linux-kernel - [PATCH 1/5] perf probe: Return a better scope DIE if there is no best scope

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Date:   Tue,  5 Nov 2019 09:16:49 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: [PATCH 1/5] perf probe: Return a better scope DIE if there is no best scope

Make find_best_scope() returns innermost DIE at given address if
there is no best matched scope DIE. Since Gcc sometimes generates
intuitively strange line info which is out of inlined function
address range, we need this fixup.

Without this, sometimes perf probe failed to probe on a line
inside an inlined function.
  # perf probe -D ksys_open:3
  Failed to find scope of probe point.
    Error: Failed to add events.

With this fix, perf probe can probe it.
  # perf probe -D ksys_open:3
  p:probe/ksys_open _text+25707308
  p:probe/ksys_open_1 _text+25710596
  p:probe/ksys_open_2 _text+25711114
  p:probe/ksys_open_3 _text+25711343
  p:probe/ksys_open_4 _text+25714058
  p:probe/ksys_open_5 _text+2819653
  p:probe/ksys_open_6 _text+2819701

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 tools/perf/util/probe-finder.c |   17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index f441e0174334..9ecea45da4ca 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -744,6 +744,16 @@ static int find_best_scope_cb(Dwarf_Die *fn_die, void *data)
 	return 0;
 }
 
+/* Return innermost DIE */
+static int find_inner_scope_cb(Dwarf_Die *fn_die, void *data)
+{
+	struct find_scope_param *fsp = data;
+
+	memcpy(fsp->die_mem, fn_die, sizeof(Dwarf_Die));
+	fsp->found = true;
+	return 1;
+}
+
 /* Find an appropriate scope fits to given conditions */
 static Dwarf_Die *find_best_scope(struct probe_finder *pf, Dwarf_Die *die_mem)
 {
@@ -755,8 +765,13 @@ static Dwarf_Die *find_best_scope(struct probe_finder *pf, Dwarf_Die *die_mem)
 		.die_mem = die_mem,
 		.found = false,
 	};
+	int ret;
 
-	cu_walk_functions_at(&pf->cu_die, pf->addr, find_best_scope_cb, &fsp);
+	ret = cu_walk_functions_at(&pf->cu_die, pf->addr, find_best_scope_cb,
+				   &fsp);
+	if (!ret && !fsp.found)
+		cu_walk_functions_at(&pf->cu_die, pf->addr,
+				     find_inner_scope_cb, &fsp);
 
 	return fsp.found ? die_mem : NULL;
 }