+{- Note [Old Area]
+~~~~~~~~~~~~~~~~~~
+There is a single call area 'Old', allocated at the extreme old
+end of the stack frame (ie just younger than the return address)
+which holds:
+ * incoming (overflow) parameters,
+ * outgoing (overflow) parameter to tail calls,
+ * outgoing (overflow) result values
+ * the update frame (if any)
+
+Its size is the max of all these requirements. On entry, the stack
+pointer will point to the youngest incoming parameter, which is not
+necessarily at the young end of the Old area.
+
+End of note -}
+