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Message-Id: <20230711222000.d316cf7fd643cb4203ea1204@kernel.org>
Date: Tue, 11 Jul 2023 22:20:00 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Georg Müller <georgmueller@....net>,
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>,
Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
"Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
regressions@...ts.linux.dev,
Arnaldo Carvalho de Melo <acme@...hat.com>,
linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf probe: read DWARF files from the correct CU
On Tue, 11 Jul 2023 09:57:45 -0300
Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> Em Thu, Jun 15, 2023 at 10:01:37PM +0200, Georg Müller escreveu:
> > After switching from dwarf_decl_file() to die_get_decl_file(), it is not
> > possible to add probes for certain functions of certain binaries:
> >
> > $ perf probe -x /usr/lib/systemd/systemd-logind match_unit_removed
> > A function DIE doesn't have decl_line. Maybe broken DWARF?
> > A function DIE doesn't have decl_line. Maybe broken DWARF?
> > Probe point 'match_unit_removed' not found.
> > Error: Failed to add events.
> >
> > The problem is that die_get_decl_file() uses the wrong CU to search for
> > the file. elfutils commit e1db5cdc9f has some good explanation for this:
> >
> > dwarf_decl_file uses dwarf_attr_integrate to get the DW_AT_decl_file
> > attribute. This means the attribute might come from a different DIE
> > in a different CU. If so, we need to use the CU associated with the
> > attribute, not the original DIE, to resolve the file name.
> >
> > This patch uses the same source of information as elfutils: use attribute
> > DW_AT_decl_file and use this CU to search for the file.
>
> Thanks, applied to the perf-tools branch, that will be submitted for
> Linux v6.5.
Thanks Arnaldo and Georg,
It sounds perfect reason why that happened. I didn't expect the case that
the attribute comes from another CU...
Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
>
> - Arnaldo
>
> > Fixes: dc9a5d2ccd5c ("perf probe: Fix to get declared file name from clang DWARF5")
> > Signed-off-by: Georg Müller <georgmueller@....net>
> > Link: https://lore.kernel.org/r/5a00d5a5-7be7-ef8a-4044-9a16249fff25@gmx.net/
> > ---
> > tools/perf/util/dwarf-aux.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
> > index b07414409771..137b3ed9897b 100644
> > --- a/tools/perf/util/dwarf-aux.c
> > +++ b/tools/perf/util/dwarf-aux.c
> > @@ -478,8 +478,10 @@ static const char *die_get_file_name(Dwarf_Die *dw_die, int idx)
> > {
> > Dwarf_Die cu_die;
> > Dwarf_Files *files;
> > + Dwarf_Attribute attr_mem;
> >
> > - if (idx < 0 || !dwarf_diecu(dw_die, &cu_die, NULL, NULL) ||
> > + if (idx < 0 || !dwarf_attr_integrate(dw_die, DW_AT_decl_file, &attr_mem) ||
> > + !dwarf_cu_die(attr_mem.cu, &cu_die, NULL, NULL, NULL, NULL, NULL, NULL) ||
> > dwarf_getsrcfiles(&cu_die, &files, NULL) != 0)
> > return NULL;
> >
> > --
> > 2.41.0
> >
>
> --
>
> - Arnaldo
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
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