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# Building BoringSSL
## Build Prerequisites
* [CMake]( 2.8.8 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
* 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
* A C compiler is required. On Windows, MSVC 12 (Visual Studio 2013) 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.
* [Go]( is required. If not found by CMake, the go
executable may be configured explicitly by setting `GO_EXECUTABLE`.
## Building
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
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](
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. Clone 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
## 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.
BoringSSL will try to use `getauxval` to discover the capabilities and, failing
that, will probe for NEON support by executing a NEON instruction and handling
any illegal-instruction signal. But some environments don't support that sort
of thing and, for them, it's possible to configure the CPU capabilities
at compile time.
If you define `OPENSSL_STATIC_ARMCAP` then you can define any of the following
to enabling the corresponding ARM feature.
* `OPENSSL_STATIC_ARMCAP_NEON` or `__ARM_NEON__` (note that the latter is set by compilers when NEON support is enabled).
Note that if a feature is enabled in this way, but not actually supported at
run-time, BoringSSL will likely crash.
# 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.