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This is however not the case if the struct has a union inside it, and `member` refers to a field inside that sub-union: struct my_inner { int a; char b[]; }; struct my_outer { char c; union { struct my_inner inner; long l; }; }; /* This will give the wrong result */ struct_size_t(struct my_outer, inner.b, n_elems); Replacing sizeof() by the offsetof() of the member fixes this. Existing users specifying non-union members should not be affected. Cc: Mark Rutland Signed-off-by: Bence Csokas --- include/linux/overflow.h | 4 ++-- include/linux/stddef.h | 8 ++++++++ 2 files changed, 10 insertions(+), 2 deletions(-) diff --git a/include/linux/overflow.h b/include/linux/overflow.h index a8cb6319b4fb..a11c1135f617 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -433,8 +433,8 @@ static __always_inline size_t __must_check size_sub(size_t minuend, size_t subtr */ #define struct_size(p, member, count) \ __builtin_choose_expr(__is_constexpr(count), \ - sizeof(*(p)) + flex_array_size(p, member, count), \ - size_add(sizeof(*(p)), flex_array_size(p, member, count))) + offsetofp((p), member) + flex_array_size(p, member, count), \ + size_add(offsetofp((p), member), flex_array_size(p, member, count))) /** * struct_size_t() - Calculate size of structure with trailing flexible array diff --git a/include/linux/stddef.h b/include/linux/stddef.h index e1851c50c89b..b8f0dbd2de55 100644 --- a/include/linux/stddef.h +++ b/include/linux/stddef.h @@ -32,6 +32,14 @@ enum { #define offsetofend(TYPE, MEMBER) \ (offsetof(TYPE, MEMBER) + sizeof_field(TYPE, MEMBER)) +/** + * offsetofp() - Get the offset of a struct field from a pointer to the struct + * + * @P: Pointer to the structure + * @MEMBER: The member within the structure to get the end offset of + */ +#define offsetofp(P, MEMBER) offsetof(typeof(*(P)), MEMBER) + /** * struct_group() - Wrap a set of declarations in a mirrored struct * base-commit: 62cc90241548d5570ee68e01aaba6506964e9811 -- 2.54.0