Re: [PATCH 13/17] parisc: Add __attribute_const__ to ffs()-family implementations

[Helge Deller]

On 8/4/25 18:44, 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 PARISC's implementations of
> ffs(), __ffs(), 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 ARCH=parisc defconfig with GCC hppa-linux-gnu 14.2.0.
>
> Link: https://github.com/KSPP/linux/issues/364 [1]
> Signed-off-by: Kees Cook <kees@xxxxxxxxxx>
> ---
>   arch/parisc/include/asm/bitops.h | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)

Acked-by: Helge Deller <deller@xxxxxx>