These patches add the __counted_by_ptr macro and then uses it in
mm/memblock.h. The name of the __counted_by_ptr attribute is the same as
__counted_by, but two different macros are needed, because of feature
skew in GCC and clang. Once the minmum versions of the compilers support
'counted_by' on both flexible array members and pointers in structs,
this macro will become obsolete.

Bill Wendling (2):
  Compiler Attributes: Add __counted_by_ptr macro
  memblock: annotate struct memblock_type with __counted_by_ptr

 include/linux/compiler_types.h | 11 +++++++++++
 include/linux/memblock.h       |  2 +-
 init/Kconfig                   |  5 +++++
 3 files changed, 17 insertions(+), 1 deletion(-)

-- 
2.52.0.rc2.455.g230fcf2819-goog

On Fri, Nov 21, 2025 at 07:39:42PM +0000, Bill Wendling wrote:
> These patches add the __counted_by_ptr macro and then uses it in
> mm/memblock.h. The name of the __counted_by_ptr attribute is the same as
> __counted_by, but two different macros are needed, because of feature
> skew in GCC and clang. Once the minmum versions of the compilers support
> 'counted_by' on both flexible array members and pointers in structs,
> this macro will become obsolete.
> 
> Bill Wendling (2):
>   Compiler Attributes: Add __counted_by_ptr macro
>   memblock: annotate struct memblock_type with __counted_by_ptr

Based on this[1] thread, I think we'll need to wait for GCC and Clang to
release with the "void *" support first, and then push the counted_by up
to that version to cover flexible arrays, pointers, and void *.

-Kees

[1] https://lore.kernel.org/lkml/20251021095447.GL3245006@noisy.programming.kicks-ass.net/

-Kees

-- 
Kees Cook

On Fri, Nov 21, 2025 at 3:25 PM Kees Cook <kees@kernel.org> wrote:
> On Fri, Nov 21, 2025 at 07:39:42PM +0000, Bill Wendling wrote:
> > These patches add the __counted_by_ptr macro and then uses it in
> > mm/memblock.h. The name of the __counted_by_ptr attribute is the same as
> > __counted_by, but two different macros are needed, because of feature
> > skew in GCC and clang. Once the minmum versions of the compilers support
> > 'counted_by' on both flexible array members and pointers in structs,
> > this macro will become obsolete.
> >
> > Bill Wendling (2):
> >   Compiler Attributes: Add __counted_by_ptr macro
> >   memblock: annotate struct memblock_type with __counted_by_ptr
>
> Based on this[1] thread, I think we'll need to wait for GCC and Clang to
> release with the "void *" support first, and then push the counted_by up
> to that version to cover flexible arrays, pointers, and void *.
>
> [1] https://lore.kernel.org/lkml/20251021095447.GL3245006@noisy.programming.kicks-ass.net/
>
Would it make sense to add it with the expected compiler version
releases so that (1) we'll be ready when the compilers are released,
and (2) people could test the new features with compiler RCs?

-bw