motiejus/hermetic_cc_toolchain
1
Fork 0
Code Releases Activity

README updates

Browse Source 
- more robust transient docker environment
- clarify platform vs subset
This commit is contained in:
Motiejus Jakštys 2022-04-21 08:31:24 +03:00
parent d4f40a19fb
commit 0e62918e88
1 changed files with 32 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

55
README.md
View File

@ -98,7 +98,8 @@ compatible with (in Bazelspeak, `target_compatible_with`) **all of the**
### Option `--toolchains=@zig_sdk//toolchain:linux_arm64_musl`
Inspect first:
Inspect first (`@platforms//cpu:aarch64` is an alias to
`@platforms//cpu:arm64`):
```
$ bazel query --output=build @zig_sdk//toolchain:linux_arm64_musl
@ -108,22 +109,16 @@ toolchain(
generator_function = "declare_toolchains",
generator_location = "toolchain/BUILD:7:19",
toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
target_compatible_with = [
"@platforms//os:linux",
"@platforms//cpu:aarch64",
"@zig_sdk//libc:unconstrained",
],
target_compatible_with = ["@platforms//os:linux", "@platforms//cpu:aarch64", "@zig_sdk//libc:unconstrained"],
toolchain = "@zig_sdk//private:aarch64-linux-musl_cc",
)
```
The above means toolchain is compatible with platforms that include
`@platforms//os:linux`, `@platforms//cpu:aarch64` (an alias to
`@platforms//cpu:arm64`) and `@zig_sdk//libc:unconstrained`. For a platform to
pick up the right toolchain, the toolchain's `target_compatible_with` must be
equivalent or a superset to the platforms `constraint_values`. Since the
toolchain is a superset (therefore, `libc:unconstrained` does not matter here),
the platform is compatible with this toolchain. As a result, `--platforms
For a platform to pick up the right toolchain, the platform's
`constraint_values` must be a subset[^1] of the toolchain's
`target_compatible_with`. Since the platform is a subset (therefore,
toolchain's `@zig_sdk//libc:unconstrained` does not matter), this toolchain is
selected for this platform. As a result, `--platforms
@zig_sdk//platform:linux_amd64` causes Bazel to select a toolchain
`@zig_sdk//platform:linux_arm64_musl` (because it satisfies all constraints),
which will compile and link the C/C++ code with musl.
@ -343,24 +338,35 @@ may apply to aarch64, but the author didn't find a need to test it (yet).
- [rules/go #2894 Per-arch_target linker flags](https://github.com/bazelbuild/rules_go/issues/2894) (CLOSED, thanks mjonaitis)
- [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)
# Testing
# Host Environments
This repository is used on the following (host) platforms:
- `linux_amd64`, a.k.a. `x86_64`.
- `linux_arm64`, a.k.a. `AArch64`.
- `darwin_amd64`, the post-PowerPC models.
- `darwin_arm64`, the M1.
The tests are running (CId) on linux-amd64, and are assuming the kernel is
configured to run arm64 binaries. There are two reasonably convenient ways to
configure arm64 emulation:
- `$ apt install qemu-user-static binfmt-support`; this should correctly setup
`binfmt_misc`.
- `$ docker run --rm --privileged multiarch/qemu-user-static --reset -p yes`.
## 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`.
A standalone Docker environment to play with bazel-zig-cc:
```
$ 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
$ docker run -e CC=/usr/bin/false -ti --rm -v "$PWD:/x" -w /x debian:bullseye-slim
# dpkg --add-architecture arm64 && apt update
# apt install --no-install-recommends -y direnv git shellcheck ca-certificates libc6:arm64
# eval "$(direnv hook bash)" && direnv allow
# ./ci/test
# ./ci/lint
```
See `ci/test` for how tests are run.
# Questions & Contributions
Project's mailing list is [~motiejus/bazel-zig-cc][mailing-list]. The mailing
@ -386,6 +392,8 @@ Many thanks to Adam Bouhenguel and his [bazel-zig-cc][ajbouh], the parent of
this repository. Also, the Zig team for making this all possible and handling
the issues promptly.
[^1]: a [mathematical subset][subset]: both can be equal.
[mailing-list]: https://lists.sr.ht/~motiejus/bazel-zig-cc
[ajbouh]: https://github.com/ajbouh/bazel-zig-cc/
[git-send-email]: https://git-send-email.io/
@ -394,3 +402,4 @@ the issues promptly.
[ubsan1]: https://github.com/ziglang/zig/issues/4830#issuecomment-605491606
[ubsan2]: https://github.com/ziglang/zig/issues/5163
[transitions]: https://docs.bazel.build/versions/main/skylark/config.html#user-defined-transitions
[subset]: https://en.wikipedia.org/wiki/Subset