amd64 default CFLAGS

[Divacky Roman]

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