This is really for anybody's FYI, and maybe Randolph if he'd like to
dig in some of the issues with me.
This is something I'm still working on, so I haven't verified my theory
just yet. But I think there is a confusion in the meaning of Save_SP
in the unwind descriptor. The document I have says:
18. Save_SP (bit 27): One if the entry value of SP is saved by this
regions entry sequence in the current frame marker (current_SP - 4);
zero otherwise.
It doesn't say that the frame has a frame base register. For this, we
have another field: