linux-kernel - Re: [PATCH 2/4] compiler_attributes.h: Add 'fallthrough' pseudo keyword for switch/case use

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Date:   Sat, 12 Oct 2019 00:25:37 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Joe Perches <joe@...ches.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Pavel Machek <pavel@....cz>,
        "Gustavo A . R . Silva" <gustavo@...eddedor.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Shawn Landden <shawn@....icu>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Miller <davem@...emloft.net>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH 2/4] compiler_attributes.h: Add 'fallthrough' pseudo
 keyword for switch/case use

On Thu, Oct 10, 2019 at 10:37 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Sat, Oct 05, 2019 at 07:17:36PM +0200, Miguel Ojeda wrote:
> > Hi Joe,
> >
> > On Sat, Oct 5, 2019 at 6:46 PM Joe Perches <joe@...ches.com> wrote:
> > >
> > > Reserve the pseudo keyword 'fallthrough' for the ability to convert the
> > > various case block /* fallthrough */ style comments to appear to be an
> > > actual reserved word with the same gcc case block missing fallthrough
> > > warning capability.
> > >
> > > All switch/case blocks now must end in one of:
> > >
> > >         break;
> > >         fallthrough;
> > >         goto <label>;
> > >         return [expression];
> > >         continue;
> > >
> > > fallthough is gcc's __attribute__((__fallthrough__)) which was introduced
> > > in gcc version 7..
> >
> > Nits: double period, missing "r" in fallthough.
> >
> > > fallthrough devolves to an empty "do {} while (0)" if the compiler
> > > version (any version less than gcc 7) does not support the attribute.
> >
> > Perhaps add a short note why (empty statement warnings maybe? I don't
> > remember them but it was months ago so maybe it changed).
> >
> > > Signed-off-by: Joe Perches <joe@...ches.com>
> > > Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> >
> > Please add Dan's Suggested-by and copy the things I wrote in the
> > commit message when I proposed this:
> >
> >   https://github.com/ojeda/linux/commit/668f011a2706ea555987e263f609a5deba9c7fc4
>
> Perhaps just take this patch directly with Miguel's authorship into the
> series and tweak the __fallthrough to fallthrough in subject and body.

Since I was going to pick it up, I would have signed-off-by anyway, but yeah ;P

Cheers,
Miguel