anchor.diff:                     (or (keywordp incoming-arguments)
                          (and incoming-arguments (not framep)))
                      block-or-tagbody-thunk)
  +           (let ((*gc-debug-scavenge-stack* t))
  +             (debug-stack-frame framep interruptp pushed-values pushed-values-register
  +                                layout-address layout-length
  +                                multiple-values incoming-arguments block-or-tagbody-thunk))
              (emergency-halt "TODO! GC SG stuff."))
            (cond (interruptp
                   (when (not framep)
  
positive.code:                                                 incoming-arguments)))
           ;; Stop after seeing a zerop frame pointer.
           (if (eql frame-pointer 0)
               (return))
           (if (not framep)
               (emergency-halt "No frame, but no end in sight?"))
           (psetf return-address (memref-unsigned-byte-64 frame-pointer 1)
                  stack-pointer (+ frame-pointer 16)
                  frame-pointer (memref-unsigned-byte-64 frame-pointer 0)
                  sg-interruptedp nil))))
    (when *gc-debug-scavenge-stack* (mumble "Done scav stack.")))
  
  (defun scan-stack-group (object)
  
negative.code:                        (other-fn-address (base-address-of-internal-pointer other-return-address))
                         (other-fn-offset (- other-return-address other-fn-address))
                         (other-fn (%%assemble-value other-fn-address +tag-function+)))
                    (when *gc-debug-scavenge-stack*
                      (mumble-hex other-return-address "oRA: " t)
                      (mumble-hex other-frame-pointer "oFP: " t)
                      (mumble-hex other-stack-pointer "oSP: " t)
                      (mumble-hex other-fn-address "oFNa: " t)
                      (mumble-hex other-fn-offset "oFNo: " t))
                    ;; Unconditionally scavenge the saved data registers.
                    (scavengef (memref-t frame-pointer -12)) ; r8
                    (scavengef (memref-t frame-pointer -11)) ; r9
  