>   Ada95 does not
>   guarantee comparisons of subprogram 'Access values. As explained
>   in [RM 3.10.2(39)], [RM 4.5.2(13)], and other places, a compiler
>   "implementation may consider two access-to-subprogram values to be
>   unequal, even though they designate the same subprogram. This might
>   be because one points directly to the subprogram, while the other
>   points to a special prologue that performs an Elaboration_Check and
>   then jumps to the subprogram." Thus, each 'Access attribute reference
>   for a given subprogram is allowed to designate a distinct wrapper if
>   needed, to support an indirect call.

If you are using GNAT compiler then you may consider the Code_Address attribute
instead of Access (see Implementation Defined Attributes in GNAT Reference Manual).