Date: Sun, 28 Sep 1997 18:33:04 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To: Chirayu Krishnappa <chirayu AT radiolink DOT net>
cc: djgpp AT delorie DOT com
Subject: Re: far pointers
In-Reply-To: <1.5.4.16.19970926194924.29cf3956@giasbga.vsnl.net.in>
Message-ID: <Pine.SUN.3.91.970928183232.423C-100000@is>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Precedence: bulk


On Fri, 26 Sep 1997, Chirayu Krishnappa wrote:

> >I'd gues that Watcom can do that because it uses a DOS extender which
> >catches all system calls and does its thing behind the scenes.  DJGPP
> 
> But a pointer dereference if not a system call, or am I mistaken?

Not necessarily.  Accessing addresses which aren't mapped into the
program's address space causes an exception in protected mode.  In
DJGPP, this exception in general causes your program to be aborted.
But a DOS extender could set up things in a way that this exception
ends up inside an exception handler set up by the extender.  When this
happens, the extender can do whatever it pleases; in particular, it
could change the address and move the data on behalf of the
application.