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[PATCH] Remove support for thread events without PTRACE_EVENT_CLONE in GDB.


Before, on systems that did not support PTRACE_EVENT_CLONE, both GDB and
GDBServer coordinated with libthread_db.so to insert breakpoints at magic
locations in libpthread.so, in order to break at thread creation and
thread death.

Support for thread events was removed from GDBServer as patch:
https://sourceware.org/ml/gdb-patches/2015-11/msg00466.html

This patch removes support for thread events in GDB.

No regressions found on Ubuntu 14.04 x86_64.

gdb/ChangeLog:
	* breakpoint.c (create_thread_event_breakpoint): Remove.
	(remove_thread_event_breakpoints): Remove.
	* linux-thread-db.c (thread_db_use_events): Remove.
	(struct thread_db_info) <td_create_bp_addr>: Remove.
	<td_death_bp_addr>: Likewise.
	<td_ta_event_addr_p>: Likewise.
	<td_ta_set_event_p>: Likewise.
	<td_ta_clear_event_p>: Likewise.
	<td_ta_event_getmsg_p>: Likewise.
	<td_thr_event_enable_p>: Likewise.
	(attach_thread): Likewise.
	(detach_thread): Likewise.
	(have_threads_callback): Likewise.
	(have_threads): Likewise.
	(enable_thread_event): Likewise.
	(enable_thread_event_reporting): Likewise.
	(try_thread_db_load_1): Remove td_ta_event_addr, td_ta_set_event,
	td_ta_clear_event, td_ta_event_getmsg, td_thr_event_enable
	initializations.
	(try_thread_db_load_1): Remove enable_thread_event_reporting call.
	(disable_thread_event_reporting): Remove.
	(record_thread): Adapt to thread_db_use_event removal.
	(detach_thread): Remove.
	(thread_db_detach): Adapt to thread_db_use_event removal.
	(check_event): Remove.
	(thread_db_wait): Adapt to thread events support removal.
	(thread_db_mourn_inferior): Likewise.
	(find_new_threads_callback): Likewise.
	(find_new_threads_once): Likewise.
	(thread_db_update_thread_list): Likewise.
---
 gdb/breakpoint.c      |  28 ----
 gdb/linux-thread-db.c | 440 +-------------------------------------------------
 2 files changed, 8 insertions(+), 460 deletions(-)

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index bc6b2ef..2a0d4fd 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -7748,34 +7748,6 @@ delete_std_terminate_breakpoint (void)
       delete_breakpoint (b);
 }
 
-struct breakpoint *
-create_thread_event_breakpoint (struct gdbarch *gdbarch, CORE_ADDR address)
-{
-  struct breakpoint *b;
-
-  b = create_internal_breakpoint (gdbarch, address, bp_thread_event,
-				  &internal_breakpoint_ops);
-
-  b->enable_state = bp_enabled;
-  /* location has to be used or breakpoint_re_set will delete me.  */
-  b->location = new_address_location (b->loc->address);
-
-  update_global_location_list_nothrow (UGLL_MAY_INSERT);
-
-  return b;
-}
-
-void
-remove_thread_event_breakpoints (void)
-{
-  struct breakpoint *b, *b_tmp;
-
-  ALL_BREAKPOINTS_SAFE (b, b_tmp)
-    if (b->type == bp_thread_event
-	&& b->loc->pspace == current_program_space)
-      delete_breakpoint (b);
-}
-
 struct lang_and_radix
   {
     enum language lang;
diff --git a/gdb/linux-thread-db.c b/gdb/linux-thread-db.c
index 229bb0b..3f5b1c1 100644
--- a/gdb/linux-thread-db.c
+++ b/gdb/linux-thread-db.c
@@ -78,16 +78,6 @@ static char *libthread_db_search_path;
    by the "set auto-load libthread-db" command.  */
 static int auto_load_thread_db = 1;
 
-/* Returns true if we need to use thread_db thread create/death event
-   breakpoints to learn about threads.  */
-
-static int
-thread_db_use_events (void)
-{
-  /* Not necessary if the kernel supports clone events.  */
-  return !linux_supports_traceclone ();
-}
-
 /* "show" command for the auto_load_thread_db configuration variable.  */
 
 static void
@@ -161,30 +151,14 @@ struct thread_db_info
      be able to ignore such stale entries.  */
   int need_stale_parent_threads_check;
 
-  /* Location of the thread creation event breakpoint.  The code at
-     this location in the child process will be called by the pthread
-     library whenever a new thread is created.  By setting a special
-     breakpoint at this location, GDB can detect when a new thread is
-     created.  We obtain this location via the td_ta_event_addr
-     call.  */
-  CORE_ADDR td_create_bp_addr;
-
-  /* Location of the thread death event breakpoint.  */
-  CORE_ADDR td_death_bp_addr;
-
   /* Pointers to the libthread_db functions.  */
 
   td_init_ftype *td_init_p;
   td_ta_new_ftype *td_ta_new_p;
   td_ta_map_lwp2thr_ftype *td_ta_map_lwp2thr_p;
   td_ta_thr_iter_ftype *td_ta_thr_iter_p;
-  td_ta_event_addr_ftype *td_ta_event_addr_p;
-  td_ta_set_event_ftype *td_ta_set_event_p;
-  td_ta_clear_event_ftype *td_ta_clear_event_p;
-  td_ta_event_getmsg_ftype * td_ta_event_getmsg_p;
   td_thr_validate_ftype *td_thr_validate_p;
   td_thr_get_info_ftype *td_thr_get_info_p;
-  td_thr_event_enable_ftype *td_thr_event_enable_p;
   td_thr_tls_get_addr_ftype *td_thr_tls_get_addr_p;
   td_thr_tlsbase_ftype *td_thr_tlsbase_p;
 };
@@ -273,12 +247,6 @@ delete_thread_db_info (int pid)
   xfree (info);
 }
 
-/* Prototypes for local functions.  */
-static int attach_thread (ptid_t ptid, const td_thrhandle_t *th_p,
-			  const td_thrinfo_t *ti_p);
-static void detach_thread (ptid_t ptid);
-
-
 /* Use "struct private_thread_info" to cache thread state.  This is
    a substantial optimization.  */
 
@@ -359,30 +327,7 @@ thread_db_err_str (td_err_e err)
       return buf;
     }
 }
-
-/* Return 1 if any threads have been registered.  There may be none if
-   the threading library is not fully initialized yet.  */
-
-static int
-have_threads_callback (struct thread_info *thread, void *args)
-{
-  int pid = * (int *) args;
-
-  if (ptid_get_pid (thread->ptid) != pid)
-    return 0;
-
-  return thread->priv != NULL;
-}
-
-static int
-have_threads (ptid_t ptid)
-{
-  int pid = ptid_get_pid (ptid);
-
-  return iterate_over_threads (have_threads_callback, &pid) != NULL;
-}
 
-
 /* Fetch the user-level thread id of PTID.  */
 
 static struct thread_info *
@@ -455,37 +400,6 @@ verbose_dlsym (void *handle, const char *name)
   return sym;
 }
 
-static td_err_e
-enable_thread_event (td_event_e event, CORE_ADDR *bp)
-{
-  td_notify_t notify;
-  td_err_e err;
-  struct thread_db_info *info;
-
-  info = get_thread_db_info (ptid_get_pid (inferior_ptid));
-
-  /* Access an lwp we know is stopped.  */
-  info->proc_handle.ptid = inferior_ptid;
-
-  /* Get the breakpoint address for thread EVENT.  */
-  err = info->td_ta_event_addr_p (info->thread_agent, event, &notify);
-  if (err != TD_OK)
-    return err;
-
-  /* Set up the breakpoint.  */
-  gdb_assert (exec_bfd);
-  (*bp) = (gdbarch_convert_from_func_ptr_addr
-	   (target_gdbarch (),
-	    /* Do proper sign extension for the target.  */
-	    (bfd_get_sign_extend_vma (exec_bfd) > 0
-	     ? (CORE_ADDR) (intptr_t) notify.u.bptaddr
-	     : (CORE_ADDR) (uintptr_t) notify.u.bptaddr),
-	    &current_target));
-  create_thread_event_breakpoint (target_gdbarch (), *bp);
-
-  return TD_OK;
-}
-
 /* Verify inferior's '\0'-terminated symbol VER_SYMBOL starts with "%d.%d" and
    return 1 if this version is lower (and not equal) to
    VER_MAJOR_MIN.VER_MINOR_MIN.  Return 0 in all other cases.  */
@@ -517,68 +431,6 @@ inferior_has_bug (const char *ver_symbol, int ver_major_min, int ver_minor_min)
   return retval;
 }
 
-static void
-enable_thread_event_reporting (void)
-{
-  td_thr_events_t events;
-  td_err_e err;
-  struct thread_db_info *info;
-
-  info = get_thread_db_info (ptid_get_pid (inferior_ptid));
-
-  /* We cannot use the thread event reporting facility if these
-     functions aren't available.  */
-  if (info->td_ta_event_addr_p == NULL
-      || info->td_ta_set_event_p == NULL
-      || info->td_ta_event_getmsg_p == NULL
-      || info->td_thr_event_enable_p == NULL)
-    return;
-
-  /* Set the process wide mask saying which events we're interested in.  */
-  td_event_emptyset (&events);
-  td_event_addset (&events, TD_CREATE);
-
-  /* There is a bug fixed between linuxthreads 2.1.3 and 2.2 by
-       commit 2e4581e4fba917f1779cd0a010a45698586c190a
-       * manager.c (pthread_exited): Correctly report event as TD_REAP
-       instead of TD_DEATH.  Fix comments.
-     where event reporting facility is broken for TD_DEATH events,
-     so don't enable it if we have glibc but a lower version.  */
-  if (!inferior_has_bug ("__linuxthreads_version", 2, 2))
-    td_event_addset (&events, TD_DEATH);
-
-  err = info->td_ta_set_event_p (info->thread_agent, &events);
-  if (err != TD_OK)
-    {
-      warning (_("Unable to set global thread event mask: %s"),
-	       thread_db_err_str (err));
-      return;
-    }
-
-  /* Delete previous thread event breakpoints, if any.  */
-  remove_thread_event_breakpoints ();
-  info->td_create_bp_addr = 0;
-  info->td_death_bp_addr = 0;
-
-  /* Set up the thread creation event.  */
-  err = enable_thread_event (TD_CREATE, &info->td_create_bp_addr);
-  if (err != TD_OK)
-    {
-      warning (_("Unable to get location for thread creation breakpoint: %s"),
-	       thread_db_err_str (err));
-      return;
-    }
-
-  /* Set up the thread death event.  */
-  err = enable_thread_event (TD_DEATH, &info->td_death_bp_addr);
-  if (err != TD_OK)
-    {
-      warning (_("Unable to get location for thread death breakpoint: %s"),
-	       thread_db_err_str (err));
-      return;
-    }
-}
-
 /* Similar as thread_db_find_new_threads_1, but try to silently ignore errors
    if appropriate.
 
@@ -716,11 +568,6 @@ try_thread_db_load_1 (struct thread_db_info *info)
   CHK (TDB_VERBOSE_DLSYM (info, td_thr_get_info));
 
   /* These are not essential.  */
-  TDB_DLSYM (info, td_ta_event_addr);
-  TDB_DLSYM (info, td_ta_set_event);
-  TDB_DLSYM (info, td_ta_clear_event);
-  TDB_DLSYM (info, td_ta_event_getmsg);
-  TDB_DLSYM (info, td_thr_event_enable);
   TDB_DLSYM (info, td_thr_tls_get_addr);
   TDB_DLSYM (info, td_thr_tlsbase);
 
@@ -784,10 +631,6 @@ try_thread_db_load_1 (struct thread_db_info *info)
   if (thread_db_list->next == NULL)
     push_target (&thread_db_ops);
 
-  /* Enable event reporting, but not when debugging a core file.  */
-  if (target_has_execution && thread_db_use_events ())
-    enable_thread_event_reporting ();
-
   return 1;
 }
 
@@ -1096,23 +939,6 @@ thread_db_load (void)
 }
 
 static void
-disable_thread_event_reporting (struct thread_db_info *info)
-{
-  if (info->td_ta_clear_event_p != NULL)
-    {
-      td_thr_events_t events;
-
-      /* Set the process wide mask saying we aren't interested in any
-	 events anymore.  */
-      td_event_fillset (&events);
-      info->td_ta_clear_event_p (info->thread_agent, &events);
-    }
-
-  info->td_create_bp_addr = 0;
-  info->td_death_bp_addr = 0;
-}
-
-static void
 check_thread_signals (void)
 {
   if (!thread_signals)
@@ -1219,75 +1045,6 @@ update_thread_state (struct private_thread_info *priv,
 		 || ti_p->ti_state == TD_THR_ZOMBIE);
 }
 
-/* Attach to a new thread.  This function is called when we receive a
-   TD_CREATE event or when we iterate over all threads and find one
-   that wasn't already in our list.  Returns true on success.  */
-
-static int
-attach_thread (ptid_t ptid, const td_thrhandle_t *th_p,
-	       const td_thrinfo_t *ti_p)
-{
-  struct thread_info *tp;
-  struct thread_db_info *info;
-
-  /* If we're being called after a TD_CREATE event, we may already
-     know about this thread.  There are two ways this can happen.  We
-     may have iterated over all threads between the thread creation
-     and the TD_CREATE event, for instance when the user has issued
-     the `info threads' command before the SIGTRAP for hitting the
-     thread creation breakpoint was reported.  Alternatively, the
-     thread may have exited and a new one been created with the same
-     thread ID.  In the first case we don't need to do anything; in
-     the second case we should discard information about the dead
-     thread and attach to the new one.  */
-  tp = find_thread_ptid (ptid);
-  if (tp != NULL)
-    {
-      /* If tp->priv is NULL, then GDB is already attached to this
-	 thread, but we do not know anything about it.  We can learn
-	 about it here.  This can only happen if we have some other
-	 way besides libthread_db to notice new threads (i.e.
-	 PTRACE_EVENT_CLONE); assume the same mechanism notices thread
-	 exit, so this can not be a stale thread recreated with the
-	 same ID.  */
-      if (tp->priv != NULL)
-	{
-	  if (!tp->priv->dying)
-	    return 0;
-
-	  delete_thread (ptid);
-	  tp = NULL;
-	}
-    }
-
-  /* Under GNU/Linux, we have to attach to each and every thread.  */
-  if (target_has_execution
-      && tp == NULL)
-    {
-      int res;
-
-      res = lin_lwp_attach_lwp (ptid_build (ptid_get_pid (ptid),
-					    ti_p->ti_lid, 0));
-      if (res < 0)
-	{
-	  /* Error, stop iterating.  */
-	  return 0;
-	}
-      else if (res > 0)
-	{
-	  /* Pretend this thread doesn't exist yet, and keep
-	     iterating.  */
-	  return 1;
-	}
-
-      /* Otherwise, we sucessfully attached to the thread.  */
-    }
-
-  info = get_thread_db_info (ptid_get_pid (ptid));
-  record_thread (info, tp, ptid, th_p, ti_p);
-  return 1;
-}
-
 /* Record a new thread in GDB's thread list.  Creates the thread's
    private info.  If TP is NULL or TP is marked as having exited,
    creates a new thread.  Otherwise, uses TP.  */
@@ -1323,16 +1080,6 @@ record_thread (struct thread_db_info *info,
   else
     tp->priv = priv;
 
-  /* Enable thread event reporting for this thread, except when
-     debugging a core file.  */
-  if (target_has_execution && thread_db_use_events () && new_thread)
-    {
-      err = info->td_thr_event_enable_p (th_p, 1);
-      if (err != TD_OK)
-	error (_("Cannot enable thread event reporting for %s: %s"),
-	       target_pid_to_str (ptid), thread_db_err_str (err));
-    }
-
   if (target_has_execution)
     check_thread_signals ();
 
@@ -1340,24 +1087,6 @@ record_thread (struct thread_db_info *info,
 }
 
 static void
-detach_thread (ptid_t ptid)
-{
-  struct thread_info *thread_info;
-
-  /* Don't delete the thread now, because it still reports as active
-     until it has executed a few instructions after the event
-     breakpoint - if we deleted it now, "info threads" would cause us
-     to re-attach to it.  Just mark it as having had a TD_DEATH
-     event.  This means that we won't delete it from our thread list
-     until we notice that it's dead (via prune_threads), or until
-     something re-uses its thread ID.  We'll report the thread exit
-     when the underlying LWP dies.  */
-  thread_info = find_thread_ptid (ptid);
-  gdb_assert (thread_info != NULL && thread_info->priv != NULL);
-  thread_info->priv->dying = 1;
-}
-
-static void
 thread_db_detach (struct target_ops *ops, const char *args, int from_tty)
 {
   struct target_ops *target_beneath = find_target_beneath (ops);
@@ -1366,21 +1095,7 @@ thread_db_detach (struct target_ops *ops, const char *args, int from_tty)
   info = get_thread_db_info (ptid_get_pid (inferior_ptid));
 
   if (info)
-    {
-      if (target_has_execution && thread_db_use_events ())
-	{
-	  disable_thread_event_reporting (info);
-
-	  /* Delete the old thread event breakpoints.  Note that
-	     unlike when mourning, we can remove them here because
-	     there's still a live inferior to poke at.  In any case,
-	     GDB will not try to insert anything in the inferior when
-	     removing a breakpoint.  */
-	  remove_thread_event_breakpoints ();
-	}
-
-      delete_thread_db_info (ptid_get_pid (inferior_ptid));
-    }
+    delete_thread_db_info (ptid_get_pid (inferior_ptid));
 
   target_beneath->to_detach (target_beneath, args, from_tty);
 
@@ -1392,101 +1107,6 @@ thread_db_detach (struct target_ops *ops, const char *args, int from_tty)
     unpush_target (&thread_db_ops);
 }
 
-/* Check if PID is currently stopped at the location of a thread event
-   breakpoint location.  If it is, read the event message and act upon
-   the event.  */
-
-static void
-check_event (ptid_t ptid)
-{
-  struct regcache *regcache = get_thread_regcache (ptid);
-  struct gdbarch *gdbarch = get_regcache_arch (regcache);
-  td_event_msg_t msg;
-  td_thrinfo_t ti;
-  td_err_e err;
-  CORE_ADDR stop_pc;
-  int loop = 0;
-  struct thread_db_info *info;
-
-  info = get_thread_db_info (ptid_get_pid (ptid));
-
-  /* Bail out early if we're not at a thread event breakpoint.  */
-  stop_pc = regcache_read_pc (regcache);
-  if (!target_supports_stopped_by_sw_breakpoint ())
-    stop_pc -= gdbarch_decr_pc_after_break (gdbarch);
-
-  if (stop_pc != info->td_create_bp_addr
-      && stop_pc != info->td_death_bp_addr)
-    return;
-
-  /* Access an lwp we know is stopped.  */
-  info->proc_handle.ptid = ptid;
-
-  /* If we have only looked at the first thread before libpthread was
-     initialized, we may not know its thread ID yet.  Make sure we do
-     before we add another thread to the list.  */
-  if (!have_threads (ptid))
-    thread_db_find_new_threads_1 (ptid);
-
-  /* If we are at a create breakpoint, we do not know what new lwp
-     was created and cannot specifically locate the event message for it.
-     We have to call td_ta_event_getmsg() to get
-     the latest message.  Since we have no way of correlating whether
-     the event message we get back corresponds to our breakpoint, we must
-     loop and read all event messages, processing them appropriately.
-     This guarantees we will process the correct message before continuing
-     from the breakpoint.
-
-     Currently, death events are not enabled.  If they are enabled,
-     the death event can use the td_thr_event_getmsg() interface to
-     get the message specifically for that lwp and avoid looping
-     below.  */
-
-  loop = 1;
-
-  do
-    {
-      err = info->td_ta_event_getmsg_p (info->thread_agent, &msg);
-      if (err != TD_OK)
-	{
-	  if (err == TD_NOMSG)
-	    return;
-
-	  error (_("Cannot get thread event message: %s"),
-		 thread_db_err_str (err));
-	}
-
-      err = info->td_thr_get_info_p (msg.th_p, &ti);
-      if (err != TD_OK)
-	error (_("Cannot get thread info: %s"), thread_db_err_str (err));
-
-      ptid = ptid_build (ptid_get_pid (ptid), ti.ti_lid, 0);
-
-      switch (msg.event)
-	{
-	case TD_CREATE:
-	  /* Call attach_thread whether or not we already know about a
-	     thread with this thread ID.  */
-	  attach_thread (ptid, msg.th_p, &ti);
-
-	  break;
-
-	case TD_DEATH:
-
-	  if (!in_thread_list (ptid))
-	    error (_("Spurious thread death event."));
-
-	  detach_thread (ptid);
-
-	  break;
-
-	default:
-	  error (_("Spurious thread event."));
-	}
-    }
-  while (loop);
-}
-
 static ptid_t
 thread_db_wait (struct target_ops *ops,
 		ptid_t ptid, struct target_waitstatus *ourstatus,
@@ -1518,17 +1138,9 @@ thread_db_wait (struct target_ops *ops,
       if (!thread_db_list)
  	unpush_target (&thread_db_ops);
 
-      /* Thread event breakpoints are deleted by
-	 update_breakpoints_after_exec.  */
-
       return ptid;
     }
 
-  if (ourstatus->kind == TARGET_WAITKIND_STOPPED
-      && ourstatus->value.sig == GDB_SIGNAL_TRAP)
-    /* Check for a thread event.  */
-    check_event (ptid);
-
   /* Fill in the thread's user-level thread id and status.  */
   thread_from_lwp (ptid);
 
@@ -1544,10 +1156,6 @@ thread_db_mourn_inferior (struct target_ops *ops)
 
   target_beneath->to_mourn_inferior (target_beneath);
 
-  /* Delete the old thread event breakpoints.  Do this after mourning
-     the inferior, so that we don't try to uninsert them.  */
-  remove_thread_event_breakpoints ();
-
   /* Detach thread_db target ops.  */
   if (!thread_db_list)
     unpush_target (ops);
@@ -1592,24 +1200,10 @@ find_new_threads_callback (const td_thrhandle_t *th_p, void *data)
 
   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.  */
-
       /* In that case, we're not stopped in a fork syscall and don't
 	 need this glibc bug workaround.  */
       info->need_stale_parent_threads_check = 0;
 
-      if (target_has_execution && thread_db_use_events ())
-	{
-	  err = info->td_thr_event_enable_p (th_p, 1);
-	  if (err != TD_OK)
-	    error (_("Cannot enable thread event reporting for LWP %d: %s"),
-		   (int) ti.ti_lid, thread_db_err_str (err));
-	}
-
       return 0;
     }
 
@@ -1627,24 +1221,7 @@ find_new_threads_callback (const td_thrhandle_t *th_p, void *data)
   ptid = ptid_build (info->pid, ti.ti_lid, 0);
   tp = find_thread_ptid (ptid);
   if (tp == NULL || tp->priv == NULL)
-    {
-      if (attach_thread (ptid, th_p, &ti))
-	cb_data->new_threads += 1;
-      else
-	/* Problem attaching this thread; perhaps it exited before we
-	   could attach it?
-	   This could mean that the thread list inside glibc itself is in
-	   inconsistent state, and libthread_db could go on looping forever
-	   (observed with glibc-2.3.6).  To prevent that, terminate
-	   iteration: thread_db_find_new_threads_2 will retry.  */
-	return 1;
-    }
-  else if (target_has_execution && !thread_db_use_events ())
-    {
-      /* Need to update this if not using the libthread_db events
-	 (particularly, the TD_DEATH event).  */
-      update_thread_state (tp->priv, &ti);
-    }
+    thread_from_lwp (ptid);
 
   return 0;
 }
@@ -1663,7 +1240,7 @@ find_new_threads_once (struct thread_db_info *info, int iteration,
   data.new_threads = 0;
 
   /* See comment in thread_db_update_thread_list.  */
-  gdb_assert (!target_has_execution || thread_db_use_events ());
+  gdb_assert (!target_has_execution);
 
   TRY
     {
@@ -1789,12 +1366,11 @@ thread_db_update_thread_list (struct target_ops *ops)
      it.  In the latter case, it's possible that a thread exits just
      at the exact time that causes GDB to get stuck in an infinite
      loop.  To avoid pausing all threads whenever the core wants to
-     refresh the thread list, if the kernel supports clone events
-     (meaning we're always already attached to all LWPs), we use
-     thread_from_lwp immediately when we see an LWP stop.  That uses
-     thread_db entry points that do not walk libpthread's thread list,
-     so should be safe, as well as more efficient.  */
-  if (target_has_execution && !thread_db_use_events ())
+     refresh the thread list, use thread_from_lwp immediately when we
+     see an LWP stop.  That uses  thread_db entry points that do not
+     walk libpthread's thread list, so should be safe, as well as
+     more efficient.  */
+  if (target_has_execution)
     ops->beneath->to_update_thread_list (ops->beneath);
   else
     thread_db_update_thread_list_td_ta_thr_iter (ops);
-- 
2.6.3


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