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SubjectRe: [PATCH v2] include/uapi/linux/swab.h: move explicit cast outside ternary
On Tue,  7 Jun 2022 17:14:22 -0700 Justin Stitt <jstitt007@gmail.com> wrote:

> A cast inside __builtin_constant_p doesn't do anything since it should evaluate
> as constant at compile time irrespective of this cast. Instead, I moved this
> cast outside the ternary to ensure the return type is as expected.
>
> For instance, if __HAVE_BUILTIN_BSWAP16__ was not defined then __swab16 is
> actually returning an `int` not a `u16` due to integer promotion as described
> by Nick in this thread. This has repercussions when building with clang
> -Wformat. This fix should solve many of these warnings.
>

ARM allmodconfig:

In file included from ./include/linux/swab.h:5,
from ./arch/arm/include/asm/opcodes.h:86,
from ./arch/arm/include/asm/bug.h:7,
from ./include/linux/bug.h:5,
from ./include/linux/mmdebug.h:5,
from ./include/linux/gfp.h:5,
from ./include/linux/slab.h:15,
from ./fs/xfs/kmem.h:9,
from ./fs/xfs/xfs_linux.h:24,
from ./fs/xfs/xfs.h:22,
from fs/xfs/scrub/agheader.c:6:
fs/xfs/scrub/agheader.c: In function 'xchk_superblock':
./include/uapi/linux/byteorder/little_endian.h:42:52: error: unsigned conversion from 'int' to 'short unsigned int' changes value from '-49265' to '16271' [-Werror=overflow]
42 | #define __cpu_to_be16(x) ((__force __be16)__swab16((x)))
| ^~~
./include/uapi/linux/swab.h:102:46: note: in definition of macro '__swab16'
102 | #define __swab16(x) (__u16)__builtin_bswap16(x)
| ^
./include/linux/byteorder/generic.h:96:21: note: in expansion of macro '__cpu_to_be16'
96 | #define cpu_to_be16 __cpu_to_be16
| ^~~~~~~~~~~~~
fs/xfs/scrub/agheader.c:158:23: note: in expansion of macro 'cpu_to_be16'
158 | vernum_mask = cpu_to_be16(~XFS_SB_VERSION_OKBITS |
| ^~~~~~~~~~~
cc1: all warnings being treated as errors
make[2]: *** [scripts/Makefile.build:249: fs/xfs/scrub/agheader.o] Error 1
make[1]: *** [scripts/Makefile.build:466: fs/xfs] Error 2
make: *** [Makefile:1839: fs] Error 2

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