Avoid weak-linking gettid on musl - #160114
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`current_os_id` uses an extern-weak `gettid` declaration so older glibc can fall back to a raw syscall. Rust-supported musl versions provide `gettid`, so musl does not need this probe. During fat LTO, LLVM can merge the weak declaration with a strong reference from another crate and keep the weak linkage. The static linker then does not extract `gettid.o` from `libc.a`, leaving the strong call without a definition. Call `gettid` directly on musl and add a regression test for the returned thread ID. This removes std's contribution to the collision; the underlying LTO linkage bug remains.
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Thanks for the pull request, and welcome! The Rust Project is excited to review your changes, and you should hear from @tgross35 (or someone else) some time within the next two weeks. Please see the contribution instructions for more information. Namely, in order to ensure the minimum review times lag, PR authors and assigned reviewers should ensure that the review label (
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Mitigates #154439.
Summary
current_os_idweak-linksgettidso older glibc can fall back to a raw syscall. Rust-supported musl versions providegettid, so musl does not need that probe.During fat LTO, LLVM can merge the weak declaration with a strong declaration from another crate and keep the weak linkage. A static linker then does not extract
gettid.ofromlibc.a, leaving the strong call without a definition.This calls
gettiddirectly on musl. It follows the musl-specific branch suggested by @tgross35 in #154439. @bjorn3 traced the underlying compiler problem to fat LTO using LLVM’s legacyModuleLinker; changing that compiler-level behavior is intentionally out of scope here, so the issue should remain open.Test
The new run-pass test builds a strong
gettiddeclaration in an auxiliary rlib that sorts afterstd, links it statically under fat LTO, and verifies that the main thread ID equals the process ID. It exits with SIGSEGV against the unpatched x86_64 musl standard library and passes with this change. The value assertion also catches targets where the bad call returns an incorrect thread ID instead of trapping.Validated with:
x86_64-unknown-linux-muslx.py fmt --checkx.py test tidyr? @tgross35