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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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Thread

perf test BPF failing on f24: fix Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-08-02 22:00 +0200
  Re: perf test BPF failing on f24: fix Alexei Starovoitov <alexei.starovoitov@gmail.com> - 2016-08-03 01:00 +0200
    Re: perf test BPF failing on f24: fix Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-08-03 04:20 +0200
      Re: perf test BPF failing on f24: fix Alexei Starovoitov <alexei.starovoitov@gmail.com> - 2016-08-03 05:00 +0200
  Re: perf test BPF failing on f24: fix "Wangnan (F)" <wangnan0@huawei.com> - 2016-08-03 05:00 +0200
    Re: perf test BPF failing on f24: fix "Wangnan (F)" <wangnan0@huawei.com> - 2016-08-03 05:50 +0200
  Re: perf test BPF failing on f24: fix "Wangnan (F)" <wangnan0@huawei.com> - 2016-08-03 10:30 +0200
    Re: perf test BPF failing on f24: fix Masami Hiramatsu <mhiramat@kernel.org> - 2016-08-03 16:50 +0200
      Re: perf test BPF failing on f24: fix Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-08-03 22:10 +0200
        Re: perf test BPF failing on f24: fix Masami Hiramatsu <mhiramat@kernel.org> - 2016-08-04 08:50 +0200
          Re: perf test BPF failing on f24: fix Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-08-04 14:50 +0200
            Re: perf test BPF failing on f24: fix Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-08-04 21:40 +0200
              Re: perf test BPF failing on f24: fix Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-08-04 23:50 +0200
                Re: perf test BPF failing on f24: fix Masami Hiramatsu <mhiramat@kernel.org> - 2016-08-05 11:50 +0200
                Re: perf test BPF failing on f24: fix Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-08-05 16:40 +0200
                Re: perf test BPF failing on f24: fix Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-08-05 18:00 +0200
                Re: perf test BPF failing on f24: fix Masami Hiramatsu <mhiramat@kernel.org> - 2016-08-06 23:10 +0200
                Re: perf test BPF failing on f24: fix Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-08-08 21:40 +0200
                [tip:perf/urgent] perf probe: Adjust map->reloc offset when finding  kernel symbol from map tip-bot for Masami Hiramatsu <tipbot@zytor.com> - 2016-08-09 21:20 +0200
      Re: perf test BPF failing on f24: fix Masami Hiramatsu <mhiramat@kernel.org> - 2016-08-04 01:10 +0200
        Re: perf test BPF failing on f24: fix "Wangnan (F)" <wangnan0@huawei.com> - 2016-08-04 04:00 +0200
          Re: perf test BPF failing on f24: fix Masami Hiramatsu <mhiramat@kernel.org> - 2016-08-04 11:00 +0200

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