%return-address-function.lisp

;;; Look for "lea -nnnn(%rip),%fn" AT the tra; if that's present, use
;;; the dispacement -nnnn to find the function.  The end of the
;;; encoded displacement is
;;; x8664::recover-fn-from-rip-disp-offset (= 7) bytes from the tra.
(defx86lapfunction %return-address-function ((r arg_z))
                                        ; extract tag  into imm0
  (extract-lisptag r imm0)
                                        ; assert first byte of imm0 = tra tag
  (cmpb ($ x8664::tag-tra) (% imm0.b))
  (jne @fail)
                                        ; assert *r = #x8d4c
  (cmpw ($ x8664::recover-fn-from-rip-word0) (@ (% r)))
  (jne @fail)
                                        ; check *(r+2) = #x2d
  (cmpb ($ x8664::recover-fn-from-rip-byte2) (@ 2 (% r)))
                                        ; copy 2 words from *(r+3) to imm0
  (movslq (@ x8664::recover-fn-from-rip-disp-offset (% r)) (% imm0))
                                        ; if cmpb failed, bail
  (jne @fail)
                                        ; load word at *(r+7+imm0) into arg_z
  (lea (@ x8664::recover-fn-from-rip-length (% imm0) (% r)) (% arg_z))
                                        ; arg_z points to the function object
  (single-value-return)
  @fail
  (movl ($ (target-nil-value)) (% arg_z.l))
  (single-value-return))