ANSI C, hardware protection, out-of-bounds pointers

Karl Botts kdb at chinet.chi.il.us
Fri Sep 15 12:53:02 AEST 1989


>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?



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