-/* Return the true size of a struct with a variable-length array field. */
-#define FLEXIBLE_ARRAY_STRUCT_SIZEOF(flexible_array_structtype, \
- flexible_array_field, \
- flexible_array_length) \
- (offsetof (flexible_array_structtype, flexible_array_field) + \
- (offsetof (flexible_array_structtype, flexible_array_field[1]) - \
- offsetof (flexible_array_structtype, flexible_array_field[0])) * \
- (flexible_array_length))
+/* Return the true aligned size of a struct whose last member is a
+ variable-length array field. (this is known as the "struct hack") */
+/* Implementation: in practice, structtype and fieldtype usually have
+ the same alignment, but we can't be sure. We need to use
+ ALIGN_SIZE to be absolutely sure of getting the correct alignment.
+ To help the compiler's optimizer, we use a ternary expression that
+ only a very stupid compiler would fail to correctly simplify. */
+#define FLEXIBLE_ARRAY_STRUCT_SIZEOF(structtype, \
+ fieldtype, \
+ fieldname, \
+ array_length) \
+(ALIGNOF (structtype) == ALIGNOF (fieldtype) \
+ ? (offsetof (structtype, fieldname) + \
+ (offsetof (structtype, fieldname[1]) - \
+ offsetof (structtype, fieldname[0])) * \
+ (array_length)) \
+ : (ALIGN_SIZE \
+ ((offsetof (structtype, fieldname) + \
+ (offsetof (structtype, fieldname[1]) - \
+ offsetof (structtype, fieldname[0])) * \
+ (array_length)), \
+ ALIGNOF (structtype))))