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SubjectRe: perf test BPF failing on f24: fix
On Tue, Aug 02, 2016 at 04:51:02PM -0300, 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 ~]#
>
> 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)

that change will break all sorts of scripts that relying on syscalls to start
with sys_
I guess we can workaround in user space, but what was the motivation to
disable kprobe attach on sys_* while it's still in kallsyms?

>
> 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:
>
> Failing (with sys_epoll_wait):
>
> [root@jouet ~]# perf test BPF
> 37: Test BPF filter :
> 37.1: Test basic BPF filtering : FAILED!
> 37.2: Test BPF prologue generation : Skip
> 37.3: Test BPF relocation checker : Skip
> [root@jouet ~]#
>
> Changing to (SyS_epoll_wait):
>
> [root@jouet ~]# perf test BPF
> 37: Test BPF filter :
> 37.1: Test basic BPF filtering : Ok
> 37.2: Test BPF prologue generation : Ok
> 37.3: Test BPF relocation checker : Ok
> [root@jouet ~]#
>
> I'm adding a fix that just makes it use SyS_epoll_wait.
>
> - Arnaldo

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