Add support for building with the Android NDK.

Previously I've been using the Linaro toolchains and just building
static binaries. However, the Linaro toolchains have a broken
pthread_rwlock_wrlock—it does nothing and then unlocking corrupts the
lock.

Building with the Android NDK avoids this.

These build instructions depend on
https://github.com/taka-no-me/android-cmake which people will need to
clone into util/ if they want to use the Android NDK.

Change-Id: Ic64919f9399af2a57e8df4fb4b3400865ddb2427
Reviewed-on: https://boringssl-review.googlesource.com/4600
Reviewed-by: Adam Langley <agl@google.com>

1 files changed, 23 insertions, 3 deletions

diff --git a/BUILDING b/BUILDING
index 8a655282..d818f950 100644
--- a/BUILDING
+++ b/BUILDING
@@ -43,17 +43,37 @@ automatically.
 Note that the default build flags in the top-level CMakeLists.txt are for
 debugging - optimisation isn't enabled.
 
-If you want to cross-compile then there are example toolchain files for 32-bit
-Intel and ARM in util/. Wipe out the build directory, recreate it and run cmake
+If you want to cross-compile then there is an example toolchain file for
+32-bit Intel in util/. Wipe out the build directory, recreate it and run cmake
 like this:
 
-  cmake -DCMAKE_TOOLCHAIN_FILE=../util/arm-toolchain.cmake -GNinja ..
+  cmake -DCMAKE_TOOLCHAIN_FILE=../util/32-bit-toolchain.cmake -GNinja ..
 
 If you want to build as a shared library, pass -DBUILD_SHARED_LIBS=1. On
 Windows, where functions need to be tagged with "dllimport" when coming from a
 shared library, define BORINGSSL_SHARED_LIBRARY in any code which #includes the
 BoringSSL headers.
 
+
+Building for Android:
+
+It's possible to build BoringSSL with the Android NDK using CMake. This has
+been tested with version 10d of the NDK.
+
+Unpack the Android NDK somewhere and export ANDROID_NDK to point to the
+directory. Clone https://github.com/taka-no-me/android-cmake into util/.
+Then make a build directory as above and run CMake *twice* like this:
+
+  cmake -DANDROID_NATIVE_API_LEVEL=android-9 \
+        -DANDROID_ABI=armeabi-v7a \
+        -DCMAKE_TOOLCHAIN_FILE=../util/android-cmake/android.toolchain.cmake \
+        -GNinja ..
+
+Once you've run that twice, ninja should produce Android-compatible binaries.
+You can replace "armeabi-v7a" in the above with "arm64-v8a" to build aarch64
+binaries.
+
+
 Known Limitations on Windows:
 
   * Versions of cmake since 3.0.2 have a bug in its Ninja generator that causes