Re: GDB support for thread-local storage

[Daniel Jacobowitz <drow@mvista.com>]

On Wed, Jun 26, 2002 at 11:56:58PM -0500, Jim Blandy wrote:
> 
> Andrew Cagney <ac131313@ges.redhat.com> writes:
> > > Doesn't libthread_db read `struct _pthread_descr_struct' from the
> > > linuxthreads library in the inferior, rather than knowing the layout
> > > itself?  So it's actually the inferior's linuxthreads library that
> > > describes its own structures' layout.
> > 
> > The structure layout will have been compiled into libthread-db.a.  It
> > implicitly knows the layout itself.
> 
> I think you're wrong here.  Could you show me the code?
> 
> (Not that the question is especially relevant to the discussion --- of
> course it could do a simple checksum check.)

You're right, and you're wrong.  For instance, td_ta_map_id2thr.c:

#include <linuxthreads/internals.h>
  struct pthread_handle_struct phc;
  if (ps_pdread (ta->ph, ta->handles + pt % pthread_threads_max, &phc,
                 sizeof (struct pthread_handle_struct)) != PS_OK)
  if (phc.h_descr == NULL)

etc.

which references:
struct pthread_handle_struct {
  struct _pthread_fastlock h_lock; /* Fast lock for sychronized access */
  pthread_descr h_descr;        /* Thread descriptor or NULL if invalid */
  char * h_bottom;              /* Lowest address in the stack thread */
};


Worse, it reads the _pthread_descr_struct from the inferior. 
_pthread_descr_struct does not describe the layout of anything; it's
the actual descriptor.  It has things like a sigjmp_buf in it.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer