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6606c8c7e8
While tracking down a problem where constant expressions used by BUILD_BUG_ON() suddenly stopped working[1], we found that an added static initializer was convincing the compiler that it couldn't track the state of the prior statically initialized value. Tracing this down found that ffs() was used in the initializer macro, but since it wasn't marked with __attribute__const__, the compiler had to assume the function might change variable states as a side-effect (which is not true for ffs(), which provides deterministic math results). Add missing __attribute_const__ annotations to generic implementations of ffs(), __ffs(), fls(), and __fls() functions. These are pure mathematical functions that always return the same result for the same input with no side effects, making them eligible for compiler optimization. Build tested with x86_64 defconfig using GCC 14.2.0, which should validate the implementations when used by ARM, ARM64, LoongArch, Microblaze, NIOS2, and SPARC32 architectures. Link: https://github.com/KSPP/linux/issues/364 [1] Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20250804164417.1612371-2-kees@kernel.org Signed-off-by: Kees Cook <kees@kernel.org> |
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