linux-hardening - [PATCH] compiler_types: Identify compiler versions for __builtin_dynamic_object

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Message-Id: <20250416172016.work.154-kees@kernel.org>
Date: Wed, 16 Apr 2025 10:20:20 -0700
From: Kees Cook <kees@...nel.org>
To: Nathan Chancellor <nathan@...nel.org>,
	Miguel Ojeda <ojeda@...nel.org>
Cc: Kees Cook <kees@...nel.org>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Marco Elver <elver@...gle.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	llvm@...ts.linux.dev,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Hendrik Farr <kernel@...rr.cc>,
	Tony Ambardar <tony.ambardar@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Uros Bizjak <ubizjak@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH] compiler_types: Identify compiler versions for __builtin_dynamic_object_size

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@...nel.org>
---
Cc: Miguel Ojeda <ojeda@...nel.org>
Cc: Nathan Chancellor <nathan@...nel.org>
Cc: Nick Desaulniers <nick.desaulniers+lkml@...il.com>
Cc: Bill Wendling <morbo@...gle.com>
Cc: Justin Stitt <justinstitt@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Marco Elver <elver@...gle.com>
Cc: Przemek Kitszel <przemyslaw.kitszel@...el.com>
Cc: llvm@...ts.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