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

Pedro Alves
2008-07-10T18:01:43Z

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