From owner-freebsd-current@FreeBSD.ORG  Wed Mar  9 18:59:13 2005
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Delivered-To: freebsd-current@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id B9CF416A4CE
	for <current@freebsd.org>; Wed,  9 Mar 2005 18:59:13 +0000 (GMT)
Received: from eva.fit.vutbr.cz (eva.fit.vutbr.cz [147.229.10.14])
	by mx1.FreeBSD.org (Postfix) with ESMTP id BA16843D2F
	for <current@freebsd.org>; Wed,  9 Mar 2005 18:59:11 +0000 (GMT)
	(envelope-from xdivac02@stud.fit.vutbr.cz)
Received: from eva.fit.vutbr.cz (localhost [127.0.0.1])
	by eva.fit.vutbr.cz (8.13.3/8.13.3) with ESMTP id j29Ix7t6011008
	(version=TLSv1/SSLv3 cipher=EDH-RSA-DES-CBC3-SHA bits=168 verify=NO)
	for <current@freebsd.org>; Wed, 9 Mar 2005 19:59:07 +0100 (CET)
Received: (from xdivac02@localhost)
	by eva.fit.vutbr.cz (8.13.3/8.13.3/Submit) id j29Ix7BP011007
	for current@freebsd.org; Wed, 9 Mar 2005 19:59:07 +0100 (CET)
Date: Wed, 9 Mar 2005 19:59:07 +0100
From: Divacky Roman <xdivac02@stud.fit.vutbr.cz>
To: current@freebsd.org
Message-ID: <20050309185907.GA10766@stud.fit.vutbr.cz>
References: <20050309092749.GA72315@stud.fit.vutbr.cz>
	<20050309170100.GG50186@hub.freebsd.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20050309170100.GG50186@hub.freebsd.org>
User-Agent: Mutt/1.4.2i
X-Scanned-By: MIMEDefang 2.49 on 147.229.10.14
Subject: Re: amd64 default CFLAGS
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
	<freebsd-current.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
	<mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
	<mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 09 Mar 2005 18:59:13 -0000

On Wed, Mar 09, 2005 at 05:01:00PM +0000, Kris Kennaway wrote:
> On Wed, Mar 09, 2005 at 10:27:49AM +0100, Divacky Roman wrote:
> > hi,
> > 
> > why is it necessary (if its at all) to have this: 
> > -mfpmath=387 -mno-sse -mno-sse2 -mno-mmx -mno-3dnow in default CFLAGS for amd64
> > architecture?
> 
> This is the default COPTFLAGS, not CFLAGS, right?  You can't use
> special instructions like sse in the kernel because they require extra
> register state operations that would cost performance.

(from sys/conf/kern.mk)
CFLAGS+= -mcmodel=kernel -mno-red-zone \
         -mfpmath=387 -mno-sse -mno-sse2 -mno-mmx -mno-3dnow \
	 -msoft-float -fno-asynchronous-unwind-tables

I'd call it CFLAGS ;)

(from sys/i386/i386/support.s)
ENTRY(sse2_pagezero)

isnt this use of sse in kernel?

why is it allowed in this case and not allowed in general. any measurements how
much does it hurt performance?

roman