From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754394AbbANQ0p (ORCPT ); Wed, 14 Jan 2015 11:26:45 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48327 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752506AbbANQ0n (ORCPT ); Wed, 14 Jan 2015 11:26:43 -0500 Date: Wed, 14 Jan 2015 17:26:27 +0100 From: Jiri Olsa To: Namhyung Kim Cc: Arnaldo Carvalho de Melo , Ingo Molnar , Peter Zijlstra , LKML , Masami Hiramatsu , David Ahern Subject: Re: [PATCH v2 4/4] perf probe: Fix probing kretprobes Message-ID: <20150114162627.GH6369@krava.redhat.com> References: <1421234288-22758-1-git-send-email-namhyung@kernel.org> <1421234288-22758-4-git-send-email-namhyung@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1421234288-22758-4-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 Wed, Jan 14, 2015 at 08:18:08PM +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. > > Reported-by: Jiri Olsa 'perf probe --add do_fork%return' inserts the probe correctly now Tested-by: Jiri Olsa thanks, jirka