linux-kernel - [PATCH -tip 4/8] perf-probe: Use the actual address instead of the symbol name

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Date:	Thu, 23 Jan 2014 02:29:55 +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 4/8] perf-probe: Use the actual address instead of the
 symbol name

Since several local symbols can have same name (e.g. t_show),
we need to use the actual address instead of symbol name for
those points. Note that this works only with debuginfo.

E.g. without this change;
----
# ./perf probe -a t_show \$vars
Added new events:
  probe:t_show         (on t_show with $vars)
  probe:t_show_1       (on t_show with $vars)
  probe:t_show_2       (on t_show with $vars)
  probe:t_show_3       (on t_show with $vars)

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

        perf record -e probe:t_show_3 -aR sleep 1
----
OK, we have 4 different t_show()s. All functions have
different arguments as below;
----
# cat /sys/kernel/debug/tracing/kprobe_events
p:probe/t_show t_show m=%di:u64 v=%si:u64
p:probe/t_show_1 t_show m=%di:u64 v=%si:u64 t=%si:u64
p:probe/t_show_2 t_show m=%di:u64 v=%si:u64 fmt=%si:u64
p:probe/t_show_3 t_show m=%di:u64 v=%si:u64 file=%si:u64
----
However, all of them have been put on the *same* address.
----
# cat /sys/kernel/debug/kprobes/list
ffffffff810d9720  k  t_show+0x0    [DISABLED]
ffffffff810d9720  k  t_show+0x0    [DISABLED]
ffffffff810d9720  k  t_show+0x0    [DISABLED]
ffffffff810d9720  k  t_show+0x0    [DISABLED]
----

With this change;
----
# ./perf probe -a t_show \$vars
Added new events:
  probe:t_show         (on t_show with $vars)
  probe:t_show_1       (on t_show with $vars)
  probe:t_show_2       (on t_show with $vars)
  probe:t_show_3       (on t_show with $vars)

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

        perf record -e probe:t_show_3 -aR sleep 1

# cat /sys/kernel/debug/tracing/kprobe_events
p:probe/t_show 0xffffffff810d9720 m=%di:u64 v=%si:u64
p:probe/t_show_1 0xffffffff810e2e40 m=%di:u64 v=%si:u64 t=%si:u64
p:probe/t_show_2 0xffffffff810ece30 m=%di:u64 v=%si:u64 fmt=%si:u64
p:probe/t_show_3 0xffffffff810f4ad0 m=%di:u64 v=%si:u64 file=%si:u64

# cat /sys/kernel/debug/kprobes/list
ffffffff810e2e40  k  t_show+0x0    [DISABLED]
ffffffff810ece30  k  t_show+0x0    [DISABLED]
ffffffff810f4ad0  k  t_show+0x0    [DISABLED]
ffffffff810d9720  k  t_show+0x0    [DISABLED]
----
This time, each event is put in different address
correctly.

Note that currently this doesn't support address-based
probe on modules (thus the probes on modules are symbol
based), since it requires relative address probe syntax
for kprobe-tracer, and it doesn't implemented yet.

One more note, this allows us to put events on correct
address, but --list option should be updated to show
correct corresponding source code.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
---
 tools/perf/util/probe-event.c |   23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 2fb4486..92ab688 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -1529,20 +1529,27 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
 	if (buf == NULL)
 		return NULL;
 
-	if (tev->uprobes)
-		len = e_snprintf(buf, MAX_CMDLEN, "%c:%s/%s %s:%s",
-				 tp->retprobe ? 'r' : 'p',
-				 tev->group, tev->event,
+	len = e_snprintf(buf, MAX_CMDLEN, "%c:%s/%s ", tp->retprobe ? 'r' : 'p',
+			 tev->group, tev->event);
+	if (len <= 0)
+		goto error;
+
+	/* Use the real address, except for kernel modules */
+	if (tp->address && !(tp->module && !tev->uprobes))
+		ret = e_snprintf(buf + len, MAX_CMDLEN, "%s%s0x%lx",
+				 tp->module ?: "", tp->module ? ":" : "",
+				 tp->address);
+	else if (tev->uprobes)
+		ret = e_snprintf(buf + len, MAX_CMDLEN, "%s:%s",
 				 tp->module, tp->symbol);
 	else
-		len = e_snprintf(buf, MAX_CMDLEN, "%c:%s/%s %s%s%s+%lu",
-				 tp->retprobe ? 'r' : 'p',
-				 tev->group, tev->event,
+		ret = e_snprintf(buf + len, MAX_CMDLEN, "%s%s%s+%lu",
 				 tp->module ?: "", tp->module ? ":" : "",
 				 tp->symbol, tp->offset);
 
-	if (len <= 0)
+	if (ret <= 0)
 		goto error;
+	len += ret;
 
 	for (i = 0; i < tev->nargs; i++) {
 		ret = synthesize_probe_trace_arg(&tev->args[i], buf + len,


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