Hi, On Wed, Oct 28, 2015, at 15:27, Rasmus Villemoes wrote: > On Wed, Oct 28 2015, Hannes Frederic Sowa <han...@stressinduktion.org> > wrote: > > > Hi Linus, > > > > On Wed, Oct 28, 2015, at 10:39, Linus Torvalds wrote: > >> Get rid of it. And I don't *ever* want to see that shit again. > > > > I don't want to give up on that this easily: > > > > In future I would like to see an interface like this. It is often hard > > to do correct overflow/wrap-around tests and it would be great if there > > are helper functions which could easily and without a lot of thinking be > > used by people to remove those problems from the kernel. > > I agree - proper overflow checking can be really hard. Quick, assuming a > and b have the same unsigned integer type, is 'a+b<a' sufficient to > check overflow? Of course not (hint: promotion rules). And as you say, > it gets even more complicated for signed types. > > A few months ago I tried posting a complete set of fallbacks for older > compilers (https://lkml.org/lkml/2015/7/19/358), but nothing really > happened. Now I know where Linus stands, so I guess I can just delete > that branch.
I actually like your approach of being type agnostic a bit more (in comparison to static inline functions), mostly because of one specific reason: The type agnostic __builtin_*_overflow function even do the correct things if you deal with types smaller than int. Imagine e.g. you want to add to unsigned chars a and b, unsigned char a, b; if (a + b < a) goto overflow; else a += b; The overflow condition will never trigger, as the comparisons will always be done in the integer domain and a + b < a is never true. I actually think that this is easy to overlook and the functions should handle that. The macro version does this quite nicely. Bye, Hannes -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
