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

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Date:   Wed, 31 Jul 2019 11:02:11 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, 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>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] compiler_attributes.h: Add 'fallthrough' pseudo
 keyword for switch/case use

On Tue, Jul 30, 2019 at 10:35:18PM -0700, Joe Perches 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];
> 
> fallthough is gcc's __attribute__((__fallthrough__)) which was introduced
> in gcc version 7..
> 
> fallthrough devolves to an empty "do {} while (0)" if the compiler version
> (any version less than gcc 7) does not support the attribute.
> 
> Signed-off-by: Joe Perches <joe@...ches.com>

_MUCH_ better than that silly comment, thanks for doing this!

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>