A problem can occure in statically linked perf when vmlinux can be found:
# perf probe --add sys_epoll_pwait
probe-definition(0): sys_epoll_pwait
symbol:sys_epoll_pwait file:(null) line:0 offset:0 return:0 lazy:(null)
0 arguments
Looking at the vmlinux_path (7 entries long)
Using /lib/modules/4.2.0-rc1+/build/vmlinux for symbols
Open Debuginfo file: /lib/modules/4.2.0-rc1+/build/vmlinux
Try to find probe point from debuginfo.
Symbol sys_epoll_pwait address found : ffffffff8122bd40
Matched function: SyS_epoll_pwait
Failed to get call frame on 0xffffffff8122bd40
An error occurred in debuginfo analysis (-2).
Error: Failed to add events. Reason: No such file or directory (Code: -2)
The reason is caused by libdw that, if libdw is statically linked, it can't
load libebl_{arch}.so reliable.
In this case it is still possible to get the address from /proc/kalksyms.
However, perf tries that only when libdw returns -EBADF.
This patch gives it another chance to utilize symbol table, even if libdw
return error code other than -EBADF.
After applying this patch:
# perf probe -nv --add sys_epoll_pwait
probe-definition(0): sys_epoll_pwait
symbol:sys_epoll_pwait file:(null) line:0 offset:0 return:0 lazy:(null)
0 arguments
Looking at the vmlinux_path (7 entries long)
Using /lib/modules/4.2.0-rc1+/build/vmlinux for symbols
Open Debuginfo file: /lib/modules/4.2.0-rc1+/build/vmlinux
Try to find probe point from debuginfo.
Symbol sys_epoll_pwait address found : ffffffff8122bd40
Matched function: SyS_epoll_pwait
Failed to get call frame on 0xffffffff8122bd40
An error occurred in debuginfo analysis (-2).
Trying to use symbols.
Opening /sys/kernel/debug/tracing/kprobe_events write=1
Added new event:
Writing event: p:probe/sys_epoll_pwait _text+2276672
probe:sys_epoll_pwait (on sys_epoll_pwait)
You can now use it in all perf tools, such as:
perf record -e probe:sys_epoll_pwait -aR sleep 1
Although libdw returns an error (Failed to get call frame),
perf tries symbol table and finally gets correct address.
Signed-off-by: Wang Nan <wangn...@huawei.com>
---
tools/perf/util/probe-event.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index fe4941a..f07374b 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -705,9 +705,10 @@ static int try_to_find_probe_trace_events(struct
perf_probe_event *pev,
}
/* Error path : ntevs < 0 */
pr_debug("An error occurred in debuginfo analysis (%d).\n", ntevs);
- if (ntevs == -EBADF) {
- pr_warning("Warning: No dwarf info found in the vmlinux - "
- "please rebuild kernel with CONFIG_DEBUG_INFO=y.\n");
+ if (ntevs < 0) {
+ if (ntevs == -EBADF)
+ pr_warning("Warning: No dwarf info found in the vmlinux
- "
+ "please rebuild kernel with
CONFIG_DEBUG_INFO=y.\n");
if (!need_dwarf) {
pr_debug("Trying to use symbols.\n");
return 0;
--
1.8.3.4
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