toolchains_llvm sysroot package generation

This repo contains the definitions and scripts to build sysroot packages for x86_64 and aarch64 (aka arm64) for use with the Bazel toolchains_llvm ruleset.

A matching text article for this repository can be found on my website: Sysroot package generation for use with toolchains_llvm

The source here is based off of the sysroot generation code in gcc-toolchain, authored by @f0rmiga.

Modifications have been made to:

• generate a valid sysroot package for use with toolchains_llvm instead of gcc-toolchain
• simplified to remove code that I didn't need
• and expanded where necessary to show how to fetch RHEL 8 specific files

Key Versions

The stock version of Dockerfile will produce a sysroot with the following library versions. If you need different versions, I encourage you to go in and make the necessary changes.

Built from source:

• kernel headers 4.18
• glibc 2.28
• libstdc++ 10.3.0

Fetched from RHEL-UBI 8 container:

• openssl
• cyrus-sasl

Building and using the sysroot packages

Use the build.sh script to build the sysroot package using Docker. The current restriction is that the container must run in x86_64. The sysroot package for other architectures are built using cross-compilation from x86_64. That is, building a sysroot package on an Apple Silicon machine is not supported at this time.

Using the build script

The entrypoint is build.sh that takes three args:

• The target architecture (x86_64 or aarch64)
• The output directory path for the generated .tar.zst file
• The target "variant". One of:
  • base, containing just the kernel, glibc, and libstdc++ files
  • ssl, containing base plus openssl and cyrus-sasl from a RHEL-UBI 8 container

./build.sh x86_64 . base
./build.sh aarch64 . base

In the end you'll have a compressed size of ~55MB for x86_64 and ~37MB for aarch64.

Using the sysroot package with toolchains_llvm

https://github.com/bazel-contrib/toolchains_llvm?tab=readme-ov-file#sysroots

WORKSPACE implementation

https://github.com/bazel-contrib/toolchains_llvm/blob/1.0.0/tests/WORKSPACE#L116

bzlmod implementation

https://github.com/bazel-contrib/toolchains_llvm/blob/1.0.0/tests/MODULE.bazel#L145