While not yet in the tree, there is a proposed patch[1] that was depending on the prior behavior of _DEFINE_FLEX, which did not have an explicit initializer. Provide this via __DEFINE_FLEX now, which can also have attributes applied (e.g. __uninitialized).
Examples of the resulting initializer behaviors can be seen here: https://godbolt.org/z/P7Go8Tr33 Link: https://lore.kernel.org/netdev/[email protected] [1] Fixes: 47e36ed78406 ("overflow: Fix direct struct member initialization in _DEFINE_FLEX()") Signed-off-by: Kees Cook <[email protected]> --- Cc: "Gustavo A. R. Silva" <[email protected]> Cc: Alexander Lobakin <[email protected]> Cc: <[email protected]> --- include/linux/overflow.h | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 7b7be27ca113..154ed0dbb43f 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -389,24 +389,37 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) struct_size((type *)NULL, member, count) /** - * _DEFINE_FLEX() - helper macro for DEFINE_FLEX() family. - * Enables caller macro to pass (different) initializer. + * __DEFINE_FLEX() - helper macro for DEFINE_FLEX() family. + * Enables caller macro to pass arbitrary trailing expressions * * @type: structure type name, including "struct" keyword. * @name: Name for a variable to define. * @member: Name of the array member. * @count: Number of elements in the array; must be compile-time const. - * @initializer: Initializer expression (e.g., pass `= { }` at minimum). + * @trailer: Trailing expressions for attributes and/or initializers. */ -#define _DEFINE_FLEX(type, name, member, count, initializer...) \ +#define __DEFINE_FLEX(type, name, member, count, trailer...) \ _Static_assert(__builtin_constant_p(count), \ "onstack flex array members require compile-time const count"); \ union { \ u8 bytes[struct_size_t(type, member, count)]; \ type obj; \ - } name##_u = { .obj initializer }; \ + } name##_u trailer; \ type *name = (type *)&name##_u +/** + * _DEFINE_FLEX() - helper macro for DEFINE_FLEX() family. + * Enables caller macro to pass (different) initializer. + * + * @type: structure type name, including "struct" keyword. + * @name: Name for a variable to define. + * @member: Name of the array member. + * @count: Number of elements in the array; must be compile-time const. + * @initializer: Initializer expression (e.g., pass `= { }` at minimum). + */ +#define _DEFINE_FLEX(type, name, member, count, initializer...) \ + __DEFINE_FLEX(type, name, member, count, = { .obj initializer }) + /** * DEFINE_RAW_FLEX() - Define an on-stack instance of structure with a trailing * flexible array member, when it does not have a __counted_by annotation. @@ -424,7 +437,7 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) * elements in array @member. */ #define DEFINE_RAW_FLEX(type, name, member, count) \ - _DEFINE_FLEX(type, name, member, count, = {}) + __DEFINE_FLEX(type, name, member, count, = { }) /** * DEFINE_FLEX() - Define an on-stack instance of structure with a trailing -- 2.34.1
