From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757054AbcHCI0e (ORCPT ); Wed, 3 Aug 2016 04:26:34 -0400 Received: from szxga01-in.huawei.com ([58.251.152.64]:30957 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754210AbcHCI0G (ORCPT ); Wed, 3 Aug 2016 04:26:06 -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 , Masami Hiramatsu From: "Wangnan (F)" Message-ID: <57A1A913.6000307@huawei.com> Date: Wed, 3 Aug 2016 16:19:31 +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=0001.0A020202.57A1A91A.0106,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 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. > 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) > > 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.