[rfc] frame->frame => frame->addr && frame->base()

[Andrew Cagney]

> Hello,
> 
> This comes from DanielB's and my discussion about dwarf2 CFA and dwarf2's frame_base vs GDB's frame->frame.
> 
> An executive summary is that the two dwarf2 frame concepts (CFA and frame_base) do not go into one GDB frame (frame->frame).
> 
> Because of this, I'd like to propose that the frame object have both:
> 
> struct frame_info
> {
>  ...
> 
> // An ISA/ABI specific address within the ``specified frame'' that is constant throughout the lifetime of the frame.  This address is used by GDB as a handle to identify this frame.  This field must be initialized as part of the creation of a frame object.  (see dwarf2 CFA)
> 
> CORE_ADDR addr;

Hmm, MichaelS has pointed out (check the code for finding a frame) that 
all we know about the existing frame->frame is that it is going to fall 
somewhere in the range of stack addresses allocated to the function.

Making for an even more in-exact science, this ``in'' has poorly defined 
boundary conditions - consider pre/post incr/decr SPs, ABIs that 
allocate beyond SP and the like.

I guess, on the bright side, we now have it ``defined''.  I'll update 
the comments then try to think of a next move (suggestions?).

Andrew