bazel-cc-sysroot-generator

This is a CLI for generating Ubuntu and macOS hermetic sysroots for use with bazel.

Usage

Prerequisites

Please make sure you have at least Python 3.12, tar, zstd, and xz-utils installed.

Generate sysroots

Create a config file named sysroot-config.toml (or .json) to define your sysroots:

[[platforms]]
os = "jammy"
archs = ["aarch64", "x86_64"]
packages = [
  "libstdc++-11-dev",
  "libstdc++6",
]
deleted_patterns = [
  "etc",
  "usr/bin",
]

[[platforms]]
os = "macos"
deleted_patterns = [
  "*Swift*",
  "*iOSSupport*",
  "usr/share",
  "usr/libexec",
]

For Ubuntu you can optionally specifiy repositories to pull from:

[[platforms]]
os = "jammy"
repositories = ["main", "universe"]
...

Run ./bazel-cc-sysroot-generator (optionally passing --config path/to/sysroot-config.toml).

This example config generates 3 sysroots in the current directory.

Note

macOS sysroots can only be generated on macOS and copy the currently selected SDK directory.

Include in bazel

Once you have generated the sysroots, you can upload them somewhere and reference them in bazel with something like:

# MODULE.bazel
bazel_dep(name = "sysroot-jammy-x86_64")
archive_override(
    module_name = "sysroot-jammy-x86_64",
    integrity = "...",
    urls = [
        "https://...",
    ],
)

And use them with a hermetic CC toolchain such as toolchains_llvm with something like:

# MODULE.bazel
llvm = use_extension("@toolchains_llvm//toolchain/extensions:llvm.bzl", "llvm")
llvm.toolchain(
    name = "llvm_toolchain",
    llvm_versions = {"": "19.1.9"},
    stdlib = {"": "dynamic-stdc++"},
)

llvm.sysroot(
    name = "llvm_toolchain",
    label = "@sysroot-jammy-x86_64",
    targets = ["linux-x86_64"],
)
use_repo(llvm, "llvm_toolchain")

register_toolchains("@llvm_toolchain//:all")

Optionally you can disable bazel's builtin CC toolchain to make sure it's an error if you accidentally use it by adding this to your .bazelrc:

common --repo_env=BAZEL_DO_NOT_DETECT_CPP_TOOLCHAIN=1

Tip

While iterating on your required packages, you can use --override_module=sysroot-jammy-x86_64=path/to/sysroot-jammy-x86_64