[PATCH 1/2] Compiler Attributes: Add __access macro

[Marco Elver <elver@google.com>]

Add support for the `__access__` attribute, which is supported since gcc
>= 11 but not currently supported by clang.

The attribute allows specifying how a function accesses memory passed
via a pointer argument (read_only, write_only, read_write, none) and
optionally the size of the access. Per [1] these annotations only affect
diagnostics, and should not affect code generation:

	"The access attribute enables the detection of invalid or unsafe
	 accesses by functions or their callers, as well as write-only
	 accesses to objects that are never read from. Such accesses may
	 be diagnosed by warnings such as -Wstringop-overflow,
	 -Wuninitialized, -Wunused, and others."

[1] https://gcc.gnu.org/onlinedocs/gcc/Common-Attributes.html#index-access

Signed-off-by: Marco Elver <elver@google.com>
---
 include/linux/compiler_attributes.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index c16d4199bf92..ef4e279e9872 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -20,6 +20,18 @@
  * Provide links to the documentation of each supported compiler, if it exists.
  */
 
+/*
+ * Optional: only supported since gcc >= 11
+ * Optional: not supported by clang
+ *
+ *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Attributes.html#index-access
+ */
+#if __has_attribute(__access__)
+# define __access(x, ...)		__attribute__((__access__(x, ## __VA_ARGS__)))
+#else
+# define __access(x, ...)
+#endif
+
 /*
  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-alias-function-attribute
  */
-- 
2.54.0.rc2.533.g4f5dca5207-goog