linux-kernel - perf test BPF failing on f24: fix

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Date:	Tue, 2 Aug 2016 16:51:02 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: perf test BPF failing on f24: fix

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@...et ~]# grep -i sys_epoll_wait /proc/kallsyms 
ffffffffbd295b50 T SyS_epoll_wait
ffffffffbd295b50 T sys_epoll_wait
[root@...et ~]#

I noticed that it is some sort of aliasing so I checked the other
variant:

[root@...et ~]# 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@...et ~]# 

Trying to use perf probe also produces the same resuls I notice when
running the perf test that is failing:

[root@...et ~]# 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@...et ~]# 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@...et ~]# 

So I am changing the BPF perf test to use the CamelCase notation alias:

Failing (with sys_epoll_wait):

[root@...et ~]# 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@...et ~]#

Changing to (SyS_epoll_wait):

[root@...et ~]# 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@...et ~]#

I'm adding a fix that just makes it use SyS_epoll_wait.

- Arnaldo