libthread_db.so question

libthread_db.so question

[Pete Huerter]

Hi,

Is it possible to use the libthread_db.so library functions to debug a
remote process and it's threads?  I.e. must the client of
libthread_db.so be running on the same host as the target process
itself?

The debugger I work on currently controls remote processes via a
ptrace-based remote debug server.   It seems that with the coming of
RedHat 9.0 the old linuxthreads interface that we are currently using is
deprecated, forcing us to move to using libthread_db.so instead.  The
debugger can debug a distributed (MPI-based) multi-threaded
(linuxthread-based OpenMP) program.  It uses a remote debug server to
control and inspect each remote node.  Must libthread_db.so be loaded by
each remote debug server?  or can the debugger load a single
libthread_db.so and use it's facilities to control the remote processes
(if a proc_service interface is implemented to them using the low level
(remote) ptrace-based interface of the remote debug server).

From reading the man pages on libthread_db.so:

"libthread_db relies on an "agent thread" in the target process for some
of its operations. The "agent thread" is a system thread started when
libthread_db attaches to a process through td_ta_new(3T) ."

Is an agent thread created for each target process?  Is the agent thread
a child thread of each target process?

I realize this is a specialized question.  If there is a better place to
direct this question, please let me know.

Thanks for your time,
--Pete Huerter.


--
Pete Huerter -- Software Engineer
STMicroelectronics, AST Portland Lab
Formerly The Portland Group, Inc.
Phone: (503) 682-2806
Fax:   (503) 682-2637

Re: libthread_db.so question

[Daniel Jacobowitz]

On Tue, Jul 15, 2003 at 12:29:14PM -0700, Pete Huerter wrote:
> Hi,
> 
> Is it possible to use the libthread_db.so library functions to debug a
> remote process and it's threads?  I.e. must the client of
> libthread_db.so be running on the same host as the target process
> itself?
> 
> The debugger I work on currently controls remote processes via a
> ptrace-based remote debug server.   It seems that with the coming of
> RedHat 9.0 the old linuxthreads interface that we are currently using is
> deprecated, forcing us to move to using libthread_db.so instead.  The
> debugger can debug a distributed (MPI-based) multi-threaded
> (linuxthread-based OpenMP) program.  It uses a remote debug server to
> control and inspect each remote node.  Must libthread_db.so be loaded by
> each remote debug server?  or can the debugger load a single
> libthread_db.so and use it's facilities to control the remote processes
> (if a proc_service interface is implemented to them using the low level
> (remote) ptrace-based interface of the remote debug server).
> 
> >From reading the man pages on libthread_db.so:
> 
> "libthread_db relies on an "agent thread" in the target process for some
> of its operations. The "agent thread" is a system thread started when
> libthread_db attaches to a process through td_ta_new(3T) ."
> 
> Is an agent thread created for each target process?  Is the agent thread
> a child thread of each target process?
> 
> I realize this is a specialized question.  If there is a better place to
> direct this question, please let me know.

I imagine you could load libthread_db on the host.  However, it's
slower, and it requires that the host be running the same glibc version
as the target.  That's why gdbserver loads libthread_db on the target
instead.

The ps_* facilities required by libthread_db are quite minimal.  The
only heavy one is symbol lookup; we use a callback to the client for
that.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer