linux-kernel - [PATCH perf/core ] [BUGFIX] perf-probe: Fix to get ummapped symbol address on kernel

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Date:	Sun, 22 Mar 2015 20:40:22 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	wangnan0@...wei.com, Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	He Kuang <hekuang@...wei.com>, namhyung@...nel.org,
	Ingo Molnar <mingo@...nel.org>
Subject: [PATCH perf/core ] [BUGFIX] perf-probe: Fix to get ummapped symbol
 address on kernel

Fix to get correctly unmapped symbol address on kernel.
This allows us to probe on syscall symbols which are aliases
of SyS_ functions with using debuginfo.

Without this fix:
  ----
  # ./perf probe -a sys_write
  Failed to find debug information for address 3b0100
  Probe point 'sys_write' not found.
    Error: Failed to add events.
  ----
The address 0x3b0100 is a mapped address, and not usable
in debuginfo.

With this fix:
  ----
  # ./perf probe -a sys_write
  Added new event:
    probe:sys_write      (on sys_write)

  You can now use it in all perf tools, such as:

          perf record -e probe:sys_write -aR sleep 1
  ----

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
---
 tools/perf/util/probe-event.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 6b95985..8feac07 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -310,7 +310,10 @@ static int find_alternative_probe_point(struct debuginfo *dinfo,
 
 	/* Find the address of given function */
 	map__for_each_symbol_by_name(map, pp->function, sym) {
-		address = sym->start;
+		if (uprobes)
+			address = sym->start;
+		else
+			address = map->unmap_ip(map, sym->start);
 		break;
 	}
 	if (!address) {

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