+ (start long)
+ ;; On platforms with small enough GC pages, this field
+ ;; will be a short. On platforms with larger ones, it'll
+ ;; be an int.
+ (bytes-used (unsigned
+ #.(if (typep sb!vm:gencgc-page-size
+ '(unsigned-byte 16))
+ 16
+ 32)))
+ (flags (unsigned 8))
+ (gen (signed 8))))