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Subject: Re: [RFC PATCH] compiler_attributes.h: Add 'fallthrough' pseudo keyword for switch/case use
To:     Peter Zijlstra <peterz@infradead.org>
CC:     Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Joe Perches <joe@perches.com>, Pavel Machek <pavel@ucw.cz>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Borislav Petkov <bp@alien8.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "Gustavo A . R . Silva" <gustavo@embeddedor.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Kan Liang <kan.liang@linux.intel.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Jiri Olsa <jolsa@redhat.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Shawn Landden <shawn@git.icu>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
From:   hpa@zytor.com
Message-ID: <0BCDEED9-0B72-4412-909F-76C20D54983E@zytor.com>
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On August 1, 2019 5:24:29 AM PDT, Peter Zijlstra <peterz@infradead=2Eorg> w=
rote:
>On Wed, Jul 31, 2019 at 11:10:36PM -0700, hpa@zytor=2Ecom wrote:
>> On July 31, 2019 4:55:47 PM PDT, Miguel Ojeda
><miguel=2Eojeda=2Esandonis@gmail=2Ecom> wrote:
>> >On Wed, Jul 31, 2019 at 11:01 PM <hpa@zytor=2Ecom> wrote:
>> >>
>> >> The standard is moving toward adding this as an attribute with the
>> >[[fallthrough]] syntax; it is in C++17, not sure when it will be in
>C
>> >be if it isn't already=2E
>> >
>> >Not yet, but it seems to be coming:
>> >
>> >  http://www=2Eopen-std=2Eorg/jtc1/sc22/wg14/www/docs/n2268=2Epdf
>> >
>> >However, even if C2x gets it, it will be quite a while until the GCC
>> >minimum version gets bumped up to that, so=2E=2E=2E
>> >
>> >Cheers,
>> >Miguel
>>=20
>> The point was that we should plan ahead in whatever we end up doing=2E
>
>By reserving 'fallthrough' as a keyword we do exactly that=2E We can then
>define it to whatever the compiler/tool at hand requires=2E
>
>Once GCC gains support for that [[attribute]] nonsense, we can detector
>that and use that over the __attribute__(())
>
>[ Also the Cxx attribute syntax is an abomination -- just a lesser one
>than reading actual comments :-) ]

I'm not disagreeing=2E=2E=2E I think using a macro makes sense=2E

Not sure if I agree about the syntax=2E=2E=2E I think it's rather friendly=
 compared to gcc's ;)
--=20
Sent from my Android device with K-9 Mail=2E Please excuse my brevity=2E