Re: [PATCH] include: sync <linux/stddef.h> with Linux

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 07.06.23 14:12, Ahmad Fatoum wrote:
> Our old definition of offsetof is not an Integer Constant Expression
> with some more recent clang versions[1]. Let's adopt the Linux
> definition as well as a number of new macros that were added as part of
> the hardening of the kernel against common out-of-bound bugs:
> 
>   - offsetofend
>   - struct_group*
>   - DECLARE_FLEX_ARRAY
> 
> Of course, we only benefit from the new macros once we start to use
> them, but that can follow now that they are available.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=14e83077d55f

I missed to add that before sending the patch out.

Let me know if I should resend.

> 
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
>  include/linux/stddef.h | 109 ++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 108 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/stddef.h b/include/linux/stddef.h
> index 1044571c3f45..88ff6f1733d2 100644
> --- a/include/linux/stddef.h
> +++ b/include/linux/stddef.h
> @@ -22,7 +22,7 @@ enum {
>  typedef unsigned short wchar_t;
>  
>  #undef offsetof
> -#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
> +#define offsetof(TYPE, MEMBER)	__builtin_offsetof(TYPE, MEMBER)
>  
>  /**
>   * sizeof_field() - Report the size of a struct field in bytes
> @@ -32,4 +32,111 @@ typedef unsigned short wchar_t;
>   */
>  #define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER))
>  
> +/**
> + * offsetofend() - Report the offset of a struct field within the struct
> + *
> + * @TYPE: The type of the structure
> + * @MEMBER: The member within the structure to get the end offset of
> + */
> +#define offsetofend(TYPE, MEMBER) \
> +	(offsetof(TYPE, MEMBER)	+ sizeof_field(TYPE, MEMBER))
> +
> +/**
> + * __struct_group() - Create a mirrored named and anonyomous struct
> + *
> + * @TAG: The tag name for the named sub-struct (usually empty)
> + * @NAME: The identifier name of the mirrored sub-struct
> + * @ATTRS: Any struct attributes (usually empty)
> + * @MEMBERS: The member declarations for the mirrored structs
> + *
> + * Used to create an anonymous union of two structs with identical layout
> + * and size: one anonymous and one named. The former's members can be used
> + * normally without sub-struct naming, and the latter can be used to
> + * reason about the start, end, and size of the group of struct members.
> + * The named struct can also be explicitly tagged for layer reuse, as well
> + * as both having struct attributes appended.
> + */
> +#define __struct_group(TAG, NAME, ATTRS, MEMBERS...) \
> +	union { \
> +		struct { MEMBERS } ATTRS; \
> +		struct TAG { MEMBERS } ATTRS NAME; \
> +	}
> +
> +/**
> + * struct_group() - Wrap a set of declarations in a mirrored struct
> + *
> + * @NAME: The identifier name of the mirrored sub-struct
> + * @MEMBERS: The member declarations for the mirrored structs
> + *
> + * Used to create an anonymous union of two structs with identical
> + * layout and size: one anonymous and one named. The former can be
> + * used normally without sub-struct naming, and the latter can be
> + * used to reason about the start, end, and size of the group of
> + * struct members.
> + */
> +#define struct_group(NAME, MEMBERS...)	\
> +	__struct_group(/* no tag */, NAME, /* no attrs */, MEMBERS)
> +
> +/**
> + * struct_group_attr() - Create a struct_group() with trailing attributes
> + *
> + * @NAME: The identifier name of the mirrored sub-struct
> + * @ATTRS: Any struct attributes to apply
> + * @MEMBERS: The member declarations for the mirrored structs
> + *
> + * Used to create an anonymous union of two structs with identical
> + * layout and size: one anonymous and one named. The former can be
> + * used normally without sub-struct naming, and the latter can be
> + * used to reason about the start, end, and size of the group of
> + * struct members. Includes structure attributes argument.
> + */
> +#define struct_group_attr(NAME, ATTRS, MEMBERS...) \
> +	__struct_group(/* no tag */, NAME, ATTRS, MEMBERS)
> +
> +/**
> + * struct_group_tagged() - Create a struct_group with a reusable tag
> + *
> + * @TAG: The tag name for the named sub-struct
> + * @NAME: The identifier name of the mirrored sub-struct
> + * @MEMBERS: The member declarations for the mirrored structs
> + *
> + * Used to create an anonymous union of two structs with identical
> + * layout and size: one anonymous and one named. The former can be
> + * used normally without sub-struct naming, and the latter can be
> + * used to reason about the start, end, and size of the group of
> + * struct members. Includes struct tag argument for the named copy,
> + * so the specified layout can be reused later.
> + */
> +#define struct_group_tagged(TAG, NAME, MEMBERS...) \
> +	__struct_group(TAG, NAME, /* no attrs */, MEMBERS)
> +
> +/**
> + * __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)	\
> +	struct { \
> +		struct { } __empty_ ## NAME; \
> +		TYPE NAME[]; \
> +	}
> +
> +/**
> + * 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(TYPE, NAME)
> +
>  #endif

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