linux-kernel - [PATCH -tip v2 5/8] perf-probe: Retry to find given address from offline dwarf

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Date:	Wed, 29 Jan 2014 09:15:02 +0000
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>, linux-kernel@...r.kernel.org,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	"David A. Long" <dave.long@...aro.org>,
	yrl.pp-manager.tt@...achi.com, Namhyung Kim <namhyung@...nel.org>
Subject: [PATCH -tip v2 5/8] perf-probe: Retry to find given address from
 offline dwarf

Retry to find the given address from offline dwarfs too.

On the KASLR enabled kernel, the kernel text section is
loaded with random offset, and debuginfo__new_online_kernel
tries to map the debuginfo with that offset. However,
perf's map object tries to make a non-randomized ummapped
address. This leads to fail looking up the appropriate
debuginfo from that address.

To solve this issue, we retry to use offline dwarfs if
possible.

Without this change;

  # ./perf probe -l
    probe:t_show         (on _stext+901288 with m v)
    probe:t_show_1       (on _stext+939624 with m v t)
    probe:t_show_2       (on _stext+980296 with m v fmt)
    probe:t_show_3       (on _stext+1014392 with m v file)

With this change;

  # ./perf probe -l
    probe:t_show         (on t_show@...ux-3/kernel/trace/ftrace.c with m v)
    probe:t_show_1       (on t_show@...ux-3/kernel/trace/trace.c with m v t)
    probe:t_show_2       (on t_show@...nel/trace/trace_printk.c with m v fmt)
    probe:t_show_3       (on t_show@...nel/trace/trace_events.c with m v file)

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
---
 tools/perf/util/probe-event.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 120954b..b35f047 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -272,6 +272,8 @@ static int kprobe_convert_to_perf_probe(struct probe_trace_point *tp,
 			 tp->offset, addr);
 
 		dinfo = debuginfo__new_online_kernel(addr);
+		if (!dinfo)	/* For kaslr kernel */
+			dinfo = open_debuginfo(tp->module);
 		if (dinfo) {
 			ret = debuginfo__find_probe_point(dinfo,
 						 (unsigned long)addr, pp);


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