188 lines
6.6 KiB
Markdown
188 lines
6.6 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-12, musl, glibc (versions 2-2.33, 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 = "0.3"
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http_archive(
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name = "bazel-zig-cc",
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sha256 = "e78a9930daa40c47fa67de7e371851452d3eedbb5f56d2904d46e2784888e21e",
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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(register = [
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"x86_64-linux-gnu.2.28",
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"x86_64-macos-gnu",
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])
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```
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The snippet 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.2.28` for `["@platforms//os:linux", "@platforms//cpu:x86_64"]`.
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- `x86_64-macos-gnu` for `["@platforms//os:macos", "@platforms//cpu:x86_64"]`.
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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` 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//... | sed -En '/.*_toolchain$/ s/.*:(.*)_toolchain$/\1/p'
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```
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Read [#Known Issues](#known-issues) before using.
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# Known Issues
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## Parallel `zig c++` invocations may fail
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**Severity: High**
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**Task:** [ziglang/zig #9431 FileNotFound when compiling macos](https://github.com/ziglang/zig/issues/9431)
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Background: there is a race when calling `zig c++`, which Bazel does a lot.
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This may fail compilation. Yours truly only reproduced it on macos with a cold
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cache. Based on that, a workaround in the toolchain exists, named
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`speed_first_safety_later`. The possible values are `auto` (default), `yes`,
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`no`.
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## relocation error with glibc < 2.32
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**Severity: High**
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**Task:** [ziglang/zig relocation error: symbol pthread_sigmask version GLIBC_2.2.5 not defined in file libc.so.6 with link time reference #7667](https://github.com/ziglang/zig/issues/7667)
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Background: one of our internal shared libraries (which we must build with glibc 2.19) does not load on an older system:
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```
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id: relocation error: /lib/x86_64-linux-gnu/libnss_uber.so.2: symbol pthread_sigmask, version GLIBC_2.2.5 not defined in file libc.so.6 with link time reference
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```
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Severity is high, because there is no known workaround: the shared library,
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when built with this toolchain, will not work on our target system.
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## fcntl64 linking error on glibc < 2.28
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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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## cgo for darwin (macos)
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**Severity: Low**
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**Task:** [rules/go #2894 Per-arch_target linker flags](https://github.com/bazelbuild/rules_go/issues/2894)
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Background: until there is a better "global" way (i.e. the task is solved), all
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`go_binary` targets destined for Darwin (macos) need an extra `gc_linkopts`
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flag:
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```
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go_binary(
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<...>
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gc_linkopts = select({
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"@platforms//os:macos": ["-s", "-w", "-buildmode=pie"],
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"//conditions:default": [],
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}),
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)
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```
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## incorrect glibc version autodetection
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**Severity: Low**
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**Task:** [ziglang/zig zig detects wrong libc version #6469](https://github.com/ziglang/zig/issues/6469)
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Background: zig detects an incorrect glibc version when not specified.
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Therefore, until the task is resolved, registering a GNU toolchain without a
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version suffix (e.g. `linux_amd64_gnu`) is not recommended. We recommend
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specifying the suffix to the oldest system that is mean to run the compiled
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binaries. This is safe, because glibc is backwards-compatible. Alternatively,
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use musl.
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# Closed issues
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- [ziglang/zig #9139 zig c++ hanging when compiling in parallel](https://github.com/ziglang/zig/issues/9139) (CLOSED)
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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)
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- [ziglang/zig #9050 golang linker segfault](https://github.com/ziglang/zig/issues/9050) (CLOSED)
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- [ziglang/zig #7917 [meta] better c/c++ toolchain compatibility](https://github.com/ziglang/zig/issues/7917) (CLOSED)
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- [ziglang/zig #7915 ar-compatible command for zig cc](https://github.com/ziglang/zig/issues/7915) (CLOSED)
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# Testing
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## linux cgo + glibc 2.19
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```
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$ bazel build --platforms @io_bazel_rules_go//go/toolchain:linux_amd64_cgo //test:hello
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$ file bazel-out/k8-fastbuild-ST-d17813c235ce/bin/test/hello_/hello
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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
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```
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## linux cgo + musl
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```
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$ bazel build \
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--platforms @io_bazel_rules_go//go/toolchain:linux_amd64_cgo \
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--extra_toolchains @zig_sdk//:linux_amd64_musl_toolchain //test:hello
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...
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$ file ../bazel-out/k8-fastbuild-ST-d17813c235ce/bin/test/hello_/hello
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../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
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$ ../bazel-out/k8-fastbuild-ST-d17813c235ce/bin/test/hello_/hello
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hello, world
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```
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## macos cgo
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```
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$ bazel build --platforms @io_bazel_rules_go//go/toolchain:darwin_amd64_cgo //test:gognu
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...
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$ file bazel-bin/test/gognu_/gognu
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bazel-bin/test/gognu_/gognu: Mach-O 64-bit x86_64 executable, flags:<NOUNDEFS|DYLDLINK|TWOLEVEL|PIE>
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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:buster-slim
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# apt update && apt install wget git -y
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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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# Credits
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Many thanks to Adam Bouhenguel and his
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[bazel-zig-cc](https://github.com/ajbouh/bazel-zig-cc/), the parent of this
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repository.
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