/* 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
