Re: [GIT PULL] fallthrough pseudo-keyword macro conversions for 5.9-rc3

[Nathan Chancellor]

On Sun, Aug 23, 2020 at 10:48:41PM -0500, Gustavo A. R. Silva wrote:
> Hi Linus,
> 
> Not sure what the problem was with my pull-request for -rc2. So, I'm giving
> this a second try because I think it is worth it.
> 
> I have build-tested this patch on 10 different architectures: x86_64, i386,
> arm64, powerpc, s390, sparc64, sh, m68k, powerpc64 and alpha (allyesconfig/
> allmodconfig for all of them). This is in linux-next already and kernel
> test robot has also helped me to successfully build-test early versions
> of this patch[2][3][4][5]. This patch does not introduce any new warnings.
> 
> Thank you
> --
> Gustavo
> 
> [1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through
> [2] https://lore.kernel.org/lkml/5f3cc99a.HgvOW3rH0mD0RmkM%25lkp@xxxxxxxxx/
> [3] https://lore.kernel.org/lkml/5f3dd1d2.l1axczH+t4hMBZ63%25lkp@xxxxxxxxx/
> [4] https://lore.kernel.org/lkml/5f3e977a.mwYHUIObbR4SHr0B%25lkp@xxxxxxxxx/
> [5] https://lore.kernel.org/lkml/5f3f9e1c.qsyb%2FaySkiXNpkO4%25lkp@xxxxxxxxx/
> 
> 
> The following changes since commit d012a7190fc1fd72ed48911e77ca97ba4521bccd:
> 
>   Linux 5.9-rc2 (2020-08-23 14:08:43 -0700)
> 
> are available in the Git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git tags/fallthrough-pseudo-keyword-5.9-rc3
> 
> for you to fetch changes up to df561f6688fef775baa341a0f5d960becd248b11:
> 
>   treewide: Use fallthrough pseudo-keyword (2020-08-23 17:36:59 -0500)
> 
> ----------------------------------------------------------------
> fallthrough pseudo-keyword macro conversions for 5.9-rc3
> 
> Hi Linus,
> 
> Please, pull the following tree-wide patch that replaces tons (2484) of
> /* fall through */ comments, and its variants, with the new pseudo-keyword
> macro fallthrough[1]. Also, remove unnecessary fall-through markings when
> it is the case.
> 
> There are currently 1167 intances of this fallthrough pseudo-keyword
> macro in mainline (5.9-rc2), that have been introduced over the last
> couple of development cycles:
> 
> $ git grep -nw 'fallthrough;' | wc -l
> 1167
> 
> The global adoption of the fallthrough pseudo-keyword is something certain
> to happen; so, better sooner than later. :) This will also save everybody's
> time and thousands of lines of unnecessarily repetitive changelog text.
> 
> After applying this patch on top of 5.9-rc2, we'll have a total of 3651
> instances of this macro:
> 
> $ git grep -nw 'fallthrough;' | wc -l
> 3651
> 
> This treewide patch doesn't address ALL fall-through markings in all
> subsystems at once because I have previously sent out patches for some of
> such subsystems separately, and I will follow up on them; however, this
> definitely contributes most of the work needed to replace all the
> fall-through markings with the fallthrough pseudo-keyword macro in the
> whole codebase.
> 
> I have build-tested this patch on 10 different architectures: x86_64, i386,
> arm64, powerpc, s390, sparc64, sh, m68k, powerpc64 and alpha (allyesconfig
> for all of them). This is in linux-next already and kernel test robot has
> also helped me to successfully build-test early versions of this
> patch[2][3][4][5].
> 
> Thanks
> --
> [1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through
> [2] https://lore.kernel.org/lkml/5f3cc99a.HgvOW3rH0mD0RmkM%25lkp@xxxxxxxxx/
> [3] https://lore.kernel.org/lkml/5f3dd1d2.l1axczH+t4hMBZ63%25lkp@xxxxxxxxx/
> [4] https://lore.kernel.org/lkml/5f3e977a.mwYHUIObbR4SHr0B%25lkp@xxxxxxxxx/
> [5] https://lore.kernel.org/lkml/5f3f9e1c.qsyb%2FaySkiXNpkO4%25lkp@xxxxxxxxx/
> 
> ----------------------------------------------------------------
> Gustavo A. R. Silva (1):
>       treewide: Use fallthrough pseudo-keyword

$ scripts/config --file arch/powerpc/configs/powernv_defconfig -e KERNEL_XZ

$ make -skj"$(nproc)" ARCH=powerpc CROSS_COMPILE=powerpc64le-linux- distclean powernv_defconfig zImage
...
In file included from arch/powerpc/boot/../../../lib/decompress_unxz.c:234,
                 from arch/powerpc/boot/decompress.c:38:
arch/powerpc/boot/../../../lib/xz/xz_dec_stream.c: In function 'dec_main':
arch/powerpc/boot/../../../lib/xz/xz_dec_stream.c:586:4: error: 'fallthrough' undeclared (first use in this function)
  586 |    fallthrough;
      |    ^~~~~~~~~~~
arch/powerpc/boot/../../../lib/xz/xz_dec_stream.c:586:4: note: each undeclared identifier is reported only once for each function it appears in
In file included from arch/powerpc/boot/../../../lib/decompress_unxz.c:235,
                 from arch/powerpc/boot/decompress.c:38:
arch/powerpc/boot/../../../lib/xz/xz_dec_lzma2.c: In function 'xz_dec_lzma2_run':
arch/powerpc/boot/../../../lib/xz/xz_dec_lzma2.c:1046:4: error: 'fallthrough' undeclared (first use in this function)
 1046 |    fallthrough;
      |    ^~~~~~~~~~~
make[2]: *** [arch/powerpc/boot/Makefile:215: arch/powerpc/boot/decompress.o] Error 1
make[2]: Target 'arch/powerpc/boot/zImage' not remade because of errors.
make[1]: *** [arch/powerpc/Makefile:295: zImage] Error 2
make: *** [Makefile:335: __build_one_by_one] Error 2
make: Target 'distclean' not remade because of errors.
make: Target 'powernv_defconfig' not remade because of errors.
make: Target 'zImage' not remade because of errors.

This will end up affecting distribution configurations such as Debian
and OpenSUSE according to my testing. I am not sure what the solution
is, the PowerPC wrapper does not set -D__KERNEL__ so I am not sure that
compiler_attributes.h can be safely included. Adding Michael and
linuxppc-dev to CC.

Cheers,
Nathan