Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!mimsy!markshome!mark
From: mark@markshome (mark weiser)
Newsgroups: comp.sys.m68k
Subject: Re: move sr/move ccr: crock
Message-ID: <5157@mimsy.UUCP>
Date: Thu, 22-Jan-87 23:51:34 EST
Article-I.D.: mimsy.5157
Posted: Thu Jan 22 23:51:34 1987
Date-Received: Fri, 23-Jan-87 03:50:30 EST
References: <809@imagen.UUCP> <1560@cit-vax.Caltech.Edu>
Sender: news@mimsy.UUCP
Reply-To: mark@markshome.UUCP (mark weiser)
Distribution: na
Organization: U of Maryland, Dept. of Computer Science, College Pk., Md. 20742
Lines: 20
Keywords: read the manuals

>In article <809@imagen.UUCP> geof@imagen.UUCP (Geoffrey Cooper) writes:
>My question is why the lords of 68k-land did this?  Presumably
>there is some lack or portability or security loophole in allowing
>a user program to look at the SR.
>
>- Geof Cooper
>  IMAGEN

This is a very nice thing motorola did for the 68010 and 68020.
It makes the processor virtualizable.  It is now possible to
write a hypervisor for a 680x0 (x!=0) which can run binary images
of other operating systems that think they have the whole machine,
and there are no non-privileged instructions which that other O.S.
can use to tell that it is being hypervised.  If it tries to tell,
by using a privileged instruction, it gets trapped and the hypervisor
can lie.
-mark
Spoken: Mark Weiser 	ARPA:	mark@mimsy.umd.edu	Phone: +1-301-454-7817
CSNet:	mark@mimsy 	UUCP:	{seismo,allegra}!mimsy!mark
USPS: Computer Science Dept., University of Maryland, College Park, MD 20742