linux-kernel - Re: [PATCH perf/core] perf intel-pt: Fix clang build failure in intel_pt_synth_pebs

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Date:   Thu, 14 May 2020 10:06:01 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: Re: [PATCH perf/core] perf intel-pt: Fix clang build failure in
 intel_pt_synth_pebs_sample

On Thu, May 14, 2020 at 10:10:30AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Wed, May 13, 2020 at 06:47:38PM -0500, Gustavo A. R. Silva escreveu:
> > Fix the following build failure generated with command 
> > $ make CC=clang HOSTCC=clang -C tools/ perf:
> > 
> > util/intel-pt.c:1802:24: error: field 'br_stack' with variable sized type 'struct branch_stack' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end]
> >                         struct branch_stack br_stack;
> >                                             ^
> > 1 error generated.
> > 
> > Fix this by reordering the members of struct br.
> 
> Yeah, I noticed that as far back as with ubuntu 16.04's clang:
> 
> clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)
> 
> util/intel-pt.c:1802:24: error: field 'br_stack' with variable sized type 'struct branch_stack' not at the end of a struct or class is a GNU
>       extension [-Werror,-Wgnu-variable-sized-type-not-at-end]
>                         struct branch_stack br_stack;
>                                             ^
> 1 error generated.
> 
> 
> Will fold this with the bug introducing the problem to avoid bisection
> problems.
> 

I agree. Also, the commit hash of the "Fixes" tag only applies to the
perf/core branch and, I guess that might create confusion.

Thanks
--
Gustavo