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To: Jonathan Mini <mini@d198-232.uoregon.edu>
cc: Mike Smith <mike@smith.net.au>, hackers@FreeBSD.ORG
Subject: Re: x86 gods; advice? Suggestions? 
In-reply-to: Your message of "Fri, 07 Nov 1997 01:44:44 -0800."
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Date: Sat, 08 Nov 1997 12:31:29 +1030
From: Mike Smith <mike@smith.net.au>
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> Mike Smith <mike@smith.net.au> stands accused of saying:
> > > What privelege level is this running at? 
> > 
> > It has to run with DPL = 0.
> 
> Why?

Because it has to in order to meet the spec.  If you're interested, or 
think you have some ideas on this, you can grab the spec from 
microsoft's website.  Make sure you get the clarification as well, as 
there's a very confusing error in one of the critical digrams...

> > > Why not just execute an illegal instruction and catch it? 
> > 
> > Because this is in the kernel context, and I've no way of knowing how 
> > to say "just for now I want illegal instructions to come here".
> 
>   Although it seems less elegant, it seems to me that it really is the best
> solution to create threads for kernel-started processes for things like
> vm86/16-bit-protected-mode BIOS calls.

Is it feasible to fork a process running in 16-bit protected mode?  I 
know the vm86 stuff works; I'm using it now.

>   What we need is an elegant way to fork a process to do something for the
> kernel. (an interesting concept when you think about it. Kind of a reverse
> syscall)

It's actually pretty easy; with any luck I'll be happy enough with the 
vm86 stuff to commit it tomorrow.

mike