summaryrefslogtreecommitdiff
path: root/gdb/solib-svr4.c
blob: 0c658ea5ab0ec6525dcf81ed5337f89555c263bc (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
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
/* Handle SVR4 shared libraries for GDB, the GNU Debugger.

   Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000,
   2001, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.

   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 "defs.h"

#include "elf/external.h"
#include "elf/common.h"
#include "elf/mips.h"

#include "symtab.h"
#include "bfd.h"
#include "symfile.h"
#include "objfiles.h"
#include "gdbcore.h"
#include "target.h"
#include "inferior.h"

#include "gdb_assert.h"

#include "solist.h"
#include "solib.h"
#include "solib-svr4.h"

#include "bfd-target.h"
#include "elf-bfd.h"
#include "exec.h"

static struct link_map_offsets *svr4_fetch_link_map_offsets (void);
static int svr4_have_link_map_offsets (void);

/* This hook is set to a function that provides native link map
   offsets if the code in solib-legacy.c is linked in.  */
struct link_map_offsets *(*legacy_svr4_fetch_link_map_offsets_hook) (void);

/* Link map info to include in an allocated so_list entry */

struct lm_info
  {
    /* Pointer to copy of link map from inferior.  The type is char *
       rather than void *, so that we may use byte offsets to find the
       various fields without the need for a cast.  */
    gdb_byte *lm;

    /* Amount by which addresses in the binary should be relocated to
       match the inferior.  This could most often be taken directly
       from lm, but when prelinking is involved and the prelink base
       address changes, we may need a different offset, we want to
       warn about the difference and compute it only once.  */
    CORE_ADDR l_addr;
  };

/* On SVR4 systems, a list of symbols in the dynamic linker where
   GDB can try to place a breakpoint to monitor shared library
   events.

   If none of these symbols are found, or other errors occur, then
   SVR4 systems will fall back to using a symbol as the "startup
   mapping complete" breakpoint address.  */

static char *solib_break_names[] =
{
  "r_debug_state",
  "_r_debug_state",
  "_dl_debug_state",
  "rtld_db_dlactivity",
  "_rtld_debug_state",

  NULL
};

#define BKPT_AT_SYMBOL 1

#if defined (BKPT_AT_SYMBOL)
static char *bkpt_names[] =
{
#ifdef SOLIB_BKPT_NAME
  SOLIB_BKPT_NAME,		/* Prefer configured name if it exists. */
#endif
  "_start",
  "__start",
  "main",
  NULL
};
#endif

static char *main_name_list[] =
{
  "main_$main",
  NULL
};

/* link map access functions */

static CORE_ADDR
LM_ADDR_FROM_LINK_MAP (struct so_list *so)
{
  struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();

  return extract_typed_address (so->lm_info->lm + lmo->l_addr_offset,
				builtin_type_void_data_ptr);
}

static int
HAS_LM_DYNAMIC_FROM_LINK_MAP ()
{
  struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();

  return lmo->l_ld_offset >= 0;
}

static CORE_ADDR
LM_DYNAMIC_FROM_LINK_MAP (struct so_list *so)
{
  struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();

  return extract_typed_address (so->lm_info->lm + lmo->l_ld_offset,
				builtin_type_void_data_ptr);
}

static CORE_ADDR
LM_ADDR_CHECK (struct so_list *so, bfd *abfd)
{
  if (so->lm_info->l_addr == (CORE_ADDR)-1)
    {
      struct bfd_section *dyninfo_sect;
      CORE_ADDR l_addr, l_dynaddr, dynaddr, align = 0x1000;

      l_addr = LM_ADDR_FROM_LINK_MAP (so);

      if (! abfd || ! HAS_LM_DYNAMIC_FROM_LINK_MAP ())
	goto set_addr;

      l_dynaddr = LM_DYNAMIC_FROM_LINK_MAP (so);

      dyninfo_sect = bfd_get_section_by_name (abfd, ".dynamic");
      if (dyninfo_sect == NULL)
	goto set_addr;

      dynaddr = bfd_section_vma (abfd, dyninfo_sect);

      if (dynaddr + l_addr != l_dynaddr)
	{
	  if (bfd_get_flavour (abfd) == bfd_target_elf_flavour)
	    {
	      Elf_Internal_Ehdr *ehdr = elf_tdata (abfd)->elf_header;
	      Elf_Internal_Phdr *phdr = elf_tdata (abfd)->phdr;
	      int i;

	      align = 1;

	      for (i = 0; i < ehdr->e_phnum; i++)
		if (phdr[i].p_type == PT_LOAD && phdr[i].p_align > align)
		  align = phdr[i].p_align;
	    }

	  /* Turn it into a mask.  */
	  align--;

	  /* If the changes match the alignment requirements, we
	     assume we're using a core file that was generated by the
	     same binary, just prelinked with a different base offset.
	     If it doesn't match, we may have a different binary, the
	     same binary with the dynamic table loaded at an unrelated
	     location, or anything, really.  To avoid regressions,
	     don't adjust the base offset in the latter case, although
	     odds are that, if things really changed, debugging won't
	     quite work.  */
	  if ((l_addr & align) == ((l_dynaddr - dynaddr) & align))
	    {
	      l_addr = l_dynaddr - dynaddr;

	      warning (_(".dynamic section for \"%s\" "
		     "is not at the expected address"), so->so_name);
	      warning (_("difference appears to be caused by prelink, "
			 "adjusting expectations"));
	    }
	  else
	    warning (_(".dynamic section for \"%s\" "
		       "is not at the expected address "
		       "(wrong library or version mismatch?)"), so->so_name);
	}

    set_addr:
      so->lm_info->l_addr = l_addr;
    }

  return so->lm_info->l_addr;
}

static CORE_ADDR
LM_NEXT (struct so_list *so)
{
  struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();

  return extract_typed_address (so->lm_info->lm + lmo->l_next_offset,
				builtin_type_void_data_ptr);
}

static CORE_ADDR
LM_NAME (struct so_list *so)
{
  struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();

  return extract_typed_address (so->lm_info->lm + lmo->l_name_offset,
				builtin_type_void_data_ptr);
}

static int
IGNORE_FIRST_LINK_MAP_ENTRY (struct so_list *so)
{
  struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();

  /* Assume that everything is a library if the dynamic loader was loaded
     late by a static executable.  */
  if (bfd_get_section_by_name (exec_bfd, ".dynamic") == NULL)
    return 0;

  return extract_typed_address (so->lm_info->lm + lmo->l_prev_offset,
				builtin_type_void_data_ptr) == 0;
}

static CORE_ADDR debug_base;	/* Base of dynamic linker structures */

/* Validity flag for debug_loader_offset.  */
static int debug_loader_offset_p;

/* Load address for the dynamic linker, inferred.  */
static CORE_ADDR debug_loader_offset;

/* Name of the dynamic linker, valid if debug_loader_offset_p.  */
static char *debug_loader_name;

/* Local function prototypes */

static int match_main (char *);

static CORE_ADDR bfd_lookup_symbol (bfd *, char *);

/*

   LOCAL FUNCTION

   bfd_lookup_symbol -- lookup the value for a specific symbol

   SYNOPSIS

   CORE_ADDR bfd_lookup_symbol (bfd *abfd, char *symname)

   DESCRIPTION

   An expensive way to lookup the value of a single symbol for
   bfd's that are only temporary anyway.  This is used by the
   shared library support to find the address of the debugger
   notification routine in the shared library.

   The returned symbol may be in a code or data section; functions
   will normally be in a code section, but may be in a data section
   if this architecture uses function descriptors.

   Note that 0 is specifically allowed as an error return (no
   such symbol).
 */

static CORE_ADDR
bfd_lookup_symbol (bfd *abfd, char *symname)
{
  long storage_needed;
  asymbol *sym;
  asymbol **symbol_table;
  unsigned int number_of_symbols;
  unsigned int i;
  struct cleanup *back_to;
  CORE_ADDR symaddr = 0;

  storage_needed = bfd_get_symtab_upper_bound (abfd);

  if (storage_needed > 0)
    {
      symbol_table = (asymbol **) xmalloc (storage_needed);
      back_to = make_cleanup (xfree, symbol_table);
      number_of_symbols = bfd_canonicalize_symtab (abfd, symbol_table);

      for (i = 0; i < number_of_symbols; i++)
	{
	  sym = *symbol_table++;
	  if (strcmp (sym->name, symname) == 0
              && (sym->section->flags & (SEC_CODE | SEC_DATA)) != 0)
	    {
	      /* BFD symbols are section relative.  */
	      symaddr = sym->value + sym->section->vma;
	      break;
	    }
	}
      do_cleanups (back_to);
    }

  if (symaddr)
    return symaddr;

  /* On FreeBSD, the dynamic linker is stripped by default.  So we'll
     have to check the dynamic string table too.  */

  storage_needed = bfd_get_dynamic_symtab_upper_bound (abfd);

  if (storage_needed > 0)
    {
      symbol_table = (asymbol **) xmalloc (storage_needed);
      back_to = make_cleanup (xfree, symbol_table);
      number_of_symbols = bfd_canonicalize_dynamic_symtab (abfd, symbol_table);

      for (i = 0; i < number_of_symbols; i++)
	{
	  sym = *symbol_table++;

	  if (strcmp (sym->name, symname) == 0
              && (sym->section->flags & (SEC_CODE | SEC_DATA)) != 0)
	    {
	      /* BFD symbols are section relative.  */
	      symaddr = sym->value + sym->section->vma;
	      break;
	    }
	}
      do_cleanups (back_to);
    }

  return symaddr;
}

/* Scan for DYNTAG in .dynamic section of ABFD. If DYNTAG is found 1 is
   returned and the corresponding PTR is set.  */

static int
scan_dyntag (int dyntag, bfd *abfd, CORE_ADDR *ptr)
{
  int arch_size, step, sect_size;
  long dyn_tag;
  CORE_ADDR dyn_ptr, dyn_addr;
  gdb_byte *bufend, *bufstart, *buf;
  Elf32_External_Dyn *x_dynp_32;
  Elf64_External_Dyn *x_dynp_64;
  struct bfd_section *sect;

  if (abfd == NULL)
    return 0;
  arch_size = bfd_get_arch_size (abfd);
  if (arch_size == -1)
   return 0;

  /* Find the start address of the .dynamic section.  */
  sect = bfd_get_section_by_name (abfd, ".dynamic");
  if (sect == NULL)
    return 0;
  dyn_addr = bfd_section_vma (abfd, sect);

  /* Read in .dynamic from the BFD.  We will get the actual value
     from memory later.  */
  sect_size = bfd_section_size (abfd, sect);
  buf = bufstart = alloca (sect_size);
  if (!bfd_get_section_contents (abfd, sect,
				 buf, 0, sect_size))
    return 0;

  /* Iterate over BUF and scan for DYNTAG.  If found, set PTR and return.  */
  step = (arch_size == 32) ? sizeof (Elf32_External_Dyn)
			   : sizeof (Elf64_External_Dyn);
  for (bufend = buf + sect_size;
       buf < bufend;
       buf += step)
  {
    if (arch_size == 32)
      {
	x_dynp_32 = (Elf32_External_Dyn *) buf;
	dyn_tag = bfd_h_get_32 (abfd, (bfd_byte *) x_dynp_32->d_tag);
	dyn_ptr = bfd_h_get_32 (abfd, (bfd_byte *) x_dynp_32->d_un.d_ptr);
      }
    else
      {
	x_dynp_64 = (Elf64_External_Dyn *) buf;
	dyn_tag = bfd_h_get_64 (abfd, (bfd_byte *) x_dynp_64->d_tag);
	dyn_ptr = bfd_h_get_64 (abfd, (bfd_byte *) x_dynp_64->d_un.d_ptr);
      }
     if (dyn_tag == DT_NULL)
       return 0;
     if (dyn_tag == dyntag)
       {
	 /* If requested, try to read the runtime value of this .dynamic
	    entry.  */
	 if (ptr)
	   {
	     gdb_byte ptr_buf[8];
	     CORE_ADDR ptr_addr;

	     ptr_addr = dyn_addr + (buf - bufstart) + arch_size / 8;
	     if (target_read_memory (ptr_addr, ptr_buf, arch_size / 8) == 0)
	       dyn_ptr = extract_typed_address (ptr_buf,
						builtin_type_void_data_ptr);
	     *ptr = dyn_ptr;
	   }
	 return 1;
       }
  }

  return 0;
}


/*

   LOCAL FUNCTION

   elf_locate_base -- locate the base address of dynamic linker structs
   for SVR4 elf targets.

   SYNOPSIS

   CORE_ADDR elf_locate_base (void)

   DESCRIPTION

   For SVR4 elf targets the address of the dynamic linker's runtime
   structure is contained within the dynamic info section in the
   executable file.  The dynamic section is also mapped into the
   inferior address space.  Because the runtime loader fills in the
   real address before starting the inferior, we have to read in the
   dynamic info section from the inferior address space.
   If there are any errors while trying to find the address, we
   silently return 0, otherwise the found address is returned.

 */

static CORE_ADDR
elf_locate_base (void)
{
  struct minimal_symbol *msymbol;
  CORE_ADDR dyn_ptr;

  /* Look for DT_MIPS_RLD_MAP first.  MIPS executables use this
     instead of DT_DEBUG, although they sometimes contain an unused
     DT_DEBUG.  */
  if (scan_dyntag (DT_MIPS_RLD_MAP, exec_bfd, &dyn_ptr))
    {
      gdb_byte *pbuf;
      int pbuf_size = TYPE_LENGTH (builtin_type_void_data_ptr);
      pbuf = alloca (pbuf_size);
      /* DT_MIPS_RLD_MAP contains a pointer to the address
	 of the dynamic link structure.  */
      if (target_read_memory (dyn_ptr, pbuf, pbuf_size))
	return 0;
      return extract_typed_address (pbuf, builtin_type_void_data_ptr);
    }

  /* Find DT_DEBUG.  */
  if (scan_dyntag (DT_DEBUG, exec_bfd, &dyn_ptr))
    return dyn_ptr;

  /* This may be a static executable.  Look for the symbol
     conventionally named _r_debug, as a last resort.  */
  msymbol = lookup_minimal_symbol ("_r_debug", NULL, symfile_objfile);
  if (msymbol != NULL)
    return SYMBOL_VALUE_ADDRESS (msymbol);

  /* DT_DEBUG entry not found.  */
  return 0;
}

/*

   LOCAL FUNCTION

   locate_base -- locate the base address of dynamic linker structs

   SYNOPSIS

   CORE_ADDR locate_base (void)

   DESCRIPTION

   For both the SunOS and SVR4 shared library implementations, if the
   inferior executable has been linked dynamically, there is a single
   address somewhere in the inferior's data space which is the key to
   locating all of the dynamic linker's runtime structures.  This
   address is the value of the debug base symbol.  The job of this
   function is to find and return that address, or to return 0 if there
   is no such address (the executable is statically linked for example).

   For SunOS, the job is almost trivial, since the dynamic linker and
   all of it's structures are statically linked to the executable at
   link time.  Thus the symbol for the address we are looking for has
   already been added to the minimal symbol table for the executable's
   objfile at the time the symbol file's symbols were read, and all we
   have to do is look it up there.  Note that we explicitly do NOT want
   to find the copies in the shared library.

   The SVR4 version is a bit more complicated because the address
   is contained somewhere in the dynamic info section.  We have to go
   to a lot more work to discover the address of the debug base symbol.
   Because of this complexity, we cache the value we find and return that
   value on subsequent invocations.  Note there is no copy in the
   executable symbol tables.

 */

static CORE_ADDR
locate_base (void)
{
  /* Check to see if we have a currently valid address, and if so, avoid
     doing all this work again and just return the cached address.  If
     we have no cached address, try to locate it in the dynamic info
     section for ELF executables.  There's no point in doing any of this
     though if we don't have some link map offsets to work with.  */

  if (debug_base == 0 && svr4_have_link_map_offsets ())
    {
      if (exec_bfd != NULL
	  && bfd_get_flavour (exec_bfd) == bfd_target_elf_flavour)
	debug_base = elf_locate_base ();
    }
  return (debug_base);
}

/* Find the first element in the inferior's dynamic link map, and
   return its address in the inferior.

   FIXME: Perhaps we should validate the info somehow, perhaps by
   checking r_version for a known version number, or r_state for
   RT_CONSISTENT.  */

static CORE_ADDR
solib_svr4_r_map (void)
{
  struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();

  return read_memory_typed_address (debug_base + lmo->r_map_offset,
				    builtin_type_void_data_ptr);
}

/* Find the link map for the dynamic linker (if it is not in the
   normal list of loaded shared objects).  */

static CORE_ADDR
solib_svr4_r_ldsomap (void)
{
  struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
  ULONGEST version;

  /* Check version, and return zero if `struct r_debug' doesn't have
     the r_ldsomap member.  */
  version = read_memory_unsigned_integer (debug_base + lmo->r_version_offset,
					  lmo->r_version_size);
  if (version < 2 || lmo->r_ldsomap_offset == -1)
    return 0;

  return read_memory_typed_address (debug_base + lmo->r_ldsomap_offset,
				    builtin_type_void_data_ptr);
}

/*

  LOCAL FUNCTION

  open_symbol_file_object

  SYNOPSIS

  void open_symbol_file_object (void *from_tty)

  DESCRIPTION

  If no open symbol file, attempt to locate and open the main symbol
  file.  On SVR4 systems, this is the first link map entry.  If its
  name is here, we can open it.  Useful when attaching to a process
  without first loading its symbol file.

  If FROM_TTYP dereferences to a non-zero integer, allow messages to
  be printed.  This parameter is a pointer rather than an int because
  open_symbol_file_object() is called via catch_errors() and
  catch_errors() requires a pointer argument. */

static int
open_symbol_file_object (void *from_ttyp)
{
  CORE_ADDR lm, l_name;
  char *filename;
  int errcode;
  int from_tty = *(int *)from_ttyp;
  struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
  int l_name_size = TYPE_LENGTH (builtin_type_void_data_ptr);
  gdb_byte *l_name_buf = xmalloc (l_name_size);
  struct cleanup *cleanups = make_cleanup (xfree, l_name_buf);

  if (symfile_objfile)
    if (!query ("Attempt to reload symbols from process? "))
      return 0;

  if ((debug_base = locate_base ()) == 0)
    return 0;	/* failed somehow... */

  /* First link map member should be the executable.  */
  lm = solib_svr4_r_map ();
  if (lm == 0)
    return 0;	/* failed somehow... */

  /* Read address of name from target memory to GDB.  */
  read_memory (lm + lmo->l_name_offset, l_name_buf, l_name_size);

  /* Convert the address to host format.  */
  l_name = extract_typed_address (l_name_buf, builtin_type_void_data_ptr);

  /* Free l_name_buf.  */
  do_cleanups (cleanups);

  if (l_name == 0)
    return 0;		/* No filename.  */

  /* Now fetch the filename from target memory.  */
  target_read_string (l_name, &filename, SO_NAME_MAX_PATH_SIZE - 1, &errcode);
  make_cleanup (xfree, filename);

  if (errcode)
    {
      warning (_("failed to read exec filename from attached file: %s"),
	       safe_strerror (errcode));
      return 0;
    }

  /* Have a pathname: read the symbol file.  */
  symbol_file_add_main (filename, from_tty);

  return 1;
}

/* If no shared library information is available from the dynamic
   linker, build a fallback list from other sources.  */

static struct so_list *
svr4_default_sos (void)
{
  struct so_list *head = NULL;
  struct so_list **link_ptr = &head;

  if (debug_loader_offset_p)
    {
      struct so_list *new = XZALLOC (struct so_list);

      new->lm_info = xmalloc (sizeof (struct lm_info));

      /* Nothing will ever check the cached copy of the link
	 map if we set l_addr.  */
      new->lm_info->l_addr = debug_loader_offset;
      new->lm_info->lm = NULL;

      strncpy (new->so_name, debug_loader_name, SO_NAME_MAX_PATH_SIZE - 1);
      new->so_name[SO_NAME_MAX_PATH_SIZE - 1] = '\0';
      strcpy (new->so_original_name, new->so_name);

      *link_ptr = new;
      link_ptr = &new->next;
    }

  return head;
}

/* LOCAL FUNCTION

   current_sos -- build a list of currently loaded shared objects

   SYNOPSIS

   struct so_list *current_sos ()

   DESCRIPTION

   Build a list of `struct so_list' objects describing the shared
   objects currently loaded in the inferior.  This list does not
   include an entry for the main executable file.

   Note that we only gather information directly available from the
   inferior --- we don't examine any of the shared library files
   themselves.  The declaration of `struct so_list' says which fields
   we provide values for.  */

static struct so_list *
svr4_current_sos (void)
{
  CORE_ADDR lm;
  struct so_list *head = 0;
  struct so_list **link_ptr = &head;
  CORE_ADDR ldsomap = 0;

  /* Make sure we've looked up the inferior's dynamic linker's base
     structure.  */
  if (! debug_base)
    {
      debug_base = locate_base ();

      /* If we can't find the dynamic linker's base structure, this
	 must not be a dynamically linked executable.  Hmm.  */
      if (! debug_base)
	return svr4_default_sos ();
    }

  /* Walk the inferior's link map list, and build our list of
     `struct so_list' nodes.  */
  lm = solib_svr4_r_map ();

  while (lm)
    {
      struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
      struct so_list *new = XZALLOC (struct so_list);
      struct cleanup *old_chain = make_cleanup (xfree, new);

      new->lm_info = xmalloc (sizeof (struct lm_info));
      make_cleanup (xfree, new->lm_info);

      new->lm_info->l_addr = (CORE_ADDR)-1;
      new->lm_info->lm = xzalloc (lmo->link_map_size);
      make_cleanup (xfree, new->lm_info->lm);

      read_memory (lm, new->lm_info->lm, lmo->link_map_size);

      lm = LM_NEXT (new);

      /* For SVR4 versions, the first entry in the link map is for the
         inferior executable, so we must ignore it.  For some versions of
         SVR4, it has no name.  For others (Solaris 2.3 for example), it
         does have a name, so we can no longer use a missing name to
         decide when to ignore it. */
      if (IGNORE_FIRST_LINK_MAP_ENTRY (new) && ldsomap == 0)
	free_so (new);
      else
	{
	  int errcode;
	  char *buffer;

	  /* Extract this shared object's name.  */
	  target_read_string (LM_NAME (new), &buffer,
			      SO_NAME_MAX_PATH_SIZE - 1, &errcode);
	  if (errcode != 0)
	    warning (_("Can't read pathname for load map: %s."),
		     safe_strerror (errcode));
	  else
	    {
	      strncpy (new->so_name, buffer, SO_NAME_MAX_PATH_SIZE - 1);
	      new->so_name[SO_NAME_MAX_PATH_SIZE - 1] = '\0';
	      strcpy (new->so_original_name, new->so_name);
	    }
	  xfree (buffer);

	  /* If this entry has no name, or its name matches the name
	     for the main executable, don't include it in the list.  */
	  if (! new->so_name[0]
	      || match_main (new->so_name))
	    free_so (new);
	  else
	    {
	      new->next = 0;
	      *link_ptr = new;
	      link_ptr = &new->next;
	    }
	}

      /* On Solaris, the dynamic linker is not in the normal list of
	 shared objects, so make sure we pick it up too.  Having
	 symbol information for the dynamic linker is quite crucial
	 for skipping dynamic linker resolver code.  */
      if (lm == 0 && ldsomap == 0)
	lm = ldsomap = solib_svr4_r_ldsomap ();

      discard_cleanups (old_chain);
    }

  if (head == NULL)
    return svr4_default_sos ();

  return head;
}

/* Get the address of the link_map for a given OBJFILE.  Loop through
   the link maps, and return the address of the one corresponding to
   the given objfile.  Note that this function takes into account that
   objfile can be the main executable, not just a shared library.  The
   main executable has always an empty name field in the linkmap.  */

CORE_ADDR
svr4_fetch_objfile_link_map (struct objfile *objfile)
{
  CORE_ADDR lm;

  if ((debug_base = locate_base ()) == 0)
    return 0;   /* failed somehow... */

  /* Position ourselves on the first link map.  */
  lm = solib_svr4_r_map ();  
  while (lm)
    {
      /* Get info on the layout of the r_debug and link_map structures. */
      struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
      int errcode;
      char *buffer;
      struct lm_info objfile_lm_info;
      struct cleanup *old_chain;
      CORE_ADDR name_address;
      int l_name_size = TYPE_LENGTH (builtin_type_void_data_ptr);
      gdb_byte *l_name_buf = xmalloc (l_name_size);
      old_chain = make_cleanup (xfree, l_name_buf);

      /* Set up the buffer to contain the portion of the link_map
         structure that gdb cares about.  Note that this is not the
         whole link_map structure.  */
      objfile_lm_info.lm = xzalloc (lmo->link_map_size);
      make_cleanup (xfree, objfile_lm_info.lm);

      /* Read the link map into our internal structure.  */
      read_memory (lm, objfile_lm_info.lm, lmo->link_map_size);

      /* Read address of name from target memory to GDB.  */
      read_memory (lm + lmo->l_name_offset, l_name_buf, l_name_size);

      /* Extract this object's name.  */
      name_address = extract_typed_address (l_name_buf,
					    builtin_type_void_data_ptr);
      target_read_string (name_address, &buffer,
      			  SO_NAME_MAX_PATH_SIZE - 1, &errcode);
      make_cleanup (xfree, buffer);
      if (errcode != 0)
	warning (_("Can't read pathname for load map: %s."),
		 safe_strerror (errcode));
      else
  	{
	  /* Is this the linkmap for the file we want?  */
	  /* If the file is not a shared library and has no name,
	     we are sure it is the main executable, so we return that.  */

	  if (buffer 
	      && ((strcmp (buffer, objfile->name) == 0)
		  || (!(objfile->flags & OBJF_SHARED) 
		      && (strcmp (buffer, "") == 0))))
  	    {
    	      do_cleanups (old_chain);
    	      return lm;
      	    }
  	}
      /* Not the file we wanted, continue checking.  */
      lm = extract_typed_address (objfile_lm_info.lm + lmo->l_next_offset,
				  builtin_type_void_data_ptr);
      do_cleanups (old_chain);
    }
  return 0;
}

/* On some systems, the only way to recognize the link map entry for
   the main executable file is by looking at its name.  Return
   non-zero iff SONAME matches one of the known main executable names.  */

static int
match_main (char *soname)
{
  char **mainp;

  for (mainp = main_name_list; *mainp != NULL; mainp++)
    {
      if (strcmp (soname, *mainp) == 0)
	return (1);
    }

  return (0);
}

/* Return 1 if PC lies in the dynamic symbol resolution code of the
   SVR4 run time loader.  */
static CORE_ADDR interp_text_sect_low;
static CORE_ADDR interp_text_sect_high;
static CORE_ADDR interp_plt_sect_low;
static CORE_ADDR interp_plt_sect_high;

int
svr4_in_dynsym_resolve_code (CORE_ADDR pc)
{
  return ((pc >= interp_text_sect_low && pc < interp_text_sect_high)
	  || (pc >= interp_plt_sect_low && pc < interp_plt_sect_high)
	  || in_plt_section (pc, NULL));
}

/* Given an executable's ABFD and target, compute the entry-point
   address.  */

static CORE_ADDR
exec_entry_point (struct bfd *abfd, struct target_ops *targ)
{
  /* KevinB wrote ... for most targets, the address returned by
     bfd_get_start_address() is the entry point for the start
     function.  But, for some targets, bfd_get_start_address() returns
     the address of a function descriptor from which the entry point
     address may be extracted.  This address is extracted by
     gdbarch_convert_from_func_ptr_addr().  The method
     gdbarch_convert_from_func_ptr_addr() is the merely the identify
     function for targets which don't use function descriptors.  */
  return gdbarch_convert_from_func_ptr_addr (current_gdbarch,
					     bfd_get_start_address (abfd),
					     targ);
}

/*

   LOCAL FUNCTION

   enable_break -- arrange for dynamic linker to hit breakpoint

   SYNOPSIS

   int enable_break (void)

   DESCRIPTION

   Both the SunOS and the SVR4 dynamic linkers have, as part of their
   debugger interface, support for arranging for the inferior to hit
   a breakpoint after mapping in the shared libraries.  This function
   enables that breakpoint.

   For SunOS, there is a special flag location (in_debugger) which we
   set to 1.  When the dynamic linker sees this flag set, it will set
   a breakpoint at a location known only to itself, after saving the
   original contents of that place and the breakpoint address itself,
   in it's own internal structures.  When we resume the inferior, it
   will eventually take a SIGTRAP when it runs into the breakpoint.
   We handle this (in a different place) by restoring the contents of
   the breakpointed location (which is only known after it stops),
   chasing around to locate the shared libraries that have been
   loaded, then resuming.

   For SVR4, the debugger interface structure contains a member (r_brk)
   which is statically initialized at the time the shared library is
   built, to the offset of a function (_r_debug_state) which is guaran-
   teed to be called once before mapping in a library, and again when
   the mapping is complete.  At the time we are examining this member,
   it contains only the unrelocated offset of the function, so we have
   to do our own relocation.  Later, when the dynamic linker actually
   runs, it relocates r_brk to be the actual address of _r_debug_state().

   The debugger interface structure also contains an enumeration which
   is set to either RT_ADD or RT_DELETE prior to changing the mapping,
   depending upon whether or not the library is being mapped or unmapped,
   and then set to RT_CONSISTENT after the library is mapped/unmapped.
 */

static int
enable_break (void)
{
#ifdef BKPT_AT_SYMBOL

  struct minimal_symbol *msymbol;
  char **bkpt_namep;
  asection *interp_sect;

  /* First, remove all the solib event breakpoints.  Their addresses
     may have changed since the last time we ran the program.  */
  remove_solib_event_breakpoints ();

  interp_text_sect_low = interp_text_sect_high = 0;
  interp_plt_sect_low = interp_plt_sect_high = 0;

  /* Find the .interp section; if not found, warn the user and drop
     into the old breakpoint at symbol code.  */
  interp_sect = bfd_get_section_by_name (exec_bfd, ".interp");
  if (interp_sect)
    {
      unsigned int interp_sect_size;
      char *buf;
      CORE_ADDR load_addr = 0;
      int load_addr_found = 0;
      struct so_list *so;
      bfd *tmp_bfd = NULL;
      struct target_ops *tmp_bfd_target;
      int tmp_fd = -1;
      char *tmp_pathname = NULL;
      CORE_ADDR sym_addr = 0;

      /* Read the contents of the .interp section into a local buffer;
         the contents specify the dynamic linker this program uses.  */
      interp_sect_size = bfd_section_size (exec_bfd, interp_sect);
      buf = alloca (interp_sect_size);
      bfd_get_section_contents (exec_bfd, interp_sect,
				buf, 0, interp_sect_size);

      /* Now we need to figure out where the dynamic linker was
         loaded so that we can load its symbols and place a breakpoint
         in the dynamic linker itself.

         This address is stored on the stack.  However, I've been unable
         to find any magic formula to find it for Solaris (appears to
         be trivial on GNU/Linux).  Therefore, we have to try an alternate
         mechanism to find the dynamic linker's base address.  */

      /* TODO drow/2006-09-12: This is somewhat fragile, because it
	 relies on read_pc.  On both Solaris and GNU/Linux we can use
	 the AT_BASE auxilliary entry, which GDB now knows how to
	 access, to find the base address.  */

      tmp_fd = solib_open (buf, &tmp_pathname);
      if (tmp_fd >= 0)
	tmp_bfd = bfd_fopen (tmp_pathname, gnutarget, FOPEN_RB, tmp_fd);

      if (tmp_bfd == NULL)
	goto bkpt_at_symbol;

      /* Make sure the dynamic linker's really a useful object.  */
      if (!bfd_check_format (tmp_bfd, bfd_object))
	{
	  warning (_("Unable to grok dynamic linker %s as an object file"), buf);
	  bfd_close (tmp_bfd);
	  goto bkpt_at_symbol;
	}

      /* Now convert the TMP_BFD into a target.  That way target, as
         well as BFD operations can be used.  Note that closing the
         target will also close the underlying bfd.  */
      tmp_bfd_target = target_bfd_reopen (tmp_bfd);

      /* On a running target, we can get the dynamic linker's base
         address from the shared library table.  */
      solib_add (NULL, 0, &current_target, auto_solib_add);
      so = master_so_list ();
      while (so)
	{
	  if (strcmp (buf, so->so_original_name) == 0)
	    {
	      load_addr_found = 1;
	      load_addr = LM_ADDR_CHECK (so, tmp_bfd);
	      break;
	    }
	  so = so->next;
	}

      /* Otherwise we find the dynamic linker's base address by examining
	 the current pc (which should point at the entry point for the
	 dynamic linker) and subtracting the offset of the entry point.  */
      if (!load_addr_found)
	{
	  load_addr = (read_pc ()
		       - exec_entry_point (tmp_bfd, tmp_bfd_target));
	  debug_loader_name = xstrdup (buf);
	  debug_loader_offset_p = 1;
	  debug_loader_offset = load_addr;
	  solib_add (NULL, 0, &current_target, auto_solib_add);
	}

      /* Record the relocated start and end address of the dynamic linker
         text and plt section for svr4_in_dynsym_resolve_code.  */
      interp_sect = bfd_get_section_by_name (tmp_bfd, ".text");
      if (interp_sect)
	{
	  interp_text_sect_low =
	    bfd_section_vma (tmp_bfd, interp_sect) + load_addr;
	  interp_text_sect_high =
	    interp_text_sect_low + bfd_section_size (tmp_bfd, interp_sect);
	}
      interp_sect = bfd_get_section_by_name (tmp_bfd, ".plt");
      if (interp_sect)
	{
	  interp_plt_sect_low =
	    bfd_section_vma (tmp_bfd, interp_sect) + load_addr;
	  interp_plt_sect_high =
	    interp_plt_sect_low + bfd_section_size (tmp_bfd, interp_sect);
	}

      /* Now try to set a breakpoint in the dynamic linker.  */
      for (bkpt_namep = solib_break_names; *bkpt_namep != NULL; bkpt_namep++)
	{
	  sym_addr = bfd_lookup_symbol (tmp_bfd, *bkpt_namep);
	  if (sym_addr != 0)
	    break;
	}

      if (sym_addr != 0)
	/* Convert 'sym_addr' from a function pointer to an address.
	   Because we pass tmp_bfd_target instead of the current
	   target, this will always produce an unrelocated value.  */
	sym_addr = gdbarch_convert_from_func_ptr_addr (current_gdbarch,
						       sym_addr,
						       tmp_bfd_target);

      /* We're done with both the temporary bfd and target.  Remember,
         closing the target closes the underlying bfd.  */
      target_close (tmp_bfd_target, 0);

      if (sym_addr != 0)
	{
	  create_solib_event_breakpoint (load_addr + sym_addr);
	  return 1;
	}

      /* For whatever reason we couldn't set a breakpoint in the dynamic
         linker.  Warn and drop into the old code.  */
    bkpt_at_symbol:
      xfree (tmp_pathname);
      warning (_("Unable to find dynamic linker breakpoint function.\n"
               "GDB will be unable to debug shared library initializers\n"
               "and track explicitly loaded dynamic code."));
    }

  /* Scan through the lists of symbols, trying to look up the symbol and
     set a breakpoint there.  Terminate loop when we/if we succeed.  */

  for (bkpt_namep = solib_break_names; *bkpt_namep != NULL; bkpt_namep++)
    {
      msymbol = lookup_minimal_symbol (*bkpt_namep, NULL, symfile_objfile);
      if ((msymbol != NULL) && (SYMBOL_VALUE_ADDRESS (msymbol) != 0))
	{
	  create_solib_event_breakpoint (SYMBOL_VALUE_ADDRESS (msymbol));
	  return 1;
	}
    }

  for (bkpt_namep = bkpt_names; *bkpt_namep != NULL; bkpt_namep++)
    {
      msymbol = lookup_minimal_symbol (*bkpt_namep, NULL, symfile_objfile);
      if ((msymbol != NULL) && (SYMBOL_VALUE_ADDRESS (msymbol) != 0))
	{
	  create_solib_event_breakpoint (SYMBOL_VALUE_ADDRESS (msymbol));
	  return 1;
	}
    }
#endif /* BKPT_AT_SYMBOL */

  return 0;
}

/*

   LOCAL FUNCTION

   special_symbol_handling -- additional shared library symbol handling

   SYNOPSIS

   void special_symbol_handling ()

   DESCRIPTION

   Once the symbols from a shared object have been loaded in the usual
   way, we are called to do any system specific symbol handling that 
   is needed.

   For SunOS4, this consisted of grunging around in the dynamic
   linkers structures to find symbol definitions for "common" symbols
   and adding them to the minimal symbol table for the runtime common
   objfile.

   However, for SVR4, there's nothing to do.

 */

static void
svr4_special_symbol_handling (void)
{
}

/* Relocate the main executable.  This function should be called upon
   stopping the inferior process at the entry point to the program. 
   The entry point from BFD is compared to the PC and if they are
   different, the main executable is relocated by the proper amount. 
   
   As written it will only attempt to relocate executables which
   lack interpreter sections.  It seems likely that only dynamic
   linker executables will get relocated, though it should work
   properly for a position-independent static executable as well.  */

static void
svr4_relocate_main_executable (void)
{
  asection *interp_sect;
  CORE_ADDR pc = read_pc ();

  /* Decide if the objfile needs to be relocated.  As indicated above,
     we will only be here when execution is stopped at the beginning
     of the program.  Relocation is necessary if the address at which
     we are presently stopped differs from the start address stored in
     the executable AND there's no interpreter section.  The condition
     regarding the interpreter section is very important because if
     there *is* an interpreter section, execution will begin there
     instead.  When there is an interpreter section, the start address
     is (presumably) used by the interpreter at some point to start
     execution of the program.

     If there is an interpreter, it is normal for it to be set to an
     arbitrary address at the outset.  The job of finding it is
     handled in enable_break().

     So, to summarize, relocations are necessary when there is no
     interpreter section and the start address obtained from the
     executable is different from the address at which GDB is
     currently stopped.
     
     [ The astute reader will note that we also test to make sure that
       the executable in question has the DYNAMIC flag set.  It is my
       opinion that this test is unnecessary (undesirable even).  It
       was added to avoid inadvertent relocation of an executable
       whose e_type member in the ELF header is not ET_DYN.  There may
       be a time in the future when it is desirable to do relocations
       on other types of files as well in which case this condition
       should either be removed or modified to accomodate the new file
       type.  (E.g, an ET_EXEC executable which has been built to be
       position-independent could safely be relocated by the OS if
       desired.  It is true that this violates the ABI, but the ABI
       has been known to be bent from time to time.)  - Kevin, Nov 2000. ]
     */

  interp_sect = bfd_get_section_by_name (exec_bfd, ".interp");
  if (interp_sect == NULL 
      && (bfd_get_file_flags (exec_bfd) & DYNAMIC) != 0
      && (exec_entry_point (exec_bfd, &exec_ops) != pc))
    {
      struct cleanup *old_chain;
      struct section_offsets *new_offsets;
      int i, changed;
      CORE_ADDR displacement;
      
      /* It is necessary to relocate the objfile.  The amount to
	 relocate by is simply the address at which we are stopped
	 minus the starting address from the executable.

	 We relocate all of the sections by the same amount.  This
	 behavior is mandated by recent editions of the System V ABI. 
	 According to the System V Application Binary Interface,
	 Edition 4.1, page 5-5:

	   ...  Though the system chooses virtual addresses for
	   individual processes, it maintains the segments' relative
	   positions.  Because position-independent code uses relative
	   addressesing between segments, the difference between
	   virtual addresses in memory must match the difference
	   between virtual addresses in the file.  The difference
	   between the virtual address of any segment in memory and
	   the corresponding virtual address in the file is thus a
	   single constant value for any one executable or shared
	   object in a given process.  This difference is the base
	   address.  One use of the base address is to relocate the
	   memory image of the program during dynamic linking.

	 The same language also appears in Edition 4.0 of the System V
	 ABI and is left unspecified in some of the earlier editions.  */

      displacement = pc - exec_entry_point (exec_bfd, &exec_ops);
      changed = 0;

      new_offsets = xcalloc (symfile_objfile->num_sections,
			     sizeof (struct section_offsets));
      old_chain = make_cleanup (xfree, new_offsets);

      for (i = 0; i < symfile_objfile->num_sections; i++)
	{
	  if (displacement != ANOFFSET (symfile_objfile->section_offsets, i))
	    changed = 1;
	  new_offsets->offsets[i] = displacement;
	}

      if (changed)
	objfile_relocate (symfile_objfile, new_offsets);

      do_cleanups (old_chain);
    }
}

/*

   GLOBAL FUNCTION

   svr4_solib_create_inferior_hook -- shared library startup support

   SYNOPSIS

   void svr4_solib_create_inferior_hook ()

   DESCRIPTION

   When gdb starts up the inferior, it nurses it along (through the
   shell) until it is ready to execute it's first instruction.  At this
   point, this function gets called via expansion of the macro
   SOLIB_CREATE_INFERIOR_HOOK.

   For SunOS executables, this first instruction is typically the
   one at "_start", or a similar text label, regardless of whether
   the executable is statically or dynamically linked.  The runtime
   startup code takes care of dynamically linking in any shared
   libraries, once gdb allows the inferior to continue.

   For SVR4 executables, this first instruction is either the first
   instruction in the dynamic linker (for dynamically linked
   executables) or the instruction at "start" for statically linked
   executables.  For dynamically linked executables, the system
   first exec's /lib/libc.so.N, which contains the dynamic linker,
   and starts it running.  The dynamic linker maps in any needed
   shared libraries, maps in the actual user executable, and then
   jumps to "start" in the user executable.

   For both SunOS shared libraries, and SVR4 shared libraries, we
   can arrange to cooperate with the dynamic linker to discover the
   names of shared libraries that are dynamically linked, and the
   base addresses to which they are linked.

   This function is responsible for discovering those names and
   addresses, and saving sufficient information about them to allow
   their symbols to be read at a later time.

   FIXME

   Between enable_break() and disable_break(), this code does not
   properly handle hitting breakpoints which the user might have
   set in the startup code or in the dynamic linker itself.  Proper
   handling will probably have to wait until the implementation is
   changed to use the "breakpoint handler function" method.

   Also, what if child has exit()ed?  Must exit loop somehow.
 */

static void
svr4_solib_create_inferior_hook (void)
{
  /* Relocate the main executable if necessary.  */
  svr4_relocate_main_executable ();

  if (!svr4_have_link_map_offsets ())
    return;

  if (!enable_break ())
    return;

#if defined(_SCO_DS)
  /* SCO needs the loop below, other systems should be using the
     special shared library breakpoints and the shared library breakpoint
     service routine.

     Now run the target.  It will eventually hit the breakpoint, at
     which point all of the libraries will have been mapped in and we
     can go groveling around in the dynamic linker structures to find
     out what we need to know about them. */

  clear_proceed_status ();
  stop_soon = STOP_QUIETLY;
  stop_signal = TARGET_SIGNAL_0;
  do
    {
      target_resume (pid_to_ptid (-1), 0, stop_signal);
      wait_for_inferior ();
    }
  while (stop_signal != TARGET_SIGNAL_TRAP);
  stop_soon = NO_STOP_QUIETLY;
#endif /* defined(_SCO_DS) */
}

static void
svr4_clear_solib (void)
{
  debug_base = 0;
  debug_loader_offset_p = 0;
  debug_loader_offset = 0;
  xfree (debug_loader_name);
  debug_loader_name = NULL;
}

static void
svr4_free_so (struct so_list *so)
{
  xfree (so->lm_info->lm);
  xfree (so->lm_info);
}


/* Clear any bits of ADDR that wouldn't fit in a target-format
   data pointer.  "Data pointer" here refers to whatever sort of
   address the dynamic linker uses to manage its sections.  At the
   moment, we don't support shared libraries on any processors where
   code and data pointers are different sizes.

   This isn't really the right solution.  What we really need here is
   a way to do arithmetic on CORE_ADDR values that respects the
   natural pointer/address correspondence.  (For example, on the MIPS,
   converting a 32-bit pointer to a 64-bit CORE_ADDR requires you to
   sign-extend the value.  There, simply truncating the bits above
   gdbarch_ptr_bit, as we do below, is no good.)  This should probably
   be a new gdbarch method or something.  */
static CORE_ADDR
svr4_truncate_ptr (CORE_ADDR addr)
{
  if (gdbarch_ptr_bit (current_gdbarch) == sizeof (CORE_ADDR) * 8)
    /* We don't need to truncate anything, and the bit twiddling below
       will fail due to overflow problems.  */
    return addr;
  else
    return addr & (((CORE_ADDR) 1 << gdbarch_ptr_bit (current_gdbarch)) - 1);
}


static void
svr4_relocate_section_addresses (struct so_list *so,
                                 struct section_table *sec)
{
  sec->addr    = svr4_truncate_ptr (sec->addr    + LM_ADDR_CHECK (so,
								  sec->bfd));
  sec->endaddr = svr4_truncate_ptr (sec->endaddr + LM_ADDR_CHECK (so,
								  sec->bfd));
}


/* Architecture-specific operations.  */

/* Per-architecture data key.  */
static struct gdbarch_data *solib_svr4_data;

struct solib_svr4_ops
{
  /* Return a description of the layout of `struct link_map'.  */
  struct link_map_offsets *(*fetch_link_map_offsets)(void);
};

/* Return a default for the architecture-specific operations.  */

static void *
solib_svr4_init (struct obstack *obstack)
{
  struct solib_svr4_ops *ops;

  ops = OBSTACK_ZALLOC (obstack, struct solib_svr4_ops);
  ops->fetch_link_map_offsets = legacy_svr4_fetch_link_map_offsets_hook;
  return ops;
}

/* Set the architecture-specific `struct link_map_offsets' fetcher for
   GDBARCH to FLMO.  */

void
set_solib_svr4_fetch_link_map_offsets (struct gdbarch *gdbarch,
                                       struct link_map_offsets *(*flmo) (void))
{
  struct solib_svr4_ops *ops = gdbarch_data (gdbarch, solib_svr4_data);

  ops->fetch_link_map_offsets = flmo;
}

/* Fetch a link_map_offsets structure using the architecture-specific
   `struct link_map_offsets' fetcher.  */

static struct link_map_offsets *
svr4_fetch_link_map_offsets (void)
{
  struct solib_svr4_ops *ops = gdbarch_data (current_gdbarch, solib_svr4_data);

  gdb_assert (ops->fetch_link_map_offsets);
  return ops->fetch_link_map_offsets ();
}

/* Return 1 if a link map offset fetcher has been defined, 0 otherwise.  */

static int
svr4_have_link_map_offsets (void)
{
  struct solib_svr4_ops *ops = gdbarch_data (current_gdbarch, solib_svr4_data);
  return (ops->fetch_link_map_offsets != NULL);
}


/* Most OS'es that have SVR4-style ELF dynamic libraries define a
   `struct r_debug' and a `struct link_map' that are binary compatible
   with the origional SVR4 implementation.  */

/* Fetch (and possibly build) an appropriate `struct link_map_offsets'
   for an ILP32 SVR4 system.  */
  
struct link_map_offsets *
svr4_ilp32_fetch_link_map_offsets (void)
{
  static struct link_map_offsets lmo;
  static struct link_map_offsets *lmp = NULL;

  if (lmp == NULL)
    {
      lmp = &lmo;

      lmo.r_version_offset = 0;
      lmo.r_version_size = 4;
      lmo.r_map_offset = 4;
      lmo.r_ldsomap_offset = 20;

      /* Everything we need is in the first 20 bytes.  */
      lmo.link_map_size = 20;
      lmo.l_addr_offset = 0;
      lmo.l_name_offset = 4;
      lmo.l_ld_offset = 8;
      lmo.l_next_offset = 12;
      lmo.l_prev_offset = 16;
    }

  return lmp;
}

/* Fetch (and possibly build) an appropriate `struct link_map_offsets'
   for an LP64 SVR4 system.  */
  
struct link_map_offsets *
svr4_lp64_fetch_link_map_offsets (void)
{
  static struct link_map_offsets lmo;
  static struct link_map_offsets *lmp = NULL;

  if (lmp == NULL)
    {
      lmp = &lmo;

      lmo.r_version_offset = 0;
      lmo.r_version_size = 4;
      lmo.r_map_offset = 8;
      lmo.r_ldsomap_offset = 40;

      /* Everything we need is in the first 40 bytes.  */
      lmo.link_map_size = 40;
      lmo.l_addr_offset = 0;
      lmo.l_name_offset = 8;
      lmo.l_ld_offset = 16;
      lmo.l_next_offset = 24;
      lmo.l_prev_offset = 32;
    }

  return lmp;
}


struct target_so_ops svr4_so_ops;

/* Lookup global symbol for ELF DSOs linked with -Bsymbolic. Those DSOs have a
   different rule for symbol lookup.  The lookup begins here in the DSO, not in
   the main executable.  */

static struct symbol *
elf_lookup_lib_symbol (const struct objfile *objfile,
		       const char *name,
		       const char *linkage_name,
		       const domain_enum domain, struct symtab **symtab)
{
  if (objfile->obfd == NULL
     || scan_dyntag (DT_SYMBOLIC, objfile->obfd, NULL) != 1)
    return NULL;

  return lookup_global_symbol_from_objfile
		(objfile, name, linkage_name, domain, symtab);
}

extern initialize_file_ftype _initialize_svr4_solib; /* -Wmissing-prototypes */

void
_initialize_svr4_solib (void)
{
  solib_svr4_data = gdbarch_data_register_pre_init (solib_svr4_init);

  svr4_so_ops.relocate_section_addresses = svr4_relocate_section_addresses;
  svr4_so_ops.free_so = svr4_free_so;
  svr4_so_ops.clear_solib = svr4_clear_solib;
  svr4_so_ops.solib_create_inferior_hook = svr4_solib_create_inferior_hook;
  svr4_so_ops.special_symbol_handling = svr4_special_symbol_handling;
  svr4_so_ops.current_sos = svr4_current_sos;
  svr4_so_ops.open_symbol_file_object = open_symbol_file_object;
  svr4_so_ops.in_dynsym_resolve_code = svr4_in_dynsym_resolve_code;
  svr4_so_ops.lookup_lib_global_symbol = elf_lookup_lib_symbol;

  /* FIXME: Don't do this here.  *_gdbarch_init() should set so_ops. */
  current_target_so_ops = &svr4_so_ops;
}