From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752107Ab3LBOtL (ORCPT ); Mon, 2 Dec 2013 09:49:11 -0500 Received: from mail-pd0-f174.google.com ([209.85.192.174]:50582 "EHLO mail-pd0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751961Ab3LBOtH (ORCPT ); Mon, 2 Dec 2013 09:49:07 -0500 Message-ID: <529C9DDF.1080401@gmail.com> Date: Mon, 02 Dec 2013 07:49:03 -0700 From: David Ahern User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.1.1 MIME-Version: 1.0 To: Masami Hiramatsu CC: acme@ghostprotocols.net, linux-kernel@vger.kernel.org, Srikar Dronamraju , Oleg Nesterov , namhyung@kernel.org, "yrl.pp-manager.tt@hitachi.com" Subject: Re: [PATCH 2/2] perf probe: Allow user to specify address within executable References: <1385942827-11637-1-git-send-email-dsahern@gmail.com> <1385942827-11637-2-git-send-email-dsahern@gmail.com> <529C259D.8010901@hitachi.com> In-Reply-To: <529C259D.8010901@hitachi.com> Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/1/13, 11:15 PM, Masami Hiramatsu wrote: > (2013/12/02 9:07), David Ahern wrote: >> Allow user to specify an address within an executable. This is useful, for >> example, in probing local functions. If the function name begins with 0x >> then try to convert the supplied name to an address. If succuessful then >> treat the function name as the address within the executable to be probed. > > Hmm, IMHO, this kind of functionality is only good for debugging. Why? perf-probe takes the function name, looks up the address in the executable, adds an offset and then pushes that address to the kernel. Why can't I have an option to jump straight to the desired address? A few use cases that come to mind: 1. Allows manual creation of return probes in kernels which do not have that support. 2. probing static functions 3. probing versioned addresses in libc -- something the current syntax does not allow because '@' is used as a field separator: $ nm /lib64/libc-2.14.90.so | grep pthread_cond_timedwait 00000000000fe6c0 t __pthread_cond_timedwait 000000000012d920 t __pthread_cond_timedwait_2_0 00000000000fe6c0 T pthread_cond_timedwait@@GLIBC_2.3.2 000000000012d920 T pthread_cond_timedwait@GLIBC_2.2.5 $ perf probe -x /lib64/libc-2.14.90.so -a 'cond_timewait=pthread_cond_timedwait' no symbols found in /lib64/libc-2.14.90.so, maybe install a debug package? Failed to load map. Error: Failed to add events. (-22) $ perf probe -x /lib64/libc-2.14.90.so -a 'cond_timewait=pthread_cond_timedwait@@GLIBC_2.3.2' Semantic error :SRC@SRC is not allowed. 4. A workaround for any other shortcomings in the interface that require patches to fix and backports to be done. backports which take time if even possible. > In that case, you should use uprobe_events interface directly. How do I do that within the context of perf? > > I recommend you to try enabing dwarf support in user space. > Perf probe is a user-friendly interface of dynamic events. I do have dwarf support enabled in perf. Are you referring to other components of userspace (like system libraries)? David