Fix sem_clockwait detection for cross-compiled builds#985
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andiradulescu wants to merge 2 commits intoastral-sh:mainfrom
Open
Fix sem_clockwait detection for cross-compiled builds#985andiradulescu wants to merge 2 commits intoastral-sh:mainfrom
andiradulescu wants to merge 2 commits intoastral-sh:mainfrom
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When cross-compiling against old glibc headers (e.g., Debian Stretch's glibc 2.24), configure cannot detect sem_clockwait (added in glibc 2.30). This causes CPython to fall back to sem_timedwait with CLOCK_REALTIME, making threading.Event.wait() hang indefinitely when the system clock jumps backward (e.g., NTP sync). Add patches that declare sem_clockwait as a weak symbol on Linux when configure didn't detect it. At runtime, the weak symbol resolves to the real function on glibc 2.30+ or to NULL on older glibc. The patched code checks this at runtime and falls back to sem_timedwait gracefully. Version-specific patches for CPython 3.10, 3.11, 3.12, and 3.13+ account for differences in the threading internals across versions.
…rom repo All version-specific patches now follow the same naming convention. The test script is kept locally for manual verification on devices.
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When cross-compiling against old glibc headers (e.g., Debian Stretch's
glibc 2.24), configure cannot detectsem_clockwait(added in glibc 2.30). This causes CPython to fall back tosem_timedwaitwith CLOCK_REALTIME, makingthreading.Event.wait()hang indefinitely when the system clock jumps backward (e.g., NTP sync).Add patches that declare
sem_clockwaitas a weak symbol on Linux when configure didn't detect it. At runtime, the weak symbol resolves to the real function onglibc 2.30+or to NULL on older glibc. The patched code checks this at runtime and falls back tosem_timedwaitgracefully.Version-specific patches for CPython 3.10, 3.11, 3.12, and 3.13+ account for differences in the threading internals across versions.
The issue was first discovered in commaai/openpilot#33993 (comment)
Test results
All patches verified by building on Debian Stretch (glibc 2.24, where
sem_clockwaitdoesn't exist in headers) and running on Debian Bookworm (glibc 2.36):Event.wait(0.1)sem_timedwaitfallbacktest-sem-clockwait.py