Xref:	news2.mv.net comp.os.msdos.djgpp:5839
From:	Charles Sandmann <sandmann AT clio DOT rice DOT edu>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Catch protection violations?
Date:	Wed, 10 Jul 1996 20:15:29 CDT
Organization:	Rice University, Houston, Texas
Lines:	29
Message-ID:	<31e455b1.sandmann@clio.rice.edu>
References:	<4rvaqo$a9 AT news2 DOT delphi DOT com>
Reply-To:	sandmann AT clio DOT rice DOT edu
NNTP-Posting-Host:	clio.rice.edu
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

> In djgpp V2., is it possible to write a handler for protection violations?

Yes, see signal() docs.   If you want more machine info, you can look at
__djgpp_exception_state.

>   movl  %eax-2^24, %ebx      ; fault if type is not cons

Should work OK.

> Second question: Is there any control over page protection? 

Sure, see mprotect().  Must be aligned on 4K pages, so pad and align.
But this only will work under a DPMI 1.0 extension provider, like
CWSDPMI.  Ignored for other providers.

> Can I load data at runtime, then set those pages to read-only? 

Sure.  Same routine as above.  Rarely used, beware of bugs.  Same
limitations.

> Does Djgpp remember the origin of read-only pages? Since they came from
> the executable image file, they don't need to be allocated any 
> 'backing store' in the page file. They don't need to be written out!

Sorry, doesn't work that way in V2.  There aren't any read-only pages
by default (since most dpmi's don't support them).  Humm, actually,
I don't think anyone has probably tried paging readonly pages.  For all
I know, CWSDPMI will puke if you try it.  Never tested it, don't remember
if I designed for it either...

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