linux-kernel - Re: [PATCH] perf: fix the probe finder location (.dwo files)

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Date:   Fri, 30 Sep 2022 10:19:00 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Henry Castro <hcvcastro@...il.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>,
        linux-perf-users <linux-perf-users@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf: fix the probe finder location (.dwo files)

Hello,

On Thu, Sep 29, 2022 at 2:00 PM Henry Castro <hcvcastro@...il.com> wrote:
>
> If the file object is compiled using -gsplit-dwarf,
> the probe finder location will fail.
>
> Signed-off-by: Henry Castro <hcvcastro@...il.com>
> ---
>  tools/perf/util/probe-finder.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index 50d861a80f57..6d7c5461251d 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -1161,7 +1161,8 @@ static int debuginfo__find_probe_location(struct debuginfo *dbg,
>         struct perf_probe_point *pp = &pf->pev->point;
>         Dwarf_Off off, noff;
>         size_t cuhl;
> -       Dwarf_Die *diep;
> +       Dwarf_Die *diep, cudie, subdie;
> +       uint8_t unit_type;
>         int ret = 0;
>
>         off = 0;
> @@ -1200,6 +1201,14 @@ static int debuginfo__find_probe_location(struct debuginfo *dbg,
>                         continue;
>                 }
>
> +               /* Check separate debug information file. */
> +               if (dwarf_cu_info(pf->cu_die.cu, NULL, &unit_type, &cudie,
> +                                 &subdie, NULL, NULL, NULL))

It seems dwarf_cu_info was introduced in elfutils 0.171 which
was released in June 2018.  I hope all the test setups have
more recent versions.


> +                       continue;
> +
> +               if (unit_type == DW_UT_skeleton)
> +                       pf->cu_die = subdie;

Is this DWARF5 thing?  Will it handle the previous version well?
IOW wouldn't dwarf_cu_info() return fail?

Anyway I think it'd be safer to do

    if (dwarf_cu_info() == 0 && unit_type == skeleton)
        pf->cu_die = subdie;

Thanks,
Namhyung


> +
>                 /* Check if target file is included. */
>                 if (pp->file)
>                         pf->fname = cu_find_realpath(&pf->cu_die, pp->file);
> --
> 2.20.1
>