Re: [PATCH v3] compiler_types: Allow opting out of __counted_by and __counted_by_ptr

[Ard Biesheuvel]

On Mon, 5 Oct 2026, at 21:20, 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 __counted_by_ptr macro 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_PTR' to turn the corresponding annotation into a no-op.
>
> Assisted-by: LLM
> Signed-off-by: Bill Wendling <morbo@xxxxxxxxxx>
> ---
> v2: Only specify __NO_COUNTED_BY_PTR. Leave __NO_COUNTED_BY until we need it.
> v3: Add the version to the Subject line.
> ---
>  include/linux/compiler_types.h | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/compiler_types.h 
> b/include/linux/compiler_types.h
> index c5921f139007..8bde6798b4ec 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -387,8 +387,13 @@ struct ftrace_likely_data {
>   *
>   *   gcc: 
> https://gcc.gnu.org/pipermail/gcc-patches/2025-April/681727.html
>   * clang: 
> https://clang.llvm.org/docs/AttributeReference.html#counted-by-counted-by-or-null-sized-by-sized-by-or-null
> + *
> + * Code that runs outside the kernel proper (e.g. the EFI stub) can 
> define
> + * __NO_COUNTED_BY_PTR to drop the annotation. Such code may also lack 
> the flag
> + * Clang needs to parse a reference to a later-declared member
> + * (-fexperimental-late-parse-attributes).
>   */
> -#ifdef CONFIG_CC_HAS_COUNTED_BY_PTR
> +#if defined(CONFIG_CC_HAS_COUNTED_BY_PTR) && 
> !defined(__NO_COUNTED_BY_PTR)
>  #define 
> __counted_by_ptr(member)	__attribute__((__counted_by__(member)))
>  #else
>  #define __counted_by_ptr(member)

Apologies, I may have been unclear.

What I would like to see here is something like

#ifndef __NO_COUNTED_BY
#define __counted_by(member)  __attribute__((....))
#define __counted_by_ptr(member)  __attribute__((....))
#else
#define __counted_by(member)
#define __counted_by_ptr(member)
#endif