linux-kernel - Re: [PATCH] perf/x86/intel: Mark expected switch fall-throughs

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Date:   Mon, 24 Jun 2019 22:37:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Joe Perches <joe@...ches.com>
Cc:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Kan Liang <kan.liang@...ux.intel.com>,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Shawn Landden <shawn@....icu>
Subject: Re: [PATCH] perf/x86/intel: Mark expected switch fall-throughs

On Mon, Jun 24, 2019 at 12:45:54PM -0700, Joe Perches wrote:
> On Mon, 2019-06-24 at 21:31 +0200, Peter Zijlstra wrote:
> > On Mon, Jun 24, 2019 at 11:19:13AM -0500, Gustavo A. R. Silva wrote:
> > > In preparation to enabling -Wimplicit-fallthrough, mark switch
> > > cases where we are expecting to fall through.
> > > 
> > > This patch fixes the following warnings:
> > > 
> > > arch/x86/events/intel/core.c: In function ‘intel_pmu_init’:
> > > arch/x86/events/intel/core.c:4959:8: warning: this statement may fall through [-Wimplicit-fallthrough=]
> > >    pmem = true;
> > >    ~~~~~^~~~~~
> > > arch/x86/events/intel/core.c:4960:2: note: here
> > >   case INTEL_FAM6_SKYLAKE_MOBILE:
> > >   ^~~~
> > > arch/x86/events/intel/core.c:5008:8: warning: this statement may fall through [-Wimplicit-fallthrough=]
> > >    pmem = true;
> > >    ~~~~~^~~~~~
> > > arch/x86/events/intel/core.c:5009:2: note: here
> > >   case INTEL_FAM6_ICELAKE_MOBILE:
> > >   ^~~~
> > > 
> > > Warning level 3 was used: -Wimplicit-fallthrough=3
> > > 
> > > This patch is part of the ongoing efforts to enable
> > > -Wimplicit-fallthrough.
> > > 
> > > Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> > 
> > I still consider it an abomination that the C parser looks at comments
> > -- other than to delete them, but OK I suppose, I'll take it.
> 
> I still believe Arnaldo's/Miguel's/Shawn's/my et al. suggestion of
> 
> #define __fallthrough __attribute__((fallthrough))
> 
> is far better.
> 
> https://lkml.org/lkml/2017/2/9/845
> https://lkml.org/lkml/2017/2/10/485
> https://lore.kernel.org/lkml/20181021171414.22674-2-miguel.ojeda.sandonis@gmail.com/
> https://lore.kernel.org/lkml/20190617155643.GA32544@amd/

Oh yes, worlds better. Please, can we haz that instead?