Date: Tue, 15 Apr 1997 22:06:16 +0200 (MET DST)
From: Mark Habersack <grendel AT hoth DOT amu DOT edu DOT pl>
Reply-To: grendel AT hoth DOT amu DOT edu DOT pl
To: Gisle Vanem <giva AT bgnett DOT no>
cc: djgpp AT delorie DOT com
Subject: Re: Using -m486
In-Reply-To: <199704151205.MAA07354@bryggen.bgnett.no>
Message-ID: <Pine.BSI.3.96.970415220235.9986A-100000@hoth.amu.edu.pl>
Organization: PPP (Pesticide Powered Pumpkins)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII

On Tue, 15 Apr 1997, Gisle Vanem wrote:

> > Hmm... The -m486 won't do what you want. It merely instructs the
> optimizer to 
> > optimize code for i486 ordering of instructions and their timings. It
> doesn't 
> > mean it will use BSWAP to swap bytes. *It will not* do that. 
> 
> I know. I should maybe clearer in my original post. My intention was to
> check (at runtime) if CPU was 486+ before running the code compiled with
> BSWAP. The BSWAP should be an inline asm function (coded using .byte xx
> since
> gas knows nothing about 486+ instructions).
In such a situation a better solution would be to write a simple utility that
would return 3 for i386 and 4 for i486 and based on the return code you would
set an environmet variable in the makefile 
> > You can hand-code these instructions where you need'em. The -m386 -m486
> *do not* 
> > choose the instruction set specific for the CPU they *seem* to select.
> -m486 
> > will still use only i386 instructions - how otherwise would programs
> compiled 
> > with -m486 run on i386? 
> 
> Gisle Vanem        ---- Nera Telecomm ASA      tel. +47-55-225633
> SW Eng.                 P.O.Box 10             fax. +47-55-225651
>                         5061 Kokstad, NORWAY   email: giva AT bgnett DOT no
>                                                       gv AT nera DOT no
>