Messages in this thread | | | From | Nick Desaulniers <> | Date | Wed, 8 Jun 2022 14:16:47 -0700 | Subject | Re: [PATCH v2] include/uapi/linux/swab.h: move explicit cast outside ternary |
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On Wed, Jun 8, 2022 at 1:09 PM Andrew Morton <akpm@linux-foundation.org> wrote: > > 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 >
Ah, I see what went wrong.
Justin added more than I requested. Compare the diffstat between: https://lore.kernel.org/llvm/CAKwvOd=-NXR5HoHwwEUZMsCt90oaADH6XHifje9n-8S8rj9SFw@mail.gmail.com/ with the v2: https://lore.kernel.org/llvm/20220608001422.26383-1-jstitt007@gmail.com/
Justin, please send a v3 dropping the changes made to the "__HAVE_BUILTIN_BSWAP*__ is defined" case; just make the changes I suggested.
In addition, please add to the commit message this snippet from Al: ``` As Al Viro notes:
You *can't* get smaller-than-int out of ? :, same as you can't get it out of addition, etc. ```
Finally, Justin, you can retest this by running: $ ARCH=arm make LLVM=1 -j72 allmodconfig fs/xfs/scrub/agheader.o with your patch applied to linux-next. (It wouldn't hurt to build the whole thing...but it's next, which is red today for ARCH=arm so nvm: https://github.com/ClangBuiltLinux/continuous-integration2/runs/6796317443?check_suite_focus=true). https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git -- Thanks, ~Nick Desaulniers
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