Re: [PATCH 1/4] locking/atomic/x86: Silence intentional wrapping addition

[Kees Cook]

On Thu, Apr 25, 2024 at 12:41:41AM +0200, Peter Zijlstra wrote:
> On Wed, Apr 24, 2024 at 12:17:34PM -0700, Kees Cook wrote:
> 
> > @@ -82,7 +83,7 @@ static __always_inline bool arch_atomic_add_negative(int i, atomic_t *v)
> >  
> >  static __always_inline int arch_atomic_add_return(int i, atomic_t *v)
> >  {
> > -	return i + xadd(&v->counter, i);
> > +	return wrapping_add(int, i, xadd(&v->counter, i));
> >  }
> >  #define arch_atomic_add_return arch_atomic_add_return
> 
> this is going to get old *real* quick :-/
> 
> This must be the ugliest possible way to annotate all this, and then
> litter the kernel with all this... urgh.

I'm expecting to have explicit wrapping type annotations soon[1], but for
the atomics, it's kind of a wash on how intrusive the annotations get. I
had originally wanted to mark the function (as I did in other cases)
rather than using the helper, but Mark preferred it this way. I'm happy
to do whatever! :)

-Kees

[1] https://github.com/llvm/llvm-project/pull/86618

-- 
Kees Cook