From: Mathieu Desnoyers Subject: Re: [PATCH 1/1] x86: fix text_poke Date: Fri, 25 Apr 2008 16:37:17 -0400 Message-ID: <20080425203717.GB25950@Krystal> References: <20080425152650.GA894@elte.hu> <20080425154854.GC3265@one.firstfloor.org> <20080425161916.GD3265@one.firstfloor.org> <20080425163035.GE9503@Krystal> <481209F2.4050908@zytor.com> <20080425170929.GA16180@Krystal> <20080425183748.GB16180@Krystal> <48123C9B.9020306@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: Andi Kleen , Linus Torvalds , Ingo Molnar , Jiri Slaby , David Miller , zdenek.kabelac@gmail.com, rjw@sisk.pl, paulmck@linux.vnet.ibm.com, akpm@linux-foundation.org, linux-ext4@vger.kernel.org, herbert@gondor.apana.org.au, penberg@cs.helsinki.fi, clameter@sgi.com, linux-kernel@vger.kernel.org, pageexec@freemail.hu, Jeremy Fitzhardinge To: "H. Peter Anvin" Return-path: Received: from tomts16.bellnexxia.net ([209.226.175.4]:60173 "EHLO tomts16-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1764695AbYDYUhU (ORCPT ); Fri, 25 Apr 2008 16:37:20 -0400 Content-Disposition: inline In-Reply-To: <48123C9B.9020306@zytor.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: * H. Peter Anvin (hpa@zytor.com) wrote: > Mathieu Desnoyers wrote: >> This epilogue should then be used on both branches of the condition, >> like this : >> if (unlikely(imv_cond(var))) { >> imv_cond_end(); >> ... >> } else { >> imv_cond_end(); >> ... >> } >> Where imv_cond_end() would look like this : >> +/* >> + * Puts a test and branch make sure the %al register and ZF are not live >> + * anymore. >> + * All asm statements clobbers the flags, but add "cc" clobber just to be >> sure. >> + * Clobbers %al. >> + */ >> +#define imv_cond_end() \ >> + do { \ >> + asm (".section __imv_cond_end,\"a\",@progbits\n\t" \ >> + _ASM_PTR "1f\n\t" \ >> + ".previous\n\t" \ >> + "1:\n\t" \ >> + : : : "a", "cc"); \ >> + } while (0) >> + > > As far as this is concerned, all you accomplish here is that gcc, if it > wants to re-use the %al value, will copy it into another register before > doing your imv_conv_end(). > Exactly, and by doing so, it will have to add instructions (mov, push..) in the instruction pattern I am looking for and therefore I will detect this and fall back on standard immediate values. Mathieu > -hpa -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68