--Hi, Cax. Sorry I failed to make my question clear. What I mean is whether in a relative clause in "I've done all that I had to do", "all" is the Object of "had" or of "do".
Similarly, what I mean is whether in a relative clause in "All that I have to do is try hard", "all" is the Object of "have" or of "do".
In the relative clause it's actually the relative pronoun that that you're interested in, right?
all that I [have / had] to do: that is the direct object of do, in the most straight forward reading. (that is assumed if omitted, of course.) But there is ambiguity, and that could also be the direct object of have (or had).