linux-kernel - Re: [RFC PATCH v1] perf build: Fix build for clang's -Wunreachable-code

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Message-ID: <CAP-5=fWFYS7-FcbyJ5Z5U2rqA7eYwwJ4dMf90TUzwJ0Shh2yxA@mail.gmail.com>
Date: Tue, 27 May 2025 13:53:37 -0700
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Adrian Hunter <adrian.hunter@...el.com>, Kan Liang <kan.liang@...ux.intel.com>, 
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [RFC PATCH v1] perf build: Fix build for clang's -Wunreachable-code

On Fri, Apr 11, 2025 at 3:14 PM Ian Rogers <irogers@...gle.com> wrote:
>
> On Fri, Apr 11, 2025 at 2:34 PM Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > Hi Ian,
> >
> > On Thu, Apr 10, 2025 at 01:26:47PM -0700, Ian Rogers wrote:
> > > Clang's unreachable code warning is able to catch bugs like the famous
> > > "goto fail" which gcc's unreachable code warning fails to warn about
> > > (it will complain about misleading indent). The changes here are
> > > sufficient to get perf building with clang with -Wunreachable code,
> > > but they don't really fix any bugs. Posting as an RFC to see if anyone
> > > things this is worth pursuing.
> >
> > I'm not sure if it's useful and don't see what kind of bugs it can
> > address.  The proposed changes don't look like an improvement.
>
> The goto fail case was in OpenSSL the code from a bad merge:
> ```
> if (...)
>   goto fail;
>   goto fail;
> ```
> Meaning the fail path was always taken and checking on the non-fail
> code never executed. Newer GCCs will warn of this because of the
> "misleading indent" but  clang won't. It is easy to imagine similar
> mistakes creeping in, so using compiler warnings to avoid the bug
> could be useful.

Ping. Thanks,
Ian