From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757554AbcHCCu3 (ORCPT ); Tue, 2 Aug 2016 22:50:29 -0400 Received: from szxga01-in.huawei.com ([58.251.152.64]:48590 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755572AbcHCCto (ORCPT ); Tue, 2 Aug 2016 22:49:44 -0400 Subject: Re: perf test BPF failing on f24: fix To: Arnaldo Carvalho de Melo References: <20160802195102.GD14639@kernel.org> CC: Linux Kernel Mailing List From: "Wangnan (F)" Message-ID: <57A159EF.7010106@huawei.com> Date: Wed, 3 Aug 2016 10:41:51 +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: <20160802195102.GD14639@kernel.org> 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=0001.0A020205.57A15A02.0089,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 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. Thank you.