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 PowerPC's implementations of fls() function. 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 ARCH=powerpc defconfig with GCC powerpc-linux-gnu 14.2.0. Link: https://github.com/KSPP/linux/issues/364 [1] Signed-off-by: Kees Cook <k...@kernel.org> --- arch/powerpc/include/asm/bitops.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/powerpc/include/asm/bitops.h b/arch/powerpc/include/asm/bitops.h index 671ecc6711e3..0d0470cd5ac3 100644 --- a/arch/powerpc/include/asm/bitops.h +++ b/arch/powerpc/include/asm/bitops.h @@ -276,7 +276,7 @@ static inline void arch___clear_bit_unlock(int nr, volatile unsigned long *addr) * fls: find last (most-significant) bit set. * Note fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32. */ -static __always_inline int fls(unsigned int x) +static __always_inline __attribute_const__ int fls(unsigned int x) { int lz; @@ -294,7 +294,7 @@ static __always_inline int fls(unsigned int x) * 32-bit fls calls. */ #ifdef CONFIG_PPC64 -static __always_inline int fls64(__u64 x) +static __always_inline __attribute_const__ int fls64(__u64 x) { int lz; -- 2.34.1