From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751857AbbALL0R (ORCPT ); Mon, 12 Jan 2015 06:26:17 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51631 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750860AbbALL0Q (ORCPT ); Mon, 12 Jan 2015 06:26:16 -0500 Date: Mon, 12 Jan 2015 12:26:04 +0100 From: Jiri Olsa To: Namhyung Kim Cc: Arnaldo Carvalho de Melo , Ingo Molnar , Peter Zijlstra , LKML , David Ahern , Masami Hiramatsu Subject: Re: [PATCH 3/4] perf probe: Fix probing kretprobes Message-ID: <20150112112604.GA4811@krava.brq.redhat.com> References: <1420886028-15135-1-git-send-email-namhyung@kernel.org> <1420886028-15135-3-git-send-email-namhyung@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1420886028-15135-3-git-send-email-namhyung@kernel.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 10, 2015 at 07:33:47PM +0900, Namhyung Kim wrote: > The commit dfef99cd0b2c ("perf probe: Use ref_reloc_sym based address > instead of the symbol name") converts kprobes to use ref_reloc_sym > (i.e. _stext) and offset instead of using symbol's name directly. So > on my system, adding do_fork ends up with like below: > > $ sudo perf probe -v --add do_fork%return > probe-definition(0): do_fork%return > symbol:do_fork file:(null) line:0 offset:0 return:1 lazy:(null) > 0 arguments > Looking at the vmlinux_path (7 entries long) > Using /lib/modules/3.17.6-1-ARCH/build/vmlinux for symbols > Could not open debuginfo. Try to use symbols. > Opening /sys/kernel/debug/tracing/kprobe_events write=1 > Added new event: > Writing event: r:probe/do_fork _stext+456136 > Failed to write event: Invalid argument > Error: Failed to add events. Reason: Operation not permitted (Code: -1) > > As you can see, the do_fork was translated to _stext+456136. This was > because to support (local) symbols that have same name. But the > problem is that kretprobe requires to be inserted at function start > point so it simply checks whether it's called with offset 0. And if > not, it'll return with -EINVAL. You can see it with dmesg. > > $ dmesg | tail -1 > [125621.764103] Return probe must be used without offset. > > So we need to use the symbol name instead of ref_reloc_sym in case of > return probes. with your patchset on top of current Arnaldo's perf/core, I'm still getting the same error: [root@krava perf]# ./perf probe -a fork_exit=do_fork%return Added new event: Failed to write event: Invalid argument Error: Failed to add events. [root@krava perf]# ./perf probe -v --add do_fork%return probe-definition(0): do_fork%return symbol:do_fork file:(null) line:0 offset:0 return:1 lazy:(null) 0 arguments Using /root/.debug/.build-id/60/4c5fd8a6c9202acac3a9e82ecd34b22b8caef6 for symbols Open Debuginfo file: /root/.debug/.build-id/60/4c5fd8a6c9202acac3a9e82ecd34b22b8caef6 Try to find probe point from debuginfo. Probe point found: do_fork+0 Found 1 probe_trace_events. Opening /sys/kernel/debug/tracing/kprobe_events write=1 Added new event: Writing event: r:probe/do_fork _text+597840 Failed to write event: Invalid argument Error: Failed to add events. Reason: Invalid argument (Code: -22) [root@krava perf]# dmesg | tail -1 [113205.738833] Return probe must be used without offset. thanks, jirka