linux-kernel - [PATCH 24/27] perf probe: Skip if the function address is 0

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Date:   Thu, 29 Sep 2016 11:35:53 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Linux Weekly News <lwn@....net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 24/27] perf probe: Skip if the function address is 0

From: Masami Hiramatsu <mhiramat@...nel.org>

Skip probes if the entry address of the target function is 0.  This can
happen when we're handling C++ debuginfo files.

E.g. without this fix, below case still fail.
  ----
  $ ./perf probe -x /usr/lib64/libstdc++.so.6 -vD is_open
  probe-definition(0): is_open
  symbol:is_open file:(null) line:0 offset:0 return:0 lazy:(null)
  0 arguments
  symbol:catch file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:throw file:(null) line:0 offset:0 return:0 lazy:(null)
  symbol:rethrow file:(null) line:0 offset:0 return:0 lazy:(null)
  Open Debuginfo file: /usr/lib/debug/usr/lib64/libstdc++.so.6.0.22.debug
  Try to find probe point from debuginfo.
  Matched function: is_open [295df]
  found inline addr: 0x8ca80
  Probe point found: is_open+0
  found inline addr: 0x8ca70
  Probe point found: is_open+0
  found inline addr: 0x8ca60
  Probe point found: is_open+0
  Matched function: is_open [6527f]
  Matched function: is_open [9fe8a]
  Probe point found: is_open+0
  Matched function: is_open [19710b]
  found inline addr: 0xecca9
  Probe point found: stdio_filebuf+57
  found inline addr: 0x0
  Probe point found: swap+0
  Matched function: is_open [19fc9d]
  Probe point found: is_open+0
  Found 7 probe_trace_events.
  p:probe_libstdc++/is_open /usr/lib64/libstdc++.so.6.0.22:0x8ca80
  p:probe_libstdc++/is_open_1 /usr/lib64/libstdc++.so.6.0.22:0x8ca70
  p:probe_libstdc++/is_open_2 /usr/lib64/libstdc++.so.6.0.22:0x8ca60
  p:probe_libstdc++/is_open_3 /usr/lib64/libstdc++.so.6.0.22:0xb0ad0
  p:probe_libstdc++/is_open_4 /usr/lib64/libstdc++.so.6.0.22:0xecca9
  Failed to synthesize probe trace event.
    Error: Failed to add events. Reason: Invalid argument (Code: -22)
  ----
This is because some instances have entry_pc == 0 (see 19710b and
19fc9d). With this fix, those are skipped.

  ----
  $ ./perf probe -x /usr/lib64/libstdc++.so.6 -D is_open
  p:probe_libstdc++/is_open /usr/lib64/libstdc++.so.6.0.22:0x8ca80
  p:probe_libstdc++/is_open_1 /usr/lib64/libstdc++.so.6.0.22:0x8ca70
  p:probe_libstdc++/is_open_2 /usr/lib64/libstdc++.so.6.0.22:0x8ca60
  p:probe_libstdc++/is_open_3 /usr/lib64/libstdc++.so.6.0.22:0xb0ad0
  p:probe_libstdc++/is_open_4 /usr/lib64/libstdc++.so.6.0.22:0xecca9
  ----

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Tested-by: Jiri Olsa <jolsa@...nel.org>
Cc: David Ahern <dsahern@...il.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/147464490707.29804.14277897643725143867.stgit@devbox
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/probe-finder.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 5fe8325e81f2..df4debe564da 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -955,6 +955,11 @@ static int probe_point_inline_cb(Dwarf_Die *in_die, void *data)
 				   dwarf_diename(in_die));
 			return -ENOENT;
 		}
+		if (addr == 0) {
+			pr_debug("%s has no valid entry address. skipped.\n",
+				 dwarf_diename(in_die));
+			return -ENOENT;
+		}
 		pf->addr = addr;
 		pf->addr += pp->offset;
 		pr_debug("found inline addr: 0x%jx\n",
@@ -998,8 +1003,13 @@ static int probe_point_search_cb(Dwarf_Die *sp_die, void *data)
 	} else if (die_is_func_instance(sp_die)) {
 		/* Instances always have the entry address */
 		dwarf_entrypc(sp_die, &pf->addr);
+		/* But in some case the entry address is 0 */
+		if (pf->addr == 0) {
+			pr_debug("%s has no entry PC. Skipped\n",
+				 dwarf_diename(sp_die));
+			param->retval = 0;
 		/* Real function */
-		if (pp->lazy_line)
+		} else if (pp->lazy_line)
 			param->retval = find_probe_point_lazy(sp_die, pf);
 		else {
 			skip_prologue(sp_die, pf);
-- 
2.7.4