Re: Signed int overflow behavior in the security context

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 1/27/07, Paul Schlie <schlie@comcast.net> wrote:
> >> On Fri, Jan 26, 2007 at 06:57:43PM -0500, Paul Schlie wrote:
> > Likewise, if the program has an uninitialized variable, the behavior
> > will differ depending on details of optimization and how variables are
> > assigned to memory.  Heap allocated for the first time might always be
> > zero (as the OS delivers it that way), turning on optimization might then
> > result in a nonzero initial value because of reuse of a register.
>
> - I would argue that in this circumstance although the resulting value may
> differ, the results are actually equivalent; as in both circumstances the
> value returned is the value associated with it's storage location; and as
> the value of all storage locations are arbitrary unless otherwise well
> specified; the result may change from run to run regardless of any applied
> optimizations.

If you read from an uninitialized variable twice you might as well get
a different result each time.  This is exactly the same issue than with
signed overflow and observable behavior - though as somebody notes
later - the uninitialized variable case doesn't stir up too many peoples
mind.

Richard.