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

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Date:   Sun, 04 Aug 2019 19:01:06 -0700
From:   Joe Perches <joe@...ches.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.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>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Neil Horman <nhorman@...driver.com>,
        David Miller <davem@...emloft.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com
Subject: Re: [RFC PATCH] compiler_attributes.h: Add 'fallthrough' pseudo
 keyword for switch/case use

On Sun, 2019-08-04 at 18:18 -0700, Nathan Chancellor wrote:
> On Sun, Aug 04, 2019 at 05:39:28PM -0700, Joe Perches wrote:
> Hi Joe,

Hi Nathan.

> This patch resolves that while adding support for the attribute.
> https://reviews.llvm.org/D64838
[]
> > The __has_attribute use is at least clang compatible.
> > https://releases.llvm.org/3.7.0/tools/clang/docs/LanguageExtensions.html
> > even if it doesn't (seem to?) work.
> 
> I was trying to follow along with this thread through the web interface
> and kind of got lost, how does it not work?

It does not work in llvm/clang mainline through
commit 305b961f64b75e73110e309341535f6d5a48ed72.

> If I apply your compiler attributes patch with D64838,
> I see fallthrough get expanded to
> __attribute__((__fallthrough__)) by the preprocessor.

Well, great.
I hope D64838 or something like it gets applied soon.
But all I could and did test was the current version.

cheers, Joe