Re: [PATCH v3] overflow: Allow mixed type arguments

[Kees Cook <keescook@chromium.org>]

On Tue, Aug 30, 2022 at 09:52:32PM +0200, Rasmus Villemoes wrote:
> On 30/08/2022 21.21, Kees Cook wrote:
> > [...]
> > + * *@d holds the results of the attempted addition, but is not considered
> > + * "safe for use" on a non-zero return value, which indicates that the
> > + * sum has overflowed or been truncated.
> 
> I don't like that wording. It makes it sound like there's some ambiguity
> or (implementation|un)-definedness involved in what the destination
> holds on overflow. The gcc documentation is perfectly clear that the
> result is the infinite-precision result truncated to N bits, with N
> being the bitwidth of d.

Hm, well, I think use of *d should be strongly discouraged on overflow.
How about just adding the specifics to the end?

 * *@d holds the result of the attempted addition, but is not considered
 * "safe for use" on a non-zero return value, which indicates that the
 * sum has overflowed or been truncated. (*@d will contain the
 * infinite-precision result truncated to the bitwidth of *@d.)

-- 
Kees Cook