From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754301Ab0ATT6d (ORCPT ); Wed, 20 Jan 2010 14:58:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754268Ab0ATT6c (ORCPT ); Wed, 20 Jan 2010 14:58:32 -0500 Received: from one.firstfloor.org ([213.235.205.2]:41911 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754213Ab0ATT6c (ORCPT ); Wed, 20 Jan 2010 14:58:32 -0500 Date: Wed, 20 Jan 2010 20:58:26 +0100 From: Andi Kleen To: Jim Keniston Cc: Andi Kleen , Avi Kivity , Pekka Enberg , Srikar Dronamraju , Peter Zijlstra , ananth@in.ibm.com, Ingo Molnar , Arnaldo Carvalho de Melo , utrace-devel , Frederic Weisbecker , Masami Hiramatsu , Maneesh Soni , Mark Wielaard , LKML Subject: Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP) Message-ID: <20100120195826.GB24355@basil.fritz.box> References: <4B545146.3080001@redhat.com> <20100118124419.GC1628@linux.vnet.ibm.com> <84144f021001180451k2a84f17x3dc24796fea986c9@mail.gmail.com> <4B5459CA.9060603@redhat.com> <4B545ACF.40203@cs.helsinki.fi> <1263852957.2266.38.camel@localhost.localdomain> <4B556855.6040800@redhat.com> <1263923265.4998.28.camel@localhost.localdomain> <87wrzc39ww.fsf@basil.nowhere.org> <1264016052.5122.40.camel@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1264016052.5122.40.camel@localhost.localdomain> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > Re: rewriting instructions that use rip-relative addressing. We do that > now. See handle_riprel_insn() in patch #2. (As far as we can tell, it > works, but we'd appreciate your review of it.) Yes, but how do you get within 2GB of it? Add lots of holes in the address space? > The instruction decoder is used only during instruction analysis, while > registering the probe -- i.e., in kernel space. Registering the user probe? That means if there's a buffer overflow in there it would be exploitable. > > > > In general the trend has been also to make traps faster in the CPU, make > > sure you're not optimizing for some old CPU here. > > I won't argue with that. What Avi seems to be proposing buys us a > speedup, but at the cost of increased complexity -- among other things, > splitting the instrumentation code between user space (in the "XOL" area > -- which would then be used for much more than XOL instruction slots) You can't have a single XOL area, at least not if you want to support shared libraries on 64bit & rip relative. > and kernel space. The splitting would presumably be handled by > higher-level code -- SystemTap, perf, or whatever. It's a neat idea, > but it seems like a v2 kind of feature. I'm not sure it can even work, unless you severly limited the allowed instructions. -Andi -- ak@linux.intel.com -- Speaking for myself only.