Date: Mon, 3 Aug 1998 19:31:04 +0000 (   )
From: "Gurunandan R. Bhat" <grbhat AT unigoa DOT ernet DOT in>
To: Hans-Bernhard Broeker <broeker AT physik DOT rwth-aachen DOT de>
Cc: djgpp AT delorie DOT com
Subject: Re: Null page Protection
In-Reply-To: <199808031106.NAA05674@acp3bf.physik.rwth-aachen.de>
Message-Id: <Pine.LNX.3.91.980803192526.4814A-100000@aditya.unigoa.ernet.in>
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On Mon, 3 Aug 1998, Hans-Bernhard Broeker wrote:

> > 	In what situations is Null page protection used, 
> > and why?
> 
> To help you catch those evil NULL pointer dereferencing errors. Many a
> DOS programmer has learned that this kind of error may actually even
> kill a hard disk (if you write via an almost-NULL pointer in 16bit
> unprotected DOS, chances are you'll hit the interrupt vector table, or
> the BIOS data area, and BOOM! it goes), so it's really a good thing to
> have.
 
But aren't all DJGPP images loaded in extended memory where the only 
thing you can clobber in the null page is your own code. What advantages 
does it serve in these situations, if any.

Thank you for your reply