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Explain the arm64 prefer-atomic gcov flag in the flags differential - #127
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The 7.2.8 arm64 allmodconfig census lists
-fprofile-update=prefer-atomicin 1445 units built by rucc and none built by gcc. The kernel's Makefile adds the flag to CFLAGS_GCOV only when it brings in no undefined symbol that the build without it lacks. On arm64 gcc turns on-moutline-atomicsby default, so its atomic counter add calls__aarch64_ldadd8_relaxand the probe fails. rucc has no outline atomics and inlines the add, so the probe passes.Before tamnd/rucc#3772 rucc also ignored the flag. Its counters are atomic adds now, which is what the kernel asks for, so the difference is only in which way each compiler does an atomic add. This adds a
[[flags]]entry with that reason.Part of #7.