Add files using upload-large-folder tool

go/src/cmd/internal/archive/archive.go

@@ -0,0 +1,503 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package archive implements reading of archive files generated by the Go
+// toolchain.
+package archive
+
+import (
+	"bufio"
+	"bytes"
+	"cmd/internal/bio"
+	"cmd/internal/goobj"
+	"errors"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+	"unicode/utf8"
+)
+
+/*
+The archive format is:
+
+First, on a line by itself
+	!<arch>
+
+Then zero or more file records. Each file record has a fixed-size one-line header
+followed by data bytes followed by an optional padding byte. The header is:
+
+	%-16s%-12d%-6d%-6d%-8o%-10d`
+	name mtime uid gid mode size
+
+(note the trailing backquote). The %-16s here means at most 16 *bytes* of
+the name, and if shorter, space padded on the right.
+*/
+
+// A Data is a reference to data stored in an object file.
+// It records the offset and size of the data, so that a client can
+// read the data only if necessary.
+type Data struct {
+	Offset int64
+	Size   int64
+}
+
+type Archive struct {
+	f       *os.File
+	Entries []Entry
+}
+
+func (a *Archive) File() *os.File { return a.f }
+
+type Entry struct {
+	Name  string
+	Type  EntryType
+	Mtime int64
+	Uid   int
+	Gid   int
+	Mode  os.FileMode
+	Data
+	Obj *GoObj // nil if this entry is not a Go object file
+}
+
+type EntryType int
+
+const (
+	EntryPkgDef EntryType = iota
+	EntryGoObj
+	EntryNativeObj
+	EntrySentinelNonObj
+)
+
+func (e *Entry) String() string {
+	return fmt.Sprintf("%s %6d/%-6d %12d %s %s",
+		(e.Mode & 0777).String(),
+		e.Uid,
+		e.Gid,
+		e.Size,
+		time.Unix(e.Mtime, 0).Format(timeFormat),
+		e.Name)
+}
+
+type GoObj struct {
+	TextHeader []byte
+	Arch       string
+	Data
+}
+
+const (
+	entryHeader = "%s%-12d%-6d%-6d%-8o%-10d`\n"
+	// In entryHeader the first entry, the name, is always printed as 16 bytes right-padded.
+	entryLen   = 16 + 12 + 6 + 6 + 8 + 10 + 1 + 1
+	timeFormat = "Jan _2 15:04 2006"
+)
+
+var (
+	archiveHeader = []byte("!<arch>\n")
+	archiveMagic  = []byte("`\n")
+	goobjHeader   = []byte("go objec") // truncated to size of archiveHeader
+
+	errCorruptArchive   = errors.New("corrupt archive")
+	errTruncatedArchive = errors.New("truncated archive")
+	errCorruptObject    = errors.New("corrupt object file")
+	errNotObject        = errors.New("unrecognized object file format")
+)
+
+type ErrGoObjOtherVersion struct{ magic []byte }
+
+func (e ErrGoObjOtherVersion) Error() string {
+	return fmt.Sprintf("go object of a different version: %q", e.magic)
+}
+
+// An objReader is an object file reader.
+type objReader struct {
+	a      *Archive
+	b      *bio.Reader
+	err    error
+	offset int64
+	limit  int64
+	tmp    [256]byte
+}
+
+func (r *objReader) init(f *os.File) {
+	r.a = &Archive{f, nil}
+	r.offset, _ = f.Seek(0, io.SeekCurrent)
+	r.limit, _ = f.Seek(0, io.SeekEnd)
+	f.Seek(r.offset, io.SeekStart)
+	r.b = bio.NewReader(f)
+}
+
+// error records that an error occurred.
+// It returns only the first error, so that an error
+// caused by an earlier error does not discard information
+// about the earlier error.
+func (r *objReader) error(err error) error {
+	if r.err == nil {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
+		r.err = err
+	}
+	// panic("corrupt") // useful for debugging
+	return r.err
+}
+
+// peek returns the next n bytes without advancing the reader.
+func (r *objReader) peek(n int) ([]byte, error) {
+	if r.err != nil {
+		return nil, r.err
+	}
+	if r.offset >= r.limit {
+		r.error(io.ErrUnexpectedEOF)
+		return nil, r.err
+	}
+	b, err := r.b.Peek(n)
+	if err != nil {
+		if err != bufio.ErrBufferFull {
+			r.error(err)
+		}
+	}
+	return b, err
+}
+
+// readByte reads and returns a byte from the input file.
+// On I/O error or EOF, it records the error but returns byte 0.
+// A sequence of 0 bytes will eventually terminate any
+// parsing state in the object file. In particular, it ends the
+// reading of a varint.
+func (r *objReader) readByte() byte {
+	if r.err != nil {
+		return 0
+	}
+	if r.offset >= r.limit {
+		r.error(io.ErrUnexpectedEOF)
+		return 0
+	}
+	b, err := r.b.ReadByte()
+	if err != nil {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
+		r.error(err)
+		b = 0
+	} else {
+		r.offset++
+	}
+	return b
+}
+
+// readFull reads exactly len(b) bytes from the input file.
+// If an error occurs, read returns the error but also
+// records it, so it is safe for callers to ignore the result
+// as long as delaying the report is not a problem.
+func (r *objReader) readFull(b []byte) error {
+	if r.err != nil {
+		return r.err
+	}
+	if r.offset+int64(len(b)) > r.limit {
+		return r.error(io.ErrUnexpectedEOF)
+	}
+	n, err := io.ReadFull(r.b, b)
+	r.offset += int64(n)
+	if err != nil {
+		return r.error(err)
+	}
+	return nil
+}
+
+// skip skips n bytes in the input.
+func (r *objReader) skip(n int64) {
+	if n < 0 {
+		r.error(fmt.Errorf("debug/goobj: internal error: misuse of skip"))
+	}
+	if n < int64(len(r.tmp)) {
+		// Since the data is so small, a just reading from the buffered
+		// reader is better than flushing the buffer and seeking.
+		r.readFull(r.tmp[:n])
+	} else if n <= int64(r.b.Buffered()) {
+		// Even though the data is not small, it has already been read.
+		// Advance the buffer instead of seeking.
+		for n > int64(len(r.tmp)) {
+			r.readFull(r.tmp[:])
+			n -= int64(len(r.tmp))
+		}
+		r.readFull(r.tmp[:n])
+	} else {
+		// Seek, giving up buffered data.
+		r.b.MustSeek(r.offset+n, io.SeekStart)
+		r.offset += n
+	}
+}
+
+// New writes to f to make a new archive.
+func New(f *os.File) (*Archive, error) {
+	_, err := f.Write(archiveHeader)
+	if err != nil {
+		return nil, err
+	}
+	return &Archive{f: f}, nil
+}
+
+// Parse parses an object file or archive from f.
+func Parse(f *os.File, verbose bool) (*Archive, error) {
+	var r objReader
+	r.init(f)
+	t, err := r.peek(8)
+	if err != nil {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
+		return nil, err
+	}
+
+	switch {
+	default:
+		return nil, errNotObject
+
+	case bytes.Equal(t, archiveHeader):
+		if err := r.parseArchive(verbose); err != nil {
+			return nil, err
+		}
+	case bytes.Equal(t, goobjHeader):
+		off := r.offset
+		o := &GoObj{}
+		if err := r.parseObject(o, r.limit-off); err != nil {
+			return nil, err
+		}
+		r.a.Entries = []Entry{{
+			Name: f.Name(),
+			Type: EntryGoObj,
+			Data: Data{off, r.limit - off},
+			Obj:  o,
+		}}
+	}
+
+	return r.a, nil
+}
+
+// trimSpace removes trailing spaces from b and returns the corresponding string.
+// This effectively parses the form used in archive headers.
+func trimSpace(b []byte) string {
+	return string(bytes.TrimRight(b, " "))
+}
+
+// parseArchive parses a Unix archive of Go object files.
+func (r *objReader) parseArchive(verbose bool) error {
+	r.readFull(r.tmp[:8]) // consume header (already checked)
+	for r.offset < r.limit {
+		if err := r.readFull(r.tmp[:60]); err != nil {
+			return err
+		}
+		data := r.tmp[:60]
+
+		// Each file is preceded by this text header (slice indices in first column):
+		//	 0:16	name
+		//	16:28 date
+		//	28:34 uid
+		//	34:40 gid
+		//	40:48 mode
+		//	48:58 size
+		//	58:60 magic - `\n
+		// We only care about name, size, and magic, unless in verbose mode.
+		// The fields are space-padded on the right.
+		// The size is in decimal.
+		// The file data - size bytes - follows the header.
+		// Headers are 2-byte aligned, so if size is odd, an extra padding
+		// byte sits between the file data and the next header.
+		// The file data that follows is padded to an even number of bytes:
+		// if size is odd, an extra padding byte is inserted betw the next header.
+		if len(data) < 60 {
+			return errTruncatedArchive
+		}
+		if !bytes.Equal(data[58:60], archiveMagic) {
+			return errCorruptArchive
+		}
+		name := trimSpace(data[0:16])
+		var err error
+		get := func(start, end, base, bitsize int) int64 {
+			if err != nil {
+				return 0
+			}
+			var v int64
+			v, err = strconv.ParseInt(trimSpace(data[start:end]), base, bitsize)
+			return v
+		}
+		size := get(48, 58, 10, 64)
+		var (
+			mtime    int64
+			uid, gid int
+			mode     os.FileMode
+		)
+		if verbose {
+			mtime = get(16, 28, 10, 64)
+			uid = int(get(28, 34, 10, 32))
+			gid = int(get(34, 40, 10, 32))
+			mode = os.FileMode(get(40, 48, 8, 32))
+		}
+		if err != nil {
+			return errCorruptArchive
+		}
+		data = data[60:]
+		fsize := size + size&1
+		if fsize < 0 || fsize < size {
+			return errCorruptArchive
+		}
+		switch name {
+		case "__.PKGDEF":
+			r.a.Entries = append(r.a.Entries, Entry{
+				Name:  name,
+				Type:  EntryPkgDef,
+				Mtime: mtime,
+				Uid:   uid,
+				Gid:   gid,
+				Mode:  mode,
+				Data:  Data{r.offset, size},
+			})
+			r.skip(size)
+		case "preferlinkext", "dynimportfail":
+			if size == 0 {
+				// These are not actual objects, but rather sentinel
+				// entries put into the archive by the Go command to
+				// be read by the linker. See #62036.
+				r.a.Entries = append(r.a.Entries, Entry{
+					Name:  name,
+					Type:  EntrySentinelNonObj,
+					Mtime: mtime,
+					Uid:   uid,
+					Gid:   gid,
+					Mode:  mode,
+					Data:  Data{r.offset, size},
+				})
+				break
+			}
+			fallthrough
+		default:
+			var typ EntryType
+			var o *GoObj
+			offset := r.offset
+			p, err := r.peek(8)
+			if err != nil {
+				return err
+			}
+			if bytes.Equal(p, goobjHeader) {
+				typ = EntryGoObj
+				o = &GoObj{}
+				err := r.parseObject(o, size)
+				if err != nil {
+					return err
+				}
+			} else {
+				typ = EntryNativeObj
+				r.skip(size)
+			}
+			r.a.Entries = append(r.a.Entries, Entry{
+				Name:  name,
+				Type:  typ,
+				Mtime: mtime,
+				Uid:   uid,
+				Gid:   gid,
+				Mode:  mode,
+				Data:  Data{offset, size},
+				Obj:   o,
+			})
+		}
+		if size&1 != 0 {
+			r.skip(1)
+		}
+	}
+	return nil
+}
+
+// parseObject parses a single Go object file.
+// The object file consists of a textual header ending in "\n!\n"
+// and then the part we want to parse begins.
+// The format of that part is defined in a comment at the top
+// of cmd/internal/goobj/objfile.go.
+func (r *objReader) parseObject(o *GoObj, size int64) error {
+	h := make([]byte, 0, 256)
+	var c1, c2, c3 byte
+	for {
+		c1, c2, c3 = c2, c3, r.readByte()
+		h = append(h, c3)
+		// The new export format can contain 0 bytes.
+		// Don't consider them errors, only look for r.err != nil.
+		if r.err != nil {
+			return errCorruptObject
+		}
+		if c1 == '\n' && c2 == '!' && c3 == '\n' {
+			break
+		}
+	}
+	o.TextHeader = h
+	hs := strings.Fields(string(h))
+	if len(hs) >= 4 {
+		o.Arch = hs[3]
+	}
+	o.Offset = r.offset
+	o.Size = size - int64(len(h))
+
+	p, err := r.peek(8)
+	if err != nil {
+		return err
+	}
+	if !bytes.Equal(p, []byte(goobj.Magic)) {
+		if bytes.HasPrefix(p, []byte("\x00go1")) && bytes.HasSuffix(p, []byte("ld")) {
+			return r.error(ErrGoObjOtherVersion{p[1:]}) // strip the \x00 byte
+		}
+		return r.error(errCorruptObject)
+	}
+	r.skip(o.Size)
+	return nil
+}
+
+// AddEntry adds an entry to the end of a, with the content from r.
+func (a *Archive) AddEntry(typ EntryType, name string, mtime int64, uid, gid int, mode os.FileMode, size int64, r io.Reader) {
+	off, err := a.f.Seek(0, io.SeekEnd)
+	if err != nil {
+		log.Fatal(err)
+	}
+	n, err := fmt.Fprintf(a.f, entryHeader, exactly16Bytes(name), mtime, uid, gid, mode, size)
+	if err != nil || n != entryLen {
+		log.Fatal("writing entry header: ", err)
+	}
+	n1, _ := io.CopyN(a.f, r, size)
+	if n1 != size {
+		log.Fatal(err)
+	}
+	if (off+size)&1 != 0 {
+		a.f.Write([]byte{0}) // pad to even byte
+	}
+	a.Entries = append(a.Entries, Entry{
+		Name:  name,
+		Type:  typ,
+		Mtime: mtime,
+		Uid:   uid,
+		Gid:   gid,
+		Mode:  mode,
+		Data:  Data{off + entryLen, size},
+	})
+}
+
+// exactly16Bytes truncates the string if necessary so it is at most 16 bytes long,
+// then pads the result with spaces to be exactly 16 bytes.
+// Fmt uses runes for its width calculation, but we need bytes in the entry header.
+func exactly16Bytes(s string) string {
+	for len(s) > 16 {
+		_, wid := utf8.DecodeLastRuneInString(s)
+		s = s[:len(s)-wid]
+	}
+	const sixteenSpaces = "                "
+	s += sixteenSpaces[:16-len(s)]
+	return s
+}
+
+// architecture-independent object file output
+const HeaderSize = 60
+
+func FormatHeader(arhdr []byte, name string, size int64) {
+	copy(arhdr[:], fmt.Sprintf("%-16s%-12d%-6d%-6d%-8o%-10d`\n", name, 0, 0, 0, 0644, size))
+}

go/src/cmd/internal/archive/archive_test.go

@@ -0,0 +1,388 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package archive
+
+import (
+	"bytes"
+	"debug/elf"
+	"debug/macho"
+	"debug/pe"
+	"fmt"
+	"internal/testenv"
+	"internal/xcoff"
+	"io"
+	"os"
+	"path/filepath"
+	"runtime"
+	"sync"
+	"testing"
+	"unicode/utf8"
+)
+
+var buildDir string
+
+func TestMain(m *testing.M) {
+	if !testenv.HasGoBuild() {
+		return
+	}
+
+	exit := m.Run()
+
+	if buildDir != "" {
+		os.RemoveAll(buildDir)
+	}
+	os.Exit(exit)
+}
+
+func copyDir(dst, src string) error {
+	err := os.MkdirAll(dst, 0777)
+	if err != nil {
+		return err
+	}
+	entries, err := os.ReadDir(src)
+	if err != nil {
+		return err
+	}
+	for _, entry := range entries {
+		err = copyFile(filepath.Join(dst, entry.Name()), filepath.Join(src, entry.Name()))
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func copyFile(dst, src string) (err error) {
+	var s, d *os.File
+	s, err = os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer s.Close()
+	d, err = os.Create(dst)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		e := d.Close()
+		if err == nil {
+			err = e
+		}
+	}()
+	_, err = io.Copy(d, s)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+var (
+	buildOnce   sync.Once
+	builtGoobjs goobjPaths
+	buildErr    error
+)
+
+type goobjPaths struct {
+	go1obj     string
+	go2obj     string
+	goarchive  string
+	cgoarchive string
+}
+
+func buildGoobj(t *testing.T) goobjPaths {
+	buildOnce.Do(func() {
+		buildErr = func() (err error) {
+			buildDir, err = os.MkdirTemp("", "TestGoobj")
+			if err != nil {
+				return err
+			}
+
+			go1obj := filepath.Join(buildDir, "go1.o")
+			go2obj := filepath.Join(buildDir, "go2.o")
+			goarchive := filepath.Join(buildDir, "go.a")
+			cgoarchive := ""
+
+			gotool, err := testenv.GoTool()
+			if err != nil {
+				return err
+			}
+
+			go1src := filepath.Join("testdata", "go1.go")
+			go2src := filepath.Join("testdata", "go2.go")
+
+			importcfgfile := filepath.Join(buildDir, "importcfg")
+			testenv.WriteImportcfg(t, importcfgfile, nil, go1src, go2src)
+
+			out, err := testenv.Command(t, gotool, "tool", "compile", "-importcfg="+importcfgfile, "-p=p", "-o", go1obj, go1src).CombinedOutput()
+			if err != nil {
+				return fmt.Errorf("go tool compile -o %s %s: %v\n%s", go1obj, go1src, err, out)
+			}
+			out, err = testenv.Command(t, gotool, "tool", "compile", "-importcfg="+importcfgfile, "-p=p", "-o", go2obj, go2src).CombinedOutput()
+			if err != nil {
+				return fmt.Errorf("go tool compile -o %s %s: %v\n%s", go2obj, go2src, err, out)
+			}
+			out, err = testenv.Command(t, gotool, "tool", "pack", "c", goarchive, go1obj, go2obj).CombinedOutput()
+			if err != nil {
+				return fmt.Errorf("go tool pack c %s %s %s: %v\n%s", goarchive, go1obj, go2obj, err, out)
+			}
+
+			if testenv.HasCGO() {
+				cgoarchive = filepath.Join(buildDir, "mycgo.a")
+				gopath := filepath.Join(buildDir, "gopath")
+				err = copyDir(filepath.Join(gopath, "src", "mycgo"), filepath.Join("testdata", "mycgo"))
+				if err == nil {
+					err = os.WriteFile(filepath.Join(gopath, "src", "mycgo", "go.mod"), []byte("module mycgo\n"), 0666)
+				}
+				if err != nil {
+					return err
+				}
+				cmd := testenv.Command(t, gotool, "build", "-buildmode=archive", "-o", cgoarchive, "-gcflags=all="+os.Getenv("GO_GCFLAGS"), "mycgo")
+				cmd.Dir = filepath.Join(gopath, "src", "mycgo")
+				cmd.Env = append(os.Environ(), "GOPATH="+gopath)
+				out, err = cmd.CombinedOutput()
+				if err != nil {
+					return fmt.Errorf("go install mycgo: %v\n%s", err, out)
+				}
+			}
+
+			builtGoobjs = goobjPaths{
+				go1obj:     go1obj,
+				go2obj:     go2obj,
+				goarchive:  goarchive,
+				cgoarchive: cgoarchive,
+			}
+			return nil
+		}()
+	})
+
+	if buildErr != nil {
+		t.Helper()
+		t.Fatal(buildErr)
+	}
+	return builtGoobjs
+}
+
+func TestParseGoobj(t *testing.T) {
+	path := buildGoobj(t).go1obj
+
+	f, err := os.Open(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+
+	a, err := Parse(f, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(a.Entries) != 2 {
+		t.Errorf("expect 2 entry, found %d", len(a.Entries))
+	}
+	for _, e := range a.Entries {
+		if e.Type == EntryPkgDef {
+			continue
+		}
+		if e.Type != EntryGoObj {
+			t.Errorf("wrong type of object: want EntryGoObj, got %v", e.Type)
+		}
+		if !bytes.Contains(e.Obj.TextHeader, []byte(runtime.GOARCH)) {
+			t.Errorf("text header does not contain GOARCH %s: %q", runtime.GOARCH, e.Obj.TextHeader)
+		}
+	}
+}
+
+func TestParseArchive(t *testing.T) {
+	path := buildGoobj(t).goarchive
+
+	f, err := os.Open(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+
+	a, err := Parse(f, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(a.Entries) != 3 {
+		t.Errorf("expect 3 entry, found %d", len(a.Entries))
+	}
+	var found1 bool
+	var found2 bool
+	for _, e := range a.Entries {
+		if e.Type == EntryPkgDef {
+			continue
+		}
+		if e.Type != EntryGoObj {
+			t.Errorf("wrong type of object: want EntryGoObj, got %v", e.Type)
+		}
+		if !bytes.Contains(e.Obj.TextHeader, []byte(runtime.GOARCH)) {
+			t.Errorf("text header does not contain GOARCH %s: %q", runtime.GOARCH, e.Obj.TextHeader)
+		}
+		if e.Name == "go1.o" {
+			found1 = true
+		}
+		if e.Name == "go2.o" {
+			found2 = true
+		}
+	}
+	if !found1 {
+		t.Errorf(`object "go1.o" not found`)
+	}
+	if !found2 {
+		t.Errorf(`object "go2.o" not found`)
+	}
+}
+
+func TestParseCGOArchive(t *testing.T) {
+	testenv.MustHaveCGO(t)
+
+	path := buildGoobj(t).cgoarchive
+
+	f, err := os.Open(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+
+	a, err := Parse(f, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	c1 := "c1"
+	c2 := "c2"
+	switch runtime.GOOS {
+	case "darwin", "ios":
+		c1 = "_" + c1
+		c2 = "_" + c2
+	case "windows":
+		if runtime.GOARCH == "386" {
+			c1 = "_" + c1
+			c2 = "_" + c2
+		}
+	case "aix":
+		c1 = "." + c1
+		c2 = "." + c2
+	}
+
+	var foundgo, found1, found2 bool
+
+	for _, e := range a.Entries {
+		switch e.Type {
+		default:
+			t.Errorf("unknown object type")
+		case EntryPkgDef:
+			continue
+		case EntryGoObj:
+			foundgo = true
+			if !bytes.Contains(e.Obj.TextHeader, []byte(runtime.GOARCH)) {
+				t.Errorf("text header does not contain GOARCH %s: %q", runtime.GOARCH, e.Obj.TextHeader)
+			}
+			continue
+		case EntryNativeObj:
+		}
+
+		obj := io.NewSectionReader(f, e.Offset, e.Size)
+		switch runtime.GOOS {
+		case "darwin", "ios":
+			mf, err := macho.NewFile(obj)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if mf.Symtab == nil {
+				continue
+			}
+			for _, s := range mf.Symtab.Syms {
+				switch s.Name {
+				case c1:
+					found1 = true
+				case c2:
+					found2 = true
+				}
+			}
+		case "windows":
+			pf, err := pe.NewFile(obj)
+			if err != nil {
+				t.Fatal(err)
+			}
+			for _, s := range pf.Symbols {
+				switch s.Name {
+				case c1:
+					found1 = true
+				case c2:
+					found2 = true
+				}
+			}
+		case "aix":
+			xf, err := xcoff.NewFile(obj)
+			if err != nil {
+				t.Fatal(err)
+			}
+			for _, s := range xf.Symbols {
+				switch s.Name {
+				case c1:
+					found1 = true
+				case c2:
+					found2 = true
+				}
+			}
+		default: // ELF
+			ef, err := elf.NewFile(obj)
+			if err != nil {
+				t.Fatal(err)
+			}
+			syms, err := ef.Symbols()
+			if err != nil {
+				t.Fatal(err)
+			}
+			for _, s := range syms {
+				switch s.Name {
+				case c1:
+					found1 = true
+				case c2:
+					found2 = true
+				}
+			}
+		}
+	}
+
+	if !foundgo {
+		t.Errorf(`go object not found`)
+	}
+	if !found1 {
+		t.Errorf(`symbol %q not found`, c1)
+	}
+	if !found2 {
+		t.Errorf(`symbol %q not found`, c2)
+	}
+}
+
+func TestExactly16Bytes(t *testing.T) {
+	var tests = []string{
+		"",
+		"a",
+		"日本語",
+		"1234567890123456",
+		"12345678901234567890",
+		"1234567890123本語4567890",
+		"12345678901234日本語567890",
+		"123456789012345日本語67890",
+		"1234567890123456日本語7890",
+		"1234567890123456日本語7日本語890",
+	}
+	for _, str := range tests {
+		got := exactly16Bytes(str)
+		if len(got) != 16 {
+			t.Errorf("exactly16Bytes(%q) is %q, length %d", str, got, len(got))
+		}
+		// Make sure it is full runes.
+		for _, c := range got {
+			if c == utf8.RuneError {
+				t.Errorf("exactly16Bytes(%q) is %q, has partial rune", str, got)
+			}
+		}
+	}
+}

go/src/cmd/internal/bio/buf.go

@@ -0,0 +1,148 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package bio implements common I/O abstractions used within the Go toolchain.
+package bio
+
+import (
+	"bufio"
+	"io"
+	"log"
+	"os"
+)
+
+// Reader implements a seekable buffered io.Reader.
+type Reader struct {
+	f *os.File
+	*bufio.Reader
+}
+
+// Writer implements a seekable buffered io.Writer.
+type Writer struct {
+	f *os.File
+	*bufio.Writer
+}
+
+// Create creates the file named name and returns a Writer
+// for that file.
+func Create(name string) (*Writer, error) {
+	f, err := os.Create(name)
+	if err != nil {
+		return nil, err
+	}
+	return &Writer{f: f, Writer: bufio.NewWriter(f)}, nil
+}
+
+// Open returns a Reader for the file named name.
+func Open(name string) (*Reader, error) {
+	f, err := os.Open(name)
+	if err != nil {
+		return nil, err
+	}
+	return NewReader(f), nil
+}
+
+// NewReader returns a Reader from an open file.
+func NewReader(f *os.File) *Reader {
+	return &Reader{f: f, Reader: bufio.NewReader(f)}
+}
+
+func (r *Reader) MustSeek(offset int64, whence int) int64 {
+	if whence == 1 {
+		offset -= int64(r.Buffered())
+	}
+	off, err := r.f.Seek(offset, whence)
+	if err != nil {
+		log.Fatalf("seeking in output: %v", err)
+	}
+	r.Reset(r.f)
+	return off
+}
+
+func (w *Writer) MustSeek(offset int64, whence int) int64 {
+	if err := w.Flush(); err != nil {
+		log.Fatalf("writing output: %v", err)
+	}
+	off, err := w.f.Seek(offset, whence)
+	if err != nil {
+		log.Fatalf("seeking in output: %v", err)
+	}
+	return off
+}
+
+func (r *Reader) Offset() int64 {
+	off, err := r.f.Seek(0, 1)
+	if err != nil {
+		log.Fatalf("seeking in output [0, 1]: %v", err)
+	}
+	off -= int64(r.Buffered())
+	return off
+}
+
+func (w *Writer) Offset() int64 {
+	if err := w.Flush(); err != nil {
+		log.Fatalf("writing output: %v", err)
+	}
+	off, err := w.f.Seek(0, 1)
+	if err != nil {
+		log.Fatalf("seeking in output [0, 1]: %v", err)
+	}
+	return off
+}
+
+func (r *Reader) Close() error {
+	return r.f.Close()
+}
+
+func (w *Writer) Close() error {
+	err := w.Flush()
+	err1 := w.f.Close()
+	if err == nil {
+		err = err1
+	}
+	return err
+}
+
+func (r *Reader) File() *os.File {
+	return r.f
+}
+
+func (w *Writer) File() *os.File {
+	return w.f
+}
+
+// Slice reads the next length bytes of r into a slice.
+//
+// This slice may be backed by mmap'ed memory. Currently, this memory
+// will never be unmapped. The second result reports whether the
+// backing memory is read-only.
+func (r *Reader) Slice(length uint64) ([]byte, bool, error) {
+	if length == 0 {
+		return []byte{}, false, nil
+	}
+
+	data, ok := r.sliceOS(length)
+	if ok {
+		return data, true, nil
+	}
+
+	data = make([]byte, length)
+	_, err := io.ReadFull(r, data)
+	if err != nil {
+		return nil, false, err
+	}
+	return data, false, nil
+}
+
+// SliceRO returns a slice containing the next length bytes of r
+// backed by a read-only mmap'd data. If the mmap cannot be
+// established (limit exceeded, region too small, etc) a nil slice
+// will be returned. If mmap succeeds, it will never be unmapped.
+func (r *Reader) SliceRO(length uint64) []byte {
+	data, ok := r.sliceOS(length)
+	if ok {
+		return data
+	}
+	return nil
+}

go/src/cmd/internal/bio/buf_mmap.go

@@ -0,0 +1,62 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix
+
+package bio
+
+import (
+	"runtime"
+	"sync/atomic"
+	"syscall"
+)
+
+// mmapLimit is the maximum number of mmaped regions to create before
+// falling back to reading into a heap-allocated slice. This exists
+// because some operating systems place a limit on the number of
+// distinct mapped regions per process. As of this writing:
+//
+//	Darwin    unlimited
+//	DragonFly   1000000 (vm.max_proc_mmap)
+//	FreeBSD   unlimited
+//	Linux         65530 (vm.max_map_count) // TODO: query /proc/sys/vm/max_map_count?
+//	NetBSD    unlimited
+//	OpenBSD   unlimited
+var mmapLimit int32 = 1<<31 - 1
+
+func init() {
+	// Linux is the only practically concerning OS.
+	if runtime.GOOS == "linux" {
+		mmapLimit = 30000
+	}
+}
+
+func (r *Reader) sliceOS(length uint64) ([]byte, bool) {
+	// For small slices, don't bother with the overhead of a
+	// mapping, especially since we have no way to unmap it.
+	const threshold = 16 << 10
+	if length < threshold {
+		return nil, false
+	}
+
+	// Have we reached the mmap limit?
+	if atomic.AddInt32(&mmapLimit, -1) < 0 {
+		atomic.AddInt32(&mmapLimit, 1)
+		return nil, false
+	}
+
+	// Page-align the offset.
+	off := r.Offset()
+	align := syscall.Getpagesize()
+	aoff := off &^ int64(align-1)
+
+	data, err := syscall.Mmap(int(r.f.Fd()), aoff, int(length+uint64(off-aoff)), syscall.PROT_READ, syscall.MAP_SHARED|syscall.MAP_FILE)
+	if err != nil {
+		return nil, false
+	}
+
+	data = data[off-aoff:]
+	r.MustSeek(int64(length), 1)
+	return data, true
+}

go/src/cmd/internal/bio/buf_nommap.go

@@ -0,0 +1,11 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !unix
+
+package bio
+
+func (r *Reader) sliceOS(length uint64) ([]byte, bool) {
+	return nil, false
+}

go/src/cmd/internal/bootstrap_test/experiment_toolid_test.go

@@ -0,0 +1,106 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build explicit
+
+package bootstrap_test
+
+import (
+	"bytes"
+	"errors"
+	"internal/testenv"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"testing"
+)
+
+// TestExperimentToolID verifies that GOEXPERIMENT settings built
+// into the toolchain influence tool ids in the Go command.
+// This test requires bootstrapping the toolchain twice, so it's very expensive.
+// It must be run explicitly with -tags=explicit.
+// Verifies go.dev/issue/33091.
+func TestExperimentToolID(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test that rebuilds the entire toolchain twice")
+	}
+	switch runtime.GOOS {
+	case "android", "ios", "js", "wasip1":
+		t.Skipf("skipping because the toolchain does not have to bootstrap on GOOS=%s", runtime.GOOS)
+	}
+
+	realGoroot := testenv.GOROOT(t)
+
+	// Set up GOROOT.
+	goroot := t.TempDir()
+	gorootSrc := filepath.Join(goroot, "src")
+	if err := overlayDir(gorootSrc, filepath.Join(realGoroot, "src")); err != nil {
+		t.Fatal(err)
+	}
+	gorootLib := filepath.Join(goroot, "lib")
+	if err := overlayDir(gorootLib, filepath.Join(realGoroot, "lib")); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(goroot, "VERSION"), []byte("go1.999"), 0666); err != nil {
+		t.Fatal(err)
+	}
+	env := append(os.Environ(), "GOROOT=", "GOROOT_BOOTSTRAP="+realGoroot)
+
+	// Use a clean cache.
+	gocache := t.TempDir()
+	env = append(env, "GOCACHE="+gocache)
+
+	// Build the toolchain without GOEXPERIMENT.
+	var makeScript string
+	switch runtime.GOOS {
+	case "windows":
+		makeScript = "make.bat"
+	case "plan9":
+		makeScript = "make.rc"
+	default:
+		makeScript = "make.bash"
+	}
+	makeScriptPath := filepath.Join(realGoroot, "src", makeScript)
+	runCmd(t, gorootSrc, env, makeScriptPath)
+
+	// Verify compiler version string.
+	goCmdPath := filepath.Join(goroot, "bin", "go")
+	gotVersion := bytes.TrimSpace(runCmd(t, gorootSrc, env, goCmdPath, "tool", "compile", "-V=full"))
+	wantVersion := []byte(`compile version go1.999`)
+	if !bytes.Equal(gotVersion, wantVersion) {
+		t.Errorf("compile version without experiment is unexpected:\ngot  %q\nwant %q", gotVersion, wantVersion)
+	}
+
+	// Build a package in a mode not handled by the make script.
+	runCmd(t, gorootSrc, env, goCmdPath, "build", "-race", "archive/tar")
+
+	// Rebuild the toolchain with GOEXPERIMENT.
+	env = append(env, "GOEXPERIMENT=fieldtrack")
+	runCmd(t, gorootSrc, env, makeScriptPath)
+
+	// Verify compiler version string.
+	gotVersion = bytes.TrimSpace(runCmd(t, gorootSrc, env, goCmdPath, "tool", "compile", "-V=full"))
+	wantVersion = []byte(`compile version go1.999 X:fieldtrack`)
+	if !bytes.Equal(gotVersion, wantVersion) {
+		t.Errorf("compile version with experiment is unexpected:\ngot  %q\nwant %q", gotVersion, wantVersion)
+	}
+
+	// Build the same package. We should not get a cache conflict.
+	runCmd(t, gorootSrc, env, goCmdPath, "build", "-race", "archive/tar")
+}
+
+func runCmd(t *testing.T, dir string, env []string, path string, args ...string) []byte {
+	cmd := exec.Command(path, args...)
+	cmd.Dir = dir
+	cmd.Env = env
+	out, err := cmd.Output()
+	if err != nil {
+		if ee, ok := errors.AsType[*exec.ExitError](err); ok {
+			out = append(out, ee.Stderr...)
+		}
+		t.Fatalf("%s failed:\n%s\n%s", cmd, out, err)
+	}
+	return out
+}

go/src/cmd/internal/bootstrap_test/overlaydir_test.go

@@ -0,0 +1,88 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package bootstrap_test
+
+import (
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// overlayDir makes a minimal-overhead copy of srcRoot in which new files may be added.
+//
+// TODO: Once we no longer need to support the misc module in GOPATH mode,
+// factor this function out into a package to reduce duplication.
+func overlayDir(dstRoot, srcRoot string) error {
+	dstRoot = filepath.Clean(dstRoot)
+	if err := os.MkdirAll(dstRoot, 0777); err != nil {
+		return err
+	}
+
+	srcRoot, err := filepath.Abs(srcRoot)
+	if err != nil {
+		return err
+	}
+
+	return filepath.WalkDir(srcRoot, func(srcPath string, entry fs.DirEntry, err error) error {
+		if err != nil || srcPath == srcRoot {
+			return err
+		}
+		if filepath.Base(srcPath) == "testdata" {
+			// We're just building, so no need to copy those.
+			return fs.SkipDir
+		}
+
+		suffix := strings.TrimPrefix(srcPath, srcRoot)
+		for len(suffix) > 0 && suffix[0] == filepath.Separator {
+			suffix = suffix[1:]
+		}
+		dstPath := filepath.Join(dstRoot, suffix)
+
+		info, err := entry.Info()
+		if err != nil {
+			return err
+		}
+		perm := info.Mode() & os.ModePerm
+		if info.Mode()&os.ModeSymlink != 0 {
+			info, err = os.Stat(srcPath)
+			if err != nil {
+				return err
+			}
+			perm = info.Mode() & os.ModePerm
+		}
+
+		// Always make copies of directories.
+		// If we add a file in the overlay, we don't want to add it in the original.
+		if info.IsDir() {
+			return os.MkdirAll(dstPath, perm|0200)
+		}
+
+		// If we can use a hard link, do that instead of copying bytes.
+		// Go builds don't like symlinks in some cases, such as go:embed.
+		if err := os.Link(srcPath, dstPath); err == nil {
+			return nil
+		}
+
+		// Otherwise, copy the bytes.
+		src, err := os.Open(srcPath)
+		if err != nil {
+			return err
+		}
+		defer src.Close()
+
+		dst, err := os.OpenFile(dstPath, os.O_WRONLY|os.O_CREATE|os.O_EXCL, perm)
+		if err != nil {
+			return err
+		}
+
+		_, err = io.Copy(dst, src)
+		if closeErr := dst.Close(); err == nil {
+			err = closeErr
+		}
+		return err
+	})
+}

go/src/cmd/internal/bootstrap_test/reboot_test.go

@@ -0,0 +1,98 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package bootstrap_test verifies that the current GOROOT can be used to bootstrap
+// itself.
+package bootstrap_test
+
+import (
+	"fmt"
+	"internal/testenv"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestRepeatBootstrap(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test that rebuilds the entire toolchain")
+	}
+	switch runtime.GOOS {
+	case "android", "ios", "js", "wasip1":
+		t.Skipf("skipping because the toolchain does not have to bootstrap on GOOS=%s", runtime.GOOS)
+	}
+
+	realGoroot := testenv.GOROOT(t)
+
+	// To ensure that bootstrapping doesn't unexpectedly depend
+	// on the Go repo's git metadata, add a fake (unreadable) git
+	// directory above the simulated GOROOT.
+	// This mimics the configuration one much have when
+	// building from distro-packaged source code
+	// (see https://go.dev/issue/54852).
+	parent := t.TempDir()
+	dotGit := filepath.Join(parent, ".git")
+	if err := os.Mkdir(dotGit, 000); err != nil {
+		t.Fatal(err)
+	}
+
+	overlayStart := time.Now()
+
+	goroot := filepath.Join(parent, "goroot")
+
+	gorootSrc := filepath.Join(goroot, "src")
+	if err := overlayDir(gorootSrc, filepath.Join(realGoroot, "src")); err != nil {
+		t.Fatal(err)
+	}
+
+	gorootLib := filepath.Join(goroot, "lib")
+	if err := overlayDir(gorootLib, filepath.Join(realGoroot, "lib")); err != nil {
+		t.Fatal(err)
+	}
+
+	t.Logf("GOROOT overlay set up in %s", time.Since(overlayStart))
+
+	if err := os.WriteFile(filepath.Join(goroot, "VERSION"), []byte(runtime.Version()), 0666); err != nil {
+		t.Fatal(err)
+	}
+
+	var makeScript string
+	switch runtime.GOOS {
+	case "windows":
+		makeScript = "make.bat"
+	case "plan9":
+		makeScript = "make.rc"
+	default:
+		makeScript = "make.bash"
+	}
+
+	var stdout strings.Builder
+	cmd := exec.Command(filepath.Join(goroot, "src", makeScript))
+	cmd.Dir = gorootSrc
+	cmd.Env = append(cmd.Environ(), "GOROOT=", "GOROOT_BOOTSTRAP="+realGoroot)
+	cmd.Stderr = os.Stderr
+	cmd.Stdout = io.MultiWriter(os.Stdout, &stdout)
+	if err := cmd.Run(); err != nil {
+		t.Fatal(err)
+	}
+
+	// Test that go.dev/issue/42563 hasn't regressed.
+	t.Run("PATH reminder", func(t *testing.T) {
+		var want string
+		switch gorootBin := filepath.Join(goroot, "bin"); runtime.GOOS {
+		default:
+			want = fmt.Sprintf("*** You need to add %s to your PATH.", gorootBin)
+		case "plan9":
+			want = fmt.Sprintf("*** You need to bind %s before /bin.", gorootBin)
+		}
+		if got := stdout.String(); !strings.Contains(got, want) {
+			t.Errorf("reminder %q is missing from %s stdout:\n%s", want, makeScript, got)
+		}
+	})
+}

go/src/cmd/internal/browser/browser.go

@@ -0,0 +1,67 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package browser provides utilities for interacting with users' browsers.
+package browser
+
+import (
+	"os"
+	"os/exec"
+	"runtime"
+	"time"
+)
+
+// Commands returns a list of possible commands to use to open a url.
+func Commands() [][]string {
+	var cmds [][]string
+	if exe := os.Getenv("BROWSER"); exe != "" {
+		cmds = append(cmds, []string{exe})
+	}
+	switch runtime.GOOS {
+	case "darwin":
+		cmds = append(cmds, []string{"/usr/bin/open"})
+	case "windows":
+		cmds = append(cmds, []string{"cmd", "/c", "start"})
+	default:
+		if os.Getenv("DISPLAY") != "" {
+			// xdg-open is only for use in a desktop environment.
+			cmds = append(cmds, []string{"xdg-open"})
+		}
+	}
+	cmds = append(cmds,
+		[]string{"chrome"},
+		[]string{"google-chrome"},
+		[]string{"chromium"},
+		[]string{"firefox"},
+	)
+	return cmds
+}
+
+// Open tries to open url in a browser and reports whether it succeeded.
+func Open(url string) bool {
+	for _, args := range Commands() {
+		cmd := exec.Command(args[0], append(args[1:], url)...)
+		if cmd.Start() == nil && appearsSuccessful(cmd, 3*time.Second) {
+			return true
+		}
+	}
+	return false
+}
+
+// appearsSuccessful reports whether the command appears to have run successfully.
+// If the command runs longer than the timeout, it's deemed successful.
+// If the command runs within the timeout, it's deemed successful if it exited cleanly.
+func appearsSuccessful(cmd *exec.Cmd, timeout time.Duration) bool {
+	errc := make(chan error, 1)
+	go func() {
+		errc <- cmd.Wait()
+	}()
+
+	select {
+	case <-time.After(timeout):
+		return true
+	case err := <-errc:
+		return err == nil
+	}
+}

go/src/cmd/internal/buildid/buildid.go

@@ -0,0 +1,343 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package buildid
+
+import (
+	"bytes"
+	"debug/elf"
+	"fmt"
+	"internal/xcoff"
+	"io"
+	"io/fs"
+	"os"
+	"strconv"
+	"strings"
+)
+
+var (
+	errBuildIDMalformed = fmt.Errorf("malformed object file")
+
+	bangArch = []byte("!<arch>")
+	pkgdef   = []byte("__.PKGDEF")
+	goobject = []byte("go object ")
+	buildid  = []byte("build id ")
+)
+
+// ReadFile reads the build ID from an archive or executable file.
+func ReadFile(name string) (id string, err error) {
+	f, err := os.Open(name)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+
+	buf := make([]byte, 8)
+	if _, err := f.ReadAt(buf, 0); err != nil {
+		return "", err
+	}
+	if string(buf) != "!<arch>\n" {
+		if string(buf) == "<bigaf>\n" {
+			return readGccgoBigArchive(name, f)
+		}
+		return readBinary(name, f)
+	}
+
+	// Read just enough of the target to fetch the build ID.
+	// The archive is expected to look like:
+	//
+	//	!<arch>
+	//	__.PKGDEF       0           0     0     644     7955      `
+	//	go object darwin amd64 devel X:none
+	//	build id "b41e5c45250e25c9fd5e9f9a1de7857ea0d41224"
+	//
+	// The variable-sized strings are GOOS, GOARCH, and the experiment list (X:none).
+	// Reading the first 1024 bytes should be plenty.
+	data := make([]byte, 1024)
+	n, err := io.ReadFull(f, data)
+	if err != nil && n == 0 {
+		return "", err
+	}
+
+	tryGccgo := func() (string, error) {
+		return readGccgoArchive(name, f)
+	}
+
+	// Archive header.
+	for i := 0; ; i++ { // returns during i==3
+		j := bytes.IndexByte(data, '\n')
+		if j < 0 {
+			return tryGccgo()
+		}
+		line := data[:j]
+		data = data[j+1:]
+		switch i {
+		case 0:
+			if !bytes.Equal(line, bangArch) {
+				return tryGccgo()
+			}
+		case 1:
+			if !bytes.HasPrefix(line, pkgdef) {
+				return tryGccgo()
+			}
+		case 2:
+			if !bytes.HasPrefix(line, goobject) {
+				return tryGccgo()
+			}
+		case 3:
+			if !bytes.HasPrefix(line, buildid) {
+				// Found the object header, just doesn't have a build id line.
+				// Treat as successful, with empty build id.
+				return "", nil
+			}
+			id, err := strconv.Unquote(string(line[len(buildid):]))
+			if err != nil {
+				return tryGccgo()
+			}
+			return id, nil
+		}
+	}
+}
+
+// readGccgoArchive tries to parse the archive as a standard Unix
+// archive file, and fetch the build ID from the _buildid.o entry.
+// The _buildid.o entry is written by (*Builder).gccgoBuildIDELFFile
+// in cmd/go/internal/work/exec.go.
+func readGccgoArchive(name string, f *os.File) (string, error) {
+	bad := func() (string, error) {
+		return "", &fs.PathError{Op: "parse", Path: name, Err: errBuildIDMalformed}
+	}
+
+	off := int64(8)
+	for {
+		if _, err := f.Seek(off, io.SeekStart); err != nil {
+			return "", err
+		}
+
+		// TODO(iant): Make a debug/ar package, and use it
+		// here and in cmd/link.
+		var hdr [60]byte
+		if _, err := io.ReadFull(f, hdr[:]); err != nil {
+			if err == io.EOF {
+				// No more entries, no build ID.
+				return "", nil
+			}
+			return "", err
+		}
+		off += 60
+
+		sizeStr := strings.TrimSpace(string(hdr[48:58]))
+		size, err := strconv.ParseInt(sizeStr, 0, 64)
+		if err != nil {
+			return bad()
+		}
+
+		name := strings.TrimSpace(string(hdr[:16]))
+		if name == "_buildid.o/" {
+			sr := io.NewSectionReader(f, off, size)
+			e, err := elf.NewFile(sr)
+			if err != nil {
+				return bad()
+			}
+			s := e.Section(".go.buildid")
+			if s == nil {
+				return bad()
+			}
+			data, err := s.Data()
+			if err != nil {
+				return bad()
+			}
+			return string(data), nil
+		}
+
+		off += size
+		if off&1 != 0 {
+			off++
+		}
+	}
+}
+
+// readGccgoBigArchive tries to parse the archive as an AIX big
+// archive file, and fetch the build ID from the _buildid.o entry.
+// The _buildid.o entry is written by (*Builder).gccgoBuildIDXCOFFFile
+// in cmd/go/internal/work/exec.go.
+func readGccgoBigArchive(name string, f *os.File) (string, error) {
+	bad := func() (string, error) {
+		return "", &fs.PathError{Op: "parse", Path: name, Err: errBuildIDMalformed}
+	}
+
+	// Read fixed-length header.
+	if _, err := f.Seek(0, io.SeekStart); err != nil {
+		return "", err
+	}
+	var flhdr [128]byte
+	if _, err := io.ReadFull(f, flhdr[:]); err != nil {
+		return "", err
+	}
+	// Read first member offset.
+	offStr := strings.TrimSpace(string(flhdr[68:88]))
+	off, err := strconv.ParseInt(offStr, 10, 64)
+	if err != nil {
+		return bad()
+	}
+	for {
+		if off == 0 {
+			// No more entries, no build ID.
+			return "", nil
+		}
+		if _, err := f.Seek(off, io.SeekStart); err != nil {
+			return "", err
+		}
+		// Read member header.
+		var hdr [112]byte
+		if _, err := io.ReadFull(f, hdr[:]); err != nil {
+			return "", err
+		}
+		// Read member name length.
+		namLenStr := strings.TrimSpace(string(hdr[108:112]))
+		namLen, err := strconv.ParseInt(namLenStr, 10, 32)
+		if err != nil {
+			return bad()
+		}
+		if namLen == 10 {
+			var nam [10]byte
+			if _, err := io.ReadFull(f, nam[:]); err != nil {
+				return "", err
+			}
+			if string(nam[:]) == "_buildid.o" {
+				sizeStr := strings.TrimSpace(string(hdr[0:20]))
+				size, err := strconv.ParseInt(sizeStr, 10, 64)
+				if err != nil {
+					return bad()
+				}
+				off += int64(len(hdr)) + namLen + 2
+				if off&1 != 0 {
+					off++
+				}
+				sr := io.NewSectionReader(f, off, size)
+				x, err := xcoff.NewFile(sr)
+				if err != nil {
+					return bad()
+				}
+				data := x.CSect(".go.buildid")
+				if data == nil {
+					return bad()
+				}
+				return string(data), nil
+			}
+		}
+
+		// Read next member offset.
+		offStr = strings.TrimSpace(string(hdr[20:40]))
+		off, err = strconv.ParseInt(offStr, 10, 64)
+		if err != nil {
+			return bad()
+		}
+	}
+}
+
+var (
+	goBuildPrefix = []byte("\xff Go build ID: \"")
+	goBuildEnd    = []byte("\"\n \xff")
+
+	elfPrefix = []byte("\x7fELF")
+
+	machoPrefixes = [][]byte{
+		{0xfe, 0xed, 0xfa, 0xce},
+		{0xfe, 0xed, 0xfa, 0xcf},
+		{0xce, 0xfa, 0xed, 0xfe},
+		{0xcf, 0xfa, 0xed, 0xfe},
+	}
+)
+
+var readSize = 32 * 1024 // changed for testing
+
+// readBinary reads the build ID from a binary.
+//
+// ELF binaries store the build ID in a proper PT_NOTE section.
+//
+// Other binary formats are not so flexible. For those, the linker
+// stores the build ID as non-instruction bytes at the very beginning
+// of the text segment, which should appear near the beginning
+// of the file. This is clumsy but fairly portable. Custom locations
+// can be added for other binary types as needed, like we did for ELF.
+func readBinary(name string, f *os.File) (id string, err error) {
+	// Read the first 32 kB of the binary file.
+	// That should be enough to find the build ID.
+	// In ELF files, the build ID is in the leading headers,
+	// which are typically less than 4 kB, not to mention 32 kB.
+	// In Mach-O files, there's no limit, so we have to parse the file.
+	// On other systems, we're trying to read enough that
+	// we get the beginning of the text segment in the read.
+	// The offset where the text segment begins in a hello
+	// world compiled for each different object format today:
+	//
+	//	Plan 9: 0x20
+	//	Windows: 0x600
+	//
+	data := make([]byte, readSize)
+	_, err = io.ReadFull(f, data)
+	if err == io.ErrUnexpectedEOF {
+		err = nil
+	}
+	if err != nil {
+		return "", err
+	}
+
+	if bytes.HasPrefix(data, elfPrefix) {
+		return readELF(name, f, data)
+	}
+	for _, m := range machoPrefixes {
+		if bytes.HasPrefix(data, m) {
+			return readMacho(name, f, data)
+		}
+	}
+	return readRaw(name, data)
+}
+
+// readRaw finds the raw build ID stored in text segment data.
+func readRaw(name string, data []byte) (id string, err error) {
+	i := bytes.Index(data, goBuildPrefix)
+	if i < 0 {
+		// Missing. Treat as successful but build ID empty.
+		return "", nil
+	}
+
+	j := bytes.Index(data[i+len(goBuildPrefix):], goBuildEnd)
+	if j < 0 {
+		return "", &fs.PathError{Op: "parse", Path: name, Err: errBuildIDMalformed}
+	}
+
+	quoted := data[i+len(goBuildPrefix)-1 : i+len(goBuildPrefix)+j+1]
+	id, err = strconv.Unquote(string(quoted))
+	if err != nil {
+		return "", &fs.PathError{Op: "parse", Path: name, Err: errBuildIDMalformed}
+	}
+	return id, nil
+}
+
+// HashToString converts the hash h to a string to be recorded
+// in package archives and binaries as part of the build ID.
+// We use the first 120 bits of the hash (5 chunks of 24 bits each) and encode
+// it in base64, resulting in a 20-byte string. Because this is only used for
+// detecting the need to rebuild installed files (not for lookups
+// in the object file cache), 120 bits are sufficient to drive the
+// probability of a false "do not need to rebuild" decision to effectively zero.
+// We embed two different hashes in archives and four in binaries,
+// so cutting to 20 bytes is a significant savings when build IDs are displayed.
+// (20*4+3 = 83 bytes compared to 64*4+3 = 259 bytes for the
+// more straightforward option of printing the entire h in base64).
+func HashToString(h [32]byte) string {
+	const b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"
+	const chunks = 5
+	var dst [chunks * 4]byte
+	for i := 0; i < chunks; i++ {
+		v := uint32(h[3*i])<<16 | uint32(h[3*i+1])<<8 | uint32(h[3*i+2])
+		dst[4*i+0] = b64[(v>>18)&0x3F]
+		dst[4*i+1] = b64[(v>>12)&0x3F]
+		dst[4*i+2] = b64[(v>>6)&0x3F]
+		dst[4*i+3] = b64[v&0x3F]
+	}
+	return string(dst[:])
+}

go/src/cmd/internal/buildid/buildid_test.go

@@ -0,0 +1,251 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package buildid
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"debug/elf"
+	"encoding/binary"
+	"internal/obscuretestdata"
+	"os"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+const (
+	expectedID = "abcdefghijklmnopqrstuvwxyz.1234567890123456789012345678901234567890123456789012345678901234"
+	newID      = "bcdefghijklmnopqrstuvwxyza.2345678901234567890123456789012345678901234567890123456789012341"
+)
+
+func TestReadFile(t *testing.T) {
+	f, err := os.CreateTemp("", "buildid-test-")
+	if err != nil {
+		t.Fatal(err)
+	}
+	tmp := f.Name()
+	defer os.Remove(tmp)
+	f.Close()
+
+	// Use obscured files to prevent Apple’s notarization service from
+	// mistaking them as candidates for notarization and rejecting the entire
+	// toolchain.
+	// See golang.org/issue/34986
+	var files = []string{
+		"p.a.base64",
+		"a.elf.base64",
+		"a.macho.base64",
+		"a.pe.base64",
+	}
+
+	for _, name := range files {
+		f, err := obscuretestdata.DecodeToTempFile("testdata/" + name)
+		if err != nil {
+			t.Errorf("obscuretestdata.DecodeToTempFile(testdata/%s): %v", name, err)
+			continue
+		}
+		defer os.Remove(f)
+		id, err := ReadFile(f)
+		if id != expectedID || err != nil {
+			t.Errorf("ReadFile(testdata/%s) = %q, %v, want %q, nil", f, id, err, expectedID)
+		}
+		old := readSize
+		readSize = 2048
+		id, err = ReadFile(f)
+		readSize = old
+		if id != expectedID || err != nil {
+			t.Errorf("ReadFile(%s) [readSize=2k] = %q, %v, want %q, nil", f, id, err, expectedID)
+		}
+
+		data, err := os.ReadFile(f)
+		if err != nil {
+			t.Fatal(err)
+		}
+		m, _, err := FindAndHash(bytes.NewReader(data), expectedID, 1024)
+		if err != nil {
+			t.Errorf("FindAndHash(%s): %v", f, err)
+			continue
+		}
+		if err := os.WriteFile(tmp, data, 0666); err != nil {
+			t.Error(err)
+			continue
+		}
+		tf, err := os.OpenFile(tmp, os.O_WRONLY, 0)
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+		err = Rewrite(tf, m, newID)
+		err2 := tf.Close()
+		if err != nil {
+			t.Errorf("Rewrite(%s): %v", f, err)
+			continue
+		}
+		if err2 != nil {
+			t.Fatal(err2)
+		}
+
+		id, err = ReadFile(tmp)
+		if id != newID || err != nil {
+			t.Errorf("ReadFile(%s after Rewrite) = %q, %v, want %q, nil", f, id, err, newID)
+		}
+
+		// Test an ELF PT_NOTE segment with an Align field of 0.
+		// Do this by rewriting the file data.
+		if strings.Contains(name, "elf") {
+			// We only expect a 64-bit ELF file.
+			if elf.Class(data[elf.EI_CLASS]) != elf.ELFCLASS64 {
+				continue
+			}
+
+			// We only expect a little-endian ELF file.
+			if elf.Data(data[elf.EI_DATA]) != elf.ELFDATA2LSB {
+				continue
+			}
+			order := binary.LittleEndian
+
+			var hdr elf.Header64
+			if err := binary.Read(bytes.NewReader(data), order, &hdr); err != nil {
+				t.Error(err)
+				continue
+			}
+
+			phoff := hdr.Phoff
+			phnum := int(hdr.Phnum)
+			phsize := uint64(hdr.Phentsize)
+
+			for i := 0; i < phnum; i++ {
+				var phdr elf.Prog64
+				if err := binary.Read(bytes.NewReader(data[phoff:]), order, &phdr); err != nil {
+					t.Error(err)
+					continue
+				}
+
+				if elf.ProgType(phdr.Type) == elf.PT_NOTE {
+					// Increase the size so we keep
+					// reading notes.
+					order.PutUint64(data[phoff+4*8:], phdr.Filesz+1)
+
+					// Clobber the Align field to zero.
+					order.PutUint64(data[phoff+6*8:], 0)
+
+					// Clobber the note type so we
+					// keep reading notes.
+					order.PutUint32(data[phdr.Off+12:], 0)
+				}
+
+				phoff += phsize
+			}
+
+			if err := os.WriteFile(tmp, data, 0666); err != nil {
+				t.Error(err)
+				continue
+			}
+
+			id, err := ReadFile(tmp)
+			// Because we clobbered the note type above,
+			// we don't expect to see a Go build ID.
+			// The issue we are testing for was a crash
+			// in Readfile; see issue #62097.
+			if id != "" || err != nil {
+				t.Errorf("ReadFile with zero ELF Align = %q, %v, want %q, nil", id, err, "")
+				continue
+			}
+		}
+	}
+}
+
+func TestFindAndHash(t *testing.T) {
+	buf := make([]byte, 64)
+	buf2 := make([]byte, 64)
+	id := make([]byte, 8)
+	zero := make([]byte, 8)
+	for i := range id {
+		id[i] = byte(i)
+	}
+	numError := 0
+	errorf := func(msg string, args ...any) {
+		t.Errorf(msg, args...)
+		if numError++; numError > 20 {
+			t.Logf("stopping after too many errors")
+			t.FailNow()
+		}
+	}
+	for bufSize := len(id); bufSize <= len(buf); bufSize++ {
+		for j := range buf {
+			for k := 0; k < 2*len(id) && j+k < len(buf); k++ {
+				for i := range buf {
+					buf[i] = 1
+				}
+				copy(buf[j:], id)
+				copy(buf[j+k:], id)
+				var m []int64
+				if j+len(id) <= j+k {
+					m = append(m, int64(j))
+				}
+				if j+k+len(id) <= len(buf) {
+					m = append(m, int64(j+k))
+				}
+				copy(buf2, buf)
+				for _, p := range m {
+					copy(buf2[p:], zero)
+				}
+				h := sha256.Sum256(buf2)
+
+				matches, hash, err := FindAndHash(bytes.NewReader(buf), string(id), bufSize)
+				if err != nil {
+					errorf("bufSize=%d j=%d k=%d: findAndHash: %v", bufSize, j, k, err)
+					continue
+				}
+				if !reflect.DeepEqual(matches, m) {
+					errorf("bufSize=%d j=%d k=%d: findAndHash: matches=%v, want %v", bufSize, j, k, matches, m)
+					continue
+				}
+				if hash != h {
+					errorf("bufSize=%d j=%d k=%d: findAndHash: matches correct, but hash=%x, want %x", bufSize, j, k, hash, h)
+				}
+			}
+		}
+	}
+}
+
+func TestExcludedReader(t *testing.T) {
+	const s = "0123456789abcdefghijklmn"
+	tests := []struct {
+		start, end int64    // excluded range
+		results    []string // expected results of reads
+	}{
+		{12, 15, []string{"0123456789", "ab\x00\x00\x00fghij", "klmn"}},                              // within one read
+		{8, 21, []string{"01234567\x00\x00", "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", "\x00lmn"}}, // across multiple reads
+		{10, 20, []string{"0123456789", "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", "klmn"}},         // a whole read
+		{0, 5, []string{"\x00\x00\x00\x00\x0056789", "abcdefghij", "klmn"}},                          // start
+		{12, 24, []string{"0123456789", "ab\x00\x00\x00\x00\x00\x00\x00\x00", "\x00\x00\x00\x00"}},   // end
+	}
+	p := make([]byte, 10)
+	for _, test := range tests {
+		r := &excludedReader{strings.NewReader(s), 0, test.start, test.end}
+		for _, res := range test.results {
+			n, err := r.Read(p)
+			if err != nil {
+				t.Errorf("read failed: %v", err)
+			}
+			if n != len(res) {
+				t.Errorf("unexpected number of bytes read: want %d, got %d", len(res), n)
+			}
+			if string(p[:n]) != res {
+				t.Errorf("unexpected bytes: want %q, got %q", res, p[:n])
+			}
+		}
+	}
+}
+
+func TestEmptyID(t *testing.T) {
+	r := strings.NewReader("aha!")
+	matches, hash, err := FindAndHash(r, "", 1000)
+	if matches != nil || hash != ([32]byte{}) || err == nil || !strings.Contains(err.Error(), "no id") {
+		t.Errorf("FindAndHash: want nil, [32]byte{}, no id specified, got %v, %v, %v", matches, hash, err)
+	}
+}

go/src/cmd/internal/buildid/note.go

@@ -0,0 +1,213 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package buildid
+
+import (
+	"bytes"
+	"debug/elf"
+	"debug/macho"
+	"encoding/binary"
+	"fmt"
+	"io"
+	"io/fs"
+	"os"
+)
+
+func readAligned4(r io.Reader, sz int32) ([]byte, error) {
+	full := (sz + 3) &^ 3
+	data := make([]byte, full)
+	_, err := io.ReadFull(r, data)
+	if err != nil {
+		return nil, err
+	}
+	data = data[:sz]
+	return data, nil
+}
+
+func ReadELFNote(filename, name string, typ int32) ([]byte, error) {
+	f, err := elf.Open(filename)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	for _, sect := range f.Sections {
+		if sect.Type != elf.SHT_NOTE {
+			continue
+		}
+		r := sect.Open()
+		for {
+			var namesize, descsize, noteType int32
+			err = binary.Read(r, f.ByteOrder, &namesize)
+			if err != nil {
+				if err == io.EOF {
+					break
+				}
+				return nil, fmt.Errorf("read namesize failed: %v", err)
+			}
+			err = binary.Read(r, f.ByteOrder, &descsize)
+			if err != nil {
+				return nil, fmt.Errorf("read descsize failed: %v", err)
+			}
+			err = binary.Read(r, f.ByteOrder, &noteType)
+			if err != nil {
+				return nil, fmt.Errorf("read type failed: %v", err)
+			}
+			noteName, err := readAligned4(r, namesize)
+			if err != nil {
+				return nil, fmt.Errorf("read name failed: %v", err)
+			}
+			desc, err := readAligned4(r, descsize)
+			if err != nil {
+				return nil, fmt.Errorf("read desc failed: %v", err)
+			}
+			if name == string(noteName) && typ == noteType {
+				return desc, nil
+			}
+		}
+	}
+	return nil, nil
+}
+
+var elfGoNote = []byte("Go\x00\x00")
+var elfGNUNote = []byte("GNU\x00")
+
+// The Go build ID is stored in a note described by an ELF PT_NOTE prog
+// header. The caller has already opened filename, to get f, and read
+// at least 4 kB out, in data.
+func readELF(name string, f *os.File, data []byte) (buildid string, err error) {
+	// Assume the note content is in the data, already read.
+	// Rewrite the ELF header to set shoff and shnum to 0, so that we can pass
+	// the data to elf.NewFile and it will decode the Prog list but not
+	// try to read the section headers and the string table from disk.
+	// That's a waste of I/O when all we care about is the Prog list
+	// and the one ELF note.
+	switch elf.Class(data[elf.EI_CLASS]) {
+	case elf.ELFCLASS32:
+		data[32], data[33], data[34], data[35] = 0, 0, 0, 0
+		data[48] = 0
+		data[49] = 0
+	case elf.ELFCLASS64:
+		data[40], data[41], data[42], data[43] = 0, 0, 0, 0
+		data[44], data[45], data[46], data[47] = 0, 0, 0, 0
+		data[60] = 0
+		data[61] = 0
+	}
+
+	const elfGoBuildIDTag = 4
+	const gnuBuildIDTag = 3
+
+	ef, err := elf.NewFile(bytes.NewReader(data))
+	if err != nil {
+		return "", &fs.PathError{Path: name, Op: "parse", Err: err}
+	}
+	var gnu string
+	for _, p := range ef.Progs {
+		if p.Type != elf.PT_NOTE || p.Filesz < 16 {
+			continue
+		}
+
+		var note []byte
+		if p.Off+p.Filesz < uint64(len(data)) {
+			note = data[p.Off : p.Off+p.Filesz]
+		} else {
+			// For some linkers, such as the Solaris linker,
+			// the buildid may not be found in data (which
+			// likely contains the first 16kB of the file)
+			// or even the first few megabytes of the file
+			// due to differences in note segment placement;
+			// in that case, extract the note data manually.
+			_, err = f.Seek(int64(p.Off), io.SeekStart)
+			if err != nil {
+				return "", err
+			}
+
+			note = make([]byte, p.Filesz)
+			_, err = io.ReadFull(f, note)
+			if err != nil {
+				return "", err
+			}
+		}
+
+		filesz := p.Filesz
+		off := p.Off
+		for filesz >= 16 {
+			nameSize := ef.ByteOrder.Uint32(note)
+			valSize := ef.ByteOrder.Uint32(note[4:])
+			tag := ef.ByteOrder.Uint32(note[8:])
+			nname := note[12:16]
+			if nameSize == 4 && 16+valSize <= uint32(len(note)) && tag == elfGoBuildIDTag && bytes.Equal(nname, elfGoNote) {
+				return string(note[16 : 16+valSize]), nil
+			}
+
+			if nameSize == 4 && 16+valSize <= uint32(len(note)) && tag == gnuBuildIDTag && bytes.Equal(nname, elfGNUNote) {
+				gnu = string(note[16 : 16+valSize])
+			}
+
+			nameSize = (nameSize + 3) &^ 3
+			valSize = (valSize + 3) &^ 3
+			notesz := uint64(12 + nameSize + valSize)
+			if filesz <= notesz {
+				break
+			}
+			off += notesz
+			align := p.Align
+			if align != 0 {
+				alignedOff := (off + align - 1) &^ (align - 1)
+				notesz += alignedOff - off
+				off = alignedOff
+			}
+			filesz -= notesz
+			note = note[notesz:]
+		}
+	}
+
+	// If we didn't find a Go note, use a GNU note if available.
+	// This is what gccgo uses.
+	if gnu != "" {
+		return gnu, nil
+	}
+
+	// No note. Treat as successful but build ID empty.
+	return "", nil
+}
+
+// The Go build ID is stored at the beginning of the Mach-O __text segment.
+// The caller has already opened filename, to get f, and read a few kB out, in data.
+// Sadly, that's not guaranteed to hold the note, because there is an arbitrary amount
+// of other junk placed in the file ahead of the main text.
+func readMacho(name string, f *os.File, data []byte) (buildid string, err error) {
+	// If the data we want has already been read, don't worry about Mach-O parsing.
+	// This is both an optimization and a hedge against the Mach-O parsing failing
+	// in the future due to, for example, the name of the __text section changing.
+	if b, err := readRaw(name, data); b != "" && err == nil {
+		return b, err
+	}
+
+	mf, err := macho.NewFile(f)
+	if err != nil {
+		return "", &fs.PathError{Path: name, Op: "parse", Err: err}
+	}
+
+	sect := mf.Section("__text")
+	if sect == nil {
+		// Every binary has a __text section. Something is wrong.
+		return "", &fs.PathError{Path: name, Op: "parse", Err: fmt.Errorf("cannot find __text section")}
+	}
+
+	// It should be in the first few bytes, but read a lot just in case,
+	// especially given our past problems on OS X with the build ID moving.
+	// There shouldn't be much difference between reading 4kB and 32kB:
+	// the hard part is getting to the data, not transferring it.
+	n := sect.Size
+	if n > uint64(readSize) {
+		n = uint64(readSize)
+	}
+	buf := make([]byte, n)
+	if _, err := f.ReadAt(buf, int64(sect.Offset)); err != nil {
+		return "", err
+	}
+
+	return readRaw(name, buf)
+}

go/src/cmd/internal/buildid/rewrite.go

@@ -0,0 +1,220 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package buildid
+
+import (
+	"bytes"
+	"cmd/internal/codesign"
+	imacho "cmd/internal/macho"
+	"crypto/sha256"
+	"debug/elf"
+	"debug/macho"
+	"fmt"
+	"io"
+)
+
+// FindAndHash reads all of r and returns the offsets of occurrences of id.
+// While reading, findAndHash also computes and returns
+// a hash of the content of r, but with occurrences of id replaced by zeros.
+// FindAndHash reads bufSize bytes from r at a time.
+// If bufSize == 0, FindAndHash uses a reasonable default.
+func FindAndHash(r io.Reader, id string, bufSize int) (matches []int64, hash [32]byte, err error) {
+	if bufSize == 0 {
+		bufSize = 31 * 1024 // bufSize+little will likely fit in 32 kB
+	}
+	if len(id) == 0 {
+		return nil, [32]byte{}, fmt.Errorf("buildid.FindAndHash: no id specified")
+	}
+	if len(id) > bufSize {
+		return nil, [32]byte{}, fmt.Errorf("buildid.FindAndHash: buffer too small")
+	}
+	zeros := make([]byte, len(id))
+	idBytes := []byte(id)
+
+	r0 := r // preserve original type of r
+
+	// For Mach-O files, we want to exclude the code signature.
+	// The code signature contains hashes of the whole file (except the signature
+	// itself), including the buildid. So the buildid cannot contain the signature.
+	r = excludeMachoCodeSignature(r)
+
+	// With the "-B gobuildid" linker option (which will be the default on some
+	// platforms), the host build ID (GNU build ID, Mach-O UUID) depends on the
+	// Go buildid. So ignore the host build ID, to avoid convergence problem.
+	r = excludeHostBuildID(r, r0)
+
+	// The strategy is to read the file through buf, looking for id,
+	// but we need to worry about what happens if id is broken up
+	// and returned in parts by two different reads.
+	// We allocate a tiny buffer (at least len(id)) and a big buffer (bufSize bytes)
+	// next to each other in memory and then copy the tail of
+	// one read into the tiny buffer before reading new data into the big buffer.
+	// The search for id is over the entire tiny+big buffer.
+	tiny := (len(id) + 127) &^ 127 // round up to 128-aligned
+	buf := make([]byte, tiny+bufSize)
+	h := sha256.New()
+	start := tiny
+	for offset := int64(0); ; {
+		// The file offset maintained by the loop corresponds to &buf[tiny].
+		// buf[start:tiny] is left over from previous iteration.
+		// After reading n bytes into buf[tiny:], we process buf[start:tiny+n].
+		n, err := io.ReadFull(r, buf[tiny:])
+		if err != io.ErrUnexpectedEOF && err != io.EOF && err != nil {
+			return nil, [32]byte{}, err
+		}
+
+		// Process any matches.
+		for {
+			i := bytes.Index(buf[start:tiny+n], idBytes)
+			if i < 0 {
+				break
+			}
+			matches = append(matches, offset+int64(start+i-tiny))
+			h.Write(buf[start : start+i])
+			h.Write(zeros)
+			start += i + len(id)
+		}
+		if n < bufSize {
+			// Did not fill buffer, must be at end of file.
+			h.Write(buf[start : tiny+n])
+			break
+		}
+
+		// Process all but final tiny bytes of buf (bufSize = len(buf)-tiny).
+		// Note that start > len(buf)-tiny is possible, if the search above
+		// found an id ending in the final tiny fringe. That's OK.
+		if start < len(buf)-tiny {
+			h.Write(buf[start : len(buf)-tiny])
+			start = len(buf) - tiny
+		}
+
+		// Slide ending tiny-sized fringe to beginning of buffer.
+		copy(buf[0:], buf[bufSize:])
+		start -= bufSize
+		offset += int64(bufSize)
+	}
+	h.Sum(hash[:0])
+	return matches, hash, nil
+}
+
+func Rewrite(w io.WriterAt, pos []int64, id string) error {
+	b := []byte(id)
+	for _, p := range pos {
+		if _, err := w.WriteAt(b, p); err != nil {
+			return err
+		}
+	}
+
+	// Update Mach-O code signature, if any.
+	if f, cmd, ok := findMachoCodeSignature(w); ok {
+		if codesign.Size(int64(cmd.Dataoff), "a.out") == int64(cmd.Datasize) {
+			// Update the signature if the size matches, so we don't need to
+			// fix up headers. Binaries generated by the Go linker should have
+			// the expected size. Otherwise skip.
+			text := f.Segment("__TEXT")
+			cs := make([]byte, cmd.Datasize)
+			codesign.Sign(cs, w.(io.Reader), "a.out", int64(cmd.Dataoff), int64(text.Offset), int64(text.Filesz), f.Type == macho.TypeExec)
+			if _, err := w.WriteAt(cs, int64(cmd.Dataoff)); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
+func excludeMachoCodeSignature(r io.Reader) io.Reader {
+	_, cmd, ok := findMachoCodeSignature(r)
+	if !ok {
+		return r
+	}
+	return &excludedReader{r, 0, int64(cmd.Dataoff), int64(cmd.Dataoff + cmd.Datasize)}
+}
+
+func excludeHostBuildID(r, r0 io.Reader) io.Reader {
+	off, sz, ok := findHostBuildID(r0)
+	if !ok {
+		return r
+	}
+	return &excludedReader{r, 0, off, off + sz}
+}
+
+// excludedReader wraps an io.Reader. Reading from it returns the bytes from
+// the underlying reader, except that when the byte offset is within the
+// range between start and end, it returns zero bytes.
+type excludedReader struct {
+	r          io.Reader
+	off        int64 // current offset
+	start, end int64 // the range to be excluded (read as zero)
+}
+
+func (r *excludedReader) Read(p []byte) (int, error) {
+	n, err := r.r.Read(p)
+	if n > 0 && r.off+int64(n) > r.start && r.off < r.end {
+		cstart := r.start - r.off
+		if cstart < 0 {
+			cstart = 0
+		}
+		cend := r.end - r.off
+		if cend > int64(n) {
+			cend = int64(n)
+		}
+		zeros := make([]byte, cend-cstart)
+		copy(p[cstart:cend], zeros)
+	}
+	r.off += int64(n)
+	return n, err
+}
+
+func findMachoCodeSignature(r any) (*macho.File, codesign.CodeSigCmd, bool) {
+	ra, ok := r.(io.ReaderAt)
+	if !ok {
+		return nil, codesign.CodeSigCmd{}, false
+	}
+	f, err := macho.NewFile(ra)
+	if err != nil {
+		return nil, codesign.CodeSigCmd{}, false
+	}
+	cmd, ok := codesign.FindCodeSigCmd(f)
+	return f, cmd, ok
+}
+
+func findHostBuildID(r io.Reader) (offset int64, size int64, ok bool) {
+	ra, ok := r.(io.ReaderAt)
+	if !ok {
+		return 0, 0, false
+	}
+
+	ef, err := elf.NewFile(ra)
+	if err == nil {
+		// ELF file. Find GNU build ID section.
+		sect := ef.Section(".note.gnu.build-id")
+		if sect == nil {
+			return 0, 0, false
+		}
+		// Skip over the 3-word note "header" and "GNU\x00".
+		return int64(sect.Offset + 16), int64(sect.Size - 16), true
+	}
+
+	mf, err := macho.NewFile(ra)
+	if err != nil {
+		return 0, 0, false
+	}
+
+	// Mach-O file. Find LC_UUID load command.
+	reader := imacho.NewLoadCmdReader(io.NewSectionReader(ra, 0, 1<<63-1), mf.ByteOrder, imacho.FileHeaderSize(mf))
+	for i := uint32(0); i < mf.Ncmd; i++ {
+		cmd, err := reader.Next()
+		if err != nil {
+			break
+		}
+		if cmd.Cmd == imacho.LC_UUID {
+			// The UUID is the data in the LC_UUID load command,
+			// skipping over the 8-byte command header.
+			return reader.Offset() + 8, int64(cmd.Len - 8), true
+		}
+	}
+	return 0, 0, false
+}

go/src/cmd/internal/codesign/codesign.go

@@ -0,0 +1,267 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package codesign provides basic functionalities for
+// ad-hoc code signing of Mach-O files.
+//
+// This is not a general tool for code-signing. It is made
+// specifically for the Go toolchain. It uses the same
+// ad-hoc signing algorithm as the Darwin linker.
+package codesign
+
+import (
+	"crypto/sha256"
+	"debug/macho"
+	"encoding/binary"
+	"io"
+
+	"cmd/internal/hash"
+)
+
+// Code signature layout.
+//
+// The code signature is a block of bytes that contains
+// a SuperBlob, which contains one or more Blobs. For ad-hoc
+// signing, a single CodeDirectory Blob suffices.
+//
+// A SuperBlob starts with its header (the binary representation
+// of the SuperBlob struct), followed by a list of (in our case,
+// one) Blobs (offset and size). A CodeDirectory Blob starts
+// with its head (the binary representation of CodeDirectory struct),
+// followed by the identifier (as a C string) and the hashes, at
+// the corresponding offsets.
+//
+// The signature data must be included in the __LINKEDIT segment.
+// In the Mach-O file header, an LC_CODE_SIGNATURE load command
+// points to the data.
+
+const (
+	pageSizeBits = 12
+	pageSize     = 1 << pageSizeBits
+)
+
+const LC_CODE_SIGNATURE = 0x1d
+
+// Constants and struct layouts are from
+// https://opensource.apple.com/source/xnu/xnu-4903.270.47/osfmk/kern/cs_blobs.h
+
+const (
+	CSMAGIC_REQUIREMENT        = 0xfade0c00 // single Requirement blob
+	CSMAGIC_REQUIREMENTS       = 0xfade0c01 // Requirements vector (internal requirements)
+	CSMAGIC_CODEDIRECTORY      = 0xfade0c02 // CodeDirectory blob
+	CSMAGIC_EMBEDDED_SIGNATURE = 0xfade0cc0 // embedded form of signature data
+	CSMAGIC_DETACHED_SIGNATURE = 0xfade0cc1 // multi-arch collection of embedded signatures
+
+	CSSLOT_CODEDIRECTORY = 0 // slot index for CodeDirectory
+)
+
+const (
+	CS_HASHTYPE_SHA1             = 1
+	CS_HASHTYPE_SHA256           = 2
+	CS_HASHTYPE_SHA256_TRUNCATED = 3
+	CS_HASHTYPE_SHA384           = 4
+)
+
+const (
+	CS_EXECSEG_MAIN_BINARY     = 0x1   // executable segment denotes main binary
+	CS_EXECSEG_ALLOW_UNSIGNED  = 0x10  // allow unsigned pages (for debugging)
+	CS_EXECSEG_DEBUGGER        = 0x20  // main binary is debugger
+	CS_EXECSEG_JIT             = 0x40  // JIT enabled
+	CS_EXECSEG_SKIP_LV         = 0x80  // skip library validation
+	CS_EXECSEG_CAN_LOAD_CDHASH = 0x100 // can bless cdhash for execution
+	CS_EXECSEG_CAN_EXEC_CDHASH = 0x200 // can execute blessed cdhash
+)
+
+type Blob struct {
+	typ    uint32 // type of entry
+	offset uint32 // offset of entry
+	// data follows
+}
+
+func (b *Blob) put(out []byte) []byte {
+	out = put32be(out, b.typ)
+	out = put32be(out, b.offset)
+	return out
+}
+
+const blobSize = 2 * 4
+
+type SuperBlob struct {
+	magic  uint32 // magic number
+	length uint32 // total length of SuperBlob
+	count  uint32 // number of index entries following
+	// blobs []Blob
+}
+
+func (s *SuperBlob) put(out []byte) []byte {
+	out = put32be(out, s.magic)
+	out = put32be(out, s.length)
+	out = put32be(out, s.count)
+	return out
+}
+
+const superBlobSize = 3 * 4
+
+type CodeDirectory struct {
+	magic         uint32 // magic number (CSMAGIC_CODEDIRECTORY)
+	length        uint32 // total length of CodeDirectory blob
+	version       uint32 // compatibility version
+	flags         uint32 // setup and mode flags
+	hashOffset    uint32 // offset of hash slot element at index zero
+	identOffset   uint32 // offset of identifier string
+	nSpecialSlots uint32 // number of special hash slots
+	nCodeSlots    uint32 // number of ordinary (code) hash slots
+	codeLimit     uint32 // limit to main image signature range
+	hashSize      uint8  // size of each hash in bytes
+	hashType      uint8  // type of hash (cdHashType* constants)
+	_pad1         uint8  // unused (must be zero)
+	pageSize      uint8  // log2(page size in bytes); 0 => infinite
+	_pad2         uint32 // unused (must be zero)
+	scatterOffset uint32
+	teamOffset    uint32
+	_pad3         uint32
+	codeLimit64   uint64
+	execSegBase   uint64
+	execSegLimit  uint64
+	execSegFlags  uint64
+	// data follows
+}
+
+func (c *CodeDirectory) put(out []byte) []byte {
+	out = put32be(out, c.magic)
+	out = put32be(out, c.length)
+	out = put32be(out, c.version)
+	out = put32be(out, c.flags)
+	out = put32be(out, c.hashOffset)
+	out = put32be(out, c.identOffset)
+	out = put32be(out, c.nSpecialSlots)
+	out = put32be(out, c.nCodeSlots)
+	out = put32be(out, c.codeLimit)
+	out = put8(out, c.hashSize)
+	out = put8(out, c.hashType)
+	out = put8(out, c._pad1)
+	out = put8(out, c.pageSize)
+	out = put32be(out, c._pad2)
+	out = put32be(out, c.scatterOffset)
+	out = put32be(out, c.teamOffset)
+	out = put32be(out, c._pad3)
+	out = put64be(out, c.codeLimit64)
+	out = put64be(out, c.execSegBase)
+	out = put64be(out, c.execSegLimit)
+	out = put64be(out, c.execSegFlags)
+	return out
+}
+
+const codeDirectorySize = 13*4 + 4 + 4*8
+
+// CodeSigCmd is Mach-O LC_CODE_SIGNATURE load command.
+type CodeSigCmd struct {
+	Cmd      uint32 // LC_CODE_SIGNATURE
+	Cmdsize  uint32 // sizeof this command (16)
+	Dataoff  uint32 // file offset of data in __LINKEDIT segment
+	Datasize uint32 // file size of data in __LINKEDIT segment
+}
+
+func FindCodeSigCmd(f *macho.File) (CodeSigCmd, bool) {
+	get32 := f.ByteOrder.Uint32
+	for _, l := range f.Loads {
+		data := l.Raw()
+		cmd := get32(data)
+		if cmd == LC_CODE_SIGNATURE {
+			return CodeSigCmd{
+				cmd,
+				get32(data[4:]),
+				get32(data[8:]),
+				get32(data[12:]),
+			}, true
+		}
+	}
+	return CodeSigCmd{}, false
+}
+
+func put32be(b []byte, x uint32) []byte { binary.BigEndian.PutUint32(b, x); return b[4:] }
+func put64be(b []byte, x uint64) []byte { binary.BigEndian.PutUint64(b, x); return b[8:] }
+func put8(b []byte, x uint8) []byte     { b[0] = x; return b[1:] }
+func puts(b, s []byte) []byte           { n := copy(b, s); return b[n:] }
+
+// Size computes the size of the code signature.
+// id is the identifier used for signing (a field in CodeDirectory blob, which
+// has no significance in ad-hoc signing).
+func Size(codeSize int64, id string) int64 {
+	nhashes := (codeSize + pageSize - 1) / pageSize
+	idOff := int64(codeDirectorySize)
+	hashOff := idOff + int64(len(id)+1)
+	cdirSz := hashOff + nhashes*hash.Size32
+	return int64(superBlobSize+blobSize) + cdirSz
+}
+
+// Sign generates an ad-hoc code signature and writes it to out.
+// out must have length at least Size(codeSize, id).
+// data is the file content without the signature, of size codeSize.
+// textOff and textSize is the file offset and size of the text segment.
+// isMain is true if this is a main executable.
+// id is the identifier used for signing (a field in CodeDirectory blob, which
+// has no significance in ad-hoc signing).
+func Sign(out []byte, data io.Reader, id string, codeSize, textOff, textSize int64, isMain bool) {
+	nhashes := (codeSize + pageSize - 1) / pageSize
+	idOff := int64(codeDirectorySize)
+	hashOff := idOff + int64(len(id)+1)
+	sz := Size(codeSize, id)
+
+	// emit blob headers
+	sb := SuperBlob{
+		magic:  CSMAGIC_EMBEDDED_SIGNATURE,
+		length: uint32(sz),
+		count:  1,
+	}
+	blob := Blob{
+		typ:    CSSLOT_CODEDIRECTORY,
+		offset: superBlobSize + blobSize,
+	}
+	cdir := CodeDirectory{
+		magic:        CSMAGIC_CODEDIRECTORY,
+		length:       uint32(sz) - (superBlobSize + blobSize),
+		version:      0x20400,
+		flags:        0x20002, // adhoc | linkerSigned
+		hashOffset:   uint32(hashOff),
+		identOffset:  uint32(idOff),
+		nCodeSlots:   uint32(nhashes),
+		codeLimit:    uint32(codeSize),
+		hashSize:     hash.Size32,
+		hashType:     CS_HASHTYPE_SHA256,
+		pageSize:     uint8(pageSizeBits),
+		execSegBase:  uint64(textOff),
+		execSegLimit: uint64(textSize),
+	}
+	if isMain {
+		cdir.execSegFlags = CS_EXECSEG_MAIN_BINARY
+	}
+
+	outp := out
+	outp = sb.put(outp)
+	outp = blob.put(outp)
+	outp = cdir.put(outp)
+
+	// emit the identifier
+	outp = puts(outp, []byte(id+"\000"))
+
+	// emit hashes
+	var buf [pageSize]byte
+	p := 0
+	for p < int(codeSize) {
+		n, err := io.ReadFull(data, buf[:])
+		if err == io.EOF {
+			break
+		}
+		if err != nil && err != io.ErrUnexpectedEOF {
+			panic(err)
+		}
+		if p+n > int(codeSize) {
+			n = int(codeSize) - p
+		}
+		p += n
+		b := sha256.Sum256(buf[:n])
+		outp = puts(outp, b[:])
+	}
+}

go/src/cmd/internal/cov/covcmd/cmddefs.go

@@ -0,0 +1,97 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package covcmd
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"internal/coverage"
+)
+
+// CoverPkgConfig is a bundle of information passed from the Go
+// command to the cover command during "go build -cover" runs. The
+// Go command creates and fills in a struct as below, then passes
+// file containing the encoded JSON for the struct to the "cover"
+// tool when instrumenting the source files in a Go package.
+type CoverPkgConfig struct {
+	// File into which cmd/cover should emit summary info
+	// when instrumentation is complete.
+	OutConfig string
+
+	// Import path for the package being instrumented.
+	PkgPath string
+
+	// Package name.
+	PkgName string
+
+	// Instrumentation granularity: one of "perfunc" or "perblock" (default)
+	Granularity string
+
+	// Module path for this package (empty if no go.mod in use)
+	ModulePath string
+
+	// Local mode indicates we're doing a coverage build or test of a
+	// package selected via local import path, e.g. "./..." or
+	// "./foo/bar" as opposed to a non-relative import path. See the
+	// corresponding field in cmd/go's PackageInternal struct for more
+	// info.
+	Local bool
+
+	// EmitMetaFile if non-empty is the path to which the cover tool should
+	// directly emit a coverage meta-data file for the package, if the
+	// package has any functions in it. The go command will pass in a value
+	// here if we've been asked to run "go test -cover" on a package that
+	// doesn't have any *_test.go files.
+	EmitMetaFile string
+}
+
+// CoverFixupConfig contains annotations/notes generated by the
+// cmd/cover tool (during instrumentation) to be passed on to the
+// compiler when the instrumented code is compiled. The cmd/cover tool
+// creates a struct of this type, JSON-encodes it, and emits the
+// result to a file, which the Go command then passes to the compiler
+// when the instrumented package is built.
+type CoverFixupConfig struct {
+	// Name of the variable (created by cmd/cover) containing the
+	// encoded meta-data for the package.
+	MetaVar string
+
+	// Length of the meta-data.
+	MetaLen int
+
+	// Hash computed by cmd/cover of the meta-data.
+	MetaHash string
+
+	// Instrumentation strategy. For now this is always set to
+	// "normal", but in the future we may add new values (for example,
+	// if panic paths are instrumented, or if the instrumenter
+	// eliminates redundant counters).
+	Strategy string
+
+	// Prefix assigned to the names of counter variables generated
+	// during instrumentation by cmd/cover.
+	CounterPrefix string
+
+	// Name chosen for the package ID variable generated during
+	// instrumentation.
+	PkgIdVar string
+
+	// Counter mode (e.g. set/count/atomic)
+	CounterMode string
+
+	// Counter granularity (perblock or perfunc).
+	CounterGranularity string
+}
+
+// MetaFileForPackage returns the expected name of the meta-data file
+// for the package whose import path is 'importPath' in cases where
+// we're using meta-data generated by the cover tool, as opposed to a
+// meta-data file created at runtime.
+func MetaFileForPackage(importPath string) string {
+	var r [32]byte
+	sum := sha256.Sum256([]byte(importPath))
+	copy(r[:], sum[:])
+	return coverage.MetaFilePref + fmt.Sprintf(".%x", r)
+}

go/src/cmd/internal/cov/mreader.go

@@ -0,0 +1,85 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cov
+
+import (
+	"cmd/internal/bio"
+	"io"
+	"os"
+)
+
+// This file contains the helper "MReader", a wrapper around bio plus
+// an "mmap'd read-only" view of the file obtained from bio.SliceRO().
+// MReader is designed to implement the io.ReaderSeeker interface.
+// Since bio.SliceOS() is not guaranteed to succeed, MReader falls back
+// on explicit reads + seeks provided by bio.Reader if needed.
+
+type MReader struct {
+	f        *os.File
+	rdr      *bio.Reader
+	fileView []byte
+	off      int64
+}
+
+func NewMreader(f *os.File) (*MReader, error) {
+	rdr := bio.NewReader(f)
+	fi, err := f.Stat()
+	if err != nil {
+		return nil, err
+	}
+	r := MReader{
+		f:        f,
+		rdr:      rdr,
+		fileView: rdr.SliceRO(uint64(fi.Size())),
+	}
+	return &r, nil
+}
+
+func (r *MReader) Read(p []byte) (int, error) {
+	if r.fileView != nil {
+		amt := len(p)
+		toread := r.fileView[r.off:]
+		if len(toread) < 1 {
+			return 0, io.EOF
+		}
+		if len(toread) < amt {
+			amt = len(toread)
+		}
+		copy(p, toread)
+		r.off += int64(amt)
+		return amt, nil
+	}
+	return io.ReadFull(r.rdr, p)
+}
+
+func (r *MReader) ReadByte() (byte, error) {
+	if r.fileView != nil {
+		toread := r.fileView[r.off:]
+		if len(toread) < 1 {
+			return 0, io.EOF
+		}
+		rv := toread[0]
+		r.off++
+		return rv, nil
+	}
+	return r.rdr.ReadByte()
+}
+
+func (r *MReader) Seek(offset int64, whence int) (int64, error) {
+	if r.fileView == nil {
+		return r.rdr.MustSeek(offset, whence), nil
+	}
+	switch whence {
+	case io.SeekStart:
+		r.off = offset
+		return offset, nil
+	case io.SeekCurrent:
+		return r.off, nil
+	case io.SeekEnd:
+		r.off = int64(len(r.fileView)) + offset
+		return r.off, nil
+	}
+	panic("other modes not implemented")
+}

go/src/cmd/internal/cov/read_test.go

@@ -0,0 +1,98 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cov_test
+
+import (
+	"cmd/internal/cov"
+	"fmt"
+	"internal/coverage"
+	"internal/coverage/decodecounter"
+	"internal/coverage/decodemeta"
+	"internal/coverage/pods"
+	"internal/testenv"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// visitor implements the CovDataVisitor interface in a very stripped
+// down way, just keeps track of interesting events.
+type visitor struct {
+	metaFileCount    int
+	counterFileCount int
+	funcCounterData  int
+	metaFuncCount    int
+}
+
+func (v *visitor) BeginPod(p pods.Pod) {}
+func (v *visitor) EndPod(p pods.Pod)   {}
+func (v *visitor) VisitMetaDataFile(mdf string, mfr *decodemeta.CoverageMetaFileReader) {
+	v.metaFileCount++
+}
+func (v *visitor) BeginCounterDataFile(cdf string, cdr *decodecounter.CounterDataReader, dirIdx int) {
+	v.counterFileCount++
+}
+func (v *visitor) EndCounterDataFile(cdf string, cdr *decodecounter.CounterDataReader, dirIdx int) {}
+func (v *visitor) VisitFuncCounterData(payload decodecounter.FuncPayload)                          { v.funcCounterData++ }
+func (v *visitor) EndCounters()                                                                    {}
+func (v *visitor) BeginPackage(pd *decodemeta.CoverageMetaDataDecoder, pkgIdx uint32)              {}
+func (v *visitor) EndPackage(pd *decodemeta.CoverageMetaDataDecoder, pkgIdx uint32)                {}
+func (v *visitor) VisitFunc(pkgIdx uint32, fnIdx uint32, fd *coverage.FuncDesc)                    { v.metaFuncCount++ }
+func (v *visitor) Finish()                                                                         {}
+
+func TestIssue58411(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// Build a tiny test program with -cover. Smallness is important;
+	// it is one of the factors that triggers issue 58411.
+	d := t.TempDir()
+	exepath := filepath.Join(d, "small.exe")
+	path := filepath.Join("testdata", "small.go")
+	cmd := testenv.Command(t, testenv.GoToolPath(t), "build",
+		"-o", exepath, "-cover", path)
+	b, err := cmd.CombinedOutput()
+	if len(b) != 0 {
+		t.Logf("## build output:\n%s", b)
+	}
+	if err != nil {
+		t.Fatalf("build error: %v", err)
+	}
+
+	// Run to produce coverage data. Note the large argument; we need a large
+	// argument (more than 4k) to trigger the bug, but the overall file
+	// has to remain small (since large files will be read with mmap).
+	covdir := filepath.Join(d, "covdata")
+	if err = os.Mkdir(covdir, 0777); err != nil {
+		t.Fatalf("creating covdir: %v", err)
+	}
+	large := fmt.Sprintf("%07999d", 0)
+	cmd = testenv.Command(t, exepath, "1", "2", "3", large)
+	cmd.Dir = covdir
+	cmd.Env = append(os.Environ(), "GOCOVERDIR="+covdir)
+	b, err = cmd.CombinedOutput()
+	if err != nil {
+		t.Logf("## run output:\n%s", b)
+		t.Fatalf("build error: %v", err)
+	}
+
+	vis := &visitor{}
+
+	// Read resulting coverage data. Without the fix, this would
+	// yield a "short read" error.
+	const verbosityLevel = 0
+	const flags = 0
+	cdr := cov.MakeCovDataReader(vis, []string{covdir}, verbosityLevel, flags, nil)
+	err = cdr.Visit()
+	if err != nil {
+		t.Fatalf("visit failed: %v", err)
+	}
+
+	// make sure we saw a few things just for grins
+	const want = "{metaFileCount:1 counterFileCount:1 funcCounterData:1 metaFuncCount:1}"
+	got := fmt.Sprintf("%+v", *vis)
+	if want != got {
+		t.Errorf("visitor contents: want %v got %v\n", want, got)
+	}
+}

go/src/cmd/internal/cov/readcovdata.go

@@ -0,0 +1,282 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cov
+
+import (
+	"cmd/internal/bio"
+	"fmt"
+	"internal/coverage"
+	"internal/coverage/decodecounter"
+	"internal/coverage/decodemeta"
+	"internal/coverage/pods"
+	"io"
+	"os"
+)
+
+// CovDataReader is a general-purpose helper/visitor object for
+// reading coverage data files in a structured way. Clients create a
+// CovDataReader to process a given collection of coverage data file
+// directories, then pass in a visitor object with methods that get
+// invoked at various important points. CovDataReader is intended
+// to facilitate common coverage data file operations such as
+// merging or intersecting data files, analyzing data files, or
+// dumping data files.
+type CovDataReader struct {
+	vis            CovDataVisitor
+	indirs         []string
+	matchpkg       func(name string) bool
+	flags          CovDataReaderFlags
+	err            error
+	verbosityLevel int
+}
+
+// MakeCovDataReader creates a CovDataReader object to process the
+// given set of input directories. Here 'vis' is a visitor object
+// providing methods to be invoked as we walk through the data,
+// 'indirs' is the set of coverage data directories to examine,
+// 'verbosityLevel' controls the level of debugging trace messages
+// (zero for off, higher for more output), 'flags' stores flags that
+// indicate what to do if errors are detected, and 'matchpkg' is a
+// caller-provided function that can be used to select specific
+// packages by name (if nil, then all packages are included).
+func MakeCovDataReader(vis CovDataVisitor, indirs []string, verbosityLevel int, flags CovDataReaderFlags, matchpkg func(name string) bool) *CovDataReader {
+	return &CovDataReader{
+		vis:            vis,
+		indirs:         indirs,
+		matchpkg:       matchpkg,
+		verbosityLevel: verbosityLevel,
+		flags:          flags,
+	}
+}
+
+// CovDataVisitor defines hooks for clients of CovDataReader. When the
+// coverage data reader makes its way through a coverage meta-data
+// file and counter data files, it will invoke the methods below to
+// hand off info to the client. The normal sequence of expected
+// visitor method invocations is:
+//
+//	for each pod P {
+//		BeginPod(p)
+//		let MF be the meta-data file for P
+//		VisitMetaDataFile(MF)
+//		for each counter data file D in P {
+//			BeginCounterDataFile(D)
+//			for each live function F in D {
+//				VisitFuncCounterData(F)
+//			}
+//			EndCounterDataFile(D)
+//		}
+//		EndCounters(MF)
+//		for each package PK in MF {
+//			BeginPackage(PK)
+//			if <PK matched according to package pattern and/or modpath> {
+//				for each function PF in PK {
+//					VisitFunc(PF)
+//				}
+//			}
+//			EndPackage(PK)
+//		}
+//		EndPod(p)
+//	}
+//	Finish()
+
+type CovDataVisitor interface {
+	// Invoked at the start and end of a given pod (a pod here is a
+	// specific coverage meta-data files with the counter data files
+	// that correspond to it).
+	BeginPod(p pods.Pod)
+	EndPod(p pods.Pod)
+
+	// Invoked when the reader is starting to examine the meta-data
+	// file for a pod. Here 'mdf' is the path of the file, and 'mfr'
+	// is an open meta-data reader.
+	VisitMetaDataFile(mdf string, mfr *decodemeta.CoverageMetaFileReader)
+
+	// Invoked when the reader processes a counter data file, first
+	// the 'begin' method at the start, then the 'end' method when
+	// we're done with the file.
+	BeginCounterDataFile(cdf string, cdr *decodecounter.CounterDataReader, dirIdx int)
+	EndCounterDataFile(cdf string, cdr *decodecounter.CounterDataReader, dirIdx int)
+
+	// Invoked once for each live function in the counter data file.
+	VisitFuncCounterData(payload decodecounter.FuncPayload)
+
+	// Invoked when we've finished processing the counter files in a
+	// POD (e.g. no more calls to VisitFuncCounterData).
+	EndCounters()
+
+	// Invoked for each package in the meta-data file for the pod,
+	// first the 'begin' method when processing of the package starts,
+	// then the 'end' method when we're done
+	BeginPackage(pd *decodemeta.CoverageMetaDataDecoder, pkgIdx uint32)
+	EndPackage(pd *decodemeta.CoverageMetaDataDecoder, pkgIdx uint32)
+
+	// Invoked for each function  the package being visited.
+	VisitFunc(pkgIdx uint32, fnIdx uint32, fd *coverage.FuncDesc)
+
+	// Invoked when all counter + meta-data file processing is complete.
+	Finish()
+}
+
+type CovDataReaderFlags uint32
+
+const (
+	CovDataReaderNoFlags CovDataReaderFlags = 0
+	PanicOnError                            = 1 << iota
+	PanicOnWarning
+)
+
+func (r *CovDataReader) Visit() error {
+	podlist, err := pods.CollectPods(r.indirs, false)
+	if err != nil {
+		return fmt.Errorf("reading inputs: %v", err)
+	}
+	if len(podlist) == 0 {
+		r.warn("no applicable files found in input directories")
+	}
+	for _, p := range podlist {
+		if err := r.visitPod(p); err != nil {
+			return err
+		}
+	}
+	r.vis.Finish()
+	return nil
+}
+
+func (r *CovDataReader) verb(vlevel int, s string, a ...any) {
+	if r.verbosityLevel >= vlevel {
+		fmt.Fprintf(os.Stderr, s, a...)
+		fmt.Fprintf(os.Stderr, "\n")
+	}
+}
+
+func (r *CovDataReader) warn(s string, a ...any) {
+	fmt.Fprintf(os.Stderr, "warning: ")
+	fmt.Fprintf(os.Stderr, s, a...)
+	fmt.Fprintf(os.Stderr, "\n")
+	if (r.flags & PanicOnWarning) != 0 {
+		panic("unexpected warning")
+	}
+}
+
+func (r *CovDataReader) fatal(s string, a ...any) error {
+	if r.err != nil {
+		return nil
+	}
+	errstr := "error: " + fmt.Sprintf(s, a...) + "\n"
+	if (r.flags & PanicOnError) != 0 {
+		fmt.Fprintf(os.Stderr, "%s", errstr)
+		panic("fatal error")
+	}
+	r.err = fmt.Errorf("%s", errstr)
+	return r.err
+}
+
+// visitPod examines a coverage data 'pod', that is, a meta-data file and
+// zero or more counter data files that refer to that meta-data file.
+func (r *CovDataReader) visitPod(p pods.Pod) error {
+	r.verb(1, "visiting pod: metafile %s with %d counter files",
+		p.MetaFile, len(p.CounterDataFiles))
+	r.vis.BeginPod(p)
+
+	// Open meta-file
+	f, err := os.Open(p.MetaFile)
+	if err != nil {
+		return r.fatal("unable to open meta-file %s", p.MetaFile)
+	}
+	defer f.Close()
+	br := bio.NewReader(f)
+	fi, err := f.Stat()
+	if err != nil {
+		return r.fatal("unable to stat metafile %s: %v", p.MetaFile, err)
+	}
+	fileView := br.SliceRO(uint64(fi.Size()))
+	br.MustSeek(0, io.SeekStart)
+
+	r.verb(1, "fileView for pod is length %d", len(fileView))
+
+	var mfr *decodemeta.CoverageMetaFileReader
+	mfr, err = decodemeta.NewCoverageMetaFileReader(f, fileView)
+	if err != nil {
+		return r.fatal("decoding meta-file %s: %s", p.MetaFile, err)
+	}
+	r.vis.VisitMetaDataFile(p.MetaFile, mfr)
+
+	processCounterDataFile := func(cdf string, k int) error {
+		cf, err := os.Open(cdf)
+		if err != nil {
+			return r.fatal("opening counter data file %s: %s", cdf, err)
+		}
+		defer cf.Close()
+		var mr *MReader
+		mr, err = NewMreader(cf)
+		if err != nil {
+			return r.fatal("creating reader for counter data file %s: %s", cdf, err)
+		}
+		var cdr *decodecounter.CounterDataReader
+		cdr, err = decodecounter.NewCounterDataReader(cdf, mr)
+		if err != nil {
+			return r.fatal("reading counter data file %s: %s", cdf, err)
+		}
+		r.vis.BeginCounterDataFile(cdf, cdr, p.Origins[k])
+		var data decodecounter.FuncPayload
+		for {
+			ok, err := cdr.NextFunc(&data)
+			if err != nil {
+				return r.fatal("reading counter data file %s: %v", cdf, err)
+			}
+			if !ok {
+				break
+			}
+			r.vis.VisitFuncCounterData(data)
+		}
+		r.vis.EndCounterDataFile(cdf, cdr, p.Origins[k])
+		return nil
+	}
+
+	// Read counter data files.
+	for k, cdf := range p.CounterDataFiles {
+		if err := processCounterDataFile(cdf, k); err != nil {
+			return err
+		}
+	}
+	r.vis.EndCounters()
+
+	// NB: packages in the meta-file will be in dependency order (basically
+	// the order in which init files execute). Do we want an additional sort
+	// pass here, say by packagepath?
+	np := uint32(mfr.NumPackages())
+	payload := []byte{}
+	for pkIdx := uint32(0); pkIdx < np; pkIdx++ {
+		var pd *decodemeta.CoverageMetaDataDecoder
+		pd, payload, err = mfr.GetPackageDecoder(pkIdx, payload)
+		if err != nil {
+			return r.fatal("reading pkg %d from meta-file %s: %s", pkIdx, p.MetaFile, err)
+		}
+		r.processPackage(p.MetaFile, pd, pkIdx)
+	}
+	r.vis.EndPod(p)
+
+	return nil
+}
+
+func (r *CovDataReader) processPackage(mfname string, pd *decodemeta.CoverageMetaDataDecoder, pkgIdx uint32) error {
+	if r.matchpkg != nil {
+		if !r.matchpkg(pd.PackagePath()) {
+			return nil
+		}
+	}
+	r.vis.BeginPackage(pd, pkgIdx)
+	nf := pd.NumFuncs()
+	var fd coverage.FuncDesc
+	for fidx := uint32(0); fidx < nf; fidx++ {
+		if err := pd.ReadFunc(fidx, &fd); err != nil {
+			return r.fatal("reading meta-data file %s: %v", mfname, err)
+		}
+		r.vis.VisitFunc(pkgIdx, fidx, &fd)
+	}
+	r.vis.EndPackage(pd, pkgIdx)
+	return nil
+}

go/src/cmd/internal/disasm/disasm.go

@@ -0,0 +1,464 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package disasm provides disassembly routines.
+//
+// It is broken out from cmd/internal/objfile so tools that don't need
+// disassembling don't need to depend on x/arch disassembler code.
+package disasm
+
+import (
+	"bufio"
+	"bytes"
+	"container/list"
+	"encoding/binary"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"regexp"
+	"sort"
+	"strings"
+	"text/tabwriter"
+
+	"cmd/internal/objfile"
+	"cmd/internal/src"
+
+	"golang.org/x/arch/arm/armasm"
+	"golang.org/x/arch/arm64/arm64asm"
+	"golang.org/x/arch/loong64/loong64asm"
+	"golang.org/x/arch/ppc64/ppc64asm"
+	"golang.org/x/arch/riscv64/riscv64asm"
+	"golang.org/x/arch/s390x/s390xasm"
+	"golang.org/x/arch/x86/x86asm"
+)
+
+// Disasm is a disassembler for a given File.
+type Disasm struct {
+	syms      []objfile.Sym    // symbols in file, sorted by address
+	pcln      objfile.Liner    // pcln table
+	text      []byte           // bytes of text segment (actual instructions)
+	textStart uint64           // start PC of text
+	textEnd   uint64           // end PC of text
+	goarch    string           // GOARCH string
+	disasm    disasmFunc       // disassembler function for goarch
+	byteOrder binary.ByteOrder // byte order for goarch
+}
+
+// DisasmForFile returns a disassembler for the file f.
+func DisasmForFile(f *objfile.File) (*Disasm, error) {
+	return disasmForEntry(f.Entries()[0])
+}
+
+func disasmForEntry(e *objfile.Entry) (*Disasm, error) {
+	syms, err := e.Symbols()
+	if err != nil {
+		return nil, err
+	}
+
+	pcln, err := e.PCLineTable()
+	if err != nil {
+		return nil, err
+	}
+
+	textStart, textBytes, err := e.Text()
+	if err != nil {
+		return nil, err
+	}
+
+	goarch := e.GOARCH()
+	disasm := disasms[goarch]
+	byteOrder := byteOrders[goarch]
+	if disasm == nil || byteOrder == nil {
+		return nil, fmt.Errorf("unsupported architecture %q", goarch)
+	}
+
+	// Filter out section symbols, overwriting syms in place.
+	keep := syms[:0]
+	for _, sym := range syms {
+		switch sym.Name {
+		case "runtime.text", "text", "_text", "runtime.etext", "etext", "_etext":
+			// drop
+		default:
+			keep = append(keep, sym)
+		}
+	}
+	syms = keep
+	d := &Disasm{
+		syms:      syms,
+		pcln:      pcln,
+		text:      textBytes,
+		textStart: textStart,
+		textEnd:   textStart + uint64(len(textBytes)),
+		goarch:    goarch,
+		disasm:    disasm,
+		byteOrder: byteOrder,
+	}
+
+	return d, nil
+}
+
+// lookup finds the symbol name containing addr.
+func (d *Disasm) lookup(addr uint64) (name string, base uint64) {
+	i := sort.Search(len(d.syms), func(i int) bool { return addr < d.syms[i].Addr })
+	if i > 0 {
+		s := d.syms[i-1]
+		if s.Addr != 0 && s.Addr <= addr && addr < s.Addr+uint64(s.Size) {
+			return s.Name, s.Addr
+		}
+	}
+	return "", 0
+}
+
+// base returns the final element in the path.
+// It works on both Windows and Unix paths,
+// regardless of host operating system.
+func base(path string) string {
+	path = path[strings.LastIndex(path, "/")+1:]
+	path = path[strings.LastIndex(path, `\`)+1:]
+	return path
+}
+
+// CachedFile contains the content of a file split into lines.
+type CachedFile struct {
+	FileName string
+	Lines    [][]byte
+}
+
+// FileCache is a simple LRU cache of file contents.
+type FileCache struct {
+	files  *list.List
+	maxLen int
+}
+
+// NewFileCache returns a FileCache which can contain up to maxLen cached file contents.
+func NewFileCache(maxLen int) *FileCache {
+	return &FileCache{
+		files:  list.New(),
+		maxLen: maxLen,
+	}
+}
+
+// Line returns the source code line for the given file and line number.
+// If the file is not already cached, reads it, inserts it into the cache,
+// and removes the least recently used file if necessary.
+// If the file is in cache, it is moved to the front of the list.
+func (fc *FileCache) Line(filename string, line int) ([]byte, error) {
+	if filepath.Ext(filename) != ".go" {
+		return nil, nil
+	}
+
+	// Clean filenames returned by src.Pos.SymFilename()
+	// or src.PosBase.SymFilename() removing
+	// the leading src.FileSymPrefix.
+	filename = strings.TrimPrefix(filename, src.FileSymPrefix)
+
+	// Expand literal "$GOROOT" rewritten by obj.AbsFile()
+	filename = filepath.Clean(os.ExpandEnv(filename))
+
+	var cf *CachedFile
+	var e *list.Element
+
+	for e = fc.files.Front(); e != nil; e = e.Next() {
+		cf = e.Value.(*CachedFile)
+		if cf.FileName == filename {
+			break
+		}
+	}
+
+	if e == nil {
+		content, err := os.ReadFile(filename)
+		if err != nil {
+			return nil, err
+		}
+
+		cf = &CachedFile{
+			FileName: filename,
+			Lines:    bytes.Split(content, []byte{'\n'}),
+		}
+		fc.files.PushFront(cf)
+
+		if fc.files.Len() >= fc.maxLen {
+			fc.files.Remove(fc.files.Back())
+		}
+	} else {
+		fc.files.MoveToFront(e)
+	}
+
+	// because //line directives can be out-of-range. (#36683)
+	if line-1 >= len(cf.Lines) || line-1 < 0 {
+		return nil, nil
+	}
+
+	return cf.Lines[line-1], nil
+}
+
+// Print prints a disassembly of the file to w.
+// If filter is non-nil, the disassembly only includes functions with names matching filter.
+// If printCode is true, the disassembly includes corresponding source lines.
+// The disassembly only includes functions that overlap the range [start, end).
+func (d *Disasm) Print(w io.Writer, filter *regexp.Regexp, start, end uint64, printCode bool, gnuAsm bool) {
+	if start < d.textStart {
+		start = d.textStart
+	}
+	if end > d.textEnd {
+		end = d.textEnd
+	}
+	printed := false
+	bw := bufio.NewWriter(w)
+
+	var fc *FileCache
+	if printCode {
+		fc = NewFileCache(8)
+	}
+
+	tw := tabwriter.NewWriter(bw, 18, 8, 1, '\t', tabwriter.StripEscape)
+	for _, sym := range d.syms {
+		symStart := sym.Addr
+		symEnd := sym.Addr + uint64(sym.Size)
+		relocs := sym.Relocs
+		if sym.Code != 'T' && sym.Code != 't' ||
+			symStart < d.textStart ||
+			symEnd <= start || end <= symStart ||
+			filter != nil && !filter.MatchString(sym.Name) {
+			continue
+		}
+		if printed {
+			fmt.Fprintf(bw, "\n")
+		}
+		printed = true
+
+		file, _, _ := d.pcln.PCToLine(sym.Addr)
+		fmt.Fprintf(bw, "TEXT %s(SB) %s\n", sym.Name, file)
+
+		if symEnd > end {
+			symEnd = end
+		}
+		code := d.text[:end-d.textStart]
+
+		var lastFile string
+		var lastLine int
+
+		d.Decode(symStart, symEnd, relocs, gnuAsm, func(pc, size uint64, file string, line int, text string) {
+			i := pc - d.textStart
+
+			if printCode {
+				if file != lastFile || line != lastLine {
+					if srcLine, err := fc.Line(file, line); err == nil {
+						fmt.Fprintf(tw, "%s%s%s\n", []byte{tabwriter.Escape}, srcLine, []byte{tabwriter.Escape})
+					}
+
+					lastFile, lastLine = file, line
+				}
+
+				fmt.Fprintf(tw, "  %#x\t", pc)
+			} else {
+				fmt.Fprintf(tw, "  %s:%d\t%#x\t", base(file), line, pc)
+			}
+
+			if size%4 != 0 || d.goarch == "386" || d.goarch == "amd64" {
+				// Print instruction as bytes.
+				fmt.Fprintf(tw, "%x", code[i:i+size])
+			} else {
+				// Print instruction as 32-bit words.
+				for j := uint64(0); j < size; j += 4 {
+					if j > 0 {
+						fmt.Fprintf(tw, " ")
+					}
+					fmt.Fprintf(tw, "%08x", d.byteOrder.Uint32(code[i+j:]))
+				}
+			}
+			fmt.Fprintf(tw, "\t%s\t\n", text)
+		})
+		tw.Flush()
+	}
+	bw.Flush()
+}
+
+// Decode disassembles the text segment range [start, end), calling f for each instruction.
+func (d *Disasm) Decode(start, end uint64, relocs []objfile.Reloc, gnuAsm bool, f func(pc, size uint64, file string, line int, text string)) {
+	if start < d.textStart {
+		start = d.textStart
+	}
+	if end > d.textEnd {
+		end = d.textEnd
+	}
+	code := d.text[:end-d.textStart]
+	lookup := d.lookup
+	for pc := start; pc < end; {
+		i := pc - d.textStart
+		text, size := d.disasm(code[i:], pc, lookup, d.byteOrder, gnuAsm)
+		file, line, _ := d.pcln.PCToLine(pc)
+		sep := "\t"
+		for len(relocs) > 0 && relocs[0].Addr < i+uint64(size) {
+			text += sep + relocs[0].Stringer.String(pc-start)
+			sep = " "
+			relocs = relocs[1:]
+		}
+		f(pc, uint64(size), file, line, text)
+		pc += uint64(size)
+	}
+}
+
+type lookupFunc = func(addr uint64) (sym string, base uint64)
+type disasmFunc func(code []byte, pc uint64, lookup lookupFunc, ord binary.ByteOrder, _ bool) (text string, size int)
+
+func disasm_386(code []byte, pc uint64, lookup lookupFunc, _ binary.ByteOrder, gnuAsm bool) (string, int) {
+	return disasm_x86(code, pc, lookup, 32, gnuAsm)
+}
+
+func disasm_amd64(code []byte, pc uint64, lookup lookupFunc, _ binary.ByteOrder, gnuAsm bool) (string, int) {
+	return disasm_x86(code, pc, lookup, 64, gnuAsm)
+}
+
+func disasm_x86(code []byte, pc uint64, lookup lookupFunc, arch int, gnuAsm bool) (string, int) {
+	inst, err := x86asm.Decode(code, arch)
+	var text string
+	size := inst.Len
+	if err != nil || size == 0 || inst.Op == 0 {
+		size = 1
+		text = "?"
+	} else {
+		if gnuAsm {
+			text = fmt.Sprintf("%-36s // %s", x86asm.GoSyntax(inst, pc, lookup), x86asm.GNUSyntax(inst, pc, nil))
+		} else {
+			text = x86asm.GoSyntax(inst, pc, lookup)
+		}
+	}
+	return text, size
+}
+
+type textReader struct {
+	code []byte
+	pc   uint64
+}
+
+func (r textReader) ReadAt(data []byte, off int64) (n int, err error) {
+	if off < 0 || uint64(off) < r.pc {
+		return 0, io.EOF
+	}
+	d := uint64(off) - r.pc
+	if d >= uint64(len(r.code)) {
+		return 0, io.EOF
+	}
+	n = copy(data, r.code[d:])
+	if n < len(data) {
+		err = io.ErrUnexpectedEOF
+	}
+	return
+}
+
+func disasm_arm(code []byte, pc uint64, lookup lookupFunc, _ binary.ByteOrder, gnuAsm bool) (string, int) {
+	inst, err := armasm.Decode(code, armasm.ModeARM)
+	var text string
+	size := inst.Len
+	if err != nil || size == 0 || inst.Op == 0 {
+		size = 4
+		text = "?"
+	} else if gnuAsm {
+		text = fmt.Sprintf("%-36s // %s", armasm.GoSyntax(inst, pc, lookup, textReader{code, pc}), armasm.GNUSyntax(inst))
+	} else {
+		text = armasm.GoSyntax(inst, pc, lookup, textReader{code, pc})
+	}
+	return text, size
+}
+
+func disasm_arm64(code []byte, pc uint64, lookup lookupFunc, byteOrder binary.ByteOrder, gnuAsm bool) (string, int) {
+	inst, err := arm64asm.Decode(code)
+	var text string
+	if err != nil || inst.Op == 0 {
+		text = "?"
+	} else if gnuAsm {
+		text = fmt.Sprintf("%-36s // %s", arm64asm.GoSyntax(inst, pc, lookup, textReader{code, pc}), arm64asm.GNUSyntax(inst))
+	} else {
+		text = arm64asm.GoSyntax(inst, pc, lookup, textReader{code, pc})
+	}
+	return text, 4
+}
+
+func disasm_loong64(code []byte, pc uint64, lookup lookupFunc, byteOrder binary.ByteOrder, gnuAsm bool) (string, int) {
+	inst, err := loong64asm.Decode(code)
+	var text string
+	if err != nil || inst.Op == 0 {
+		text = "?"
+	} else if gnuAsm {
+		text = fmt.Sprintf("%-36s // %s", loong64asm.GoSyntax(inst, pc, lookup), loong64asm.GNUSyntax(inst))
+	} else {
+		text = loong64asm.GoSyntax(inst, pc, lookup)
+	}
+	return text, 4
+}
+
+func disasm_ppc64(code []byte, pc uint64, lookup lookupFunc, byteOrder binary.ByteOrder, gnuAsm bool) (string, int) {
+	inst, err := ppc64asm.Decode(code, byteOrder)
+	var text string
+	size := inst.Len
+	if err != nil || size == 0 {
+		size = 4
+		text = "?"
+	} else {
+		if gnuAsm {
+			text = fmt.Sprintf("%-36s // %s", ppc64asm.GoSyntax(inst, pc, lookup), ppc64asm.GNUSyntax(inst, pc))
+		} else {
+			text = ppc64asm.GoSyntax(inst, pc, lookup)
+		}
+	}
+	return text, size
+}
+
+func disasm_riscv64(code []byte, pc uint64, lookup lookupFunc, byteOrder binary.ByteOrder, gnuAsm bool) (string, int) {
+	inst, err := riscv64asm.Decode(code)
+	var text string
+	size := inst.Len
+	if err != nil || inst.Op == 0 {
+		size = 2
+		text = "?"
+	} else if gnuAsm {
+		text = fmt.Sprintf("%-36s // %s", riscv64asm.GoSyntax(inst, pc, lookup, textReader{code, pc}), riscv64asm.GNUSyntax(inst))
+	} else {
+		text = riscv64asm.GoSyntax(inst, pc, lookup, textReader{code, pc})
+	}
+	return text, size
+}
+
+func disasm_s390x(code []byte, pc uint64, lookup lookupFunc, _ binary.ByteOrder, gnuAsm bool) (string, int) {
+	inst, err := s390xasm.Decode(code)
+	var text string
+	size := inst.Len
+	if err != nil || size == 0 || inst.Op == 0 {
+		size = 2
+		text = "?"
+	} else {
+		if gnuAsm {
+			text = fmt.Sprintf("%-36s // %s", s390xasm.GoSyntax(inst, pc, lookup), s390xasm.GNUSyntax(inst, pc))
+		} else {
+			text = s390xasm.GoSyntax(inst, pc, lookup)
+		}
+	}
+	return text, size
+}
+
+var disasms = map[string]disasmFunc{
+	"386":     disasm_386,
+	"amd64":   disasm_amd64,
+	"arm":     disasm_arm,
+	"arm64":   disasm_arm64,
+	"loong64": disasm_loong64,
+	"ppc64":   disasm_ppc64,
+	"ppc64le": disasm_ppc64,
+	"riscv64": disasm_riscv64,
+	"s390x":   disasm_s390x,
+}
+
+var byteOrders = map[string]binary.ByteOrder{
+	"386":     binary.LittleEndian,
+	"amd64":   binary.LittleEndian,
+	"arm":     binary.LittleEndian,
+	"arm64":   binary.LittleEndian,
+	"loong64": binary.LittleEndian,
+	"ppc64":   binary.BigEndian,
+	"ppc64le": binary.LittleEndian,
+	"riscv64": binary.LittleEndian,
+	"s390x":   binary.BigEndian,
+}

go/src/cmd/internal/dwarf/dwarf.go

@@ -0,0 +1,1695 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package dwarf generates DWARF debugging information.
+// DWARF generation is split between the compiler and the linker,
+// this package contains the shared code.
+package dwarf
+
+import (
+	"bytes"
+	"cmd/internal/src"
+	"cmp"
+	"errors"
+	"fmt"
+	"internal/buildcfg"
+	"os/exec"
+	"slices"
+	"strconv"
+	"strings"
+)
+
+// InfoPrefix is the prefix for all the symbols containing DWARF info entries.
+const InfoPrefix = "go:info."
+
+// ConstInfoPrefix is the prefix for all symbols containing DWARF info
+// entries that contain constants.
+const ConstInfoPrefix = "go:constinfo."
+
+// CUInfoPrefix is the prefix for symbols containing information to
+// populate the DWARF compilation unit info entries.
+const CUInfoPrefix = "go:cuinfo."
+
+// Used to form the symbol name assigned to the DWARF "abstract subprogram"
+// info entry for a function
+const AbstractFuncSuffix = "$abstract"
+
+// Controls logging/debugging for selected aspects of DWARF subprogram
+// generation (functions, scopes).
+var logDwarf bool
+
+// Sym represents a symbol.
+type Sym any
+
+// A Var represents a local variable or a function parameter.
+type Var struct {
+	Name          string
+	Tag           int // Either DW_TAG_variable or DW_TAG_formal_parameter
+	WithLoclist   bool
+	IsReturnValue bool
+	IsInlFormal   bool
+	DictIndex     uint16 // index of the dictionary entry describing the type of this variable
+	StackOffset   int32
+	// This package can't use the ssa package, so it can't mention ssa.FuncDebug,
+	// so indirect through a closure.
+	PutLocationList func(listSym, startPC Sym)
+	Scope           int32
+	Type            Sym
+	DeclFile        string
+	DeclLine        uint
+	DeclCol         uint
+	InlIndex        int32 // subtract 1 to form real index into InlTree
+	ChildIndex      int32 // child DIE index in abstract function
+	IsInAbstract    bool  // variable exists in abstract function
+	ClosureOffset   int64 // if non-zero this is the offset of this variable in the closure struct
+}
+
+// A Scope represents a lexical scope. All variables declared within a
+// scope will only be visible to instructions covered by the scope.
+// Lexical scopes are contiguous in source files but can end up being
+// compiled to discontiguous blocks of instructions in the executable.
+// The Ranges field lists all the blocks of instructions that belong
+// in this scope.
+type Scope struct {
+	Parent int32
+	Ranges []Range
+	Vars   []*Var
+}
+
+// A Range represents a half-open interval [Start, End).
+type Range struct {
+	Start, End int64
+}
+
+// This container is used by the PutFunc* variants below when
+// creating the DWARF subprogram DIE(s) for a function.
+type FnState struct {
+	Name          string
+	Info          Sym
+	Loc           Sym
+	Ranges        Sym
+	Absfn         Sym
+	StartPC       Sym
+	StartPos      src.Pos
+	Size          int64
+	External      bool
+	Scopes        []Scope
+	InlCalls      InlCalls
+	UseBASEntries bool
+
+	dictIndexToOffset []int64
+}
+
+func EnableLogging(doit bool) {
+	logDwarf = doit
+}
+
+// MergeRanges creates a new range list by merging the ranges from
+// its two arguments, then returns the new list.
+func MergeRanges(in1, in2 []Range) []Range {
+	out := make([]Range, 0, len(in1)+len(in2))
+	i, j := 0, 0
+	for {
+		var cur Range
+		if i < len(in2) && j < len(in1) {
+			if in2[i].Start < in1[j].Start {
+				cur = in2[i]
+				i++
+			} else {
+				cur = in1[j]
+				j++
+			}
+		} else if i < len(in2) {
+			cur = in2[i]
+			i++
+		} else if j < len(in1) {
+			cur = in1[j]
+			j++
+		} else {
+			break
+		}
+
+		if n := len(out); n > 0 && cur.Start <= out[n-1].End {
+			out[n-1].End = cur.End
+		} else {
+			out = append(out, cur)
+		}
+	}
+
+	return out
+}
+
+// UnifyRanges merges the ranges from 'c' into the list of ranges for 's'.
+func (s *Scope) UnifyRanges(c *Scope) {
+	s.Ranges = MergeRanges(s.Ranges, c.Ranges)
+}
+
+// AppendRange adds r to s, if r is non-empty.
+// If possible, it extends the last Range in s.Ranges; if not, it creates a new one.
+func (s *Scope) AppendRange(r Range) {
+	if r.End <= r.Start {
+		return
+	}
+	i := len(s.Ranges)
+	if i > 0 && s.Ranges[i-1].End == r.Start {
+		s.Ranges[i-1].End = r.End
+		return
+	}
+	s.Ranges = append(s.Ranges, r)
+}
+
+type InlCalls struct {
+	Calls []InlCall
+}
+
+type InlCall struct {
+	// index into ctx.InlTree describing the call inlined here
+	InlIndex int
+
+	// Position of the inlined call site.
+	CallPos src.Pos
+
+	// Dwarf abstract subroutine symbol (really *obj.LSym).
+	AbsFunSym Sym
+
+	// Indices of child inlines within Calls array above.
+	Children []int
+
+	// entries in this list are PAUTO's created by the inliner to
+	// capture the promoted formals and locals of the inlined callee.
+	InlVars []*Var
+
+	// PC ranges for this inlined call.
+	Ranges []Range
+
+	// Root call (not a child of some other call).
+	Root bool
+}
+
+// A Context specifies how to add data to a Sym.
+type Context interface {
+	PtrSize() int
+	Size(s Sym) int64
+	AddInt(s Sym, size int, i int64)
+	AddBytes(s Sym, b []byte)
+	AddAddress(s Sym, t any, ofs int64)
+	AddCURelativeAddress(s Sym, t any, ofs int64)
+	AddSectionOffset(s Sym, size int, t any, ofs int64)
+	AddDWARFAddrSectionOffset(s Sym, t any, ofs int64)
+	AddIndirectTextRef(s Sym, t any)
+	CurrentOffset(s Sym) int64
+	RecordDclReference(from Sym, to Sym, dclIdx int, inlIndex int)
+	RecordChildDieOffsets(s Sym, vars []*Var, offsets []int32)
+	AddString(s Sym, v string)
+	Logf(format string, args ...any)
+}
+
+// AppendUleb128 appends v to b using DWARF's unsigned LEB128 encoding.
+func AppendUleb128(b []byte, v uint64) []byte {
+	for {
+		c := uint8(v & 0x7f)
+		v >>= 7
+		if v != 0 {
+			c |= 0x80
+		}
+		b = append(b, c)
+		if c&0x80 == 0 {
+			break
+		}
+	}
+	return b
+}
+
+// AppendSleb128 appends v to b using DWARF's signed LEB128 encoding.
+func AppendSleb128(b []byte, v int64) []byte {
+	for {
+		c := uint8(v & 0x7f)
+		s := uint8(v & 0x40)
+		v >>= 7
+		if (v != -1 || s == 0) && (v != 0 || s != 0) {
+			c |= 0x80
+		}
+		b = append(b, c)
+		if c&0x80 == 0 {
+			break
+		}
+	}
+	return b
+}
+
+// sevenbits contains all unsigned seven bit numbers, indexed by their value.
+var sevenbits = [...]byte{
+	0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
+	0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
+	0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
+	0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
+	0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
+	0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f,
+	0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
+	0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f,
+}
+
+// sevenBitU returns the unsigned LEB128 encoding of v if v is seven bits and nil otherwise.
+// The contents of the returned slice must not be modified.
+func sevenBitU(v int64) []byte {
+	if uint64(v) < uint64(len(sevenbits)) {
+		return sevenbits[v : v+1]
+	}
+	return nil
+}
+
+// sevenBitS returns the signed LEB128 encoding of v if v is seven bits and nil otherwise.
+// The contents of the returned slice must not be modified.
+func sevenBitS(v int64) []byte {
+	if uint64(v) <= 63 {
+		return sevenbits[v : v+1]
+	}
+	if uint64(-v) <= 64 {
+		return sevenbits[128+v : 128+v+1]
+	}
+	return nil
+}
+
+// Uleb128put appends v to s using DWARF's unsigned LEB128 encoding.
+func Uleb128put(ctxt Context, s Sym, v int64) {
+	b := sevenBitU(v)
+	if b == nil {
+		var encbuf [20]byte
+		b = AppendUleb128(encbuf[:0], uint64(v))
+	}
+	ctxt.AddBytes(s, b)
+}
+
+// Sleb128put appends v to s using DWARF's signed LEB128 encoding.
+func Sleb128put(ctxt Context, s Sym, v int64) {
+	b := sevenBitS(v)
+	if b == nil {
+		var encbuf [20]byte
+		b = AppendSleb128(encbuf[:0], v)
+	}
+	ctxt.AddBytes(s, b)
+}
+
+/*
+ * Defining Abbrevs. This is hardcoded on a per-platform basis (that is,
+ * each platform will see a fixed abbrev table for all objects); the number
+ * of abbrev entries is fairly small (compared to C++ objects).  The DWARF
+ * spec places no restriction on the ordering of attributes in the
+ * Abbrevs and DIEs, and we will always write them out in the order
+ * of declaration in the abbrev.
+ */
+type dwAttrForm struct {
+	attr uint16
+	form uint8
+}
+
+// Go-specific type attributes.
+const (
+	DW_AT_go_kind = 0x2900
+	DW_AT_go_key  = 0x2901
+	DW_AT_go_elem = 0x2902
+	// Attribute for DW_TAG_member of a struct type.
+	// Nonzero value indicates the struct field is an embedded field.
+	DW_AT_go_embedded_field = 0x2903
+	DW_AT_go_runtime_type   = 0x2904
+
+	DW_AT_go_package_name   = 0x2905 // Attribute for DW_TAG_compile_unit
+	DW_AT_go_dict_index     = 0x2906 // Attribute for DW_TAG_typedef_type, index of the dictionary entry describing the real type of this type shape
+	DW_AT_go_closure_offset = 0x2907 // Attribute for DW_TAG_variable, offset in the closure struct where this captured variable resides
+
+	DW_AT_internal_location = 253 // params and locals; not emitted
+)
+
+// Index into the abbrevs table below.
+const (
+	DW_ABRV_NULL = iota
+	DW_ABRV_COMPUNIT
+	DW_ABRV_COMPUNIT_TEXTLESS
+	DW_ABRV_FUNCTION
+	DW_ABRV_WRAPPER
+	DW_ABRV_FUNCTION_ABSTRACT
+	DW_ABRV_FUNCTION_CONCRETE
+	DW_ABRV_WRAPPER_CONCRETE
+	DW_ABRV_INLINED_SUBROUTINE
+	DW_ABRV_INLINED_SUBROUTINE_RANGES
+	DW_ABRV_VARIABLE
+	DW_ABRV_INT_CONSTANT
+	DW_ABRV_LEXICAL_BLOCK_RANGES
+	DW_ABRV_LEXICAL_BLOCK_SIMPLE
+	DW_ABRV_STRUCTFIELD
+	DW_ABRV_FUNCTYPEPARAM
+	DW_ABRV_FUNCTYPEOUTPARAM
+	DW_ABRV_DOTDOTDOT
+	DW_ABRV_ARRAYRANGE
+	DW_ABRV_NULLTYPE
+	DW_ABRV_BASETYPE
+	DW_ABRV_ARRAYTYPE
+	DW_ABRV_CHANTYPE
+	DW_ABRV_FUNCTYPE
+	DW_ABRV_IFACETYPE
+	DW_ABRV_MAPTYPE
+	DW_ABRV_PTRTYPE
+	DW_ABRV_BARE_PTRTYPE // only for void*, no DW_AT_type attr to please gdb 6.
+	DW_ABRV_SLICETYPE
+	DW_ABRV_STRINGTYPE
+	DW_ABRV_STRUCTTYPE
+	DW_ABRV_TYPEDECL
+	DW_ABRV_DICT_INDEX
+	DW_ABRV_PUTVAR_START
+)
+
+type dwAbbrev struct {
+	tag      uint8
+	children uint8
+	attr     []dwAttrForm
+}
+
+var abbrevsFinalized bool
+
+// expandPseudoForm takes an input DW_FORM_xxx value and translates it
+// into a version- and platform-appropriate concrete form. Existing
+// concrete/real DW_FORM values are left untouched. For the moment the
+// only platform-specific pseudo-form is DW_FORM_udata_pseudo, which
+// gets expanded to DW_FORM_data4 on Darwin and DW_FORM_udata
+// everywhere else. See issue #31459 for more context. Then we have a
+// pair of pseudo-forms for lo and hi PC attributes, which are
+// expanded differently depending on whether we're generating DWARF
+// version 4 or 5.
+func expandPseudoForm(form uint8) uint8 {
+	switch form {
+	case DW_FORM_udata_pseudo:
+		expandedForm := DW_FORM_udata
+		if buildcfg.GOOS == "darwin" || buildcfg.GOOS == "ios" {
+			expandedForm = DW_FORM_data4
+		}
+		return uint8(expandedForm)
+	case DW_FORM_lo_pc_pseudo:
+		if buildcfg.Experiment.Dwarf5 {
+			return DW_FORM_addrx
+		}
+		return DW_FORM_addr
+	case DW_FORM_hi_pc_pseudo:
+		if buildcfg.Experiment.Dwarf5 {
+			return DW_FORM_udata
+		}
+		return DW_FORM_addr
+	default:
+		return form
+	}
+}
+
+// Abbrevs returns the finalized abbrev array for the platform,
+// expanding any DW_FORM pseudo-ops to real values.
+func Abbrevs() []dwAbbrev {
+	if abbrevsFinalized {
+		return abbrevs
+	}
+	abbrevs = append(abbrevs, putvarAbbrevs...)
+	for i := 1; i < len(abbrevs); i++ {
+		for j := 0; j < len(abbrevs[i].attr); j++ {
+			abbrevs[i].attr[j].form = expandPseudoForm(abbrevs[i].attr[j].form)
+		}
+	}
+	if buildcfg.Experiment.Dwarf5 {
+		// Tack on a new DW_AT_addr_base attribute to the compunit DIE,
+		// which will point to the offset in the .debug_addr section
+		// containing entries for this comp unit (this attr gets
+		// fixed up in the linker).
+		for i := 1; i < len(abbrevs); i++ {
+			haveLo := false
+			for j := 0; j < len(abbrevs[i].attr); j++ {
+				if abbrevs[i].attr[j].attr == DW_AT_low_pc {
+					haveLo = true
+				}
+			}
+			if abbrevs[i].tag == DW_TAG_compile_unit && haveLo {
+				abbrevs[i].attr = append(abbrevs[i].attr,
+					dwAttrForm{DW_AT_addr_base, DW_FORM_sec_offset})
+			}
+		}
+	}
+
+	abbrevsFinalized = true
+	return abbrevs
+}
+
+// abbrevs is a raw table of abbrev entries; it needs to be post-processed
+// by the Abbrevs() function above prior to being consumed, to expand
+// the 'pseudo-form' entries below to real DWARF form values.
+
+var abbrevs = []dwAbbrev{
+	/* The mandatory DW_ABRV_NULL entry. */
+	{0, 0, []dwAttrForm{}},
+
+	/* COMPUNIT */
+	{
+		DW_TAG_compile_unit,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_language, DW_FORM_data1},
+			{DW_AT_stmt_list, DW_FORM_sec_offset},
+			{DW_AT_low_pc, DW_FORM_addr},
+			{DW_AT_ranges, DW_FORM_sec_offset},
+			{DW_AT_comp_dir, DW_FORM_string},
+			{DW_AT_producer, DW_FORM_string},
+			{DW_AT_go_package_name, DW_FORM_string},
+			// NB: DWARF5 adds DW_AT_addr_base here.
+		},
+	},
+
+	/* COMPUNIT_TEXTLESS */
+	{
+		DW_TAG_compile_unit,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_language, DW_FORM_data1},
+			{DW_AT_comp_dir, DW_FORM_string},
+			{DW_AT_producer, DW_FORM_string},
+			{DW_AT_go_package_name, DW_FORM_string},
+		},
+	},
+
+	/* FUNCTION */
+	{
+		DW_TAG_subprogram,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_low_pc, DW_FORM_lo_pc_pseudo},
+			{DW_AT_high_pc, DW_FORM_hi_pc_pseudo},
+			{DW_AT_frame_base, DW_FORM_block1},
+			{DW_AT_decl_file, DW_FORM_data4},
+			{DW_AT_decl_line, DW_FORM_udata},
+			{DW_AT_external, DW_FORM_flag},
+		},
+	},
+
+	/* WRAPPER */
+	{
+		DW_TAG_subprogram,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_low_pc, DW_FORM_lo_pc_pseudo},
+			{DW_AT_high_pc, DW_FORM_hi_pc_pseudo},
+			{DW_AT_frame_base, DW_FORM_block1},
+			{DW_AT_trampoline, DW_FORM_flag},
+		},
+	},
+
+	/* FUNCTION_ABSTRACT */
+	{
+		DW_TAG_subprogram,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_inline, DW_FORM_data1},
+			{DW_AT_decl_line, DW_FORM_udata},
+			{DW_AT_external, DW_FORM_flag},
+		},
+	},
+
+	/* FUNCTION_CONCRETE */
+	{
+		DW_TAG_subprogram,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_abstract_origin, DW_FORM_ref_addr},
+			{DW_AT_low_pc, DW_FORM_lo_pc_pseudo},
+			{DW_AT_high_pc, DW_FORM_hi_pc_pseudo},
+			{DW_AT_frame_base, DW_FORM_block1},
+		},
+	},
+
+	/* WRAPPER_CONCRETE */
+	{
+		DW_TAG_subprogram,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_abstract_origin, DW_FORM_ref_addr},
+			{DW_AT_low_pc, DW_FORM_lo_pc_pseudo},
+			{DW_AT_high_pc, DW_FORM_hi_pc_pseudo},
+			{DW_AT_frame_base, DW_FORM_block1},
+			{DW_AT_trampoline, DW_FORM_flag},
+		},
+	},
+
+	/* INLINED_SUBROUTINE */
+	{
+		DW_TAG_inlined_subroutine,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_abstract_origin, DW_FORM_ref_addr},
+			{DW_AT_low_pc, DW_FORM_lo_pc_pseudo},
+			{DW_AT_high_pc, DW_FORM_hi_pc_pseudo},
+			{DW_AT_call_file, DW_FORM_data4},
+			{DW_AT_call_line, DW_FORM_udata_pseudo}, // pseudo-form
+		},
+	},
+
+	/* INLINED_SUBROUTINE_RANGES */
+	{
+		DW_TAG_inlined_subroutine,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_abstract_origin, DW_FORM_ref_addr},
+			{DW_AT_ranges, DW_FORM_sec_offset},
+			{DW_AT_call_file, DW_FORM_data4},
+			{DW_AT_call_line, DW_FORM_udata_pseudo}, // pseudo-form
+		},
+	},
+
+	/* VARIABLE */
+	{
+		DW_TAG_variable,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_location, DW_FORM_block1},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_external, DW_FORM_flag},
+		},
+	},
+
+	/* INT CONSTANT */
+	{
+		DW_TAG_constant,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_const_value, DW_FORM_sdata},
+		},
+	},
+
+	/* LEXICAL_BLOCK_RANGES */
+	{
+		DW_TAG_lexical_block,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_ranges, DW_FORM_sec_offset},
+		},
+	},
+
+	/* LEXICAL_BLOCK_SIMPLE */
+	{
+		DW_TAG_lexical_block,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			// Note: unused if we are generating DWARF 5, we
+			// use the ranges form even if there is a singleton range.
+			{DW_AT_low_pc, DW_FORM_addr},
+			{DW_AT_high_pc, DW_FORM_addr},
+		},
+	},
+
+	/* STRUCTFIELD */
+	{
+		DW_TAG_member,
+		DW_CHILDREN_no,
+		// This abbrev is special-cased by the linker (unlike other DIEs
+		// we don't want a loader.Sym created for this DIE).
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_data_member_location, DW_FORM_udata},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_go_embedded_field, DW_FORM_flag},
+		},
+	},
+
+	/* FUNCTYPEPARAM */
+	{
+		DW_TAG_formal_parameter,
+		DW_CHILDREN_no,
+
+		// No name!
+		// This abbrev is special-cased by the linker (unlike other DIEs
+		// we don't want a loader.Sym created for this DIE).
+		[]dwAttrForm{
+			{DW_AT_type, DW_FORM_ref_addr},
+		},
+	},
+
+	/* FUNCTYPEOUTPARAM */
+	{
+		DW_TAG_formal_parameter,
+		DW_CHILDREN_no,
+
+		// No name!
+		// This abbrev is special-cased by the linker (unlike other DIEs
+		// we don't want a loader.Sym created for this DIE).
+		[]dwAttrForm{
+			{DW_AT_variable_parameter, DW_FORM_flag},
+			{DW_AT_type, DW_FORM_ref_addr},
+		},
+	},
+
+	/* DOTDOTDOT */
+	{
+		DW_TAG_unspecified_parameters,
+		DW_CHILDREN_no,
+		// No name.
+		// This abbrev is special-cased by the linker (unlike other DIEs
+		// we don't want a loader.Sym created for this DIE).
+		[]dwAttrForm{},
+	},
+
+	/* ARRAYRANGE */
+	{
+		DW_TAG_subrange_type,
+		DW_CHILDREN_no,
+
+		// No name!
+		// This abbrev is special-cased by the linker (unlike other DIEs
+		// we don't want a loader.Sym created for this DIE).
+		[]dwAttrForm{
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_count, DW_FORM_udata},
+		},
+	},
+
+	// Below here are the types considered public by ispubtype
+	/* NULLTYPE */
+	{
+		DW_TAG_unspecified_type,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+		},
+	},
+
+	/* BASETYPE */
+	{
+		DW_TAG_base_type,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_encoding, DW_FORM_data1},
+			{DW_AT_byte_size, DW_FORM_data1},
+			{DW_AT_go_kind, DW_FORM_data1},
+			{DW_AT_go_runtime_type, DW_FORM_addr},
+		},
+	},
+
+	/* ARRAYTYPE */
+	// child is subrange with upper bound
+	{
+		DW_TAG_array_type,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_byte_size, DW_FORM_udata},
+			{DW_AT_go_kind, DW_FORM_data1},
+			{DW_AT_go_runtime_type, DW_FORM_addr},
+		},
+	},
+
+	/* CHANTYPE */
+	{
+		DW_TAG_typedef,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_go_kind, DW_FORM_data1},
+			{DW_AT_go_runtime_type, DW_FORM_addr},
+			{DW_AT_go_elem, DW_FORM_ref_addr},
+		},
+	},
+
+	/* FUNCTYPE */
+	{
+		DW_TAG_subroutine_type,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_byte_size, DW_FORM_udata},
+			{DW_AT_go_kind, DW_FORM_data1},
+			{DW_AT_go_runtime_type, DW_FORM_addr},
+		},
+	},
+
+	/* IFACETYPE */
+	{
+		DW_TAG_typedef,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_go_kind, DW_FORM_data1},
+			{DW_AT_go_runtime_type, DW_FORM_addr},
+		},
+	},
+
+	/* MAPTYPE */
+	{
+		DW_TAG_typedef,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_go_kind, DW_FORM_data1},
+			{DW_AT_go_runtime_type, DW_FORM_addr},
+			{DW_AT_go_key, DW_FORM_ref_addr},
+			{DW_AT_go_elem, DW_FORM_ref_addr},
+		},
+	},
+
+	/* PTRTYPE */
+	{
+		DW_TAG_pointer_type,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_go_kind, DW_FORM_data1},
+			{DW_AT_go_runtime_type, DW_FORM_addr},
+		},
+	},
+
+	/* BARE_PTRTYPE */
+	{
+		DW_TAG_pointer_type,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_go_runtime_type, DW_FORM_addr},
+		},
+	},
+
+	/* SLICETYPE */
+	{
+		DW_TAG_structure_type,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_byte_size, DW_FORM_udata},
+			{DW_AT_go_kind, DW_FORM_data1},
+			{DW_AT_go_runtime_type, DW_FORM_addr},
+			{DW_AT_go_elem, DW_FORM_ref_addr},
+		},
+	},
+
+	/* STRINGTYPE */
+	{
+		DW_TAG_structure_type,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_byte_size, DW_FORM_udata},
+			{DW_AT_go_kind, DW_FORM_data1},
+			{DW_AT_go_runtime_type, DW_FORM_addr},
+		},
+	},
+
+	/* STRUCTTYPE */
+	{
+		DW_TAG_structure_type,
+		DW_CHILDREN_yes,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_byte_size, DW_FORM_udata},
+			{DW_AT_go_kind, DW_FORM_data1},
+			{DW_AT_go_runtime_type, DW_FORM_addr},
+		},
+	},
+
+	/* TYPEDECL */
+	{
+		DW_TAG_typedef,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_type, DW_FORM_ref_addr},
+		},
+	},
+
+	/* DICT_INDEX */
+	{
+		DW_TAG_typedef,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_go_dict_index, DW_FORM_udata},
+		},
+	},
+}
+
+// GetAbbrev returns the contents of the .debug_abbrev section.
+func GetAbbrev() []byte {
+	abbrevs := Abbrevs()
+	var buf []byte
+	for i := 1; i < len(abbrevs); i++ {
+		// See section 7.5.3
+		buf = AppendUleb128(buf, uint64(i))
+		buf = AppendUleb128(buf, uint64(abbrevs[i].tag))
+		buf = append(buf, abbrevs[i].children)
+		for _, f := range abbrevs[i].attr {
+			buf = AppendUleb128(buf, uint64(f.attr))
+			buf = AppendUleb128(buf, uint64(f.form))
+		}
+		buf = append(buf, 0, 0)
+	}
+	return append(buf, 0)
+}
+
+/*
+ * Debugging Information Entries and their attributes.
+ */
+
+// DWAttr represents an attribute of a DWDie.
+//
+// For DW_CLS_string and _block, value should contain the length, and
+// data the data, for _reference, value is 0 and data is a DWDie* to
+// the referenced instance, for all others, value is the whole thing
+// and data is null.
+type DWAttr struct {
+	Link  *DWAttr
+	Atr   uint16 // DW_AT_
+	Cls   uint8  // DW_CLS_
+	Value int64
+	Data  any
+}
+
+// DWDie represents a DWARF debug info entry.
+type DWDie struct {
+	Abbrev int
+	Link   *DWDie
+	Child  *DWDie
+	Attr   *DWAttr
+	Sym    Sym
+}
+
+func putattr(ctxt Context, s Sym, abbrev int, form int, cls int, value int64, data any) error {
+	switch form {
+	case DW_FORM_addr: // address
+		// Allow nil addresses for DW_AT_go_runtime_type.
+		if data == nil && value == 0 {
+			ctxt.AddInt(s, ctxt.PtrSize(), 0)
+			break
+		}
+		if cls == DW_CLS_GO_TYPEREF {
+			ctxt.AddSectionOffset(s, ctxt.PtrSize(), data, value)
+			break
+		}
+		ctxt.AddAddress(s, data, value)
+
+	case DW_FORM_block1: // block
+		if cls == DW_CLS_ADDRESS {
+			ctxt.AddInt(s, 1, int64(1+ctxt.PtrSize()))
+			ctxt.AddInt(s, 1, DW_OP_addr)
+			ctxt.AddAddress(s, data, 0)
+			break
+		}
+
+		value &= 0xff
+		ctxt.AddInt(s, 1, value)
+		p := data.([]byte)[:value]
+		ctxt.AddBytes(s, p)
+
+	case DW_FORM_block2: // block
+		value &= 0xffff
+
+		ctxt.AddInt(s, 2, value)
+		p := data.([]byte)[:value]
+		ctxt.AddBytes(s, p)
+
+	case DW_FORM_block4: // block
+		value &= 0xffffffff
+
+		ctxt.AddInt(s, 4, value)
+		p := data.([]byte)[:value]
+		ctxt.AddBytes(s, p)
+
+	case DW_FORM_block: // block
+		Uleb128put(ctxt, s, value)
+
+		p := data.([]byte)[:value]
+		ctxt.AddBytes(s, p)
+
+	case DW_FORM_data1: // constant
+		ctxt.AddInt(s, 1, value)
+
+	case DW_FORM_data2: // constant
+		ctxt.AddInt(s, 2, value)
+
+	case DW_FORM_data4: // constant, {line,loclist,mac,rangelist}ptr
+		if cls == DW_CLS_PTR { // DW_AT_stmt_list and DW_AT_ranges
+			ctxt.AddDWARFAddrSectionOffset(s, data, value)
+			break
+		}
+		ctxt.AddInt(s, 4, value)
+
+	case DW_FORM_data8: // constant, {line,loclist,mac,rangelist}ptr
+		ctxt.AddInt(s, 8, value)
+
+	case DW_FORM_sdata: // constant
+		Sleb128put(ctxt, s, value)
+
+	case DW_FORM_udata: // constant
+		Uleb128put(ctxt, s, value)
+
+	case DW_FORM_string: // string
+		str := data.(string)
+		ctxt.AddString(s, str)
+		// TODO(ribrdb): verify padded strings are never used and remove this
+		for i := int64(len(str)); i < value; i++ {
+			ctxt.AddInt(s, 1, 0)
+		}
+
+	case DW_FORM_flag: // flag
+		if value != 0 {
+			ctxt.AddInt(s, 1, 1)
+		} else {
+			ctxt.AddInt(s, 1, 0)
+		}
+
+	// As of DWARF 3 the ref_addr is always 32 bits, unless emitting a large
+	// (> 4 GB of debug info aka "64-bit") unit, which we don't implement.
+	case DW_FORM_ref_addr: // reference to a DIE in the .info section
+		fallthrough
+	case DW_FORM_sec_offset: // offset into a DWARF section other than .info
+		if data == nil {
+			return fmt.Errorf("dwarf: null reference in %d", abbrev)
+		}
+		ctxt.AddDWARFAddrSectionOffset(s, data, value)
+
+	case DW_FORM_addrx: // index into .debug_addr section
+		ctxt.AddIndirectTextRef(s, data)
+
+	case DW_FORM_ref1, // reference within the compilation unit
+		DW_FORM_ref2,      // reference
+		DW_FORM_ref4,      // reference
+		DW_FORM_ref8,      // reference
+		DW_FORM_ref_udata, // reference
+
+		DW_FORM_strp,     // string
+		DW_FORM_indirect: // (see Section 7.5.3)
+		fallthrough
+	default:
+		return fmt.Errorf("dwarf: unsupported attribute form %d / class %d", form, cls)
+	}
+	return nil
+}
+
+// PutAttrs writes the attributes for a DIE to symbol 's'.
+//
+// Note that we can (and do) add arbitrary attributes to a DIE, but
+// only the ones actually listed in the Abbrev will be written out.
+func PutAttrs(ctxt Context, s Sym, abbrev int, attr *DWAttr) {
+	abbrevs := Abbrevs()
+Outer:
+	for _, f := range abbrevs[abbrev].attr {
+		for ap := attr; ap != nil; ap = ap.Link {
+			if ap.Atr == f.attr {
+				putattr(ctxt, s, abbrev, int(f.form), int(ap.Cls), ap.Value, ap.Data)
+				continue Outer
+			}
+		}
+
+		putattr(ctxt, s, abbrev, int(f.form), 0, 0, nil)
+	}
+}
+
+// HasChildren reports whether 'die' uses an abbrev that supports children.
+func HasChildren(die *DWDie) bool {
+	abbrevs := Abbrevs()
+	return abbrevs[die.Abbrev].children != 0
+}
+
+// PutIntConst writes a DIE for an integer constant
+func PutIntConst(ctxt Context, info, typ Sym, name string, val int64) {
+	Uleb128put(ctxt, info, DW_ABRV_INT_CONSTANT)
+	putattr(ctxt, info, DW_ABRV_INT_CONSTANT, DW_FORM_string, DW_CLS_STRING, int64(len(name)), name)
+	putattr(ctxt, info, DW_ABRV_INT_CONSTANT, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, typ)
+	putattr(ctxt, info, DW_ABRV_INT_CONSTANT, DW_FORM_sdata, DW_CLS_CONSTANT, val, nil)
+}
+
+// PutGlobal writes a DIE for a global variable.
+func PutGlobal(ctxt Context, info, typ, gvar Sym, name string) {
+	Uleb128put(ctxt, info, DW_ABRV_VARIABLE)
+	putattr(ctxt, info, DW_ABRV_VARIABLE, DW_FORM_string, DW_CLS_STRING, int64(len(name)), name)
+	putattr(ctxt, info, DW_ABRV_VARIABLE, DW_FORM_block1, DW_CLS_ADDRESS, 0, gvar)
+	putattr(ctxt, info, DW_ABRV_VARIABLE, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, typ)
+	putattr(ctxt, info, DW_ABRV_VARIABLE, DW_FORM_flag, DW_CLS_FLAG, 1, nil)
+}
+
+// PutBasedRanges writes a range table to sym. All addresses in ranges are
+// relative to some base address, which must be arranged by the caller
+// (e.g., with a DW_AT_low_pc attribute, or in a BASE-prefixed range).
+func PutBasedRanges(ctxt Context, sym Sym, ranges []Range) {
+	ps := ctxt.PtrSize()
+	// Write ranges.
+	for _, r := range ranges {
+		ctxt.AddInt(sym, ps, r.Start)
+		ctxt.AddInt(sym, ps, r.End)
+	}
+	// Write trailer.
+	ctxt.AddInt(sym, ps, 0)
+	ctxt.AddInt(sym, ps, 0)
+}
+
+// PutRngListRanges writes a DWARF5-style set of rangelist entries to sym,
+// using base as a starting/base address.
+func PutRngListRanges(ctxt Context, sym Sym, base Sym, ranges []Range) {
+	addULEB128 := func(v int64) {
+		b := sevenBitU(v)
+		if b == nil {
+			var encbuf [20]byte
+			b = AppendUleb128(encbuf[:0], uint64(v))
+		}
+		ctxt.AddBytes(sym, b)
+	}
+	// First entry is base address.
+	ctxt.AddInt(sym, 1, DW_RLE_base_addressx)
+	ctxt.AddIndirectTextRef(sym, base)
+	// Remaining entries are .debug_rnglist offset pairs
+	for _, r := range ranges {
+		ctxt.AddInt(sym, 1, DW_RLE_offset_pair)
+		addULEB128(r.Start)
+		addULEB128(r.End)
+	}
+	// Terminator to mark end of list
+	ctxt.AddInt(sym, 1, DW_RLE_end_of_list)
+}
+
+// PutRanges writes a range table to s.Ranges.
+// All addresses in ranges are relative to s.base.
+func (s *FnState) PutRanges(ctxt Context, ranges []Range) {
+	ps := ctxt.PtrSize()
+	sym, base := s.Ranges, s.StartPC
+
+	if buildcfg.Experiment.Dwarf5 {
+		PutRngListRanges(ctxt, sym, base, ranges)
+		return
+	}
+
+	if s.UseBASEntries {
+		// Using a Base Address Selection Entry reduces the number of relocations, but
+		// this is not done on macOS because it is not supported by dsymutil/dwarfdump/lldb
+		ctxt.AddInt(sym, ps, -1)
+		ctxt.AddAddress(sym, base, 0)
+		PutBasedRanges(ctxt, sym, ranges)
+		return
+	}
+
+	// Write ranges full of relocations
+	for _, r := range ranges {
+		ctxt.AddCURelativeAddress(sym, base, r.Start)
+		ctxt.AddCURelativeAddress(sym, base, r.End)
+	}
+	// Write trailer.
+	ctxt.AddInt(sym, ps, 0)
+	ctxt.AddInt(sym, ps, 0)
+}
+
+// Return TRUE if the inlined call in the specified slot is empty,
+// meaning it has a zero-length range (no instructions), and all
+// of its children are empty.
+func isEmptyInlinedCall(slot int, calls *InlCalls) bool {
+	ic := &calls.Calls[slot]
+	if ic.InlIndex == -2 {
+		return true
+	}
+	live := false
+	for _, k := range ic.Children {
+		if !isEmptyInlinedCall(k, calls) {
+			live = true
+		}
+	}
+	if len(ic.Ranges) > 0 {
+		live = true
+	}
+	if !live {
+		ic.InlIndex = -2
+	}
+	return !live
+}
+
+// Slot -1:    return top-level inlines.
+// Slot >= 0:  return children of that slot.
+func inlChildren(slot int, calls *InlCalls) []int {
+	var kids []int
+	if slot != -1 {
+		for _, k := range calls.Calls[slot].Children {
+			if !isEmptyInlinedCall(k, calls) {
+				kids = append(kids, k)
+			}
+		}
+	} else {
+		for k := 0; k < len(calls.Calls); k += 1 {
+			if calls.Calls[k].Root && !isEmptyInlinedCall(k, calls) {
+				kids = append(kids, k)
+			}
+		}
+	}
+	return kids
+}
+
+func inlinedVarTable(inlcalls *InlCalls) map[*Var]bool {
+	vars := make(map[*Var]bool)
+	for _, ic := range inlcalls.Calls {
+		for _, v := range ic.InlVars {
+			vars[v] = true
+		}
+	}
+	return vars
+}
+
+// The s.Scopes slice contains variables were originally part of the
+// function being emitted, as well as variables that were imported
+// from various callee functions during the inlining process. This
+// function prunes out any variables from the latter category (since
+// they will be emitted as part of DWARF inlined_subroutine DIEs) and
+// then generates scopes for vars in the former category.
+func putPrunedScopes(ctxt Context, s *FnState, fnabbrev int) error {
+	if len(s.Scopes) == 0 {
+		return nil
+	}
+	scopes := make([]Scope, len(s.Scopes), len(s.Scopes))
+	pvars := inlinedVarTable(&s.InlCalls)
+	for k, s := range s.Scopes {
+		var pruned Scope = Scope{Parent: s.Parent, Ranges: s.Ranges}
+		for i := 0; i < len(s.Vars); i++ {
+			_, found := pvars[s.Vars[i]]
+			if !found {
+				pruned.Vars = append(pruned.Vars, s.Vars[i])
+			}
+		}
+		slices.SortFunc(pruned.Vars, byChildIndexCmp)
+		scopes[k] = pruned
+	}
+
+	s.dictIndexToOffset = putparamtypes(ctxt, s, scopes, fnabbrev)
+
+	var encbuf [20]byte
+	if putscope(ctxt, s, scopes, 0, fnabbrev, encbuf[:0]) < int32(len(scopes)) {
+		return errors.New("multiple toplevel scopes")
+	}
+	return nil
+}
+
+// Emit DWARF attributes and child DIEs for an 'abstract' subprogram.
+// The abstract subprogram DIE for a function contains its
+// location-independent attributes (name, type, etc). Other instances
+// of the function (any inlined copy of it, or the single out-of-line
+// 'concrete' instance) will contain a pointer back to this abstract
+// DIE (as a space-saving measure, so that name/type etc doesn't have
+// to be repeated for each inlined copy).
+func PutAbstractFunc(ctxt Context, s *FnState) error {
+	if logDwarf {
+		ctxt.Logf("PutAbstractFunc(%v)\n", s.Absfn)
+	}
+
+	abbrev := DW_ABRV_FUNCTION_ABSTRACT
+	Uleb128put(ctxt, s.Absfn, int64(abbrev))
+
+	fullname := s.Name
+	if strings.HasPrefix(s.Name, `"".`) {
+		return fmt.Errorf("unqualified symbol name: %v", s.Name)
+	}
+	putattr(ctxt, s.Absfn, abbrev, DW_FORM_string, DW_CLS_STRING, int64(len(fullname)), fullname)
+
+	// DW_AT_inlined value
+	putattr(ctxt, s.Absfn, abbrev, DW_FORM_data1, DW_CLS_CONSTANT, int64(DW_INL_inlined), nil)
+
+	// TODO(mdempsky): Shouldn't we write out StartPos.FileIndex() too?
+	putattr(ctxt, s.Absfn, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(s.StartPos.RelLine()), nil)
+
+	var ev int64
+	if s.External {
+		ev = 1
+	}
+	putattr(ctxt, s.Absfn, abbrev, DW_FORM_flag, DW_CLS_FLAG, ev, 0)
+
+	// Child variables (may be empty)
+	var flattened []*Var
+
+	// This slice will hold the offset in bytes for each child var DIE
+	// with respect to the start of the parent subprogram DIE.
+	var offsets []int32
+
+	// Scopes/vars
+	if len(s.Scopes) > 0 {
+		// For abstract subprogram DIEs we want to flatten out scope info:
+		// lexical scope DIEs contain range and/or hi/lo PC attributes,
+		// which we explicitly don't want for the abstract subprogram DIE.
+		pvars := inlinedVarTable(&s.InlCalls)
+		for _, scope := range s.Scopes {
+			for i := 0; i < len(scope.Vars); i++ {
+				_, found := pvars[scope.Vars[i]]
+				if found || !scope.Vars[i].IsInAbstract {
+					continue
+				}
+				flattened = append(flattened, scope.Vars[i])
+			}
+		}
+		if len(flattened) > 0 {
+			slices.SortFunc(flattened, byChildIndexCmp)
+
+			if logDwarf {
+				ctxt.Logf("putAbstractScope(%v): vars:", s.Info)
+				for i, v := range flattened {
+					ctxt.Logf(" %d:%s", i, v.Name)
+				}
+				ctxt.Logf("\n")
+			}
+
+			// This slice will hold the offset in bytes for each child
+			// variable DIE with respect to the start of the parent
+			// subprogram DIE.
+			for _, v := range flattened {
+				offsets = append(offsets, int32(ctxt.CurrentOffset(s.Absfn)))
+				putAbstractVar(ctxt, s.Absfn, v)
+			}
+		}
+	}
+	ctxt.RecordChildDieOffsets(s.Absfn, flattened, offsets)
+
+	Uleb128put(ctxt, s.Absfn, 0)
+	return nil
+}
+
+// dwarfFileIndex returns the DWARF file index value for the file associated
+// with pos.
+func dwarfFileIndex(pos src.Pos) int64 {
+	return int64(1 + pos.FileIndex())
+}
+
+// Emit DWARF attributes and child DIEs for an inlined subroutine. The
+// first attribute of an inlined subroutine DIE is a reference back to
+// its corresponding 'abstract' DIE (containing location-independent
+// attributes such as name, type, etc). Inlined subroutine DIEs can
+// have other inlined subroutine DIEs as children.
+func putInlinedFunc(ctxt Context, s *FnState, callIdx int) error {
+	ic := s.InlCalls.Calls[callIdx]
+	callee := ic.AbsFunSym
+
+	// For DWARF 5, we always use the ranges form of the abbrev, since
+	// it is more compact than using explicit hi/lo PC attrs.  See
+	// issue #72821 for more on why this makes sense.
+	abbrev := DW_ABRV_INLINED_SUBROUTINE_RANGES
+	if len(ic.Ranges) == 1 && !buildcfg.Experiment.Dwarf5 {
+		abbrev = DW_ABRV_INLINED_SUBROUTINE
+	}
+	Uleb128put(ctxt, s.Info, int64(abbrev))
+
+	if logDwarf {
+		ctxt.Logf("putInlinedFunc(callee=%v,abbrev=%d)\n", callee, abbrev)
+	}
+
+	// Abstract origin.
+	putattr(ctxt, s.Info, abbrev, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, callee)
+
+	if abbrev == DW_ABRV_INLINED_SUBROUTINE_RANGES {
+		putattr(ctxt, s.Info, abbrev, DW_FORM_sec_offset, DW_CLS_PTR, ctxt.Size(s.Ranges), s.Ranges)
+		s.PutRanges(ctxt, ic.Ranges)
+	} else {
+		st := ic.Ranges[0].Start
+		en := ic.Ranges[0].End
+		emitHiLoPc(ctxt, abbrev, s, st, en)
+	}
+
+	// Emit call file, line attrs.
+	putattr(ctxt, s.Info, abbrev, DW_FORM_data4, DW_CLS_CONSTANT, dwarfFileIndex(ic.CallPos), nil)
+	form := int(expandPseudoForm(DW_FORM_udata_pseudo))
+	putattr(ctxt, s.Info, abbrev, form, DW_CLS_CONSTANT, int64(ic.CallPos.RelLine()), nil)
+
+	// Variables associated with this inlined routine instance.
+	vars := ic.InlVars
+	slices.SortFunc(vars, byChildIndexCmp)
+	inlIndex := ic.InlIndex
+	var encbuf [20]byte
+	for _, v := range vars {
+		if !v.IsInAbstract {
+			continue
+		}
+		putvar(ctxt, s, v, callee, abbrev, inlIndex, encbuf[:0])
+	}
+
+	// Children of this inline.
+	for _, sib := range inlChildren(callIdx, &s.InlCalls) {
+		err := putInlinedFunc(ctxt, s, sib)
+		if err != nil {
+			return err
+		}
+	}
+
+	Uleb128put(ctxt, s.Info, 0)
+	return nil
+}
+
+func emitHiLoPc(ctxt Context, abbrev int, fns *FnState, st int64, en int64) {
+	if buildcfg.Experiment.Dwarf5 {
+		putattr(ctxt, fns.Info, abbrev, DW_FORM_addrx, DW_CLS_CONSTANT, st, fns.StartPC)
+		putattr(ctxt, fns.Info, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, en, 0)
+	} else {
+		putattr(ctxt, fns.Info, abbrev, DW_FORM_addr, DW_CLS_ADDRESS, st, fns.StartPC)
+		putattr(ctxt, fns.Info, abbrev, DW_FORM_addr, DW_CLS_ADDRESS, en, fns.StartPC)
+	}
+}
+
+// Emit DWARF attributes and child DIEs for a 'concrete' subprogram,
+// meaning the out-of-line copy of a function that was inlined at some
+// point during the compilation of its containing package. The first
+// attribute for a concrete DIE is a reference to the 'abstract' DIE
+// for the function (which holds location-independent attributes such
+// as name, type), then the remainder of the attributes are specific
+// to this instance (location, frame base, etc).
+func PutConcreteFunc(ctxt Context, s *FnState, isWrapper bool, fncount int) error {
+	if logDwarf {
+		ctxt.Logf("PutConcreteFunc(%v)\n", s.Info)
+	}
+	abbrev := DW_ABRV_FUNCTION_CONCRETE
+	if isWrapper {
+		abbrev = DW_ABRV_WRAPPER_CONCRETE
+	}
+	Uleb128put(ctxt, s.Info, int64(abbrev))
+
+	// Abstract origin.
+	putattr(ctxt, s.Info, abbrev, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, s.Absfn)
+
+	// Start/end PC.
+	emitHiLoPc(ctxt, abbrev, s, 0, s.Size)
+
+	// cfa / frame base
+	putattr(ctxt, s.Info, abbrev, DW_FORM_block1, DW_CLS_BLOCK, 1, []byte{DW_OP_call_frame_cfa})
+
+	if isWrapper {
+		putattr(ctxt, s.Info, abbrev, DW_FORM_flag, DW_CLS_FLAG, int64(1), 0)
+	}
+
+	// Scopes
+	if err := putPrunedScopes(ctxt, s, abbrev); err != nil {
+		return err
+	}
+
+	// Inlined subroutines.
+	for _, sib := range inlChildren(-1, &s.InlCalls) {
+		err := putInlinedFunc(ctxt, s, sib)
+		if err != nil {
+			return err
+		}
+	}
+
+	Uleb128put(ctxt, s.Info, 0)
+	return nil
+}
+
+// Emit DWARF attributes and child DIEs for a subprogram. Here
+// 'default' implies that the function in question was not inlined
+// when its containing package was compiled (hence there is no need to
+// emit an abstract version for it to use as a base for inlined
+// routine records).
+func PutDefaultFunc(ctxt Context, s *FnState, isWrapper bool) error {
+	if logDwarf {
+		ctxt.Logf("PutDefaultFunc(%v)\n", s.Info)
+	}
+	abbrev := DW_ABRV_FUNCTION
+	if isWrapper {
+		abbrev = DW_ABRV_WRAPPER
+	}
+	Uleb128put(ctxt, s.Info, int64(abbrev))
+
+	name := s.Name
+	if strings.HasPrefix(name, `"".`) {
+		return fmt.Errorf("unqualified symbol name: %v", name)
+	}
+
+	putattr(ctxt, s.Info, DW_ABRV_FUNCTION, DW_FORM_string, DW_CLS_STRING, int64(len(name)), name)
+	emitHiLoPc(ctxt, abbrev, s, 0, s.Size)
+	putattr(ctxt, s.Info, abbrev, DW_FORM_block1, DW_CLS_BLOCK, 1, []byte{DW_OP_call_frame_cfa})
+	if isWrapper {
+		putattr(ctxt, s.Info, abbrev, DW_FORM_flag, DW_CLS_FLAG, int64(1), 0)
+	} else {
+		putattr(ctxt, s.Info, abbrev, DW_FORM_data4, DW_CLS_CONSTANT, dwarfFileIndex(s.StartPos), nil)
+		putattr(ctxt, s.Info, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(s.StartPos.RelLine()), nil)
+
+		var ev int64
+		if s.External {
+			ev = 1
+		}
+		putattr(ctxt, s.Info, abbrev, DW_FORM_flag, DW_CLS_FLAG, ev, 0)
+	}
+
+	// Scopes
+	if err := putPrunedScopes(ctxt, s, abbrev); err != nil {
+		return err
+	}
+
+	// Inlined subroutines.
+	for _, sib := range inlChildren(-1, &s.InlCalls) {
+		err := putInlinedFunc(ctxt, s, sib)
+		if err != nil {
+			return err
+		}
+	}
+
+	Uleb128put(ctxt, s.Info, 0)
+	return nil
+}
+
+// putparamtypes writes typedef DIEs for any parametric types that are used by this function.
+func putparamtypes(ctxt Context, s *FnState, scopes []Scope, fnabbrev int) []int64 {
+	if fnabbrev == DW_ABRV_FUNCTION_CONCRETE {
+		return nil
+	}
+
+	maxDictIndex := uint16(0)
+
+	for i := range scopes {
+		for _, v := range scopes[i].Vars {
+			if v.DictIndex > maxDictIndex {
+				maxDictIndex = v.DictIndex
+			}
+		}
+	}
+
+	if maxDictIndex == 0 {
+		return nil
+	}
+
+	dictIndexToOffset := make([]int64, maxDictIndex)
+
+	for i := range scopes {
+		for _, v := range scopes[i].Vars {
+			if v.DictIndex == 0 || dictIndexToOffset[v.DictIndex-1] != 0 {
+				continue
+			}
+
+			dictIndexToOffset[v.DictIndex-1] = ctxt.CurrentOffset(s.Info)
+
+			Uleb128put(ctxt, s.Info, int64(DW_ABRV_DICT_INDEX))
+			n := fmt.Sprintf(".param%d", v.DictIndex-1)
+			putattr(ctxt, s.Info, DW_ABRV_DICT_INDEX, DW_FORM_string, DW_CLS_STRING, int64(len(n)), n)
+			putattr(ctxt, s.Info, DW_ABRV_DICT_INDEX, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, v.Type)
+			putattr(ctxt, s.Info, DW_ABRV_DICT_INDEX, DW_FORM_udata, DW_CLS_CONSTANT, int64(v.DictIndex-1), nil)
+		}
+	}
+
+	return dictIndexToOffset
+}
+
+func putscope(ctxt Context, s *FnState, scopes []Scope, curscope int32, fnabbrev int, encbuf []byte) int32 {
+
+	if logDwarf {
+		ctxt.Logf("putscope(%v,%d): vars:", s.Info, curscope)
+		for i, v := range scopes[curscope].Vars {
+			ctxt.Logf(" %d:%d:%s", i, v.ChildIndex, v.Name)
+		}
+		ctxt.Logf("\n")
+	}
+
+	for _, v := range scopes[curscope].Vars {
+		putvar(ctxt, s, v, s.Absfn, fnabbrev, -1, encbuf)
+	}
+	this := curscope
+	curscope++
+	for curscope < int32(len(scopes)) {
+		scope := scopes[curscope]
+		if scope.Parent != this {
+			return curscope
+		}
+
+		if len(scopes[curscope].Vars) == 0 {
+			curscope = putscope(ctxt, s, scopes, curscope, fnabbrev, encbuf)
+			continue
+		}
+
+		// For DWARF 5, we always use the ranges form of the abbrev, since
+		// it is more compact than using explicit hi/lo PC attrs.  See
+		// issue #72821 for more on why this makes sense.
+		if len(scope.Ranges) == 1 && !buildcfg.Experiment.Dwarf5 {
+			Uleb128put(ctxt, s.Info, DW_ABRV_LEXICAL_BLOCK_SIMPLE)
+			putattr(ctxt, s.Info, DW_ABRV_LEXICAL_BLOCK_SIMPLE, DW_FORM_addr, DW_CLS_ADDRESS, scope.Ranges[0].Start, s.StartPC)
+			putattr(ctxt, s.Info, DW_ABRV_LEXICAL_BLOCK_SIMPLE, DW_FORM_addr, DW_CLS_ADDRESS, scope.Ranges[0].End, s.StartPC)
+		} else {
+			Uleb128put(ctxt, s.Info, DW_ABRV_LEXICAL_BLOCK_RANGES)
+			putattr(ctxt, s.Info, DW_ABRV_LEXICAL_BLOCK_RANGES, DW_FORM_sec_offset, DW_CLS_PTR, ctxt.Size(s.Ranges), s.Ranges)
+
+			s.PutRanges(ctxt, scope.Ranges)
+		}
+
+		curscope = putscope(ctxt, s, scopes, curscope, fnabbrev, encbuf)
+
+		Uleb128put(ctxt, s.Info, 0)
+	}
+	return curscope
+}
+
+func concreteVar(fnabbrev int, v *Var) bool {
+	concrete := true
+	switch fnabbrev {
+	case DW_ABRV_FUNCTION, DW_ABRV_WRAPPER:
+		concrete = false
+	case DW_ABRV_FUNCTION_CONCRETE, DW_ABRV_WRAPPER_CONCRETE:
+		// If we're emitting a concrete subprogram DIE and the variable
+		// in question is not part of the corresponding abstract function DIE,
+		// then use the default (non-concrete) abbrev for this param.
+		if !v.IsInAbstract {
+			concrete = false
+		}
+	case DW_ABRV_INLINED_SUBROUTINE, DW_ABRV_INLINED_SUBROUTINE_RANGES:
+	default:
+		panic("should never happen")
+	}
+	return concrete
+}
+
+// Emit DWARF attributes for a variable belonging to an 'abstract' subprogram.
+func putAbstractVar(ctxt Context, info Sym, v *Var) {
+	// The contents of this functions are used to generate putAbstractVarAbbrev automatically, see TestPutVarAbbrevGenerator.
+	abbrev := putAbstractVarAbbrev(v)
+	Uleb128put(ctxt, info, int64(abbrev))
+	putattr(ctxt, info, abbrev, DW_FORM_string, DW_CLS_STRING, int64(len(v.Name)), v.Name) // DW_AT_name
+
+	// Isreturn attribute if this is a param
+	if v.Tag == DW_TAG_formal_parameter {
+		var isReturn int64
+		if v.IsReturnValue {
+			isReturn = 1
+		}
+		putattr(ctxt, info, abbrev, DW_FORM_flag, DW_CLS_FLAG, isReturn, nil) // DW_AT_variable_parameter
+	}
+
+	// Line
+	if v.Tag == DW_TAG_variable {
+		// See issue 23374 for more on why decl line is skipped for abs params.
+		putattr(ctxt, info, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(v.DeclLine), nil) // DW_AT_decl_line
+	}
+
+	// Type
+	putattr(ctxt, info, abbrev, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, v.Type) // DW_AT_type
+
+	// Var has no children => no terminator
+}
+
+func putvar(ctxt Context, s *FnState, v *Var, absfn Sym, fnabbrev, inlIndex int, encbuf []byte) {
+	// The contents of this functions are used to generate putvarAbbrev automatically, see TestPutVarAbbrevGenerator.
+	concrete := concreteVar(fnabbrev, v)
+	hasParametricType := !concrete && (v.DictIndex > 0 && s.dictIndexToOffset != nil && s.dictIndexToOffset[v.DictIndex-1] != 0)
+	withLoclist := v.WithLoclist && v.PutLocationList != nil
+
+	abbrev := putvarAbbrev(v, concrete, withLoclist)
+	Uleb128put(ctxt, s.Info, int64(abbrev))
+
+	// Abstract origin for concrete / inlined case
+	if concrete {
+		// Here we are making a reference to a child DIE of an abstract
+		// function subprogram DIE. The child DIE has no LSym, so instead
+		// after the call to 'putattr' below we make a call to register
+		// the child DIE reference.
+		putattr(ctxt, s.Info, abbrev, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, absfn) // DW_AT_abstract_origin
+		ctxt.RecordDclReference(s.Info, absfn, int(v.ChildIndex), inlIndex)
+	} else {
+		// Var name, line for abstract and default cases
+		n := v.Name
+		putattr(ctxt, s.Info, abbrev, DW_FORM_string, DW_CLS_STRING, int64(len(n)), n) // DW_AT_name
+		if v.Tag == DW_TAG_formal_parameter {
+			var isReturn int64
+			if v.IsReturnValue {
+				isReturn = 1
+			}
+			putattr(ctxt, s.Info, abbrev, DW_FORM_flag, DW_CLS_FLAG, isReturn, nil) // DW_AT_variable_parameter
+		}
+		putattr(ctxt, s.Info, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(v.DeclLine), nil) // DW_AT_decl_line
+		if hasParametricType {
+			// If the type of this variable is parametric use the entry emitted by putparamtypes
+			putattr(ctxt, s.Info, abbrev, DW_FORM_ref_addr, DW_CLS_REFERENCE, s.dictIndexToOffset[v.DictIndex-1], s.Info) // DW_AT_type
+		} else {
+			putattr(ctxt, s.Info, abbrev, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, v.Type) // DW_AT_type
+		}
+
+		if v.ClosureOffset > 0 {
+			putattr(ctxt, s.Info, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, v.ClosureOffset, nil) // DW_AT_go_closure_offset
+		}
+	}
+
+	if withLoclist {
+		putattr(ctxt, s.Info, abbrev, DW_FORM_sec_offset, DW_CLS_PTR, ctxt.Size(s.Loc), s.Loc) // DW_AT_location
+		v.PutLocationList(s.Loc, s.StartPC)
+	} else {
+		loc := encbuf[:0]
+		switch {
+		case v.WithLoclist:
+			break // no location
+		case v.StackOffset == 0:
+			loc = append(loc, DW_OP_call_frame_cfa)
+		default:
+			loc = append(loc, DW_OP_fbreg)
+			loc = AppendSleb128(loc, int64(v.StackOffset))
+		}
+		putattr(ctxt, s.Info, abbrev, DW_FORM_block1, DW_CLS_BLOCK, int64(len(loc)), loc) // DW_AT_location
+	}
+
+	// Var has no children => no terminator
+}
+
+// byChildIndexCmp compares two *dwarf.Var by child index.
+func byChildIndexCmp(a, b *Var) int { return cmp.Compare(a.ChildIndex, b.ChildIndex) }
+
+// IsDWARFEnabledOnAIXLd returns true if DWARF is possible on the
+// current extld.
+// AIX ld doesn't support DWARF with -bnoobjreorder with version
+// prior to 7.2.2.
+func IsDWARFEnabledOnAIXLd(extld []string) (bool, error) {
+	name, args := extld[0], extld[1:]
+	args = append(args, "-Wl,-V")
+	out, err := exec.Command(name, args...).CombinedOutput()
+	if err != nil {
+		// The normal output should display ld version and
+		// then fails because ".main" is not defined:
+		// ld: 0711-317 ERROR: Undefined symbol: .main
+		if !bytes.Contains(out, []byte("0711-317")) {
+			return false, fmt.Errorf("%s -Wl,-V failed: %v\n%s", extld, err, out)
+		}
+	}
+	// gcc -Wl,-V output should be:
+	//   /usr/bin/ld: LD X.X.X(date)
+	//   ...
+	out = bytes.TrimPrefix(out, []byte("/usr/bin/ld: LD "))
+	vers := string(bytes.Split(out, []byte("("))[0])
+	subvers := strings.Split(vers, ".")
+	if len(subvers) != 3 {
+		return false, fmt.Errorf("cannot parse %s -Wl,-V (%s): %v\n", extld, out, err)
+	}
+	if v, err := strconv.Atoi(subvers[0]); err != nil || v < 7 {
+		return false, nil
+	} else if v > 7 {
+		return true, nil
+	}
+	if v, err := strconv.Atoi(subvers[1]); err != nil || v < 2 {
+		return false, nil
+	} else if v > 2 {
+		return true, nil
+	}
+	if v, err := strconv.Atoi(subvers[2]); err != nil || v < 2 {
+		return false, nil
+	}
+	return true, nil
+}

go/src/cmd/internal/dwarf/dwarf_defs.go

@@ -0,0 +1,550 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package dwarf
+
+// Cut, pasted, tr-and-awk'ed from tables in
+// http://dwarfstd.org/doc/Dwarf3.pdf
+
+// Table 18
+const (
+	DW_TAG_array_type               = 0x01
+	DW_TAG_class_type               = 0x02
+	DW_TAG_entry_point              = 0x03
+	DW_TAG_enumeration_type         = 0x04
+	DW_TAG_formal_parameter         = 0x05
+	DW_TAG_imported_declaration     = 0x08
+	DW_TAG_label                    = 0x0a
+	DW_TAG_lexical_block            = 0x0b
+	DW_TAG_member                   = 0x0d
+	DW_TAG_pointer_type             = 0x0f
+	DW_TAG_reference_type           = 0x10
+	DW_TAG_compile_unit             = 0x11
+	DW_TAG_string_type              = 0x12
+	DW_TAG_structure_type           = 0x13
+	DW_TAG_subroutine_type          = 0x15
+	DW_TAG_typedef                  = 0x16
+	DW_TAG_union_type               = 0x17
+	DW_TAG_unspecified_parameters   = 0x18
+	DW_TAG_variant                  = 0x19
+	DW_TAG_common_block             = 0x1a
+	DW_TAG_common_inclusion         = 0x1b
+	DW_TAG_inheritance              = 0x1c
+	DW_TAG_inlined_subroutine       = 0x1d
+	DW_TAG_module                   = 0x1e
+	DW_TAG_ptr_to_member_type       = 0x1f
+	DW_TAG_set_type                 = 0x20
+	DW_TAG_subrange_type            = 0x21
+	DW_TAG_with_stmt                = 0x22
+	DW_TAG_access_declaration       = 0x23
+	DW_TAG_base_type                = 0x24
+	DW_TAG_catch_block              = 0x25
+	DW_TAG_const_type               = 0x26
+	DW_TAG_constant                 = 0x27
+	DW_TAG_enumerator               = 0x28
+	DW_TAG_file_type                = 0x29
+	DW_TAG_friend                   = 0x2a
+	DW_TAG_namelist                 = 0x2b
+	DW_TAG_namelist_item            = 0x2c
+	DW_TAG_packed_type              = 0x2d
+	DW_TAG_subprogram               = 0x2e
+	DW_TAG_template_type_parameter  = 0x2f
+	DW_TAG_template_value_parameter = 0x30
+	DW_TAG_thrown_type              = 0x31
+	DW_TAG_try_block                = 0x32
+	DW_TAG_variant_part             = 0x33
+	DW_TAG_variable                 = 0x34
+	DW_TAG_volatile_type            = 0x35
+	// Dwarf3
+	DW_TAG_dwarf_procedure  = 0x36
+	DW_TAG_restrict_type    = 0x37
+	DW_TAG_interface_type   = 0x38
+	DW_TAG_namespace        = 0x39
+	DW_TAG_imported_module  = 0x3a
+	DW_TAG_unspecified_type = 0x3b
+	DW_TAG_partial_unit     = 0x3c
+	DW_TAG_imported_unit    = 0x3d
+	DW_TAG_condition        = 0x3f
+	DW_TAG_shared_type      = 0x40
+	// Dwarf4
+	DW_TAG_type_unit             = 0x41
+	DW_TAG_rvalue_reference_type = 0x42
+	DW_TAG_template_alias        = 0x43
+
+	// User defined
+	DW_TAG_lo_user = 0x4080
+	DW_TAG_hi_user = 0xffff
+)
+
+// Table 19
+const (
+	DW_CHILDREN_no  = 0x00
+	DW_CHILDREN_yes = 0x01
+)
+
+// Not from the spec, but logically belongs here
+const (
+	DW_CLS_ADDRESS = 0x01 + iota
+	DW_CLS_BLOCK
+	DW_CLS_CONSTANT
+	DW_CLS_FLAG
+	DW_CLS_PTR // lineptr, loclistptr, macptr, rangelistptr
+	DW_CLS_REFERENCE
+	DW_CLS_ADDRLOC
+	DW_CLS_STRING
+
+	// Go-specific internal hackery.
+	DW_CLS_GO_TYPEREF
+)
+
+// Table 20
+const (
+	DW_AT_sibling              = 0x01 // reference
+	DW_AT_location             = 0x02 // block, loclistptr
+	DW_AT_name                 = 0x03 // string
+	DW_AT_ordering             = 0x09 // constant
+	DW_AT_byte_size            = 0x0b // block, constant, reference
+	DW_AT_bit_offset           = 0x0c // block, constant, reference
+	DW_AT_bit_size             = 0x0d // block, constant, reference
+	DW_AT_stmt_list            = 0x10 // lineptr
+	DW_AT_low_pc               = 0x11 // address
+	DW_AT_high_pc              = 0x12 // address
+	DW_AT_language             = 0x13 // constant
+	DW_AT_discr                = 0x15 // reference
+	DW_AT_discr_value          = 0x16 // constant
+	DW_AT_visibility           = 0x17 // constant
+	DW_AT_import               = 0x18 // reference
+	DW_AT_string_length        = 0x19 // block, loclistptr
+	DW_AT_common_reference     = 0x1a // reference
+	DW_AT_comp_dir             = 0x1b // string
+	DW_AT_const_value          = 0x1c // block, constant, string
+	DW_AT_containing_type      = 0x1d // reference
+	DW_AT_default_value        = 0x1e // reference
+	DW_AT_inline               = 0x20 // constant
+	DW_AT_is_optional          = 0x21 // flag
+	DW_AT_lower_bound          = 0x22 // block, constant, reference
+	DW_AT_producer             = 0x25 // string
+	DW_AT_prototyped           = 0x27 // flag
+	DW_AT_return_addr          = 0x2a // block, loclistptr
+	DW_AT_start_scope          = 0x2c // constant
+	DW_AT_bit_stride           = 0x2e // constant
+	DW_AT_upper_bound          = 0x2f // block, constant, reference
+	DW_AT_abstract_origin      = 0x31 // reference
+	DW_AT_accessibility        = 0x32 // constant
+	DW_AT_address_class        = 0x33 // constant
+	DW_AT_artificial           = 0x34 // flag
+	DW_AT_base_types           = 0x35 // reference
+	DW_AT_calling_convention   = 0x36 // constant
+	DW_AT_count                = 0x37 // block, constant, reference
+	DW_AT_data_member_location = 0x38 // block, constant, loclistptr
+	DW_AT_decl_column          = 0x39 // constant
+	DW_AT_decl_file            = 0x3a // constant
+	DW_AT_decl_line            = 0x3b // constant
+	DW_AT_declaration          = 0x3c // flag
+	DW_AT_discr_list           = 0x3d // block
+	DW_AT_encoding             = 0x3e // constant
+	DW_AT_external             = 0x3f // flag
+	DW_AT_frame_base           = 0x40 // block, loclistptr
+	DW_AT_friend               = 0x41 // reference
+	DW_AT_identifier_case      = 0x42 // constant
+	DW_AT_macro_info           = 0x43 // macptr
+	DW_AT_namelist_item        = 0x44 // block
+	DW_AT_priority             = 0x45 // reference
+	DW_AT_segment              = 0x46 // block, loclistptr
+	DW_AT_specification        = 0x47 // reference
+	DW_AT_static_link          = 0x48 // block, loclistptr
+	DW_AT_type                 = 0x49 // reference
+	DW_AT_use_location         = 0x4a // block, loclistptr
+	DW_AT_variable_parameter   = 0x4b // flag
+	DW_AT_virtuality           = 0x4c // constant
+	DW_AT_vtable_elem_location = 0x4d // block, loclistptr
+	// Dwarf3
+	DW_AT_allocated      = 0x4e // block, constant, reference
+	DW_AT_associated     = 0x4f // block, constant, reference
+	DW_AT_data_location  = 0x50 // block
+	DW_AT_byte_stride    = 0x51 // block, constant, reference
+	DW_AT_entry_pc       = 0x52 // address
+	DW_AT_use_UTF8       = 0x53 // flag
+	DW_AT_extension      = 0x54 // reference
+	DW_AT_ranges         = 0x55 // rangelistptr
+	DW_AT_trampoline     = 0x56 // address, flag, reference, string
+	DW_AT_call_column    = 0x57 // constant
+	DW_AT_call_file      = 0x58 // constant
+	DW_AT_call_line      = 0x59 // constant
+	DW_AT_description    = 0x5a // string
+	DW_AT_binary_scale   = 0x5b // constant
+	DW_AT_decimal_scale  = 0x5c // constant
+	DW_AT_small          = 0x5d // reference
+	DW_AT_decimal_sign   = 0x5e // constant
+	DW_AT_digit_count    = 0x5f // constant
+	DW_AT_picture_string = 0x60 // string
+	DW_AT_mutable        = 0x61 // flag
+	DW_AT_threads_scaled = 0x62 // flag
+	DW_AT_explicit       = 0x63 // flag
+	DW_AT_object_pointer = 0x64 // reference
+	DW_AT_endianity      = 0x65 // constant
+	DW_AT_elemental      = 0x66 // flag
+	DW_AT_pure           = 0x67 // flag
+	DW_AT_recursive      = 0x68 // flag
+	DW_AT_addr_base      = 0x73 // addrptr
+
+	DW_AT_lo_user = 0x2000 // ---
+	DW_AT_hi_user = 0x3fff // ---
+)
+
+// Table 21
+const (
+	DW_FORM_addr      = 0x01 // address
+	DW_FORM_block2    = 0x03 // block
+	DW_FORM_block4    = 0x04 // block
+	DW_FORM_data2     = 0x05 // constant
+	DW_FORM_data4     = 0x06 // constant, lineptr, loclistptr, macptr, rangelistptr
+	DW_FORM_data8     = 0x07 // constant, lineptr, loclistptr, macptr, rangelistptr
+	DW_FORM_string    = 0x08 // string
+	DW_FORM_block     = 0x09 // block
+	DW_FORM_block1    = 0x0a // block
+	DW_FORM_data1     = 0x0b // constant
+	DW_FORM_flag      = 0x0c // flag
+	DW_FORM_sdata     = 0x0d // constant
+	DW_FORM_strp      = 0x0e // string
+	DW_FORM_udata     = 0x0f // constant
+	DW_FORM_ref_addr  = 0x10 // reference
+	DW_FORM_ref1      = 0x11 // reference
+	DW_FORM_ref2      = 0x12 // reference
+	DW_FORM_ref4      = 0x13 // reference
+	DW_FORM_ref8      = 0x14 // reference
+	DW_FORM_ref_udata = 0x15 // reference
+	DW_FORM_indirect  = 0x16 // (see Section 7.5.3)
+	// Dwarf4
+	DW_FORM_sec_offset   = 0x17 // lineptr, loclistptr, macptr, rangelistptr
+	DW_FORM_exprloc      = 0x18 // exprloc
+	DW_FORM_flag_present = 0x19 // flag
+	// Dwarf5
+	DW_FORM_addrx = 0x1b
+	// Pseudo-form: expanded to data4 on IOS, udata elsewhere.
+	DW_FORM_udata_pseudo = 0x99
+	// Pseudo-form: expands to DW_FORM_addrx in DWARF5, DW_FORM_addr in DWARF4
+	DW_FORM_lo_pc_pseudo = 0x9a
+	// Pseudo-form: expands to DW_FORM_udata in DWARF5, DW_FORM_addr in DWARF4
+	DW_FORM_hi_pc_pseudo = 0x9b
+)
+
+// Table 24 (#operands, notes)
+const (
+	DW_OP_addr                = 0x03 // 1 constant address (size target specific)
+	DW_OP_deref               = 0x06 // 0
+	DW_OP_const1u             = 0x08 // 1 1-byte constant
+	DW_OP_const1s             = 0x09 // 1 1-byte constant
+	DW_OP_const2u             = 0x0a // 1 2-byte constant
+	DW_OP_const2s             = 0x0b // 1 2-byte constant
+	DW_OP_const4u             = 0x0c // 1 4-byte constant
+	DW_OP_const4s             = 0x0d // 1 4-byte constant
+	DW_OP_const8u             = 0x0e // 1 8-byte constant
+	DW_OP_const8s             = 0x0f // 1 8-byte constant
+	DW_OP_constu              = 0x10 // 1 ULEB128 constant
+	DW_OP_consts              = 0x11 // 1 SLEB128 constant
+	DW_OP_dup                 = 0x12 // 0
+	DW_OP_drop                = 0x13 // 0
+	DW_OP_over                = 0x14 // 0
+	DW_OP_pick                = 0x15 // 1 1-byte stack index
+	DW_OP_swap                = 0x16 // 0
+	DW_OP_rot                 = 0x17 // 0
+	DW_OP_xderef              = 0x18 // 0
+	DW_OP_abs                 = 0x19 // 0
+	DW_OP_and                 = 0x1a // 0
+	DW_OP_div                 = 0x1b // 0
+	DW_OP_minus               = 0x1c // 0
+	DW_OP_mod                 = 0x1d // 0
+	DW_OP_mul                 = 0x1e // 0
+	DW_OP_neg                 = 0x1f // 0
+	DW_OP_not                 = 0x20 // 0
+	DW_OP_or                  = 0x21 // 0
+	DW_OP_plus                = 0x22 // 0
+	DW_OP_plus_uconst         = 0x23 // 1 ULEB128 addend
+	DW_OP_shl                 = 0x24 // 0
+	DW_OP_shr                 = 0x25 // 0
+	DW_OP_shra                = 0x26 // 0
+	DW_OP_xor                 = 0x27 // 0
+	DW_OP_skip                = 0x2f // 1 signed 2-byte constant
+	DW_OP_bra                 = 0x28 // 1 signed 2-byte constant
+	DW_OP_eq                  = 0x29 // 0
+	DW_OP_ge                  = 0x2a // 0
+	DW_OP_gt                  = 0x2b // 0
+	DW_OP_le                  = 0x2c // 0
+	DW_OP_lt                  = 0x2d // 0
+	DW_OP_ne                  = 0x2e // 0
+	DW_OP_lit0                = 0x30 // 0 ...
+	DW_OP_lit31               = 0x4f // 0 literals 0..31 = (DW_OP_lit0 + literal)
+	DW_OP_reg0                = 0x50 // 0 ..
+	DW_OP_reg31               = 0x6f // 0 reg 0..31 = (DW_OP_reg0 + regnum)
+	DW_OP_breg0               = 0x70 // 1 ...
+	DW_OP_breg31              = 0x8f // 1 SLEB128 offset base register 0..31 = (DW_OP_breg0 + regnum)
+	DW_OP_regx                = 0x90 // 1 ULEB128 register
+	DW_OP_fbreg               = 0x91 // 1 SLEB128 offset
+	DW_OP_bregx               = 0x92 // 2 ULEB128 register followed by SLEB128 offset
+	DW_OP_piece               = 0x93 // 1 ULEB128 size of piece addressed
+	DW_OP_deref_size          = 0x94 // 1 1-byte size of data retrieved
+	DW_OP_xderef_size         = 0x95 // 1 1-byte size of data retrieved
+	DW_OP_nop                 = 0x96 // 0
+	DW_OP_push_object_address = 0x97 // 0
+	DW_OP_call2               = 0x98 // 1 2-byte offset of DIE
+	DW_OP_call4               = 0x99 // 1 4-byte offset of DIE
+	DW_OP_call_ref            = 0x9a // 1 4- or 8-byte offset of DIE
+	DW_OP_form_tls_address    = 0x9b // 0
+	DW_OP_call_frame_cfa      = 0x9c // 0
+	DW_OP_bit_piece           = 0x9d // 2
+	DW_OP_lo_user             = 0xe0
+	DW_OP_hi_user             = 0xff
+)
+
+// Table 25
+const (
+	DW_ATE_address         = 0x01
+	DW_ATE_boolean         = 0x02
+	DW_ATE_complex_float   = 0x03
+	DW_ATE_float           = 0x04
+	DW_ATE_signed          = 0x05
+	DW_ATE_signed_char     = 0x06
+	DW_ATE_unsigned        = 0x07
+	DW_ATE_unsigned_char   = 0x08
+	DW_ATE_imaginary_float = 0x09
+	DW_ATE_packed_decimal  = 0x0a
+	DW_ATE_numeric_string  = 0x0b
+	DW_ATE_edited          = 0x0c
+	DW_ATE_signed_fixed    = 0x0d
+	DW_ATE_unsigned_fixed  = 0x0e
+	DW_ATE_decimal_float   = 0x0f
+	DW_ATE_lo_user         = 0x80
+	DW_ATE_hi_user         = 0xff
+)
+
+// Table 26
+const (
+	DW_DS_unsigned           = 0x01
+	DW_DS_leading_overpunch  = 0x02
+	DW_DS_trailing_overpunch = 0x03
+	DW_DS_leading_separate   = 0x04
+	DW_DS_trailing_separate  = 0x05
+)
+
+// Table 27
+const (
+	DW_END_default = 0x00
+	DW_END_big     = 0x01
+	DW_END_little  = 0x02
+	DW_END_lo_user = 0x40
+	DW_END_hi_user = 0xff
+)
+
+// Table 28
+const (
+	DW_ACCESS_public    = 0x01
+	DW_ACCESS_protected = 0x02
+	DW_ACCESS_private   = 0x03
+)
+
+// Table 29
+const (
+	DW_VIS_local     = 0x01
+	DW_VIS_exported  = 0x02
+	DW_VIS_qualified = 0x03
+)
+
+// Table 30
+const (
+	DW_VIRTUALITY_none         = 0x00
+	DW_VIRTUALITY_virtual      = 0x01
+	DW_VIRTUALITY_pure_virtual = 0x02
+)
+
+// Table 31
+const (
+	DW_LANG_C89         = 0x0001
+	DW_LANG_C           = 0x0002
+	DW_LANG_Ada83       = 0x0003
+	DW_LANG_C_plus_plus = 0x0004
+	DW_LANG_Cobol74     = 0x0005
+	DW_LANG_Cobol85     = 0x0006
+	DW_LANG_Fortran77   = 0x0007
+	DW_LANG_Fortran90   = 0x0008
+	DW_LANG_Pascal83    = 0x0009
+	DW_LANG_Modula2     = 0x000a
+	// Dwarf3
+	DW_LANG_Java           = 0x000b
+	DW_LANG_C99            = 0x000c
+	DW_LANG_Ada95          = 0x000d
+	DW_LANG_Fortran95      = 0x000e
+	DW_LANG_PLI            = 0x000f
+	DW_LANG_ObjC           = 0x0010
+	DW_LANG_ObjC_plus_plus = 0x0011
+	DW_LANG_UPC            = 0x0012
+	DW_LANG_D              = 0x0013
+	// Dwarf4
+	DW_LANG_Python = 0x0014
+	// Dwarf5
+	DW_LANG_Go = 0x0016
+
+	DW_LANG_lo_user = 0x8000
+	DW_LANG_hi_user = 0xffff
+)
+
+// Table 32
+const (
+	DW_ID_case_sensitive   = 0x00
+	DW_ID_up_case          = 0x01
+	DW_ID_down_case        = 0x02
+	DW_ID_case_insensitive = 0x03
+)
+
+// Table 33
+const (
+	DW_CC_normal  = 0x01
+	DW_CC_program = 0x02
+	DW_CC_nocall  = 0x03
+	DW_CC_lo_user = 0x40
+	DW_CC_hi_user = 0xff
+)
+
+// Table 34
+const (
+	DW_INL_not_inlined          = 0x00
+	DW_INL_inlined              = 0x01
+	DW_INL_declared_not_inlined = 0x02
+	DW_INL_declared_inlined     = 0x03
+)
+
+// Table 35
+const (
+	DW_ORD_row_major = 0x00
+	DW_ORD_col_major = 0x01
+)
+
+// Table 36
+const (
+	DW_DSC_label = 0x00
+	DW_DSC_range = 0x01
+)
+
+// Table 37
+const (
+	DW_LNS_copy             = 0x01
+	DW_LNS_advance_pc       = 0x02
+	DW_LNS_advance_line     = 0x03
+	DW_LNS_set_file         = 0x04
+	DW_LNS_set_column       = 0x05
+	DW_LNS_negate_stmt      = 0x06
+	DW_LNS_set_basic_block  = 0x07
+	DW_LNS_const_add_pc     = 0x08
+	DW_LNS_fixed_advance_pc = 0x09
+	// Dwarf3
+	DW_LNS_set_prologue_end   = 0x0a
+	DW_LNS_set_epilogue_begin = 0x0b
+	DW_LNS_set_isa            = 0x0c
+)
+
+// Table 38
+const (
+	DW_LNE_end_sequence = 0x01
+	DW_LNE_set_address  = 0x02
+	DW_LNE_define_file  = 0x03
+	DW_LNE_lo_user      = 0x80
+	DW_LNE_hi_user      = 0xff
+)
+
+// Table 7.25 (DWARF version 5), containing the encodings for the
+// .debug_rnglists entry formats.
+const (
+	DW_RLE_end_of_list   = 0x0
+	DW_RLE_base_addressx = 0x1
+	DW_RLE_startx_endx   = 0x2
+	DW_RLE_startx_length = 0x3
+	DW_RLE_offset_pair   = 0x4
+	DW_RLE_base_address  = 0x5
+	DW_RLE_start_end     = 0x6
+	DW_RLE_start_length  = 0x7
+)
+
+// Table 7.10 (DWARF version 5), containing the encodings for the
+// .debug_loclists entry formats.
+const (
+	DW_LLE_end_of_list      = 0x0
+	DW_LLE_base_addressx    = 0x1
+	DW_LLE_startx_endx      = 0x2
+	DW_LLE_startx_length    = 0x3
+	DW_LLE_offset_pair      = 0x4
+	DW_LLE_default_location = 0x5
+	DW_LLE_base_address     = 0x6
+	DW_LLE_start_end        = 0x7
+	DW_LLE_start_length     = 0x8
+)
+
+// Table 7.27 (DWARF version 5), containing the encodings for the
+// line number header entry formats.
+const (
+	DW_LNCT_path            = 0x01
+	DW_LNCT_directory_index = 0x02
+	DW_LNCT_timestamp       = 0x03
+	DW_LNCT_size            = 0x04
+	DW_LNCT_md5             = 0x05
+	DW_LNCT_lo_user         = 0x2000
+	DW_LNCT_hi_user         = 0x3fff
+)
+
+// Table 7.2 (DWARF version 5), dwarf unit type encodings.
+const (
+	DW_UT_compile       = 0x01
+	DW_UT_type          = 0x02
+	DW_UT_partial       = 0x03
+	DW_UT_skeleton      = 0x04
+	DW_UT_split_compile = 0x05
+	DW_UT_split_type    = 0x06
+	DW_UT_lo_user       = 0x80
+	DW_UT_hi_user       = 0xff
+)
+
+// Table 39
+const (
+	DW_MACINFO_define     = 0x01
+	DW_MACINFO_undef      = 0x02
+	DW_MACINFO_start_file = 0x03
+	DW_MACINFO_end_file   = 0x04
+	DW_MACINFO_vendor_ext = 0xff
+)
+
+// Table 40.
+const (
+	// operand,...
+	DW_CFA_nop              = 0x00
+	DW_CFA_set_loc          = 0x01 // address
+	DW_CFA_advance_loc1     = 0x02 // 1-byte delta
+	DW_CFA_advance_loc2     = 0x03 // 2-byte delta
+	DW_CFA_advance_loc4     = 0x04 // 4-byte delta
+	DW_CFA_offset_extended  = 0x05 // ULEB128 register, ULEB128 offset
+	DW_CFA_restore_extended = 0x06 // ULEB128 register
+	DW_CFA_undefined        = 0x07 // ULEB128 register
+	DW_CFA_same_value       = 0x08 // ULEB128 register
+	DW_CFA_register         = 0x09 // ULEB128 register, ULEB128 register
+	DW_CFA_remember_state   = 0x0a
+	DW_CFA_restore_state    = 0x0b
+
+	DW_CFA_def_cfa            = 0x0c // ULEB128 register, ULEB128 offset
+	DW_CFA_def_cfa_register   = 0x0d // ULEB128 register
+	DW_CFA_def_cfa_offset     = 0x0e // ULEB128 offset
+	DW_CFA_def_cfa_expression = 0x0f // BLOCK
+	DW_CFA_expression         = 0x10 // ULEB128 register, BLOCK
+	DW_CFA_offset_extended_sf = 0x11 // ULEB128 register, SLEB128 offset
+	DW_CFA_def_cfa_sf         = 0x12 // ULEB128 register, SLEB128 offset
+	DW_CFA_def_cfa_offset_sf  = 0x13 // SLEB128 offset
+	DW_CFA_val_offset         = 0x14 // ULEB128, ULEB128
+	DW_CFA_val_offset_sf      = 0x15 // ULEB128, SLEB128
+	DW_CFA_val_expression     = 0x16 // ULEB128, BLOCK
+
+	DW_CFA_lo_user = 0x1c
+	DW_CFA_hi_user = 0x3f
+
+	// Opcodes that take an addend operand.
+	DW_CFA_advance_loc = 0x1 << 6 // +delta
+	DW_CFA_offset      = 0x2 << 6 // +register (ULEB128 offset)
+	DW_CFA_restore     = 0x3 << 6 // +register
+)

go/src/cmd/internal/dwarf/dwarf_test.go

@@ -0,0 +1,38 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package dwarf
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestSevenBitEnc128(t *testing.T) {
+	t.Run("unsigned", func(t *testing.T) {
+		for v := int64(-255); v < 255; v++ {
+			s := sevenBitU(v)
+			if s == nil {
+				continue
+			}
+			b := AppendUleb128(nil, uint64(v))
+			if !reflect.DeepEqual(b, s) {
+				t.Errorf("sevenBitU(%d) = %v but AppendUleb128(%d) = %v", v, s, v, b)
+			}
+		}
+	})
+
+	t.Run("signed", func(t *testing.T) {
+		for v := int64(-255); v < 255; v++ {
+			s := sevenBitS(v)
+			if s == nil {
+				continue
+			}
+			b := AppendSleb128(nil, v)
+			if !reflect.DeepEqual(b, s) {
+				t.Errorf("sevenBitS(%d) = %v but AppendSleb128(%d) = %v", v, s, v, b)
+			}
+		}
+	})
+}

go/src/cmd/internal/dwarf/putvarabbrevgen.go

@@ -0,0 +1,201 @@
+// Code generated by TestPutVarAbbrevGenerator. DO NOT EDIT.
+// Regenerate using go test -run TestPutVarAbbrevGenerator -generate instead.
+
+package dwarf
+
+var putvarAbbrevs = []dwAbbrev{
+	{
+		DW_TAG_variable,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_decl_line, DW_FORM_udata},
+			{DW_AT_type, DW_FORM_ref_addr},
+		},
+	},
+	{
+		DW_TAG_formal_parameter,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_variable_parameter, DW_FORM_flag},
+			{DW_AT_type, DW_FORM_ref_addr},
+		},
+	},
+	{
+		DW_TAG_variable,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_abstract_origin, DW_FORM_ref_addr},
+			{DW_AT_location, DW_FORM_sec_offset},
+		},
+	},
+	{
+		DW_TAG_variable,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_abstract_origin, DW_FORM_ref_addr},
+			{DW_AT_location, DW_FORM_block1},
+		},
+	},
+	{
+		DW_TAG_variable,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_decl_line, DW_FORM_udata},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_go_closure_offset, DW_FORM_udata},
+			{DW_AT_location, DW_FORM_sec_offset},
+		},
+	},
+	{
+		DW_TAG_variable,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_decl_line, DW_FORM_udata},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_go_closure_offset, DW_FORM_udata},
+			{DW_AT_location, DW_FORM_block1},
+		},
+	},
+	{
+		DW_TAG_variable,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_decl_line, DW_FORM_udata},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_location, DW_FORM_sec_offset},
+		},
+	},
+	{
+		DW_TAG_variable,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_decl_line, DW_FORM_udata},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_location, DW_FORM_block1},
+		},
+	},
+	{
+		DW_TAG_formal_parameter,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_abstract_origin, DW_FORM_ref_addr},
+			{DW_AT_location, DW_FORM_sec_offset},
+		},
+	},
+	{
+		DW_TAG_formal_parameter,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_abstract_origin, DW_FORM_ref_addr},
+			{DW_AT_location, DW_FORM_block1},
+		},
+	},
+	{
+		DW_TAG_formal_parameter,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_variable_parameter, DW_FORM_flag},
+			{DW_AT_decl_line, DW_FORM_udata},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_go_closure_offset, DW_FORM_udata},
+			{DW_AT_location, DW_FORM_sec_offset},
+		},
+	},
+	{
+		DW_TAG_formal_parameter,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_variable_parameter, DW_FORM_flag},
+			{DW_AT_decl_line, DW_FORM_udata},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_go_closure_offset, DW_FORM_udata},
+			{DW_AT_location, DW_FORM_block1},
+		},
+	},
+	{
+		DW_TAG_formal_parameter,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_variable_parameter, DW_FORM_flag},
+			{DW_AT_decl_line, DW_FORM_udata},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_location, DW_FORM_sec_offset},
+		},
+	},
+	{
+		DW_TAG_formal_parameter,
+		DW_CHILDREN_no,
+		[]dwAttrForm{
+			{DW_AT_name, DW_FORM_string},
+			{DW_AT_variable_parameter, DW_FORM_flag},
+			{DW_AT_decl_line, DW_FORM_udata},
+			{DW_AT_type, DW_FORM_ref_addr},
+			{DW_AT_location, DW_FORM_block1},
+		},
+	},
+}
+
+func putAbstractVarAbbrev(v *Var) int {
+	if v.Tag == DW_TAG_variable {
+		return DW_ABRV_PUTVAR_START + 0
+	} else {
+		return DW_ABRV_PUTVAR_START + 1
+	}
+}
+
+func putvarAbbrev(v *Var, concrete, withLoclist bool) int {
+	if v.Tag == DW_TAG_variable {
+		if concrete {
+			if withLoclist {
+				return DW_ABRV_PUTVAR_START + 2
+			} else {
+				return DW_ABRV_PUTVAR_START + 3
+			}
+		} else {
+			if v.ClosureOffset > 0 {
+				if withLoclist {
+					return DW_ABRV_PUTVAR_START + 4
+				} else {
+					return DW_ABRV_PUTVAR_START + 5
+				}
+			} else {
+				if withLoclist {
+					return DW_ABRV_PUTVAR_START + 6
+				} else {
+					return DW_ABRV_PUTVAR_START + 7
+				}
+			}
+		}
+	} else {
+		if concrete {
+			if withLoclist {
+				return DW_ABRV_PUTVAR_START + 8
+			} else {
+				return DW_ABRV_PUTVAR_START + 9
+			}
+		} else {
+			if v.ClosureOffset > 0 {
+				if withLoclist {
+					return DW_ABRV_PUTVAR_START + 10
+				} else {
+					return DW_ABRV_PUTVAR_START + 11
+				}
+			} else {
+				if withLoclist {
+					return DW_ABRV_PUTVAR_START + 12
+				} else {
+					return DW_ABRV_PUTVAR_START + 13
+				}
+			}
+		}
+	}
+}

go/src/cmd/internal/dwarf/putvarabbrevgen_test.go

@@ -0,0 +1,316 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package dwarf
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"go/ast"
+	"go/format"
+	"go/parser"
+	"go/printer"
+	"go/token"
+	"os"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+const pvagenfile = "./putvarabbrevgen.go"
+
+var pvaDoGenerate bool
+
+func TestMain(m *testing.M) {
+	flag.BoolVar(&pvaDoGenerate, "generate", false, "regenerates "+pvagenfile)
+	flag.Parse()
+	os.Exit(m.Run())
+
+}
+
+// TestPutVarAbbrevGenerator checks that putvarabbrevgen.go is kept in sync
+// with the contents of functions putvar and putAbstractVar. If test flag -generate
+// is specified the file is regenerated instead.
+//
+// The block of code in putvar and putAbstractVar that picks the correct
+// abbrev is also generated automatically by this function by looking at all
+// the possible paths in their CFG and the order in which putattr is called.
+//
+// There are some restrictions on how putattr can be used in putvar and
+// putAbstractVar:
+//
+//  1. it shouldn't appear inside a for or switch statements
+//  2. it can appear within any number of nested if/else statements but the
+//     conditionals must not change after putvarAbbrev/putAbstractVarAbbrev
+//     are called
+//  3. the form argument of putattr must be a compile time constant
+//  4. each putattr call must be followed by a comment containing the name of
+//     the attribute it is setting
+//
+// TestPutVarAbbrevGenerator will fail if (1) or (4) are not respected and
+// the generated code will not compile if (3) is violated. Violating (2)
+// will result in code silently wrong code (which will usually be detected
+// by one of the tests that parse debug_info).
+func TestPutVarAbbrevGenerator(t *testing.T) {
+	spvagenfile := pvagenerate(t)
+
+	if pvaDoGenerate {
+		err := os.WriteFile(pvagenfile, []byte(spvagenfile), 0660)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return
+	}
+
+	slurp := func(name string) string {
+		out, err := os.ReadFile(name)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return string(out)
+	}
+
+	if spvagenfile != slurp(pvagenfile) {
+		t.Error(pvagenfile + " is out of date")
+	}
+
+}
+
+func pvagenerate(t *testing.T) string {
+	var fset token.FileSet
+	f, err := parser.ParseFile(&fset, "./dwarf.go", nil, parser.ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+	cm := ast.NewCommentMap(&fset, f, f.Comments)
+	abbrevs := make(map[string]int)
+	funcs := map[string]ast.Stmt{}
+	for _, decl := range f.Decls {
+		decl, ok := decl.(*ast.FuncDecl)
+		if !ok || decl.Body == nil {
+			continue
+		}
+		if decl.Name.Name == "putvar" || decl.Name.Name == "putAbstractVar" {
+			// construct the simplified CFG
+			pvagraph, _ := pvacfgbody(t, &fset, cm, decl.Body.List)
+			funcs[decl.Name.Name+"Abbrev"] = pvacfgvisit(pvagraph, abbrevs)
+		}
+	}
+	abbrevslice := make([]string, len(abbrevs))
+	for abbrev, n := range abbrevs {
+		abbrevslice[n] = abbrev
+	}
+
+	buf := new(bytes.Buffer)
+	fmt.Fprint(buf, `// Code generated by TestPutVarAbbrevGenerator. DO NOT EDIT.
+// Regenerate using go test -run TestPutVarAbbrevGenerator -generate instead.
+
+package dwarf
+
+var putvarAbbrevs = []dwAbbrev{
+`)
+
+	for _, abbrev := range abbrevslice {
+		fmt.Fprint(buf, abbrev+",\n")
+	}
+
+	fmt.Fprint(buf, "\n}\n\n")
+
+	fmt.Fprint(buf, "func putAbstractVarAbbrev(v *Var) int {\n")
+	format.Node(buf, &token.FileSet{}, funcs["putAbstractVarAbbrev"])
+	fmt.Fprint(buf, "}\n\n")
+
+	fmt.Fprint(buf, "func putvarAbbrev(v *Var, concrete, withLoclist bool) int {\n")
+	format.Node(buf, &token.FileSet{}, funcs["putvarAbbrev"])
+	fmt.Fprint(buf, "}\n")
+
+	out, err := format.Source(buf.Bytes())
+	if err != nil {
+		t.Log(string(buf.Bytes()))
+		t.Fatal(err)
+	}
+
+	return string(out)
+}
+
+type pvacfgnode struct {
+	attr, form string
+
+	cond      ast.Expr
+	then, els *pvacfgnode
+}
+
+// pvacfgbody generates a simplified CFG for a slice of statements,
+// containing only calls to putattr and the if statements affecting them.
+func pvacfgbody(t *testing.T, fset *token.FileSet, cm ast.CommentMap, body []ast.Stmt) (start, end *pvacfgnode) {
+	add := func(n *pvacfgnode) {
+		if start == nil || end == nil {
+			start = n
+			end = n
+		} else {
+			end.then = n
+			end = n
+		}
+	}
+	for _, stmt := range body {
+		switch stmt := stmt.(type) {
+		case *ast.ExprStmt:
+			if x, _ := stmt.X.(*ast.CallExpr); x != nil {
+				funstr := exprToString(x.Fun)
+				if funstr == "putattr" {
+					form, _ := x.Args[3].(*ast.Ident)
+					if form == nil {
+						t.Fatalf("%s invalid use of putattr", fset.Position(x.Pos()))
+					}
+					cmt := findLineComment(cm, stmt)
+					if cmt == nil {
+						t.Fatalf("%s invalid use of putattr (no comment containing the attribute name)", fset.Position(x.Pos()))
+					}
+					add(&pvacfgnode{attr: strings.TrimSpace(cmt.Text[2:]), form: form.Name})
+				}
+			}
+		case *ast.IfStmt:
+			ifStart, ifEnd := pvacfgif(t, fset, cm, stmt)
+			if ifStart != nil {
+				add(ifStart)
+				end = ifEnd
+			}
+		default:
+			// check that nothing under this contains a putattr call
+			ast.Inspect(stmt, func(n ast.Node) bool {
+				if call, _ := n.(*ast.CallExpr); call != nil {
+					if exprToString(call.Fun) == "putattr" {
+						t.Fatalf("%s use of putattr in unsupported block", fset.Position(call.Pos()))
+					}
+				}
+				return true
+			})
+		}
+	}
+	return start, end
+}
+
+func pvacfgif(t *testing.T, fset *token.FileSet, cm ast.CommentMap, ifstmt *ast.IfStmt) (start, end *pvacfgnode) {
+	thenStart, thenEnd := pvacfgbody(t, fset, cm, ifstmt.Body.List)
+	var elseStart, elseEnd *pvacfgnode
+	if ifstmt.Else != nil {
+		switch els := ifstmt.Else.(type) {
+		case *ast.IfStmt:
+			elseStart, elseEnd = pvacfgif(t, fset, cm, els)
+		case *ast.BlockStmt:
+			elseStart, elseEnd = pvacfgbody(t, fset, cm, els.List)
+		default:
+			t.Fatalf("%s: unexpected statement %T", fset.Position(els.Pos()), els)
+		}
+	}
+
+	if thenStart != nil && elseStart != nil && thenStart == thenEnd && elseStart == elseEnd && thenStart.form == elseStart.form && thenStart.attr == elseStart.attr {
+		return thenStart, thenEnd
+	}
+
+	if thenStart != nil || elseStart != nil {
+		start = &pvacfgnode{cond: ifstmt.Cond}
+		end = &pvacfgnode{}
+		if thenStart != nil {
+			start.then = thenStart
+			thenEnd.then = end
+		} else {
+			start.then = end
+		}
+		if elseStart != nil {
+			start.els = elseStart
+			elseEnd.then = end
+		} else {
+			start.els = end
+		}
+	}
+	return start, end
+}
+
+func exprToString(t ast.Expr) string {
+	var buf bytes.Buffer
+	printer.Fprint(&buf, token.NewFileSet(), t)
+	return buf.String()
+}
+
+// findLineComment finds the line comment for statement stmt.
+func findLineComment(cm ast.CommentMap, stmt *ast.ExprStmt) *ast.Comment {
+	var r *ast.Comment
+	for _, cmtg := range cm[stmt] {
+		for _, cmt := range cmtg.List {
+			if cmt.Slash > stmt.Pos() {
+				if r != nil {
+					return nil
+				}
+				r = cmt
+			}
+		}
+	}
+	return r
+}
+
+// pvacfgvisit visits the CFG depth first, populates abbrevs with all
+// possible dwAbbrev definitions and returns a tree of if/else statements
+// that picks the correct abbrev.
+func pvacfgvisit(pvacfg *pvacfgnode, abbrevs map[string]int) ast.Stmt {
+	r := &ast.IfStmt{Cond: &ast.BinaryExpr{
+		Op: token.EQL,
+		X:  &ast.SelectorExpr{X: &ast.Ident{Name: "v"}, Sel: &ast.Ident{Name: "Tag"}},
+		Y:  &ast.Ident{Name: "DW_TAG_variable"}}}
+	r.Body = &ast.BlockStmt{List: []ast.Stmt{
+		pvacfgvisitnode(pvacfg, "DW_TAG_variable", []*pvacfgnode{}, abbrevs),
+	}}
+	r.Else = &ast.BlockStmt{List: []ast.Stmt{
+		pvacfgvisitnode(pvacfg, "DW_TAG_formal_parameter", []*pvacfgnode{}, abbrevs),
+	}}
+	return r
+}
+
+func pvacfgvisitnode(pvacfg *pvacfgnode, tag string, path []*pvacfgnode, abbrevs map[string]int) ast.Stmt {
+	if pvacfg == nil {
+		abbrev := toabbrev(tag, path)
+		if _, ok := abbrevs[abbrev]; !ok {
+			abbrevs[abbrev] = len(abbrevs)
+		}
+		return &ast.ReturnStmt{
+			Results: []ast.Expr{&ast.BinaryExpr{
+				Op: token.ADD,
+				X:  &ast.Ident{Name: "DW_ABRV_PUTVAR_START"},
+				Y:  &ast.BasicLit{Kind: token.INT, Value: strconv.Itoa(abbrevs[abbrev])}}}}
+	}
+	if pvacfg.attr != "" {
+		return pvacfgvisitnode(pvacfg.then, tag, append(path, pvacfg), abbrevs)
+	} else if pvacfg.cond != nil {
+		if bx, _ := pvacfg.cond.(*ast.BinaryExpr); bx != nil && bx.Op == token.EQL && exprToString(bx.X) == "v.Tag" {
+			// this condition is "v.Tag == Xxx", check the value of 'tag'
+			y := exprToString(bx.Y)
+			if y == tag {
+				return pvacfgvisitnode(pvacfg.then, tag, path, abbrevs)
+			} else {
+				return pvacfgvisitnode(pvacfg.els, tag, path, abbrevs)
+			}
+		} else {
+			r := &ast.IfStmt{Cond: pvacfg.cond}
+			r.Body = &ast.BlockStmt{List: []ast.Stmt{pvacfgvisitnode(pvacfg.then, tag, path, abbrevs)}}
+			r.Else = &ast.BlockStmt{List: []ast.Stmt{pvacfgvisitnode(pvacfg.els, tag, path, abbrevs)}}
+			return r
+		}
+	} else {
+		return pvacfgvisitnode(pvacfg.then, tag, path, abbrevs)
+	}
+}
+
+func toabbrev(tag string, path []*pvacfgnode) string {
+	buf := new(bytes.Buffer)
+	fmt.Fprintf(buf, "{\n%s,\nDW_CHILDREN_no,\n[]dwAttrForm{\n", tag)
+	for _, node := range path {
+		if node.cond == nil {
+			fmt.Fprintf(buf, "{%s, %s},\n", node.attr, node.form)
+
+		}
+	}
+	fmt.Fprint(buf, "},\n}")
+	return buf.String()
+}

go/src/cmd/internal/edit/edit.go

@@ -0,0 +1,93 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package edit implements buffered position-based editing of byte slices.
+package edit
+
+import (
+	"fmt"
+	"sort"
+)
+
+// A Buffer is a queue of edits to apply to a given byte slice.
+type Buffer struct {
+	old []byte
+	q   edits
+}
+
+// An edit records a single text modification: change the bytes in [start,end) to new.
+type edit struct {
+	start int
+	end   int
+	new   string
+}
+
+// An edits is a list of edits that is sortable by start offset, breaking ties by end offset.
+type edits []edit
+
+func (x edits) Len() int      { return len(x) }
+func (x edits) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
+func (x edits) Less(i, j int) bool {
+	if x[i].start != x[j].start {
+		return x[i].start < x[j].start
+	}
+	return x[i].end < x[j].end
+}
+
+// NewBuffer returns a new buffer to accumulate changes to an initial data slice.
+// The returned buffer maintains a reference to the data, so the caller must ensure
+// the data is not modified until after the Buffer is done being used.
+func NewBuffer(data []byte) *Buffer {
+	return &Buffer{old: data}
+}
+
+func (b *Buffer) Insert(pos int, new string) {
+	if pos < 0 || pos > len(b.old) {
+		panic("invalid edit position")
+	}
+	b.q = append(b.q, edit{pos, pos, new})
+}
+
+func (b *Buffer) Delete(start, end int) {
+	if end < start || start < 0 || end > len(b.old) {
+		panic("invalid edit position")
+	}
+	b.q = append(b.q, edit{start, end, ""})
+}
+
+func (b *Buffer) Replace(start, end int, new string) {
+	if end < start || start < 0 || end > len(b.old) {
+		panic("invalid edit position")
+	}
+	b.q = append(b.q, edit{start, end, new})
+}
+
+// Bytes returns a new byte slice containing the original data
+// with the queued edits applied.
+func (b *Buffer) Bytes() []byte {
+	// Sort edits by starting position and then by ending position.
+	// Breaking ties by ending position allows insertions at point x
+	// to be applied before a replacement of the text at [x, y).
+	sort.Stable(b.q)
+
+	var new []byte
+	offset := 0
+	for i, e := range b.q {
+		if e.start < offset {
+			e0 := b.q[i-1]
+			panic(fmt.Sprintf("overlapping edits: [%d,%d)->%q, [%d,%d)->%q", e0.start, e0.end, e0.new, e.start, e.end, e.new))
+		}
+		new = append(new, b.old[offset:e.start]...)
+		offset = e.end
+		new = append(new, e.new...)
+	}
+	new = append(new, b.old[offset:]...)
+	return new
+}
+
+// String returns a string containing the original data
+// with the queued edits applied.
+func (b *Buffer) String() string {
+	return string(b.Bytes())
+}

go/src/cmd/internal/edit/edit_test.go

@@ -0,0 +1,28 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package edit
+
+import "testing"
+
+func TestEdit(t *testing.T) {
+	b := NewBuffer([]byte("0123456789"))
+	b.Insert(8, ",7½,")
+	b.Replace(9, 10, "the-end")
+	b.Insert(10, "!")
+	b.Insert(4, "3.14,")
+	b.Insert(4, "π,")
+	b.Insert(4, "3.15,")
+	b.Replace(3, 4, "three,")
+	want := "012three,3.14,π,3.15,4567,7½,8the-end!"
+
+	s := b.String()
+	if s != want {
+		t.Errorf("b.String() = %q, want %q", s, want)
+	}
+	sb := b.Bytes()
+	if string(sb) != want {
+		t.Errorf("b.Bytes() = %q, want %q", sb, want)
+	}
+}

go/src/cmd/internal/fuzztest/script_test.go

@@ -0,0 +1,22 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package fuzztest
+
+import (
+	"cmd/internal/script/scripttest"
+	"flag"
+	"internal/testenv"
+	"testing"
+)
+
+//go:generate go test cmd/internal/fuzztest -v -run=TestScript/README --fixreadme
+
+var fixReadme = flag.Bool("fixreadme", false, "if true, update README for script tests")
+
+func TestScript(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+	testenv.SkipIfShortAndSlow(t)
+	scripttest.RunToolScriptTest(t, nil, "testdata/script", *fixReadme)
+}

go/src/cmd/internal/fuzztest/testdata/script/README

@@ -0,0 +1,286 @@
+This file is generated by 'go generate'. DO NOT EDIT.
+
+This directory holds test scripts *.txt run during 'go test cmd/<toolname>'.
+To run a specific script foo.txt
+
+	go test cmd/<toolname> -run=Script/^foo$
+
+In general script files should have short names: a few words,
+ not whole sentences.
+The first word should be the general category of behavior being tested,
+often the name of a go subcommand (build, link, compile, ...) or concept (vendor, pattern).
+
+Each script is a text archive (go doc internal/txtar).
+The script begins with an actual command script to run
+followed by the content of zero or more supporting files to
+create in the script's temporary file system before it starts executing.
+
+As an example, run_hello.txt says:
+
+	# hello world
+	go run hello.go
+	stderr 'hello world'
+	! stdout .
+
+	-- hello.go --
+	package main
+	func main() { println("hello world") }
+
+Each script runs in a fresh temporary work directory tree, available to scripts as $WORK.
+Scripts also have access to other environment variables, including:
+
+	GOARCH=<target GOARCH>
+	GOOS=<target GOOS>
+	TMPDIR=$WORK/tmp
+	devnull=<value of os.DevNull>
+	goversion=<current Go version; for example, 1.12>
+
+On Plan 9, the variables $path and $home are set instead of $PATH and $HOME.
+On Windows, the variables $USERPROFILE and $TMP are set instead of
+$HOME and $TMPDIR.
+
+The lines at the top of the script are a sequence of commands to be executed by
+a small script engine configured in .../cmd/internal/script/scripttest/run.go (not the system shell).
+
+Each line of a script is parsed into a sequence of space-separated command
+words, with environment variable expansion within each word and # marking
+an end-of-line comment. Additional variables named ':' and '/' are expanded
+within script arguments (expanding to the value of os.PathListSeparator and
+os.PathSeparator respectively) but are not inherited in subprocess environments.
+
+Adding single quotes around text keeps spaces in that text from being treated
+as word separators and also disables environment variable expansion. Inside a
+single-quoted block of text, a repeated single quote indicates a literal single
+quote, as in:
+
+    'Don''t communicate by sharing memory.'
+
+A line beginning with # is a comment and conventionally explains what is being
+done or tested at the start of a new section of the script.
+
+Commands are executed one at a time, and errors are checked for each command;
+if any command fails unexpectedly, no subsequent commands in the script are
+executed. The command prefix ! indicates that the command on the rest of the
+line (typically go or a matching predicate) must fail instead of succeeding.
+The command prefix ? indicates that the command may or may not succeed, but the
+script should continue regardless.
+
+The command prefix [cond] indicates that the command on the rest of the line
+should only run when the condition is satisfied.
+
+A condition can be negated: [!root] means to run the rest of the line only if
+the user is not root. Multiple conditions may be given for a single command,
+for example, '[linux] [amd64] skip'. The command will run if all conditions are
+satisfied.
+
+When TestScript runs a script and the script fails, by default TestScript shows
+the execution of the most recent phase of the script (since the last # comment)
+and only shows the # comments for earlier phases.
+
+Note also that in reported output, the actual name of the per-script temporary directory
+has been consistently replaced with the literal string $WORK.
+
+The available commands are:
+cat files...
+	concatenate files and print to the script's stdout buffer
+
+
+cc args...
+	run the platform C compiler
+
+
+cd dir
+	change the working directory
+
+
+chmod perm paths...
+	change file mode bits
+
+	Changes the permissions of the named files or directories to
+	be equal to perm.
+	Only numerical permissions are supported.
+
+cmp [-q] file1 file2
+	compare files for differences
+
+	By convention, file1 is the actual data and file2 is the
+	expected data.
+	The command succeeds if the file contents are identical.
+	File1 can be 'stdout' or 'stderr' to compare the stdout or
+	stderr buffer from the most recent command.
+
+cmpenv [-q] file1 file2
+	compare files for differences, with environment expansion
+
+	By convention, file1 is the actual data and file2 is the
+	expected data.
+	The command succeeds if the file contents are identical
+	after substituting variables from the script environment.
+	File1 can be 'stdout' or 'stderr' to compare the script's
+	stdout or stderr buffer.
+
+cp src... dst
+	copy files to a target file or directory
+
+	src can include 'stdout' or 'stderr' to copy from the
+	script's stdout or stderr buffer.
+
+echo string...
+	display a line of text
+
+
+env [key[=value]...]
+	set or log the values of environment variables
+
+	With no arguments, print the script environment to the log.
+	Otherwise, add the listed key=value pairs to the environment
+	or print the listed keys.
+
+exec program [args...] [&]
+	run an executable program with arguments
+
+	Note that 'exec' does not terminate the script (unlike Unix
+	shells).
+
+exists [-readonly] [-exec] file...
+	check that files exist
+
+
+go [args...] [&]
+	run the 'go' program provided by the script host
+
+
+grep [-count=N] [-q] 'pattern' file
+	find lines in a file that match a pattern
+
+	The command succeeds if at least one match (or the exact
+	count, if given) is found.
+	The -q flag suppresses printing of matches.
+
+help [-v] name...
+	log help text for commands and conditions
+
+	To display help for a specific condition, enclose it in
+	brackets: 'help [amd64]'.
+	To display complete documentation when listing all commands,
+	pass the -v flag.
+
+mkdir path...
+	create directories, if they do not already exist
+
+	Unlike Unix mkdir, parent directories are always created if
+	needed.
+
+mv old new
+	rename a file or directory to a new path
+
+	OS-specific restrictions may apply when old and new are in
+	different directories.
+
+replace [old new]... file
+	replace strings in a file
+
+	The 'old' and 'new' arguments are unquoted as if in quoted
+	Go strings.
+
+rm path...
+	remove a file or directory
+
+	If the path is a directory, its contents are removed
+	recursively.
+
+skip [msg]
+	skip the current test
+
+
+sleep duration [&]
+	sleep for a specified duration
+
+	The duration must be given as a Go time.Duration string.
+
+stderr [-count=N] [-q] 'pattern' file
+	find lines in the stderr buffer that match a pattern
+
+	The command succeeds if at least one match (or the exact
+	count, if given) is found.
+	The -q flag suppresses printing of matches.
+
+stdout [-count=N] [-q] 'pattern' file
+	find lines in the stdout buffer that match a pattern
+
+	The command succeeds if at least one match (or the exact
+	count, if given) is found.
+	The -q flag suppresses printing of matches.
+
+stop [msg]
+	stop execution of the script
+
+	The message is written to the script log, but no error is
+	reported from the script engine.
+
+symlink path -> target
+	create a symlink
+
+	Creates path as a symlink to target.
+	The '->' token (like in 'ls -l' output on Unix) is required.
+
+wait 
+	wait for completion of background commands
+
+	Waits for all background commands to complete.
+	The output (and any error) from each command is printed to
+	the log in the order in which the commands were started.
+	After the call to 'wait', the script's stdout and stderr
+	buffers contain the concatenation of the background
+	commands' outputs.
+
+
+
+The available conditions are:
+[GOARCH:*]
+	runtime.GOARCH == <suffix>
+[GODEBUG:*]
+	GODEBUG contains <suffix>
+[GOEXPERIMENT:*]
+	GOEXPERIMENT <suffix> is enabled
+[GOOS:*]
+	runtime.GOOS == <suffix>
+[asan]
+	GOOS/GOARCH supports -asan
+[buildmode:*]
+	go supports -buildmode=<suffix>
+[cgo]
+	host CGO_ENABLED
+[cgolinkext]
+	platform requires external linking for cgo
+[compiler:*]
+	runtime.Compiler == <suffix>
+[cross]
+	cmd/go GOOS/GOARCH != GOHOSTOS/GOHOSTARCH
+[exec:*]
+	<suffix> names an executable in the test binary's PATH
+[fuzz]
+	GOOS/GOARCH supports -fuzz
+[fuzz-instrumented]
+	GOOS/GOARCH supports -fuzz with instrumentation
+[go-builder]
+	GO_BUILDER_NAME is non-empty
+[link]
+	testenv.HasLink()
+[msan]
+	GOOS/GOARCH supports -msan
+[mustlinkext]
+	platform always requires external linking
+[pielinkext]
+	platform requires external linking for PIE
+[race]
+	GOOS/GOARCH supports -race
+[root]
+	os.Geteuid() == 0
+[short]
+	testing.Short()
+[symlink]
+	testenv.HasSymlink()
+[verbose]
+	testing.Verbose()
+

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz.txt

@@ -0,0 +1,503 @@
+[!fuzz] skip
+[short] skip
+env GOCACHE=$WORK/cache
+
+# This test uses -vet=off to suppress vet, as vet's "tests" analyzer would
+# otherwise statically report the problems we are trying to observe dynamically.
+
+# Test that running a fuzz target that returns without failing or calling
+# f.Fuzz fails and causes a non-zero exit status.
+! go test -vet=off noop_fuzz_test.go
+! stdout ^ok
+stdout FAIL
+
+# Test that fuzzing a fuzz target that returns without failing or calling
+# f.Fuzz fails and causes a non-zero exit status.
+! go test -vet=off -fuzz=Fuzz -fuzztime=1x noop_fuzz_test.go
+! stdout ^ok
+stdout FAIL
+
+# Test that calling f.Error in a fuzz target causes a non-zero exit status.
+! go test -vet=off -fuzz=Fuzz -fuzztime=1x error_fuzz_test.go
+! stdout ^ok
+stdout FAIL
+
+# Test that calling f.Fatal in a fuzz target causes a non-zero exit status.
+! go test -vet=off fatal_fuzz_test.go
+! stdout ^ok
+stdout FAIL
+
+# Test that successful test exits cleanly.
+go test -vet=off success_fuzz_test.go
+stdout ^ok
+! stdout FAIL
+
+# Test that successful fuzzing exits cleanly.
+go test -vet=off -fuzz=Fuzz -fuzztime=1x success_fuzz_test.go
+stdout ok
+! stdout FAIL
+
+# Test that calling f.Fatal while fuzzing causes a non-zero exit status.
+! go test -vet=off -fuzz=Fuzz -fuzztime=1x fatal_fuzz_test.go
+! stdout ^ok
+stdout FAIL
+
+# Test error with seed corpus in f.Fuzz
+! go test -vet=off -run Fuzz_error -vet=off fuzz_add_test.go
+! stdout ^ok
+stdout FAIL
+stdout 'error here'
+
+[short] stop
+
+# Test that calling panic(nil) in a fuzz target causes a non-zero exit status.
+! go test -vet=off panic_fuzz_test.go
+! stdout ^ok
+stdout FAIL
+
+# Test that skipped test exits cleanly.
+go test -vet=off skipped_fuzz_test.go
+stdout ok
+! stdout FAIL
+
+# Test that f.Fatal within f.Fuzz panics
+! go test -vet=off fatal_fuzz_fn_fuzz_test.go
+! stdout ^ok
+! stdout 'fatal here'
+stdout FAIL
+stdout 'fuzz target'
+
+# Test that f.Error within f.Fuzz panics
+! go test -vet=off error_fuzz_fn_fuzz_test.go
+! stdout ^ok
+! stdout 'error here'
+stdout FAIL
+stdout 'fuzz target'
+
+# Test that f.Fail within f.Fuzz panics
+! go test -vet=off fail_fuzz_fn_fuzz_test.go
+! stdout ^ok
+stdout FAIL
+stdout 'fuzz target'
+
+# Test that f.Skip within f.Fuzz panics
+! go test -vet=off skip_fuzz_fn_fuzz_test.go
+! stdout ^ok
+! stdout 'skip here'
+stdout FAIL
+stdout 'fuzz target'
+
+# Test that f.Skipped within f.Fuzz panics
+! go test -vet=off skipped_fuzz_fn_fuzz_test.go
+! stdout ^ok
+! stdout 'f.Skipped is'
+stdout FAIL
+stdout 'fuzz target'
+stdout 't.Skipped is false'
+
+# Test that runtime.Goexit within the fuzz function is an error.
+! go test -vet=off goexit_fuzz_fn_fuzz_test.go
+! stdout ^ok
+stdout FAIL
+
+# Test that a call to f.Fatal after the Fuzz func is executed.
+! go test -vet=off fatal_after_fuzz_func_fuzz_test.go
+! stdout ok
+stdout FAIL
+
+# Test that missing *T in f.Fuzz causes a non-zero exit status.
+! go test -vet=off incomplete_fuzz_call_fuzz_test.go
+! stdout ^ok
+stdout FAIL
+
+# Test that a panic in the Cleanup func is executed.
+! go test -vet=off cleanup_fuzz_test.go
+! stdout ^ok
+stdout FAIL
+stdout 'failed some precondition'
+
+# Test success with seed corpus in f.Fuzz
+go test -vet=off -run Fuzz_pass -vet=off fuzz_add_test.go
+stdout ok
+! stdout FAIL
+! stdout 'off by one error'
+
+# Test fatal with seed corpus in f.Fuzz
+! go test -vet=off -run Fuzz_fatal -vet=off fuzz_add_test.go
+! stdout ^ok
+stdout FAIL
+stdout 'fatal here'
+
+# Test panic with seed corpus in f.Fuzz
+! go test -vet=off -run Fuzz_panic -vet=off fuzz_add_test.go
+! stdout ^ok
+stdout FAIL
+stdout 'off by one error'
+
+# Test panic(nil) with seed corpus in f.Fuzz
+! go test -vet=off -run Fuzz_nilPanic -vet=off fuzz_add_test.go
+! stdout ^ok
+stdout FAIL
+
+# Test panic with unsupported seed corpus
+! go test -vet=off -run Fuzz_unsupported -vet=off fuzz_add_test.go
+! stdout ^ok
+stdout FAIL
+
+# Test panic with different number of args to f.Add
+! go test -vet=off -run Fuzz_addDifferentNumber -vet=off fuzz_add_test.go
+! stdout ^ok
+stdout FAIL
+
+# Test panic with different type of args to f.Add
+! go test -vet=off -run Fuzz_addDifferentType -vet=off fuzz_add_test.go
+! stdout ^ok
+stdout FAIL
+
+# Test that the wrong type given with f.Add will fail.
+! go test -vet=off -run Fuzz_wrongType -vet=off fuzz_add_test.go
+! stdout ^ok
+stdout '\[string int\], want \[\[\]uint8 int8\]'
+stdout FAIL
+
+# Test fatal with testdata seed corpus
+! go test -vet=off -run Fuzz_fail corpustesting/fuzz_testdata_corpus_test.go
+! stdout ^ok
+stdout FAIL
+stdout 'fatal here'
+
+# Test pass with testdata seed corpus
+go test -vet=off -run Fuzz_pass corpustesting/fuzz_testdata_corpus_test.go
+stdout ok
+! stdout FAIL
+! stdout 'fatal here'
+
+# Test pass with testdata and f.Add seed corpus
+go test -vet=off -run Fuzz_passString corpustesting/fuzz_testdata_corpus_test.go
+stdout ok
+! stdout FAIL
+
+# Fuzzing pass with testdata and f.Add seed corpus (skip running tests first)
+go test -vet=off -run=None -fuzz=Fuzz_passString corpustesting/fuzz_testdata_corpus_test.go -fuzztime=10x
+stdout ok
+! stdout FAIL
+
+# Fuzzing pass with testdata and f.Add seed corpus
+go test -vet=off -run=Fuzz_passString -fuzz=Fuzz_passString corpustesting/fuzz_testdata_corpus_test.go -fuzztime=10x
+stdout ok
+! stdout FAIL
+
+# Test panic with malformed seed corpus
+! go test -vet=off -run Fuzz_fail corpustesting/fuzz_testdata_corpus_test.go
+! stdout ^ok
+stdout FAIL
+
+# Test pass with file in other nested testdata directory
+go test -vet=off -run Fuzz_inNestedDir corpustesting/fuzz_testdata_corpus_test.go
+stdout ok
+! stdout FAIL
+! stdout 'fatal here'
+
+# Test fails with file containing wrong type
+! go test -vet=off -run Fuzz_wrongType corpustesting/fuzz_testdata_corpus_test.go
+! stdout ^ok
+stdout FAIL
+
+-- noop_fuzz_test.go --
+package noop_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {}
+
+-- error_fuzz_test.go --
+package error_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Error("error in target")
+}
+
+-- fatal_fuzz_test.go --
+package fatal_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Fatal("fatal in target")
+}
+
+-- panic_fuzz_test.go --
+package panic_fuzz
+
+import "testing"
+
+func Fuzz_panic(f *testing.F) {
+    panic(nil)
+}
+
+-- success_fuzz_test.go --
+package success_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Fuzz(func (*testing.T, []byte) {})
+}
+
+-- skipped_fuzz_test.go --
+package skipped_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Skip()
+}
+
+-- fatal_fuzz_fn_fuzz_test.go --
+package fatal_fuzz_fn_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Add([]byte("aa"))
+    f.Fuzz(func(t *testing.T, b []byte) {
+        f.Fatal("fatal here")
+    })
+}
+
+-- error_fuzz_fn_fuzz_test.go --
+package error_fuzz_fn_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Add([]byte("aa"))
+    f.Fuzz(func(t *testing.T, b []byte) {
+        f.Error("error here")
+    })
+}
+
+-- fail_fuzz_fn_fuzz_test.go --
+package skip_fuzz_fn_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Add([]byte("aa"))
+    f.Fuzz(func(t *testing.T, b []byte) {
+        f.Fail()
+    })
+}
+
+-- skip_fuzz_fn_fuzz_test.go --
+package skip_fuzz_fn_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Add([]byte("aa"))
+    f.Fuzz(func(t *testing.T, b []byte) {
+        f.Skip("skip here")
+    })
+}
+
+-- skipped_fuzz_fn_fuzz_test.go --
+package skipped_fuzz_fn_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Add([]byte("aa"))
+    f.Fuzz(func(t *testing.T, b []byte) {
+        t.Logf("t.Skipped is %t\n", t.Skipped())
+        t.Logf("f.Skipped is %t\n", f.Skipped())
+    })
+}
+
+-- goexit_fuzz_fn_fuzz_test.go --
+package goexit_fuzz_fn_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Add([]byte("aa"))
+    f.Fuzz(func(t *testing.T, b []byte) {
+        runtime.Goexit()
+    })
+}
+
+-- fatal_after_fuzz_func_fuzz_test.go --
+package fatal_after_fuzz_func_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Fuzz(func(t *testing.T, b []byte) {
+        // no-op
+    })
+    f.Fatal("this shouldn't be called")
+}
+
+-- incomplete_fuzz_call_fuzz_test.go --
+package incomplete_fuzz_call_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Fuzz(func(b []byte) {
+        // this is missing *testing.T as the first param, so should panic
+    })
+}
+
+-- cleanup_fuzz_test.go --
+package cleanup_fuzz_test
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Cleanup(func() {
+        panic("failed some precondition")
+    })
+    f.Fuzz(func(t *testing.T, b []byte) {
+        // no-op
+    })
+}
+
+-- fuzz_add_test.go --
+package fuzz_add
+
+import "testing"
+
+func add(f *testing.F) {
+    f.Helper()
+    f.Add([]byte("123"))
+    f.Add([]byte("12345"))
+    f.Add([]byte(""))
+}
+
+func Fuzz_pass(f *testing.F) {
+    add(f)
+    f.Fuzz(func(t *testing.T, b []byte) {
+        if len(b) == -1 {
+            t.Fatal("fatal here") // will not be executed
+        }
+    })
+}
+
+func Fuzz_error(f *testing.F) {
+    add(f)
+    f.Fuzz(func(t *testing.T, b []byte) {
+        if len(b) == 3 {
+            t.Error("error here")
+        }
+    })
+}
+
+func Fuzz_fatal(f *testing.F) {
+    add(f)
+    f.Fuzz(func(t *testing.T, b []byte) {
+        if len(b) == 0 {
+            t.Fatal("fatal here")
+        }
+    })
+}
+
+func Fuzz_panic(f *testing.F) {
+    add(f)
+    f.Fuzz(func(t *testing.T, b []byte) {
+        if len(b) == 5 {
+            panic("off by one error")
+        }
+    })
+}
+
+func Fuzz_nilPanic(f *testing.F) {
+    add(f)
+    f.Fuzz(func(t *testing.T, b []byte) {
+        if len(b) == 3 {
+            panic(nil)
+        }
+    })
+}
+
+func Fuzz_unsupported(f *testing.F) {
+    m := make(map[string]bool)
+    f.Add(m)
+    f.Fuzz(func(*testing.T, []byte) {})
+}
+
+func Fuzz_addDifferentNumber(f *testing.F) {
+    f.Add([]byte("a"))
+    f.Add([]byte("a"), []byte("b"))
+    f.Fuzz(func(*testing.T, []byte) {})
+}
+
+func Fuzz_addDifferentType(f *testing.F) {
+    f.Add(false)
+    f.Add(1234)
+    f.Fuzz(func(*testing.T, []byte) {})
+}
+
+func Fuzz_wrongType(f *testing.F) {
+    f.Add("hello", 50)
+    f.Fuzz(func(*testing.T, []byte, int8) {})
+}
+
+-- corpustesting/fuzz_testdata_corpus_test.go --
+package fuzz_testdata_corpus
+
+import "testing"
+
+func fuzzFn(f *testing.F) {
+    f.Helper()
+    f.Fuzz(func(t *testing.T, b []byte) {
+        if string(b) == "12345" {
+            t.Fatal("fatal here")
+        }
+    })
+}
+
+func Fuzz_fail(f *testing.F) {
+    fuzzFn(f)
+}
+
+func Fuzz_pass(f *testing.F) {
+    fuzzFn(f)
+}
+
+func Fuzz_passString(f *testing.F) {
+    f.Add("some seed corpus")
+    f.Fuzz(func(*testing.T, string) {})
+}
+
+func Fuzz_panic(f *testing.F) {
+    f.Fuzz(func(t *testing.T, b []byte) {})
+}
+
+func Fuzz_inNestedDir(f *testing.F) {
+    f.Fuzz(func(t *testing.T, b []byte) {})
+}
+
+func Fuzz_wrongType(f *testing.F) {
+    f.Fuzz(func(t *testing.T, b []byte) {})
+}
+
+-- corpustesting/testdata/fuzz/Fuzz_fail/1 --
+go test fuzz v1
+[]byte("12345")
+-- corpustesting/testdata/fuzz/Fuzz_pass/1 --
+go test fuzz v1
+[]byte("00000")
+-- corpustesting/testdata/fuzz/Fuzz_passString/1 --
+go test fuzz v1
+string("hello")
+-- corpustesting/testdata/fuzz/Fuzz_panic/1 --
+malformed
+-- corpustesting/testdata/fuzz/Fuzz_inNestedDir/anotherdir/1 --
+go test fuzz v1
+[]byte("12345")
+-- corpustesting/testdata/fuzz/Fuzz_wrongType/1 --
+go test fuzz v1
+int("00000")

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_cache.txt

@@ -0,0 +1,97 @@
+[!fuzz-instrumented] skip
+
+[short] skip
+env GOCACHE=$WORK/cache
+
+# Fuzz cache should not exist after a regular test run.
+go test .
+exists $GOCACHE
+! exists $GOCACHE/fuzz
+
+# Fuzzing should write interesting values to the cache.
+go test -fuzz=FuzzY -fuzztime=100x .
+go run ./contains_files $GOCACHE/fuzz/example.com/y/FuzzY
+
+# 'go clean -cache' should not delete the fuzz cache.
+go clean -cache
+exists $GOCACHE/fuzz
+
+# 'go clean -fuzzcache' should delete the fuzz cache but not the build cache.
+go build -x ./empty
+stderr '(compile|gccgo)( |\.exe).*empty.go'
+go clean -fuzzcache
+! exists $GOCACHE/fuzz
+go build -x ./empty
+! stderr '(compile|gccgo)( |\.exe).*empty.go'
+
+# Fuzzing indicates that one new interesting value was found with an empty
+# corpus, and the total size of the cache is now 1.
+go clean -fuzzcache
+go test -fuzz=FuzzEmpty -fuzztime=10000x .
+stdout 'new interesting: 1'
+stdout 'total: 1'
+
+# Fuzzing again with a small fuzztime does not find any other interesting
+# values but still indicates that the cache size is 1.
+go test -fuzz=FuzzEmpty -fuzztime=2x .
+stdout 'new interesting: 0'
+stdout 'total: 1'
+
+! go clean -fuzzcache example.com/y
+stderr 'go: clean -fuzzcache cannot be used with package arguments'
+
+-- go.mod --
+module example.com/y
+
+go 1.16
+-- y_test.go --
+package y
+
+import (
+	"io"
+	"testing"
+)
+
+func FuzzEmpty(f *testing.F) {
+    f.Fuzz(func (*testing.T, []byte) {})
+}
+
+func FuzzY(f *testing.F) {
+	f.Add([]byte("y"))
+	f.Fuzz(func(t *testing.T, b []byte) { Y(io.Discard, b) })
+}
+-- y.go --
+package y
+
+import (
+	"bytes"
+	"io"
+)
+
+func Y(w io.Writer, b []byte) {
+	if !bytes.Equal(b, []byte("y")) {
+		w.Write([]byte("not equal"))
+	}
+}
+-- empty/empty.go --
+package empty
+-- contains_files/contains_files.go --
+package main
+
+import (
+	"fmt"
+	"path/filepath"
+	"io/ioutil"
+	"os"
+)
+
+func main() {
+	infos, err := ioutil.ReadDir(filepath.Clean(os.Args[1]))
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	if len(infos) == 0 {
+		os.Exit(1)
+	}
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_cgo.txt

@@ -0,0 +1,28 @@
+[!fuzz] skip
+[!cgo] skip
+[short] skip
+env GOCACHE=$WORK/cache
+
+# Test that fuzzing works with cgo (issue 65169)
+
+go test -fuzz=. -fuzztime=1x
+stdout ok
+! stdout FAIL
+
+-- go.mod --
+module example.com/p
+
+go 1.20
+-- c.go --
+package p
+
+import "C"
+-- c_test.go --
+package p
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+	f.Add(0)
+	f.Fuzz(func(t *testing.T, x int) {})
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_chatty.txt

@@ -0,0 +1,103 @@
+[!fuzz] skip
+[short] skip
+env GOCACHE=$WORK/cache
+
+# Run chatty fuzz targets with an error.
+! go test -v chatty_error_fuzz_test.go
+! stdout '^ok'
+stdout 'FAIL'
+stdout 'error in target'
+
+# Run chatty fuzz targets with a fatal.
+! go test -v chatty_fatal_fuzz_test.go
+! stdout '^ok'
+stdout 'FAIL'
+stdout 'fatal in target'
+
+# Run chatty fuzz target with a panic
+! go test -v chatty_panic_fuzz_test.go
+! stdout ^ok
+stdout FAIL
+stdout 'this is bad'
+
+# Run skipped chatty fuzz targets.
+go test -v chatty_skipped_fuzz_test.go
+stdout ok
+stdout SKIP
+! stdout FAIL
+
+# Run successful chatty fuzz targets.
+go test -v chatty_fuzz_test.go
+stdout ok
+stdout PASS
+stdout 'all good here'
+! stdout FAIL
+
+# Fuzz successful chatty fuzz target that includes a separate unit test.
+go test -v chatty_with_test_fuzz_test.go -fuzz=Fuzz -fuzztime=1x
+stdout ok
+stdout PASS
+! stdout FAIL
+stdout -count=1 'all good here'
+# Verify that the unit test is only run once.
+stdout -count=1 'logged foo'
+
+-- chatty_error_fuzz_test.go --
+package chatty_error_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Error("error in target")
+}
+
+-- chatty_fatal_fuzz_test.go --
+package chatty_fatal_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Fatal("fatal in target")
+}
+
+-- chatty_panic_fuzz_test.go --
+package chatty_panic_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    panic("this is bad")
+}
+
+-- chatty_skipped_fuzz_test.go --
+package chatty_skipped_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Skip()
+}
+
+-- chatty_fuzz_test.go --
+package chatty_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+    f.Log("all good here")
+    f.Fuzz(func(*testing.T, []byte) {})
+}
+
+-- chatty_with_test_fuzz_test.go --
+package chatty_with_test_fuzz
+
+import "testing"
+
+func TestFoo(t *testing.T) {
+    t.Log("logged foo")
+}
+
+func Fuzz(f *testing.F) {
+    f.Log("all good here")
+    f.Fuzz(func(*testing.T, []byte) {})
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_cleanup.txt

@@ -0,0 +1,67 @@
+[!fuzz] skip
+[short] skip
+env GOCACHE=$WORK/cache
+
+# Cleanup should run after F.Skip.
+go test -run=FuzzTargetSkip
+stdout cleanup
+
+# Cleanup should run after F.Fatal.
+! go test -run=FuzzTargetFatal
+stdout cleanup
+
+# Cleanup should run after an unexpected runtime.Goexit.
+! go test -run=FuzzTargetGoexit
+stdout cleanup
+
+# Cleanup should run after panic.
+! go test -run=FuzzTargetPanic
+stdout cleanup
+
+# Cleanup should run in fuzz function on seed corpus.
+go test -v -run=FuzzFunction
+stdout '(?s)inner.*outer'
+
+# TODO(jayconrod): test cleanup while fuzzing. For now, the worker process's
+# stdout and stderr is connected to the coordinator's, but it should eventually
+# be connected to os.DevNull, so we wouldn't see t.Log output.
+
+-- go.mod --
+module cleanup
+
+go 1.15
+-- cleanup_test.go --
+package cleanup
+
+import (
+	"runtime"
+	"testing"
+)
+
+func FuzzTargetSkip(f *testing.F) {
+	f.Cleanup(func() { f.Log("cleanup") })
+	f.Skip()
+}
+
+func FuzzTargetFatal(f *testing.F) {
+	f.Cleanup(func() { f.Log("cleanup") })
+	f.Fatal()
+}
+
+func FuzzTargetGoexit(f *testing.F) {
+	f.Cleanup(func() { f.Log("cleanup") })
+	runtime.Goexit()
+}
+
+func FuzzTargetPanic(f *testing.F) {
+	f.Cleanup(func() { f.Log("cleanup") })
+	panic("oh no")
+}
+
+func FuzzFunction(f *testing.F) {
+	f.Add([]byte{0})
+	f.Cleanup(func() { f.Log("outer") })
+	f.Fuzz(func(t *testing.T, b []byte) {
+		t.Cleanup(func() { t.Logf("inner") })
+	})
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_context.txt

@@ -0,0 +1,47 @@
+[!fuzz] skip
+[short] skip
+env GOCACHE=$WORK/cache
+
+# Test fuzz.Context.
+go test -vet=off context_fuzz_test.go
+stdout ^ok
+! stdout FAIL
+
+go test -vet=off -fuzz=Fuzz -fuzztime=1x context_fuzz_test.go
+stdout ok
+! stdout FAIL
+
+-- context_fuzz_test.go --
+package context_fuzz
+
+import (
+	"context"
+	"errors"
+	"testing"
+)
+
+func Fuzz(f *testing.F) {
+	ctx := f.Context()
+	if err := ctx.Err(); err != nil {
+		f.Fatalf("expected non-canceled context, got %v", err)
+	}
+
+	f.Fuzz(func(t *testing.T, data []byte) {
+		innerCtx := t.Context()
+		if err := innerCtx.Err(); err != nil {
+			t.Fatalf("expected inner test to not inherit canceled context, got %v", err)
+		}
+
+		t.Cleanup(func() {
+			if !errors.Is(innerCtx.Err(), context.Canceled) {
+				t.Fatal("expected context of inner test to be canceled after its fuzz function finished")
+			}
+		})
+	})
+
+	f.Cleanup(func() {
+		if !errors.Is(ctx.Err(), context.Canceled) {
+			f.Fatal("expected context canceled before cleanup")
+		}
+	})
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_cov.txt

@@ -0,0 +1,36 @@
+# Test that coverage instrumentation is working. Without the instrumentation
+# it is _extremely_ unlikely that the fuzzer would produce this particular
+# input in any reasonable amount of time.
+
+[short] skip
+[!fuzz-instrumented] skip
+env GOCACHE=$WORK/cache
+
+# TODO(#51484): enabled debugging info to help diagnose a deadlock in the fuzzer
+env GODEBUG=fuzzdebug=1
+! go test -fuzz=FuzzCov -v
+! stderr 'cov instrumentation working'
+
+-- go.mod --
+module test
+
+-- cov_test.go --
+package cov
+
+import "testing"
+
+func FuzzCov(f *testing.F) {
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if len(b) == 8 &&
+			b[0] == 'h' &&
+			b[1] == 'e' &&
+			b[2] == 'l' &&
+			b[3] == 'l' &&
+			b[4] == 'o' &&
+			b[5] == ' ' &&
+			b[6] == ':' &&
+			b[7] == ')' {
+			panic("cov instrumentation working")
+		}
+	})
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_deadline.txt

@@ -0,0 +1,46 @@
+[!fuzz] skip
+[short] skip
+env GOCACHE=$WORK/cache
+
+# Warm up the build cache with GOMAXPROCS unrestricted.
+go test -c -o $devnull
+
+# For the fuzzing phase, we reduce GOMAXPROCS to avoid consuming too many
+# resources during the test. Ideally this would just free up resources to run
+# other parallel tests more quickly, but unfortunately it is actually necessary
+# in some 32-bit environments to prevent the fuzzing engine from running out of
+# address space (see https://go.dev/issue/65434).
+env GOMAXPROCS=2
+
+# The fuzz function should be able to detect whether -timeout
+# was set with T.Deadline. Note there is no F.Deadline, and
+# there is no timeout while fuzzing, even if -fuzztime is set.
+go test -run=FuzzDeadline -wantdeadline=true # -timeout defaults to 10m
+go test -run=FuzzDeadline -timeout=0 -wantdeadline=false
+! go test -run=FuzzDeadline -timeout=1s -wantdeadline=false
+go test -run=FuzzDeadline -timeout=1s -wantdeadline=true
+go test -fuzz=FuzzDeadline -timeout=0 -fuzztime=1s -wantdeadline=false
+go test -fuzz=FuzzDeadline -timeout=0 -fuzztime=100x -wantdeadline=false
+
+-- go.mod --
+module fuzz
+
+go 1.16
+-- fuzz_deadline_test.go --
+package fuzz_test
+
+import (
+	"flag"
+	"testing"
+)
+
+var wantDeadline = flag.Bool("wantdeadline", false, "whether the test should have a deadline")
+
+func FuzzDeadline(f *testing.F) {
+	f.Add("run once")
+	f.Fuzz(func (t *testing.T, _ string) {
+		if _, hasDeadline := t.Deadline(); hasDeadline != *wantDeadline {
+			t.Fatalf("function got %v; want %v", hasDeadline, *wantDeadline)
+		}
+	})
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_dup_cache.txt

@@ -0,0 +1,53 @@
+[!fuzz] skip
+[short] skip
+env GOCACHE=$WORK/cache
+
+# This test checks that cached corpus loading properly handles duplicate entries (this can
+# happen when a f.Add value has a duplicate entry in the cached corpus.) Duplicate entries
+# should be discarded, and the rest of the cache should be loaded as normal.
+
+env GOCACHE=$WORK/cache
+env GODEBUG=fuzzdebug=1
+
+mkdir -p $GOCACHE/fuzz/fuzztest/FuzzTarget
+go run ./populate $GOCACHE/fuzz/fuzztest/FuzzTarget
+
+go test -fuzz=FuzzTarget -fuzztime=10x .
+stdout 'entries: 5'
+
+-- go.mod --
+module fuzztest
+
+go 1.17
+
+-- fuzz_test.go --
+package fuzz
+
+import "testing"
+
+func FuzzTarget(f *testing.F) {
+    f.Add(int(0))
+    f.Fuzz(func(t *testing.T, _ int) {})
+}
+
+-- populate/main.go --
+package main
+
+import (
+    "path/filepath"
+	"fmt"
+	"os"
+)
+
+func main() {
+	for i := 0; i < 10; i++ {
+		b := byte(0)
+		if i > 5 {
+			b = byte(i)
+		}
+        tmpl := "go test fuzz v1\nint(%d)\n"
+		if err := os.WriteFile(filepath.Join(os.Args[1], fmt.Sprint(i)), []byte(fmt.Sprintf(tmpl, b)), 0777); err != nil {
+			panic(err)
+		}
+	}
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_err_deadlock.txt

@@ -0,0 +1,50 @@
+[short] skip
+[!fuzz-instrumented] skip
+
+env GOCACHE=$WORK/cache
+! go test -fuzz=FuzzDead -v
+# This is a somewhat inexact check, but since we don't prefix the error with anything
+# and as the error suffix is platform dependent, this is the best we can do. In the
+# deadlock failure case, the test will just deadlock and timeout anyway, so it should
+# be clear that that failure mode is different.
+stdout 'open'
+
+-- go.mod --
+module test
+
+-- cov_test.go --
+package dead
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func FuzzDead(f *testing.F) {
+	go func() {
+		c := filepath.Join(os.Getenv("GOCACHE"), "fuzz", "test", "FuzzDead")
+		t := time.NewTicker(time.Second)
+		for range t.C {
+			files, _ := os.ReadDir(c)
+			if len(files) > 0 {
+				os.RemoveAll(c)
+			}
+		}
+	}()
+
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if len(b) == 8 &&
+			b[0] == 'h' &&
+			b[1] == 'e' &&
+			b[2] == 'l' &&
+			b[3] == 'l' &&
+			b[4] == 'o' &&
+			b[5] == ' ' &&
+			b[6] == ':' &&
+			b[7] == ')' {
+			return
+		}
+	})
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_fuzztime.txt

@@ -0,0 +1,129 @@
+skip # a 5s timeout is never going to be reliable (go.dev/issue/72140)
+
+[!fuzz] skip
+[short] skip
+env GOCACHE=$WORK/cache
+
+# There are no seed values, so 'go test' should finish quickly.
+go test
+
+# For the fuzzing phase, we reduce GOMAXPROCS to avoid consuming too many
+# resources during the test. Ideally this would just free up resources to run
+# other parallel tests more quickly, but unfortunately it is actually necessary
+# in some 32-bit environments to prevent the fuzzing engine from running out of
+# address space (see https://go.dev/issue/65434).
+env GOMAXPROCS=2
+
+# Fuzzing should exit 0 after fuzztime, even if timeout is short.
+go test -timeout=3s -fuzz=FuzzFast -fuzztime=5s
+
+# We should see the same behavior when invoking the test binary directly.
+go test -c
+exec ./fuzz.test$GOEXE -test.timeout=3s -test.fuzz=FuzzFast -test.fuzztime=5s -test.parallel=1 -test.fuzzcachedir=$WORK/cache
+
+# Timeout should not cause inputs to be written as crashers.
+! exists testdata/fuzz
+
+# When we use fuzztime with an "x" suffix, it runs a specific number of times.
+# This fuzz function creates a file with a unique name ($pid.$count) on each
+# run. We count the files to find the number of runs.
+mkdir count
+go test -fuzz=FuzzTestCount -fuzztime=1000x -fuzzminimizetime=1x
+go run check_file_count.go count 1000
+
+# When we use fuzzminimizetime with an "x" suffix, it runs a specific number of
+# times while minimizing. This fuzz function creates a file with a unique name
+# ($pid.$count) on each run once the first crash has been found. That means that
+# there should be one file for each execution of the fuzz function during
+# minimization, so we count these to determine how many times minimization was
+# run.
+mkdir minimizecount
+! go test -fuzz=FuzzMinimizeCount -fuzzminimizetime=3x -parallel=1
+go run check_file_count.go minimizecount 3
+
+-- go.mod --
+module fuzz
+
+go 1.16
+-- fuzz_fast_test.go --
+package fuzz_test
+
+import "testing"
+
+func FuzzFast(f *testing.F) {
+	f.Fuzz(func (*testing.T, []byte) {})
+}
+-- fuzz_count_test.go --
+package fuzz
+
+import (
+	"fmt"
+	"os"
+	"testing"
+)
+
+func FuzzTestCount(f *testing.F) {
+	pid := os.Getpid()
+	n := 0
+	f.Fuzz(func(t *testing.T, _ []byte) {
+		name := fmt.Sprintf("count/%v.%d", pid, n)
+		if err := os.WriteFile(name, nil, 0666); err != nil {
+			t.Fatal(err)
+		}
+		n++
+	})
+}
+-- fuzz_minimize_count_test.go --
+package fuzz
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"testing"
+)
+
+func FuzzMinimizeCount(f *testing.F) {
+	pid := os.Getpid()
+	n := 0
+	seed := bytes.Repeat([]byte("a"), 357)
+	f.Add(seed)
+	crashFound := false
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if crashFound {
+			name := fmt.Sprintf("minimizecount/%v.%d", pid, n)
+			if err := os.WriteFile(name, nil, 0666); err != nil {
+				t.Fatal(err)
+			}
+			n++
+		}
+		if !bytes.Equal(b, seed) {  // this should happen right away
+			crashFound = true
+			t.Error("minimize this!")
+		}
+	})
+}
+-- check_file_count.go --
+// +build ignore
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+)
+
+func main() {
+	dir, err := os.ReadDir(os.Args[1])
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	got := len(dir)
+	want, _ := strconv.Atoi(os.Args[2])
+	if got != want {
+		fmt.Fprintf(os.Stderr, "got %d files; want %d\n", got, want)
+		os.Exit(1)
+	}
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_io_error.txt

@@ -0,0 +1,102 @@
+# Test that when the coordinator experiences an I/O error communicating
+# with a worker, the coordinator stops the worker and reports the error.
+# The coordinator should not record a crasher.
+#
+# We simulate an I/O error in the test by writing garbage to fuzz_out.
+# This is unlikely, but possible. It's difficult to simulate interruptions
+# due to ^C and EOF errors which are more common. We don't report those.
+[short] skip
+[!fuzz] skip
+env GOCACHE=$WORK/cache
+
+# If the I/O error occurs before F.Fuzz is called, the coordinator should
+# stop the worker and say that.
+! go test -fuzz=FuzzClosePipeBefore -parallel=1
+stdout '\s*fuzzing process terminated without fuzzing:'
+! stdout 'communicating with fuzzing process'
+! exists testdata
+
+# If the I/O error occurs after F.Fuzz is called (unlikely), just exit.
+# It's hard to distinguish this case from the worker being interrupted by ^C
+# or exiting with status 0 (which it should do when interrupted by ^C).
+! go test -fuzz=FuzzClosePipeAfter -parallel=1
+stdout '^\s*communicating with fuzzing process: invalid character ''!'' looking for beginning of value$'
+! exists testdata
+
+-- go.mod --
+module test
+
+go 1.17
+-- io_error_test.go --
+package io_error
+
+import (
+	"flag"
+	"testing"
+	"time"
+)
+
+func isWorker() bool {
+	f := flag.Lookup("test.fuzzworker")
+	if f == nil {
+		return false
+	}
+	get, ok := f.Value.(flag.Getter)
+	if !ok {
+		return false
+	}
+	return get.Get() == interface{}(true)
+}
+
+func FuzzClosePipeBefore(f *testing.F) {
+	if isWorker() {
+		sendGarbageToCoordinator(f)
+		time.Sleep(3600 * time.Second) // pause until coordinator terminates the process
+	}
+	f.Fuzz(func(*testing.T, []byte) {})
+}
+
+func FuzzClosePipeAfter(f *testing.F) {
+	f.Fuzz(func(t *testing.T, _ []byte) {
+		if isWorker() {
+			sendGarbageToCoordinator(t)
+			time.Sleep(3600 * time.Second) // pause until coordinator terminates the process
+		}
+	})
+}
+-- io_error_windows_test.go --
+package io_error
+
+import (
+	"fmt"
+	"os"
+	"testing"
+)
+
+func sendGarbageToCoordinator(tb testing.TB) {
+	v := os.Getenv("GO_TEST_FUZZ_WORKER_HANDLES")
+	var fuzzInFD, fuzzOutFD uintptr
+	if _, err := fmt.Sscanf(v, "%x,%x", &fuzzInFD, &fuzzOutFD); err != nil {
+		tb.Fatalf("parsing GO_TEST_FUZZ_WORKER_HANDLES: %v", err)
+	}
+	f := os.NewFile(fuzzOutFD, "fuzz_out")
+	if _, err := f.Write([]byte("!!")); err != nil {
+		tb.Fatalf("writing fuzz_out: %v", err)
+	}
+}
+-- io_error_notwindows_test.go --
+// +build !windows
+
+package io_error
+
+import (
+	"os"
+	"testing"
+)
+
+func sendGarbageToCoordinator(tb testing.TB) {
+	f := os.NewFile(4, "fuzz_out")
+	if _, err := f.Write([]byte("!!")); err != nil {
+		tb.Fatalf("writing fuzz_out: %v", err)
+	}
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_limit_dup_entry.txt

@@ -0,0 +1,37 @@
+[!fuzz] skip
+[short] skip
+env GOCACHE=$WORK/cache
+
+# FuzzA attempts to cause the mutator to create duplicate inputs that generate
+# new coverage. Previously this would trigger a corner case when the fuzzer
+# had an execution limit, causing it to deadlock and sit in the coordinator
+# loop indefinitely, failing to exit once the limit had been exhausted.
+
+go test -fuzz=FuzzA -fuzztime=100x -parallel=1
+
+-- go.mod --
+module m
+
+go 1.16
+-- fuzz_test.go --
+package fuzz_test
+
+import (
+	"fmt"
+	"testing"
+)
+
+func FuzzA(f *testing.F) {
+	f.Add([]byte("seed"))
+	i := 0
+	f.Fuzz(func(t *testing.T, b []byte) {
+		i++
+		if string(b) == "seed" {
+			if i == 0 {
+				fmt.Println("a")
+			} else if i > 1 {
+				fmt.Println("b")
+			}
+		}
+	})
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_match.txt

@@ -0,0 +1,40 @@
+[!fuzz] skip
+[short] skip
+env GOCACHE=$WORK/cache
+
+# Matches only fuzz targets to test.
+go test standalone_fuzz_test.go
+! stdout '^ok.*\[no tests to run\]'
+stdout '^ok'
+
+# Matches only for fuzzing.
+go test -fuzz Fuzz -fuzztime 1x standalone_fuzz_test.go
+! stdout '^ok.*\[no tests to run\]'
+stdout '^ok'
+
+# Matches none for fuzzing but will run the fuzz target as a test.
+go test -fuzz ThisWillNotMatch -fuzztime 1x standalone_fuzz_test.go
+! stdout '^ok.*no tests to run'
+stdout '^ok'
+stdout 'no fuzz tests to fuzz'
+
+[short] stop
+
+# Matches only fuzz targets to test with -run.
+go test -run Fuzz standalone_fuzz_test.go
+! stdout '^ok.*\[no tests to run\]'
+stdout '^ok'
+
+# Matches no fuzz targets.
+go test -run ThisWillNotMatch standalone_fuzz_test.go
+stdout '^ok.*no tests to run'
+! stdout 'no fuzz tests to fuzz'
+
+-- standalone_fuzz_test.go --
+package standalone_fuzz
+
+import "testing"
+
+func Fuzz(f *testing.F) {
+	f.Fuzz(func (*testing.T, []byte) {})
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_minimize.txt

@@ -0,0 +1,203 @@
+[!fuzz] skip
+[short] skip
+
+# We clean the fuzz cache during this test. Don't clean the user's cache.
+env GOCACHE=$WORK/gocache
+
+# Test that fuzzminimizetime cannot be negative seconds
+! go test -fuzz=FuzzMinimizerRecoverable -run=FuzzMinimizerRecoverable -fuzztime=10000x -fuzzminimizetime=-1ms .
+! stdout '^ok'
+! stdout 'contains a non-zero byte'
+stdout 'invalid duration'
+stdout FAIL
+
+# Test that fuzzminimizetime cannot be negative times
+! go test -fuzz=FuzzMinimizerRecoverable -run=FuzzMinimizerRecoverable -fuzztime=10000x -fuzzminimizetime=-1x .
+! stdout '^ok'
+! stdout 'contains a non-zero byte'
+stdout 'invalid count'
+stdout FAIL
+
+# Test that fuzzminimizetime can be zero seconds, and minimization is disabled
+! go test -fuzz=FuzzMinimizeZeroDurationSet -run=FuzzMinimizeZeroDurationSet -fuzztime=10000x -fuzzminimizetime=0s .
+! stdout '^ok'
+! stdout 'minimizing'
+stdout 'there was an Error'
+stdout FAIL
+
+# Test that fuzzminimizetime can be zero times, and minimization is disabled
+! go test -fuzz=FuzzMinimizeZeroLimitSet -run=FuzzMinimizeZeroLimitSet -fuzztime=10000x -fuzzminimizetime=0x .
+! stdout '^ok'
+! stdout 'minimizing'
+stdout -count=1 'there was an Error'
+stdout FAIL
+
+# Test that minimization is working for recoverable errors.
+! go test -fuzz=FuzzMinimizerRecoverable -run=FuzzMinimizerRecoverable -fuzztime=10000x .
+! stdout '^ok'
+stdout 'got the minimum size!'
+# The error message that was printed should be for the one written to testdata.
+stdout 'contains a non-zero byte of length 50'
+stdout FAIL
+
+# Check that the bytes written to testdata are of length 50 (the minimum size)
+go run ./check_testdata FuzzMinimizerRecoverable 50
+
+# Test that re-running the minimized value causes a crash.
+! go test -run=FuzzMinimizerRecoverable .
+rm testdata
+
+# Test that minimization is working for recoverable errors. Run it with -v this
+# time to ensure the command line output still looks right.
+! go test -v -fuzz=FuzzMinimizerRecoverable -run=FuzzMinimizerRecoverable -fuzztime=10000x .
+! stdout '^ok'
+stdout 'got the minimum size!'
+# The error message that was printed should be for the one written to testdata.
+stdout 'contains a non-zero byte of length 50'
+stdout FAIL
+
+# Check that the bytes written to testdata are of length 50 (the minimum size)
+go run ./check_testdata FuzzMinimizerRecoverable 50
+
+# Test that re-running the minimized value causes a crash.
+! go test -run=FuzzMinimizerRecoverable .
+rm testdata
+
+# Test that minimization doesn't run for non-recoverable errors.
+! go test -fuzz=FuzzMinimizerNonrecoverable -run=FuzzMinimizerNonrecoverable -fuzztime=10000x .
+! stdout '^ok'
+! stdout 'minimizing'
+stdout -count=1 '^\s+fuzzing process hung or terminated unexpectedly: exit status 99'
+stdout FAIL
+
+# Check that re-running the value causes a crash.
+! go test -run=FuzzMinimizerNonrecoverable .
+rm testdata
+
+# Clear the fuzzing cache. There may already be minimized inputs that would
+# interfere with the next stage of the test.
+go clean -fuzzcache
+
+# Test that minimization can be cancelled by fuzzminimizetime and the latest
+# crash will still be logged and written to testdata.
+! go test -fuzz=FuzzMinimizerRecoverable -run=FuzzMinimizerRecoverable -fuzztime=100x -fuzzminimizetime=1x .
+! stdout '^ok'
+stdout 'testdata[/\\]fuzz[/\\]FuzzMinimizerRecoverable[/\\]'
+! stdout 'got the minimum size!'  # it shouldn't have had enough time to minimize it
+stdout FAIL
+
+# Test that re-running the unminimized value causes a crash.
+! go test -run=FuzzMinimizerRecoverable .
+
+# TODO(jayconrod,katiehockman): add a test which verifies that the right bytes
+# are written to testdata in the case of an interrupt during minimization.
+
+-- go.mod --
+module example.com/y
+
+go 1.16
+-- y_test.go --
+package y
+
+import (
+	"os"
+	"testing"
+)
+
+func FuzzMinimizeZeroDurationSet(f *testing.F) {
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if len(b) > 5 {
+			t.Errorf("there was an Error")
+		}
+	})
+}
+
+func FuzzMinimizeZeroLimitSet(f *testing.F) {
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if len(b) > 5 {
+			t.Errorf("there was an Error")
+		}
+	})
+}
+
+func FuzzMinimizerRecoverable(f *testing.F) {
+	f.Add(make([]byte, 100))
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if len(b) < 50 {
+			// Make sure that b is large enough that it can be minimized
+			return
+		}
+		// Given the randomness of the mutations, this should allow the
+		// minimizer to trim down the value a bit.
+		for _, n := range b {
+			if n != 0 {
+				if len(b) == 50 {
+					t.Log("got the minimum size!")
+				}
+				t.Fatalf("contains a non-zero byte of length %d", len(b))
+			}
+		}
+	})
+}
+
+func FuzzMinimizerNonrecoverable(f *testing.F) {
+	f.Fuzz(func(t *testing.T, b []byte) {
+		os.Exit(99)
+	})
+}
+-- empty/empty.go --
+package empty
+-- check_testdata/check_testdata.go --
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strconv"
+)
+
+func main() {
+	target := os.Args[1]
+	numBytes, err := strconv.Atoi(os.Args[2])
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+
+	// Open the file in testdata (there should only be one)
+	dir := fmt.Sprintf("testdata/fuzz/%s", target)
+	files, err := ioutil.ReadDir(dir)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	if len(files) != 1 {
+		fmt.Fprintf(os.Stderr, "expected one file, got %d", len(files))
+		os.Exit(1)
+	}
+	got, err := ioutil.ReadFile(filepath.Join(dir, files[0].Name()))
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+
+	// Trim the newline at the end of the file
+	got = bytes.TrimSpace(got)
+
+	// Make sure that there were exactly 100 bytes written to the corpus entry
+	prefix := []byte("[]byte(")
+	i := bytes.Index(got, prefix)
+	gotBytes := got[i+len(prefix) : len(got)-1]
+	s, err := strconv.Unquote(string(gotBytes))
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	if want, got := numBytes, len(s); want != got {
+		fmt.Fprintf(os.Stderr, "want %d bytes, got %d\n", want, got)
+		os.Exit(1)
+	}
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_minimize_dirty_cov.txt

@@ -0,0 +1,85 @@
+# Test that minimization doesn't use dirty coverage snapshots when it
+# is unable to actually minimize the input. We do this by checking that
+# an expected value appears in the cache. If a dirty coverage map is used
+# (i.e. the coverage map generated during the last minimization step,
+# rather than the map provided with the initial input) then this value
+# is unlikely to appear in the cache, since the map generated during
+# the last minimization step should not increase the coverage.
+
+[short] skip
+[!fuzz-instrumented] skip
+
+env GOCACHE=$WORK/gocache
+go test -fuzz=FuzzCovMin -fuzztime=500000x -test.fuzzcachedir=$GOCACHE/fuzz
+go run check_file/main.go $GOCACHE/fuzz/FuzzCovMin ab
+
+-- go.mod --
+module test
+
+-- covmin_test.go --
+package covmin
+
+import "testing"
+
+func FuzzCovMin(f *testing.F) {
+	f.Add([]byte("aa"))
+	f.Fuzz(func(t *testing.T, data []byte) {
+		if len(data) == 2 && data[0] == 'a' && data[1] == 'b' {
+			return
+		}
+	})
+}
+
+-- check_file/main.go --
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strconv"
+)
+
+func checkFile(name, expected string) (bool, error) {
+	data, err := os.ReadFile(name)
+	if err != nil {
+		return false, err
+	}
+	for _, line := range bytes.Split(data, []byte("\n")) {
+		m := valRe.FindSubmatch(line)
+		if m == nil {
+			continue
+		}
+		fmt.Println(strconv.Unquote(string(m[1])))
+		if s, err := strconv.Unquote(string(m[1])); err != nil {
+			return false, err
+		} else if s == expected {
+			return true, nil
+		}
+	}
+	return false, nil
+}
+
+var valRe = regexp.MustCompile(`^\[\]byte\(([^)]+)\)$`)
+
+func main() {
+	dir, expected := os.Args[1], os.Args[2]
+	ents, err := os.ReadDir(dir)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	for _, ent := range ents {
+		name := filepath.Join(dir, ent.Name())
+		if good, err := checkFile(name, expected); err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		} else if good {
+			os.Exit(0)
+		}
+	}
+	fmt.Fprintln(os.Stderr, "input over minimized")
+	os.Exit(1)
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_minimize_interesting.txt

@@ -0,0 +1,230 @@
+[short] skip
+[!fuzz-instrumented] skip
+
+# Test that when an interesting value is discovered (one that expands coverage),
+# the fuzzing engine minimizes it before writing it to the cache.
+#
+# The program below starts with a seed value of length 100, but more coverage
+# will be found for any value other than the seed. We should end with a value
+# in the cache of length 1 (the minimizer currently does not produce empty
+# strings). check_cache.go confirms that.
+#
+# We would like to verify that ALL values in the cache were minimized to a
+# length of 1, but this isn't always possible when new coverage is found in
+# functions called by testing or internal/fuzz in the background.
+
+go test -c -fuzz=.  # Build using shared build cache for speed.
+env GOCACHE=$WORK/gocache
+exec ./fuzz.test$GOEXE -test.fuzzcachedir=$GOCACHE/fuzz -test.fuzz=FuzzMinCache -test.fuzztime=1000x
+go run check_cache/check_cache.go $GOCACHE/fuzz/FuzzMinCache
+
+# Test that minimization occurs for a crash that appears while minimizing a
+# newly found interesting input. There must be only one worker for this test to
+# be flaky like we want.
+! exec ./fuzz.test$GOEXE -test.fuzzcachedir=$GOCACHE/fuzz -test.fuzz=FuzzMinimizerCrashInMinimization -test.run=^$ -test.fuzztime=10000x -test.parallel=1
+! stdout '^ok'
+stdout -count=1 'got the minimum size!'
+stdout -count=1 'bad input'
+stdout FAIL
+# Check that the input written to testdata will reproduce the error, and is the
+# smallest possible.
+go run check_testdata/check_testdata.go FuzzMinimizerCrashInMinimization 1
+
+# Test that a nonrecoverable error that occurs while minimizing an interesting
+# input is reported correctly.
+! exec ./fuzz.test$GOEXE -test.fuzzcachedir=$GOCACHE/fuzz -test.fuzz=FuzzMinimizerNonrecoverableCrashInMinimization -test.run=^$ -test.fuzztime=10000x -test.parallel=1
+! stdout '^ok'
+stdout -count=1 'fuzzing process hung or terminated unexpectedly while minimizing'
+stdout -count=1 'EOF'
+stdout FAIL
+# Check that the input written to testdata will reproduce the error.
+go run check_testdata/check_testdata.go FuzzMinimizerNonrecoverableCrashInMinimization 1
+
+-- go.mod --
+module fuzz
+
+go 1.17
+-- y.go --
+package fuzz
+
+import (
+	"bytes"
+	"io"
+)
+
+func Y(w io.Writer, s string) {
+	if !bytes.Equal([]byte(s), []byte("y")) {
+		w.Write([]byte("not equal"))
+	}
+}
+-- fuzz_test.go --
+package fuzz
+
+import (
+	"bytes"
+	"os"
+	"testing"
+)
+
+func FuzzMinimizerCrashInMinimization(f *testing.F) {
+	seed := bytes.Repeat([]byte{255}, 100)
+	f.Add(seed)
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if bytes.Equal(seed, b) {
+			return
+		}
+		t.Error("bad input")
+		if len(b) == 1 {
+			t.Error("got the minimum size!")
+		}
+	})
+}
+
+var fuzzing bool
+
+func FuzzMinimizerNonrecoverableCrashInMinimization(f *testing.F) {
+	seed := bytes.Repeat([]byte{255}, 100)
+	f.Add(seed)
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if bytes.Equal(seed, b) {
+			return
+		} else if len(b) == 1 {
+			os.Exit(1)
+		}
+	})
+}
+
+func FuzzMinCache(f *testing.F) {
+	seed := bytes.Repeat([]byte("a"), 20)
+	f.Add(seed)
+	f.Fuzz(func(t *testing.T, buf []byte) {
+		if bytes.Equal(buf, seed) {
+			return
+		}
+	})
+}
+-- check_testdata/check_testdata.go --
+//go:build ignore
+// +build ignore
+
+// check_testdata.go checks that the string written
+// is not longer than the provided length.
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strconv"
+)
+
+func main() {
+	wantLen, err := strconv.Atoi(os.Args[2])
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	testName := os.Args[1]
+	dir := filepath.Join("testdata/fuzz", testName)
+
+	files, err := ioutil.ReadDir(dir)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+
+	if len(files) == 0 {
+		fmt.Fprintf(os.Stderr, "expect at least one failure to be written to testdata\n")
+		os.Exit(1)
+	}
+
+	for _, f := range files {
+		data, err := ioutil.ReadFile(filepath.Join(dir, f.Name()))
+		if err != nil {
+			panic(err)
+		}
+		var containsVal bool
+		for _, line := range bytes.Split(data, []byte("\n")) {
+			m := valRe.FindSubmatch(line)
+			if m == nil {
+				continue
+			}
+			containsVal = true
+			s, err := strconv.Unquote(string(m[1]))
+			if err != nil {
+				panic(err)
+			}
+			if len(s) != wantLen {
+				fmt.Fprintf(os.Stderr, "expect length %d, got %d (%q)\n", wantLen, len(s), line)
+				os.Exit(1)
+			}
+		}
+		if !containsVal {
+			fmt.Fprintln(os.Stderr, "corpus file contained no values")
+			os.Exit(1)
+		}
+	}
+}
+
+var valRe = regexp.MustCompile(`^\[\]byte\(([^)]+)\)$`)
+
+-- check_cache/check_cache.go --
+//go:build ignore
+// +build ignore
+
+// check_cache.go checks that each file in the cached corpus has a []byte
+// of length at most 1. This verifies that at least one cached input is minimized.
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strconv"
+)
+
+func main() {
+	dir := os.Args[1]
+	ents, err := os.ReadDir(dir)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	for _, ent := range ents {
+		name := filepath.Join(dir, ent.Name())
+		if good, err := checkCacheFile(name); err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		} else if good {
+			os.Exit(0)
+		}
+	}
+	fmt.Fprintln(os.Stderr, "no cached inputs were minimized")
+	os.Exit(1)
+}
+
+func checkCacheFile(name string) (good bool, err error) {
+	data, err := os.ReadFile(name)
+	if err != nil {
+		return false, err
+	}
+	for _, line := range bytes.Split(data, []byte("\n")) {
+		m := valRe.FindSubmatch(line)
+		if m == nil {
+			continue
+		}
+		if s, err := strconv.Unquote(string(m[1])); err != nil {
+			return false, err
+		} else if len(s) <= 1 {
+			return true, nil
+		}
+	}
+	return false, nil
+}
+
+var valRe = regexp.MustCompile(`^\[\]byte\(([^)]+)\)$`)

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_multiple.txt

@@ -0,0 +1,50 @@
+# This test checks that 'go test' prints a reasonable error when fuzzing is
+# enabled, and multiple package or multiple fuzz targets match.
+# TODO(#46312): support fuzzing multiple targets in multiple packages.
+
+[!fuzz] skip
+[short] skip
+env GOCACHE=$WORK/cache
+
+# With fuzzing disabled, multiple targets can be tested.
+go test ./...
+
+# With fuzzing enabled, at most one package may be tested,
+# even if only one package contains fuzz targets.
+! go test -fuzz=. ./...
+stderr '^cannot use -fuzz flag with multiple packages$'
+! go test -fuzz=. ./zero ./one
+stderr '^cannot use -fuzz flag with multiple packages$'
+go test -fuzz=. -fuzztime=1x ./one
+
+# With fuzzing enabled, at most one target in the same package may match.
+! go test -fuzz=. ./two
+stdout '^testing: will not fuzz, -fuzz matches more than one fuzz test: \[FuzzOne FuzzTwo\]$'
+go test -fuzz=FuzzTwo -fuzztime=1x ./two
+
+-- go.mod --
+module fuzz
+
+go 1.18
+-- zero/zero.go --
+package zero
+-- one/one_test.go --
+package one
+
+import "testing"
+
+func FuzzOne(f *testing.F) {
+  f.Fuzz(func(*testing.T, []byte) {})
+}
+-- two/two_test.go --
+package two
+
+import "testing"
+
+func FuzzOne(f *testing.F) {
+  f.Fuzz(func(*testing.T, []byte) {})
+}
+
+func FuzzTwo(f *testing.F) {
+  f.Fuzz(func(*testing.T, []byte) {})
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_mutate_crash.txt

@@ -0,0 +1,323 @@
+[!fuzz] skip
+
+# Tests that a crash caused by a mutator-discovered input writes the bad input
+# to testdata, and fails+reports correctly. This tests the end-to-end behavior
+# of the mutator finding a crash while fuzzing, adding it as a regression test
+# to the seed corpus in testdata, and failing the next time the test is run.
+
+[short] skip
+env GOCACHE=$WORK/cache
+
+# Running the seed corpus for all of the targets should pass the first
+# time, since nothing in the seed corpus will cause a crash.
+go test
+
+# Running the fuzzer should find a crashing input quickly.
+! go test -fuzz=FuzzWithBug -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzWithBug[/\\]'
+stdout 'this input caused a crash!'
+go run check_testdata.go FuzzWithBug
+
+# Now, the failing bytes should have been added to the seed corpus for
+# the target, and should fail when run without fuzzing.
+! go test
+stdout 'FuzzWithBug/[a-f0-9]{16}'
+stdout 'this input caused a crash!'
+
+! go test -run=FuzzWithNilPanic -fuzz=FuzzWithNilPanic -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzWithNilPanic[/\\]'
+stdout 'panic called with nil argument|test executed panic.nil. or runtime.Goexit'
+go run check_testdata.go FuzzWithNilPanic
+
+! go test -run=FuzzWithGoexit -fuzz=FuzzWithGoexit -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzWithGoexit[/\\]'
+stdout 'runtime.Goexit'
+go run check_testdata.go FuzzWithGoexit
+
+! go test -run=FuzzWithFail -fuzz=FuzzWithFail -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzWithFail[/\\]'
+go run check_testdata.go FuzzWithFail
+
+! go test -run=FuzzWithLogFail -fuzz=FuzzWithLogFail -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzWithLogFail[/\\]'
+stdout 'logged something'
+go run check_testdata.go FuzzWithLogFail
+
+! go test -run=FuzzWithErrorf -fuzz=FuzzWithErrorf -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzWithErrorf[/\\]'
+stdout 'errorf was called here'
+go run check_testdata.go FuzzWithErrorf
+
+! go test -run=FuzzWithFatalf -fuzz=FuzzWithFatalf -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzWithFatalf[/\\]'
+stdout 'fatalf was called here'
+go run check_testdata.go FuzzWithFatalf
+
+! go test -run=FuzzWithBadExit -fuzz=FuzzWithBadExit -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzWithBadExit[/\\]'
+stdout '^\s+fuzzing process hung or terminated unexpectedly: exit status'
+go run check_testdata.go FuzzWithBadExit
+
+! go test -run=FuzzDeadlock -fuzz=FuzzDeadlock -fuzztime=100x -fuzzminimizetime=0x
+stdout 'testdata[/\\]fuzz[/\\]FuzzDeadlock[/\\]'
+stdout '^\s+fuzzing process hung or terminated unexpectedly: exit status'
+go run check_testdata.go FuzzDeadlock
+
+# Running the fuzzer should find a crashing input quickly for fuzzing two types.
+! go test -run=FuzzWithTwoTypes -fuzz=FuzzWithTwoTypes -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzWithTwoTypes[/\\]'
+stdout 'these inputs caused a crash!'
+go run check_testdata.go FuzzWithTwoTypes
+
+# Running the fuzzer should find a crashing input quickly for an integer.
+! go test -run=FuzzInt -fuzz=FuzzInt -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzInt[/\\]'
+stdout 'this input caused a crash!'
+go run check_testdata.go FuzzInt
+
+! go test -run=FuzzUint -fuzz=FuzzUint -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzUint[/\\]'
+stdout 'this input caused a crash!'
+go run check_testdata.go FuzzUint
+
+# Running the fuzzer should find a crashing input quickly for a bool.
+! go test -run=FuzzBool -fuzz=FuzzBool -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzBool[/\\]'
+stdout 'this input caused a crash!'
+go run check_testdata.go FuzzBool
+
+# Running the fuzzer should find a crashing input quickly for a float.
+! go test -run=FuzzFloat -fuzz=FuzzFloat -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzFloat[/\\]'
+stdout 'this input caused a crash!'
+go run check_testdata.go FuzzFloat
+
+# Running the fuzzer should find a crashing input quickly for a byte.
+! go test -run=FuzzByte -fuzz=FuzzByte -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzByte[/\\]'
+stdout 'this input caused a crash!'
+go run check_testdata.go FuzzByte
+
+# Running the fuzzer should find a crashing input quickly for a rune.
+! go test -run=FuzzRune -fuzz=FuzzRune -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzRune[/\\]'
+stdout 'this input caused a crash!'
+go run check_testdata.go FuzzRune
+
+# Running the fuzzer should find a crashing input quickly for a string.
+! go test -run=FuzzString -fuzz=FuzzString -fuzztime=100x -fuzzminimizetime=1000x
+stdout 'testdata[/\\]fuzz[/\\]FuzzString[/\\]'
+stdout 'this input caused a crash!'
+go run check_testdata.go FuzzString
+
+-- go.mod --
+module m
+
+go 1.16
+-- fuzz_crash_test.go --
+package fuzz_crash
+
+import (
+	"os"
+	"runtime"
+	"testing"
+)
+
+func FuzzWithBug(f *testing.F) {
+	f.Add([]byte("aa"))
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if string(b) != "aa" {
+			panic("this input caused a crash!")
+		}
+	})
+}
+
+func FuzzWithNilPanic(f *testing.F) {
+	f.Add([]byte("aa"))
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if string(b) != "aa" {
+			panic(nil)
+		}
+	})
+}
+
+func FuzzWithGoexit(f *testing.F) {
+	f.Add([]byte("aa"))
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if string(b) != "aa" {
+			runtime.Goexit()
+		}
+	})
+}
+
+func FuzzWithFail(f *testing.F) {
+	f.Add([]byte("aa"))
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if string(b) != "aa" {
+			t.Fail()
+		}
+	})
+}
+
+func FuzzWithLogFail(f *testing.F) {
+	f.Add([]byte("aa"))
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if string(b) != "aa" {
+			t.Log("logged something")
+			t.Fail()
+		}
+	})
+}
+
+func FuzzWithErrorf(f *testing.F) {
+	f.Add([]byte("aa"))
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if string(b) != "aa" {
+			t.Errorf("errorf was called here")
+		}
+	})
+}
+
+func FuzzWithFatalf(f *testing.F) {
+	f.Add([]byte("aa"))
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if string(b) != "aa" {
+			t.Fatalf("fatalf was called here")
+		}
+	})
+}
+
+func FuzzWithBadExit(f *testing.F) {
+	f.Add([]byte("aa"))
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if string(b) != "aa" {
+			os.Exit(1)
+		}
+	})
+}
+
+func FuzzDeadlock(f *testing.F) {
+	f.Add(int(0))
+	f.Fuzz(func(t *testing.T, n int) {
+		if n != 0 {
+			select {}
+		}
+	})
+}
+
+func FuzzWithTwoTypes(f *testing.F) {
+	f.Fuzz(func(t *testing.T, a, b []byte) {
+		if len(a) > 0 && len(b) > 0 {
+			panic("these inputs caused a crash!")
+		}
+	})
+}
+
+func FuzzInt(f *testing.F) {
+	f.Add(0)
+	f.Fuzz(func(t *testing.T, a int) {
+		if a != 0 {
+			panic("this input caused a crash!")
+		}
+	})
+}
+
+func FuzzUint(f *testing.F) {
+	f.Add(uint(0))
+	f.Fuzz(func(t *testing.T, a uint) {
+		if a != 0 {
+			panic("this input caused a crash!")
+		}
+	})
+}
+
+func FuzzBool(f *testing.F) {
+	f.Add(false)
+	f.Fuzz(func(t *testing.T, a bool) {
+		if a {
+			panic("this input caused a crash!")
+		}
+	})
+}
+
+func FuzzFloat(f *testing.F) {
+	f.Fuzz(func(t *testing.T, a float64) {
+		if a != 0 {
+			panic("this input caused a crash!")
+		}
+	})
+}
+
+func FuzzByte(f *testing.F) {
+	f.Add(byte(0))
+	f.Fuzz(func(t *testing.T, a byte) {
+		if a != 0 {
+			panic("this input caused a crash!")
+		}
+	})
+}
+
+func FuzzRune(f *testing.F) {
+	f.Add(rune(0))
+	f.Fuzz(func(t *testing.T, a rune) {
+		if a != 0 {
+			panic("this input caused a crash!")
+		}
+	})
+}
+
+func FuzzString(f *testing.F) {
+	f.Add("")
+	f.Fuzz(func(t *testing.T, a string) {
+		if a != "" {
+			panic("this input caused a crash!")
+		}
+	})
+}
+
+-- check_testdata.go --
+// +build ignore
+
+package main
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+func main() {
+	target := os.Args[1]
+	dir := filepath.Join("testdata/fuzz", target)
+
+	files, err := ioutil.ReadDir(dir)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+
+	if len(files) == 0 {
+		fmt.Fprintf(os.Stderr, "expect at least one new mutation to be written to testdata\n")
+		os.Exit(1)
+	}
+
+	fname := files[0].Name()
+	contents, err := ioutil.ReadFile(filepath.Join(dir, fname))
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	if bytes.Equal(contents, []byte("aa")) {
+		fmt.Fprintf(os.Stderr, "newly written testdata entry was not mutated\n")
+		os.Exit(1)
+	}
+	// The hash of the bytes in the file should match the filename.
+	h := []byte(fmt.Sprintf("%x", sha256.Sum256(contents)))
+	if !bytes.HasPrefix(h, []byte(fname)) {
+		fmt.Fprintf(os.Stderr, "hash of bytes %q does not match filename %q\n", h, fname)
+		os.Exit(1)
+	}
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_mutate_fail.txt

@@ -0,0 +1,103 @@
+[!fuzz] skip
+
+# Check that if a worker does not call F.Fuzz or calls F.Fail first,
+# 'go test' exits non-zero and no crasher is recorded.
+
+[short] skip
+env GOCACHE=$WORK/cache
+
+! go test -fuzz=FuzzReturn
+! exists testdata
+
+! go test -fuzz=FuzzSkip
+! exists testdata
+
+! go test -fuzz=FuzzFail
+! exists testdata
+
+! go test -fuzz=FuzzPanic
+! exists testdata
+
+! go test -fuzz=FuzzNilPanic
+! exists testdata
+
+! go test -fuzz=FuzzGoexit
+! exists testdata
+
+! go test -fuzz=FuzzExit
+! exists testdata
+
+-- go.mod --
+module m
+
+go 1.17
+-- fuzz_fail_test.go --
+package fuzz_fail
+
+import (
+	"flag"
+	"os"
+	"runtime"
+	"testing"
+)
+
+func isWorker() bool {
+	f := flag.Lookup("test.fuzzworker")
+	if f == nil {
+		return false
+	}
+	get, ok := f.Value.(flag.Getter)
+	if !ok {
+		return false
+	}
+	return get.Get() == interface{}(true)
+}
+
+func FuzzReturn(f *testing.F) {
+	if isWorker() {
+		return
+	}
+	f.Fuzz(func(*testing.T, []byte) {})
+}
+
+func FuzzSkip(f *testing.F) {
+	if isWorker() {
+		f.Skip()
+	}
+	f.Fuzz(func(*testing.T, []byte) {})
+}
+
+func FuzzFail(f *testing.F) {
+	if isWorker() {
+		f.Fail()
+	}
+	f.Fuzz(func(*testing.T, []byte) {})
+}
+
+func FuzzPanic(f *testing.F) {
+	if isWorker() {
+		panic("nope")
+	}
+	f.Fuzz(func(*testing.T, []byte) {})
+}
+
+func FuzzNilPanic(f *testing.F) {
+	if isWorker() {
+		panic(nil)
+	}
+	f.Fuzz(func(*testing.T, []byte) {})
+}
+
+func FuzzGoexit(f *testing.F) {
+	if isWorker() {
+		runtime.Goexit()
+	}
+	f.Fuzz(func(*testing.T, []byte) {})
+}
+
+func FuzzExit(f *testing.F) {
+	if isWorker() {
+		os.Exit(99)
+	}
+	f.Fuzz(func(*testing.T, []byte) {})
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_mutator.txt

@@ -0,0 +1,166 @@
+[!fuzz] skip
+
+# Test basic fuzzing mutator behavior.
+#
+# fuzz_test.go has two fuzz targets (FuzzA, FuzzB) which both add a seed value.
+# Each fuzz function writes the input to a log file. The coordinator and worker
+# use separate log files. check_logs.go verifies that the coordinator only
+# tests seed values and the worker tests mutated values on the fuzz target.
+
+[short] skip
+env GOCACHE=$WORK/cache
+
+go test -fuzz=FuzzA -fuzztime=100x -parallel=1 -log=fuzz
+go run check_logs.go fuzz fuzz.worker
+
+# TODO(b/181800488): remove -parallel=1, here and below. For now, when a
+# crash is found, all workers keep running, wasting resources and reducing
+# the number of executions available to the minimizer, increasing flakiness.
+
+# Test that the mutator is good enough to find several unique mutations.
+! go test -fuzz=FuzzMutator -parallel=1 -fuzztime=100x mutator_test.go
+! stdout '^ok'
+stdout FAIL
+stdout 'mutator found enough unique mutations'
+
+-- go.mod --
+module m
+
+go 1.16
+-- fuzz_test.go --
+package fuzz_test
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"testing"
+)
+
+var (
+	logPath = flag.String("log", "", "path to log file")
+	logFile *os.File
+)
+
+func TestMain(m *testing.M) {
+	flag.Parse()
+	var err error
+	logFile, err = os.OpenFile(*logPath, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
+	if os.IsExist(err) {
+		*logPath += ".worker"
+		logFile, err = os.OpenFile(*logPath, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
+	}
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	os.Exit(m.Run())
+}
+
+func FuzzA(f *testing.F) {
+	f.Add([]byte("seed"))
+	f.Fuzz(func(t *testing.T, b []byte) {
+		fmt.Fprintf(logFile, "FuzzA %q\n", b)
+	})
+}
+
+func FuzzB(f *testing.F) {
+	f.Add([]byte("seed"))
+	f.Fuzz(func(t *testing.T, b []byte) {
+		fmt.Fprintf(logFile, "FuzzB %q\n", b)
+	})
+}
+
+-- check_logs.go --
+// +build ignore
+
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+)
+
+func main() {
+	coordPath, workerPath := os.Args[1], os.Args[2]
+
+	coordLog, err := os.Open(coordPath)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	defer coordLog.Close()
+	if err := checkCoordLog(coordLog); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+
+	workerLog, err := os.Open(workerPath)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	defer workerLog.Close()
+	if err := checkWorkerLog(workerLog); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
+
+func checkCoordLog(r io.Reader) error {
+	b, err := io.ReadAll(r)
+	if err != nil {
+		return err
+	}
+	if string(bytes.TrimSpace(b)) != `FuzzB "seed"` {
+		return fmt.Errorf("coordinator: did not test FuzzB seed")
+	}
+	return nil
+}
+
+func checkWorkerLog(r io.Reader) error {
+	scan := bufio.NewScanner(r)
+	var sawAMutant bool
+	for scan.Scan() {
+		line := scan.Text()
+		if !strings.HasPrefix(line, "FuzzA ") {
+			return fmt.Errorf("worker: tested something other than target: %s", line)
+		}
+		if strings.TrimPrefix(line, "FuzzA ") != `"seed"` {
+			sawAMutant = true
+		}
+	}
+	if err := scan.Err(); err != nil && err != bufio.ErrTooLong {
+		return err
+	}
+	if !sawAMutant {
+		return fmt.Errorf("worker: did not test any mutants")
+	}
+	return nil
+}
+-- mutator_test.go --
+package fuzz_test
+
+import (
+	"testing"
+)
+
+// TODO(katiehockman): re-work this test once we have a better fuzzing engine
+// (ie. more mutations, and compiler instrumentation)
+func FuzzMutator(f *testing.F) {
+	// TODO(katiehockman): simplify this once we can dedupe crashes (e.g.
+	// replace map with calls to panic, and simply count the number of crashes
+	// that were added to testdata)
+	crashes := make(map[string]bool)
+	// No seed corpus initiated
+	f.Fuzz(func(t *testing.T, b []byte) {
+		crashes[string(b)] = true
+		if len(crashes) >= 10 {
+			panic("mutator found enough unique mutations")
+		}
+	})
+}

go/src/cmd/internal/fuzztest/testdata/script/test_fuzz_mutator_repeat.txt

@@ -0,0 +1,75 @@
+# TODO(jayconrod): support shared memory on more platforms.
+[!GOOS:darwin] [!GOOS:linux] [!GOOS:windows] skip
+
+# Verify that the fuzzing engine records the actual crashing input, even when
+# a worker process terminates without communicating the crashing input back
+# to the coordinator.
+
+[short] skip
+env GOCACHE=$WORK/cache
+
+# Start fuzzing. The worker crashes after 100 iterations.
+# The fuzz function writes the crashing input to "want" before exiting.
+# The fuzzing engine reconstructs the crashing input and saves it to testdata.
+! exists want
+! go test -fuzz=. -parallel=1 -fuzztime=110x -fuzzminimizetime=10x -v
+stdout '^\s+fuzzing process hung or terminated unexpectedly: exit status'
+stdout 'Failing input written to testdata'
+
+# Run the fuzz target without fuzzing. The fuzz function is called with the
+# crashing input in testdata. The test passes if that input is identical to
+# the one saved in "want".
+exists want
+go test -want=want
+
+-- go.mod --
+module fuzz
+
+go 1.17
+-- fuzz_test.go --
+package fuzz
+
+import (
+	"bytes"
+	"flag"
+	"os"
+	"testing"
+)
+
+var wantFlag = flag.String("want", "", "file containing previous crashing input")
+
+func FuzzRepeat(f *testing.F) {
+	i := 0
+	f.Fuzz(func(t *testing.T, b []byte) {
+		i++
+		if i == 100 {
+			f, err := os.OpenFile("want", os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0666)
+			if err != nil {
+				// Couldn't create the file. Return without crashing, and try
+				// again.
+				i--
+				t.Skip(err)
+			}
+			if _, err := f.Write(b); err != nil {
+				// We already created the file, so if we failed to write it
+				// there's not much we can do. The test will fail anyway, but
+				// at least make sure the error is logged to stdout.
+				t.Fatal(err)
+			}
+			if err := f.Close(); err != nil {
+				t.Fatal(err)
+			}
+			os.Exit(1) // crash without communicating
+		}
+
+		if *wantFlag != "" {
+			want, err := os.ReadFile(*wantFlag)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if !bytes.Equal(want, b) {
+				t.Fatalf("inputs are not equal!\n got: %q\nwant:%q", b, want)
+			}
+		}
+	})
+}