to require GCC to construct all integer constants using code, even if it takes more instructions (the maximum is six). You typically use this option to build a shared library dynamic loader. Itself a shared library, it must relocate itself in memory before it can find the variables and constants in its own data segment. -mbwx -mno-bwx -mcix -mno-cix -mfix -mno-fix -mmax -mno-max Indicate whether GCC should generate code to use the optional BWX, CIX, FIX and MAX instruction sets. The default is to use the instruction sets supported by the CPU type specified via -mcpu= option or that of the CPU on which GCC was built if none is specified. -mfloat-vax -mfloat-ieee Generate code that uses (does not use) VAX F and G floating-point arithmetic instead of IEEE single and double precision. -mexplicit-relocs -mno-explicit-relocs Older Alpha assemblers provided no way to generate symbol relocations except via assembler macros. Use of these macros does not allow optimal instruction scheduling. GNU binutils as of version 2.12 supports a new syntax that allows the compiler to explicitly mark which relocations should apply to which instructions. This option is mostly useful for debugging, as GCC detects the capabilities of the assembler when it is built and sets the default accordingly. -msmall-data -mlarge-data When -mexplicit-relocs is in effect, static data is accessed via gp-relative relocations. When -msmall-data is used, objects 8 bytes long or smaller are placed in a small data area (the ".sdata" and ".sbss" sections) and are accessed via 16-bit relocations off of the $gp register. This limits the size of the small data area to 64KB, but allows the variables to be directly accessed via a single instruction. The default is -mlarge-data. With this option the data area is limited to just below 2GB. Programs that require more than 2GB of data must use "malloc" or "mmap" to allocate the data in the heap instead of in the program's data segment. When generating code for shared libraries, -fpic implies -msmall-data and -fPIC implies -mlarge-data. -msmall-text -mlarge-text When -msmall-text is used, the compiler assumes that the code of the entire program (or shared library) fits in 4MB, and is thus reachable with a branch instruction. When -msmall-data is used, the compiler can assume that all local symbols share the same $gp value, and thus reduce the number of instructions required for a function call from 4 to 1. The default is -mlarge-text. -mcpu=cpu_type Set the instruction set and instruction scheduling parameters for machine type cpu_type. You can specify either the EV style name or the corresponding chip number. GCC supports scheduling parameters for the EV4, EV5 and EV6 family of processors and chooses the default values for the instruction set from the processor you specify. If you do not specify a processor type, GCC defaults to the processor on which the compiler was built. Supported values for cpu_type are ev4 ev45 21064 Schedules as an EV4 and has no instruction set extensions. ev5 21164 Schedules as an EV5 and has no instruction set extensions. ev56 21164a Schedules as an EV5 and supports the BWX extension. pca56 21164pc 21164PC Schedules as an EV5 and supports the BWX and MAX extensions. ev6 21264 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions. ev67 21264a Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions. Native toolchains also support the value native, which selects the best architecture option for the host processor. -mcpu=native has no effect if GCC does not recognize the processor. -mtune=cpu_type Set only the instruction scheduling parameters for machine type cpu_type. The instruction set is not changed. Native toolchains also support the value native, which selects the best architecture option for the host processor. -mtune=native has no effect if GCC does not recognize the processor. -mmemory-latency=time Sets the latency the scheduler should assume for typical memory references as seen by the application. This number is highly dependent on the memory access patterns used by the application and the size of the external cache on the machine. Valid options for time are number A decimal number representing clock cycles. L1 L2 L3 main The compiler contains estimates of the number of clock cycles for "typical" EV4 & EV5 hardware for the Level 1, 2 & 3 caches (also called Dcache, Scache, and Bcache), as well as to main memory. Note that L3 is only valid for EV5. eBPF Options -mframe-limit=bytes This specifies the hard limit for frame sizes, in bytes. Currently, the value that can be specified should be less than or equal to 32767. Defaults to whatever limit is imposed by the version of the Linux kernel targeted. -mkernel=version This specifies the minimum version of the kernel that will run the compiled program. GCC uses this version to determine which instructions to use, what kernel helpers to allow, etc. Currently, version can be one of 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 4.10, 4.11, 4.12, 4.13, 4.14, 4.15, 4.16, 4.17, 4.18, 4.19, 4.20, 5.0, 5.1, 5.2, latest and native. -mbig-endian Generate code for a big-endian target. -mlittle-endian Generate code for a little-endian target. This is the default. -mjmpext Enable generation of extra conditional-branch instructions. Enabled for CPU v2 and above. -mjmp32 Enable 32-bit jump instructions. Enabled for CPU v3 and above. -malu32 Enable 32-bit ALU instructions. Enabled for CPU v3 and above. -mcpu=version This specifies which version of the eBPF ISA to target. Newer versions may not be supported by all kernels. The default is v3. Supported values for version are: v1 The first stable eBPF ISA with no special features or extensions. v2 Supports the jump extensions, as in -mjmpext. v3 All features of v2, plus: -<32-bit jump operations, as in -mjmp32> -<32-bit ALU operations, as in -malu32> -mco-re Enable BPF Compile Once - Run Everywhere (CO-RE) support. Requires and is implied by -gbtf. -mno-co-re Disable BPF Compile Once - Run Everywhere (CO-RE) support. BPF CO- RE support is enabled by default when generating BTF debug information for the BPF target. -mxbpf Generate code for an expanded version of BPF, which relaxes some of the restrictions imposed by the BPF architecture: -<Save and restore callee-saved registers at function entry and> exit, respectively. FR30 Options These options are defined specifically for the FR30 port. -msmall-model Use the small address space model. This can produce smaller code, but it does assume that all symbolic values and addresses fit into a 20-bit range. -mno-lsim Assume that runtime support has been provided and so there is no need to include the simulator library (libsim.a) on the linker command line. FT32 Options These options are defined specifically for the FT32 port. -msim Specifies that the program will be run on the simulator. This causes an alternate runtime startup and library to be linked. You must not use this option when generating programs that will run on real hardware; you must provide your own runtime library for whatever I/O functions are needed. -mlra Enable Local Register Allocation. This is still experimental for FT32, so by default the compiler uses standard reload. -mnodiv Do not use div and mod instructions. -mft32b Enable use of the extended instructions of the FT32B processor. -mcompress Compress all code using the Ft32B code compression scheme. -mnopm Do not generate code that reads program memory. FRV Options -mgpr-32 Only use the first 32 general-purpose registers. -mgpr-64 Use all 64 general-purpose registers. -mfpr-32 Use only the first 32 floating-point registers. -mfpr-64 Use all 64 floating-point registers. -mhard-float Use hardware instructions for floating-point operations. -msoft-float Use library routines for floating-point operations. -malloc-cc Dynamically allocate condition code registers. -mfixed-cc Do not try to dynamically allocate condition code registers, only use "icc0" and "fcc0". -mdword Change ABI to use double word insns. -mno-dword Do not use double word instructions. -mdouble Use floating-point double instructions. -mno-double Do not use floating-point double instructions. -mmedia Use media instructions. -mno-media Do not use media instructions. -mmuladd Use multiply and add/subtract instructions. -mno-muladd Do not use multiply and add/subtract instructions. -mfdpic Select the FDPIC ABI, which uses function descriptors to represent pointers to functions. Without any PIC/PIE-related options, it implies -fPIE. With -fpic or -fpie, it assumes GOT entries and small data are within a 12-bit range from the GOT base address; with -fPIC or -fPIE, GOT offsets are computed with 32 bits. With a bfin-elf target, this option implies -msim. -minline-plt Enable inlining of PLT entries in function calls to functions that are not known to bind locally. It has no effect without -mfdpic. It's enabled by default if optimizing for speed and compiling for shared libraries (i.e., -fPIC or -fpic), or when an optimization option such as -O3 or above is present in the command line. -mTLS Assume a large TLS segment when generating thread-local code. -mtls Do not assume a large TLS segment when generating thread-local code. -mgprel-ro Enable the use of "GPREL" relocations in the FDPIC ABI for data that is known to be in read-only sections. It's enabled by default, except for -fpic or -fpie: even though it may help make the global offset table smaller, it trades 1 instruction for 4. With -fPIC or -fPIE, it trades 3 instructions for 4, one of which may be shared by multiple symbols, and it avoids the need for a GOT entry for the referenced symbol, so it's more likely to be a win. If it is not, -mno-gprel-ro can be used to disable it. -multilib-library-pic Link with the (library, not FD) pic libraries. It's implied by -mlibrary-pic, as well as by -fPIC and -fpic without -mfdpic. You should never have to use it explicitly. -mlinked-fp Follow the EABI requirement of always creating a frame pointer whenever a stack frame is allocated. This option is enabled by default and can be disabled with -mno-linked-fp. -mlong-calls Use indirect addressing to call functions outside the current compilation unit. This allows the functions to be placed anywhere within the 32-bit address space. -malign-labels Try to align labels to an 8-byte boundary by inserting NOPs into the previous packet. This option only has an effect when VLIW packing is enabled. It doesn't create new packets; it merely adds NOPs to existing ones. -mlibrary-pic Generate position-independent EABI code. -macc-4 Use only the first four media accumulator registers. -macc-8 Use all eight media accumulator registers. -mpack Pack VLIW instructions. -mno-pack Do not pack VLIW instructions. -mno-eflags Do not mark ABI switches in e_flags. -mcond-move Enable the use of conditional-move instructions (default). This switch is mainly for debugging the compiler and will likely be removed in a future version. -mno-cond-move Disable the use of conditional-move instructions. This switch is mainly for debugging the compiler and will likely be removed in a future version. -mscc Enable the use of conditional set instructions (default). This switch is mainly for debugging the compiler and will likely be removed in a future version. -mno-scc Disable the use of conditional set instructions. This switch is mainly for debugging the compiler and will likely be removed in a future version. -mcond-exec Enable the use of conditional execution (default). This switch is mainly for debugging the compiler and will likely be removed in a future version. -mno-cond-exec Disable the use of conditional execution. This switch is mainly for debugging the compiler and will likely be removed in a future version. -mvliw-branch Run a pass to pack branches into VLIW instructions (default). This switch is mainly for debugging the compiler and will likely be removed in a future version. -mno-vliw-branch Do not run a pass to pack branches into VLIW instructions. This switch is mainly for debugging the compiler and will likely be removed in a future version. -mmulti-cond-exec Enable optimization of "&&" and "||" in conditional execution (default). This switch is mainly for debugging the compiler and will likely be removed in a future version. -mno-multi-cond-exec Disable optimization of "&&" and "||" in conditional execution. This switch is mainly for debugging the compiler and will likely be removed in a future version. -mnested-cond-exec Enable nested conditional execution optimizations (default). This switch is mainly for debugging the compiler and will likely be removed in a future version. -mno-nested-cond-exec Disable nested conditional execution optimizations. This switch is mainly for debugging the compiler and will likely be removed in a future version. -moptimize-membar This switch removes redundant "membar" instructions from the compiler-generated code. It is enabled by default. -mno-optimize-membar This switch disables the automatic removal of redundant "membar" instructions from the generated code. -mtomcat-stats Cause gas to print out tomcat statistics. -mcpu=cpu Select the processor type for which to generate code. Possible values are frv, fr550, tomcat, fr500, fr450, fr405, fr400, fr300 and simple. GNU/Linux Options These -m options are defined for GNU/Linux targets: -mglibc Use the GNU C library. This is the default except on *-*-linux-*uclibc*, *-*-linux-*musl* and *-*-linux-*android* targets. -muclibc Use uClibc C library. This is the default on *-*-linux-*uclibc* targets. -mmusl Use the musl C library. This is the default on *-*-linux-*musl* targets. -mbionic Use Bionic C library. This is the default on *-*-linux-*android* targets. -mandroid Compile code compatible with Android platform. This is the default on *-*-linux-*android* targets. When compiling, this option enables -mbionic, -fPIC, -fno-exceptions and -fno-rtti by default. When linking, this option makes the GCC driver pass Android-specific options to the linker. Finally, this option causes the preprocessor macro "__ANDROID__" to be defined. -tno-android-cc Disable compilation effects of -mandroid, i.e., do not enable -mbionic, -fPIC, -fno-exceptions and -fno-rtti by default. -tno-android-ld Disable linking effects of -mandroid, i.e., pass standard Linux linking options to the linker. H8/300 Options These -m options are defined for the H8/300 implementations: -mrelax Shorten some address references at link time, when possible; uses the linker option -relax. -mh Generate code for the H8/300H. -ms Generate code for the H8S. -mn Generate code for the H8S and H8/300H in the normal mode. This switch must be used either with -mh or -ms. -ms2600 Generate code for the H8S/2600. This switch must be used with -ms. -mexr Extended registers are stored on stack before execution of function with monitor attribute. Default option is -mexr. This option is valid only for H8S targets. -mno-exr Extended registers are not stored on stack before execution of function with monitor attribute. Default option is -mno-exr. This option is valid only for H8S targets. -mint32 Make "int" data 32 bits by default. -malign-300 On the H8/300H and H8S, use the same alignment rules as for the H8/300. The default for the H8/300H and H8S is to align longs and floats on 4-byte boundaries. -malign-300 causes them to be aligned on 2-byte boundaries. This option has no effect on the H8/300. HPPA Options These -m options are defined for the HPPA family of computers: -march=architecture-type Generate code for the specified architecture. The choices for architecture-type are 1.0 for PA 1.0, 1.1 for PA 1.1, and 2.0 for PA 2.0 processors. Refer to /usr/lib/sched.models on an HP-UX system to determine the proper architecture option for your machine. Code compiled for lower numbered architectures runs on higher numbered architectures, but not the other way around. -mpa-risc-1-0 -mpa-risc-1-1 -mpa-risc-2-0 Synonyms for -march=1.0, -march=1.1, and -march=2.0 respectively. -matomic-libcalls Generate libcalls for atomic loads and stores when sync libcalls are disabled. This option is enabled by default. It only affects the generation of atomic libcalls by the HPPA backend. Both the sync and libatomic libcall implementations use locking. As a result, processor stores are not atomic with respect to other atomic operations. Processor loads up to DImode are atomic with respect to other atomic operations provided they are implemented as a single access. The PA-RISC architecture does not support any atomic operations in hardware except for the "ldcw" instruction. Thus, all atomic support is implemented using sync and atomic libcalls. Sync libcall support is in libgcc.a. Atomic libcall support is in libatomic. This option generates "__atomic_exchange" calls for atomic stores. It also provides special handling for atomic DImode accesses on 32-bit targets. -mbig-switch Does nothing. Preserved for backward compatibility. -mcaller-copies The caller copies function arguments passed by hidden reference. This option should be used with care as it is not compatible with the default 32-bit runtime. However, only aggregates larger than eight bytes are passed by hidden reference and the option provides better compatibility with OpenMP. -mcoherent-ldcw Use ldcw/ldcd coherent cache-control hint. -mdisable-fpregs Disable floating-point registers. Equivalent to "-msoft-float". -mdisable-indexing Prevent the compiler from using indexing address modes. This avoids some rather obscure problems when compiling MIG generated code under MACH. -mfast-indirect-calls Generate code that assumes calls never cross space boundaries. This allows GCC to emit code that performs faster indirect calls. This option does not work in the presence of shared libraries or nested functions. -mfixed-range=register-range Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. -mgas Enable the use of assembler directives only GAS understands. -mgnu-ld Use options specific to GNU ld. This passes -shared to ld when building a shared library. It is the default when GCC is configured, explicitly or implicitly, with the GNU linker. This option does not affect which ld is called; it only changes what parameters are passed to that ld. The ld that is called is determined by the --with-ld configure option, GCC's program search path, and finally by the user's PATH. The linker used by GCC can be printed using which `gcc -print-prog-name=ld`. This option is only available on the 64-bit HP-UX GCC, i.e. configured with hppa*64*-*-hpux*. -mhp-ld Use options specific to HP ld. This passes -b to ld when building a shared library and passes +Accept TypeMismatch to ld on all links. It is the default when GCC is configured, explicitly or implicitly, with the HP linker. This option does not affect which ld is called; it only changes what parameters are passed to that ld. The ld that is called is determined by the --with-ld configure option, GCC's program search path, and finally by the user's PATH. The linker used by GCC can be printed using which `gcc -print-prog-name=ld`. This option is only available on the 64-bit HP-UX GCC, i.e. configured with hppa*64*-*-hpux*. -mlinker-opt Enable the optimization pass in the HP-UX linker. Note this makes symbolic debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9 linkers in which they give bogus error messages when linking some programs. -mlong-calls Generate code that uses long call sequences. This ensures that a call is always able to reach linker generated stubs. The default is to generate long calls only when the distance from the call site to the beginning of the function or translation unit, as the case may be, exceeds a predefined limit set by the branch type being used. The limits for normal calls are 7,600,000 and 240,000 bytes, respectively for the PA 2.0 and PA 1.X architectures. Sibcalls are always limited at 240,000 bytes. Distances are measured from the beginning of functions when using the -ffunction-sections option, or when using the -mgas and -mno-portable-runtime options together under HP-UX with the SOM linker. It is normally not desirable to use this option as it degrades performance. However, it may be useful in large applications, particularly when partial linking is used to build the application. The types of long calls used depends on the capabilities of the assembler and linker, and the type of code being generated. The impact on systems that support long absolute calls, and long pic symbol-difference or pc-relative calls should be relatively small. However, an indirect call is used on 32-bit ELF systems in pic code and it is quite long. -mlong-load-store Generate 3-instruction load and store sequences as sometimes required by the HP-UX 10 linker. This is equivalent to the +k option to the HP compilers. -mjump-in-delay This option is ignored and provided for compatibility purposes only. -mno-space-regs Generate code that assumes the target has no space registers. This allows GCC to generate faster indirect calls and use unscaled index address modes. Such code is suitable for level 0 PA systems and kernels. -mordered Assume memory references are ordered and barriers are not needed. -mportable-runtime Use the portable calling conventions proposed by HP for ELF systems. -mschedule=cpu-type Schedule code according to the constraints for the machine type cpu-type. The choices for cpu-type are 700 7100, 7100LC, 7200, 7300 and 8000. Refer to /usr/lib/sched.models on an HP-UX system to determine the proper scheduling option for your machine. The default scheduling is 8000. -msio Generate the predefine, "_SIO", for server IO. The default is -mwsio. This generates the predefines, "__hp9000s700", "__hp9000s700__" and "_WSIO", for workstation IO. These options are available under HP-UX and HI-UX. -msoft-float Generate output containing library calls for floating point. Warning: the requisite libraries are not available for all HPPA targets. Normally the facilities of the machine's usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. -msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a, the library that comes with GCC, with -msoft-float in order for this to work. -msoft-mult Use software integer multiplication. This disables the use of the "xmpyu" instruction. -munix=unix-std Generate compiler predefines and select a startfile for the specified UNIX standard. The choices for unix-std are 93, 95 and 98. 93 is supported on all HP-UX versions. 95 is available on HP- UX 10.10 and later. 98 is available on HP-UX 11.11 and later. The default values are 93 for HP-UX 10.00, 95 for HP-UX 10.10 though to 11.00, and 98 for HP-UX 11.11 and later. -munix=93 provides the same predefines as GCC 3.3 and 3.4. -munix=95 provides additional predefines for "XOPEN_UNIX" and "_XOPEN_SOURCE_EXTENDED", and the startfile unix95.o. -munix=98 provides additional predefines for "_XOPEN_UNIX", "_XOPEN_SOURCE_EXTENDED", "_INCLUDE__STDC_A1_SOURCE" and "_INCLUDE_XOPEN_SOURCE_500", and the startfile unix98.o. It is important to note that this option changes the interfaces for various library routines. It also affects the operational behavior of the C library. Thus, extreme care is needed in using this option. Library code that is intended to operate with more than one UNIX standard must test, set and restore the variable "__xpg4_extended_mask" as appropriate. Most GNU software doesn't provide this capability. -nolibdld Suppress the generation of link options to search libdld.sl when the -static option is specified on HP-UX 10 and later. -static The HP-UX implementation of setlocale in libc has a dependency on libdld.sl. There isn't an archive version of libdld.sl. Thus, when the -static option is specified, special link options are needed to resolve this dependency. On HP-UX 10 and later, the GCC driver adds the necessary options to link with libdld.sl when the -static option is specified. This causes the resulting binary to be dynamic. On the 64-bit port, the linkers generate dynamic binaries by default in any case. The -nolibdld option can be used to prevent the GCC driver from adding these link options. -threads Add support for multithreading with the dce thread library under HP-UX. This option sets flags for both the preprocessor and linker. IA-64 Options These are the -m options defined for the Intel IA-64 architecture. -mbig-endian Generate code for a big-endian target. This is the default for HP- UX. -mlittle-endian Generate code for a little-endian target. This is the default for AIX5 and GNU/Linux. -mgnu-as -mno-gnu-as Generate (or don't) code for the GNU assembler. This is the default. -mgnu-ld -mno-gnu-ld Generate (or don't) code for the GNU linker. This is the default. -mno-pic Generate code that does not use a global pointer register. The result is not position independent code, and violates the IA-64 ABI. -mvolatile-asm-stop -mno-volatile-asm-stop Generate (or don't) a stop bit immediately before and after volatile asm statements. -mregister-names -mno-register-names Generate (or don't) in, loc, and out register names for the stacked registers. This may make assembler output more readable. -mno-sdata -msdata Disable (or enable) optimizations that use the small data section. This may be useful for working around optimizer bugs. -mconstant-gp Generate code that uses a single constant global pointer value. This is useful when compiling kernel code. -mauto-pic Generate code that is self-relocatable. This implies -mconstant-gp. This is useful when compiling firmware code. -minline-float-divide-min-latency Generate code for inline divides of floating-point values using the minimum latency algorithm. -minline-float-divide-max-throughput Generate code for inline divides of floating-point values using the maximum throughput algorithm. -mno-inline-float-divide Do not generate inline code for divides of floating-point values. -minline-int-divide-min-latency Generate code for inline divides of integer values using the minimum latency algorithm. -minline-int-divide-max-throughput Generate code for inline divides of integer values using the maximum throughput algorithm. -mno-inline-int-divide Do not generate inline code for divides of integer values. -minline-sqrt-min-latency Generate code for inline square roots using the minimum latency algorithm. -minline-sqrt-max-throughput Generate code for inline square roots using the maximum throughput algorithm. -mno-inline-sqrt Do not generate inline code for "sqrt". -mfused-madd -mno-fused-madd Do (don't) generate code that uses the fused multiply/add or multiply/subtract instructions. The default is to use these instructions. -mno-dwarf2-asm -mdwarf2-asm Don't (or do) generate assembler code for the DWARF line number debugging info. This may be useful when not using the GNU assembler. -mearly-stop-bits -mno-early-stop-bits Allow stop bits to be placed earlier than immediately preceding the instruction that triggered the stop bit. This can improve instruction scheduling, but does not always do so. -mfixed-range=register-range Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. -mtls-size=tls-size Specify bit size of immediate TLS offsets. Valid values are 14, 22, and 64. -mtune=cpu-type Tune the instruction scheduling for a particular CPU, Valid values are itanium, itanium1, merced, itanium2, and mckinley. -milp32 -mlp64 Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits. These are HP-UX specific flags. -mno-sched-br-data-spec -msched-br-data-spec (Dis/En)able data speculative scheduling before reload. This results in generation of "ld.a" instructions and the corresponding check instructions ("ld.c" / "chk.a"). The default setting is disabled. -msched-ar-data-spec -mno-sched-ar-data-spec (En/Dis)able data speculative scheduling after reload. This results in generation of "ld.a" instructions and the corresponding check instructions ("ld.c" / "chk.a"). The default setting is enabled. -mno-sched-control-spec -msched-control-spec (Dis/En)able control speculative scheduling. This feature is available only during region scheduling (i.e. before reload). This results in generation of the "ld.s" instructions and the corresponding check instructions "chk.s". The default setting is disabled. -msched-br-in-data-spec -mno-sched-br-in-data-spec (En/Dis)able speculative scheduling of the instructions that are dependent on the data speculative loads before reload. This is effective only with -msched-br-data-spec enabled. The default setting is enabled. -msched-ar-in-data-spec -mno-sched-ar-in-data-spec (En/Dis)able speculative scheduling of the instructions that are dependent on the data speculative loads after reload. This is effective only with -msched-ar-data-spec enabled. The default setting is enabled. -msched-in-control-spec -mno-sched-in-control-spec (En/Dis)able speculative scheduling of the instructions that are dependent on the control speculative loads. This is effective only with -msched-control-spec enabled. The default setting is enabled. -mno-sched-prefer-non-data-spec-insns -msched-prefer-non-data-spec-insns If enabled, data-speculative instructions are chosen for schedule only if there are no other choices at the moment. This makes the use of the data speculation much more conservative. The default setting is disabled. -mno-sched-prefer-non-control-spec-insns -msched-prefer-non-control-spec-insns If enabled, control-speculative instructions are chosen for schedule only if there are no other choices at the moment. This makes the use of the control speculation much more conservative. The default setting is disabled. -mno-sched-count-spec-in-critical-path -msched-count-spec-in-critical-path If enabled, speculative dependencies are considered during computation of the instructions priorities. This makes the use of the speculation a bit more conservative. The default setting is disabled. -msched-spec-ldc Use a simple data speculation check. This option is on by default. -msched-control-spec-ldc Use a simple check for control speculation. This option is on by default. -msched-stop-bits-after-every-cycle Place a stop bit after every cycle when scheduling. This option is on by default. -msched-fp-mem-deps-zero-cost Assume that floating-point stores and loads are not likely to cause a conflict when placed into the same instruction group. This option is disabled by default. -msel-sched-dont-check-control-spec Generate checks for control speculation in selective scheduling. This flag is disabled by default. -msched-max-memory-insns=max-insns Limit on the number of memory insns per instruction group, giving lower priority to subsequent memory insns attempting to schedule in the same instruction group. Frequently useful to prevent cache bank conflicts. The default value is 1. -msched-max-memory-insns-hard-limit Makes the limit specified by msched-max-memory-insns a hard limit, disallowing more than that number in an instruction group. Otherwise, the limit is "soft", meaning that non-memory operations are preferred when the limit is reached, but memory operations may still be scheduled. LM32 Options These -m options are defined for the LatticeMico32 architecture: -mbarrel-shift-enabled Enable barrel-shift instructions. -mdivide-enabled Enable divide and modulus instructions. -mmultiply-enabled Enable multiply instructions. -msign-extend-enabled Enable sign extend instructions. -muser-enabled Enable user-defined instructions. LoongArch Options These command-line options are defined for LoongArch targets: -march=cpu-type Generate instructions for the machine type cpu-type. In contrast to -mtune=cpu-type, which merely tunes the generated code for the specified cpu-type, -march=cpu-type allows GCC to generate code that may not run at all on processors other than the one indicated. Specifying -march=cpu-type implies -mtune=cpu-type, except where noted otherwise. The choices for cpu-type are: native This selects the CPU to generate code for at compilation time by determining the processor type of the compiling machine. Using -march=native enables all instruction subsets supported by the local machine (hence the result might not run on different machines). Using -mtune=native produces code optimized for the local machine under the constraints of the selected instruction set. loongarch64 A generic CPU with 64-bit extensions. la464 LoongArch LA464 CPU with LBT, LSX, LASX, LVZ. -mtune=cpu-type Optimize the output for the given processor, specified by microarchitecture name. -mabi=base-abi-type Generate code for the specified calling convention. base-abi-type can be one of: lp64d Uses 64-bit general purpose registers and 32/64-bit floating- point registers for parameter passing. Data model is LP64, where int is 32 bits, while long int and pointers are 64 bits. lp64f Uses 64-bit general purpose registers and 32-bit floating-point registers for parameter passing. Data model is LP64, where int is 32 bits, while long int and pointers are 64 bits. lp64s Uses 64-bit general purpose registers and no floating-point registers for parameter passing. Data model is LP64, where int is 32 bits, while long int and pointers are 64 bits. -mfpu=fpu-type Generate code for the specified FPU type, which can be one of: 64 Allow the use of hardware floating-point instructions for 32-bit and 64-bit operations. 32 Allow the use of hardware floating-point instructions for 32-bit operations. none 0 Prevent the use of hardware floating-point instructions. -msoft-float Force -mfpu=none and prevents the use of floating-point registers for parameter passing. This option may change the target ABI. -msingle-float Force -mfpu=32 and allow the use of 32-bit floating-point registers for parameter passing. This option may change the target ABI. -mdouble-float Force -mfpu=64 and allow the use of 32/64-bit floating-point registers for parameter passing. This option may change the target ABI. -mbranch-cost=n Set the cost of branches to roughly n instructions. -mcheck-zero-division -mno-check-zero-divison Trap (do not trap) on integer division by zero. The default is -mcheck-zero-division for -O0 or -Og, and -mno-check-zero-division for other optimization levels. -mcond-move-int -mno-cond-move-int Conditional moves for integral data in general-purpose registers are enabled (disabled). The default is -mcond-move-int. -mcond-move-float -mno-cond-move-float Conditional moves for floating-point registers are enabled (disabled). The default is -mcond-move-float. -mmemcpy -mno-memcpy Force (do not force) the use of "memcpy" for non-trivial block moves. The default is -mno-memcpy, which allows GCC to inline most constant-sized copies. Setting optimization level to -Os also forces the use of "memcpy", but -mno-memcpy may override this behavior if explicitly specified, regardless of the order these options on the command line. -mstrict-align -mno-strict-align Avoid or allow generating memory accesses that may not be aligned on a natural object boundary as described in the architecture specification. The default is -mno-strict-align. -msmall-data-limit=number Put global and static data smaller than number bytes into a special section (on some targets). The default value is 0. -mmax-inline-memcpy-size=n Inline all block moves (such as calls to "memcpy" or structure copies) less than or equal to n bytes. The default value of n is 1024. -mcmodel=code-model Set the code model to one of: tiny-static (Not implemented yet) tiny (Not implemented yet) normal The text segment must be within 128MB addressing space. The data segment must be within 2GB addressing space. medium The text segment and data segment must be within 2GB addressing space. large (Not implemented yet) extreme This mode does not limit the size of the code segment and data segment. The -mcmodel=extreme option is incompatible with -fplt and -mno-explicit-relocs. The default code model is "normal". -mexplicit-relocs -mno-explicit-relocs Use or do not use assembler relocation operators when dealing with symbolic addresses. The alternative is to use assembler macros instead, which may limit optimization. The default value for the option is determined during GCC build-time by detecting corresponding assembler support: "-mexplicit-relocs" if said support is present, "-mno-explicit-relocs" otherwise. This option is mostly useful for debugging, or interoperation with assemblers different from the build-time one. -mdirect-extern-access -mno-direct-extern-access Do not use or use GOT to access external symbols. The default is -mno-direct-extern-access: GOT is used for external symbols with default visibility, but not used for other external symbols. With -mdirect-extern-access, GOT is not used and all external symbols are PC-relatively addressed. It is only suitable for environments where no dynamic link is performed, like firmwares, OS kernels, executables linked with -static or -static-pie. -mdirect-extern-access is not compatible with -fPIC or -fpic. M32C Options -mcpu=name Select the CPU for which code is generated. name may be one of r8c for the R8C/Tiny series, m16c for the M16C (up to /60) series, m32cm for the M16C/80 series, or m32c for the M32C/80 series. -msim Specifies that the program will be run on the simulator. This causes an alternate runtime library to be linked in which supports, for example, file I/O. You must not use this option when generating programs that will run on real hardware; you must provide your own runtime library for whatever I/O functions are needed. -memregs=number Specifies the number of memory-based pseudo-registers GCC uses during code generation. These pseudo-registers are used like real registers, so there is a tradeoff between GCC's ability to fit the code into available registers, and the performance penalty of using memory instead of registers. Note that all modules in a program must be compiled with the same value for this option. Because of that, you must not use this option with GCC's default runtime libraries. M32R/D Options These -m options are defined for Renesas M32R/D architectures: -m32r2 Generate code for the M32R/2. -m32rx Generate code for the M32R/X. -m32r Generate code for the M32R. This is the default. -mmodel=small Assume all objects live in the lower 16MB of memory (so that their addresses can be loaded with the "ld24" instruction), and assume all subroutines are reachable with the "bl" instruction. This is the default. The addressability of a particular object can be set with the "model" attribute. -mmodel=medium Assume objects may be anywhere in the 32-bit address space (the compiler generates "seth/add3" instructions to load their addresses), and assume all subroutines are reachable with the "bl" instruction. -mmodel=large Assume objects may be anywhere in the 32-bit address space (the compiler generates "seth/add3" instructions to load their addresses), and assume subroutines may not be reachable with the "bl" instruction (the compiler generates the much slower "seth/add3/jl" instruction sequence). -msdata=none Disable use of the small data area. Variables are put into one of ".data", ".bss", or ".rodata" (unless the "section" attribute has been specified). This is the default. The small data area consists of sections ".sdata" and ".sbss". Objects may be explicitly put in the small data area with the "section" attribute using one of these sections. -msdata=sdata Put small global and static data in the small data area, but do not generate special code to reference them. -msdata=use Put small global and static data in the small data area, and generate special instructions to reference them. -G num Put global and static objects less than or equal to num bytes into the small data or BSS sections instead of the normal data or BSS sections. The default value of num is 8. The -msdata option must be set to one of sdata or use for this option to have any effect. All modules should be compiled with the same -G num value. Compiling with different values of num may or may not work; if it doesn't the linker gives an error message---incorrect code is not generated. -mdebug Makes the M32R-specific code in the compiler display some statistics that might help in debugging programs. -malign-loops Align all loops to a 32-byte boundary. -mno-align-loops Do not enforce a 32-byte alignment for loops. This is the default. -missue-rate=number Issue number instructions per cycle. number can only be 1 or 2. -mbranch-cost=number number can only be 1 or 2. If it is 1 then branches are preferred over conditional code, if it is 2, then the opposite applies. -mflush-trap=number Specifies the trap number to use to flush the cache. The default is 12. Valid numbers are between 0 and 15 inclusive. -mno-flush-trap Specifies that the cache cannot be flushed by using a trap. -mflush-func=name Specifies the name of the operating system function to call to flush the cache. The default is _flush_cache, but a function call is only used if a trap is not available. -mno-flush-func Indicates that there is no OS function for flushing the cache. M680x0 Options These are the -m options defined for M680x0 and ColdFire processors. The default settings depend on which architecture was selected when the compiler was configured; the defaults for the most common choices are given below. -march=arch Generate code for a specific M680x0 or ColdFire instruction set architecture. Permissible values of arch for M680x0 architectures are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32. ColdFire architectures are selected according to Freescale's ISA classification and the permissible values are: isaa, isaaplus, isab and isac. GCC defines a macro "__mcfarch__" whenever it is generating code for a ColdFire target. The arch in this macro is one of the -march arguments given above. When used together, -march and -mtune select code that runs on a family of similar processors but that is optimized for a particular microarchitecture. -mcpu=cpu Generate code for a specific M680x0 or ColdFire processor. The M680x0 cpus are: 68000, 68010, 68020, 68030, 68040, 68060, 68302, 68332 and cpu32. The ColdFire cpus are given by the table below, which also classifies the CPUs into families: Family : -mcpu arguments 51 : 51 51ac 51ag 51cn 51em 51je 51jf 51jg 51jm 51mm 51qe 51qm 5206 : 5202 5204 5206 5206e : 5206e 5208 : 5207 5208 5211a : 5210a 5211a 5213 : 5211 5212 5213 5216 : 5214 5216 52235 : 52230 52231 52232 52233 52234 52235 5225 : 5224 5225 52259 : 52252 52254 52255 52256 52258 52259 5235 : 5232 5233 5234 5235 523x 5249 : 5249 5250 : 5250 5271 : 5270 5271 5272 : 5272 5275 : 5274 5275 5282 : 5280 5281 5282 528x 53017 : 53011 53012 53013 53014 53015 53016 53017 5307 : 5307 5329 : 5327 5328 5329 532x 5373 : 5372 5373 537x 5407 : 5407 5475 : 5470 5471 5472 5473 5474 5475 547x 5480 5481 5482 5483 5484 5485 -mcpu=cpu overrides -march=arch if arch is compatible with cpu. Other combinations of -mcpu and -march are rejected. GCC defines the macro "__mcf_cpu_cpu" when ColdFire target cpu is selected. It also defines "__mcf_family_family", where the value of family is given by the table above. -mtune=tune Tune the code for a particular microarchitecture within the constraints set by -march and -mcpu. The M680x0 microarchitectures are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32. The ColdFire microarchitectures are: cfv1, cfv2, cfv3, cfv4 and cfv4e. You can also use -mtune=68020-40 for code that needs to run relatively well on 68020, 68030 and 68040 targets. -mtune=68020-60 is similar but includes 68060 targets as well. These two options select the same tuning decisions as -m68020-40 and -m68020-60 respectively. GCC defines the macros "__mcarch" and "__mcarch__" when tuning for 680x0 architecture arch. It also defines "mcarch" unless either -ansi or a non-GNU -std option is used. If GCC is tuning for a range of architectures, as selected by -mtune=68020-40 or -mtune=68020-60, it defines the macros for every architecture in the range. GCC also defines the macro "__muarch__" when tuning for ColdFire microarchitecture uarch, where uarch is one of the arguments given above. -m68000 -mc68000 Generate output for a 68000. This is the default when the compiler is configured for 68000-based systems. It is equivalent to -march=68000. Use this option for microcontrollers with a 68000 or EC000 core, including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356. -m68010 Generate output for a 68010. This is the default when the compiler is configured for 68010-based systems. It is equivalent to -march=68010. -m68020 -mc68020 Generate output for a 68020. This is the default when the compiler is configured for 68020-based systems. It is equivalent to -march=68020. -m68030 Generate output for a 68030. This is the default when the compiler is configured for 68030-based systems. It is equivalent to -march=68030. -m68040 Generate output for a 68040. This is the default when the compiler is configured for 68040-based systems. It is equivalent to -march=68040. This option inhibits the use of 68881/68882 instructions that have to be emulated by software on the 68040. Use this option if your 68040 does not have code to emulate those instructions. -m68060 Generate output for a 68060. This is the default when the compiler is configured for 68060-based systems. It is equivalent to -march=68060. This option inhibits the use of 68020 and 68881/68882 instructions that have to be emulated by software on the 68060. Use this option if your 68060 does not have code to emulate those instructions. -mcpu32 Generate output for a CPU32. This is the default when the compiler is configured for CPU32-based systems. It is equivalent to -march=cpu32. Use this option for microcontrollers with a CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, 68336, 68340, 68341, 68349 and 68360. -m5200 Generate output for a 520X ColdFire CPU. This is the default when the compiler is configured for 520X-based systems. It is equivalent to -mcpu=5206, and is now deprecated in favor of that option. Use this option for microcontroller with a 5200 core, including the MCF5202, MCF5203, MCF5204 and MCF5206. -m5206e Generate output for a 5206e ColdFire CPU. The option is now deprecated in favor of the equivalent -mcpu=5206e. -m528x Generate output for a member of the ColdFire 528X family. The option is now deprecated in favor of the equivalent -mcpu=528x. -m5307 Generate output for a ColdFire 5307 CPU. The option is now deprecated in favor of the equivalent -mcpu=5307. -m5407 Generate output for a ColdFire 5407 CPU. The option is now deprecated in favor of the equivalent -mcpu=5407. -mcfv4e Generate output for a ColdFire V4e family CPU (e.g. 547x/548x). This includes use of hardware floating-point instructions. The option is equivalent to -mcpu=547x, and is now deprecated in favor of that option. -m68020-40 Generate output for a 68040, without using any of the new instructions. This results in code that can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The generated code does use the 68881 instructions that are emulated on the 68040. The option is equivalent to -march=68020 -mtune=68020-40. -m68020-60 Generate output for a 68060, without using any of the new instructions. This results in code that can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The generated code does use the 68881 instructions that are emulated on the 68060. The option is equivalent to -march=68020 -mtune=68020-60. -mhard-float -m68881 Generate floating-point instructions. This is the default for 68020 and above, and for ColdFire devices that have an FPU. It defines the macro "__HAVE_68881__" on M680x0 targets and "__mcffpu__" on ColdFire targets. -msoft-float Do not generate floating-point instructions; use library calls instead. This is the default for 68000, 68010, and 68832 targets. It is also the default for ColdFire devices that have no FPU. -mdiv -mno-div Generate (do not generate) ColdFire hardware divide and remainder instructions. If -march is used without -mcpu, the default is "on" for ColdFire architectures and "off" for M680x0 architectures. Otherwise, the default is taken from the target CPU (either the default CPU, or the one specified by -mcpu). For example, the default is "off" for -mcpu=5206 and "on" for -mcpu=5206e. GCC defines the macro "__mcfhwdiv__" when this option is enabled. -mshort Consider type "int" to be 16 bits wide, like "short int". Additionally, parameters passed on the stack are also aligned to a 16-bit boundary even on targets whose API mandates promotion to 32-bit. -mno-short Do not consider type "int" to be 16 bits wide. This is the default. -mnobitfield -mno-bitfield Do not use the bit-field instructions. The -m68000, -mcpu32 and -m5200 options imply -mnobitfield. -mbitfield Do use the bit-field instructions. The -m68020 option implies -mbitfield. This is the default if you use a configuration designed for a 68020. -mrtd Use a different function-calling convention, in which functions that take a fixed number of arguments return with the "rtd" instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no need to pop the arguments there. This calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. Also, you must provide function prototypes for all functions that take variable numbers of arguments (including "printf"); otherwise incorrect code is generated for calls to those functions. In addition, seriously incorrect code results if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.) The "rtd" instruction is supported by the 68010, 68020, 68030, 68040, 68060 and CPU32 processors, but not by the 68000 or 5200. The default is -mno-rtd. -malign-int -mno-align-int Control whether GCC aligns "int", "long", "long long", "float", "double", and "long double" variables on a 32-bit boundary (-malign-int) or a 16-bit boundary (-mno-align-int). Aligning variables on 32-bit boundaries produces code that runs somewhat faster on processors with 32-bit busses at the expense of more memory. Warning: if you use the -malign-int switch, GCC aligns structures containing the above types differently than most published application binary interface specifications for the m68k. Use the pc-relative addressing mode of the 68000 directly, instead of using a global offset table. At present, this option implies -fpic, allowing at most a 16-bit offset for pc-relative addressing. -fPIC is not presently supported with -mpcrel, though this could be supported for 68020 and higher processors. -mno-strict-align -mstrict-align Do not (do) assume that unaligned memory references are handled by the system. -msep-data Generate code that allows the data segment to be located in a different area of memory from the text segment. This allows for execute-in-place in an environment without virtual memory management. This option implies -fPIC. -mno-sep-data Generate code that assumes that the data segment follows the text segment. This is the default. -mid-shared-library Generate code that supports shared libraries via the library ID method. This allows for execute-in-place and shared libraries in an environment without virtual memory management. This option implies -fPIC. -mno-id-shared-library Generate code that doesn't assume ID-based shared libraries are being used. This is the default. -mshared-library-id=n Specifies the identification number of the ID-based shared library being compiled. Specifying a value of 0 generates more compact code; specifying other values forces the allocation of that number to the current library, but is no more space- or time-efficient than omitting this option. -mxgot -mno-xgot When generating position-independent code for ColdFire, generate code that works if the GOT has more than 8192 entries. This code is larger and slower than code generated without this option. On M680x0 processors, this option is not needed; -fPIC suffices. GCC normally uses a single instruction to load values from the GOT. While this is relatively efficient, it only works if the GOT is smaller than about 64k. Anything larger causes the linker to report an error such as: relocation truncated to fit: R_68K_GOT16O foobar If this happens, you should recompile your code with -mxgot. It should then work with very large GOTs. However, code generated with -mxgot is less efficient, since it takes 4 instructions to fetch the value of a global symbol. Note that some linkers, including newer versions of the GNU linker, can create multiple GOTs and sort GOT entries. If you have such a linker, you should only need to use -mxgot when compiling a single object file that accesses more than 8192 GOT entries. Very few do. These options have no effect unless GCC is generating position- independent code. -mlong-jump-table-offsets Use 32-bit offsets in "switch" tables. The default is to use 16-bit offsets. MCore Options These are the -m options defined for the Motorola M*Core processors. -mhardlit -mno-hardlit Inline constants into the code stream if it can be done in two instructions or less. -mdiv -mno-div Use the divide instruction. (Enabled by default). -mrelax-immediate -mno-relax-immediate Allow arbitrary-sized immediates in bit operations. -mwide-bitfields -mno-wide-bitfields Always treat bit-fields as "int"-sized. -m4byte-functions -mno-4byte-functions Force all functions to be aligned to a 4-byte boundary. -mcallgraph-data -mno-callgraph-data Emit callgraph information. -mslow-bytes -mno-slow-bytes Prefer word access when reading byte quantities. -mlittle-endian -mbig-endian Generate code for a little-endian target. -m210 -m340 Generate code for the 210 processor. -mno-lsim Assume that runtime support has been provided and so omit the simulator library (libsim.a) from the linker command line. -mstack-increment=size Set the maximum amount for a single stack increment operation. Large values can increase the speed of programs that contain functions that need a large amount of stack space, but they can also trigger a segmentation fault if the stack is extended too much. The default value is 0x1000. MicroBlaze Options -msoft-float Use software emulation for floating point (default). -mhard-float Use hardware floating-point instructions. -mmemcpy Do not optimize block moves, use "memcpy". -mno-clearbss This option is deprecated. Use -fno-zero-initialized-in-bss instead. -mcpu=cpu-type Use features of, and schedule code for, the given CPU. Supported values are in the format vX.YY.Z, where X is a major version, YY is the minor version, and Z is compatibility code. Example values are v3.00.a, v4.00.b, v5.00.a, v5.00.b, v6.00.a. -mxl-soft-mul Use software multiply emulation (default). -mxl-soft-div Use software emulation for divides (default). -mxl-barrel-shift Use the hardware barrel shifter. -mxl-pattern-compare Use pattern compare instructions. -msmall-divides Use table lookup optimization for small signed integer divisions. -mxl-stack-check This option is deprecated. Use -fstack-check instead. -mxl-gp-opt Use GP-relative ".sdata"/".sbss" sections. -mxl-multiply-high Use multiply high instructions for high part of 32x32 multiply. -mxl-float-convert Use hardware floating-point conversion instructions. -mxl-float-sqrt Use hardware floating-point square root instruction. -mbig-endian Generate code for a big-endian target. -mlittle-endian Generate code for a little-endian target. -mxl-reorder Use reorder instructions (swap and byte reversed load/store). -mxl-mode-app-model Select application model app-model. Valid models are executable normal executable (default), uses startup code crt0.o. xmdstub for use with Xilinx Microprocessor Debugger (XMD) based software intrusive debug agent called xmdstub. This uses startup file crt1.o and sets the start address of the program to 0x800. bootstrap for applications that are loaded using a bootloader. This model uses startup file crt2.o which does not contain a processor reset vector handler. This is suitable for transferring control on a processor reset to the bootloader rather than the application. novectors for applications that do not require any of the MicroBlaze vectors. This option may be useful for applications running within a monitoring application. This model uses crt3.o as a startup file. Option -xl-mode-app-model is a deprecated alias for -mxl-mode-app- model. -mpic-data-is-text-relative Assume that the displacement between the text and data segments is fixed at static link time. This allows data to be referenced by offset from start of text address instead of GOT since PC-relative addressing is not supported. MIPS Options -EB Generate big-endian code. -EL Generate little-endian code. This is the default for mips*el-*-* configurations. -march=arch Generate code that runs on arch, which can be the name of a generic MIPS ISA, or the name of a particular processor. The ISA names are: mips1, mips2, mips3, mips4, mips32, mips32r2, mips32r3, mips32r5, mips32r6, mips64, mips64r2, mips64r3, mips64r5 and mips64r6. The processor names are: 4kc, 4km, 4kp, 4ksc, 4kec, 4kem, 4kep, 4ksd, 5kc, 5kf, 20kc, 24kc, 24kf2_1, 24kf1_1, 24kec, 24kef2_1, 24kef1_1, 34kc, 34kf2_1, 34kf1_1, 34kn, 74kc, 74kf2_1, 74kf1_1, 74kf3_2, 1004kc, 1004kf2_1, 1004kf1_1, i6400, i6500, interaptiv, loongson2e, loongson2f, loongson3a, gs464, gs464e, gs264e, m4k, m14k, m14kc, m14ke, m14kec, m5100, m5101, octeon, octeon+, octeon2, octeon3, orion, p5600, p6600, r2000, r3000, r3900, r4000, r4400, r4600, r4650, r4700, r5900, r6000, r8000, rm7000, rm9000, r10000, r12000, r14000, r16000, sb1, sr71000, vr4100, vr4111, vr4120, vr4130, vr4300, vr5000, vr5400, vr5500, xlr and xlp. The special value from-abi selects the most compatible architecture for the selected ABI (that is, mips1 for 32-bit ABIs and mips3 for 64-bit ABIs). The native Linux/GNU toolchain also supports the value native, which selects the best architecture option for the host processor. -march=native has no effect if GCC does not recognize the processor. In processor names, a final 000 can be abbreviated as k (for example, -march=r2k). Prefixes are optional, and vr may be written r. Names of the form nf2_1 refer to processors with FPUs clocked at half the rate of the core, names of the form nf1_1 refer to processors with FPUs clocked at the same rate as the core, and names of the form nf3_2 refer to processors with FPUs clocked a ratio of 3:2 with respect to the core. For compatibility reasons, nf is accepted as a synonym for nf2_1 while nx and bfx are accepted as synonyms for nf1_1. GCC defines two macros based on the value of this option. The first is "_MIPS_ARCH", which gives the name of target architecture, as a string. The second has the form "_MIPS_ARCH_foo", where foo is the capitalized value of "_MIPS_ARCH". For example, -march=r2000 sets "_MIPS_ARCH" to "r2000" and defines the macro "_MIPS_ARCH_R2000". Note that the "_MIPS_ARCH" macro uses the processor names given above. In other words, it has the full prefix and does not abbreviate 000 as k. In the case of from-abi, the macro names the resolved architecture (either "mips1" or "mips3"). It names the default architecture when no -march option is given. -mtune=arch Optimize for arch. Among other things, this option controls the way instructions are scheduled, and the perceived cost of arithmetic operations. The list of arch values is the same as for -march. When this option is not used, GCC optimizes for the processor specified by -march. By using -march and -mtune together, it is possible to generate code that runs on a family of processors, but optimize the code for one particular member of that family. -mtune defines the macros "_MIPS_TUNE" and "_MIPS_TUNE_foo", which work in the same way as the -march ones described above. -mips1 Equivalent to -march=mips1. -mips2 Equivalent to -march=mips2. -mips3 Equivalent to -march=mips3. -mips4 Equivalent to -march=mips4. -mips32 Equivalent to -march=mips32. -mips32r3 Equivalent to -march=mips32r3. -mips32r5 Equivalent to -march=mips32r5. -mips32r6 Equivalent to -march=mips32r6. -mips64 Equivalent to -march=mips64. -mips64r2 Equivalent to -march=mips64r2. -mips64r3 Equivalent to -march=mips64r3. -mips64r5 Equivalent to -march=mips64r5. -mips64r6 Equivalent to -march=mips64r6. -mips16 -mno-mips16 Generate (do not generate) MIPS16 code. If GCC is targeting a MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE. MIPS16 code generation can also be controlled on a per-function basis by means of "mips16" and "nomips16" attributes. -mflip-mips16 Generate MIPS16 code on alternating functions. This option is provided for regression testing of mixed MIPS16/non-MIPS16 code generation, and is not intended for ordinary use in compiling user code. -minterlink-compressed -mno-interlink-compressed Require (do not require) that code using the standard (uncompressed) MIPS ISA be link-compatible with MIPS16 and microMIPS code, and vice versa. For example, code using the standard ISA encoding cannot jump directly to MIPS16 or microMIPS code; it must either use a call or an indirect jump. -minterlink-compressed therefore disables direct jumps unless GCC knows that the target of the jump is not compressed. -minterlink-mips16 -mno-interlink-mips16 Aliases of -minterlink-compressed and -mno-interlink-compressed. These options predate the microMIPS ASE and are retained for backwards compatibility. -mabi=32 -mabi=o64 -mabi=n32 -mabi=64 -mabi=eabi Generate code for the given ABI. Note that the EABI has a 32-bit and a 64-bit variant. GCC normally generates 64-bit code when you select a 64-bit architecture, but you can use -mgp32 to get 32-bit code instead. For information about the O64 ABI, see <https://gcc.gnu.org/projects/mipso64-abi.html>. GCC supports a variant of the o32 ABI in which floating-point registers are 64 rather than 32 bits wide. You can select this combination with -mabi=32 -mfp64. This ABI relies on the "mthc1" and "mfhc1" instructions and is therefore only supported for MIPS32R2, MIPS32R3 and MIPS32R5 processors. The register assignments for arguments and return values remain the same, but each scalar value is passed in a single 64-bit register rather than a pair of 32-bit registers. For example, scalar floating-point values are returned in $f0 only, not a $f0/$f1 pair. The set of call-saved registers also remains the same in that the even-numbered double-precision registers are saved. Two additional variants of the o32 ABI are supported to enable a transition from 32-bit to 64-bit registers. These are FPXX (-mfpxx) and FP64A (-mfp64 -mno-odd-spreg). The FPXX extension mandates that all code must execute correctly when run using 32-bit or 64-bit registers. The code can be interlinked with either FP32 or FP64, but not both. The FP64A extension is similar to the FP64 extension but forbids the use of odd-numbered single-precision registers. This can be used in conjunction with the "FRE" mode of FPUs in MIPS32R5 processors and allows both FP32 and FP64A code to interlink and run in the same process without changing FPU modes. -mabicalls -mno-abicalls Generate (do not generate) code that is suitable for SVR4-style dynamic objects. -mabicalls is the default for SVR4-based systems. -mshared -mno-shared Generate (do not generate) code that is fully position-independent, and that can therefore be linked into shared libraries. This option only affects -mabicalls. All -mabicalls code has traditionally been position-independent, regardless of options like -fPIC and -fpic. However, as an extension, the GNU toolchain allows executables to use absolute accesses for locally-binding symbols. It can also use shorter GP initialization sequences and generate direct calls to locally- defined functions. This mode is selected by -mno-shared. -mno-shared depends on binutils 2.16 or higher and generates objects that can only be linked by the GNU linker. However, the option does not affect the ABI of the final executable; it only affects the ABI of relocatable objects. Using -mno-shared generally makes executables both smaller and quicker. -mshared is the default. -mplt -mno-plt Assume (do not assume) that the static and dynamic linkers support PLTs and copy relocations. This option only affects -mno-shared -mabicalls. For the n64 ABI, this option has no effect without -msym32. You can make -mplt the default by configuring GCC with --with-mips-plt. The default is -mno-plt otherwise. -mxgot -mno-xgot Lift (do not lift) the usual restrictions on the size of the global offset table. GCC normally uses a single instruction to load values from the GOT. While this is relatively efficient, it only works if the GOT is smaller than about 64k. Anything larger causes the linker to report an error such as: relocation truncated to fit: R_MIPS_GOT16 foobar If this happens, you should recompile your code with -mxgot. This works with very large GOTs, although the code is also less efficient, since it takes three instructions to fetch the value of a global symbol. Note that some linkers can create multiple GOTs. If you have such a linker, you should only need to use -mxgot when a single object file accesses more than 64k's worth of GOT entries. Very few do. These options have no effect unless GCC is generating position independent code. -mgp32 Assume that general-purpose registers are 32 bits wide. -mgp64 Assume that general-purpose registers are 64 bits wide. -mfp32 Assume that floating-point registers are 32 bits wide. -mfp64 Assume that floating-point registers are 64 bits wide. -mfpxx Do not assume the width of floating-point registers. -mhard-float Use floating-point coprocessor instructions. -msoft-float Do not use floating-point coprocessor instructions. Implement floating-point calculations using library calls instead. -mno-float Equivalent to -msoft-float, but additionally asserts that the program being compiled does not perform any floating-point operations. This option is presently supported only by some bare- metal MIPS configurations, where it may select a special set of libraries that lack all floating-point support (including, for example, the floating-point "printf" formats). If code compiled with -mno-float accidentally contains floating-point operations, it is likely to suffer a link-time or run-time failure. -msingle-float Assume that the floating-point coprocessor only supports single- precision operations. -mdouble-float Assume that the floating-point coprocessor supports double- precision operations. This is the default. -modd-spreg -mno-odd-spreg Enable the use of odd-numbered single-precision floating-point registers for the o32 ABI. This is the default for processors that are known to support these registers. When using the o32 FPXX ABI, -mno-odd-spreg is set by default. -mabs=2008 -mabs=legacy These options control the treatment of the special not-a-number (NaN) IEEE 754 floating-point data with the "abs.fmt" and "neg.fmt" machine instructions. By default or when -mabs=legacy is used the legacy treatment is selected. In this case these instructions are considered arithmetic and avoided where correct operation is required and the input operand might be a NaN. A longer sequence of instructions that manipulate the sign bit of floating-point datum manually is used instead unless the -ffinite-math-only option has also been specified. The -mabs=2008 option selects the IEEE 754-2008 treatment. In this case these instructions are considered non-arithmetic and therefore operating correctly in all cases, including in particular where the input operand is a NaN. These instructions are therefore always used for the respective operations. -mnan=2008 -mnan=legacy These options control the encoding of the special not-a-number (NaN) IEEE 754 floating-point data. The -mnan=legacy option selects the legacy encoding. In this case quiet NaNs (qNaNs) are denoted by the first bit of their trailing significand field being 0, whereas signaling NaNs (sNaNs) are denoted by the first bit of their trailing significand field being 1. The -mnan=2008 option selects the IEEE 754-2008 encoding. In this case qNaNs are denoted by the first bit of their trailing significand field being 1, whereas sNaNs are denoted by the first bit of their trailing significand field being 0. The default is -mnan=legacy unless GCC has been configured with --with-nan=2008. -mllsc -mno-llsc Use (do not use) ll, sc, and sync instructions to implement atomic memory built-in functions. When neither option is specified, GCC uses the instructions if the target architecture supports them. -mllsc is useful if the runtime environment can emulate the instructions and -mno-llsc can be useful when compiling for nonstandard ISAs. You can make either option the default by configuring GCC with --with-llsc and --without-llsc respectively. --with-llsc is the default for some configurations; see the installation documentation for details. -mdsp -mno-dsp Use (do not use) revision 1 of the MIPS DSP ASE. This option defines the preprocessor macro "__mips_dsp". It also defines "__mips_dsp_rev" to 1. -mdspr2 -mno-dspr2 Use (do not use) revision 2 of the MIPS DSP ASE. This option defines the preprocessor macros "__mips_dsp" and "__mips_dspr2". It also defines "__mips_dsp_rev" to 2. -msmartmips -mno-smartmips Use (do not use) the MIPS SmartMIPS ASE. -mpaired-single -mno-paired-single Use (do not use) paired-single floating-point instructions. This option requires hardware floating-point support to be enabled. -mdmx -mno-mdmx Use (do not use) MIPS Digital Media Extension instructions. This option can only be used when generating 64-bit code and requires hardware floating-point support to be enabled. -mips3d -mno-mips3d Use (do not use) the MIPS-3D ASE. The option -mips3d implies -mpaired-single. -mmicromips -mno-micromips Generate (do not generate) microMIPS code. MicroMIPS code generation can also be controlled on a per-function basis by means of "micromips" and "nomicromips" attributes. -mmt -mno-mt Use (do not use) MT Multithreading instructions. -mmcu -mno-mcu Use (do not use) the MIPS MCU ASE instructions. -meva -mno-eva Use (do not use) the MIPS Enhanced Virtual Addressing instructions. -mvirt -mno-virt Use (do not use) the MIPS Virtualization (VZ) instructions. -mxpa -mno-xpa Use (do not use) the MIPS eXtended Physical Address (XPA) instructions. -mcrc -mno-crc Use (do not use) the MIPS Cyclic Redundancy Check (CRC) instructions. -mginv -mno-ginv Use (do not use) the MIPS Global INValidate (GINV) instructions. -mloongson-mmi -mno-loongson-mmi Use (do not use) the MIPS Loongson MultiMedia extensions Instructions (MMI). -mloongson-ext -mno-loongson-ext Use (do not use) the MIPS Loongson EXTensions (EXT) instructions. -mloongson-ext2 -mno-loongson-ext2 Use (do not use) the MIPS Loongson EXTensions r2 (EXT2) instructions. -mlong64 Force "long" types to be 64 bits wide. See -mlong32 for an explanation of the default and the way that the pointer size is determined. -mlong32 Force "long", "int", and pointer types to be 32 bits wide. The default size of "int"s, "long"s and pointers depends on the ABI. All the supported ABIs use 32-bit "int"s. The n64 ABI uses 64-bit "long"s, as does the 64-bit EABI; the others use 32-bit "long"s. Pointers are the same size as "long"s, or the same size as integer registers, whichever is smaller. -msym32 -mno-sym32 Assume (do not assume) that all symbols have 32-bit values, regardless of the selected ABI. This option is useful in combination with -mabi=64 and -mno-abicalls because it allows GCC to generate shorter and faster references to symbolic addresses. -G num Put definitions of externally-visible data in a small data section if that data is no bigger than num bytes. GCC can then generate more efficient accesses to the data; see -mgpopt for details. The default -G option depends on the configuration. -mlocal-sdata -mno-local-sdata Extend (do not extend) the -G behavior to local data too, such as to static variables in C. -mlocal-sdata is the default for all configurations. If the linker complains that an application is using too much small data, you might want to try rebuilding the less performance- critical parts with -mno-local-sdata. You might also want to build large libraries with -mno-local-sdata, so that the libraries leave more room for the main program. -mextern-sdata -mno-extern-sdata Assume (do not assume) that externally-defined data is in a small data section if the size of that data is within the -G limit. -mextern-sdata is the default for all configurations. If you compile a module Mod with -mextern-sdata -G num -mgpopt, and Mod references a variable Var that is no bigger than num bytes, you must make sure that Var is placed in a small data section. If Var is defined by another module, you must either compile that module with a high-enough -G setting or attach a "section" attribute to Var's definition. If Var is common, you must link the application with a high-enough -G setting. The easiest way of satisfying these restrictions is to compile and link every module with the same -G option. However, you may wish to build a library that supports several different small data limits. You can do this by compiling the library with the highest supported -G setting and additionally using -mno-extern-sdata to stop the library from making assumptions about externally-defined data. -mgpopt -mno-gpopt Use (do not use) GP-relative accesses for symbols that are known to be in a small data section; see -G, -mlocal-sdata and -mextern-sdata. -mgpopt is the default for all configurations. -mno-gpopt is useful for cases where the $gp register might not hold the value of "_gp". For example, if the code is part of a library that might be used in a boot monitor, programs that call boot monitor routines pass an unknown value in $gp. (In such situations, the boot monitor itself is usually compiled with -G0.) -mno-gpopt implies -mno-local-sdata and -mno-extern-sdata. -membedded-data -mno-embedded-data Allocate variables to the read-only data section first if possible, then next in the small data section if possible, otherwise in data. This gives slightly slower code than the default, but reduces the amount of RAM required when executing, and thus may be preferred for some embedded systems. -muninit-const-in-rodata -mno-uninit-const-in-rodata Put uninitialized "const" variables in the read-only data section. This option is only meaningful in conjunction with -membedded-data. -mcode-readable=setting Specify whether GCC may generate code that reads from executable sections. There are three possible settings: -mcode-readable=yes Instructions may freely access executable sections. This is the default setting. -mcode-readable=pcrel MIPS16 PC-relative load instructions can access executable sections, but other instructions must not do so. This option is useful on 4KSc and 4KSd processors when the code TLBs have the Read Inhibit bit set. It is also useful on processors that can be configured to have a dual instruction/data SRAM interface and that, like the M4K, automatically redirect PC- relative loads to the instruction RAM. -mcode-readable=no Instructions must not access executable sections. This option can be useful on targets that are configured to have a dual instruction/data SRAM interface but that (unlike the M4K) do not automatically redirect PC-relative loads to the instruction RAM. -msplit-addresses -mno-split-addresses Enable (disable) use of the "%hi()" and "%lo()" assembler relocation operators. This option has been superseded by -mexplicit-relocs but is retained for backwards compatibility. -mexplicit-relocs -mno-explicit-relocs Use (do not use) assembler relocation operators when dealing with symbolic addresses. The alternative, selected by -mno-explicit-relocs, is to use assembler macros instead. -mexplicit-relocs is the default if GCC was configured to use an assembler that supports relocation operators. -mcheck-zero-division -mno-check-zero-division Trap (do not trap) on integer division by zero. The default is -mcheck-zero-division. -mdivide-traps -mdivide-breaks MIPS systems check for division by zero by generating either a conditional trap or a break instruction. Using traps results in smaller code, but is only supported on MIPS II and later. Also, some versions of the Linux kernel have a bug that prevents trap from generating the proper signal ("SIGFPE"). Use -mdivide-traps to allow conditional traps on architectures that support them and -mdivide-breaks to force the use of breaks. The default is usually -mdivide-traps, but this can be overridden at configure time using --with-divide=breaks. Divide-by-zero checks can be completely disabled using -mno-check-zero-division. -mload-store-pairs -mno-load-store-pairs Enable (disable) an optimization that pairs consecutive load or store instructions to enable load/store bonding. This option is enabled by default but only takes effect when the selected architecture is known to support bonding. -munaligned-access -mno-unaligned-access Enable (disable) direct unaligned access for MIPS Release 6. MIPSr6 requires load/store unaligned-access support, by hardware or trap&emulate. So -mno-unaligned-access may be needed by kernel. -mmemcpy -mno-memcpy Force (do not force) the use of "memcpy" for non-trivial block moves. The default is -mno-memcpy, which allows GCC to inline most constant-sized copies. -mlong-calls -mno-long-calls Disable (do not disable) use of the "jal" instruction. Calling functions using "jal" is more efficient but requires the caller and callee to be in the same 256 megabyte segment. This option has no effect on abicalls code. The default is -mno-long-calls. -mmad -mno-mad Enable (disable) use of the "mad", "madu" and "mul" instructions, as provided by the R4650 ISA. -mimadd -mno-imadd Enable (disable) use of the "madd" and "msub" integer instructions. The default is -mimadd on architectures that support "madd" and "msub" except for the 74k architecture where it was found to generate slower code. -mfused-madd -mno-fused-madd Enable (disable) use of the floating-point multiply-accumulate instructions, when they are available. The default is -mfused-madd. On the R8000 CPU when multiply-accumulate instructions are used, the intermediate product is calculated to infinite precision and is not subject to the FCSR Flush to Zero bit. This may be undesirable in some circumstances. On other processors the result is numerically identical to the equivalent computation using separate multiply, add, subtract and negate instructions. -nocpp Tell the MIPS assembler to not run its preprocessor over user assembler files (with a .s suffix) when assembling them. -mfix-24k -mno-fix-24k Work around the 24K E48 (lost data on stores during refill) errata. The workarounds are implemented by the assembler rather than by GCC. -mfix-r4000 -mno-fix-r4000 Work around certain R4000 CPU errata: - A double-word or a variable shift may give an incorrect result if executed immediately after starting an integer division. - A double-word or a variable shift may give an incorrect result if executed while an integer multiplication is in progress. - An integer division may give an incorrect result if started in a delay slot of a taken branch or a jump. -mfix-r4400 -mno-fix-r4400 Work around certain R4400 CPU errata: - A double-word or a variable shift may give an incorrect result if executed immediately after starting an integer division. -mfix-r10000 -mno-fix-r10000 Work around certain R10000 errata: - "ll"/"sc" sequences may not behave atomically on revisions prior to 3.0. They may deadlock on revisions 2.6 and earlier. This option can only be used if the target architecture supports branch-likely instructions. -mfix-r10000 is the default when -march=r10000 is used; -mno-fix-r10000 is the default otherwise. -mfix-r5900 -mno-fix-r5900 Do not attempt to schedule the preceding instruction into the delay slot of a branch instruction placed at the end of a short loop of six instructions or fewer and always schedule a "nop" instruction there instead. The short loop bug under certain conditions causes loops to execute only once or twice, due to a hardware bug in the R5900 chip. The workaround is implemented by the assembler rather than by GCC. -mfix-rm7000 -mno-fix-rm7000 Work around the RM7000 "dmult"/"dmultu" errata. The workarounds are implemented by the assembler rather than by GCC. -mfix-vr4120 -mno-fix-vr4120 Work around certain VR4120 errata: - "dmultu" does not always produce the correct result. - "div" and "ddiv" do not always produce the correct result if one of the operands is negative. The workarounds for the division errata rely on special functions in libgcc.a. At present, these functions are only provided by the "mips64vr*-elf" configurations. Other VR4120 errata require a NOP to be inserted between certain pairs of instructions. These errata are handled by the assembler, not by GCC itself. -mfix-vr4130 Work around the VR4130 "mflo"/"mfhi" errata. The workarounds are implemented by the assembler rather than by GCC, although GCC avoids using "mflo" and "mfhi" if the VR4130 "macc", "macchi", "dmacc" and "dmacchi" instructions are available instead. -mfix-sb1 -mno-fix-sb1 Work around certain SB-1 CPU core errata. (This flag currently works around the SB-1 revision 2 "F1" and "F2" floating-point errata.) -mr10k-cache-barrier=setting Specify whether GCC should insert cache barriers to avoid the side effects of speculation on R10K processors. In common with many processors, the R10K tries to predict the outcome of a conditional branch and speculatively executes instructions from the "taken" branch. It later aborts these instructions if the predicted outcome is wrong. However, on the R10K, even aborted instructions can have side effects. This problem only affects kernel stores and, depending on the system, kernel loads. As an example, a speculatively-executed store may load the target memory into cache and mark the cache line as dirty, even if the store itself is later aborted. If a DMA operation writes to the same area of memory before the "dirty" line is flushed, the cached data overwrites the DMA-ed data. See the R10K processor manual for a full description, including other potential problems. One workaround is to insert cache barrier instructions before every memory access that might be speculatively executed and that might have side effects even if aborted. -mr10k-cache-barrier=setting controls GCC's implementation of this workaround. It assumes that aborted accesses to any byte in the following regions does not have side effects: 1. the memory occupied by the current function's stack frame; 2. the memory occupied by an incoming stack argument; 3. the memory occupied by an object with a link-time-constant address. It is the kernel's responsibility to ensure that speculative accesses to these regions are indeed safe. If the input program contains a function declaration such as: void foo (void); then the implementation of "foo" must allow "j foo" and "jal foo" to be executed speculatively. GCC honors this restriction for functions it compiles itself. It expects non-GCC functions (such as hand-written assembly code) to do the same. The option has three forms: -mr10k-cache-barrier=load-store Insert a cache barrier before a load or store that might be speculatively executed and that might have side effects even if aborted. -mr10k-cache-barrier=store Insert a cache barrier before a store that might be speculatively executed and that might have side effects even if aborted. -mr10k-cache-barrier=none Disable the insertion of cache barriers. This is the default setting. -mflush-func=func -mno-flush-func Specifies the function to call to flush the I and D caches, or to not call any such function. If called, the function must take the same arguments as the common "_flush_func", that is, the address of the memory range for which the cache is being flushed, the size of the memory range, and the number 3 (to flush both caches). The default depends on the target GCC was configured for, but commonly is either "_flush_func" or "__cpu_flush". mbranch-cost=num Set the cost of branches to roughly num "simple" instructions. This cost is only a heuristic and is not guaranteed to produce consistent results across releases. A zero cost redundantly selects the default, which is based on the -mtune setting. -mbranch-likely -mno-branch-likely Enable or disable use of Branch Likely instructions, regardless of the default for the selected architecture. By default, Branch Likely instructions may be generated if they are supported by the selected architecture. An exception is for the MIPS32 and MIPS64 architectures and processors that implement those architectures; for those, Branch Likely instructions are not be generated by default because the MIPS32 and MIPS64 architectures specifically deprecate their use. -mcompact-branches=never -mcompact-branches=optimal -mcompact-branches=always These options control which form of branches will be generated. The default is -mcompact-branches=optimal. The -mcompact-branches=never option ensures that compact branch instructions will never be generated. The -mcompact-branches=always option ensures that a compact branch instruction will be generated if available for MIPS Release 6 onwards. If a compact branch instruction is not available (or pre-R6), a delay slot form of the branch will be used instead. If it is used for MIPS16/microMIPS targets, it will be just ignored now. The behaviour for MIPS16/microMIPS may change in future, since they do have some compact branch instructions. The -mcompact-branches=optimal option will cause a delay slot branch to be used if one is available in the current ISA and the delay slot is successfully filled. If the delay slot is not filled, a compact branch will be chosen if one is available. -mfp-exceptions -mno-fp-exceptions Specifies whether FP exceptions are enabled. This affects how FP instructions are scheduled for some processors. The default is that FP exceptions are enabled. For instance, on the SB-1, if FP exceptions are disabled, and we are emitting 64-bit code, then we can use both FP pipes. Otherwise, we can only use one FP pipe. -mvr4130-align -mno-vr4130-align The VR4130 pipeline is two-way superscalar, but can only issue two instructions together if the first one is 8-byte aligned. When this option is enabled, GCC aligns pairs of instructions that it thinks should execute in parallel. This option only has an effect when optimizing for the VR4130. It normally makes code faster, but at the expense of making it bigger. It is enabled by default at optimization level -O3. -msynci -mno-synci Enable (disable) generation of "synci" instructions on architectures that support it. The "synci" instructions (if enabled) are generated when "__builtin___clear_cache" is compiled. This option defaults to -mno-synci, but the default can be overridden by configuring GCC with --with-synci. When compiling code for single processor systems, it is generally safe to use "synci". However, on many multi-core (SMP) systems, it does not invalidate the instruction caches on all cores and may lead to undefined behavior. -mrelax-pic-calls -mno-relax-pic-calls Try to turn PIC calls that are normally dispatched via register $25 into direct calls. This is only possible if the linker can resolve the destination at link time and if the destination is within range for a direct call. -mrelax-pic-calls is the default if GCC was configured to use an assembler and a linker that support the ".reloc" assembly directive and -mexplicit-relocs is in effect. With -mno-explicit-relocs, this optimization can be performed by the assembler and the linker alone without help from the compiler. -mmcount-ra-address -mno-mcount-ra-address Emit (do not emit) code that allows "_mcount" to modify the calling function's return address. When enabled, this option extends the usual "_mcount" interface with a new ra-address parameter, which has type "intptr_t *" and is passed in register $12. "_mcount" can then modify the return address by doing both of the following: * Returning the new address in register $31. * Storing the new address in "*ra-address", if ra-address is nonnull. The default is -mno-mcount-ra-address. -mframe-header-opt -mno-frame-header-opt Enable (disable) frame header optimization in the o32 ABI. When using the o32 ABI, calling functions will allocate 16 bytes on the stack for the called function to write out register arguments. When enabled, this optimization will suppress the allocation of the frame header if it can be determined that it is unused. This optimization is off by default at all optimization levels. -mlxc1-sxc1 -mno-lxc1-sxc1 When applicable, enable (disable) the generation of "lwxc1", "swxc1", "ldxc1", "sdxc1" instructions. Enabled by default. -mmadd4 -mno-madd4 When applicable, enable (disable) the generation of 4-operand "madd.s", "madd.d" and related instructions. Enabled by default. MMIX Options These options are defined for the MMIX: -mlibfuncs -mno-libfuncs Specify that intrinsic library functions are being compiled, passing all values in registers, no matter the size. -mepsilon -mno-epsilon Generate floating-point comparison instructions that compare with respect to the "rE" epsilon register. -mabi=mmixware -mabi=gnu Generate code that passes function parameters and return values that (in the called function) are seen as registers $0 and up, as opposed to the GNU ABI which uses global registers $231 and up. -mzero-extend -mno-zero-extend When reading data from memory in sizes shorter than 64 bits, use (do not use) zero-extending load instructions by default, rather than sign-extending ones. -mknuthdiv -mno-knuthdiv Make the result of a division yielding a remainder have the same sign as the divisor. With the default, -mno-knuthdiv, the sign of the remainder follows the sign of the dividend. Both methods are arithmetically valid, the latter being almost exclusively used. -mtoplevel-symbols -mno-toplevel-symbols Prepend (do not prepend) a : to all global symbols, so the assembly code can be used with the "PREFIX" assembly directive. -melf Generate an executable in the ELF format, rather than the default mmo format used by the mmix simulator. -mbranch-predict -mno-branch-predict Use (do not use) the probable-branch instructions, when static branch prediction indicates a probable branch. -mbase-addresses -mno-base-addresses Generate (do not generate) code that uses base addresses. Using a base address automatically generates a request (handled by the assembler and the linker) for a constant to be set up in a global register. The register is used for one or more base address requests within the range 0 to 255 from the value held in the register. The generally leads to short and fast code, but the number of different data items that can be addressed is limited. This means that a program that uses lots of static data may require -mno-base-addresses. -msingle-exit -mno-single-exit Force (do not force) generated code to have a single exit point in each function. MN10300 Options These -m options are defined for Matsushita MN10300 architectures: -mmult-bug Generate code to avoid bugs in the multiply instructions for the MN10300 processors. This is the default. -mno-mult-bug Do not generate code to avoid bugs in the multiply instructions for the MN10300 processors. -mam33 Generate code using features specific to the AM33 processor. -mno-am33 Do not generate code using features specific to the AM33 processor. This is the default. -mam33-2 Generate code using features specific to the AM33/2.0 processor. -mam34 Generate code using features specific to the AM34 processor. -mtune=cpu-type Use the timing characteristics of the indicated CPU type when scheduling instructions. This does not change the targeted processor type. The CPU type must be one of mn10300, am33, am33-2 or am34. -mreturn-pointer-on-d0 When generating a function that returns a pointer, return the pointer in both "a0" and "d0". Otherwise, the pointer is returned only in "a0", and attempts to call such functions without a prototype result in errors. Note that this option is on by default; use -mno-return-pointer-on-d0 to disable it. -mno-crt0 Do not link in the C run-time initialization object file. -mrelax Indicate to the linker that it should perform a relaxation optimization pass to shorten branches, calls and absolute memory addresses. This option only has an effect when used on the command line for the final link step. This option makes symbolic debugging impossible. -mliw Allow the compiler to generate Long Instruction Word instructions if the target is the AM33 or later. This is the default. This option defines the preprocessor macro "__LIW__". -mno-liw Do not allow the compiler to generate Long Instruction Word instructions. This option defines the preprocessor macro "__NO_LIW__". -msetlb Allow the compiler to generate the SETLB and Lcc instructions if the target is the AM33 or later. This is the default. This option defines the preprocessor macro "__SETLB__". -mno-setlb Do not allow the compiler to generate SETLB or Lcc instructions. This option defines the preprocessor macro "__NO_SETLB__". Moxie Options -meb Generate big-endian code. This is the default for moxie-*-* configurations. -mel Generate little-endian code. -mmul.x Generate mul.x and umul.x instructions. This is the default for moxiebox-*-* configurations. -mno-crt0 Do not link in the C run-time initialization object file. MSP430 Options These options are defined for the MSP430: -masm-hex Force assembly output to always use hex constants. Normally such constants are signed decimals, but this option is available for testsuite and/or aesthetic purposes. -mmcu= Select the MCU to target. This is used to create a C preprocessor symbol based upon the MCU name, converted to upper case and pre- and post-fixed with __. This in turn is used by the msp430.h header file to select an MCU-specific supplementary header file. The option also sets the ISA to use. If the MCU name is one that is known to only support the 430 ISA then that is selected, otherwise the 430X ISA is selected. A generic MCU name of msp430 can also be used to select the 430 ISA. Similarly the generic msp430x MCU name selects the 430X ISA. In addition an MCU-specific linker script is added to the linker command line. The script's name is the name of the MCU with .ld appended. Thus specifying -mmcu=xxx on the gcc command line defines the C preprocessor symbol "__XXX__" and cause the linker to search for a script called xxx.ld. The ISA and hardware multiply supported for the different MCUs is hard-coded into GCC. However, an external devices.csv file can be used to extend device support beyond those that have been hard- coded. GCC searches for the devices.csv file using the following methods in the given precedence order, where the first method takes precendence over the second which takes precedence over the third. Include path specified with "-I" and "-L" devices.csv will be searched for in each of the directories specified by include paths and linker library search paths. Path specified by the environment variable MSP430_GCC_INCLUDE_DIR Define the value of the global environment variable MSP430_GCC_INCLUDE_DIR to the full path to the directory containing devices.csv, and GCC will search this directory for devices.csv. If devices.csv is found, this directory will also be registered as an include path, and linker library path. Header files and linker scripts in this directory can therefore be used without manually specifying "-I" and "-L" on the command line. The msp430-elf{,bare}/include/devices directory Finally, GCC will examine msp430-elf{,bare}/include/devices from the toolchain root directory. This directory does not exist in a default installation, but if the user has created it and copied devices.csv there, then the MCU data will be read. As above, this directory will also be registered as an include path, and linker library path. If none of the above search methods find devices.csv, then the hard-coded MCU data is used. -mwarn-mcu -mno-warn-mcu This option enables or disables warnings about conflicts between the MCU name specified by the -mmcu option and the ISA set by the -mcpu option and/or the hardware multiply support set by the -mhwmult option. It also toggles warnings about unrecognized MCU names. This option is on by default. -mcpu= Specifies the ISA to use. Accepted values are msp430, msp430x and msp430xv2. This option is deprecated. The -mmcu= option should be used to select the ISA. -msim Link to the simulator runtime libraries and linker script. Overrides any scripts that would be selected by the -mmcu= option. -mlarge Use large-model addressing (20-bit pointers, 20-bit "size_t"). -msmall Use small-model addressing (16-bit pointers, 16-bit "size_t"). -mrelax This option is passed to the assembler and linker, and allows the linker to perform certain optimizations that cannot be done until the final link. mhwmult= Describes the type of hardware multiply supported by the target. Accepted values are none for no hardware multiply, 16bit for the original 16-bit-only multiply supported by early MCUs. 32bit for the 16/32-bit multiply supported by later MCUs and f5series for the 16/32-bit multiply supported by F5-series MCUs. A value of auto can also be given. This tells GCC to deduce the hardware multiply support based upon the MCU name provided by the -mmcu option. If no -mmcu option is specified or if the MCU name is not recognized then no hardware multiply support is assumed. "auto" is the default setting. Hardware multiplies are normally performed by calling a library routine. This saves space in the generated code. When compiling at -O3 or higher however the hardware multiplier is invoked inline. This makes for bigger, but faster code. The hardware multiply routines disable interrupts whilst running and restore the previous interrupt state when they finish. This makes them safe to use inside interrupt handlers as well as in normal code. -minrt Enable the use of a minimum runtime environment - no static initializers or constructors. This is intended for memory- constrained devices. The compiler includes special symbols in some objects that tell the linker and runtime which code fragments are required. -mtiny-printf Enable reduced code size "printf" and "puts" library functions. The tiny implementations of these functions are not reentrant, so must be used with caution in multi-threaded applications. Support for streams has been removed and the string to be printed will always be sent to stdout via the "write" syscall. The string is not buffered before it is sent to write. This option requires Newlib Nano IO, so GCC must be configured with --enable-newlib-nano-formatted-io. -mmax-inline-shift= This option takes an integer between 0 and 64 inclusive, and sets the maximum number of inline shift instructions which should be emitted to perform a shift operation by a constant amount. When this value needs to be exceeded, an mspabi helper function is used instead. The default value is 4. This only affects cases where a shift by multiple positions cannot be completed with a single instruction (e.g. all shifts >1 on the 430 ISA). Shifts of a 32-bit value are at least twice as costly, so the value passed for this option is divided by 2 and the resulting value used instead. -mcode-region= -mdata-region= These options tell the compiler where to place functions and data that do not have one of the "lower", "upper", "either" or "section" attributes. Possible values are "lower", "upper", "either" or "any". The first three behave like the corresponding attribute. The fourth possible value - "any" - is the default. It leaves placement entirely up to the linker script and how it assigns the standard sections (".text", ".data", etc) to the memory regions. -msilicon-errata= This option passes on a request to assembler to enable the fixes for the named silicon errata. -msilicon-errata-warn= This option passes on a request to the assembler to enable warning messages when a silicon errata might need to be applied. -mwarn-devices-csv -mno-warn-devices-csv Warn if devices.csv is not found or there are problem parsing it (default: on). NDS32 Options These options are defined for NDS32 implementations: -mbig-endian Generate code in big-endian mode. -mlittle-endian Generate code in little-endian mode. -mreduced-regs Use reduced-set registers for register allocation. -mfull-regs Use full-set registers for register allocation. -mcmov Generate conditional move instructions. -mno-cmov Do not generate conditional move instructions. -mext-perf Generate performance extension instructions. -mno-ext-perf Do not generate performance extension instructions. -mext-perf2 Generate performance extension 2 instructions. -mno-ext-perf2 Do not generate performance extension 2 instructions. -mext-string Generate string extension instructions. -mno-ext-string Do not generate string extension instructions. -mv3push Generate v3 push25/pop25 instructions. -mno-v3push Do not generate v3 push25/pop25 instructions. -m16-bit Generate 16-bit instructions. -mno-16-bit Do not generate 16-bit instructions. -misr-vector-size=num Specify the size of each interrupt vector, which must be 4 or 16. -mcache-block-size=num Specify the size of each cache block, which must be a power of 2 between 4 and 512. -march=arch Specify the name of the target architecture. -mcmodel=code-model Set the code model to one of small All the data and read-only data segments must be within 512KB addressing space. The text segment must be within 16MB addressing space. medium The data segment must be within 512KB while the read-only data segment can be within 4GB addressing space. The text segment should be still within 16MB addressing space. large All the text and data segments can be within 4GB addressing space. -mctor-dtor Enable constructor/destructor feature. -mrelax Guide linker to relax instructions. Nios II Options These are the options defined for the Altera Nios II processor. -G num Put global and static objects less than or equal to num bytes into the small data or BSS sections instead of the normal data or BSS sections. The default value of num is 8. -mgpopt=option -mgpopt -mno-gpopt Generate (do not generate) GP-relative accesses. The following option names are recognized: none Do not generate GP-relative accesses. local Generate GP-relative accesses for small data objects that are not external, weak, or uninitialized common symbols. Also use GP-relative addressing for objects that have been explicitly placed in a small data section via a "section" attribute. global As for local, but also generate GP-relative accesses for small data objects that are external, weak, or common. If you use this option, you must ensure that all parts of your program (including libraries) are compiled with the same -G setting. data Generate GP-relative accesses for all data objects in the program. If you use this option, the entire data and BSS segments of your program must fit in 64K of memory and you must use an appropriate linker script to allocate them within the addressable range of the global pointer. all Generate GP-relative addresses for function pointers as well as data pointers. If you use this option, the entire text, data, and BSS segments of your program must fit in 64K of memory and you must use an appropriate linker script to allocate them within the addressable range of the global pointer. -mgpopt is equivalent to -mgpopt=local, and -mno-gpopt is equivalent to -mgpopt=none. The default is -mgpopt except when -fpic or -fPIC is specified to generate position-independent code. Note that the Nios II ABI does not permit GP-relative accesses from shared libraries. You may need to specify -mno-gpopt explicitly when building programs that include large amounts of small data, including large GOT data sections. In this case, the 16-bit offset for GP-relative addressing may not be large enough to allow access to the entire small data section. -mgprel-sec=regexp This option specifies additional section names that can be accessed via GP-relative addressing. It is most useful in conjunction with "section" attributes on variable declarations and a custom linker script. The regexp is a POSIX Extended Regular Expression. This option does not affect the behavior of the -G option, and the specified sections are in addition to the standard ".sdata" and ".sbss" small-data sections that are recognized by -mgpopt. -mr0rel-sec=regexp This option specifies names of sections that can be accessed via a 16-bit offset from "r0"; that is, in the low 32K or high 32K of the 32-bit address space. It is most useful in conjunction with "section" attributes on variable declarations and a custom linker script. The regexp is a POSIX Extended Regular Expression. In contrast to the use of GP-relative addressing for small data, zero-based addressing is never generated by default and there are no conventional section names used in standard linker scripts for sections in the low or high areas of memory. -mel -meb Generate little-endian (default) or big-endian (experimental) code, respectively. -march=arch This specifies the name of the target Nios II architecture. GCC uses this name to determine what kind of instructions it can emit when generating assembly code. Permissible names are: r1, r2. The preprocessor macro "__nios2_arch__" is available to programs, with value 1 or 2, indicating the targeted ISA level. -mbypass-cache -mno-bypass-cache Force all load and store instructions to always bypass cache by using I/O variants of the instructions. The default is not to bypass the cache. -mno-cache-volatile -mcache-volatile Volatile memory access bypass the cache using the I/O variants of the load and store instructions. The default is not to bypass the cache. -mno-fast-sw-div -mfast-sw-div Do not use table-based fast divide for small numbers. The default is to use the fast divide at -O3 and above. -mno-hw-mul -mhw-mul -mno-hw-mulx -mhw-mulx -mno-hw-div -mhw-div Enable or disable emitting "mul", "mulx" and "div" family of instructions by the compiler. The default is to emit "mul" and not emit "div" and "mulx". -mbmx -mno-bmx -mcdx -mno-cdx Enable or disable generation of Nios II R2 BMX (bit manipulation) and CDX (code density) instructions. Enabling these instructions also requires -march=r2. Since these instructions are optional extensions to the R2 architecture, the default is not to emit them. -mcustom-insn=N -mno-custom-insn Each -mcustom-insn=N option enables use of a custom instruction with encoding N when generating code that uses insn. For example, -mcustom-fadds=253 generates custom instruction 253 for single- precision floating-point add operations instead of the default behavior of using a library call. The following values of insn are supported. Except as otherwise noted, floating-point operations are expected to be implemented with normal IEEE 754 semantics and correspond directly to the C operators or the equivalent GCC built-in functions. Single-precision floating point: fadds, fsubs, fdivs, fmuls Binary arithmetic operations. fnegs Unary negation. fabss Unary absolute value. fcmpeqs, fcmpges, fcmpgts, fcmples, fcmplts, fcmpnes Comparison operations. fmins, fmaxs Floating-point minimum and maximum. These instructions are only generated if -ffinite-math-only is specified. fsqrts Unary square root operation. fcoss, fsins, ftans, fatans, fexps, flogs Floating-point trigonometric and exponential functions. These instructions are only generated if -funsafe-math-optimizations is also specified. Double-precision floating point: faddd, fsubd, fdivd, fmuld Binary arithmetic operations. fnegd Unary negation. fabsd Unary absolute value. fcmpeqd, fcmpged, fcmpgtd, fcmpled, fcmpltd, fcmpned Comparison operations. fmind, fmaxd Double-precision minimum and maximum. These instructions are only generated if -ffinite-math-only is specified. fsqrtd Unary square root operation. fcosd, fsind, ftand, fatand, fexpd, flogd Double-precision trigonometric and exponential functions. These instructions are only generated if -funsafe-math-optimizations is also specified. Conversions: fextsd Conversion from single precision to double precision. ftruncds Conversion from double precision to single precision. fixsi, fixsu, fixdi, fixdu Conversion from floating point to signed or unsigned integer types, with truncation towards zero. round Conversion from single-precision floating point to signed integer, rounding to the nearest integer and ties away from zero. This corresponds to the "__builtin_lroundf" function when -fno-math-errno is used. floatis, floatus, floatid, floatud Conversion from signed or unsigned integer types to floating- point types. In addition, all of the following transfer instructions for internal registers X and Y must be provided to use any of the double-precision floating-point instructions. Custom instructions taking two double-precision source operands expect the first operand in the 64-bit register X. The other operand (or only operand of a unary operation) is given to the custom arithmetic instruction with the least significant half in source register src1 and the most significant half in src2. A custom instruction that returns a double-precision result returns the most significant 32 bits in the destination register and the other half in 32-bit register Y. GCC automatically generates the necessary code sequences to write register X and/or read register Y when double- precision floating-point instructions are used. fwrx Write src1 into the least significant half of X and src2 into the most significant half of X. fwry Write src1 into Y. frdxhi, frdxlo Read the most or least (respectively) significant half of X and store it in dest. frdy Read the value of Y and store it into dest. Note that you can gain more local control over generation of Nios II custom instructions by using the "target("custom-insn=N")" and "target("no-custom-insn")" function attributes or pragmas. -mcustom-fpu-cfg=name This option enables a predefined, named set of custom instruction encodings (see -mcustom-insn above). Currently, the following sets are defined: -mcustom-fpu-cfg=60-1 is equivalent to: -mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254 -fsingle-precision-constant -mcustom-fpu-cfg=60-2 is equivalent to: -mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254 -mcustom-fdivs=255 -fsingle-precision-constant -mcustom-fpu-cfg=72-3 is equivalent to: -mcustom-floatus=243 -mcustom-fixsi=244 -mcustom-floatis=245 -mcustom-fcmpgts=246 -mcustom-fcmples=249 -mcustom-fcmpeqs=250 -mcustom-fcmpnes=251 -mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254 -mcustom-fdivs=255 -fsingle-precision-constant -mcustom-fpu-cfg=fph2 is equivalent to: -mcustom-fabss=224 -mcustom-fnegs=225 -mcustom-fcmpnes=226 -mcustom-fcmpeqs=227 -mcustom-fcmpges=228 -mcustom-fcmpgts=229 -mcustom-fcmples=230 -mcustom-fcmplts=231 -mcustom-fmaxs=232 -mcustom-fmins=233 -mcustom-round=248 -mcustom-fixsi=249 -mcustom-floatis=250 -mcustom-fsqrts=251 -mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254 -mcustom-fdivs=255 Custom instruction assignments given by individual -mcustom-insn= options override those given by -mcustom-fpu-cfg=, regardless of the order of the options on the command line. Note that you can gain more local control over selection of a FPU configuration by using the "target("custom-fpu-cfg=name")" function attribute or pragma. The name fph2 is an abbreviation for Nios II Floating Point Hardware 2 Component. Please note that the custom instructions enabled by -mcustom-fmins=233 and -mcustom-fmaxs=234 are only generated if -ffinite-math-only is specified. The custom instruction enabled by -mcustom-round=248 is only generated if -fno-math-errno is specified. In contrast to the other configurations, -fsingle-precision-constant is not set. These additional -m options are available for the Altera Nios II ELF (bare-metal) target: -mhal Link with HAL BSP. This suppresses linking with the GCC-provided C runtime startup and termination code, and is typically used in conjunction with -msys-crt0= to specify the location of the alternate startup code provided by the HAL BSP. -msmallc Link with a limited version of the C library, -lsmallc, rather than Newlib. -msys-crt0=startfile startfile is the file name of the startfile (crt0) to use when linking. This option is only useful in conjunction with -mhal. -msys-lib=systemlib systemlib is the library name of the library that provides low- level system calls required by the C library, e.g. "read" and "write". This option is typically used to link with a library provided by a HAL BSP. Nvidia PTX Options These options are defined for Nvidia PTX: -m64 Ignored, but preserved for backward compatibility. Only 64-bit ABI is supported. -march=architecture-string Generate code for the specified PTX ISA target architecture (e.g. sm_35). Valid architecture strings are sm_30, sm_35, sm_53, sm_70, sm_75 and sm_80. The default depends on how the compiler has been configured, see --with-arch. This option sets the value of the preprocessor macro "__PTX_SM__"; for instance, for sm_35, it has the value 350. -misa=architecture-string Alias of -march=. -march-map=architecture-string Select the closest available -march= value that is not more capable. For instance, for -march-map=sm_50 select -march=sm_35, and for -march-map=sm_53 select -march=sm_53. -mptx=version-string Generate code for the specified PTX ISA version (e.g. 7.0). Valid version strings include 3.1, 6.0, 6.3, and 7.0. The default PTX ISA version is 6.0, unless a higher version is required for specified PTX ISA target architecture via option -march=. This option sets the values of the preprocessor macros "__PTX_ISA_VERSION_MAJOR__" and "__PTX_ISA_VERSION_MINOR__"; for instance, for 3.1 the macros have the values 3 and 1, respectively. -mmainkernel Link in code for a __main kernel. This is for stand-alone instead of offloading execution. -moptimize Apply partitioned execution optimizations. This is the default when any level of optimization is selected. -msoft-stack Generate code that does not use ".local" memory directly for stack storage. Instead, a per-warp stack pointer is maintained explicitly. This enables variable-length stack allocation (with variable-length arrays or "alloca"), and when global memory is used for underlying storage, makes it possible to access automatic variables from other threads, or with atomic instructions. This code generation variant is used for OpenMP offloading, but the option is exposed on its own for the purpose of testing the compiler; to generate code suitable for linking into programs using OpenMP offloading, use option -mgomp. -muniform-simt Switch to code generation variant that allows to execute all threads in each warp, while maintaining memory state and side effects as if only one thread in each warp was active outside of OpenMP SIMD regions. All atomic operations and calls to runtime (malloc, free, vprintf) are conditionally executed (iff current lane index equals the master lane index), and the register being assigned is copied via a shuffle instruction from the master lane. Outside of SIMD regions lane 0 is the master; inside, each thread sees itself as the master. Shared memory array "int __nvptx_uni[]" stores all-zeros or all-ones bitmasks for each warp, indicating current mode (0 outside of SIMD regions). Each thread can bitwise- and the bitmask at position "tid.y" with current lane index to compute the master lane index. -mgomp Generate code for use in OpenMP offloading: enables -msoft-stack and -muniform-simt options, and selects corresponding multilib variant. OpenRISC Options These options are defined for OpenRISC: -mboard=name Configure a board specific runtime. This will be passed to the linker for newlib board library linking. The default is "or1ksim". -mnewlib This option is ignored; it is for compatibility purposes only. This used to select linker and preprocessor options for use with newlib. -msoft-div -mhard-div Select software or hardware divide ("l.div", "l.divu") instructions. This default is hardware divide. -msoft-mul -mhard-mul Select software or hardware multiply ("l.mul", "l.muli") instructions. This default is hardware multiply. -msoft-float -mhard-float Select software or hardware for floating point operations. The default is software. -mdouble-float When -mhard-float is selected, enables generation of double- precision floating point instructions. By default functions from libgcc are used to perform double-precision floating point operations. -munordered-float When -mhard-float is selected, enables generation of unordered floating point compare and set flag ("lf.sfun*") instructions. By default functions from libgcc are used to perform unordered floating point compare and set flag operations. -mcmov Enable generation of conditional move ("l.cmov") instructions. By default the equivalent will be generated using set and branch. -mror Enable generation of rotate right ("l.ror") instructions. By default functions from libgcc are used to perform rotate right operations. -mrori Enable generation of rotate right with immediate ("l.rori") instructions. By default functions from libgcc are used to perform rotate right with immediate operations. -msext Enable generation of sign extension ("l.ext*") instructions. By default memory loads are used to perform sign extension. -msfimm Enable generation of compare and set flag with immediate ("l.sf*i") instructions. By default extra instructions will be generated to store the immediate to a register first. -mshftimm Enable generation of shift with immediate ("l.srai", "l.srli", "l.slli") instructions. By default extra instructions will be generated to store the immediate to a register first. -mcmodel=small Generate OpenRISC code for the small model: The GOT is limited to 64k. This is the default model. -mcmodel=large Generate OpenRISC code for the large model: The GOT may grow up to 4G in size. PDP-11 Options These options are defined for the PDP-11: -mfpu Use hardware FPP floating point. This is the default. (FIS floating point on the PDP-11/40 is not supported.) Implies -m45. -msoft-float Do not use hardware floating point. -mac0 Return floating-point results in ac0 (fr0 in Unix assembler syntax). -mno-ac0 Return floating-point results in memory. This is the default. -m40 Generate code for a PDP-11/40. Implies -msoft-float -mno-split. -m45 Generate code for a PDP-11/45. This is the default. -m10 Generate code for a PDP-11/10. Implies -msoft-float -mno-split. -mint16 -mno-int32 Use 16-bit "int". This is the default. -mint32 -mno-int16 Use 32-bit "int". -msplit Target has split instruction and data space. Implies -m45. -munix-asm Use Unix assembler syntax. -mdec-asm Use DEC assembler syntax. -mgnu-asm Use GNU assembler syntax. This is the default. -mlra Use the new LRA register allocator. By default, the old "reload" allocator is used. PowerPC Options These are listed under PRU Options These command-line options are defined for PRU target: -minrt Link with a minimum runtime environment, with no support for static initializers and constructors. Using this option can significantly reduce the size of the final ELF binary. Beware that the compiler could still generate code with static initializers and constructors. It is up to the programmer to ensure that the source program will not use those features. -mmcu=mcu Specify the PRU MCU variant to use. Check Newlib for the exact list of supported MCUs. -mno-relax Make GCC pass the --no-relax command-line option to the linker instead of the --relax option. -mloop Allow (or do not allow) GCC to use the LOOP instruction. -mabi=variant Specify the ABI variant to output code for. -mabi=ti selects the unmodified TI ABI while -mabi=gnu selects a GNU variant that copes more naturally with certain GCC assumptions. These are the differences: Function Pointer Size TI ABI specifies that function (code) pointers are 16-bit, whereas GNU supports only 32-bit data and code pointers. Optional Return Value Pointer Function return values larger than 64 bits are passed by using a hidden pointer as the first argument of the function. TI ABI, though, mandates that the pointer can be NULL in case the caller is not using the returned value. GNU always passes and expects a valid return value pointer. The current -mabi=ti implementation simply raises a compile error when any of the above code constructs is detected. As a consequence the standard C library cannot be built and it is omitted when linking with -mabi=ti. Relaxation is a GNU feature and for safety reasons is disabled when using -mabi=ti. The TI toolchain does not emit relocations for QBBx instructions, so the GNU linker cannot adjust them when shortening adjacent LDI32 pseudo instructions. RISC-V Options These command-line options are defined for RISC-V targets: -mbranch-cost=n Set the cost of branches to roughly n instructions. -mplt -mno-plt When generating PIC code, do or don't allow the use of PLTs. Ignored for non-PIC. The default is -mplt. -mabi=ABI-string Specify integer and floating-point calling convention. ABI-string contains two parts: the size of integer types and the registers used for floating-point types. For example -march=rv64ifd -mabi=lp64d means that long and pointers are 64-bit (implicitly defining int to be 32-bit), and that floating-point values up to 64 bits wide are passed in F registers. Contrast this with -march=rv64ifd -mabi=lp64f, which still allows the compiler to generate code that uses the F and D extensions but only allows floating-point values up to 32 bits long to be passed in registers; or -march=rv64ifd -mabi=lp64, in which no floating-point arguments will be passed in registers. The default for this argument is system dependent, users who want a specific calling convention should specify one explicitly. The valid calling conventions are: ilp32, ilp32f, ilp32d, lp64, lp64f, and lp64d. Some calling conventions are impossible to implement on some ISAs: for example, -march=rv32if -mabi=ilp32d is invalid because the ABI requires 64-bit values be passed in F registers, but F registers are only 32 bits wide. There is also the ilp32e ABI that can only be used with the rv32e architecture. This ABI is not well specified at present, and is subject to change. -mfdiv -mno-fdiv Do or don't use hardware floating-point divide and square root instructions. This requires the F or D extensions for floating- point registers. The default is to use them if the specified architecture has these instructions. -mdiv -mno-div Do or don't use hardware instructions for integer division. This requires the M extension. The default is to use them if the specified architecture has these instructions. -misa-spec=ISA-spec-string Specify the version of the RISC-V Unprivileged (formerly User- Level) ISA specification to produce code conforming to. The possibilities for ISA-spec-string are: 2.2 Produce code conforming to version 2.2. 20190608 Produce code conforming to version 20190608. 20191213 Produce code conforming to version 20191213. The default is -misa-spec=20191213 unless GCC has been configured with --with-isa-spec= specifying a different default version. -march=ISA-string Generate code for given RISC-V ISA (e.g. rv64im). ISA strings must be lower-case. Examples include rv64i, rv32g, rv32e, and rv32imaf. When -march= is not specified, use the setting from -mcpu. If both -march and -mcpu= are not specified, the default for this argument is system dependent, users who want a specific architecture extensions should specify one explicitly. -mcpu=processor-string Use architecture of and optimize the output for the given processor, specified by particular CPU name. Permissible values for this option are: sifive-e20, sifive-e21, sifive-e24, sifive-e31, sifive-e34, sifive-e76, sifive-s21, sifive-s51, sifive-s54, sifive-s76, sifive-u54, and sifive-u74. -mtune=processor-string Optimize the output for the given processor, specified by microarchitecture or particular CPU name. Permissible values for this option are: rocket, sifive-3-series, sifive-5-series, sifive-7-series, thead-c906, size, and all valid options for -mcpu=. When -mtune= is not specified, use the setting from -mcpu, the default is rocket if both are not specified. The size choice is not intended for use by end-users. This is used when -Os is specified. It overrides the instruction cost info provided by -mtune=, but does not override the pipeline info. This helps reduce code size while still giving good performance. -mpreferred-stack-boundary=num Attempt to keep the stack boundary aligned to a 2 raised to num byte boundary. If -mpreferred-stack-boundary is not specified, the default is 4 (16 bytes or 128-bits). Warning: If you use this switch, then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules. -msmall-data-limit=n Put global and static data smaller than n bytes into a special section (on some targets). -msave-restore -mno-save-restore Do or don't use smaller but slower prologue and epilogue code that uses library function calls. The default is to use fast inline prologues and epilogues. -minline-atomics -mno-inline-atomics Do or don't use smaller but slower subword atomic emulation code that uses libatomic function calls. The default is to use fast inline subword atomics that do not require libatomic. -mshorten-memrefs -mno-shorten-memrefs Do or do not attempt to make more use of compressed load/store instructions by replacing a load/store of 'base register + large offset' with a new load/store of 'new base + small offset'. If the new base gets stored in a compressed register, then the new load/store can be compressed. Currently targets 32-bit integer load/stores only. -mstrict-align -mno-strict-align Do not or do generate unaligned memory accesses. The default is set depending on whether the processor we are optimizing for supports fast unaligned access or not. -mcmodel=medlow Generate code for the medium-low code model. The program and its statically defined symbols must lie within a single 2 GiB address range and must lie between absolute addresses -2 GiB and +2 GiB. Programs can be statically or dynamically linked. This is the default code model. -mcmodel=medany Generate code for the medium-any code model. The program and its statically defined symbols must be within any single 2 GiB address range. Programs can be statically or dynamically linked. The code generated by the medium-any code model is position- independent, but is not guaranteed to function correctly when linked into position-independent executables or libraries. -mexplicit-relocs -mno-exlicit-relocs Use or do not use assembler relocation operators when dealing with symbolic addresses. The alternative is to use assembler macros instead, which may limit optimization. -mrelax -mno-relax Take advantage of linker relaxations to reduce the number of instructions required to materialize symbol addresses. The default is to take advantage of linker relaxations. -mriscv-attribute -mno-riscv-attribute Emit (do not emit) RISC-V attribute to record extra information into ELF objects. This feature requires at least binutils 2.32. -mcsr-check -mno-csr-check Enables or disables the CSR checking. -malign-data=type Control how GCC aligns variables and constants of array, structure, or union types. Supported values for type are xlen which uses x register width as the alignment value, and natural which uses natural alignment. xlen is the default. -mbig-endian Generate big-endian code. This is the default when GCC is configured for a riscv64be-*-* or riscv32be-*-* target. -mlittle-endian Generate little-endian code. This is the default when GCC is configured for a riscv64-*-* or riscv32-*-* but not a riscv64be-*-* or riscv32be-*-* target. -mstack-protector-guard=guard -mstack-protector-guard-reg=reg -mstack-protector-guard-offset=offset Generate stack protection code using canary at guard. Supported locations are global for a global canary or tls for per-thread canary in the TLS block. With the latter choice the options -mstack-protector-guard-reg=reg and -mstack-protector-guard-offset=offset furthermore specify which register to use as base register for reading the canary, and from what offset from that base register. There is no default register or offset as this is entirely for use within the Linux kernel. RL78 Options -msim Links in additional target libraries to support operation within a simulator. -mmul=none -mmul=g10 -mmul=g13 -mmul=g14 -mmul=rl78 Specifies the type of hardware multiplication and division support to be used. The simplest is "none", which uses software for both multiplication and division. This is the default. The "g13" value is for the hardware multiply/divide peripheral found on the RL78/G13 (S2 core) targets. The "g14" value selects the use of the multiplication and division instructions supported by the RL78/G14 (S3 core) parts. The value "rl78" is an alias for "g14" and the value "mg10" is an alias for "none". In addition a C preprocessor macro is defined, based upon the setting of this option. Possible values are: "__RL78_MUL_NONE__", "__RL78_MUL_G13__" or "__RL78_MUL_G14__". -mcpu=g10 -mcpu=g13 -mcpu=g14 -mcpu=rl78 Specifies the RL78 core to target. The default is the G14 core, also known as an S3 core or just RL78. The G13 or S2 core does not have multiply or divide instructions, instead it uses a hardware peripheral for these operations. The G10 or S1 core does not have register banks, so it uses a different calling convention. If this option is set it also selects the type of hardware multiply support to use, unless this is overridden by an explicit -mmul=none option on the command line. Thus specifying -mcpu=g13 enables the use of the G13 hardware multiply peripheral and specifying -mcpu=g10 disables the use of hardware multiplications altogether. Note, although the RL78/G14 core is the default target, specifying -mcpu=g14 or -mcpu=rl78 on the command line does change the behavior of the toolchain since it also enables G14 hardware multiply support. If these options are not specified on the command line then software multiplication routines will be used even though the code targets the RL78 core. This is for backwards compatibility with older toolchains which did not have hardware multiply and divide support. In addition a C preprocessor macro is defined, based upon the setting of this option. Possible values are: "__RL78_G10__", "__RL78_G13__" or "__RL78_G14__". -mg10 -mg13 -mg14 -mrl78 These are aliases for the corresponding -mcpu= option. They are provided for backwards compatibility. -mallregs Allow the compiler to use all of the available registers. By default registers "r24..r31" are reserved for use in interrupt handlers. With this option enabled these registers can be used in ordinary functions as well. -m64bit-doubles -m32bit-doubles Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits (-m32bit-doubles) in size. The default is -m32bit-doubles. -msave-mduc-in-interrupts -mno-save-mduc-in-interrupts Specifies that interrupt handler functions should preserve the MDUC registers. This is only necessary if normal code might use the MDUC registers, for example because it performs multiplication and division operations. The default is to ignore the MDUC registers as this makes the interrupt handlers faster. The target option -mg13 needs to be passed for this to work as this feature is only available on the G13 target (S2 core). The MDUC registers will only be saved if the interrupt handler performs a multiplication or division operation or it calls another function. IBM RS/6000 and PowerPC Options These -m options are defined for the IBM RS/6000 and PowerPC: -mpowerpc-gpopt -mno-powerpc-gpopt -mpowerpc-gfxopt -mno-powerpc-gfxopt -mpowerpc64 -mno-powerpc64 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd -mfprnd -mno-fprnd -mcmpb -mno-cmpb -mhard-dfp -mno-hard-dfp You use these options to specify which instructions are available on the processor you are using. The default value of these options is determined when configuring GCC. Specifying the -mcpu=cpu_type overrides the specification of these options. We recommend you use the -mcpu=cpu_type option rather than the options listed above. Specifying -mpowerpc-gpopt allows GCC to use the optional PowerPC architecture instructions in the General Purpose group, including floating-point square root. Specifying -mpowerpc-gfxopt allows GCC to use the optional PowerPC architecture instructions in the Graphics group, including floating-point select. The -mmfcrf option allows GCC to generate the move from condition register field instruction implemented on the POWER4 processor and other processors that support the PowerPC V2.01 architecture. The -mpopcntb option allows GCC to generate the popcount and double- precision FP reciprocal estimate instruction implemented on the POWER5 processor and other processors that support the PowerPC V2.02 architecture. The -mpopcntd option allows GCC to generate the popcount instruction implemented on the POWER7 processor and other processors that support the PowerPC V2.06 architecture. The -mfprnd option allows GCC to generate the FP round to integer instructions implemented on the POWER5+ processor and other processors that support the PowerPC V2.03 architecture. The -mcmpb option allows GCC to generate the compare bytes instruction implemented on the POWER6 processor and other processors that support the PowerPC V2.05 architecture. The -mhard-dfp option allows GCC to generate the decimal floating-point instructions implemented on some POWER processors. The -mpowerpc64 option allows GCC to generate the additional 64-bit instructions that are found in the full PowerPC64 architecture and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to -mno-powerpc64. -mcpu=cpu_type Set architecture type, register usage, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are 401, 403, 405, 405fp, 440, 440fp, 464, 464fp, 476, 476fp, 505, 601, 602, 603, 603e, 604, 604e, 620, 630, 740, 7400, 7450, 750, 801, 821, 823, 860, 970, 8540, a2, e300c2, e300c3, e500mc, e500mc64, e5500, e6500, ec603e, G3, G4, G5, titan, power3, power4, power5, power5+, power6, power6x, power7, power8, power9, power10, powerpc, powerpc64, powerpc64le, rs64, and native. -mcpu=powerpc, -mcpu=powerpc64, and -mcpu=powerpc64le specify pure 32-bit PowerPC (either endian), 64-bit big endian PowerPC and 64-bit little endian PowerPC architecture machine types, with an appropriate, generic processor model assumed for scheduling purposes. Specifying native as cpu type detects and selects the architecture option that corresponds to the host processor of the system performing the compilation. -mcpu=native has no effect if GCC does not recognize the processor. The other options specify a specific processor. Code generated under those options runs best on that processor, and may not run at all on others. The -mcpu options automatically enable or disable the following options: -maltivec -mfprnd -mhard-float -mmfcrf -mmultiple -mpopcntb -mpopcntd -mpowerpc64 -mpowerpc-gpopt -mpowerpc-gfxopt -mmulhw -mdlmzb -mmfpgpr -mvsx -mcrypto -mhtm -mpower8-fusion -mpower8-vector -mquad-memory -mquad-memory-atomic -mfloat128 -mfloat128-hardware -mprefixed -mpcrel -mmma -mrop-protect The particular options set for any particular CPU varies between compiler versions, depending on what setting seems to produce optimal code for that CPU; it doesn't necessarily reflect the actual hardware's capabilities. If you wish to set an individual option to a particular value, you may specify it after the -mcpu option, like -mcpu=970 -mno-altivec. On AIX, the -maltivec and -mpowerpc64 options are not enabled or disabled by the -mcpu option at present because AIX does not have full support for these options. You may still enable or disable them individually if you're sure it'll work in your environment. -mtune=cpu_type Set the instruction scheduling parameters for machine type cpu_type, but do not set the architecture type or register usage, as -mcpu=cpu_type does. The same values for cpu_type are used for -mtune as for -mcpu. If both are specified, the code generated uses the architecture and registers set by -mcpu, but the scheduling parameters set by -mtune. -mcmodel=small Generate PowerPC64 code for the small model: The TOC is limited to 64k. -mcmodel=medium Generate PowerPC64 code for the medium model: The TOC and other static data may be up to a total of 4G in size. This is the default for 64-bit Linux. -mcmodel=large Generate PowerPC64 code for the large model: The TOC may be up to 4G in size. Other data and code is only limited by the 64-bit address space. -maltivec -mno-altivec Generate code that uses (does not use) AltiVec instructions, and also enable the use of built-in functions that allow more direct access to the AltiVec instruction set. You may also need to set -mabi=altivec to adjust the current ABI with AltiVec ABI enhancements. When -maltivec is used, the element order for AltiVec intrinsics such as "vec_splat", "vec_extract", and "vec_insert" match array element order corresponding to the endianness of the target. That is, element zero identifies the leftmost element in a vector register when targeting a big-endian platform, and identifies the rightmost element in a vector register when targeting a little- endian platform. -mvrsave -mno-vrsave Generate VRSAVE instructions when generating AltiVec code. -msecure-plt Generate code that allows ld and ld.so to build executables and shared libraries with non-executable ".plt" and ".got" sections. This is a PowerPC 32-bit SYSV ABI option. -mbss-plt Generate code that uses a BSS ".plt" section that ld.so fills in, and requires ".plt" and ".got" sections that are both writable and executable. This is a PowerPC 32-bit SYSV ABI option. -misel -mno-isel This switch enables or disables the generation of ISEL instructions. -mvsx -mno-vsx Generate code that uses (does not use) vector/scalar (VSX) instructions, and also enable the use of built-in functions that allow more direct access to the VSX instruction set. -mcrypto -mno-crypto Enable the use (disable) of the built-in functions that allow direct access to the cryptographic instructions that were added in version 2.07 of the PowerPC ISA. -mhtm -mno-htm Enable (disable) the use of the built-in functions that allow direct access to the Hardware Transactional Memory (HTM) instructions that were added in version 2.07 of the PowerPC ISA. -mpower8-fusion -mno-power8-fusion Generate code that keeps (does not keeps) some integer operations adjacent so that the instructions can be fused together on power8 and later processors. -mpower8-vector -mno-power8-vector Generate code that uses (does not use) the vector and scalar instructions that were added in version 2.07 of the PowerPC ISA. Also enable the use of built-in functions that allow more direct access to the vector instructions. -mquad-memory -mno-quad-memory Generate code that uses (does not use) the non-atomic quad word memory instructions. The -mquad-memory option requires use of 64-bit mode. -mquad-memory-atomic -mno-quad-memory-atomic Generate code that uses (does not use) the atomic quad word memory instructions. The -mquad-memory-atomic option requires use of 64-bit mode. -mfloat128 -mno-float128 Enable/disable the __float128 keyword for IEEE 128-bit floating point and use either software emulation for IEEE 128-bit floating point or hardware instructions. The VSX instruction set (-mvsx) must be enabled to use the IEEE 128-bit floating point support. The IEEE 128-bit floating point is only supported on Linux. The default for -mfloat128 is enabled on PowerPC Linux systems using the VSX instruction set, and disabled on other systems. If you use the ISA 3.0 instruction set (-mpower9-vector or -mcpu=power9) on a 64-bit system, the IEEE 128-bit floating point support will also enable the generation of ISA 3.0 IEEE 128-bit floating point instructions. Otherwise, if you do not specify to generate ISA 3.0 instructions or you are targeting a 32-bit big endian system, IEEE 128-bit floating point will be done with software emulation. -mfloat128-hardware -mno-float128-hardware Enable/disable using ISA 3.0 hardware instructions to support the __float128 data type. The default for -mfloat128-hardware is enabled on PowerPC Linux systems using the ISA 3.0 instruction set, and disabled on other systems. -m32 -m64 Generate code for 32-bit or 64-bit environments of Darwin and SVR4 targets (including GNU/Linux). The 32-bit environment sets int, long and pointer to 32 bits and generates code that runs on any PowerPC variant. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits, and generates code for PowerPC64, as for -mpowerpc64. -mfull-toc -mno-fp-in-toc -mno-sum-in-toc -mminimal-toc Modify generation of the TOC (Table Of Contents), which is created for every executable file. The -mfull-toc option is selected by default. In that case, GCC allocates at least one TOC entry for each unique non-automatic variable reference in your program. GCC also places floating-point constants in the TOC. However, only 16,384 entries are available in the TOC. If you receive a linker error message that saying you have overflowed the available TOC space, you can reduce the amount of TOC space used with the -mno-fp-in-toc and -mno-sum-in-toc options. -mno-fp-in-toc prevents GCC from putting floating-point constants in the TOC and -mno-sum-in-toc forces GCC to generate code to calculate the sum of an address and a constant at run time instead of putting that sum into the TOC. You may specify one or both of these options. Each causes GCC to produce very slightly slower and larger code at the expense of conserving TOC space. If you still run out of space in the TOC even when you specify both of these options, specify -mminimal-toc instead. This option causes GCC to make only one TOC entry for every file. When you specify this option, GCC produces code that is slower and larger but which uses extremely little TOC space. You may wish to use this option only on files that contain less frequently-executed code. -maix64 -maix32 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit "long" type, and the infrastructure needed to support them. Specifying -maix64 implies -mpowerpc64, while -maix32 disables the 64-bit ABI and implies -mno-powerpc64. GCC defaults to -maix32. -mxl-compat -mno-xl-compat Produce code that conforms more closely to IBM XL compiler semantics when using AIX-compatible ABI. Pass floating-point arguments to prototyped functions beyond the register save area (RSA) on the stack in addition to argument FPRs. Do not assume that most significant double in 128-bit long double value is properly rounded when comparing values and converting to double. Use XL symbol names for long double support routines. The AIX calling convention was extended but not initially documented to handle an obscure K&R C case of calling a function that takes the address of its arguments with fewer arguments than declared. IBM XL compilers access floating-point arguments that do not fit in the RSA from the stack when a subroutine is compiled without optimization. Because always storing floating-point arguments on the stack is inefficient and rarely needed, this option is not enabled by default and only is necessary when calling subroutines compiled by IBM XL compilers without optimization. -mpe Support IBM RS/6000 SP Parallel Environment (PE). Link an application written to use message passing with special startup code to enable the application to run. The system must have PE installed in the standard location (/usr/lpp/ppe.poe/), or the specs file must be overridden with the -specs= option to specify the appropriate directory location. The Parallel Environment does not support threads, so the -mpe option and the -pthread option are incompatible. -malign-natural -malign-power On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option -malign-natural overrides the ABI-defined alignment of larger types, such as floating-point doubles, on their natural size-based boundary. The option -malign-power instructs GCC to follow the ABI-specified alignment rules. GCC defaults to the standard alignment defined in the ABI. On 64-bit Darwin, natural alignment is the default, and -malign-power is not supported. -msoft-float -mhard-float Generate code that does not use (uses) the floating-point register set. Software floating-point emulation is provided if you use the -msoft-float option, and pass the option to GCC when linking. -mmultiple -mno-multiple Generate code that uses (does not use) the load multiple word instructions and the store multiple word instructions. These instructions are generated by default on POWER systems, and not generated on PowerPC systems. Do not use -mmultiple on little- endian PowerPC systems, since those instructions do not work when the processor is in little-endian mode. The exceptions are PPC740 and PPC750 which permit these instructions in little-endian mode. -mupdate -mno-update Generate code that uses (does not use) the load or store instructions that update the base register to the address of the calculated memory location. These instructions are generated by default. If you use -mno-update, there is a small window between the time that the stack pointer is updated and the address of the previous frame is stored, which means code that walks the stack frame across interrupts or signals may get corrupted data. -mavoid-indexed-addresses -mno-avoid-indexed-addresses Generate code that tries to avoid (not avoid) the use of indexed load or store instructions. These instructions can incur a performance penalty on Power6 processors in certain situations, such as when stepping through large arrays that cross a 16M boundary. This option is enabled by default when targeting Power6 and disabled otherwise. -mfused-madd -mno-fused-madd Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. The machine-dependent -mfused-madd option is now mapped to the machine-independent -ffp-contract=fast option, and -mno-fused-madd is mapped to -ffp-contract=off. -mmulhw -mno-mulhw Generate code that uses (does not use) the half-word multiply and multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors. These instructions are generated by default when targeting those processors. -mdlmzb -mno-dlmzb Generate code that uses (does not use) the string-search dlmzb instruction on the IBM 405, 440, 464 and 476 processors. This instruction is generated by default when targeting those processors. -mno-bit-align -mbit-align On System V.4 and embedded PowerPC systems do not (do) force structures and unions that contain bit-fields to be aligned to the base type of the bit-field. For example, by default a structure containing nothing but 8 "unsigned" bit-fields of length 1 is aligned to a 4-byte boundary and has a size of 4 bytes. By using -mno-bit-align, the structure is aligned to a 1-byte boundary and is 1 byte in size. -mno-strict-align -mstrict-align On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory references are handled by the system. -mrelocatable -mno-relocatable Generate code that allows (does not allow) a static executable to be relocated to a different address at run time. A simple embedded PowerPC system loader should relocate the entire contents of ".got2" and 4-byte locations listed in the ".fixup" section, a table of 32-bit addresses generated by this option. For this to work, all objects linked together must be compiled with -mrelocatable or -mrelocatable-lib. -mrelocatable code aligns the stack to an 8-byte boundary. -mrelocatable-lib -mno-relocatable-lib Like -mrelocatable, -mrelocatable-lib generates a ".fixup" section to allow static executables to be relocated at run time, but -mrelocatable-lib does not use the smaller stack alignment of -mrelocatable. Objects compiled with -mrelocatable-lib may be linked with objects compiled with any combination of the -mrelocatable options. -mno-toc -mtoc On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains a pointer to a global area pointing to the addresses used in the program. -mlittle -mlittle-endian On System V.4 and embedded PowerPC systems compile code for the processor in little-endian mode. The -mlittle-endian option is the same as -mlittle. -mbig -mbig-endian On System V.4 and embedded PowerPC systems compile code for the processor in big-endian mode. The -mbig-endian option is the same as -mbig. -mdynamic-no-pic On Darwin and Mac OS X systems, compile code so that it is not relocatable, but that its external references are relocatable. The resulting code is suitable for applications, but not shared libraries. -msingle-pic-base Treat the register used for PIC addressing as read-only, rather than loading it in the prologue for each function. The runtime system is responsible for initializing this register with an appropriate value before execution begins. -mprioritize-restricted-insns=priority This option controls the priority that is assigned to dispatch-slot restricted instructions during the second scheduling pass. The argument priority takes the value 0, 1, or 2 to assign no, highest, or second-highest (respectively) priority to dispatch-slot restricted instructions. -msched-costly-dep=dependence_type This option controls which dependences are considered costly by the target during instruction scheduling. The argument dependence_type takes one of the following values: no No dependence is costly. all All dependences are costly. true_store_to_load A true dependence from store to load is costly. store_to_load Any dependence from store to load is costly. number Any dependence for which the latency is greater than or equal to number is costly. -minsert-sched-nops=scheme This option controls which NOP insertion scheme is used during the second scheduling pass. The argument scheme takes one of the following values: no Don't insert NOPs. pad Pad with NOPs any dispatch group that has vacant issue slots, according to the scheduler's grouping. regroup_exact Insert NOPs to force costly dependent insns into separate groups. Insert exactly as many NOPs as needed to force an insn to a new group, according to the estimated processor grouping. number Insert NOPs to force costly dependent insns into separate groups. Insert number NOPs to force an insn to a new group. -mcall-sysv On System V.4 and embedded PowerPC systems compile code using calling conventions that adhere to the March 1995 draft of the System V Application Binary Interface, PowerPC processor supplement. This is the default unless you configured GCC using powerpc-*-eabiaix. -mcall-sysv-eabi -mcall-eabi Specify both -mcall-sysv and -meabi options. -mcall-sysv-noeabi Specify both -mcall-sysv and -mno-eabi options. -mcall-aixdesc On System V.4 and embedded PowerPC systems compile code for the AIX operating system. -mcall-linux On System V.4 and embedded PowerPC systems compile code for the Linux-based GNU system. -mcall-freebsd On System V.4 and embedded PowerPC systems compile code for the FreeBSD operating system. -mcall-netbsd On System V.4 and embedded PowerPC systems compile code for the NetBSD operating system. -mcall-openbsd On System V.4 and embedded PowerPC systems compile code for the OpenBSD operating system. -mtraceback=traceback_type Select the type of traceback table. Valid values for traceback_type are full, part, and no. -maix-struct-return Return all structures in memory (as specified by the AIX ABI). -msvr4-struct-return Return structures smaller than 8 bytes in registers (as specified by the SVR4 ABI). -mabi=abi-type Extend the current ABI with a particular extension, or remove such extension. Valid values are: altivec, no-altivec, ibmlongdouble, ieeelongdouble, elfv1, elfv2, and for AIX: vec-extabi, vec-default. -mabi=ibmlongdouble Change the current ABI to use IBM extended-precision long double. This is not likely to work if your system defaults to using IEEE extended-precision long double. If you change the long double type from IEEE extended-precision, the compiler will issue a warning unless you use the -Wno-psabi option. Requires -mlong-double-128 to be enabled. -mabi=ieeelongdouble Change the current ABI to use IEEE extended-precision long double. This is not likely to work if your system defaults to using IBM extended-precision long double. If you change the long double type from IBM extended-precision, the compiler will issue a warning unless you use the -Wno-psabi option. Requires -mlong-double-128 to be enabled. -mabi=elfv1 Change the current ABI to use the ELFv1 ABI. This is the default ABI for big-endian PowerPC 64-bit Linux. Overriding the default ABI requires special system support and is likely to fail in spectacular ways. -mabi=elfv2 Change the current ABI to use the ELFv2 ABI. This is the default ABI for little-endian PowerPC 64-bit Linux. Overriding the default ABI requires special system support and is likely to fail in spectacular ways. -mgnu-attribute -mno-gnu-attribute Emit .gnu_attribute assembly directives to set tag/value pairs in a .gnu.attributes section that specify ABI variations in function parameters or return values. -mprototype -mno-prototype On System V.4 and embedded PowerPC systems assume that all calls to variable argument functions are properly prototyped. Otherwise, the compiler must insert an instruction before every non-prototyped call to set or clear bit 6 of the condition code register ("CR") to indicate whether floating-point values are passed in the floating- point registers in case the function takes variable arguments. With -mprototype, only calls to prototyped variable argument functions set or clear the bit. -msim On embedded PowerPC systems, assume that the startup module is called sim-crt0.o and that the standard C libraries are libsim.a and libc.a. This is the default for powerpc-*-eabisim configurations. -mmvme On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C libraries are libmvme.a and libc.a. -mads On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C libraries are libads.a and libc.a. -myellowknife On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C libraries are libyk.a and libc.a. -mvxworks On System V.4 and embedded PowerPC systems, specify that you are compiling for a VxWorks system. -memb On embedded PowerPC systems, set the "PPC_EMB" bit in the ELF flags header to indicate that eabi extended relocations are used. -meabi -mno-eabi On System V.4 and embedded PowerPC systems do (do not) adhere to the Embedded Applications Binary Interface (EABI), which is a set of modifications to the System V.4 specifications. Selecting -meabi means that the stack is aligned to an 8-byte boundary, a function "__eabi" is called from "main" to set up the EABI environment, and the -msdata option can use both "r2" and "r13" to point to two separate small data areas. Selecting -mno-eabi means that the stack is aligned to a 16-byte boundary, no EABI initialization function is called from "main", and the -msdata option only uses "r13" to point to a single small data area. The -meabi option is on by default if you configured GCC using one of the powerpc*-*-eabi* options. -msdata=eabi On System V.4 and embedded PowerPC systems, put small initialized "const" global and static data in the ".sdata2" section, which is pointed to by register "r2". Put small initialized non-"const" global and static data in the ".sdata" section, which is pointed to by register "r13". Put small uninitialized global and static data in the ".sbss" section, which is adjacent to the ".sdata" section. The -msdata=eabi option is incompatible with the -mrelocatable option. The -msdata=eabi option also sets the -memb option. -msdata=sysv On System V.4 and embedded PowerPC systems, put small global and static data in the ".sdata" section, which is pointed to by register "r13". Put small uninitialized global and static data in the ".sbss" section, which is adjacent to the ".sdata" section. The -msdata=sysv option is incompatible with the -mrelocatable option. -msdata=default -msdata On System V.4 and embedded PowerPC systems, if -meabi is used, compile code the same as -msdata=eabi, otherwise compile code the same as -msdata=sysv. -msdata=data On System V.4 and embedded PowerPC systems, put small global data in the ".sdata" section. Put small uninitialized global data in the ".sbss" section. Do not use register "r13" to address small data however. This is the default behavior unless other -msdata options are used. -msdata=none -mno-sdata On embedded PowerPC systems, put all initialized global and static data in the ".data" section, and all uninitialized data in the ".bss" section. -mreadonly-in-sdata Put read-only objects in the ".sdata" section as well. This is the default. -mblock-move-inline-limit=num Inline all block moves (such as calls to "memcpy" or structure copies) less than or equal to num bytes. The minimum value for num is 32 bytes on 32-bit targets and 64 bytes on 64-bit targets. The default value is target-specific. -mblock-compare-inline-limit=num Generate non-looping inline code for all block compares (such as calls to "memcmp" or structure compares) less than or equal to num bytes. If num is 0, all inline expansion (non-loop and loop) of block compare is disabled. The default value is target-specific. -mblock-compare-inline-loop-limit=num Generate an inline expansion using loop code for all block compares that are less than or equal to num bytes, but greater than the limit for non-loop inline block compare expansion. If the block length is not constant, at most num bytes will be compared before "memcmp" is called to compare the remainder of the block. The default value is target-specific. -mstring-compare-inline-limit=num Compare at most num string bytes with inline code. If the difference or end of string is not found at the end of the inline compare a call to "strcmp" or "strncmp" will take care of the rest of the comparison. The default is 64 bytes. -G num On embedded PowerPC systems, put global and static items less than or equal to num bytes into the small data or BSS sections instead of the normal data or BSS section. By default, num is 8. The -G num switch is also passed to the linker. All modules should be compiled with the same -G num value. -mregnames -mno-regnames On System V.4 and embedded PowerPC systems do (do not) emit register names in the assembly language output using symbolic forms. -mlongcall -mno-longcall By default assume that all calls are far away so that a longer and more expensive calling sequence is required. This is required for calls farther than 32 megabytes (33,554,432 bytes) from the current location. A short call is generated if the compiler knows the call cannot be that far away. This setting can be overridden by the "shortcall" function attribute, or by "#pragma longcall(0)". Some linkers are capable of detecting out-of-range calls and generating glue code on the fly. On these systems, long calls are unnecessary and generate slower code. As of this writing, the AIX linker can do this, as can the GNU linker for PowerPC/64. It is planned to add this feature to the GNU linker for 32-bit PowerPC systems as well. On PowerPC64 ELFv2 and 32-bit PowerPC systems with newer GNU linkers, GCC can generate long calls using an inline PLT call sequence (see -mpltseq). PowerPC with -mbss-plt and PowerPC64 ELFv1 (big-endian) do not support inline PLT calls. On Darwin/PPC systems, "#pragma longcall" generates "jbsr callee, L42", plus a branch island (glue code). The two target addresses represent the callee and the branch island. The Darwin/PPC linker prefers the first address and generates a "bl callee" if the PPC "bl" instruction reaches the callee directly; otherwise, the linker generates "bl L42" to call the branch island. The branch island is appended to the body of the calling function; it computes the full 32-bit address of the callee and jumps to it. On Mach-O (Darwin) systems, this option directs the compiler emit to the glue for every direct call, and the Darwin linker decides whether to use or discard it. In the future, GCC may ignore all longcall specifications when the linker is known to generate glue. -mpltseq -mno-pltseq Implement (do not implement) -fno-plt and long calls using an inline PLT call sequence that supports lazy linking and long calls to functions in dlopen'd shared libraries. Inline PLT calls are only supported on PowerPC64 ELFv2 and 32-bit PowerPC systems with newer GNU linkers, and are enabled by default if the support is detected when configuring GCC, and, in the case of 32-bit PowerPC, if GCC is configured with --enable-secureplt. -mpltseq code and -mbss-plt 32-bit PowerPC relocatable objects may not be linked together. -mtls-markers -mno-tls-markers Mark (do not mark) calls to "__tls_get_addr" with a relocation specifying the function argument. The relocation allows the linker to reliably associate function call with argument setup instructions for TLS optimization, which in turn allows GCC to better schedule the sequence. -mrecip -mno-recip This option enables use of the reciprocal estimate and reciprocal square root estimate instructions with additional Newton-Raphson steps to increase precision instead of doing a divide or square root and divide for floating-point arguments. You should use the -ffast-math option when using -mrecip (or at least -funsafe-math-optimizations, -ffinite-math-only, -freciprocal-math and -fno-trapping-math). Note that while the throughput of the sequence is generally higher than the throughput of the non- reciprocal instruction, the precision of the sequence can be decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994) for reciprocal square roots. -mrecip=opt This option controls which reciprocal estimate instructions may be used. opt is a comma-separated list of options, which may be preceded by a "!" to invert the option: all Enable all estimate instructions. default Enable the default instructions, equivalent to -mrecip. none Disable all estimate instructions, equivalent to -mno-recip. div Enable the reciprocal approximation instructions for both single and double precision. divf Enable the single-precision reciprocal approximation instructions. divd Enable the double-precision reciprocal approximation instructions. rsqrt Enable the reciprocal square root approximation instructions for both single and double precision. rsqrtf Enable the single-precision reciprocal square root approximation instructions. rsqrtd Enable the double-precision reciprocal square root approximation instructions. So, for example, -mrecip=all,!rsqrtd enables all of the reciprocal estimate instructions, except for the "FRSQRTE", "XSRSQRTEDP", and "XVRSQRTEDP" instructions which handle the double-precision reciprocal square root calculations. -mrecip-precision -mno-recip-precision Assume (do not assume) that the reciprocal estimate instructions provide higher-precision estimates than is mandated by the PowerPC ABI. Selecting -mcpu=power6, -mcpu=power7 or -mcpu=power8 automatically selects -mrecip-precision. The double-precision square root estimate instructions are not generated by default on low-precision machines, since they do not provide an estimate that converges after three steps. -mveclibabi=type Specifies the ABI type to use for vectorizing intrinsics using an external library. The only type supported at present is mass, which specifies to use IBM's Mathematical Acceleration Subsystem (MASS) libraries for vectorizing intrinsics using external libraries. GCC currently emits calls to "acosd2", "acosf4", "acoshd2", "acoshf4", "asind2", "asinf4", "asinhd2", "asinhf4", "atan2d2", "atan2f4", "atand2", "atanf4", "atanhd2", "atanhf4", "cbrtd2", "cbrtf4", "cosd2", "cosf4", "coshd2", "coshf4", "erfcd2", "erfcf4", "erfd2", "erff4", "exp2d2", "exp2f4", "expd2", "expf4", "expm1d2", "expm1f4", "hypotd2", "hypotf4", "lgammad2", "lgammaf4", "log10d2", "log10f4", "log1pd2", "log1pf4", "log2d2", "log2f4", "logd2", "logf4", "powd2", "powf4", "sind2", "sinf4", "sinhd2", "sinhf4", "sqrtd2", "sqrtf4", "tand2", "tanf4", "tanhd2", and "tanhf4" when generating code for power7. Both -ftree-vectorize and -funsafe-math-optimizations must also be enabled. The MASS libraries must be specified at link time. -mfriz -mno-friz Generate (do not generate) the "friz" instruction when the -funsafe-math-optimizations option is used to optimize rounding of floating-point values to 64-bit integer and back to floating point. The "friz" instruction does not return the same value if the floating-point number is too large to fit in an integer. -mpointers-to-nested-functions -mno-pointers-to-nested-functions Generate (do not generate) code to load up the static chain register ("r11") when calling through a pointer on AIX and 64-bit Linux systems where a function pointer points to a 3-word descriptor giving the function address, TOC value to be loaded in register "r2", and static chain value to be loaded in register "r11". The -mpointers-to-nested-functions is on by default. You cannot call through pointers to nested functions or pointers to functions compiled in other languages that use the static chain if you use -mno-pointers-to-nested-functions. -msave-toc-indirect -mno-save-toc-indirect Generate (do not generate) code to save the TOC value in the reserved stack location in the function prologue if the function calls through a pointer on AIX and 64-bit Linux systems. If the TOC value is not saved in the prologue, it is saved just before the call through the pointer. The -mno-save-toc-indirect option is the default. -mcompat-align-parm -mno-compat-align-parm Generate (do not generate) code to pass structure parameters with a maximum alignment of 64 bits, for compatibility with older versions of GCC. Older versions of GCC (prior to 4.9.0) incorrectly did not align a structure parameter on a 128-bit boundary when that structure contained a member requiring 128-bit alignment. This is corrected in more recent versions of GCC. This option may be used to generate code that is compatible with functions compiled with older versions of GCC. The -mno-compat-align-parm option is the default. -mstack-protector-guard=guard -mstack-protector-guard-reg=reg -mstack-protector-guard-offset=offset -mstack-protector-guard-symbol=symbol Generate stack protection code using canary at guard. Supported locations are global for global canary or tls for per-thread canary in the TLS block (the default with GNU libc version 2.4 or later). With the latter choice the options -mstack-protector-guard-reg=reg and -mstack-protector-guard-offset=offset furthermore specify which register to use as base register for reading the canary, and from what offset from that base register. The default for those is as specified in the relevant ABI. -mstack-protector-guard-symbol=symbol overrides the offset with a symbol reference to a canary in the TLS block. -mpcrel -mno-pcrel Generate (do not generate) pc-relative addressing. The -mpcrel option requires that the medium code model (-mcmodel=medium) and prefixed addressing (-mprefixed) options are enabled. -mprefixed -mno-prefixed Generate (do not generate) addressing modes using prefixed load and store instructions. The -mprefixed option requires that the option -mcpu=power10 (or later) is enabled. -mmma -mno-mma Generate (do not generate) the MMA instructions. The -mma option requires that the option -mcpu=power10 (or later) is enabled. -mrop-protect -mno-rop-protect Generate (do not generate) ROP protection instructions when the target processor supports them. Currently this option disables the shrink-wrap optimization (-fshrink-wrap). -mprivileged -mno-privileged Generate (do not generate) code that will run in privileged state. -mblock-ops-unaligned-vsx -mno-block-ops-unaligned-vsx Generate (do not generate) unaligned vsx loads and stores for inline expansion of "memcpy" and "memmove". --param rs6000-vect-unroll-limit= The vectorizer will check with target information to determine whether it would be beneficial to unroll the main vectorized loop and by how much. This parameter sets the upper bound of how much the vectorizer will unroll the main loop. The default value is four. RX Options These command-line options are defined for RX targets: -m64bit-doubles -m32bit-doubles Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits (-m32bit-doubles) in size. The default is -m32bit-doubles. Note RX floating-point hardware only works on 32-bit values, which is why the default is -m32bit-doubles. -fpu -nofpu Enables (-fpu) or disables (-nofpu) the use of RX floating-point hardware. The default is enabled for the RX600 series and disabled for the RX200 series. Floating-point instructions are only generated for 32-bit floating- point values, however, so the FPU hardware is not used for doubles if the -m64bit-doubles option is used. Note If the -fpu option is enabled then -funsafe-math-optimizations is also enabled automatically. This is because the RX FPU instructions are themselves unsafe. -mcpu=name Selects the type of RX CPU to be targeted. Currently three types are supported, the generic RX600 and RX200 series hardware and the specific RX610 CPU. The default is RX600. The only difference between RX600 and RX610 is that the RX610 does not support the "MVTIPL" instruction. The RX200 series does not have a hardware floating-point unit and so -nofpu is enabled by default when this type is selected. -mbig-endian-data -mlittle-endian-data Store data (but not code) in the big-endian format. The default is -mlittle-endian-data, i.e. to store data in the little-endian format. -msmall-data-limit=N Specifies the maximum size in bytes of global and static variables which can be placed into the small data area. Using the small data area can lead to smaller and faster code, but the size of area is limited and it is up to the programmer to ensure that the area does not overflow. Also when the small data area is used one of the RX's registers (usually "r13") is reserved for use pointing to this area, so it is no longer available for use by the compiler. This could result in slower and/or larger code if variables are pushed onto the stack instead of being held in this register. Note, common variables (variables that have not been initialized) and constants are not placed into the small data area as they are assigned to other sections in the output executable. The default value is zero, which disables this feature. Note, this feature is not enabled by default with higher optimization levels (-O2 etc) because of the potentially detrimental effects of reserving a register. It is up to the programmer to experiment and discover whether this feature is of benefit to their program. See the description of the -mpid option for a description of how the actual register to hold the small data area pointer is chosen. -msim -mno-sim Use the simulator runtime. The default is to use the libgloss board-specific runtime. -mas100-syntax -mno-as100-syntax When generating assembler output use a syntax that is compatible with Renesas's AS100 assembler. This syntax can also be handled by the GAS assembler, but it has some restrictions so it is not generated by default. -mmax-constant-size=N Specifies the maximum size, in bytes, of a constant that can be used as an operand in a RX instruction. Although the RX instruction set does allow constants of up to 4 bytes in length to be used in instructions, a longer value equates to a longer instruction. Thus in some circumstances it can be beneficial to restrict the size of constants that are used in instructions. Constants that are too big are instead placed into a constant pool and referenced via register indirection. The value N can be between 0 and 4. A value of 0 (the default) or 4 means that constants of any size are allowed. -mrelax Enable linker relaxation. Linker relaxation is a process whereby the linker attempts to reduce the size of a program by finding shorter versions of various instructions. Disabled by default. -mint-register=N Specify the number of registers to reserve for fast interrupt handler functions. The value N can be between 0 and 4. A value of 1 means that register "r13" is reserved for the exclusive use of fast interrupt handlers. A value of 2 reserves "r13" and "r12". A value of 3 reserves "r13", "r12" and "r11", and a value of 4 reserves "r13" through "r10". A value of 0, the default, does not reserve any registers. -msave-acc-in-interrupts Specifies that interrupt handler functions should preserve the accumulator register. This is only necessary if normal code might use the accumulator register, for example because it performs 64-bit multiplications. The default is to ignore the accumulator as this makes the interrupt handlers faster. -mpid -mno-pid Enables the generation of position independent data. When enabled any access to constant data is done via an offset from a base address held in a register. This allows the location of constant data to be determined at run time without requiring the executable to be relocated, which is a benefit to embedded applications with tight memory constraints. Data that can be modified is not affected by this option. Note, using this feature reserves a register, usually "r13", for the constant data base address. This can result in slower and/or larger code, especially in complicated functions. The actual register chosen to hold the constant data base address depends upon whether the -msmall-data-limit and/or the -mint-register command-line options are enabled. Starting with register "r13" and proceeding downwards, registers are allocated first to satisfy the requirements of -mint-register, then -mpid and finally -msmall-data-limit. Thus it is possible for the small data area register to be "r8" if both -mint-register=4 and -mpid are specified on the command line. By default this feature is not enabled. The default can be restored via the -mno-pid command-line option. -mno-warn-multiple-fast-interrupts -mwarn-multiple-fast-interrupts Prevents GCC from issuing a warning message if it finds more than one fast interrupt handler when it is compiling a file. The default is to issue a warning for each extra fast interrupt handler found, as the RX only supports one such interrupt. -mallow-string-insns -mno-allow-string-insns Enables or disables the use of the string manipulation instructions "SMOVF", "SCMPU", "SMOVB", "SMOVU", "SUNTIL" "SWHILE" and also the "RMPA" instruction. These instructions may prefetch data, which is not safe to do if accessing an I/O register. (See section 12.2.7 of the RX62N Group User's Manual for more information). The default is to allow these instructions, but it is not possible for GCC to reliably detect all circumstances where a string instruction might be used to access an I/O register, so their use cannot be disabled automatically. Instead it is reliant upon the programmer to use the -mno-allow-string-insns option if their program accesses I/O space. When the instructions are enabled GCC defines the C preprocessor symbol "__RX_ALLOW_STRING_INSNS__", otherwise it defines the symbol "__RX_DISALLOW_STRING_INSNS__". -mjsr -mno-jsr Use only (or not only) "JSR" instructions to access functions. This option can be used when code size exceeds the range of "BSR" instructions. Note that -mno-jsr does not mean to not use "JSR" but instead means that any type of branch may be used. Note: The generic GCC command-line option -ffixed-reg has special significance to the RX port when used with the "interrupt" function attribute. This attribute indicates a function intended to process fast interrupts. GCC ensures that it only uses the registers "r10", "r11", "r12" and/or "r13" and only provided that the normal use of the corresponding registers have been restricted via the -ffixed-reg or -mint-register command-line options. S/390 and zSeries Options These are the -m options defined for the S/390 and zSeries architecture. -mhard-float -msoft-float Use (do not use) the hardware floating-point instructions and registers for floating-point operations. When -msoft-float is specified, functions in libgcc.a are used to perform floating-point operations. When -mhard-float is specified, the compiler generates IEEE floating-point instructions. This is the default. -mhard-dfp -mno-hard-dfp Use (do not use) the hardware decimal-floating-point instructions for decimal-floating-point operations. When -mno-hard-dfp is specified, functions in libgcc.a are used to perform decimal- floating-point operations. When -mhard-dfp is specified, the compiler generates decimal-floating-point hardware instructions. This is the default for -march=z9-ec or higher. -mlong-double-64 -mlong-double-128 These switches control the size of "long double" type. A size of 64 bits makes the "long double" type equivalent to the "double" type. This is the default. -mbackchain -mno-backchain Store (do not store) the address of the caller's frame as backchain pointer into the callee's stack frame. A backchain may be needed to allow debugging using tools that do not understand DWARF call frame information. When -mno-packed-stack is in effect, the backchain pointer is stored at the bottom of the stack frame; when -mpacked-stack is in effect, the backchain is placed into the topmost word of the 96/160 byte register save area. In general, code compiled with -mbackchain is call-compatible with code compiled with -mno-backchain; however, use of the backchain for debugging purposes usually requires that the whole binary is built with -mbackchain. Note that the combination of -mbackchain, -mpacked-stack and -mhard-float is not supported. In order to build a linux kernel use -msoft-float. The default is to not maintain the backchain. -mpacked-stack -mno-packed-stack Use (do not use) the packed stack layout. When -mno-packed-stack is specified, the compiler uses the all fields of the 96/160 byte register save area only for their default purpose; unused fields still take up stack space. When -mpacked-stack is specified, register save slots are densely packed at the top of the register save area; unused space is reused for other purposes, allowing for more efficient use of the available stack space. However, when -mbackchain is also in effect, the topmost word of the save area is always used to store the backchain, and the return address register is always saved two words below the backchain. As long as the stack frame backchain is not used, code generated with -mpacked-stack is call-compatible with code generated with -mno-packed-stack. Note that some non-FSF releases of GCC 2.95 for S/390 or zSeries generated code that uses the stack frame backchain at run time, not just for debugging purposes. Such code is not call-compatible with code compiled with -mpacked-stack. Also, note that the combination of -mbackchain, -mpacked-stack and -mhard-float is not supported. In order to build a linux kernel use -msoft-float. The default is to not use the packed stack layout. -msmall-exec -mno-small-exec Generate (or do not generate) code using the "bras" instruction to do subroutine calls. This only works reliably if the total executable size does not exceed 64k. The default is to use the "basr" instruction instead, which does not have this limitation. -m64 -m31 When -m31 is specified, generate code compliant to the GNU/Linux for S/390 ABI. When -m64 is specified, generate code compliant to the GNU/Linux for zSeries ABI. This allows GCC in particular to generate 64-bit instructions. For the s390 targets, the default is -m31, while the s390x targets default to -m64. -mzarch -mesa When -mzarch is specified, generate code using the instructions available on z/Architecture. When -mesa is specified, generate code using the instructions available on ESA/390. Note that -mesa is not possible with -m64. When generating code compliant to the GNU/Linux for S/390 ABI, the default is -mesa. When generating code compliant to the GNU/Linux for zSeries ABI, the default is -mzarch. -mhtm -mno-htm The -mhtm option enables a set of builtins making use of instructions available with the transactional execution facility introduced with the IBM zEnterprise EC12 machine generation S/390 System z Built-in Functions. -mhtm is enabled by default when using -march=zEC12. -mvx -mno-vx When -mvx is specified, generate code using the instructions available with the vector extension facility introduced with the IBM z13 machine generation. This option changes the ABI for some vector type values with regard to alignment and calling conventions. In case vector type values are being used in an ABI- relevant context a GAS .gnu_attribute command will be added to mark the resulting binary with the ABI used. -mvx is enabled by default when using -march=z13. -mzvector -mno-zvector The -mzvector option enables vector language extensions and builtins using instructions available with the vector extension facility introduced with the IBM z13 machine generation. This option adds support for vector to be used as a keyword to define vector type variables and arguments. vector is only available when GNU extensions are enabled. It will not be expanded when requesting strict standard compliance e.g. with -std=c99. In addition to the GCC low-level builtins -mzvector enables a set of builtins added for compatibility with AltiVec-style implementations like Power and Cell. In order to make use of these builtins the header file vecintrin.h needs to be included. -mzvector is disabled by default. -mmvcle -mno-mvcle Generate (or do not generate) code using the "mvcle" instruction to perform block moves. When -mno-mvcle is specified, use a "mvc" loop instead. This is the default unless optimizing for size. -mdebug -mno-debug Print (or do not print) additional debug information when compiling. The default is to not print debug information. -march=cpu-type Generate code that runs on cpu-type, which is the name of a system representing a certain processor type. Possible values for cpu- type are z900/arch5, z990/arch6, z9-109, z9-ec/arch7, z10/arch8, z196/arch9, zEC12, z13/arch11, z14/arch12, z15/arch13, z16/arch14, and native. The default is -march=z900. Specifying native as cpu type can be used to select the best architecture option for the host processor. -march=native has no effect if GCC does not recognize the processor. -mtune=cpu-type Tune to cpu-type everything applicable about the generated code, except for the ABI and the set of available instructions. The list of cpu-type values is the same as for -march. The default is the value used for -march. -mtpf-trace -mno-tpf-trace Generate code that adds (does not add) in TPF OS specific branches to trace routines in the operating system. This option is off by default, even when compiling for the TPF OS. -mtpf-trace-skip -mno-tpf-trace-skip Generate code that changes (does not change) the default branch targets enabled by -mtpf-trace to point to specialized trace routines providing the ability of selectively skipping function trace entries for the TPF OS. This option is off by default, even when compiling for the TPF OS and specifying -mtpf-trace. -mfused-madd -mno-fused-madd Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. -mwarn-framesize=framesize Emit a warning if the current function exceeds the given frame size. Because this is a compile-time check it doesn't need to be a real problem when the program runs. It is intended to identify functions that most probably cause a stack overflow. It is useful to be used in an environment with limited stack size e.g. the linux kernel. -mwarn-dynamicstack Emit a warning if the function calls "alloca" or uses dynamically- sized arrays. This is generally a bad idea with a limited stack size. -mstack-guard=stack-guard -mstack-size=stack-size If these options are provided the S/390 back end emits additional instructions in the function prologue that trigger a trap if the stack size is stack-guard bytes above the stack-size (remember that the stack on S/390 grows downward). If the stack-guard option is omitted the smallest power of 2 larger than the frame size of the compiled function is chosen. These options are intended to be used to help debugging stack overflow problems. The additionally emitted code causes only little overhead and hence can also be used in production-like systems without greater performance degradation. The given values have to be exact powers of 2 and stack-size has to be greater than stack-guard without exceeding 64k. In order to be efficient the extra code makes the assumption that the stack starts at an address aligned to the value given by stack-size. The stack- guard option can only be used in conjunction with stack-size. -mhotpatch=pre-halfwords,post-halfwords If the hotpatch option is enabled, a "hot-patching" function prologue is generated for all functions in the compilation unit. The funtion label is prepended with the given number of two-byte NOP instructions (pre-halfwords, maximum 1000000). After the label, 2 * post-halfwords bytes are appended, using the largest NOP like instructions the architecture allows (maximum 1000000). If both arguments are zero, hotpatching is disabled. This option can be overridden for individual functions with the "hotpatch" attribute. SH Options These -m options are defined for the SH implementations: -m1 Generate code for the SH1. -m2 Generate code for the SH2. -m2e Generate code for the SH2e. -m2a-nofpu Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way that the floating-point unit is not used. -m2a-single-only Generate code for the SH2a-FPU, in such a way that no double- precision floating-point operations are used. -m2a-single Generate code for the SH2a-FPU assuming the floating-point unit is in single-precision mode by default. -m2a Generate code for the SH2a-FPU assuming the floating-point unit is in double-precision mode by default. -m3 Generate code for the SH3. -m3e Generate code for the SH3e. -m4-nofpu Generate code for the SH4 without a floating-point unit. -m4-single-only Generate code for the SH4 with a floating-point unit that only supports single-precision arithmetic. -m4-single Generate code for the SH4 assuming the floating-point unit is in single-precision mode by default. -m4 Generate code for the SH4. -m4-100 Generate code for SH4-100. -m4-100-nofpu Generate code for SH4-100 in such a way that the floating-point unit is not used. -m4-100-single Generate code for SH4-100 assuming the floating-point unit is in single-precision mode by default. -m4-100-single-only Generate code for SH4-100 in such a way that no double-precision floating-point operations are used. -m4-200 Generate code for SH4-200. -m4-200-nofpu Generate code for SH4-200 without in such a way that the floating- point unit is not used. -m4-200-single Generate code for SH4-200 assuming the floating-point unit is in single-precision mode by default. -m4-200-single-only Generate code for SH4-200 in such a way that no double-precision floating-point operations are used. -m4-300 Generate code for SH4-300. -m4-300-nofpu Generate code for SH4-300 without in such a way that the floating- point unit is not used. -m4-300-single Generate code for SH4-300 in such a way that no double-precision floating-point operations are used. -m4-300-single-only Generate code for SH4-300 in such a way that no double-precision floating-point operations are used. -m4-340 Generate code for SH4-340 (no MMU, no FPU). -m4-500 Generate code for SH4-500 (no FPU). Passes -isa=sh4-nofpu to the assembler. -m4a-nofpu Generate code for the SH4al-dsp, or for a SH4a in such a way that the floating-point unit is not used. -m4a-single-only Generate code for the SH4a, in such a way that no double-precision floating-point operations are used. -m4a-single Generate code for the SH4a assuming the floating-point unit is in single-precision mode by default. -m4a Generate code for the SH4a. -m4al Same as -m4a-nofpu, except that it implicitly passes -dsp to the assembler. GCC doesn't generate any DSP instructions at the moment. -mb Compile code for the processor in big-endian mode. -ml Compile code for the processor in little-endian mode. -mdalign Align doubles at 64-bit boundaries. Note that this changes the calling conventions, and thus some functions from the standard C library do not work unless you recompile it first with -mdalign. -mrelax Shorten some address references at link time, when possible; uses the linker option -relax. -mbigtable Use 32-bit offsets in "switch" tables. The default is to use 16-bit offsets. -mbitops Enable the use of bit manipulation instructions on SH2A. -mfmovd Enable the use of the instruction "fmovd". Check -mdalign for alignment constraints. -mrenesas Comply with the calling conventions defined by Renesas. -mno-renesas Comply with the calling conventions defined for GCC before the Renesas conventions were available. This option is the default for all targets of the SH toolchain. -mnomacsave Mark the "MAC" register as call-clobbered, even if -mrenesas is given. -mieee -mno-ieee Control the IEEE compliance of floating-point comparisons, which affects the handling of cases where the result of a comparison is unordered. By default -mieee is implicitly enabled. If -ffinite-math-only is enabled -mno-ieee is implicitly set, which results in faster floating-point greater-equal and less-equal comparisons. The implicit settings can be overridden by specifying either -mieee or -mno-ieee. -minline-ic_invalidate Inline code to invalidate instruction cache entries after setting up nested function trampolines. This option has no effect if -musermode is in effect and the selected code generation option (e.g. -m4) does not allow the use of the "icbi" instruction. If the selected code generation option does not allow the use of the "icbi" instruction, and -musermode is not in effect, the inlined code manipulates the instruction cache address array directly with an associative write. This not only requires privileged mode at run time, but it also fails if the cache line had been mapped via the TLB and has become unmapped. -misize Dump instruction size and location in the assembly code. -mpadstruct This option is deprecated. It pads structures to multiple of 4 bytes, which is incompatible with the SH ABI. -matomic-model=model Sets the model of atomic operations and additional parameters as a comma separated list. For details on the atomic built-in functions see __atomic Builtins. The following models and parameters are supported: none Disable compiler generated atomic sequences and emit library calls for atomic operations. This is the default if the target is not "sh*-*-linux*". soft-gusa Generate GNU/Linux compatible gUSA software atomic sequences for the atomic built-in functions. The generated atomic sequences require additional support from the interrupt/exception handling code of the system and are only suitable for SH3* and SH4* single-core systems. This option is enabled by default when the target is "sh*-*-linux*" and SH3* or SH4*. When the target is SH4A, this option also partially utilizes the hardware atomic instructions "movli.l" and "movco.l" to create more efficient code, unless strict is specified. soft-tcb Generate software atomic sequences that use a variable in the thread control block. This is a variation of the gUSA sequences which can also be used on SH1* and SH2* targets. The generated atomic sequences require additional support from the interrupt/exception handling code of the system and are only suitable for single-core systems. When using this model, the gbr-offset= parameter has to be specified as well. soft-imask Generate software atomic sequences that temporarily disable interrupts by setting "SR.IMASK = 1111". This model works only when the program runs in privileged mode and is only suitable for single-core systems. Additional support from the interrupt/exception handling code of the system is not required. This model is enabled by default when the target is "sh*-*-linux*" and SH1* or SH2*. hard-llcs Generate hardware atomic sequences using the "movli.l" and "movco.l" instructions only. This is only available on SH4A and is suitable for multi-core systems. Since the hardware instructions support only 32 bit atomic variables access to 8 or 16 bit variables is emulated with 32 bit accesses. Code compiled with this option is also compatible with other software atomic model interrupt/exception handling systems if executed on an SH4A system. Additional support from the interrupt/exception handling code of the system is not required for this model. gbr-offset= This parameter specifies the offset in bytes of the variable in the thread control block structure that should be used by the generated atomic sequences when the soft-tcb model has been selected. For other models this parameter is ignored. The specified value must be an integer multiple of four and in the range 0-1020. strict This parameter prevents mixed usage of multiple atomic models, even if they are compatible, and makes the compiler generate atomic sequences of the specified model only. -mtas Generate the "tas.b" opcode for "__atomic_test_and_set". Notice that depending on the particular hardware and software configuration this can degrade overall performance due to the operand cache line flushes that are implied by the "tas.b" instruction. On multi-core SH4A processors the "tas.b" instruction must be used with caution since it can result in data corruption for certain cache configurations. -mprefergot When generating position-independent code, emit function calls using the Global Offset Table instead of the Procedure Linkage Table. -musermode -mno-usermode Don't allow (allow) the compiler generating privileged mode code. Specifying -musermode also implies -mno-inline-ic_invalidate if the inlined code would not work in user mode. -musermode is the default when the target is "sh*-*-linux*". If the target is SH1* or SH2* -musermode has no effect, since there is no user mode. -multcost=number Set the cost to assume for a multiply insn. -mdiv=strategy Set the division strategy to be used for integer division operations. strategy can be one of: call-div1 Calls a library function that uses the single-step division instruction "div1" to perform the operation. Division by zero calculates an unspecified result and does not trap. This is the default except for SH4, SH2A and SHcompact. call-fp Calls a library function that performs the operation in double precision floating point. Division by zero causes a floating- point exception. This is the default for SHcompact with FPU. Specifying this for targets that do not have a double precision FPU defaults to "call-div1". call-table Calls a library function that uses a lookup table for small divisors and the "div1" instruction with case distinction for larger divisors. Division by zero calculates an unspecified result and does not trap. This is the default for SH4. Specifying this for targets that do not have dynamic shift instructions defaults to "call-div1". When a division strategy has not been specified the default strategy is selected based on the current target. For SH2A the default strategy is to use the "divs" and "divu" instructions instead of library function calls. -maccumulate-outgoing-args Reserve space once for outgoing arguments in the function prologue rather than around each call. Generally beneficial for performance and size. Also needed for unwinding to avoid changing the stack frame around conditional code. -mdivsi3_libfunc=name Set the name of the library function used for 32-bit signed division to name. This only affects the name used in the call division strategies, and the compiler still expects the same sets of input/output/clobbered registers as if this option were not present. -mfixed-range=register-range Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. -mbranch-cost=num Assume num to be the cost for a branch instruction. Higher numbers make the compiler try to generate more branch-free code if possible. If not specified the value is selected depending on the processor type that is being compiled for. -mzdcbranch -mno-zdcbranch Assume (do not assume) that zero displacement conditional branch instructions "bt" and "bf" are fast. If -mzdcbranch is specified, the compiler prefers zero displacement branch code sequences. This is enabled by default when generating code for SH4 and SH4A. It can be explicitly disabled by specifying -mno-zdcbranch. -mcbranch-force-delay-slot Force the usage of delay slots for conditional branches, which stuffs the delay slot with a "nop" if a suitable instruction cannot be found. By default this option is disabled. It can be enabled to work around hardware bugs as found in the original SH7055. -mfused-madd -mno-fused-madd Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. The machine-dependent -mfused-madd option is now mapped to the machine-independent -ffp-contract=fast option, and -mno-fused-madd is mapped to -ffp-contract=off. -mfsca -mno-fsca Allow or disallow the compiler to emit the "fsca" instruction for sine and cosine approximations. The option -mfsca must be used in combination with -funsafe-math-optimizations. It is enabled by default when generating code for SH4A. Using -mno-fsca disables sine and cosine approximations even if -funsafe-math-optimizations is in effect. -mfsrra -mno-fsrra Allow or disallow the compiler to emit the "fsrra" instruction for reciprocal square root approximations. The option -mfsrra must be used in combination with -funsafe-math-optimizations and -ffinite-math-only. It is enabled by default when generating code for SH4A. Using -mno-fsrra disables reciprocal square root approximations even if -funsafe-math-optimizations and -ffinite-math-only are in effect. -mpretend-cmove Prefer zero-displacement conditional branches for conditional move instruction patterns. This can result in faster code on the SH4 processor. -mfdpic Generate code using the FDPIC ABI. Solaris 2 Options These -m options are supported on Solaris 2: -mclear-hwcap -mclear-hwcap tells the compiler to remove the hardware capabilities generated by the Solaris assembler. This is only necessary when object files use ISA extensions not supported by the current machine, but check at runtime whether or not to use them. -mimpure-text -mimpure-text, used in addition to -shared, tells the compiler to not pass -z text to the linker when linking a shared object. Using this option, you can link position-dependent code into a shared object. -mimpure-text suppresses the "relocations remain against allocatable but non-writable sections" linker error message. However, the necessary relocations trigger copy-on-write, and the shared object is not actually shared across processes. Instead of using -mimpure-text, you should compile all source code with -fpic or -fPIC. These switches are supported in addition to the above on Solaris 2: -pthreads This is a synonym for -pthread. SPARC Options These -m options are supported on the SPARC: -mno-app-regs -mapp-regs Specify -mapp-regs to generate output using the global registers 2 through 4, which the SPARC SVR4 ABI reserves for applications. Like the global register 1, each global register 2 through 4 is then treated as an allocable register that is clobbered by function calls. This is the default. To be fully SVR4 ABI-compliant at the cost of some performance loss, specify -mno-app-regs. You should compile libraries and system software with this option. -mflat -mno-flat With -mflat, the compiler does not generate save/restore instructions and uses a "flat" or single register window model. This model is compatible with the regular register window model. The local registers and the input registers (0--5) are still treated as "call-saved" registers and are saved on the stack as needed. With -mno-flat (the default), the compiler generates save/restore instructions (except for leaf functions). This is the normal operating mode. -mfpu -mhard-float Generate output containing floating-point instructions. This is the default. -mno-fpu -msoft-float Generate output containing library calls for floating point. Warning: the requisite libraries are not available for all SPARC targets. Normally the facilities of the machine's usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. The embedded targets sparc-*-aout and sparclite-*-* do provide software floating-point support. -msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a, the library that comes with GCC, with -msoft-float in order for this to work. -mhard-quad-float Generate output containing quad-word (long double) floating-point instructions. -msoft-quad-float Generate output containing library calls for quad-word (long double) floating-point instructions. The functions called are those specified in the SPARC ABI. This is the default. As of this writing, there are no SPARC implementations that have hardware support for the quad-word floating-point instructions. They all invoke a trap handler for one of these instructions, and then the trap handler emulates the effect of the instruction. Because of the trap handler overhead, this is much slower than calling the ABI library routines. Thus the -msoft-quad-float option is the default. -mno-unaligned-doubles -munaligned-doubles Assume that doubles have 8-byte alignment. This is the default. With -munaligned-doubles, GCC assumes that doubles have 8-byte alignment only if they are contained in another type, or if they have an absolute address. Otherwise, it assumes they have 4-byte alignment. Specifying this option avoids some rare compatibility problems with code generated by other compilers. It is not the default because it results in a performance loss, especially for floating-point code. -muser-mode -mno-user-mode Do not generate code that can only run in supervisor mode. This is relevant only for the "casa" instruction emitted for the LEON3 processor. This is the default. -mfaster-structs -mno-faster-structs With -mfaster-structs, the compiler assumes that structures should have 8-byte alignment. This enables the use of pairs of "ldd" and "std" instructions for copies in structure assignment, in place of twice as many "ld" and "st" pairs. However, the use of this changed alignment directly violates the SPARC ABI. Thus, it's intended only for use on targets where the developer acknowledges that their resulting code is not directly in line with the rules of the ABI. -mstd-struct-return -mno-std-struct-return With -mstd-struct-return, the compiler generates checking code in functions returning structures or unions to detect size mismatches between the two sides of function calls, as per the 32-bit ABI. The default is -mno-std-struct-return. This option has no effect in 64-bit mode. -mlra -mno-lra Enable Local Register Allocation. This is the default for SPARC since GCC 7 so -mno-lra needs to be passed to get old Reload. -mcpu=cpu_type Set the instruction set, register set, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are v7, cypress, v8, supersparc, hypersparc, leon, leon3, leon3v7, leon5, sparclite, f930, f934, sparclite86x, sparclet, tsc701, v9, ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4, niagara7 and m8. Native Solaris and GNU/Linux toolchains also support the value native, which selects the best architecture option for the host processor. -mcpu=native has no effect if GCC does not recognize the processor. Default instruction scheduling parameters are used for values that select an architecture and not an implementation. These are v7, v8, sparclite, sparclet, v9. Here is a list of each supported architecture and their supported implementations. v7 cypress, leon3v7 v8 supersparc, hypersparc, leon, leon3, leon5 sparclite f930, f934, sparclite86x sparclet tsc701 v9 ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4, niagara7, m8 By default (unless configured otherwise), GCC generates code for the V7 variant of the SPARC architecture. With -mcpu=cypress, the compiler additionally optimizes it for the Cypress CY7C602 chip, as used in the SPARCStation/SPARCServer 3xx series. This is also appropriate for the older SPARCStation 1, 2, IPX etc. With -mcpu=v8, GCC generates code for the V8 variant of the SPARC architecture. The only difference from V7 code is that the compiler emits the integer multiply and integer divide instructions which exist in SPARC-V8 but not in SPARC-V7. With -mcpu=supersparc, the compiler additionally optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000 series. With -mcpu=sparclite, GCC generates code for the SPARClite variant of the SPARC architecture. This adds the integer multiply, integer divide step and scan ("ffs") instructions which exist in SPARClite but not in SPARC-V7. With -mcpu=f930, the compiler additionally optimizes it for the Fujitsu MB86930 chip, which is the original SPARClite, with no FPU. With -mcpu=f934, the compiler additionally optimizes it for the Fujitsu MB86934 chip, which is the more recent SPARClite with FPU. With -mcpu=sparclet, GCC generates code for the SPARClet variant of the SPARC architecture. This adds the integer multiply, multiply/accumulate, integer divide step and scan ("ffs") instructions which exist in SPARClet but not in SPARC-V7. With -mcpu=tsc701, the compiler additionally optimizes it for the TEMIC SPARClet chip. With -mcpu=v9, GCC generates code for the V9 variant of the SPARC architecture. This adds 64-bit integer and floating-point move instructions, 3 additional floating-point condition code registers and conditional move instructions. With -mcpu=ultrasparc, the compiler additionally optimizes it for the Sun UltraSPARC I/II/IIi chips. With -mcpu=ultrasparc3, the compiler additionally optimizes it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With -mcpu=niagara, the compiler additionally optimizes it for Sun UltraSPARC T1 chips. With -mcpu=niagara2, the compiler additionally optimizes it for Sun UltraSPARC T2 chips. With -mcpu=niagara3, the compiler additionally optimizes it for Sun UltraSPARC T3 chips. With -mcpu=niagara4, the compiler additionally optimizes it for Sun UltraSPARC T4 chips. With -mcpu=niagara7, the compiler additionally optimizes it for Oracle SPARC M7 chips. With -mcpu=m8, the compiler additionally optimizes it for Oracle M8 chips. -mtune=cpu_type Set the instruction scheduling parameters for machine type cpu_type, but do not set the instruction set or register set that the option -mcpu=cpu_type does. The same values for -mcpu=cpu_type can be used for -mtune=cpu_type, but the only useful values are those that select a particular CPU implementation. Those are cypress, supersparc, hypersparc, leon, leon3, leon3v7, leon5, f930, f934, sparclite86x, tsc701, ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4, niagara7 and m8. With native Solaris and GNU/Linux toolchains, native can also be used. -mv8plus -mno-v8plus With -mv8plus, GCC generates code for the SPARC-V8+ ABI. The difference from the V8 ABI is that the global and out registers are considered 64 bits wide. This is enabled by default on Solaris in 32-bit mode for all SPARC-V9 processors. -mvis -mno-vis With -mvis, GCC generates code that takes advantage of the UltraSPARC Visual Instruction Set extensions. The default is -mno-vis. -mvis2 -mno-vis2 With -mvis2, GCC generates code that takes advantage of version 2.0 of the UltraSPARC Visual Instruction Set extensions. The default is -mvis2 when targeting a cpu that supports such instructions, such as UltraSPARC-III and later. Setting -mvis2 also sets -mvis. -mvis3 -mno-vis3 With -mvis3, GCC generates code that takes advantage of version 3.0 of the UltraSPARC Visual Instruction Set extensions. The default is -mvis3 when targeting a cpu that supports such instructions, such as niagara-3 and later. Setting -mvis3 also sets -mvis2 and -mvis. -mvis4 -mno-vis4 With -mvis4, GCC generates code that takes advantage of version 4.0 of the UltraSPARC Visual Instruction Set extensions. The default is -mvis4 when targeting a cpu that supports such instructions, such as niagara-7 and later. Setting -mvis4 also sets -mvis3, -mvis2 and -mvis. -mvis4b -mno-vis4b With -mvis4b, GCC generates code that takes advantage of version 4.0 of the UltraSPARC Visual Instruction Set extensions, plus the additional VIS instructions introduced in the Oracle SPARC Architecture 2017. The default is -mvis4b when targeting a cpu that supports such instructions, such as m8 and later. Setting -mvis4b also sets -mvis4, -mvis3, -mvis2 and -mvis. -mcbcond -mno-cbcond With -mcbcond, GCC generates code that takes advantage of the UltraSPARC Compare-and-Branch-on-Condition instructions. The default is -mcbcond when targeting a CPU that supports such instructions, such as Niagara-4 and later. -mfmaf -mno-fmaf With -mfmaf, GCC generates code that takes advantage of the UltraSPARC Fused Multiply-Add Floating-point instructions. The default is -mfmaf when targeting a CPU that supports such instructions, such as Niagara-3 and later. -mfsmuld -mno-fsmuld With -mfsmuld, GCC generates code that takes advantage of the Floating-point Multiply Single to Double (FsMULd) instruction. The default is -mfsmuld when targeting a CPU supporting the architecture versions V8 or V9 with FPU except -mcpu=leon. -mpopc -mno-popc With -mpopc, GCC generates code that takes advantage of the UltraSPARC Population Count instruction. The default is -mpopc when targeting a CPU that supports such an instruction, such as Niagara-2 and later. -msubxc -mno-subxc With -msubxc, GCC generates code that takes advantage of the UltraSPARC Subtract-Extended-with-Carry instruction. The default is -msubxc when targeting a CPU that supports such an instruction, such as Niagara-7 and later. -mfix-at697f Enable the documented workaround for the single erratum of the Atmel AT697F processor (which corresponds to erratum #13 of the AT697E processor). -mfix-ut699 Enable the documented workarounds for the floating-point errata and the data cache nullify errata of the UT699 processor. -mfix-ut700 Enable the documented workaround for the back-to-back store errata of the UT699E/UT700 processor. -mfix-gr712rc Enable the documented workaround for the back-to-back store errata of the GR712RC processor. These -m options are supported in addition to the above on SPARC-V9 processors in 64-bit environments: -m32 -m64 Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits. -mcmodel=which Set the code model to one of medlow The Medium/Low code model: 64-bit addresses, programs must be linked in the low 32 bits of memory. Programs can be statically or dynamically linked. medmid The Medium/Middle code model: 64-bit addresses, programs must be linked in the low 44 bits of memory, the text and data segments must be less than 2GB in size and the data segment must be located within 2GB of the text segment. medany The Medium/Anywhere code model: 64-bit addresses, programs may be linked anywhere in memory, the text and data segments must be less than 2GB in size and the data segment must be located within 2GB of the text segment. embmedany The Medium/Anywhere code model for embedded systems: 64-bit addresses, the text and data segments must be less than 2GB in size, both starting anywhere in memory (determined at link time). The global register %g4 points to the base of the data segment. Programs are statically linked and PIC is not supported. -mmemory-model=mem-model Set the memory model in force on the processor to one of default The default memory model for the processor and operating system. rmo Relaxed Memory Order pso Partial Store Order tso Total Store Order sc Sequential Consistency These memory models are formally defined in Appendix D of the SPARC-V9 architecture manual, as set in the processor's "PSTATE.MM" field. -mstack-bias -mno-stack-bias With -mstack-bias, GCC assumes that the stack pointer, and frame pointer if present, are offset by -2047 which must be added back when making stack frame references. This is the default in 64-bit mode. Otherwise, assume no such offset is present. Options for System V These additional options are available on System V Release 4 for compatibility with other compilers on those systems: -G Create a shared object. It is recommended that -symbolic or -shared be used instead. -Qy Identify the versions of each tool used by the compiler, in a ".ident" assembler directive in the output. -Qn Refrain from adding ".ident" directives to the output file (this is the default). -YP,dirs Search the directories dirs, and no others, for libraries specified with -l. -Ym,dir Look in the directory dir to find the M4 preprocessor. The assembler uses this option. V850 Options These -m options are defined for V850 implementations: -mlong-calls -mno-long-calls Treat all calls as being far away (near). If calls are assumed to be far away, the compiler always loads the function's address into a register, and calls indirect through the pointer. -mno-ep -mep Do not optimize (do optimize) basic blocks that use the same index pointer 4 or more times to copy pointer into the "ep" register, and use the shorter "sld" and "sst" instructions. The -mep option is on by default if you optimize. -mno-prolog-function -mprolog-function Do not use (do use) external functions to save and restore registers at the prologue and epilogue of a function. The external functions are slower, but use less code space if more than one function saves the same number of registers. The -mprolog-function option is on by default if you optimize. -mspace Try to make the code as small as possible. At present, this just turns on the -mep and -mprolog-function options. -mtda=n Put static or global variables whose size is n bytes or less into the tiny data area that register "ep" points to. The tiny data area can hold up to 256 bytes in total (128 bytes for byte references). -msda=n Put static or global variables whose size is n bytes or less into the small data area that register "gp" points to. The small data area can hold up to 64 kilobytes. -mzda=n Put static or global variables whose size is n bytes or less into the first 32 kilobytes of memory. -mv850 Specify that the target processor is the V850. -mv850e3v5 Specify that the target processor is the V850E3V5. The preprocessor constant "__v850e3v5__" is defined if this option is used. -mv850e2v4 Specify that the target processor is the V850E3V5. This is an alias for the -mv850e3v5 option. -mv850e2v3 Specify that the target processor is the V850E2V3. The preprocessor constant "__v850e2v3__" is defined if this option is used. -mv850e2 Specify that the target processor is the V850E2. The preprocessor constant "__v850e2__" is defined if this option is used. -mv850e1 Specify that the target processor is the V850E1. The preprocessor constants "__v850e1__" and "__v850e__" are defined if this option is used. -mv850es Specify that the target processor is the V850ES. This is an alias for the -mv850e1 option. -mv850e Specify that the target processor is the V850E. The preprocessor constant "__v850e__" is defined if this option is used. If neither -mv850 nor -mv850e nor -mv850e1 nor -mv850e2 nor -mv850e2v3 nor -mv850e3v5 are defined then a default target processor is chosen and the relevant __v850*__ preprocessor constant is defined. The preprocessor constants "__v850" and "__v851__" are always defined, regardless of which processor variant is the target. -mdisable-callt -mno-disable-callt This option suppresses generation of the "CALLT" instruction for the v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the v850 architecture. This option is enabled by default when the RH850 ABI is in use (see -mrh850-abi), and disabled by default when the GCC ABI is in use. If "CALLT" instructions are being generated then the C preprocessor symbol "__V850_CALLT__" is defined. -mrelax -mno-relax Pass on (or do not pass on) the -mrelax command-line option to the assembler. -mlong-jumps -mno-long-jumps Disable (or re-enable) the generation of PC-relative jump instructions. -msoft-float -mhard-float Disable (or re-enable) the generation of hardware floating point instructions. This option is only significant when the target architecture is V850E2V3 or higher. If hardware floating point instructions are being generated then the C preprocessor symbol "__FPU_OK__" is defined, otherwise the symbol "__NO_FPU__" is defined. -mloop Enables the use of the e3v5 LOOP instruction. The use of this instruction is not enabled by default when the e3v5 architecture is selected because its use is still experimental. -mrh850-abi -mghs Enables support for the RH850 version of the V850 ABI. This is the default. With this version of the ABI the following rules apply: * Integer sized structures and unions are returned via a memory pointer rather than a register. * Large structures and unions (more than 8 bytes in size) are passed by value. * Functions are aligned to 16-bit boundaries. * The -m8byte-align command-line option is supported. * The -mdisable-callt command-line option is enabled by default. The -mno-disable-callt command-line option is not supported. When this version of the ABI is enabled the C preprocessor symbol "__V850_RH850_ABI__" is defined. -mgcc-abi Enables support for the old GCC version of the V850 ABI. With this version of the ABI the following rules apply: * Integer sized structures and unions are returned in register "r10". * Large structures and unions (more than 8 bytes in size) are passed by reference. * Functions are aligned to 32-bit boundaries, unless optimizing for size. * The -m8byte-align command-line option is not supported. * The -mdisable-callt command-line option is supported but not enabled by default. When this version of the ABI is enabled the C preprocessor symbol "__V850_GCC_ABI__" is defined. -m8byte-align -mno-8byte-align Enables support for "double" and "long long" types to be aligned on 8-byte boundaries. The default is to restrict the alignment of all objects to at most 4-bytes. When -m8byte-align is in effect the C preprocessor symbol "__V850_8BYTE_ALIGN__" is defined. -mbig-switch Generate code suitable for big switch tables. Use this option only if the assembler/linker complain about out of range branches within a switch table. -mapp-regs This option causes r2 and r5 to be used in the code generated by the compiler. This setting is the default. -mno-app-regs This option causes r2 and r5 to be treated as fixed registers. VAX Options These -m options are defined for the VAX: -munix Do not output certain jump instructions ("aobleq" and so on) that the Unix assembler for the VAX cannot handle across long ranges. -mgnu Do output those jump instructions, on the assumption that the GNU assembler is being used. -mg Output code for G-format floating-point numbers instead of D-format. -mlra -mno-lra Enable Local Register Allocation. This is still experimental for the VAX, so by default the compiler uses standard reload. Visium Options -mdebug A program which performs file I/O and is destined to run on an MCM target should be linked with this option. It causes the libraries libc.a and libdebug.a to be linked. The program should be run on the target under the control of the GDB remote debugging stub. -msim A program which performs file I/O and is destined to run on the simulator should be linked with option. This causes libraries libc.a and libsim.a to be linked. -mfpu -mhard-float Generate code containing floating-point instructions. This is the default. -mno-fpu -msoft-float Generate code containing library calls for floating-point. -msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a, the library that comes with GCC, with -msoft-float in order for this to work. -mcpu=cpu_type Set the instruction set, register set, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are mcm, gr5 and gr6. mcm is a synonym of gr5 present for backward compatibility. By default (unless configured otherwise), GCC generates code for the GR5 variant of the Visium architecture. With -mcpu=gr6, GCC generates code for the GR6 variant of the Visium architecture. The only difference from GR5 code is that the compiler will generate block move instructions. -mtune=cpu_type Set the instruction scheduling parameters for machine type cpu_type, but do not set the instruction set or register set that the option -mcpu=cpu_type would. -msv-mode Generate code for the supervisor mode, where there are no restrictions on the access to general registers. This is the default. -muser-mode Generate code for the user mode, where the access to some general registers is forbidden: on the GR5, registers r24 to r31 cannot be accessed in this mode; on the GR6, only registers r29 to r31 are affected. VMS Options These -m options are defined for the VMS implementations: -mvms-return-codes Return VMS condition codes from "main". The default is to return POSIX-style condition (e.g. error) codes. -mdebug-main=prefix Flag the first routine whose name starts with prefix as the main routine for the debugger. -mmalloc64 Default to 64-bit memory allocation routines. -mpointer-size=size Set the default size of pointers. Possible options for size are 32 or short for 32 bit pointers, 64 or long for 64 bit pointers, and no for supporting only 32 bit pointers. The later option disables "pragma pointer_size". VxWorks Options The options in this section are defined for all VxWorks targets. Options specific to the target hardware are listed with the other options for that target. -mrtp GCC can generate code for both VxWorks kernels and real time processes (RTPs). This option switches from the former to the latter. It also defines the preprocessor macro "__RTP__". -non-static Link an RTP executable against shared libraries rather than static libraries. The options -static and -shared can also be used for RTPs; -static is the default. -Bstatic -Bdynamic These options are passed down to the linker. They are defined for compatibility with Diab. -Xbind-lazy Enable lazy binding of function calls. This option is equivalent to -Wl,-z,now and is defined for compatibility with Diab. -Xbind-now Disable lazy binding of function calls. This option is the default and is defined for compatibility with Diab. x86 Options These -m options are defined for the x86 family of computers. -march=cpu-type Generate instructions for the machine type cpu-type. In contrast to -mtune=cpu-type, which merely tunes the generated code for the specified cpu-type, -march=cpu-type allows GCC to generate code that may not run at all on processors other than the one indicated. Specifying -march=cpu-type implies -mtune=cpu-type, except where noted otherwise. The choices for cpu-type are: native This selects the CPU to generate code for at compilation time by determining the processor type of the compiling machine. Using -march=native enables all instruction subsets supported by the local machine (hence the result might not run on different machines). Using -mtune=native produces code optimized for the local machine under the constraints of the selected instruction set. x86-64 A generic CPU with 64-bit extensions. x86-64-v2 x86-64-v3 x86-64-v4 These choices for cpu-type select the corresponding micro- architecture level from the x86-64 psABI. On ABIs other than the x86-64 psABI they select the same CPU features as the x86-64 psABI documents for the particular micro-architecture level. Since these cpu-type values do not have a corresponding -mtune setting, using -march with these values enables generic tuning. Specific tuning can be enabled using the -mtune=other-cpu-type option with an appropriate other-cpu-type value. i386 Original Intel i386 CPU. i486 Intel i486 CPU. (No scheduling is implemented for this chip.) i586 pentium Intel Pentium CPU with no MMX support. lakemont Intel Lakemont MCU, based on Intel Pentium CPU. pentium-mmx Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support. pentiumpro Intel Pentium Pro CPU. i686 When used with -march, the Pentium Pro instruction set is used, so the code runs on all i686 family chips. When used with -mtune, it has the same meaning as generic. pentium2 Intel Pentium II CPU, based on Pentium Pro core with MMX and FXSR instruction set support. pentium3 pentium3m Intel Pentium III CPU, based on Pentium Pro core with MMX, FXSR and SSE instruction set support. pentium-m Intel Pentium M; low-power version of Intel Pentium III CPU with MMX, SSE, SSE2 and FXSR instruction set support. Used by Centrino notebooks. pentium4 pentium4m Intel Pentium 4 CPU with MMX, SSE, SSE2 and FXSR instruction set support. prescott Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2, SSE3 and FXSR instruction set support. nocona Improved version of Intel Pentium 4 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and FXSR instruction set support. core2 Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, CX16, SAHF and FXSR instruction set support. nehalem Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF and FXSR instruction set support. westmere Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR and PCLMUL instruction set support. sandybridge Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE and PCLMUL instruction set support. ivybridge Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND and F16C instruction set support. haswell Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE and HLE instruction set support. broadwell Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX and PREFETCHW instruction set support. skylake Intel Skylake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES and SGX instruction set support. bonnell Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3 and SSSE3 instruction set support. silvermont Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, PCLMUL, PREFETCHW and RDRND instruction set support. goldmont Intel Goldmont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, PCLMUL, PREFETCHW, RDRND, AES, SHA, RDSEED, XSAVE, XSAVEC, XSAVES, XSAVEOPT, CLFLUSHOPT and FSGSBASE instruction set support. goldmont-plus Intel Goldmont Plus CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, PCLMUL, PREFETCHW, RDRND, AES, SHA, RDSEED, XSAVE, XSAVEC, XSAVES, XSAVEOPT, CLFLUSHOPT, FSGSBASE, PTWRITE, RDPID and SGX instruction set support. tremont Intel Tremont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, PCLMUL, PREFETCHW, RDRND, AES, SHA, RDSEED, XSAVE, XSAVEC, XSAVES, XSAVEOPT, CLFLUSHOPT, FSGSBASE, PTWRITE, RDPID, SGX, CLWB, GFNI-SSE, MOVDIRI, MOVDIR64B, CLDEMOTE and WAITPKG instruction set support. sierraforest Intel Sierra Forest CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW, PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT, FSGSBASE, PTWRITE, RDPID, SGX, GFNI-SSE, CLWB, MOVDIRI, MOVDIR64B, CLDEMOTE, WAITPKG, ADCX, AVX, AVX2, BMI, BMI2, F16C, FMA, LZCNT, PCONFIG, PKU, VAES, VPCLMULQDQ, SERIALIZE, HRESET, KL, WIDEKL, AVX-VNNI, AVXIFMA, AVXVNNIINT8, AVXNECONVERT, CMPCCXADD, ENQCMD and UINTR instruction set support. grandridge Intel Grand Ridge CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW, PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT, FSGSBASE, PTWRITE, RDPID, SGX, GFNI-SSE, CLWB, MOVDIRI, MOVDIR64B, CLDEMOTE, WAITPKG, ADCX, AVX, AVX2, BMI, BMI2, F16C, FMA, LZCNT, PCONFIG, PKU, VAES, VPCLMULQDQ, SERIALIZE, HRESET, KL, WIDEKL, AVX-VNNI, AVXIFMA, AVXVNNIINT8, AVXNECONVERT, CMPCCXADD, ENQCMD, UINTR and RAOINT instruction set support. knl Intel Knight's Landing CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AVX512PF, AVX512ER, AVX512F, AVX512CD and PREFETCHWT1 instruction set support. knm Intel Knights Mill CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AVX512PF, AVX512ER, AVX512F, AVX512CD and PREFETCHWT1, AVX5124VNNIW, AVX5124FMAPS and AVX512VPOPCNTDQ instruction set support. skylake-avx512 Intel Skylake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL, AVX512BW, AVX512DQ and AVX512CD instruction set support. cannonlake Intel Cannonlake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA and SHA instruction set support. icelake-client Intel Icelake Client CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2 , VPCLMULQDQ, AVX512BITALG, RDPID and AVX512VPOPCNTDQ instruction set support. icelake-server Intel Icelake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2 , VPCLMULQDQ, AVX512BITALG, RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD and CLWB instruction set support. cascadelake Intel Cascadelake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL, AVX512BW, AVX512DQ, AVX512CD and AVX512VNNI instruction set support. cooperlake Intel cooperlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL, AVX512BW, AVX512DQ, AVX512CD, AVX512VNNI and AVX512BF16 instruction set support. tigerlake Intel Tigerlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2, VPCLMULQDQ, AVX512BITALG, RDPID, AVX512VPOPCNTDQ, MOVDIRI, MOVDIR64B, CLWB, AVX512VP2INTERSECT and KEYLOCKER instruction set support. sapphirerapids Intel sapphirerapids CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2, VPCLMULQDQ, AVX512BITALG, RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD, CLWB, MOVDIRI, MOVDIR64B, ENQCMD, CLDEMOTE, PTWRITE, WAITPKG, SERIALIZE, TSXLDTRK, UINTR, AMX-BF16, AMX-TILE, AMX-INT8, AVX-VNNI, AVX512-FP16 and AVX512BF16 instruction set support. alderlake Intel Alderlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW, PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT, FSGSBASE, PTWRITE, RDPID, SGX, GFNI-SSE, CLWB, MOVDIRI, MOVDIR64B, CLDEMOTE, WAITPKG, ADCX, AVX, AVX2, BMI, BMI2, F16C, FMA, LZCNT, PCONFIG, PKU, VAES, VPCLMULQDQ, SERIALIZE, HRESET, KL, WIDEKL and AVX-VNNI instruction set support. rocketlake Intel Rocketlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3 , SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2, VPCLMULQDQ, AVX512BITALG, RDPID and AVX512VPOPCNTDQ instruction set support. graniterapids Intel graniterapids CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2, VPCLMULQDQ, AVX512BITALG, RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD, CLWB, MOVDIRI, MOVDIR64B, ENQCMD, CLDEMOTE, PTWRITE, WAITPKG, SERIALIZE, TSXLDTRK, UINTR, AMX-BF16, AMX-TILE, AMX-INT8, AVX-VNNI, AVX512-FP16, AVX512BF16, AMX-FP16 and PREFETCHI instruction set support. graniterapids-d Intel graniterapids D CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2, VPCLMULQDQ, AVX512BITALG, RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD, CLWB, MOVDIRI, MOVDIR64B, ENQCMD, CLDEMOTE, PTWRITE, WAITPKG, SERIALIZE, TSXLDTRK, UINTR, AMX-BF16, AMX-TILE, AMX-INT8, AVX-VNNI, AVX512FP16, AVX512BF16, AMX-FP16, PREFETCHI and AMX-COMPLEX instruction set support. k6 AMD K6 CPU with MMX instruction set support. k6-2 k6-3 Improved versions of AMD K6 CPU with MMX and 3DNow! instruction set support. athlon athlon-tbird AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow! and SSE prefetch instructions support. athlon-4 athlon-xp athlon-mp Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow! and full SSE instruction set support. k8 opteron athlon64 athlon-fx Processors based on the AMD K8 core with x86-64 instruction set support, including the AMD Opteron, Athlon 64, and Athlon 64 FX processors. (This supersets MMX, SSE, SSE2, 3DNow!, enhanced 3DNow! and 64-bit instruction set extensions.) k8-sse3 opteron-sse3 athlon64-sse3 Improved versions of AMD K8 cores with SSE3 instruction set support. amdfam10 barcelona CPUs based on AMD Family 10h cores with x86-64 instruction set support. (This supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!, enhanced 3DNow!, ABM and 64-bit instruction set extensions.) bdver1 CPUs based on AMD Family 15h cores with x86-64 instruction set support. (This supersets FMA4, AVX, XOP, LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.) bdver2 AMD Family 15h core based CPUs with x86-64 instruction set support. (This supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP, LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.) bdver3 AMD Family 15h core based CPUs with x86-64 instruction set support. (This supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, XOP, LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.) bdver4 AMD Family 15h core based CPUs with x86-64 instruction set support. (This supersets BMI, BMI2, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, AVX2, XOP, LWP, AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.) znver1 AMD Family 17h core based CPUs with x86-64 instruction set support. (This supersets BMI, BMI2, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, and 64-bit instruction set extensions.) znver2 AMD Family 17h core based CPUs with x86-64 instruction set support. (This supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID, WBNOINVD, and 64-bit instruction set extensions.) znver3 AMD Family 19h core based CPUs with x86-64 instruction set support. (This supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID, WBNOINVD, PKU, VPCLMULQDQ, VAES, and 64-bit instruction set extensions.) znver4 AMD Family 19h core based CPUs with x86-64 instruction set support. (This supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID, WBNOINVD, PKU, VPCLMULQDQ, VAES, AVX512F, AVX512DQ, AVX512IFMA, AVX512CD, AVX512BW, AVX512VL, AVX512BF16, AVX512VBMI, AVX512VBMI2, AVX512VNNI, AVX512BITALG, AVX512VPOPCNTDQ, GFNI and 64-bit instruction set extensions.) btver1 CPUs based on AMD Family 14h cores with x86-64 instruction set support. (This supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A, CX16, ABM and 64-bit instruction set extensions.) btver2 CPUs based on AMD Family 16h cores with x86-64 instruction set support. This includes MOVBE, F16C, BMI, AVX, PCLMUL, AES, SSE4.2, SSE4.1, CX16, ABM, SSE4A, SSSE3, SSE3, SSE2, SSE, MMX and 64-bit instruction set extensions. winchip-c6 IDT WinChip C6 CPU, dealt in same way as i486 with additional MMX instruction set support. winchip2 IDT WinChip 2 CPU, dealt in same way as i486 with additional MMX and 3DNow! instruction set support. c3 VIA C3 CPU with MMX and 3DNow! instruction set support. (No scheduling is implemented for this chip.) c3-2 VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set support. (No scheduling is implemented for this chip.) c7 VIA C7 (Esther) CPU with MMX, SSE, SSE2 and SSE3 instruction set support. (No scheduling is implemented for this chip.) samuel-2 VIA Eden Samuel 2 CPU with MMX and 3DNow! instruction set support. (No scheduling is implemented for this chip.) nehemiah VIA Eden Nehemiah CPU with MMX and SSE instruction set support. (No scheduling is implemented for this chip.) esther VIA Eden Esther CPU with MMX, SSE, SSE2 and SSE3 instruction set support. (No scheduling is implemented for this chip.) eden-x2 VIA Eden X2 CPU with x86-64, MMX, SSE, SSE2 and SSE3 instruction set support. (No scheduling is implemented for this chip.) eden-x4 VIA Eden X4 CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, AVX and AVX2 instruction set support. (No scheduling is implemented for this chip.) nano Generic VIA Nano CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3 instruction set support. (No scheduling is implemented for this chip.) nano-1000 VIA Nano 1xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3 instruction set support. (No scheduling is implemented for this chip.) nano-2000 VIA Nano 2xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3 instruction set support. (No scheduling is implemented for this chip.) nano-3000 VIA Nano 3xxx CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1 instruction set support. (No scheduling is implemented for this chip.) nano-x2 VIA Nano Dual Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1 instruction set support. (No scheduling is implemented for this chip.) nano-x4 VIA Nano Quad Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1 instruction set support. (No scheduling is implemented for this chip.) lujiazui ZHAOXIN lujiazui CPU with x86-64, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, AVX, POPCNT, AES, PCLMUL, RDRND, XSAVE, XSAVEOPT, FSGSBASE, CX16, ABM, BMI, BMI2, F16C, FXSR, RDSEED instruction set support. geode AMD Geode embedded processor with MMX and 3DNow! instruction set support. -mtune=cpu-type Tune to cpu-type everything applicable about the generated code, except for the ABI and the set of available instructions. While picking a specific cpu-type schedules things appropriately for that particular chip, the compiler does not generate any code that cannot run on the default machine type unless you use a -march=cpu- type option. For example, if GCC is configured for i686-pc-linux-gnu then -mtune=pentium4 generates code that is tuned for Pentium 4 but still runs on i686 machines. The choices for cpu-type are the same as for -march. In addition, -mtune supports 2 extra choices for cpu-type: generic Produce code optimized for the most common IA32/AMD64/EM64T processors. If you know the CPU on which your code will run, then you should use the corresponding -mtune or -march option instead of -mtune=generic. But, if you do not know exactly what CPU users of your application will have, then you should use this option. As new processors are deployed in the marketplace, the behavior of this option will change. Therefore, if you upgrade to a newer version of GCC, code generation controlled by this option will change to reflect the processors that are most common at the time that version of GCC is released. There is no -march=generic option because -march indicates the instruction set the compiler can use, and there is no generic instruction set applicable to all processors. In contrast, -mtune indicates the processor (or, in this case, collection of processors) for which the code is optimized. intel Produce code optimized for the most current Intel processors, which are Haswell and Silvermont for this version of GCC. If you know the CPU on which your code will run, then you should use the corresponding -mtune or -march option instead of -mtune=intel. But, if you want your application performs better on both Haswell and Silvermont, then you should use this option. As new Intel processors are deployed in the marketplace, the behavior of this option will change. Therefore, if you upgrade to a newer version of GCC, code generation controlled by this option will change to reflect the most current Intel processors at the time that version of GCC is released. There is no -march=intel option because -march indicates the instruction set the compiler can use, and there is no common instruction set applicable to all processors. In contrast, -mtune indicates the processor (or, in this case, collection of processors) for which the code is optimized. -mcpu=cpu-type A deprecated synonym for -mtune. -mfpmath=unit Generate floating-point arithmetic for selected unit unit. The choices for unit are: 387 Use the standard 387 floating-point coprocessor present on the majority of chips and emulated otherwise. Code compiled with this option runs almost everywhere. The temporary results are computed in 80-bit precision instead of the precision specified by the type, resulting in slightly different results compared to most of other chips. See -ffloat-store for more detailed description. This is the default choice for non-Darwin x86-32 targets. sse Use scalar floating-point instructions present in the SSE instruction set. This instruction set is supported by Pentium III and newer chips, and in the AMD line by Athlon-4, Athlon XP and Athlon MP chips. The earlier version of the SSE instruction set supports only single-precision arithmetic, thus the double and extended-precision arithmetic are still done using 387. A later version, present only in Pentium 4 and AMD x86-64 chips, supports double-precision arithmetic too. For the x86-32 compiler, you must use -march=cpu-type, -msse or -msse2 switches to enable SSE extensions and make this option effective. For the x86-64 compiler, these extensions are enabled by default. The resulting code should be considerably faster in the majority of cases and avoid the numerical instability problems of 387 code, but may break some existing code that expects temporaries to be 80 bits. This is the default choice for the x86-64 compiler, Darwin x86-32 targets, and the default choice for x86-32 targets with the SSE2 instruction set when -ffast-math is enabled. sse,387 sse+387 both Attempt to utilize both instruction sets at once. This effectively doubles the amount of available registers, and on chips with separate execution units for 387 and SSE the execution resources too. Use this option with care, as it is still experimental, because the GCC register allocator does not model separate functional units well, resulting in unstable performance. -masm=dialect Output assembly instructions using selected dialect. Also affects which dialect is used for basic "asm" and extended "asm". Supported choices (in dialect order) are att or intel. The default is att. Darwin does not support intel. -mieee-fp -mno-ieee-fp Control whether or not the compiler uses IEEE floating-point comparisons. These correctly handle the case where the result of a comparison is unordered. -m80387 -mhard-float Generate output containing 80387 instructions for floating point. -mno-80387 -msoft-float Generate output containing library calls for floating point. Warning: the requisite libraries are not part of GCC. Normally the facilities of the machine's usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross- compilation. On machines where a function returns floating-point results in the 80387 register stack, some floating-point opcodes may be emitted even if -msoft-float is used. -mno-fp-ret-in-387 Do not use the FPU registers for return values of functions. The usual calling convention has functions return values of types "float" and "double" in an FPU register, even if there is no FPU. The idea is that the operating system should emulate an FPU. The option -mno-fp-ret-in-387 causes such values to be returned in ordinary CPU registers instead. -mno-fancy-math-387 Some 387 emulators do not support the "sin", "cos" and "sqrt" instructions for the 387. Specify this option to avoid generating those instructions. This option is overridden when -march indicates that the target CPU always has an FPU and so the instruction does not need emulation. These instructions are not generated unless you also use the -funsafe-math-optimizations switch. -malign-double -mno-align-double Control whether GCC aligns "double", "long double", and "long long" variables on a two-word boundary or a one-word boundary. Aligning "double" variables on a two-word boundary produces code that runs somewhat faster on a Pentium at the expense of more memory. On x86-64, -malign-double is enabled by default. Warning: if you use the -malign-double switch, structures containing the above types are aligned differently than the published application binary interface specifications for the x86-32 and are not binary compatible with structures in code compiled without that switch. -m96bit-long-double -m128bit-long-double These switches control the size of "long double" type. The x86-32 application binary interface specifies the size to be 96 bits, so -m96bit-long-double is the default in 32-bit mode. Modern architectures (Pentium and newer) prefer "long double" to be aligned to an 8- or 16-byte boundary. In arrays or structures conforming to the ABI, this is not possible. So specifying -m128bit-long-double aligns "long double" to a 16-byte boundary by padding the "long double" with an additional 32-bit zero. In the x86-64 compiler, -m128bit-long-double is the default choice as its ABI specifies that "long double" is aligned on 16-byte boundary. Notice that neither of these options enable any extra precision over the x87 standard of 80 bits for a "long double". Warning: if you override the default value for your target ABI, this changes the size of structures and arrays containing "long double" variables, as well as modifying the function calling convention for functions taking "long double". Hence they are not binary-compatible with code compiled without that switch. -mlong-double-64 -mlong-double-80 -mlong-double-128 These switches control the size of "long double" type. A size of 64 bits makes the "long double" type equivalent to the "double" type. This is the default for 32-bit Bionic C library. A size of 128 bits makes the "long double" type equivalent to the "__float128" type. This is the default for 64-bit Bionic C library. Warning: if you override the default value for your target ABI, this changes the size of structures and arrays containing "long double" variables, as well as modifying the function calling convention for functions taking "long double". Hence they are not binary-compatible with code compiled without that switch. -malign-data=type Control how GCC aligns variables. Supported values for type are compat uses increased alignment value compatible uses GCC 4.8 and earlier, abi uses alignment value as specified by the psABI, and cacheline uses increased alignment value to match the cache line size. compat is the default. -mlarge-data-threshold=threshold When -mcmodel=medium is specified, data objects larger than threshold are placed in the large data section. This value must be the same across all objects linked into the binary, and defaults to 65535. -mrtd Use a different function-calling convention, in which functions that take a fixed number of arguments return with the "ret num" instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no need to pop the arguments there. You can specify that an individual function is called with this calling sequence with the function attribute "stdcall". You can also override the -mrtd option by using the function attribute "cdecl". Warning: this calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. Also, you must provide function prototypes for all functions that take variable numbers of arguments (including "printf"); otherwise incorrect code is generated for calls to those functions. In addition, seriously incorrect code results if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.) -mregparm=num Control how many registers are used to pass integer arguments. By default, no registers are used to pass arguments, and at most 3 registers can be used. You can control this behavior for a specific function by using the function attribute "regparm". Warning: if you use this switch, and num is nonzero, then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules. -msseregparm Use SSE register passing conventions for float and double arguments and return values. You can control this behavior for a specific function by using the function attribute "sseregparm". Warning: if you use this switch then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules. -mvect8-ret-in-mem Return 8-byte vectors in memory instead of MMX registers. This is the default on VxWorks to match the ABI of the Sun Studio compilers until version 12. Only use this option if you need to remain compatible with existing code produced by those previous compiler versions or older versions of GCC. -mpc32 -mpc64 -mpc80 Set 80387 floating-point precision to 32, 64 or 80 bits. When -mpc32 is specified, the significands of results of floating-point operations are rounded to 24 bits (single precision); -mpc64 rounds the significands of results of floating-point operations to 53 bits (double precision) and -mpc80 rounds the significands of results of floating-point operations to 64 bits (extended double precision), which is the default. When this option is used, floating-point operations in higher precisions are not available to the programmer without setting the FPU control word explicitly. Setting the rounding of floating-point operations to less than the default 80 bits can speed some programs by 2% or more. Note that some mathematical libraries assume that extended-precision (80-bit) floating-point operations are enabled by default; routines in such libraries could suffer significant loss of accuracy, typically through so-called "catastrophic cancellation", when this option is used to set the precision to less than extended precision. -mdaz-ftz The flush-to-zero (FTZ) and denormals-are-zero (DAZ) flags in the MXCSR register are used to control floating-point calculations.SSE and AVX instructions including scalar and vector instructions could benefit from enabling the FTZ and DAZ flags when -mdaz-ftz is specified. Don't set FTZ/DAZ flags when -mno-daz-ftz or -shared is specified, -mdaz-ftz will set FTZ/DAZ flags even with -shared. -mstackrealign Realign the stack at entry. On the x86, the -mstackrealign option generates an alternate prologue and epilogue that realigns the run- time stack if necessary. This supports mixing legacy codes that keep 4-byte stack alignment with modern codes that keep 16-byte stack alignment for SSE compatibility. See also the attribute "force_align_arg_pointer", applicable to individual functions. -mpreferred-stack-boundary=num Attempt to keep the stack boundary aligned to a 2 raised to num byte boundary. If -mpreferred-stack-boundary is not specified, the default is 4 (16 bytes or 128 bits). Warning: When generating code for the x86-64 architecture with SSE extensions disabled, -mpreferred-stack-boundary=3 can be used to keep the stack boundary aligned to 8 byte boundary. Since x86-64 ABI require 16 byte stack alignment, this is ABI incompatible and intended to be used in controlled environment where stack space is important limitation. This option leads to wrong code when functions compiled with 16 byte stack alignment (such as functions from a standard library) are called with misaligned stack. In this case, SSE instructions may lead to misaligned memory access traps. In addition, variable arguments are handled incorrectly for 16 byte aligned objects (including x87 long double and __int128), leading to wrong results. You must build all modules with -mpreferred-stack-boundary=3, including any libraries. This includes the system libraries and startup modules. -mincoming-stack-boundary=num Assume the incoming stack is aligned to a 2 raised to num byte boundary. If -mincoming-stack-boundary is not specified, the one specified by -mpreferred-stack-boundary is used. On Pentium and Pentium Pro, "double" and "long double" values should be aligned to an 8-byte boundary (see -malign-double) or suffer significant run time performance penalties. On Pentium III, the Streaming SIMD Extension (SSE) data type "__m128" may not work properly if it is not 16-byte aligned. To ensure proper alignment of this values on the stack, the stack boundary must be as aligned as that required by any value stored on the stack. Further, every function must be generated such that it keeps the stack aligned. Thus calling a function compiled with a higher preferred stack boundary from a function compiled with a lower preferred stack boundary most likely misaligns the stack. It is recommended that libraries that use callbacks always use the default setting. This extra alignment does consume extra stack space, and generally increases code size. Code that is sensitive to stack space usage, such as embedded systems and operating system kernels, may want to reduce the preferred alignment to -mpreferred-stack-boundary=2. -mmmx -msse -msse2 -msse3 -mssse3 -msse4 -msse4a -msse4.1 -msse4.2 -mavx -mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -mavx512vl -mavx512bw -mavx512dq -mavx512ifma -mavx512vbmi -msha -maes -mpclmul -mclflushopt -mclwb -mfsgsbase -mptwrite -mrdrnd -mf16c -mfma -mpconfig -mwbnoinvd -mfma4 -mprfchw -mrdpid -mprefetchwt1 -mrdseed -msgx -mxop -mlwp -m3dnow -m3dnowa -mpopcnt -mabm -madx -mbmi -mbmi2 -mlzcnt -mfxsr -mxsave -mxsaveopt -mxsavec -mxsaves -mrtm -mhle -mtbm -mmwaitx -mclzero -mpku -mavx512vbmi2 -mavx512bf16 -mavx512fp16 -mgfni -mvaes -mwaitpkg -mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b -menqcmd -muintr -mtsxldtrk -mavx512vpopcntdq -mavx512vp2intersect -mavx5124fmaps -mavx512vnni -mavxvnni -mavx5124vnniw -mcldemote -mserialize -mamx-tile -mamx-int8 -mamx-bf16 -mhreset -mkl -mwidekl -mavxifma -mavxvnniint8 -mavxneconvert -mcmpccxadd -mamx-fp16 -mprefetchi -mraoint -mamx-complex These switches enable the use of instructions in the MMX, SSE, SSE2, SSE3, SSSE3, SSE4, SSE4A, SSE4.1, SSE4.2, AVX, AVX2, AVX512F, AVX512PF, AVX512ER, AVX512CD, AVX512VL, AVX512BW, AVX512DQ, AVX512IFMA, AVX512VBMI, SHA, AES, PCLMUL, CLFLUSHOPT, CLWB, FSGSBASE, PTWRITE, RDRND, F16C, FMA, PCONFIG, WBNOINVD, FMA4, PREFETCHW, RDPID, PREFETCHWT1, RDSEED, SGX, XOP, LWP, 3DNow!, enhanced 3DNow!, POPCNT, ABM, ADX, BMI, BMI2, LZCNT, FXSR, XSAVE, XSAVEOPT, XSAVEC, XSAVES, RTM, HLE, TBM, MWAITX, CLZERO, PKU, AVX512VBMI2, GFNI, VAES, WAITPKG, VPCLMULQDQ, AVX512BITALG, MOVDIRI, MOVDIR64B, AVX512BF16, ENQCMD, AVX512VPOPCNTDQ, AVX5124FMAPS, AVX512VNNI, AVX5124VNNIW, SERIALIZE, UINTR, HRESET, AMXTILE, AMXINT8, AMXBF16, KL, WIDEKL, AVXVNNI, AVX512-FP16, AVXIFMA, AVXVNNIINT8, AVXNECONVERT, CMPCCXADD, AMX-FP16, PREFETCHI, RAOINT, AMX-COMPLEX or CLDEMOTE extended instruction sets. Each has a corresponding -mno- option to disable use of these instructions. These extensions are also available as built-in functions: see x86 Built-in Functions, for details of the functions enabled and disabled by these switches. To generate SSE/SSE2 instructions automatically from floating-point code (as opposed to 387 instructions), see -mfpmath=sse. GCC depresses SSEx instructions when -mavx is used. Instead, it generates new AVX instructions or AVX equivalence for all SSEx instructions when needed. These options enable GCC to use these extended instructions in generated code, even without -mfpmath=sse. Applications that perform run-time CPU detection must compile separate files for each supported architecture, using the appropriate flags. In particular, the file containing the CPU detection code should be compiled without these options. -mdump-tune-features This option instructs GCC to dump the names of the x86 performance tuning features and default settings. The names can be used in -mtune-ctrl=feature-list. -mtune-ctrl=feature-list This option is used to do fine grain control of x86 code generation features. feature-list is a comma separated list of feature names. See also -mdump-tune-features. When specified, the feature is turned on if it is not preceded with ^, otherwise, it is turned off. -mtune-ctrl=feature-list is intended to be used by GCC developers. Using it may lead to code paths not covered by testing and can potentially result in compiler ICEs or runtime errors. -mno-default This option instructs GCC to turn off all tunable features. See also -mtune-ctrl=feature-list and -mdump-tune-features. -mcld This option instructs GCC to emit a "cld" instruction in the prologue of functions that use string instructions. String instructions depend on the DF flag to select between autoincrement or autodecrement mode. While the ABI specifies the DF flag to be cleared on function entry, some operating systems violate this specification by not clearing the DF flag in their exception dispatchers. The exception handler can be invoked with the DF flag set, which leads to wrong direction mode when string instructions are used. This option can be enabled by default on 32-bit x86 targets by configuring GCC with the --enable-cld configure option. Generation of "cld" instructions can be suppressed with the -mno-cld compiler option in this case. -mvzeroupper This option instructs GCC to emit a "vzeroupper" instruction before a transfer of control flow out of the function to minimize the AVX to SSE transition penalty as well as remove unnecessary "zeroupper" intrinsics. -mprefer-avx128 This option instructs GCC to use 128-bit AVX instructions instead of 256-bit AVX instructions in the auto-vectorizer. -mprefer-vector-width=opt This option instructs GCC to use opt-bit vector width in instructions instead of default on the selected platform. -mmove-max=bits This option instructs GCC to set the maximum number of bits can be moved from memory to memory efficiently to bits. The valid bits are 128, 256 and 512. -mstore-max=bits This option instructs GCC to set the maximum number of bits can be stored to memory efficiently to bits. The valid bits are 128, 256 and 512. none No extra limitations applied to GCC other than defined by the selected platform. 128 Prefer 128-bit vector width for instructions. 256 Prefer 256-bit vector width for instructions. 512 Prefer 512-bit vector width for instructions. -mcx16 This option enables GCC to generate "CMPXCHG16B" instructions in 64-bit code to implement compare-and-exchange operations on 16-byte aligned 128-bit objects. This is useful for atomic updates of data structures exceeding one machine word in size. The compiler uses this instruction to implement __sync Builtins. However, for __atomic Builtins operating on 128-bit integers, a library call is always used. -msahf This option enables generation of "SAHF" instructions in 64-bit code. Early Intel Pentium 4 CPUs with Intel 64 support, prior to the introduction of Pentium 4 G1 step in December 2005, lacked the "LAHF" and "SAHF" instructions which are supported by AMD64. These are load and store instructions, respectively, for certain status flags. In 64-bit mode, the "SAHF" instruction is used to optimize "fmod", "drem", and "remainder" built-in functions; see Other Builtins for details. -mmovbe This option enables use of the "movbe" instruction to implement "__builtin_bswap32" and "__builtin_bswap64". -mshstk The -mshstk option enables shadow stack built-in functions from x86 Control-flow Enforcement Technology (CET). -mcrc32 This option enables built-in functions "__builtin_ia32_crc32qi", "__builtin_ia32_crc32hi", "__builtin_ia32_crc32si" and "__builtin_ia32_crc32di" to generate the "crc32" machine instruction. -mmwait This option enables built-in functions "__builtin_ia32_monitor", and "__builtin_ia32_mwait" to generate the "monitor" and "mwait" machine instructions. -mrecip This option enables use of "RCPSS" and "RSQRTSS" instructions (and their vectorized variants "RCPPS" and "RSQRTPS") with an additional Newton-Raphson step to increase precision instead of "DIVSS" and "SQRTSS" (and their vectorized variants) for single-precision floating-point arguments. These instructions are generated only when -funsafe-math-optimizations is enabled together with -ffinite-math-only and -fno-trapping-math. Note that while the throughput of the sequence is higher than the throughput of the non-reciprocal instruction, the precision of the sequence can be decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994). Note that GCC implements "1.0f/sqrtf(x)" in terms of "RSQRTSS" (or "RSQRTPS") already with -ffast-math (or the above option combination), and doesn't need -mrecip. Also note that GCC emits the above sequence with additional Newton- Raphson step for vectorized single-float division and vectorized "sqrtf(x)" already with -ffast-math (or the above option combination), and doesn't need -mrecip. -mrecip=opt This option controls which reciprocal estimate instructions may be used. opt is a comma-separated list of options, which may be preceded by a ! to invert the option: all Enable all estimate instructions. default Enable the default instructions, equivalent to -mrecip. none Disable all estimate instructions, equivalent to -mno-recip. div Enable the approximation for scalar division. vec-div Enable the approximation for vectorized division. sqrt Enable the approximation for scalar square root. vec-sqrt Enable the approximation for vectorized square root. So, for example, -mrecip=all,!sqrt enables all of the reciprocal approximations, except for square root. -mveclibabi=type Specifies the ABI type to use for vectorizing intrinsics using an external library. Supported values for type are svml for the Intel short vector math library and acml for the AMD math core library. To use this option, both -ftree-vectorize and -funsafe-math-optimizations have to be enabled, and an SVML or ACML ABI-compatible library must be specified at link time. GCC currently emits calls to "vmldExp2", "vmldLn2", "vmldLog102", "vmldPow2", "vmldTanh2", "vmldTan2", "vmldAtan2", "vmldAtanh2", "vmldCbrt2", "vmldSinh2", "vmldSin2", "vmldAsinh2", "vmldAsin2", "vmldCosh2", "vmldCos2", "vmldAcosh2", "vmldAcos2", "vmlsExp4", "vmlsLn4", "vmlsLog104", "vmlsPow4", "vmlsTanh4", "vmlsTan4", "vmlsAtan4", "vmlsAtanh4", "vmlsCbrt4", "vmlsSinh4", "vmlsSin4", "vmlsAsinh4", "vmlsAsin4", "vmlsCosh4", "vmlsCos4", "vmlsAcosh4" and "vmlsAcos4" for corresponding function type when -mveclibabi=svml is used, and "__vrd2_sin", "__vrd2_cos", "__vrd2_exp", "__vrd2_log", "__vrd2_log2", "__vrd2_log10", "__vrs4_sinf", "__vrs4_cosf", "__vrs4_expf", "__vrs4_logf", "__vrs4_log2f", "__vrs4_log10f" and "__vrs4_powf" for the corresponding function type when -mveclibabi=acml is used. -mabi=name Generate code for the specified calling convention. Permissible values are sysv for the ABI used on GNU/Linux and other systems, and ms for the Microsoft ABI. The default is to use the Microsoft ABI when targeting Microsoft Windows and the SysV ABI on all other systems. You can control this behavior for specific functions by using the function attributes "ms_abi" and "sysv_abi". -mforce-indirect-call Force all calls to functions to be indirect. This is useful when using Intel Processor Trace where it generates more precise timing information for function calls. -mmanual-endbr Insert ENDBR instruction at function entry only via the "cf_check" function attribute. This is useful when used with the option -fcf-protection=branch to control ENDBR insertion at the function entry. -mcet-switch By default, CET instrumentation is turned off on switch statements that use a jump table and indirect branch track is disabled. Since jump tables are stored in read-only memory, this does not result in a direct loss of hardening. But if the jump table index is attacker-controlled, the indirect jump may not be constrained by CET. This option turns on CET instrumentation to enable indirect branch track for switch statements with jump tables which leads to the jump targets reachable via any indirect jumps. -mcall-ms2sysv-xlogues Due to differences in 64-bit ABIs, any Microsoft ABI function that calls a System V ABI function must consider RSI, RDI and XMM6-15 as clobbered. By default, the code for saving and restoring these registers is emitted inline, resulting in fairly lengthy prologues and epilogues. Using -mcall-ms2sysv-xlogues emits prologues and epilogues that use stubs in the static portion of libgcc to perform these saves and restores, thus reducing function size at the cost of a few extra instructions. -mtls-dialect=type Generate code to access thread-local storage using the gnu or gnu2 conventions. gnu is the conservative default; gnu2 is more efficient, but it may add compile- and run-time requirements that cannot be satisfied on all systems. -mpush-args -mno-push-args Use PUSH operations to store outgoing parameters. This method is shorter and usually equally fast as method using SUB/MOV operations and is enabled by default. In some cases disabling it may improve performance because of improved scheduling and reduced dependencies. -maccumulate-outgoing-args If enabled, the maximum amount of space required for outgoing arguments is computed in the function prologue. This is faster on most modern CPUs because of reduced dependencies, improved scheduling and reduced stack usage when the preferred stack boundary is not equal to 2. The drawback is a notable increase in code size. This switch implies -mno-push-args. -mthreads Support thread-safe exception handling on MinGW. Programs that rely on thread-safe exception handling must compile and link all code with the -mthreads option. When compiling, -mthreads defines -D_MT; when linking, it links in a special thread helper library -lmingwthrd which cleans up per-thread exception-handling data. -mms-bitfields -mno-ms-bitfields Enable/disable bit-field layout compatible with the native Microsoft Windows compiler. If "packed" is used on a structure, or if bit-fields are used, it may be that the Microsoft ABI lays out the structure differently than the way GCC normally does. Particularly when moving packed data between functions compiled with GCC and the native Microsoft compiler (either via function call or as data in a file), it may be necessary to access either format. This option is enabled by default for Microsoft Windows targets. This behavior can also be controlled locally by use of variable or type attributes. For more information, see x86 Variable Attributes and x86 Type Attributes. The Microsoft structure layout algorithm is fairly simple with the exception of the bit-field packing. The padding and alignment of members of structures and whether a bit-field can straddle a storage-unit boundary are determine by these rules: 1. Structure members are stored sequentially in the order in which they are declared: the first member has the lowest memory address and the last member the highest. 2. Every data object has an alignment requirement. The alignment requirement for all data except structures, unions, and arrays is either the size of the object or the current packing size (specified with either the "aligned" attribute or the "pack" pragma), whichever is less. For structures, unions, and arrays, the alignment requirement is the largest alignment requirement of its members. Every object is allocated an offset so that: offset % alignment_requirement == 0 3. Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte allocation unit if the integral types are the same size and if the next bit-field fits into the current allocation unit without crossing the boundary imposed by the common alignment requirements of the bit-fields. MSVC interprets zero-length bit-fields in the following ways: 1. If a zero-length bit-field is inserted between two bit-fields that are normally coalesced, the bit-fields are not coalesced. For example: struct { unsigned long bf_1 : 12; unsigned long : 0; unsigned long bf_2 : 12; } t1; The size of "t1" is 8 bytes with the zero-length bit-field. If the zero-length bit-field were removed, "t1"'s size would be 4 bytes. 2. If a zero-length bit-field is inserted after a bit-field, "foo", and the alignment of the zero-length bit-field is greater than the member that follows it, "bar", "bar" is aligned as the type of the zero-length bit-field. For example: struct { char foo : 4; short : 0; char bar; } t2; struct { char foo : 4; short : 0; double bar; } t3; For "t2", "bar" is placed at offset 2, rather than offset 1. Accordingly, the size of "t2" is 4. For "t3", the zero-length bit-field does not affect the alignment of "bar" or, as a result, the size of the structure. Taking this into account, it is important to note the following: 1. If a zero-length bit-field follows a normal bit-field, the type of the zero-length bit-field may affect the alignment of the structure as whole. For example, "t2" has a size of 4 bytes, since the zero-length bit-field follows a normal bit-field, and is of type short. 2. Even if a zero-length bit-field is not followed by a normal bit-field, it may still affect the alignment of the structure: struct { char foo : 6; long : 0; } t4; Here, "t4" takes up 4 bytes. 3. Zero-length bit-fields following non-bit-field members are ignored: struct { char foo; long : 0; char bar; } t5; Here, "t5" takes up 2 bytes. -mno-align-stringops Do not align the destination of inlined string operations. This switch reduces code size and improves performance in case the destination is already aligned, but GCC doesn't know about it. -minline-all-stringops By default GCC inlines string operations only when the destination is known to be aligned to least a 4-byte boundary. This enables more inlining and increases code size, but may improve performance of code that depends on fast "memcpy" and "memset" for short lengths. The option enables inline expansion of "strlen" for all pointer alignments. -minline-stringops-dynamically For string operations of unknown size, use run-time checks with inline code for small blocks and a library call for large blocks. -mstringop-strategy=alg Override the internal decision heuristic for the particular algorithm to use for inlining string operations. The allowed values for alg are: rep_byte rep_4byte rep_8byte Expand using i386 "rep" prefix of the specified size. byte_loop loop unrolled_loop Expand into an inline loop. libcall Always use a library call. -mmemcpy-strategy=strategy Override the internal decision heuristic to decide if "__builtin_memcpy" should be inlined and what inline algorithm to use when the expected size of the copy operation is known. strategy is a comma-separated list of alg:max_size:dest_align triplets. alg is specified in -mstringop-strategy, max_size specifies the max byte size with which inline algorithm alg is allowed. For the last triplet, the max_size must be "-1". The max_size of the triplets in the list must be specified in increasing order. The minimal byte size for alg is 0 for the first triplet and "max_size + 1" of the preceding range. -mmemset-strategy=strategy The option is similar to -mmemcpy-strategy= except that it is to control "__builtin_memset" expansion. -momit-leaf-frame-pointer Don't keep the frame pointer in a register for leaf functions. This avoids the instructions to save, set up, and restore frame pointers and makes an extra register available in leaf functions. The option -fomit-leaf-frame-pointer removes the frame pointer for leaf functions, which might make debugging harder. -mtls-direct-seg-refs -mno-tls-direct-seg-refs Controls whether TLS variables may be accessed with offsets from the TLS segment register (%gs for 32-bit, %fs for 64-bit), or whether the thread base pointer must be added. Whether or not this is valid depends on the operating system, and whether it maps the segment to cover the entire TLS area. For systems that use the GNU C Library, the default is on. -msse2avx -mno-sse2avx Specify that the assembler should encode SSE instructions with VEX prefix. The option -mavx turns this on by default. -mfentry -mno-fentry If profiling is active (-pg), put the profiling counter call before the prologue. Note: On x86 architectures the attribute "ms_hook_prologue" isn't possible at the moment for -mfentry and -pg. -mrecord-mcount -mno-record-mcount If profiling is active (-pg), generate a __mcount_loc section that contains pointers to each profiling call. This is useful for automatically patching and out calls. -mnop-mcount -mno-nop-mcount If profiling is active (-pg), generate the calls to the profiling functions as NOPs. This is useful when they should be patched in later dynamically. This is likely only useful together with -mrecord-mcount. -minstrument-return=type Instrument function exit in -pg -mfentry instrumented functions with call to specified function. This only instruments true returns ending with ret, but not sibling calls ending with jump. Valid types are none to not instrument, call to generate a call to __return__, or nop5 to generate a 5 byte nop. -mrecord-return -mno-record-return Generate a __return_loc section pointing to all return instrumentation code. -mfentry-name=name Set name of __fentry__ symbol called at function entry for -pg -mfentry functions. -mfentry-section=name Set name of section to record -mrecord-mcount calls (default __mcount_loc). -mskip-rax-setup -mno-skip-rax-setup When generating code for the x86-64 architecture with SSE extensions disabled, -mskip-rax-setup can be used to skip setting up RAX register when there are no variable arguments passed in vector registers. Warning: Since RAX register is used to avoid unnecessarily saving vector registers on stack when passing variable arguments, the impacts of this option are callees may waste some stack space, misbehave or jump to a random location. GCC 4.4 or newer don't have those issues, regardless the RAX register value. -m8bit-idiv -mno-8bit-idiv On some processors, like Intel Atom, 8-bit unsigned integer divide is much faster than 32-bit/64-bit integer divide. This option generates a run-time check. If both dividend and divisor are within range of 0 to 255, 8-bit unsigned integer divide is used instead of 32-bit/64-bit integer divide. -mavx256-split-unaligned-load -mavx256-split-unaligned-store Split 32-byte AVX unaligned load and store. -mstack-protector-guard=guard -mstack-protector-guard-reg=reg -mstack-protector-guard-offset=offset Generate stack protection code using canary at guard. Supported locations are global for global canary or tls for per-thread canary in the TLS block (the default). This option has effect only when -fstack-protector or -fstack-protector-all is specified. With the latter choice the options -mstack-protector-guard-reg=reg and -mstack-protector-guard-offset=offset furthermore specify which segment register (%fs or %gs) to use as base register for reading the canary, and from what offset from that base register. The default for those is as specified in the relevant ABI. -mgeneral-regs-only Generate code that uses only the general-purpose registers. This prevents the compiler from using floating-point, vector, mask and bound registers. -mrelax-cmpxchg-loop When emitting a compare-and-swap loop for __sync Builtins and __atomic Builtins lacking a native instruction, optimize for the highly contended case by issuing an atomic load before the "CMPXCHG" instruction, and using the "PAUSE" instruction to save CPU power when restarting the loop. -mindirect-branch=choice Convert indirect call and jump with choice. The default is keep, which keeps indirect call and jump unmodified. thunk converts indirect call and jump to call and return thunk. thunk-inline converts indirect call and jump to inlined call and return thunk. thunk-extern converts indirect call and jump to external call and return thunk provided in a separate object file. You can control this behavior for a specific function by using the function attribute "indirect_branch". Note that -mcmodel=large is incompatible with -mindirect-branch=thunk and -mindirect-branch=thunk-extern since the thunk function may not be reachable in the large code model. Note that -mindirect-branch=thunk-extern is compatible with -fcf-protection=branch since the external thunk can be made to enable control-flow check. -mfunction-return=choice Convert function return with choice. The default is keep, which keeps function return unmodified. thunk converts function return to call and return thunk. thunk-inline converts function return to inlined call and return thunk. thunk-extern converts function return to external call and return thunk provided in a separate object file. You can control this behavior for a specific function by using the function attribute "function_return". Note that -mindirect-return=thunk-extern is compatible with -fcf-protection=branch since the external thunk can be made to enable control-flow check. Note that -mcmodel=large is incompatible with -mfunction-return=thunk and -mfunction-return=thunk-extern since the thunk function may not be reachable in the large code model. -mindirect-branch-register Force indirect call and jump via register. -mharden-sls=choice Generate code to mitigate against straight line speculation (SLS) with choice. The default is none which disables all SLS hardening. return enables SLS hardening for function returns. indirect-jmp enables SLS hardening for indirect jumps. all enables all SLS hardening. -mindirect-branch-cs-prefix Add CS prefix to call and jmp to indirect thunk with branch target in r8-r15 registers so that the call and jmp instruction length is 6 bytes to allow them to be replaced with lfence; call *%r8-r15 or lfence; jmp *%r8-r15 at run-time. These -m switches are supported in addition to the above on x86-64 processors in 64-bit environments. -m32 -m64 -mx32 -m16 -miamcu Generate code for a 16-bit, 32-bit or 64-bit environment. The -m32 option sets "int", "long", and pointer types to 32 bits, and generates code that runs in 32-bit mode. The -m64 option sets "int" to 32 bits and "long" and pointer types to 64 bits, and generates code for the x86-64 architecture. For Darwin only the -m64 option also turns off the -fno-pic and -mdynamic-no-pic options. The -mx32 option sets "int", "long", and pointer types to 32 bits, and generates code for the x86-64 architecture. The -m16 option is the same as -m32, except for that it outputs the ".code16gcc" assembly directive at the beginning of the assembly output so that the binary can run in 16-bit mode. The -miamcu option generates code which conforms to Intel MCU psABI. It requires the -m32 option to be turned on. -mno-red-zone Do not use a so-called "red zone" for x86-64 code. The red zone is mandated by the x86-64 ABI; it is a 128-byte area beyond the location of the stack pointer that is not modified by signal or interrupt handlers and therefore can be used for temporary data without adjusting the stack pointer. The flag -mno-red-zone disables this red zone. -mcmodel=small Generate code for the small code model: the program and its symbols must be linked in the lower 2 GB of the address space. Pointers are 64 bits. Programs can be statically or dynamically linked. This is the default code model. -mcmodel=kernel Generate code for the kernel code model. The kernel runs in the negative 2 GB of the address space. This model has to be used for Linux kernel code. -mcmodel=medium Generate code for the medium model: the program is linked in the lower 2 GB of the address space. Small symbols are also placed there. Symbols with sizes larger than -mlarge-data-threshold are put into large data or BSS sections and can be located above 2GB. Programs can be statically or dynamically linked. -mcmodel=large Generate code for the large model. This model makes no assumptions about addresses and sizes of sections. -maddress-mode=long Generate code for long address mode. This is only supported for 64-bit and x32 environments. It is the default address mode for 64-bit environments. -maddress-mode=short Generate code for short address mode. This is only supported for 32-bit and x32 environments. It is the default address mode for 32-bit and x32 environments. -mneeded -mno-needed Emit GNU_PROPERTY_X86_ISA_1_NEEDED GNU property for Linux target to indicate the micro-architecture ISA level required to execute the binary. -mno-direct-extern-access Without -fpic nor -fPIC, always use the GOT pointer to access external symbols. With -fpic or -fPIC, treat access to protected symbols as local symbols. The default is -mdirect-extern-access. Warning: shared libraries compiled with -mno-direct-extern-access and executable compiled with -mdirect-extern-access may not be binary compatible if protected symbols are used in shared libraries and executable. -munroll-only-small-loops Controls conservative small loop unrolling. It is default enabled by O2, and unrolls loop with less than 4 insns by 1 time. Explicit -f[no-]unroll-[all-]loops would disable this flag to avoid any unintended unrolling behavior that user does not want. -mlam=choice LAM(linear-address masking) allows special bits in the pointer to be used for metadata. The default is none. With u48, pointer bits in positions 62:48 can be used for metadata; With u57, pointer bits in positions 62:57 can be used for metadata. x86 Windows Options These additional options are available for Microsoft Windows targets: -mconsole This option specifies that a console application is to be generated, by instructing the linker to set the PE header subsystem type required for console applications. This option is available for Cygwin and MinGW targets and is enabled by default on those targets. -mdll This option is available for Cygwin and MinGW targets. It specifies that a DLL---a dynamic link library---is to be generated, enabling the selection of the required runtime startup object and entry point. -mnop-fun-dllimport This option is available for Cygwin and MinGW targets. It specifies that the "dllimport" attribute should be ignored. -mthreads This option is available for MinGW targets. It specifies that MinGW-specific thread support is to be used. -municode This option is available for MinGW-w64 targets. It causes the "UNICODE" preprocessor macro to be predefined, and chooses Unicode- capable runtime startup code. -mwin32 This option is available for Cygwin and MinGW targets. It specifies that the typical Microsoft Windows predefined macros are to be set in the pre-processor, but does not influence the choice of runtime library/startup code. -mwindows This option is available for Cygwin and MinGW targets. It specifies that a GUI application is to be generated by instructing the linker to set the PE header subsystem type appropriately. -fno-set-stack-executable This option is available for MinGW targets. It specifies that the executable flag for the stack used by nested functions isn't set. This is necessary for binaries running in kernel mode of Microsoft Windows, as there the User32 API, which is used to set executable privileges, isn't available. -fwritable-relocated-rdata This option is available for MinGW and Cygwin targets. It specifies that relocated-data in read-only section is put into the ".data" section. This is a necessary for older runtimes not supporting modification of ".rdata" sections for pseudo-relocation. -mpe-aligned-commons This option is available for Cygwin and MinGW targets. It specifies that the GNU extension to the PE file format that permits the correct alignment of COMMON variables should be used when generating code. It is enabled by default if GCC detects that the target assembler found during configuration supports the feature. See also under x86 Options for standard options. Xstormy16 Options These options are defined for Xstormy16: -msim Choose startup files and linker script suitable for the simulator. Xtensa Options These options are supported for Xtensa targets: -mconst16 -mno-const16 Enable or disable use of "CONST16" instructions for loading constant values. The "CONST16" instruction is currently not a standard option from Tensilica. When enabled, "CONST16" instructions are always used in place of the standard "L32R" instructions. The use of "CONST16" is enabled by default only if the "L32R" instruction is not available. -mfused-madd -mno-fused-madd Enable or disable use of fused multiply/add and multiply/subtract instructions in the floating-point option. This has no effect if the floating-point option is not also enabled. Disabling fused multiply/add and multiply/subtract instructions forces the compiler to use separate instructions for the multiply and add/subtract operations. This may be desirable in some cases where strict IEEE 754-compliant results are required: the fused multiply add/subtract instructions do not round the intermediate result, thereby producing results with more bits of precision than specified by the IEEE standard. Disabling fused multiply add/subtract instructions also ensures that the program output is not sensitive to the compiler's ability to combine multiply and add/subtract operations. -mserialize-volatile -mno-serialize-volatile When this option is enabled, GCC inserts "MEMW" instructions before "volatile" memory references to guarantee sequential consistency. The default is -mserialize-volatile. Use -mno-serialize-volatile to omit the "MEMW" instructions. -mforce-no-pic For targets, like GNU/Linux, where all user-mode Xtensa code must be position-independent code (PIC), this option disables PIC for compiling kernel code. -mtext-section-literals -mno-text-section-literals These options control the treatment of literal pools. The default is -mno-text-section-literals, which places literals in a separate section in the output file. This allows the literal pool to be placed in a data RAM/ROM, and it also allows the linker to combine literal pools from separate object files to remove redundant literals and improve code size. With -mtext-section-literals, the literals are interspersed in the text section in order to keep them as close as possible to their references. This may be necessary for large assembly files. Literals for each function are placed right before that function. -mauto-litpools -mno-auto-litpools These options control the treatment of literal pools. The default is -mno-auto-litpools, which places literals in a separate section in the output file unless -mtext-section-literals is used. With -mauto-litpools the literals are interspersed in the text section by the assembler. Compiler does not produce explicit ".literal" directives and loads literals into registers with "MOVI" instructions instead of "L32R" to let the assembler do relaxation and place literals as necessary. This option allows assembler to create several literal pools per function and assemble very big functions, which may not be possible with -mtext-section-literals. -mtarget-align -mno-target-align When this option is enabled, GCC instructs the assembler to automatically align instructions to reduce branch penalties at the expense of some code density. The assembler attempts to widen density instructions to align branch targets and the instructions following call instructions. If there are not enough preceding safe density instructions to align a target, no widening is performed. The default is -mtarget-align. These options do not affect the treatment of auto-aligned instructions like "LOOP", which the assembler always aligns, either by widening density instructions or by inserting NOP instructions. -mlongcalls -mno-longcalls When this option is enabled, GCC instructs the assembler to translate direct calls to indirect calls unless it can determine that the target of a direct call is in the range allowed by the call instruction. This translation typically occurs for calls to functions in other source files. Specifically, the assembler translates a direct "CALL" instruction into an "L32R" followed by a "CALLX" instruction. The default is -mno-longcalls. This option should be used in programs where the call target can potentially be out of range. This option is implemented in the assembler, not the compiler, so the assembly code generated by GCC still shows direct call instructions---look at the disassembled object code to see the actual instructions. Note that the assembler uses an indirect call for every cross-file call, not just those that really are out of range. -mabi=name Generate code for the specified ABI. Permissible values are: call0, windowed. Default ABI is chosen by the Xtensa core configuration. -mabi=call0 When this option is enabled function parameters are passed in registers "a2" through "a7", registers "a12" through "a15" are caller-saved, and register "a15" may be used as a frame pointer. When this version of the ABI is enabled the C preprocessor symbol "__XTENSA_CALL0_ABI__" is defined. -mabi=windowed When this option is enabled function parameters are passed in registers "a10" through "a15", and called function rotates register window by 8 registers on entry so that its arguments are found in registers "a2" through "a7". Register "a7" may be used as a frame pointer. Register window is rotated 8 registers back upon return. When this version of the ABI is enabled the C preprocessor symbol "__XTENSA_WINDOWED_ABI__" is defined. -mextra-l32r-costs=n Specify an extra cost of instruction RAM/ROM access for "L32R" instructions, in clock cycles. This affects, when optimizing for speed, whether loading a constant from literal pool using "L32R" or synthesizing the constant from a small one with a couple of arithmetic instructions. The default value is 0. zSeries Options These are listed under ENVIRONMENT This section describes several environment variables that affect how GCC operates. Some of them work by specifying directories or prefixes to use when searching for various kinds of files. Some are used to specify other aspects of the compilation environment. Note that you can also specify places to search using options such as -B, -I and -L. These take precedence over places specified using environment variables, which in turn take precedence over those specified by the configuration of GCC. LANG LC_CTYPE LC_MESSAGES LC_ALL These environment variables control the way that GCC uses localization information which allows GCC to work with different national conventions. GCC inspects the locale categories LC_CTYPE and LC_MESSAGES if it has been configured to do so. These locale categories can be set to any value supported by your installation. A typical value is en_GB.UTF-8 for English in the United Kingdom encoded in UTF-8. The LC_CTYPE environment variable specifies character classification. GCC uses it to determine the character boundaries in a string; this is needed for some multibyte encodings that contain quote and escape characters that are otherwise interpreted as a string end or escape. The LC_MESSAGES environment variable specifies the language to use in diagnostic messages. If the LC_ALL environment variable is set, it overrides the value of LC_CTYPE and LC_MESSAGES; otherwise, LC_CTYPE and LC_MESSAGES default to the value of the LANG environment variable. If none of these variables are set, GCC defaults to traditional C English behavior. TMPDIR If TMPDIR is set, it specifies the directory to use for temporary files. GCC uses temporary files to hold the output of one stage of compilation which is to be used as input to the next stage: for example, the output of the preprocessor, which is the input to the compiler proper. GCC_COMPARE_DEBUG Setting GCC_COMPARE_DEBUG is nearly equivalent to passing -fcompare-debug to the compiler driver. See the documentation of this option for more details. GCC_EXEC_PREFIX If GCC_EXEC_PREFIX is set, it specifies a prefix to use in the names of the subprograms executed by the compiler. No slash is added when this prefix is combined with the name of a subprogram, but you can specify a prefix that ends with a slash if you wish. If GCC_EXEC_PREFIX is not set, GCC attempts to figure out an appropriate prefix to use based on the pathname it is invoked with. If GCC cannot find the subprogram using the specified prefix, it tries looking in the usual places for the subprogram. The default value of GCC_EXEC_PREFIX is prefix/lib/gcc/ where prefix is the prefix to the installed compiler. In many cases prefix is the value of "prefix" when you ran the configure script. Other prefixes specified with -B take precedence over this prefix. This prefix is also used for finding files such as crt0.o that are used for linking. In addition, the prefix is used in an unusual way in finding the directories to search for header files. For each of the standard directories whose name normally begins with /usr/local/lib/gcc (more precisely, with the value of GCC_INCLUDE_DIR), GCC tries replacing that beginning with the specified prefix to produce an alternate directory name. Thus, with -Bfoo/, GCC searches foo/bar just before it searches the standard directory /usr/local/lib/bar. If a standard directory begins with the configured prefix then the value of prefix is replaced by GCC_EXEC_PREFIX when looking for header files. COMPILER_PATH The value of COMPILER_PATH is a colon-separated list of directories, much like PATH. GCC tries the directories thus specified when searching for subprograms, if it cannot find the subprograms using GCC_EXEC_PREFIX. LIBRARY_PATH The value of LIBRARY_PATH is a colon-separated list of directories, much like PATH. When configured as a native compiler, GCC tries the directories thus specified when searching for special linker files, if it cannot find them using GCC_EXEC_PREFIX. Linking using GCC also uses these directories when searching for ordinary libraries for the -l option (but directories specified with -L come first). LANG This variable is used to pass locale information to the compiler. One way in which this information is used is to determine the character set to be used when character literals, string literals and comments are parsed in C and C++. When the compiler is configured to allow multibyte characters, the following values for LANG are recognized: C-JIS Recognize JIS characters. C-SJIS Recognize SJIS characters. C-EUCJP Recognize EUCJP characters. If LANG is not defined, or if it has some other value, then the compiler uses "mblen" and "mbtowc" as defined by the default locale to recognize and translate multibyte characters. GCC_EXTRA_DIAGNOSTIC_OUTPUT If GCC_EXTRA_DIAGNOSTIC_OUTPUT is set to one of the following values, then additional text will be emitted to stderr when fix-it hints are emitted. -fdiagnostics-parseable-fixits and -fno-diagnostics-parseable-fixits take precedence over this environment variable. fixits-v1 Emit parseable fix-it hints, equivalent to -fdiagnostics-parseable-fixits. In particular, columns are expressed as a count of bytes, starting at byte 1 for the initial column. fixits-v2 As "fixits-v1", but columns are expressed as display columns, as per -fdiagnostics-column-unit=display. Some additional environment variables affect the behavior of the preprocessor. CPATH C_INCLUDE_PATH CPLUS_INCLUDE_PATH OBJC_INCLUDE_PATH Each variable's value is a list of directories separated by a special character, much like PATH, in which to look for header files. The special character, "PATH_SEPARATOR", is target- dependent and determined at GCC build time. For Microsoft Windows- based targets it is a semicolon, and for almost all other targets it is a colon. CPATH specifies a list of directories to be searched as if specified with -I, but after any paths given with -I options on the command line. This environment variable is used regardless of which language is being preprocessed. The remaining environment variables apply only when preprocessing the particular language indicated. Each specifies a list of directories to be searched as if specified with -isystem, but after any paths given with -isystem options on the command line. In all these variables, an empty element instructs the compiler to search its current working directory. Empty elements can appear at the beginning or end of a path. For instance, if the value of CPATH is ":/special/include", that has the same effect as -I. -I/special/include. DEPENDENCIES_OUTPUT If this variable is set, its value specifies how to output dependencies for Make based on the non-system header files processed by the compiler. System header files are ignored in the dependency output. The value of DEPENDENCIES_OUTPUT can be just a file name, in which case the Make rules are written to that file, guessing the target name from the source file name. Or the value can have the form file target, in which case the rules are written to file file using target as the target name. In other words, this environment variable is equivalent to combining the options -MM and -MF, with an optional -MT switch too. SUNPRO_DEPENDENCIES This variable is the same as DEPENDENCIES_OUTPUT (see above), except that system header files are not ignored, so it implies -M rather than -MM. However, the dependence on the main input file is omitted. SOURCE_DATE_EPOCH If this variable is set, its value specifies a UNIX timestamp to be used in replacement of the current date and time in the "__DATE__" and "__TIME__" macros, so that the embedded timestamps become reproducible. The value of SOURCE_DATE_EPOCH must be a UNIX timestamp, defined as the number of seconds (excluding leap seconds) since 01 Jan 1970 00:00:00 represented in ASCII; identical to the output of "date +%s" on GNU/Linux and other systems that support the %s extension in the "date" command. The value should be a known timestamp such as the last modification time of the source or package and it should be set by the build process. BUGS For instructions on reporting bugs, see <https://github.com/Homebrew/homebrew-core/issues>. FOOTNOTES 1. On some systems, gcc -shared needs to build supplementary stub code for constructors to work. On multi-libbed systems, gcc -shared must select the correct support libraries to link against. Failing to supply the correct flags may lead to subtle defects. Supplying them in cases where they are not necessary is innocuous. -shared suppresses the addition of startup code to alter the floating-point environment as done with -ffast-math, -Ofast or -funsafe-math-optimizations on some targets. SEE ALSO gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), as(1), ld(1), gdb(1) and the Info entries for gcc, cpp, as, ld, binutils and gdb. AUTHOR See the Info entry for gcc, or <https://gcc.gnu.org/onlinedocs/gcc/Contributors.html>, for contributors to GCC. COPYRIGHT Copyright (c) 1988-2023 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being "GNU General Public License" and "Funding Free Software", the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the gfdl(7) man page. (a) The FSF's Front-Cover Text is: A GNU Manual (b) The FSF's Back-Cover Text is: You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development. gcc-13 2023-07-27 GCC(1)
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dtls_client
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redis-server
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flake8
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jiwer
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kbxutil
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unxz
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xz is a general-purpose data compression tool with command line syntax similar to gzip(1) and bzip2(1). The native file format is the .xz format, but the legacy .lzma format used by LZMA Utils and raw compressed streams with no container format headers are also supported. In addition, decompression of the .lz format used by lzip is supported. xz compresses or decompresses each file according to the selected operation mode. If no files are given or file is -, xz reads from standard input and writes the processed data to standard output. xz will refuse (display an error and skip the file) to write compressed data to standard output if it is a terminal. Similarly, xz will refuse to read compressed data from standard input if it is a terminal. Unless --stdout is specified, files other than - are written to a new file whose name is derived from the source file name: • When compressing, the suffix of the target file format (.xz or .lzma) is appended to the source filename to get the target filename. • When decompressing, the .xz, .lzma, or .lz suffix is removed from the filename to get the target filename. xz also recognizes the suffixes .txz and .tlz, and replaces them with the .tar suffix. If the target file already exists, an error is displayed and the file is skipped. Unless writing to standard output, xz will display a warning and skip the file if any of the following applies: • File is not a regular file. Symbolic links are not followed, and thus they are not considered to be regular files. • File has more than one hard link. • File has setuid, setgid, or sticky bit set. • The operation mode is set to compress and the file already has a suffix of the target file format (.xz or .txz when compressing to the .xz format, and .lzma or .tlz when compressing to the .lzma format). • The operation mode is set to decompress and the file doesn't have a suffix of any of the supported file formats (.xz, .txz, .lzma, .tlz, or .lz). After successfully compressing or decompressing the file, xz copies the owner, group, permissions, access time, and modification time from the source file to the target file. If copying the group fails, the permissions are modified so that the target file doesn't become accessible to users who didn't have permission to access the source file. xz doesn't support copying other metadata like access control lists or extended attributes yet. Once the target file has been successfully closed, the source file is removed unless --keep was specified. The source file is never removed if the output is written to standard output or if an error occurs. Sending SIGINFO or SIGUSR1 to the xz process makes it print progress information to standard error. This has only limited use since when standard error is a terminal, using --verbose will display an automatically updating progress indicator. Memory usage The memory usage of xz varies from a few hundred kilobytes to several gigabytes depending on the compression settings. The settings used when compressing a file determine the memory requirements of the decompressor. Typically the decompressor needs 5 % to 20 % of the amount of memory that the compressor needed when creating the file. For example, decompressing a file created with xz -9 currently requires 65 MiB of memory. Still, it is possible to have .xz files that require several gigabytes of memory to decompress. Especially users of older systems may find the possibility of very large memory usage annoying. To prevent uncomfortable surprises, xz has a built-in memory usage limiter, which is disabled by default. While some operating systems provide ways to limit the memory usage of processes, relying on it wasn't deemed to be flexible enough (for example, using ulimit(1) to limit virtual memory tends to cripple mmap(2)). The memory usage limiter can be enabled with the command line option --memlimit=limit. Often it is more convenient to enable the limiter by default by setting the environment variable XZ_DEFAULTS, for example, XZ_DEFAULTS=--memlimit=150MiB. It is possible to set the limits separately for compression and decompression by using --memlimit-compress=limit and --memlimit-decompress=limit. Using these two options outside XZ_DEFAULTS is rarely useful because a single run of xz cannot do both compression and decompression and --memlimit=limit (or -M limit) is shorter to type on the command line. If the specified memory usage limit is exceeded when decompressing, xz will display an error and decompressing the file will fail. If the limit is exceeded when compressing, xz will try to scale the settings down so that the limit is no longer exceeded (except when using --format=raw or --no-adjust). This way the operation won't fail unless the limit is very small. The scaling of the settings is done in steps that don't match the compression level presets, for example, if the limit is only slightly less than the amount required for xz -9, the settings will be scaled down only a little, not all the way down to xz -8. Concatenation and padding with .xz files It is possible to concatenate .xz files as is. xz will decompress such files as if they were a single .xz file. It is possible to insert padding between the concatenated parts or after the last part. The padding must consist of null bytes and the size of the padding must be a multiple of four bytes. This can be useful, for example, if the .xz file is stored on a medium that measures file sizes in 512-byte blocks. Concatenation and padding are not allowed with .lzma files or raw streams.
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xz, unxz, xzcat, lzma, unlzma, lzcat - Compress or decompress .xz and .lzma files
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xz [option...] [file...] COMMAND ALIASES unxz is equivalent to xz --decompress. xzcat is equivalent to xz --decompress --stdout. lzma is equivalent to xz --format=lzma. unlzma is equivalent to xz --format=lzma --decompress. lzcat is equivalent to xz --format=lzma --decompress --stdout. When writing scripts that need to decompress files, it is recommended to always use the name xz with appropriate arguments (xz -d or xz -dc) instead of the names unxz and xzcat.
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Integer suffixes and special values In most places where an integer argument is expected, an optional suffix is supported to easily indicate large integers. There must be no space between the integer and the suffix. KiB Multiply the integer by 1,024 (2^10). Ki, k, kB, K, and KB are accepted as synonyms for KiB. MiB Multiply the integer by 1,048,576 (2^20). Mi, m, M, and MB are accepted as synonyms for MiB. GiB Multiply the integer by 1,073,741,824 (2^30). Gi, g, G, and GB are accepted as synonyms for GiB. The special value max can be used to indicate the maximum integer value supported by the option. Operation mode If multiple operation mode options are given, the last one takes effect. -z, --compress Compress. This is the default operation mode when no operation mode option is specified and no other operation mode is implied from the command name (for example, unxz implies --decompress). -d, --decompress, --uncompress Decompress. -t, --test Test the integrity of compressed files. This option is equivalent to --decompress --stdout except that the decompressed data is discarded instead of being written to standard output. No files are created or removed. -l, --list Print information about compressed files. No uncompressed output is produced, and no files are created or removed. In list mode, the program cannot read the compressed data from standard input or from other unseekable sources. The default listing shows basic information about files, one file per line. To get more detailed information, use also the --verbose option. For even more information, use --verbose twice, but note that this may be slow, because getting all the extra information requires many seeks. The width of verbose output exceeds 80 characters, so piping the output to, for example, less -S may be convenient if the terminal isn't wide enough. The exact output may vary between xz versions and different locales. For machine-readable output, --robot --list should be used. Operation modifiers -k, --keep Don't delete the input files. Since xz 5.2.6, this option also makes xz compress or decompress even if the input is a symbolic link to a regular file, has more than one hard link, or has the setuid, setgid, or sticky bit set. The setuid, setgid, and sticky bits are not copied to the target file. In earlier versions this was only done with --force. -f, --force This option has several effects: • If the target file already exists, delete it before compressing or decompressing. • Compress or decompress even if the input is a symbolic link to a regular file, has more than one hard link, or has the setuid, setgid, or sticky bit set. The setuid, setgid, and sticky bits are not copied to the target file. • When used with --decompress --stdout and xz cannot recognize the type of the source file, copy the source file as is to standard output. This allows xzcat --force to be used like cat(1) for files that have not been compressed with xz. Note that in future, xz might support new compressed file formats, which may make xz decompress more types of files instead of copying them as is to standard output. --format=format can be used to restrict xz to decompress only a single file format. -c, --stdout, --to-stdout Write the compressed or decompressed data to standard output instead of a file. This implies --keep. --single-stream Decompress only the first .xz stream, and silently ignore possible remaining input data following the stream. Normally such trailing garbage makes xz display an error. xz never decompresses more than one stream from .lzma files or raw streams, but this option still makes xz ignore the possible trailing data after the .lzma file or raw stream. This option has no effect if the operation mode is not --decompress or --test. --no-sparse Disable creation of sparse files. By default, if decompressing into a regular file, xz tries to make the file sparse if the decompressed data contains long sequences of binary zeros. It also works when writing to standard output as long as standard output is connected to a regular file and certain additional conditions are met to make it safe. Creating sparse files may save disk space and speed up the decompression by reducing the amount of disk I/O. -S .suf, --suffix=.suf When compressing, use .suf as the suffix for the target file instead of .xz or .lzma. If not writing to standard output and the source file already has the suffix .suf, a warning is displayed and the file is skipped. When decompressing, recognize files with the suffix .suf in addition to files with the .xz, .txz, .lzma, .tlz, or .lz suffix. If the source file has the suffix .suf, the suffix is removed to get the target filename. When compressing or decompressing raw streams (--format=raw), the suffix must always be specified unless writing to standard output, because there is no default suffix for raw streams. --files[=file] Read the filenames to process from file; if file is omitted, filenames are read from standard input. Filenames must be terminated with the newline character. A dash (-) is taken as a regular filename; it doesn't mean standard input. If filenames are given also as command line arguments, they are processed before the filenames read from file. --files0[=file] This is identical to --files[=file] except that each filename must be terminated with the null character. Basic file format and compression options -F format, --format=format Specify the file format to compress or decompress: auto This is the default. When compressing, auto is equivalent to xz. When decompressing, the format of the input file is automatically detected. Note that raw streams (created with --format=raw) cannot be auto- detected. xz Compress to the .xz file format, or accept only .xz files when decompressing. lzma, alone Compress to the legacy .lzma file format, or accept only .lzma files when decompressing. The alternative name alone is provided for backwards compatibility with LZMA Utils. lzip Accept only .lz files when decompressing. Compression is not supported. The .lz format version 0 and the unextended version 1 are supported. Version 0 files were produced by lzip 1.3 and older. Such files aren't common but may be found from file archives as a few source packages were released in this format. People might have old personal files in this format too. Decompression support for the format version 0 was removed in lzip 1.18. lzip 1.4 and later create files in the format version 1. The sync flush marker extension to the format version 1 was added in lzip 1.6. This extension is rarely used and isn't supported by xz (diagnosed as corrupt input). raw Compress or uncompress a raw stream (no headers). This is meant for advanced users only. To decode raw streams, you need use --format=raw and explicitly specify the filter chain, which normally would have been stored in the container headers. -C check, --check=check Specify the type of the integrity check. The check is calculated from the uncompressed data and stored in the .xz file. This option has an effect only when compressing into the .xz format; the .lzma format doesn't support integrity checks. The integrity check (if any) is verified when the .xz file is decompressed. Supported check types: none Don't calculate an integrity check at all. This is usually a bad idea. This can be useful when integrity of the data is verified by other means anyway. crc32 Calculate CRC32 using the polynomial from IEEE-802.3 (Ethernet). crc64 Calculate CRC64 using the polynomial from ECMA-182. This is the default, since it is slightly better than CRC32 at detecting damaged files and the speed difference is negligible. sha256 Calculate SHA-256. This is somewhat slower than CRC32 and CRC64. Integrity of the .xz headers is always verified with CRC32. It is not possible to change or disable it. --ignore-check Don't verify the integrity check of the compressed data when decompressing. The CRC32 values in the .xz headers will still be verified normally. Do not use this option unless you know what you are doing. Possible reasons to use this option: • Trying to recover data from a corrupt .xz file. • Speeding up decompression. This matters mostly with SHA-256 or with files that have compressed extremely well. It's recommended to not use this option for this purpose unless the file integrity is verified externally in some other way. -0 ... -9 Select a compression preset level. The default is -6. If multiple preset levels are specified, the last one takes effect. If a custom filter chain was already specified, setting a compression preset level clears the custom filter chain. The differences between the presets are more significant than with gzip(1) and bzip2(1). The selected compression settings determine the memory requirements of the decompressor, thus using a too high preset level might make it painful to decompress the file on an old system with little RAM. Specifically, it's not a good idea to blindly use -9 for everything like it often is with gzip(1) and bzip2(1). -0 ... -3 These are somewhat fast presets. -0 is sometimes faster than gzip -9 while compressing much better. The higher ones often have speed comparable to bzip2(1) with comparable or better compression ratio, although the results depend a lot on the type of data being compressed. -4 ... -6 Good to very good compression while keeping decompressor memory usage reasonable even for old systems. -6 is the default, which is usually a good choice for distributing files that need to be decompressible even on systems with only 16 MiB RAM. (-5e or -6e may be worth considering too. See --extreme.) -7 ... -9 These are like -6 but with higher compressor and decompressor memory requirements. These are useful only when compressing files bigger than 8 MiB, 16 MiB, and 32 MiB, respectively. On the same hardware, the decompression speed is approximately a constant number of bytes of compressed data per second. In other words, the better the compression, the faster the decompression will usually be. This also means that the amount of uncompressed output produced per second can vary a lot. The following table summarises the features of the presets: Preset DictSize CompCPU CompMem DecMem -0 256 KiB 0 3 MiB 1 MiB -1 1 MiB 1 9 MiB 2 MiB -2 2 MiB 2 17 MiB 3 MiB -3 4 MiB 3 32 MiB 5 MiB -4 4 MiB 4 48 MiB 5 MiB -5 8 MiB 5 94 MiB 9 MiB -6 8 MiB 6 94 MiB 9 MiB -7 16 MiB 6 186 MiB 17 MiB -8 32 MiB 6 370 MiB 33 MiB -9 64 MiB 6 674 MiB 65 MiB Column descriptions: • DictSize is the LZMA2 dictionary size. It is waste of memory to use a dictionary bigger than the size of the uncompressed file. This is why it is good to avoid using the presets -7 ... -9 when there's no real need for them. At -6 and lower, the amount of memory wasted is usually low enough to not matter. • CompCPU is a simplified representation of the LZMA2 settings that affect compression speed. The dictionary size affects speed too, so while CompCPU is the same for levels -6 ... -9, higher levels still tend to be a little slower. To get even slower and thus possibly better compression, see --extreme. • CompMem contains the compressor memory requirements in the single-threaded mode. It may vary slightly between xz versions. • DecMem contains the decompressor memory requirements. That is, the compression settings determine the memory requirements of the decompressor. The exact decompressor memory usage is slightly more than the LZMA2 dictionary size, but the values in the table have been rounded up to the next full MiB. Memory requirements of the multi-threaded mode are significantly higher than that of the single-threaded mode. With the default value of --block-size, each thread needs 3*3*DictSize plus CompMem or DecMem. For example, four threads with preset -6 needs 660–670 MiB of memory. -e, --extreme Use a slower variant of the selected compression preset level (-0 ... -9) to hopefully get a little bit better compression ratio, but with bad luck this can also make it worse. Decompressor memory usage is not affected, but compressor memory usage increases a little at preset levels -0 ... -3. Since there are two presets with dictionary sizes 4 MiB and 8 MiB, the presets -3e and -5e use slightly faster settings (lower CompCPU) than -4e and -6e, respectively. That way no two presets are identical. Preset DictSize CompCPU CompMem DecMem -0e 256 KiB 8 4 MiB 1 MiB -1e 1 MiB 8 13 MiB 2 MiB -2e 2 MiB 8 25 MiB 3 MiB -3e 4 MiB 7 48 MiB 5 MiB -4e 4 MiB 8 48 MiB 5 MiB -5e 8 MiB 7 94 MiB 9 MiB -6e 8 MiB 8 94 MiB 9 MiB -7e 16 MiB 8 186 MiB 17 MiB -8e 32 MiB 8 370 MiB 33 MiB -9e 64 MiB 8 674 MiB 65 MiB For example, there are a total of four presets that use 8 MiB dictionary, whose order from the fastest to the slowest is -5, -6, -5e, and -6e. --fast --best These are somewhat misleading aliases for -0 and -9, respectively. These are provided only for backwards compatibility with LZMA Utils. Avoid using these options. --block-size=size When compressing to the .xz format, split the input data into blocks of size bytes. The blocks are compressed independently from each other, which helps with multi-threading and makes limited random-access decompression possible. This option is typically used to override the default block size in multi- threaded mode, but this option can be used in single-threaded mode too. In multi-threaded mode about three times size bytes will be allocated in each thread for buffering input and output. The default size is three times the LZMA2 dictionary size or 1 MiB, whichever is more. Typically a good value is 2–4 times the size of the LZMA2 dictionary or at least 1 MiB. Using size less than the LZMA2 dictionary size is waste of RAM because then the LZMA2 dictionary buffer will never get fully used. In multi-threaded mode, the sizes of the blocks are stored in the block headers. This size information is required for multi-threaded decompression. In single-threaded mode no block splitting is done by default. Setting this option doesn't affect memory usage. No size information is stored in block headers, thus files created in single-threaded mode won't be identical to files created in multi-threaded mode. The lack of size information also means that xz won't be able decompress the files in multi-threaded mode. --block-list=items When compressing to the .xz format, start a new block with an optional custom filter chain after the given intervals of uncompressed data. The items are a comma-separated list. Each item consists of an optional filter chain number between 0 and 9 followed by a colon (:) and a required size of uncompressed data. Omitting an item (two or more consecutive commas) is a shorthand to use the size and filters of the previous item. If the input file is bigger than the sum of the sizes in items, the last item is repeated until the end of the file. A special value of 0 may be used as the last size to indicate that the rest of the file should be encoded as a single block. An alternative filter chain for each block can be specified in combination with the --filters1=filters ... --filters9=filters options. These options define filter chains with an identifier between 1–9. Filter chain 0 can be used to refer to the default filter chain, which is the same as not specifying a filter chain. The filter chain identifier can be used before the uncompressed size, followed by a colon (:). For example, if one specifies --block-list=1:2MiB,3:2MiB,2:4MiB,,2MiB,0:4MiB then blocks will be created using: • The filter chain specified by --filters1 and 2 MiB input • The filter chain specified by --filters3 and 2 MiB input • The filter chain specified by --filters2 and 4 MiB input • The filter chain specified by --filters2 and 4 MiB input • The default filter chain and 2 MiB input • The default filter chain and 4 MiB input for every block until end of input. If one specifies a size that exceeds the encoder's block size (either the default value in threaded mode or the value specified with --block-size=size), the encoder will create additional blocks while keeping the boundaries specified in items. For example, if one specifies --block-size=10MiB --block-list=5MiB,10MiB,8MiB,12MiB,24MiB and the input file is 80 MiB, one will get 11 blocks: 5, 10, 8, 10, 2, 10, 10, 4, 10, 10, and 1 MiB. In multi-threaded mode the sizes of the blocks are stored in the block headers. This isn't done in single-threaded mode, so the encoded output won't be identical to that of the multi-threaded mode. --flush-timeout=timeout When compressing, if more than timeout milliseconds (a positive integer) has passed since the previous flush and reading more input would block, all the pending input data is flushed from the encoder and made available in the output stream. This can be useful if xz is used to compress data that is streamed over a network. Small timeout values make the data available at the receiving end with a small delay, but large timeout values give better compression ratio. This feature is disabled by default. If this option is specified more than once, the last one takes effect. The special timeout value of 0 can be used to explicitly disable this feature. This feature is not available on non-POSIX systems. This feature is still experimental. Currently xz is unsuitable for decompressing the stream in real time due to how xz does buffering. --memlimit-compress=limit Set a memory usage limit for compression. If this option is specified multiple times, the last one takes effect. If the compression settings exceed the limit, xz will attempt to adjust the settings downwards so that the limit is no longer exceeded and display a notice that automatic adjustment was done. The adjustments are done in this order: reducing the number of threads, switching to single-threaded mode if even one thread in multi-threaded mode exceeds the limit, and finally reducing the LZMA2 dictionary size. When compressing with --format=raw or if --no-adjust has been specified, only the number of threads may be reduced since it can be done without affecting the compressed output. If the limit cannot be met even with the adjustments described above, an error is displayed and xz will exit with exit status 1. The limit can be specified in multiple ways: • The limit can be an absolute value in bytes. Using an integer suffix like MiB can be useful. Example: --memlimit-compress=80MiB • The limit can be specified as a percentage of total physical memory (RAM). This can be useful especially when setting the XZ_DEFAULTS environment variable in a shell initialization script that is shared between different computers. That way the limit is automatically bigger on systems with more memory. Example: --memlimit-compress=70% • The limit can be reset back to its default value by setting it to 0. This is currently equivalent to setting the limit to max (no memory usage limit). For 32-bit xz there is a special case: if the limit would be over 4020 MiB, the limit is set to 4020 MiB. On MIPS32 2000 MiB is used instead. (The values 0 and max aren't affected by this. A similar feature doesn't exist for decompression.) This can be helpful when a 32-bit executable has access to 4 GiB address space (2 GiB on MIPS32) while hopefully doing no harm in other situations. See also the section Memory usage. --memlimit-decompress=limit Set a memory usage limit for decompression. This also affects the --list mode. If the operation is not possible without exceeding the limit, xz will display an error and decompressing the file will fail. See --memlimit-compress=limit for possible ways to specify the limit. --memlimit-mt-decompress=limit Set a memory usage limit for multi-threaded decompression. This can only affect the number of threads; this will never make xz refuse to decompress a file. If limit is too low to allow any multi-threading, the limit is ignored and xz will continue in single-threaded mode. Note that if also --memlimit-decompress is used, it will always apply to both single-threaded and multi- threaded modes, and so the effective limit for multi-threading will never be higher than the limit set with --memlimit-decompress. In contrast to the other memory usage limit options, --memlimit-mt-decompress=limit has a system-specific default limit. xz --info-memory can be used to see the current value. This option and its default value exist because without any limit the threaded decompressor could end up allocating an insane amount of memory with some input files. If the default limit is too low on your system, feel free to increase the limit but never set it to a value larger than the amount of usable RAM as with appropriate input files xz will attempt to use that amount of memory even with a low number of threads. Running out of memory or swapping will not improve decompression performance. See --memlimit-compress=limit for possible ways to specify the limit. Setting limit to 0 resets the limit to the default system-specific value. -M limit, --memlimit=limit, --memory=limit This is equivalent to specifying --memlimit-compress=limit --memlimit-decompress=limit --memlimit-mt-decompress=limit. --no-adjust Display an error and exit if the memory usage limit cannot be met without adjusting settings that affect the compressed output. That is, this prevents xz from switching the encoder from multi-threaded mode to single-threaded mode and from reducing the LZMA2 dictionary size. Even when this option is used the number of threads may be reduced to meet the memory usage limit as that won't affect the compressed output. Automatic adjusting is always disabled when creating raw streams (--format=raw). -T threads, --threads=threads Specify the number of worker threads to use. Setting threads to a special value 0 makes xz use up to as many threads as the processor(s) on the system support. The actual number of threads can be fewer than threads if the input file is not big enough for threading with the given settings or if using more threads would exceed the memory usage limit. The single-threaded and multi-threaded compressors produce different output. Single-threaded compressor will give the smallest file size but only the output from the multi-threaded compressor can be decompressed using multiple threads. Setting threads to 1 will use the single-threaded mode. Setting threads to any other value, including 0, will use the multi-threaded compressor even if the system supports only one hardware thread. (xz 5.2.x used single-threaded mode in this situation.) To use multi-threaded mode with only one thread, set threads to +1. The + prefix has no effect with values other than 1. A memory usage limit can still make xz switch to single-threaded mode unless --no-adjust is used. Support for the + prefix was added in xz 5.4.0. If an automatic number of threads has been requested and no memory usage limit has been specified, then a system-specific default soft limit will be used to possibly limit the number of threads. It is a soft limit in sense that it is ignored if the number of threads becomes one, thus a soft limit will never stop xz from compressing or decompressing. This default soft limit will not make xz switch from multi-threaded mode to single- threaded mode. The active limits can be seen with xz --info-memory. Currently the only threading method is to split the input into blocks and compress them independently from each other. The default block size depends on the compression level and can be overridden with the --block-size=size option. Threaded decompression only works on files that contain multiple blocks with size information in block headers. All large enough files compressed in multi-threaded mode meet this condition, but files compressed in single-threaded mode don't even if --block-size=size has been used. The default value for threads is 0. In xz 5.4.x and older the default is 1. Custom compressor filter chains A custom filter chain allows specifying the compression settings in detail instead of relying on the settings associated to the presets. When a custom filter chain is specified, preset options (-0 ... -9 and --extreme) earlier on the command line are forgotten. If a preset option is specified after one or more custom filter chain options, the new preset takes effect and the custom filter chain options specified earlier are forgotten. A filter chain is comparable to piping on the command line. When compressing, the uncompressed input goes to the first filter, whose output goes to the next filter (if any). The output of the last filter gets written to the compressed file. The maximum number of filters in the chain is four, but typically a filter chain has only one or two filters. Many filters have limitations on where they can be in the filter chain: some filters can work only as the last filter in the chain, some only as a non-last filter, and some work in any position in the chain. Depending on the filter, this limitation is either inherent to the filter design or exists to prevent security issues. A custom filter chain can be specified in two different ways. The options --filters=filters and --filters1=filters ... --filters9=filters allow specifying an entire filter chain in one option using the liblzma filter string syntax. Alternatively, a filter chain can be specified by using one or more individual filter options in the order they are wanted in the filter chain. That is, the order of the individual filter options is significant! When decoding raw streams (--format=raw), the filter chain must be specified in the same order as it was specified when compressing. Any individual filter or preset options specified before the full chain option (--filters=filters) will be forgotten. Individual filters specified after the full chain option will reset the filter chain. Both the full and individual filter options take filter-specific options as a comma-separated list. Extra commas in options are ignored. Every option has a default value, so specify those you want to change. To see the whole filter chain and options, use xz -vv (that is, use --verbose twice). This works also for viewing the filter chain options used by presets. --filters=filters Specify the full filter chain or a preset in a single option. Each filter can be separated by spaces or two dashes (--). filters may need to be quoted on the shell command line so it is parsed as a single option. To denote options, use : or =. A preset can be prefixed with a - and followed with zero or more flags. The only supported flag is e to apply the same options as --extreme. --filters1=filters ... --filters9=filters Specify up to nine additional filter chains that can be used with --block-list. For example, when compressing an archive with executable files followed by text files, the executable part could use a filter chain with a BCJ filter and the text part only the LZMA2 filter. --filters-help Display a help message describing how to specify presets and custom filter chains in the --filters and --filters1=filters ... --filters9=filters options, and exit successfully. --lzma1[=options] --lzma2[=options] Add LZMA1 or LZMA2 filter to the filter chain. These filters can be used only as the last filter in the chain. LZMA1 is a legacy filter, which is supported almost solely due to the legacy .lzma file format, which supports only LZMA1. LZMA2 is an updated version of LZMA1 to fix some practical issues of LZMA1. The .xz format uses LZMA2 and doesn't support LZMA1 at all. Compression speed and ratios of LZMA1 and LZMA2 are practically the same. LZMA1 and LZMA2 share the same set of options: preset=preset Reset all LZMA1 or LZMA2 options to preset. Preset consist of an integer, which may be followed by single- letter preset modifiers. The integer can be from 0 to 9, matching the command line options -0 ... -9. The only supported modifier is currently e, which matches --extreme. If no preset is specified, the default values of LZMA1 or LZMA2 options are taken from the preset 6. dict=size Dictionary (history buffer) size indicates how many bytes of the recently processed uncompressed data is kept in memory. The algorithm tries to find repeating byte sequences (matches) in the uncompressed data, and replace them with references to the data currently in the dictionary. The bigger the dictionary, the higher is the chance to find a match. Thus, increasing dictionary size usually improves compression ratio, but a dictionary bigger than the uncompressed file is waste of memory. Typical dictionary size is from 64 KiB to 64 MiB. The minimum is 4 KiB. The maximum for compression is currently 1.5 GiB (1536 MiB). The decompressor already supports dictionaries up to one byte less than 4 GiB, which is the maximum for the LZMA1 and LZMA2 stream formats. Dictionary size and match finder (mf) together determine the memory usage of the LZMA1 or LZMA2 encoder. The same (or bigger) dictionary size is required for decompressing that was used when compressing, thus the memory usage of the decoder is determined by the dictionary size used when compressing. The .xz headers store the dictionary size either as 2^n or 2^n + 2^(n-1), so these sizes are somewhat preferred for compression. Other sizes will get rounded up when stored in the .xz headers. lc=lc Specify the number of literal context bits. The minimum is 0 and the maximum is 4; the default is 3. In addition, the sum of lc and lp must not exceed 4. All bytes that cannot be encoded as matches are encoded as literals. That is, literals are simply 8-bit bytes that are encoded one at a time. The literal coding makes an assumption that the highest lc bits of the previous uncompressed byte correlate with the next byte. For example, in typical English text, an upper-case letter is often followed by a lower-case letter, and a lower-case letter is usually followed by another lower-case letter. In the US-ASCII character set, the highest three bits are 010 for upper-case letters and 011 for lower-case letters. When lc is at least 3, the literal coding can take advantage of this property in the uncompressed data. The default value (3) is usually good. If you want maximum compression, test lc=4. Sometimes it helps a little, and sometimes it makes compression worse. If it makes it worse, test lc=2 too. lp=lp Specify the number of literal position bits. The minimum is 0 and the maximum is 4; the default is 0. Lp affects what kind of alignment in the uncompressed data is assumed when encoding literals. See pb below for more information about alignment. pb=pb Specify the number of position bits. The minimum is 0 and the maximum is 4; the default is 2. Pb affects what kind of alignment in the uncompressed data is assumed in general. The default means four-byte alignment (2^pb=2^2=4), which is often a good choice when there's no better guess. When the alignment is known, setting pb accordingly may reduce the file size a little. For example, with text files having one-byte alignment (US-ASCII, ISO-8859-*, UTF-8), setting pb=0 can improve compression slightly. For UTF-16 text, pb=1 is a good choice. If the alignment is an odd number like 3 bytes, pb=0 might be the best choice. Even though the assumed alignment can be adjusted with pb and lp, LZMA1 and LZMA2 still slightly favor 16-byte alignment. It might be worth taking into account when designing file formats that are likely to be often compressed with LZMA1 or LZMA2. mf=mf Match finder has a major effect on encoder speed, memory usage, and compression ratio. Usually Hash Chain match finders are faster than Binary Tree match finders. The default depends on the preset: 0 uses hc3, 1–3 use hc4, and the rest use bt4. The following match finders are supported. The memory usage formulas below are rough approximations, which are closest to the reality when dict is a power of two. hc3 Hash Chain with 2- and 3-byte hashing Minimum value for nice: 3 Memory usage: dict * 7.5 (if dict <= 16 MiB); dict * 5.5 + 64 MiB (if dict > 16 MiB) hc4 Hash Chain with 2-, 3-, and 4-byte hashing Minimum value for nice: 4 Memory usage: dict * 7.5 (if dict <= 32 MiB); dict * 6.5 (if dict > 32 MiB) bt2 Binary Tree with 2-byte hashing Minimum value for nice: 2 Memory usage: dict * 9.5 bt3 Binary Tree with 2- and 3-byte hashing Minimum value for nice: 3 Memory usage: dict * 11.5 (if dict <= 16 MiB); dict * 9.5 + 64 MiB (if dict > 16 MiB) bt4 Binary Tree with 2-, 3-, and 4-byte hashing Minimum value for nice: 4 Memory usage: dict * 11.5 (if dict <= 32 MiB); dict * 10.5 (if dict > 32 MiB) mode=mode Compression mode specifies the method to analyze the data produced by the match finder. Supported modes are fast and normal. The default is fast for presets 0–3 and normal for presets 4–9. Usually fast is used with Hash Chain match finders and normal with Binary Tree match finders. This is also what the presets do. nice=nice Specify what is considered to be a nice length for a match. Once a match of at least nice bytes is found, the algorithm stops looking for possibly better matches. Nice can be 2–273 bytes. Higher values tend to give better compression ratio at the expense of speed. The default depends on the preset. depth=depth Specify the maximum search depth in the match finder. The default is the special value of 0, which makes the compressor determine a reasonable depth from mf and nice. Reasonable depth for Hash Chains is 4–100 and 16–1000 for Binary Trees. Using very high values for depth can make the encoder extremely slow with some files. Avoid setting the depth over 1000 unless you are prepared to interrupt the compression in case it is taking far too long. When decoding raw streams (--format=raw), LZMA2 needs only the dictionary size. LZMA1 needs also lc, lp, and pb. --x86[=options] --arm[=options] --armthumb[=options] --arm64[=options] --powerpc[=options] --ia64[=options] --sparc[=options] --riscv[=options] Add a branch/call/jump (BCJ) filter to the filter chain. These filters can be used only as a non-last filter in the filter chain. A BCJ filter converts relative addresses in the machine code to their absolute counterparts. This doesn't change the size of the data but it increases redundancy, which can help LZMA2 to produce 0–15 % smaller .xz file. The BCJ filters are always reversible, so using a BCJ filter for wrong type of data doesn't cause any data loss, although it may make the compression ratio slightly worse. The BCJ filters are very fast and use an insignificant amount of memory. These BCJ filters have known problems related to the compression ratio: • Some types of files containing executable code (for example, object files, static libraries, and Linux kernel modules) have the addresses in the instructions filled with filler values. These BCJ filters will still do the address conversion, which will make the compression worse with these files. • If a BCJ filter is applied on an archive, it is possible that it makes the compression ratio worse than not using a BCJ filter. For example, if there are similar or even identical executables then filtering will likely make the files less similar and thus compression is worse. The contents of non- executable files in the same archive can matter too. In practice one has to try with and without a BCJ filter to see which is better in each situation. Different instruction sets have different alignment: the executable file must be aligned to a multiple of this value in the input data to make the filter work. Filter Alignment Notes x86 1 32-bit or 64-bit x86 ARM 4 ARM-Thumb 2 ARM64 4 4096-byte alignment is best PowerPC 4 Big endian only IA-64 16 Itanium SPARC 4 RISC-V 2 Since the BCJ-filtered data is usually compressed with LZMA2, the compression ratio may be improved slightly if the LZMA2 options are set to match the alignment of the selected BCJ filter. Examples: • IA-64 filter has 16-byte alignment so pb=4,lp=4,lc=0 is good with LZMA2 (2^4=16). • RISC-V code has 2-byte or 4-byte alignment depending on whether the file contains 16-bit compressed instructions (the C extension). When 16-bit instructions are used, pb=2,lp=1,lc=3 or pb=1,lp=1,lc=3 is good. When 16-bit instructions aren't present, pb=2,lp=2,lc=2 is the best. readelf -h can be used to check if "RVC" appears on the "Flags" line. • ARM64 is always 4-byte aligned so pb=2,lp=2,lc=2 is the best. • The x86 filter is an exception. It's usually good to stick to LZMA2's defaults (pb=2,lp=0,lc=3) when compressing x86 executables. All BCJ filters support the same options: start=offset Specify the start offset that is used when converting between relative and absolute addresses. The offset must be a multiple of the alignment of the filter (see the table above). The default is zero. In practice, the default is good; specifying a custom offset is almost never useful. --delta[=options] Add the Delta filter to the filter chain. The Delta filter can be only used as a non-last filter in the filter chain. Currently only simple byte-wise delta calculation is supported. It can be useful when compressing, for example, uncompressed bitmap images or uncompressed PCM audio. However, special purpose algorithms may give significantly better results than Delta + LZMA2. This is true especially with audio, which compresses faster and better, for example, with flac(1). Supported options: dist=distance Specify the distance of the delta calculation in bytes. distance must be 1–256. The default is 1. For example, with dist=2 and eight-byte input A1 B1 A2 B3 A3 B5 A4 B7, the output will be A1 B1 01 02 01 02 01 02. Other options -q, --quiet Suppress warnings and notices. Specify this twice to suppress errors too. This option has no effect on the exit status. That is, even if a warning was suppressed, the exit status to indicate a warning is still used. -v, --verbose Be verbose. If standard error is connected to a terminal, xz will display a progress indicator. Specifying --verbose twice will give even more verbose output. The progress indicator shows the following information: • Completion percentage is shown if the size of the input file is known. That is, the percentage cannot be shown in pipes. • Amount of compressed data produced (compressing) or consumed (decompressing). • Amount of uncompressed data consumed (compressing) or produced (decompressing). • Compression ratio, which is calculated by dividing the amount of compressed data processed so far by the amount of uncompressed data processed so far. • Compression or decompression speed. This is measured as the amount of uncompressed data consumed (compression) or produced (decompression) per second. It is shown after a few seconds have passed since xz started processing the file. • Elapsed time in the format M:SS or H:MM:SS. • Estimated remaining time is shown only when the size of the input file is known and a couple of seconds have already passed since xz started processing the file. The time is shown in a less precise format which never has any colons, for example, 2 min 30 s. When standard error is not a terminal, --verbose will make xz print the filename, compressed size, uncompressed size, compression ratio, and possibly also the speed and elapsed time on a single line to standard error after compressing or decompressing the file. The speed and elapsed time are included only when the operation took at least a few seconds. If the operation didn't finish, for example, due to user interruption, also the completion percentage is printed if the size of the input file is known. -Q, --no-warn Don't set the exit status to 2 even if a condition worth a warning was detected. This option doesn't affect the verbosity level, thus both --quiet and --no-warn have to be used to not display warnings and to not alter the exit status. --robot Print messages in a machine-parsable format. This is intended to ease writing frontends that want to use xz instead of liblzma, which may be the case with various scripts. The output with this option enabled is meant to be stable across xz releases. See the section ROBOT MODE for details. --info-memory Display, in human-readable format, how much physical memory (RAM) and how many processor threads xz thinks the system has and the memory usage limits for compression and decompression, and exit successfully. -h, --help Display a help message describing the most commonly used options, and exit successfully. -H, --long-help Display a help message describing all features of xz, and exit successfully -V, --version Display the version number of xz and liblzma in human readable format. To get machine-parsable output, specify --robot before --version. ROBOT MODE The robot mode is activated with the --robot option. It makes the output of xz easier to parse by other programs. Currently --robot is supported only together with --list, --filters-help, --info-memory, and --version. It will be supported for compression and decompression in the future. List mode xz --robot --list uses tab-separated output. The first column of every line has a string that indicates the type of the information found on that line: name This is always the first line when starting to list a file. The second column on the line is the filename. file This line contains overall information about the .xz file. This line is always printed after the name line. stream This line type is used only when --verbose was specified. There are as many stream lines as there are streams in the .xz file. block This line type is used only when --verbose was specified. There are as many block lines as there are blocks in the .xz file. The block lines are shown after all the stream lines; different line types are not interleaved. summary This line type is used only when --verbose was specified twice. This line is printed after all block lines. Like the file line, the summary line contains overall information about the .xz file. totals This line is always the very last line of the list output. It shows the total counts and sizes. The columns of the file lines: 2. Number of streams in the file 3. Total number of blocks in the stream(s) 4. Compressed size of the file 5. Uncompressed size of the file 6. Compression ratio, for example, 0.123. If ratio is over 9.999, three dashes (---) are displayed instead of the ratio. 7. Comma-separated list of integrity check names. The following strings are used for the known check types: None, CRC32, CRC64, and SHA-256. For unknown check types, Unknown-N is used, where N is the Check ID as a decimal number (one or two digits). 8. Total size of stream padding in the file The columns of the stream lines: 2. Stream number (the first stream is 1) 3. Number of blocks in the stream 4. Compressed start offset 5. Uncompressed start offset 6. Compressed size (does not include stream padding) 7. Uncompressed size 8. Compression ratio 9. Name of the integrity check 10. Size of stream padding The columns of the block lines: 2. Number of the stream containing this block 3. Block number relative to the beginning of the stream (the first block is 1) 4. Block number relative to the beginning of the file 5. Compressed start offset relative to the beginning of the file 6. Uncompressed start offset relative to the beginning of the file 7. Total compressed size of the block (includes headers) 8. Uncompressed size 9. Compression ratio 10. Name of the integrity check If --verbose was specified twice, additional columns are included on the block lines. These are not displayed with a single --verbose, because getting this information requires many seeks and can thus be slow: 11. Value of the integrity check in hexadecimal 12. Block header size 13. Block flags: c indicates that compressed size is present, and u indicates that uncompressed size is present. If the flag is not set, a dash (-) is shown instead to keep the string length fixed. New flags may be added to the end of the string in the future. 14. Size of the actual compressed data in the block (this excludes the block header, block padding, and check fields) 15. Amount of memory (in bytes) required to decompress this block with this xz version 16. Filter chain. Note that most of the options used at compression time cannot be known, because only the options that are needed for decompression are stored in the .xz headers. The columns of the summary lines: 2. Amount of memory (in bytes) required to decompress this file with this xz version 3. yes or no indicating if all block headers have both compressed size and uncompressed size stored in them Since xz 5.1.2alpha: 4. Minimum xz version required to decompress the file The columns of the totals line: 2. Number of streams 3. Number of blocks 4. Compressed size 5. Uncompressed size 6. Average compression ratio 7. Comma-separated list of integrity check names that were present in the files 8. Stream padding size 9. Number of files. This is here to keep the order of the earlier columns the same as on file lines. If --verbose was specified twice, additional columns are included on the totals line: 10. Maximum amount of memory (in bytes) required to decompress the files with this xz version 11. yes or no indicating if all block headers have both compressed size and uncompressed size stored in them Since xz 5.1.2alpha: 12. Minimum xz version required to decompress the file Future versions may add new line types and new columns can be added to the existing line types, but the existing columns won't be changed. Filters help xz --robot --filters-help prints the supported filters in the following format: filter:option=<value>,option=<value>... filter Name of the filter option Name of a filter specific option value Numeric value ranges appear as <min-max>. String value choices are shown within < > and separated by a | character. Each filter is printed on its own line. Memory limit information xz --robot --info-memory prints a single line with multiple tab- separated columns: 1. Total amount of physical memory (RAM) in bytes. 2. Memory usage limit for compression in bytes (--memlimit-compress). A special value of 0 indicates the default setting which for single-threaded mode is the same as no limit. 3. Memory usage limit for decompression in bytes (--memlimit-decompress). A special value of 0 indicates the default setting which for single-threaded mode is the same as no limit. 4. Since xz 5.3.4alpha: Memory usage for multi-threaded decompression in bytes (--memlimit-mt-decompress). This is never zero because a system-specific default value shown in the column 5 is used if no limit has been specified explicitly. This is also never greater than the value in the column 3 even if a larger value has been specified with --memlimit-mt-decompress. 5. Since xz 5.3.4alpha: A system-specific default memory usage limit that is used to limit the number of threads when compressing with an automatic number of threads (--threads=0) and no memory usage limit has been specified (--memlimit-compress). This is also used as the default value for --memlimit-mt-decompress. 6. Since xz 5.3.4alpha: Number of available processor threads. In the future, the output of xz --robot --info-memory may have more columns, but never more than a single line. Version xz --robot --version prints the version number of xz and liblzma in the following format: XZ_VERSION=XYYYZZZS LIBLZMA_VERSION=XYYYZZZS X Major version. YYY Minor version. Even numbers are stable. Odd numbers are alpha or beta versions. ZZZ Patch level for stable releases or just a counter for development releases. S Stability. 0 is alpha, 1 is beta, and 2 is stable. S should be always 2 when YYY is even. XYYYZZZS are the same on both lines if xz and liblzma are from the same XZ Utils release. Examples: 4.999.9beta is 49990091 and 5.0.0 is 50000002. EXIT STATUS 0 All is good. 1 An error occurred. 2 Something worth a warning occurred, but no actual errors occurred. Notices (not warnings or errors) printed on standard error don't affect the exit status. ENVIRONMENT xz parses space-separated lists of options from the environment variables XZ_DEFAULTS and XZ_OPT, in this order, before parsing the options from the command line. Note that only options are parsed from the environment variables; all non-options are silently ignored. Parsing is done with getopt_long(3) which is used also for the command line arguments. XZ_DEFAULTS User-specific or system-wide default options. Typically this is set in a shell initialization script to enable xz's memory usage limiter by default. Excluding shell initialization scripts and similar special cases, scripts must never set or unset XZ_DEFAULTS. XZ_OPT This is for passing options to xz when it is not possible to set the options directly on the xz command line. This is the case when xz is run by a script or tool, for example, GNU tar(1): XZ_OPT=-2v tar caf foo.tar.xz foo Scripts may use XZ_OPT, for example, to set script-specific default compression options. It is still recommended to allow users to override XZ_OPT if that is reasonable. For example, in sh(1) scripts one may use something like this: XZ_OPT=${XZ_OPT-"-7e"} export XZ_OPT LZMA UTILS COMPATIBILITY The command line syntax of xz is practically a superset of lzma, unlzma, and lzcat as found from LZMA Utils 4.32.x. In most cases, it is possible to replace LZMA Utils with XZ Utils without breaking existing scripts. There are some incompatibilities though, which may sometimes cause problems. Compression preset levels The numbering of the compression level presets is not identical in xz and LZMA Utils. The most important difference is how dictionary sizes are mapped to different presets. Dictionary size is roughly equal to the decompressor memory usage. Level xz LZMA Utils -0 256 KiB N/A -1 1 MiB 64 KiB -2 2 MiB 1 MiB -3 4 MiB 512 KiB -4 4 MiB 1 MiB -5 8 MiB 2 MiB -6 8 MiB 4 MiB -7 16 MiB 8 MiB -8 32 MiB 16 MiB -9 64 MiB 32 MiB The dictionary size differences affect the compressor memory usage too, but there are some other differences between LZMA Utils and XZ Utils, which make the difference even bigger: Level xz LZMA Utils 4.32.x -0 3 MiB N/A -1 9 MiB 2 MiB -2 17 MiB 12 MiB -3 32 MiB 12 MiB -4 48 MiB 16 MiB -5 94 MiB 26 MiB -6 94 MiB 45 MiB -7 186 MiB 83 MiB -8 370 MiB 159 MiB -9 674 MiB 311 MiB The default preset level in LZMA Utils is -7 while in XZ Utils it is -6, so both use an 8 MiB dictionary by default. Streamed vs. non-streamed .lzma files The uncompressed size of the file can be stored in the .lzma header. LZMA Utils does that when compressing regular files. The alternative is to mark that uncompressed size is unknown and use end-of-payload marker to indicate where the decompressor should stop. LZMA Utils uses this method when uncompressed size isn't known, which is the case, for example, in pipes. xz supports decompressing .lzma files with or without end-of-payload marker, but all .lzma files created by xz will use end-of-payload marker and have uncompressed size marked as unknown in the .lzma header. This may be a problem in some uncommon situations. For example, a .lzma decompressor in an embedded device might work only with files that have known uncompressed size. If you hit this problem, you need to use LZMA Utils or LZMA SDK to create .lzma files with known uncompressed size. Unsupported .lzma files The .lzma format allows lc values up to 8, and lp values up to 4. LZMA Utils can decompress files with any lc and lp, but always creates files with lc=3 and lp=0. Creating files with other lc and lp is possible with xz and with LZMA SDK. The implementation of the LZMA1 filter in liblzma requires that the sum of lc and lp must not exceed 4. Thus, .lzma files, which exceed this limitation, cannot be decompressed with xz. LZMA Utils creates only .lzma files which have a dictionary size of 2^n (a power of 2) but accepts files with any dictionary size. liblzma accepts only .lzma files which have a dictionary size of 2^n or 2^n + 2^(n-1). This is to decrease false positives when detecting .lzma files. These limitations shouldn't be a problem in practice, since practically all .lzma files have been compressed with settings that liblzma will accept. Trailing garbage When decompressing, LZMA Utils silently ignore everything after the first .lzma stream. In most situations, this is a bug. This also means that LZMA Utils don't support decompressing concatenated .lzma files. If there is data left after the first .lzma stream, xz considers the file to be corrupt unless --single-stream was used. This may break obscure scripts which have assumed that trailing garbage is ignored. NOTES Compressed output may vary The exact compressed output produced from the same uncompressed input file may vary between XZ Utils versions even if compression options are identical. This is because the encoder can be improved (faster or better compression) without affecting the file format. The output can vary even between different builds of the same XZ Utils version, if different build options are used. The above means that once --rsyncable has been implemented, the resulting files won't necessarily be rsyncable unless both old and new files have been compressed with the same xz version. This problem can be fixed if a part of the encoder implementation is frozen to keep rsyncable output stable across xz versions. Embedded .xz decompressors Embedded .xz decompressor implementations like XZ Embedded don't necessarily support files created with integrity check types other than none and crc32. Since the default is --check=crc64, you must use --check=none or --check=crc32 when creating files for embedded systems. Outside embedded systems, all .xz format decompressors support all the check types, or at least are able to decompress the file without verifying the integrity check if the particular check is not supported. XZ Embedded supports BCJ filters, but only with the default start offset.
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Basics Compress the file foo into foo.xz using the default compression level (-6), and remove foo if compression is successful: xz foo Decompress bar.xz into bar and don't remove bar.xz even if decompression is successful: xz -dk bar.xz Create baz.tar.xz with the preset -4e (-4 --extreme), which is slower than the default -6, but needs less memory for compression and decompression (48 MiB and 5 MiB, respectively): tar cf - baz | xz -4e > baz.tar.xz A mix of compressed and uncompressed files can be decompressed to standard output with a single command: xz -dcf a.txt b.txt.xz c.txt d.txt.lzma > abcd.txt Parallel compression of many files On GNU and *BSD, find(1) and xargs(1) can be used to parallelize compression of many files: find . -type f \! -name '*.xz' -print0 \ | xargs -0r -P4 -n16 xz -T1 The -P option to xargs(1) sets the number of parallel xz processes. The best value for the -n option depends on how many files there are to be compressed. If there are only a couple of files, the value should probably be 1; with tens of thousands of files, 100 or even more may be appropriate to reduce the number of xz processes that xargs(1) will eventually create. The option -T1 for xz is there to force it to single-threaded mode, because xargs(1) is used to control the amount of parallelization. Robot mode Calculate how many bytes have been saved in total after compressing multiple files: xz --robot --list *.xz | awk '/^totals/{print $5-$4}' A script may want to know that it is using new enough xz. The following sh(1) script checks that the version number of the xz tool is at least 5.0.0. This method is compatible with old beta versions, which didn't support the --robot option: if ! eval "$(xz --robot --version 2> /dev/null)" || [ "$XZ_VERSION" -lt 50000002 ]; then echo "Your xz is too old." fi unset XZ_VERSION LIBLZMA_VERSION Set a memory usage limit for decompression using XZ_OPT, but if a limit has already been set, don't increase it: NEWLIM=$((123 << 20)) # 123 MiB OLDLIM=$(xz --robot --info-memory | cut -f3) if [ $OLDLIM -eq 0 -o $OLDLIM -gt $NEWLIM ]; then XZ_OPT="$XZ_OPT --memlimit-decompress=$NEWLIM" export XZ_OPT fi Custom compressor filter chains The simplest use for custom filter chains is customizing a LZMA2 preset. This can be useful, because the presets cover only a subset of the potentially useful combinations of compression settings. The CompCPU columns of the tables from the descriptions of the options -0 ... -9 and --extreme are useful when customizing LZMA2 presets. Here are the relevant parts collected from those two tables: Preset CompCPU -0 0 -1 1 -2 2 -3 3 -4 4 -5 5 -6 6 -5e 7 -6e 8 If you know that a file requires somewhat big dictionary (for example, 32 MiB) to compress well, but you want to compress it quicker than xz -8 would do, a preset with a low CompCPU value (for example, 1) can be modified to use a bigger dictionary: xz --lzma2=preset=1,dict=32MiB foo.tar With certain files, the above command may be faster than xz -6 while compressing significantly better. However, it must be emphasized that only some files benefit from a big dictionary while keeping the CompCPU value low. The most obvious situation, where a big dictionary can help a lot, is an archive containing very similar files of at least a few megabytes each. The dictionary size has to be significantly bigger than any individual file to allow LZMA2 to take full advantage of the similarities between consecutive files. If very high compressor and decompressor memory usage is fine, and the file being compressed is at least several hundred megabytes, it may be useful to use an even bigger dictionary than the 64 MiB that xz -9 would use: xz -vv --lzma2=dict=192MiB big_foo.tar Using -vv (--verbose --verbose) like in the above example can be useful to see the memory requirements of the compressor and decompressor. Remember that using a dictionary bigger than the size of the uncompressed file is waste of memory, so the above command isn't useful for small files. Sometimes the compression time doesn't matter, but the decompressor memory usage has to be kept low, for example, to make it possible to decompress the file on an embedded system. The following command uses -6e (-6 --extreme) as a base and sets the dictionary to only 64 KiB. The resulting file can be decompressed with XZ Embedded (that's why there is --check=crc32) using about 100 KiB of memory. xz --check=crc32 --lzma2=preset=6e,dict=64KiB foo If you want to squeeze out as many bytes as possible, adjusting the number of literal context bits (lc) and number of position bits (pb) can sometimes help. Adjusting the number of literal position bits (lp) might help too, but usually lc and pb are more important. For example, a source code archive contains mostly US-ASCII text, so something like the following might give slightly (like 0.1 %) smaller file than xz -6e (try also without lc=4): xz --lzma2=preset=6e,pb=0,lc=4 source_code.tar Using another filter together with LZMA2 can improve compression with certain file types. For example, to compress a x86-32 or x86-64 shared library using the x86 BCJ filter: xz --x86 --lzma2 libfoo.so Note that the order of the filter options is significant. If --x86 is specified after --lzma2, xz will give an error, because there cannot be any filter after LZMA2, and also because the x86 BCJ filter cannot be used as the last filter in the chain. The Delta filter together with LZMA2 can give good results with bitmap images. It should usually beat PNG, which has a few more advanced filters than simple delta but uses Deflate for the actual compression. The image has to be saved in uncompressed format, for example, as uncompressed TIFF. The distance parameter of the Delta filter is set to match the number of bytes per pixel in the image. For example, 24-bit RGB bitmap needs dist=3, and it is also good to pass pb=0 to LZMA2 to accommodate the three-byte alignment: xz --delta=dist=3 --lzma2=pb=0 foo.tiff If multiple images have been put into a single archive (for example, .tar), the Delta filter will work on that too as long as all images have the same number of bytes per pixel. SEE ALSO xzdec(1), xzdiff(1), xzgrep(1), xzless(1), xzmore(1), gzip(1), bzip2(1), 7z(1) XZ Utils: <https://tukaani.org/xz/> XZ Embedded: <https://tukaani.org/xz/embedded.html> LZMA SDK: <https://7-zip.org/sdk.html> Tukaani 2024-04-08 XZ(1)
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hwloc-distrib
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hwloc-distrib generates a series of CPU masks corresponding to a distribution of a given number of elements over the topology of the machine. The distribution is done recursively from the top of the hierarchy (or from the level specified by option --from) down to the bottom of the hierarchy (or down to the level specified by option --to, or until only one element remains), splitting the number of elements at each encountered hierarchy level not ignored by options --ignore. This can e.g. be used to distribute a set of processes hierarchically according to the topology of a machine. These masks can be used with hwloc-bind(1). NOTE: It is highly recommended that you read the hwloc(7) overview page before reading this man page. Most of the concepts described in hwloc(7) directly apply to the hwloc-bind utility.
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hwloc-distrib - Build a number of cpu masks distributed on the system
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hwloc-distrib [options] <integer>
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--single Singlify each output to a single CPU. --taskset Show CPU set strings in the format recognized by the taskset command-line program instead of hwloc-specific CPU set string format. -v --verbose Verbose messages. -i <path>, --input <path> Read the topology from <path> instead of discovering the topology of the local machine. If <path> is a file, it may be a XML file exported by a previous hwloc program. If <path> is "-", the standard input may be used as a XML file. On Linux, <path> may be a directory containing the topology files gathered from another machine topology with hwloc-gather- topology. On x86, <path> may be a directory containing a cpuid dump gathered with hwloc-gather-cpuid. When the archivemount program is available, <path> may also be a tarball containing such Linux or x86 topology files. -i <specification>, --input <specification> Simulate a fake hierarchy (instead of discovering the topology on the local machine). If <specification> is "node:2 pu:3", the topology will contain two NUMA nodes with 3 processing units in each of them. The <specification> string must end with a number of PUs. --if <format>, --input-format <format> Enforce the input in the given format, among xml, fsroot, cpuid and synthetic. --ignore <type> Ignore all objects of type <type> in the topology. --from <type> Distribute starting from objects of the given type instead of from the top of the topology hierarchy, i.e. ignoring the structure given by objects above. <type> cannot be among NUMANode, I/O or Misc types. --to <type> Distribute down to objects of the given type instead of down to the bottom of the topology hierarchy, i.e. ignoring the structure given by objects below. This may be useful if some latitude is desired for the binding, e.g. just bind several processes to each package without specifying a single core for each of them. <type> cannot be among NUMANode, I/O or Misc types. --at <type> Distribute among objects of the given type. This is equivalent to specifying both --from and --to at the same time. --reverse Distribute by starting with the last objects first, and singlify CPU sets by keeping the last bit (instead of the first bit). --restrict <cpuset> Restrict the topology to the given cpuset. This removes some PUs and their now-child-less parents. Beware that restricting the PUs in a topology may change the logical indexes of many objects, including NUMA nodes. --restrict nodeset=<nodeset> Restrict the topology to the given nodeset (unless --restrict-flags specifies something different). This removes some NUMA nodes and their now-child-less parents. Beware that restricting the NUMA nodes in a topology may change the logical indexes of many objects, including PUs. --restrict-flags <flags> Enforce flags when restricting the topology. Flags may be given as numeric values or as a comma-separated list of flag names that are passed to hwloc_topology_restrict(). Those names may be substrings of actual flag names as long as a single one matches, for instance bynodeset,memless. The default is 0 (or none). --disallowed Include objects disallowed by administrative limitations. --version Report version and exit. -h --help Display help message and exit.
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hwloc-distrib's operation is best described through several examples. If 4 processes have to be distributed across a machine, their CPU masks may be obtained with: $ hwloc-distrib 4 0x0000000f 0x00000f00 0x000000f0 0x0000f000 To distribute only among the second package, the topology should be restricted: $ hwloc-distrib --restrict $(hwloc-calc package:1) 4 0x00000010 0x00000020 0x00000040 0x00000080 To get a single processor of each CPU masks (prevent migration in case of binding) $ hwloc-distrib 4 --single 0x00000001 0x00000100 0x00000010 0x00001000 Each output line may be converted independently with hwloc-calc: $ hwloc-distrib 4 --single | hwloc-calc --taskset 0x1 0x100 0x10 0x1000 To convert the output into a list of processors that may be passed to dplace -c inside a mpirun command line: $ hwloc-distrib 4 --single | xargs hwloc-calc --pulist 0,8,4,16 RETURN VALUE Upon successful execution, hwloc-distrib displays one or more CPU mask strings. The return value is 0. hwloc-distrib will return nonzero if any kind of error occurs, such as (but not limited to) failure to parse the command line. SEE ALSO hwloc(7) 2.10.0 December 4, 2023 HWLOC-DISTRIB(1)
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datacopy
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datacopy is a utility distributed with FreeTDS. datacopy will move table data from one server to another without the need for intermediate files. datacopy is much faster and more efficient than is freebcp out/in. datacopy makes use of the db-lib bcp API built into FreeTDS. This API is also available to application developers. datacopy can be used to migrate data between Sybase ASE and SQL Server or vice versa.
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datacopy – move table data between two servers
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datacopy [-vdE] {-t | -a | -c owner} [-b batchsize] [-p packetsize] [-S server/username/password/database/table_or_view] [-D server/username/password/database/table] [-T textsize]
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-t Truncate target table before loading data. -a Append data to target table. -c owner Create the target table with the same schema as the source table. datacopy will submit a ‘CREATE TABLE’ command on the target server using the specified owner in the command, e.g. ‘CREATE TABLE owner.table (...).’ -b batchsize The number of rows per batch of data copied. Each batch of data is effectively 'committed' to the database. The default is 1000. -p packetsize The number of bytes, per network packet, sent to and from the servers. Increased packet size can enhance performance. -T textsize Specify size of TEXT/IMAGE column from network. -v Produce verbose output, including diagnostic timings. -d Produce freetds TDSDUMP output. (Serious debug only!) -S server/username/password/database/table_or_view The connection information for the source server and the location/name of the table (or view) to be copied. If not specified, datacopy prompts the user for the information. -D server/username/password/database/table The connection information for the destination server and the location/name of the target table. If not specified, datacopy prompts the user for the information. -E Keep identity values. SEE ALSO freebcp(1), defncopy(1), bsqldb(1), tsql(1), FreeTDS User Guide. HISTORY datacopy first appeared in FreeTDS 0.64. AUTHORS The datacopy utility was written by Bill Thompson ⟨thompbil@exchange.uk.ml.com⟩. FreeTDS 1.4.21 March 25, 2015 FreeTDS 1.4.21
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libav-merge-next-commit
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gen_key
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fido2-cred
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fido2-cred makes or verifies a FIDO2 credential. A credential type may be es256 (denoting ECDSA over NIST P-256 with SHA-256), rs256 (denoting 2048-bit RSA with PKCS#1.5 padding and SHA-256), or eddsa (denoting EDDSA over Curve25519 with SHA-512). If type is not specified, es256 is assumed. When making a credential, the authenticator may require the user to authenticate with a PIN. If the -q option is not specified, fido2-cred will prompt the user for the PIN. If a tty is available, fido2-cred will use it to obtain the PIN. Otherwise, stdin is used. The input of fido2-cred is defined by the parameters of the credential to be made/verified. See the INPUT FORMAT section for details. The output of fido2-cred is defined by the result of the selected operation. See the OUTPUT FORMAT section for details. If a credential is successfully created or verified, fido2-cred exits 0. Otherwise, fido2-cred exits 1. The options are as follows: -M Tells fido2-cred to make a new credential on device. -V Tells fido2-cred to verify a credential. -b Request the credential's “largeBlobKey”, a 32-byte symmetric key associated with the generated credential. -c cred_protect If making a credential, set the credential's protection level to cred_protect, where cred_protect is the credential's protection level in decimal notation. Please refer to <fido/param.h> for the set of possible values. If verifying a credential, check whether the credential's protection level was signed by the authenticator as cred_protect. -d Causes fido2-cred to emit debugging output on stderr. -h If making a credential, enable the FIDO2 hmac-secret extension. If verifying a credential, check whether the extension data bit was signed by the authenticator. -i input_file Tells fido2-cred to read the parameters of the credential from input_file instead of stdin. -o output_file Tells fido2-cred to write output on output_file instead of stdout. -q Tells fido2-cred to be quiet. If a PIN is required and -q is specified, fido2-cred will fail. -r Create a resident credential. Resident credentials are called “discoverable credentials” in CTAP 2.1. -u Create a U2F credential. By default, fido2-cred will use FIDO2 if supported by the authenticator, and fallback to U2F otherwise. -v If making a credential, request user verification. If verifying a credential, check whether the user verification bit was signed by the authenticator. -w Tells fido2-cred that the first line of input when making a credential shall be interpreted as unhashed client data. This is required by Windows Hello, which calculates the client data hash internally. INPUT FORMAT The input of fido2-cred consists of base64 blobs and UTF-8 strings separated by newline characters ('\n'). When making a credential, fido2-cred expects its input to consist of: 1. client data hash (base64 blob); 2. relying party id (UTF-8 string); 3. user name (UTF-8 string); 4. user id (base64 blob). When verifying a credential, fido2-cred expects its input to consist of: 1. client data hash (base64 blob); 2. relying party id (UTF-8 string); 3. credential format (UTF-8 string); 4. authenticator data (base64 blob); 5. credential id (base64 blob); 6. attestation signature (base64 blob); 7. attestation certificate (optional, base64 blob). UTF-8 strings passed to fido2-cred must not contain embedded newline or NUL characters. OUTPUT FORMAT The output of fido2-cred consists of base64 blobs, UTF-8 strings, and PEM-encoded public keys separated by newline characters ('\n'). Upon the successful generation of a credential, fido2-cred outputs: 1. client data hash (base64 blob); 2. relying party id (UTF-8 string); 3. credential format (UTF-8 string); 4. authenticator data (base64 blob); 5. credential id (base64 blob); 6. attestation signature (base64 blob); 7. attestation certificate, if present (base64 blob). 8. the credential's associated 32-byte symmetric key (“largeBlobKey”), if present (base64 blob). Upon the successful verification of a credential, fido2-cred outputs: 1. credential id (base64 blob); 2. PEM-encoded credential key.
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fido2-cred – make/verify a FIDO2 credential
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fido2-cred -M [-bdhqruvw] [-c cred_protect] [-i input_file] [-o output_file] device [type] fido2-cred -V [-dhv] [-c cred_protect] [-i input_file] [-o output_file] [type]
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Create a new es256 credential on /dev/hidraw5, verify it, and save the id and the public key of the credential in cred: $ echo credential challenge | openssl sha256 -binary | base64 > cred_param $ echo relying party >> cred_param $ echo user name >> cred_param $ dd if=/dev/urandom bs=1 count=32 | base64 >> cred_param $ fido2-cred -M -i cred_param /dev/hidraw5 | fido2-cred -V -o cred SEE ALSO fido2-assert(1), fido2-token(1) CAVEATS Please note that fido2-cred handles Basic Attestation and Self Attestation transparently. In the case of Basic Attestation, the validity of the authenticator's attestation certificate is not verified. macOS 14.5 July 3, 2023 macOS 14.5
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mysqldumpslow
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The MySQL slow query log contains information about queries that take a long time to execute (see Section 5.4.5, “The Slow Query Log”). mysqldumpslow parses MySQL slow query log files and summarizes their contents. Normally, mysqldumpslow groups queries that are similar except for the particular values of number and string data values. It “abstracts” these values to N and 'S' when displaying summary output. To modify value abstracting behavior, use the -a and -n options. Invoke mysqldumpslow like this: mysqldumpslow [options] [log_file ...] Example output with no options given: Reading mysql slow query log from /usr/local/mysql/data/mysqld83-slow.log Count: 1 Time=4.32s (4s) Lock=0.00s (0s) Rows=0.0 (0), root[root]@localhost insert into t2 select * from t1 Count: 3 Time=2.53s (7s) Lock=0.00s (0s) Rows=0.0 (0), root[root]@localhost insert into t2 select * from t1 limit N Count: 3 Time=2.13s (6s) Lock=0.00s (0s) Rows=0.0 (0), root[root]@localhost insert into t1 select * from t1 mysqldumpslow supports the following options. • --help ┌────────────────────┬────────┐ │Command-Line Format │ --help │ └────────────────────┴────────┘ Display a help message and exit. • -a Do not abstract all numbers to N and strings to 'S'. • --debug, -d ┌────────────────────┬─────────┐ │Command-Line Format │ --debug │ └────────────────────┴─────────┘ Run in debug mode. This option is available only if MySQL was built using WITH_DEBUG. MySQL release binaries provided by Oracle are not built using this option. • -g pattern ┌─────┬────────┐ │Type │ String │ └─────┴────────┘ Consider only queries that match the (grep-style) pattern. • -h host_name ┌──────────────┬────────┐ │Type │ String │ ├──────────────┼────────┤ │Default Value │ * │ └──────────────┴────────┘ Host name of MySQL server for *-slow.log file name. The value can contain a wildcard. The default is * (match all). • -i name ┌─────┬────────┐ │Type │ String │ └─────┴────────┘ Name of server instance (if using mysql.server startup script). • -l Do not subtract lock time from total time. • -n N ┌─────┬─────────┐ │Type │ Numeric │ └─────┴─────────┘ Abstract numbers with at least N digits within names. • -r Reverse the sort order. • -s sort_type ┌──────────────┬────────┐ │Type │ String │ ├──────────────┼────────┤ │Default Value │ at │ └──────────────┴────────┘ How to sort the output. The value of sort_type should be chosen from the following list: • t, at: Sort by query time or average query time • l, al: Sort by lock time or average lock time • r, ar: Sort by rows sent or average rows sent • c: Sort by count By default, mysqldumpslow sorts by average query time (equivalent to -s at). • -t N ┌─────┬─────────┐ │Type │ Numeric │ └─────┴─────────┘ Display only the first N queries in the output. • --verbose, -v ┌────────────────────┬───────────┐ │Command-Line Format │ --verbose │ └────────────────────┴───────────┘ Verbose mode. Print more information about what the program does. COPYRIGHT Copyright © 1997, 2023, Oracle and/or its affiliates. This documentation is free software; you can redistribute it and/or modify it only under the terms of the GNU General Public License as published by the Free Software Foundation; version 2 of the License. This documentation is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with the program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA or see http://www.gnu.org/licenses/. SEE ALSO For more information, please refer to the MySQL Reference Manual, which may already be installed locally and which is also available online at http://dev.mysql.com/doc/. AUTHOR Oracle Corporation (http://dev.mysql.com/). MySQL 8.3 11/23/2023 MYSQLDUMPSLOW(1)
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mysqldumpslow - Summarize slow query log files
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mysqldumpslow [options] [log_file ...]
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grpc_objective_c_plugin
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mysqld
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mysqld, also known as MySQL Server, is a single multithreaded program that does most of the work in a MySQL installation. It does not spawn additional processes. MySQL Server manages access to the MySQL data directory that contains databases and tables. The data directory is also the default location for other information such as log files and status files. Note Some installation packages contain a debugging version of the server named mysqld-debug. Invoke this version instead of mysqld for debugging support, memory allocation checking, and trace file support (see Section 5.9.1.2, “Creating Trace Files”). When MySQL server starts, it listens for network connections from client programs and manages access to databases on behalf of those clients. The mysqld program has many options that can be specified at startup. For a complete list of options, run this command: mysqld --verbose --help MySQL Server also has a set of system variables that affect its operation as it runs. System variables can be set at server startup, and many of them can be changed at runtime to effect dynamic server reconfiguration. MySQL Server also has a set of status variables that provide information about its operation. You can monitor these status variables to access runtime performance characteristics. For a full description of MySQL Server command options, system variables, and status variables, see Section 5.1, “The MySQL Server”. For information about installing MySQL and setting up the initial configuration, see Chapter 2, Installing and Upgrading MySQL. COPYRIGHT Copyright © 1997, 2023, Oracle and/or its affiliates. This documentation is free software; you can redistribute it and/or modify it only under the terms of the GNU General Public License as published by the Free Software Foundation; version 2 of the License. This documentation is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with the program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA or see http://www.gnu.org/licenses/. SEE ALSO For more information, please refer to the MySQL Reference Manual, which may already be installed locally and which is also available online at http://dev.mysql.com/doc/. AUTHOR Oracle Corporation (http://dev.mysql.com/). MySQL 8.3 11/23/2023 MYSQLD(8)
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mysqld - the MySQL server
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mysqld [options]
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freetype-config
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freetype-config returns information needed for compiling and linking programs with the FreeType library, such as linker flags and compilation parameters. Alternatively, it can be used to query information about the FreeType library version installed on the system, such as the installation (directory path) prefix or the FreeType version number. If pkg-config(1) is found in the path, freetype-config acts as a wrapper for pkg-config. This program is part of the FreeType package.
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freetype-config - Get information about a libfreetype installation
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freetype-config [options]
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There are two types of options: output/display selection options, and path override options. Output selection options Only one of the output selection options should be given at each program invocation. --prefix Return the prefix value of the installed FreeType library (the default prefix will be `/usr' in most cases for distribution- installed packages). --exec-prefix Return the executable prefix value of the installed FreeType library (will often be the same as the prefix value). --ftversion Return the FreeType version number, directly derived from file `freetype.h'. --version Return the `libtool version' of the FreeType library. --libtool Return the library name for linking with libtool. --libs Return compiler flags for linking with the installed FreeType library. --cflags Return compiler flags for compiling against the installed FreeType library. --static Make command line options display flags for static linking. --help Show help and exit. Path override options These affect any selected output option, except the libtool version returned by --version. --prefix=PREFIX Override --prefix value with PREFIX. This also sets --exec-prefix=PREFIX if option --exec-prefix is not explicitly given. --exec-prefix=EPREFIX Override --exec-prefix value with EPREFIX. BUGS In case the libraries FreeType links to are located in non-standard directories, and pkg-config(1) is not available, the output from option --libs might be incomplete. It is thus recommended to use the pkg-config(1) interface instead, which is able to correctly resolve all dependencies. Setting --exec-prefix (either explicitly or implicitly) might return incorrect results if combined with option --static. The same problem can occur if you set the SYSROOT environment variable. AUTHOR This manual page was contributed by Nis Martensen <nis.martensen@web.de>, with further refinements from the FreeType team. FreeType 2.13.2 August 2023 FREETYPE-CONFIG(1)
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fbectest
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pip3
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exrmultipart
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gpg-error
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b2sum
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Print or check BLAKE2b (512-bit) checksums. With no FILE, or when FILE is -, read standard input. Mandatory arguments to long options are mandatory for short options too. -b, --binary read in binary mode -c, --check read checksums from the FILEs and check them -l, --length=BITS digest length in bits; must not exceed the max for the blake2 algorithm and must be a multiple of 8 --tag create a BSD-style checksum -t, --text read in text mode (default) -z, --zero end each output line with NUL, not newline, and disable file name escaping The following five options are useful only when verifying checksums: --ignore-missing don't fail or report status for missing files --quiet don't print OK for each successfully verified file --status don't output anything, status code shows success --strict exit non-zero for improperly formatted checksum lines -w, --warn warn about improperly formatted checksum lines --help display this help and exit --version output version information and exit The sums are computed as described in RFC 7693. When checking, the input should be a former output of this program. The default mode is to print a line with: checksum, a space, a character indicating input mode ('*' for binary, ' ' for text or where binary is insignificant), and name for each FILE. Note: There is no difference between binary mode and text mode on GNU systems. AUTHOR Written by Padraig Brady and Samuel Neves. REPORTING BUGS GNU coreutils online help: <https://www.gnu.org/software/coreutils/> Report any translation bugs to <https://translationproject.org/team/> COPYRIGHT Copyright © 2023 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. SEE ALSO cksum(1) Full documentation <https://www.gnu.org/software/coreutils/b2sum> or available locally via: info '(coreutils) b2sum invocation' GNU coreutils 9.3 April 2023 B2SUM(1)
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b2sum - compute and check BLAKE2 message digest
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b2sum [OPTION]... [FILE]...
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gr2fonttest
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crlutil
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gcov-13
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gcov is a test coverage program. Use it in concert with GCC to analyze your programs to help create more efficient, faster running code and to discover untested parts of your program. You can use gcov as a profiling tool to help discover where your optimization efforts will best affect your code. You can also use gcov along with the other profiling tool, gprof, to assess which parts of your code use the greatest amount of computing time. Profiling tools help you analyze your code's performance. Using a profiler such as gcov or gprof, you can find out some basic performance statistics, such as: * how often each line of code executes * what lines of code are actually executed * how much computing time each section of code uses Once you know these things about how your code works when compiled, you can look at each module to see which modules should be optimized. gcov helps you determine where to work on optimization. Software developers also use coverage testing in concert with testsuites, to make sure software is actually good enough for a release. Testsuites can verify that a program works as expected; a coverage program tests to see how much of the program is exercised by the testsuite. Developers can then determine what kinds of test cases need to be added to the testsuites to create both better testing and a better final product. You should compile your code without optimization if you plan to use gcov because the optimization, by combining some lines of code into one function, may not give you as much information as you need to look for `hot spots' where the code is using a great deal of computer time. Likewise, because gcov accumulates statistics by line (at the lowest resolution), it works best with a programming style that places only one statement on each line. If you use complicated macros that expand to loops or to other control structures, the statistics are less helpful---they only report on the line where the macro call appears. If your complex macros behave like functions, you can replace them with inline functions to solve this problem. gcov creates a logfile called sourcefile.gcov which indicates how many times each line of a source file sourcefile.c has executed. You can use these logfiles along with gprof to aid in fine-tuning the performance of your programs. gprof gives timing information you can use along with the information you get from gcov. gcov works only on code compiled with GCC. It is not compatible with any other profiling or test coverage mechanism.
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gcov - coverage testing tool
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gcov [-v|--version] [-h|--help] [-a|--all-blocks] [-b|--branch-probabilities] [-c|--branch-counts] [-d|--display-progress] [-f|--function-summaries] [-j|--json-format] [-H|--human-readable] [-k|--use-colors] [-l|--long-file-names] [-m|--demangled-names] [-n|--no-output] [-o|--object-directory directory|file] [-p|--preserve-paths] [-q|--use-hotness-colors] [-r|--relative-only] [-s|--source-prefix directory] [-t|--stdout] [-u|--unconditional-branches] [-x|--hash-filenames] files
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-a --all-blocks Write individual execution counts for every basic block. Normally gcov outputs execution counts only for the main blocks of a line. With this option you can determine if blocks within a single line are not being executed. -b --branch-probabilities Write branch frequencies to the output file, and write branch summary info to the standard output. This option allows you to see how often each branch in your program was taken. Unconditional branches will not be shown, unless the -u option is given. -c --branch-counts Write branch frequencies as the number of branches taken, rather than the percentage of branches taken. -d --display-progress Display the progress on the standard output. -f --function-summaries Output summaries for each function in addition to the file level summary. -h --help Display help about using gcov (on the standard output), and exit without doing any further processing. -j --json-format Output gcov file in an easy-to-parse JSON intermediate format which does not require source code for generation. The JSON file is compressed with gzip compression algorithm and the files have .gcov.json.gz extension. Structure of the JSON is following: { "current_working_directory": "foo/bar", "data_file": "a.out", "format_version": "1", "gcc_version": "11.1.1 20210510" "files": ["$file"] } Fields of the root element have following semantics: * current_working_directory: working directory where a compilation unit was compiled * data_file: name of the data file (GCDA) * format_version: semantic version of the format * gcc_version: version of the GCC compiler Each file has the following form: { "file": "a.c", "functions": ["$function"], "lines": ["$line"] } Fields of the file element have following semantics: * file_name: name of the source file Each function has the following form: { "blocks": 2, "blocks_executed": 2, "demangled_name": "foo", "end_column": 1, "end_line": 4, "execution_count": 1, "name": "foo", "start_column": 5, "start_line": 1 } Fields of the function element have following semantics: * blocks: number of blocks that are in the function * blocks_executed: number of executed blocks of the function * demangled_name: demangled name of the function * end_column: column in the source file where the function ends * end_line: line in the source file where the function ends * execution_count: number of executions of the function * name: name of the function * start_column: column in the source file where the function begins * start_line: line in the source file where the function begins Note that line numbers and column numbers number from 1. In the current implementation, start_line and start_column do not include any template parameters and the leading return type but that this is likely to be fixed in the future. Each line has the following form: { "branches": ["$branch"], "count": 2, "line_number": 15, "unexecuted_block": false, "function_name": "foo", } Branches are present only with -b option. Fields of the line element have following semantics: * count: number of executions of the line * line_number: line number * unexecuted_block: flag whether the line contains an unexecuted block (not all statements on the line are executed) * function_name: a name of a function this line belongs to (for a line with an inlined statements can be not set) Each branch has the following form: { "count": 11, "fallthrough": true, "throw": false } Fields of the branch element have following semantics: * count: number of executions of the branch * fallthrough: true when the branch is a fall through branch * throw: true when the branch is an exceptional branch -H --human-readable Write counts in human readable format (like 24.6k). -k --use-colors Use colors for lines of code that have zero coverage. We use red color for non-exceptional lines and cyan for exceptional. Same colors are used for basic blocks with -a option. -l --long-file-names Create long file names for included source files. For example, if the header file x.h contains code, and was included in the file a.c, then running gcov on the file a.c will produce an output file called a.c##x.h.gcov instead of x.h.gcov. This can be useful if x.h is included in multiple source files and you want to see the individual contributions. If you use the -p option, both the including and included file names will be complete path names. -m --demangled-names Display demangled function names in output. The default is to show mangled function names. -n --no-output Do not create the gcov output file. -o directory|file --object-directory directory --object-file file Specify either the directory containing the gcov data files, or the object path name. The .gcno, and .gcda data files are searched for using this option. If a directory is specified, the data files are in that directory and named after the input file name, without its extension. If a file is specified here, the data files are named after that file, without its extension. -p --preserve-paths Preserve complete path information in the names of generated .gcov files. Without this option, just the filename component is used. With this option, all directories are used, with / characters translated to # characters, . directory components removed and unremoveable .. components renamed to ^. This is useful if sourcefiles are in several different directories. -q --use-hotness-colors Emit perf-like colored output for hot lines. Legend of the color scale is printed at the very beginning of the output file. -r --relative-only Only output information about source files with a relative pathname (after source prefix elision). Absolute paths are usually system header files and coverage of any inline functions therein is normally uninteresting. -s directory --source-prefix directory A prefix for source file names to remove when generating the output coverage files. This option is useful when building in a separate directory, and the pathname to the source directory is not wanted when determining the output file names. Note that this prefix detection is applied before determining whether the source file is absolute. -t --stdout Output to standard output instead of output files. -u --unconditional-branches When branch probabilities are given, include those of unconditional branches. Unconditional branches are normally not interesting. -v --version Display the gcov version number (on the standard output), and exit without doing any further processing. -w --verbose Print verbose informations related to basic blocks and arcs. -x --hash-filenames When using --preserve-paths, gcov uses the full pathname of the source files to create an output filename. This can lead to long filenames that can overflow filesystem limits. This option creates names of the form source-file##md5.gcov, where the source-file component is the final filename part and the md5 component is calculated from the full mangled name that would have been used otherwise. The option is an alternative to the --preserve-paths on systems which have a filesystem limit. gcov should be run with the current directory the same as that when you invoked the compiler. Otherwise it will not be able to locate the source files. gcov produces files called mangledname.gcov in the current directory. These contain the coverage information of the source file they correspond to. One .gcov file is produced for each source (or header) file containing code, which was compiled to produce the data files. The mangledname part of the output file name is usually simply the source file name, but can be something more complicated if the -l or -p options are given. Refer to those options for details. If you invoke gcov with multiple input files, the contributions from each input file are summed. Typically you would invoke it with the same list of files as the final link of your executable. The .gcov files contain the : separated fields along with program source code. The format is <execution_count>:<line_number>:<source line text> Additional block information may succeed each line, when requested by command line option. The execution_count is - for lines containing no code. Unexecuted lines are marked ##### or =====, depending on whether they are reachable by non-exceptional paths or only exceptional paths such as C++ exception handlers, respectively. Given the -a option, unexecuted blocks are marked $$$$$ or %%%%%, depending on whether a basic block is reachable via non-exceptional or exceptional paths. Executed basic blocks having a statement with zero execution_count end with * character and are colored with magenta color with the -k option. This functionality is not supported in Ada. Note that GCC can completely remove the bodies of functions that are not needed -- for instance if they are inlined everywhere. Such functions are marked with -, which can be confusing. Use the -fkeep-inline-functions and -fkeep-static-functions options to retain these functions and allow gcov to properly show their execution_count. Some lines of information at the start have line_number of zero. These preamble lines are of the form -:0:<tag>:<value> The ordering and number of these preamble lines will be augmented as gcov development progresses --- do not rely on them remaining unchanged. Use tag to locate a particular preamble line. The additional block information is of the form <tag> <information> The information is human readable, but designed to be simple enough for machine parsing too. When printing percentages, 0% and 100% are only printed when the values are exactly 0% and 100% respectively. Other values which would conventionally be rounded to 0% or 100% are instead printed as the nearest non-boundary value. When using gcov, you must first compile your program with a special GCC option --coverage. This tells the compiler to generate additional information needed by gcov (basically a flow graph of the program) and also includes additional code in the object files for generating the extra profiling information needed by gcov. These additional files are placed in the directory where the object file is located. Running the program will cause profile output to be generated. For each source file compiled with -fprofile-arcs, an accompanying .gcda file will be placed in the object file directory. Running gcov with your program's source file names as arguments will now produce a listing of the code along with frequency of execution for each line. For example, if your program is called tmp.cpp, this is what you see when you use the basic gcov facility: $ g++ --coverage tmp.cpp -c $ g++ --coverage tmp.o $ a.out $ gcov tmp.cpp -m File 'tmp.cpp' Lines executed:92.86% of 14 Creating 'tmp.cpp.gcov' The file tmp.cpp.gcov contains output from gcov. Here is a sample: -: 0:Source:tmp.cpp -: 0:Working directory:/home/gcc/testcase -: 0:Graph:tmp.gcno -: 0:Data:tmp.gcda -: 0:Runs:1 -: 0:Programs:1 -: 1:#include <stdio.h> -: 2: -: 3:template<class T> -: 4:class Foo -: 5:{ -: 6: public: 1*: 7: Foo(): b (1000) {} ------------------ Foo<char>::Foo(): #####: 7: Foo(): b (1000) {} ------------------ Foo<int>::Foo(): 1: 7: Foo(): b (1000) {} ------------------ 2*: 8: void inc () { b++; } ------------------ Foo<char>::inc(): #####: 8: void inc () { b++; } ------------------ Foo<int>::inc(): 2: 8: void inc () { b++; } ------------------ -: 9: -: 10: private: -: 11: int b; -: 12:}; -: 13: -: 14:template class Foo<int>; -: 15:template class Foo<char>; -: 16: -: 17:int 1: 18:main (void) -: 19:{ -: 20: int i, total; 1: 21: Foo<int> counter; -: 22: 1: 23: counter.inc(); 1: 24: counter.inc(); 1: 25: total = 0; -: 26: 11: 27: for (i = 0; i < 10; i++) 10: 28: total += i; -: 29: 1*: 30: int v = total > 100 ? 1 : 2; -: 31: 1: 32: if (total != 45) #####: 33: printf ("Failure\n"); -: 34: else 1: 35: printf ("Success\n"); 1: 36: return 0; -: 37:} Note that line 7 is shown in the report multiple times. First occurrence presents total number of execution of the line and the next two belong to instances of class Foo constructors. As you can also see, line 30 contains some unexecuted basic blocks and thus execution count has asterisk symbol. When you use the -a option, you will get individual block counts, and the output looks like this: -: 0:Source:tmp.cpp -: 0:Working directory:/home/gcc/testcase -: 0:Graph:tmp.gcno -: 0:Data:tmp.gcda -: 0:Runs:1 -: 0:Programs:1 -: 1:#include <stdio.h> -: 2: -: 3:template<class T> -: 4:class Foo -: 5:{ -: 6: public: 1*: 7: Foo(): b (1000) {} ------------------ Foo<char>::Foo(): #####: 7: Foo(): b (1000) {} ------------------ Foo<int>::Foo(): 1: 7: Foo(): b (1000) {} ------------------ 2*: 8: void inc () { b++; } ------------------ Foo<char>::inc(): #####: 8: void inc () { b++; } ------------------ Foo<int>::inc(): 2: 8: void inc () { b++; } ------------------ -: 9: -: 10: private: -: 11: int b; -: 12:}; -: 13: -: 14:template class Foo<int>; -: 15:template class Foo<char>; -: 16: -: 17:int 1: 18:main (void) -: 19:{ -: 20: int i, total; 1: 21: Foo<int> counter; 1: 21-block 0 -: 22: 1: 23: counter.inc(); 1: 23-block 0 1: 24: counter.inc(); 1: 24-block 0 1: 25: total = 0; -: 26: 11: 27: for (i = 0; i < 10; i++) 1: 27-block 0 11: 27-block 1 10: 28: total += i; 10: 28-block 0 -: 29: 1*: 30: int v = total > 100 ? 1 : 2; 1: 30-block 0 %%%%%: 30-block 1 1: 30-block 2 -: 31: 1: 32: if (total != 45) 1: 32-block 0 #####: 33: printf ("Failure\n"); %%%%%: 33-block 0 -: 34: else 1: 35: printf ("Success\n"); 1: 35-block 0 1: 36: return 0; 1: 36-block 0 -: 37:} In this mode, each basic block is only shown on one line -- the last line of the block. A multi-line block will only contribute to the execution count of that last line, and other lines will not be shown to contain code, unless previous blocks end on those lines. The total execution count of a line is shown and subsequent lines show the execution counts for individual blocks that end on that line. After each block, the branch and call counts of the block will be shown, if the -b option is given. Because of the way GCC instruments calls, a call count can be shown after a line with no individual blocks. As you can see, line 33 contains a basic block that was not executed. When you use the -b option, your output looks like this: -: 0:Source:tmp.cpp -: 0:Working directory:/home/gcc/testcase -: 0:Graph:tmp.gcno -: 0:Data:tmp.gcda -: 0:Runs:1 -: 0:Programs:1 -: 1:#include <stdio.h> -: 2: -: 3:template<class T> -: 4:class Foo -: 5:{ -: 6: public: 1*: 7: Foo(): b (1000) {} ------------------ Foo<char>::Foo(): function Foo<char>::Foo() called 0 returned 0% blocks executed 0% #####: 7: Foo(): b (1000) {} ------------------ Foo<int>::Foo(): function Foo<int>::Foo() called 1 returned 100% blocks executed 100% 1: 7: Foo(): b (1000) {} ------------------ 2*: 8: void inc () { b++; } ------------------ Foo<char>::inc(): function Foo<char>::inc() called 0 returned 0% blocks executed 0% #####: 8: void inc () { b++; } ------------------ Foo<int>::inc(): function Foo<int>::inc() called 2 returned 100% blocks executed 100% 2: 8: void inc () { b++; } ------------------ -: 9: -: 10: private: -: 11: int b; -: 12:}; -: 13: -: 14:template class Foo<int>; -: 15:template class Foo<char>; -: 16: -: 17:int function main called 1 returned 100% blocks executed 81% 1: 18:main (void) -: 19:{ -: 20: int i, total; 1: 21: Foo<int> counter; call 0 returned 100% branch 1 taken 100% (fallthrough) branch 2 taken 0% (throw) -: 22: 1: 23: counter.inc(); call 0 returned 100% branch 1 taken 100% (fallthrough) branch 2 taken 0% (throw) 1: 24: counter.inc(); call 0 returned 100% branch 1 taken 100% (fallthrough) branch 2 taken 0% (throw) 1: 25: total = 0; -: 26: 11: 27: for (i = 0; i < 10; i++) branch 0 taken 91% (fallthrough) branch 1 taken 9% 10: 28: total += i; -: 29: 1*: 30: int v = total > 100 ? 1 : 2; branch 0 taken 0% (fallthrough) branch 1 taken 100% -: 31: 1: 32: if (total != 45) branch 0 taken 0% (fallthrough) branch 1 taken 100% #####: 33: printf ("Failure\n"); call 0 never executed branch 1 never executed branch 2 never executed -: 34: else 1: 35: printf ("Success\n"); call 0 returned 100% branch 1 taken 100% (fallthrough) branch 2 taken 0% (throw) 1: 36: return 0; -: 37:} For each function, a line is printed showing how many times the function is called, how many times it returns and what percentage of the function's blocks were executed. For each basic block, a line is printed after the last line of the basic block describing the branch or call that ends the basic block. There can be multiple branches and calls listed for a single source line if there are multiple basic blocks that end on that line. In this case, the branches and calls are each given a number. There is no simple way to map these branches and calls back to source constructs. In general, though, the lowest numbered branch or call will correspond to the leftmost construct on the source line. For a branch, if it was executed at least once, then a percentage indicating the number of times the branch was taken divided by the number of times the branch was executed will be printed. Otherwise, the message "never executed" is printed. For a call, if it was executed at least once, then a percentage indicating the number of times the call returned divided by the number of times the call was executed will be printed. This will usually be 100%, but may be less for functions that call "exit" or "longjmp", and thus may not return every time they are called. The execution counts are cumulative. If the example program were executed again without removing the .gcda file, the count for the number of times each line in the source was executed would be added to the results of the previous run(s). This is potentially useful in several ways. For example, it could be used to accumulate data over a number of program runs as part of a test verification suite, or to provide more accurate long-term information over a large number of program runs. The data in the .gcda files is saved immediately before the program exits. For each source file compiled with -fprofile-arcs, the profiling code first attempts to read in an existing .gcda file; if the file doesn't match the executable (differing number of basic block counts) it will ignore the contents of the file. It then adds in the new execution counts and finally writes the data to the file. Using gcov with GCC Optimization If you plan to use gcov to help optimize your code, you must first compile your program with a special GCC option --coverage. Aside from that, you can use any other GCC options; but if you want to prove that every single line in your program was executed, you should not compile with optimization at the same time. On some machines the optimizer can eliminate some simple code lines by combining them with other lines. For example, code like this: if (a != b) c = 1; else c = 0; can be compiled into one instruction on some machines. In this case, there is no way for gcov to calculate separate execution counts for each line because there isn't separate code for each line. Hence the gcov output looks like this if you compiled the program with optimization: 100: 12:if (a != b) 100: 13: c = 1; 100: 14:else 100: 15: c = 0; The output shows that this block of code, combined by optimization, executed 100 times. In one sense this result is correct, because there was only one instruction representing all four of these lines. However, the output does not indicate how many times the result was 0 and how many times the result was 1. Inlineable functions can create unexpected line counts. Line counts are shown for the source code of the inlineable function, but what is shown depends on where the function is inlined, or if it is not inlined at all. If the function is not inlined, the compiler must emit an out of line copy of the function, in any object file that needs it. If fileA.o and fileB.o both contain out of line bodies of a particular inlineable function, they will also both contain coverage counts for that function. When fileA.o and fileB.o are linked together, the linker will, on many systems, select one of those out of line bodies for all calls to that function, and remove or ignore the other. Unfortunately, it will not remove the coverage counters for the unused function body. Hence when instrumented, all but one use of that function will show zero counts. If the function is inlined in several places, the block structure in each location might not be the same. For instance, a condition might now be calculable at compile time in some instances. Because the coverage of all the uses of the inline function will be shown for the same source lines, the line counts themselves might seem inconsistent. Long-running applications can use the "__gcov_reset" and "__gcov_dump" facilities to restrict profile collection to the program region of interest. Calling "__gcov_reset(void)" will clear all run-time profile counters to zero, and calling "__gcov_dump(void)" will cause the profile information collected at that point to be dumped to .gcda output files. Instrumented applications use a static destructor with priority 99 to invoke the "__gcov_dump" function. Thus "__gcov_dump" is executed after all user defined static destructors, as well as handlers registered with "atexit". If an executable loads a dynamic shared object via dlopen functionality, -Wl,--dynamic-list-data is needed to dump all profile data. Profiling run-time library reports various errors related to profile manipulation and profile saving. Errors are printed into standard error output or GCOV_ERROR_FILE file, if environment variable is used. In order to terminate immediately after an errors occurs set GCOV_EXIT_AT_ERROR environment variable. That can help users to find profile clashing which leads to a misleading profile. SEE ALSO gpl(7), gfdl(7), fsf-funding(7), gcc(1) and the Info entry for gcc. COPYRIGHT Copyright (c) 1996-2023 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being "GNU General Public License" and "Funding Free Software", the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the gfdl(7) man page. (a) The FSF's Front-Cover Text is: A GNU Manual (b) The FSF's Back-Cover Text is: You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development. gcc-13.2.0 2023-07-27 GCOV(1)
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venc_data_dump
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enc_recon_frame_test
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zipmerge
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zipmerge merges the source zip archives source-zip into the target zip archive target-zip. By default, files in the source zip archives overwrite existing files of the same name in the target zip archive. Supported options: -D Ignore directory components in file name comparisons. This option is slow for archives with many files. -h Display a short help message and exit. -I Ignore case in file name comparisons This option is slow for archives with many files. -i Ask before overwriting files. See also -s. -k Do not compress files that were uncompressed in source-zip, otherwise they are compressed with the default compression method. -S Do not overwrite files that have the same size and CRC32 in both the source and target archives. -s When -i is given, do not ask before overwriting files that have the same size and CRC32. -V Display version information and exit. EXIT STATUS zipmerge exits 0 on success and >1 if an error occurred. SEE ALSO zipcmp(1), ziptool(1), libzip(3) HISTORY zipmerge was added in libzip 0.6. AUTHORS Dieter Baron <dillo@nih.at> and Thomas Klausner <tk@giga.or.at> CAVEATS zipmerge uses one open file descriptor per zip archive. If you need to merge a lot of zip archives, check your shell's file descriptor ulimit and either increase it or run zipmerge multiple times with e.g. 1000 source zip archives each time. macOS 14.5 December 5, 2022 macOS 14.5
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zipmerge – merge zip archives
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zipmerge [-DhIiSsV] target-zip source-zip [source-zip ...]
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env_parallel.csh
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mysqlrouter
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• mysqlrouter Option Summaries • mysqlrouter Option Descriptions MySQL Router accepts command line options that are passed into mysqlrouter to affect its behavior, or to bootstrap router based on an InnoDB Cluster. When starting Router, you can optionally use --config to pass in the main configuration file's location (otherwise the default location is used) and --extra-config for an additional configuration file. Bootstrapping command line options affect the generated files and directories that are used when starting MySQL Router. mysqlrouter Option Summariesmysqlrouter Option Descriptions • --version, -V ┌────────────────────┬────────────────┐ │Command-Line Format │ --version , -V │ └────────────────────┴────────────────┘ Displays the version number and related information of the application, and exits. For example: $> mysqlrouter --version MySQL Router v8.1.0 on Linux (64-bit) (GPL community edition) • --help, -? ┌────────────────────┬─────────────┐ │Command-Line Format │ --help , -? │ └────────────────────┴─────────────┘ Display help and informative information, and exit. The --help option has an added benefit. Along with the explanation of each of the options, the --help option also displays the paths used to find the configuration file, and also several default paths. The following excerpt of the --help output shows an example from a Ubuntu 16.04 machine: $> mysqlrouter --help ... Start MySQL Router. Configuration read from the following files in the given order (enclosed in parentheses means not available for reading): (/etc/mysqlrouter/mysqlrouter.conf) /home/philip/.mysqlrouter.conf Plugin Path: /usr/lib/x86_64-linux-gnu/mysqlrouter Default Log Directory: /var/log/mysqlrouter Default Persistent Data Directory: /var/lib/mysqlrouter Default Runtime State Directory: /run/mysqlrouter Usage: mysqlrouter [-V|--version] [-?|--help] ... The configuration section shows the order for the paths that may be used for reading the configuration file. In this case, only the second file is accessible. • --bootstrap URI, -B URI ┌────────────────────┬─────────────────────────┐ │Command-Line Format │ --bootstrap URI, -B URI │ ├────────────────────┼─────────────────────────┤ │Type │ String │ └────────────────────┴─────────────────────────┘ The main option to perform a bootstrap of MySQL Router by connecting to the InnoDB Cluster metadata server at the URI provided. MySQL Router configures itself based on the information retrieved from the InnoDB Cluster metadata server. A password is prompted for if needed. If a username is not provided as part of the URI then the default user name "root" is used. See Connecting Using URI-Like Connection Strings[1] for information on using a path to specify a server instance. Note While --bootstrap accepts a URI for TCP/IP connections, using the --bootstrap-socket option with a local Unix domain socket name replaces the "host:port" part of the URI passed to the --bootstrap option with the socket on the same machine. By default, the bootstrap process performs a system-wide configuration of MySQL Router. Only one instance of MySQL Router can be configured for system-wide operation. The system instance of MySQL Router has a router_name of "system". If additional instances are desired, use the --directory option to create self-contained MySQL Router installations. URI: a server instance from an InnoDB Cluster to fetch metadata information from. If the provided URI is a read-only instance, MySQL Router automatically reconnects to a read-write instance in the InnoDB Cluster so it can register MySQL Router. If a configuration file already exists when you start MySQL Router with the --bootstrap, the existing router_id in that file is reused, and a reconfiguration process occurs. The configuration file is regenerated from scratch and the MySQL Router's metadata server account is recreated, although with the same name. During the reconfiguration process, all changes made to an existing configuration file are discarded. To customize a configuration file and still retain the ability of automatic reconfiguration (bootstrapping), you can use the --extra-config command line option to specify an additional configuration file that is read after the main configuration file. These configuration options are used because this extra configuration file is loaded after the main configuration file. The bootstrap process creates a new MySQL user account with a randomly generated password to use by that specific MySQL Router instance. This account is used by MySQL Router when connecting to the metadata server and InnoDB cluster to fetch information about its current state. For detailed information about this user including how its password is stored and the MySQL privilege it requires, see documentation for the MySQL user option. The generated configuration file is named mysqlrouter.conf, and its location depends on the type of instance being configured, the system, and the package. For system-wide installations, the generated configuration file is added to the system's configuration directory such as /etc or %PROGRAMDATA%\MySQL\MySQL Router\. Executing mysqlrouter --help will display this location. The --user option is required if executing a bootstrap with a super user (uid=0). Although not recommended, forcing the super user is possible by passing its name as an argument such as --user=root. The minimum GRANT permissions required to execute --boostrap are: GRANT CREATE USER ON *.* TO 'bootstrapuser'@'%' WITH GRANT OPTION; GRANT SELECT, INSERT, UPDATE, DELETE, EXECUTE ON mysql_innodb_cluster_metadata.* TO 'bootstrapuser'@'%'; GRANT SELECT ON mysql.user TO 'bootstrapuser'@'%'; GRANT SELECT ON performance_schema.replication_group_members TO 'bootstrapuser'@'%'; GRANT SELECT ON performance_schema.replication_group_member_stats TO 'bootstrapuser'@'%'; GRANT SELECT ON performance_schema.global_variables TO 'bootstrapuser'@'%'; Using --bootstrap adds default values to the generated MySQL Router configuration file, and some of these default values depend on other conditions. Listed below are some of the conditions that affect the generated default values, where default is defined by passing in --bootstrap by itself. Table 4.2. Conditions that affect default --bootstrap values ┌───────────────────┬────────────────────────────┐ │Condition │ Description │ ├───────────────────┼────────────────────────────┤ │--conf-base-port │ Modifies generated │ │ │ bind_port values for each │ │ │ connection type. By │ │ │ default, generated │ │ │ bind_port values are as │ │ │ follows: For the classic │ │ │ protocol, Read-Write uses │ │ │ 6446 and Read-Only uses │ │ │ 6447, and for the X │ │ │ protocol Read-Write uses │ │ │ 6448 and Read-Only uses │ │ │ 6449. Setting │ │ │ --conf-base-port to 0 │ │ │ changes the default │ │ │ bind_port values to the │ │ │ following defaults: For │ │ │ the classic protocol, │ │ │ Read-Write uses 6446 and │ │ │ Read-Only uses 6447, and │ │ │ for the X protocol │ │ │ Read-Write uses 64460 and │ │ │ Read-Only uses 64470. │ ├───────────────────┼────────────────────────────┤ │--conf-use-sockets │ Inserts socket definitions │ │ │ for each connection type. │ ├───────────────────┼────────────────────────────┤ │--conf-skip-tcp │ TCP/IP connection │ │ │ definitions are not │ │ │ defined. │ ├───────────────────┼────────────────────────────┤ │--directory │ Affects all file paths, │ │ │ and also generates │ │ │ additional files. │ ├───────────────────┼────────────────────────────┤ │Other │ This list is not │ │ │ exhaustive, other options │ │ │ and conditions also affect │ │ │ the generated values. │ └───────────────────┴────────────────────────────┘ • --bootstrap-socket socket_name ┌────────────────────┬────────────────────┐ │Command-Line Format │ --bootstrap-socket │ │ │ socket_name │ ├────────────────────┼────────────────────┤ │Platform Specific │ Linux │ └────────────────────┴────────────────────┘ Used in conjunction with --bootstrap to bootstrap using a local Unix domain socket instead of TCP/IP. The --bootstrap-socket value replaces the "host:port" part in the --bootstrap definition with the assigned socket name for connecting to the MySQL metadata server using Unix domain sockets. This is the MySQL instance that is being bootstrapped from, and this instance must be on the same machine if sockets are used. For additional details about how bootstrapping works, see --bootstrap. This option is different than the --conf-use-sockets command line option that sets the socket configuration file option during the bootstrap process. This option is not available on Windows. • --directory dir_path, -d dir_path ┌────────────────────┬──────────────────────────┐ │Command-Line Format │ --directory dir_path, -d │ │ │ dir_path │ ├────────────────────┼──────────────────────────┤ │Type │ String │ └────────────────────┴──────────────────────────┘ Specifies that a self-contained MySQL Router installation will be created at the defined directory instead of configuring the system-wide router instance. This also allows multiple router instances to be created on the same system. The self-contained directory structure for Router is: $path/start.sh $path/stop.sh $path/mysqlrouter.pid $path/mysqlrouter.conf $path/mysqlrouter.key $path/run $path/run/keyring $path/data $path/log $path/log/mysqlrouter.log If this option is specified, the keyring file is stored under the runtime state directory of that instance, under run/ in the specified directory, as opposed to the system-wide runtime state directory. If --conf-use-sockets is also enabled then the generated socket files are also added to this directory. • --master-key-writer ┌────────────────────┬─────────────────────┐ │Command-Line Format │ --master-key-writer │ │ │ file_path │ ├────────────────────┼─────────────────────┤ │Type │ String │ └────────────────────┴─────────────────────┘ This optional bootstrap option accepts a script that reads the master key from STDIN. It also uses the ROUTER_ID environment variable set by MySQL Router before the master-key-writer script is called. The master-key-writer and master-key-reader options must be used together, and using them means the master_key_file option must not be defined in mysqlrouter.conf as the master key is not written to the mysqlrouter.key master key file. This is also written to the generated MySQL Router configuration file as the master-key-writer [DEFAULT] option. Example contents of a bash script named writer.sh used in our example: #!/bin/bash KID_=$(keyctl padd user ${ROUTER_ID} @us <&0) Example usage: $> mysqlrouter --bootstrap=127.0.0.1:3310 --master-key-reader=./reader.sh --master-key-writer=./writer.sh This also affects the generated mysqlrouter.conf, for example: [DEFAULT] ... master-key-reader=reader.sh master-key-writer=writer.sh • --master-key-reader ┌────────────────────┬─────────────────────┐ │Command-Line Format │ --master-key-reader │ │ │ file_path │ ├────────────────────┼─────────────────────┤ │Type │ String │ └────────────────────┴─────────────────────┘ This optional bootstrap option accepts a script that writes the master key to STDOUT. It also uses the ROUTER_ID environment variable set by MySQL Router before the master-key-reader script is called. The master-key-reader and master-key-writer options must be used together, and using them means the master_key_file option must not be defined in mysqlrouter.conf as the master key is not written to the mysqlrouter.key master key file, and instead uses the value provided by this option's script. This is also written to the generated MySQL Router configuration file as the master-key-reader [DEFAULT] option. Example contents of a bash script named reader.sh used in our example: #!/bin/bash KID_=$(keyctl search @us user ${ROUTER_ID} 2>/dev/null) if [ ! -z $KID_ ]; then keyctl pipe $KID_ fi Example usage: $> mysqlrouter --bootstrap=127.0.0.1:3310 --master-key-reader=./reader.sh # Or, multiple hosts--master-key-writer=./writer.sh This also affects the generated mysqlrouter.conf, for example: [DEFAULT] ... master-key-reader=reader.sh master-key-writer=writer.sh • --strict ┌────────────────────┬──────────┐ │Command-Line Format │ --strict │ ├────────────────────┼──────────┤ │Type │ String │ └────────────────────┴──────────┘ Enables strict mode, which for example causes the bootstrap --account user verification check to stop the bootstrap process rather than only emit a warning and continue if the supplied user does not pass the check. • --account ┌────────────────────┬────────────────────┐ │Command-Line Format │ --account username │ ├────────────────────┼────────────────────┤ │Type │ String │ └────────────────────┴────────────────────┘ A bootstrap option to specify the MySQL user to use, which either reuses an existing MySQL user account or creates one; behavior controlled by the related --account-create option. With --account, usage favors ease of management over ease of deployment as multiple routers may share the same account, and the username and password are manually defined rather than auto-generated. Setting this option triggers a password prompt for this account regardless of whether the password is available in the keyring. Bootstrapping without passing --account does not recreate an existing MySQL server account. Using this option assumes the user has sufficient access rights for Router because the bootstrap process does not attempt to add missing grants to existing accounts. The bootstrap process does verify the permissions and outputs information to the console of the failed check. The bootstrap process continues despite these failed checks unless the optional --strict option is also used. Example required permissions: GRANT USAGE ON *.* TO `theuser`@`%` GRANT SELECT, EXECUTE ON `mysql_innodb_cluster_metadata`.* TO `theuser`@`%` GRANT INSERT, UPDATE, DELETE ON `mysql_innodb_cluster_metadata`.`routers` TO `theuser`@`%` GRANT INSERT, UPDATE, DELETE ON `mysql_innodb_cluster_metadata`.`v2_routers` TO `theuser`@`%` GRANT SELECT ON `performance_schema`.`global_variables` TO `theuser`@`%` GRANT SELECT ON `performance_schema`.`replication_group_member_stats` TO `theuser`@`%` GRANT SELECT ON `performance_schema`.`replication_group_members` TO `theuser`@`%` A password is not accepted from the command-line. For example, passing in "foo:bar" assumes "foo:bar" is the desired username rather than user foo with the password bar. • --account-create ┌────────────────────┬────────────────────────────┐ │Command-Line Format │ --account-create behavior │ ├────────────────────┼────────────────────────────┤ │Type │ String │ ├────────────────────┼────────────────────────────┤ │Default Value │ if-not-exists │ ├────────────────────┼────────────────────────────┤ │Valid Values │ if-not-exists always never │ └────────────────────┴────────────────────────────┘ Specify the account creation policy to help guard against accidentally bootstrapping with the wrong user account. Potential values are: • if-not-exists (default): Bootstrap either way; reuse the account if it exists, otherwise create it. • always: Only bootstrap if the account does not already exist; and create it. • never: Only bootstrap if the account already exists; and reuse it. This option requires that the --account option is also used, and that --account-host is not used. • --account-host ┌────────────────────┬────────────────┐ │Command-Line Format │ --account-host │ │ │ host_pattern │ ├────────────────────┼────────────────┤ │Type │ String │ ├────────────────────┼────────────────┤ │Default Value │ % │ └────────────────────┴────────────────┘ The host pattern used for accounts created by MySQL Router during the bootstrap process. This is optional and defaults to '%'. Pass in this option multiple times to define multiple patterns, in which case the generated MySQL accounts use the same password. Note Router does not perform sanity checking and does not ensure that the pattern authorizes Router to connect. Note Bootstrapping reuses existing Router accounts by dropping and recreating the user, and this user recreation process applies to every host. Examples: # One host $> mysqlrouter --bootstrap localhost:3310 --account-host host1 # Or, multiple hosts $> mysqlrouter --bootstrap localhost:3310 --account-host host1 --account-host host2 --account-host host3 • --conf-use-sockets ┌────────────────────┬────────────────────┐ │Command-Line Format │ --conf-use-sockets │ ├────────────────────┼────────────────────┤ │Platform Specific │ Linux │ └────────────────────┴────────────────────┘ Enables local Unix domain sockets. This option is used while bootstrapping, and enabling it adds the socket option to the generated configuration file. The name of the generated socket file depends on the mode and protocol options. With the classic protocol enabled, the file is named mysql.sock in read-write mode, and mysqlro.sock in read-only mode. With the X Protocol enabled, the file is named mysqlx.sock in read-write mode, and mysqlxro.sock in read-only mode. This option is not available on Windows. • --conf-use-gr-notifications ┌────────────────────┬─────────────────────────────┐ │Command-Line Format │ --conf-use-gr-notifications │ └────────────────────┴─────────────────────────────┘ Enables the use_gr_notifications [metadata_cache] option during bootstrap. When enabled, Router is asynchronously notified about most cluster changes. See use_gr_notifications for more information. In addition, using this option sets ttl=60 and auth_cache_refresh_interval=60. • --pid-file path ┌────────────────────┬─────────────────┐ │Command-Line Format │ --pid-file path │ ├────────────────────┼─────────────────┤ │Type │ String │ └────────────────────┴─────────────────┘ Sets location of the PID file. This can be set in three different ways (in order of precedence): this --pid-file command-line option, setting pid_file in Router's configuration file, or defining the ROUTER_PID environment variable. If --bootstrap is specified, then setting --pid-file causes Router to fail. This is unlike ROUTER_PID and the pid_file configuration option, which are ignored if --bootstrap is specified. If --bootstrap is not specified, then the following cause Router to fail: the --pid-file already exists, pid_file or ROUTER_PID are set but empty, or if Router can't write the PID file. • --report-host ┌────────────────────┬────────────────────────┐ │Command-Line Format │ --report-host hostname │ ├────────────────────┼────────────────────────┤ │Type │ String │ └────────────────────┴────────────────────────┘ Optionally define Router's hostname instead of relying on auto-detection to determine the externally visible hostname registered to metadata during the bootstrap process. Router does not check or confirm that the supplied hostname is reachable, but does use RFC 1123 to validate host names, and RFC 2181 to validate addresses. The supplied hostname is written to the host_name field of the mysql_innodb_cluster_metadata.hosts table in the MySQL InnoDB cluster metadata store. • --conf-skip-tcp ┌────────────────────┬─────────────────┐ │Command-Line Format │ --conf-skip-tcp │ ├────────────────────┼─────────────────┤ │Platform Specific │ Linux │ └────────────────────┴─────────────────┘ Skips configuration of a TCP port for listening to incoming connections. See also --conf-use-sockets. This option is not available on Windows. • --conf-base-port port_num ┌────────────────────┬───────────────────────────┐ │Command-Line Format │ --conf-base-port port_num │ ├────────────────────┼───────────────────────────┤ │Type │ Integer │ └────────────────────┴───────────────────────────┘ Base (first) value used for the listening TCP ports by setting bind_port for each bootstrapped route. This value is used for the classic read-write route, and each additional allocated port is incremented by a value of one. The port order set is classic read-write / read-only, and then x read-write / read-only. Setting --conf-base-port to 0 changes the default bind_port values to the following defaults, which were as follows: For the classic protocol, Read-Write uses 6446 and Read-Only uses 6447, and for the X protocol Read-Write uses 64460 and Read-Only uses 64470. Example usage: # Example without --conf-base-port $> mysqlrouter --bootstrap root@localhost:3310 ... Classic MySQL protocol connections to cluster 'devCluster': - Read/Write Connections: localhost:6446 - Read/Only Connections: localhost:6447 X protocol connections to cluster 'devCluster': - Read/Write Connections: localhost:6448 - Read/Only Connections: localhost:6449 # Example demonstrating --conf-base-port set to 0 $> mysqlrouter --bootstrap root@localhost:3310 --conf-base-port 0 ... Classic MySQL protocol connections to cluster 'devCluster': - Read/Write Connections: localhost:6446 - Read/Only Connections: localhost:6447 X protocol connections to cluster 'devCluster': - Read/Write Connections: localhost:64460 - Read/Only Connections: localhost:64470 • --conf-bind-address address ┌────────────────────┬─────────────────────┐ │Command-Line Format │ --conf-bind-address │ │ │ address │ ├────────────────────┼─────────────────────┤ │Type │ String │ ├────────────────────┼─────────────────────┤ │Default Value │ 0.0.0.0 │ └────────────────────┴─────────────────────┘ Modifies the bind_address value set by --bootstrap in the generated Router configuration file. By default, bootstrapping sets bind_address=0.0.0.0 for each route, and this option changes that value. Note The default bind_address value is 127.0.0.1 if bind_address is not defined. • --read-timeout num_seconds ┌────────────────────┬────────────────────────────┐ │Command-Line Format │ --read-timeout num_seconds │ ├────────────────────┼────────────────────────────┤ │Type │ Integer │ ├────────────────────┼────────────────────────────┤ │Default Value │ 30 │ └────────────────────┴────────────────────────────┘ Number of seconds before read operations to a metadata server are considered timed out. This affects read operations during both the bootstrap process, and also affects normal MySQL Router operations by setting the associated read_timeout option in the generated mysqlrouter.conf. This option is set under the [DEFAULT] namespace. • --connect-timeout num_seconds ┌────────────────────┬───────────────────┐ │Command-Line Format │ --connect-timeout │ │ │ num_seconds │ ├────────────────────┼───────────────────┤ │Type │ Integer │ ├────────────────────┼───────────────────┤ │Default Value │ 30 │ └────────────────────┴───────────────────┘ Number of seconds before connection attempts to a metadata server are considered timed out. This affects connections during both the bootstrap process, and also affects normal MySQL Router operations by setting the associated connect_timeout option in the generated mysqlrouter.conf. There are two connect_timeout variants. The metadata server variant is defined under the [DEFAULT] namespace, while the MySQL server variant is defined under the [routing] namespace. • --user {user_name|user_id}, -u {user_name|user_id} ┌────────────────────┬─────────────────────────┐ │Command-Line Format │ --user │ │ │ {user_name|user_id}, -u │ │ │ {user_name|user_id} │ ├────────────────────┼─────────────────────────┤ │Platform Specific │ Linux │ ├────────────────────┼─────────────────────────┤ │Type │ String │ └────────────────────┴─────────────────────────┘ Run mysqlrouter as the user having the name user_name or the numeric user ID user_id. “User” in this context refers to a system login account, not a MySQL user listed in the grant tables. When bootstrapping, all generated files are owned by this user, and this also sets the associated user option. This system user is defined in the configuration file under the [DEFAULT] namespace. For additional information, see the user option's documentation that --user configures. The --user option is required if executing a bootstrap as a super user (uid=0). Although not recommended, forcing the super user is possible by passing its name as an argument, such as --user=root. This option is not available on Windows. • --name router_name ┌────────────────────┬────────────────────┐ │Command-Line Format │ --name router_name │ ├────────────────────┼────────────────────┤ │Type │ String │ ├────────────────────┼────────────────────┤ │Default Value │ system │ └────────────────────┴────────────────────┘ On initial bootstrap, specifies a symbolic name for a self-contained Router instance. This option is optional, and is used with --directory. When creating multiple instances, the names must be unique. • --force-password-validation ┌────────────────────┬─────────────────────────────┐ │Command-Line Format │ --force-password-validation │ ├────────────────────┼─────────────────────────────┤ │Platform Specific │ Linux │ └────────────────────┴─────────────────────────────┘ By default, MySQL Router skips the MySQL Server's validate_password mechanism and instead Router generates and uses a STRONG password based on known validate_password default settings. This is because validate_password can be configured by the user and Router can not take into account unusual custom settings. This option ensures that password validation (validate_password) is not skipped for generated passwords, and it is disabled by default. • --password-retries num_retries ┌────────────────────┬────────────────────┐ │Command-Line Format │ --password-retries │ │ │ num_retries │ ├────────────────────┼────────────────────┤ │Type │ Integer │ ├────────────────────┼────────────────────┤ │Default Value │ 20 │ ├────────────────────┼────────────────────┤ │Minimum Value │ 1 │ ├────────────────────┼────────────────────┤ │Maximum Value │ 10000 │ └────────────────────┴────────────────────┘ Specifies the number of times MySQL Router should attempt to generate a password when creating user account with the password validation rules. The default value is 20. The valid range is 1 to 10000. The most likely reason for failure is due to custom validate_password settings with unusual requirements such as a 50 character minimum. In that fail scenario, either --force-password-validation is set to true and/or the mysql_native_password MySQL Server plugin is disabled (this plugin allows bypassing validation). • --force ┌────────────────────┬─────────┐ │Command-Line Format │ --force │ └────────────────────┴─────────┘ Force a reconfiguration over a previously configured router instance on the host. • --ssl-mode mode ┌────────────────────┬────────────────────┐ │Command-Line Format │ --ssl-mode mode │ ├────────────────────┼────────────────────┤ │Type │ String │ ├────────────────────┼────────────────────┤ │Default Value │ PREFERRED │ ├────────────────────┼────────────────────┤ │Valid Values │ PREFERRED DISABLED │ │ │ REQUIRED VERIFY_CA │ │ │ VERIFY_IDENTITY │ └────────────────────┴────────────────────┘ SSL connection mode for use during bootstrap and normal operation when connecting to the metadata server. Analogous to --ssl-mode in the mysql client. During bootstrap, all connections to metadata servers made by the Router will use the SSL options specified. If ssl_mode is not specified in the configuration, it will default to PREFERRED. During normal operation, after Router is launched, its Metadata Cache plugin will read and honor all configured SSL settings. When set to a value other than the default (PREFERRED), an ssl_mode entry is inserted under the [metadata_cache] section in the generated configuration file. Available values are DISABLED, PREFERRED, REQUIRED, VERIFY_CA, and VERIFY_IDENTITY. PREFERRED is the default value. As with the mysql client, this value is case-insensitive. The configuration file equivalent is documented separately at ssl_mode. • --ssl-cert file_path ┌────────────────────┬─────────────────────┐ │Command-Line Format │ --ssl-key file_path │ ├────────────────────┼─────────────────────┤ │Type │ String │ └────────────────────┴─────────────────────┘ The path name of the SSL public key certificate file in PEM format. This is used to facilitate client-side authentication during the bootstrap process. This directly matches and uses functionality of the MySQL client's --ssl-cert option. Like --ssl-key, this option is only used during bootstrap that uses a root account. It is useful when the root account was created with REQUIRE X509, and therefore logging in as root requires the client to authenticate itself. • --ssl-key file_path ┌────────────────────┬─────────────────────┐ │Command-Line Format │ --ssl-key file_path │ ├────────────────────┼─────────────────────┤ │Type │ String │ └────────────────────┴─────────────────────┘ The path name of the SSL private key file in PEM format. This is used to facilitate client-side authentication during the bootstrap process. This directly matches and uses functionality of the MySQL client's --ssl-key option. Like --ssl-cert, this option is only used during a bootstrap process that uses a root account. It is useful when the root account was created with REQUIRE X509, and therefore logging in as root requires the client to authenticate itself. • --ssl-cipher ciphers ┌────────────────────┬──────────────────────┐ │Command-Line Format │ --ssl-cipher ciphers │ ├────────────────────┼──────────────────────┤ │Type │ String │ ├────────────────────┼──────────────────────┤ │Default Value │ │ └────────────────────┴──────────────────────┘ A colon-separated (":") list of SSL ciphers to allow, if SSL is enabled. • --tls-version versions ┌────────────────────┬────────────────────────┐ │Command-Line Format │ --tls-version versions │ ├────────────────────┼────────────────────────┤ │Type │ String │ ├────────────────────┼────────────────────────┤ │Default Value │ │ └────────────────────┴────────────────────────┘ A comma-separated (",") list of TLS versions to request, if SSL is enabled. • --ssl-ca file_path ┌────────────────────┬────────────────────┐ │Command-Line Format │ --ssl-ca file_path │ ├────────────────────┼────────────────────┤ │Type │ String │ ├────────────────────┼────────────────────┤ │Default Value │ │ └────────────────────┴────────────────────┘ Path to the SSL CA file to verify a server's certificate against. • --ssl-capath dir_path ┌────────────────────┬───────────────────────┐ │Command-Line Format │ --ssl-capath dir_path │ ├────────────────────┼───────────────────────┤ │Type │ String │ ├────────────────────┼───────────────────────┤ │Default Value │ │ └────────────────────┴───────────────────────┘ Path to directory containing the SSL CA files to verify a server's certificate against. • --ssl-crl file_path ┌────────────────────┬─────────────────────┐ │Command-Line Format │ --ssl-crl file_path │ ├────────────────────┼─────────────────────┤ │Type │ String │ ├────────────────────┼─────────────────────┤ │Default Value │ │ └────────────────────┴─────────────────────┘ Path to the SSL CRL file to use when verifying a server's certificate. • --ssl-crlpath dir_path ┌────────────────────┬────────────────────────┐ │Command-Line Format │ --ssl-crlpath dir_path │ ├────────────────────┼────────────────────────┤ │Type │ String │ ├────────────────────┼────────────────────────┤ │Default Value │ │ └────────────────────┴────────────────────────┘ Path to the directory containing SSL CRL files to use when verifying a server's certificate. • --config file_path, -c file_path ┌────────────────────┬────────────────────────┐ │Command-Line Format │ --config file_path, -c │ │ │ file_path │ └────────────────────┴────────────────────────┘ Used to provide a path and file name for the configuration file to use. Use this option if you want to use a configuration file located in a folder other than the default locations. When used with --bootstrap, and if the configuration file already exists, a copy of the current file is saved with a .bak extension if the generated configuration file contents is different than the original. Existing .bak files are overwritten. • --extra-config file_path, -a file_path ┌────────────────────┬───────────────────────────┐ │Command-Line Format │ --extra-config file_path, │ │ │ -a file_path │ └────────────────────┴───────────────────────────┘ Used to provide an optional, additional configuration file to use. Use this option if you want to split the configuration file into two parts for testing, multiple instances of the application running on the same machine, etc. This configuration file is read after the main configuration file. If there are conflicts (an option is set in multiple configuration files), values from the file that is loaded last is used. • --install-service ┌────────────────────┬───────────────────┐ │Command-Line Format │ --install-service │ │ │ [service_name] │ ├────────────────────┼───────────────────┤ │Platform Specific │ Windows │ └────────────────────┴───────────────────┘ Install Router as a Windows service that automatically starts when Windows starts. The service name defaults to MySQLRouter. This installation process does not validate configuration files passed in via --config. This option is only available on Windows. • --install-service-manual ┌────────────────────┬──────────────────────────┐ │Command-Line Format │ --install-service-manual │ │ │ [service_name] │ ├────────────────────┼──────────────────────────┤ │Platform Specific │ Windows │ └────────────────────┴──────────────────────────┘ Install MySQL Router as a Windows service that can be manually started. The service name defaults to MySQLRouter. This option is only available on Windows. • --remove-service ┌────────────────────┬──────────────────┐ │Command-Line Format │ --remove-service │ │ │ [service_name] │ ├────────────────────┼──────────────────┤ │Platform Specific │ Windows │ └────────────────────┴──────────────────┘ Remove the Router Windows service; service name defaults to MySQLRouter. This option is only available on Windows. • --service ┌────────────────────┬───────────┐ │Command-Line Format │ --service │ ├────────────────────┼───────────┤ │Platform Specific │ Windows │ └────────────────────┴───────────┘ Start Router as a Windows service. This is a private option, meaning it is only meant to be used by the Windows Service when launching Router as a service. This option is only available on Windows. • --update-credentials-section ┌────────────────────┬──────────────────────────────┐ │Command-Line Format │ --update-credentials-section │ │ │ section_name │ ├────────────────────┼──────────────────────────────┤ │Platform Specific │ Windows │ └────────────────────┴──────────────────────────────┘ This option is only available on Windows, and refers to its password vault. • --conf-target-cluster ┌────────────────────┬───────────────────────┐ │Command-Line Format │ --conf-target-cluster │ │ │ value │ ├────────────────────┼───────────────────────┤ │Type │ String │ ├────────────────────┼───────────────────────┤ │Valid Values │ current primary │ └────────────────────┴───────────────────────┘ Sets the target_cluster metadata MySQL Router option. Accepts one of the following strings: • current: sets target_cluster to the cluster containing the node being bootstrapped against. It defines it as the cluster's UUID value. If this is also the Primary, it does not dynamically follow role changes like the primary does; instead it remains static. • primary: sets target_cluster to the primary cluster, including when it changes at runtime. See also --config-target-cluster-by-name, which sets the target_cluster to a specific static cluster name. Note Bootstrapping against a ClusterSet[2] requires the cluster_type Router configuration option set to gr. • --conf-set-option ┌────────────────────┬──────────────────────────────────────────────────┐ │Command-Line Format │ --conf-set-option │ │ │ section_name[:optional_section_key].option=value │ ├────────────────────┼──────────────────────────────────────────────────┤ │Type │ String │ └────────────────────┴──────────────────────────────────────────────────┘ Sets a value for a generated configuration option during bootstrap; this can set a value for any bootstrapped option, for example: $> mysqlrouter -B 127.0.0.1:5000 \ --directory=dir1 \ --conf-set-option=logger.level=debug \ --conf-set-option=routing:test_rw.max_connect_errors=0 \ --conf-set-option=routing:test_ro.max_connect_errors=0 Those commands alter the default values for those specific options by defining them as such: [logger] level=debug [routing:test_rw] ... max_connect_errors=0 ... [routing:test_ro] ... max_connect_errors=0 ... --conf-set-option definitions take precedence over option specific parameters to set specific value. For example, if both --connect-timeout=X and --conf-set-option=DEFAULT.connect_timeout=Y are specified when bootstrapping, the connect_timeout is set to Y in the generated configuration file. • --conf-target-cluster-by-name ┌────────────────────┬───────────────────────────────┐ │Command-Line Format │ --conf-target-cluster-by-name │ │ │ clusterName │ ├────────────────────┼───────────────────────────────┤ │Type │ String │ └────────────────────┴───────────────────────────────┘ Sets the target_cluster metadata MySQL Router option to a specific cluster name. Or, instead use --conf-target-cluster to assign a dynamic cluster type, such as primary. • --remove-credentials-section section_name ┌────────────────────┬──────────────────────────────┐ │Command-Line Format │ --remove-credentials-section │ │ │ section_name │ ├────────────────────┼──────────────────────────────┤ │Platform Specific │ Windows │ └────────────────────┴──────────────────────────────┘ Remove the credentials for a given section. This option is only available on Windows, and refers to its password vault. • --clear-all-credentials ┌────────────────────┬─────────────────────────┐ │Command-Line Format │ --clear-all-credentials │ ├────────────────────┼─────────────────────────┤ │Platform Specific │ Windows │ └────────────────────┴─────────────────────────┘ Clear the password vault by removing all credentials stored in it. This option is only available on Windows, and refers to its password vault. • --disable-rest ┌────────────────────┬────────────────┐ │Command-Line Format │ --disable-rest │ └────────────────────┴────────────────┘ By default, configuration details for the MySQL Router REST API web service functionality are added to the generated mysqlrouter.conf file at bootstrap; and this parameter means those details are not added. This does not disable REST API functionality, as the REST API functionality can be manually configured (to enable it) later on. • --https-port ┌────────────────────┬────────────────────┐ │Command-Line Format │ --https-port value │ ├────────────────────┼────────────────────┤ │Type │ Integer │ ├────────────────────┼────────────────────┤ │Default Value │ 8443 │ ├────────────────────┼────────────────────┤ │Minimum Value │ 1 │ ├────────────────────┼────────────────────┤ │Maximum Value │ 65535 │ └────────────────────┴────────────────────┘ Optionally define the HTTP server's port for the MySQL Router REST API under the [http_server] section in generated mysqlrouter.conf at bootstrap. It defaults to 8443. Availability of the port is not checked. COPYRIGHT Copyright © 2006, 2023, Oracle and/or its affiliates. This documentation is free software; you can redistribute it and/or modify it only under the terms of the GNU General Public License as published by the Free Software Foundation; version 2 of the License. This documentation is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with the program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA or see http://www.gnu.org/licenses/. NOTES 1. Connecting Using URI-Like Connection Strings https://dev.mysql.com/doc/refman/8.2/en/connecting-using-uri-or- key-value-pairs.html#connecting-using-uri 2. ClusterSet https://dev.mysql.com/doc/mysql-shell/8.3/en/innodb-clusterset.html AUTHOR Oracle Corporation (http://dev.mysql.com/). MySQL 8.1 11/22/2023 MYSQLROUTER(1)
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mysqlrouter - MySQL Router
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mysqlrouter [options]
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distro
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gnutls-serv
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Server program that listens to incoming TLS connections.
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gnutls-serv - GnuTLS server
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gnutls-serv [-flags] [-flag [value]] [--option-name[[=| ]value]] All arguments must be options.
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-d num, --debug=num Enable debugging. This option takes an integer number as its argument. The value of num is constrained to being: in the range 0 through 9999 Specifies the debug level. --sni-hostname=str Server's hostname for server name extension. Server name of type host_name that the server will recognise as its own. If the server receives client hello with different name, it will send a warning-level unrecognized_name alert. --sni-hostname-fatal Send fatal alert on sni-hostname mismatch. --alpn=str Specify ALPN protocol to be enabled by the server. This option may appear an unlimited number of times. Specify the (textual) ALPN protocol for the server to use. --alpn-fatal Send fatal alert on non-matching ALPN name. --noticket Don't accept session tickets. --earlydata Accept early data. --maxearlydata=num The maximum early data size to accept. This option takes an integer number as its argument. The value of num is constrained to being: in the range 1 through 2147483648 --nocookie Don't require cookie on DTLS sessions. -g, --generate Generate Diffie-Hellman parameters. -q, --quiet Suppress some messages. --nodb Do not use a resumption database. --http Act as an HTTP server. --echo Act as an Echo server. --crlf Do not replace CRLF by LF in Echo server mode. -u, --udp Use DTLS (datagram TLS) over UDP. --mtu=num Set MTU for datagram TLS. This option takes an integer number as its argument. The value of num is constrained to being: in the range 0 through 17000 --srtp-profiles=str Offer SRTP profiles. -a, --disable-client-cert Do not request a client certificate. This option must not appear in combination with any of the following options: require-client-cert. -r, --require-client-cert Require a client certificate. This option before 3.6.0 used to imply --verify-client-cert. Since 3.6.0 it will no longer verify the certificate by default. --verify-client-cert If a client certificate is sent then verify it. Do not require, but if a client certificate is sent then verify it and close the connection if invalid. --compress-cert=str Compress certificate. This option may appear an unlimited number of times. This option sets a supported compression method for certificate compression. -b, --heartbeat Activate heartbeat support. Regularly ping client via heartbeat extension messages --x509fmtder Use DER format for certificates to read from. --priority=str Priorities string. TLS algorithms and protocols to enable. You can use predefined sets of ciphersuites such as PERFORMANCE, NORMAL, SECURE128, SECURE256. The default is NORMAL. Check the GnuTLS manual on section “Priority strings” for more information on allowed keywords --dhparams=file DH params file to use. --x509cafile=str Certificate file or PKCS #11 URL to use. --x509crlfile=file CRL file to use. --pgpkeyfile=file PGP Key file to use. NOTE: THIS OPTION IS DEPRECATED --x509keyfile=str X.509 key file or PKCS #11 URL to use. This option may appear an unlimited number of times. Specify the private key file or URI to use; it must correspond to the certificate specified in --x509certfile. Multiple keys and certificates can be specified with this option and in that case each occurrence of keyfile must be followed by the corresponding x509certfile or vice-versa. --x509certfile=str X.509 Certificate file or PKCS #11 URL to use. This option may appear an unlimited number of times. Specify the certificate file or URI to use; it must correspond to the key specified in --x509keyfile. Multiple keys and certificates can be specified with this option and in that case each occurrence of keyfile must be followed by the corresponding x509certfile or vice-versa. --x509dsakeyfile This is an alias for the --x509keyfile option. NOTE: THIS OPTION IS DEPRECATED --x509dsacertfile This is an alias for the --x509certfile option. NOTE: THIS OPTION IS DEPRECATED --x509ecckeyfile This is an alias for the --x509keyfile option. NOTE: THIS OPTION IS DEPRECATED --x509ecccertfile This is an alias for the --x509certfile option. NOTE: THIS OPTION IS DEPRECATED --rawpkkeyfile=str Private key file (PKCS #8 or PKCS #12) or PKCS #11 URL to use. This option may appear an unlimited number of times. Specify the private key file or URI to use; it must correspond to the raw public-key specified in --rawpkfile. Multiple key pairs can be specified with this option and in that case each occurrence of keyfile must be followed by the corresponding rawpkfile or vice-versa. In order to instruct the application to negotiate raw public keys one must enable the respective certificate types via the priority strings (i.e. CTYPE-CLI-* and CTYPE-SRV-* flags). Check the GnuTLS manual on section “Priority strings” for more information on how to set certificate types. --rawpkfile=str Raw public-key file to use. This option may appear an unlimited number of times. This option must appear in combination with the following options: rawpkkeyfile. Specify the raw public-key file to use; it must correspond to the private key specified in --rawpkkeyfile. Multiple key pairs can be specified with this option and in that case each occurrence of keyfile must be followed by the corresponding rawpkfile or vice-versa. In order to instruct the application to negotiate raw public keys one must enable the respective certificate types via the priority strings (i.e. CTYPE-CLI-* and CTYPE-SRV-* flags). Check the GnuTLS manual on section “Priority strings” for more information on how to set certificate types. --srppasswd=file SRP password file to use. --srppasswdconf=file SRP password configuration file to use. --pskpasswd=file PSK password file to use. --pskhint=str PSK identity hint to use. --ocsp-response=str The OCSP response to send to client. This option may appear an unlimited number of times. If the client requested an OCSP response, return data from this file to the client. --ignore-ocsp-response-errors Ignore any errors when setting the OCSP response. That option instructs gnutls to not attempt to match the provided OCSP responses with the certificates. -p num, --port=num The port to connect to. This option takes an integer number as its argument. -l, --list Print a list of the supported algorithms and modes. Print a list of the supported algorithms and modes. If a priority string is given then only the enabled ciphersuites are shown. --provider=file Specify the PKCS #11 provider library. This will override the default options in /etc/gnutls/pkcs11.conf --keymatexport=str Label used for exporting keying material. --keymatexportsize=num Size of the exported keying material. This option takes an integer number as its argument. --recordsize=num The maximum record size to advertise. This option takes an integer number as its argument. The value of num is constrained to being: in the range 0 through 16384 --httpdata=file The data used as HTTP response. --timeout=num The timeout period for server. This option takes an integer number as its argument. --attime=timestamp Perform validation at the timestamp instead of the system time. timestamp is an instance in time encoded as Unix time or in a human readable timestring such as "29 Feb 2004", "2004-02-29". Full documentation available at <https://www.gnu.org/software/coreutils/manual/html_node/Date-input-formats.html> or locally via info '(coreutils) date invocation'. -v arg, --version=arg Output version of program and exit. The default mode is `v', a simple version. The `c' mode will print copyright information and `n' will print the full copyright notice. -h, --help Display usage information and exit. -!, --more-help Pass the extended usage information through a pager.
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Running your own TLS server based on GnuTLS can be useful when debugging clients and/or GnuTLS itself. This section describes how to use gnutls-serv as a simple HTTPS server. The most basic server can be started as: gnutls-serv --http --priority "NORMAL:+ANON-ECDH:+ANON-DH" It will only support anonymous ciphersuites, which many TLS clients refuse to use. The next step is to add support for X.509. First we generate a CA: $ certtool --generate-privkey > x509-ca-key.pem $ echo 'cn = GnuTLS test CA' > ca.tmpl $ echo 'ca' >> ca.tmpl $ echo 'cert_signing_key' >> ca.tmpl $ certtool --generate-self-signed --load-privkey x509-ca-key.pem --template ca.tmpl --outfile x509-ca.pem Then generate a server certificate. Remember to change the dns_name value to the name of your server host, or skip that command to avoid the field. $ certtool --generate-privkey > x509-server-key.pem $ echo 'organization = GnuTLS test server' > server.tmpl $ echo 'cn = test.gnutls.org' >> server.tmpl $ echo 'tls_www_server' >> server.tmpl $ echo 'encryption_key' >> server.tmpl $ echo 'signing_key' >> server.tmpl $ echo 'dns_name = test.gnutls.org' >> server.tmpl $ certtool --generate-certificate --load-privkey x509-server-key.pem --load-ca-certificate x509-ca.pem --load-ca-privkey x509-ca-key.pem --template server.tmpl --outfile x509-server.pem For use in the client, you may want to generate a client certificate as well. $ certtool --generate-privkey > x509-client-key.pem $ echo 'cn = GnuTLS test client' > client.tmpl $ echo 'tls_www_client' >> client.tmpl $ echo 'encryption_key' >> client.tmpl $ echo 'signing_key' >> client.tmpl $ certtool --generate-certificate --load-privkey x509-client-key.pem --load-ca-certificate x509-ca.pem --load-ca-privkey x509-ca-key.pem --template client.tmpl --outfile x509-client.pem To be able to import the client key/certificate into some applications, you will need to convert them into a PKCS#12 structure. This also encrypts the security sensitive key with a password. $ certtool --to-p12 --load-ca-certificate x509-ca.pem --load-privkey x509-client-key.pem --load-certificate x509-client.pem --outder --outfile x509-client.p12 For icing, we'll create a proxy certificate for the client too. $ certtool --generate-privkey > x509-proxy-key.pem $ echo 'cn = GnuTLS test client proxy' > proxy.tmpl $ certtool --generate-proxy --load-privkey x509-proxy-key.pem --load-ca-certificate x509-client.pem --load-ca-privkey x509-client-key.pem --load-certificate x509-client.pem --template proxy.tmpl --outfile x509-proxy.pem Then start the server again: $ gnutls-serv --http --x509cafile x509-ca.pem --x509keyfile x509-server-key.pem --x509certfile x509-server.pem Try connecting to the server using your web browser. Note that the server listens to port 5556 by default. While you are at it, to allow connections using ECDSA, you can also create a ECDSA key and certificate for the server. These credentials will be used in the final example below. $ certtool --generate-privkey --ecdsa > x509-server-key-ecc.pem $ certtool --generate-certificate --load-privkey x509-server-key-ecc.pem --load-ca-certificate x509-ca.pem --load-ca-privkey x509-ca-key.pem --template server.tmpl --outfile x509-server-ecc.pem The next step is to add support for SRP authentication. This requires an SRP password file created with srptool. To start the server with SRP support: gnutls-serv --http --priority NORMAL:+SRP-RSA:+SRP --srppasswdconf srp-tpasswd.conf --srppasswd srp-passwd.txt Let's also start a server with support for PSK. This would require a password file created with psktool. gnutls-serv --http --priority NORMAL:+ECDHE-PSK:+PSK --pskpasswd psk-passwd.txt If you want a server with support for raw public-keys we can also add these credentials. Note however that there is no identity information linked to these keys as is the case with regular x509 certificates. Authentication must be done via different means. Also we need to explicitly enable raw public-key certificates via the priority strings. gnutls-serv --http --priority NORMAL:+CTYPE-CLI-RAWPK:+CTYPE-SRV-RAWPK --rawpkfile srv.rawpk.pem --rawpkkeyfile srv.key.pem Finally, we start the server with all the earlier parameters and you get this command: gnutls-serv --http --priority NORMAL:+PSK:+SRP:+CTYPE-CLI-RAWPK:+CTYPE-SRV-RAWPK --x509cafile x509-ca.pem --x509keyfile x509-server-key.pem --x509certfile x509-server.pem --x509keyfile x509-server-key-ecc.pem --x509certfile x509-server-ecc.pem --srppasswdconf srp-tpasswd.conf --srppasswd srp-passwd.txt --pskpasswd psk-passwd.txt --rawpkfile srv.rawpk.pem --rawpkkeyfile srv.key.pem EXIT STATUS One of the following exit values will be returned: 0 (EXIT_SUCCESS) Successful program execution. 1 (EXIT_FAILURE) The operation failed or the command syntax was not valid. SEE ALSO gnutls-cli-debug(1), gnutls-cli(1) AUTHORS COPYRIGHT Copyright (C) 2020-2023 Free Software Foundation, and others all rights reserved. This program is released under the terms of the GNU General Public License, version 3 or later BUGS Please send bug reports to: bugs@gnutls.org 3.8.4 19 Mar 2024 gnutls-serv(1)
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grm
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This manual page documents the GNU version of rm. rm removes each specified file. By default, it does not remove directories. If the -I or --interactive=once option is given, and there are more than three files or the -r, -R, or --recursive are given, then rm prompts the user for whether to proceed with the entire operation. If the response is not affirmative, the entire command is aborted. Otherwise, if a file is unwritable, standard input is a terminal, and the -f or --force option is not given, or the -i or --interactive=always option is given, rm prompts the user for whether to remove the file. If the response is not affirmative, the file is skipped.
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rm - remove files or directories
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rm [OPTION]... [FILE]...
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Remove (unlink) the FILE(s). -f, --force ignore nonexistent files and arguments, never prompt -i prompt before every removal -I prompt once before removing more than three files, or when removing recursively; less intrusive than -i, while still giving protection against most mistakes --interactive[=WHEN] prompt according to WHEN: never, once (-I), or always (-i); without WHEN, prompt always --one-file-system when removing a hierarchy recursively, skip any directory that is on a file system different from that of the corresponding command line argument --no-preserve-root do not treat '/' specially --preserve-root[=all] do not remove '/' (default); with 'all', reject any command line argument on a separate device from its parent -r, -R, --recursive remove directories and their contents recursively -d, --dir remove empty directories -v, --verbose explain what is being done --help display this help and exit --version output version information and exit By default, rm does not remove directories. Use the --recursive (-r or -R) option to remove each listed directory, too, along with all of its contents. To remove a file whose name starts with a '-', for example '-foo', use one of these commands: rm -- -foo rm ./-foo Note that if you use rm to remove a file, it might be possible to recover some of its contents, given sufficient expertise and/or time. For greater assurance that the contents are truly unrecoverable, consider using shred(1). AUTHOR Written by Paul Rubin, David MacKenzie, Richard M. Stallman, and Jim Meyering. REPORTING BUGS GNU coreutils online help: <https://www.gnu.org/software/coreutils/> Report any translation bugs to <https://translationproject.org/team/> COPYRIGHT Copyright © 2023 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. SEE ALSO unlink(1), unlink(2), chattr(1), shred(1) Full documentation <https://www.gnu.org/software/coreutils/rm> or available locally via: info '(coreutils) rm invocation' GNU coreutils 9.3 April 2023 RM(1)
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ssl_pthread_server
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tor-resolve
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tor-resolve is a simple script to connect to a SOCKS proxy that knows about the SOCKS RESOLVE command, hand it a hostname, and return an IP address. By default, tor-resolve uses the Tor server running on 127.0.0.1 on SOCKS port 9050. If this isn’t what you want, you should specify an explicit sockshost and/or socksport on the command line.
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tor-resolve - resolve a hostname to an IP address via tor
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tor-resolve [-4|-5] [-v] [-x] [-p socksport] hostname [sockshost[:socksport]]
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-v Display verbose output. -x Perform a reverse lookup: get the PTR record for an IPv4 address. -5 Use the SOCKS5 protocol. (Default) -4 Use the SOCKS4a protocol rather than the default SOCKS5 protocol. Doesn’t support reverse DNS. -p socksport Override the default SOCKS port without setting the hostname. SEE ALSO tor(1), torify(1). For protocol details, see: https://spec.torproject.org/socks-extensions AUTHOR Peter Palfrader Author. Tor 12/08/2023 TOR-RESOLVE(1)
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aarch64-apple-darwin23-gcc-13
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exr_to_pq
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exrmultiview
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pcre2test
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If pcre2test is given two filename arguments, it reads from the first and writes to the second. If the first name is "-", input is taken from the standard input. If pcre2test is given only one argument, it reads from that file and writes to stdout. Otherwise, it reads from stdin and writes to stdout. When pcre2test is built, a configuration option can specify that it should be linked with the libreadline or libedit library. When this is done, if the input is from a terminal, it is read using the readline() function. This provides line-editing and history facilities. The output from the -help option states whether or not readline() will be used. The program handles any number of tests, each of which consists of a set of input lines. Each set starts with a regular expression pattern, followed by any number of subject lines to be matched against that pattern. In between sets of test data, command lines that begin with # may appear. This file format, with some restrictions, can also be processed by the perltest.sh script that is distributed with PCRE2 as a means of checking that the behaviour of PCRE2 and Perl is the same. For a specification of perltest.sh, see the comments near its beginning. See also the #perltest command below. When the input is a terminal, pcre2test prompts for each line of input, using "re>" to prompt for regular expression patterns, and "data>" to prompt for subject lines. Command lines starting with # can be entered only in response to the "re>" prompt. Each subject line is matched separately and independently. If you want to do multi-line matches, you have to use the \n escape sequence (or \r or \r\n, etc., depending on the newline setting) in a single line of input to encode the newline sequences. There is no limit on the length of subject lines; the input buffer is automatically extended if it is too small. There are replication features that makes it possible to generate long repetitive pattern or subject lines without having to supply them explicitly. An empty line or the end of the file signals the end of the subject lines for a test, at which point a new pattern or command line is expected if there is still input to be read. COMMAND LINES In between sets of test data, a line that begins with # is interpreted as a command line. If the first character is followed by white space or an exclamation mark, the line is treated as a comment, and ignored. Otherwise, the following commands are recognized: #forbid_utf Subsequent patterns automatically have the PCRE2_NEVER_UTF and PCRE2_NEVER_UCP options set, which locks out the use of the PCRE2_UTF and PCRE2_UCP options and the use of (*UTF) and (*UCP) at the start of patterns. This command also forces an error if a subsequent pattern contains any occurrences of \P, \p, or \X, which are still supported when PCRE2_UTF is not set, but which require Unicode property support to be included in the library. This is a trigger guard that is used in test files to ensure that UTF or Unicode property tests are not accidentally added to files that are used when Unicode support is not included in the library. Setting PCRE2_NEVER_UTF and PCRE2_NEVER_UCP as a default can also be obtained by the use of #pattern; the difference is that #forbid_utf cannot be unset, and the automatic options are not displayed in pattern information, to avoid cluttering up test output. #load <filename> This command is used to load a set of precompiled patterns from a file, as described in the section entitled "Saving and restoring compiled patterns" below. #loadtables <filename> This command is used to load a set of binary character tables that can be accessed by the tables=3 qualifier. Such tables can be created by the pcre2_dftables program with the -b option. #newline_default [<newline-list>] When PCRE2 is built, a default newline convention can be specified. This determines which characters and/or character pairs are recognized as indicating a newline in a pattern or subject string. The default can be overridden when a pattern is compiled. The standard test files contain tests of various newline conventions, but the majority of the tests expect a single linefeed to be recognized as a newline by default. Without special action the tests would fail when PCRE2 is compiled with either CR or CRLF as the default newline. The #newline_default command specifies a list of newline types that are acceptable as the default. The types must be one of CR, LF, CRLF, ANYCRLF, ANY, or NUL (in upper or lower case), for example: #newline_default LF Any anyCRLF If the default newline is in the list, this command has no effect. Otherwise, except when testing the POSIX API, a newline modifier that specifies the first newline convention in the list (LF in the above example) is added to any pattern that does not already have a newline modifier. If the newline list is empty, the feature is turned off. This command is present in a number of the standard test input files. When the POSIX API is being tested there is no way to override the default newline convention, though it is possible to set the newline convention from within the pattern. A warning is given if the posix or posix_nosub modifier is used when #newline_default would set a default for the non-POSIX API. #pattern <modifier-list> This command sets a default modifier list that applies to all subsequent patterns. Modifiers on a pattern can change these settings. #perltest This line is used in test files that can also be processed by perltest.sh to confirm that Perl gives the same results as PCRE2. Subsequent tests are checked for the use of pcre2test features that are incompatible with the perltest.sh script. Patterns must use '/' as their delimiter, and only certain modifiers are supported. Comment lines, #pattern commands, and #subject commands that set or unset "mark" are recognized and acted on. The #perltest, #forbid_utf, and #newline_default commands, which are needed in the relevant pcre2test files, are silently ignored. All other command lines are ignored, but give a warning message. The #perltest command helps detect tests that are accidentally put in the wrong file or use the wrong delimiter. For more details of the perltest.sh script see the comments it contains. #pop [<modifiers>] #popcopy [<modifiers>] These commands are used to manipulate the stack of compiled patterns, as described in the section entitled "Saving and restoring compiled patterns" below. #save <filename> This command is used to save a set of compiled patterns to a file, as described in the section entitled "Saving and restoring compiled patterns" below. #subject <modifier-list> This command sets a default modifier list that applies to all subsequent subject lines. Modifiers on a subject line can change these settings. MODIFIER SYNTAX Modifier lists are used with both pattern and subject lines. Items in a list are separated by commas followed by optional white space. Trailing whitespace in a modifier list is ignored. Some modifiers may be given for both patterns and subject lines, whereas others are valid only for one or the other. Each modifier has a long name, for example "anchored", and some of them must be followed by an equals sign and a value, for example, "offset=12". Values cannot contain comma characters, but may contain spaces. Modifiers that do not take values may be preceded by a minus sign to turn off a previous setting. A few of the more common modifiers can also be specified as single letters, for example "i" for "caseless". In documentation, following the Perl convention, these are written with a slash ("the /i modifier") for clarity. Abbreviated modifiers must all be concatenated in the first item of a modifier list. If the first item is not recognized as a long modifier name, it is interpreted as a sequence of these abbreviations. For example: /abc/ig,newline=cr,jit=3 This is a pattern line whose modifier list starts with two one-letter modifiers (/i and /g). The lower-case abbreviated modifiers are the same as used in Perl. PATTERN SYNTAX A pattern line must start with one of the following characters (common symbols, excluding pattern meta-characters): / ! " ' ` - = _ : ; , % & @ ~ This is interpreted as the pattern's delimiter. A regular expression may be continued over several input lines, in which case the newline characters are included within it. It is possible to include the delimiter as a literal within the pattern by escaping it with a backslash, for example /abc\/def/ If you do this, the escape and the delimiter form part of the pattern, but since the delimiters are all non-alphanumeric, the inclusion of the backslash does not affect the pattern's interpretation. Note, however, that this trick does not work within \Q...\E literal bracketing because the backslash will itself be interpreted as a literal. If the terminating delimiter is immediately followed by a backslash, for example, /abc/\ a backslash is added to the end of the pattern. This is done to provide a way of testing the error condition that arises if a pattern finishes with a backslash, because /abc\/ is interpreted as the first line of a pattern that starts with "abc/", causing pcre2test to read the next line as a continuation of the regular expression. A pattern can be followed by a modifier list (details below). SUBJECT LINE SYNTAX Before each subject line is passed to pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match(), leading and trailing white space is removed, and the line is scanned for backslash escapes, unless the subject_literal modifier was set for the pattern. The following provide a means of encoding non-printing characters in a visible way: \a alarm (BEL, \x07) \b backspace (\x08) \e escape (\x27) \f form feed (\x0c) \n newline (\x0a) \r carriage return (\x0d) \t tab (\x09) \v vertical tab (\x0b) \nnn octal character (up to 3 octal digits); always a byte unless > 255 in UTF-8 or 16-bit or 32-bit mode \o{dd...} octal character (any number of octal digits} \xhh hexadecimal byte (up to 2 hex digits) \x{hh...} hexadecimal character (any number of hex digits) The use of \x{hh...} is not dependent on the use of the utf modifier on the pattern. It is recognized always. There may be any number of hexadecimal digits inside the braces; invalid values provoke error messages. Note that \xhh specifies one byte rather than one character in UTF-8 mode; this makes it possible to construct invalid UTF-8 sequences for testing purposes. On the other hand, \x{hh} is interpreted as a UTF-8 character in UTF-8 mode, generating more than one byte if the value is greater than 127. When testing the 8-bit library not in UTF-8 mode, \x{hh} generates one byte for values less than 256, and causes an error for greater values. In UTF-16 mode, all 4-digit \x{hhhh} values are accepted. This makes it possible to construct invalid UTF-16 sequences for testing purposes. In UTF-32 mode, all 4- to 8-digit \x{...} values are accepted. This makes it possible to construct invalid UTF-32 sequences for testing purposes. There is a special backslash sequence that specifies replication of one or more characters: \[<characters>]{<count>} This makes it possible to test long strings without having to provide them as part of the file. For example: \[abc]{4} is converted to "abcabcabcabc". This feature does not support nesting. To include a closing square bracket in the characters, code it as \x5D. A backslash followed by an equals sign marks the end of the subject string and the start of a modifier list. For example: abc\=notbol,notempty If the subject string is empty and \= is followed by whitespace, the line is treated as a comment line, and is not used for matching. For example: \= This is a comment. abc\= This is an invalid modifier list. A backslash followed by any other non-alphanumeric character just escapes that character. A backslash followed by anything else causes an error. However, if the very last character in the line is a backslash (and there is no modifier list), it is ignored. This gives a way of passing an empty line as data, since a real empty line terminates the data input. If the subject_literal modifier is set for a pattern, all subject lines that follow are treated as literals, with no special treatment of backslashes. No replication is possible, and any subject modifiers must be set as defaults by a #subject command. PATTERN MODIFIERS There are several types of modifier that can appear in pattern lines. Except where noted below, they may also be used in #pattern commands. A pattern's modifier list can add to or override default modifiers that were set by a previous #pattern command. Setting compilation options The following modifiers set options for pcre2_compile(). Most of them set bits in the options argument of that function, but those whose names start with PCRE2_EXTRA are additional options that are set in the compile context. Some of these options have single-letter abbreviations. There is special handling for /x: if a second x is present, PCRE2_EXTENDED is converted into PCRE2_EXTENDED_MORE as in Perl. A third appearance adds PCRE2_EXTENDED as well, though this makes no difference to the way pcre2_compile() behaves. See pcre2api for a description of the effects of these options. allow_empty_class set PCRE2_ALLOW_EMPTY_CLASS allow_lookaround_bsk set PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK allow_surrogate_escapes set PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES alt_bsux set PCRE2_ALT_BSUX alt_circumflex set PCRE2_ALT_CIRCUMFLEX alt_verbnames set PCRE2_ALT_VERBNAMES anchored set PCRE2_ANCHORED /a ascii_all set all ASCII options ascii_bsd set PCRE2_EXTRA_ASCII_BSD ascii_bss set PCRE2_EXTRA_ASCII_BSS ascii_bsw set PCRE2_EXTRA_ASCII_BSW ascii_digit set PCRE2_EXTRA_ASCII_DIGIT ascii_posix set PCRE2_EXTRA_ASCII_POSIX auto_callout set PCRE2_AUTO_CALLOUT bad_escape_is_literal set PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL /i caseless set PCRE2_CASELESS /r caseless_restrict set PCRE2_EXTRA_CASELESS_RESTRICT dollar_endonly set PCRE2_DOLLAR_ENDONLY /s dotall set PCRE2_DOTALL dupnames set PCRE2_DUPNAMES endanchored set PCRE2_ENDANCHORED escaped_cr_is_lf set PCRE2_EXTRA_ESCAPED_CR_IS_LF /x extended set PCRE2_EXTENDED /xx extended_more set PCRE2_EXTENDED_MORE extra_alt_bsux set PCRE2_EXTRA_ALT_BSUX firstline set PCRE2_FIRSTLINE literal set PCRE2_LITERAL match_line set PCRE2_EXTRA_MATCH_LINE match_invalid_utf set PCRE2_MATCH_INVALID_UTF match_unset_backref set PCRE2_MATCH_UNSET_BACKREF match_word set PCRE2_EXTRA_MATCH_WORD /m multiline set PCRE2_MULTILINE never_backslash_c set PCRE2_NEVER_BACKSLASH_C never_ucp set PCRE2_NEVER_UCP never_utf set PCRE2_NEVER_UTF /n no_auto_capture set PCRE2_NO_AUTO_CAPTURE no_auto_possess set PCRE2_NO_AUTO_POSSESS no_dotstar_anchor set PCRE2_NO_DOTSTAR_ANCHOR no_start_optimize set PCRE2_NO_START_OPTIMIZE no_utf_check set PCRE2_NO_UTF_CHECK ucp set PCRE2_UCP ungreedy set PCRE2_UNGREEDY use_offset_limit set PCRE2_USE_OFFSET_LIMIT utf set PCRE2_UTF As well as turning on the PCRE2_UTF option, the utf modifier causes all non-printing characters in output strings to be printed using the \x{hh...} notation. Otherwise, those less than 0x100 are output in hex without the curly brackets. Setting utf in 16-bit or 32-bit mode also causes pattern and subject strings to be translated to UTF-16 or UTF-32, respectively, before being passed to library functions. Setting compilation controls The following modifiers affect the compilation process or request information about the pattern. There are single-letter abbreviations for some that are heavily used in the test files. bsr=[anycrlf|unicode] specify \R handling /B bincode show binary code without lengths callout_info show callout information convert=<options> request foreign pattern conversion convert_glob_escape=c set glob escape character convert_glob_separator=c set glob separator character convert_length set convert buffer length debug same as info,fullbincode framesize show matching frame size fullbincode show binary code with lengths /I info show info about compiled pattern hex unquoted characters are hexadecimal jit[=<number>] use JIT jitfast use JIT fast path jitverify verify JIT use locale=<name> use this locale max_pattern_compiled ) set maximum compiled pattern _length=<n> ) length (bytes) max_pattern_length=<n> set maximum pattern length (code units) max_varlookbehind=<n> set maximum variable lookbehind length memory show memory used newline=<type> set newline type null_context compile with a NULL context null_pattern pass pattern as NULL parens_nest_limit=<n> set maximum parentheses depth posix use the POSIX API posix_nosub use the POSIX API with REG_NOSUB push push compiled pattern onto the stack pushcopy push a copy onto the stack stackguard=<number> test the stackguard feature subject_literal treat all subject lines as literal tables=[0|1|2|3] select internal tables use_length do not zero-terminate the pattern utf8_input treat input as UTF-8 The effects of these modifiers are described in the following sections. Newline and \R handling The bsr modifier specifies what \R in a pattern should match. If it is set to "anycrlf", \R matches CR, LF, or CRLF only. If it is set to "unicode", \R matches any Unicode newline sequence. The default can be specified when PCRE2 is built; if it is not, the default is set to Unicode. The newline modifier specifies which characters are to be interpreted as newlines, both in the pattern and in subject lines. The type must be one of CR, LF, CRLF, ANYCRLF, ANY, or NUL (in upper or lower case). Information about a pattern The debug modifier is a shorthand for info,fullbincode, requesting all available information. The bincode modifier causes a representation of the compiled code to be output after compilation. This information does not contain length and offset values, which ensures that the same output is generated for different internal link sizes and different code unit widths. By using bincode, the same regression tests can be used in different environments. The fullbincode modifier, by contrast, does include length and offset values. This is used in a few special tests that run only for specific code unit widths and link sizes, and is also useful for one-off tests. The info modifier requests information about the compiled pattern (whether it is anchored, has a fixed first character, and so on). The information is obtained from the pcre2_pattern_info() function. Here are some typical examples: re> /(?i)(^a|^b)/m,info Capture group count = 1 Compile options: multiline Overall options: caseless multiline First code unit at start or follows newline Subject length lower bound = 1 re> /(?i)abc/info Capture group count = 0 Compile options: <none> Overall options: caseless First code unit = 'a' (caseless) Last code unit = 'c' (caseless) Subject length lower bound = 3 "Compile options" are those specified by modifiers; "overall options" have added options that are taken or deduced from the pattern. If both sets of options are the same, just a single "options" line is output; if there are no options, the line is omitted. "First code unit" is where any match must start; if there is more than one they are listed as "starting code units". "Last code unit" is the last literal code unit that must be present in any match. This is not necessarily the last character. These lines are omitted if no starting or ending code units are recorded. The subject length line is omitted when no_start_optimize is set because the minimum length is not calculated when it can never be used. The framesize modifier shows the size, in bytes, of each storage frame used by pcre2_match() for handling backtracking. The size depends on the number of capturing parentheses in the pattern. A vector of these frames is used at matching time; its overall size is shown when the heaframes_size subject modifier is set. The callout_info modifier requests information about all the callouts in the pattern. A list of them is output at the end of any other information that is requested. For each callout, either its number or string is given, followed by the item that follows it in the pattern. Passing a NULL context Normally, pcre2test passes a context block to pcre2_compile(). If the null_context modifier is set, however, NULL is passed. This is for testing that pcre2_compile() behaves correctly in this case (it uses default values). Passing a NULL pattern The null_pattern modifier is for testing the behaviour of pcre2_compile() when the pattern argument is NULL. The length value passed is the default PCRE2_ZERO_TERMINATED unless use_length is set. Any length other than zero causes an error. Specifying pattern characters in hexadecimal The hex modifier specifies that the characters of the pattern, except for substrings enclosed in single or double quotes, are to be interpreted as pairs of hexadecimal digits. This feature is provided as a way of creating patterns that contain binary zeros and other non- printing characters. White space is permitted between pairs of digits. For example, this pattern contains three characters: /ab 32 59/hex Parts of such a pattern are taken literally if quoted. This pattern contains nine characters, only two of which are specified in hexadecimal: /ab "literal" 32/hex Either single or double quotes may be used. There is no way of including the delimiter within a substring. The hex and expand modifiers are mutually exclusive. Specifying the pattern's length By default, patterns are passed to the compiling functions as zero- terminated strings but can be passed by length instead of being zero- terminated. The use_length modifier causes this to happen. Using a length happens automatically (whether or not use_length is set) when hex is set, because patterns specified in hexadecimal may contain binary zeros. If hex or use_length is used with the POSIX wrapper API (see "Using the POSIX wrapper API" below), the REG_PEND extension is used to pass the pattern's length. Specifying a maximum for variable lookbehinds Variable lookbehind assertions are supported only if, for each one, there is a maximum length (in characters) that it can match. There is a limit on this, whose default can be set at build time, with an ultimate default of 255. The max_varlookbehind modifier uses the pcre2_set_max_varlookbehind() function to change the limit. Lookbehinds whose branches each match a fixed length are limited to 65535 characters per branch. Specifying wide characters in 16-bit and 32-bit modes In 16-bit and 32-bit modes, all input is automatically treated as UTF-8 and translated to UTF-16 or UTF-32 when the utf modifier is set. For testing the 16-bit and 32-bit libraries in non-UTF mode, the utf8_input modifier can be used. It is mutually exclusive with utf. Input lines are interpreted as UTF-8 as a means of specifying wide characters. More details are given in "Input encoding" above. Generating long repetitive patterns Some tests use long patterns that are very repetitive. Instead of creating a very long input line for such a pattern, you can use a special repetition feature, similar to the one described for subject lines above. If the expand modifier is present on a pattern, parts of the pattern that have the form \[<characters>]{<count>} are expanded before the pattern is passed to pcre2_compile(). For example, \[AB]{6000} is expanded to "ABAB..." 6000 times. This construction cannot be nested. An initial "\[" sequence is recognized only if "]{" followed by decimal digits and "}" is found later in the pattern. If not, the characters remain in the pattern unaltered. The expand and hex modifiers are mutually exclusive. If part of an expanded pattern looks like an expansion, but is really part of the actual pattern, unwanted expansion can be avoided by giving two values in the quantifier. For example, \[AB]{6000,6000} is not recognized as an expansion item. If the info modifier is set on an expanded pattern, the result of the expansion is included in the information that is output. JIT compilation Just-in-time (JIT) compiling is a heavyweight optimization that can greatly speed up pattern matching. See the pcre2jit documentation for details. JIT compiling happens, optionally, after a pattern has been successfully compiled into an internal form. The JIT compiler converts this to optimized machine code. It needs to know whether the match-time options PCRE2_PARTIAL_HARD and PCRE2_PARTIAL_SOFT are going to be used, because different code is generated for the different cases. See the partial modifier in "Subject Modifiers" below for details of how these options are specified for each match attempt. JIT compilation is requested by the jit pattern modifier, which may optionally be followed by an equals sign and a number in the range 0 to 7. The three bits that make up the number specify which of the three JIT operating modes are to be compiled: 1 compile JIT code for non-partial matching 2 compile JIT code for soft partial matching 4 compile JIT code for hard partial matching The possible values for the jit modifier are therefore: 0 disable JIT 1 normal matching only 2 soft partial matching only 3 normal and soft partial matching 4 hard partial matching only 6 soft and hard partial matching only 7 all three modes If no number is given, 7 is assumed. The phrase "partial matching" means a call to pcre2_match() with either the PCRE2_PARTIAL_SOFT or the PCRE2_PARTIAL_HARD option set. Note that such a call may return a complete match; the options enable the possibility of a partial match, but do not require it. Note also that if you request JIT compilation only for partial matching (for example, jit=2) but do not set the partial modifier on a subject line, that match will not use JIT code because none was compiled for non-partial matching. If JIT compilation is successful, the compiled JIT code will automatically be used when an appropriate type of match is run, except when incompatible run-time options are specified. For more details, see the pcre2jit documentation. See also the jitstack modifier below for a way of setting the size of the JIT stack. If the jitfast modifier is specified, matching is done using the JIT "fast path" interface, pcre2_jit_match(), which skips some of the sanity checks that are done by pcre2_match(), and of course does not work when JIT is not supported. If jitfast is specified without jit, jit=7 is assumed. If the jitverify modifier is specified, information about the compiled pattern shows whether JIT compilation was or was not successful. If jitverify is specified without jit, jit=7 is assumed. If JIT compilation is successful when jitverify is set, the text "(JIT)" is added to the first output line after a match or non match when JIT- compiled code was actually used in the match. Setting a locale The locale modifier must specify the name of a locale, for example: /pattern/locale=fr_FR The given locale is set, pcre2_maketables() is called to build a set of character tables for the locale, and this is then passed to pcre2_compile() when compiling the regular expression. The same tables are used when matching the following subject lines. The locale modifier applies only to the pattern on which it appears, but can be given in a #pattern command if a default is needed. Setting a locale and alternate character tables are mutually exclusive. Showing pattern memory The memory modifier causes the size in bytes of the memory used to hold the compiled pattern to be output. This does not include the size of the pcre2_code block; it is just the actual compiled data. If the pattern is subsequently passed to the JIT compiler, the size of the JIT compiled code is also output. Here is an example: re> /a(b)c/jit,memory Memory allocation (code space): 21 Memory allocation (JIT code): 1910 Limiting nested parentheses The parens_nest_limit modifier sets a limit on the depth of nested parentheses in a pattern. Breaching the limit causes a compilation error. The default for the library is set when PCRE2 is built, but pcre2test sets its own default of 220, which is required for running the standard test suite. Limiting the pattern length The max_pattern_length modifier sets a limit, in code units, to the length of pattern that pcre2_compile() will accept. Breaching the limit causes a compilation error. The default is the largest number a PCRE2_SIZE variable can hold (essentially unlimited). Limiting the size of a compiled pattern The max_pattern_compiled_length modifier sets a limit, in bytes, to the amount of memory used by a compiled pattern. Breaching the limit causes a compilation error. The default is the largest number a PCRE2_SIZE variable can hold (essentially unlimited). Using the POSIX wrapper API The posix and posix_nosub modifiers cause pcre2test to call PCRE2 via the POSIX wrapper API rather than its native API. When posix_nosub is used, the POSIX option REG_NOSUB is passed to regcomp(). The POSIX wrapper supports only the 8-bit library. Note that it does not imply POSIX matching semantics; for more detail see the pcre2posix documentation. The following pattern modifiers set options for the regcomp() function: caseless REG_ICASE multiline REG_NEWLINE dotall REG_DOTALL ) ungreedy REG_UNGREEDY ) These options are not part of ucp REG_UCP ) the POSIX standard utf REG_UTF8 ) The regerror_buffsize modifier specifies a size for the error buffer that is passed to regerror() in the event of a compilation error. For example: /abc/posix,regerror_buffsize=20 This provides a means of testing the behaviour of regerror() when the buffer is too small for the error message. If this modifier has not been set, a large buffer is used. The aftertext and allaftertext subject modifiers work as described below. All other modifiers are either ignored, with a warning message, or cause an error. The pattern is passed to regcomp() as a zero-terminated string by default, but if the use_length or hex modifiers are set, the REG_PEND extension is used to pass it by length. Testing the stack guard feature The stackguard modifier is used to test the use of pcre2_set_compile_recursion_guard(), a function that is provided to enable stack availability to be checked during compilation (see the pcre2api documentation for details). If the number specified by the modifier is greater than zero, pcre2_set_compile_recursion_guard() is called to set up callback from pcre2_compile() to a local function. The argument it receives is the current nesting parenthesis depth; if this is greater than the value given by the modifier, non-zero is returned, causing the compilation to be aborted. Using alternative character tables The value specified for the tables modifier must be one of the digits 0, 1, 2, or 3. It causes a specific set of built-in character tables to be passed to pcre2_compile(). This is used in the PCRE2 tests to check behaviour with different character tables. The digit specifies the tables as follows: 0 do not pass any special character tables 1 the default ASCII tables, as distributed in pcre2_chartables.c.dist 2 a set of tables defining ISO 8859 characters 3 a set of tables loaded by the #loadtables command In tables 2, some characters whose codes are greater than 128 are identified as letters, digits, spaces, etc. Tables 3 can be used only after a #loadtables command has loaded them from a binary file. Setting alternate character tables and a locale are mutually exclusive. Setting certain match controls The following modifiers are really subject modifiers, and are described under "Subject Modifiers" below. However, they may be included in a pattern's modifier list, in which case they are applied to every subject line that is processed with that pattern. These modifiers do not affect the compilation process. aftertext show text after match allaftertext show text after captures allcaptures show all captures allvector show the entire ovector allusedtext show all consulted text altglobal alternative global matching /g global global matching heapframes_size show match data heapframes size jitstack=<n> set size of JIT stack mark show mark values replace=<string> specify a replacement string startchar show starting character when relevant substitute_callout use substitution callouts substitute_extended use PCRE2_SUBSTITUTE_EXTENDED substitute_literal use PCRE2_SUBSTITUTE_LITERAL substitute_matched use PCRE2_SUBSTITUTE_MATCHED substitute_overflow_length use PCRE2_SUBSTITUTE_OVERFLOW_LENGTH substitute_replacement_only use PCRE2_SUBSTITUTE_REPLACEMENT_ONLY substitute_skip=<n> skip substitution <n> substitute_stop=<n> skip substitution <n> and following substitute_unknown_unset use PCRE2_SUBSTITUTE_UNKNOWN_UNSET substitute_unset_empty use PCRE2_SUBSTITUTE_UNSET_EMPTY These modifiers may not appear in a #pattern command. If you want them as defaults, set them in a #subject command. Specifying literal subject lines If the subject_literal modifier is present on a pattern, all the subject lines that it matches are taken as literal strings, with no interpretation of backslashes. It is not possible to set subject modifiers on such lines, but any that are set as defaults by a #subject command are recognized. Saving a compiled pattern When a pattern with the push modifier is successfully compiled, it is pushed onto a stack of compiled patterns, and pcre2test expects the next line to contain a new pattern (or a command) instead of a subject line. This facility is used when saving compiled patterns to a file, as described in the section entitled "Saving and restoring compiled patterns" below. If pushcopy is used instead of push, a copy of the compiled pattern is stacked, leaving the original as current, ready to match the following input lines. This provides a way of testing the pcre2_code_copy() function. The push and pushcopy modifiers are incompatible with compilation modifiers such as global that act at match time. Any that are specified are ignored (for the stacked copy), with a warning message, except for replace, which causes an error. Note that jitverify, which is allowed, does not carry through to any subsequent matching that uses a stacked pattern. Testing foreign pattern conversion The experimental foreign pattern conversion functions in PCRE2 can be tested by setting the convert modifier. Its argument is a colon- separated list of options, which set the equivalent option for the pcre2_pattern_convert() function: glob PCRE2_CONVERT_GLOB glob_no_starstar PCRE2_CONVERT_GLOB_NO_STARSTAR glob_no_wild_separator PCRE2_CONVERT_GLOB_NO_WILD_SEPARATOR posix_basic PCRE2_CONVERT_POSIX_BASIC posix_extended PCRE2_CONVERT_POSIX_EXTENDED unset Unset all options The "unset" value is useful for turning off a default that has been set by a #pattern command. When one of these options is set, the input pattern is passed to pcre2_pattern_convert(). If the conversion is successful, the result is reflected in the output and then passed to pcre2_compile(). The normal utf and no_utf_check options, if set, cause the PCRE2_CONVERT_UTF and PCRE2_CONVERT_NO_UTF_CHECK options to be passed to pcre2_pattern_convert(). By default, the conversion function is allowed to allocate a buffer for its output. However, if the convert_length modifier is set to a value greater than zero, pcre2test passes a buffer of the given length. This makes it possible to test the length check. The convert_glob_escape and convert_glob_separator modifiers can be used to specify the escape and separator characters for glob processing, overriding the defaults, which are operating-system dependent. SUBJECT MODIFIERS The modifiers that can appear in subject lines and the #subject command are of two types. Setting match options The following modifiers set options for pcre2_match() or pcre2_dfa_match(). See pcreapi for a description of their effects. anchored set PCRE2_ANCHORED endanchored set PCRE2_ENDANCHORED dfa_restart set PCRE2_DFA_RESTART dfa_shortest set PCRE2_DFA_SHORTEST disable_recurseloop_check set PCRE2_DISABLE_RECURSELOOP_CHECK no_jit set PCRE2_NO_JIT no_utf_check set PCRE2_NO_UTF_CHECK notbol set PCRE2_NOTBOL notempty set PCRE2_NOTEMPTY notempty_atstart set PCRE2_NOTEMPTY_ATSTART noteol set PCRE2_NOTEOL partial_hard (or ph) set PCRE2_PARTIAL_HARD partial_soft (or ps) set PCRE2_PARTIAL_SOFT The partial matching modifiers are provided with abbreviations because they appear frequently in tests. If the posix or posix_nosub modifier was present on the pattern, causing the POSIX wrapper API to be used, the only option-setting modifiers that have any effect are notbol, notempty, and noteol, causing REG_NOTBOL, REG_NOTEMPTY, and REG_NOTEOL, respectively, to be passed to regexec(). The other modifiers are ignored, with a warning message. There is one additional modifier that can be used with the POSIX wrapper. It is ignored (with a warning) if used for non-POSIX matching. posix_startend=<n>[:<m>] This causes the subject string to be passed to regexec() using the REG_STARTEND option, which uses offsets to specify which part of the string is searched. If only one number is given, the end offset is passed as the end of the subject string. For more detail of REG_STARTEND, see the pcre2posix documentation. If the subject string contains binary zeros (coded as escapes such as \x{00} because pcre2test does not support actual binary zeros in its input), you must use posix_startend to specify its length. Setting match controls The following modifiers affect the matching process or request additional information. Some of them may also be specified on a pattern line (see above), in which case they apply to every subject line that is matched against that pattern, but can be overridden by modifiers on the subject. aftertext show text after match allaftertext show text after captures allcaptures show all captures allvector show the entire ovector allusedtext show all consulted text (non-JIT only) altglobal alternative global matching callout_capture show captures at callout time callout_data=<n> set a value to pass via callouts callout_error=<n>[:<m>] control callout error callout_extra show extra callout information callout_fail=<n>[:<m>] control callout failure callout_no_where do not show position of a callout callout_none do not supply a callout function copy=<number or name> copy captured substring depth_limit=<n> set a depth limit dfa use pcre2_dfa_match() find_limits find heap, match and depth limits find_limits_noheap find match and depth limits get=<number or name> extract captured substring getall extract all captured substrings /g global global matching heapframes_size show match data heapframes size heap_limit=<n> set a limit on heap memory (Kbytes) jitstack=<n> set size of JIT stack mark show mark values match_limit=<n> set a match limit memory show heap memory usage null_context match with a NULL context null_replacement substitute with NULL replacement null_subject match with NULL subject offset=<n> set starting offset offset_limit=<n> set offset limit ovector=<n> set size of output vector recursion_limit=<n> obsolete synonym for depth_limit replace=<string> specify a replacement string startchar show startchar when relevant startoffset=<n> same as offset=<n> substitute_callout use substitution callouts substitute_extedded use PCRE2_SUBSTITUTE_EXTENDED substitute_literal use PCRE2_SUBSTITUTE_LITERAL substitute_matched use PCRE2_SUBSTITUTE_MATCHED substitute_overflow_length use PCRE2_SUBSTITUTE_OVERFLOW_LENGTH substitute_replacement_only use PCRE2_SUBSTITUTE_REPLACEMENT_ONLY substitute_skip=<n> skip substitution number n substitute_stop=<n> skip substitution number n and greater substitute_unknown_unset use PCRE2_SUBSTITUTE_UNKNOWN_UNSET substitute_unset_empty use PCRE2_SUBSTITUTE_UNSET_EMPTY zero_terminate pass the subject as zero-terminated The effects of these modifiers are described in the following sections. When matching via the POSIX wrapper API, the aftertext, allaftertext, and ovector subject modifiers work as described below. All other modifiers are either ignored, with a warning message, or cause an error. Showing more text The aftertext modifier requests that as well as outputting the part of the subject string that matched the entire pattern, pcre2test should in addition output the remainder of the subject string. This is useful for tests where the subject contains multiple copies of the same substring. The allaftertext modifier requests the same action for captured substrings as well as the main matched substring. In each case the remainder is output on the following line with a plus character following the capture number. The allusedtext modifier requests that all the text that was consulted during a successful pattern match by the interpreter should be shown, for both full and partial matches. This feature is not supported for JIT matching, and if requested with JIT it is ignored (with a warning message). Setting this modifier affects the output if there is a lookbehind at the start of a match, or, for a complete match, a lookahead at the end, or if \K is used in the pattern. Characters that precede or follow the start and end of the actual match are indicated in the output by '<' or '>' characters underneath them. Here is an example: re> /(?<=pqr)abc(?=xyz)/ data> 123pqrabcxyz456\=allusedtext 0: pqrabcxyz <<< >>> data> 123pqrabcxy\=ph,allusedtext Partial match: pqrabcxy <<< The first, complete match shows that the matched string is "abc", with the preceding and following strings "pqr" and "xyz" having been consulted during the match (when processing the assertions). The partial match can indicate only the preceding string. The startchar modifier requests that the starting character for the match be indicated, if it is different to the start of the matched string. The only time when this occurs is when \K has been processed as part of the match. In this situation, the output for the matched string is displayed from the starting character instead of from the match point, with circumflex characters under the earlier characters. For example: re> /abc\Kxyz/ data> abcxyz\=startchar 0: abcxyz ^^^ Unlike allusedtext, the startchar modifier can be used with JIT. However, these two modifiers are mutually exclusive. Showing the value of all capture groups The allcaptures modifier requests that the values of all potential captured parentheses be output after a match. By default, only those up to the highest one actually used in the match are output (corresponding to the return code from pcre2_match()). Groups that did not take part in the match are output as "<unset>". This modifier is not relevant for DFA matching (which does no capturing) and does not apply when replace is specified; it is ignored, with a warning message, if present. Showing the entire ovector, for all outcomes The allvector modifier requests that the entire ovector be shown, whatever the outcome of the match. Compare allcaptures, which shows only up to the maximum number of capture groups for the pattern, and then only for a successful complete non-DFA match. This modifier, which acts after any match result, and also for DFA matching, provides a means of checking that there are no unexpected modifications to ovector fields. Before each match attempt, the ovector is filled with a special value, and if this is found in both elements of a capturing pair, "<unchanged>" is output. After a successful match, this applies to all groups after the maximum capture group for the pattern. In other cases it applies to the entire ovector. After a partial match, the first two elements are the only ones that should be set. After a DFA match, the amount of ovector that is used depends on the number of matches that were found. Testing pattern callouts A callout function is supplied when pcre2test calls the library matching functions, unless callout_none is specified. Its behaviour can be controlled by various modifiers listed above whose names begin with callout_. Details are given in the section entitled "Callouts" below. Testing callouts from pcre2_substitute() is described separately in "Testing the substitution function" below. Finding all matches in a string Searching for all possible matches within a subject can be requested by the global or altglobal modifier. After finding a match, the matching function is called again to search the remainder of the subject. The difference between global and altglobal is that the former uses the start_offset argument to pcre2_match() or pcre2_dfa_match() to start searching at a new point within the entire string (which is what Perl does), whereas the latter passes over a shortened subject. This makes a difference to the matching process if the pattern begins with a lookbehind assertion (including \b or \B). If an empty string is matched, the next match is done with the PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED flags set, in order to search for another, non-empty, match at the same point in the subject. If this match fails, the start offset is advanced, and the normal match is retried. This imitates the way Perl handles such cases when using the /g modifier or the split() function. Normally, the start offset is advanced by one character, but if the newline convention recognizes CRLF as a newline, and the current character is CR followed by LF, an advance of two characters occurs. Testing substring extraction functions The copy and get modifiers can be used to test the pcre2_substring_copy_xxx() and pcre2_substring_get_xxx() functions. They can be given more than once, and each can specify a capture group name or number, for example: abcd\=copy=1,copy=3,get=G1 If the #subject command is used to set default copy and/or get lists, these can be unset by specifying a negative number to cancel all numbered groups and an empty name to cancel all named groups. The getall modifier tests pcre2_substring_list_get(), which extracts all captured substrings. If the subject line is successfully matched, the substrings extracted by the convenience functions are output with C, G, or L after the string number instead of a colon. This is in addition to the normal full list. The string length (that is, the return from the extraction function) is given in parentheses after each substring, followed by the name when the extraction was by name. Testing the substitution function If the replace modifier is set, the pcre2_substitute() function is called instead of one of the matching functions (or after one call of pcre2_match() in the case of PCRE2_SUBSTITUTE_MATCHED). Note that replacement strings cannot contain commas, because a comma signifies the end of a modifier. This is not thought to be an issue in a test program. Specifying a completely empty replacement string disables this modifier. However, it is possible to specify an empty replacement by providing a buffer length, as described below, for an otherwise empty replacement. Unlike subject strings, pcre2test does not process replacement strings for escape sequences. In UTF mode, a replacement string is checked to see if it is a valid UTF-8 string. If so, it is correctly converted to a UTF string of the appropriate code unit width. If it is not a valid UTF-8 string, the individual code units are copied directly. This provides a means of passing an invalid UTF-8 string for testing purposes. The following modifiers set options (in additional to the normal match options) for pcre2_substitute(): global PCRE2_SUBSTITUTE_GLOBAL substitute_extended PCRE2_SUBSTITUTE_EXTENDED substitute_literal PCRE2_SUBSTITUTE_LITERAL substitute_matched PCRE2_SUBSTITUTE_MATCHED substitute_overflow_length PCRE2_SUBSTITUTE_OVERFLOW_LENGTH substitute_replacement_only PCRE2_SUBSTITUTE_REPLACEMENT_ONLY substitute_unknown_unset PCRE2_SUBSTITUTE_UNKNOWN_UNSET substitute_unset_empty PCRE2_SUBSTITUTE_UNSET_EMPTY See the pcre2api documentation for details of these options. After a successful substitution, the modified string is output, preceded by the number of replacements. This may be zero if there were no matches. Here is a simple example of a substitution test: /abc/replace=xxx =abc=abc= 1: =xxx=abc= =abc=abc=\=global 2: =xxx=xxx= Subject and replacement strings should be kept relatively short (fewer than 256 characters) for substitution tests, as fixed-size buffers are used. To make it easy to test for buffer overflow, if the replacement string starts with a number in square brackets, that number is passed to pcre2_substitute() as the size of the output buffer, with the replacement string starting at the next character. Here is an example that tests the edge case: /abc/ 123abc123\=replace=[10]XYZ 1: 123XYZ123 123abc123\=replace=[9]XYZ Failed: error -47: no more memory The default action of pcre2_substitute() is to return PCRE2_ERROR_NOMEMORY when the output buffer is too small. However, if the PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option is set (by using the substitute_overflow_length modifier), pcre2_substitute() continues to go through the motions of matching and substituting (but not doing any callouts), in order to compute the size of buffer that is required. When this happens, pcre2test shows the required buffer length (which includes space for the trailing zero) as part of the error message. For example: /abc/substitute_overflow_length 123abc123\=replace=[9]XYZ Failed: error -47: no more memory: 10 code units are needed A replacement string is ignored with POSIX and DFA matching. Specifying partial matching provokes an error return ("bad option value") from pcre2_substitute(). Testing substitute callouts If the substitute_callout modifier is set, a substitution callout function is set up. The null_context modifier must not be set, because the address of the callout function is passed in a match context. When the callout function is called (after each substitution), details of the input and output strings are output. For example: /abc/g,replace=<$0>,substitute_callout abcdefabcpqr 1(1) Old 0 3 "abc" New 0 5 "<abc>" 2(1) Old 6 9 "abc" New 8 13 "<abc>" 2: <abc>def<abc>pqr The first number on each callout line is the count of matches. The parenthesized number is the number of pairs that are set in the ovector (that is, one more than the number of capturing groups that were set). Then are listed the offsets of the old substring, its contents, and the same for the replacement. By default, the substitution callout function returns zero, which accepts the replacement and causes matching to continue if /g was used. Two further modifiers can be used to test other return values. If substitute_skip is set to a value greater than zero the callout function returns +1 for the match of that number, and similarly substitute_stop returns -1. These cause the replacement to be rejected, and -1 causes no further matching to take place. If either of them are set, substitute_callout is assumed. For example: /abc/g,replace=<$0>,substitute_skip=1 abcdefabcpqr 1(1) Old 0 3 "abc" New 0 5 "<abc> SKIPPED" 2(1) Old 6 9 "abc" New 6 11 "<abc>" 2: abcdef<abc>pqr abcdefabcpqr\=substitute_stop=1 1(1) Old 0 3 "abc" New 0 5 "<abc> STOPPED" 1: abcdefabcpqr If both are set for the same number, stop takes precedence. Only a single skip or stop is supported, which is sufficient for testing that the feature works. Setting the JIT stack size The jitstack modifier provides a way of setting the maximum stack size that is used by the just-in-time optimization code. It is ignored if JIT optimization is not being used. The value is a number of kibibytes (units of 1024 bytes). Setting zero reverts to the default of 32KiB. Providing a stack that is larger than the default is necessary only for very complicated patterns. If jitstack is set non-zero on a subject line it overrides any value that was set on the pattern. Setting heap, match, and depth limits The heap_limit, match_limit, and depth_limit modifiers set the appropriate limits in the match context. These values are ignored when the find_limits or find_limits_noheap modifier is specified. Finding minimum limits If the find_limits modifier is present on a subject line, pcre2test calls the relevant matching function several times, setting different values in the match context via pcre2_set_heap_limit(), pcre2_set_match_limit(), or pcre2_set_depth_limit() until it finds the smallest value for each parameter that allows the match to complete without a "limit exceeded" error. The match itself may succeed or fail. An alternative modifier, find_limits_noheap, omits the heap limit. This is used in the standard tests, because the minimum heap limit varies between systems. If JIT is being used, only the match limit is relevant, and the other two are automatically omitted. When using this modifier, the pattern should not contain any limit settings such as (*LIMIT_MATCH=...) within it. If such a setting is present and is lower than the minimum matching value, the minimum value cannot be found because pcre2_set_match_limit() etc. are only able to reduce the value of an in-pattern limit; they cannot increase it. For non-DFA matching, the minimum depth_limit number is a measure of how much nested backtracking happens (that is, how deeply the pattern's tree is searched). In the case of DFA matching, depth_limit controls the depth of recursive calls of the internal function that is used for handling pattern recursion, lookaround assertions, and atomic groups. For non-DFA matching, the match_limit number is a measure of the amount of backtracking that takes place, and learning the minimum value can be instructive. For most simple matches, the number is quite small, but for patterns with very large numbers of matching possibilities, it can become large very quickly with increasing length of subject string. In the case of DFA matching, match_limit controls the total number of calls, both recursive and non-recursive, to the internal matching function, thus controlling the overall amount of computing resource that is used. For both kinds of matching, the heap_limit number, which is in kibibytes (units of 1024 bytes), limits the amount of heap memory used for matching. Showing MARK names The mark modifier causes the names from backtracking control verbs that are returned from calls to pcre2_match() to be displayed. If a mark is returned for a match, non-match, or partial match, pcre2test shows it. For a match, it is on a line by itself, tagged with "MK:". Otherwise, it is added to the non-match message. Showing memory usage The memory modifier causes pcre2test to log the sizes of all heap memory allocation and freeing calls that occur during a call to pcre2_match() or pcre2_dfa_match(). In the latter case, heap memory is used only when a match requires more internal workspace that the default allocation on the stack, so in many cases there will be no output. No heap memory is allocated during matching with JIT. For this modifier to work, the null_context modifier must not be set on both the pattern and the subject, though it can be set on one or the other. Showing the heap frame overall vector size The heapframes_size modifier is relevant for matches using pcre2_match() without JIT. After a match has run (whether successful or not) the size, in bytes, of the allocated heap frames vector that is left attached to the match data block is shown. If the matching action involved several calls to pcre2_match() (for example, global matching or for timing) only the final value is shown. This modifier is ignored, with a warning, for POSIX or DFA matching. JIT matching does not use the heap frames vector, so the size is always zero, unless there was a previous non-JIT match. Note that specifing a size of zero for the output vector (see below) causes pcre2test to free its match data block (and associated heap frames vector) and allocate a new one. Setting a starting offset The offset modifier sets an offset in the subject string at which matching starts. Its value is a number of code units, not characters. Setting an offset limit The offset_limit modifier sets a limit for unanchored matches. If a match cannot be found starting at or before this offset in the subject, a "no match" return is given. The data value is a number of code units, not characters. When this modifier is used, the use_offset_limit modifier must have been set for the pattern; if not, an error is generated. Setting the size of the output vector The ovector modifier applies only to the subject line in which it appears, though of course it can also be used to set a default in a #subject command. It specifies the number of pairs of offsets that are available for storing matching information. The default is 15. A value of zero is useful when testing the POSIX API because it causes regexec() to be called with a NULL capture vector. When not testing the POSIX API, a value of zero is used to cause pcre2_match_data_create_from_pattern() to be called, in order to create a new match block of exactly the right size for the pattern. (It is not possible to create a match block with a zero-length ovector; there is always at least one pair of offsets.) The old match data block is freed. Passing the subject as zero-terminated By default, the subject string is passed to a native API matching function with its correct length. In order to test the facility for passing a zero-terminated string, the zero_terminate modifier is provided. It causes the length to be passed as PCRE2_ZERO_TERMINATED. When matching via the POSIX interface, this modifier is ignored, with a warning. When testing pcre2_substitute(), this modifier also has the effect of passing the replacement string as zero-terminated. Passing a NULL context, subject, or replacement Normally, pcre2test passes a context block to pcre2_match(), pcre2_dfa_match(), pcre2_jit_match() or pcre2_substitute(). If the null_context modifier is set, however, NULL is passed. This is for testing that the matching and substitution functions behave correctly in this case (they use default values). This modifier cannot be used with the find_limits, find_limits_noheap, or substitute_callout modifiers. Similarly, for testing purposes, if the null_subject or null_replacement modifier is set, the subject or replacement string pointers are passed as NULL, respectively, to the relevant functions. THE ALTERNATIVE MATCHING FUNCTION By default, pcre2test uses the standard PCRE2 matching function, pcre2_match() to match each subject line. PCRE2 also supports an alternative matching function, pcre2_dfa_match(), which operates in a different way, and has some restrictions. The differences between the two functions are described in the pcre2matching documentation. If the dfa modifier is set, the alternative matching function is used. This function finds all possible matches at a given point in the subject. If, however, the dfa_shortest modifier is set, processing stops after the first match is found. This is always the shortest possible match. DEFAULT OUTPUT FROM pcre2test This section describes the output when the normal matching function, pcre2_match(), is being used. When a match succeeds, pcre2test outputs the list of captured substrings, starting with number 0 for the string that matched the whole pattern. Otherwise, it outputs "No match" when the return is PCRE2_ERROR_NOMATCH, or "Partial match:" followed by the partially matching substring when the return is PCRE2_ERROR_PARTIAL. (Note that this is the entire substring that was inspected during the partial match; it may include characters before the actual match start if a lookbehind assertion, \K, \b, or \B was involved.) For any other return, pcre2test outputs the PCRE2 negative error number and a short descriptive phrase. If the error is a failed UTF string check, the code unit offset of the start of the failing character is also output. Here is an example of an interactive pcre2test run. $ pcre2test PCRE2 version 10.22 2016-07-29 re> /^abc(\d+)/ data> abc123 0: abc123 1: 123 data> xyz No match Unset capturing substrings that are not followed by one that is set are not shown by pcre2test unless the allcaptures modifier is specified. In the following example, there are two capturing substrings, but when the first data line is matched, the second, unset substring is not shown. An "internal" unset substring is shown as "<unset>", as for the second data line. re> /(a)|(b)/ data> a 0: a 1: a data> b 0: b 1: <unset> 2: b If the strings contain any non-printing characters, they are output as \xhh escapes if the value is less than 256 and UTF mode is not set. Otherwise they are output as \x{hh...} escapes. See below for the definition of non-printing characters. If the aftertext modifier is set, the output for substring 0 is followed by the rest of the subject string, identified by "0+" like this: re> /cat/aftertext data> cataract 0: cat 0+ aract If global matching is requested, the results of successive matching attempts are output in sequence, like this: re> /\Bi(\w\w)/g data> Mississippi 0: iss 1: ss 0: iss 1: ss 0: ipp 1: pp "No match" is output only if the first match attempt fails. Here is an example of a failure message (the offset 4 that is specified by the offset modifier is past the end of the subject string): re> /xyz/ data> xyz\=offset=4 Error -24 (bad offset value) Note that whereas patterns can be continued over several lines (a plain ">" prompt is used for continuations), subject lines may not. However newlines can be included in a subject by means of the \n escape (or \r, \r\n, etc., depending on the newline sequence setting). OUTPUT FROM THE ALTERNATIVE MATCHING FUNCTION When the alternative matching function, pcre2_dfa_match(), is used, the output consists of a list of all the matches that start at the first point in the subject where there is at least one match. For example: re> /(tang|tangerine|tan)/ data> yellow tangerine\=dfa 0: tangerine 1: tang 2: tan Using the normal matching function on this data finds only "tang". The longest matching string is always given first (and numbered zero). After a PCRE2_ERROR_PARTIAL return, the output is "Partial match:", followed by the partially matching substring. Note that this is the entire substring that was inspected during the partial match; it may include characters before the actual match start if a lookbehind assertion, \b, or \B was involved. (\K is not supported for DFA matching.) If global matching is requested, the search for further matches resumes at the end of the longest match. For example: re> /(tang|tangerine|tan)/g data> yellow tangerine and tangy sultana\=dfa 0: tangerine 1: tang 2: tan 0: tang 1: tan 0: tan The alternative matching function does not support substring capture, so the modifiers that are concerned with captured substrings are not relevant. RESTARTING AFTER A PARTIAL MATCH When the alternative matching function has given the PCRE2_ERROR_PARTIAL return, indicating that the subject partially matched the pattern, you can restart the match with additional subject data by means of the dfa_restart modifier. For example: re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/ data> 23ja\=ps,dfa Partial match: 23ja data> n05\=dfa,dfa_restart 0: n05 For further information about partial matching, see the pcre2partial documentation. CALLOUTS If the pattern contains any callout requests, pcre2test's callout function is called during matching unless callout_none is specified. This works with both matching functions, and with JIT, though there are some differences in behaviour. The output for callouts with numerical arguments and those with string arguments is slightly different. Callouts with numerical arguments By default, the callout function displays the callout number, the start and current positions in the subject text at the callout time, and the next pattern item to be tested. For example: --->pqrabcdef 0 ^ ^ \d This output indicates that callout number 0 occurred for a match attempt starting at the fourth character of the subject string, when the pointer was at the seventh character, and when the next pattern item was \d. Just one circumflex is output if the start and current positions are the same, or if the current position precedes the start position, which can happen if the callout is in a lookbehind assertion. Callouts numbered 255 are assumed to be automatic callouts, inserted as a result of the auto_callout pattern modifier. In this case, instead of showing the callout number, the offset in the pattern, preceded by a plus, is output. For example: re> /\d?[A-E]\*/auto_callout data> E* --->E* +0 ^ \d? +3 ^ [A-E] +8 ^^ \* +10 ^ ^ 0: E* If a pattern contains (*MARK) items, an additional line is output whenever a change of latest mark is passed to the callout function. For example: re> /a(*MARK:X)bc/auto_callout data> abc --->abc +0 ^ a +1 ^^ (*MARK:X) +10 ^^ b Latest Mark: X +11 ^ ^ c +12 ^ ^ 0: abc The mark changes between matching "a" and "b", but stays the same for the rest of the match, so nothing more is output. If, as a result of backtracking, the mark reverts to being unset, the text "<unset>" is output. Callouts with string arguments The output for a callout with a string argument is similar, except that instead of outputting a callout number before the position indicators, the callout string and its offset in the pattern string are output before the reflection of the subject string, and the subject string is reflected for each callout. For example: re> /^ab(?C'first')cd(?C"second")ef/ data> abcdefg Callout (7): 'first' --->abcdefg ^ ^ c Callout (20): "second" --->abcdefg ^ ^ e 0: abcdef Callout modifiers The callout function in pcre2test returns zero (carry on matching) by default, but you can use a callout_fail modifier in a subject line to change this and other parameters of the callout (see below). If the callout_capture modifier is set, the current captured groups are output when a callout occurs. This is useful only for non-DFA matching, as pcre2_dfa_match() does not support capturing, so no captures are ever shown. The normal callout output, showing the callout number or pattern offset (as described above) is suppressed if the callout_no_where modifier is set. When using the interpretive matching function pcre2_match() without JIT, setting the callout_extra modifier causes additional output from pcre2test's callout function to be generated. For the first callout in a match attempt at a new starting position in the subject, "New match attempt" is output. If there has been a backtrack since the last callout (or start of matching if this is the first callout), "Backtrack" is output, followed by "No other matching paths" if the backtrack ended the previous match attempt. For example: re> /(a+)b/auto_callout,no_start_optimize,no_auto_possess data> aac\=callout_extra New match attempt --->aac +0 ^ ( +1 ^ a+ +3 ^ ^ ) +4 ^ ^ b Backtrack --->aac +3 ^^ ) +4 ^^ b Backtrack No other matching paths New match attempt --->aac +0 ^ ( +1 ^ a+ +3 ^^ ) +4 ^^ b Backtrack No other matching paths New match attempt --->aac +0 ^ ( +1 ^ a+ Backtrack No other matching paths New match attempt --->aac +0 ^ ( +1 ^ a+ No match Notice that various optimizations must be turned off if you want all possible matching paths to be scanned. If no_start_optimize is not used, there is an immediate "no match", without any callouts, because the starting optimization fails to find "b" in the subject, which it knows must be present for any match. If no_auto_possess is not used, the "a+" item is turned into "a++", which reduces the number of backtracks. The callout_extra modifier has no effect if used with the DFA matching function, or with JIT. Return values from callouts The default return from the callout function is zero, which allows matching to continue. The callout_fail modifier can be given one or two numbers. If there is only one number, 1 is returned instead of 0 (causing matching to backtrack) when a callout of that number is reached. If two numbers (<n>:<m>) are given, 1 is returned when callout <n> is reached and there have been at least <m> callouts. The callout_error modifier is similar, except that PCRE2_ERROR_CALLOUT is returned, causing the entire matching process to be aborted. If both these modifiers are set for the same callout number, callout_error takes precedence. Note that callouts with string arguments are always given the number zero. The callout_data modifier can be given an unsigned or a negative number. This is set as the "user data" that is passed to the matching function, and passed back when the callout function is invoked. Any value other than zero is used as a return from pcre2test's callout function. Inserting callouts can be helpful when using pcre2test to check complicated regular expressions. For further information about callouts, see the pcre2callout documentation. NON-PRINTING CHARACTERS When pcre2test is outputting text in the compiled version of a pattern, bytes other than 32-126 are always treated as non-printing characters and are therefore shown as hex escapes. When pcre2test is outputting text that is a matched part of a subject string, it behaves in the same way, unless a different locale has been set for the pattern (using the locale modifier). In this case, the isprint() function is used to distinguish printing and non-printing characters. SAVING AND RESTORING COMPILED PATTERNS It is possible to save compiled patterns on disc or elsewhere, and reload them later, subject to a number of restrictions. JIT data cannot be saved. The host on which the patterns are reloaded must be running the same version of PCRE2, with the same code unit width, and must also have the same endianness, pointer width and PCRE2_SIZE type. Before compiled patterns can be saved they must be serialized, that is, converted to a stream of bytes. A single byte stream may contain any number of compiled patterns, but they must all use the same character tables. A single copy of the tables is included in the byte stream (its size is 1088 bytes). The functions whose names begin with pcre2_serialize_ are used for serializing and de-serializing. They are described in the pcre2serialize documentation. In this section we describe the features of pcre2test that can be used to test these functions. Note that "serialization" in PCRE2 does not convert compiled patterns to an abstract format like Java or .NET. It just makes a reloadable byte code stream. Hence the restrictions on reloading mentioned above. In pcre2test, when a pattern with push modifier is successfully compiled, it is pushed onto a stack of compiled patterns, and pcre2test expects the next line to contain a new pattern (or command) instead of a subject line. By contrast, the pushcopy modifier causes a copy of the compiled pattern to be stacked, leaving the original available for immediate matching. By using push and/or pushcopy, a number of patterns can be compiled and retained. These modifiers are incompatible with posix, and control modifiers that act at match time are ignored (with a message) for the stacked patterns. The jitverify modifier applies only at compile time. The command #save <filename> causes all the stacked patterns to be serialized and the result written to the named file. Afterwards, all the stacked patterns are freed. The command #load <filename> reads the data in the file, and then arranges for it to be de- serialized, with the resulting compiled patterns added to the pattern stack. The pattern on the top of the stack can be retrieved by the #pop command, which must be followed by lines of subjects that are to be matched with the pattern, terminated as usual by an empty line or end of file. This command may be followed by a modifier list containing only control modifiers that act after a pattern has been compiled. In particular, hex, posix, posix_nosub, push, and pushcopy are not allowed, nor are any option-setting modifiers. The JIT modifiers are, however permitted. Here is an example that saves and reloads two patterns. /abc/push /xyz/push #save tempfile #load tempfile #pop info xyz #pop jit,bincode abc If jitverify is used with #pop, it does not automatically imply jit, which is different behaviour from when it is used on a pattern. The #popcopy command is analogous to the pushcopy modifier in that it makes current a copy of the topmost stack pattern, leaving the original still on the stack. SEE ALSO pcre2(3), pcre2api(3), pcre2callout(3), pcre2jit, pcre2matching(3), pcre2partial(d), pcre2pattern(3), pcre2serialize(3). AUTHOR Philip Hazel Retired from University Computing Service Cambridge, England. REVISION Last updated: 24 April 2024 Copyright (c) 1997-2024 University of Cambridge. PCRE 10.44 24 April 2024 PCRE2TEST(1)
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pcre2test - a program for testing Perl-compatible regular expressions.
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pcre2test [options] [input file [output file]] pcre2test is a test program for the PCRE2 regular expression libraries, but it can also be used for experimenting with regular expressions. This document describes the features of the test program; for details of the regular expressions themselves, see the pcre2pattern documentation. For details of the PCRE2 library function calls and their options, see the pcre2api documentation. The input for pcre2test is a sequence of regular expression patterns and subject strings to be matched. There are also command lines for setting defaults and controlling some special actions. The output shows the result of each match attempt. Modifiers on external or internal command lines, the patterns, and the subject lines specify PCRE2 function options, control how the subject is processed, and what output is produced. There are many obscure modifiers, some of which are specifically designed for use in conjunction with the test script and data files that are distributed as part of PCRE2. All the modifiers are documented here, some without much justification, but many of them are unlikely to be of use except when testing the libraries. PCRE2's 8-BIT, 16-BIT AND 32-BIT LIBRARIES Different versions of the PCRE2 library can be built to support character strings that are encoded in 8-bit, 16-bit, or 32-bit code units. One, two, or all three of these libraries may be simultaneously installed. The pcre2test program can be used to test all the libraries. However, its own input and output are always in 8-bit format. When testing the 16-bit or 32-bit libraries, patterns and subject strings are converted to 16-bit or 32-bit format before being passed to the library functions. Results are converted back to 8-bit code units for output. In the rest of this document, the names of library functions and structures are given in generic form, for example, pcre2_compile(). The actual names used in the libraries have a suffix _8, _16, or _32, as appropriate. INPUT ENCODING Input to pcre2test is processed line by line, either by calling the C library's fgets() function, or via the libreadline or libedit library. In some Windows environments character 26 (hex 1A) causes an immediate end of file, and no further data is read, so this character should be avoided unless you really want that action. The input is processed using C's string functions, so must not contain binary zeros, even though in Unix-like environments, fgets() treats any bytes other than newline as data characters. An error is generated if a binary zero is encountered. By default subject lines are processed for backslash escapes, which makes it possible to include any data value in strings that are passed to the library for matching. For patterns, there is a facility for specifying some or all of the 8-bit input characters as hexadecimal pairs, which makes it possible to include binary zeros. Input for the 16-bit and 32-bit libraries When testing the 16-bit or 32-bit libraries, there is a need to be able to generate character code points greater than 255 in the strings that are passed to the library. For subject lines, backslash escapes can be used. In addition, when the utf modifier (see "Setting compilation options" below) is set, the pattern and any following subject lines are interpreted as UTF-8 strings and translated to UTF-16 or UTF-32 as appropriate. For non-UTF testing of wide characters, the utf8_input modifier can be used. This is mutually exclusive with utf, and is allowed only in 16-bit or 32-bit mode. It causes the pattern and following subject lines to be treated as UTF-8 according to the original definition (RFC 2279), which allows for character values up to 0x7fffffff. Each character is placed in one 16-bit or 32-bit code unit (in the 16-bit case, values greater than 0xffff cause an error to occur). UTF-8 (in its original definition) is not capable of encoding values greater than 0x7fffffff, but such values can be handled by the 32-bit library. When testing this library in non-UTF mode with utf8_input set, if any character is preceded by the byte 0xff (which is an invalid byte in UTF-8) 0x80000000 is added to the character's value. This is the only way of passing such code points in a pattern string. For subject strings, using an escape sequence is preferable. COMMAND LINE OPTIONS -8 If the 8-bit library has been built, this option causes it to be used (this is the default). If the 8-bit library has not been built, this option causes an error. -16 If the 16-bit library has been built, this option causes it to be used. If the 8-bit library has not been built, this is the default. If the 16-bit library has not been built, this option causes an error. -32 If the 32-bit library has been built, this option causes it to be used. If no other library has been built, this is the default. If the 32-bit library has not been built, this option causes an error. -ac Behave as if each pattern has the auto_callout modifier, that is, insert automatic callouts into every pattern that is compiled. -AC As for -ac, but in addition behave as if each subject line has the callout_extra modifier, that is, show additional information from callouts. -b Behave as if each pattern has the fullbincode modifier; the full internal binary form of the pattern is output after compilation. -C Output the version number of the PCRE2 library, and all available information about the optional features that are included, and then exit with zero exit code. All other options are ignored. If both -C and -LM are present, whichever is first is recognized. -C option Output information about a specific build-time option, then exit. This functionality is intended for use in scripts such as RunTest. The following options output the value and set the exit code as indicated: ebcdic-nl the code for LF (= NL) in an EBCDIC environment: 0x15 or 0x25 0 if used in an ASCII environment exit code is always 0 linksize the configured internal link size (2, 3, or 4) exit code is set to the link size newline the default newline setting: CR, LF, CRLF, ANYCRLF, ANY, or NUL exit code is always 0 bsr the default setting for what \R matches: ANYCRLF or ANY exit code is always 0 The following options output 1 for true or 0 for false, and set the exit code to the same value: backslash-C \C is supported (not locked out) ebcdic compiled for an EBCDIC environment jit just-in-time support is available pcre2-16 the 16-bit library was built pcre2-32 the 32-bit library was built pcre2-8 the 8-bit library was built unicode Unicode support is available If an unknown option is given, an error message is output; the exit code is 0. -d Behave as if each pattern has the debug modifier; the internal form and information about the compiled pattern is output after compilation; -d is equivalent to -b -i. -dfa Behave as if each subject line has the dfa modifier; matching is done using the pcre2_dfa_match() function instead of the default pcre2_match(). -error number[,number,...] Call pcre2_get_error_message() for each of the error numbers in the comma-separated list, display the resulting messages on the standard output, then exit with zero exit code. The numbers may be positive or negative. This is a convenience facility for PCRE2 maintainers. -help Output a brief summary these options and then exit. -i Behave as if each pattern has the info modifier; information about the compiled pattern is given after compilation. -jit Behave as if each pattern line has the jit modifier; after successful compilation, each pattern is passed to the just- in-time compiler, if available. -jitfast Behave as if each pattern line has the jitfast modifier; after successful compilation, each pattern is passed to the just-in-time compiler, if available, and each subject line is passed directly to the JIT matcher via its "fast path". -jitverify Behave as if each pattern line has the jitverify modifier; after successful compilation, each pattern is passed to the just-in-time compiler, if available, and the use of JIT for matching is verified. -LM List modifiers: write a list of available pattern and subject modifiers to the standard output, then exit with zero exit code. All other options are ignored. If both -C and any -Lx options are present, whichever is first is recognized. -LP List properties: write a list of recognized Unicode properties to the standard output, then exit with zero exit code. All other options are ignored. If both -C and any -Lx options are present, whichever is first is recognized. -LS List scripts: write a list of recognized Unicode script names to the standard output, then exit with zero exit code. All other options are ignored. If both -C and any -Lx options are present, whichever is first is recognized. -pattern modifier-list Behave as if each pattern line contains the given modifiers. -q Do not output the version number of pcre2test at the start of execution. -S size On Unix-like systems, set the size of the run-time stack to size mebibytes (units of 1024*1024 bytes). -subject modifier-list Behave as if each subject line contains the given modifiers. -t Run each compile and match many times with a timer, and output the resulting times per compile or match. When JIT is used, separate times are given for the initial compile and the JIT compile. You can control the number of iterations that are used for timing by following -t with a number (as a separate item on the command line). For example, "-t 1000" iterates 1000 times. The default is to iterate 500,000 times. -tm This is like -t except that it times only the matching phase, not the compile phase. -T -TM These behave like -t and -tm, but in addition, at the end of a run, the total times for all compiles and matches are output. -version Output the PCRE2 version number and then exit.
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mysql_config
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mysql_config provides you with useful information for compiling your MySQL client and connecting it to MySQL. It is a shell script, so it is available only on Unix and Unix-like systems. Note pkg-config can be used as an alternative to mysql_config for obtaining information such as compiler flags or link libraries required to compile MySQL applications. For more information, see Building C API Client Programs Using pkg-config[1]. mysql_config supports the following options. • --cflags C Compiler flags to find include files and critical compiler flags and defines used when compiling the libmysqlclient library. The options returned are tied to the specific compiler that was used when the library was created and might clash with the settings for your own compiler. Use --include for more portable options that contain only include paths. • --cxxflags Like --cflags, but for C++ compiler flags. • --include Compiler options to find MySQL include files. • --libs Libraries and options required to link with the MySQL client library. • --libs_r Libraries and options required to link with the thread-safe MySQL client library. In MySQL 8.3, all client libraries are thread-safe, so this option need not be used. The --libs option can be used in all cases. • --plugindir The default plugin directory path name, defined when configuring MySQL. • --port The default TCP/IP port number, defined when configuring MySQL. • --socket The default Unix socket file, defined when configuring MySQL. • --variable=var_name Display the value of the named configuration variable. Permitted var_name values are pkgincludedir (the header file directory), pkglibdir (the library directory), and plugindir (the plugin directory). • --version Version number for the MySQL distribution. If you invoke mysql_config with no options, it displays a list of all options that it supports, and their values: $> mysql_config Usage: /usr/local/mysql/bin/mysql_config [options] Options: --cflags [-I/usr/local/mysql/include/mysql -mcpu=pentiumpro] --cxxflags [-I/usr/local/mysql/include/mysql -mcpu=pentiumpro] --include [-I/usr/local/mysql/include/mysql] --libs [-L/usr/local/mysql/lib/mysql -lmysqlclient -lpthread -lm -lrt -lssl -lcrypto -ldl] --libs_r [-L/usr/local/mysql/lib/mysql -lmysqlclient_r -lpthread -lm -lrt -lssl -lcrypto -ldl] --plugindir [/usr/local/mysql/lib/plugin] --socket [/tmp/mysql.sock] --port [3306] --version [5.8.0-m17] --variable=VAR VAR is one of: pkgincludedir [/usr/local/mysql/include] pkglibdir [/usr/local/mysql/lib] plugindir [/usr/local/mysql/lib/plugin] You can use mysql_config within a command line using backticks to include the output that it produces for particular options. For example, to compile and link a MySQL client program, use mysql_config as follows: gcc -c `mysql_config --cflags` progname.c gcc -o progname progname.o `mysql_config --libs` COPYRIGHT Copyright © 1997, 2023, Oracle and/or its affiliates. This documentation is free software; you can redistribute it and/or modify it only under the terms of the GNU General Public License as published by the Free Software Foundation; version 2 of the License. This documentation is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with the program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA or see http://www.gnu.org/licenses/. NOTES 1. Building C API Client Programs Using pkg-config https://dev.mysql.com/doc/c-api/8.2/en/c-api-building-clients-pkg- config.html SEE ALSO For more information, please refer to the MySQL Reference Manual, which may already be installed locally and which is also available online at http://dev.mysql.com/doc/. AUTHOR Oracle Corporation (http://dev.mysql.com/). MySQL 8.3 11/23/2023 MYSQL_CONFIG(1)
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mysql_config - display options for compiling clients
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mysql_config options
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gdbus-codegen
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fc-validate
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cjpeg
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cjpeg compresses the named image file, or the standard input if no file is named, and produces a JPEG/JFIF file on the standard output. The currently supported input file formats are: PPM (PBMPLUS color format), PGM (PBMPLUS grayscale format), BMP, GIF, and Targa.
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cjpeg - compress an image file to a JPEG file
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cjpeg [ options ] [ filename ]
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All switch names may be abbreviated; for example, -grayscale may be written -gray or -gr. Most of the "basic" switches can be abbreviated to as little as one letter. Upper and lower case are equivalent (thus -BMP is the same as -bmp). British spellings are also accepted (e.g., -greyscale), though for brevity these are not mentioned below. The basic switches are: -quality N[,...] Scale quantization tables to adjust image quality. Quality is 0 (worst) to 100 (best); default is 75. (See below for more info.) -grayscale Create monochrome JPEG file from color input. By saying -grayscale, you'll get a smaller JPEG file that takes less time to process. -rgb Create RGB JPEG file. Using this switch suppresses the conversion from RGB colorspace input to the default YCbCr JPEG colorspace. -optimize Perform optimization of entropy encoding parameters. Without this, default encoding parameters are used. -optimize usually makes the JPEG file a little smaller, but cjpeg runs somewhat slower and needs much more memory. Image quality and speed of decompression are unaffected by -optimize. -progressive Create progressive JPEG file (see below). -targa Input file is Targa format. Targa files that contain an "identification" field will not be automatically recognized by cjpeg; for such files you must specify -targa to make cjpeg treat the input as Targa format. For most Targa files, you won't need this switch. The -quality switch lets you trade off compressed file size against quality of the reconstructed image: the higher the quality setting, the larger the JPEG file, and the closer the output image will be to the original input. Normally you want to use the lowest quality setting (smallest file) that decompresses into something visually indistinguishable from the original image. For this purpose the quality setting should generally be between 50 and 95 (the default is 75) for photographic images. If you see defects at -quality 75, then go up 5 or 10 counts at a time until you are happy with the output image. (The optimal setting will vary from one image to another.) -quality 100 will generate a quantization table of all 1's, minimizing loss in the quantization step (but there is still information loss in subsampling, as well as roundoff error.) For most images, specifying a quality value above about 95 will increase the size of the compressed file dramatically, and while the quality gain from these higher quality values is measurable (using metrics such as PSNR or SSIM), it is rarely perceivable by human vision. In the other direction, quality values below 50 will produce very small files of low image quality. Settings around 5 to 10 might be useful in preparing an index of a large image library, for example. Try -quality 2 (or so) for some amusing Cubist effects. (Note: quality values below about 25 generate 2-byte quantization tables, which are considered optional in the JPEG standard. cjpeg emits a warning message when you give such a quality value, because some other JPEG programs may be unable to decode the resulting file. Use -baseline if you need to ensure compatibility at low quality values.) The -quality option has been extended in this version of cjpeg to support separate quality settings for luminance and chrominance (or, in general, separate settings for every quantization table slot.) The principle is the same as chrominance subsampling: since the human eye is more sensitive to spatial changes in brightness than spatial changes in color, the chrominance components can be quantized more than the luminance components without incurring any visible image quality loss. However, unlike subsampling, this feature reduces data in the frequency domain instead of the spatial domain, which allows for more fine- grained control. This option is useful in quality-sensitive applications, for which the artifacts generated by subsampling may be unacceptable. The -quality option accepts a comma-separated list of parameters, which respectively refer to the quality levels that should be assigned to the quantization table slots. If there are more q-table slots than parameters, then the last parameter is replicated. Thus, if only one quality parameter is given, this is used for both luminance and chrominance (slots 0 and 1, respectively), preserving the legacy behavior of cjpeg v6b and prior. More (or customized) quantization tables can be set with the -qtables option and assigned to components with the -qslots option (see the "wizard" switches below.) JPEG files generated with separate luminance and chrominance quality are fully compliant with standard JPEG decoders. CAUTION: For this setting to be useful, be sure to pass an argument of -sample 1x1 to cjpeg to disable chrominance subsampling. Otherwise, the default subsampling level (2x2, AKA "4:2:0") will be used. The -progressive switch creates a "progressive JPEG" file. In this type of JPEG file, the data is stored in multiple scans of increasing quality. If the file is being transmitted over a slow communications link, the decoder can use the first scan to display a low-quality image very quickly, and can then improve the display with each subsequent scan. The final image is exactly equivalent to a standard JPEG file of the same quality setting, and the total file size is about the same --- often a little smaller. Switches for advanced users: -precision N Create JPEG file with N-bit data precision. N is 8, 12, or 16; default is 8. If N is 16, then -lossless must also be specified. Caution: 12-bit and 16-bit JPEG is not yet widely implemented, so many decoders will be unable to view a 12-bit or 16-bit JPEG file at all. -lossless psv[,Pt] Create a lossless JPEG file using the specified predictor selection value (1 through 7) and optional point transform (0 through precision - 1, where precision is the JPEG data precision in bits). A point transform value of 0 (the default) is necessary in order to create a fully lossless JPEG file. (A non-zero point transform value right-shifts the input samples by the specified number of bits, which is effectively a form of lossy color quantization.) Caution: lossless JPEG is not yet widely implemented, so many decoders will be unable to view a lossless JPEG file at all. In most cases, compressing and decompressing a lossless JPEG file is considerably slower than compressing and decompressing a lossy JPEG file, and lossless JPEG files are much larger than lossy JPEG files. Also note that the following features will be unavailable when compressing or decompressing a lossless JPEG file: - Quality/quantization table selection - Color space conversion (the JPEG image will use the same color space as the input image) - Color quantization - DCT/IDCT algorithm selection - Smoothing - Downsampling/upsampling - IDCT scaling - Partial image decompression - Transformations using jpegtran Any switches used to enable or configure those features will be ignored. -arithmetic Use arithmetic coding. Caution: arithmetic coded JPEG is not yet widely implemented, so many decoders will be unable to view an arithmetic coded JPEG file at all. -dct int Use accurate integer DCT method (default). -dct fast Use less accurate integer DCT method [legacy feature]. When the Independent JPEG Group's software was first released in 1991, the compression time for a 1-megapixel JPEG image on a mainstream PC was measured in minutes. Thus, the fast integer DCT algorithm provided noticeable performance benefits. On modern CPUs running libjpeg-turbo, however, the compression time for a 1-megapixel JPEG image is measured in milliseconds, and thus the performance benefits of the fast algorithm are much less noticeable. On modern x86/x86-64 CPUs that support AVX2 instructions, the fast and int methods have similar performance. On other types of CPUs, the fast method is generally about 5-15% faster than the int method. For quality levels of 90 and below, there should be little or no perceptible quality difference between the two algorithms. For quality levels above 90, however, the difference between the fast and int methods becomes more pronounced. With quality=97, for instance, the fast method incurs generally about a 1-3 dB loss in PSNR relative to the int method, but this can be larger for some images. Do not use the fast method with quality levels above 97. The algorithm often degenerates at quality=98 and above and can actually produce a more lossy image than if lower quality levels had been used. Also, in libjpeg-turbo, the fast method is not fully accelerated for quality levels above 97, so it will be slower than the int method. -dct float Use floating-point DCT method [legacy feature]. The float method does not produce significantly more accurate results than the int method, and it is much slower. The float method may also give different results on different machines due to varying roundoff behavior, whereas the integer methods should give the same results on all machines. -icc file Embed ICC color management profile contained in the specified file. -restart N Emit a JPEG restart marker every N MCU rows, or every N MCU blocks (samples in lossless mode) if "B" is attached to the number. -restart 0 (the default) means no restart markers. -smooth N Smooth the input image to eliminate dithering noise. N, ranging from 1 to 100, indicates the strength of smoothing. 0 (the default) means no smoothing. -maxmemory N Set limit for amount of memory to use in processing large images. Value is in thousands of bytes, or millions of bytes if "M" is attached to the number. For example, -max 4m selects 4000000 bytes. If more space is needed, an error will occur. -outfile name Send output image to the named file, not to standard output. -memdst Compress to memory instead of a file. This feature was implemented mainly as a way of testing the in-memory destination manager (jpeg_mem_dest()), but it is also useful for benchmarking, since it reduces the I/O overhead. -report Report compression progress. -strict Treat all warnings as fatal. Enabling this option will cause the compressor to abort if an LZW-compressed GIF input image contains incomplete or corrupt image data. -verbose Enable debug printout. More -v's give more output. Also, version information is printed at startup. -debug Same as -verbose. -version Print version information and exit. The -restart option inserts extra markers that allow a JPEG decoder to resynchronize after a transmission error. Without restart markers, any damage to a compressed file will usually ruin the image from the point of the error to the end of the image; with restart markers, the damage is usually confined to the portion of the image up to the next restart marker. Of course, the restart markers occupy extra space. We recommend -restart 1 for images that will be transmitted across unreliable networks such as Usenet. The -smooth option filters the input to eliminate fine-scale noise. This is often useful when converting dithered images to JPEG: a moderate smoothing factor of 10 to 50 gets rid of dithering patterns in the input file, resulting in a smaller JPEG file and a better-looking image. Too large a smoothing factor will visibly blur the image, however. Switches for wizards: -baseline Force baseline-compatible quantization tables to be generated. This clamps quantization values to 8 bits even at low quality settings. (This switch is poorly named, since it does not ensure that the output is actually baseline JPEG. For example, you can use -baseline and -progressive together.) -qtables file Use the quantization tables given in the specified text file. -qslots N[,...] Select which quantization table to use for each color component. -sample HxV[,...] Set JPEG sampling factors for each color component. -scans file Use the scan script given in the specified text file. The "wizard" switches are intended for experimentation with JPEG. If you don't know what you are doing, don't use them. These switches are documented further in the file wizard.txt.
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This example compresses the PPM file foo.ppm with a quality factor of 60 and saves the output as foo.jpg: cjpeg -quality 60 foo.ppm > foo.jpg HINTS Color GIF files are not the ideal input for JPEG; JPEG is really intended for compressing full-color (24-bit) images. In particular, don't try to convert cartoons, line drawings, and other images that have only a few distinct colors. GIF works great on these, JPEG does not. If you want to convert a GIF to JPEG, you should experiment with cjpeg's -quality and -smooth options to get a satisfactory conversion. -smooth 10 or so is often helpful. Avoid running an image through a series of JPEG compression/decompression cycles. Image quality loss will accumulate; after ten or so cycles the image may be noticeably worse than it was after one cycle. It's best to use a lossless format while manipulating an image, then convert to JPEG format when you are ready to file the image away. The -optimize option to cjpeg is worth using when you are making a "final" version for posting or archiving. It's also a win when you are using low quality settings to make very small JPEG files; the percentage improvement is often a lot more than it is on larger files. (At present, -optimize mode is always selected when generating progressive JPEG files.) ENVIRONMENT JPEGMEM If this environment variable is set, its value is the default memory limit. The value is specified as described for the -maxmemory switch. JPEGMEM overrides the default value specified when the program was compiled, and itself is overridden by an explicit -maxmemory. SEE ALSO djpeg(1), jpegtran(1), rdjpgcom(1), wrjpgcom(1) ppm(5), pgm(5) Wallace, Gregory K. "The JPEG Still Picture Compression Standard", Communications of the ACM, April 1991 (vol. 34, no. 4), pp. 30-44. AUTHOR Independent JPEG Group This file was modified by The libjpeg-turbo Project to include only information relevant to libjpeg-turbo, to wordsmith certain sections, and to describe features not present in libjpeg. ISSUES Not all variants of BMP and Targa file formats are supported. The -targa switch is not a bug, it's a feature. (It would be a bug if the Targa format designers had not been clueless.) 14 Dec 2023 CJPEG(1)
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autom4te
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Run GNU M4 on the FILES, avoiding useless runs. Output the traces if tracing, the frozen file if freezing, otherwise the expansion of the FILES. If some of the FILES are named 'FILE.m4f' they are considered to be M4 frozen files of all the previous files (which are therefore not loaded). If 'FILE.m4f' is not found, then 'FILE.m4' will be used, together with all the previous files. Some files may be optional, i.e., will only be processed if found in the include path, but then must end in '.m4?'; the question mark is not part of the actual file name. Operation modes: -h, --help print this help, then exit -V, --version print version number, then exit -v, --verbose verbosely report processing -d, --debug don't remove temporary files -o, --output=FILE save output in FILE (defaults to '-', stdout) -f, --force don't rely on cached values -W, --warnings=CATEGORY report the warnings falling in CATEGORY (comma-separated list accepted) -l, --language=LANG specify the set of M4 macros to use -C, --cache=DIRECTORY preserve results for future runs in DIRECTORY --no-cache disable the cache -m, --mode=OCTAL change the non trace output file mode (0666) -M, --melt don't use M4 frozen files Languages include: 'Autoconf' create Autoconf configure scripts 'Autotest' create Autotest test suites 'M4sh' create M4sh shell scripts 'M4sugar' create M4sugar output Warning categories are: cross cross compilation issues gnu GNU coding standards (default in gnu and gnits modes) obsolete obsolete features or constructions (default) override user redefinitions of Automake rules or variables portability portability issues (default in gnu and gnits modes) portability-recursive nested Make variables (default with -Wportability) extra-portability extra portability issues related to obscure tools syntax dubious syntactic constructs (default) unsupported unsupported or incomplete features (default) -W also understands: all turn on all the warnings none turn off all the warnings no-CATEGORY turn off warnings in CATEGORY error treat all enabled warnings as errors The environment variables 'M4' and 'WARNINGS' are honored. Library directories: -B, --prepend-include=DIR prepend directory DIR to search path -I, --include=DIR append directory DIR to search path Tracing: -t, --trace=MACRO[:FORMAT] report the MACRO invocations -p, --preselect=MACRO prepare to trace MACRO in a future run Freezing: -F, --freeze produce an M4 frozen state file for FILES FORMAT defaults to '$f:$l:$n:$%', and can use the following escapes: $$ literal $ $f file where macro was called $l line where macro was called $d nesting depth of macro call $n name of the macro $NUM argument NUM, unquoted and with newlines $SEP@ all arguments, with newlines, quoted, and separated by SEP $SEP* all arguments, with newlines, unquoted, and separated by SEP $SEP% all arguments, without newlines, unquoted, and separated by SEP SEP can be empty for the default (comma for @ and *, colon for %), a single character for that character, or {STRING} to use a string. AUTHOR Written by Akim Demaille. REPORTING BUGS Report bugs to <bug-autoconf@gnu.org>, or via Savannah: <https://savannah.gnu.org/support/?group=autoconf>. COPYRIGHT Copyright © 2023 Free Software Foundation, Inc. License GPLv3+/Autoconf: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>, <https://gnu.org/licenses/exceptions.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. SEE ALSO autoconf(1), automake(1), autoreconf(1), autoupdate(1), autoheader(1), autoscan(1), config.guess(1), config.sub(1), ifnames(1), libtool(1). The full documentation for Autoconf is maintained as a Texinfo manual. To read the manual locally, use the command info autoconf You can also consult the Web version of the manual at <https://gnu.org/software/autoconf/manual/>. GNU Autoconf 2.72 December 2023 AUTOM4TE(1)
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autom4te - Generate files and scripts thanks to M4
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autom4te [OPTION]... [FILES]
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mpg123
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mpg123 reads one or more files (or standard input if ``-'' is specified) or URLs and plays them on the audio device (default) or outputs them to stdout. file/URL is assumed to be an MPEG audio bit stream. OPERANDS The following operands are supported: file(s) The path name(s) of one or more input files. They must be valid MPEG-1.0/2.0/2.5 audio layer 1, 2 or 3 bit streams. If a dash ``-'' is specified, MPEG data will be read from the standard input. Furthermore, any name starting with ``http://'' or ``https://'' is recognized as URL (see next section), while a leading ``file://'' is being stripped for normal local file access, for consistency (since mpg123 1.30.1).
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mpg123 - play audio MPEG 1.0/2.0/2.5 stream (layers 1, 2 and 3)
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mpg123 [ options ] file-or-URL...
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mpg123 options may be either the traditional POSIX one letter options, or the GNU style long options. POSIX style options start with a single ``-'', while GNU long options start with ``--''. Option arguments (if needed) follow separated by whitespace (not ``=''). Note that some options can be absent from your installation when disabled in the build process. INPUT OPTIONS -k num, --skip num Skip first num frames. By default the decoding starts at the first frame. -n num, --frames num Decode only num frames. By default the complete stream is decoded. --fuzzy Enable fuzzy seeks (guessing byte offsets or using approximate seek points from Xing TOC). Without that, seeks need a first scan through the file before they can jump at positions. You can decide here: sample-accurate operation with gapless features or faster (fuzzy) seeking. -y, --no-resync Do NOT try to resync and continue decoding if an error occurs in the input file. Normally, mpg123 tries to keep the playback alive at all costs, including skipping invalid material and searching new header when something goes wrong. With this switch you can make it bail out on data errors (and perhaps spare your ears a bad time). Note that this switch has been renamed from --resync. The old name still works, but is not advertised or recommended to use (subject to removal in future). -F, --no-frankenstein Disable support for Frankenstein streams. Normally, mpg123 stays true to the concept of MPEG audio being just a concatenation of MPEG frames. It will continue decoding even if the type of MPEG frames varies wildly. With this switch, it will only decode the input as long as it does not change its character (from layer I to layer III, changing sampling rate, from mono to stereo), silently assuming end of stream on such occasion. The switch also stops decoding of compatible MPEG frames if there was an Info frame (Xing header, Lame tag) that contained a length of the track in MPEG frames. This comes a bit closer to the notion of a MP3 file as a defined collection of MPEG frames that belong together, but gets rid of the flexibility that can be fun at times but mostly is hell for the programmer of the parser and decoder ... --network backend Select network backend (helper program), choices are usually auto, wget, and curl. Auto means to try the first available backend. --resync-limit bytes Set number of bytes to search for valid MPEG data once lost in stream; <0 means search whole stream. If you know there are huge chunks of invalid data in your files... here is your hammer. Note: Only since version 1.14 this also increases the amount of junk skipped on beginning. -u auth, --auth auth HTTP authentication to use when receiving files via HTTP. The format used is user:password. Mpg123 will clear this quickly, but it may still appear in sight of other users or even just in your shell history. You may seek alternative ways to specify that to your network backend. --auth-file authfile Provide the authentication info via given file instead of command line directly. --ignore-mime Ignore MIME types given by HTTP server. If you know better and want mpg123 to decode something the server thinks is image/png, then just do it. --no-icy-meta Do not accept ICY meta data. --streamdump filename Dump a copy of the input data (as read by libmpg123) to the given file. This enables you to store a web stream to disk while playing, or just create a concatenation of the local files you play for ... why not? --icy-interval bytes This setting enables you to play a stream dump containing ICY metadata at the given interval in bytes (the value of the icy- metaint HTTP response header). Without it, such a stream will play, but will cause regular decoding glitches with resync. --no-seekbuffer Disable the default micro-buffering of non-seekable streams that gives the parser a safer footing. -@ file, --list file Read filenames and/or URLs of MPEG audio streams from the specified file in addition to the ones specified on the command line (if any). Note that file can be either an ordinary file, a dash ``-'' to indicate that a list of filenames/URLs is to be read from the standard input, or an URL pointing to a an appropriate list file. Note: only one -@ option can be used (if more than one is specified, only the last one will be recognized). Furthermore, for HTTP resources, the MIME type information will be used to re-open an actual MPEG stream as such instead of treating it as playlist file. So you could just always use -@ for web resources without bothering if it is a playlist or already the resolved stream address. -l n, --listentry n Of the playlist, play specified entry only. n is the number of entry starting at 1. A value of 0 is the default and means playing the whole list, a negative value means showing of the list of titles with their numbers... --continue Enable playlist continuation mode. This changes frame skipping to apply only to the first track and also continues to play following tracks in playlist after the selected one. Also, the option to play a number of frames only applies to the whole playlist. Basically, this tries to treat the playlist more like one big stream (like, an audio book). The current track number in list (1-based) and frame number (0-based) are printed at exit (useful if you interrupted playback and want to continue later). Note that the continuation info is printed to standard output unless the switch for piping audio data to standard out is used. Also, it really makes sense to work with actual playlist files instead of lists of file names as arguments, to keep track positions consistent. --loop times for looping track(s) a certain number of times, < 0 means infinite loop (not with --random!). --keep-open For remote control mode: Keep loaded file open after reaching end. --timeout seconds Timeout in (integer) seconds before declaring a stream dead (if <= 0, wait forever). -z, --shuffle Shuffle play. Randomly shuffles the order of files specified on the command line, or in the list file. -Z, --random Continuous random play. Keeps picking a random file from the command line or the play list. Unlike shuffle play above, random play never ends, and plays individual songs more than once. -i, --index Index / scan through the track before playback. This fills the index table for seeking (if enabled in libmpg123) and may make the operating system cache the file contents for smoother operating on playback. --index-size size Set the number of entries in the seek frame index table. --preframes num Set the number of frames to be read as lead-in before a seeked- to position. This serves to fill the layer 3 bit reservoir, which is needed to faithfully reproduce a certain sample at a certain position. Note that for layer 3, a minimum of 1 is enforced (because of frame overlap), and for layer 1 and 2, this is limited to 2 (no bit reservoir in that case, but engine spin- up anyway). OUTPUT and PROCESSING OPTIONS -o module, --output module Select audio output module. You can provide a comma-separated list to use the first one that works. Also see -a. --list-modules List the available modules. --list-devices List the available output devices for given output module. If there is no functionality to list devices in the chosen module, an error will be printed and mpg123 will exit with a non-zero code. -a dev, --audiodevice dev Specify the audio device to use. The default as well as the possible values depend on the active output. For the JACK output, a comma-separated list of ports to connect to (for each channel) can be specified. -s, --stdout The decoded audio samples are written to standard output, instead of playing them through the audio device. This option must be used if your audio hardware is not supported by mpg123. The output format per default is raw (headerless) linear PCM audio data, 16 bit, stereo, host byte order (you can force mono or 8bit). -O file, --outfile Write raw output into a file (instead of simply redirecting standard output to a file with the shell). -w file, --wav Write output as WAV file. This will cause the MPEG stream to be decoded and saved as file file , or standard output if - is used as file name. You can also use --au and --cdr for AU and CDR format, respectively. Note that WAV/AU writing to non-seekable files, or redirected stdout, needs some thought. Since 1.16.0, the logic changed to writing the header with the first actual data. This avoids spurious WAV headers in a pipe, for example. The result of decoding nothing to WAV/AU is a file consisting just of the header when it is seekable and really nothing when not (not even a header). Correctly writing data with prophetic headers to stdout is no easy business. --au file Does not play the MPEG file but writes it to file in SUN audio format. If - is used as the filename, the AU file is written to stdout. See paragraph about WAV writing for header fun with non- seekable streams. --cdr file Does not play the MPEG file but writes it to file as a CDR file. If - is used as the filename, the CDR file is written to stdout. --reopen Forces reopen of the audiodevice after ever song --cpu decoder-type Selects a certain decoder (optimized for specific CPU), for example i586 or MMX. The list of available decoders can vary; depending on the build and what your CPU supports. This option is only available when the build actually includes several optimized decoders. --test-cpu Tests your CPU and prints a list of possible choices for --cpu. --list-cpu Lists all available decoder choices, regardless of support by your CPU. -g gain, --gain gain [DEPRECATED] Set audio hardware output gain (default: don't change). The unit of the gain value is hardware and output module dependent. (This parameter is only provided for backwards compatibility and may be removed in the future without prior notice. Use the audio player for playing and a mixer app for mixing, UNIX style!) -f factor, --scale factor Change scale factor (default: 32768). --rva-mix, --rva-radio Enable RVA (relative volume adjustment) using the values stored for ReplayGain radio mode / mix mode with all tracks roughly equal loudness. The first valid information found in ID3V2 Tags (Comment named RVA or the RVA2 frame) or ReplayGain header in Lame/Info Tag is used. --rva-album, --rva-audiophile Enable RVA (relative volume adjustment) using the values stored for ReplayGain audiophile mode / album mode with usually the effect of adjusting album loudness but keeping relative loudness inside album. The first valid information found in ID3V2 Tags (Comment named RVA_ALBUM or the RVA2 frame) or ReplayGain header in Lame/Info Tag is used. -0, --single0; -1, --single1 Decode only channel 0 (left) or channel 1 (right), respectively. These options are available for stereo MPEG streams only. -m, --mono, --mix, --singlemix Mix both channels / decode mono. It takes less CPU time than full stereo decoding. --stereo Force stereo output -r rate, --rate rate Set sample rate (default: automatic). You may want to change this if you need a constant bitrate independent of the mpeg stream rate. mpg123 automagically converts the rate. You should then combine this with --stereo or --mono. --resample method Set resampling method to employ if forcing an output rate. Choices (case-insensitive) are NtoM, dirty, and fine. The fine resampler is the default. It employs libsyn123's low-latency fairly efficient resampler to postprocess the output from libmpg123 instead of the fast but very crude NtoM decoder (drop sample method) that mpg123 offers since decades. If you are really low on CPU time, choose NtoM, as the resampler usually needs more time than the MPEG decoder itself. The mpg123 program is smart enough to combine the 2to1 or 4to1 downsampling modes with the postprocessing for extreme downsampling. -2, --2to1; -4, --4to1 Performs a downsampling of ratio 2:1 (22 kHz from 44.1 kHz) or 4:1 (11 kHz) on the output stream, respectively. Saves some CPU cycles, but of course throws away the high frequencies, as the decoder does not bother producing them. --pitch value Set a pitch change (speedup/down, 0 is neutral; 0.05 is 5% speedup). When not enforcing an output rate, this changes the output sampling rate, so it only works in the range your audio system/hardware supports. When you combine this with a fixed output rate, it modifies a software resampling ratio instead. --8bit Forces 8bit output --float Forces f32 encoding -e enc, --encoding enc Choose output sample encoding. Possible values look like f32 (32-bit floating point), s32 (32-bit signed integer), u32 (32-bit unsigned integer) and the variants with different numbers of bits (s24, u24, s16, u16, s8, u8) and also special variants like ulaw and alaw 8-bit. See the output of mpg123's longhelp for actually available encodings. -d n, --doublespeed n Only play every n'th frame. This will cause the MPEG stream to be played n times faster, which can be used for special effects. Can also be combined with the --halfspeed option to play 3 out of 4 frames etc. Don't expect great sound quality when using this option. -h n, --halfspeed n Play each frame n times. This will cause the MPEG stream to be played at 1/n'th speed (n times slower), which can be used for special effects. Can also be combined with the --doublespeed option to double every third frame or things like that. Don't expect great sound quality when using this option. -E file, --equalizer Enables equalization, taken from file. The file needs to contain 32 lines of data, additional comment lines may be prefixed with #. Each data line consists of two floating-point entries, separated by whitespace. They specify the multipliers for left and right channel of a certain frequency band, respectively. The first line corresponds to the lowest, the 32nd to the highest frequency band. Note that you can control the equalizer interactively with the generic control interface. Also note that these are the 32 bands of the MPEG codec, not spaced like you would see for a usual graphic equalizer. The upside is that there is zero computational cost in addition to decoding. The downside is that you roughly have bass in band 0, (upper) mids in band 1, treble in all others. --gapless Enable code that cuts (junk) samples at beginning and end of tracks, enabling gapless transitions between MPEG files when encoder padding and codec delays would prevent it. This is enabled per default beginning with mpg123 version 1.0.0 . --no-gapless Disable the gapless code. That gives you MP3 decodings that include encoder delay and padding plus mpg123's decoder delay. --no-infoframe Do not parse the Xing/Lame/VBR/Info frame, decode it instead just like a stupid old MP3 hardware player. This implies disabling of gapless playback as the necessary information is in said metadata frame. -D n, --delay n Insert a delay of n seconds before each track. -o h, --headphones Direct audio output to the headphone connector (some hardware only; AIX, HP, SUN). -o s, --speaker Direct audio output to the speaker (some hardware only; AIX, HP, SUN). -o l, --lineout Direct audio output to the line-out connector (some hardware only; AIX, HP, SUN). -b size, --buffer size Use an audio output buffer of size Kbytes. This is useful to bypass short periods of heavy system activity, which would normally cause the audio output to be interrupted. You should specify a buffer size of at least 1024 (i.e. 1 Mb, which equals about 6 seconds of audio data) or more; less than about 300 does not make much sense. The default is 0, which turns buffering off. --preload fraction Wait for the buffer to be filled to fraction before starting playback (fraction between 0 and 1). You can tune this prebuffering to either get faster sound to your ears or safer uninterrupted web radio. Default is 0.2 (wait for 20 % of buffer to be full, changed from 1 in version 1.23). --devbuffer seconds Set device buffer in seconds; <= 0 means default value. This is the small buffer between the application and the audio backend, possibly directly related to hardware buffers. --smooth Keep buffer over track boundaries -- meaning, do not empty the buffer between tracks for possibly some added smoothness. MISC OPTIONS -t, --test Test mode. The audio stream is decoded, but no output occurs. -c, --check Check for filter range violations (clipping), and report them for each frame if any occur. -v, --verbose Increase the verbosity level. For example, displays the frame numbers during decoding. -q, --quiet Quiet. Suppress diagnostic messages. -C, --control Enable terminal control keys. This is enabled automatically if a terminal is detected. By default use 's' or the space bar to stop/restart (pause, unpause) playback, 'f' to jump forward to the next song, 'b' to jump back to the beginning of the song, ',' to rewind, '.' to fast forward, and 'q' to quit. Type 'h' for a full list of available controls. The A-B loop feature with key 'o' changes the preset loop interval to the interval between two presses of 'o', the third press (or 'p') ending the looped playback. The key 'p' will use the updated loop interval after that. --no-control Disable terminal control even if terminal is detected. --title In an xterm, rxvt, screen, iris-ansi (compatible, TERM environment variable is examined), change the window's title to the name of song currently playing. --pauseloop seconds Set the length of the loop interval in terminal control fixed looping mode, away from the default of 0.5 seconds, as a floating point number. This value can be overwritten at runtime using the A-B loop feature. --name name Set the name of this instance, possibly used in various places. This sets the client name for JACK output. --long-tag Display ID3 tag info always in long format with one line per item (artist, title, ...) --utf8 Regardless of environment, print metadata in UTF-8 (otherwise, when not using UTF-8 locale, you'll get ASCII stripdown). -R, --remote Activate generic control interface. mpg123 will then read and execute commands from stdin. Basic usage is ``load <filename> '' to play some file and the obvious ``pause'', ``command. ``jump <frame>'' will jump/seek to a given point (MPEG frame number). Issue ``help'' to get a full list of commands and syntax. --remote-err Print responses for generic control mode to standard error, not standard out. This is automatically triggered when using -s. --fifo path Create a fifo / named pipe on the given path and use that for reading commands instead of standard input. --aggressive Tries to get higher priority -T, --realtime Tries to gain realtime priority. This option usually requires root privileges to have any effect. -?, --help Shows short usage instructions. --longhelp Shows long usage instructions. --version Print the version string. --libversion Print version information on the mpg123 libraries being used (libmpg123, libout123, libsyn123). HTTP SUPPORT In addition to reading MPEG audio streams from ordinary files and from the standard input, mpg123 supports retrieval of MPEG audio streams or playlists via the HTTP protocol, which is used in the World Wide Web (WWW). Such files are specified using a so-called URL, which starts with http:// or https://. When a file with that prefix is encountered, mpg123 since 1.30.0 will by default call an external helper program (either wget(1) or curl(1), see the --network option) to retrieve the resource. You can configure access via a proxy server using the standard environment variables those programs support. The --proxy option that mpg123 before 1.30.0 used for its internal network code is gone in the default build now and will probably disappear for good with 1.31.1. Note that, in order to play MPEG audio files from a WWW server, it is necessary that the connection to that server is fast enough. For example, a 128 kbit/s MPEG file requires the network connection to be at least 128 kbit/s (16 kbyte/s) plus protocol overhead. If you suffer from short network outages, you should try the -b option (buffer) to bypass such outages. If your network connection is generally not fast enough to retrieve MPEG audio files in realtime, you can first download the files to your local harddisk (e.g. using wget(1)) and then play them from there. Streams with embedded ICY metadata are supported, the interval being communicated via HTTP headers or --icy-interval. INTERRUPT When in terminal control mode, you can quit via pressing the q key, while any time you can abort mpg123 by pressing Ctrl-C. If not in terminal control mode, this will skip to the next file (if any). If you want to abort playing immediately in that case, press Ctrl-C twice in short succession (within about one second). Note that the result of quitting mpg123 pressing Ctrl-C might not be audible immediately, due to audio data buffering in the audio device. This delay is system dependent, but it is usually not more than one or two seconds. PLAYBACK STATUS LINE In verbose mode, mpg123 updates a line with various information centering around the current playback position. On any decent terminal, the line also works as a progress bar in the current file by reversing video for a fraction of the line according to the current position. An example for a full line is this: > 0291+0955 00:01.68+00:28.22 [00:05.30] mix 100=085 192 kb/s 576 B acc 18 clip p+0.014 The information consists of, in order: > single-character playback state (``>'' for playing, ``='' for pausing/looping, ``_'' for stopped) 0291+0955 current frame offset and number of remaining frames after the plus sign 00:01.68+00:28.22 current position from and remaining time in human terms (hours, minutes, seconds) [00:05.30] fill of the output buffer in terms of playback time, if the buffer is enabled mix selected RVA mode (possible values: mix, alb (album), and --- (neutral, off)) 100=085 set volume and the RVA-modified effective volume after the equal sign 192 kb/s current bitrate 576 B size of current frame in bytes acc if positions are accurate, possible values are ``acc'' for accurate positions or ``fuz'' for fuzzy (with guessed byte offsets using mean frame size) 18 clip amount of clipped samples, non-zero only if decoder reports that (generic does, some optimized ones not) p+0.014 pitch change (increased/decreased playback sampling rate on user request) NOTES MPEG audio decoding requires a good deal of CPU performance, especially layer-3. To decode it in realtime, you should have at least an i486DX4, Pentium, Alpha, SuperSparc or equivalent processor. You can also use the -m option to decode mono only, which reduces the CPU load somewhat for layer-3 streams. See also the -2 and -4 options. If everything else fails, have mpg123 decode to a file and then use an appropriate utility to play that file with less CPU load. Most probably you can configure mpg123 to produce a format suitable for your audio device (see above about encodings and sampling rates). If your system is generally fast enough to decode in realtime, but there are sometimes periods of heavy system load (such as cronjobs, users logging in remotely, starting of ``big'' programs etc.) causing the audio output to be interrupted, then you should use the -b option to use a buffer of reasonable size (at least 1000 Kbytes). EXIT CODE Up to version 1.25.x, mpg123 always returned exit code 0 also for complete junk on the input side. Fatal errors were only considered for output. With version 1.26.0, this changed to the behaviour described below. When not using the remote control interface (which returns input errors as text messages), the process exit code is zero (success) only if all tracks in a playlist had at least one frame parsed, even if it did not decode cleanly, or are empty, MPEG-wise (perhaps only metadata, or really an empty file). When you decode nothing, nothing is the result and that is fine. When a track later aborts because of parser errors or breakdown of the network communication, this is treated as end of a track, but does not make the process as such fail. One really bad (or non-existing) stream in the playlist results in a non-zero error code, consistent with other UNIX tools. An error in audio output results in the process ending with a non-zero exit code immediately, regardless of how much data has been successfully played before. The forgiveness is only on the input side. BUGS Mostly MPEG-1 layer 2 and 3 are tested in real life. Please report any issues and provide test files to help fixing them. No CRC error checking is performed. But the decoder is built and tested to behave nicely with damaged streams. Mostly, damaged frames will just be silent. Some platforms lack audio hardware support; you may be able to use the -s switch to feed the decoded data to a program that can play it on your audio device. AUTHORS Maintainer: Thomas Orgis <maintainer@mpg123.org>, <thomas@orgis.org> Original Creator: Michael Hipp Uses code or ideas from various people, see the AUTHORS file accompanying the source code. LICENSE mpg123 is licensed under the GNU Lesser/Library General Public License, LGPL, version 2.1 . WEBSITE http://www.mpg123.org http://sourceforge.net/projects/mpg123 11 Jul 2022 mpg123(1)
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nvim
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nvim is a text editor based on Vim. Start nvim followed by any number of options and/or files: nvim [options] [file ...] Commands in nvim begin with colon (‘:’). Type ":help subject" to get help on a specific subject. Use <Tab> and CTRL-D to complete subjects (":help cmdline-completion"). The "quickref" help section is a condensed reference of editor features: :help quickref If you are new to Vim/Nvim, start with the 30-minute tutorial: :Tutor After installing/updating Nvim, it's a good idea to run the self-check: :checkhealth file ... File(s) to edit. Opens one buffer per file. To switch between buffers, use the :next and :previous commands. - Reads text from standard input until EOF, then opens a buffer with that text. User input is read from standard error, which should be a terminal.
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nvim – edit text
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nvim [options] [file ...] nvim [options] - nvim [options] -t tag nvim [options] -q [errorfile]
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-t tag Finds tag in the tags file, the associated file becomes the current file and the associated command is executed. Cursor is positioned at the tag location in the file. :help tag-commands -q [errorfile] QuickFix mode. Display the first error in errorfile. If errorfile is omitted, the value of the 'errorfile' option is used (defaults to errors.err). Further errors can be jumped to with the :cnext command. :help quickfix -- End of options. Remaining arguments are treated as literal file names, including filenames starting with hyphen (‘-’). -e Ex mode, reading stdin as Ex commands. :help Ex-mode -E Ex mode, reading stdin as text. :help Ex-mode -es Silent (non-interactive) Ex mode, reading stdin as Ex commands. Useful for scripting because it does NOT start a UI, unlike -e. :help silent-mode -Es Silent (non-interactive) Ex mode, reading stdin as text. Useful for scripting because it does NOT start a UI, unlike -E. :help silent-mode -d Diff mode. Show the difference between two to eight files, similar to sdiff(1). :help diff -R Read-only mode. Sets the 'readonly' option. Implies -n. Buffers can still be edited, but cannot be written to disk if already associated with a file. To overwrite a file, add an exclamation mark to the relevant Ex command, such as :w!. :help 'readonly' -m Resets the 'write' option, to disable file modifications. Writing to a file is disabled, but buffers can still be modified. -M Resets the 'write' and 'modifiable' options, to disable file and buffer modifications. -b Binary mode. :help edit-binary -A Arabic mode. Sets the 'arabic' option. -H Hebrew mode. Sets the 'hkmap' and 'rightleft' options. -V[N][file] Verbose mode. Prints debug messages. N is the 'verbose' level, defaults to 10. If file is specified, append messages to file instead of printing them. :help 'verbose' -D Vimscript debug mode. Started when executing the first command from a script. :help debug-mode -n Disable the use of swap files. Sets the 'updatecount' option to 0. Can be useful for editing files on a slow medium. -r [file] Recovery mode. If file is omitted then list swap files with recovery information. Otherwise the swap file file is used to recover a crashed session. The swap file has the same name as the file it's associated with, but with ‘.swp’ appended. :help recovery -L [file] Alias for -r. -u vimrc Use vimrc instead of the default ~/.config/nvim/init.vim. If vimrc is NORC, do not load any initialization files (except plugins). If vimrc is NONE, loading plugins is also skipped. :help initialization -i shada Use shada instead of the default ~/.local/state/nvim/shada/main.shada. If shada is NONE, do not read or write a ShaDa file. :help shada --noplugin Skip loading plugins. Implied by -u NONE. --clean Start Nvim with "factory defaults" (no user config and plugins, no shada). :help --clean -o[N] Open N windows stacked horizontally. If N is omitted, open one window for each file. If N is less than the number of file arguments, allocate windows for the first N files and hide the rest. -O[N] Like -o, but tile windows vertically. -p[N] Like -o, but for tab pages. +[linenum] For the first file, position the cursor on line linenum. If linenum is omitted, position the cursor on the last line of the file. +5 and -c 5 on the command-line are equivalent to :5 inside nvim. +/[pattern] For the first file, position the cursor on the first occurrence of pattern. If pattern is omitted, the most recent search pattern is used (if any). +/foo and -c /foo on the command-line are equivalent to /foo and :/foo inside nvim. :help search-pattern +command, -c command Execute command after reading the first file. Up to 10 instances allowed. "+foo" and -c "foo" are equivalent. --cmd command Like -c, but execute command before processing any vimrc. Up to 10 instances of these can be used independently from instances of -c. -l script [args] Execute Lua script with optional [args] after processing any preceding Nvim startup arguments. All [args] are treated as script arguments and are passed literally to Lua, that is, -l stops processing of Nvim arguments. :help -l -S [session] Execute session after the first file argument has been read. If session filename ends with .lua it is executed as Lua instead of Vimscript. Equivalent to -c "source session". session cannot start with a hyphen (‘-’). If session is omitted then Session.vim is used, if found. :help session-file -s scriptin Read normal mode commands from scriptin. The same can be done with the command :source! scriptin. If the end of the file is reached before nvim exits, further characters are read from the keyboard. -w scriptout Append all typed characters to scriptout. Can be used for creating a script to be used with -s or :source!. -W scriptout Like -w, but truncate scriptout. --startuptime file During startup, append timing messages to file. Can be used to diagnose slow startup times. --api-info Dump API metadata serialized to msgpack and exit. --embed Use standard input and standard output as a msgpack-rpc channel. :help --embed --headless Do not start a UI. When supplied with --embed this implies that the embedding application does not intend to (immediately) start a UI. Also useful for "scraping" messages in a pipe. :help --headless --listen address Start RPC server on this pipe or TCP socket. -h, --help Print usage information and exit. -v, --version Print version information and exit. ENVIRONMENT NVIM_LOG_FILE Low-level log file, usually found at ~/.local/state/nvim/log. :help $NVIM_LOG_FILE VIM Used to locate user files, such as init.vim. System- dependent. :help $VIM VIMRUNTIME Used to locate runtime files (documentation, syntax highlighting, etc.). XDG_CONFIG_HOME Path to the user-local configuration directory, see FILES. Defaults to ~/.config. :help xdg XDG_STATE_HOME Like XDG_CONFIG_HOME, but used to store data not generally edited by the user, namely swap, backup, and ShaDa files. Defaults to ~/.local/state. :help xdg XDG_DATA_HOME Like XDG_CONFIG_HOME, but used to store data not generally edited by the user, things like runtime files. Defaults to ~/.local/share. :help xdg VIMINIT Ex commands to be executed at startup. :help VIMINIT SHELL Used to initialize the 'shell' option, which decides the default shell used by features like :terminal, :!, and system(). FILES ~/.config/nvim/init.vim User-local nvim configuration file. ~/.config/nvim User-local nvim configuration directory. See also XDG_CONFIG_HOME. $VIM/sysinit.vim System-global nvim configuration file. $VIM System-global nvim runtime directory. AUTHORS Nvim was started by Thiago de Arruda. Most of Vim was written by Bram Moolenaar. Vim is based on Stevie, worked on by Tim Thompson, Tony Andrews, and G.R. (Fred) Walter. :help credits macOS 14.5 December 17, 2017 macOS 14.5
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jpegtran
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jpegtran performs various useful transformations of JPEG files. It can translate the coded representation from one variant of JPEG to another, for example from baseline JPEG to progressive JPEG or vice versa. It can also perform some rearrangements of the image data, for example turning an image from landscape to portrait format by rotation. For EXIF files and JPEG files containing Exif data, you may prefer to use exiftran instead. jpegtran works by rearranging the compressed data (DCT coefficients), without ever fully decoding the image. Therefore, its transformations are lossless: there is no image degradation at all, which would not be true if you used djpeg followed by cjpeg to accomplish the same conversion. But by the same token, jpegtran cannot perform lossy operations such as changing the image quality. However, while the image data is losslessly transformed, metadata can be removed. See the -copy option for specifics. jpegtran reads the named JPEG/JFIF file, or the standard input if no file is named, and produces a JPEG/JFIF file on the standard output.
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jpegtran - lossless transformation of JPEG files
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jpegtran [ options ] [ filename ]
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All switch names may be abbreviated; for example, -optimize may be written -opt or -o. Upper and lower case are equivalent. British spellings are also accepted (e.g., -optimise), though for brevity these are not mentioned below. To specify the coded JPEG representation used in the output file, jpegtran accepts a subset of the switches recognized by cjpeg: -optimize Perform optimization of entropy encoding parameters. -progressive Create progressive JPEG file. -restart N Emit a JPEG restart marker every N MCU rows, or every N MCU blocks if "B" is attached to the number. -arithmetic Use arithmetic coding. -scans file Use the scan script given in the specified text file. See cjpeg(1) for more details about these switches. If you specify none of these switches, you get a plain baseline-JPEG output file. The quality setting and so forth are determined by the input file. The image can be losslessly transformed by giving one of these switches: -flip horizontal Mirror image horizontally (left-right). -flip vertical Mirror image vertically (top-bottom). -rotate 90 Rotate image 90 degrees clockwise. -rotate 180 Rotate image 180 degrees. -rotate 270 Rotate image 270 degrees clockwise (or 90 ccw). -transpose Transpose image (across UL-to-LR axis). -transverse Transverse transpose (across UR-to-LL axis). The transpose transformation has no restrictions regarding image dimensions. The other transformations operate rather oddly if the image dimensions are not a multiple of the iMCU size (usually 8 or 16 pixels), because they can only transform complete blocks of DCT coefficient data in the desired way. jpegtran's default behavior when transforming an odd-size image is designed to preserve exact reversibility and mathematical consistency of the transformation set. As stated, transpose is able to flip the entire image area. Horizontal mirroring leaves any partial iMCU column at the right edge untouched, but is able to flip all rows of the image. Similarly, vertical mirroring leaves any partial iMCU row at the bottom edge untouched, but is able to flip all columns. The other transforms can be built up as sequences of transpose and flip operations; for consistency, their actions on edge pixels are defined to be the same as the end result of the corresponding transpose-and-flip sequence. For practical use, you may prefer to discard any untransformable edge pixels rather than having a strange-looking strip along the right and/or bottom edges of a transformed image. To do this, add the -trim switch: -trim Drop non-transformable edge blocks. Obviously, a transformation with -trim is not reversible, so strictly speaking jpegtran with this switch is not lossless. Also, the expected mathematical equivalences between the transformations no longer hold. For example, -rot 270 -trim trims only the bottom edge, but -rot 90 -trim followed by -rot 180 -trim trims both edges. -perfect If you are only interested in perfect transformations, add the -perfect switch. This causes jpegtran to fail with an error if the transformation is not perfect. For example, you may want to do (jpegtran -rot 90 -perfect foo.jpg || djpeg foo.jpg | pnmflip -r90 | cjpeg) to do a perfect rotation, if available, or an approximated one if not. This version of jpegtran also offers a lossless crop option, which discards data outside of a given image region but losslessly preserves what is inside. Like the rotate and flip transforms, lossless crop is restricted by the current JPEG format; the upper left corner of the selected region must fall on an iMCU boundary. If it doesn't, then it is silently moved up and/or left to the nearest iMCU boundary (the lower right corner is unchanged.) Thus, the output image covers at least the requested region, but it may cover more. The adjustment of the region dimensions may be optionally disabled by attaching an The image can be losslessly cropped by giving the switch: -crop WxH+X+Y Crop the image to a rectangular region of width W and height H, starting at point X,Y. The lossless crop feature discards data outside of a given image region but losslessly preserves what is inside. Like the rotate and flip transforms, lossless crop is restricted by the current JPEG format; the upper left corner of the selected region must fall on an iMCU boundary. If it doesn't, then it is silently moved up and/or left to the nearest iMCU boundary (the lower right corner is unchanged.) If W or H is larger than the width/height of the input image, then the output image is expanded in size, and the expanded region is filled in with zeros (neutral gray). Attaching an 'f' character ("flatten") to the width number will cause each block in the expanded region to be filled in with the DC coefficient of the nearest block in the input image rather than grayed out. Attaching an 'r' character ("reflect") to the width number will cause the expanded region to be filled in with repeated reflections of the input image rather than grayed out. A complementary lossless wipe option is provided to discard (gray out) data inside a given image region while losslessly preserving what is outside: -wipe WxH+X+Y Wipe (gray out) a rectangular region of width W and height H from the input image, starting at point X,Y. Attaching an 'f' character ("flatten") to the width number will cause the region to be filled with the average of adjacent blocks rather than grayed out. If the wipe region and the region outside the wipe region, when adjusted to the nearest iMCU boundary, form two horizontally adjacent rectangles, then attaching an 'r' character ("reflect") to the width number will cause the wipe region to be filled with repeated reflections of the outside region rather than grayed out. A lossless drop option is also provided, which allows another JPEG image to be inserted ("dropped") into the input image data at a given position, replacing the existing image data at that position: -drop +X+Y filename Drop (insert) another image at point X,Y Both the input image and the drop image must have the same subsampling level. It is best if they also have the same quantization (quality.) Otherwise, the quantization of the output image will be adapted to accommodate the higher of the input image quality and the drop image quality. The trim option can be used with the drop option to requantize the drop image to match the input image. Note that a grayscale image can be dropped into a full-color image or vice versa, as long as the full-color image has no vertical subsampling. If the input image is grayscale and the drop image is full-color, then the chrominance channels from the drop image will be discarded. Other not-strictly-lossless transformation switches are: -grayscale Force grayscale output. This option discards the chrominance channels if the input image is YCbCr (ie, a standard color JPEG), resulting in a grayscale JPEG file. The luminance channel is preserved exactly, so this is a better method of reducing to grayscale than decompression, conversion, and recompression. This switch is particularly handy for fixing a monochrome picture that was mistakenly encoded as a color JPEG. (In such a case, the space savings from getting rid of the near-empty chroma channels won't be large; but the decoding time for a grayscale JPEG is substantially less than that for a color JPEG.) jpegtran also recognizes these switches that control what to do with "extra" markers, such as comment blocks: -copy none Copy no extra markers from source file. This setting suppresses all comments and other metadata in the source file. -copy comments Copy only comment markers. This setting copies comments from the source file but discards any other metadata. -copy icc Copy only ICC profile markers. This setting copies the ICC profile from the source file but discards any other metadata. -copy all Copy all extra markers. This setting preserves miscellaneous markers found in the source file, such as JFIF thumbnails, Exif data, and Photoshop settings. In some files, these extra markers can be sizable. Note that this option will copy thumbnails as-is; they will not be transformed. The default behavior is -copy comments. (Note: in IJG releases v6 and v6a, jpegtran always did the equivalent of -copy none.) Additional switches recognized by jpegtran are: -icc file Embed ICC color management profile contained in the specified file. Note that this will cause jpegtran to ignore any APP2 markers in the input file, even if -copy all or -copy icc is specified. -maxmemory N Set limit for amount of memory to use in processing large images. Value is in thousands of bytes, or millions of bytes if "M" is attached to the number. For example, -max 4m selects 4000000 bytes. If more space is needed, an error will occur. -maxscans N Abort if the input image contains more than N scans. This feature demonstrates a method by which applications can guard against denial-of-service attacks instigated by specially- crafted malformed JPEG images containing numerous scans with missing image data or image data consisting only of "EOB runs" (a feature of progressive JPEG images that allows potentially hundreds of thousands of adjoining zero-value pixels to be represented using only a few bytes.) Attempting to transform such malformed JPEG images can cause excessive CPU activity, since the decompressor must fully process each scan (even if the scan is corrupt) before it can proceed to the next scan. -outfile name Send output image to the named file, not to standard output. -report Report transformation progress. -strict Treat all warnings as fatal. This feature also demonstrates a method by which applications can guard against attacks instigated by specially-crafted malformed JPEG images. Enabling this option will cause the decompressor to abort if the input image contains incomplete or corrupt image data. -verbose Enable debug printout. More -v's give more output. Also, version information is printed at startup. -debug Same as -verbose. -version Print version information and exit.
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This example converts a baseline JPEG file to progressive form: jpegtran -progressive foo.jpg > fooprog.jpg This example rotates an image 90 degrees clockwise, discarding any unrotatable edge pixels: jpegtran -rot 90 -trim foo.jpg > foo90.jpg ENVIRONMENT JPEGMEM If this environment variable is set, its value is the default memory limit. The value is specified as described for the -maxmemory switch. JPEGMEM overrides the default value specified when the program was compiled, and itself is overridden by an explicit -maxmemory. SEE ALSO cjpeg(1), djpeg(1), rdjpgcom(1), wrjpgcom(1) Wallace, Gregory K. "The JPEG Still Picture Compression Standard", Communications of the ACM, April 1991 (vol. 34, no. 4), pp. 30-44. AUTHOR Independent JPEG Group This file was modified by The libjpeg-turbo Project to include only information relevant to libjpeg-turbo and to wordsmith certain sections. BUGS The transform options can't transform odd-size images perfectly. Use -trim or -perfect if you don't like the results. The entire image is read into memory and then written out again, even in cases where this isn't really necessary. Expect swapping on large images, especially when using the more complex transform options. 13 July 2021 JPEGTRAN(1)
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transformers-cli
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redis-cli
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protoc-27.1.0
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exrmaketiled
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srt-ffplay
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query_compile_time_config
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lstopo
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lstopo and lstopo-no-graphics are capable of displaying a topological map of the system in a variety of different output formats. The only difference between lstopo and lstopo-no-graphics is that graphical outputs are only supported by lstopo, to reduce dependencies on external libraries. hwloc-ls is identical to lstopo-no-graphics. The filename specified directly implies the output format that will be used; see the OUTPUT FORMATS section, below. Output formats that support color will indicate specific characteristics about individual CPUs by their color; see the COLORS section, below. OUTPUT FORMATS By default, if no output filename is specified, the output is sent to a graphical window if possible in the current environment (DISPLAY environment variable set on Unix, etc.). Otherwise, a text summary is displayed in the console. The console is also used when the program runs from a terminal and the output is redirected to a pipe or file. These default behaviors may be changed by passing --of console to force console mode or --of window for graphical window. The filename on the command line usually determines the format of the output. There are a few filenames that indicate specific output formats and devices (e.g., a filename of "-" will output a text summary to stdout), but most filenames indicate the desired output format by their suffix (e.g., "topo.png" will output a PNG-format file). The format of the output may also be changed with "--of". For instance, "--of pdf" will generate a PDF-format file on the standard output, while "--of fig toto" will output a Xfig-format file named "toto". The list of currently supported formats is given below. Any of them may be used with "--of" or as a filename suffix. default Send the output to a window or to the console depending on the environment. window Send the output to a graphical window. console Send a text summary to stdout. Binding or unallowed processors are only annotated in this mode if verbose; see the COLORS section, below. ascii Output an ASCII art representation of the map (formerly called txt). If outputting to stdout and if colors are supported on the terminal, the output will be colorized. tikz or tex Output a LaTeX tikzpicture representation of the map that can be compiled with a LaTeX compiler. fig Output a representation of the map that can be loaded in Xfig. svg Output a SVG representation of the map, using Cairo (by default, if supported) or a native SVG backend (fallback, always supported). See cairosvg and nativesvg below. cairosvg or svg(cairo) If lstopo was compiled with the proper support, output a SVG representation of the map using Cairo. nativesvg or svg(native) Output a SVG representation of the map using the native SVG backend. It may be less pretty than the Cairo output, but it is always supported, and SVG objects have attributes for identifying and manipulating them. See dynamic_SVG_example.html for an example. pdf If lstopo was compiled with the proper support, lstopo outputs a PDF representation of the map. ps If lstopo was compiled with the proper support, lstopo outputs a Postscript representation of the map. png If lstopo was compiled with the proper support, lstopo outputs a PNG representation of the map. synthetic If the topology is symmetric (which requires that the root object has its symmetric_subtree field set), lstopo outputs a synthetic description string. This output may be reused as an input synthetic topology description later. See also the Synthetic topologies section in the documentation. Note that Misc and I/O devices are ignored during this export. xml lstopo outputs an XML representation of the map. It may be reused later, even on another machine, with lstopo --input, the HWLOC_XMLFILE environment variable, or the hwloc_topology_set_xml() function. The following special names may be used: - Send a text summary to stdout. /dev/stdout Send a text summary to stdout. It is effectively the same as specifying "-". -.<format> If the entire filename is "-.<format>", lstopo behaves as if "--of <format> -" was given, which means a file of the given format is sent to the standard output. See the output of "lstopo --help" for a specific list of what graphical output formats are supported in your hwloc installation. GRAPHICAL OUTPUT The graphical output is made of nested boxes representing the inclusion of objects in the hierarchy of resources. Usually a Machine box contains one or several Package boxes, that contain multiple Core boxes, with one or several PUs each. Caches Caches are displayed in a slightly different manner because they do not actually include computing resources such as cores. For instance, a L2 Cache shared by a pair of Cores is drawn as a Cache box on top of two Core boxes (instead of having Core boxes inside the Cache box). NUMA nodes and Memory-side Caches By default, NUMA nodes boxes are drawn on top of their local computing resources. For instance, a processor Package containing one NUMA node and four Cores is displayed as a Package box containing the NUMA node box above four Core boxes. If a NUMA node is local to the L3 Cache, the NUMA node is displayed above that Cache box. All this specific drawing strategy for memory objects may be disabled by passing command- line option --children-order plain. If multiple NUMA nodes are attached to the same parent object, they are displayed inside an additional unnamed memory box. If some Memory-side Caches exist in front of some NUMA nodes, they are drawn as boxes immediately above them. PCI bridges, PCI devices and OS devices The PCI hierarchy is not drawn as a set of included boxes but rather as a tree of bridges (that may actually be switches) with links between them. The tree starts with a small square on the left for the hostbridge or root complex. It ends with PCI device boxes on the right. Intermediate PCI bridges/switches may appear as additional small squares in the middle. PCI devices on the right of the tree are boxes containing their PCI bus ID (such as 00:02.3). They may also contain sub-boxes for OS device objects such as a network interface eth0 or a CUDA GPU cuda0. When there is a single link (horizontal line) on the right of a PCI bridge, it means that a single device or bridge is connected on the secondary PCI bus behind that bridge. When there is a vertical line, it means that multiple devices and/or bridges are connected to the same secondary PCI bus. The datarate of a PCI link may be written (in GB/s) right below its drawn line (if the operating system and/or libraries are able to report that information). This datarate is the currently configured speed of the entire PCI link (sum of the bandwidth of all PCI lanes in that link). It may change during execution since some devices are able to slow their PCI links down when idle. LAYOUT In its graphical output, lstopo uses simple rectangular heuristics to try to achieve a 4/3 ratio between width and height. Although the hierarchy of resources is properly reflected, the exact physical organization (NUMA distances, rings, complete graphs, etc.) is currently ignored. The layout of a level may be changed with --vert, --horiz, and --rect to force a parent object to arrange its children in vertical, horizontal or rectangular manners respectively. The position of Memory, I/O and Misc children with respect to other children objects may be changed using --children-order. This effectivement divides children into multiple sections. The layout of children is first computed inside each section, before sections are placed inside (or below) the parent box. The vertical/horizontal/rectangular layout of these additional sections may also be configured through --children-order. COLORS Individual CPUs and NUMA nodes are colored in the graphical output formats to indicate different characteristics: Green The topology is reported as seen by a specific process (see --pid), and the given CPU or NUMA node is in this process CPU or Memory binding mask. White The CPU or NUMA node is in the allowed set (see below). If the topology is reported as seen by a specific process (see --pid), the object is also not in this process binding mask. Red The CPU or NUMA node is not in the allowed set (see below). The "allowed set" is the set of CPUs or NUMA nodes to which the current process is allowed to bind. The allowed set is usually either inherited from the parent process or set by administrative qpolicies on the system. Linux cpusets are one example of limiting the allowed set for a process and its children to be less than the full set of CPUs or NUMA nodes on the system. Different processes may therefore have different CPUs or NUMA nodes in the allowed set. Hence, invoking lstopo in different contexts and/or as different users may display different colors for the same individual CPUs (e.g., running lstopo in one context may show a specific CPU as red, but running lstopo in a different context may show the same CPU as white). Some lstopo output modes, e.g. the console mode (default non-graphical output), do not support colors at all. The console mode displays the above characteristics by appending text to each PU line if verbose messages are enabled. CUSTOM COLORS The colors of different kinds of boxes may be configured with --palette. The color of each object in the graphical output may also be enforced by specifying a "lstopoStyle" info attribute in that object. Its value should be a semi-colon separated list of "<attribute>=#rrggbb" where rr, gg and bb are the RGB components of a color, each between 0 and 255, in hexadecimal (00 to ff). <attribute> may be Background Sets the background color of the main object box. Text Sets the color of the text showing the object name, type, index, etc. Text2 Sets the color of the additional text near the object, for instance the link speed behind a PCI bridge. The "lstopoStyle" info may be added to a temporarily-saved XML topologies with hwloc-annotate, or with hwloc_obj_add_info(). For instance, to display all core objects in blue (with white names): lstopo save.xml hwloc-annotate save.xml save.xml core:all info lstopoStyle "Background=#0000ff;Text=#ffffff" lstopo -i save.xml
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lstopo, lstopo-no-graphics, hwloc-ls - Show the topology of the system
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lstopo [ options ]... [ filename ] lstopo-no-graphics [ options ]... [ filename ] hwloc-ls [ options ]... [ filename ] Note that hwloc(7) provides a detailed explanation of the hwloc system; it should be read before reading this man page
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--of <format>, --output-format <format> Enforce the output in the given format. See the OUTPUT FORMATS section below. -i <path>, --input <path> Read the topology from <path> instead of discovering the topology of the local machine. If <path> is a file, it may be a XML file exported by a previous hwloc program. If <path> is "-", the standard input may be used as a XML file. On Linux, <path> may be a directory containing the topology files gathered from another machine topology with hwloc-gather- topology. On x86, <path> may be a directory containing a cpuid dump gathered with hwloc-gather-cpuid. When the archivemount program is available, <path> may also be a tarball containing such Linux or x86 topology files. -i <specification>, --input <specification> Simulate a fake hierarchy (instead of discovering the topology on the local machine). If <specification> is "node:2 pu:3", the topology will contain two NUMA nodes with 3 processing units in each of them. The <specification> string must end with a number of PUs. --if <format>, --input-format <format> Enforce the input in the given format, among xml, fsroot, cpuid and synthetic. --export-xml-flags <flags> Enforce flags when exporting to the XML format. Flags may be given as numeric values or as a comma-separated list of flag names that are passed to hwloc_topology_export_xml(). Those names may be substrings of actual flag names as long as a single one matches. A value of 1 (or v1) reverts to the format of hwloc v1.x. The default is 0 (or none). --export-synthetic-flags <flags> Enforce flags when exporting to the synthetic format. Flags may be given as numeric values or as a comma-separated list of flag names that are passed to hwloc_topology_export_synthetic(). Those names may be substrings of actual flag names as long as a single one matches. A value of 2 (or no_attr) reverts to the format of hwloc v1.9. A value of 3 (or no_ext,no_attr) reverts to the original minimalistic format (before v1.9). The default is 0 (or none). -v --verbose Include additional detail. The hwloc-info tool may be used to display even more information about specific objects. -q --quiet -s --silent Reduce the amount of details to show. --distances Only display distance matrices. --distances-transform <links|merge-switch-ports|transitive-closure> Try applying a transformation to distances structures before displaying them. See hwloc_distances_transform() for details. More transformations may be applied using hwloc-annotate(1) (and it may save their output to XML). --memattrs Only display memory attributes. All of them are displayed (while the default textual output selects memory attribute details depending on the verbosity level). --cpukinds Only display CPU kinds. CPU kinds are displayed in order, starting from the most energy efficient ones up to the rather higher performance and power hungry ones. --windows-processor-groups On Windows, only show information about processor groups. All of them are displayed, while the default verbose output only shows them if there are more than one. -f --force If the destination file already exists, overwrite it. -l --logical Display hwloc logical indexes of all objects, with prefix "L#". By default, both logical and physical/OS indexes are displayed for PUs and NUMA nodes, logical only for cores, dies and packages, and no index for other types. -p --physical Display OS/physical indexes of all objects, with prefix "P#". By default, both logical and physical/OS indexes are displayed for PUs and NUMA nodes, logical only for cores, dies and packages, and no index for other types. --logical-index-prefix <prefix> Replace " L#" with the given prefix for logical indexes. --os-index-prefix <prefix> Replace " P#" with the given prefix for physical/OS indexes. -c --cpuset Display the cpuset of each object. -C --cpuset-only Only display the cpuset of each object; do not display anything else about the object. --taskset Show CPU set strings in the format recognized by the taskset command-line program instead of hwloc-specific CPU set string format. This option should be combined with --cpuset or --cpuset-only, otherwise it will imply --cpuset. --only <type> Only show objects of the given type in the textual output. <type> may contain a filter to select specific objects among the type. For instance --only NUMA[HBM] only shows NUMA nodes marked with subtype "HBM", while --only "numa[mcdram]" only shows MCDRAM NUMA nodes on KNL. --filter <type>:<kind>, --filter <type> Filter objects of type <type>, or of any type if <type> is "all". "io", "cache" and "icache" are also supported. <kind> specifies the filtering behavior. If "none" or not specified, all objects of the given type are removed. If "all", all objects are kept as usual. If "structure", objects are kept when they bring structure to the topology. If "important" (only applicable to I/O), only important objects are kept. See hwloc_topology_set_type_filter() for more details. hwloc supports filtering any type except PUs and NUMA nodes. lstopo also offers PU and NUMA node filtering by hiding them in the graphical and textual outputs, but any object included in them (for instance Misc) will be hidden as well. Note that PUs and NUMA nodes may not be ignored in the XML output. Note also that the top-level object type cannot be ignored (usually Machine or System). --ignore <type> This is the old way to specify --filter <type>:none. --no-smt Ignore PUs. This is identical to --filter PU:none. --no-caches Do not show caches. This is identical to --filter cache:none. --no-useless-caches This is identical to --filter cache:structure. --no-icaches This is identical to --filter icache:none. --disallowed Include objects disallowed by administrative limitations (e.g Cgroups on Linux). Offline PUs and NUMA nodes are still ignored. --allow <all|local|0xff|nodeset=0xf0> Include objects disallowed by administrative limitations (implies --disallowed) and also change the set of allowed ones. If local is given, only objects available to the current process are allowed (default behavior when loading from the native operating system backend). It may be useful if the topology was created by another process (with different administrative restrictions such as Linux Cgroups) and loaded here loaded from XML or synthetic. This case implies --thissystem. If all, all objects are allowed. If a bitmap is given as a hexadecimal string, it is used as the set of allowed PUs. If a bitmap is given after prefix nodeset=, it is the set of allowed NUMA nodes. --flags <flags> Enforce topology flags. Flags may be given as numeric values or as a comma-separated list of flag names that are passed to hwloc_topology_set_flags(). Those names may be substrings of actual flag names as long as a single one matches, for instance disallowed,thissystem_allowed. The default is 8 (or import). --merge Do not show levels that do not have a hierarchical impact. This sets HWLOC_TYPE_FILTER_KEEP_STRUCTURE for all object types. This is identical to --filter all:structure. --no-factorize --no-factorize=<type> Never factorize identical objects in the graphical output. If an object type is given, only factorizing of these objects is disabled. This only applies to normal CPU-side objects, it is independent from PCI collapsing. --factorize --factorize=[<type>,]<N>[,<L>[,<F>] Factorize identical children in the graphical output (enabled by default). If <N> is specified (4 by default), factorizing only occurs when there are strictly more than N identical children. If <L> and <F> are specified, they set the numbers of first and last children to keep after factorizing. If an object type is given, only factorizing of these objects is configured. This only applies to normal CPU-side object, it is independent from PCI collapsing. --no-collapse Do not collapse identical PCI devices. By default, identical sibling PCI devices (such as many virtual functions inside a single physical device) are collapsed. --no-cpukinds Do not show different kinds of CPUs in the graphical output. By default, when supported, different types of lines, thickness and bold font may be used to display PU boxes of different kinds. --restrict <cpuset> Restrict the topology to the given cpuset. This removes some PUs and their now-child-less parents. Beware that restricting the PUs in a topology may change the logical indexes of many objects, including NUMA nodes. --restrict nodeset=<nodeset> Restrict the topology to the given nodeset. (unless --restrict-flags specifies something different). This removes some NUMA nodes and their now-child-less parents. Beware that restricting the NUMA nodes in a topology may change the logical indexes of many objects, including PUs. --restrict binding Restrict the topology to the current process binding. This option requires the use of the actual current machine topology (or any other topology with --thissystem or with HWLOC_THISSYSTEM set to 1 in the environment). Beware that restricting the topology may change the logical indexes of many objects, including PUs and NUMA nodes. --restrict-flags <flags> Enforce flags when restricting the topology. Flags may be given as numeric values or as a comma-separated list of flag names that are passed to hwloc_topology_restrict(). Those names may be substrings of actual flag names as long as a single one matches, for instance bynodeset,memless. The default is 0 (or none). --no-io Do not show any I/O device or bridge. This is identical to --filter io:none. By default, common devices (GPUs, NICs, block devices, ...) and interesting bridges/switches are shown. --no-bridges Do not show any I/O bridge except hostbridges. This is identical to --filter bridge:none. By default, common devices (GPUs, NICs, block devices, ...) and interesting bridges/switches are shown. --whole-io Show all I/O devices and bridges. This is identical to --filter io:all. By default, only common devices (GPUs, NICs, block devices, ...) and interesting bridges/switches are shown. --thissystem Assume that the selected backend provides the topology for the system on which we are running. This is useful when loading a custom topology such as an XML file and using --restrict binding or --allow all. --pid <pid> Detect topology as seen by process <pid>, i.e. as if process <pid> did the discovery itself. Note that this can for instance change the set of allowed processors. Also show this process current CPU and Memory binding by marking the corresponding PUs and NUMA nodes (in Green in the graphical output, see the COLORS section below, or by appending (binding) to the verbose text output). If 0 is given as pid, the current binding for the lstopo process will be shown. --ps --top Show existing processes as misc objects in the output. To avoid uselessly cluttering the output, only processes that are restricted to some part of the machine are shown. On Linux, kernel threads are not shown. If many processes appear, the output may become hard to read anyway, making the hwloc-ps program more practical. See --misc-from for a customizable variant using hwloc-ps. --misc-from <file> Add Misc objects as described in <file> containing entries such as: name=myMisc1 cpuset=0x5 name=myMisc2 cpuset=0x7 subtype=myOptionalSubtype This is useful for combining with hwloc-ps --lstopo-misc (see EXAMPLES below) because hwloc-ps is far more customizable than lstopo's --top option. --children-order <order> Change the order of the different kinds of children with respect to their parent in the graphical output. <order> may be a comma-separated list of keywords among: memory:above displays memory children above other children (and above the parent if it is a cache). PUs are therefore below their local NUMA nodes, like hwloc 1.x did. io:right and misc:right place I/O or Misc children on the right of CPU children. io:below and misc:below place I/O or Misc children below CPU children. plain places everything not specified together with normal CPU children. If only plain is specified, lstopo displays the topology in a basic manner that strictly matches the actual tree: Memory, I/O and Misc children are listed below their parent just like any other child. PUs are therefore on the side of their local NUMA nodes, below a common ancestor. This output may result in strange layouts since the size of Memory, CPU and I/O children may be very different, causing the placement algorithm to poorly arrange them in rows. The default order is memory:above,io:right,misc:right which means Memory children are above CPU children while I/O and Misc are together on the right. Up to hwloc 2.5, the default was rather to memory:above,plain. Additionally, memory:above, io:right, io:below, misc:right and misc:below may be suffixed with :horiz, :vert or :rect to force the horizontal, vertical or rectangular layout of children inside these sections. See also the GRAPHICAL OUTPUT and LAYOUT sections below. --fontsize <size> Set the size of text font in the graphical output. The default is 10. Boxes are scaled according to the text size. The LSTOPO_TEXT_XSCALE environment variable may be used to further scale the width of boxes (its default value is 1.0). The --fontsize option is ignored in the ASCII backend. --gridsize <size> Set the margin between elements in the graphical output. The default is 7. It was 10 prior to hwloc 2.1. This option is ignored in the ASCII backend. --linespacing <size> Set the spacing between lines of text in the graphical output. The default is 4. The option was included in --gridsize prior to hwloc 2.1 (and its default was 10). This option is ignored in the ASCII backend. --thickness <size> Set the thickness of lines and boxes in the graphical output. The default is 1. This option is ignored in the ASCII backend. --horiz, --horiz=<type1,...> Force a horizontal graphical layout instead of nearly 4/3 ratio in the graphical output. If a comma-separated list of object types is given, the layout only applies to the corresponding container objects. Ignored for bridges since their children are always vertically aligned. --vert, --vert=<type1,...> Force a vertical graphical layout instead of nearly 4/3 ratio in the graphical output. If a comma-separated list of object types is given, the layout only applies to the corresponding container objects. --rect, --rect=<type1,...> Force a rectangular graphical layout with nearly 4/3 ratio in the graphical output. If a comma-separated list of object types is given, the layout only applies to the corresponding container objects. Ignored for bridges since their children are always vertically aligned. --no-text, --no-text=<type1,...> Do not display any text in boxes in the graphical output. If a comma-separated list of object types is given, text is disabled for the corresponding objects. This is mostly useful for removing text from Group objects. --text, --text=<type1,...> Display text in boxes in the graphical output (default). If a comma-separated list of object types is given, text is reenabled for the corresponding objects (if it was previously disabled with --no-text). --no-index, --no-index=<type1,...> Do not show object indexes in the graphical output. If a comma- separated list of object types is given, indexes are disabled for the corresponding objects. --index, --index=<type1,...> Show object indexes in the graphical output (default). If a comma-separated list of object types is given, indexes are reenabled for the corresponding objects (if they were previously disabled with --no-index). --no-attrs, --no-attrs=<type1,...> Do not show object attributes (such as memory size, cache size, PCI bus ID, PCI link speed, etc.) in the graphical output. If a comma-separated list of object types is given, attributes are disabled for the corresponding objects. --attrs, --attrs=<type1,...> Show object attributes (such as memory size, cache size, PCI bus ID, PCI link speed, etc.) in the graphical output (default). If a comma-separated list of object types is given, attributes are reenabled for the corresponding objects (if they were previously disabled with --no-attrs). --no-legend Remove all text legend lines at the bottom of the graphical output. --no-default-legend Remove default text legend lines at the bottom of the graphical output. User-added legend lines with --append-legend or the "lstopoLegend" info are still displayed if any. --append-legend <line> Append the line of text to the bottom of the legend in the graphical output. If adding multiple lines, each line should be given separately by passing this option multiple times. Additional legend lines may also be specified inside the topology using the "lstopoLegend" info attributes on the topology root object. --grey, --greyscale Use greyscale instead of colors in the graphical output. --palette <grey|greyscale|defaut|colors|white|none> Change the color palette. Passing grey or greyscale is identical to passing --grey or --greyscale. Passing white or none uses white instead of colors for all box backgrounds. Passing default or colors reverts back to the default color palette. --palette type=#rrggbb Replace the color of the given box type with the given 3x8bit hexadecimal RGB combination (e.g. #ff0000 is red). Existing types are machine, group, package, group_in_package, die, core, pu, numanode, memories (box containing multiple memory children), cache, pcidev, osdev, bridge, and misc. See also CUSTOM COLOR below for customizing individual objects. --binding-color <none|#rrggbb> Do not colorize PUs and NUMA nodes according to the binding in the graphical output. Or change the color to the given 3x8bit hexadecimal RGB combination (e.g. #ff0000 is red). --disallowed-color <none|#rrggbb> Do not colorize disallowed PUs and NUMA nodes in the graphical output. Or change the color to the given 3x8bit hexadecimal RGB combination (e.g. #00ff00 is green). --top-color <none|#rrggbb> Do not colorize task objects in the graphical output when --top is given. Or change the color to the given 3x8bit hexadecimal RGB combination (e.g. #0000ff is blue). This is actually applied to Misc objects of subtype Process or Thread. --version Report version and exit. -h --help Display help message and exit.
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To display the machine topology in textual mode: lstopo-no-graphics To display the machine topology in ascii-art mode: lstopo-no-graphics -.ascii To display in graphical mode (assuming that the DISPLAY environment variable is set to a relevant value): lstopo To export the topology to a PNG file: lstopo file.png To export an XML file on a machine and later display the corresponding graphical output on another machine: machine1$ lstopo file.xml <transfer file.xml from machine1 to machine2> machine2$ lstopo --input file.xml To save the current machine topology to XML and later reload it faster while still considering it as the current machine: $ lstopo file.xml <...> $ lstopo --input file.xml --thissystem To restrict an XML topology to only physical processors 0, 1, 4 and 5: lstopo --input file.xml --restrict 0x33 newfile.xml To restrict an XML topology to only numa node whose logical index is 1: lstopo --input file.xml --restrict $(hwloc-calc --input file.xml node:1) newfile.xml To display a summary of the topology: lstopo -s To get more details about the topology: lstopo -v To only show cores: lstopo --only core To show cpusets: lstopo --cpuset To only show the cpusets of package: lstopo --only package --cpuset-only Simulate a fake hierarchy; this example shows with 2 NUMA nodes of 2 processor units: lstopo --input "node:2 2" To count the number of logical processors in the system lstopo --only pu | wc -l To append the kernel release and version to the graphical legend: lstopo --append-legend "Kernel release: $(uname -r)" --append-legend "Kernel version: $(uname -v)" To show where a process and its children are bound by combining with hwloc-ps: hwloc-ps --pid-children 23 --lstopo-misc - | lstopo --misc-from - NOTES lstopo displays memory and cache sizes with units such as kB (1 kilobyte = 1000 bytes) or GB (1 gigabyte = 1000*1000*1000 bytes) while it actually means KiB (1 kibibyte = 1024 bytes) or GiB (1 gibibytes = 1024*1024*1024 bytes) . SEE ALSO hwloc(7), hwloc-info(1), hwloc-bind(1), hwloc-annotate(1), hwloc-ps(1), hwloc-gather-topology(1), hwloc-gather-cpuid(1) 2.10.0 December 4, 2023 LSTOPO(1)
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libpng16-config
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xcodeproj
| null | null | null | null | null |
freebcp
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freebcp is a utility program distributed with FreeTDS. freebcp replicates (in part at least) the functionality of the bcp utility programs distributed by Sybase and Microsoft. freebcp makes use of the DB-Library bcp API provided by FreeTDS. This API is also available to application developers. The manual pages or online help for Sybase or SQL Server can be referenced for more detailed information on bcp functionality. TABLES AND FILES database The name of the database containing object to be copied. Optional if the table/view is in the default database for username. schema The schema of the object being copied. If not provided, the default schema for username is used. object The name of the database object you wish to access, typically a table. It can also be a view. All views can be read; some can be written, subject to constraints. With queryout, object can also be an SQL query. in Copy data from a host file to a database table. out Copy data from a database table to a host file. queryout indicates that table_name is in fact SQL, rather than a database object. freebcp will execute the query and write the results to a file. (It is a good idea to have the query return one and only one result set.) datafile The name of an operating system file.
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freebcp – bulk loading utility for Sybase and Microsoft databases
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freebcp [[⟨database⟩.]⟨owner⟩.]⟨object_name⟩ {in | [query]out} datafile {-c | -n | -f formatfile} [-S servername] [-D dbname] [-U username] [-P password] [-b batchsize] [-F firstrow] [-L lastrow] [-e errfile] [-I interfaces] [-m maxerror] [-t field_term] [-r row_term] [-h hints] [-T textsize] [-A packet_size] [-O options] [-i inputfile] [-o outputfile] [-C charset] [-EdVv]
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-A packet_size Set the size of a TDS packet to packet_size. Not sure why you would want to do this, except as an experiment. -D dbname The name of the default database to use. Overrides default database associated with the login account. Causes freebcp to issue a USE dbname command immediately after logging in, before commencing BCP operations. -E Write the data in datafile to the table's IDENTITY column. Without this flag, the identity data present in the datafile will be ignored, and new IDENTITY values will be generated for the imported rows. -F firstrow The first row to copy from the input file or database table. The default is the first row, row 1. -I interfaces The name and location of the interfaces file to search when connecting to servername. Overrides freetds.conf. -L lastrow The last row to copy from an input file or database table. The default is the last row. -O options SQL text to set connection options prior to the bcp operation. If options is a valid filename, the SQL is read from the file instead. Sometimes needed for queryout. Example: -O `SET QUOTED_IDENTIFIER ON'. -P password The password associated with username. -S servername The name of the Database Server to which to connect. -T textsize For text or image columns, set the maximum number of characters to request from the server. Defaults to the setting in freetds.conf. If not specified anywhere, defaults to the full size of the data. -U username A database login name. For TDS 7+ connections, a domain login is attempted if username is not provided. -b batchsize The number of rows per batch of data copied. Batching applies only when you are bulk copying into the database. Each batch of data is effectively “committed” into the database. The default value for batchsize is 1000. -c The host data file is (or will be) in "character" format, i.e., a text file. Encoding is determined by the client charset attribute in freetds.conf. -d Turn off any logging. (Unintuitive, perhaps.) -e errfile Write errors to errfile. For uploads. Includes line and column information, and the row data. -f formatfile The format of the host data file is described by formatfile. The layout of formatfile is identical to that understood by the Sybase and Microsoft bcp utilities, but is too complicated to describe here. -h hints Set bcp hints. For valid values, cf. bcp_options() in the FreeTDS Reference Manual. -m maxerror Stop after encountering maxerror errors. Default 10. -n The host data file is in “native” format. This is a format that freebcp will be able to process, but is not portable or readable. -r row_term The row terminator for a character file. May be more than one character. Default is newline ('\n'). Cf. -c, above. -t field_term The field terminator for character file. Also known as a column delimiter. May be more than one character. Default is tab ('\t'). Cf. -c, above. -v -V Print the version information and exit. -i inputfile Read input data from file specified. -o outputfile Write output data to file specified. -C charset Specify character set to use to talk to server. ENVIRONMENT DSQUERY default servername NOTES When connecting to a Sybase database server, it is required that the TDS 5.0 protocol be used. When connecting to a Microsoft SQL Server 2000 database server, the TDS 7 (or later) protocol is required. Sybase and Microsoft define different versions of the bcp portion of TDS 4.2. Because FreeTDS has no way of knowing which type of server it's connected to, freebcp does not support version 4.2 of the TDS protocol. HISTORY freebcp first appeared in FreeTDS 0.60 AUTHORS The freebcp utility was written by Bill Thompson ⟨thompbil@exchange.uk.ml.com⟩ BUGS Currently, there is no support for text data types in freebcp, when SQL Server 2000 is the target server. FreeTDS 1.4.21 March 25, 2015 FreeTDS 1.4.21
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dertimetest
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gsha256sum
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Print or check SHA256 (256-bit) checksums. With no FILE, or when FILE is -, read standard input. -b, --binary read in binary mode -c, --check read checksums from the FILEs and check them --tag create a BSD-style checksum -t, --text read in text mode (default) -z, --zero end each output line with NUL, not newline, and disable file name escaping The following five options are useful only when verifying checksums: --ignore-missing don't fail or report status for missing files --quiet don't print OK for each successfully verified file --status don't output anything, status code shows success --strict exit non-zero for improperly formatted checksum lines -w, --warn warn about improperly formatted checksum lines --help display this help and exit --version output version information and exit The sums are computed as described in FIPS-180-2. When checking, the input should be a former output of this program. The default mode is to print a line with: checksum, a space, a character indicating input mode ('*' for binary, ' ' for text or where binary is insignificant), and name for each FILE. Note: There is no difference between binary mode and text mode on GNU systems. AUTHOR Written by Ulrich Drepper, Scott Miller, and David Madore. REPORTING BUGS GNU coreutils online help: <https://www.gnu.org/software/coreutils/> Report any translation bugs to <https://translationproject.org/team/> COPYRIGHT Copyright © 2023 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. SEE ALSO cksum(1) Full documentation <https://www.gnu.org/software/coreutils/sha256sum> or available locally via: info '(coreutils) sha2 utilities' GNU coreutils 9.3 April 2023 SHA256SUM(1)
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sha256sum - compute and check SHA256 message digest
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sha256sum [OPTION]... [FILE]...
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pod2text
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pod2text is a wrapper script around the Pod::Text and its subclasses. It uses them to generate formatted text from POD source. It can optionally use either termcap sequences or ANSI color escape sequences to format the text. input is the file to read for POD source (the POD can be embedded in code). If input isn't given, it defaults to "STDIN". output, if given, is the file to which to write the formatted output. If output isn't given, the formatted output is written to "STDOUT". Several POD files can be processed in the same pod2text invocation (saving module load and compile times) by providing multiple pairs of input and output files on the command line. By default, the output encoding is the same as the encoding of the input file, or UTF-8 if that encoding is not set (except on EBCDIC systems). See the -e option to explicitly set the output encoding and "Encoding" in Pod::Text for more discussion.
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pod2text - Convert POD data to formatted ASCII text
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pod2text [-aclostu] [--code] [-e encoding] [--errors=style] [--guesswork=rule[,rule...]] [-i indent] [-q quotes] [--nourls] [--stderr] [-w width] [input [output ...]] pod2text -h
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Each option is annotated with the version of podlators in which that option was added with its current meaning. -a, --alt [1.00] Use an alternate output format that, among other things, uses a different heading style and marks "=item" entries with a colon in the left margin. --code [1.11] Include any non-POD text from the input file in the output as well. Useful for viewing code documented with POD blocks with the POD rendered and the code left intact. -c, --color [1.00] Format the output with ANSI color escape sequences. Using this option requires that Term::ANSIColor be installed on your system. -e encoding, --encoding=encoding [5.00] Specifies the encoding of the output. encoding must be an encoding recognized by the Encode module (see Encode::Supported). If the output contains characters that cannot be represented in this encoding, that is an error that will be reported as configured by the "errors" option. If error handling is other than "die", the unrepresentable character will be replaced with the Encode substitution character (normally "?"). WARNING: The input encoding of the POD source is independent from the output encoding, and setting this option does not affect the interpretation of the POD input. Unless your POD source is US- ASCII, its encoding should be declared with the "=encoding" command in the source, as near to the top of the file as possible. If this is not done, Pod::Simple will will attempt to guess the encoding and may be successful if it's Latin-1 or UTF-8, but it will produce warnings. See perlpod(1) for more information. --errors=style [2.5.0] Set the error handling style. "die" says to throw an exception on any POD formatting error. "stderr" says to report errors on standard error, but not to throw an exception. "pod" says to include a POD ERRORS section in the resulting documentation summarizing the errors. "none" ignores POD errors entirely, as much as possible. The default is "die". --guesswork=rule[,rule...] [5.01] By default, pod2text applies some default formatting rules based on guesswork and regular expressions that are intended to make writing Perl documentation easier and require less explicit markup. These rules may not always be appropriate, particularly for documentation that isn't about Perl. This option allows turning all or some of it off. The special rule "all" enables all guesswork. This is also the default for backward compatibility reasons. The special rule "none" disables all guesswork. Otherwise, the value of this option should be a comma-separated list of one or more of the following keywords: quoting If no guesswork is enabled, any text enclosed in C<> is surrounded by double quotes in nroff (terminal) output unless the contents are already quoted. When this guesswork is enabled, quote marks will also be suppressed for Perl variables, function names, function calls, numbers, and hex constants. Any unknown guesswork name is silently ignored (for potential future compatibility), so be careful about spelling. -i indent, --indent=indent [1.00] Set the number of spaces to indent regular text, and the default indentation for "=over" blocks. Defaults to 4 spaces if this option isn't given. -h, --help [1.00] Print out usage information and exit. -l, --loose [1.00] Print a blank line after a "=head1" heading. Normally, no blank line is printed after "=head1", although one is still printed after "=head2", because this is the expected formatting for manual pages; if you're formatting arbitrary text documents, using this option is recommended. -m width, --left-margin=width, --margin=width [1.24] The width of the left margin in spaces. Defaults to 0. This is the margin for all text, including headings, not the amount by which regular text is indented; for the latter, see -i option. --nourls [2.5.0] Normally, L<> formatting codes with a URL but anchor text are formatted to show both the anchor text and the URL. In other words: L<foo|http://example.com/> is formatted as: foo <http://example.com/> This flag, if given, suppresses the URL when anchor text is given, so this example would be formatted as just "foo". This can produce less cluttered output in cases where the URLs are not particularly important. -o, --overstrike [1.06] Format the output with overstrike printing. Bold text is rendered as character, backspace, character. Italics and file names are rendered as underscore, backspace, character. Many pagers, such as less, know how to convert this to bold or underlined text. -q quotes, --quotes=quotes [4.00] Sets the quote marks used to surround C<> text to quotes. If quotes is a single character, it is used as both the left and right quote. Otherwise, it is split in half, and the first half of the string is used as the left quote and the second is used as the right quote. quotes may also be set to the special value "none", in which case no quote marks are added around C<> text. -s, --sentence [1.00] Assume each sentence ends with two spaces and try to preserve that spacing. Without this option, all consecutive whitespace in non-verbatim paragraphs is compressed into a single space. --stderr [2.1.3] By default, pod2text dies if any errors are detected in the POD input. If --stderr is given and no --errors flag is present, errors are sent to standard error, but pod2text does not abort. This is equivalent to "--errors=stderr" and is supported for backward compatibility. -t, --termcap [1.00] Try to determine the width of the screen and the bold and underline sequences for the terminal from termcap, and use that information in formatting the output. Output will be wrapped at two columns less than the width of your terminal device. Using this option requires that your system have a termcap file somewhere where Term::Cap can find it and requires that your system support termios. With this option, the output of pod2text will contain terminal control sequences for your current terminal type. -u, --utf8 [2.2.0] Set the output encoding to UTF-8. This is equivalent to "--encoding=UTF-8" and is supported for backward compatibility. -w, --width=width, -width [1.00] The column at which to wrap text on the right-hand side. Defaults to 76, unless -t is given, in which case it's two columns less than the width of your terminal device. EXIT STATUS As long as all documents processed result in some output, even if that output includes errata (a "POD ERRORS" section generated with "--errors=pod"), pod2text will exit with status 0. If any of the documents being processed do not result in an output document, pod2text will exit with status 1. If there are syntax errors in a POD document being processed and the error handling style is set to the default of "die", pod2text will abort immediately with exit status 255. DIAGNOSTICS If pod2text fails with errors, see Pod::Text and Pod::Simple for information about what those errors might mean. Internally, it can also produce the following diagnostics: -c (--color) requires Term::ANSIColor be installed (F) -c or --color were given, but Term::ANSIColor could not be loaded. Unknown option: %s (F) An unknown command line option was given. In addition, other Getopt::Long error messages may result from invalid command-line options. ENVIRONMENT COLUMNS If -t is given, pod2text will take the current width of your screen from this environment variable, if available. It overrides terminal width information in TERMCAP. TERMCAP If -t is given, pod2text will use the contents of this environment variable if available to determine the correct formatting sequences for your current terminal device. AUTHOR Russ Allbery <rra@cpan.org>. COPYRIGHT AND LICENSE Copyright 1999-2001, 2004, 2006, 2008, 2010, 2012-2019, 2022 Russ Allbery <rra@cpan.org> This program is free software; you may redistribute it and/or modify it under the same terms as Perl itself. SEE ALSO Encode::Supported, Pod::Text, Pod::Text::Color, Pod::Text::Overstrike, Pod::Text::Termcap, Pod::Simple, perlpod(1) The current version of this script is always available from its web site at <https://www.eyrie.org/~eagle/software/podlators/>. It is also part of the Perl core distribution as of 5.6.0. perl v5.38.2 2023-11-28 POD2TEXT(1)
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addbuiltin
| null | null | null | null | null |
dart
| null | null | null | null | null |
nltk
| null | null | null | null | null |
imageio_remove_bin
| null | null | null | null | null |
xzegrep
|
xzgrep invokes grep(1) on uncompressed contents of files. The formats of the files are determined from the filename suffixes. Any file with a suffix supported by xz(1), gzip(1), bzip2(1), lzop(1), zstd(1), or lz4(1) will be decompressed; all other files are assumed to be uncompressed. If no files are specified or file is - then standard input is read. When reading from standard input, only files supported by xz(1) are decompressed. Other files are assumed to be in uncompressed form already. Most options of grep(1) are supported. However, the following options are not supported: -r, --recursive -R, --dereference-recursive -d, --directories=action -Z, --null -z, --null-data --include=glob --exclude=glob --exclude-from=file --exclude-dir=glob xzegrep is an alias for xzgrep -E. xzfgrep is an alias for xzgrep -F. The commands lzgrep, lzegrep, and lzfgrep are provided for backward compatibility with LZMA Utils. EXIT STATUS 0 At least one match was found from at least one of the input files. No errors occurred. 1 No matches were found from any of the input files. No errors occurred. >1 One or more errors occurred. It is unknown if matches were found. ENVIRONMENT GREP If GREP is set to a non-empty value, it is used instead of grep, grep -E, or grep -F. SEE ALSO grep(1), xz(1), gzip(1), bzip2(1), lzop(1), zstd(1), lz4(1), zgrep(1) Tukaani 2024-02-13 XZGREP(1)
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xzgrep - search possibly-compressed files for patterns
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xzgrep [option...] [pattern_list] [file...] xzegrep ... xzfgrep ... lzgrep ... lzegrep ... lzfgrep ...
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sem
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GNU sem is an alias for GNU parallel --semaphore. GNU sem acts as a counting semaphore. When GNU sem is called with command it starts the command in the background. When num number of commands are running in the background, GNU sem waits for one of these to complete before starting the command. GNU sem does not read any arguments to build the command (no -a, :::, and ::::). It simply waits for a semaphore to become available and then runs the command given. Before looking at the options you may want to check out the examples after the list of options. That will give you an idea of what GNU sem is capable of.
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sem - semaphore for executing shell command lines in parallel
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sem [--fg] [--id <id>] [--semaphoretimeout <secs>] [-j <num>] [--wait] command
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command Command to execute. The command may be followed by arguments for the command. --bg Run command in background thus GNU sem will not wait for completion of the command before exiting. This is the default. In toilet analogy: GNU sem waits for a toilet to be available, gives the toilet to a person, and exits immediately. See also: --fg --jobs N -j N --max-procs N -P N Run up to N commands in parallel. Default is 1 thus acting like a mutex. In toilet analogy: -j is the number of toilets. --jobs +N -j +N --max-procs +N -P +N Add N to the number of CPU cores. Run up to this many jobs in parallel. For compute intensive jobs -j +0 is useful as it will run number-of-cpu-cores jobs simultaneously. --jobs -N -j -N --max-procs -N -P -N Subtract N from the number of CPU cores. Run up to this many jobs in parallel. If the evaluated number is less than 1 then 1 will be used. See also --use-cpus-instead-of-cores. --jobs N% -j N% --max-procs N% -P N% Multiply N% with the number of CPU cores. Run up to this many jobs in parallel. If the evaluated number is less than 1 then 1 will be used. See also --use-cpus-instead-of-cores. --jobs procfile -j procfile --max-procs procfile -P procfile Read parameter from file. Use the content of procfile as parameter for -j. E.g. procfile could contain the string 100% or +2 or 10. --pipe Pass stdin (standard input) to command. If command read from stdin (standard input), use --pipe. --semaphorename name --id name Use name as the name of the semaphore. Default is the name of the controlling tty (output from tty). The default normally works as expected when used interactively, but when used in a script name should be set. $$ or my_task_name are often a good value. The semaphore is stored in ~/.parallel/semaphores/ In toilet analogy the name corresponds to different types of toilets: e.g. male, female, customer, staff. --fg Do not put command in background. In toilet analogy: GNU sem waits for a toilet to be available, takes a person to the toilet, waits for the person to finish, and exits. --semaphoretimeout secs --st secs If secs > 0: If the semaphore is not released within secs seconds, take it anyway. If secs < 0: If the semaphore is not released within secs seconds, exit. In toilet analogy: secs > 0: If no toilet becomes available within secs seconds, pee on the floor. secs < 0: If no toilet becomes available within secs seconds, exit without doing anything. --wait Wait for all commands to complete. In toilet analogy: Wait until all toilets are empty, then exit. UNDERSTANDING A SEMAPHORE Try the following example: sem -j 2 'sleep 1;echo 1 finished'; echo sem 1 exited sem -j 2 'sleep 2;echo 2 finished'; echo sem 2 exited sem -j 2 'sleep 3;echo 3 finished'; echo sem 3 exited sem -j 2 'sleep 4;echo 4 finished'; echo sem 4 exited sem --wait; echo sem --wait done In toilet analogy this uses 2 toilets (-j 2). GNU sem takes '1' to a toilet, and exits immediately. While '1' is sleeping, another GNU sem takes '2' to a toilet, and exits immediately. While '1' and '2' are sleeping, another GNU sem waits for a free toilet. When '1' finishes, a toilet becomes available, and this GNU sem stops waiting, and takes '3' to a toilet, and exits immediately. While '2' and '3' are sleeping, another GNU sem waits for a free toilet. When '2' finishes, a toilet becomes available, and this GNU sem stops waiting, and takes '4' to a toilet, and exits immediately. Finally another GNU sem waits for all toilets to become free. EXAMPLE: Gzipping *.log Run one gzip process per CPU core. Block until a CPU core becomes available. for i in *.log ; do echo $i sem -j+0 gzip $i ";" echo done done sem --wait EXAMPLE: Protecting pod2html from itself pod2html creates two files: pod2htmd.tmp and pod2htmi.tmp which it does not clean up. It uses these two files for a short time. But if you run multiple pod2html in parallel (e.g. in a Makefile with make -j) there is a risk that two different instances of pod2html will write to the files at the same time: # This may fail due to shared pod2htmd.tmp/pod2htmi.tmp files foo.html: pod2html foo.pod --outfile foo.html bar.html: pod2html bar.pod --outfile bar.html $ make -j foo.html bar.html You need to protect pod2html from running twice at the same time. sem running as a mutex will make sure only one runs: foo.html: sem --id pod2html pod2html foo.pod --outfile foo.html bar.html: sem --id pod2html pod2html bar.pod --outfile bar.html clean: foo.html bar.html sem --id pod2html --wait rm -f pod2htmd.tmp pod2htmi.tmp $ make -j foo.html bar.html clean BUGS None known. REPORTING BUGS Report bugs to <bug-parallel@gnu.org>. AUTHOR Copyright (C) 2010-2024 Ole Tange, http://ole.tange.dk and Free Software Foundation, Inc. LICENSE This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or at your option any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. Documentation license I Permission is granted to copy, distribute and/or modify this documentation under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the file LICENSES/GFDL-1.3-or-later.txt. Documentation license II You are free: to Share to copy, distribute and transmit the work to Remix to adapt the work Under the following conditions: Attribution You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work). Share Alike If you alter, transform, or build upon this work, you may distribute the resulting work only under the same, similar or a compatible license. With the understanding that: Waiver Any of the above conditions can be waived if you get permission from the copyright holder. Public Domain Where the work or any of its elements is in the public domain under applicable law, that status is in no way affected by the license. Other Rights In no way are any of the following rights affected by the license: • Your fair dealing or fair use rights, or other applicable copyright exceptions and limitations; • The author's moral rights; • Rights other persons may have either in the work itself or in how the work is used, such as publicity or privacy rights. Notice For any reuse or distribution, you must make clear to others the license terms of this work. A copy of the full license is included in the file as LICENCES/CC-BY-SA-4.0.txt DEPENDENCIES GNU sem uses Perl, and the Perl modules Getopt::Long, Symbol, Fcntl. SEE ALSO parallel(1) 20240522 2024-06-22 SEM(1)
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pinentry-tty
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gsettings
| null | null | null | null | null |
btoa
| null | null | null | null | null |
jxl_from_tree
| null | null | null | null | null |
pngfix
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isql
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isql and iusql are command-line tools allowing users to execute SQL interactively or in batches. The tools provide several useful features, including an option to generate output wrapped in an HTML table. iusql is the same as isql but includes built-in Unicode support. Some data sources only work with iusql. An important difference between the two tools is that isql connects using SQLConnect and iusql connects using SQLDriverConnect. ARGUMENTS DSN The Data Source Name (DSN) used to connect to the SQL database. unixODBC looks for the specified DSN in /etc/odbc.ini and $HOME/.odbc.ini, with the latter taking precedence. When searching the configuration files, unixODBC looks for a bare name. If the DSN begins with a semicolon, it is treated as a connection string. The connection string can contain a DSN and/or other semicolon-separated parameters. USER Specifies the database user or role under which the connection should be made. This parameter overrides any UID specified in the data source configuration files. PASSWORD Password required to access the database for the specified USER. This parameter overrides any PASSWORD specified in the data source configuration files. When using iusql, passwords containing semicolons should be escaped with braces (curly brackets) and terminated with a semicolon. Refer to the Examples section below for syntax. "ConnectionString" A connection string starting with DSN=, DRIVER= or FILEDSN= will be passed unchanged to SQLDriverConnect. This option allows for the use of more complex syntax in a connection string than would otherwise be possible by just using DSN, UID and PWD. It also (and this was the main reason for its inclusion) allows passwords to contain semicolons without having to add complex escape syntax to the existing code.
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isql, iusql - unixODBC interactive SQL command-line tools
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isql DSN [USER [PASSWORD]] [options] iusql DSN [USER [PASSWORD]] [options] iusql "ConnectionString" [options]
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-b Run 'isql' in non-interactive batch mode. In this mode, 'isql' processes from standard input, expecting one SQL command per line. -dDELIMITER Delimit columns with the specified delimiter. -xHEX Delimit columns with the character represented in hexadecimal by HEX. The hexadecimal code must be in the format 0xNN (e.g. 0x09 for the TAB character). -w Format the result as an HTML table. -c Output the names of the columns on the first row. This option can only be used with the -d or -x options. -mNUM Limit the column display width to NUM characters. -lLOCALE Set the character locale to LOCALE. -q Wrap the character fields in double quotes. -3 Use calls from ODBC version 3. -n Process multiple lines of SQL, terminated with the GO command. -e Use SQLExecDirect instead of Prepare. -k Use SQLDriverConnect. -v Enable verbose mode, fully describing all errors. This option is useful for debugging. --version Display the program version. -LNUM Set the maximum number of characters displayed from a character field to NUM. The default value is 300 characters. COMMANDS This section briefly describes some isql and iusql run-time commands. help List all tables in the database. help table List all columns in the table. help help List all help options.
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A bare DSN: $ iusql WebDB MyID MyPWD -w -b < My.sql Connects to the WebDB DSN as user MyID with password MyPWD, then executes the commands in the My.sql file and returns the results wrapped in an HTML table. Each line in My.sql must only contain one SQL command, except for the last line, which must be blank (unless the -n option is specified). A DSN in a connection string: Note the leading semicolon on the connection string. $ iusql ";DSN=WebDB" MyID MyPWD -w -b < My.sql Options in the DSN may be overridden in the connection string: $ iusql ";DSN=WebDB;Driver=PostgreSQL ODBC;UID=MyID;PASSWORD=secret;Debug=1;CommLog=1" -v A string DSN: A string DSN may be provided in its entirety, with no file DSN reference at all: $ iusql ";Driver=PostgreSQL Unicode;UID=MyID;PASSWORD=secret" -v A password containing a semicolon (iusql): $ iusql WebDB MyID '{My;PWD};' $ iusql 'DSN=WebDB;UID=MyID;PWD={My;PWD};' TROUBLESHOOTING Cryptic error messages Re-run isql or iusql with the -v flag to get more information from errors, and/or enable Trace mode in odbcinst.ini. Missing driver definition Check that the driver name specified by the Driver entry in the odbc.ini data-source definition is present in odbcinst.ini and exactly matches the odbcinst.ini [section name]. Unloadable or incompatible driver If the ODBC driver is properly specified for the data source, it is possible that the driver is not loadable. Check for mix-ups between Unicode and ANSI drivers, and verify the driver paths in the odbcinst.ini [section name]. Unicode data sources with ANSI clients Some data sources are Unicode-only and require the use of iusql. If isql reports [IM002][unixODBC][Driver Manager]Data source name not found and no default driver specified [ISQL]ERROR: Could not SQLConnect but the data source and driver required are listed by odbcinst -q -d and odbcinst -q -s then try iusql. FILES /etc/odbc.ini Configuration file containing system-wide Data Source Name (DSN) definitions. See odbc.ini(5) for more information. $HOME/.odbc.ini Configuration file containing user-specific Data Source Name (DSN) definitions. See odbc.ini(5) for more information. SEE ALSO unixODBC(7), odbcinst(1), odbc.ini(5) "The unixODBC Administrator Manual (HTML)" AUTHORS The authors of unixODBC are Peter Harvey <pharvey@codebydesign.com> and Nick Gorham <nick@lurcher.org>. For a full list of contributors, refer to the AUTHORS file. COPYRIGHT unixODBC is licensed under the GNU Lesser General Public License. For details about the license, see the COPYING file. version 2.3.12 Thu 14 Jan 2021 isql(1)
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pdfattach
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Pdfattach adds a new embedded file (attachment) to an existing Portable Document Format (PDF) file.
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pdfattach - Portable Document Format (PDF) document embedded file creator (version 3.03)
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pdfattach [options] input-PDF-file file-to-attach output-PDF-file
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-replace Replace embedded file with same name (if it exists) -v Print copyright and version information. -h Print usage information. (-help and --help are equivalent.) EXIT CODES 0 No error. 1 Error opening input PDF file. 2 Error opening file to attach. 3 Output file already exists. 3 There is already an attached file with that name. 5 Error saving the output file. AUTHOR The pdfattach software and documentation are copyright 2019 The Poppler developers SEE ALSO pdfdetach(1), pdfimages(1), pdfinfo(1), pdftocairo(1), pdftohtml(1), pdftoppm(1), pdftops(1), pdftotext(1) pdfseparate(1), pdfsig(1), pdfunite(1) 10 Febuary 2019 pdfattach(1)
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butteraugli_main
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mysqltest_safe_process
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gfalse
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Exit with a status code indicating failure. --help display this help and exit --version output version information and exit NOTE: your shell may have its own version of false, which usually supersedes the version described here. Please refer to your shell's documentation for details about the options it supports. AUTHOR Written by Jim Meyering. REPORTING BUGS GNU coreutils online help: <https://www.gnu.org/software/coreutils/> Report any translation bugs to <https://translationproject.org/team/> COPYRIGHT Copyright © 2023 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. SEE ALSO Full documentation <https://www.gnu.org/software/coreutils/false> or available locally via: info '(coreutils) false invocation' GNU coreutils 9.3 April 2023 FALSE(1)
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false - do nothing, unsuccessfully
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false [ignored command line arguments] false OPTION
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shapeclustering
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env_parallel.tcsh
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glib-compile-schemas
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shtab
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webpmux
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This manual page documents the webpmux command. webpmux can be used to create/extract from animated WebP files, as well as to add/extract/strip XMP/EXIF metadata and ICC profile. If a single file name (not starting with the character '-') is supplied as the argument, the command line arguments are actually tokenized from this file. This allows for easy scripting or using a large number of arguments.
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webpmux - create animated WebP files from non-animated WebP images, extract frames from animated WebP images, and manage XMP/EXIF metadata and ICC profile.
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webpmux -get GET_OPTIONS INPUT -o OUTPUT webpmux -set SET_OPTIONS INPUT -o OUTPUT webpmux -strip STRIP_OPTIONS INPUT -o OUTPUT webpmux -frame FRAME_OPTIONS [ -frame ... ] [ -loop LOOP_COUNT ] [ -bgcolor BACKGROUND_COLOR ] -o OUTPUT webpmux -duration DURATION OPTIONS [ -duration ... ] INPUT -o OUTPUT webpmux -info INPUT webpmux [-h|-help] webpmux -version webpmux argument_file_name
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GET_OPTIONS (-get): icc Get ICC profile. exif Get EXIF metadata. xmp Get XMP metadata. frame n Get nth frame from an animated image. (n = 0 has a special meaning: last frame). SET_OPTIONS (-set) loop loop_count Set loop count on an animated file. Where: 'loop_count' must be in range [0, 65535]. bgcolor A,R,G,B Set the background color of the canvas on an animated file. where: 'A', 'R', 'G' and 'B' are integers in the range 0 to 255 specifying the Alpha, Red, Green and Blue component values respectively. icc file.icc Set ICC profile. Where: 'file.icc' contains the ICC profile to be set. exif file.exif Set EXIF metadata. Where: 'file.exif' contains the EXIF metadata to be set. xmp file.xmp Set XMP metadata. Where: 'file.xmp' contains the XMP metadata to be set. STRIP_OPTIONS (-strip) icc Strip ICC profile. exif Strip EXIF metadata. xmp Strip XMP metadata. DURATION_OPTIONS (-duration) Amend the duration of a specific interval of frames. This option is only effective on animated WebP and has no effect on a single-frame file. duration[,start[,end]] Where: duration is the duration for the interval in milliseconds (mandatory). Must be non-negative. start is the starting frame index of the interval (optional). end is the ending frame index (inclusive) of the interval (optional). The three typical usages of this option are: -duration d set the duration to 'd' for the whole animation. -duration d,f set the duration of frame 'f' to 'd'. -duration d,start,end set the duration to 'd' for the whole [start,end] interval. Note that the frames outside of the [start, end] interval will remain untouched. The 'end' value '0' has the special meaning 'last frame of the animation'. Reminder: frame indexing starts at '1'. FRAME_OPTIONS (-frame) Create an animated WebP file from multiple (non-animated) WebP images. file_i +di[+xi+yi[+mi[bi]]] Where: 'file_i' is the i'th frame (WebP format), 'xi','yi' specify the image offset for this frame, 'di' is the pause duration before next frame, 'mi' is the dispose method for this frame (0 for NONE or 1 for BACKGROUND) and 'bi' is the blending method for this frame (+b for BLEND or -b for NO_BLEND). Argument 'bi' can be omitted and will default to +b (BLEND). Also, 'mi' can be omitted if 'bi' is omitted and will default to 0 (NONE). Finally, if 'mi' and 'bi' are omitted then 'xi' and 'yi' can be omitted and will default to +0+0. -loop n Loop the frames n number of times. 0 indicates the frames should loop forever. Valid range is 0 to 65535 [Default: 0 (infinite)]. -bgcolor A,R,G,B Background color of the canvas. where: 'A', 'R', 'G' and 'B' are integers in the range 0 to 255 specifying the Alpha, Red, Green and Blue component values respectively [Default: 255,255,255,255]. INPUT Input file in WebP format. OUTPUT (-o) Output file in WebP format. Note: The nature of EXIF, XMP and ICC data is not checked and is assumed to be valid. BUGS Please report all bugs to the issue tracker: https://bugs.chromium.org/p/webp Patches welcome! See this page to get started: https://www.webmproject.org/code/contribute/submitting-patches/
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Add ICC profile: webpmux -set icc image_profile.icc in.webp -o icc_container.webp Extract ICC profile: webpmux -get icc icc_container.webp -o image_profile.icc Strip ICC profile: webpmux -strip icc icc_container.webp -o without_icc.webp Add XMP metadata: webpmux -set xmp image_metadata.xmp in.webp -o xmp_container.webp Extract XMP metadata: webpmux -get xmp xmp_container.webp -o image_metadata.xmp Strip XMP metadata: webpmux -strip xmp xmp_container.webp -o without_xmp.webp Add EXIF metadata: webpmux -set exif image_metadata.exif in.webp -o exif_container.webp Extract EXIF metadata: webpmux -get exif exif_container.webp -o image_metadata.exif Strip EXIF metadata: webpmux -strip exif exif_container.webp -o without_exif.webp Create an animated WebP file from 3 (non-animated) WebP images: webpmux -frame 1.webp +100 -frame 2.webp +100+50+50 -frame 3.webp +100+50+50+1+b -loop 10 -bgcolor 255,255,255,255 -o anim_container.webp Get the 2nd frame from an animated WebP file: webpmux -get frame 2 anim_container.webp -o frame_2.webp Using -get/-set/-strip with input file name starting with '-': webpmux -set icc image_profile.icc -o icc_container.webp -- ---in.webp webpmux -get icc -o image_profile.icc -- ---icc_container.webp webpmux -strip icc -o without_icc.webp -- ---icc_container.webp AUTHORS webpmux is a part of libwebp and was written by the WebP team. The latest source tree is available at https://chromium.googlesource.com/webm/libwebp This manual page was written by Vikas Arora <vikaas.arora@gmail.com>, for the Debian project (and may be used by others). SEE ALSO cwebp(1), dwebp(1), gif2webp(1) Please refer to https://developers.google.com/speed/webp/ for additional information. November 17, 2021 WEBPMUX(1)
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mpg123-id3dump
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bltest
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fc-query
| null | null | null | null | null |
pk_verify
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brotli
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undill
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cargo
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This program is a package manager and build tool for the Rust language, available at <https://rust-lang.org>. COMMANDS Build Commands cargo-bench(1) Execute benchmarks of a package. cargo-build(1) Compile a package. cargo-check(1) Check a local package and all of its dependencies for errors. cargo-clean(1) Remove artifacts that Cargo has generated in the past. cargo-doc(1) Build a package’s documentation. cargo-fetch(1) Fetch dependencies of a package from the network. cargo-fix(1) Automatically fix lint warnings reported by rustc. cargo-run(1) Run a binary or example of the local package. cargo-rustc(1) Compile a package, and pass extra options to the compiler. cargo-rustdoc(1) Build a package’s documentation, using specified custom flags. cargo-test(1) Execute unit and integration tests of a package. Manifest Commands cargo-generate-lockfile(1) Generate Cargo.lock for a project. cargo-locate-project(1) Print a JSON representation of a Cargo.toml file’s location. cargo-metadata(1) Output the resolved dependencies of a package in machine-readable format. cargo-pkgid(1) Print a fully qualified package specification. cargo-tree(1) Display a tree visualization of a dependency graph. cargo-update(1) Update dependencies as recorded in the local lock file. cargo-vendor(1) Vendor all dependencies locally. cargo-verify-project(1) Check correctness of crate manifest. Package Commands cargo-init(1) Create a new Cargo package in an existing directory. cargo-install(1) Build and install a Rust binary. cargo-new(1) Create a new Cargo package. cargo-search(1) Search packages in crates.io. cargo-uninstall(1) Remove a Rust binary. Publishing Commands cargo-login(1) Save an API token from the registry locally. cargo-logout(1) Remove an API token from the registry locally. cargo-owner(1) Manage the owners of a crate on the registry. cargo-package(1) Assemble the local package into a distributable tarball. cargo-publish(1) Upload a package to the registry. cargo-yank(1) Remove a pushed crate from the index. General Commands cargo-help(1) Display help information about Cargo. cargo-version(1) Show version information.
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cargo — The Rust package manager
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cargo [options] command [args] cargo [options] --version cargo [options] --list cargo [options] --help cargo [options] --explain code
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Special Options -V, --version Print version info and exit. If used with --verbose, prints extra information. --list List all installed Cargo subcommands. If used with --verbose, prints extra information. --explain code Run rustc --explain CODE which will print out a detailed explanation of an error message (for example, E0004). Display Options -v, --verbose Use verbose output. May be specified twice for “very verbose” output which includes extra output such as dependency warnings and build script output. May also be specified with the term.verbose config value <https://doc.rust-lang.org/cargo/reference/config.html>. -q, --quiet Do not print cargo log messages. May also be specified with the term.quiet config value <https://doc.rust-lang.org/cargo/reference/config.html>. --color when Control when colored output is used. Valid values: • auto (default): Automatically detect if color support is available on the terminal. • always: Always display colors. • never: Never display colors. May also be specified with the term.color config value <https://doc.rust-lang.org/cargo/reference/config.html>. Manifest Options --frozen, --locked Either of these flags requires that the Cargo.lock file is up-to-date. If the lock file is missing, or it needs to be updated, Cargo will exit with an error. The --frozen flag also prevents Cargo from attempting to access the network to determine if it is out-of-date. These may be used in environments where you want to assert that the Cargo.lock file is up-to-date (such as a CI build) or want to avoid network access. --offline Prevents Cargo from accessing the network for any reason. Without this flag, Cargo will stop with an error if it needs to access the network and the network is not available. With this flag, Cargo will attempt to proceed without the network if possible. Beware that this may result in different dependency resolution than online mode. Cargo will restrict itself to crates that are downloaded locally, even if there might be a newer version as indicated in the local copy of the index. See the cargo-fetch(1) command to download dependencies before going offline. May also be specified with the net.offline config value <https://doc.rust-lang.org/cargo/reference/config.html>. Common Options +toolchain If Cargo has been installed with rustup, and the first argument to cargo begins with +, it will be interpreted as a rustup toolchain name (such as +stable or +nightly). See the rustup documentation <https://rust-lang.github.io/rustup/overrides.html> for more information about how toolchain overrides work. --config KEY=VALUE or PATH Overrides a Cargo configuration value. The argument should be in TOML syntax of KEY=VALUE, or provided as a path to an extra configuration file. This flag may be specified multiple times. See the command-line overrides section <https://doc.rust-lang.org/cargo/reference/config.html#command-line-overrides> for more information. -C PATH Changes the current working directory before executing any specified operations. This affects things like where cargo looks by default for the project manifest (Cargo.toml), as well as the directories searched for discovering .cargo/config.toml, for example. This option must appear before the command name, for example cargo -C path/to/my-project build. This option is only available on the nightly channel <https://doc.rust-lang.org/book/appendix-07-nightly-rust.html> and requires the -Z unstable-options flag to enable (see #10098 <https://github.com/rust-lang/cargo/issues/10098>). -h, --help Prints help information. -Z flag Unstable (nightly-only) flags to Cargo. Run cargo -Z help for details. ENVIRONMENT See the reference <https://doc.rust-lang.org/cargo/reference/environment-variables.html> for details on environment variables that Cargo reads. EXIT STATUS • 0: Cargo succeeded. • 101: Cargo failed to complete. FILES ~/.cargo/ Default location for Cargo’s “home” directory where it stores various files. The location can be changed with the CARGO_HOME environment variable. $CARGO_HOME/bin/ Binaries installed by cargo-install(1) will be located here. If using rustup <https://rust-lang.github.io/rustup/>, executables distributed with Rust are also located here. $CARGO_HOME/config.toml The global configuration file. See the reference <https://doc.rust-lang.org/cargo/reference/config.html> for more information about configuration files. .cargo/config.toml Cargo automatically searches for a file named .cargo/config.toml in the current directory, and all parent directories. These configuration files will be merged with the global configuration file. $CARGO_HOME/credentials.toml Private authentication information for logging in to a registry. $CARGO_HOME/registry/ This directory contains cached downloads of the registry index and any downloaded dependencies. $CARGO_HOME/git/ This directory contains cached downloads of git dependencies. Please note that the internal structure of the $CARGO_HOME directory is not stable yet and may be subject to change.
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1. Build a local package and all of its dependencies: cargo build 2. Build a package with optimizations: cargo build --release 3. Run tests for a cross-compiled target: cargo test --target i686-unknown-linux-gnu 4. Create a new package that builds an executable: cargo new foobar 5. Create a package in the current directory: mkdir foo && cd foo cargo init . 6. Learn about a command’s options and usage: cargo help clean BUGS See <https://github.com/rust-lang/cargo/issues> for issues. SEE ALSO rustc(1), rustdoc(1) CARGO(1)
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