FRAME_CHAIN() -> frame_id_unwind() ?

[Andrew Cagney]

Hello,

This, I think, is the missing piece in making the frame code fully 
recursive.

A frame ID provides a frame unique identifer.  It includes the frame's 
stack address (for all stacks, the IA64 has two stacks) and the frame's 
code pointer.  A frame ID can be used for things like find a 
dummy-frame's data, or find the selected frame after a frame cache flush.

By asking the next frame to unwind the frame ID we get that unique 
identifier.  FRAME_CHAIN() only returns the frame pointer on the main 
stack so it, in the long run, isn't going to be sufficient.

Initially, for old code, frame_id_unwind() method would look something like:

	frame_id.base = FRAME_CHAIN() or FRAME_FP()
	frame_id.pc = FRAME_SAVED_PC(); /* aka frame_pc_unwind() */

And for a dummy-frame, it would be even simpler:

	// prev_id saved when dummy frame was created
	return dummy_frame->prev_id;

The CFI code could be implemented to do something equivalent.

This will give us:

	frame_register_unwind()
	frame_pc_unwind()
	frame_id_unwind()

Thoughts, at least on the principle?

Andrew