From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934899AbcHEJqF (ORCPT ); Fri, 5 Aug 2016 05:46:05 -0400 Received: from mail.kernel.org ([198.145.29.136]:49546 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934069AbcHEJqA (ORCPT ); Fri, 5 Aug 2016 05:46:00 -0400 Date: Fri, 5 Aug 2016 18:45:50 +0900 From: Masami Hiramatsu To: Arnaldo Carvalho de Melo Cc: Arnaldo Carvalho de Melo , Masami Hiramatsu , "Wangnan (F)" , Alexei Starovoitov , Linux Kernel Mailing List Subject: Re: perf test BPF failing on f24: fix Message-Id: <20160805184550.33ffa7a6989fad3940187d7e@kernel.org> In-Reply-To: <20160804214724.GL14639@kernel.org> References: <20160802195102.GD14639@kernel.org> <57A1A913.6000307@huawei.com> <20160803234557.29f43f755b7e14c634a54a9a@kernel.org> <20160803200415.GG14639@kernel.org> <20160804153221.8aa29dfc5533b14089bd7470@kernel.org> <20160804124857.GH14639@kernel.org> <20160804193656.GK14639@kernel.org> <20160804214724.GL14639@kernel.org> 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 Thu, 4 Aug 2016 18:47:24 -0300 Arnaldo Carvalho de Melo wrote: > Em Thu, Aug 04, 2016 at 04:36:56PM -0300, Arnaldo Carvalho de Melo escreveu: > > So: > > > > int err = debuginfo__get_text_offset(dbg, &baseaddr); > > > > is returning 0, no relocation, its dwarf_addrdie() that is not finding > > SyS_epoll_wait from its address. > > > > Trying to figure out why dwarf_addrdie(0xffffffffbd295b50) fails... > > So, trying to use that vmlinux with objdump to do disassembly I found > that I need to do some offsetting, and after calculating it, this made > things works for me: > > diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c > index f2d9ff064e2d..9b95754f28ed 100644 > --- a/tools/perf/util/probe-finder.c > +++ b/tools/perf/util/probe-finder.c > @@ -1486,6 +1486,8 @@ retry: > /* Find cu die */ > if (!dwarf_addrdie(dbg->dbg, (Dwarf_Addr)addr, &cudie)) { > if (!reloc && debuginfo__get_text_offset(dbg, &baseaddr) == 0) { > + if (baseaddr == 0) > + baseaddr = -0x3c000000; Hmm, strange... what's this magic number ...? Actually debuginfo__get_text_offset() is for kernel modules and it relocate the offset. But I guess sys_epoll_wait is in the kernel. > addr += baseaddr; > reloc = true; > goto retry; > > ---------------- > > With it, which is not a proper fix, of course, we get: > > [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 ~]# > > Which, using -v shows it "finding" the alias: > > [root@jouet ~]# 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 : ffffffffbd295b50 > Matched function: SyS_epoll_wait > found inline addr: 0xffffffff81295ee7 > Probe point found: compat_SyS_epoll_pwait+151 > found inline addr: 0xffffffff81295cca > Probe point found: SyS_epoll_pwait+138 > found inline addr: 0xffffffff81295b50 > Probe point found: SyS_epoll_wait+0 Mine shows ---- Using /usr/lib/debug/lib/modules/4.6.4-301.fc24.x86_64/vmlinux for symbols Open Debuginfo file: /usr/lib/debug/lib/modules/4.6.4-301.fc24.x86_64/vmlinux Try to find probe point from debuginfo. Symbol sys_epoll_wait address found : ffffffff81292d60 <-(*) Matched function: SyS_epoll_wait found inline addr: 0xffffffff812930f3 Probe point found: compat_SyS_epoll_pwait+147 found inline addr: 0xffffffff81292ed6 Probe point found: SyS_epoll_pwait+134 found inline addr: 0xffffffff81292d60 Probe point found: SyS_epoll_wait+0 Found 3 probe_trace_events. ----- See the symbol address calcurated from symbol map, in successful case the address exactly same address of SyS_epoll_wait. This indicates something might wrong in the symbol map. (maybe KASLR?) Could you check what happen if nokaslr is passed to your kernel? Thank you, > Found 3 probe_trace_events. > Opening /sys/kernel/debug/tracing//kprobe_events write=1 > Writing event: p:probe/sys_epoll_wait _text+2711271 > Writing event: p:probe/sys_epoll_wait_1 _text+2710730 > Writing event: p:probe/sys_epoll_wait_2 _text+2710352 > 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 ~]# > > ---------- > > Now to figure out why baseaddr is returning as zero... > > - Arnaldo -- Masami Hiramatsu