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 = "v0.6.1"

http_archive(
    name = "bazel-zig-cc",
    sha256 = "6969858b7f142a0629c61aea4338fca1c81f4e137892464a96bfe9a42ed74821",
    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()

# Or, if you are using this in production, you probably want more control:
zig_register_toolchains(
    version = "<...>",
    url_formats = [
        "https://example.internal/zig/zig-{host_platform}-{version}.tar.xz",
    ],
    host_platform_sha256 = { ... },
)

And this to .bazelrc:

build --incompatible_enable_cc_toolchain_resolution
build --extra_toolchains @zig_sdk//toolchain:linux_amd64_gnu.2.19
build --extra_toolchains @zig_sdk//toolchain:linux_arm64_gnu.2.28
build --extra_toolchains @zig_sdk//toolchain:darwin_amd64
build --extra_toolchains @zig_sdk//toolchain:darwin_arm64

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

• x86_64-linux-gnu.2.19 for ["@platforms//os:linux", "@platforms//cpu:x86_64"].
• x86_64-linux-gnu.2.28 for ["@platforms//os:linux", "@platforms//cpu:aarch64"].
• x86_64-macos-gnu for ["@platforms//os:macos", "@platforms//cpu:x86_64"].
• aarch64-macos-gnu for ["@platforms//os:macos", "@platforms//cpu:aarch64"].

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

$ bazel query @zig_sdk//toolchain/...

Specifying non-default toolchains

You may explicitly request Bazel to use a specific toolchain, even though a different one is registered using --extra_toolchains <toolchain> in .bazelrc. For example, if you wish to compile a specific binary (or run tests) on linux/amd64/musl, you may specify:

--extra_toolchains @zig_sdk//toolchain:linux_amd64_musl

UBSAN and "SIGILL: Illegal Instruction"

zig cc differs from "mainstream" compilers by enabling UBSAN by default. Which means your program may compile successfully and crash with:

SIGILL: illegal instruction

This is by design: it encourages program authors to fix the undefined behavior. There are many ways to find the undefined behavior.

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 any time soon, but patches implementing those will be accepted. See Questions & Contributions on how to contribute.

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.

OSX: sysroot

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

OSX: different OS targets (Catalina -- Monterey)

Zig 0.9.0 may target macos.10 (Catalina), macos.11 (Big Sur) or macos.12 (Monterey). It currently targets the lowest version, without ability to change it.

Known Issues In Upstream

This section lists issues that I've stumbled into when using zig cc, and is outside of 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

• ziglang/zig #10386 zig cc regression in 0.9.0(CLOSED, thanks Xavier)
• ziglang/zig #10312 macho: fail if requested -framework is not found (CLOSED, thanks kubkon)
• ziglang/zig #10299 [darwin aarch64 cgo] regression (CLOSED, thanks kubkon)
• ziglang/zig #10297 [darwin x86_64 cgo] regression (CLOSED, thanks kubkon)
• ziglang/zig #9431 FileNotFound when compiling macos (CLOSED, thanks andrewrk)
• ziglang/zig #9139 zig c++ hanging when compiling in parallel (CLOSED, thanks andrewrk)
• ziglang/zig #9050 golang linker segfault (CLOSED, thanks kubkon)
• ziglang/zig #7917 [meta] better c/c++ toolchain compatibility (CLOSED, thanks andrewrk)
• ziglang/zig #7915 ar-compatible command for zig cc (CLOSED, thanks andrewrk)
• ziglang/zig #7667 misplaced relocated glibc stubs (pthread_sigmask) (CLOSED, thanks mjonaitis and andrewrk)
• rules/go #2894 Per-arch_target linker flags (CLOSED, thanks mjonaitis)
• golang/go #46644 cmd/link: with CC=zig: SIGSERV when cross-compiling to darwin/amd64 (CLOSED, thanks kubkon)

Testing

Transient docker environment

First of all, make sure that your kernel is configured to run arm64 binaries. You can either apt install qemu-user-static binfmt-support; this should setup binfmt_misc to handle arm64 binaries. Or you can use this handy dockerized script docker run --rm --privileged multiarch/qemu-user-static --reset -p yes.

$ docker run -e CC=/usr/bin/false -ti --rm -v $(git rev-parse --show-toplevel):/x -w /x debian:bullseye-slim
# dpkg --add-architecture arm64 && apt update && apt install -y direnv git shellcheck libc6:arm64
# . .envrc
# ./ci/test
# ./ci/lint

See ci/test for how tests are run.

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.