On Mon, Aug 04, 2025 at 09:43:59AM -0700, Kees Cook wrote: > 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 C-SKY's 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. LGTM.
Acked-by: Guo Ren <[email protected]> > > Build tested ARCH=csky defconfig with GCC csky-linux 15.1.0. > > Link: https://github.com/KSPP/linux/issues/364 [1] > Signed-off-by: Kees Cook <[email protected]> > --- > arch/csky/include/asm/bitops.h | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/arch/csky/include/asm/bitops.h b/arch/csky/include/asm/bitops.h > index 72e1b2aa29a0..80d67eee6e86 100644 > --- a/arch/csky/include/asm/bitops.h > +++ b/arch/csky/include/asm/bitops.h > @@ -9,7 +9,7 @@ > /* > * asm-generic/bitops/ffs.h > */ > -static inline int ffs(int x) > +static inline __attribute_const__ int ffs(int x) > { > if (!x) > return 0; > @@ -26,7 +26,7 @@ static inline int ffs(int x) > /* > * asm-generic/bitops/__ffs.h > */ > -static __always_inline unsigned long __ffs(unsigned long x) > +static __always_inline __attribute_const__ unsigned long __ffs(unsigned long > x) > { > asm volatile ( > "brev %0\n" > @@ -39,7 +39,7 @@ static __always_inline unsigned long __ffs(unsigned long x) > /* > * asm-generic/bitops/fls.h > */ > -static __always_inline int fls(unsigned int x) > +static __always_inline __attribute_const__ int fls(unsigned int x) > { > asm volatile( > "ff1 %0\n" > @@ -52,7 +52,7 @@ static __always_inline int fls(unsigned int x) > /* > * asm-generic/bitops/__fls.h > */ > -static __always_inline unsigned long __fls(unsigned long x) > +static __always_inline __attribute_const__ unsigned long __fls(unsigned long > x) > { > return fls(x) - 1; > } > -- > 2.34.1 > >
