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The term “#define”, when the line breaking happens to put at the beginning of a line, confuses markdown. This change escapes the '#'. Change-Id: I8300324f9e8c7561f32aba6fa29c0132a188a58b
86 lines
4.1 KiB
Markdown
86 lines
4.1 KiB
Markdown
# Incorporating BoringSSL into a project
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**Note**: if your target project is not a Google project then first read the
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[main README](/README.md) about the purpose of BoringSSL.
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## Directory layout
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Typically projects create a `third_party/boringssl` directory to put
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BoringSSL-specific files into. The source code of BoringSSL itself goes into
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`third_party/boringssl/src`, either by copying or as a
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[submodule](https://git-scm.com/docs/git-submodule).
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It's generally a mistake to put BoringSSL's source code into
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`third_party/boringssl` directly because pre-built files and custom build files
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need to go somewhere and merging these with the BoringSSL source code makes
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updating things more complex.
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## Build support
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BoringSSL is designed to work with many different build systems. Currently,
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different projects use [GYP](https://gyp.gsrc.io/),
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[GN](https://chromium.googlesource.com/chromium/src/+/master/tools/gn/docs/quick_start.md),
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[Bazel](http://bazel.io/) and [Make](https://www.gnu.org/software/make/) to
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build BoringSSL, without too much pain.
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The development build system is CMake and the CMake build knows how to
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automatically generate the intermediate files that BoringSSL needs. However,
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outside of the CMake environment, these intermediates are generated once and
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checked into the incorporating project's source repository. This avoids
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incorporating projects needing to support Perl and Go in their build systems.
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The script [`util/generate_build_files.py`](/util/generate_build_files.py)
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expects to be run from the `third_party/boringssl` directory and to find the
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BoringSSL source code in `src/`. You should pass it a single argument: the name
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of the build system that you're using. If you don't use any of the supported
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build systems then you should augment `generate_build_files.py` with support
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for it.
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The script will pregenerate the intermediate files (see
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[BUILDING.md](/BUILDING.md) for details about which tools will need to be
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installed) and output helper files for that build system. It doesn't generate a
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complete build script, just file and test lists, which change often. For
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example, see the
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[file](https://code.google.com/p/chromium/codesearch#chromium/src/third_party/boringssl/BUILD.generated.gni)
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and
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[test](https://code.google.com/p/chromium/codesearch#chromium/src/third_party/boringssl/BUILD.generated_tests.gni)
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lists generated for GN in Chromium.
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## Defines
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BoringSSL does not present a lot of configurability in order to reduce the
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number of configurations that need to be tested. But there are a couple of
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\#defines that you may wish to set:
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`OPENSSL_NO_ASM` prevents the use of assembly code (although it's up to you to
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ensure that the build system doesn't link it in if you wish to reduce binary
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size). This will have a significant performance impact but can be useful if you
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wish to use tools like
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[AddressSanitizer](http://clang.llvm.org/docs/AddressSanitizer.html) that
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interact poorly with assembly code.
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`OPENSSL_SMALL` removes some code that is especially large at some performance
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cost.
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## Symbols
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You cannot link multiple versions of BoringSSL or OpenSSL into a single binary
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without dealing with symbol conflicts. If you are statically linking multiple
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versions together, there's not a lot that can be done because C doesn't have a
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module system.
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If you are using multiple versions in a single binary, in different shared
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objects, ensure you build BoringSSL with `-fvisibility=hidden` and do not
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export any of BoringSSL's symbols. This will prevent any collisions with other
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verisons that may be included in other shared objects. Note that this requires
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that all callers of BoringSSL APIs live in the same shared object as BoringSSL.
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If you require that BoringSSL APIs be used across shared object boundaries,
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continue to build with `-fvisibility=hidden` but define
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`BORINGSSL_SHARED_LIBRARY` in both BoringSSL and consumers. BoringSSL's own
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source files (but *not* consumers' source files) must also build with
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`BORINGSSL_IMPLEMENTATION` defined. This will export BoringSSL's public symbols
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in the resulting shared object while hiding private symbols. However note that,
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as with a static link, this precludes dynamically linking with another version
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of BoringSSL or OpenSSL.
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