[RFC v2] perf: probe_finder: continue if atleast one probe point found

[Joel Fernandes]

From: Joel Fernandes <agnel.joel@xxxxxxxxx>

Sometimes for inline functions, perf probe can fail such as if an arguments are
requested at probe points. This is probably because when the compiler inlines,
for some instances it optimizes away arguments. Either way, the DWARF has
missing arguments for certain probe points of inline functions causing 'perf
probe' to fail. I noticed this when probing the C library that ships with my
distribution. With the following patch I am successfully able to record uprobe
events with arguments.
v2 changes: Corrected commit message to mention uprobe.

Test
----
 ./perf probe \
   -k ./vmlinux -s ./ -x /lib/x86_64-linux-gnu/libc.so.6 -a 'malloc bytes' -v

Without the patch
-----------------
Matched function: __libc_malloc
found inline addr: 0x831a6
Probe point found: malloc_atfork+150
Searching 'bytes' variable in context.
Converting variable bytes into trace event.
bytes type is long unsigned int.
found inline addr: 0x844a0
Probe point found: __libc_malloc+0
Searching 'bytes' variable in context.
Converting variable bytes into trace event.
bytes type is long unsigned int.
found inline addr: 0x8463b
Probe point found: __malloc_get_state+11
Searching 'bytes' variable in context.
Failed to find 'bytes' in this function.
An error occurred in debuginfo analysis (-2).
  Error: Failed to add events. Reason: No such file or directory (Code: -2)

With the patch
--------------
Open Debuginfo file: /usr/lib/debug/lib/x86_64-linux-gnu/libc-2.21.so
Try to find probe point from debuginfo.
Symbol malloc address found : 844a0
Matched function: __libc_malloc
found inline addr: 0x831a6
Probe point found: malloc_atfork+150
Searching 'bytes' variable in context.
Converting variable bytes into trace event.
bytes type is long unsigned int.
found inline addr: 0x844a0
Probe point found: __libc_malloc+0
Searching 'bytes' variable in context.
Converting variable bytes into trace event.
bytes type is long unsigned int.
found inline addr: 0x8463b
Probe point found: __malloc_get_state+11
Searching 'bytes' variable in context.
Failed to find 'bytes' in this function.
Probe point error, ignoring. Atleast one probe point found
found inline addr: 0x84bba
Probe point found: __libc_realloc+410
Searching 'bytes' variable in context.
Failed to find 'bytes' in this function.
Probe point error, ignoring. Atleast one probe point found
found inline addr: 0x84d08
...
Probe point error, ignoring. Atleast one probe point found
Found 3 probe_trace_events.
Opening /sys/kernel/debug/tracing//uprobe_events write=1
Writing event: p:probe_libc/malloc /lib/x86_64-linux-gnu/libc-2.21.so:0x831a6 bytes=%bp:u64
Writing event: p:probe_libc/malloc_1 /lib/x86_64-linux-gnu/libc-2.21.so:0x844a0 bytes=%di:u64
Writing event: p:probe_libc/malloc_2 /lib/x86_64-linux-gnu/libc-2.21.so:0x85af7 bytes=%di:u64
Added new events:
  probe_libc:malloc    (on malloc in /lib/x86_64-linux-gnu/libc-2.21.so with bytes)
  probe_libc:malloc_1  (on malloc in /lib/x86_64-linux-gnu/libc-2.21.so with bytes)
  probe_libc:malloc_2  (on malloc in /lib/x86_64-linux-gnu/libc-2.21.so with bytes)

Signed-off-by: Joel Fernandes <agnel.joel@xxxxxxxxx>
---
 tools/perf/util/probe-finder.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 4ce5c5e..3ac9481 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -1255,6 +1255,10 @@ end:
 	if (ret) {
 		clear_probe_trace_event(tev);
 		tf->ntevs--;
+		if (tf->ntevs != 0) {
+			pr_debug("Ignoring error as atleast one probe point found.\n");
+			ret = 0;
+		}
 	}
 	free(args);
 	return ret;
-- 
2.5.0