Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
overflow: Introduce __DEFINE_FLEX for having no initializer
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/20250520205920.2134829-9-anthony.l.nguyen@intel.com [1]
Fixes: 47e36ed78406 ("overflow: Fix direct struct member initialization in _DEFINE_FLEX()")
Signed-off-by: Kees Cook <kees@kernel.org>
+21
-8
+21
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include/linux/overflow.h
+21
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include/linux/overflow.h
···
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struct_size((type *)NULL, member, count)
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/**
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* __DEFINE_FLEX() - helper macro for DEFINE_FLEX() family.
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* Enables caller macro to pass arbitrary trailing expressions
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*
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* @type: structure type name, including "struct" keyword.
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* @name: Name for a variable to define.
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* @member: Name of the array member.
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* @count: Number of elements in the array; must be compile-time const.
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* @trailer: Trailing expressions for attributes and/or initializers.
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*/
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#define __DEFINE_FLEX(type, name, member, count, trailer...) \
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_Static_assert(__builtin_constant_p(count), \
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"onstack flex array members require compile-time const count"); \
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union { \
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u8 bytes[struct_size_t(type, member, count)]; \
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type obj; \
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} name##_u trailer; \
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type *name = (type *)&name##_u
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/**
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* _DEFINE_FLEX() - helper macro for DEFINE_FLEX() family.
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* Enables caller macro to pass (different) initializer.
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*
···
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* @initializer: Initializer expression (e.g., pass `= { }` at minimum).
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*/
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#define _DEFINE_FLEX(type, name, member, count, initializer...) \
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_Static_assert(__builtin_constant_p(count), \
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"onstack flex array members require compile-time const count"); \
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union { \
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u8 bytes[struct_size_t(type, member, count)]; \
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type obj; \
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} name##_u = { .obj initializer }; \
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type *name = (type *)&name##_u
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__DEFINE_FLEX(type, name, member, count, = { .obj initializer })
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/**
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* DEFINE_RAW_FLEX() - Define an on-stack instance of structure with a trailing
···
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* elements in array @member.
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*/
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#define DEFINE_RAW_FLEX(type, name, member, count) \
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_DEFINE_FLEX(type, name, member, count, = {})
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__DEFINE_FLEX(type, name, member, count, = { })
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/**
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* DEFINE_FLEX() - Define an on-stack instance of structure with a trailing