On Wed, Apr 24, 2024 at 03:45:07PM -0700, Kees Cook wrote:
> 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
This is arse-about-face. Signed stuff wraps per -fno-strict-overflow.
We've been writing code for years under that assumption.
You want to mark the non-wrapping case.
