SilcUInt32 silc_stack_pop(SilcStack stack);

    Pop the top of the stack upwards which reveals the previous stack frame
    and becomes the top of the stack.  After popping, memory allocated in
    the old frame is freed.  For each silc_stack_push call there must be
    silc_stack_pop call to free all memory (in reality any memory is not
    freed but within the stack it is).  This returns the stack pointer of
    old frame after popping and caller may check that it is same as
    returned by the silc_stack_push.  If it they differ, some routine
    has called silc_stack_push but has not called silc_stack_pop, or
    silc_stack_pop has been called too many times.  Application should
    treat this as a fatal error, as it is a bug in the application code.

    If `stack' is NULL this call has no effect.

    This example saves the stack pointer which is checked when popping
    the current stack frame.  If the stack pointer differs then someone
    has pushed the stack frame but forgot to pop it (or has called it
    too many times).

    sp = silc_stack_push(stack, NULL);
    silc_foo_parse_packet(packet, stack);
    if (silc_stack_pop(stack) != sp)
      fatal("corrupted stack");