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 <lkp@intel.com>
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 <jchrist@linux.ibm.com>
Reviewed-by: Juergen Christ <jchrist@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

diff --git a/arch/s390/include/asm/bitops.h b/arch/s390/include/asm/bitops.h
index 9dfb687ba62009ef01da5cbefe73bcee2a5c5b9e..9bc70acbac9ec48ae92a4a4937e8e1dc70c0acf9 100644 (file)
--- 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;
        }
 }