':param function_addr_a: The address of the first function (in the first binary)
:param function_addr_b: The address of the second function (in the second binary)
:returns: the FunctionDiff of the two functions'

def get_function_diff(self, function_addr_a, function_addr_b):

    pair = (function_addr_a, function_addr_b)
    if (pair not in self._function_diffs):
        function_a = self.cfg_a.kb.functions.function(function_addr_a)
        function_b = self.cfg_b.kb.functions.function(function_addr_b)
        self._function_diffs[pair] = FunctionDiff(function_a, function_b, self)
    return self._function_diffs[pair]
