Path: utzoo!attcan!uunet!husc6!necntc!ima!johnl
From: johnl@ima.ISC.COM (John R. Levine)
Newsgroups: comp.arch
Subject: Re: Is the Intel memory model safe from NO-ONE ?!?
Message-ID: <1021@ima.ISC.COM>
Date: 13 May 88 17:48:09 GMT
References: <353@cf-cm.UUCP> <3095@edm.UUCP> <20618@think.UUCP> <1988May12.162207.16764@utzoo.uucp>
Reply-To: johnl@ima.UUCP (John R. Levine)
Organization: Not much
Lines: 15

In article <1988May12.162207.16764@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
> I know of no machine, offhand, whose hardware has any notion of a "user
> handler".

Funny you should mention that. On the 286 and 386, traps can go to
"conformant" segments that run in the protection domain of the caller. You
could imagine a generic zero-divide handler that looked around to see what
mode it is in and jumps off accordingly. Considering the cost of even the
microcode-assisted context switches on the 286, it probably wouldn't be a bad
idea. I have no idea whether any actual 286 or 386 operating systems do that,
though.
-- 
John R. Levine, IECC, PO Box 349, Cambridge MA 02238-0349, +1 617 492 3869
{ ihnp4 | decvax | cbosgd | harvard | yale }!ima!johnl, Levine@YALE.something
Rome fell, Babylon fell, Scarsdale will have its turn.  -G. B. Shaw