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Android Native Development Kit (NDK)

The NDK allows Android application developers to include native code in their Android application packages, compiled as JNI shared libraries.

Discussions related to the Android NDK happen on the android-ndk Google Group.

Building the NDK

Note: This document is for developers of the NDK, not developers that use the NDK.

Both Linux and Windows host binaries are built on Linux machines. Windows host binaries are built via MinGW cross compiler. Systems without a working MinGW compiler can use build/tools/build-mingw64-toolchain.sh to generate their own and be added to the PATH for build scripts to discover.

Building binaries for Mac OS X requires at least 10.8.

Target headers and binaries are built on Linux.

Components

The NDK consists of three parts: host binaries, target prebuilts, and others (build system, docs, samples, tests).

Host Binaries

  • toolchains/ contains GCC and Clang toolchains.
    • $TOOLCHAIN/config.mk contains ARCH and ABIS this toolchain can handle.
    • $TOOLCHAIN/setup.mk contains toolchain-specific default CFLAGS/LDFLAGS when this toolchain is used.
  • binutils/ contains the standalone binutils installation for use with Clang.
  • host-tools/ contains build dependencies and additional tools.
    • make, awk, python, yasm, and for Windows: cmp.exe and echo.exe
    • ndk-depends, ndk-stack and ndk-gdb can also be found here.

Target Headers and Binaries

  • platforms/android-N/arch-$ARCH_NAME/ contains headers and libraries for each API level.
    • The build system sets --sysroot to one of these directories based on user-specified APP_ABI and APP_PLATFORM.
  • sources/cxx-stl/$STL contains the headers and libraries for the various C++ STLs.
  • gdbserver/ contains gdbserver.

Others

  • build/ contains the ndk-build system and scripts to rebuild NDK.
  • docs/
  • sources/ contains modules useful in samples and apps via $(call import-module, $MODULE)
  • tests/

Prerequisites

  • AOSP NDK Repository

    • Check out the branch master-ndk
    ```bash
    repo init -u https://android.googlesource.com/platform/manifest \
        -b master-ndk
    
    # Googlers, use
    repo init -u \
        persistent-https://android.git.corp.google.com/platform/manifest \
        -b master-ndk
    ```
    
  • Additional Linux Dependencies (available from apt):

    • texinfo
    • gcc-mingw32
    • wine
    • bison
    • flex
    • dmake
    • libtool
    • pbzip2
  • Mac OS X also requires Xcode.

Host/Target prebuilts

For Linux or Darwin:

$ python checkbuild.py --no-package

For Windows, from Linux:

$ python checkbuild.py --system windows

checkbuild.py also accepts a variety of other options to speed up local builds, namely --arch and --module.

Packaging

The simplest way to package an NDK on Linux is to just omit the --no-package flag when running checkbuild.py. This will take a little longer though, so it may not be desired for day to day development.

If you need to re-run just the packaging step without going through a build, packaging is handled by build/tools/package.py.

Testing

Running the NDK tests requires a complete NDK package (see previous steps). From the NDK source directory (not the extracted package):

$ NDK=/path/to/extracted/ndk python tests/run-all.py --abi $ABI_TO_TEST

To run the tests with Clang, use the option --toolchain clang.

The full test suite includes tests which run on a device or emulator, so you’ll need to have adb in your path and ANDROID_SERIAL set if more than one device/emulator is connected. If you do not have a device capable of running the tests, you can run just the build or awk test suites with the --suite flag.

The libc++ tests are not currently integrated into the main NDK tests. To run the libc++ tests:

$ NDK=/path/to/extracted/ndk sources/cxx-stl/llvm-libc++/llvm/ndk-test.sh $ABI

Note that these tests are far from failure free (especially on 32-bit ARM). In general, most of these tests are locale related and fail because we don’t support anything beyond the C locale. The ARM32 specific failures are because the libgcc unwinder does not get along with the LLVM unwinder. The test config file ($NDK/sources/cxx-stl/llvm-libc++/libcxx/test/libcxx/ndk/test/config.py) can be modified to use -lc++_static before -lgcc and the tests will then work on ARM (but will take considerably longer to run).

Yes, this does mean that exception handling will often fail when using c++_shared on ARM32. We should fix this ASAP, but this actually is not a regression from r10e.