Date: Wed, 9 Mar 2005 19:59:07 +0100 From: Divacky Roman <xdivac02@stud.fit.vutbr.cz> To: current@freebsd.org Subject: Re: amd64 default CFLAGS Message-ID: <20050309185907.GA10766@stud.fit.vutbr.cz> In-Reply-To: <20050309170100.GG50186@hub.freebsd.org> References: <20050309092749.GA72315@stud.fit.vutbr.cz> <20050309170100.GG50186@hub.freebsd.org>
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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
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