aboutsummaryrefslogtreecommitdiff
path: root/gdb/gdbserver/thread-db.c
blob: 372cdbcad61c8a1071da3c13ceaf8e241a667984 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
/* Thread management interface, for the remote server for GDB.
   Copyright (C) 2002, 2004, 2005, 2006, 2007, 2008, 2009, 2010
   Free Software Foundation, Inc.

   Contributed by MontaVista Software.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "server.h"

#include "linux-low.h"

extern int debug_threads;

static int thread_db_use_events;

#include "gdb_proc_service.h"
#include "../gdb_thread_db.h"

#ifndef USE_LIBTHREAD_DB_DIRECTLY
#include <dlfcn.h>
#endif

#include <stdint.h>
#include <limits.h>
#include <ctype.h>

struct thread_db
{
  /* Structure that identifies the child process for the
     <proc_service.h> interface.  */
  struct ps_prochandle proc_handle;

  /* Connection to the libthread_db library.  */
  td_thragent_t *thread_agent;

  /* If this flag has been set, we've already asked GDB for all
     symbols we might need; assume symbol cache misses are
     failures.  */
  int all_symbols_looked_up;

#ifndef USE_LIBTHREAD_DB_DIRECTLY
  /* Handle of the libthread_db from dlopen.  */
  void *handle;
#endif

  /* 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.  Note that if the
     running kernel supports tracing clones, then we don't need to use
     (and in fact don't use) this magic thread event breakpoint to
     learn about threads.  */
  struct breakpoint *td_create_bp;

  /* Addresses of libthread_db functions.  */
  td_err_e (*td_ta_new_p) (struct ps_prochandle * ps, td_thragent_t **ta);
  td_err_e (*td_ta_event_getmsg_p) (const td_thragent_t *ta,
				    td_event_msg_t *msg);
  td_err_e (*td_ta_set_event_p) (const td_thragent_t *ta,
				 td_thr_events_t *event);
  td_err_e (*td_ta_event_addr_p) (const td_thragent_t *ta,
				  td_event_e event, td_notify_t *ptr);
  td_err_e (*td_ta_map_lwp2thr_p) (const td_thragent_t *ta, lwpid_t lwpid,
				   td_thrhandle_t *th);
  td_err_e (*td_thr_get_info_p) (const td_thrhandle_t *th,
				 td_thrinfo_t *infop);
  td_err_e (*td_thr_event_enable_p) (const td_thrhandle_t *th, int event);
  td_err_e (*td_ta_thr_iter_p) (const td_thragent_t *ta,
				td_thr_iter_f *callback, void *cbdata_p,
				td_thr_state_e state, int ti_pri,
				sigset_t *ti_sigmask_p,
				unsigned int ti_user_flags);
  td_err_e (*td_thr_tls_get_addr_p) (const td_thrhandle_t *th,
				     psaddr_t map_address,
				     size_t offset, psaddr_t *address);
  const char ** (*td_symbol_list_p) (void);
};

static char *libthread_db_search_path;

static int find_one_thread (ptid_t);
static int find_new_threads_callback (const td_thrhandle_t *th_p, void *data);

static const char *
thread_db_err_str (td_err_e err)
{
  static char buf[64];

  switch (err)
    {
    case TD_OK:
      return "generic 'call succeeded'";
    case TD_ERR:
      return "generic error";
    case TD_NOTHR:
      return "no thread to satisfy query";
    case TD_NOSV:
      return "no sync handle to satisfy query";
    case TD_NOLWP:
      return "no LWP to satisfy query";
    case TD_BADPH:
      return "invalid process handle";
    case TD_BADTH:
      return "invalid thread handle";
    case TD_BADSH:
      return "invalid synchronization handle";
    case TD_BADTA:
      return "invalid thread agent";
    case TD_BADKEY:
      return "invalid key";
    case TD_NOMSG:
      return "no event message for getmsg";
    case TD_NOFPREGS:
      return "FPU register set not available";
    case TD_NOLIBTHREAD:
      return "application not linked with libthread";
    case TD_NOEVENT:
      return "requested event is not supported";
    case TD_NOCAPAB:
      return "capability not available";
    case TD_DBERR:
      return "debugger service failed";
    case TD_NOAPLIC:
      return "operation not applicable to";
    case TD_NOTSD:
      return "no thread-specific data for this thread";
    case TD_MALLOC:
      return "malloc failed";
    case TD_PARTIALREG:
      return "only part of register set was written/read";
    case TD_NOXREGS:
      return "X register set not available for this thread";
#ifdef HAVE_TD_VERSION
    case TD_VERSION:
      return "version mismatch between libthread_db and libpthread";
#endif
    default:
      xsnprintf (buf, sizeof (buf), "unknown thread_db error '%d'", err);
      return buf;
    }
}

#if 0
static char *
thread_db_state_str (td_thr_state_e state)
{
  static char buf[64];

  switch (state)
    {
    case TD_THR_STOPPED:
      return "stopped by debugger";
    case TD_THR_RUN:
      return "runnable";
    case TD_THR_ACTIVE:
      return "active";
    case TD_THR_ZOMBIE:
      return "zombie";
    case TD_THR_SLEEP:
      return "sleeping";
    case TD_THR_STOPPED_ASLEEP:
      return "stopped by debugger AND blocked";
    default:
      xsnprintf (buf, sizeof (buf), "unknown thread_db state %d", state);
      return buf;
    }
}
#endif

static int
thread_db_create_event (CORE_ADDR where)
{
  td_event_msg_t msg;
  td_err_e err;
  struct lwp_info *lwp;
  struct thread_db *thread_db = current_process ()->private->thread_db;

  if (thread_db->td_ta_event_getmsg_p == NULL)
    fatal ("unexpected thread_db->td_ta_event_getmsg_p == NULL");

  if (debug_threads)
    fprintf (stderr, "Thread creation event.\n");

  /* FIXME: This assumes we don't get another event.
     In the LinuxThreads implementation, this is safe,
     because all events come from the manager thread
     (except for its own creation, of course).  */
  err = thread_db->td_ta_event_getmsg_p (thread_db->thread_agent, &msg);
  if (err != TD_OK)
    fprintf (stderr, "thread getmsg err: %s\n",
	     thread_db_err_str (err));

  /* If we do not know about the main thread yet, this would be a good time to
     find it.  We need to do this to pick up the main thread before any newly
     created threads.  */
  lwp = get_thread_lwp (current_inferior);
  if (lwp->thread_known == 0)
    find_one_thread (lwp->head.id);

  /* msg.event == TD_EVENT_CREATE */

  find_new_threads_callback (msg.th_p, NULL);

  return 0;
}

static int
thread_db_enable_reporting (void)
{
  td_thr_events_t events;
  td_notify_t notify;
  td_err_e err;
  struct thread_db *thread_db = current_process ()->private->thread_db;

  if (thread_db->td_ta_set_event_p == NULL
      || thread_db->td_ta_event_addr_p == NULL
      || thread_db->td_ta_event_getmsg_p == NULL)
    /* This libthread_db is missing required support.  */
    return 0;

  /* Set the process wide mask saying which events we're interested in.  */
  td_event_emptyset (&events);
  td_event_addset (&events, TD_CREATE);

  err = thread_db->td_ta_set_event_p (thread_db->thread_agent, &events);
  if (err != TD_OK)
    {
      warning ("Unable to set global thread event mask: %s",
	       thread_db_err_str (err));
      return 0;
    }

  /* Get address for thread creation breakpoint.  */
  err = thread_db->td_ta_event_addr_p (thread_db->thread_agent, TD_CREATE,
				       &notify);
  if (err != TD_OK)
    {
      warning ("Unable to get location for thread creation breakpoint: %s",
	       thread_db_err_str (err));
      return 0;
    }
  thread_db->td_create_bp
    = set_breakpoint_at ((CORE_ADDR) (unsigned long) notify.u.bptaddr,
			 thread_db_create_event);

  return 1;
}

static int
find_one_thread (ptid_t ptid)
{
  td_thrhandle_t th;
  td_thrinfo_t ti;
  td_err_e err;
  struct thread_info *inferior;
  struct lwp_info *lwp;
  struct thread_db *thread_db = current_process ()->private->thread_db;
  int lwpid = ptid_get_lwp (ptid);

  inferior = (struct thread_info *) find_inferior_id (&all_threads, ptid);
  lwp = get_thread_lwp (inferior);
  if (lwp->thread_known)
    return 1;

  /* Get information about this thread.  */
  err = thread_db->td_ta_map_lwp2thr_p (thread_db->thread_agent, lwpid, &th);
  if (err != TD_OK)
    error ("Cannot get thread handle for LWP %d: %s",
	   lwpid, thread_db_err_str (err));

  err = thread_db->td_thr_get_info_p (&th, &ti);
  if (err != TD_OK)
    error ("Cannot get thread info for LWP %d: %s",
	   lwpid, thread_db_err_str (err));

  if (debug_threads)
    fprintf (stderr, "Found thread %ld (LWP %d)\n",
	     ti.ti_tid, ti.ti_lid);

  if (lwpid != ti.ti_lid)
    {
      warning ("PID mismatch!  Expected %ld, got %ld",
	       (long) lwpid, (long) ti.ti_lid);
      return 0;
    }

  if (thread_db_use_events)
    {
      err = thread_db->td_thr_event_enable_p (&th, 1);
      if (err != TD_OK)
	error ("Cannot enable thread event reporting for %d: %s",
	       ti.ti_lid, thread_db_err_str (err));
    }

  /* If the new thread ID is zero, a final thread ID will be available
     later.  Do not enable thread debugging yet.  */
  if (ti.ti_tid == 0)
    return 0;

  lwp->thread_known = 1;
  lwp->th = th;

  return 1;
}

/* Attach a thread.  Return true on success.  */

static int
attach_thread (const td_thrhandle_t *th_p, td_thrinfo_t *ti_p)
{
  struct lwp_info *lwp;

  if (debug_threads)
    fprintf (stderr, "Attaching to thread %ld (LWP %d)\n",
	     ti_p->ti_tid, ti_p->ti_lid);
  linux_attach_lwp (ti_p->ti_lid);
  lwp = find_lwp_pid (pid_to_ptid (ti_p->ti_lid));
  if (lwp == NULL)
    {
      warning ("Could not attach to thread %ld (LWP %d)\n",
	       ti_p->ti_tid, ti_p->ti_lid);
      return 0;
    }

  lwp->thread_known = 1;
  lwp->th = *th_p;

  if (thread_db_use_events)
    {
      td_err_e err;
      struct thread_db *thread_db = current_process ()->private->thread_db;

      err = thread_db->td_thr_event_enable_p (th_p, 1);
      if (err != TD_OK)
	error ("Cannot enable thread event reporting for %d: %s",
	       ti_p->ti_lid, thread_db_err_str (err));
    }

  return 1;
}

/* Attach thread if we haven't seen it yet.
   Increment *COUNTER if we have attached a new thread.
   Return false on failure.  */

static int
maybe_attach_thread (const td_thrhandle_t *th_p, td_thrinfo_t *ti_p,
		     int *counter)
{
  struct lwp_info *lwp;

  lwp = find_lwp_pid (pid_to_ptid (ti_p->ti_lid));
  if (lwp != NULL)
    return 1;

  if (!attach_thread (th_p, ti_p))
    return 0;

  if (counter != NULL)
    *counter += 1;

  return 1;
}

static int
find_new_threads_callback (const td_thrhandle_t *th_p, void *data)
{
  td_thrinfo_t ti;
  td_err_e err;
  struct thread_db *thread_db = current_process ()->private->thread_db;

  err = thread_db->td_thr_get_info_p (th_p, &ti);
  if (err != TD_OK)
    error ("Cannot get thread info: %s", thread_db_err_str (err));

  /* Check for zombies.  */
  if (ti.ti_state == TD_THR_UNKNOWN || ti.ti_state == TD_THR_ZOMBIE)
    return 0;

  if (!maybe_attach_thread (th_p, &ti, (int *) data))
    {
      /* Terminate iteration early: we might be looking at stale data in
	 the inferior.  The thread_db_find_new_threads will retry.  */
      return 1;
    }

  return 0;
}

static void
thread_db_find_new_threads (void)
{
  td_err_e err;
  ptid_t ptid = ((struct inferior_list_entry *) current_inferior)->id;
  struct thread_db *thread_db = current_process ()->private->thread_db;
  int loop, iteration;

  /* This function is only called when we first initialize thread_db.
     First locate the initial thread.  If it is not ready for
     debugging yet, then stop.  */
  if (find_one_thread (ptid) == 0)
    return;

  /* Require 4 successive iterations which do not find any new threads.
     The 4 is a heuristic: there is an inherent race here, and I have
     seen that 2 iterations in a row are not always sufficient to
     "capture" all threads.  */
  for (loop = 0, iteration = 0; loop < 4; ++loop, ++iteration)
    {
      int new_thread_count = 0;

      /* Iterate over all user-space threads to discover new threads.  */
      err = thread_db->td_ta_thr_iter_p (thread_db->thread_agent,
					 find_new_threads_callback,
					 &new_thread_count,
					 TD_THR_ANY_STATE, TD_THR_LOWEST_PRIORITY,
					 TD_SIGNO_MASK, TD_THR_ANY_USER_FLAGS);
      if (debug_threads)
	fprintf (stderr, "Found %d threads in iteration %d.\n",
		 new_thread_count, iteration);

      if (new_thread_count != 0)
	{
	  /* Found new threads.  Restart iteration from beginning.  */
	  loop = -1;
	}
    }
  if (err != TD_OK)
    error ("Cannot find new threads: %s", thread_db_err_str (err));
}

/* Cache all future symbols that thread_db might request.  We can not
   request symbols at arbitrary states in the remote protocol, only
   when the client tells us that new symbols are available.  So when
   we load the thread library, make sure to check the entire list.  */

static void
thread_db_look_up_symbols (void)
{
  struct thread_db *thread_db = current_process ()->private->thread_db;
  const char **sym_list;
  CORE_ADDR unused;

  for (sym_list = thread_db->td_symbol_list_p (); *sym_list; sym_list++)
    look_up_one_symbol (*sym_list, &unused, 1);

  /* We're not interested in any other libraries loaded after this
     point, only in symbols in libpthread.so.  */
  thread_db->all_symbols_looked_up = 1;
}

int
thread_db_look_up_one_symbol (const char *name, CORE_ADDR *addrp)
{
  struct thread_db *thread_db = current_process ()->private->thread_db;
  int may_ask_gdb = !thread_db->all_symbols_looked_up;

  /* If we've passed the call to thread_db_look_up_symbols, then
     anything not in the cache must not exist; we're not interested
     in any libraries loaded after that point, only in symbols in
     libpthread.so.  It might not be an appropriate time to look
     up a symbol, e.g. while we're trying to fetch registers.  */
  return look_up_one_symbol (name, addrp, may_ask_gdb);
}

int
thread_db_get_tls_address (struct thread_info *thread, CORE_ADDR offset,
			   CORE_ADDR load_module, CORE_ADDR *address)
{
  psaddr_t addr;
  td_err_e err;
  struct lwp_info *lwp;
  struct thread_info *saved_inferior;
  struct process_info *proc;
  struct thread_db *thread_db;

  proc = get_thread_process (thread);
  thread_db = proc->private->thread_db;

  /* If the thread layer is not (yet) initialized, fail.  */
  if (!thread_db->all_symbols_looked_up)
    return TD_ERR;

  if (thread_db->td_thr_tls_get_addr_p == NULL)
    return -1;

  lwp = get_thread_lwp (thread);
  if (!lwp->thread_known)
    find_one_thread (lwp->head.id);
  if (!lwp->thread_known)
    return TD_NOTHR;

  saved_inferior = current_inferior;
  current_inferior = thread;
  /* Note the cast through uintptr_t: this interface only works if
     a target address fits in a psaddr_t, which is a host pointer.
     So a 32-bit debugger can not access 64-bit TLS through this.  */
  err = thread_db->td_thr_tls_get_addr_p (&lwp->th,
					  (psaddr_t) (uintptr_t) load_module,
					  offset, &addr);
  current_inferior = saved_inferior;
  if (err == TD_OK)
    {
      *address = (CORE_ADDR) (uintptr_t) addr;
      return 0;
    }
  else
    return err;
}

#ifdef USE_LIBTHREAD_DB_DIRECTLY

static int
thread_db_load_search (void)
{
  td_err_e err;
  struct thread_db *tdb;
  struct process_info *proc = current_process ();

  if (proc->private->thread_db != NULL)
    fatal ("unexpected: proc->private->thread_db != NULL");

  tdb = xcalloc (1, sizeof (*tdb));
  proc->private->thread_db = tdb;

  tdb->td_ta_new_p = &td_ta_new;

  /* Attempt to open a connection to the thread library.  */
  err = tdb->td_ta_new_p (&tdb->proc_handle, &tdb->thread_agent);
  if (err != TD_OK)
    {
      if (debug_threads)
	fprintf (stderr, "td_ta_new(): %s\n", thread_db_err_str (err));
      free (tdb);
      proc->private->thread_db = NULL;
      return 0;
    }

  tdb->td_ta_map_lwp2thr_p = &td_ta_map_lwp2thr;
  tdb->td_thr_get_info_p = &td_thr_get_info;
  tdb->td_ta_thr_iter_p = &td_ta_thr_iter;
  tdb->td_symbol_list_p = &td_symbol_list;

  /* This is required only when thread_db_use_events is on.  */
  tdb->td_thr_event_enable_p = &td_thr_event_enable;

  /* These are not essential.  */
  tdb->td_ta_event_addr_p = &td_ta_event_addr;
  tdb->td_ta_set_event_p = &td_ta_set_event;
  tdb->td_ta_event_getmsg_p = &td_ta_event_getmsg;
  tdb->td_thr_tls_get_addr_p = &td_thr_tls_get_addr;

  return 1;
}

#else

static int
try_thread_db_load_1 (void *handle)
{
  td_err_e err;
  struct thread_db *tdb;
  struct process_info *proc = current_process ();

  if (proc->private->thread_db != NULL)
    fatal ("unexpected: proc->private->thread_db != NULL");

  tdb = xcalloc (1, sizeof (*tdb));
  proc->private->thread_db = tdb;

  tdb->handle = handle;

  /* Initialize pointers to the dynamic library functions we will use.
     Essential functions first.  */

#define CHK(required, a)					\
  do								\
    {								\
      if ((a) == NULL)						\
	{							\
	  if (debug_threads)					\
	    fprintf (stderr, "dlsym: %s\n", dlerror ());	\
	  if (required)						\
	    {							\
	      free (tdb);					\
	      proc->private->thread_db = NULL;			\
	      return 0;						\
	    }							\
	}							\
    }								\
  while (0)

  CHK (1, tdb->td_ta_new_p = dlsym (handle, "td_ta_new"));

  /* Attempt to open a connection to the thread library.  */
  err = tdb->td_ta_new_p (&tdb->proc_handle, &tdb->thread_agent);
  if (err != TD_OK)
    {
      if (debug_threads)
	fprintf (stderr, "td_ta_new(): %s\n", thread_db_err_str (err));
      free (tdb);
      proc->private->thread_db = NULL;
      return 0;
    }

  CHK (1, tdb->td_ta_map_lwp2thr_p = dlsym (handle, "td_ta_map_lwp2thr"));
  CHK (1, tdb->td_thr_get_info_p = dlsym (handle, "td_thr_get_info"));
  CHK (1, tdb->td_ta_thr_iter_p = dlsym (handle, "td_ta_thr_iter"));
  CHK (1, tdb->td_symbol_list_p = dlsym (handle, "td_symbol_list"));

  /* This is required only when thread_db_use_events is on.  */
  CHK (thread_db_use_events,
       tdb->td_thr_event_enable_p = dlsym (handle, "td_thr_event_enable"));

  /* These are not essential.  */
  CHK (0, tdb->td_ta_event_addr_p = dlsym (handle, "td_ta_event_addr"));
  CHK (0, tdb->td_ta_set_event_p = dlsym (handle, "td_ta_set_event"));
  CHK (0, tdb->td_ta_event_getmsg_p = dlsym (handle, "td_ta_event_getmsg"));
  CHK (0, tdb->td_thr_tls_get_addr_p = dlsym (handle, "td_thr_tls_get_addr"));

#undef CHK

  return 1;
}

#ifdef HAVE_DLADDR

/* Lookup a library in which given symbol resides.
   Note: this is looking in the GDBSERVER process, not in the inferior.
   Returns library name, or NULL.  */

static const char *
dladdr_to_soname (const void *addr)
{
  Dl_info info;

  if (dladdr (addr, &info) != 0)
    return info.dli_fname;
  return NULL;
}

#endif

static int
try_thread_db_load (const char *library)
{
  void *handle;

  if (debug_threads)
    fprintf (stderr, "Trying host libthread_db library: %s.\n",
	     library);
  handle = dlopen (library, RTLD_NOW);
  if (handle == NULL)
    {
      if (debug_threads)
	fprintf (stderr, "dlopen failed: %s.\n", dlerror ());
      return 0;
    }

#ifdef HAVE_DLADDR
  if (debug_threads && strchr (library, '/') == NULL)
    {
      void *td_init;

      td_init = dlsym (handle, "td_init");
      if (td_init != NULL)
	{
	  const char *const libpath = dladdr_to_soname (td_init);

	  if (libpath != NULL)
	    fprintf (stderr, "Host %s resolved to: %s.\n",
		     library, libpath);
	}
    }
#endif

  if (try_thread_db_load_1 (handle))
    return 1;

  /* This library "refused" to work on current inferior.  */
  dlclose (handle);
  return 0;
}

static int
thread_db_load_search (void)
{
  char path[PATH_MAX];
  const char *search_path;
  int rc = 0;

  if (libthread_db_search_path == NULL)
    libthread_db_search_path = xstrdup (LIBTHREAD_DB_SEARCH_PATH);

  search_path = libthread_db_search_path;
  while (*search_path)
    {
      const char *end = strchr (search_path, ':');
      if (end)
	{
	  size_t len = end - search_path;
	  if (len + 1 + strlen (LIBTHREAD_DB_SO) + 1 > sizeof (path))
	    {
	      char *cp = xmalloc (len + 1);
	      memcpy (cp, search_path, len);
	      cp[len] = '\0';
	      warning ("libthread_db_search_path component too long, "
		       "ignored: %s.", cp);
	      free (cp);
	      search_path += len + 1;
	      continue;
	    }
	  memcpy (path, search_path, len);
	  path[len] = '\0';
	  search_path += len + 1;
	}
      else
	{
	  size_t len = strlen (search_path);

	  if (len + 1 + strlen (LIBTHREAD_DB_SO) + 1 > sizeof (path))
	    {
	      warning ("libthread_db_search_path component too long,"
		       " ignored: %s.", search_path);
	      break;
	    }
	  memcpy (path, search_path, len + 1);
	  search_path += len;
	}
      strcat (path, "/");
      strcat (path, LIBTHREAD_DB_SO);
      if (debug_threads)
	fprintf (stderr, "thread_db_load_search trying %s\n", path);
      if (try_thread_db_load (path))
	{
	  rc = 1;
	  break;
	}
    }
  if (rc == 0)
    rc = try_thread_db_load (LIBTHREAD_DB_SO);

  if (debug_threads)
    fprintf (stderr, "thread_db_load_search returning %d\n", rc);
  return rc;
}

#endif  /* USE_LIBTHREAD_DB_DIRECTLY */

int
thread_db_init (int use_events)
{
  struct process_info *proc = current_process ();

  /* FIXME drow/2004-10-16: This is the "overall process ID", which
     GNU/Linux calls tgid, "thread group ID".  When we support
     attaching to threads, the original thread may not be the correct
     thread.  We would have to get the process ID from /proc for NPTL.
     For LinuxThreads we could do something similar: follow the chain
     of parent processes until we find the highest one we're attached
     to, and use its tgid.

     This isn't the only place in gdbserver that assumes that the first
     process in the list is the thread group leader.  */

  thread_db_use_events = use_events;

  if (thread_db_load_search ())
    {
      if (use_events && thread_db_enable_reporting () == 0)
	{
	  /* Keep trying; maybe event reporting will work later.  */
	  thread_db_mourn (proc);
	  return 0;
	}
      thread_db_find_new_threads ();
      thread_db_look_up_symbols ();
      return 1;
    }

  return 0;
}

static int
any_thread_of (struct inferior_list_entry *entry, void *args)
{
  int *pid_p = args;

  if (ptid_get_pid (entry->id) == *pid_p)
    return 1;

  return 0;
}

static void
switch_to_process (struct process_info *proc)
{
  int pid = pid_of (proc);

  current_inferior =
    (struct thread_info *) find_inferior (&all_threads,
					  any_thread_of, &pid);
}

/* Disconnect from libthread_db and free resources.  */

static void
disable_thread_event_reporting (struct process_info *proc)
{
  struct thread_db *thread_db = proc->private->thread_db;
  if (thread_db)
    {
      td_err_e (*td_ta_clear_event_p) (const td_thragent_t *ta,
				       td_thr_events_t *event);

#ifndef USE_LIBTHREAD_DB_DIRECTLY
      td_ta_clear_event_p = dlsym (thread_db->handle, "td_ta_clear_event");
#else
      td_ta_clear_event_p = &td_ta_clear_event;
#endif

      if (td_ta_clear_event_p != NULL)
	{
	  struct thread_info *saved_inferior = current_inferior;
	  td_thr_events_t events;

	  switch_to_process (proc);

	  /* Set the process wide mask saying we aren't interested
	     in any events anymore.  */
	  td_event_fillset (&events);
	  (*td_ta_clear_event_p) (thread_db->thread_agent, &events);

	  current_inferior = saved_inferior;
	}
    }
}

static void
remove_thread_event_breakpoints (struct process_info *proc)
{
  struct thread_db *thread_db = proc->private->thread_db;

  if (thread_db->td_create_bp != NULL)
    {
      struct thread_info *saved_inferior = current_inferior;

      switch_to_process (proc);

      delete_breakpoint (thread_db->td_create_bp);
      thread_db->td_create_bp = NULL;

      current_inferior = saved_inferior;
    }
}

void
thread_db_detach (struct process_info *proc)
{
  struct thread_db *thread_db = proc->private->thread_db;

  if (thread_db)
    {
      disable_thread_event_reporting (proc);
      remove_thread_event_breakpoints (proc);
    }
}

/* Disconnect from libthread_db and free resources.  */

void
thread_db_mourn (struct process_info *proc)
{
  struct thread_db *thread_db = proc->private->thread_db;
  if (thread_db)
    {
      td_err_e (*td_ta_delete_p) (td_thragent_t *);

#ifndef USE_LIBTHREAD_DB_DIRECTLY
      td_ta_delete_p = dlsym (thread_db->handle, "td_ta_delete");
#else
      td_ta_delete_p = &td_ta_delete;
#endif

      if (td_ta_delete_p != NULL)
	(*td_ta_delete_p) (thread_db->thread_agent);

#ifndef USE_LIBTHREAD_DB_DIRECTLY
      dlclose (thread_db->handle);
#endif  /* USE_LIBTHREAD_DB_DIRECTLY  */

      free (thread_db);
      proc->private->thread_db = NULL;
    }
}

/* Handle "set libthread-db-search-path" monitor command and return 1.
   For any other command, return 0.  */

int
thread_db_handle_monitor_command (char *mon)
{
  if (strncmp (mon, "set libthread-db-search-path ", 29) == 0)
    {
      const char *cp = mon + 29;

      if (libthread_db_search_path != NULL)
	free (libthread_db_search_path);

      /* Skip leading space (if any).  */
      while (isspace (*cp))
	++cp;

      libthread_db_search_path = xstrdup (cp);

      monitor_output ("libthread-db-search-path set to `");
      monitor_output (libthread_db_search_path);
      monitor_output ("'\n");
      return 1;
    }

  /* Tell server.c to perform default processing.  */
  return 0;
}