Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1754518AbcKUQDC (ORCPT <rfc822;w@1wt.eu>);
        Mon, 21 Nov 2016 11:03:02 -0500
Received: from terminus.zytor.com ([198.137.202.10]:41144 "EHLO mail.zytor.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1752580AbcKUQDB (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 21 Nov 2016 11:03:01 -0500
Subject: Re: What exactly do 32-bit x86 exceptions push on the stack in the CS
 slot?
To: Andy Lutomirski <luto@kernel.org>, tedheadster@gmail.com,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Brian Gerst <brgerst@gmail.com>, George Spelvin <linux@horizon.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        X86 ML <x86@kernel.org>
References: <CALCETrUqdp=rEKX4gdSpJYder3q0g_yxdRE9APw8MgerXvnB=w@mail.gmail.com>
 <4152ADD4-3F2D-46B2-B545-082C734C7640@zytor.com>
From: "H. Peter Anvin" <hpa@zytor.com>
Message-ID: <6e5a0f8b-31e3-8ed7-62f7-f9f28f73f503@zytor.com>
Date: Mon, 21 Nov 2016 07:58:28 -0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101
 Thunderbird/45.4.0
MIME-Version: 1.0
In-Reply-To: <4152ADD4-3F2D-46B2-B545-082C734C7640@zytor.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 354
Lines: 11

On 11/20/16 20:54, hpa@zytor.com wrote:
> 
> I believe i686+ writes zero, older CPUs leave unchanged.
> 

I should point out that, at least from my memory, the same applies to
instructions like "movl <seg>".  I can't even remember for sure how the
behavior differs between "movl <seg>,<reg32>" and "movl <seg>,<mem>";
I'd have to do some digging.

	-hpa