linux-kernel - Re: [PATCH v2] perf: fix the probe finder location (.dwo files)

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Date:   Tue, 4 Oct 2022 11:54:19 -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>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v2] perf: fix the probe finder location (.dwo files)

Cc + Masami

On Mon, Oct 3, 2022 at 11:10 AM 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>
> ---
>
> > Anyway I think it'd be safer to do
> >
> >    if (dwarf_cu_info() == 0 && unit_type == skeleton)
> >        pf->cu_die = subdie;
>
> Thank you, I have modifed the patch :)
>
>
>  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..b27039f5f04b 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;

They will be unused for earlier elfutils.

>         int ret = 0;
>
>         off = 0;
> @@ -1200,6 +1201,14 @@ static int debuginfo__find_probe_location(struct debuginfo *dbg,
>                         continue;
>                 }
>
> +#if _ELFUTILS_VERSION >= 171

Nit, I think we use _ELFUTILS_PREREQ(0, 171).

> +               /* Check separate debug information file. */
> +               if (dwarf_cu_info(pf->cu_die.cu, NULL, &unit_type,
> +                                 &cudie, &subdie, NULL, NULL, NULL) == 0
> +                   && unit_type == DW_UT_skeleton)
> +                       pf->cu_die = subdie;
> +#endif

How about making it a separate function with 2 versions
depending on the elfutils?  Then you can have the variables
only if they are used.

Something like get_source_from_debuginfod() in the same
file.

Thanks,
Namhyung


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