From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932657AbcHCOql (ORCPT ); Wed, 3 Aug 2016 10:46:41 -0400 Received: from mail.kernel.org ([198.145.29.136]:48036 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753598AbcHCOqj (ORCPT ); Wed, 3 Aug 2016 10:46:39 -0400 Date: Wed, 3 Aug 2016 23:45:57 +0900 From: Masami Hiramatsu To: "Wangnan (F)" Cc: Arnaldo Carvalho de Melo , Linux Kernel Mailing List , Masami Hiramatsu Subject: Re: perf test BPF failing on f24: fix Message-Id: <20160803234557.29f43f755b7e14c634a54a9a@kernel.org> In-Reply-To: <57A1A913.6000307@huawei.com> References: <20160802195102.GD14639@kernel.org> <57A1A913.6000307@huawei.com> X-Mailer: Sylpheed 3.5.0 (GTK+ 2.24.30; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 3 Aug 2016 16:19:31 +0800 "Wangnan (F)" wrote: > 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. As below result shown, perf probe tries to fallback, but it seems to fail to find corresponding debuginfo entry... > > [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. So, at least I should investigate it. Thanks, > > [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. > -- Masami Hiramatsu