linux-kernel - Re: Change x86 prefix order

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Message-ID: <20061206170030.GA543@lucon.org>
Date:	Wed, 6 Dec 2006 09:00:30 -0800
From:	"H. J. Lu" <hjl@...on.org>
To:	Randy Dunlap <rdunlap@...otime.net>
Cc:	gcc@....gnu.org, GNU C Library <libc-alpha@...rces.redhat.com>,
	linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: Change x86 prefix order

On Wed, Dec 06, 2006 at 08:43:17AM -0800, Randy Dunlap wrote:
> On Tue, 5 Dec 2006 23:00:14 -0800 H. J. Lu wrote:
> 
> > On x86, the order of prefix SEG_PREFIX, ADDR_PREFIX, DATA_PREFIX and
> > LOCKREP_PREFIX isn't fixed. Currently, gas generates
> > 
> > LOCKREP_PREFIX ADDR_PREFIX DATA_PREFIX SEG_PREFIX
> > 
> > I will check in a patch:
> > 
> > http://sourceware.org/ml/binutils/2006-12/msg00054.html
> > 
> > tomorrow and change gas to generate
> > 
> > SEG_PREFIX ADDR_PREFIX DATA_PREFIX LOCKREP_PREFIX
> 
> Hi,
> Could you provide a "why" for this in addition to the
> "what", please?

LOCKREP_PREFIX is also used as SIMD prefix. DATA_PREFIX can be used as
either SIMD prefix or data size prefix for SIMD instructions. The new
order

SEG_PREFIX ADDR_PREFIX DATA_PREFIX LOCKREP_PREFIX

will make SIMD prefixes close to SIMD opcode.

H.J.
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