From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755444Ab1HKAV6 (ORCPT ); Wed, 10 Aug 2011 20:21:58 -0400 Received: from mail7.hitachi.co.jp ([133.145.228.42]:54686 "EHLO mail7.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754655Ab1HKAV4 (ORCPT ); Wed, 10 Aug 2011 20:21:56 -0400 X-AuditID: b753bd60-9ea82ba000000655-d5-4e4320a09bb8 X-AuditID: b753bd60-9ea82ba000000655-d5-4e4320a09bb8 Message-ID: <4E43209D.7090104@hitachi.com> Date: Thu, 11 Aug 2011 09:21:49 +0900 From: Masami Hiramatsu Organization: Systems Development Lab., Hitachi, Ltd., Japan User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:5.0) Gecko/20110624 Thunderbird/5.0 MIME-Version: 1.0 To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Thomas Gleixner , Peter Zijlstra , Frederic Weisbecker , Arnaldo Carvalho de Melo , Jason Baron , yrl.pp-manager.tt@hitachi.com Subject: Re: [PATCH 0/5][RFC] kprobes/ftrace: Have kprobes use ftrace on ftrace nops References: <20110810162222.017387055@goodmis.org> In-Reply-To: <20110810162222.017387055@goodmis.org> Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Steven, Thanks for this nice feature! (2011/08/11 1:22), Steven Rostedt wrote: > Hi All, > > I started working on adding the -mfentry switch to ftrace, which > allows us to remove the frame pointers requirement from function tracing > as well as makes mcount (fentry) work just better. > > But when I did this in another branch, I noticed that I broke kprobes > in its most common usage. The attaching a probe at the beginning of > a function to use get to its parameters. > > So I started this branch. This branch is to have kprobes use ftrace > directly when a probe is attached to a ftrace nop. Currently, kprobes > will just error when that happens. With this patch set, it will hook > into the ftrace infrastructure and use ftrace instead. This is more > like an optimized probe as no breakpoints need to be set. A call to > the function is done directly via the mcount trampoline. If ftrace > pt_regs is implemented for an arch, kprobes gets this feature for free. I agreed this idea, this looks good to me too :) With -fentry, this can improve dynamic trace events very much. BTW (OT), it seems that current kprobe data structure becomes a bit fat. Maybe what we need is just a "holder of hooking handler" as what ftrace provides, not a full storage data structure of copied instrucutions. Perhaps, we'd better diet the kprobe structure for transparency of hooking infrastructure. > The first patch is just a clean up that I need to push out to get rid > of the annoying compile warning about initialized variables that > gcc can't tell have been initialized. > > The next two patches have ftrace pass both the ftrace_ops structure > and the pt_regs to the callback function that is registered with ftrace. > > The last two patches have kprobes interact with ftrace and use the > ftrace infrastructure instead. > > I only did this for x86_64, and will do it for x86_32 and PPC64 if everyone > agrees with this approach. Then I could find people to do it for other > archs :) OK, I'll review this soon! Thank you! -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com