Re: [non-stop] 08/10 linux native support

[Pedro Alves <pedro@codesourcery.com>]

On Thursday 10 July 2008 18:15:18, Daniel Jacobowitz wrote:
> On Thu, Jul 10, 2008 at 04:27:49PM +0100, Pedro Alves wrote:
> > > This (the thread_db_attach_lwp version) looks reasonable to me.  Ugly,
> > > but reasonable.  Why do we need the parent's data?
> >
> > Due to this:
> >
> >  (gdb) r&
> >  Starting program: /home/pedro/gdb/tests/threads32
> >  (gdb) [Thread debugging using libthread_db enabled]
> >  [New Thread 0xf7df0b90 (LWP 24154)]
> >  [New Thread 0xf75efb90 (LWP 24155)]
> >  info threads
> >    3 Thread 0xf75efb90 (LWP 24155)  (running)
> >    2 Thread 0xf7df0b90 (LWP 24154)  (running)
> >  * 1 LWP 24151  (running)
>
> Why didn't this thread get identified at the shared library event,
> when libthread_db was loaded?  It already existed by then, being the
> main thread.

Because we hit this in find_new_threads_callback:

  if (ti.ti_tid == 0)
    {
      /* A thread ID of zero means that this is the main thread, but
	 glibc has not yet initialized thread-local storage and the
	 pthread library.  We do not know what the thread's TID will
	 be yet.  Just enable event reporting and otherwise ignore
	 it.  */

#0  find_new_threads_callback (th_p=0xffb316c4, data=0x0) at ../../src/gdb/linux-thread-db.c:1011
#1  0xf7dfbb59 in ?? () from /lib32/libthread_db.so.1
#2  0xf7dfbc11 in td_ta_thr_iter () from /lib32/libthread_db.so.1
#3  0x080a8dec in thread_db_find_new_threads () at ../../src/gdb/linux-thread-db.c:1044
#4  0x080a8371 in check_for_thread_db () at ../../src/gdb/linux-thread-db.c:665
#5  0x080a83af in thread_db_new_objfile (objfile=0x84a6cf8) at ../../src/gdb/linux-thread-db.c:679
...

That's from here:

649       /* Now attempt to open a connection to the thread library.  */
650       err = td_ta_new_p (&proc_handle, &thread_agent);
651       switch (err)
652         {
653         case TD_NOLIBTHREAD:
654           /* No thread library was detected.  */
655           break;
656
657         case TD_OK:
658           printf_unfiltered (_("[Thread debugging using libthread_db enabled]\n"));
659
660           /* The thread library was detected.  Activate the thread_db target.  */
661           push_target (&thread_db_ops);
662           using_thread_db = 1;
663
664           enable_thread_event_reporting ();
665           thread_db_find_new_threads ();
666           break;

-- 
Pedro Alves