bootstrap: Detect musl hosts #144092

Gelbpunkt · 2025-07-17T22:48:44Z

Currently, all non-Android Linux hosts are assumed to be using glibc. This obviously isn't very portable and will currently result in downloading a stage0 toolchain for glibc even on musl hosts.

There are multiple ways to detect musl somewhat reliably, but the easiest option is to check for the python target, which is exposed in sys.implementation._multiarch and has values like "x86_64-linux-gnu" or "powerpc64le-linux-musl".

rustbot · 2025-07-17T22:48:48Z

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Gelbpunkt · 2025-07-17T22:51:18Z

The alternative I would suggest is to check ldd --version for the string musl, but that would require a larger, more intrusive change, since it outputs to stderr, while the current command execution code only accounts for stdout. I think the python target is sufficient.

Kobzol · 2025-07-18T06:02:58Z

Is there a way to get this information in Python with public (i.e. not _) API?

Gelbpunkt · 2025-07-18T06:33:27Z

Is there a way to get this information in Python with public (i.e. not _) API?

sysconfig.get_config_var("MULTIARCH") would also work, although from what I read in some cpython issues, SOABI is probably the preferred config var to check.

Kobzol · 2025-07-18T07:09:56Z

Ok. This looks simple enough. If it causes any trouble, we can later wrap it in a try/except block. There are some CPU architectures for which we have a GNU build, but don't have a MUSL build though:

~$ rustup target list -q | grep -e "-linux-gnu$"
aarch64-unknown-linux-gnu
i586-unknown-linux-gnu
i686-unknown-linux-gnu
loongarch64-unknown-linux-gnu
powerpc-unknown-linux-gnu
powerpc64-unknown-linux-gnu
powerpc64le-unknown-linux-gnu
riscv64gc-unknown-linux-gnu
s390x-unknown-linux-gnu
sparc64-unknown-linux-gnu
x86_64-unknown-linux-gnu
~$ rustup target list -q | grep -e "-linux-musl$"
aarch64-unknown-linux-musl
i586-unknown-linux-musl
i686-unknown-linux-musl
loongarch64-unknown-linux-musl
powerpc64le-unknown-linux-musl
riscv64gc-unknown-linux-musl
x86_64-unknown-linux-musl

Not sure if anyone runs bootstrap on s390x/sparc/powerpc/powerpc64...

If I understand it correctly, if -gnu stage0 is downloaded on a MUSL system, it's useless, because your system doesn't have glibc at all? In that case the missing architectures wouldn't be an issue, as bootstrap wouldn't work on them before anyway.

r? @Kobzol

Gelbpunkt · 2025-07-18T07:22:12Z

Not sure if anyone runs bootstrap on s390x/sparc/powerpc/powerpc64...

I'm running it on powerpc64(le) at the moment x)

If I understand it correctly, if -gnu stage0 is downloaded on a MUSL system, it's useless, because your system doesn't have glibc at all?

Correct, the stage0 is completely useless and cannot be executed.

I would be very surprised to see someone with a Python build for musl bootstrapping rustc with glibc as their system libc.

Kobzol · 2025-07-18T07:26:06Z

I'm running it on powerpc64(le) at the moment x)

Well the le variant has a musl build :)

Ok, I agree that the described situation should be quite rare. Let's try.

@bors r+ rollup

bors · 2025-07-18T07:26:09Z

📌 Commit 2e99b18 has been approved by Kobzol

It is now in the queue for this repository.

Gelbpunkt · 2025-07-18T07:27:41Z

Should I really not change it to use sysconfig.get_config_var("SOABI")? I'm fine either way, just want to make sure you're okay with this as is

Gelbpunkt · 2025-07-18T07:28:12Z

Well the le variant has a musl build :)

And here's the output on powerpc64-unknown-linux-musl host with this PR:

RuntimeError: src/stage0 doesn't contain a checksum for dist/2025-06-24/rust-std-beta-powerpc64-unknown-linux-musl.tar.xz. Pre-built artifacts might not be available for this target at this time, see https://doc.rust-lang.org/nightly/rustc/platform-support.html for more information.

Kobzol · 2025-07-18T07:33:36Z

Should I really not change it to use sysconfig.get_config_var("SOABI")? I'm fine either way, just want to make sure you're okay with this as is

Oh, I misunderstood your earlier comment, I somehow thought that "SOABI" refers to the way the arch is checked in the current version of this PR. In that case yes, please switch to the approach using public API.

@bors r-

Currently, all non-Android Linux hosts are assumed to be using glibc. This obviously isn't very portable and will currently result in downloading a stage0 toolchain for glibc even on musl hosts. There are multiple ways to detect musl somewhat reliably, but the easiest option is to check for the python SOABI config variable, which has values like "cpython-313-x86_64-linux-gnu" or "cpython-313-powerpc64-linux-musl". Signed-off-by: Jens Reidel <adrian@travitia.xyz>

Gelbpunkt · 2025-07-18T07:40:40Z

Changed it to use SOABI :)

@rustbot ready

Kobzol · 2025-07-18T07:41:27Z

Thanks!

@bors r+ rollup

bors · 2025-07-18T07:41:30Z

📌 Commit 9e4f777 has been approved by Kobzol

It is now in the queue for this repository.

Rollup of 10 pull requests Successful merges: - #141076 (fix Zip unsoundness (again)) - #142444 (adding run-make test to autodiff) - #143704 (Be a bit more careful around exotic cycles in in the inliner) - #144073 (Don't test panic=unwind in panic_main.rs on Fuchsia) - #144083 (miri sleep tests: increase slack) - #144092 (bootstrap: Detect musl hosts) - #144098 (Do not lint private-in-public for RPITIT) - #144103 (Rename `emit_unless` to `emit_unless_delay`) - #144108 (Ignore tests/run-make/link-eh-frame-terminator/rmake.rs when cross-compiling) - #144115 (fix outdated comment) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #144092 - Gelbpunkt:musl-stage0, r=Kobzol bootstrap: Detect musl hosts Currently, all non-Android Linux hosts are assumed to be using glibc. This obviously isn't very portable and will currently result in downloading a stage0 toolchain for glibc even on musl hosts. There are multiple ways to detect musl somewhat reliably, but the easiest option is to check for the python target, which is exposed in `sys.implementation._multiarch` and has values like "x86_64-linux-gnu" or "powerpc64le-linux-musl".

Rollup of 10 pull requests Successful merges: - rust-lang/rust#141076 (fix Zip unsoundness (again)) - rust-lang/rust#142444 (adding run-make test to autodiff) - rust-lang/rust#143704 (Be a bit more careful around exotic cycles in in the inliner) - rust-lang/rust#144073 (Don't test panic=unwind in panic_main.rs on Fuchsia) - rust-lang/rust#144083 (miri sleep tests: increase slack) - rust-lang/rust#144092 (bootstrap: Detect musl hosts) - rust-lang/rust#144098 (Do not lint private-in-public for RPITIT) - rust-lang/rust#144103 (Rename `emit_unless` to `emit_unless_delay`) - rust-lang/rust#144108 (Ignore tests/run-make/link-eh-frame-terminator/rmake.rs when cross-compiling) - rust-lang/rust#144115 (fix outdated comment) r? `@ghost` `@rustbot` modify labels: rollup

rustbot assigned albertlarsan68 Jul 17, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-bootstrap Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap) labels Jul 17, 2025

rustbot assigned Kobzol and unassigned albertlarsan68 Jul 18, 2025

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 18, 2025

bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Jul 18, 2025

Gelbpunkt force-pushed the musl-stage0 branch from 2e99b18 to 9e4f777 Compare July 18, 2025 07:40

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 18, 2025

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 18, 2025

matthiaskrgr mentioned this pull request Jul 19, 2025

Rollup of 10 pull requests #144166

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bors merged commit 870d429 into rust-lang:master Jul 19, 2025
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rustbot added this to the 1.90.0 milestone Jul 19, 2025

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bootstrap: Detect musl hosts #144092

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