linux-kernel - Re: [gustavoars-linux:for-next/clang-fallthrough 1/1] warning: fallthrough annotation in unreachable code/

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Message-ID: <YQw2P8esj8PMNRQn@Ryzen-9-3900X.localdomain>
Date:   Thu, 5 Aug 2021 12:04:31 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     kernel test robot <lkp@...el.com>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        clang-built-linux@...glegroups.com, kbuild-all@...ts.01.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [gustavoars-linux:for-next/clang-fallthrough 1/1] warning:
 fallthrough annotation in unreachable code/

On Thu, Aug 05, 2021 at 02:21:34PM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git for-next/clang-fallthrough
> head:   58d0d2d2e7dc1b1a4997bb9c47d6cf428f2d3a00
> commit: 58d0d2d2e7dc1b1a4997bb9c47d6cf428f2d3a00 [1/1] Revert "Revert "Makefile: Enable -Wimplicit-fallthrough for Clang""
> config: hexagon-randconfig-r023-20210804 (attached as .config)
> compiler: clang version 12.0.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git/commit/?id=58d0d2d2e7dc1b1a4997bb9c47d6cf428f2d3a00
>         git remote add gustavoars-linux https://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git
>         git fetch --no-tags gustavoars-linux for-next/clang-fallthrough
>         git checkout 58d0d2d2e7dc1b1a4997bb9c47d6cf428f2d3a00
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=hexagon 
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@...el.com>
> 
> All warnings (new ones prefixed by >>):
> 
> >> warning: fallthrough annotation in unreachable code [-Wimplicit-fallthrough]
> >> warning: fallthrough annotation in unreachable code [-Wimplicit-fallthrough]
>    2 warnings generated.

With a newer version of clang that shows proper line numbers:

sound/core/pcm_native.c:3812:3: warning: fallthrough annotation in unreachable code [-Wimplicit-fallthrough]
                fallthrough;
                ^
include/linux/compiler_attributes.h:211:41: note: expanded from macro 'fallthrough'
# define fallthrough                    __attribute__((__fallthrough__))
                                        ^
sound/core/pcm_native.c:3820:3: warning: fallthrough annotation in unreachable code [-Wimplicit-fallthrough]
                fallthrough;
                ^
include/linux/compiler_attributes.h:211:41: note: expanded from macro 'fallthrough'
# define fallthrough                    __attribute__((__fallthrough__))
                                        ^
2 warnings generated.

Which is already being tracked: https://github.com/ClangBuiltLinux/linux/issues/1429

Cheers,
Nathan