From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753793Ab2EBXkg (ORCPT ); Wed, 2 May 2012 19:40:36 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:4813 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752213Ab2EBXkf (ORCPT ); Wed, 2 May 2012 19:40:35 -0400 X-Authority-Analysis: v=2.0 cv=N/Wr5hBB c=1 sm=0 a=ZycB6UtQUfgMyuk2+PxD7w==:17 a=XQbtiDEiEegA:10 a=uEXl3daXtzsA:10 a=5SG0PmZfjMsA:10 a=Q9fys5e9bTEA:10 a=wI1-Dj-GET37w66_tpsA:9 a=PUjeQqilurYA:10 a=ZycB6UtQUfgMyuk2+PxD7w==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.80.29 Message-ID: <1336002032.14207.52.camel@gandalf.stny.rr.com> Subject: Re: [PATCH 6/9][RFC] kprobes: Allow probe on ftrace reserved text (but move it) From: Steven Rostedt To: "Frank Ch. Eigler" Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Frederic Weisbecker , Masami Hiramatsu , "H. Peter Anvin" Date: Wed, 02 May 2012 19:40:32 -0400 In-Reply-To: References: <20120502192418.024103772@goodmis.org> <20120502193237.321234712@goodmis.org> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.2.2-1 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2012-05-02 at 16:40 -0400, Frank Ch. Eigler wrote: > rostedt wrote: > > > [...] Added KPROBE_FLAG_MOVED (as suggested by Masami) that is set > > when the address is moved to get around an ftrace nop. [...] > > Steve, perhaps my earlier comments on this got lost during the mailing > list outage. I saw it, but it didn't really specify what you wanted. Here's your comment: > I suspect Masami intended that this flag is later used during int3 > processing to subtract MCOUNT_INSN_SIZE back out from the pt_regs->ip > during kprobe_handler() if this flag was set. This is what I thought too, but to me it sounded like Masami could do the work. I was just setting up a flag to make it possible. > > The gist is that a KPROBE_FLAG_MOVED being set this way accomplishes > very little since nothing is looking for that flag. Instead, you > should patch {arch/*}/kernel/kprobe.c kprobe_handler() to subtract > MCOUNT_INSN_SIZE back out from pt_regs->ip if KPROBE_FLAG_MOVED was > set. That way, kprobes clients need do not perceive the int3 movement. I basically thought that Masami wanted me to add the flag, and then others could look for this and do the adjustment. I'm not the kprobes author. I was just adding a flag that Masami and others could use to do such updates. I'm not sure if the adjustment is fine with everyone, as it may cause repercussions that I don't know about. Perhaps that could be another patch (want to write it?) -- Steve