Re: [PATCH v2 1/2] Compiler Attributes: Add __counted_by_ptr macro

[Kees Cook]

On Fri, Jan 16, 2026 at 09:35:16AM +0100, Peter Zijlstra wrote:
> On Fri, Nov 21, 2025 at 10:47:45PM +0100, Miguel Ojeda wrote:
> > On Fri, Nov 21, 2025 at 8:55 PM Bill Wendling <morbo@xxxxxxxxxx> wrote:
> > >
> > > +/*
> > > + * Optional: only supported since clang >= 21
> > > + *
> > > + * clang: https://github.com/llvm/llvm-project/pull/137250
> > > + */
> > > +#ifdef CONFIG_CC_HAS_COUNTED_BY_FOR_POINTER
> > > +#define __counted_by_ptr(member)       __attribute__((__counted_by__(member)))
> > > +#else
> > > +#define __counted_by_ptr(member)
> > > +#endif
> > 
> > I guess there is a reason for this name, but it sounds to me a bit
> > like the thing between parenthesis is a pointer, i.e. that perhaps it
> > is the pointee that one that counts.
> > 
> > Hmm... what about `__ptr_counted_by`?
> 
> Kees promised to drop this attribute once GCC-16 releases by basically
> doing 's/__counted_by_ptr/__counted_by/' and unifying things again.

Yeah, this will effectively raise "counted_by" support to GCC 16 (from
15) and to Clang 22 (from 20). I'd still prefer to keep the earlier
support, but we'll see how it goes.

-Kees

-- 
Kees Cook