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Bazel zig cc toolchain

This is a C/C++ toolchain that can (cross-)compile C/C++ programs. It contains clang-13, musl, glibc (versions 2-2.34, selectable), all in a ~40MB package. Read here about zig-cc; the rest of the README will present how to use this toolchain from Bazel.

Usage

Add this to your WORKSPACE:

BAZEL_ZIG_CC_VERSION = "v0.4.0-rc2"

http_archive(
    name = "bazel-zig-cc",
    sha256 = "3fd0a8ed10adaa49cdb709a9ecb05990c9762849f6098412e205e3a2260fecc4",
    strip_prefix = "bazel-zig-cc-{}".format(BAZEL_ZIG_CC_VERSION),
    urls = ["https://git.sr.ht/~motiejus/bazel-zig-cc/archive/{}.tar.gz".format(BAZEL_ZIG_CC_VERSION)],
)

load("@bazel-zig-cc//toolchain:defs.bzl", zig_register_toolchains = "register_toolchains")

zig_register_toolchains(register = [
    "x86_64-linux-gnu.2.28",
    "x86_64-macos-gnu",
])

The snippet above will download the zig toolchain and register it for the following platforms:

  • x86_64-linux-gnu.2.28 for ["@platforms//os:linux", "@platforms//cpu:x86_64"].
  • x86_64-macos-gnu for ["@platforms//os:macos", "@platforms//cpu:x86_64"].

Note that both Go and Bazel naming schemes are accepted. For convenience with Go, the following Go-style toolchain aliases are created:

Bazel (zig) name Go name
x86_64 amd64
aarch64 arm64
macos darwin

For example, the toolchain linux_amd64_gnu is aliased to x86_64-linux-gnu.2.28. To find out which toolchains can be registered or used, run:

$ bazel query @zig_sdk//... | sed -En '/.*_toolchain$/ s/.*:(.*)_toolchain$/\1/p'

Known Issues in bazel-zig-cc

These are the things you may stumble into when using bazel-zig-cc. I am unlikely to implement them, but patches implementing those will be accepted. See Questions & Contributions on how to contribute.

OSX: sysroot

MacOS SDK (--sysroot) may be necessary for non-trivial programs (and is required for all cgo darwin/arm64 ones). Read Jakub's comment about it. Support for OSX sysroot is currently not implemented.

OSX: different OS targets (Catalina -- Monterey)

Since zig 0.9.0 zig may target macos.10 (Catalina), macos.11 (Big Sur) or macos.12 (Monterey). It currently targets the lowest version.

Zig cache

Currently zig cache is in $HOME so bazel clean --expunge does not clear the zig cache. Zig's cache should be stored somewhere in the project's path.

Alternative download URLs

Currently zig is downloaded from dl.jakstys.lt, which is nuts. One should provide a way to specify alternative URLs for the zig toolchain.

Bazel toolchain target locations

The path to Bazel toolchains is @zig_sdk//:<toolchain>_toolchain. It should be moved to @zig_sdk//toolchain:<toolchain> or similar; so the user-facing targets are in their own namespace.

Known Issues in upstream

This section lists issues that I've stumbled into when using zig cc, and is outside of control bazel-zig-cc's control.

using glibc 2.27 or older

Severity: Low

Task: ziglang/zig #9485 glibc 2.27 or older: fcntl64 not found, but zig's glibc headers refer it

Background: when glibc 2.27 or older is selected, it may miss fcntl64. A workaround is applied for x86_64, but not for aarch64. The same workaround may apply to aarch64, but the author didn't find a need to test it (yet).

Closed upstream issues

Testing

linux cgo + glibc 2.28

$ bazel build --platforms @io_bazel_rules_go//go/toolchain:linux_amd64_cgo //test:hello
$ file bazel-out/k8-fastbuild-ST-d17813c235ce/bin/test/hello_/hello
bazel-out/k8-fastbuild-ST-d17813c235ce/bin/test/hello_/hello: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.0.0, Go BuildID=redacted, with debug_info, not stripped

linux cgo + musl

$ bazel build \
    --platforms @io_bazel_rules_go//go/toolchain:linux_amd64_cgo \
    --extra_toolchains @zig_sdk//:linux_amd64_musl_toolchain //test:hello
...
$ file ../bazel-out/k8-fastbuild-ST-d17813c235ce/bin/test/hello_/hello
../bazel-out/k8-fastbuild-ST-d17813c235ce/bin/test/hello_/hello: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked, Go BuildID=redacted, with debug_info, not stripped
$ ../bazel-out/k8-fastbuild-ST-d17813c235ce/bin/test/hello_/hello
hello, world

macos cgo

$ bazel build --platforms @io_bazel_rules_go//go/toolchain:darwin_amd64_cgo //test:hello
...
$ file bazel-bin/test/hello_/hello
bazel-bin/test/hello_/hello: Mach-O 64-bit x86_64 executable, flags:<NOUNDEFS|DYLDLINK|TWOLEVEL|PIE>

Transient docker environment

$ docker run -e CC=/usr/bin/false -ti --rm -v $(pwd):/x -w /x debian:bullseye-slim
# apt update && apt install direnv git -y
# . .envrc

And run the bazel build commands above. Take a look at .build.yml and see how CI does it.

Future & Roadmap

This section lists things that I think will happen at some point: either by myself, or my colleagues, or outside contributors.

Questions & Contributions

Project's mailing list is ~motiejus/bazel-zig-cc. The mailing list is used for:

  • announcements (I am aiming to send an email with every release).
  • user discussions.
  • raising issues.
  • contributions.

I will generally respond to emails about issues. I may even be able to fix them. However, no promises: you are much more likely (and welcome!) to get it fixed by submitting a patch.

To contribute, send your patches to the mailing list, as described in git-send-email.io or via Sourcehut web UI.

Copyright is retained by the contributors.

Thanks

Many thanks to Adam Bouhenguel and his bazel-zig-cc, the parent of this repository. Also, the Zig team for making this all possible and handling the issues promptly.