From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 9288 invoked by alias); 13 Feb 2003 08:20:39 -0000 Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Archive: List-Post: List-Help: Sender: gcc-owner@gcc.gnu.org Received: (qmail 9173 invoked from network); 13 Feb 2003 08:20:38 -0000 Received: from unknown (HELO mx2.redhat.com) (12.150.115.133) by 172.16.49.205 with SMTP; 13 Feb 2003 08:20:38 -0000 Received: from int-mx2.corp.redhat.com (int-mx2.corp.redhat.com [172.16.27.26]) by mx2.redhat.com (8.11.6/8.11.6) with ESMTP id h1D8EN108266; Thu, 13 Feb 2003 03:14:23 -0500 Received: from potter.sfbay.redhat.com (potter.sfbay.redhat.com [172.16.27.15]) by int-mx2.corp.redhat.com (8.11.6/8.11.6) with ESMTP id h1D8KZn30377; Thu, 13 Feb 2003 03:20:35 -0500 Received: from localhost.localdomain (frothingslosh.sfbay.redhat.com [172.16.24.27]) by potter.sfbay.redhat.com (8.11.6/8.11.6) with ESMTP id h1D8KZQ26723; Thu, 13 Feb 2003 00:20:35 -0800 Received: (from rth@localhost) by localhost.localdomain (8.11.6/8.11.6) id h1D8KZX11624; Thu, 13 Feb 2003 00:20:35 -0800 X-Authentication-Warning: localhost.localdomain: rth set sender to rth@redhat.com using -f Date: Thu, 13 Feb 2003 08:59:00 -0000 From: Richard Henderson To: John David Anglin Cc: Franz.Sirl-kernel@lauterbach.com, gcc@gcc.gnu.org, gianni@scaramanga.co.uk Subject: Re: Altivec + 16 byte alignment Message-ID: <20030213082035.GB11557@redhat.com> Mail-Followup-To: Richard Henderson , John David Anglin , Franz.Sirl-kernel@lauterbach.com, gcc@gcc.gnu.org, gianni@scaramanga.co.uk References: <20030213003118.GK29744@redhat.com> <200302130614.h1D6EVhk019444@hiauly1.hia.nrc.ca> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200302130614.h1D6EVhk019444@hiauly1.hia.nrc.ca> User-Agent: Mutt/1.4i X-SW-Source: 2003-02/txt/msg00892.txt.bz2 On Thu, Feb 13, 2003 at 01:14:30AM -0500, John David Anglin wrote: > > PREFERRED_STACK_BOUNDARY is a suggestion. The theory is that > > *if* every object file is compiled with this, that we'll get > > some speedup at runtime, due to fewer misalignment fixups. > > > > But it is *not* ABI mandated, and you have to assume that > > someone somewhere may not honor this. > > Yes, it is. No. That is not the purpose of PREFERRED_STACK_BOUNDARY. The ABI mandated quantity is STACK_BOUNDARY. > I guess you are saying that STACK_BOUNDARY really should be 512... If that's what the ABI mandates, yes. > Can you describe under what > circumstances if any gcc will not be able to align to the preferred > stack boundary? None. That's not the point. > Looking at the documentation, it says that STACK_BOUNDARY should be set > to the *minimum* alignment enforced by hardware for the stack pointer > on the machine. It doesn't say the ABI mandated value. Then the docs need updating. > When STACK_BOUNDARY is set to 64, there is one fill word in the frame > as a result of the starting frame offset and the need to align it to a > STACK_BOUNDARY. If STACK_BOUNDARY were set to 512, we would have 15 > fill words. Eh? Is the stack pointer aligned or not? r~