Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753877Ab2FEXh4 (ORCPT ); Tue, 5 Jun 2012 19:37:56 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:2763 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753825Ab2FEXhz (ORCPT ); Tue, 5 Jun 2012 19:37:55 -0400 X-Authority-Analysis: v=2.0 cv=T6AOvo2Q c=1 sm=0 a=ZycB6UtQUfgMyuk2+PxD7w==:17 a=XQbtiDEiEegA:10 a=MiGSmKHM__4A:10 a=5SG0PmZfjMsA:10 a=Q9fys5e9bTEA:10 a=meVymXHHAAAA:8 a=ayC55rCoAAAA:8 a=yzjbzWvirs0ToGFTdAIA:9 a=PUjeQqilurYA:10 a=ZycB6UtQUfgMyuk2+PxD7w==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.80.29 Message-ID: <1338939470.13348.541.camel@gandalf.stny.rr.com> Subject: Re: [PATCH -tip v2 3/9] ftrace/x86: Support SAVE_REGS feature on i386 From: Steven Rostedt To: "Frank Ch. Eigler" Cc: Masami Hiramatsu , linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Ananth N Mavinakayanahalli , Andrew Morton , Frederic Weisbecker , yrl.pp-manager.tt@hitachi.com Date: Tue, 05 Jun 2012 19:37:50 -0400 In-Reply-To: <20120605212411.GC11575@redhat.com> References: <20120605102734.27845.43401.stgit@localhost.localdomain> <20120605102802.27845.49309.stgit@localhost.localdomain> <1338928666.13348.538.camel@gandalf.stny.rr.com> <20120605212411.GC11575@redhat.com> 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 Content-Length: 1159 Lines: 35 On Tue, 2012-06-05 at 17:24 -0400, Frank Ch. Eigler wrote: > Hi - > > On Tue, Jun 05, 2012 at 04:37:46PM -0400, Steven Rostedt wrote: > > [...] > > I'm not sure we really need to restore all the regs. I'll keep this for > > now, but for an optimization, we can just restore the ones that mcount > > mcount needs to. > > > > Or do you expect kprobes to change any of theses? > > That would be the way for a kprobe to modify variables/values that > happen to be in the registers. In systemtap, for example: > > # stap -g -e 'probe kernel.function("foo") { $bar = 1 }' > And why would we want to allow this? Modifying variables with probes is another way to lead to disaster. If the system did not intend for a variable to be a certain value, why let someone change it? What real world example leads to external sources modifying internal core variables? With the obvious exception of rootkits. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/