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

[David Laight <david.laight.linux@gmail.com>]

On Tue, 21 Apr 2026 21:03:47 +0200
Marco Elver <elver@google.com> wrote:

> 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

No need to the initial 'x', you can just do:
# define __access(...)		__attribute__((__access__(__VA_ARGS__)))

Putting the actual syntax in the comment would help, eg as:
	__access__(read_only|read_write|write_only|none, param_number[, size])

	David

> +
>  /*
>   *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-alias-function-attribute
>   */