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.
  • $TOOLCHAIN/setup.mk contains toolchain-specific default CFLAGS/LDFLAGS when this toolchain is used.
• prebuilt/$HOST_TAG 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-$VERSION/arch-$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/$STL contains the headers and libraries for the various C++ STLs.
• prebuilt/android-$ARCH/gdbserver contains gdbserver.

Others

• build/ contains the ndk-build system and scripts to rebuild NDK.
• sources/android and sources/third_party contain modules that can be used in apps (cpufeatures, native_app_glue, etc) via $(call import-module, $MODULE)
• tests/

Prerequisites

• AOSP NDK Repository

  • Check out the branch master-ndk

    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):

  • bison
  • flex
  • libtool
  • mingw-w64
  • pbzip2 (optional, improves packaging times)
  • texinfo

• Mac OS X also requires Xcode.

Host/Target prebuilts

For Linux or Darwin:

$ python checkbuild.py

For Windows, from Linux:

$ python checkbuild.py --system windows  # Or windows64.

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

Packaging

By default, checkbuild.py will also package the NDK and run basic tests. To skip the packaging step, use the --no-package flag. Note that running the tests does require the packaging step.

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 GCC, use the option --toolchain 4.9.

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. In general, most of these tests are locale related and fail because we don't support anything beyond the C locale.