linux-kernel - Re: [PATCH] Makefile: Convert -Wimplicit-fallthrough=3 to just -Wimplicit-fallthrough for clang

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Message-ID: <CAKwvOdmAj34xDcMUn7Fu_aXdtD-7xHjHuU20qY=rFcr_Kz7gpg@mail.gmail.com>
Date:   Mon, 12 Aug 2019 09:28:15 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] Makefile: Convert -Wimplicit-fallthrough=3 to just
 -Wimplicit-fallthrough for clang

On Sat, Aug 10, 2019 at 8:06 PM Joe Perches <joe@...ches.com> wrote:
>
> On Sat, 2019-08-10 at 19:04 -0700, Nathan Chancellor wrote:
> > On a tangential note, how are you planning on doing the fallthrough
> > comment to attribute conversion? The reason I ask is clang does not
> > support the comment annotations, meaning that when Nathan Huckleberry's
> > patch is applied to clang (which has been accepted [1]), we are going
> > to get slammed by the warnings. I just ran an x86 defconfig build at
> > 296d05cb0d3c with his patch applied and I see 27673 instances of this
> > warning... (mostly coming from some header files so nothing crazy but it
> > will be super noisy).
> >
> > If you have something to share like a script or patch, I'd be happy to
> > test it locally.
> >
> > [1]: https://reviews.llvm.org/D64838
>
> Something like this patch:
>
> https://lore.kernel.org/patchwork/patch/1108577/
>
> Maybe use:
>
> #define fallthrough [[fallthrough]]

Isn't [[fallthrough]] the C++ style attribute?  **eek** Seems to be a
waste for Clang to implement __attribute__((fallthrough)) just as we
switch the kernel to not use it.  Also, I'd recommend making the
preprocessor define all caps to help folks recognize it's a
preprocessor define.
-- 
Thanks,
~Nick Desaulniers