Re: [PATCH 1/2] stddef: Allow attributes to be used when creating flex arrays

[Gustavo A. R. Silva]

On 2/9/24 19:16, Kees Cook wrote:
> With the coming support for the __counted_by struct member attribute, we
> will need a way to add such annotations to the places where
> DECLARE_FLEX_ARRAY() is used. Introduce DECLARE_FLEX_ARRAY_ATTR() which
> takes a third argument: the attributes to apply to the flexible array.
>
> Cc: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Keith Packard <keithp@xxxxxxxxxx>
> Cc: Miguel Ojeda <ojeda@xxxxxxxxxx>
> Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
> Cc: Dmitry Antipov <dmantipov@xxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Nice!

Reviewed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>

Thanks
--
Gustavo

> ---
>   include/linux/stddef.h      | 16 ++++++++++++++--
>   include/uapi/linux/stddef.h | 25 +++++++++++++++++++------
>   2 files changed, 33 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/stddef.h b/include/linux/stddef.h
> index 929d67710cc5..eb51f6727ecf 100644
> --- a/include/linux/stddef.h
> +++ b/include/linux/stddef.h
> @@ -81,8 +81,20 @@ enum {
>   	__struct_group(TAG, NAME, /* no attrs */, MEMBERS)
>   
>   /**
> - * DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
> + * DECLARE_FLEX_ARRAY_ATTR() - Declare a flexible array usable in a union
> + * @TYPE: The type of each flexible array element
> + * @NAME: The name of the flexible array member
> + * @ATTRS: The list of member attributes to apply
>    *
> + * In order to have a flexible array member in a union or alone in a
> + * struct, it needs to be wrapped in an anonymous struct with at least 1
> + * named member, but that member can be empty.
> + */
> +#define DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, ATTRS) \
> +	__DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, ATTRS)
> +
> +/**
> + * DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
>    * @TYPE: The type of each flexible array element
>    * @NAME: The name of the flexible array member
>    *
> @@ -91,6 +103,6 @@ enum {
>    * named member, but that member can be empty.
>    */
>   #define DECLARE_FLEX_ARRAY(TYPE, NAME) \
> -	__DECLARE_FLEX_ARRAY(TYPE, NAME)
> +	DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, /* no attributes */)
>   
>   #endif
> diff --git a/include/uapi/linux/stddef.h b/include/uapi/linux/stddef.h
> index 2ec6f35cda32..5499c08ad011 100644
> --- a/include/uapi/linux/stddef.h
> +++ b/include/uapi/linux/stddef.h
> @@ -31,24 +31,37 @@
>   
>   #ifdef __cplusplus
>   /* sizeof(struct{}) is 1 in C++, not 0, can't use C version of the macro. */
> -#define __DECLARE_FLEX_ARRAY(T, member)	\
> -	T member[0]
> +#define __DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, ATTRS)	\
> +	TYPE NAME[0] ATTRS
> +#define __DECLARE_FLEX_ARRAY(TYPE, NAME)		\
> +	__DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, /* no attributes */)
>   #else
>   /**
> - * __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
> - *
> + * __DECLARE_FLEX_ARRAY_ATTR() - Declare a flexible array usable in a union
>    * @TYPE: The type of each flexible array element
>    * @NAME: The name of the flexible array member
> + * @ATTRS: The list of member attributes to apply
>    *
>    * In order to have a flexible array member in a union or alone in a
>    * struct, it needs to be wrapped in an anonymous struct with at least 1
>    * named member, but that member can be empty.
>    */
> -#define __DECLARE_FLEX_ARRAY(TYPE, NAME)	\
> +#define __DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, ATTRS)	\
>   	struct { \
>   		struct { } __empty_ ## NAME; \
> -		TYPE NAME[]; \
> +		TYPE NAME[] ATTRS; \
>   	}
> +/**
> + * __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
> + * @TYPE: The type of each flexible array element
> + * @NAME: The name of the flexible array member
> + *
> + * In order to have a flexible array member in a union or alone in a
> + * struct, it needs to be wrapped in an anonymous struct with at least 1
> + * named member, but that member can be empty.
> + */
> +#define __DECLARE_FLEX_ARRAY(TYPE, NAME)	\
> +	__DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, /* no attributes */)
>   #endif
>   
>   #ifndef __counted_by