aboutsummaryrefslogtreecommitdiffstats
path: root/src/UnwindCursor.hpp
blob: 90683164ff242c647a3b8d633194962a28e73ee4 (plain) (blame)
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
//===------------------------- UnwindCursor.hpp ---------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//
// C++ interface to lower levels of libuwind
//===----------------------------------------------------------------------===//

#ifndef __UNWINDCURSOR_HPP__
#define __UNWINDCURSOR_HPP__

#include <algorithm>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unwind.h>

#ifdef __APPLE__
  #include <mach-o/dyld.h>
#endif

#include "config.h"

#include "AddressSpace.hpp"
#include "CompactUnwinder.hpp"
#include "config.h"
#include "DwarfInstructions.hpp"
#include "EHHeaderParser.hpp"
#include "libunwind.h"
#include "Registers.hpp"
#include "Unwind-EHABI.h"

namespace libunwind {

#if _LIBUNWIND_SUPPORT_DWARF_UNWIND
/// Cache of recently found FDEs.
template <typename A>
class _LIBUNWIND_HIDDEN DwarfFDECache {
  typedef typename A::pint_t pint_t;
public:
  static pint_t findFDE(pint_t mh, pint_t pc);
  static void add(pint_t mh, pint_t ip_start, pint_t ip_end, pint_t fde);
  static void removeAllIn(pint_t mh);
  static void iterateCacheEntries(void (*func)(unw_word_t ip_start,
                                               unw_word_t ip_end,
                                               unw_word_t fde, unw_word_t mh));

private:

  struct entry {
    pint_t mh;
    pint_t ip_start;
    pint_t ip_end;
    pint_t fde;
  };

  // These fields are all static to avoid needing an initializer.
  // There is only one instance of this class per process.
  static pthread_rwlock_t _lock;
#ifdef __APPLE__
  static void dyldUnloadHook(const struct mach_header *mh, intptr_t slide);
  static bool _registeredForDyldUnloads;
#endif
  // Can't use std::vector<> here because this code is below libc++.
  static entry *_buffer;
  static entry *_bufferUsed;
  static entry *_bufferEnd;
  static entry _initialBuffer[64];
};

template <typename A>
typename DwarfFDECache<A>::entry *
DwarfFDECache<A>::_buffer = _initialBuffer;

template <typename A>
typename DwarfFDECache<A>::entry *
DwarfFDECache<A>::_bufferUsed = _initialBuffer;

template <typename A>
typename DwarfFDECache<A>::entry *
DwarfFDECache<A>::_bufferEnd = &_initialBuffer[64];

template <typename A>
typename DwarfFDECache<A>::entry DwarfFDECache<A>::_initialBuffer[64];

template <typename A>
pthread_rwlock_t DwarfFDECache<A>::_lock = PTHREAD_RWLOCK_INITIALIZER;

#ifdef __APPLE__
template <typename A>
bool DwarfFDECache<A>::_registeredForDyldUnloads = false;
#endif

template <typename A>
typename A::pint_t DwarfFDECache<A>::findFDE(pint_t mh, pint_t pc) {
  pint_t result = 0;
  _LIBUNWIND_LOG_NON_ZERO(::pthread_rwlock_rdlock(&_lock));
  for (entry *p = _buffer; p < _bufferUsed; ++p) {
    if ((mh == p->mh) || (mh == 0)) {
      if ((p->ip_start <= pc) && (pc < p->ip_end)) {
        result = p->fde;
        break;
      }
    }
  }
  _LIBUNWIND_LOG_NON_ZERO(::pthread_rwlock_unlock(&_lock));
  return result;
}

template <typename A>
void DwarfFDECache<A>::add(pint_t mh, pint_t ip_start, pint_t ip_end,
                           pint_t fde) {
#if !defined(_LIBUNWIND_NO_HEAP)
  _LIBUNWIND_LOG_NON_ZERO(::pthread_rwlock_wrlock(&_lock));
  if (_bufferUsed >= _bufferEnd) {
    size_t oldSize = (size_t)(_bufferEnd - _buffer);
    size_t newSize = oldSize * 4;
    // Can't use operator new (we are below it).
    entry *newBuffer = (entry *)malloc(newSize * sizeof(entry));
    memcpy(newBuffer, _buffer, oldSize * sizeof(entry));
    if (_buffer != _initialBuffer)
      free(_buffer);
    _buffer = newBuffer;
    _bufferUsed = &newBuffer[oldSize];
    _bufferEnd = &newBuffer[newSize];
  }
  _bufferUsed->mh = mh;
  _bufferUsed->ip_start = ip_start;
  _bufferUsed->ip_end = ip_end;
  _bufferUsed->fde = fde;
  ++_bufferUsed;
#ifdef __APPLE__
  if (!_registeredForDyldUnloads) {
    _dyld_register_func_for_remove_image(&dyldUnloadHook);
    _registeredForDyldUnloads = true;
  }
#endif
  _LIBUNWIND_LOG_NON_ZERO(::pthread_rwlock_unlock(&_lock));
#endif
}

template <typename A>
void DwarfFDECache<A>::removeAllIn(pint_t mh) {
  _LIBUNWIND_LOG_NON_ZERO(::pthread_rwlock_wrlock(&_lock));
  entry *d = _buffer;
  for (const entry *s = _buffer; s < _bufferUsed; ++s) {
    if (s->mh != mh) {
      if (d != s)
        *d = *s;
      ++d;
    }
  }
  _bufferUsed = d;
  _LIBUNWIND_LOG_NON_ZERO(::pthread_rwlock_unlock(&_lock));
}

#ifdef __APPLE__
template <typename A>
void DwarfFDECache<A>::dyldUnloadHook(const struct mach_header *mh, intptr_t ) {
  removeAllIn((pint_t) mh);
}
#endif

template <typename A>
void DwarfFDECache<A>::iterateCacheEntries(void (*func)(
    unw_word_t ip_start, unw_word_t ip_end, unw_word_t fde, unw_word_t mh)) {
  _LIBUNWIND_LOG_NON_ZERO(::pthread_rwlock_wrlock(&_lock));
  for (entry *p = _buffer; p < _bufferUsed; ++p) {
    (*func)(p->ip_start, p->ip_end, p->fde, p->mh);
  }
  _LIBUNWIND_LOG_NON_ZERO(::pthread_rwlock_unlock(&_lock));
}
#endif // _LIBUNWIND_SUPPORT_DWARF_UNWIND


#define arrayoffsetof(type, index, field) ((size_t)(&((type *)0)[index].field))

#if _LIBUNWIND_SUPPORT_COMPACT_UNWIND
template <typename A> class UnwindSectionHeader {
public:
  UnwindSectionHeader(A &addressSpace, typename A::pint_t addr)
      : _addressSpace(addressSpace), _addr(addr) {}

  uint32_t version() const {
    return _addressSpace.get32(_addr +
                               offsetof(unwind_info_section_header, version));
  }
  uint32_t commonEncodingsArraySectionOffset() const {
    return _addressSpace.get32(_addr +
                               offsetof(unwind_info_section_header,
                                        commonEncodingsArraySectionOffset));
  }
  uint32_t commonEncodingsArrayCount() const {
    return _addressSpace.get32(_addr + offsetof(unwind_info_section_header,
                                                commonEncodingsArrayCount));
  }
  uint32_t personalityArraySectionOffset() const {
    return _addressSpace.get32(_addr + offsetof(unwind_info_section_header,
                                                personalityArraySectionOffset));
  }
  uint32_t personalityArrayCount() const {
    return _addressSpace.get32(
        _addr + offsetof(unwind_info_section_header, personalityArrayCount));
  }
  uint32_t indexSectionOffset() const {
    return _addressSpace.get32(
        _addr + offsetof(unwind_info_section_header, indexSectionOffset));
  }
  uint32_t indexCount() const {
    return _addressSpace.get32(
        _addr + offsetof(unwind_info_section_header, indexCount));
  }

private:
  A                     &_addressSpace;
  typename A::pint_t     _addr;
};

template <typename A> class UnwindSectionIndexArray {
public:
  UnwindSectionIndexArray(A &addressSpace, typename A::pint_t addr)
      : _addressSpace(addressSpace), _addr(addr) {}

  uint32_t functionOffset(uint32_t index) const {
    return _addressSpace.get32(
        _addr + arrayoffsetof(unwind_info_section_header_index_entry, index,
                              functionOffset));
  }
  uint32_t secondLevelPagesSectionOffset(uint32_t index) const {
    return _addressSpace.get32(
        _addr + arrayoffsetof(unwind_info_section_header_index_entry, index,
                              secondLevelPagesSectionOffset));
  }
  uint32_t lsdaIndexArraySectionOffset(uint32_t index) const {
    return _addressSpace.get32(
        _addr + arrayoffsetof(unwind_info_section_header_index_entry, index,
                              lsdaIndexArraySectionOffset));
  }

private:
  A                   &_addressSpace;
  typename A::pint_t   _addr;
};

template <typename A> class UnwindSectionRegularPageHeader {
public:
  UnwindSectionRegularPageHeader(A &addressSpace, typename A::pint_t addr)
      : _addressSpace(addressSpace), _addr(addr) {}

  uint32_t kind() const {
    return _addressSpace.get32(
        _addr + offsetof(unwind_info_regular_second_level_page_header, kind));
  }
  uint16_t entryPageOffset() const {
    return _addressSpace.get16(
        _addr + offsetof(unwind_info_regular_second_level_page_header,
                         entryPageOffset));
  }
  uint16_t entryCount() const {
    return _addressSpace.get16(
        _addr +
        offsetof(unwind_info_regular_second_level_page_header, entryCount));
  }

private:
  A &_addressSpace;
  typename A::pint_t _addr;
};

template <typename A> class UnwindSectionRegularArray {
public:
  UnwindSectionRegularArray(A &addressSpace, typename A::pint_t addr)
      : _addressSpace(addressSpace), _addr(addr) {}

  uint32_t functionOffset(uint32_t index) const {
    return _addressSpace.get32(
        _addr + arrayoffsetof(unwind_info_regular_second_level_entry, index,
                              functionOffset));
  }
  uint32_t encoding(uint32_t index) const {
    return _addressSpace.get32(
        _addr +
        arrayoffsetof(unwind_info_regular_second_level_entry, index, encoding));
  }

private:
  A &_addressSpace;
  typename A::pint_t _addr;
};

template <typename A> class UnwindSectionCompressedPageHeader {
public:
  UnwindSectionCompressedPageHeader(A &addressSpace, typename A::pint_t addr)
      : _addressSpace(addressSpace), _addr(addr) {}

  uint32_t kind() const {
    return _addressSpace.get32(
        _addr +
        offsetof(unwind_info_compressed_second_level_page_header, kind));
  }
  uint16_t entryPageOffset() const {
    return _addressSpace.get16(
        _addr + offsetof(unwind_info_compressed_second_level_page_header,
                         entryPageOffset));
  }
  uint16_t entryCount() const {
    return _addressSpace.get16(
        _addr +
        offsetof(unwind_info_compressed_second_level_page_header, entryCount));
  }
  uint16_t encodingsPageOffset() const {
    return _addressSpace.get16(
        _addr + offsetof(unwind_info_compressed_second_level_page_header,
                         encodingsPageOffset));
  }
  uint16_t encodingsCount() const {
    return _addressSpace.get16(
        _addr + offsetof(unwind_info_compressed_second_level_page_header,
                         encodingsCount));
  }

private:
  A &_addressSpace;
  typename A::pint_t _addr;
};

template <typename A> class UnwindSectionCompressedArray {
public:
  UnwindSectionCompressedArray(A &addressSpace, typename A::pint_t addr)
      : _addressSpace(addressSpace), _addr(addr) {}

  uint32_t functionOffset(uint32_t index) const {
    return UNWIND_INFO_COMPRESSED_ENTRY_FUNC_OFFSET(
        _addressSpace.get32(_addr + index * sizeof(uint32_t)));
  }
  uint16_t encodingIndex(uint32_t index) const {
    return UNWIND_INFO_COMPRESSED_ENTRY_ENCODING_INDEX(
        _addressSpace.get32(_addr + index * sizeof(uint32_t)));
  }

private:
  A &_addressSpace;
  typename A::pint_t _addr;
};

template <typename A> class UnwindSectionLsdaArray {
public:
  UnwindSectionLsdaArray(A &addressSpace, typename A::pint_t addr)
      : _addressSpace(addressSpace), _addr(addr) {}

  uint32_t functionOffset(uint32_t index) const {
    return _addressSpace.get32(
        _addr + arrayoffsetof(unwind_info_section_header_lsda_index_entry,
                              index, functionOffset));
  }
  uint32_t lsdaOffset(uint32_t index) const {
    return _addressSpace.get32(
        _addr + arrayoffsetof(unwind_info_section_header_lsda_index_entry,
                              index, lsdaOffset));
  }

private:
  A                   &_addressSpace;
  typename A::pint_t   _addr;
};
#endif // _LIBUNWIND_SUPPORT_COMPACT_UNWIND

class _LIBUNWIND_HIDDEN AbstractUnwindCursor {
public:
  // NOTE: provide a class specific placement deallocation function (S5.3.4 p20)
  // This avoids an unnecessary dependency to libc++abi.
  void operator delete(void *, size_t) {}

  virtual ~AbstractUnwindCursor() {}
  virtual bool validReg(int) { _LIBUNWIND_ABORT("validReg not implemented"); }
  virtual unw_word_t getReg(int) { _LIBUNWIND_ABORT("getReg not implemented"); }
  virtual void setReg(int, unw_word_t) {
    _LIBUNWIND_ABORT("setReg not implemented");
  }
  virtual bool validFloatReg(int) {
    _LIBUNWIND_ABORT("validFloatReg not implemented");
  }
  virtual unw_fpreg_t getFloatReg(int) {
    _LIBUNWIND_ABORT("getFloatReg not implemented");
  }
  virtual void setFloatReg(int, unw_fpreg_t) {
    _LIBUNWIND_ABORT("setFloatReg not implemented");
  }
  virtual int step() { _LIBUNWIND_ABORT("step not implemented"); }
  virtual void getInfo(unw_proc_info_t *) {
    _LIBUNWIND_ABORT("getInfo not implemented");
  }
  virtual void jumpto() { _LIBUNWIND_ABORT("jumpto not implemented"); }
  virtual bool isSignalFrame() {
    _LIBUNWIND_ABORT("isSignalFrame not implemented");
  }
  virtual bool getFunctionName(char *, size_t, unw_word_t *) {
    _LIBUNWIND_ABORT("getFunctionName not implemented");
  }
  virtual void setInfoBasedOnIPRegister(bool = false) {
    _LIBUNWIND_ABORT("setInfoBasedOnIPRegister not implemented");
  }
  virtual const char *getRegisterName(int) {
    _LIBUNWIND_ABORT("getRegisterName not implemented");
  }
#ifdef __arm__
  virtual void saveVFPAsX() { _LIBUNWIND_ABORT("saveVFPAsX not implemented"); }
#endif
};

/// UnwindCursor contains all state (including all register values) during
/// an unwind.  This is normally stack allocated inside a unw_cursor_t.
template <typename A, typename R>
class UnwindCursor : public AbstractUnwindCursor{
  typedef typename A::pint_t pint_t;
public:
                      UnwindCursor(unw_context_t *context, A &as);
                      UnwindCursor(A &as, void *threadArg);
  virtual             ~UnwindCursor() {}
  virtual bool        validReg(int);
  virtual unw_word_t  getReg(int);
  virtual void        setReg(int, unw_word_t);
  virtual bool        validFloatReg(int);
  virtual unw_fpreg_t getFloatReg(int);
  virtual void        setFloatReg(int, unw_fpreg_t);
  virtual int         step();
  virtual void        getInfo(unw_proc_info_t *);
  virtual void        jumpto();
  virtual bool        isSignalFrame();
  virtual bool        getFunctionName(char *buf, size_t len, unw_word_t *off);
  virtual void        setInfoBasedOnIPRegister(bool isReturnAddress = false);
  virtual const char *getRegisterName(int num);
#ifdef __arm__
  virtual void        saveVFPAsX();
#endif

private:

#if _LIBUNWIND_ARM_EHABI
  bool getInfoFromEHABISection(pint_t pc, const UnwindInfoSections &sects);

  int stepWithEHABI() {
    size_t len = 0;
    size_t off = 0;
    // FIXME: Calling decode_eht_entry() here is violating the libunwind
    // abstraction layer.
    const uint32_t *ehtp =
        decode_eht_entry(reinterpret_cast<const uint32_t *>(_info.unwind_info),
                         &off, &len);
    if (_Unwind_VRS_Interpret((_Unwind_Context *)this, ehtp, off, len) !=
            _URC_CONTINUE_UNWIND)
      return UNW_STEP_END;
    return UNW_STEP_SUCCESS;
  }
#endif

#if _LIBUNWIND_SUPPORT_DWARF_UNWIND
  bool getInfoFromDwarfSection(pint_t pc, const UnwindInfoSections &sects,
                                            uint32_t fdeSectionOffsetHint=0);
  int stepWithDwarfFDE() {
    return DwarfInstructions<A, R>::stepWithDwarf(_addressSpace,
                                              (pint_t)this->getReg(UNW_REG_IP),
                                              (pint_t)_info.unwind_info,
                                              _registers);
  }
#endif

#if _LIBUNWIND_SUPPORT_COMPACT_UNWIND
  bool getInfoFromCompactEncodingSection(pint_t pc,
                                            const UnwindInfoSections &sects);
  int stepWithCompactEncoding() {
  #if _LIBUNWIND_SUPPORT_DWARF_UNWIND
    if ( compactSaysUseDwarf() )
      return stepWithDwarfFDE();
  #endif
    R dummy;
    return stepWithCompactEncoding(dummy);
  }

  int stepWithCompactEncoding(Registers_x86_64 &) {
    return CompactUnwinder_x86_64<A>::stepWithCompactEncoding(
        _info.format, _info.start_ip, _addressSpace, _registers);
  }

  int stepWithCompactEncoding(Registers_x86 &) {
    return CompactUnwinder_x86<A>::stepWithCompactEncoding(
        _info.format, (uint32_t)_info.start_ip, _addressSpace, _registers);
  }

  int stepWithCompactEncoding(Registers_ppc &) {
    return UNW_EINVAL;
  }

  int stepWithCompactEncoding(Registers_arm64 &) {
    return CompactUnwinder_arm64<A>::stepWithCompactEncoding(
        _info.format, _info.start_ip, _addressSpace, _registers);
  }

  bool compactSaysUseDwarf(uint32_t *offset=NULL) const {
    R dummy;
    return compactSaysUseDwarf(dummy, offset);
  }

  bool compactSaysUseDwarf(Registers_x86_64 &, uint32_t *offset) const {
    if ((_info.format & UNWIND_X86_64_MODE_MASK) == UNWIND_X86_64_MODE_DWARF) {
      if (offset)
        *offset = (_info.format & UNWIND_X86_64_DWARF_SECTION_OFFSET);
      return true;
    }
    return false;
  }

  bool compactSaysUseDwarf(Registers_x86 &, uint32_t *offset) const {
    if ((_info.format & UNWIND_X86_MODE_MASK) == UNWIND_X86_MODE_DWARF) {
      if (offset)
        *offset = (_info.format & UNWIND_X86_DWARF_SECTION_OFFSET);
      return true;
    }
    return false;
  }

  bool compactSaysUseDwarf(Registers_ppc &, uint32_t *) const {
    return true;
  }

  bool compactSaysUseDwarf(Registers_arm64 &, uint32_t *offset) const {
    if ((_info.format & UNWIND_ARM64_MODE_MASK) == UNWIND_ARM64_MODE_DWARF) {
      if (offset)
        *offset = (_info.format & UNWIND_ARM64_DWARF_SECTION_OFFSET);
      return true;
    }
    return false;
  }
#endif // _LIBUNWIND_SUPPORT_COMPACT_UNWIND

#if _LIBUNWIND_SUPPORT_DWARF_UNWIND
  compact_unwind_encoding_t dwarfEncoding() const {
    R dummy;
    return dwarfEncoding(dummy);
  }

  compact_unwind_encoding_t dwarfEncoding(Registers_x86_64 &) const {
    return UNWIND_X86_64_MODE_DWARF;
  }

  compact_unwind_encoding_t dwarfEncoding(Registers_x86 &) const {
    return UNWIND_X86_MODE_DWARF;
  }

  compact_unwind_encoding_t dwarfEncoding(Registers_ppc &) const {
    return 0;
  }

  compact_unwind_encoding_t dwarfEncoding(Registers_arm64 &) const {
    return UNWIND_ARM64_MODE_DWARF;
  }

  compact_unwind_encoding_t dwarfEncoding(Registers_or1k &) const {
    return 0;
  }
#endif // _LIBUNWIND_SUPPORT_DWARF_UNWIND


  A               &_addressSpace;
  R                _registers;
  unw_proc_info_t  _info;
  bool             _unwindInfoMissing;
  bool             _isSignalFrame;
};


template <typename A, typename R>
UnwindCursor<A, R>::UnwindCursor(unw_context_t *context, A &as)
    : _addressSpace(as), _registers(context), _unwindInfoMissing(false),
      _isSignalFrame(false) {
  static_assert(sizeof(UnwindCursor<A, R>) < sizeof(unw_cursor_t),
                "UnwindCursor<> does not fit in unw_cursor_t");
  memset(&_info, 0, sizeof(_info));
}

template <typename A, typename R>
UnwindCursor<A, R>::UnwindCursor(A &as, void *)
    : _addressSpace(as), _unwindInfoMissing(false), _isSignalFrame(false) {
  memset(&_info, 0, sizeof(_info));
  // FIXME
  // fill in _registers from thread arg
}


template <typename A, typename R>
bool UnwindCursor<A, R>::validReg(int regNum) {
  return _registers.validRegister(regNum);
}

template <typename A, typename R>
unw_word_t UnwindCursor<A, R>::getReg(int regNum) {
  return _registers.getRegister(regNum);
}

template <typename A, typename R>
void UnwindCursor<A, R>::setReg(int regNum, unw_word_t value) {
  _registers.setRegister(regNum, (typename A::pint_t)value);
}

template <typename A, typename R>
bool UnwindCursor<A, R>::validFloatReg(int regNum) {
  return _registers.validFloatRegister(regNum);
}

template <typename A, typename R>
unw_fpreg_t UnwindCursor<A, R>::getFloatReg(int regNum) {
  return _registers.getFloatRegister(regNum);
}

template <typename A, typename R>
void UnwindCursor<A, R>::setFloatReg(int regNum, unw_fpreg_t value) {
  _registers.setFloatRegister(regNum, value);
}

template <typename A, typename R> void UnwindCursor<A, R>::jumpto() {
  _registers.jumpto();
}

#ifdef __arm__
template <typename A, typename R> void UnwindCursor<A, R>::saveVFPAsX() {
  _registers.saveVFPAsX();
}
#endif

template <typename A, typename R>
const char *UnwindCursor<A, R>::getRegisterName(int regNum) {
  return _registers.getRegisterName(regNum);
}

template <typename A, typename R> bool UnwindCursor<A, R>::isSignalFrame() {
  return _isSignalFrame;
}

#if _LIBUNWIND_ARM_EHABI
struct EHABIIndexEntry {
  uint32_t functionOffset;
  uint32_t data;
};

template<typename A>
struct EHABISectionIterator {
  typedef EHABISectionIterator _Self;

  typedef std::random_access_iterator_tag iterator_category;
  typedef typename A::pint_t value_type;
  typedef typename A::pint_t* pointer;
  typedef typename A::pint_t& reference;
  typedef size_t size_type;
  typedef size_t difference_type;

  static _Self begin(A& addressSpace, const UnwindInfoSections& sects) {
    return _Self(addressSpace, sects, 0);
  }
  static _Self end(A& addressSpace, const UnwindInfoSections& sects) {
    return _Self(addressSpace, sects, sects.arm_section_length);
  }

  EHABISectionIterator(A& addressSpace, const UnwindInfoSections& sects, size_t i)
      : _i(i), _addressSpace(&addressSpace), _sects(&sects) {}

  _Self& operator++() { ++_i; return *this; }
  _Self& operator+=(size_t a) { _i += a; return *this; }
  _Self& operator--() { assert(_i > 0); --_i; return *this; }
  _Self& operator-=(size_t a) { assert(_i >= a); _i -= a; return *this; }

  _Self operator+(size_t a) { _Self out = *this; out._i += a; return out; }
  _Self operator-(size_t a) { assert(_i >= a); _Self out = *this; out._i -= a; return out; }

  size_t operator-(const _Self& other) { return _i - other._i; }

  bool operator==(const _Self& other) const {
    assert(_addressSpace == other._addressSpace);
    assert(_sects == other._sects);
    return _i == other._i;
  }

  typename A::pint_t operator*() const { return functionAddress(); }

  typename A::pint_t functionAddress() const {
    typename A::pint_t indexAddr = _sects->arm_section + arrayoffsetof(
        EHABIIndexEntry, _i, functionOffset);
    return indexAddr + signExtendPrel31(_addressSpace->get32(indexAddr));
  }

  typename A::pint_t dataAddress() {
    typename A::pint_t indexAddr = _sects->arm_section + arrayoffsetof(
        EHABIIndexEntry, _i, data);
    return indexAddr;
  }

 private:
  size_t _i;
  A* _addressSpace;
  const UnwindInfoSections* _sects;
};

template <typename A, typename R>
bool UnwindCursor<A, R>::getInfoFromEHABISection(
    pint_t pc,
    const UnwindInfoSections &sects) {
  EHABISectionIterator<A> begin =
      EHABISectionIterator<A>::begin(_addressSpace, sects);
  EHABISectionIterator<A> end =
      EHABISectionIterator<A>::end(_addressSpace, sects);

  EHABISectionIterator<A> itNextPC = std::upper_bound(begin, end, pc);
  if (itNextPC == begin || itNextPC == end)
    return false;
  EHABISectionIterator<A> itThisPC = itNextPC - 1;

  pint_t thisPC = itThisPC.functionAddress();
  pint_t nextPC = itNextPC.functionAddress();
  pint_t indexDataAddr = itThisPC.dataAddress();

  if (indexDataAddr == 0)
    return false;

  uint32_t indexData = _addressSpace.get32(indexDataAddr);
  if (indexData == UNW_EXIDX_CANTUNWIND)
    return false;

  // If the high bit is set, the exception handling table entry is inline inside
  // the index table entry on the second word (aka |indexDataAddr|). Otherwise,
  // the table points at an offset in the exception handling table (section 5 EHABI).
  pint_t exceptionTableAddr;
  uint32_t exceptionTableData;
  bool isSingleWordEHT;
  if (indexData & 0x80000000) {
    exceptionTableAddr = indexDataAddr;
    // TODO(ajwong): Should this data be 0?
    exceptionTableData = indexData;
    isSingleWordEHT = true;
  } else {
    exceptionTableAddr = indexDataAddr + signExtendPrel31(indexData);
    exceptionTableData = _addressSpace.get32(exceptionTableAddr);
    isSingleWordEHT = false;
  }

  // Now we know the 3 things:
  //   exceptionTableAddr -- exception handler table entry.
  //   exceptionTableData -- the data inside the first word of the eht entry.
  //   isSingleWordEHT -- whether the entry is in the index.
  unw_word_t personalityRoutine = 0xbadf00d;
  bool scope32 = false;
  uintptr_t lsda;

  // If the high bit in the exception handling table entry is set, the entry is
  // in compact form (section 6.3 EHABI).
  if (exceptionTableData & 0x80000000) {
    // Grab the index of the personality routine from the compact form.
    uint32_t choice = (exceptionTableData & 0x0f000000) >> 24;
    uint32_t extraWords = 0;
    switch (choice) {
      case 0:
        personalityRoutine = (unw_word_t) &__aeabi_unwind_cpp_pr0;
        extraWords = 0;
        scope32 = false;
        lsda = isSingleWordEHT ? 0 : (exceptionTableAddr + 4);
        break;
      case 1:
        personalityRoutine = (unw_word_t) &__aeabi_unwind_cpp_pr1;
        extraWords = (exceptionTableData & 0x00ff0000) >> 16;
        scope32 = false;
        lsda = exceptionTableAddr + (extraWords + 1) * 4;
        break;
      case 2:
        personalityRoutine = (unw_word_t) &__aeabi_unwind_cpp_pr2;
        extraWords = (exceptionTableData & 0x00ff0000) >> 16;
        scope32 = true;
        lsda = exceptionTableAddr + (extraWords + 1) * 4;
        break;
      default:
        _LIBUNWIND_ABORT("unknown personality routine");
        return false;
    }

    if (isSingleWordEHT) {
      if (extraWords != 0) {
        _LIBUNWIND_ABORT("index inlined table detected but pr function "
                         "requires extra words");
        return false;
      }
    }
  } else {
    pint_t personalityAddr =
        exceptionTableAddr + signExtendPrel31(exceptionTableData);
    personalityRoutine = personalityAddr;

    // ARM EHABI # 6.2, # 9.2
    //
    //  +---- ehtp
    //  v
    // +--------------------------------------+
    // | +--------+--------+--------+-------+ |
    // | |0| prel31 to personalityRoutine   | |
    // | +--------+--------+--------+-------+ |
    // | |      N |      unwind opcodes     | |  <-- UnwindData
    // | +--------+--------+--------+-------+ |
    // | | Word 2        unwind opcodes     | |
    // | +--------+--------+--------+-------+ |
    // | ...                                  |
    // | +--------+--------+--------+-------+ |
    // | | Word N        unwind opcodes     | |
    // | +--------+--------+--------+-------+ |
    // | | LSDA                             | |  <-- lsda
    // | | ...                              | |
    // | +--------+--------+--------+-------+ |
    // +--------------------------------------+

    uint32_t *UnwindData = reinterpret_cast<uint32_t*>(exceptionTableAddr) + 1;
    uint32_t FirstDataWord = *UnwindData;
    size_t N = ((FirstDataWord >> 24) & 0xff);
    size_t NDataWords = N + 1;
    lsda = reinterpret_cast<uintptr_t>(UnwindData + NDataWords);
  }

  _info.start_ip = thisPC;
  _info.end_ip = nextPC;
  _info.handler = personalityRoutine;
  _info.unwind_info = exceptionTableAddr;
  _info.lsda = lsda;
  // flags is pr_cache.additional. See EHABI #7.2 for definition of bit 0.
  _info.flags = isSingleWordEHT ? 1 : 0 | scope32 ? 0x2 : 0;  // Use enum?

  return true;
}
#endif

#if _LIBUNWIND_SUPPORT_DWARF_UNWIND
template <typename A, typename R>
bool UnwindCursor<A, R>::getInfoFromDwarfSection(pint_t pc,
                                                const UnwindInfoSections &sects,
                                                uint32_t fdeSectionOffsetHint) {
  typename CFI_Parser<A>::FDE_Info fdeInfo;
  typename CFI_Parser<A>::CIE_Info cieInfo;
  bool foundFDE = false;
  bool foundInCache = false;
  // If compact encoding table gave offset into dwarf section, go directly there
  if (fdeSectionOffsetHint != 0) {
    foundFDE = CFI_Parser<A>::findFDE(_addressSpace, pc, sects.dwarf_section,
                                    (uint32_t)sects.dwarf_section_length,
                                    sects.dwarf_section + fdeSectionOffsetHint,
                                    &fdeInfo, &cieInfo);
  }
#if _LIBUNWIND_SUPPORT_DWARF_INDEX
  if (!foundFDE && (sects.dwarf_index_section != 0)) {
    foundFDE = EHHeaderParser<A>::findFDE(
        _addressSpace, pc, sects.dwarf_index_section,
        (uint32_t)sects.dwarf_index_section_length, &fdeInfo, &cieInfo);
  }
#endif
  if (!foundFDE) {
    // otherwise, search cache of previously found FDEs.
    pint_t cachedFDE = DwarfFDECache<A>::findFDE(sects.dso_base, pc);
    if (cachedFDE != 0) {
      foundFDE =
          CFI_Parser<A>::findFDE(_addressSpace, pc, sects.dwarf_section,
                                 (uint32_t)sects.dwarf_section_length,
                                 cachedFDE, &fdeInfo, &cieInfo);
      foundInCache = foundFDE;
    }
  }
  if (!foundFDE) {
    // Still not found, do full scan of __eh_frame section.
    foundFDE = CFI_Parser<A>::findFDE(_addressSpace, pc, sects.dwarf_section,
                                      (uint32_t)sects.dwarf_section_length, 0,
                                      &fdeInfo, &cieInfo);
  }
  if (foundFDE) {
    typename CFI_Parser<A>::PrologInfo prolog;
    if (CFI_Parser<A>::parseFDEInstructions(_addressSpace, fdeInfo, cieInfo, pc,
                                            &prolog)) {
      // Save off parsed FDE info
      _info.start_ip          = fdeInfo.pcStart;
      _info.end_ip            = fdeInfo.pcEnd;
      _info.lsda              = fdeInfo.lsda;
      _info.handler           = cieInfo.personality;
      _info.gp                = prolog.spExtraArgSize;
      _info.flags             = 0;
      _info.format            = dwarfEncoding();
      _info.unwind_info       = fdeInfo.fdeStart;
      _info.unwind_info_size  = (uint32_t)fdeInfo.fdeLength;
      _info.extra             = (unw_word_t) sects.dso_base;

      // Add to cache (to make next lookup faster) if we had no hint
      // and there was no index.
      if (!foundInCache && (fdeSectionOffsetHint == 0)) {
  #if _LIBUNWIND_SUPPORT_DWARF_INDEX
        if (sects.dwarf_index_section == 0)
  #endif
        DwarfFDECache<A>::add(sects.dso_base, fdeInfo.pcStart, fdeInfo.pcEnd,
                              fdeInfo.fdeStart);
      }
      return true;
    }
  }
  //_LIBUNWIND_DEBUG_LOG("can't find/use FDE for pc=0x%llX\n", (uint64_t)pc);
  return false;
}
#endif // _LIBUNWIND_SUPPORT_DWARF_UNWIND


#if _LIBUNWIND_SUPPORT_COMPACT_UNWIND
template <typename A, typename R>
bool UnwindCursor<A, R>::getInfoFromCompactEncodingSection(pint_t pc,
                                              const UnwindInfoSections &sects) {
  const bool log = false;
  if (log)
    fprintf(stderr, "getInfoFromCompactEncodingSection(pc=0x%llX, mh=0x%llX)\n",
            (uint64_t)pc, (uint64_t)sects.dso_base);

  const UnwindSectionHeader<A> sectionHeader(_addressSpace,
                                                sects.compact_unwind_section);
  if (sectionHeader.version() != UNWIND_SECTION_VERSION)
    return false;

  // do a binary search of top level index to find page with unwind info
  pint_t targetFunctionOffset = pc - sects.dso_base;
  const UnwindSectionIndexArray<A> topIndex(_addressSpace,
                                           sects.compact_unwind_section
                                         + sectionHeader.indexSectionOffset());
  uint32_t low = 0;
  uint32_t high = sectionHeader.indexCount();
  uint32_t last = high - 1;
  while (low < high) {
    uint32_t mid = (low + high) / 2;
    //if ( log ) fprintf(stderr, "\tmid=%d, low=%d, high=%d, *mid=0x%08X\n",
    //mid, low, high, topIndex.functionOffset(mid));
    if (topIndex.functionOffset(mid) <= targetFunctionOffset) {
      if ((mid == last) ||
          (topIndex.functionOffset(mid + 1) > targetFunctionOffset)) {
        low = mid;
        break;
      } else {
        low = mid + 1;
      }
    } else {
      high = mid;
    }
  }
  const uint32_t firstLevelFunctionOffset = topIndex.functionOffset(low);
  const uint32_t firstLevelNextPageFunctionOffset =
      topIndex.functionOffset(low + 1);
  const pint_t secondLevelAddr =
      sects.compact_unwind_section + topIndex.secondLevelPagesSectionOffset(low);
  const pint_t lsdaArrayStartAddr =
      sects.compact_unwind_section + topIndex.lsdaIndexArraySectionOffset(low);
  const pint_t lsdaArrayEndAddr =
      sects.compact_unwind_section + topIndex.lsdaIndexArraySectionOffset(low+1);
  if (log)
    fprintf(stderr, "\tfirst level search for result index=%d "
                    "to secondLevelAddr=0x%llX\n",
                    low, (uint64_t) secondLevelAddr);
  // do a binary search of second level page index
  uint32_t encoding = 0;
  pint_t funcStart = 0;
  pint_t funcEnd = 0;
  pint_t lsda = 0;
  pint_t personality = 0;
  uint32_t pageKind = _addressSpace.get32(secondLevelAddr);
  if (pageKind == UNWIND_SECOND_LEVEL_REGULAR) {
    // regular page
    UnwindSectionRegularPageHeader<A> pageHeader(_addressSpace,
                                                 secondLevelAddr);
    UnwindSectionRegularArray<A> pageIndex(
        _addressSpace, secondLevelAddr + pageHeader.entryPageOffset());
    // binary search looks for entry with e where index[e].offset <= pc <
    // index[e+1].offset
    if (log)
      fprintf(stderr, "\tbinary search for targetFunctionOffset=0x%08llX in "
                      "regular page starting at secondLevelAddr=0x%llX\n",
              (uint64_t) targetFunctionOffset, (uint64_t) secondLevelAddr);
    low = 0;
    high = pageHeader.entryCount();
    while (low < high) {
      uint32_t mid = (low + high) / 2;
      if (pageIndex.functionOffset(mid) <= targetFunctionOffset) {
        if (mid == (uint32_t)(pageHeader.entryCount() - 1)) {
          // at end of table
          low = mid;
          funcEnd = firstLevelNextPageFunctionOffset + sects.dso_base;
          break;
        } else if (pageIndex.functionOffset(mid + 1) > targetFunctionOffset) {
          // next is too big, so we found it
          low = mid;
          funcEnd = pageIndex.functionOffset(low + 1) + sects.dso_base;
          break;
        } else {
          low = mid + 1;
        }
      } else {
        high = mid;
      }
    }
    encoding = pageIndex.encoding(low);
    funcStart = pageIndex.functionOffset(low) + sects.dso_base;
    if (pc < funcStart) {
      if (log)
        fprintf(
            stderr,
            "\tpc not in table, pc=0x%llX, funcStart=0x%llX, funcEnd=0x%llX\n",
            (uint64_t) pc, (uint64_t) funcStart, (uint64_t) funcEnd);
      return false;
    }
    if (pc > funcEnd) {
      if (log)
        fprintf(
            stderr,
            "\tpc not in table, pc=0x%llX, funcStart=0x%llX, funcEnd=0x%llX\n",
            (uint64_t) pc, (uint64_t) funcStart, (uint64_t) funcEnd);
      return false;
    }
  } else if (pageKind == UNWIND_SECOND_LEVEL_COMPRESSED) {
    // compressed page
    UnwindSectionCompressedPageHeader<A> pageHeader(_addressSpace,
                                                    secondLevelAddr);
    UnwindSectionCompressedArray<A> pageIndex(
        _addressSpace, secondLevelAddr + pageHeader.entryPageOffset());
    const uint32_t targetFunctionPageOffset =
        (uint32_t)(targetFunctionOffset - firstLevelFunctionOffset);
    // binary search looks for entry with e where index[e].offset <= pc <
    // index[e+1].offset
    if (log)
      fprintf(stderr, "\tbinary search of compressed page starting at "
                      "secondLevelAddr=0x%llX\n",
              (uint64_t) secondLevelAddr);
    low = 0;
    last = pageHeader.entryCount() - 1;
    high = pageHeader.entryCount();
    while (low < high) {
      uint32_t mid = (low + high) / 2;
      if (pageIndex.functionOffset(mid) <= targetFunctionPageOffset) {
        if ((mid == last) ||
            (pageIndex.functionOffset(mid + 1) > targetFunctionPageOffset)) {
          low = mid;
          break;
        } else {
          low = mid + 1;
        }
      } else {
        high = mid;
      }
    }
    funcStart = pageIndex.functionOffset(low) + firstLevelFunctionOffset
                                                              + sects.dso_base;
    if (low < last)
      funcEnd =
          pageIndex.functionOffset(low + 1) + firstLevelFunctionOffset
                                                              + sects.dso_base;
    else
      funcEnd = firstLevelNextPageFunctionOffset + sects.dso_base;
    if (pc < funcStart) {
      _LIBUNWIND_DEBUG_LOG("malformed __unwind_info, pc=0x%llX not in second  "
                           "level compressed unwind table. funcStart=0x%llX\n",
                            (uint64_t) pc, (uint64_t) funcStart);
      return false;
    }
    if (pc > funcEnd) {
      _LIBUNWIND_DEBUG_LOG("malformed __unwind_info, pc=0x%llX not in second  "
                          "level compressed unwind table. funcEnd=0x%llX\n",
                           (uint64_t) pc, (uint64_t) funcEnd);
      return false;
    }
    uint16_t encodingIndex = pageIndex.encodingIndex(low);
    if (encodingIndex < sectionHeader.commonEncodingsArrayCount()) {
      // encoding is in common table in section header
      encoding = _addressSpace.get32(
          sects.compact_unwind_section +
          sectionHeader.commonEncodingsArraySectionOffset() +
          encodingIndex * sizeof(uint32_t));
    } else {
      // encoding is in page specific table
      uint16_t pageEncodingIndex =
          encodingIndex - (uint16_t)sectionHeader.commonEncodingsArrayCount();
      encoding = _addressSpace.get32(secondLevelAddr +
                                     pageHeader.encodingsPageOffset() +
                                     pageEncodingIndex * sizeof(uint32_t));
    }
  } else {
    _LIBUNWIND_DEBUG_LOG("malformed __unwind_info at 0x%0llX bad second "
                         "level page\n",
                          (uint64_t) sects.compact_unwind_section);
    return false;
  }

  // look up LSDA, if encoding says function has one
  if (encoding & UNWIND_HAS_LSDA) {
    UnwindSectionLsdaArray<A> lsdaIndex(_addressSpace, lsdaArrayStartAddr);
    uint32_t funcStartOffset = (uint32_t)(funcStart - sects.dso_base);
    low = 0;
    high = (uint32_t)(lsdaArrayEndAddr - lsdaArrayStartAddr) /
                    sizeof(unwind_info_section_header_lsda_index_entry);
    // binary search looks for entry with exact match for functionOffset
    if (log)
      fprintf(stderr,
              "\tbinary search of lsda table for targetFunctionOffset=0x%08X\n",
              funcStartOffset);
    while (low < high) {
      uint32_t mid = (low + high) / 2;
      if (lsdaIndex.functionOffset(mid) == funcStartOffset) {
        lsda = lsdaIndex.lsdaOffset(mid) + sects.dso_base;
        break;
      } else if (lsdaIndex.functionOffset(mid) < funcStartOffset) {
        low = mid + 1;
      } else {
        high = mid;
      }
    }
    if (lsda == 0) {
      _LIBUNWIND_DEBUG_LOG("found encoding 0x%08X with HAS_LSDA bit set for "
                    "pc=0x%0llX, but lsda table has no entry\n",
                    encoding, (uint64_t) pc);
      return false;
    }
  }

  // extact personality routine, if encoding says function has one
  uint32_t personalityIndex = (encoding & UNWIND_PERSONALITY_MASK) >>
                              (__builtin_ctz(UNWIND_PERSONALITY_MASK));
  if (personalityIndex != 0) {
    --personalityIndex; // change 1-based to zero-based index
    if (personalityIndex > sectionHeader.personalityArrayCount()) {
      _LIBUNWIND_DEBUG_LOG("found encoding 0x%08X with personality index %d,  "
                            "but personality table has only %d entires\n",
                            encoding, personalityIndex,
                            sectionHeader.personalityArrayCount());
      return false;
    }
    int32_t personalityDelta = (int32_t)_addressSpace.get32(
        sects.compact_unwind_section +
        sectionHeader.personalityArraySectionOffset() +
        personalityIndex * sizeof(uint32_t));
    pint_t personalityPointer = sects.dso_base + (pint_t)personalityDelta;
    personality = _addressSpace.getP(personalityPointer);
    if (log)
      fprintf(stderr, "getInfoFromCompactEncodingSection(pc=0x%llX), "
                      "personalityDelta=0x%08X, personality=0x%08llX\n",
              (uint64_t) pc, personalityDelta, (uint64_t) personality);
  }

  if (log)
    fprintf(stderr, "getInfoFromCompactEncodingSection(pc=0x%llX), "
                    "encoding=0x%08X, lsda=0x%08llX for funcStart=0x%llX\n",
            (uint64_t) pc, encoding, (uint64_t) lsda, (uint64_t) funcStart);
  _info.start_ip = funcStart;
  _info.end_ip = funcEnd;
  _info.lsda = lsda;
  _info.handler = personality;
  _info.gp = 0;
  _info.flags = 0;
  _info.format = encoding;
  _info.unwind_info = 0;
  _info.unwind_info_size = 0;
  _info.extra = sects.dso_base;
  return true;
}
#endif // _LIBUNWIND_SUPPORT_COMPACT_UNWIND


template <typename A, typename R>
void UnwindCursor<A, R>::setInfoBasedOnIPRegister(bool isReturnAddress) {
  pint_t pc = (pint_t)this->getReg(UNW_REG_IP);
#if _LIBUNWIND_ARM_EHABI
  // Remove the thumb bit so the IP represents the actual instruction address.
  // This matches the behaviour of _Unwind_GetIP on arm.
  pc &= (pint_t)~0x1;
#endif

  // If the last line of a function is a "throw" the compiler sometimes
  // emits no instructions after the call to __cxa_throw.  This means
  // the return address is actually the start of the next function.
  // To disambiguate this, back up the pc when we know it is a return
  // address.
  if (isReturnAddress)
    --pc;

  // Ask address space object to find unwind sections for this pc.
  UnwindInfoSections sects;
  if (_addressSpace.findUnwindSections(pc, sects)) {
#if _LIBUNWIND_SUPPORT_COMPACT_UNWIND
    // If there is a compact unwind encoding table, look there first.
    if (sects.compact_unwind_section != 0) {
      if (this->getInfoFromCompactEncodingSection(pc, sects)) {
  #if _LIBUNWIND_SUPPORT_DWARF_UNWIND
        // Found info in table, done unless encoding says to use dwarf.
        uint32_t dwarfOffset;
        if ((sects.dwarf_section != 0) && compactSaysUseDwarf(&dwarfOffset)) {
          if (this->getInfoFromDwarfSection(pc, sects, dwarfOffset)) {
            // found info in dwarf, done
            return;
          }
        }
  #endif
        // If unwind table has entry, but entry says there is no unwind info,
        // record that we have no unwind info.
        if (_info.format == 0)
          _unwindInfoMissing = true;
        return;
      }
    }
#endif // _LIBUNWIND_SUPPORT_COMPACT_UNWIND

#if _LIBUNWIND_SUPPORT_DWARF_UNWIND
    // If there is dwarf unwind info, look there next.
    if (sects.dwarf_section != 0) {
      if (this->getInfoFromDwarfSection(pc, sects)) {
        // found info in dwarf, done
        return;
      }
    }
#endif

#if _LIBUNWIND_ARM_EHABI
    // If there is ARM EHABI unwind info, look there next.
    if (sects.arm_section != 0 && this->getInfoFromEHABISection(pc, sects))
      return;
#endif
  }

#if _LIBUNWIND_SUPPORT_DWARF_UNWIND
  // There is no static unwind info for this pc. Look to see if an FDE was
  // dynamically registered for it.
  pint_t cachedFDE = DwarfFDECache<A>::findFDE(0, pc);
  if (cachedFDE != 0) {
    CFI_Parser<LocalAddressSpace>::FDE_Info fdeInfo;
    CFI_Parser<LocalAddressSpace>::CIE_Info cieInfo;
    const char *msg = CFI_Parser<A>::decodeFDE(_addressSpace,
                                                cachedFDE, &fdeInfo, &cieInfo);
    if (msg == NULL) {
      typename CFI_Parser<A>::PrologInfo prolog;
      if (CFI_Parser<A>::parseFDEInstructions(_addressSpace, fdeInfo, cieInfo,
                                                                pc, &prolog)) {
        // save off parsed FDE info
        _info.start_ip         = fdeInfo.pcStart;
        _info.end_ip           = fdeInfo.pcEnd;
        _info.lsda             = fdeInfo.lsda;
        _info.handler          = cieInfo.personality;
        _info.gp               = prolog.spExtraArgSize;
                                  // Some frameless functions need SP
                                  // altered when resuming in function.
        _info.flags            = 0;
        _info.format           = dwarfEncoding();
        _info.unwind_info      = fdeInfo.fdeStart;
        _info.unwind_info_size = (uint32_t)fdeInfo.fdeLength;
        _info.extra            = 0;
        return;
      }
    }
  }

  // Lastly, ask AddressSpace object about platform specific ways to locate
  // other FDEs.
  pint_t fde;
  if (_addressSpace.findOtherFDE(pc, fde)) {
    CFI_Parser<LocalAddressSpace>::FDE_Info fdeInfo;
    CFI_Parser<LocalAddressSpace>::CIE_Info cieInfo;
    if (!CFI_Parser<A>::decodeFDE(_addressSpace, fde, &fdeInfo, &cieInfo)) {
      // Double check this FDE is for a function that includes the pc.
      if ((fdeInfo.pcStart <= pc) && (pc < fdeInfo.pcEnd)) {
        typename CFI_Parser<A>::PrologInfo prolog;
        if (CFI_Parser<A>::parseFDEInstructions(_addressSpace, fdeInfo,
                                                cieInfo, pc, &prolog)) {
          // save off parsed FDE info
          _info.start_ip         = fdeInfo.pcStart;
          _info.end_ip           = fdeInfo.pcEnd;
          _info.lsda             = fdeInfo.lsda;
          _info.handler          = cieInfo.personality;
          _info.gp               = prolog.spExtraArgSize;
          _info.flags            = 0;
          _info.format           = dwarfEncoding();
          _info.unwind_info      = fdeInfo.fdeStart;
          _info.unwind_info_size = (uint32_t)fdeInfo.fdeLength;
          _info.extra            = 0;
          return;
        }
      }
    }
  }
#endif // #if _LIBUNWIND_SUPPORT_DWARF_UNWIND

  // no unwind info, flag that we can't reliably unwind
  _unwindInfoMissing = true;
}

template <typename A, typename R>
int UnwindCursor<A, R>::step() {
  // Bottom of stack is defined is when unwind info cannot be found.
  if (_unwindInfoMissing)
    return UNW_STEP_END;

  // Use unwinding info to modify register set as if function returned.
  int result;
#if _LIBUNWIND_SUPPORT_COMPACT_UNWIND
  result = this->stepWithCompactEncoding();
#elif _LIBUNWIND_SUPPORT_DWARF_UNWIND
  result = this->stepWithDwarfFDE();
#elif _LIBUNWIND_ARM_EHABI
  result = this->stepWithEHABI();
#else
  #error Need _LIBUNWIND_SUPPORT_COMPACT_UNWIND or \
              _LIBUNWIND_SUPPORT_DWARF_UNWIND or \
              _LIBUNWIND_ARM_EHABI
#endif

  // update info based on new PC
  if (result == UNW_STEP_SUCCESS) {
    this->setInfoBasedOnIPRegister(true);
    if (_unwindInfoMissing)
      return UNW_STEP_END;
    if (_info.gp)
      setReg(UNW_REG_SP, getReg(UNW_REG_SP) + _info.gp);
  }

  return result;
}

template <typename A, typename R>
void UnwindCursor<A, R>::getInfo(unw_proc_info_t *info) {
  *info = _info;
}

template <typename A, typename R>
bool UnwindCursor<A, R>::getFunctionName(char *buf, size_t bufLen,
                                                           unw_word_t *offset) {
  return _addressSpace.findFunctionName((pint_t)this->getReg(UNW_REG_IP),
                                         buf, bufLen, offset);
}

} // namespace libunwind

#endif // __UNWINDCURSOR_HPP__