The patch titled
Subject: byteswap-try-to-avoid-__builtin_constant_p-gcc-bug-v2-fix
has been added to the -mm tree. Its filename is
byteswap-try-to-avoid-__builtin_constant_p-gcc-bug-v2-fix.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/byteswap-try-to-avoid-__builtin_constant_p-gcc-bug-v2-fix.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/byteswap-try-to-avoid-__builtin_constant_p-gcc-bug-v2-fix.patch
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From: Arnd Bergmann <arnd@xxxxxxxx>
Subject: byteswap-try-to-avoid-__builtin_constant_p-gcc-bug-v2-fix
> > > net/tipc/name_distr.c: In function 'tipc_named_process_backlog':
> > > net/tipc/name_distr.c:330: warning: format '%u' expects type 'unsigned int', but argument 3 has type 'unsigned int'
> > > net/tipc/name_distr.c:330: warning: format '%u' expects type 'unsigned int', but argument 4 has type 'unsigned int'
> > > net/tipc/name_distr.c:330: warning: format '%u' expects type 'unsigned int', but argument 5 has type 'unsigned int'
> > > net/tipc/name_distr.c:330: warning: format '%u' expects type 'unsigned int', but argument 7 has type 'unsigned int'
> >
> > I've built a few thousand kernels (arm32 with gcc-6.1) with the patch applied,
> > but didn't see this one. What target architecture and compiler version produced
> > this? Does it go away if you add a (__u32) cast? I don't even know what the
> > warning is trying to tell me.
>
> heh, I didn't actually read it.
>
> Hopefully we can write this off as a gcc-4.4.4 glitch. 4.8.4 is OK.
Ah, old compiler. I've tried gcc-4.3 now on ARM, and I don't get this warning
(just a lot "may be used uninitialized"), but unlike gcc-4.4, my version doesn't
actually get into the code path I have changed because __builtin_bswap32 was only
introduced with 4.4.
I don't have gcc-4.4 and 4.5 here, but the warning does show up with 4.6, 4.7
and 4.8:
drivers/soc/sunxi/sunxi_sram.c: In function `sunxi_sram_show':
drivers/soc/sunxi/sunxi_sram.c:103:7: warning: format `%x' expects argument of type `unsigned int', but argument 3 has type `unsigned int' [-Wformat=]
4.8 is probably still common enough that we should try to address this.
This change addresses the problem for me with ARM gcc-4.8, but adding
two more type casts. This also makes the 16/32/64 bit swaps all
look the same. I would expect this to also have the same effect on 4.4.
Link: http://lkml.kernel.org/r/12243652.bxSxEgjgfk@wuerfel
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> # on gcc-5.3
Cc: Quinn Tran <quinn.tran@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/uapi/linux/swab.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff -puN include/uapi/linux/swab.h~byteswap-try-to-avoid-__builtin_constant_p-gcc-bug-v2-fix include/uapi/linux/swab.h
--- a/include/uapi/linux/swab.h~byteswap-try-to-avoid-__builtin_constant_p-gcc-bug-v2-fix
+++ a/include/uapi/linux/swab.h
@@ -97,7 +97,7 @@ static inline __attribute_const__ __u32
* @x: value to byteswap
*/
#ifdef __HAVE_BUILTIN_BSWAP16__
-#define __swab16(x) __builtin_bswap16((__u16)(x))
+#define __swab16(x) (__u16)__builtin_bswap16((__u16)(x))
#else
#define __swab16(x) \
(__builtin_constant_p((__u16)(x)) ? \
@@ -110,7 +110,7 @@ static inline __attribute_const__ __u32
* @x: value to byteswap
*/
#ifdef __HAVE_BUILTIN_BSWAP32__
-#define __swab32(x) __builtin_bswap32((__u32)(x))
+#define __swab32(x) (__u32)__builtin_bswap32((__u32)(x))
#else
#define __swab32(x) \
(__builtin_constant_p((__u32)(x)) ? \
_
Patches currently in -mm which might be from arnd@xxxxxxxx are
byteswap-try-to-avoid-__builtin_constant_p-gcc-bug-v2.patch
byteswap-try-to-avoid-__builtin_constant_p-gcc-bug-v2-fix.patch
kernel-padata-hide-unused-functions.patch
drm-amdgpu-make-amdgpu_mn_get-wait-for-mmap_sem-killable-fix.patch
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