Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!tut.cis.ohio-state.edu!att!chinet!kdb
From: kdb@chinet.chi.il.us (Karl Botts)
Newsgroups: comp.std.c
Subject: Re: ANSI C, hardware protection, out-of-bounds pointers
Message-ID: <9584@chinet.chi.il.us>
Date: 15 Sep 89 02:53:02 GMT
References: <427@maytag.waterloo.edu> <1989Sep5.175411.25203@utzoo.uucp> <9520@chinet.chi.il.us> <10997@smoke.BRL.MIL>
Reply-To: kdb@chinet.chi.il.us (Karl Botts)
Organization: Chinet - Public Access Unix
Lines: 17

>Even in such cases, it still wouldn't help with arrays of large objects,
>because first-1 would point many bytes below the start of the allocated
>data block.

No argument.  I think I said something about the size of the objects in my
original message.

>Just don't use first-1.  It's not that hard to avoid.

No argument again -- I would never do it myself.  It has been done,
however.  Take a look at yyparse.c the way it handles the stack pointers (I
think they are called "yyvs" and "yypvs" or something like that.)  I don't
have a machine where meerly mentioning, as opposed to dereferencing, an OOB
pointer will cause an exception, but such machines exist and I suspect that
YACC parsers would fail under certain circumstances on such machines.  I'm
out on a bit of a limb here, but I'd be interested if anybody has had such
an experience?