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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_STDDEF_H
#define _LINUX_STDDEF_H
#include <uapi/linux/stddef.h>
#undef NULL
#define NULL ((void *)0)
enum {
false = 0,
true = 1
};
#undef offsetof
#define offsetof(TYPE, MEMBER) __builtin_offsetof(TYPE, MEMBER)
/**
* sizeof_field() - Report the size of a struct field in bytes
*
* @TYPE: The structure containing the field of interest
* @MEMBER: The field to return the size of
*/
#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() - 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) \
__DECLARE_FLEX_ARRAY(TYPE, NAME)
/**
* __TRAILING_OVERLAP() - Overlap a flexible-array member with trailing
* members.
*
* Creates a union between a flexible-array member (FAM) in a struct and a set
* of additional members that would otherwise follow it.
*
* Beware that, as this helper encloses TYPE NAME and MEMBERS in the same
* union, designated initializers for MEMBERS may overwrite portions
* previously initialized through NAME.
*
* For example::
*
* struct flex {
* size_t count;
* u8 fam[];
* };
*
* struct composite {
* ...
* __TRAILING_OVERLAP(struct flex, flex, fam, __packed,
* u8 data;
* );
* } __packed;
*
* static struct composite comp = {
* .flex = {
* .count = 1,
* },
* .data = 2,
* };
*
* In the example above, .flex and .data initialize different views of the same
* union storage. Since .data is initialized last, it _may_ overwrite portions
* previously initialized through .flex, leading to .flex.count being zeroed
* out.
*
* A couple of alternatives are shown below.
*
* a) Initialize only one view of the overlapped storage and assign the rest
* at runtime::
*
* static struct composite comp = {
* .flex = {
* .count = 1,
* },
* };
*
* static void foo(void)
* {
* comp.data = 2;
* ...
* }
*
* b) Alternatively, replace designated initializers with runtime assignments::
*
* static void foo(void)
* {
* struct composite comp;
*
* comp.flex.count = 1;
* comp.data = 2;
* ...
* }
*
* Compiler Explorer test code: https://godbolt.org/z/voM4E36dT
*
* For another example of the above see commit 5e54510a9389 ("acpi: nfit:
* intel: avoid multiple -Wflex-array-member-not-at-end warnings")
*
* Link: https://git.kernel.org/linus/5e54510a9389caa9
*
* @TYPE: Flexible structure type name, including "struct" keyword.
* @NAME: Name for a variable to define.
* @FAM: The flexible-array member within @TYPE
* @ATTRS: Any struct attributes (usually empty)
* @MEMBERS: Trailing overlapping members.
*/
#define __TRAILING_OVERLAP(TYPE, NAME, FAM, ATTRS, MEMBERS) \
union { \
TYPE NAME; \
struct { \
unsigned char __offset_to_FAM[offsetof(TYPE, FAM)]; \
MEMBERS \
} ATTRS; \
}
/**
* TRAILING_OVERLAP() - Overlap a flexible-array member with trailing members.
*
* Creates a union between a flexible-array member (FAM) in a struct and a set
* of additional members that would otherwise follow it.
*
* @TYPE: Flexible structure type name, including "struct" keyword.
* @NAME: Name for a variable to define.
* @FAM: The flexible-array member within @TYPE
* @MEMBERS: Trailing overlapping members.
*/
#define TRAILING_OVERLAP(TYPE, NAME, FAM, MEMBERS) \
__TRAILING_OVERLAP(TYPE, NAME, FAM, /* no attrs */, MEMBERS)
#endif
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