From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752501AbdI2TQK (ORCPT <rfc822;w@1wt.eu>);
        Fri, 29 Sep 2017 15:16:10 -0400
Received: from mx1.redhat.com ([209.132.183.28]:57660 "EHLO mx1.redhat.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1752338AbdI2TQJ (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 29 Sep 2017 15:16:09 -0400
DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com F01984E4CA
Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com
Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=jpoimboe@redhat.com
Date: Fri, 29 Sep 2017 14:16:07 -0500
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, X86 ML <x86@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86: use register variable to get stack pointer value
Message-ID: <20170929191607.nfl2nat6xi4mpb6f@treble>
References: <20170929141537.29167-1-aryabinin@virtuozzo.com>
 <20170929153828.rtxwllhsjgiaeaos@treble>
 <CALCETrUZN=bEbBYwohM+oALu+MG7-SJUAG5_Fr4ppNVQ_SFMAg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <CALCETrUZN=bEbBYwohM+oALu+MG7-SJUAG5_Fr4ppNVQ_SFMAg@mail.gmail.com>
User-Agent: Mutt/1.6.0.1 (2016-04-01)
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Fri, 29 Sep 2017 19:16:09 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, Sep 29, 2017 at 11:37:52AM -0700, Andy Lutomirski wrote:
> On Fri, Sep 29, 2017 at 8:38 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > On Fri, Sep 29, 2017 at 05:15:36PM +0300, Andrey Ryabinin wrote:
> >> Currently we use current_stack_pointer() function to get the value
> >> of the stack pointer register. Since commit f5caf621ee35
> >> ("x86/asm: Fix inline asm call constraints for Clang") we have stack
> >> register variable declared. It can be used instead of current_stack_pointer()
> >> function which allows to optimize away some excessive "mov %rsp, %<dst>"
> >> instructions:
> >>
> >> -mov    %rsp,%rdx
> >> -sub    %rdx,%rax
> >> -cmp    $0x3fff,%rax
> >> -ja     ffffffff810722fd <ist_begin_non_atomic+0x2d>
> >>
> >> +sub    %rsp,%rax
> >> +cmp    $0x3fff,%rax
> >> +ja     ffffffff810722fa <ist_begin_non_atomic+0x2a>
> >>
> >> Remove current_stack_pointer(), rename __asm_call_sp to current_stack_pointer
> >> and use it instead of removed function.
> >>
> >> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> >
> > Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
> 
> 
> Ok with me.  As an alternative, you could leave it as
> current_stack_pointer(), but either way is fine.

Good point, I think changing current_stack_pointer() to return the
global variable would be cleaner.

-- 
Josh