From owner-freebsd-hackers@FreeBSD.ORG  Thu Jan 13 21:57:20 2011
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 02CC0106564A
	for <freebsd-hackers@freebsd.org>; Thu, 13 Jan 2011 21:57:20 +0000 (UTC)
	(envelope-from joerg@britannica.bec.de)
Received: from mo-p00-ob.rzone.de (mo-p00-ob.rzone.de [81.169.146.161])
	by mx1.freebsd.org (Postfix) with ESMTP id 624508FC14
	for <freebsd-hackers@freebsd.org>; Thu, 13 Jan 2011 21:57:19 +0000 (UTC)
X-RZG-AUTH: :JiIXek6mfvEEUpFQdo7Fj1/zg48CFjWjQv0cW+St/nW/YPAwtil3kVlq3myX
X-RZG-CLASS-ID: mo00
Received: from britannica.bec.de
	(dslb-088-074-063-088.pools.arcor-ip.net [88.74.63.88])
	by post.strato.de (jimi mo49) (RZmta 24.9)
	with (DHE-RSA-AES128-SHA encrypted) ESMTP id Y05860n0DKCHm3 ;
	Thu, 13 Jan 2011 22:57:16 +0100 (MET)
Received: by britannica.bec.de (sSMTP sendmail emulation);
	Thu, 13 Jan 2011 22:57:15 +0100
Date: Thu, 13 Jan 2011 22:57:15 +0100
From: Joerg Sonnenberger <joerg@britannica.bec.de>
To: freebsd-hackers@freebsd.org, FreeBSD Hackers <hackers@freebsd.org>
Message-ID: <20110113215713.GB5278@britannica.bec.de>
Mail-Followup-To: freebsd-hackers@freebsd.org,
	FreeBSD Hackers <hackers@freebsd.org>
References: <AANLkTikrsHUO3M+fvo0kO+3dPq8OHu5L2zBf3fa3jL2x@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <AANLkTikrsHUO3M+fvo0kO+3dPq8OHu5L2zBf3fa3jL2x@mail.gmail.com>
User-Agent: Mutt/1.5.20 (2009-06-14)
Cc: 
Subject: Re: What does the FreeBSD/i386 ABI say about stack alignment?
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
	<freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>, 
	<mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 13 Jan 2011 21:57:20 -0000

On Thu, Jan 13, 2011 at 12:19:00PM -0500, Ryan Stone wrote:
> I've been trying to get an application compiled with gcc 4.5.1 running
> on FreeBSD 8.1, but it's been crashing during startup with a SIGBUS.
> It turns out that the problem is that gcc is issuing SSE
> instructions(in my case, a movdqa) that assume that the stack will be
> aligned to a 16-byte boundary.  It seems that Linux/i386 guarantees
> this, and I worry that gcc has extended this assumption to all i386
> architectures.  I'm assuming that FreeBSD doesn't make any such
> promises based on the fact that I'm getting crashes.

FreeBSD follows the original SYSV ABI. Linux at some point silently
decided to redefine the ABI to fit their mindset. I think you want to
use a combination of -mpreferred-stack-boundary=4 and
-mincoming-stack-boundary=2.

Joerg