Messages in this thread | | | Date | Wed, 3 Aug 2016 23:45:57 +0900 | From | Masami Hiramatsu <> | Subject | Re: perf test BPF failing on f24: fix |
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On Wed, 3 Aug 2016 16:19:31 +0800 "Wangnan (F)" <wangnan0@huawei.com> wrote:
> 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.
As below result shown, perf probe tries to fallback, but it seems to fail to find corresponding debuginfo entry...
> > [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.
So, at least I should investigate it.
Thanks,
> > [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. >
-- Masami Hiramatsu <mhiramat@kernel.org>
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