aboutsummaryrefslogtreecommitdiffstats
path: root/ELF/OutputSections.cpp
blob: 2aa814524d6be2d22179b00fc4862284205c90b4 (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
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
//===- OutputSections.cpp -------------------------------------------------===//
//
//                             The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "OutputSections.h"
#include "Config.h"
#include "SymbolTable.h"
#include "Target.h"
#include "llvm/Support/MathExtras.h"

using namespace llvm;
using namespace llvm::object;
using namespace llvm::support::endian;
using namespace llvm::ELF;

using namespace lld;
using namespace lld::elf2;

bool elf2::HasGotOffRel = false;

template <class ELFT>
OutputSectionBase<ELFT>::OutputSectionBase(StringRef Name, uint32_t Type,
                                           uintX_t Flags)
    : Name(Name) {
  memset(&Header, 0, sizeof(Elf_Shdr));
  Header.sh_type = Type;
  Header.sh_flags = Flags;
}

template <class ELFT>
GotPltSection<ELFT>::GotPltSection()
    : OutputSectionBase<ELFT>(".got.plt", SHT_PROGBITS, SHF_ALLOC | SHF_WRITE) {
  this->Header.sh_addralign = sizeof(uintX_t);
}

template <class ELFT> void GotPltSection<ELFT>::addEntry(SymbolBody *Sym) {
  Sym->GotPltIndex = Target->getGotPltHeaderEntriesNum() + Entries.size();
  Entries.push_back(Sym);
}

template <class ELFT> bool GotPltSection<ELFT>::empty() const {
  return Entries.empty();
}

template <class ELFT>
typename GotPltSection<ELFT>::uintX_t
GotPltSection<ELFT>::getEntryAddr(const SymbolBody &B) const {
  return this->getVA() + B.GotPltIndex * sizeof(uintX_t);
}

template <class ELFT> void GotPltSection<ELFT>::finalize() {
  this->Header.sh_size =
      (Target->getGotPltHeaderEntriesNum() + Entries.size()) * sizeof(uintX_t);
}

template <class ELFT> void GotPltSection<ELFT>::writeTo(uint8_t *Buf) {
  Target->writeGotPltHeaderEntries(Buf);
  Buf += Target->getGotPltHeaderEntriesNum() * sizeof(uintX_t);
  for (const SymbolBody *B : Entries) {
    Target->writeGotPltEntry(Buf, Out<ELFT>::Plt->getEntryAddr(*B));
    Buf += sizeof(uintX_t);
  }
}

template <class ELFT>
GotSection<ELFT>::GotSection()
    : OutputSectionBase<ELFT>(".got", SHT_PROGBITS, SHF_ALLOC | SHF_WRITE) {
  if (Config->EMachine == EM_MIPS)
    this->Header.sh_flags |= SHF_MIPS_GPREL;
  this->Header.sh_addralign = sizeof(uintX_t);
}

template <class ELFT> void GotSection<ELFT>::addEntry(SymbolBody *Sym) {
  Sym->GotIndex = Target->getGotHeaderEntriesNum() + Entries.size();
  Entries.push_back(Sym);
}

template <class ELFT> bool GotSection<ELFT>::addDynTlsEntry(SymbolBody *Sym) {
  if (Sym->hasGlobalDynIndex())
    return false;
  Sym->GlobalDynIndex = Target->getGotHeaderEntriesNum() + Entries.size();
  // Global Dynamic TLS entries take two GOT slots.
  Entries.push_back(Sym);
  Entries.push_back(nullptr);
  return true;
}

template <class ELFT> bool GotSection<ELFT>::addCurrentModuleTlsIndex() {
  if (LocalTlsIndexOff != uint32_t(-1))
    return false;
  Entries.push_back(nullptr);
  Entries.push_back(nullptr);
  LocalTlsIndexOff = (Entries.size() - 2) * sizeof(uintX_t);
  return true;
}

template <class ELFT>
typename GotSection<ELFT>::uintX_t
GotSection<ELFT>::getEntryAddr(const SymbolBody &B) const {
  return this->getVA() + B.GotIndex * sizeof(uintX_t);
}

template <class ELFT>
typename GotSection<ELFT>::uintX_t
GotSection<ELFT>::getGlobalDynAddr(const SymbolBody &B) const {
  return this->getVA() + B.GlobalDynIndex * sizeof(uintX_t);
}

template <class ELFT>
const SymbolBody *GotSection<ELFT>::getMipsFirstGlobalEntry() const {
  return Entries.empty() ? nullptr : Entries.front();
}

template <class ELFT>
unsigned GotSection<ELFT>::getMipsLocalEntriesNum() const {
  // TODO: Update when the support of GOT entries for local symbols is added.
  return Target->getGotHeaderEntriesNum();
}

template <class ELFT> void GotSection<ELFT>::finalize() {
  this->Header.sh_size =
      (Target->getGotHeaderEntriesNum() + Entries.size()) * sizeof(uintX_t);
}

template <class ELFT> void GotSection<ELFT>::writeTo(uint8_t *Buf) {
  Target->writeGotHeaderEntries(Buf);
  Buf += Target->getGotHeaderEntriesNum() * sizeof(uintX_t);
  for (const SymbolBody *B : Entries) {
    uint8_t *Entry = Buf;
    Buf += sizeof(uintX_t);
    if (!B)
      continue;
    // MIPS has special rules to fill up GOT entries.
    // See "Global Offset Table" in Chapter 5 in the following document
    // for detailed description:
    // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
    // As the first approach, we can just store addresses for all symbols.
    if (Config->EMachine != EM_MIPS && canBePreempted(B, false))
      continue; // The dynamic linker will take care of it.
    uintX_t VA = getSymVA<ELFT>(*B);
    write<uintX_t, ELFT::TargetEndianness, sizeof(uintX_t)>(Entry, VA);
  }
}

template <class ELFT>
PltSection<ELFT>::PltSection()
    : OutputSectionBase<ELFT>(".plt", SHT_PROGBITS, SHF_ALLOC | SHF_EXECINSTR) {
  this->Header.sh_addralign = 16;
}

template <class ELFT> void PltSection<ELFT>::writeTo(uint8_t *Buf) {
  size_t Off = 0;
  bool LazyReloc = Target->supportsLazyRelocations();
  if (LazyReloc) {
    // First write PLT[0] entry which is special.
    Target->writePltZeroEntry(Buf, Out<ELFT>::GotPlt->getVA(), this->getVA());
    Off += Target->getPltZeroEntrySize();
  }
  for (auto &I : Entries) {
    const SymbolBody *E = I.first;
    unsigned RelOff = I.second;
    uint64_t GotVA =
        LazyReloc ? Out<ELFT>::GotPlt->getVA() : Out<ELFT>::Got->getVA();
    uint64_t GotE = LazyReloc ? Out<ELFT>::GotPlt->getEntryAddr(*E)
                              : Out<ELFT>::Got->getEntryAddr(*E);
    uint64_t Plt = this->getVA() + Off;
    Target->writePltEntry(Buf + Off, GotVA, GotE, Plt, E->PltIndex, RelOff);
    Off += Target->getPltEntrySize();
  }
}

template <class ELFT> void PltSection<ELFT>::addEntry(SymbolBody *Sym) {
  Sym->PltIndex = Entries.size();
  unsigned RelOff = Target->supportsLazyRelocations()
                        ? Out<ELFT>::RelaPlt->getRelocOffset()
                        : Out<ELFT>::RelaDyn->getRelocOffset();
  Entries.push_back(std::make_pair(Sym, RelOff));
}

template <class ELFT>
typename PltSection<ELFT>::uintX_t
PltSection<ELFT>::getEntryAddr(const SymbolBody &B) const {
  return this->getVA() + Target->getPltZeroEntrySize() +
         B.PltIndex * Target->getPltEntrySize();
}

template <class ELFT> void PltSection<ELFT>::finalize() {
  this->Header.sh_size = Target->getPltZeroEntrySize() +
                         Entries.size() * Target->getPltEntrySize();
}

template <class ELFT>
RelocationSection<ELFT>::RelocationSection(StringRef Name, bool IsRela)
    : OutputSectionBase<ELFT>(Name, IsRela ? SHT_RELA : SHT_REL, SHF_ALLOC),
      IsRela(IsRela) {
  this->Header.sh_entsize = IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
  this->Header.sh_addralign = ELFT::Is64Bits ? 8 : 4;
}

// Applies corresponding symbol and type for dynamic tls relocation.
// Returns true if relocation was handled.
template <class ELFT>
bool RelocationSection<ELFT>::applyTlsDynamicReloc(SymbolBody *Body,
                                                   uint32_t Type, Elf_Rel *P,
                                                   Elf_Rel *N) {
  if (Target->isTlsLocalDynamicReloc(Type)) {
    P->setSymbolAndType(0, Target->getTlsModuleIndexReloc(), Config->Mips64EL);
    P->r_offset = Out<ELFT>::Got->getLocalTlsIndexVA();
    return true;
  }

  if (!Body || !Target->isTlsGlobalDynamicReloc(Type))
    return false;

  if (Target->isTlsOptimized(Type, Body)) {
    P->setSymbolAndType(Body->DynamicSymbolTableIndex,
                        Target->getTlsGotReloc(), Config->Mips64EL);
    P->r_offset = Out<ELFT>::Got->getEntryAddr(*Body);
    return true;
  }

  P->setSymbolAndType(Body->DynamicSymbolTableIndex,
                      Target->getTlsModuleIndexReloc(), Config->Mips64EL);
  P->r_offset = Out<ELFT>::Got->getGlobalDynAddr(*Body);
  N->setSymbolAndType(Body->DynamicSymbolTableIndex,
                      Target->getTlsOffsetReloc(), Config->Mips64EL);
  N->r_offset = Out<ELFT>::Got->getGlobalDynAddr(*Body) + sizeof(uintX_t);
  return true;
}

template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *Buf) {
  for (const DynamicReloc<ELFT> &Rel : Relocs) {
    auto *P = reinterpret_cast<Elf_Rel *>(Buf);
    Buf += IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);

    // Skip placeholder for global dynamic TLS relocation pair. It was already
    // handled by the previous relocation.
    if (!Rel.C)
      continue;

    InputSectionBase<ELFT> &C = *Rel.C;
    const Elf_Rel &RI = *Rel.RI;
    uint32_t SymIndex = RI.getSymbol(Config->Mips64EL);
    const ObjectFile<ELFT> &File = *C.getFile();
    SymbolBody *Body = File.getSymbolBody(SymIndex);
    if (Body)
      Body = Body->repl();

    uint32_t Type = RI.getType(Config->Mips64EL);
    if (applyTlsDynamicReloc(Body, Type, P, reinterpret_cast<Elf_Rel *>(Buf)))
      continue;
    bool NeedsCopy = Body && Target->needsCopyRel(Type, *Body);
    bool NeedsGot = Body && Target->relocNeedsGot(Type, *Body);
    bool CBP = canBePreempted(Body, NeedsGot);
    bool LazyReloc = Body && Target->supportsLazyRelocations() &&
                     Target->relocNeedsPlt(Type, *Body);
    bool IsDynRelative = Type == Target->getRelativeReloc();

    unsigned Sym = CBP ? Body->DynamicSymbolTableIndex : 0;
    unsigned Reloc;
    if (!CBP && Body && isGnuIFunc<ELFT>(*Body))
      Reloc = Target->getIRelativeReloc();
    else if (!CBP || IsDynRelative)
      Reloc = Target->getRelativeReloc();
    else if (LazyReloc)
      Reloc = Target->getPltReloc();
    else if (NeedsGot)
      Reloc = Body->isTls() ? Target->getTlsGotReloc() : Target->getGotReloc();
    else if (NeedsCopy)
      Reloc = Target->getCopyReloc();
    else
      Reloc = Target->getDynReloc(Type);
    P->setSymbolAndType(Sym, Reloc, Config->Mips64EL);

    if (LazyReloc)
      P->r_offset = Out<ELFT>::GotPlt->getEntryAddr(*Body);
    else if (NeedsGot)
      P->r_offset = Out<ELFT>::Got->getEntryAddr(*Body);
    else if (NeedsCopy)
      P->r_offset = Out<ELFT>::Bss->getVA() +
                    cast<SharedSymbol<ELFT>>(Body)->OffsetInBss;
    else
      P->r_offset = C.getOffset(RI.r_offset) + C.OutSec->getVA();

    uintX_t OrigAddend = 0;
    if (IsRela && !NeedsGot)
      OrigAddend = static_cast<const Elf_Rela &>(RI).r_addend;

    uintX_t Addend;
    if (NeedsCopy)
      Addend = 0;
    else if (CBP || IsDynRelative)
      Addend = OrigAddend;
    else if (Body)
      Addend = getSymVA<ELFT>(*Body) + OrigAddend;
    else if (IsRela)
      Addend =
          getLocalRelTarget(File, static_cast<const Elf_Rela &>(RI),
                            getAddend<ELFT>(static_cast<const Elf_Rela &>(RI)));
    else
      Addend = getLocalRelTarget(File, RI, 0);

    if (IsRela)
      static_cast<Elf_Rela *>(P)->r_addend = Addend;
  }
}

template <class ELFT> unsigned RelocationSection<ELFT>::getRelocOffset() {
  const unsigned EntrySize = IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
  return EntrySize * Relocs.size();
}

template <class ELFT> void RelocationSection<ELFT>::finalize() {
  this->Header.sh_link = Static ? Out<ELFT>::SymTab->SectionIndex
                                : Out<ELFT>::DynSymTab->SectionIndex;
  this->Header.sh_size = Relocs.size() * this->Header.sh_entsize;
}

template <class ELFT>
InterpSection<ELFT>::InterpSection()
    : OutputSectionBase<ELFT>(".interp", SHT_PROGBITS, SHF_ALLOC) {
  this->Header.sh_size = Config->DynamicLinker.size() + 1;
  this->Header.sh_addralign = 1;
}

template <class ELFT>
void OutputSectionBase<ELFT>::writeHeaderTo(Elf_Shdr *SHdr) {
  Header.sh_name = Out<ELFT>::ShStrTab->addString(Name);
  *SHdr = Header;
}

template <class ELFT> void InterpSection<ELFT>::writeTo(uint8_t *Buf) {
  memcpy(Buf, Config->DynamicLinker.data(), Config->DynamicLinker.size());
}

template <class ELFT>
HashTableSection<ELFT>::HashTableSection()
    : OutputSectionBase<ELFT>(".hash", SHT_HASH, SHF_ALLOC) {
  this->Header.sh_entsize = sizeof(Elf_Word);
  this->Header.sh_addralign = sizeof(Elf_Word);
}

static uint32_t hashSysv(StringRef Name) {
  uint32_t H = 0;
  for (char C : Name) {
    H = (H << 4) + C;
    uint32_t G = H & 0xf0000000;
    if (G)
      H ^= G >> 24;
    H &= ~G;
  }
  return H;
}

template <class ELFT> void HashTableSection<ELFT>::finalize() {
  this->Header.sh_link = Out<ELFT>::DynSymTab->SectionIndex;

  unsigned NumEntries = 2;                 // nbucket and nchain.
  NumEntries += Out<ELFT>::DynSymTab->getNumSymbols(); // The chain entries.

  // Create as many buckets as there are symbols.
  // FIXME: This is simplistic. We can try to optimize it, but implementing
  // support for SHT_GNU_HASH is probably even more profitable.
  NumEntries += Out<ELFT>::DynSymTab->getNumSymbols();
  this->Header.sh_size = NumEntries * sizeof(Elf_Word);
}

template <class ELFT> void HashTableSection<ELFT>::writeTo(uint8_t *Buf) {
  unsigned NumSymbols = Out<ELFT>::DynSymTab->getNumSymbols();
  auto *P = reinterpret_cast<Elf_Word *>(Buf);
  *P++ = NumSymbols; // nbucket
  *P++ = NumSymbols; // nchain

  Elf_Word *Buckets = P;
  Elf_Word *Chains = P + NumSymbols;

  for (SymbolBody *Body : Out<ELFT>::DynSymTab->getSymbols()) {
    StringRef Name = Body->getName();
    unsigned I = Body->DynamicSymbolTableIndex;
    uint32_t Hash = hashSysv(Name) % NumSymbols;
    Chains[I] = Buckets[Hash];
    Buckets[Hash] = I;
  }
}

static uint32_t hashGnu(StringRef Name) {
  uint32_t H = 5381;
  for (uint8_t C : Name)
    H = (H << 5) + H + C;
  return H;
}

template <class ELFT>
GnuHashTableSection<ELFT>::GnuHashTableSection()
    : OutputSectionBase<ELFT>(".gnu.hash", SHT_GNU_HASH, SHF_ALLOC) {
  this->Header.sh_entsize = ELFT::Is64Bits ? 0 : 4;
  this->Header.sh_addralign = ELFT::Is64Bits ? 8 : 4;
}

template <class ELFT>
unsigned GnuHashTableSection<ELFT>::calcNBuckets(unsigned NumHashed) {
  if (!NumHashed)
    return 0;

  // These values are prime numbers which are not greater than 2^(N-1) + 1.
  // In result, for any particular NumHashed we return a prime number
  // which is not greater than NumHashed.
  static const unsigned Primes[] = {
      1,   1,    3,    3,    7,    13,    31,    61,    127,   251,
      509, 1021, 2039, 4093, 8191, 16381, 32749, 65521, 131071};

  return Primes[std::min<unsigned>(Log2_32_Ceil(NumHashed),
                                   array_lengthof(Primes) - 1)];
}

// Bloom filter estimation: at least 8 bits for each hashed symbol.
// GNU Hash table requirement: it should be a power of 2,
//   the minimum value is 1, even for an empty table.
// Expected results for a 32-bit target:
//   calcMaskWords(0..4)   = 1
//   calcMaskWords(5..8)   = 2
//   calcMaskWords(9..16)  = 4
// For a 64-bit target:
//   calcMaskWords(0..8)   = 1
//   calcMaskWords(9..16)  = 2
//   calcMaskWords(17..32) = 4
template <class ELFT>
unsigned GnuHashTableSection<ELFT>::calcMaskWords(unsigned NumHashed) {
  if (!NumHashed)
    return 1;
  return NextPowerOf2((NumHashed - 1) / sizeof(Elf_Off));
}

template <class ELFT> void GnuHashTableSection<ELFT>::finalize() {
  unsigned NumHashed = HashedSymbols.size();
  NBuckets = calcNBuckets(NumHashed);
  MaskWords = calcMaskWords(NumHashed);
  // Second hash shift estimation: just predefined values.
  Shift2 = ELFT::Is64Bits ? 6 : 5;

  this->Header.sh_link = Out<ELFT>::DynSymTab->SectionIndex;
  this->Header.sh_size = sizeof(Elf_Word) * 4            // Header
                         + sizeof(Elf_Off) * MaskWords   // Bloom Filter
                         + sizeof(Elf_Word) * NBuckets   // Hash Buckets
                         + sizeof(Elf_Word) * NumHashed; // Hash Values
}

template <class ELFT> void GnuHashTableSection<ELFT>::writeTo(uint8_t *Buf) {
  writeHeader(Buf);
  if (HashedSymbols.empty())
    return;
  writeBloomFilter(Buf);
  writeHashTable(Buf);
}

template <class ELFT>
void GnuHashTableSection<ELFT>::writeHeader(uint8_t *&Buf) {
  auto *P = reinterpret_cast<Elf_Word *>(Buf);
  *P++ = NBuckets;
  *P++ = Out<ELFT>::DynSymTab->getNumSymbols() - HashedSymbols.size();
  *P++ = MaskWords;
  *P++ = Shift2;
  Buf = reinterpret_cast<uint8_t *>(P);
}

template <class ELFT>
void GnuHashTableSection<ELFT>::writeBloomFilter(uint8_t *&Buf) {
  unsigned C = sizeof(Elf_Off) * 8;

  auto *Masks = reinterpret_cast<Elf_Off *>(Buf);
  for (const HashedSymbolData &Item : HashedSymbols) {
    size_t Pos = (Item.Hash / C) & (MaskWords - 1);
    uintX_t V = (uintX_t(1) << (Item.Hash % C)) |
                (uintX_t(1) << ((Item.Hash >> Shift2) % C));
    Masks[Pos] |= V;
  }
  Buf += sizeof(Elf_Off) * MaskWords;
}

template <class ELFT>
void GnuHashTableSection<ELFT>::writeHashTable(uint8_t *Buf) {
  Elf_Word *Buckets = reinterpret_cast<Elf_Word *>(Buf);
  Elf_Word *Values = Buckets + NBuckets;

  int PrevBucket = -1;
  int I = 0;
  for (const HashedSymbolData &Item : HashedSymbols) {
    int Bucket = Item.Hash % NBuckets;
    assert(PrevBucket <= Bucket);
    if (Bucket != PrevBucket) {
      Buckets[Bucket] = Item.Body->DynamicSymbolTableIndex;
      PrevBucket = Bucket;
      if (I > 0)
        Values[I - 1] |= 1;
    }
    Values[I] = Item.Hash & ~1;
    ++I;
  }
  if (I > 0)
    Values[I - 1] |= 1;
}

static bool includeInGnuHashTable(SymbolBody *B) {
  // Assume that includeInDynamicSymtab() is already checked.
  return !B->isUndefined();
}

template <class ELFT>
void GnuHashTableSection<ELFT>::addSymbols(std::vector<SymbolBody *> &Symbols) {
  std::vector<SymbolBody *> NotHashed;
  NotHashed.reserve(Symbols.size());
  HashedSymbols.reserve(Symbols.size());
  for (SymbolBody *B : Symbols) {
    if (includeInGnuHashTable(B))
      HashedSymbols.push_back(HashedSymbolData{B, hashGnu(B->getName())});
    else
      NotHashed.push_back(B);
  }
  if (HashedSymbols.empty())
    return;

  unsigned NBuckets = calcNBuckets(HashedSymbols.size());
  std::stable_sort(HashedSymbols.begin(), HashedSymbols.end(),
                   [&](const HashedSymbolData &L, const HashedSymbolData &R) {
                     return L.Hash % NBuckets < R.Hash % NBuckets;
                   });

  Symbols = std::move(NotHashed);
  for (const HashedSymbolData &Item : HashedSymbols)
    Symbols.push_back(Item.Body);
}

template <class ELFT>
DynamicSection<ELFT>::DynamicSection(SymbolTable<ELFT> &SymTab)
    : OutputSectionBase<ELFT>(".dynamic", SHT_DYNAMIC, SHF_ALLOC | SHF_WRITE),
      SymTab(SymTab) {
  Elf_Shdr &Header = this->Header;
  Header.sh_addralign = ELFT::Is64Bits ? 8 : 4;
  Header.sh_entsize = ELFT::Is64Bits ? 16 : 8;

  // .dynamic section is not writable on MIPS.
  // See "Special Section" in Chapter 4 in the following document:
  // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
  if (Config->EMachine == EM_MIPS)
    Header.sh_flags = SHF_ALLOC;
}

template <class ELFT> void DynamicSection<ELFT>::finalize() {
  if (this->Header.sh_size)
    return; // Already finalized.

  Elf_Shdr &Header = this->Header;
  Header.sh_link = Out<ELFT>::DynStrTab->SectionIndex;

  unsigned NumEntries = 0;
  if (Out<ELFT>::RelaDyn->hasRelocs()) {
    ++NumEntries; // DT_RELA / DT_REL
    ++NumEntries; // DT_RELASZ / DT_RELSZ
    ++NumEntries; // DT_RELAENT / DT_RELENT
  }
  if (Out<ELFT>::RelaPlt && Out<ELFT>::RelaPlt->hasRelocs()) {
    ++NumEntries; // DT_JMPREL
    ++NumEntries; // DT_PLTRELSZ
    ++NumEntries; // DT_PLTGOT / DT_MIPS_PLTGOT
    ++NumEntries; // DT_PLTREL
  }

  ++NumEntries; // DT_SYMTAB
  ++NumEntries; // DT_SYMENT
  ++NumEntries; // DT_STRTAB
  ++NumEntries; // DT_STRSZ
  if (Out<ELFT>::GnuHashTab)
    ++NumEntries; // DT_GNU_HASH
  if (Out<ELFT>::HashTab)
    ++NumEntries; // DT_HASH

  if (!Config->RPath.empty()) {
    ++NumEntries; // DT_RUNPATH / DT_RPATH
    Out<ELFT>::DynStrTab->reserve(Config->RPath);
  }

  if (!Config->SoName.empty()) {
    ++NumEntries; // DT_SONAME
    Out<ELFT>::DynStrTab->reserve(Config->SoName);
  }

  if (PreInitArraySec)
    NumEntries += 2;
  if (InitArraySec)
    NumEntries += 2;
  if (FiniArraySec)
    NumEntries += 2;

  for (const std::unique_ptr<SharedFile<ELFT>> &F : SymTab.getSharedFiles()) {
    if (!F->isNeeded())
      continue;
    Out<ELFT>::DynStrTab->reserve(F->getSoName());
    ++NumEntries;
  }

  if (Symbol *S = SymTab.getSymbols().lookup(Config->Init))
    InitSym = S->Body;
  if (Symbol *S = SymTab.getSymbols().lookup(Config->Fini))
    FiniSym = S->Body;
  if (InitSym)
    ++NumEntries; // DT_INIT
  if (FiniSym)
    ++NumEntries; // DT_FINI

  if (Config->Bsymbolic)
    DtFlags |= DF_SYMBOLIC;
  if (Config->ZNodelete)
    DtFlags1 |= DF_1_NODELETE;
  if (Config->ZNow) {
    DtFlags |= DF_BIND_NOW;
    DtFlags1 |= DF_1_NOW;
  }
  if (Config->ZOrigin) {
    DtFlags |= DF_ORIGIN;
    DtFlags1 |= DF_1_ORIGIN;
  }

  if (DtFlags)
    ++NumEntries; // DT_FLAGS
  if (DtFlags1)
    ++NumEntries; // DT_FLAGS_1

  if (!Config->Entry.empty())
    ++NumEntries; // DT_DEBUG

  if (Config->EMachine == EM_MIPS) {
    ++NumEntries; // DT_MIPS_RLD_VERSION
    ++NumEntries; // DT_MIPS_FLAGS
    ++NumEntries; // DT_MIPS_BASE_ADDRESS
    ++NumEntries; // DT_MIPS_SYMTABNO
    ++NumEntries; // DT_MIPS_LOCAL_GOTNO
    ++NumEntries; // DT_MIPS_GOTSYM;
    ++NumEntries; // DT_PLTGOT
    if (Out<ELFT>::MipsRldMap)
      ++NumEntries; // DT_MIPS_RLD_MAP
  }

  ++NumEntries; // DT_NULL

  Header.sh_size = NumEntries * Header.sh_entsize;
}

template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *Buf) {
  auto *P = reinterpret_cast<Elf_Dyn *>(Buf);

  auto WritePtr = [&](int32_t Tag, uint64_t Val) {
    P->d_tag = Tag;
    P->d_un.d_ptr = Val;
    ++P;
  };

  auto WriteVal = [&](int32_t Tag, uint32_t Val) {
    P->d_tag = Tag;
    P->d_un.d_val = Val;
    ++P;
  };

  if (Out<ELFT>::RelaDyn->hasRelocs()) {
    bool IsRela = Out<ELFT>::RelaDyn->isRela();
    WritePtr(IsRela ? DT_RELA : DT_REL, Out<ELFT>::RelaDyn->getVA());
    WriteVal(IsRela ? DT_RELASZ : DT_RELSZ, Out<ELFT>::RelaDyn->getSize());
    WriteVal(IsRela ? DT_RELAENT : DT_RELENT,
             IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel));
  }
  if (Out<ELFT>::RelaPlt && Out<ELFT>::RelaPlt->hasRelocs()) {
    WritePtr(DT_JMPREL, Out<ELFT>::RelaPlt->getVA());
    WriteVal(DT_PLTRELSZ, Out<ELFT>::RelaPlt->getSize());
    // On MIPS, the address of the .got.plt section is stored in
    // the DT_MIPS_PLTGOT entry because the DT_PLTGOT entry points to
    // the .got section. See "Dynamic Section" in the following document:
    // https://sourceware.org/ml/binutils/2008-07/txt00000.txt
    WritePtr((Config->EMachine == EM_MIPS) ? DT_MIPS_PLTGOT : DT_PLTGOT,
             Out<ELFT>::GotPlt->getVA());
    WriteVal(DT_PLTREL, Out<ELFT>::RelaPlt->isRela() ? DT_RELA : DT_REL);
  }

  WritePtr(DT_SYMTAB, Out<ELFT>::DynSymTab->getVA());
  WritePtr(DT_SYMENT, sizeof(Elf_Sym));
  WritePtr(DT_STRTAB, Out<ELFT>::DynStrTab->getVA());
  WriteVal(DT_STRSZ, Out<ELFT>::DynStrTab->getSize());
  if (Out<ELFT>::GnuHashTab)
    WritePtr(DT_GNU_HASH, Out<ELFT>::GnuHashTab->getVA());
  if (Out<ELFT>::HashTab)
    WritePtr(DT_HASH, Out<ELFT>::HashTab->getVA());

  // If --enable-new-dtags is set, lld emits DT_RUNPATH
  // instead of DT_RPATH. The two tags are functionally
  // equivalent except for the following:
  // - DT_RUNPATH is searched after LD_LIBRARY_PATH, while
  //   DT_RPATH is searched before.
  // - DT_RUNPATH is used only to search for direct
  //   dependencies of the object it's contained in, while
  //   DT_RPATH is used for indirect dependencies as well.
  if (!Config->RPath.empty())
    WriteVal(Config->EnableNewDtags ? DT_RUNPATH : DT_RPATH,
             Out<ELFT>::DynStrTab->addString(Config->RPath));

  if (!Config->SoName.empty())
    WriteVal(DT_SONAME, Out<ELFT>::DynStrTab->addString(Config->SoName));

  auto WriteArray = [&](int32_t T1, int32_t T2,
                        const OutputSectionBase<ELFT> *Sec) {
    if (!Sec)
      return;
    WritePtr(T1, Sec->getVA());
    WriteVal(T2, Sec->getSize());
  };
  WriteArray(DT_PREINIT_ARRAY, DT_PREINIT_ARRAYSZ, PreInitArraySec);
  WriteArray(DT_INIT_ARRAY, DT_INIT_ARRAYSZ, InitArraySec);
  WriteArray(DT_FINI_ARRAY, DT_FINI_ARRAYSZ, FiniArraySec);

  for (const std::unique_ptr<SharedFile<ELFT>> &F : SymTab.getSharedFiles())
    if (F->isNeeded())
      WriteVal(DT_NEEDED, Out<ELFT>::DynStrTab->addString(F->getSoName()));

  if (InitSym)
    WritePtr(DT_INIT, getSymVA<ELFT>(*InitSym));
  if (FiniSym)
    WritePtr(DT_FINI, getSymVA<ELFT>(*FiniSym));
  if (DtFlags)
    WriteVal(DT_FLAGS, DtFlags);
  if (DtFlags1)
    WriteVal(DT_FLAGS_1, DtFlags1);
  if (!Config->Entry.empty())
    WriteVal(DT_DEBUG, 0);

  // See "Dynamic Section" in Chapter 5 in the following document
  // for detailed description:
  // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
  if (Config->EMachine == EM_MIPS) {
    WriteVal(DT_MIPS_RLD_VERSION, 1);
    WriteVal(DT_MIPS_FLAGS, RHF_NOTPOT);
    WritePtr(DT_MIPS_BASE_ADDRESS, Target->getVAStart());
    WriteVal(DT_MIPS_SYMTABNO, Out<ELFT>::DynSymTab->getNumSymbols());
    WriteVal(DT_MIPS_LOCAL_GOTNO, Out<ELFT>::Got->getMipsLocalEntriesNum());
    if (const SymbolBody *B = Out<ELFT>::Got->getMipsFirstGlobalEntry())
      WriteVal(DT_MIPS_GOTSYM, B->DynamicSymbolTableIndex);
    else
      WriteVal(DT_MIPS_GOTSYM, Out<ELFT>::DynSymTab->getNumSymbols());
    WritePtr(DT_PLTGOT, Out<ELFT>::Got->getVA());
    if (Out<ELFT>::MipsRldMap)
      WritePtr(DT_MIPS_RLD_MAP, Out<ELFT>::MipsRldMap->getVA());
  }

  WriteVal(DT_NULL, 0);
}

template <class ELFT>
OutputSection<ELFT>::OutputSection(StringRef Name, uint32_t Type,
                                   uintX_t Flags)
    : OutputSectionBase<ELFT>(Name, Type, Flags) {}

template <class ELFT>
void OutputSection<ELFT>::addSection(InputSectionBase<ELFT> *C) {
  auto *S = cast<InputSection<ELFT>>(C);
  Sections.push_back(S);
  S->OutSec = this;
  uint32_t Align = S->getAlign();
  if (Align > this->Header.sh_addralign)
    this->Header.sh_addralign = Align;

  uintX_t Off = this->Header.sh_size;
  Off = align(Off, Align);
  S->OutSecOff = Off;
  Off += S->getSize();
  this->Header.sh_size = Off;
}

template <class ELFT>
typename ELFFile<ELFT>::uintX_t elf2::getSymVA(const SymbolBody &S) {
  switch (S.kind()) {
  case SymbolBody::DefinedSyntheticKind: {
    auto &D = cast<DefinedSynthetic<ELFT>>(S);
    return D.Section.getVA() + D.Value;
  }
  case SymbolBody::DefinedRegularKind: {
    const auto &DR = cast<DefinedRegular<ELFT>>(S);
    InputSectionBase<ELFT> *SC = DR.Section;
    if (!SC)
      return DR.Sym.st_value;

    // Symbol offsets for AMDGPU need to be the offset in bytes of the symbol
    // from the beginning of the section.
    if (Config->EMachine == EM_AMDGPU)
      return SC->getOffset(DR.Sym);
    if (DR.Sym.getType() == STT_TLS)
      return SC->OutSec->getVA() + SC->getOffset(DR.Sym) -
             Out<ELFT>::TlsPhdr->p_vaddr;
    return SC->OutSec->getVA() + SC->getOffset(DR.Sym);
  }
  case SymbolBody::DefinedCommonKind:
    return Out<ELFT>::Bss->getVA() + cast<DefinedCommon>(S).OffsetInBss;
  case SymbolBody::SharedKind: {
    auto &SS = cast<SharedSymbol<ELFT>>(S);
    if (SS.NeedsCopy)
      return Out<ELFT>::Bss->getVA() + SS.OffsetInBss;
    return 0;
  }
  case SymbolBody::UndefinedElfKind:
  case SymbolBody::UndefinedKind:
    return 0;
  case SymbolBody::LazyKind:
    assert(S.isUsedInRegularObj() && "Lazy symbol reached writer");
    return 0;
  }
  llvm_unreachable("Invalid symbol kind");
}

// Returns a VA which a relocatin RI refers to. Used only for local symbols.
// For non-local symbols, use getSymVA instead.
template <class ELFT, bool IsRela>
typename ELFFile<ELFT>::uintX_t
elf2::getLocalRelTarget(const ObjectFile<ELFT> &File,
                        const Elf_Rel_Impl<ELFT, IsRela> &RI,
                        typename ELFFile<ELFT>::uintX_t Addend) {
  typedef typename ELFFile<ELFT>::Elf_Sym Elf_Sym;
  typedef typename ELFFile<ELFT>::uintX_t uintX_t;

  // PPC64 has a special relocation representing the TOC base pointer
  // that does not have a corresponding symbol.
  if (Config->EMachine == EM_PPC64 && RI.getType(false) == R_PPC64_TOC)
    return getPPC64TocBase() + Addend;

  const Elf_Sym *Sym =
      File.getObj().getRelocationSymbol(&RI, File.getSymbolTable());

  if (!Sym)
    error("Unsupported relocation without symbol");

  InputSectionBase<ELFT> *Section = File.getSection(*Sym);

  if (Sym->getType() == STT_TLS)
    return (Section->OutSec->getVA() + Section->getOffset(*Sym) + Addend) -
           Out<ELFT>::TlsPhdr->p_vaddr;

  // According to the ELF spec reference to a local symbol from outside
  // the group are not allowed. Unfortunately .eh_frame breaks that rule
  // and must be treated specially. For now we just replace the symbol with
  // 0.
  if (Section == &InputSection<ELFT>::Discarded || !Section->isLive())
    return Addend;

  uintX_t VA = Section->OutSec->getVA();
  if (isa<InputSection<ELFT>>(Section))
    return VA + Section->getOffset(*Sym) + Addend;

  uintX_t Offset = Sym->st_value;
  if (Sym->getType() == STT_SECTION) {
    Offset += Addend;
    Addend = 0;
  }
  return VA + Section->getOffset(Offset) + Addend;
}

// Returns true if a symbol can be replaced at load-time by a symbol
// with the same name defined in other ELF executable or DSO.
bool elf2::canBePreempted(const SymbolBody *Body, bool NeedsGot) {
  if (!Body)
    return false;  // Body is a local symbol.
  if (Body->isShared())
    return true;

  if (Body->isUndefined()) {
    if (!Body->isWeak())
      return true;

    // This is an horrible corner case. Ideally we would like to say that any
    // undefined symbol can be preempted so that the dynamic linker has a
    // chance of finding it at runtime.
    //
    // The problem is that the code sequence used to test for weak undef
    // functions looks like
    // if (func) func()
    // If the code is -fPIC the first reference is a load from the got and
    // everything works.
    // If the code is not -fPIC there is no reasonable way to solve it:
    // * A relocation writing to the text segment will fail (it is ro).
    // * A copy relocation doesn't work for functions.
    // * The trick of using a plt entry as the address would fail here since
    //   the plt entry would have a non zero address.
    // Since we cannot do anything better, we just resolve the symbol to 0 and
    // don't produce a dynamic relocation.
    //
    // As an extra hack, assume that if we are producing a shared library the
    // user knows what he or she is doing and can handle a dynamic relocation.
    return Config->Shared || NeedsGot;
  }
  if (!Config->Shared)
    return false;
  return Body->getVisibility() == STV_DEFAULT;
}

template <class ELFT> void OutputSection<ELFT>::writeTo(uint8_t *Buf) {
  for (InputSection<ELFT> *C : Sections)
    C->writeTo(Buf);
}

template <class ELFT>
EHOutputSection<ELFT>::EHOutputSection(StringRef Name, uint32_t Type,
                                       uintX_t Flags)
    : OutputSectionBase<ELFT>(Name, Type, Flags) {}

template <class ELFT>
EHRegion<ELFT>::EHRegion(EHInputSection<ELFT> *S, unsigned Index)
    : S(S), Index(Index) {}

template <class ELFT> StringRef EHRegion<ELFT>::data() const {
  ArrayRef<uint8_t> SecData = S->getSectionData();
  ArrayRef<std::pair<uintX_t, uintX_t>> Offsets = S->Offsets;
  size_t Start = Offsets[Index].first;
  size_t End =
      Index == Offsets.size() - 1 ? SecData.size() : Offsets[Index + 1].first;
  return StringRef((const char *)SecData.data() + Start, End - Start);
}

template <class ELFT>
Cie<ELFT>::Cie(EHInputSection<ELFT> *S, unsigned Index)
    : EHRegion<ELFT>(S, Index) {}

template <class ELFT>
template <bool IsRela>
void EHOutputSection<ELFT>::addSectionAux(
    EHInputSection<ELFT> *S,
    iterator_range<const Elf_Rel_Impl<ELFT, IsRela> *> Rels) {
  const endianness E = ELFT::TargetEndianness;

  S->OutSec = this;
  uint32_t Align = S->getAlign();
  if (Align > this->Header.sh_addralign)
    this->Header.sh_addralign = Align;

  Sections.push_back(S);

  ArrayRef<uint8_t> SecData = S->getSectionData();
  ArrayRef<uint8_t> D = SecData;
  uintX_t Offset = 0;
  auto RelI = Rels.begin();
  auto RelE = Rels.end();

  DenseMap<unsigned, unsigned> OffsetToIndex;
  while (!D.empty()) {
    unsigned Index = S->Offsets.size();
    S->Offsets.push_back(std::make_pair(Offset, -1));

    uintX_t Length = readEntryLength(D);
    StringRef Entry((const char *)D.data(), Length);

    while (RelI != RelE && RelI->r_offset < Offset)
      ++RelI;
    uintX_t NextOffset = Offset + Length;
    bool HasReloc = RelI != RelE && RelI->r_offset < NextOffset;

    uint32_t ID = read32<E>(D.data() + 4);
    if (ID == 0) {
      // CIE
      Cie<ELFT> C(S, Index);

      StringRef Personality;
      if (HasReloc) {
        uint32_t SymIndex = RelI->getSymbol(Config->Mips64EL);
        SymbolBody &Body = *S->getFile()->getSymbolBody(SymIndex)->repl();
        Personality = Body.getName();
      }

      std::pair<StringRef, StringRef> CieInfo(Entry, Personality);
      auto P = CieMap.insert(std::make_pair(CieInfo, Cies.size()));
      if (P.second) {
        Cies.push_back(C);
        this->Header.sh_size += align(Length, sizeof(uintX_t));
      }
      OffsetToIndex[Offset] = P.first->second;
    } else {
      if (!HasReloc)
        error("FDE doesn't reference another section");
      InputSectionBase<ELFT> *Target = S->getRelocTarget(*RelI);
      if (Target != &InputSection<ELFT>::Discarded && Target->isLive()) {
        uint32_t CieOffset = Offset + 4 - ID;
        auto I = OffsetToIndex.find(CieOffset);
        if (I == OffsetToIndex.end())
          error("Invalid CIE reference");
        Cies[I->second].Fdes.push_back(EHRegion<ELFT>(S, Index));
        this->Header.sh_size += align(Length, sizeof(uintX_t));
      }
    }

    Offset = NextOffset;
    D = D.slice(Length);
  }
}

template <class ELFT>
typename EHOutputSection<ELFT>::uintX_t
EHOutputSection<ELFT>::readEntryLength(ArrayRef<uint8_t> D) {
  const endianness E = ELFT::TargetEndianness;

  if (D.size() < 4)
    error("Truncated CIE/FDE length");
  uint64_t Len = read32<E>(D.data());
  if (Len < UINT32_MAX) {
    if (Len > (UINT32_MAX - 4))
      error("CIE/FIE size is too large");
    if (Len + 4 > D.size())
      error("CIE/FIE ends past the end of the section");
    return Len + 4;
  }

  if (D.size() < 12)
    error("Truncated CIE/FDE length");
  Len = read64<E>(D.data() + 4);
  if (Len > (UINT64_MAX - 12))
    error("CIE/FIE size is too large");
  if (Len + 12 > D.size())
    error("CIE/FIE ends past the end of the section");
  return Len + 12;
}

template <class ELFT>
void EHOutputSection<ELFT>::addSection(InputSectionBase<ELFT> *C) {
  auto *S = cast<EHInputSection<ELFT>>(C);
  const Elf_Shdr *RelSec = S->RelocSection;
  if (!RelSec)
    return addSectionAux(
        S, make_range((const Elf_Rela *)nullptr, (const Elf_Rela *)nullptr));
  ELFFile<ELFT> &Obj = S->getFile()->getObj();
  if (RelSec->sh_type == SHT_RELA)
    return addSectionAux(S, Obj.relas(RelSec));
  return addSectionAux(S, Obj.rels(RelSec));
}

template <class ELFT>
static typename ELFFile<ELFT>::uintX_t writeAlignedCieOrFde(StringRef Data,
                                                            uint8_t *Buf) {
  typedef typename ELFFile<ELFT>::uintX_t uintX_t;
  const endianness E = ELFT::TargetEndianness;
  uint64_t Len = align(Data.size(), sizeof(uintX_t));
  write32<E>(Buf, Len - 4);
  memcpy(Buf + 4, Data.data() + 4, Data.size() - 4);
  return Len;
}

template <class ELFT> void EHOutputSection<ELFT>::writeTo(uint8_t *Buf) {
  const endianness E = ELFT::TargetEndianness;
  size_t Offset = 0;
  for (const Cie<ELFT> &C : Cies) {
    size_t CieOffset = Offset;

    uintX_t CIELen = writeAlignedCieOrFde<ELFT>(C.data(), Buf + Offset);
    C.S->Offsets[C.Index].second = Offset;
    Offset += CIELen;

    for (const EHRegion<ELFT> &F : C.Fdes) {
      uintX_t Len = writeAlignedCieOrFde<ELFT>(F.data(), Buf + Offset);
      write32<E>(Buf + Offset + 4, Offset + 4 - CieOffset); // Pointer
      F.S->Offsets[F.Index].second = Offset;
      Offset += Len;
    }
  }

  for (EHInputSection<ELFT> *S : Sections) {
    const Elf_Shdr *RelSec = S->RelocSection;
    if (!RelSec)
      continue;
    ELFFile<ELFT> &EObj = S->getFile()->getObj();
    if (RelSec->sh_type == SHT_RELA)
      S->relocate(Buf, nullptr, EObj.relas(RelSec));
    else
      S->relocate(Buf, nullptr, EObj.rels(RelSec));
  }
}

template <class ELFT>
MergeOutputSection<ELFT>::MergeOutputSection(StringRef Name, uint32_t Type,
                                             uintX_t Flags)
    : OutputSectionBase<ELFT>(Name, Type, Flags) {}

template <class ELFT> void MergeOutputSection<ELFT>::writeTo(uint8_t *Buf) {
  if (shouldTailMerge()) {
    StringRef Data = Builder.data();
    memcpy(Buf, Data.data(), Data.size());
    return;
  }
  for (const std::pair<StringRef, size_t> &P : Builder.getMap()) {
    StringRef Data = P.first;
    memcpy(Buf + P.second, Data.data(), Data.size());
  }
}

static size_t findNull(StringRef S, size_t EntSize) {
  // Optimize the common case.
  if (EntSize == 1)
    return S.find(0);

  for (unsigned I = 0, N = S.size(); I != N; I += EntSize) {
    const char *B = S.begin() + I;
    if (std::all_of(B, B + EntSize, [](char C) { return C == 0; }))
      return I;
  }
  return StringRef::npos;
}

template <class ELFT>
void MergeOutputSection<ELFT>::addSection(InputSectionBase<ELFT> *C) {
  auto *S = cast<MergeInputSection<ELFT>>(C);
  S->OutSec = this;
  uint32_t Align = S->getAlign();
  if (Align > this->Header.sh_addralign)
    this->Header.sh_addralign = Align;

  ArrayRef<uint8_t> D = S->getSectionData();
  StringRef Data((const char *)D.data(), D.size());
  uintX_t EntSize = S->getSectionHdr()->sh_entsize;

  if (this->Header.sh_flags & SHF_STRINGS) {
    uintX_t Offset = 0;
    while (!Data.empty()) {
      size_t End = findNull(Data, EntSize);
      if (End == StringRef::npos)
        error("String is not null terminated");
      StringRef Entry = Data.substr(0, End + EntSize);
      uintX_t OutputOffset = Builder.add(Entry);
      if (shouldTailMerge())
        OutputOffset = -1;
      S->Offsets.push_back(std::make_pair(Offset, OutputOffset));
      uintX_t Size = End + EntSize;
      Data = Data.substr(Size);
      Offset += Size;
    }
  } else {
    for (unsigned I = 0, N = Data.size(); I != N; I += EntSize) {
      StringRef Entry = Data.substr(I, EntSize);
      size_t OutputOffset = Builder.add(Entry);
      S->Offsets.push_back(std::make_pair(I, OutputOffset));
    }
  }
}

template <class ELFT>
unsigned MergeOutputSection<ELFT>::getOffset(StringRef Val) {
  return Builder.getOffset(Val);
}

template <class ELFT> bool MergeOutputSection<ELFT>::shouldTailMerge() const {
  return Config->Optimize >= 2 && this->Header.sh_flags & SHF_STRINGS;
}

template <class ELFT> void MergeOutputSection<ELFT>::finalize() {
  if (shouldTailMerge())
    Builder.finalize();
  this->Header.sh_size = Builder.getSize();
}

template <class ELFT>
StringTableSection<ELFT>::StringTableSection(StringRef Name, bool Dynamic)
    : OutputSectionBase<ELFT>(Name, SHT_STRTAB,
                              Dynamic ? (uintX_t)SHF_ALLOC : 0),
      Dynamic(Dynamic) {
  this->Header.sh_addralign = 1;
}

// String tables are created in two phases. First you call reserve()
// to reserve room in the string table, and then call addString() to actually
// add that string.
//
// Why two phases? We want to know the size of the string table as early as
// possible to fix file layout. So we have separated finalize(), which
// determines the size of the section, from writeTo(), which writes the section
// contents to the output buffer. If we merge reserve() with addString(),
// we need a plumbing work for finalize() and writeTo() so that offsets
// we obtained in the former function can be written in the latter.
// This design eliminated that need.
template <class ELFT> void StringTableSection<ELFT>::reserve(StringRef S) {
  Reserved += S.size() + 1; // +1 for NUL
}

// Adds a string to the string table. You must call reserve() with the
// same string before calling addString().
template <class ELFT> size_t StringTableSection<ELFT>::addString(StringRef S) {
  size_t Pos = Used;
  Strings.push_back(S);
  Used += S.size() + 1;
  Reserved -= S.size() + 1;
  assert((int64_t)Reserved >= 0);
  return Pos;
}

template <class ELFT> void StringTableSection<ELFT>::writeTo(uint8_t *Buf) {
  // ELF string tables start with NUL byte, so advance the pointer by one.
  ++Buf;
  for (StringRef S : Strings) {
    memcpy(Buf, S.data(), S.size());
    Buf += S.size() + 1;
  }
}

template <class ELFT>
bool elf2::shouldKeepInSymtab(const ObjectFile<ELFT> &File, StringRef SymName,
                              const typename ELFFile<ELFT>::Elf_Sym &Sym) {
  if (Sym.getType() == STT_SECTION)
    return false;

  InputSectionBase<ELFT> *Sec = File.getSection(Sym);
  // If sym references a section in a discarded group, don't keep it.
  if (Sec == &InputSection<ELFT>::Discarded)
    return false;

  if (Config->DiscardNone)
    return true;

  // In ELF assembly .L symbols are normally discarded by the assembler.
  // If the assembler fails to do so, the linker discards them if
  // * --discard-locals is used.
  // * The symbol is in a SHF_MERGE section, which is normally the reason for
  //   the assembler keeping the .L symbol.
  if (!SymName.startswith(".L") && !SymName.empty())
    return true;

  if (Config->DiscardLocals)
    return false;

  return !(Sec->getSectionHdr()->sh_flags & SHF_MERGE);
}

template <class ELFT>
SymbolTableSection<ELFT>::SymbolTableSection(
    SymbolTable<ELFT> &Table, StringTableSection<ELFT> &StrTabSec)
    : OutputSectionBase<ELFT>(StrTabSec.isDynamic() ? ".dynsym" : ".symtab",
                              StrTabSec.isDynamic() ? SHT_DYNSYM : SHT_SYMTAB,
                              StrTabSec.isDynamic() ? (uintX_t)SHF_ALLOC : 0),
      Table(Table), StrTabSec(StrTabSec) {
  this->Header.sh_entsize = sizeof(Elf_Sym);
  this->Header.sh_addralign = ELFT::Is64Bits ? 8 : 4;
}

// Orders symbols according to their positions in the GOT,
// in compliance with MIPS ABI rules.
// See "Global Offset Table" in Chapter 5 in the following document
// for detailed description:
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
static bool sortMipsSymbols(SymbolBody *L, SymbolBody *R) {
  if (!L->isInGot() || !R->isInGot())
    return R->isInGot();
  return L->GotIndex < R->GotIndex;
}

template <class ELFT> void SymbolTableSection<ELFT>::finalize() {
  if (this->Header.sh_size)
    return; // Already finalized.

  this->Header.sh_size = getNumSymbols() * sizeof(Elf_Sym);
  this->Header.sh_link = StrTabSec.SectionIndex;
  this->Header.sh_info = NumLocals + 1;

  if (!StrTabSec.isDynamic()) {
    std::stable_sort(Symbols.begin(), Symbols.end(),
                     [](SymbolBody *L, SymbolBody *R) {
                       return getSymbolBinding(L) == STB_LOCAL &&
                              getSymbolBinding(R) != STB_LOCAL;
                     });
    return;
  }
  if (Out<ELFT>::GnuHashTab)
    // NB: It also sorts Symbols to meet the GNU hash table requirements.
    Out<ELFT>::GnuHashTab->addSymbols(Symbols);
  else if (Config->EMachine == EM_MIPS)
    std::stable_sort(Symbols.begin(), Symbols.end(), sortMipsSymbols);
  size_t I = 0;
  for (SymbolBody *B : Symbols)
    B->DynamicSymbolTableIndex = ++I;
}

template <class ELFT>
void SymbolTableSection<ELFT>::addLocalSymbol(StringRef Name) {
  StrTabSec.reserve(Name);
  ++NumVisible;
  ++NumLocals;
}

template <class ELFT>
void SymbolTableSection<ELFT>::addSymbol(SymbolBody *Body) {
  StrTabSec.reserve(Body->getName());
  Symbols.push_back(Body);
  ++NumVisible;
}

template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *Buf) {
  Buf += sizeof(Elf_Sym);

  // All symbols with STB_LOCAL binding precede the weak and global symbols.
  // .dynsym only contains global symbols.
  if (!Config->DiscardAll && !StrTabSec.isDynamic())
    writeLocalSymbols(Buf);

  writeGlobalSymbols(Buf);
}

template <class ELFT>
void SymbolTableSection<ELFT>::writeLocalSymbols(uint8_t *&Buf) {
  // Iterate over all input object files to copy their local symbols
  // to the output symbol table pointed by Buf.
  for (const std::unique_ptr<ObjectFile<ELFT>> &File : Table.getObjectFiles()) {
    Elf_Sym_Range Syms = File->getLocalSymbols();
    for (const Elf_Sym &Sym : Syms) {
      ErrorOr<StringRef> SymNameOrErr = Sym.getName(File->getStringTable());
      error(SymNameOrErr);
      StringRef SymName = *SymNameOrErr;
      if (!shouldKeepInSymtab<ELFT>(*File, SymName, Sym))
        continue;

      auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
      uintX_t VA = 0;
      if (Sym.st_shndx == SHN_ABS) {
        ESym->st_shndx = SHN_ABS;
        VA = Sym.st_value;
      } else {
        InputSectionBase<ELFT> *Section = File->getSection(Sym);
        if (!Section->isLive())
          continue;
        const OutputSectionBase<ELFT> *OutSec = Section->OutSec;
        ESym->st_shndx = OutSec->SectionIndex;
        VA = Section->getOffset(Sym);
        // Symbol offsets for AMDGPU need to be the offset in bytes of the
        // symbol from the beginning of the section.
        if (Config->EMachine != EM_AMDGPU)
          VA += OutSec->getVA();
      }
      ESym->st_name = StrTabSec.addString(SymName);
      ESym->st_size = Sym.st_size;
      ESym->setBindingAndType(Sym.getBinding(), Sym.getType());
      ESym->st_value = VA;
      Buf += sizeof(*ESym);
    }
  }
}

template <class ELFT>
static const typename llvm::object::ELFFile<ELFT>::Elf_Sym *
getElfSym(SymbolBody &Body) {
  if (auto *EBody = dyn_cast<DefinedElf<ELFT>>(&Body))
    return &EBody->Sym;
  if (auto *EBody = dyn_cast<UndefinedElf<ELFT>>(&Body))
    return &EBody->Sym;
  return nullptr;
}

template <class ELFT>
void SymbolTableSection<ELFT>::writeGlobalSymbols(uint8_t *Buf) {
  // Write the internal symbol table contents to the output symbol table
  // pointed by Buf.
  auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
  for (SymbolBody *Body : Symbols) {
    const OutputSectionBase<ELFT> *OutSec = nullptr;

    switch (Body->kind()) {
    case SymbolBody::DefinedSyntheticKind:
      OutSec = &cast<DefinedSynthetic<ELFT>>(Body)->Section;
      break;
    case SymbolBody::DefinedRegularKind: {
      auto *Sym = cast<DefinedRegular<ELFT>>(Body->repl());
      if (InputSectionBase<ELFT> *Sec = Sym->Section) {
        if (!Sec->isLive())
          continue;
        OutSec = Sec->OutSec;
      }
      break;
    }
    case SymbolBody::DefinedCommonKind:
      OutSec = Out<ELFT>::Bss;
      break;
    case SymbolBody::SharedKind: {
      if (cast<SharedSymbol<ELFT>>(Body)->NeedsCopy)
        OutSec = Out<ELFT>::Bss;
      break;
    }
    case SymbolBody::UndefinedElfKind:
    case SymbolBody::UndefinedKind:
    case SymbolBody::LazyKind:
      break;
    }

    StringRef Name = Body->getName();
    ESym->st_name = StrTabSec.addString(Name);

    unsigned char Type = STT_NOTYPE;
    uintX_t Size = 0;
    if (const Elf_Sym *InputSym = getElfSym<ELFT>(*Body)) {
      Type = InputSym->getType();
      Size = InputSym->st_size;
    } else if (auto *C = dyn_cast<DefinedCommon>(Body)) {
      Type = STT_OBJECT;
      Size = C->Size;
    }

    ESym->setBindingAndType(getSymbolBinding(Body), Type);
    ESym->st_size = Size;
    ESym->setVisibility(Body->getVisibility());
    ESym->st_value = getSymVA<ELFT>(*Body);

    if (OutSec)
      ESym->st_shndx = OutSec->SectionIndex;
    else if (isa<DefinedRegular<ELFT>>(Body))
      ESym->st_shndx = SHN_ABS;

    ++ESym;
  }
}

template <class ELFT>
uint8_t SymbolTableSection<ELFT>::getSymbolBinding(SymbolBody *Body) {
  uint8_t Visibility = Body->getVisibility();
  if (Visibility != STV_DEFAULT && Visibility != STV_PROTECTED)
    return STB_LOCAL;
  if (const Elf_Sym *ESym = getElfSym<ELFT>(*Body))
    return ESym->getBinding();
  if (isa<DefinedSynthetic<ELFT>>(Body))
    return STB_LOCAL;
  return Body->isWeak() ? STB_WEAK : STB_GLOBAL;
}

template <class ELFT>
MipsReginfoOutputSection<ELFT>::MipsReginfoOutputSection()
    : OutputSectionBase<ELFT>(".reginfo", SHT_MIPS_REGINFO, SHF_ALLOC) {
  this->Header.sh_addralign = 4;
  this->Header.sh_entsize = sizeof(Elf_Mips_RegInfo);
  this->Header.sh_size = sizeof(Elf_Mips_RegInfo);
}

template <class ELFT>
void MipsReginfoOutputSection<ELFT>::writeTo(uint8_t *Buf) {
  auto *R = reinterpret_cast<Elf_Mips_RegInfo *>(Buf);
  R->ri_gp_value = getMipsGpAddr<ELFT>();
  R->ri_gprmask = GprMask;
}

template <class ELFT>
void MipsReginfoOutputSection<ELFT>::addSection(InputSectionBase<ELFT> *C) {
  // Copy input object file's .reginfo gprmask to output.
  auto *S = cast<MipsReginfoInputSection<ELFT>>(C);
  GprMask |= S->Reginfo->ri_gprmask;
}

namespace lld {
namespace elf2 {
template class OutputSectionBase<ELF32LE>;
template class OutputSectionBase<ELF32BE>;
template class OutputSectionBase<ELF64LE>;
template class OutputSectionBase<ELF64BE>;

template class GotPltSection<ELF32LE>;
template class GotPltSection<ELF32BE>;
template class GotPltSection<ELF64LE>;
template class GotPltSection<ELF64BE>;

template class GotSection<ELF32LE>;
template class GotSection<ELF32BE>;
template class GotSection<ELF64LE>;
template class GotSection<ELF64BE>;

template class PltSection<ELF32LE>;
template class PltSection<ELF32BE>;
template class PltSection<ELF64LE>;
template class PltSection<ELF64BE>;

template class RelocationSection<ELF32LE>;
template class RelocationSection<ELF32BE>;
template class RelocationSection<ELF64LE>;
template class RelocationSection<ELF64BE>;

template class InterpSection<ELF32LE>;
template class InterpSection<ELF32BE>;
template class InterpSection<ELF64LE>;
template class InterpSection<ELF64BE>;

template class GnuHashTableSection<ELF32LE>;
template class GnuHashTableSection<ELF32BE>;
template class GnuHashTableSection<ELF64LE>;
template class GnuHashTableSection<ELF64BE>;

template class HashTableSection<ELF32LE>;
template class HashTableSection<ELF32BE>;
template class HashTableSection<ELF64LE>;
template class HashTableSection<ELF64BE>;

template class DynamicSection<ELF32LE>;
template class DynamicSection<ELF32BE>;
template class DynamicSection<ELF64LE>;
template class DynamicSection<ELF64BE>;

template class OutputSection<ELF32LE>;
template class OutputSection<ELF32BE>;
template class OutputSection<ELF64LE>;
template class OutputSection<ELF64BE>;

template class EHOutputSection<ELF32LE>;
template class EHOutputSection<ELF32BE>;
template class EHOutputSection<ELF64LE>;
template class EHOutputSection<ELF64BE>;

template class MipsReginfoOutputSection<ELF32LE>;
template class MipsReginfoOutputSection<ELF32BE>;
template class MipsReginfoOutputSection<ELF64LE>;
template class MipsReginfoOutputSection<ELF64BE>;

template class MergeOutputSection<ELF32LE>;
template class MergeOutputSection<ELF32BE>;
template class MergeOutputSection<ELF64LE>;
template class MergeOutputSection<ELF64BE>;

template class StringTableSection<ELF32LE>;
template class StringTableSection<ELF32BE>;
template class StringTableSection<ELF64LE>;
template class StringTableSection<ELF64BE>;

template class SymbolTableSection<ELF32LE>;
template class SymbolTableSection<ELF32BE>;
template class SymbolTableSection<ELF64LE>;
template class SymbolTableSection<ELF64BE>;

template ELFFile<ELF32LE>::uintX_t getSymVA<ELF32LE>(const SymbolBody &);
template ELFFile<ELF32BE>::uintX_t getSymVA<ELF32BE>(const SymbolBody &);
template ELFFile<ELF64LE>::uintX_t getSymVA<ELF64LE>(const SymbolBody &);
template ELFFile<ELF64BE>::uintX_t getSymVA<ELF64BE>(const SymbolBody &);

template ELFFile<ELF32LE>::uintX_t
getLocalRelTarget(const ObjectFile<ELF32LE> &,
                  const ELFFile<ELF32LE>::Elf_Rel &,
                  ELFFile<ELF32LE>::uintX_t Addend);
template ELFFile<ELF32BE>::uintX_t
getLocalRelTarget(const ObjectFile<ELF32BE> &,
                  const ELFFile<ELF32BE>::Elf_Rel &,
                  ELFFile<ELF32BE>::uintX_t Addend);
template ELFFile<ELF64LE>::uintX_t
getLocalRelTarget(const ObjectFile<ELF64LE> &,
                  const ELFFile<ELF64LE>::Elf_Rel &,
                  ELFFile<ELF64LE>::uintX_t Addend);
template ELFFile<ELF64BE>::uintX_t
getLocalRelTarget(const ObjectFile<ELF64BE> &,
                  const ELFFile<ELF64BE>::Elf_Rel &,
                  ELFFile<ELF64BE>::uintX_t Addend);

template bool shouldKeepInSymtab<ELF32LE>(const ObjectFile<ELF32LE> &,
                                          StringRef,
                                          const ELFFile<ELF32LE>::Elf_Sym &);
template bool shouldKeepInSymtab<ELF32BE>(const ObjectFile<ELF32BE> &,
                                          StringRef,
                                          const ELFFile<ELF32BE>::Elf_Sym &);
template bool shouldKeepInSymtab<ELF64LE>(const ObjectFile<ELF64LE> &,
                                          StringRef,
                                          const ELFFile<ELF64LE>::Elf_Sym &);
template bool shouldKeepInSymtab<ELF64BE>(const ObjectFile<ELF64BE> &,
                                          StringRef,
                                          const ELFFile<ELF64BE>::Elf_Sym &);
}
}