linux-kernel - Re: [PATCH v2 2/4] perf tools: Use dynamic register set for Dwarf unwind

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Date:   Tue, 17 May 2022 19:03:22 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     James Clark <james.clark@....com>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        broonie@...nel.org, acme@...nel.org, german.gomez@....com,
        mathieu.poirier@...aro.org, john.garry@...wei.com,
        Will Deacon <will@...nel.org>,
        Mike Leach <mike.leach@...aro.org>,
        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@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/4] perf tools: Use dynamic register set for Dwarf
 unwind

On Tue, May 17, 2022 at 11:20:03AM +0100, James Clark wrote:
> Architectures can detect availability of extra registers at
> runtime so use this more complete set for unwinding. This
> will include the VG register on arm64 in a later commit.
> 
> If the function isn't implemented then PERF_REGS_MASK is
> returned and there is no change.
> 
> Signed-off-by: James Clark <james.clark@....com>

This patch looks good to me:
Reviewed-by: Leo Yan <leo.yan@...aro.org>

Just curious, do you think should update the test (e.g.
arch/arm64/tests/dwarf-unwind.c) to use arch__user_reg_mask()?

Thanks,
Leo

> ---
>  tools/perf/util/evsel.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 5fd7924f8eb3..787bbcbcd2ae 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -896,7 +896,7 @@ static void __evsel__config_callchain(struct evsel *evsel, struct record_opts *o
>  					   "specifying a subset with --user-regs may render DWARF unwinding unreliable, "
>  					   "so the minimal registers set (IP, SP) is explicitly forced.\n");
>  			} else {
> -				attr->sample_regs_user |= PERF_REGS_MASK;
> +				attr->sample_regs_user |= arch__user_reg_mask();
>  			}
>  			attr->sample_stack_user = param->dump_size;
>  			attr->exclude_callchain_user = 1;
> -- 
> 2.28.0
>