Clarify when __builtin_dynamic_object_size() is available. All our
supported Clang versions support it. GCC 12 and later support it. Link
to documentation for both.

Signed-off-by: Kees Cook <kees@kernel.org>
---
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <nick.desaulniers+lkml@gmail.com>
Cc: Bill Wendling <morbo@google.com>
Cc: Justin Stitt <justinstitt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Marco Elver <elver@google.com>
Cc: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Cc: llvm@lists.linux.dev
---
 include/linux/compiler_types.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 501cffddc2f4..20881cc761fa 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -449,6 +449,11 @@ struct ftrace_likely_data {
 /*
  * When the size of an allocated object is needed, use the best available
  * mechanism to find it. (For cases where sizeof() cannot be used.)
+ *
+ * Optional: only supported since gcc >= 12
+ *
+ *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Object-Size-Checking.html
+ * clang: https://clang.llvm.org/docs/LanguageExtensions.html#evaluating-object-size
  */
 #if __has_builtin(__builtin_dynamic_object_size)
 #define __struct_size(p)	__builtin_dynamic_object_size(p, 0)
-- 
2.34.1

On Wed, 16 Apr 2025 10:20:20 -0700, Kees Cook wrote:
> Clarify when __builtin_dynamic_object_size() is available. All our
> supported Clang versions support it. GCC 12 and later support it. Link
> to documentation for both.
> 
> 

Applied to for-next/hardening, thanks!

[1/1] compiler_types: Identify compiler versions for __builtin_dynamic_object_size
      https://git.kernel.org/kees/c/833dd6a6a1b1

Take care,

-- 
Kees Cook

On Wed, Apr 16, 2025 at 7:20 PM Kees Cook <kees@kernel.org> wrote:
>
> Clarify when __builtin_dynamic_object_size() is available. All our
> supported Clang versions support it. GCC 12 and later support it. Link
> to documentation for both.
>
> Signed-off-by: Kees Cook <kees@kernel.org>

Looks good to me, thanks!

If you/someone is taking it through their tree:

Acked-by: Miguel Ojeda <ojeda@kernel.org>

Cheers,
Miguel