Understanding GDB frames

[Maxim Grigoriev]

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