Android NDK x86-64 instruction set support
===

Introduction:
-------------

Android NDK r[TBD] added support for the '`x86-64`' ABI, that allows native code to
run on Android-based devices running on CPUs supporting the x86-64 instruction
set.

The Android x86-64 ABI itself is fully specified in docs/CPU-ARCH-ABIS.html.

Overview:
---------

Generating machine code is simple: just add 'x86-64' to your APP_ABI
definition in your Application.mk file, for example:

        APP_ABI := armeabi armeabi-v7a x86 x86-64

Alternatively, you can use:

        APP_ABI := all

will generate machine code for all supported ABIs with this NDK. Doing so
will ensure that your application package contains libraries for all target
ABIs. Note that this has an impact on package size, since each ABI will
correspond to its own set of native libraries built from the same sources.

The default ABI is still '`armeabi`', if unspecified in your project.

As you would expect, generated libraries will go into `$PROJECT/libs/x86-64/`,
and will be embedded into your .apk under `/lib/x86-64/`.

And just like other ABIs, the Android package manager will extract these
libraries on a *compatible* x86-64 based device automatically at install
time, to put them under <dataPath>/lib, where <dataPath> is the
application's private data directory.

Similarly, the Google Play server is capable of filtering applications
based on the native libraries they embed and your device's target CPU.

Debugging with ndk-gdb should work exactly as described under docs/NDK-GDB.html.

Standalone-toolchain:
---------------------

It is possible to use the x86-64 toolchain with NDK in stand-alone mode.
See docs/STANDALONE-TOOLCHAIN.html for more details. Briefly speaking,
it is now possible to run:

      $NDK/build/tools/make-standalone-toolchain.sh --arch=x86_64 --install-dir=<path>

The toolchain binaries have the `x86_64-linux-android- prefix`.


Compatibility:
--------------

The minimal native API level provided by official Android x86-64 platform
builds is [TBD], which corresponds to all the native APIs provided by
Android [TBD], i.e. [TBD]-desert.

You won't have to change anything to your project files if you target an older
API level: the NDK build script will automatically select the right set of
native platform headers/libraries for you.