[commit] Allow inspection of a bad frame

[Andrew Cagney]

Hello,

See:  Lazy get_frame_id()
http://sources.redhat.com/ml/gdb/2003-03/msg00240.html

This patch delays the verification of a frame's ID until a further 
unwind is requested.  By doing this, it becomes possible to `step onto' 
a bad frame, and hence examine things like its registers.  Previously, 
GDB would refuse to go near such a frame, making examination impossible :-(

+  /* The unwound frame ID is validate at the start of this function,
+     as part of the logic to decide if that frame should be further
+     unwound, and not here while the prev frame is being created.
+     Doing this makes it possible for the user to examine a frame that
+     has an invalid frame ID.
+
+     The very old VAX frame_args_address_correct() method noted: [...]
+     For the sake of argument, suppose that the stack is somewhat
+     trashed (which is one reason that "info frame" exists).  So,
+     return 0 (indicating we don't know the address of the arglist) if
+     we don't know what frame this frame calls.  */

This change only applies to the new unwinders, and hence, can only 
affect the d10v.

It does not implement the lazy ID and infrun.c changes also mentioned in 
that post.

committed,
Andrew
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