Commit 2bbdcf02 authored by Gustavo A. R. Silva's avatar Gustavo A. R. Silva Committed by Kees Cook
Browse files

stddef: Introduce __TRAILING_OVERLAP() 



Introduce underlying __TRAILING_OVERLAP() macro to let callers apply
atributes to trailing overlapping members.

For instance, the code below:

| struct flex {
| 	size_t count;
| 	int data[];
| };

| struct {
| 	struct flex f;
| 	struct foo a;
| 	struct boo b;
| } __packed instance;

can now be changed to the following, and preserve the __packed
attribute:

| __TRAILING_OVERLAP(struct flex, f, data, __packed,
| 	struct foo a;
| 	struct boo b;
| ) instance;

Signed-off-by: default avatarGustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/f80c529b239ce11f0a51f714fe00ddf839e05f5e.1758115257.git.gustavoars@kernel.org


Signed-off-by: default avatarKees Cook <kees@kernel.org>
parent 413187f7

include/linux/stddef.h

+19 −3
Original line number Diff line number Diff line
@@ -94,7 +94,8 @@ enum { 
	__DECLARE_FLEX_ARRAY(TYPE, NAME)



/**

 * TRAILING_OVERLAP() - Overlap a flexible-array member with trailing members.

 * __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.
@@ -102,15 +103,30 @@ enum { 
 * @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, 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