Differential D52502

libc: Have memcmp test what's actually required by the standard
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Authored by emaste on Sep 12 2025, 4:23 PM.

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fuz
jilles
imp
markj

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rG79e4dfe2a5f7: libc: Have memcmp test what the standard requires
rGe0eaabb80d17: libc: Have memcmp test what the standard requires

Summary

libc's C memcmp currently returns the difference in byte values rather than just -1/0/1 as the AArch64 assembly implementation, and many non-FreeBSD implementations, do.

It is a bug for a user to expect memcmp to return the difference in the byte values as the compiler is free to inline memcmp() with an implementation that does not do this. Change the test to validate only what the standard requires.

PR: 289084

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rG FreeBSD src repository

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Tests Not Applicable

Event Timeline

emaste requested review of this revision.Sep 12 2025, 4:23 PM

emaste created this revision.

emaste added inline comments.

lib/libc/tests/string/memcmp_test.c
48

markj accepted this revision.Sep 12 2025, 5:59 PM

This revision is now accepted and ready to land.Sep 12 2025, 5:59 PM

Yeah sure why not.

Closed by commit rGe0eaabb80d17: libc: Have memcmp test what the standard requires (authored by emaste). · Explain WhySep 13 2025, 7:30 PM

This revision was automatically updated to reflect the committed changes.

emaste added a commit: rGe0eaabb80d17: libc: Have memcmp test what the standard requires.

emaste added a commit: rG79e4dfe2a5f7: libc: Have memcmp test what the standard requires.Sep 16 2025, 5:35 PM

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lib/

libc/

tests/

string/

12 lines

Diff 161983

lib/libc/tests/string/memcmp_test.c

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