[PATCH] C undefined behavior fix

[Paul Mackerras]

Joe Buck writes:

> There is already such a project under development: see
> 
> http://gcc.gnu.org/projects/bp/main.html
> 
> This is a modification to gcc that implements pointers as triples.
> While there is a performance penalty for doing this, it can completely
> eliminate the problem of exploitable buffer overflows.  However, programs
> that violate the rules of ISO C by generating out-of-range pointers will
> fail.

What will it do if I cast a pointer to unsigned long?  Or if I cast an
unsigned long to a pointer?  The kernel does both of these things, and
in a lot of places.

Part of my beef with what gcc-3 is doing is that I take a pointer,
cast it to unsigned long, do something to it, cast it back to a
pointer, and gcc _still_ thinks it's knows what I am doing.  It
doesn't.

Paul.