funcalling foreign function pointers

I'm trying to emulate the behavior of LispWork's
DEFINE-FOREIGN-FUNCALLABLE [1] in Allegro CL 6.2.  The current
definition I have is

(def-foreign-funcallable int-caller :int ((x :int)))

  ==>

(defun int-caller (fptr x)
  (system::ff-funcall fptr ':int ':int))

But this segv's.  I obtained system::ff-funcall from the macroexpansion
of def-foreign-call exhibited in the manual, but there are a few
differences I'd like to make a note of first:

;; This taken from def-foreign-call macroexpansion
(system::ff-funcall
  (load-time-value
    (excl::determine-foreign-address '("foo" :language :c)
                                     2
                                     nil))
  '(:int (integer * *))
  x
  '((* :char)
    (array character (*)))
  y
  '(:int (integer * *)))

As you can see, there is a lot more information here.  The conversion of 
:int to '(:int (integer * *)) is done by the def-foreign-call macro, for
example.  Also, the return value of excl::determine-foreign-address is
something like: #("foo" 1078448336 134570392 2 1075560002)
where the function pointers I am getting are just integers (and when I
try to use ff-funcall with them, it segv's as well).

So my question basically boils down to:
 (a) Is there some proper interface for this functionality that I am
     missing?
 (b) If not, how do I go about using what is available?  Do I need to
     deduce (:int (integer * *)) from :int?  How do I obtain a
     function pointer object suitable for ff-funcall's consumption?

Thanks

P.S. I am not sure whether I am subscribed to this list yet or not, so
please CC me on replies.

[1]

In LispWorks, this looks like,

(fli:define-foreign-funcallable int-caller ((x :int))
 :result-type :int)

(int-caller (fli:make-pointer :symbol-name "IntAbs") -100)

(Drawn from KnowledgeBase article under FLI ``Implementing COM...'')

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