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

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Date:   Fri, 30 Jun 2023 11:11:48 +0200
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
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>
CC:     <linux-perf-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kernel@...s.com>, Vincent Whitchurch <vincent.whitchurch@...s.com>
Subject: [PATCH v2] perf: unwind: Fix symfs with libdw

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.

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