Datasets:
Devilishcode
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hacking

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| v v |
| classes.dex nativelib.so |
| | | |
+---------+----------------+---------+
| |
+---------+----------------+---------+
| | | |
| +----v-----+ +--v--+ |
| | dexopt | | JNI | |
| +----+-----+ +-----+ |
| | |
| +----v-----+ +----------+ |
| | app.odex +-----> dalvikvm | |
| +----------+ +----------+ |
+------------------------------------+
```
It's 2014. The Nexus 6 has a processor with not just one but four 2.7GHz
cores and 3 GB of RAM. Its 32GB of storage allows for much more code to be
stored, and so the JIT compilation is replaced by a complete Ahead-Of-Time
(AOT) compilation. ODEX files no longer contain Dalvik code. They contain
binary code and become OAT (allegedly "of-ahead-time") files. This
compilation adds another layer of optimizations, a fact that will come back
in Section 3.4. We will call the binary ODEX files OAT instead of ODEX, but
they still use the file ending .odex. They are technically ELF shared
objects with some additional metadata, but they are meant to only run with
the Android Runtime (ART). It replaces the dalvikvm and can handle oat
files.
On the developers' side, the pipeline of javac-to-plugins-to-dx also sees
changes: Jack and Jill replace the whole stack, unifying compilation and
optimizations. Android apps are fast(er).
```txt
+-------------+ +-------------+
| source.java | | library.jar |
++------------+ ++------------+
| |
| | +------------+
| | | source.cpp |
| | ++-----------+
| | |
+v-----------------v-+ +v-----------+
| jack | | NDK |
| and | | |
| jill | | |
+---------+----+-----+ +--+---------+
| |
| | above is accessible to developers
----------+----------------+-----------
| | below is running on devices
| |
+---------+----------------+---------+
| APK | | |
| v v |
| classes.dex nativelib.so |
| | | |
+---------+----------------+---------+
| |
+---------+----------------+---------+
| ART | | |
| +----v-----+ +--v--+ |
| | dex2oat | | JNI | |
| | | +-----+ |
| | full | +----------+ |
| | AOT----+-----> app.odex | |
| | | +----------+ |
| +----------+ |
+------------------------------------+
```
It's 2017. The Xperia XZ1 has eight 2.3GHz cores and 4GB RAM. Lessons were
learned. First, getting rid of the Java compiler is rolled back and instead
ProGuard's functionality is included in the R8/D8 compiler suite that
consumes Java bytecode. Kotlin is added as the preferred language.
It also turned out that compiling all of an app's code during installation
can take a while, even with all those cores available. And, of course, all
apps have to be recompiled after system updates, which eats performance
like Android codename snacks. JIT is re-introduced, and profile-based
compilation is added. The compilation profiles track per app which methods
should be compiled ahead-of time, for example, after a system update. This
saves resources.
```txt
+-------------+ +-------------+
| source.java | | library.jar |
++------------+ ++------------+
| |
| +-----------+ | +------------+
| | source.kt | | | source.cpp |
| ++----------+ | ++-----------+
| | | |
+v--v-----------+ | |
| javac/kotlinc | | |
+---------+-----+ | |
| | |
+---------v--------v-+ +v-----------+
| R8/D8 | | NDK |
| includes ProGuard | | |
| shrinking and | | |
| renaming | | |