From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932185AbcHCC5z (ORCPT ); Tue, 2 Aug 2016 22:57:55 -0400 Received: from mail-pf0-f173.google.com ([209.85.192.173]:35598 "EHLO mail-pf0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755572AbcHCC5r (ORCPT ); Tue, 2 Aug 2016 22:57:47 -0400 Date: Tue, 2 Aug 2016 19:57:42 -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: <20160803025739.GA30416@ast-mbp.thefacebook.com> References: <20160802195102.GD14639@kernel.org> <20160802210331.GA20688@ast-mbp.thefacebook.com> <20160803021534.GE14639@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160803021534.GE14639@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 11:15:34PM -0300, Arnaldo Carvalho de Melo wrote: > Em Tue, Aug 02, 2016 at 02:03:33PM -0700, Alexei Starovoitov escreveu: > > 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_ > > Is there a promise that internal kernel functions will not change names? > > > 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? > > Was it disabled? What I noticed whas that the sys_epoll_wait wasn't > present in the DWARF info present in the vmlinux file, which would be > good for others to confirm, which I'll check on other machines here at > home, tomorrow. as far as I can see sys_ and SyS_ both present in kallsyms, so kprobe infra should recognize both, the question is why perf decided to ingore sys_ version?