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    SubjectRe: perf test BPF failing on f24: fix
    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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