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>

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

CMakeLists.txt

@@ -2,9 +2,16 @@ cmake_minimum_required (VERSION 2.8.10)
 
 project (BoringSSL)
 
-find_package(Perl REQUIRED)
+if(ANDROID)
+  # Android-NDK CMake files reconfigure the path and so Go and Perl won't be
+  # found. However, ninja will still find them in $PATH if we just name them.
+  set(PERL_EXECUTABLE "perl")
+  set(GO_EXECUTABLE "go")
+else()
+  find_package(Perl REQUIRED)
+  find_program(GO_EXECUTABLE go)
+endif()
 
-find_program(GO_EXECUTABLE go)
 if (NOT GO_EXECUTABLE)
   message(FATAL_ERROR "Could not find Go")
 endif()
@@ -97,12 +104,21 @@ elseif (${CMAKE_SYSTEM_PROCESSOR} STREQUAL "i686")
   set(ARCH "x86")
 elseif (${CMAKE_SYSTEM_PROCESSOR} STREQUAL "arm")
   set(ARCH "arm")
+elseif (${CMAKE_SYSTEM_PROCESSOR} STREQUAL "armv7-a")
+  set(ARCH "arm")
 elseif (${CMAKE_SYSTEM_PROCESSOR} STREQUAL "aarch64")
   set(ARCH "aarch64")
 else()
   message(FATAL_ERROR "Unknown processor:" ${CMAKE_SYSTEM_PROCESSOR})
 endif()
 
+if (ANDROID AND ${ARCH} STREQUAL "arm")
+  # The Android-NDK CMake files somehow fail to set the -march flag for
+  # assembly files. Without this flag, the compiler believes that it's
+  # building for ARMv5.
+  set(CMAKE_ASM_FLAGS "${CMAKE_ASM_FLAGS} -march=armv7-a")
+endif()
+
 if (${ARCH} STREQUAL "x86" AND APPLE)
   # With CMake 2.8.x, ${CMAKE_SYSTEM_PROCESSOR} evalutes to i386 on OS X,
   # but clang defaults to 64-bit builds on OS X unless otherwise told.

crypto/CMakeLists.txt

@@ -191,7 +191,7 @@ add_library(
   $<TARGET_OBJECTS:pkcs8>
 )
 
-if(NOT MSVC)
+if(NOT MSVC AND NOT ANDROID)
   target_link_libraries(crypto pthread)
 endif()
 

crypto/cpu-arm.c

@@ -30,9 +30,6 @@
 
 unsigned long getauxval(unsigned long type) __attribute__((weak));
 
-static const unsigned long AT_HWCAP = 16;
-static const unsigned long AT_HWCAP2 = 26;
-
 char CRYPTO_is_NEON_capable(void) {
   return (OPENSSL_armcap_P & ARMV7_NEON) != 0;
 }
@@ -136,6 +133,7 @@ void OPENSSL_cpuid_setup(void) {
     return;
   }
 
+  static const unsigned long AT_HWCAP = 16;
   unsigned long hwcap = getauxval(AT_HWCAP);
 
 #if defined(OPENSSL_ARM)
@@ -146,6 +144,7 @@ void OPENSSL_cpuid_setup(void) {
 
   /* In 32-bit mode, the ARMv8 feature bits are in a different aux vector
    * value. */
+  static const unsigned long AT_HWCAP2 = 26;
   hwcap = getauxval(AT_HWCAP2);
 
   /* See /usr/include/asm/hwcap.h on an ARM installation for the source of

tool/CMakeLists.txt

@@ -15,7 +15,7 @@ add_executable(
   transport_common.cc
 )
 
-if (APPLE OR WIN32)
+if (APPLE OR WIN32 OR ANDROID)
   target_link_libraries(bssl ssl crypto)
 else()
   target_link_libraries(bssl ssl crypto -lrt)

util/aarch64-toolchain.cmake

@@ -1,6 +0,0 @@
-set(CMAKE_SYSTEM_NAME Linux)
-set(CMAKE_SYSTEM_VERSION 1)
-set(CMAKE_SYSTEM_PROCESSOR "aarch64")
-set(CMAKE_CXX_COMPILER "/opt/gcc-linaro-4.9-2014.11-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-g++")
-set(CMAKE_C_COMPILER "/opt/gcc-linaro-4.9-2014.11-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-gcc")
-set(CMAKE_EXE_LINKER_FLAGS "-static")

util/arm-toolchain.cmake

@@ -1,6 +0,0 @@
-set(CMAKE_SYSTEM_NAME Linux)
-set(CMAKE_SYSTEM_VERSION 1)
-set(CMAKE_SYSTEM_PROCESSOR "arm")
-set(CMAKE_CXX_COMPILER "/opt/gcc-linaro-4.9-2014.11-x86_64_arm-linux-gnueabihf/bin/arm-linux-gnueabihf-g++")
-set(CMAKE_C_COMPILER "/opt/gcc-linaro-4.9-2014.11-x86_64_arm-linux-gnueabihf/bin/arm-linux-gnueabihf-gcc")
-set(CMAKE_EXE_LINKER_FLAGS "-static")