linux-kernel - [PATCH v2 2/2] perf probe: read DWARF files from the correct CU

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Date:   Wed, 28 Jun 2023 10:23:21 +0200
From:   Georg Müller <georgmueller@....net>
To:     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>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     Georg Müller <georgmueller@....net>,
        regressions@...ts.linux.dev,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] perf probe: read DWARF files from the correct CU

After switching from dwarf_decl_file() to die_get_decl_file(), it is not
possible to add probes for certain functions:

 $ 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.

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