ppc64 gdbserver NPTL problem

ppc64 gdbserver NPTL problem

[Dmitry S. Vasilchenko]

Hello!

I have met some problems with gdbserver and multithread debugging.
The problem is that on ppc64 td_ta_event_addr from glibc returns the
pointer to function descriptor, not the address of the function. As a
result, gdbserver installs breakpoint at the memory address in .opd
section, not at the function glibs expects. So gdbserver will never
receive information about new threads creation on ppc64.

It is easy to fix, but I am not sure, maybe this should be fixed in
glibc. Your thoughts?

from gdb/gdbserver/thread-tb.c:
/* ************************************ */
static int
thread_db_enable_reporting ()
{
...
  /* Get address for thread creation breakpoint.  */
  err = td_ta_event_addr (thread_agent, TD_CREATE, &notify);
...
  set_breakpoint_at ((CORE_ADDR) (unsigned long) notify.u.bptaddr,
                     thread_db_create_event);


From glibc, nptl_db/td_ta_event_addr.c:
/* ************************************ */
td_err_e
td_ta_event_addr (const td_thragent_t *ta_arg,
                  td_event_e event, td_notify_t *addr)
{
...
      err = DB_GET_SYMBOL (taddr, ta, __nptl_create_event);
...
      addr->u.bptaddr = taddr;

--
Best regards,
Dmitry Vasilchenko

Re: ppc64 gdbserver NPTL problem

[Andreas Schwab]

"Dmitry S. Vasilchenko" <newdimm@gmail.com> writes:

> I have met some problems with gdbserver and multithread debugging.
> The problem is that on ppc64 td_ta_event_addr from glibc returns the
> pointer to function descriptor, not the address of the function. As a
> result, gdbserver installs breakpoint at the memory address in .opd
> section, not at the function glibs expects. So gdbserver will never
> receive information about new threads creation on ppc64.
>
> It is easy to fix, but I am not sure, maybe this should be fixed in
> glibc. Your thoughts?

I think gdbserver needs to do the equivalent of
gdbarch_convert_from_func_ptr_addr, as it is done in
linux-thread-db.c:enable_thread_event.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
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