doubleyou/bazel-toolchain

LLVM toolchain for bazel

LLVM toolchain for Bazel

To use this toolchain, include this section in your WORKSPACE:

# Change master to the git tag you want.
http_archive(
    name = "com_grail_bazel_toolchain",
    strip_prefix = "bazel-toolchain-master",
    urls = ["https://github.com/grailbio/bazel-toolchain/archive/master.tar.gz"],
)

load("@com_grail_bazel_toolchain//toolchain:rules.bzl", "llvm_toolchain")

llvm_toolchain(
    name = "llvm_toolchain",
    llvm_version = "7.0.0",
)

You can use the toolchain in your builds with --crosstool_top=@llvm_toolchain//:toolchain

The toolchain can automatically detect your OS type, and use the right pre-built binary distribution from llvm.org. The detection is currently based on host OS and is not perfect, so some distributions, docker based sandboxed builds, and remote execution builds will need toolchains configured manually through the distribution attribute. We expect the detection logic to grow through community contributions. We welcome PRs! 😄

See in-code documentation in rules.bzl for available attributes to llvm_toolchain.

For making changes to default settings for these toolchains, edit the CROSSTOOL.tpl file. The file is in ASCII protobuf format.

https://github.com/bazelbuild/bazel/wiki/About-the-CROSSTOOL

Notes:

• The LLVM toolchain archive is downloaded and extracted in the named repository. People elsewhere have used wrapper scripts to avoid symlinking and get better control of the environment in which the toolchain binaries are run.

• A sysroot can be specified through the sysroot attribute. This can be either a path on the user's system, or a bazel filegroup like label. One way to create a sysroot is to use docker export to get a single archive of the entire filesystem for the image you want. Another way is to use the build scripts provided by the Chromium project.

• Sandboxing the toolchain introduces a significant overhead (100ms per action). To overcome this, one can use --experimental_sandbox_base=/dev/shm. However, not all environments might have enough shared memory available to load all the files in memory. That is why we have templated the paths to the toolchain as absolute paths. When running bazel actions, these paths will be available from inside the sandbox as part of the / read-only mount.

• The toolchain is known to also work with rules_go, both with absolute and relative paths.

Other examples of toolchain configuration:

https://github.com/bazelbuild/bazel/wiki/Building-with-a-custom-toolchain

https://github.com/vsco/bazel-toolchains