bazel_bootlin

Provides hermetic Bazel C/C++ toolchains based on Buildroot toolchains provided by Bootlin.

Usage

WORKSPACE

To incorporate bazel_bootlin toolchains into your project, copy the following into your WORKSPACE file.

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

http_archive(
    name = "bazel_bootlin",
    # See release page for latest version url and sha.
)

load("@bazel_bootlin//toolchains:toolchains.bzl", "bootlin_all_toolchain_deps")

bootlin_all_toolchain_deps()

This will bring all of the available toolchains (and their associated platform definitions) into your project. The toolchains will only be downloaded when actually utilized, but if you prefer, you can only import a specific toolchain:

load("@bazel_bootlin//toolchains:toolchains.bzl", "bootlin_toolchain_deps")

bootlin_toolchain_deps(
    architecture = "x86-64-core-i7",
    cstdlib = "glibc",
    buildroot_version = "2020.08-1",
)

• architecture - refers to the architecture string used by Bootlin.
• cstdlib - refers to the cstdlib string used by bootlin.
• buildroot_version - refers to the Buildroot version string used by Bootlin.

Available Toolchains

Currently bazel_bootlin only provides the "glibc--stable" version of the following Bootlin toolchains:

Architecture	cstdlib	Buildroot Version
x86-64	glibc	2022.08-1, 2021.11-5
x86-64-core-i7	glibc	2020.08-1
aarch64	glibc, musl	2021.11-1, 2020.08-1
armv7-eabihf	glibc	2020.08-1
riscv64-lp64d	glibc	2024.02-1

This list is easily expanded. If a toolchain of interest isn't available feel free to submit and issue, or alternatively take a look at _AVAILABLE_TOOLCHAINS in setup_toolchains.py and create a pull request. Don't forget to actually run setup_toolchains.py after adding a toolchain and before submitting a PR:

bazel run //:setup_toolchains

Platforms

bazel_bootlin defines a different platform for each toolchain that is included. The platforms specify constraint_value for the canonical @platforms//os:os and @platforms//cpu:cpu constraint_setting:

platform(
    name = "{architecture}-linux-{cstdlib}-{buildroot_version}",
    constraint_values = [
        "@platforms//cpu:{architecture}",
        "@platforms//os:linux",
        "@bazel_bootlin//platforms:{buildroot_version}",
    ],
)

Specifying one of these platforms will cause Bazel to use the corresponding toolchain during build.

Building With Toolchain

In order to enable toolchain selection via platforms, Bazel requires a special flag along with the target platform:

bazel build --incompatible_enable_cc_toolchain_resolution --platforms=@bazel_bootlin//platforms:{architecture}-linux-{cstdlib}-{buildroot_version} //...

The ergonomics can be improved by placing the flags in a .bazelrc file:

build --incompatible_enable_cc_toolchain_resolution
build --platforms=@bazel_bootlin//platforms:{architecture}-linux-{cstdlib}-{buildroot_version}

Then a simple bazel build //... will utilize the desired toolchain.