Re: GCC optimizes integer overflow: bug or feature?

[Paolo Bonzini <bonzini at gnu dot org>]

> By the way, as I've tried to describe here:
> <http://cert.uni-stuttgart.de/advisories/c-integer-overflow.php>
> variable range tracking can result in reintroduction of
> supposedly-fixed security vulnerabilities. 8-(

Interesting read.  I agree with the proposed fix; however, note that GCC 
does not make the result of overflowing signed left-shifts undefined, 
exactly because in this case the overflow is relied upon by too many 
existing programs (and also because left shifts are inherently a bitwise 
operation, with well defined overflowing behavior on the most 
significant bits).

Paolo