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 10:10:30 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
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

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.

 
> Clang version 11.0.0 was used.
> 
> Fixes: f283f293a60d ("perf tools: Replace zero-length array with flexible-array")
> Reported-by: Ian Rogers <irogers@...gle.com>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
> Here to fix what I break. :)
> 
>  tools/perf/util/intel-pt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c
> index f17b1e769ae4..b34179e3926f 100644
> --- a/tools/perf/util/intel-pt.c
> +++ b/tools/perf/util/intel-pt.c
> @@ -1799,8 +1799,8 @@ static int intel_pt_synth_pebs_sample(struct intel_pt_queue *ptq)
>  
>  	if (sample_type & PERF_SAMPLE_BRANCH_STACK) {
>  		struct {
> -			struct branch_stack br_stack;
>  			struct branch_entry entries[LBRS_MAX];
> +			struct branch_stack br_stack;
>  		} br;
>  
>  		if (items->mask[INTEL_PT_LBR_0_POS] ||
> -- 
> 2.26.2
> 

-- 

- Arnaldo