Date: Thu, 10 Mar 2005 16:47:56 +0000 From: Kris Kennaway <kris@FreeBSD.org> To: Divacky Roman <xdivac02@stud.fit.vutbr.cz> Cc: current@freebsd.org Subject: Re: amd64 default CFLAGS Message-ID: <20050310164756.GB34206@hub.freebsd.org> In-Reply-To: <20050309185907.GA10766@stud.fit.vutbr.cz> References: <20050309092749.GA72315@stud.fit.vutbr.cz> <20050309170100.GG50186@hub.freebsd.org> <20050309185907.GA10766@stud.fit.vutbr.cz>
next in thread | previous in thread | raw e-mail | index | archive | help
On Wed, Mar 09, 2005 at 07:59:07PM +0100, Divacky Roman wrote: > 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 ;) kern.mk is only used for kernel + module builds. > (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? This has been discussed before; see the archives. Kris
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20050310164756.GB34206>