# Building BoringSSL ## Build Prerequisites The standalone CMake build is primarily intended for developers. If embedding BoringSSL into another project with a pre-existing build system, see [INCORPORATING.md](/INCORPORATING.md). Unless otherwise noted, build tools must at most five years old, matching [Abseil guidelines](https://abseil.io/about/compatibility). If in doubt, use the most recent stable version of each tool. * [CMake](https://cmake.org/download/) 2.8.12 or later is required. Note we will begin requiring CMake 3.0 in 2019. * A recent version of Perl is required. On Windows, [Active State Perl](http://www.activestate.com/activeperl/) has been reported to work, as has MSYS Perl. [Strawberry Perl](http://strawberryperl.com/) 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`. * Building with [Ninja](https://ninja-build.org/) instead of Make is recommended, because it makes builds faster. On Windows, CMake's Visual Studio generator may also work, but it not tested regularly and requires recent versions of CMake for assembly support. * On Windows only, [NASM](https://www.nasm.us/) is required. If not found by CMake, it may be configured explicitly by setting `CMAKE_ASM_NASM_COMPILER`. * C and C++ compilers with C++11 support are 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. * The most recent stable version of [Go](https://golang.org/dl/) is required. Note Go is exempt from the five year support window. If not found by CMake, the go executable may be configured explicitly by setting `GO_EXECUTABLE`. * On x86_64 Linux, the tests have an optional [libunwind](https://www.nongnu.org/libunwind/) dependency to test the assembly more thoroughly. ## Building Using Ninja (note the 'N' is capitalized in the cmake invocation): mkdir build cd build cmake -GNinja .. ninja Using Make (does not work on Windows): mkdir build cd build cmake .. make 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 `#include`s 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](https://cmake.org/cmake/help/v3.4/manual/cmake-variables.7.html) 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. Recent versions of the NDK include a CMake toolchain file which works with CMake 3.6.0 or later. This has been tested with version r16b 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=${ANDROID_NDK}/build/cmake/android.toolchain.cmake \ -DANDROID_NATIVE_API_LEVEL=16 \ -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 the documentation in the toolchain file. ### 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. ### Building with Prefixed Symbols BoringSSL's build system has experimental support for adding a custom prefix to all symbols. This can be useful when linking multiple versions of BoringSSL in the same project to avoid symbol conflicts. In order to build with prefixed symbols, the `BORINGSSL_PREFIX` CMake variable should specify the prefix to add to all symbols, and the `BORINGSSL_PREFIX_SYMBOLS` CMake variable should specify the path to a file which contains a list of symbols which should be prefixed (one per line; comments are supported with `#`). In other words, `cmake .. -DBORINGSSL_PREFIX=MY_CUSTOM_PREFIX -DBORINGSSL_PREFIX_SYMBOLS=/path/to/symbols.txt` will configure the build to add the prefix `MY_CUSTOM_PREFIX` to all of the symbols listed in `/path/to/symbols.txt`. It is currently the caller's responsibility to create and maintain the list of symbols to be prefixed. Alternatively, `util/read_symbols.go` reads the list of exported symbols from a `.a` file, and can be used in a build script to generate the symbol list on the fly (by building without prefixing, using `read_symbols.go` to construct a symbol list, and then building again with prefixing). This mechanism is under development and may change over time. Please contact the BoringSSL maintainers if making use of it. ## 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 http://www.cmake.org/Bug/view.php?id=15253. * 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. * `OPENSSL_STATIC_ARMCAP_NEON` * `OPENSSL_STATIC_ARMCAP_AES` * `OPENSSL_STATIC_ARMCAP_SHA1` * `OPENSSL_STATIC_ARMCAP_SHA256` * `OPENSSL_STATIC_ARMCAP_PMULL` Note that if a feature is enabled in this way, but not actually supported at run-time, BoringSSL will likely crash. ## Binary Size The implementations of some algorithms require a trade-off between binary size and performance. For instance, BoringSSL's fastest P-256 implementation uses a 148 KiB pre-computed table. To optimize instead for binary size, pass `-DOPENSSL_SMALL=1` to CMake or define the `OPENSSL_SMALL` preprocessor symbol. # 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.