linux-kernel - [PATCH] Compiler Attributes: counted_by: Adjust name and identifier expansion

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Message-Id: <20230817200558.never.077-kees@kernel.org>
Date:   Thu, 17 Aug 2023 13:06:03 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Miguel Ojeda <ojeda@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Tom Rix <trix@...hat.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        linux-hardening@...r.kernel.org
Subject: [PATCH] Compiler Attributes: counted_by: Adjust name and identifier expansion

GCC and Clang's current RFCs name this attribute "counted_by", and have
moved away from using a string for the member name. Update the kernel's
macros to match. Additionally provide a UAPI no-op macro for UAPI structs
that will gain annotations.

Cc: Miguel Ojeda <ojeda@...nel.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Fixes: dd06e72e68bc ("Compiler Attributes: Add __counted_by macro")
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/linux/compiler_attributes.h | 26 +++++++++++++-------------
 include/uapi/linux/stddef.h         |  4 ++++
 2 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 00efa35c350f..74716a407aac 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -94,6 +94,19 @@
 # define __copy(symbol)
 #endif
 
+/*
+ * Optional: only supported since gcc >= 14
+ * Optional: only supported since clang >= 17
+ *
+ *   gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
+ * clang: https://reviews.llvm.org/D148381
+ */
+#if __has_attribute(__counted_by__)
+# define __counted_by(member)		__attribute__((__counted_by__(member)))
+#else
+# define __counted_by(member)
+#endif
+
 /*
  * Optional: not supported by gcc
  * Optional: only supported since clang >= 14.0
@@ -129,19 +142,6 @@
 # define __designated_init
 #endif
 
-/*
- * Optional: only supported since gcc >= 14
- * Optional: only supported since clang >= 17
- *
- *   gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
- * clang: https://reviews.llvm.org/D148381
- */
-#if __has_attribute(__element_count__)
-# define __counted_by(member)		__attribute__((__element_count__(#member)))
-#else
-# define __counted_by(member)
-#endif
-
 /*
  * Optional: only supported since clang >= 14.0
  *
diff --git a/include/uapi/linux/stddef.h b/include/uapi/linux/stddef.h
index 7837ba4fe728..7c3fc3980881 100644
--- a/include/uapi/linux/stddef.h
+++ b/include/uapi/linux/stddef.h
@@ -45,3 +45,7 @@
 		TYPE NAME[]; \
 	}
 #endif
+
+#ifndef __counted_by
+#define __counted_by(m)
+#endif
-- 
2.34.1