From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755770AbcHCDrd (ORCPT ); Tue, 2 Aug 2016 23:47:33 -0400 Received: from szxga01-in.huawei.com ([58.251.152.64]:35593 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751860AbcHCDrZ (ORCPT ); Tue, 2 Aug 2016 23:47:25 -0400 Subject: Re: perf test BPF failing on f24: fix To: Arnaldo Carvalho de Melo References: <20160802195102.GD14639@kernel.org> <57A159EF.7010106@huawei.com> CC: Linux Kernel Mailing List From: "Wangnan (F)" Message-ID: <57A16807.9010901@huawei.com> Date: Wed, 3 Aug 2016 11:41:59 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 MIME-Version: 1.0 In-Reply-To: <57A159EF.7010106@huawei.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.111.66.109] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A020206.57A16811.0027,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2013-06-18 04:22:30, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 1866986e63a8cef48643d1d1874fbc2f Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2016/8/3 10:41, Wangnan (F) wrote: > > > 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 >> # >> >> 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 ~]# > > I also see no sys_epoll_wait in output of 'readelf -wi', but I can't > reproduce the whole problem. > >> 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. > > For me: > > # uname -r > 4.7.0 > > # perf probe -v sys_epoll_wait > probe-definition(0): sys_epoll_wait > symbol:sys_epoll_wait file:(null) line:0 offset:0 return:0 lazy:(null) > 0 arguments > Looking at the vmlinux_path (8 entries long) > Using /lib/modules/4.7.0/build/vmlinux for symbols > Open Debuginfo file: /lib/modules/4.7.0/build/vmlinux > Try to find probe point from debuginfo. > Symbol sys_epoll_wait address found : ffffffff81281240 > Matched function: SyS_epoll_wait > found inline addr: 0xffffffff81281240 > Probe point found: SyS_epoll_wait+0 > found inline addr: 0xffffffff812813a7 > Probe point found: SyS_epoll_pwait+135 > found inline addr: 0xffffffff8128157a > Probe point found: compat_SyS_epoll_pwait+154 > Found 3 probe_trace_events. > Opening /sys/kernel/debug/tracing//kprobe_events write=1 > Writing event: p:probe/sys_epoll_wait _text+2626112 > Writing event: p:probe/sys_epoll_wait_1 _text+2626471 > Writing event: p:probe/sys_epoll_wait_2 _text+2626938 > 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 > > > I'll try different kernel version and kconfig. > Still unable reproduce. I tried tip/core/core, which is '4.7.0+'. I also turns off CONFIG_DEBUG_INFO. In this case, testcase BPF prologue fails as expected, and basic BPF test is okay. After removing vmlinux, with kallsyms information 'perf probe sys_epoll_wait' sets only 1 kprobe, but it still works. I think there is a bug in your vmlinux. Could you please do a bisect to find which commit causes this problem? Thank you.