Andy,
I agree, completely, with your description of the challenge,
thank you for focusing the discussion on that problem statement.
Question:
Is it required (by the "ABI") that a user program has everything
on the stack for user-space XSAVE/XRESTOR to get back
to the state of the program just before receiving the signal?
My understanding is that there are programs that do this.
However, if it is not guaranteed to work, that could greatly simplify
what we are required to put on the signal stack.
thanks,
-Len