From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753671AbbAUSEk (ORCPT ); Wed, 21 Jan 2015 13:04:40 -0500 Received: from cantor2.suse.de ([195.135.220.15]:58739 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752733AbbAUSEd (ORCPT ); Wed, 21 Jan 2015 13:04:33 -0500 Date: Wed, 21 Jan 2015 19:04:30 +0100 From: Borislav Petkov To: Alexander van Heukelum Cc: Denys Vlasenko , Andy Lutomirski , X86 ML , Linux Kernel Mailing List , Frederic Weisbecker , Oleg Nesterov , Rik van Riel Subject: Re: [PATCHv2 1/4] x86_64: cleanup THREAD_INFO(reg,offset) macro Message-ID: <20150121180429.GB31527@pd.tnic> References: <1421581520-2816-1-git-send-email-heukelum@fastmail.fm> <1421581520-2816-2-git-send-email-heukelum@fastmail.fm> <1421857209.171127.216796445.0DC88E13@webmail.messagingengine.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1421857209.171127.216796445.0DC88E13@webmail.messagingengine.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 21, 2015 at 05:20:09PM +0100, Alexander van Heukelum wrote: > On Wed, Jan 21, 2015, at 14:40, Denys Vlasenko wrote: > > On Sun, Jan 18, 2015 at 12:45 PM, Alexander van Heukelum > > wrote: > > > The macro THREAD_INFO(reg,offset) is used in assembly to compute the > > > offset between the user ptregs and the thread_info struct. Change > > > the macro and all its uses so that offset is given as the current > > > top of stack in the pt_regs frame. The generated code is identical. > > > > What is the purpose of doing this? > > > > I don't mean to say that it's pointless, but it is also not obvious > > why it's better than the code before patch. > > Just because I had a hard time understanding what the offset > parameter means. Turns out Borislav did another variant in his > patchset. Quoting him from the commit message which made > that the change: > > Semi-mysterious expressions THREAD_INFO(%rsp,RIP) - "why RIP??" > > are now replaced by more logical THREAD_INFO(%rsp,SIZEOF_PTREGS) - > > "rsp is SIZEOF_PTREGS bytes below the top, calculate > > thread_info's address using that information" > > Borislav expresses "offset" as an offset from the stack's page > boundary,while I chose the offset from the start of struct > pt_regs on the stack. I've never done any such thing :-) s/Borislav/Denys/g. -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. --