GDB internals: thread infos

[Fabrice Gautier <Fabrice_Gautier at sdesigns dot com>]

Hi,

I'm trying to understand how gdb retrieve thread information, thread frame
and thread pc.

I started in the info_threads_command  function.

So there in order to retrieve thread $pc it call the
functionswitch_to_thread which I presume do only a frame switch.

So here is this function:

static void
switch_to_thread (pid)
     int pid;
{
  if (pid == inferior_pid)
    return;

  inferior_pid = pid;
  flush_cached_frames ();
  registers_changed ();
  stop_pc = read_pc ();
  select_frame (get_current_frame (), 0);
}

I assume that inferior_pid should contain the thread id of the current
selected thread.
Then I have a few questions:

What does the registers_changed() should do and where is it defined?

Which pc does the read_pc command should return? The one of the inferior_pid
thread ?

Then in the get_current_frame function, it ends up calling:
	current_frame = create_new_frame (read_fp (), read_pc ());

What frame pointer should read_fp() return? I presume this is the one of the
thread we are switching too. right?
idem for read_pc(). But at what point is there an interaction with the
target to get effectively those values.

-- 
Fabrice Gautier
fabrice_gautier@sdesigns.com