linux-kernel - [PATCH] perf probe: Fix failure to add multiple probes without debuginfo

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Date:	Thu, 19 Mar 2015 17:23:43 +0800
From:	He Kuang <hekuang@...wei.com>
To:	<acme@...nel.org>, <masami.hiramatsu.pt@...achi.com>,
	<a.p.zijlstra@...llo.nl>, <mingo@...hat.com>, <namhyung@...nel.org>
CC:	<wangnan0@...wei.com>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] perf probe: Fix failure to add multiple probes without debuginfo

From: hekuang <hekuang@...o.com>

Perf tries to find probe function addresses from map when debuginfo
could not be found.

To the first added function, the value of ref_reloc_sym was set in
maps__set_kallsyms_ref_reloc_sym() and can be obtained from
host_machine->kmaps->maps. After that, new maps are added to
host_machine->kmaps->maps in dso__load_kcore(), all these new added maps
do not have a valid ref_reloc_sym.

When adding a second function, get_target_map() may get a map without
valid ref_reloc_sym, and raise the error "Relocated base symbol is not
found".

Fix this by getting ref_reloc_sym from machine->vmlinux_maps.

This problem can be reproduced as following:

  $ perf probe --add='sys_write' --add='sys_open'
  Relocated base symbol is not found!
    Error: Failed to add events.

After this patch:

  $ perf probe --add='sys_write' --add='sys_open'
  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

  Added new event:
    probe:sys_open       (on sys_open)

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

      perf record -e probe:sys_open -aR sleep 1

Signed-off-by: He Kuang <hekuang@...wei.com>
---
 tools/perf/util/probe-event.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index c5e1338..75d41ee 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -2540,7 +2540,19 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
 	}
 
 	if (!pev->uprobes && !pp->retprobe) {
-		kmap = map__kmap(map);
+		struct machine *machine;
+		struct map *vmlinux_map = NULL;
+
+		if (map->groups && map->groups->machine) {
+			machine = map->groups->machine;
+			vmlinux_map = machine->vmlinux_maps[MAP__FUNCTION];
+		}
+
+		if (vmlinux_map)
+			kmap = map__kmap(vmlinux_map);
+		else
+			kmap = map__kmap(map);
+
 		reloc_sym = kmap->ref_reloc_sym;
 		if (!reloc_sym) {
 			pr_warning("Relocated base symbol is not found!\n");
-- 
2.3.3.220.g9ab698f

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