Xref:	news2.mv.net comp.os.msdos.djgpp:5802
From:	jrubin AT bix DOT com (jrubin)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Catch protection violations?
Date:	10 Jul 1996 04:16:24 GMT
Organization:	BIX
Lines:	16
Message-ID:	<4rvaqo$a9@news2.delphi.com>
NNTP-Posting-Host:	bix.com
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?
My application is a Scheme compiler. It would be nice to encode an
object's type in the high bits of the address. For example, a pointer to
a cons cell would be represented as 2^26 + <true address>. When only that
type is legal, the generated code would do:
  movl  %eax-2^24, %ebx      ; fault if type is not cons

Second question: Is there any control over page protection? Can I
load data at runtime, then set those pages to read-only? This would
be done to simplify debugging.

Third, a question about paging:
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!

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