aboutsummaryrefslogtreecommitdiffstats
path: root/COFF/Writer.cpp
blob: 36ef87de4263e59e4aa584e36ea5fc59b42cde39 (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
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
//===- Writer.cpp ---------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "Writer.h"
#include "Config.h"
#include "DLL.h"
#include "InputFiles.h"
#include "MapFile.h"
#include "PDB.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Memory.h"
#include "lld/Common/Threads.h"
#include "lld/Common/Timer.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Support/BinaryStreamReader.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/FileOutputBuffer.h"
#include "llvm/Support/Parallel.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/RandomNumberGenerator.h"
#include "llvm/Support/xxhash.h"
#include <algorithm>
#include <cstdio>
#include <map>
#include <memory>
#include <utility>

using namespace llvm;
using namespace llvm::COFF;
using namespace llvm::object;
using namespace llvm::support;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::coff;

/* To re-generate DOSProgram:
$ cat > /tmp/DOSProgram.asm
org 0
        ; Copy cs to ds.
        push cs
        pop ds
        ; Point ds:dx at the $-terminated string.
        mov dx, str
        ; Int 21/AH=09h: Write string to standard output.
        mov ah, 0x9
        int 0x21
        ; Int 21/AH=4Ch: Exit with return code (in AL).
        mov ax, 0x4C01
        int 0x21
str:
        db 'This program cannot be run in DOS mode.$'
align 8, db 0
$ nasm -fbin /tmp/DOSProgram.asm -o /tmp/DOSProgram.bin
$ xxd -i /tmp/DOSProgram.bin
*/
static unsigned char dosProgram[] = {
  0x0e, 0x1f, 0xba, 0x0e, 0x00, 0xb4, 0x09, 0xcd, 0x21, 0xb8, 0x01, 0x4c,
  0xcd, 0x21, 0x54, 0x68, 0x69, 0x73, 0x20, 0x70, 0x72, 0x6f, 0x67, 0x72,
  0x61, 0x6d, 0x20, 0x63, 0x61, 0x6e, 0x6e, 0x6f, 0x74, 0x20, 0x62, 0x65,
  0x20, 0x72, 0x75, 0x6e, 0x20, 0x69, 0x6e, 0x20, 0x44, 0x4f, 0x53, 0x20,
  0x6d, 0x6f, 0x64, 0x65, 0x2e, 0x24, 0x00, 0x00
};
static_assert(sizeof(dosProgram) % 8 == 0,
              "DOSProgram size must be multiple of 8");

static const int dosStubSize = sizeof(dos_header) + sizeof(dosProgram);
static_assert(dosStubSize % 8 == 0, "DOSStub size must be multiple of 8");

static const int numberOfDataDirectory = 16;

// Global vector of all output sections. After output sections are finalized,
// this can be indexed by Chunk::getOutputSection.
static std::vector<OutputSection *> outputSections;

OutputSection *Chunk::getOutputSection() const {
  return osidx == 0 ? nullptr : outputSections[osidx - 1];
}

namespace {

class DebugDirectoryChunk : public NonSectionChunk {
public:
  DebugDirectoryChunk(const std::vector<Chunk *> &r, bool writeRepro)
      : records(r), writeRepro(writeRepro) {}

  size_t getSize() const override {
    return (records.size() + int(writeRepro)) * sizeof(debug_directory);
  }

  void writeTo(uint8_t *b) const override {
    auto *d = reinterpret_cast<debug_directory *>(b);

    for (const Chunk *record : records) {
      OutputSection *os = record->getOutputSection();
      uint64_t offs = os->getFileOff() + (record->getRVA() - os->getRVA());
      fillEntry(d, COFF::IMAGE_DEBUG_TYPE_CODEVIEW, record->getSize(),
                record->getRVA(), offs);
      ++d;
    }

    if (writeRepro) {
      // FIXME: The COFF spec allows either a 0-sized entry to just say
      // "the timestamp field is really a hash", or a 4-byte size field
      // followed by that many bytes containing a longer hash (with the
      // lowest 4 bytes usually being the timestamp in little-endian order).
      // Consider storing the full 8 bytes computed by xxHash64 here.
      fillEntry(d, COFF::IMAGE_DEBUG_TYPE_REPRO, 0, 0, 0);
    }
  }

  void setTimeDateStamp(uint32_t timeDateStamp) {
    for (support::ulittle32_t *tds : timeDateStamps)
      *tds = timeDateStamp;
  }

private:
  void fillEntry(debug_directory *d, COFF::DebugType debugType, size_t size,
                 uint64_t rva, uint64_t offs) const {
    d->Characteristics = 0;
    d->TimeDateStamp = 0;
    d->MajorVersion = 0;
    d->MinorVersion = 0;
    d->Type = debugType;
    d->SizeOfData = size;
    d->AddressOfRawData = rva;
    d->PointerToRawData = offs;

    timeDateStamps.push_back(&d->TimeDateStamp);
  }

  mutable std::vector<support::ulittle32_t *> timeDateStamps;
  const std::vector<Chunk *> &records;
  bool writeRepro;
};

class CVDebugRecordChunk : public NonSectionChunk {
public:
  size_t getSize() const override {
    return sizeof(codeview::DebugInfo) + config->pdbAltPath.size() + 1;
  }

  void writeTo(uint8_t *b) const override {
    // Save off the DebugInfo entry to backfill the file signature (build id)
    // in Writer::writeBuildId
    buildId = reinterpret_cast<codeview::DebugInfo *>(b);

    // variable sized field (PDB Path)
    char *p = reinterpret_cast<char *>(b + sizeof(*buildId));
    if (!config->pdbAltPath.empty())
      memcpy(p, config->pdbAltPath.data(), config->pdbAltPath.size());
    p[config->pdbAltPath.size()] = '\0';
  }

  mutable codeview::DebugInfo *buildId = nullptr;
};

// PartialSection represents a group of chunks that contribute to an
// OutputSection. Collating a collection of PartialSections of same name and
// characteristics constitutes the OutputSection.
class PartialSectionKey {
public:
  StringRef name;
  unsigned characteristics;

  bool operator<(const PartialSectionKey &other) const {
    int c = name.compare(other.name);
    if (c == 1)
      return false;
    if (c == 0)
      return characteristics < other.characteristics;
    return true;
  }
};

// The writer writes a SymbolTable result to a file.
class Writer {
public:
  Writer() : buffer(errorHandler().outputBuffer) {}
  void run();

private:
  void createSections();
  void createMiscChunks();
  void createImportTables();
  void appendImportThunks();
  void locateImportTables();
  void createExportTable();
  void mergeSections();
  void removeUnusedSections();
  void assignAddresses();
  void finalizeAddresses();
  void removeEmptySections();
  void assignOutputSectionIndices();
  void createSymbolAndStringTable();
  void openFile(StringRef outputPath);
  template <typename PEHeaderTy> void writeHeader();
  void createSEHTable();
  void createRuntimePseudoRelocs();
  void insertCtorDtorSymbols();
  void createGuardCFTables();
  void markSymbolsForRVATable(ObjFile *file,
                              ArrayRef<SectionChunk *> symIdxChunks,
                              SymbolRVASet &tableSymbols);
  void maybeAddRVATable(SymbolRVASet tableSymbols, StringRef tableSym,
                        StringRef countSym);
  void setSectionPermissions();
  void writeSections();
  void writeBuildId();
  void sortExceptionTable();
  void sortCRTSectionChunks(std::vector<Chunk *> &chunks);
  void addSyntheticIdata();
  void fixPartialSectionChars(StringRef name, uint32_t chars);
  bool fixGnuImportChunks();
  PartialSection *createPartialSection(StringRef name, uint32_t outChars);
  PartialSection *findPartialSection(StringRef name, uint32_t outChars);

  llvm::Optional<coff_symbol16> createSymbol(Defined *d);
  size_t addEntryToStringTable(StringRef str);

  OutputSection *findSection(StringRef name);
  void addBaserels();
  void addBaserelBlocks(std::vector<Baserel> &v);

  uint32_t getSizeOfInitializedData();

  std::unique_ptr<FileOutputBuffer> &buffer;
  std::map<PartialSectionKey, PartialSection *> partialSections;
  std::vector<char> strtab;
  std::vector<llvm::object::coff_symbol16> outputSymtab;
  IdataContents idata;
  Chunk *importTableStart = nullptr;
  uint64_t importTableSize = 0;
  Chunk *iatStart = nullptr;
  uint64_t iatSize = 0;
  DelayLoadContents delayIdata;
  EdataContents edata;
  bool setNoSEHCharacteristic = false;

  DebugDirectoryChunk *debugDirectory = nullptr;
  std::vector<Chunk *> debugRecords;
  CVDebugRecordChunk *buildId = nullptr;
  ArrayRef<uint8_t> sectionTable;

  uint64_t fileSize;
  uint32_t pointerToSymbolTable = 0;
  uint64_t sizeOfImage;
  uint64_t sizeOfHeaders;

  OutputSection *textSec;
  OutputSection *rdataSec;
  OutputSection *buildidSec;
  OutputSection *dataSec;
  OutputSection *pdataSec;
  OutputSection *idataSec;
  OutputSection *edataSec;
  OutputSection *didatSec;
  OutputSection *rsrcSec;
  OutputSection *relocSec;
  OutputSection *ctorsSec;
  OutputSection *dtorsSec;

  // The first and last .pdata sections in the output file.
  //
  // We need to keep track of the location of .pdata in whichever section it
  // gets merged into so that we can sort its contents and emit a correct data
  // directory entry for the exception table. This is also the case for some
  // other sections (such as .edata) but because the contents of those sections
  // are entirely linker-generated we can keep track of their locations using
  // the chunks that the linker creates. All .pdata chunks come from input
  // files, so we need to keep track of them separately.
  Chunk *firstPdata = nullptr;
  Chunk *lastPdata;
};
} // anonymous namespace

namespace lld {
namespace coff {

static Timer codeLayoutTimer("Code Layout", Timer::root());
static Timer diskCommitTimer("Commit Output File", Timer::root());

void writeResult() { Writer().run(); }

void OutputSection::addChunk(Chunk *c) {
  chunks.push_back(c);
}

void OutputSection::insertChunkAtStart(Chunk *c) {
  chunks.insert(chunks.begin(), c);
}

void OutputSection::setPermissions(uint32_t c) {
  header.Characteristics &= ~permMask;
  header.Characteristics |= c;
}

void OutputSection::merge(OutputSection *other) {
  chunks.insert(chunks.end(), other->chunks.begin(), other->chunks.end());
  other->chunks.clear();
  contribSections.insert(contribSections.end(), other->contribSections.begin(),
                         other->contribSections.end());
  other->contribSections.clear();
}

// Write the section header to a given buffer.
void OutputSection::writeHeaderTo(uint8_t *buf) {
  auto *hdr = reinterpret_cast<coff_section *>(buf);
  *hdr = header;
  if (stringTableOff) {
    // If name is too long, write offset into the string table as a name.
    sprintf(hdr->Name, "/%d", stringTableOff);
  } else {
    assert(!config->debug || name.size() <= COFF::NameSize ||
           (hdr->Characteristics & IMAGE_SCN_MEM_DISCARDABLE) == 0);
    strncpy(hdr->Name, name.data(),
            std::min(name.size(), (size_t)COFF::NameSize));
  }
}

void OutputSection::addContributingPartialSection(PartialSection *sec) {
  contribSections.push_back(sec);
}

} // namespace coff
} // namespace lld

// Check whether the target address S is in range from a relocation
// of type relType at address P.
static bool isInRange(uint16_t relType, uint64_t s, uint64_t p, int margin) {
  if (config->machine == ARMNT) {
    int64_t diff = AbsoluteDifference(s, p + 4) + margin;
    switch (relType) {
    case IMAGE_REL_ARM_BRANCH20T:
      return isInt<21>(diff);
    case IMAGE_REL_ARM_BRANCH24T:
    case IMAGE_REL_ARM_BLX23T:
      return isInt<25>(diff);
    default:
      return true;
    }
  } else if (config->machine == ARM64) {
    int64_t diff = AbsoluteDifference(s, p) + margin;
    switch (relType) {
    case IMAGE_REL_ARM64_BRANCH26:
      return isInt<28>(diff);
    case IMAGE_REL_ARM64_BRANCH19:
      return isInt<21>(diff);
    case IMAGE_REL_ARM64_BRANCH14:
      return isInt<16>(diff);
    default:
      return true;
    }
  } else {
    llvm_unreachable("Unexpected architecture");
  }
}

// Return the last thunk for the given target if it is in range,
// or create a new one.
static std::pair<Defined *, bool>
getThunk(DenseMap<uint64_t, Defined *> &lastThunks, Defined *target, uint64_t p,
         uint16_t type, int margin) {
  Defined *&lastThunk = lastThunks[target->getRVA()];
  if (lastThunk && isInRange(type, lastThunk->getRVA(), p, margin))
    return {lastThunk, false};
  Chunk *c;
  switch (config->machine) {
  case ARMNT:
    c = make<RangeExtensionThunkARM>(target);
    break;
  case ARM64:
    c = make<RangeExtensionThunkARM64>(target);
    break;
  default:
    llvm_unreachable("Unexpected architecture");
  }
  Defined *d = make<DefinedSynthetic>("", c);
  lastThunk = d;
  return {d, true};
}

// This checks all relocations, and for any relocation which isn't in range
// it adds a thunk after the section chunk that contains the relocation.
// If the latest thunk for the specific target is in range, that is used
// instead of creating a new thunk. All range checks are done with the
// specified margin, to make sure that relocations that originally are in
// range, but only barely, also get thunks - in case other added thunks makes
// the target go out of range.
//
// After adding thunks, we verify that all relocations are in range (with
// no extra margin requirements). If this failed, we restart (throwing away
// the previously created thunks) and retry with a wider margin.
static bool createThunks(OutputSection *os, int margin) {
  bool addressesChanged = false;
  DenseMap<uint64_t, Defined *> lastThunks;
  DenseMap<std::pair<ObjFile *, Defined *>, uint32_t> thunkSymtabIndices;
  size_t thunksSize = 0;
  // Recheck Chunks.size() each iteration, since we can insert more
  // elements into it.
  for (size_t i = 0; i != os->chunks.size(); ++i) {
    SectionChunk *sc = dyn_cast_or_null<SectionChunk>(os->chunks[i]);
    if (!sc)
      continue;
    size_t thunkInsertionSpot = i + 1;

    // Try to get a good enough estimate of where new thunks will be placed.
    // Offset this by the size of the new thunks added so far, to make the
    // estimate slightly better.
    size_t thunkInsertionRVA = sc->getRVA() + sc->getSize() + thunksSize;
    ObjFile *file = sc->file;
    std::vector<std::pair<uint32_t, uint32_t>> relocReplacements;
    ArrayRef<coff_relocation> originalRelocs =
        file->getCOFFObj()->getRelocations(sc->header);
    for (size_t j = 0, e = originalRelocs.size(); j < e; ++j) {
      const coff_relocation &rel = originalRelocs[j];
      Symbol *relocTarget = file->getSymbol(rel.SymbolTableIndex);

      // The estimate of the source address P should be pretty accurate,
      // but we don't know whether the target Symbol address should be
      // offset by thunksSize or not (or by some of thunksSize but not all of
      // it), giving us some uncertainty once we have added one thunk.
      uint64_t p = sc->getRVA() + rel.VirtualAddress + thunksSize;

      Defined *sym = dyn_cast_or_null<Defined>(relocTarget);
      if (!sym)
        continue;

      uint64_t s = sym->getRVA();

      if (isInRange(rel.Type, s, p, margin))
        continue;

      // If the target isn't in range, hook it up to an existing or new
      // thunk.
      Defined *thunk;
      bool wasNew;
      std::tie(thunk, wasNew) = getThunk(lastThunks, sym, p, rel.Type, margin);
      if (wasNew) {
        Chunk *thunkChunk = thunk->getChunk();
        thunkChunk->setRVA(
            thunkInsertionRVA); // Estimate of where it will be located.
        os->chunks.insert(os->chunks.begin() + thunkInsertionSpot, thunkChunk);
        thunkInsertionSpot++;
        thunksSize += thunkChunk->getSize();
        thunkInsertionRVA += thunkChunk->getSize();
        addressesChanged = true;
      }

      // To redirect the relocation, add a symbol to the parent object file's
      // symbol table, and replace the relocation symbol table index with the
      // new index.
      auto insertion = thunkSymtabIndices.insert({{file, thunk}, ~0U});
      uint32_t &thunkSymbolIndex = insertion.first->second;
      if (insertion.second)
        thunkSymbolIndex = file->addRangeThunkSymbol(thunk);
      relocReplacements.push_back({j, thunkSymbolIndex});
    }

    // Get a writable copy of this section's relocations so they can be
    // modified. If the relocations point into the object file, allocate new
    // memory. Otherwise, this must be previously allocated memory that can be
    // modified in place.
    ArrayRef<coff_relocation> curRelocs = sc->getRelocs();
    MutableArrayRef<coff_relocation> newRelocs;
    if (originalRelocs.data() == curRelocs.data()) {
      newRelocs = makeMutableArrayRef(
          bAlloc.Allocate<coff_relocation>(originalRelocs.size()),
          originalRelocs.size());
    } else {
      newRelocs = makeMutableArrayRef(
          const_cast<coff_relocation *>(curRelocs.data()), curRelocs.size());
    }

    // Copy each relocation, but replace the symbol table indices which need
    // thunks.
    auto nextReplacement = relocReplacements.begin();
    auto endReplacement = relocReplacements.end();
    for (size_t i = 0, e = originalRelocs.size(); i != e; ++i) {
      newRelocs[i] = originalRelocs[i];
      if (nextReplacement != endReplacement && nextReplacement->first == i) {
        newRelocs[i].SymbolTableIndex = nextReplacement->second;
        ++nextReplacement;
      }
    }

    sc->setRelocs(newRelocs);
  }
  return addressesChanged;
}

// Verify that all relocations are in range, with no extra margin requirements.
static bool verifyRanges(const std::vector<Chunk *> chunks) {
  for (Chunk *c : chunks) {
    SectionChunk *sc = dyn_cast_or_null<SectionChunk>(c);
    if (!sc)
      continue;

    ArrayRef<coff_relocation> relocs = sc->getRelocs();
    for (size_t j = 0, e = relocs.size(); j < e; ++j) {
      const coff_relocation &rel = relocs[j];
      Symbol *relocTarget = sc->file->getSymbol(rel.SymbolTableIndex);

      Defined *sym = dyn_cast_or_null<Defined>(relocTarget);
      if (!sym)
        continue;

      uint64_t p = sc->getRVA() + rel.VirtualAddress;
      uint64_t s = sym->getRVA();

      if (!isInRange(rel.Type, s, p, 0))
        return false;
    }
  }
  return true;
}

// Assign addresses and add thunks if necessary.
void Writer::finalizeAddresses() {
  assignAddresses();
  if (config->machine != ARMNT && config->machine != ARM64)
    return;

  size_t origNumChunks = 0;
  for (OutputSection *sec : outputSections) {
    sec->origChunks = sec->chunks;
    origNumChunks += sec->chunks.size();
  }

  int pass = 0;
  int margin = 1024 * 100;
  while (true) {
    // First check whether we need thunks at all, or if the previous pass of
    // adding them turned out ok.
    bool rangesOk = true;
    size_t numChunks = 0;
    for (OutputSection *sec : outputSections) {
      if (!verifyRanges(sec->chunks)) {
        rangesOk = false;
        break;
      }
      numChunks += sec->chunks.size();
    }
    if (rangesOk) {
      if (pass > 0)
        log("Added " + Twine(numChunks - origNumChunks) + " thunks with " +
            "margin " + Twine(margin) + " in " + Twine(pass) + " passes");
      return;
    }

    if (pass >= 10)
      fatal("adding thunks hasn't converged after " + Twine(pass) + " passes");

    if (pass > 0) {
      // If the previous pass didn't work out, reset everything back to the
      // original conditions before retrying with a wider margin. This should
      // ideally never happen under real circumstances.
      for (OutputSection *sec : outputSections)
        sec->chunks = sec->origChunks;
      margin *= 2;
    }

    // Try adding thunks everywhere where it is needed, with a margin
    // to avoid things going out of range due to the added thunks.
    bool addressesChanged = false;
    for (OutputSection *sec : outputSections)
      addressesChanged |= createThunks(sec, margin);
    // If the verification above thought we needed thunks, we should have
    // added some.
    assert(addressesChanged);

    // Recalculate the layout for the whole image (and verify the ranges at
    // the start of the next round).
    assignAddresses();

    pass++;
  }
}

// The main function of the writer.
void Writer::run() {
  ScopedTimer t1(codeLayoutTimer);

  createImportTables();
  createSections();
  createMiscChunks();
  appendImportThunks();
  createExportTable();
  mergeSections();
  removeUnusedSections();
  finalizeAddresses();
  removeEmptySections();
  assignOutputSectionIndices();
  setSectionPermissions();
  createSymbolAndStringTable();

  if (fileSize > UINT32_MAX)
    fatal("image size (" + Twine(fileSize) + ") " +
        "exceeds maximum allowable size (" + Twine(UINT32_MAX) + ")");

  openFile(config->outputFile);
  if (config->is64()) {
    writeHeader<pe32plus_header>();
  } else {
    writeHeader<pe32_header>();
  }
  writeSections();
  sortExceptionTable();

  t1.stop();

  if (!config->pdbPath.empty() && config->debug) {
    assert(buildId);
    createPDB(symtab, outputSections, sectionTable, buildId->buildId);
  }
  writeBuildId();

  writeMapFile(outputSections);

  ScopedTimer t2(diskCommitTimer);
  if (auto e = buffer->commit())
    fatal("failed to write the output file: " + toString(std::move(e)));
}

static StringRef getOutputSectionName(StringRef name) {
  StringRef s = name.split('$').first;

  // Treat a later period as a separator for MinGW, for sections like
  // ".ctors.01234".
  return s.substr(0, s.find('.', 1));
}

// For /order.
static void sortBySectionOrder(std::vector<Chunk *> &chunks) {
  auto getPriority = [](const Chunk *c) {
    if (auto *sec = dyn_cast<SectionChunk>(c))
      if (sec->sym)
        return config->order.lookup(sec->sym->getName());
    return 0;
  };

  llvm::stable_sort(chunks, [=](const Chunk *a, const Chunk *b) {
    return getPriority(a) < getPriority(b);
  });
}

// Change the characteristics of existing PartialSections that belong to the
// section Name to Chars.
void Writer::fixPartialSectionChars(StringRef name, uint32_t chars) {
  for (auto it : partialSections) {
    PartialSection *pSec = it.second;
    StringRef curName = pSec->name;
    if (!curName.consume_front(name) ||
        (!curName.empty() && !curName.startswith("$")))
      continue;
    if (pSec->characteristics == chars)
      continue;
    PartialSection *destSec = createPartialSection(pSec->name, chars);
    destSec->chunks.insert(destSec->chunks.end(), pSec->chunks.begin(),
                           pSec->chunks.end());
    pSec->chunks.clear();
  }
}

// Sort concrete section chunks from GNU import libraries.
//
// GNU binutils doesn't use short import files, but instead produces import
// libraries that consist of object files, with section chunks for the .idata$*
// sections. These are linked just as regular static libraries. Each import
// library consists of one header object, one object file for every imported
// symbol, and one trailer object. In order for the .idata tables/lists to
// be formed correctly, the section chunks within each .idata$* section need
// to be grouped by library, and sorted alphabetically within each library
// (which makes sure the header comes first and the trailer last).
bool Writer::fixGnuImportChunks() {
  uint32_t rdata = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ;

  // Make sure all .idata$* section chunks are mapped as RDATA in order to
  // be sorted into the same sections as our own synthesized .idata chunks.
  fixPartialSectionChars(".idata", rdata);

  bool hasIdata = false;
  // Sort all .idata$* chunks, grouping chunks from the same library,
  // with alphabetical ordering of the object fils within a library.
  for (auto it : partialSections) {
    PartialSection *pSec = it.second;
    if (!pSec->name.startswith(".idata"))
      continue;

    if (!pSec->chunks.empty())
      hasIdata = true;
    llvm::stable_sort(pSec->chunks, [&](Chunk *s, Chunk *t) {
      SectionChunk *sc1 = dyn_cast_or_null<SectionChunk>(s);
      SectionChunk *sc2 = dyn_cast_or_null<SectionChunk>(t);
      if (!sc1 || !sc2) {
        // if SC1, order them ascending. If SC2 or both null,
        // S is not less than T.
        return sc1 != nullptr;
      }
      // Make a string with "libraryname/objectfile" for sorting, achieving
      // both grouping by library and sorting of objects within a library,
      // at once.
      std::string key1 =
          (sc1->file->parentName + "/" + sc1->file->getName()).str();
      std::string key2 =
          (sc2->file->parentName + "/" + sc2->file->getName()).str();
      return key1 < key2;
    });
  }
  return hasIdata;
}

// Add generated idata chunks, for imported symbols and DLLs, and a
// terminator in .idata$2.
void Writer::addSyntheticIdata() {
  uint32_t rdata = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ;
  idata.create();

  // Add the .idata content in the right section groups, to allow
  // chunks from other linked in object files to be grouped together.
  // See Microsoft PE/COFF spec 5.4 for details.
  auto add = [&](StringRef n, std::vector<Chunk *> &v) {
    PartialSection *pSec = createPartialSection(n, rdata);
    pSec->chunks.insert(pSec->chunks.end(), v.begin(), v.end());
  };

  // The loader assumes a specific order of data.
  // Add each type in the correct order.
  add(".idata$2", idata.dirs);
  add(".idata$4", idata.lookups);
  add(".idata$5", idata.addresses);
  add(".idata$6", idata.hints);
  add(".idata$7", idata.dllNames);
}

// Locate the first Chunk and size of the import directory list and the
// IAT.
void Writer::locateImportTables() {
  uint32_t rdata = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ;

  if (PartialSection *importDirs = findPartialSection(".idata$2", rdata)) {
    if (!importDirs->chunks.empty())
      importTableStart = importDirs->chunks.front();
    for (Chunk *c : importDirs->chunks)
      importTableSize += c->getSize();
  }

  if (PartialSection *importAddresses = findPartialSection(".idata$5", rdata)) {
    if (!importAddresses->chunks.empty())
      iatStart = importAddresses->chunks.front();
    for (Chunk *c : importAddresses->chunks)
      iatSize += c->getSize();
  }
}

// Create output section objects and add them to OutputSections.
void Writer::createSections() {
  // First, create the builtin sections.
  const uint32_t data = IMAGE_SCN_CNT_INITIALIZED_DATA;
  const uint32_t bss = IMAGE_SCN_CNT_UNINITIALIZED_DATA;
  const uint32_t code = IMAGE_SCN_CNT_CODE;
  const uint32_t discardable = IMAGE_SCN_MEM_DISCARDABLE;
  const uint32_t r = IMAGE_SCN_MEM_READ;
  const uint32_t w = IMAGE_SCN_MEM_WRITE;
  const uint32_t x = IMAGE_SCN_MEM_EXECUTE;

  SmallDenseMap<std::pair<StringRef, uint32_t>, OutputSection *> sections;
  auto createSection = [&](StringRef name, uint32_t outChars) {
    OutputSection *&sec = sections[{name, outChars}];
    if (!sec) {
      sec = make<OutputSection>(name, outChars);
      outputSections.push_back(sec);
    }
    return sec;
  };

  // Try to match the section order used by link.exe.
  textSec = createSection(".text", code | r | x);
  createSection(".bss", bss | r | w);
  rdataSec = createSection(".rdata", data | r);
  buildidSec = createSection(".buildid", data | r);
  dataSec = createSection(".data", data | r | w);
  pdataSec = createSection(".pdata", data | r);
  idataSec = createSection(".idata", data | r);
  edataSec = createSection(".edata", data | r);
  didatSec = createSection(".didat", data | r);
  rsrcSec = createSection(".rsrc", data | r);
  relocSec = createSection(".reloc", data | discardable | r);
  ctorsSec = createSection(".ctors", data | r | w);
  dtorsSec = createSection(".dtors", data | r | w);

  // Then bin chunks by name and output characteristics.
  for (Chunk *c : symtab->getChunks()) {
    auto *sc = dyn_cast<SectionChunk>(c);
    if (sc && !sc->live) {
      if (config->verbose)
        sc->printDiscardedMessage();
      continue;
    }
    StringRef name = c->getSectionName();
    // On MinGW, comdat groups are formed by putting the comdat group name
    // after the '$' in the section name. Such a section name suffix shouldn't
    // imply separate alphabetical sorting of those section chunks though.
    if (config->mingw && sc && sc->isCOMDAT())
      name = name.split('$').first;
    PartialSection *pSec = createPartialSection(name,
                                                c->getOutputCharacteristics());
    pSec->chunks.push_back(c);
  }

  fixPartialSectionChars(".rsrc", data | r);
  // Even in non MinGW cases, we might need to link against GNU import
  // libraries.
  bool hasIdata = fixGnuImportChunks();
  if (!idata.empty())
    hasIdata = true;

  if (hasIdata)
    addSyntheticIdata();

  // Process an /order option.
  if (!config->order.empty())
    for (auto it : partialSections)
      sortBySectionOrder(it.second->chunks);

  if (hasIdata)
    locateImportTables();

  // Then create an OutputSection for each section.
  // '$' and all following characters in input section names are
  // discarded when determining output section. So, .text$foo
  // contributes to .text, for example. See PE/COFF spec 3.2.
  for (auto it : partialSections) {
    PartialSection *pSec = it.second;
    StringRef name = getOutputSectionName(pSec->name);
    uint32_t outChars = pSec->characteristics;

    if (name == ".CRT") {
      // In link.exe, there is a special case for the I386 target where .CRT
      // sections are treated as if they have output characteristics DATA | R if
      // their characteristics are DATA | R | W. This implements the same
      // special case for all architectures.
      outChars = data | r;

      log("Processing section " + pSec->name + " -> " + name);

      sortCRTSectionChunks(pSec->chunks);
    }

    OutputSection *sec = createSection(name, outChars);
    for (Chunk *c : pSec->chunks)
      sec->addChunk(c);

    sec->addContributingPartialSection(pSec);
  }

  // Finally, move some output sections to the end.
  auto sectionOrder = [&](const OutputSection *s) {
    // Move DISCARDABLE (or non-memory-mapped) sections to the end of file
    // because the loader cannot handle holes. Stripping can remove other
    // discardable ones than .reloc, which is first of them (created early).
    if (s->header.Characteristics & IMAGE_SCN_MEM_DISCARDABLE)
      return 2;
    // .rsrc should come at the end of the non-discardable sections because its
    // size may change by the Win32 UpdateResources() function, causing
    // subsequent sections to move (see https://crbug.com/827082).
    if (s == rsrcSec)
      return 1;
    return 0;
  };
  llvm::stable_sort(outputSections,
                    [&](const OutputSection *s, const OutputSection *t) {
                      return sectionOrder(s) < sectionOrder(t);
                    });
}

void Writer::createMiscChunks() {
  for (MergeChunk *p : MergeChunk::instances) {
    if (p) {
      p->finalizeContents();
      rdataSec->addChunk(p);
    }
  }

  // Create thunks for locally-dllimported symbols.
  if (!symtab->localImportChunks.empty()) {
    for (Chunk *c : symtab->localImportChunks)
      rdataSec->addChunk(c);
  }

  // Create Debug Information Chunks
  OutputSection *debugInfoSec = config->mingw ? buildidSec : rdataSec;
  if (config->debug || config->repro) {
    debugDirectory = make<DebugDirectoryChunk>(debugRecords, config->repro);
    debugInfoSec->addChunk(debugDirectory);
  }

  if (config->debug) {
    // Make a CVDebugRecordChunk even when /DEBUG:CV is not specified.  We
    // output a PDB no matter what, and this chunk provides the only means of
    // allowing a debugger to match a PDB and an executable.  So we need it even
    // if we're ultimately not going to write CodeView data to the PDB.
    buildId = make<CVDebugRecordChunk>();
    debugRecords.push_back(buildId);

    for (Chunk *c : debugRecords)
      debugInfoSec->addChunk(c);
  }

  // Create SEH table. x86-only.
  if (config->safeSEH)
    createSEHTable();

  // Create /guard:cf tables if requested.
  if (config->guardCF != GuardCFLevel::Off)
    createGuardCFTables();

  if (config->mingw) {
    createRuntimePseudoRelocs();

    insertCtorDtorSymbols();
  }
}

// Create .idata section for the DLL-imported symbol table.
// The format of this section is inherently Windows-specific.
// IdataContents class abstracted away the details for us,
// so we just let it create chunks and add them to the section.
void Writer::createImportTables() {
  // Initialize DLLOrder so that import entries are ordered in
  // the same order as in the command line. (That affects DLL
  // initialization order, and this ordering is MSVC-compatible.)
  for (ImportFile *file : ImportFile::instances) {
    if (!file->live)
      continue;

    std::string dll = StringRef(file->dllName).lower();
    if (config->dllOrder.count(dll) == 0)
      config->dllOrder[dll] = config->dllOrder.size();

    if (file->impSym && !isa<DefinedImportData>(file->impSym))
      fatal(toString(*file->impSym) + " was replaced");
    DefinedImportData *impSym = cast_or_null<DefinedImportData>(file->impSym);
    if (config->delayLoads.count(StringRef(file->dllName).lower())) {
      if (!file->thunkSym)
        fatal("cannot delay-load " + toString(file) +
              " due to import of data: " + toString(*impSym));
      delayIdata.add(impSym);
    } else {
      idata.add(impSym);
    }
  }
}

void Writer::appendImportThunks() {
  if (ImportFile::instances.empty())
    return;

  for (ImportFile *file : ImportFile::instances) {
    if (!file->live)
      continue;

    if (!file->thunkSym)
      continue;

    if (!isa<DefinedImportThunk>(file->thunkSym))
      fatal(toString(*file->thunkSym) + " was replaced");
    DefinedImportThunk *thunk = cast<DefinedImportThunk>(file->thunkSym);
    if (file->thunkLive)
      textSec->addChunk(thunk->getChunk());
  }

  if (!delayIdata.empty()) {
    Defined *helper = cast<Defined>(config->delayLoadHelper);
    delayIdata.create(helper);
    for (Chunk *c : delayIdata.getChunks())
      didatSec->addChunk(c);
    for (Chunk *c : delayIdata.getDataChunks())
      dataSec->addChunk(c);
    for (Chunk *c : delayIdata.getCodeChunks())
      textSec->addChunk(c);
  }
}

void Writer::createExportTable() {
  if (config->exports.empty())
    return;
  for (Chunk *c : edata.chunks)
    edataSec->addChunk(c);
}

void Writer::removeUnusedSections() {
  // Remove sections that we can be sure won't get content, to avoid
  // allocating space for their section headers.
  auto isUnused = [this](OutputSection *s) {
    if (s == relocSec)
      return false; // This section is populated later.
    // MergeChunks have zero size at this point, as their size is finalized
    // later. Only remove sections that have no Chunks at all.
    return s->chunks.empty();
  };
  outputSections.erase(
      std::remove_if(outputSections.begin(), outputSections.end(), isUnused),
      outputSections.end());
}

// The Windows loader doesn't seem to like empty sections,
// so we remove them if any.
void Writer::removeEmptySections() {
  auto isEmpty = [](OutputSection *s) { return s->getVirtualSize() == 0; };
  outputSections.erase(
      std::remove_if(outputSections.begin(), outputSections.end(), isEmpty),
      outputSections.end());
}

void Writer::assignOutputSectionIndices() {
  // Assign final output section indices, and assign each chunk to its output
  // section.
  uint32_t idx = 1;
  for (OutputSection *os : outputSections) {
    os->sectionIndex = idx;
    for (Chunk *c : os->chunks)
      c->setOutputSectionIdx(idx);
    ++idx;
  }

  // Merge chunks are containers of chunks, so assign those an output section
  // too.
  for (MergeChunk *mc : MergeChunk::instances)
    if (mc)
      for (SectionChunk *sc : mc->sections)
        if (sc && sc->live)
          sc->setOutputSectionIdx(mc->getOutputSectionIdx());
}

size_t Writer::addEntryToStringTable(StringRef str) {
  assert(str.size() > COFF::NameSize);
  size_t offsetOfEntry = strtab.size() + 4; // +4 for the size field
  strtab.insert(strtab.end(), str.begin(), str.end());
  strtab.push_back('\0');
  return offsetOfEntry;
}

Optional<coff_symbol16> Writer::createSymbol(Defined *def) {
  coff_symbol16 sym;
  switch (def->kind()) {
  case Symbol::DefinedAbsoluteKind:
    sym.Value = def->getRVA();
    sym.SectionNumber = IMAGE_SYM_ABSOLUTE;
    break;
  case Symbol::DefinedSyntheticKind:
    // Relative symbols are unrepresentable in a COFF symbol table.
    return None;
  default: {
    // Don't write symbols that won't be written to the output to the symbol
    // table.
    Chunk *c = def->getChunk();
    if (!c)
      return None;
    OutputSection *os = c->getOutputSection();
    if (!os)
      return None;

    sym.Value = def->getRVA() - os->getRVA();
    sym.SectionNumber = os->sectionIndex;
    break;
  }
  }

  StringRef name = def->getName();
  if (name.size() > COFF::NameSize) {
    sym.Name.Offset.Zeroes = 0;
    sym.Name.Offset.Offset = addEntryToStringTable(name);
  } else {
    memset(sym.Name.ShortName, 0, COFF::NameSize);
    memcpy(sym.Name.ShortName, name.data(), name.size());
  }

  if (auto *d = dyn_cast<DefinedCOFF>(def)) {
    COFFSymbolRef ref = d->getCOFFSymbol();
    sym.Type = ref.getType();
    sym.StorageClass = ref.getStorageClass();
  } else {
    sym.Type = IMAGE_SYM_TYPE_NULL;
    sym.StorageClass = IMAGE_SYM_CLASS_EXTERNAL;
  }
  sym.NumberOfAuxSymbols = 0;
  return sym;
}

void Writer::createSymbolAndStringTable() {
  // PE/COFF images are limited to 8 byte section names. Longer names can be
  // supported by writing a non-standard string table, but this string table is
  // not mapped at runtime and the long names will therefore be inaccessible.
  // link.exe always truncates section names to 8 bytes, whereas binutils always
  // preserves long section names via the string table. LLD adopts a hybrid
  // solution where discardable sections have long names preserved and
  // non-discardable sections have their names truncated, to ensure that any
  // section which is mapped at runtime also has its name mapped at runtime.
  for (OutputSection *sec : outputSections) {
    if (sec->name.size() <= COFF::NameSize)
      continue;
    if ((sec->header.Characteristics & IMAGE_SCN_MEM_DISCARDABLE) == 0)
      continue;
    sec->setStringTableOff(addEntryToStringTable(sec->name));
  }

  if (config->debugDwarf || config->debugSymtab) {
    for (ObjFile *file : ObjFile::instances) {
      for (Symbol *b : file->getSymbols()) {
        auto *d = dyn_cast_or_null<Defined>(b);
        if (!d || d->writtenToSymtab)
          continue;
        d->writtenToSymtab = true;

        if (Optional<coff_symbol16> sym = createSymbol(d))
          outputSymtab.push_back(*sym);
      }
    }
  }

  if (outputSymtab.empty() && strtab.empty())
    return;

  // We position the symbol table to be adjacent to the end of the last section.
  uint64_t fileOff = fileSize;
  pointerToSymbolTable = fileOff;
  fileOff += outputSymtab.size() * sizeof(coff_symbol16);
  fileOff += 4 + strtab.size();
  fileSize = alignTo(fileOff, config->fileAlign);
}

void Writer::mergeSections() {
  if (!pdataSec->chunks.empty()) {
    firstPdata = pdataSec->chunks.front();
    lastPdata = pdataSec->chunks.back();
  }

  for (auto &p : config->merge) {
    StringRef toName = p.second;
    if (p.first == toName)
      continue;
    StringSet<> names;
    while (1) {
      if (!names.insert(toName).second)
        fatal("/merge: cycle found for section '" + p.first + "'");
      auto i = config->merge.find(toName);
      if (i == config->merge.end())
        break;
      toName = i->second;
    }
    OutputSection *from = findSection(p.first);
    OutputSection *to = findSection(toName);
    if (!from)
      continue;
    if (!to) {
      from->name = toName;
      continue;
    }
    to->merge(from);
  }
}

// Visits all sections to assign incremental, non-overlapping RVAs and
// file offsets.
void Writer::assignAddresses() {
  sizeOfHeaders = dosStubSize + sizeof(PEMagic) + sizeof(coff_file_header) +
                  sizeof(data_directory) * numberOfDataDirectory +
                  sizeof(coff_section) * outputSections.size();
  sizeOfHeaders +=
      config->is64() ? sizeof(pe32plus_header) : sizeof(pe32_header);
  sizeOfHeaders = alignTo(sizeOfHeaders, config->fileAlign);
  uint64_t rva = pageSize; // The first page is kept unmapped.
  fileSize = sizeOfHeaders;

  for (OutputSection *sec : outputSections) {
    if (sec == relocSec)
      addBaserels();
    uint64_t rawSize = 0, virtualSize = 0;
    sec->header.VirtualAddress = rva;

    // If /FUNCTIONPADMIN is used, functions are padded in order to create a
    // hotpatchable image.
    const bool isCodeSection =
        (sec->header.Characteristics & IMAGE_SCN_CNT_CODE) &&
        (sec->header.Characteristics & IMAGE_SCN_MEM_READ) &&
        (sec->header.Characteristics & IMAGE_SCN_MEM_EXECUTE);
    uint32_t padding = isCodeSection ? config->functionPadMin : 0;

    for (Chunk *c : sec->chunks) {
      if (padding && c->isHotPatchable())
        virtualSize += padding;
      virtualSize = alignTo(virtualSize, c->getAlignment());
      c->setRVA(rva + virtualSize);
      virtualSize += c->getSize();
      if (c->hasData)
        rawSize = alignTo(virtualSize, config->fileAlign);
    }
    if (virtualSize > UINT32_MAX)
      error("section larger than 4 GiB: " + sec->name);
    sec->header.VirtualSize = virtualSize;
    sec->header.SizeOfRawData = rawSize;
    if (rawSize != 0)
      sec->header.PointerToRawData = fileSize;
    rva += alignTo(virtualSize, pageSize);
    fileSize += alignTo(rawSize, config->fileAlign);
  }
  sizeOfImage = alignTo(rva, pageSize);

  // Assign addresses to sections in MergeChunks.
  for (MergeChunk *mc : MergeChunk::instances)
    if (mc)
      mc->assignSubsectionRVAs();
}

template <typename PEHeaderTy> void Writer::writeHeader() {
  // Write DOS header. For backwards compatibility, the first part of a PE/COFF
  // executable consists of an MS-DOS MZ executable. If the executable is run
  // under DOS, that program gets run (usually to just print an error message).
  // When run under Windows, the loader looks at AddressOfNewExeHeader and uses
  // the PE header instead.
  uint8_t *buf = buffer->getBufferStart();
  auto *dos = reinterpret_cast<dos_header *>(buf);
  buf += sizeof(dos_header);
  dos->Magic[0] = 'M';
  dos->Magic[1] = 'Z';
  dos->UsedBytesInTheLastPage = dosStubSize % 512;
  dos->FileSizeInPages = divideCeil(dosStubSize, 512);
  dos->HeaderSizeInParagraphs = sizeof(dos_header) / 16;

  dos->AddressOfRelocationTable = sizeof(dos_header);
  dos->AddressOfNewExeHeader = dosStubSize;

  // Write DOS program.
  memcpy(buf, dosProgram, sizeof(dosProgram));
  buf += sizeof(dosProgram);

  // Write PE magic
  memcpy(buf, PEMagic, sizeof(PEMagic));
  buf += sizeof(PEMagic);

  // Write COFF header
  auto *coff = reinterpret_cast<coff_file_header *>(buf);
  buf += sizeof(*coff);
  coff->Machine = config->machine;
  coff->NumberOfSections = outputSections.size();
  coff->Characteristics = IMAGE_FILE_EXECUTABLE_IMAGE;
  if (config->largeAddressAware)
    coff->Characteristics |= IMAGE_FILE_LARGE_ADDRESS_AWARE;
  if (!config->is64())
    coff->Characteristics |= IMAGE_FILE_32BIT_MACHINE;
  if (config->dll)
    coff->Characteristics |= IMAGE_FILE_DLL;
  if (!config->relocatable)
    coff->Characteristics |= IMAGE_FILE_RELOCS_STRIPPED;
  if (config->swaprunCD)
    coff->Characteristics |= IMAGE_FILE_REMOVABLE_RUN_FROM_SWAP;
  if (config->swaprunNet)
    coff->Characteristics |= IMAGE_FILE_NET_RUN_FROM_SWAP;
  coff->SizeOfOptionalHeader =
      sizeof(PEHeaderTy) + sizeof(data_directory) * numberOfDataDirectory;

  // Write PE header
  auto *pe = reinterpret_cast<PEHeaderTy *>(buf);
  buf += sizeof(*pe);
  pe->Magic = config->is64() ? PE32Header::PE32_PLUS : PE32Header::PE32;

  // If {Major,Minor}LinkerVersion is left at 0.0, then for some
  // reason signing the resulting PE file with Authenticode produces a
  // signature that fails to validate on Windows 7 (but is OK on 10).
  // Set it to 14.0, which is what VS2015 outputs, and which avoids
  // that problem.
  pe->MajorLinkerVersion = 14;
  pe->MinorLinkerVersion = 0;

  pe->ImageBase = config->imageBase;
  pe->SectionAlignment = pageSize;
  pe->FileAlignment = config->fileAlign;
  pe->MajorImageVersion = config->majorImageVersion;
  pe->MinorImageVersion = config->minorImageVersion;
  pe->MajorOperatingSystemVersion = config->majorOSVersion;
  pe->MinorOperatingSystemVersion = config->minorOSVersion;
  pe->MajorSubsystemVersion = config->majorOSVersion;
  pe->MinorSubsystemVersion = config->minorOSVersion;
  pe->Subsystem = config->subsystem;
  pe->SizeOfImage = sizeOfImage;
  pe->SizeOfHeaders = sizeOfHeaders;
  if (!config->noEntry) {
    Defined *entry = cast<Defined>(config->entry);
    pe->AddressOfEntryPoint = entry->getRVA();
    // Pointer to thumb code must have the LSB set, so adjust it.
    if (config->machine == ARMNT)
      pe->AddressOfEntryPoint |= 1;
  }
  pe->SizeOfStackReserve = config->stackReserve;
  pe->SizeOfStackCommit = config->stackCommit;
  pe->SizeOfHeapReserve = config->heapReserve;
  pe->SizeOfHeapCommit = config->heapCommit;
  if (config->appContainer)
    pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_APPCONTAINER;
  if (config->dynamicBase)
    pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_DYNAMIC_BASE;
  if (config->highEntropyVA)
    pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_HIGH_ENTROPY_VA;
  if (!config->allowBind)
    pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NO_BIND;
  if (config->nxCompat)
    pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NX_COMPAT;
  if (!config->allowIsolation)
    pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NO_ISOLATION;
  if (config->guardCF != GuardCFLevel::Off)
    pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_GUARD_CF;
  if (config->integrityCheck)
    pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_FORCE_INTEGRITY;
  if (setNoSEHCharacteristic)
    pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NO_SEH;
  if (config->terminalServerAware)
    pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_TERMINAL_SERVER_AWARE;
  pe->NumberOfRvaAndSize = numberOfDataDirectory;
  if (textSec->getVirtualSize()) {
    pe->BaseOfCode = textSec->getRVA();
    pe->SizeOfCode = textSec->getRawSize();
  }
  pe->SizeOfInitializedData = getSizeOfInitializedData();

  // Write data directory
  auto *dir = reinterpret_cast<data_directory *>(buf);
  buf += sizeof(*dir) * numberOfDataDirectory;
  if (!config->exports.empty()) {
    dir[EXPORT_TABLE].RelativeVirtualAddress = edata.getRVA();
    dir[EXPORT_TABLE].Size = edata.getSize();
  }
  if (importTableStart) {
    dir[IMPORT_TABLE].RelativeVirtualAddress = importTableStart->getRVA();
    dir[IMPORT_TABLE].Size = importTableSize;
  }
  if (iatStart) {
    dir[IAT].RelativeVirtualAddress = iatStart->getRVA();
    dir[IAT].Size = iatSize;
  }
  if (rsrcSec->getVirtualSize()) {
    dir[RESOURCE_TABLE].RelativeVirtualAddress = rsrcSec->getRVA();
    dir[RESOURCE_TABLE].Size = rsrcSec->getVirtualSize();
  }
  if (firstPdata) {
    dir[EXCEPTION_TABLE].RelativeVirtualAddress = firstPdata->getRVA();
    dir[EXCEPTION_TABLE].Size =
        lastPdata->getRVA() + lastPdata->getSize() - firstPdata->getRVA();
  }
  if (relocSec->getVirtualSize()) {
    dir[BASE_RELOCATION_TABLE].RelativeVirtualAddress = relocSec->getRVA();
    dir[BASE_RELOCATION_TABLE].Size = relocSec->getVirtualSize();
  }
  if (Symbol *sym = symtab->findUnderscore("_tls_used")) {
    if (Defined *b = dyn_cast<Defined>(sym)) {
      dir[TLS_TABLE].RelativeVirtualAddress = b->getRVA();
      dir[TLS_TABLE].Size = config->is64()
                                ? sizeof(object::coff_tls_directory64)
                                : sizeof(object::coff_tls_directory32);
    }
  }
  if (debugDirectory) {
    dir[DEBUG_DIRECTORY].RelativeVirtualAddress = debugDirectory->getRVA();
    dir[DEBUG_DIRECTORY].Size = debugDirectory->getSize();
  }
  if (Symbol *sym = symtab->findUnderscore("_load_config_used")) {
    if (auto *b = dyn_cast<DefinedRegular>(sym)) {
      SectionChunk *sc = b->getChunk();
      assert(b->getRVA() >= sc->getRVA());
      uint64_t offsetInChunk = b->getRVA() - sc->getRVA();
      if (!sc->hasData || offsetInChunk + 4 > sc->getSize())
        fatal("_load_config_used is malformed");

      ArrayRef<uint8_t> secContents = sc->getContents();
      uint32_t loadConfigSize =
          *reinterpret_cast<const ulittle32_t *>(&secContents[offsetInChunk]);
      if (offsetInChunk + loadConfigSize > sc->getSize())
        fatal("_load_config_used is too large");
      dir[LOAD_CONFIG_TABLE].RelativeVirtualAddress = b->getRVA();
      dir[LOAD_CONFIG_TABLE].Size = loadConfigSize;
    }
  }
  if (!delayIdata.empty()) {
    dir[DELAY_IMPORT_DESCRIPTOR].RelativeVirtualAddress =
        delayIdata.getDirRVA();
    dir[DELAY_IMPORT_DESCRIPTOR].Size = delayIdata.getDirSize();
  }

  // Write section table
  for (OutputSection *sec : outputSections) {
    sec->writeHeaderTo(buf);
    buf += sizeof(coff_section);
  }
  sectionTable = ArrayRef<uint8_t>(
      buf - outputSections.size() * sizeof(coff_section), buf);

  if (outputSymtab.empty() && strtab.empty())
    return;

  coff->PointerToSymbolTable = pointerToSymbolTable;
  uint32_t numberOfSymbols = outputSymtab.size();
  coff->NumberOfSymbols = numberOfSymbols;
  auto *symbolTable = reinterpret_cast<coff_symbol16 *>(
      buffer->getBufferStart() + coff->PointerToSymbolTable);
  for (size_t i = 0; i != numberOfSymbols; ++i)
    symbolTable[i] = outputSymtab[i];
  // Create the string table, it follows immediately after the symbol table.
  // The first 4 bytes is length including itself.
  buf = reinterpret_cast<uint8_t *>(&symbolTable[numberOfSymbols]);
  write32le(buf, strtab.size() + 4);
  if (!strtab.empty())
    memcpy(buf + 4, strtab.data(), strtab.size());
}

void Writer::openFile(StringRef path) {
  buffer = CHECK(
      FileOutputBuffer::create(path, fileSize, FileOutputBuffer::F_executable),
      "failed to open " + path);
}

void Writer::createSEHTable() {
  SymbolRVASet handlers;
  for (ObjFile *file : ObjFile::instances) {
    if (!file->hasSafeSEH())
      error("/safeseh: " + file->getName() + " is not compatible with SEH");
    markSymbolsForRVATable(file, file->getSXDataChunks(), handlers);
  }

  // Set the "no SEH" characteristic if there really were no handlers, or if
  // there is no load config object to point to the table of handlers.
  setNoSEHCharacteristic =
      handlers.empty() || !symtab->findUnderscore("_load_config_used");

  maybeAddRVATable(std::move(handlers), "__safe_se_handler_table",
                   "__safe_se_handler_count");
}

// Add a symbol to an RVA set. Two symbols may have the same RVA, but an RVA set
// cannot contain duplicates. Therefore, the set is uniqued by Chunk and the
// symbol's offset into that Chunk.
static void addSymbolToRVASet(SymbolRVASet &rvaSet, Defined *s) {
  Chunk *c = s->getChunk();
  if (auto *sc = dyn_cast<SectionChunk>(c))
    c = sc->repl; // Look through ICF replacement.
  uint32_t off = s->getRVA() - (c ? c->getRVA() : 0);
  rvaSet.insert({c, off});
}

// Given a symbol, add it to the GFIDs table if it is a live, defined, function
// symbol in an executable section.
static void maybeAddAddressTakenFunction(SymbolRVASet &addressTakenSyms,
                                         Symbol *s) {
  if (!s)
    return;

  switch (s->kind()) {
  case Symbol::DefinedLocalImportKind:
  case Symbol::DefinedImportDataKind:
    // Defines an __imp_ pointer, so it is data, so it is ignored.
    break;
  case Symbol::DefinedCommonKind:
    // Common is always data, so it is ignored.
    break;
  case Symbol::DefinedAbsoluteKind:
  case Symbol::DefinedSyntheticKind:
    // Absolute is never code, synthetic generally isn't and usually isn't
    // determinable.
    break;
  case Symbol::LazyKind:
  case Symbol::UndefinedKind:
    // Undefined symbols resolve to zero, so they don't have an RVA. Lazy
    // symbols shouldn't have relocations.
    break;

  case Symbol::DefinedImportThunkKind:
    // Thunks are always code, include them.
    addSymbolToRVASet(addressTakenSyms, cast<Defined>(s));
    break;

  case Symbol::DefinedRegularKind: {
    // This is a regular, defined, symbol from a COFF file. Mark the symbol as
    // address taken if the symbol type is function and it's in an executable
    // section.
    auto *d = cast<DefinedRegular>(s);
    if (d->getCOFFSymbol().getComplexType() == COFF::IMAGE_SYM_DTYPE_FUNCTION) {
      SectionChunk *sc = dyn_cast<SectionChunk>(d->getChunk());
      if (sc && sc->live &&
          sc->getOutputCharacteristics() & IMAGE_SCN_MEM_EXECUTE)
        addSymbolToRVASet(addressTakenSyms, d);
    }
    break;
  }
  }
}

// Visit all relocations from all section contributions of this object file and
// mark the relocation target as address-taken.
static void markSymbolsWithRelocations(ObjFile *file,
                                       SymbolRVASet &usedSymbols) {
  for (Chunk *c : file->getChunks()) {
    // We only care about live section chunks. Common chunks and other chunks
    // don't generally contain relocations.
    SectionChunk *sc = dyn_cast<SectionChunk>(c);
    if (!sc || !sc->live)
      continue;

    for (const coff_relocation &reloc : sc->getRelocs()) {
      if (config->machine == I386 && reloc.Type == COFF::IMAGE_REL_I386_REL32)
        // Ignore relative relocations on x86. On x86_64 they can't be ignored
        // since they're also used to compute absolute addresses.
        continue;

      Symbol *ref = sc->file->getSymbol(reloc.SymbolTableIndex);
      maybeAddAddressTakenFunction(usedSymbols, ref);
    }
  }
}

// Create the guard function id table. This is a table of RVAs of all
// address-taken functions. It is sorted and uniqued, just like the safe SEH
// table.
void Writer::createGuardCFTables() {
  SymbolRVASet addressTakenSyms;
  SymbolRVASet longJmpTargets;
  for (ObjFile *file : ObjFile::instances) {
    // If the object was compiled with /guard:cf, the address taken symbols
    // are in .gfids$y sections, and the longjmp targets are in .gljmp$y
    // sections. If the object was not compiled with /guard:cf, we assume there
    // were no setjmp targets, and that all code symbols with relocations are
    // possibly address-taken.
    if (file->hasGuardCF()) {
      markSymbolsForRVATable(file, file->getGuardFidChunks(), addressTakenSyms);
      markSymbolsForRVATable(file, file->getGuardLJmpChunks(), longJmpTargets);
    } else {
      markSymbolsWithRelocations(file, addressTakenSyms);
    }
  }

  // Mark the image entry as address-taken.
  if (config->entry)
    maybeAddAddressTakenFunction(addressTakenSyms, config->entry);

  // Mark exported symbols in executable sections as address-taken.
  for (Export &e : config->exports)
    maybeAddAddressTakenFunction(addressTakenSyms, e.sym);

  // Ensure sections referenced in the gfid table are 16-byte aligned.
  for (const ChunkAndOffset &c : addressTakenSyms)
    if (c.inputChunk->getAlignment() < 16)
      c.inputChunk->setAlignment(16);

  maybeAddRVATable(std::move(addressTakenSyms), "__guard_fids_table",
                   "__guard_fids_count");

  // Add the longjmp target table unless the user told us not to.
  if (config->guardCF == GuardCFLevel::Full)
    maybeAddRVATable(std::move(longJmpTargets), "__guard_longjmp_table",
                     "__guard_longjmp_count");

  // Set __guard_flags, which will be used in the load config to indicate that
  // /guard:cf was enabled.
  uint32_t guardFlags = uint32_t(coff_guard_flags::CFInstrumented) |
                        uint32_t(coff_guard_flags::HasFidTable);
  if (config->guardCF == GuardCFLevel::Full)
    guardFlags |= uint32_t(coff_guard_flags::HasLongJmpTable);
  Symbol *flagSym = symtab->findUnderscore("__guard_flags");
  cast<DefinedAbsolute>(flagSym)->setVA(guardFlags);
}

// Take a list of input sections containing symbol table indices and add those
// symbols to an RVA table. The challenge is that symbol RVAs are not known and
// depend on the table size, so we can't directly build a set of integers.
void Writer::markSymbolsForRVATable(ObjFile *file,
                                    ArrayRef<SectionChunk *> symIdxChunks,
                                    SymbolRVASet &tableSymbols) {
  for (SectionChunk *c : symIdxChunks) {
    // Skip sections discarded by linker GC. This comes up when a .gfids section
    // is associated with something like a vtable and the vtable is discarded.
    // In this case, the associated gfids section is discarded, and we don't
    // mark the virtual member functions as address-taken by the vtable.
    if (!c->live)
      continue;

    // Validate that the contents look like symbol table indices.
    ArrayRef<uint8_t> data = c->getContents();
    if (data.size() % 4 != 0) {
      warn("ignoring " + c->getSectionName() +
           " symbol table index section in object " + toString(file));
      continue;
    }

    // Read each symbol table index and check if that symbol was included in the
    // final link. If so, add it to the table symbol set.
    ArrayRef<ulittle32_t> symIndices(
        reinterpret_cast<const ulittle32_t *>(data.data()), data.size() / 4);
    ArrayRef<Symbol *> objSymbols = file->getSymbols();
    for (uint32_t symIndex : symIndices) {
      if (symIndex >= objSymbols.size()) {
        warn("ignoring invalid symbol table index in section " +
             c->getSectionName() + " in object " + toString(file));
        continue;
      }
      if (Symbol *s = objSymbols[symIndex]) {
        if (s->isLive())
          addSymbolToRVASet(tableSymbols, cast<Defined>(s));
      }
    }
  }
}

// Replace the absolute table symbol with a synthetic symbol pointing to
// tableChunk so that we can emit base relocations for it and resolve section
// relative relocations.
void Writer::maybeAddRVATable(SymbolRVASet tableSymbols, StringRef tableSym,
                              StringRef countSym) {
  if (tableSymbols.empty())
    return;

  RVATableChunk *tableChunk = make<RVATableChunk>(std::move(tableSymbols));
  rdataSec->addChunk(tableChunk);

  Symbol *t = symtab->findUnderscore(tableSym);
  Symbol *c = symtab->findUnderscore(countSym);
  replaceSymbol<DefinedSynthetic>(t, t->getName(), tableChunk);
  cast<DefinedAbsolute>(c)->setVA(tableChunk->getSize() / 4);
}

// MinGW specific. Gather all relocations that are imported from a DLL even
// though the code didn't expect it to, produce the table that the runtime
// uses for fixing them up, and provide the synthetic symbols that the
// runtime uses for finding the table.
void Writer::createRuntimePseudoRelocs() {
  std::vector<RuntimePseudoReloc> rels;

  for (Chunk *c : symtab->getChunks()) {
    auto *sc = dyn_cast<SectionChunk>(c);
    if (!sc || !sc->live)
      continue;
    sc->getRuntimePseudoRelocs(rels);
  }

  if (!rels.empty())
    log("Writing " + Twine(rels.size()) + " runtime pseudo relocations");
  PseudoRelocTableChunk *table = make<PseudoRelocTableChunk>(rels);
  rdataSec->addChunk(table);
  EmptyChunk *endOfList = make<EmptyChunk>();
  rdataSec->addChunk(endOfList);

  Symbol *headSym = symtab->findUnderscore("__RUNTIME_PSEUDO_RELOC_LIST__");
  Symbol *endSym = symtab->findUnderscore("__RUNTIME_PSEUDO_RELOC_LIST_END__");
  replaceSymbol<DefinedSynthetic>(headSym, headSym->getName(), table);
  replaceSymbol<DefinedSynthetic>(endSym, endSym->getName(), endOfList);
}

// MinGW specific.
// The MinGW .ctors and .dtors lists have sentinels at each end;
// a (uintptr_t)-1 at the start and a (uintptr_t)0 at the end.
// There's a symbol pointing to the start sentinel pointer, __CTOR_LIST__
// and __DTOR_LIST__ respectively.
void Writer::insertCtorDtorSymbols() {
  AbsolutePointerChunk *ctorListHead = make<AbsolutePointerChunk>(-1);
  AbsolutePointerChunk *ctorListEnd = make<AbsolutePointerChunk>(0);
  AbsolutePointerChunk *dtorListHead = make<AbsolutePointerChunk>(-1);
  AbsolutePointerChunk *dtorListEnd = make<AbsolutePointerChunk>(0);
  ctorsSec->insertChunkAtStart(ctorListHead);
  ctorsSec->addChunk(ctorListEnd);
  dtorsSec->insertChunkAtStart(dtorListHead);
  dtorsSec->addChunk(dtorListEnd);

  Symbol *ctorListSym = symtab->findUnderscore("__CTOR_LIST__");
  Symbol *dtorListSym = symtab->findUnderscore("__DTOR_LIST__");
  replaceSymbol<DefinedSynthetic>(ctorListSym, ctorListSym->getName(),
                                  ctorListHead);
  replaceSymbol<DefinedSynthetic>(dtorListSym, dtorListSym->getName(),
                                  dtorListHead);
}

// Handles /section options to allow users to overwrite
// section attributes.
void Writer::setSectionPermissions() {
  for (auto &p : config->section) {
    StringRef name = p.first;
    uint32_t perm = p.second;
    for (OutputSection *sec : outputSections)
      if (sec->name == name)
        sec->setPermissions(perm);
  }
}

// Write section contents to a mmap'ed file.
void Writer::writeSections() {
  // Record the number of sections to apply section index relocations
  // against absolute symbols. See applySecIdx in Chunks.cpp..
  DefinedAbsolute::numOutputSections = outputSections.size();

  uint8_t *buf = buffer->getBufferStart();
  for (OutputSection *sec : outputSections) {
    uint8_t *secBuf = buf + sec->getFileOff();
    // Fill gaps between functions in .text with INT3 instructions
    // instead of leaving as NUL bytes (which can be interpreted as
    // ADD instructions).
    if (sec->header.Characteristics & IMAGE_SCN_CNT_CODE)
      memset(secBuf, 0xCC, sec->getRawSize());
    parallelForEach(sec->chunks, [&](Chunk *c) {
      c->writeTo(secBuf + c->getRVA() - sec->getRVA());
    });
  }
}

void Writer::writeBuildId() {
  // There are two important parts to the build ID.
  // 1) If building with debug info, the COFF debug directory contains a
  //    timestamp as well as a Guid and Age of the PDB.
  // 2) In all cases, the PE COFF file header also contains a timestamp.
  // For reproducibility, instead of a timestamp we want to use a hash of the
  // PE contents.
  if (config->debug) {
    assert(buildId && "BuildId is not set!");
    // BuildId->BuildId was filled in when the PDB was written.
  }

  // At this point the only fields in the COFF file which remain unset are the
  // "timestamp" in the COFF file header, and the ones in the coff debug
  // directory.  Now we can hash the file and write that hash to the various
  // timestamp fields in the file.
  StringRef outputFileData(
      reinterpret_cast<const char *>(buffer->getBufferStart()),
      buffer->getBufferSize());

  uint32_t timestamp = config->timestamp;
  uint64_t hash = 0;
  bool generateSyntheticBuildId =
      config->mingw && config->debug && config->pdbPath.empty();

  if (config->repro || generateSyntheticBuildId)
    hash = xxHash64(outputFileData);

  if (config->repro)
    timestamp = static_cast<uint32_t>(hash);

  if (generateSyntheticBuildId) {
    // For MinGW builds without a PDB file, we still generate a build id
    // to allow associating a crash dump to the executable.
    buildId->buildId->PDB70.CVSignature = OMF::Signature::PDB70;
    buildId->buildId->PDB70.Age = 1;
    memcpy(buildId->buildId->PDB70.Signature, &hash, 8);
    // xxhash only gives us 8 bytes, so put some fixed data in the other half.
    memcpy(&buildId->buildId->PDB70.Signature[8], "LLD PDB.", 8);
  }

  if (debugDirectory)
    debugDirectory->setTimeDateStamp(timestamp);

  uint8_t *buf = buffer->getBufferStart();
  buf += dosStubSize + sizeof(PEMagic);
  object::coff_file_header *coffHeader =
      reinterpret_cast<coff_file_header *>(buf);
  coffHeader->TimeDateStamp = timestamp;
}

// Sort .pdata section contents according to PE/COFF spec 5.5.
void Writer::sortExceptionTable() {
  if (!firstPdata)
    return;
  // We assume .pdata contains function table entries only.
  auto bufAddr = [&](Chunk *c) {
    OutputSection *os = c->getOutputSection();
    return buffer->getBufferStart() + os->getFileOff() + c->getRVA() -
           os->getRVA();
  };
  uint8_t *begin = bufAddr(firstPdata);
  uint8_t *end = bufAddr(lastPdata) + lastPdata->getSize();
  if (config->machine == AMD64) {
    struct Entry { ulittle32_t begin, end, unwind; };
    parallelSort(
        MutableArrayRef<Entry>((Entry *)begin, (Entry *)end),
        [](const Entry &a, const Entry &b) { return a.begin < b.begin; });
    return;
  }
  if (config->machine == ARMNT || config->machine == ARM64) {
    struct Entry { ulittle32_t begin, unwind; };
    parallelSort(
        MutableArrayRef<Entry>((Entry *)begin, (Entry *)end),
        [](const Entry &a, const Entry &b) { return a.begin < b.begin; });
    return;
  }
  errs() << "warning: don't know how to handle .pdata.\n";
}

// The CRT section contains, among other things, the array of function
// pointers that initialize every global variable that is not trivially
// constructed. The CRT calls them one after the other prior to invoking
// main().
//
// As per C++ spec, 3.6.2/2.3,
// "Variables with ordered initialization defined within a single
// translation unit shall be initialized in the order of their definitions
// in the translation unit"
//
// It is therefore critical to sort the chunks containing the function
// pointers in the order that they are listed in the object file (top to
// bottom), otherwise global objects might not be initialized in the
// correct order.
void Writer::sortCRTSectionChunks(std::vector<Chunk *> &chunks) {
  auto sectionChunkOrder = [](const Chunk *a, const Chunk *b) {
    auto sa = dyn_cast<SectionChunk>(a);
    auto sb = dyn_cast<SectionChunk>(b);
    assert(sa && sb && "Non-section chunks in CRT section!");

    StringRef sAObj = sa->file->mb.getBufferIdentifier();
    StringRef sBObj = sb->file->mb.getBufferIdentifier();

    return sAObj == sBObj && sa->getSectionNumber() < sb->getSectionNumber();
  };
  llvm::stable_sort(chunks, sectionChunkOrder);

  if (config->verbose) {
    for (auto &c : chunks) {
      auto sc = dyn_cast<SectionChunk>(c);
      log("  " + sc->file->mb.getBufferIdentifier().str() +
          ", SectionID: " + Twine(sc->getSectionNumber()));
    }
  }
}

OutputSection *Writer::findSection(StringRef name) {
  for (OutputSection *sec : outputSections)
    if (sec->name == name)
      return sec;
  return nullptr;
}

uint32_t Writer::getSizeOfInitializedData() {
  uint32_t res = 0;
  for (OutputSection *s : outputSections)
    if (s->header.Characteristics & IMAGE_SCN_CNT_INITIALIZED_DATA)
      res += s->getRawSize();
  return res;
}

// Add base relocations to .reloc section.
void Writer::addBaserels() {
  if (!config->relocatable)
    return;
  relocSec->chunks.clear();
  std::vector<Baserel> v;
  for (OutputSection *sec : outputSections) {
    if (sec->header.Characteristics & IMAGE_SCN_MEM_DISCARDABLE)
      continue;
    // Collect all locations for base relocations.
    for (Chunk *c : sec->chunks)
      c->getBaserels(&v);
    // Add the addresses to .reloc section.
    if (!v.empty())
      addBaserelBlocks(v);
    v.clear();
  }
}

// Add addresses to .reloc section. Note that addresses are grouped by page.
void Writer::addBaserelBlocks(std::vector<Baserel> &v) {
  const uint32_t mask = ~uint32_t(pageSize - 1);
  uint32_t page = v[0].rva & mask;
  size_t i = 0, j = 1;
  for (size_t e = v.size(); j < e; ++j) {
    uint32_t p = v[j].rva & mask;
    if (p == page)
      continue;
    relocSec->addChunk(make<BaserelChunk>(page, &v[i], &v[0] + j));
    i = j;
    page = p;
  }
  if (i == j)
    return;
  relocSec->addChunk(make<BaserelChunk>(page, &v[i], &v[0] + j));
}

PartialSection *Writer::createPartialSection(StringRef name,
                                             uint32_t outChars) {
  PartialSection *&pSec = partialSections[{name, outChars}];
  if (pSec)
    return pSec;
  pSec = make<PartialSection>(name, outChars);
  return pSec;
}

PartialSection *Writer::findPartialSection(StringRef name, uint32_t outChars) {
  auto it = partialSections.find({name, outChars});
  if (it != partialSections.end())
    return it->second;
  return nullptr;
}