t is, in most cases, RET points to an
               object of exactly the size of the type specified when CIF
               was constructed.  However, integral types narrower than
               the system register size are widened.  In these cases
               your program may assume that RET points to an 'ffi_arg'
               object.

          ARGS
               A vector of pointers to memory holding the arguments to
               the function.

          USER_DATA
               The same USER_DATA that was passed to
               'ffi_prep_closure_loc'.

     'ffi_prep_closure_loc' will return 'FFI_OK' if everything went ok,
     and one of the other 'ffi_status' values on error.

     After calling 'ffi_prep_closure_loc', you can cast CODELOC to the
     appropriate pointer-to-function type.

   You may see old code referring to 'ffi_prep_closure'.  This function
is deprecated, as it cannot handle the need for separate writable and
executable addresses.