[PATCH] perf probe: Fix module probing with shortname

Wang Nan
2015-09-22T03:35:12Z

After commit 3d39ac538629e4f00a6e1c38d46346f1b8e69505 ("perf machine:
No need to have two DSOs lists"), perf probe with module short name doesn't
work again. For example:

# lsmod | grep e1000e
e1000e 233472 0

# cat /proc/modules | grep e1000e
e1000e 233472 0 - Live 0xffffffffa0073000

# cat /proc/kallsyms | grep '\<e1000e_up\>'
ffffffffa0093860 t e1000e_up[e1000e]

# perf probe -v -m e1000e --add e1000e_up
probe-definition(0): e1000e_up
symbol:e1000e_up file:(null) line:0 offset:0 return:0 lazy:(null)
0 arguments
Failed to find module e1000e.
Could not open debuginfo. Try to use symbols.
Looking at the vmlinux_path (7 entries long)
Using /lib/modules/4.2.0-rc7+/build/vmlinux for symbols
e1000e_up is out of .text, skip it.
Error: Failed to add events. Reason: No such file or directory (Code: -2)

This is caused by a misunderstood of dso->kernel in kernel_get_module_dso()
that, for kernel module, dso->kernel is DSO_TYPE_USER. dso->kernel is DSO_TYPE_KERNEL
iff dso is vmlinux.

This patch fix 'perf probe -m' with an ad-hoc way.

After this patch:

# perf probe -v -m e1000e --add e1000e_up
probe-definition(0): e1000e_up
symbol:e1000e_up file:(null) line:0 offset:0 return:0 lazy:(null)
0 arguments
Open Debuginfo file: /lib/modules/4.2.0-rc7+/kernel/drivers/net/ethernet/intel/e1000e/e1000e.ko
Try to find probe point from debuginfo.
Matched function: e1000e_up
Probe point found: e1000e_up+0
Found 1 probe_trace_events.
Opening /sys/kernel/debug/tracing//kprobe_events write=1
Writing event: p:probe/e1000e_up e1000e:e1000e_up+0
Added new event:
probe:e1000e_up (on e1000e_up in e1000e)

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

perf record -e probe:e1000e_up -aR sleep 1

# perf probe -l
Failed to find debug information for address ffffffffa0093860
probe:e1000e_up (on e1000e_up in e1000e)

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
---

I think there may be other places where dso->kernel is misused.
machine__process_kernel_mmap_event() may be one of them. If I understand
correctly, 'dso->kernel && is_kernel_module(dso->long_name)' should always
false theoretically. However, I don't have enough time to check whether that
code really cause problem.

---
tools/perf/util/probe-event.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 2b78e8f..c7d6d3d 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -270,7 +270,7 @@ static int kernel_get_module_dso(const char *module, struct dso **pdso)

if (module) {
list_for_each_entry(dso, &host_machine->dsos.head, node) {
- if (!dso->kernel)
+ if (dso->kernel)
continue;
if (strncmp(dso->short_name + 1, module,
dso->short_name_len - 2) == 0)
--
1.8.3.4