linux-kernel - [PATCH] perf probe: Fix failure to probe events on arm

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Date:	Mon, 15 Jun 2015 08:06:53 +0000
From:	He Kuang <hekuang@...wei.com>
To:	<a.p.zijlstra@...llo.nl>, <mingo@...hat.com>, <acme@...nel.org>,
	<masami.hiramatsu.pt@...achi.com>, <namhyung@...nel.org>
CC:	<wangnan0@...wei.com>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] perf probe: Fix failure to probe events on arm

Fix failure to probe events on arm, problem is introduced by commit
5a51fcd1f30c ("perf probe: Skip kernel symbols which is out of
.text"). For some architectures, label '_etext' is not in the .text
section(in .notes section for arm/arm64). Label out of .text section is
not loaded as symbols and we got a zero value when look up its address,
which causes all events be wrongly skiped.

This patch uses kernel map->end when failed to get the address of
'_etext' and fixes the problem.

Problem can be reproduced on arm as following:

  # perf probe --add='generic_perform_write'
  generic_perform_write+0 is out of .text, skip it.
  Probe point 'generic_perform_write' not found.
    Error: Failed to add events. Reason: No such file or directory (Code: -2)

After this patch:

  # perf probe --add='generic_perform_write'
  Added new event:
    probe:generic_perform_write (on generic_perform_write)

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

    perf record -e probe:generic_perform_write -aR sleep 1

Signed-off-by: He Kuang <hekuang@...wei.com>
---
 tools/perf/util/probe-event.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index daa24a2..ee26961 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -575,8 +575,22 @@ static int post_process_probe_trace_events(struct probe_trace_event *tevs,
 		pr_warning("Relocated base symbol is not found!\n");
 		return -EINVAL;
 	}
-	/* Get the address of _etext for checking non-probable text symbol */
+	/* Get the address of _etext for checking non-probable text symbol,
+	   for some architectures (e.g. arm, arm64), _etext is out of .text
+	   section and not loaded as symbols, use kernel map->end instead.
+	 */
 	etext_addr = kernel_get_symbol_address_by_name("_etext", false);
+	if (etext_addr == 0) {
+		struct map *map;
+
+		map = kernel_get_module_map(NULL);
+		if (!map) {
+			pr_err("Failed to get a map for kernel\n");
+			return -EINVAL;
+		}
+
+		etext_addr = map->end;
+	}
 
 	for (i = 0; i < ntevs; i++) {
 		if (tevs[i].point.address && !tevs[i].point.retprobe) {
-- 
1.8.5.2

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