From:	"Charles Sandmann" <sandmann AT clio DOT rice DOT edu>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: C Library: mmap() function
Date:	Wed, 27 Sep 2000 17:06:01
Organization:	Aspen Technology, Inc.
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> I understand that DPMI is not supposed to provide support for mmap().  Can
> we extend it? (or is that just _not_ done?)

DPMI 1.0 provides enough functionality to implement mmap().  You would need
to provide a user supplied page fault handler.

> Windows: does DJGPP under Windows rely on the OS for virtual memory
> management?  If so, then there's probably not much to be done about it,
> right?

You could write VXDs to extend Window's DPMI features.  Borland did this,
but they were a partial solution and buggy.

> CWSDPMI: can this server be extended to provide mmap() functionality?

If someone had the motivation, time and skills additional DPMI 1.0 features
could be added to CWSDPMI.  In particular, you would need to support the
alternate exception frames described in the DPMI 1.0 document.  Exceptions
handlers are hard to debug - since if you make a mistake the machine 
reboots leaving no trace of why it rebooted.

You would then need to modify the DJGPP exception handling code to use
DPMI 1.0 frames if they were available.  Again, very painful debugging.

So, it's feasible, but very unlikely anyone will do this.

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