235 lines
9.1 KiB
Markdown
235 lines
9.1 KiB
Markdown
[](https://builds.sr.ht/~motiejus/bazel-zig-cc)
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# Bazel zig cc toolchain
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This is a C/C++ toolchain that can (cross-)compile C/C++ programs. It contains
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clang-13, musl, glibc (versions 2-2.34, selectable), all in a ~40MB package.
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Read
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[here](https://andrewkelley.me/post/zig-cc-powerful-drop-in-replacement-gcc-clang.html)
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about zig-cc; the rest of the README will present how to use this toolchain
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from Bazel.
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# Usage
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Add this to your `WORKSPACE`:
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```
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BAZEL_ZIG_CC_VERSION = "v0.4.5"
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http_archive(
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name = "bazel-zig-cc",
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sha256 = "5888e46c3a6089d4a79b6a5cac8c397e3642ed732910cec8a1011986d68a112b",
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strip_prefix = "bazel-zig-cc-{}".format(BAZEL_ZIG_CC_VERSION),
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urls = ["https://git.sr.ht/~motiejus/bazel-zig-cc/archive/{}.tar.gz".format(BAZEL_ZIG_CC_VERSION)],
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)
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load("@bazel-zig-cc//toolchain:defs.bzl", zig_register_toolchains = "register_toolchains")
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zig_register_toolchains()
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```
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And this to `.bazelrc`:
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```
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build --incompatible_enable_cc_toolchain_resolution
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build --extra_toolchains @zig_sdk//:linux_amd64_gnu.2.19_toolchain
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build --extra_toolchains @zig_sdk//:linux_arm64_gnu.2.28_toolchain
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build --extra_toolchains @zig_sdk//:darwin_amd64_toolchain
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build --extra_toolchains @zig_sdk//:darwin_arm64_toolchain
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```
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The snippets above will download the zig toolchain and register it for the
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following platforms:
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- `x86_64-linux-gnu.2.19` for `["@platforms//os:linux", "@platforms//cpu:x86_64"]`.
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- `x86_64-linux-gnu.2.28` for `["@platforms//os:linux", "@platforms//cpu:aarch64"]`.
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- `x86_64-macos-gnu` for `["@platforms//os:macos", "@platforms//cpu:x86_64"]`.
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- `aarch64-macos-gnu` for `["@platforms//os:macos", "@platforms//cpu:aarch64"]`.
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Note that both Go and Bazel naming schemes are accepted. For convenience with
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Go, the following Go-style toolchain aliases are created:
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|Bazel (zig) name | Go name |
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|---------------- | -------- |
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|`x86_64` | `amd64` |
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|`aarch64` | `arm64` |
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|`macos` | `darwin` |
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For example, the toolchain `linux_amd64_gnu.2.28` is aliased to
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`x86_64-linux-gnu.2.28`. To find out which toolchains can be registered or
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used, run:
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```
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$ bazel query @zig_sdk//... | grep _toolchain$
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```
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## Specifying non-default toolchains
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You may explicitly request Bazel to use a specific toolchain, even though a
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different one is registered using `--extra_toolchains <toolchain>` in
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`.bazelrc`. For example, if you wish to compile a specific binary (or run
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tests) on linux/amd64/musl, you may specify:
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```
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--extra_toolchains @zig_sdk//:linux_amd64_musl_toolchain
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```
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## UBSAN and "SIGILL: Illegal Instruction"
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`zig cc` differs from "mainstream" compilers by [enabling UBSAN by
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default][ubsan1]. Which means your program may compile successfully and crash
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with:
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```
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SIGILL: illegal instruction
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```
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This is by design: it encourages program authors to fix the undefined behavior.
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There are [many ways][ubsan2] to find the undefined behavior.
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# Known Issues In bazel-zig-cc
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These are the things you may stumble into when using bazel-zig-cc. I am
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unlikely to implement them any time soon, but patches implementing those will
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be accepted. See [Questions & Contributions](#questions-amp-contributions) on
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how to contribute.
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## Zig cache
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Currently zig cache is in `$HOME`, so `bazel clean --expunge` does not clear
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the zig cache. Zig's cache should be stored somewhere in the project's path.
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## Alternative download URLs
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Currently zig is downloaded from
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[dl.jakstys.lt/zig](https://dl.jakstys.lt/zig/), which is nuts. One should
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provide a way to specify alternative URLs for the zig toolchain.
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## Toolchain and platform target locations
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The path to Bazel toolchains is `@zig_sdk//:<toolchain>_toolchain`. It should
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be moved to `@zig_sdk//toolchain:<toolchain>` or similar; so the user-facing
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targets are in their own namespace.
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Likewise, platforms are `@zig_sdk//:<platform>_platform`, and should be moved
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to `@zig_sdk//:platform:<platform>`.
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## OSX: sysroot
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For non-trivial programs (and for all darwin/arm64 cgo programs) MacOS SDK may
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be necessary. Read [Jakub's comment][sysroot] about it. Support for OSX sysroot
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is currently not implemented.
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## OSX: different OS targets (Catalina -- Monterey)
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[Zig 0.9.0](https://ziglang.org/download/0.9.0/release-notes.html#macOS) may
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target macos.10 (Catalina), macos.11 (Big Sur) or macos.12 (Monterey). It
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currently targets the lowest version, without ability to change it.
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# Known Issues In Upstream
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This section lists issues that I've stumbled into when using `zig cc`, and is
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outside of bazel-zig-cc's control.
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## using glibc 2.27 or older
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**Severity: Low**
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Task: [ziglang/zig #9485 glibc 2.27 or older: fcntl64 not found, but zig's glibc headers refer it](https://github.com/ziglang/zig/issues/9485)
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Background: when glibc 2.27 or older is selected, it may miss `fcntl64`. A
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workaround is applied for `x86_64`, but not for aarch64. The same workaround
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may apply to aarch64, but the author didn't find a need to test it (yet).
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# Closed Upstream Issues
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- [ziglang/zig #10386 zig cc regression in 0.9.0](https://github.com/ziglang/zig/issues/10386)(CLOSED, thanks Xavier)
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- [ziglang/zig #10312 macho: fail if requested -framework is not found](https://github.com/ziglang/zig/pull/10312) (CLOSED, thanks kubkon)
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- [ziglang/zig #10299 [darwin aarch64 cgo] regression](https://github.com/ziglang/zig/issues/10299) (CLOSED, thanks kubkon)
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- [ziglang/zig #10297 [darwin x86_64 cgo] regression](https://github.com/ziglang/zig/issues/10297) (CLOSED, thanks kubkon)
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- [ziglang/zig #9431 FileNotFound when compiling macos](https://github.com/ziglang/zig/issues/9431) (CLOSED, thanks andrewrk)
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- [ziglang/zig #9139 zig c++ hanging when compiling in parallel](https://github.com/ziglang/zig/issues/9139) (CLOSED, thanks andrewrk)
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- [ziglang/zig #9050 golang linker segfault](https://github.com/ziglang/zig/issues/9050) (CLOSED, thanks kubkon)
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- [ziglang/zig #7917 [meta] better c/c++ toolchain compatibility](https://github.com/ziglang/zig/issues/7917) (CLOSED, thanks andrewrk)
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- [ziglang/zig #7915 ar-compatible command for zig cc](https://github.com/ziglang/zig/issues/7915) (CLOSED, thanks andrewrk)
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- [ziglang/zig #7667 misplaced relocated glibc stubs (pthread_sigmask)](https://github.com/ziglang/zig/issues/7667) (CLOSED, thanks mjonaitis and andrewrk)
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- [rules/go #2894 Per-arch_target linker flags](https://github.com/bazelbuild/rules_go/issues/2894) (CLOSED, thanks mjonaitis)
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- [golang/go #46644 cmd/link: with CC=zig: SIGSERV when cross-compiling to darwin/amd64](https://github.com/golang/go/issues/46644) (CLOSED, thanks kubkon)
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# Testing
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## build & run linux cgo + glibc
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```
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$ bazel build --platforms @zig_sdk//:linux_amd64_platform //test/go:go
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$ file bazel-out/k8-opt-ST-d17813c235ce/bin/test/go/go_/go
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bazel-out/k8-opt-ST-d17813c235ce/bin/test/go/go_/go: 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
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$ bazel-out/k8-opt-ST-d17813c235ce/bin/test/go/go_/go
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hello, world
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```
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## test linux cgo + musl on arm64 (under qemu-aarch64)
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```
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$ bazel test \
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--config=qemu-aarch64 \
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--platforms @zig_sdk//:linux_arm64_platform \
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--extra_toolchains @zig_sdk//:linux_arm64_musl_toolchain //test/...
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...
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INFO: Build completed successfully, 10 total actions
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//test/go:go_test PASSED in 0.2s
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```
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## macos cgo
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```
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$ bazel build --platforms @zig_sdk//:darwin_amd64_platform //test/go:go
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...
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$ file bazel-out/k8-opt-ST-d17813c235ce/bin/test/go/go_/go
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bazel-out/k8-opt-ST-d17813c235ce/bin/test/go/go_/go: Mach-O 64-bit x86_64 executable, flags:<NOUNDEFS|DYLDLINK|TWOLEVEL|PIE|HAS_TLV_DESCRIPTORS>
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```
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## Transient docker environment
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```
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$ docker run -e CC=/usr/bin/false -ti --rm -v $(pwd):/x -w /x debian:bullseye-slim
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# apt update && apt install -y direnv git
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# . .envrc
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```
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And run the `bazel build` commands above. Take a look at `.build.yml` and see
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how CI does it.
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# Questions & Contributions
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Project's mailing list is [~motiejus/bazel-zig-cc][mailing-list]. The mailing
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list is used for:
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- announcements (I am aiming to send an email with every release).
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- user discussions.
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- raising issues.
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- contributions.
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I will generally respond to emails about issues. I may even be able to fix
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them. However, no promises: you are much more likely (and welcome!) to get it
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fixed by submitting a patch.
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To contribute, send your patches to the mailing list, as described in
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[git-send-email.io][git-send-email] or via [Sourcehut web UI][video].
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Copyright is retained by the contributors.
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# Thanks
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Many thanks to Adam Bouhenguel and his [bazel-zig-cc][ajbouh], the parent of
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this repository. Also, the Zig team for making this all possible and handling
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the issues promptly.
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[mailing-list]: https://lists.sr.ht/~motiejus/bazel-zig-cc
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[ajbouh]: https://github.com/ajbouh/bazel-zig-cc/
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[git-send-email]: https://git-send-email.io/
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[video]: https://spacepub.space/w/no6jnhHeUrt2E5ST168tRL
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[sysroot]: https://github.com/ziglang/zig/issues/10299#issuecomment-989153750
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[ubsan1]: https://github.com/ziglang/zig/issues/4830#issuecomment-605491606
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[ubsan2]: https://github.com/ziglang/zig/issues/5163
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