From a9f859b516ac98c06b0d24e691fceab32a9665d5 Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Tue, 16 Sep 2025 15:48:00 +0200 Subject: [PATCH] s390/bitops: Limit return value range of __flogr() With the recent ffs() and ffs64() optimization a logical AND operation was removed, which allowed the compiler to tell the return value range of both functions. This may lead to compile warnings as reported by the kernel test robot: drivers/infiniband/hw/mlx5/mr.c: In function 'mlx5r_cache_create_ent_locked': >> drivers/infiniband/hw/mlx5/mr.c:840:31: warning: 'sprintf' may write a terminating nul past the end of the destination [-Wformat-overflow=] 840 | sprintf(ent->name, "%d", order); | ^ In function 'mlx5_mkey_cache_debugfs_add_ent', inlined from 'mlx5r_cache_create_ent_locked' at drivers/infiniband/hw/mlx5/mr.c:930:3: drivers/infiniband/hw/mlx5/mr.c:840:9: note: 'sprintf' output between 2 and 5 bytes into a destination of size 4 840 | sprintf(ent->name, "%d", order); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Add the AND operation again to address the warning. From a correctness point of view the AND operation is not necessary, however there is no other way to tell the compiler that the returned value of the flogr inline assembly is in the range of 0..64. This increases the kernel image size by 566 bytes (defconfig, gcc 15.2.0). Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-kbuild-all/202508211859.UoYsJbLN-lkp@intel.com/ Fixes: de88e74889a3 ("s390/bitops: Slightly optimize ffs() and fls64()") Suggested-by: Juergen Christ Reviewed-by: Juergen Christ Signed-off-by: Heiko Carstens Signed-off-by: Alexander Gordeev --- arch/s390/include/asm/bitops.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/s390/include/asm/bitops.h b/arch/s390/include/asm/bitops.h index 9dfb687ba6200..9bc70acbac9ec 100644 --- a/arch/s390/include/asm/bitops.h +++ b/arch/s390/include/asm/bitops.h @@ -169,7 +169,7 @@ static __always_inline unsigned char __flogr(unsigned long word) asm volatile( " flogr %[rp],%[rp]\n" : [rp] "+d" (rp.pair) : : "cc"); - return rp.even; + return rp.even & 127; } } -- 2.47.3