include/linux/stddef.h

#ifndef _LINUX_STDDEF_H
#define _LINUX_STDDEF_H

#undef NULL
#define NULL ((void *)0)

#undef offsetof
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)

/**
 * __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[]; \
	}

#endif