Understanding GDB frames

[Maxim Grigoriev <maxim at tensilica dot com>]

I experience some difficulties in finding a precise definition
of gdb frames.

Any help on choosing the right answer among the list provided
by me at the end of this message will be highly appreciated.

QUESTION
========

The program (frame.c) is

#include <stdio.h>

int frame_number = 1;

int f11(int b)
{
       int a;

       printf("f11() frame number %d\n", frame_number++);

       a = b + 1;
       b--;
       if (b != 0)
         {
           printf("f11() will be called recursively\n");
           f11(b);
         }
       return a;   /* <-- BP set here.  */
}

int f1(int a)
{
       return f11(a);
}

int main()
{
       int a = 1;
       int i;

       for (i = 0; i <2; i++)
         a = f11(a);

       a = f11(1);
       a = f1(1);

       return 0;
}

The gdb command file "CMD":

   break frame.c:18
   run
   continue
   continue
   continue
   continue
   kill
   quit

was used to run a gdb session like this :
   gdb <executable> --command=CMD

Let's define that "frames A and B are the same" if

   frame_id_eq ( A->this_id, B->this_id ) == true

The breakpoit has been set at line 18 and hit 5 times.
Execution control has been subsequently taken by
gdb in five frames numbered 1, 2, 3, 4, and 5.

According to the definition of GDB frames,
which statement is correct ?

ANSWERS
=======

1) All frames 1, 2, 3, 4, and 5 are the same;
2) All frames 1, 2, 3, 4, and 5 are different from each other;
3) Frames 1,2, and 4 are the same. Frames 3 and 5 are
  different from 1, 2, 4 and from each other;
4) It's implementation-dependent. While doing architecture ports,
  people decide how to implement frame_id-related functions
  to compare frames;
5) Other ( explanation would be appreciated ).

-- Maxim