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fix: detect musl libc when downloading python-build-standalone - #2889
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`platform.libc_ver()` only ever reports glibc and returns `("", "")` on
musl systems, so `"musl" in platform.libc_ver()` was never true and musl
hosts (e.g. Alpine) always selected the `gnu` python-build-standalone
asset, which won't run.
Detect musl by shelling out to `ldd --version`, which prints "musl libc"
on musl-based systems. This probes the actual system loader rather than
the host Python's linkage, so it stays correct even when cibuildwheel
runs under a relocatable/statically-linked interpreter. Falls back to
glibc when `ldd` is unavailable.
Assisted-by: ClaudeCode:claude-opus-4.8
Assisted-by: ClaudeCode:claude-opus-4.8
joerick
approved these changes
Jun 3, 2026
joerick
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Thanks. Not sure how I ended up with the libc_ver() approach!
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The current check is never true. Using
('', '')might assume musl for something like portable Python, so used a more complex check.🤖 AI text below 🤖
Problem
platform.libc_ver()only ever reports glibc — it returns("", "")on musl systems. The musl detection inpython_build_standalone.py:could therefore never be true, so musl hosts (e.g. Alpine) always selected the
gnupython-build-standalone asset, which won't run there.Fix
Detect musl by shelling out to
ldd --version, which printsmusl libcon musl-based systems (andGLIBC/GNU libcon glibc). This probes the actual system loader rather than the host Python's linkage, so it stays correct even when cibuildwheel runs under a relocatable/statically-linked interpreter (including a python-build-standalone one). Falls back to glibc whenlddis unavailable.Adds unit tests for musl/glibc/missing-
ldddetection and the resulting libc identifier.