From owner-freebsd-emulation  Wed Sep 10 18:05:18 1997
Return-Path: <owner-freebsd-emulation>
Received: (from root@localhost)
          by hub.freebsd.org (8.8.7/8.8.7) id SAA11934
          for emulation-outgoing; Wed, 10 Sep 1997 18:05:18 -0700 (PDT)
Received: from kithrup.com (kithrup.com [205.179.156.40])
          by hub.freebsd.org (8.8.7/8.8.7) with ESMTP id SAA11929
          for <emulation@FreeBSD.ORG>; Wed, 10 Sep 1997 18:05:12 -0700 (PDT)
Received: (from sef@localhost) by kithrup.com (8.8.5/8.6.6) id SAA09151; Wed, 10 Sep 1997 18:05:10 -0700 (PDT)
Date: Wed, 10 Sep 1997 18:05:10 -0700 (PDT)
From: Sean Eric Fagan <sef@Kithrup.COM>
Message-Id: <199709110105.SAA09151@kithrup.com>
To: gallatin@CS.Duke.EDU, grog@lemis.com
Subject: Re: Net posting: SCO gets Linux emulation
Cc: emulation@FreeBSD.ORG, jkh@time.cdrom.com, mike@smith.net.au,
        sos@sos.freebsd.dk
Sender: owner-freebsd-emulation@FreeBSD.ORG
X-Loop: FreeBSD.org
Precedence: bulk

>> Well, its somewhat interesting because it runs entirely in userland
>> and traps system calls via a SEGV handler.
>Ugh.  Is this what we have come to expect of SCO?

That is both unfair and rude.  (Bit of a warning here... I've known the
author ever since I interviewed at SCO, and I happen to like him.)

I looked at the program; it's interesting, but not terribly exciting.
However, I might have done the iBCS2 emulation the same way, if I could
have -- however, trapping the system call vector in a user-mode program is
hard.  If 386BSD had used a different entry vector...

Mike also probably would have done the program using LDT manipulation,
except for the fact that the IDT is global.

>> And because of this, I imagine that its a good bit slower.  Also,
>> their '$LINUX_ROOT' path remapping is interesting if only for its
>> flexibility, but their choice of what paths to remap is very
>> haphazard compared with the {Free,Net}BSD approach.
>Doesn't sound like a serious implementation effort to me.

To a large degree, it isn't.  He did it as a quick&dirty way to be able to
run the Linux port of Acrobat Reader (there is/was no SCO version), and
apparantly convinced SCO to allow him to release it under a Berkeley-style
license.

All told, it probably took Mike about a day to write this.

Perhaps you should add support for kernel-mode vm86 drivers before you start
to insult Mike's efforts.  (He had done this about six months before I left
SCO; he decided that they were too slow to be generally usable.  However,
SCO doesn't have the problem that FreeBSD does, in getting documentation for
cards.)

Sean.