Add Masami to Cc list. He knowns debug info.
Please see below...
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
#
As I have said in another mail, although I don't know why,
I don't think the missing of sys_epoll_wait is the root cause
of your failure.
I did a bisect search and found commit
83460ec8dcac14142e7860a01fa59c267ac4657c:
"syscalls.h: use gcc alias instead of assembler aliases for syscalls"
After this commit, sys_xxx symbols is gone from output of 'readelf -wi'.
It is
introduced in v3.13.
But:
[root@jouet ~]# grep -i sys_epoll_wait /proc/kallsyms
ffffffffbd295b50 T SyS_ep
oll_wait
ffffffffbd295b50 T sys_epoll_wait
[root@jouet ~]#
If we remove vmlinux, perf should use /proc/kallsyms. I think
the failure would gone. The problem is: when symbol searching
fail using vmlinux, should we fallback to kallsyms? However,
this is another question.
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 ~]#
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.
[root@jouet ~]# perf probe SyS_epoll_wait
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
[root@jouet ~]#
So I am changing the BPF perf test to use the CamelCase notation alias:
Changing to SyS_xxx is okay, byt we still need to know the root
cause.
Thank you.