On 2016/8/3 3:51, Arnaldo Carvalho de Melo wrote:
Hi Wang,
Something changed and a function used in a perf test for BPF is
not anymore appearing on vmlinux, albeit still available on
/proc/kallsyms:
# readelf -wi /lib/modules/4.7.0+/build/vmlinux | grep -w sys_epoll_wait
#
But:
[root@jouet ~]# grep -i sys_epoll_wait /proc/kallsyms
ffffffffbd295b50 T SyS_epoll_wait
ffffffffbd295b50 T sys_epoll_wait
[root@jouet ~]#
I noticed that it is some sort of aliasing so I checked the other
variant:
[root@jouet ~]# readelf -wi /lib/modules/4.7.0+/build/vmlinux | grep -w
SyS_epoll_wait
<2bc9b85> DW_AT_name : (indirect string, offset: 0xe7524):
SyS_epoll_wait
[root@jouet ~]#
I also see no sys_epoll_wait in output of 'readelf -wi', but I can't
reproduce the whole problem.
Trying to use perf probe also produces the same resuls I notice when
running the perf test that is failing:
[root@jouet ~]# perf probe sys_epoll_wait
Failed to find debug information for address ffffffffbd295b50
Probe point 'sys_epoll_wait' not found.
Error: Failed to add events.
For me:
# uname -r
4.7.0
# perf probe -v sys_epoll_wait
probe-definition(0): sys_epoll_wait
symbol:sys_epoll_wait file:(null) line:0 offset:0 return:0 lazy:(null)
0 arguments
Looking at the vmlinux_path (8 entries long)
Using /lib/modules/4.7.0/build/vmlinux for symbols
Open Debuginfo file: /lib/modules/4.7.0/build/vmlinux
Try to find probe point from debuginfo.
Symbol sys_epoll_wait address found : ffffffff81281240
Matched function: SyS_epoll_wait
found inline addr: 0xffffffff81281240
Probe point found: SyS_epoll_wait+0
found inline addr: 0xffffffff812813a7
Probe point found: SyS_epoll_pwait+135
found inline addr: 0xffffffff8128157a
Probe point found: compat_SyS_epoll_pwait+154
Found 3 probe_trace_events.
Opening /sys/kernel/debug/tracing//kprobe_events write=1
Writing event: p:probe/sys_epoll_wait _text+2626112
Writing event: p:probe/sys_epoll_wait_1 _text+2626471
Writing event: p:probe/sys_epoll_wait_2 _text+2626938
Added new events:
probe:sys_epoll_wait (on sys_epoll_wait)
probe:sys_epoll_wait_1 (on sys_epoll_wait)
probe:sys_epoll_wait_2 (on sys_epoll_wait)
You can now use it in all perf tools, such as:
perf record -e probe:sys_epoll_wait_2 -aR sleep 1
I'll try different kernel version and kconfig.
Thank you.
