From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751892AbbANCCM (ORCPT ); Tue, 13 Jan 2015 21:02:12 -0500 Received: from lgeamrelo04.lge.com ([156.147.1.127]:46876 "EHLO lgeamrelo04.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751004AbbANCCL (ORCPT ); Tue, 13 Jan 2015 21:02:11 -0500 X-Original-SENDERIP: 10.177.220.203 X-Original-MAILFROM: namhyung@kernel.org Date: Wed, 14 Jan 2015 10:59:39 +0900 From: Namhyung Kim To: Masami Hiramatsu Cc: Arnaldo Carvalho de Melo , Ingo Molnar , Peter Zijlstra , Jiri Olsa , LKML , David Ahern Subject: Re: [PATCH 3/4] perf probe: Fix probing kretprobes Message-ID: <20150114015939.GD800@sejong> References: <1420886028-15135-1-git-send-email-namhyung@kernel.org> <1420886028-15135-3-git-send-email-namhyung@kernel.org> <54B3BC75.2060500@hitachi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <54B3BC75.2060500@hitachi.com> 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 Mon, Jan 12, 2015 at 09:22:13PM +0900, Masami Hiramatsu wrote: > (2015/01/10 19:33), 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. > > Thanks, but as I pointed in previous mail, this patch fixes just one > code path which doesn't use debuginfo. With debuginfo, perf-probe > executes try_to_find_probe_trace_events() to analyze debuginfo. > We can just skip calling it for retprobes, but I prefer to keep > it works. So just skipping conversion in post_process_probe_trace_events() > is better. Ah, missed that. I only tested on my laptop which has no debuginfo. I will add the check into the post_process_probe_trace_events(). Thanks, Namhyung