From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756705AbZBKKTH (ORCPT ); Wed, 11 Feb 2009 05:19:07 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752086AbZBKKSz (ORCPT ); Wed, 11 Feb 2009 05:18:55 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:45451 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752432AbZBKKSy (ORCPT ); Wed, 11 Feb 2009 05:18:54 -0500 Date: Wed, 11 Feb 2009 11:18:46 +0100 From: Ingo Molnar To: Tejun Heo Cc: Brian Gerst , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] x86: Pass in pt_regs pointer for syscalls that need it Message-ID: <20090211101846.GH20518@elte.hu> References: <1234277507-4987-1-git-send-email-brgerst@gmail.com> <1234277507-4987-3-git-send-email-brgerst@gmail.com> <4992812B.1050800@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4992812B.1050800@kernel.org> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Tejun Heo wrote: > Hello, Brian. > > Brian Gerst wrote: > > Some syscalls need to access the pt_regs structure, either to copy > > user register state or to modifiy it. This patch adds stubs to load > > the address of the pt_regs struct into the %eax register, and changes > > the syscalls to regparm(1) to receive the pt_regs pointer as the > > first argument. > > Heh... neat. Just one question. > > > -asmlinkage long sys_iopl(unsigned long regsp) > > +ptregscall long sys_iopl(struct pt_regs *regs, unsigned int level) > > { > > - struct pt_regs *regs = (struct pt_regs *)®sp; > > - unsigned int level = regs->bx; > > Here and at other places where the function takes more than one > arguments, wouldn't it be better to just take *regs and use other > parameters from regs? That way we won't have to worry about gcc > corrupting register frame at all and I think it's cleaner that way. Hm, gcc cannot corrupt register arguments only on-stack arguments - but your suggestion nevertheless makes sense as an optimization. I'd suggest this to be done as a separate patch though, both for regression analysis reasons (easier to bisect - the patch is large enough already) and from a size/performance analysis POV. (so we can see the benefits in isolation) Ingo