Building BoringSSL

Build Prerequisites

  • CMake 2.8.11 or later is required.

  • Perl 5.6.1 or later is required. On Windows, Active State Perl has been reported to work, as has MSYS Perl. Strawberry Perl also works but it adds GCC to PATH, which can confuse some build tools when identifying the compiler (removing C:\Strawberry\c\bin from PATH should resolve any problems). If Perl is not found by CMake, it may be configured explicitly by setting PERL_EXECUTABLE.

  • On Windows you currently must use Ninja to build; on other platforms, it is not required, but recommended, because it makes builds faster.

  • If you need to build Ninja from source, then a recent version of Python is required (Python 2.7.5 works).

  • On Windows only, Yasm is required. If not found by CMake, it may be configured explicitly by setting CMAKE_ASM_NASM_COMPILER.

  • A C compiler is required. On Windows, MSVC 14 (Visual Studio 2015) or later with Platform SDK 8.1 or later are supported. Recent versions of GCC (4.8+) and Clang should work on non-Windows platforms, and maybe on Windows too. To build the tests, you also need a C++ compiler with C++11 support.

  • Go is required. If not found by CMake, the go executable may be configured explicitly by setting GO_EXECUTABLE.

  • To build the x86 and x86_64 assembly, your assembler must support AVX2 instructions and MOVBE. If using GNU binutils, you must have 2.22 or later


Using Ninja (note the ‘N’ is capitalized in the cmake invocation):

mkdir build
cd build
cmake -GNinja ..

Using Make (does not work on Windows):

mkdir build
cd build
cmake ..

You usually don't need to run cmake again after changing CMakeLists.txt files because the build scripts will detect changes to them and rebuild themselves automatically.

Note that the default build flags in the top-level CMakeLists.txt are for debugging—optimisation isn't enabled. Pass -DCMAKE_BUILD_TYPE=Release to cmake to configure a release build.

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/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.

In order to serve environments where code-size is important as well as those where performance is the overriding concern, OPENSSL_SMALL can be defined to remove some code that is especially large.

See CMake's documentation for other variables which may be used to configure the build.

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. Then make a build directory as above and run CMake like this:

cmake -DANDROID_ABI=armeabi-v7a \
      -DCMAKE_TOOLCHAIN_FILE=../third_party/android-cmake/android.toolchain.cmake \
      -GNinja ..

Once you've run that, Ninja should produce Android-compatible binaries. You can replace armeabi-v7a in the above with arm64-v8a and use API level 21 or higher to build aarch64 binaries.

For other options, see android-cmake's documentation.

Building for iOS

To build for iOS, pass -DCMAKE_OSX_SYSROOT=iphoneos and -DCMAKE_OSX_ARCHITECTURES=ARCH to CMake, where ARCH is the desired architecture, matching values used in the -arch flag in Apple's toolchain.

Passing multiple architectures for a multiple-architecture build is not supported.

Known Limitations on Windows

  • Versions of CMake since 3.0.2 have a bug in its Ninja generator that causes yasm to output warnings

    yasm: warning: can open only one input file, only the last file will be processed

    These warnings can be safely ignored. The cmake bug is

  • CMake can generate Visual Studio projects, but the generated project files don't have steps for assembling the assembly language source files, so they currently cannot be used to build BoringSSL.

Embedded ARM

ARM, unlike Intel, does not have an instruction that allows applications to discover the capabilities of the processor. Instead, the capability information has to be provided by the operating system somehow.

By default, on Linux-based systems, BoringSSL will try to use getauxval and /proc to discover the capabilities. But some environments don‘t support that sort of thing and, for them, it’s possible to configure the CPU capabilities at compile time.

On iOS or builds which define OPENSSL_STATIC_ARMCAP, features will be determined based on the __ARM_NEON__ and __ARM_FEATURE_CRYPTO preprocessor symbols reported by the compiler. These values are usually controlled by the -march flag. You can also define any of the following to enable the corresponding ARM feature.


Note that if a feature is enabled in this way, but not actually supported at run-time, BoringSSL will likely crash.

Assembling ARMv8 with Clang

In order to support the ARMv8 crypto instructions, Clang requires that the architecture be armv8-a+crypto. However, setting that as a general build flag would allow the compiler to assume that crypto instructions are always supported, even without testing for them.

It's possible to set the architecture in an assembly file using the .arch directive, but only very recent versions of Clang support this. If BORINGSSL_CLANG_SUPPORTS_DOT_ARCH is defined then .arch directives will be used with Clang, otherwise you may need to craft acceptable assembler flags.

Running tests

There are two sets of tests: the C/C++ tests and the blackbox tests. For former are built by Ninja and can be run from the top-level directory with go run util/all_tests.go. The latter have to be run separately by running go test from within ssl/test/runner.

Both sets of tests may also be run with ninja -C build run_tests, but CMake 3.2 or later is required to avoid Ninja's output buffering.