From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756553AbcHBW6M (ORCPT ); Tue, 2 Aug 2016 18:58:12 -0400 Received: from mail-pf0-f175.google.com ([209.85.192.175]:35750 "EHLO mail-pf0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752316AbcHBW57 (ORCPT ); Tue, 2 Aug 2016 18:57:59 -0400 Date: Tue, 2 Aug 2016 14:03:33 -0700 From: Alexei Starovoitov To: Arnaldo Carvalho de Melo Cc: Wang Nan , Linux Kernel Mailing List , brendan.d.gregg@gmail.com, bblanco@plumgrid.com Subject: Re: perf test BPF failing on f24: fix Message-ID: <20160802210331.GA20688@ast-mbp.thefacebook.com> References: <20160802195102.GD14639@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160802195102.GD14639@kernel.org> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 02, 2016 at 04:51:02PM -0300, 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 ~]# > > 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) that change will break all sorts of scripts that relying on syscalls to start with sys_ I guess we can workaround in user space, but what was the motivation to disable kprobe attach on sys_* while it's still in kallsyms? > > 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: > > Failing (with sys_epoll_wait): > > [root@jouet ~]# 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@jouet ~]# > > Changing to (SyS_epoll_wait): > > [root@jouet ~]# 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@jouet ~]# > > I'm adding a fix that just makes it use SyS_epoll_wait. > > - Arnaldo