Re: [PATCH] compiler_types: Allow opting out of __counted_by and __counted_by_ptr

[Ard Biesheuvel]

Hi Bill,

On Mon, 5 Oct 2026, at 12:25, Bill Wendling wrote:
> Code that runs outside the kernel proper, such as the EFI stub, gets
> nothing out of the counted_by annotations: the bounds checks they feed
> (FORTIFY_SOURCE, UBSAN_BOUNDS) are already disabled there.
>
> The annotations can also break the build. A __counted_by_ptr() that
> names a member declared after the pointer needs Clang's
> '-fexperimental-late-parse-attributes', which the top-level Makefile
> adds to 'KBUILD_CFLAGS'. The x86 EFI stub builds its own cflags and does
> not get that flag, so it fails as soon as such a struct is pulled in
> through a common header.
>
> Overriding the macros from a Makefile doesn't work:
> 'compiler_types.h' is pulled in with '-include', which is processed
> after all -D/-U options, so it re-establishes the definitions. Follow
> the '__NO_FORTIFY' precedent instead: let a build define
> '__NO_COUNTED_BY' or '__NO_COUNTED_BY_PTR' to turn the corresponding
> annotation into a no-op.  The two are kept separate but parallel so they
> can be folded together once all supported compilers handle
> '__counted_by' on pointers.
>

I'd prefer a single macro here - if there is ever a case where we need to
turn off one but not the other, we can revisit.

Otherwise, this looks good to me - thanks.