Infinite backtrace on arm

[Andrew Cagney]

> The problem is that there's not much GDB can do with hand-coded
> assembly functions.
> 
> However, GDB ought to be able to detect and stop that loop without any
> of this.  It seems to me that the problem is not two frames with the
> same PC, but two frames with their PC "saved" in the same place - i.e.
> GDB failing to figure out where the PC is saved.  This is made a little
> tricky in current versions of GDB, because the PC is normally unwound
> using frame_pc_unwind (which doesn't tell us where it was saved, since
> the interface doesn't assume it's a single normal register), and the
> core code doesn't have a concept of a "PC register" any more.
> 
> Andrew, any idea on how to do this?

Before anything else, find out what a current GDB does - its code to 
detect a "corrupt stack" is now much improved.

Andrew