Date: Fri, 14 Jan 2011 00:00:52 +0200 From: Kostik Belousov <kostikbel@gmail.com> To: FreeBSD Hackers <hackers@freebsd.org> Subject: Re: What does the FreeBSD/i386 ABI say about stack alignment? Message-ID: <20110113220052.GL2518@deviant.kiev.zoral.com.ua> In-Reply-To: <20110113215713.GB5278@britannica.bec.de> References: <AANLkTikrsHUO3M%2Bfvo0kO%2B3dPq8OHu5L2zBf3fa3jL2x@mail.gmail.com> <20110113215713.GB5278@britannica.bec.de>
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--VSJGZE3ajDCqFLUt Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Jan 13, 2011 at 10:57:15PM +0100, Joerg Sonnenberger wrote: > 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. >=20 > 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=3D4 and > -mincoming-stack-boundary=3D2. I think gcc [*] requires 16-byte alignment. Also, it follows the policy of not changing the stack alignment through the calls. What you see is a plain bug in FreeBSD, when a developer (me) tried to adopt to newer ABI but failed. * Might be not gcc in our tree, but definitely newer gcc releases. --VSJGZE3ajDCqFLUt Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (FreeBSD) iEYEARECAAYFAk0vdhQACgkQC3+MBN1Mb4j0SACgtUvjulBMeaNmpyWyg3Hv2UGP R7sAmwW4wOyAnlt9+EYIjXw71TR49W45 =W2jt -----END PGP SIGNATURE----- --VSJGZE3ajDCqFLUt--
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