On Tue, Apr 22, 2025 at 11:21:36AM -0600, Gustavo A. R. Silva wrote:
> Add new STACK_FLEX_ARRAY_SIZE() helper to get the size of a
> flexible-array member defined using DEFINE_FLEX()/DEFINE_RAW_FLEX()
> at compile time.
>
> This is essentially the same as ARRAY_SIZE() but for on-stack
> flexible-array members.
>
> Signed-off-by: Gustavo A. R. Silva <gustavo...@kernel.org>
> ---
> include/linux/overflow.h | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> index 6ee67c20b575..5b2e0cc9aba2 100644
> --- a/include/linux/overflow.h
> +++ b/include/linux/overflow.h
> @@ -420,6 +420,7 @@ static inline size_t __must_check size_sub(size_t
> minuend, size_t subtrahend)
> * flexible array member.
> * Use __struct_size(@name) to get compile-time size of it afterwards.
> * Use __member_size(@name->member) to get compile-time size of @name
> members.
> + * Use STACK_FLEX_ARRAY_SIZE(@name, @member) to get compile-time size of
> array @member.
Instead of "size of" how about "number of elements in"
> */
> #define DEFINE_RAW_FLEX(type, name, member, count) \
> _DEFINE_FLEX(type, name, member, count, = {})
> @@ -438,8 +439,20 @@ static inline size_t __must_check size_sub(size_t
> minuend, size_t subtrahend)
> * flexible array member.
> * Use __struct_size(@NAME) to get compile-time size of it afterwards.
> * Use __member_size(@NAME->member) to get compile-time size of @NAME
> members.
> + * Use STACK_FLEX_ARRAY_SIZE(@name, @member) to get compile-time size of
> array @member.
Same here.
> */
> #define DEFINE_FLEX(TYPE, NAME, MEMBER, COUNTER, COUNT) \
> _DEFINE_FLEX(TYPE, NAME, MEMBER, COUNT, = { .obj.COUNTER = COUNT, })
>
> +/**
> + * STACK_FLEX_ARRAY_SIZE() - helper macro for DEFINE_FLEX() family.
> + * Returns the number of elements in @array.
Which matches these docs.
> + *
> + * @name: Name for a variable defined in DEFINE_RAW_FLEX()/DEFINE_FLEX().
> + * @array: Name of the array member.
> + */
> +#define STACK_FLEX_ARRAY_SIZE(name, array)
> \
> + (__member_size((name)->array) / sizeof(*(name)->array) +
> \
> + __must_be_array((name)->array))
> +
> #endif /* __LINUX_OVERFLOW_H */
> --
> 2.43.0
>
--
Kees Cook
