From:	pavenis AT lanet DOT lv
Message-ID:	<B0000104700@stargate.astr.lu.lv>
To:	eplmst AT lu DOT erisoft DOT se (Martin Stromberg), djgpp AT delorie DOT com
Date:	Mon, 11 Oct 1999 12:19:24 +0300
MIME-Version:	1.0
Subject:	Re: Problems using signals
In-reply-to:	<7tqeh0$ktf$1@antares.lu.erisoft.se>
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On 10 Oct 99, at 16:22, Martin Stromberg wrote:

> Eli Zaretskii (eliz AT is DOT elta DOT co DOT il) wrote:
> : The way it works is as follows.  The keyboard interrupt handler
> : invalidates the DS selector by resetting its limit to the first page
> : (a.k.a. null page) only, saves the original limit in a special
> : variable, sets a flag which indicates that Ctrl-C was seen, and then
> : does an IRET.  Since all data is above the null page, we are
> : guaranteed that the first time the program touches any of its data, it
> : will trigger a GPF.  The GPF exception handler, also set up by the
> : startup code, sees that the exception is really a fake one generated
> : by Ctrl-C, so it restores the DS limit to its original value and then
> : does a "raise(SIGINT);".
> 
> Nice explanation, but how can this work in WINDOZE where there isn't any
> NULL page?
> 

Under Win9X DPMI server You cannot protect NULL page against 
access (so You cannot catch NULL pointer dereferencing).
That doesn't meen that there is no such page.

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