linux-kernel - Re: [PATCH v2] perf: unwind: Fix symfs with libdw

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Message-ID: <CAM9d7cjF+g5Ww22bDviHqFa42dC1JjhGw1cM7POvTziY2wyCgA@mail.gmail.com>
Date:   Sat, 1 Jul 2023 11:13:32 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>
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>,
        Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...s.com
Subject: Re: [PATCH v2] perf: unwind: Fix symfs with libdw

Hello,

On Fri, Jun 30, 2023 at 2:11 AM Vincent Whitchurch
<vincent.whitchurch@...s.com> wrote:
>
> Pass the full path including the symfs (if any) to libdw.  Without this
> unwinding fails with errors like this when a symfs is used:
>
>   unwind: failed with 'No such file or directory'"
>
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>
> ---
> I posted this last year but didn't receive any comments.  This patch is
> still needed in current mainline so here is a rebased version, fixing
> some merge conflicts.

Sorry that you didn't get any feedback.  Looks like a real problem.

>
> Changes in v2:
> - Rebased to v6.4.
> - Link to v1: https://lore.kernel.org/lkml/20221125112743.2285759-1-vincent.whitchurch@axis.com/

In general, you'd better base your perf tools changes on the
perf/perf-tools (for fixes) or perf/perf-tools-next (for new features)
in git.kernel.org.  But it seems this change applies cleanly.

> ---
>  tools/perf/util/unwind-libdw.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
> index bdccfc511b7e2..30a63d819d74e 100644
> --- a/tools/perf/util/unwind-libdw.c
> +++ b/tools/perf/util/unwind-libdw.c
> @@ -66,9 +66,13 @@ static int __report_module(struct addr_location *al, u64 ip,
>                         mod = 0;
>         }
>
> -       if (!mod)
> -               mod = dwfl_report_elf(ui->dwfl, dso->short_name, dso->long_name, -1,
> +       if (!mod) {
> +               char filename[PATH_MAX];
> +
> +               __symbol__join_symfs(filename, sizeof(filename), dso->long_name);

As __symbol__join_symfs() will have dso->long_name when symfs
is not set, I don't think it changes the behavior, so

Acked-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung


> +               mod = dwfl_report_elf(ui->dwfl, dso->short_name, filename, -1,
>                                       map__start(al->map) - map__pgoff(al->map), false);
> +       }
>         if (!mod) {
>                 char filename[PATH_MAX];
>
>
> ---
> base-commit: 6995e2de6891c724bfeb2db33d7b87775f913ad1
> change-id: 20230630-perf-libdw-symfs-9adb29f4df7d
>
> Best regards,
> --
> Vincent Whitchurch <vincent.whitchurch@...s.com>
>