1//===- llvm/MC/WinCOFFObjectWriter.cpp ------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file contains an implementation of a Win32 COFF object file writer.
10//
11//===----------------------------------------------------------------------===//
12
13#include "llvm/ADT/DenseMap.h"
14#include "llvm/ADT/DenseSet.h"
15#include "llvm/ADT/STLExtras.h"
16#include "llvm/ADT/SmallString.h"
17#include "llvm/ADT/SmallVector.h"
18#include "llvm/ADT/StringRef.h"
19#include "llvm/ADT/Twine.h"
20#include "llvm/BinaryFormat/COFF.h"
21#include "llvm/MC/MCAsmLayout.h"
22#include "llvm/MC/MCAssembler.h"
23#include "llvm/MC/MCContext.h"
24#include "llvm/MC/MCExpr.h"
25#include "llvm/MC/MCFixup.h"
26#include "llvm/MC/MCFragment.h"
27#include "llvm/MC/MCObjectWriter.h"
28#include "llvm/MC/MCSection.h"
29#include "llvm/MC/MCSectionCOFF.h"
30#include "llvm/MC/MCSymbol.h"
31#include "llvm/MC/MCSymbolCOFF.h"
32#include "llvm/MC/MCValue.h"
33#include "llvm/MC/MCWinCOFFObjectWriter.h"
34#include "llvm/MC/StringTableBuilder.h"
35#include "llvm/Support/CRC.h"
36#include "llvm/Support/Casting.h"
37#include "llvm/Support/EndianStream.h"
38#include "llvm/Support/ErrorHandling.h"
39#include "llvm/Support/LEB128.h"
40#include "llvm/Support/MathExtras.h"
41#include "llvm/Support/raw_ostream.h"
42#include <algorithm>
43#include <cassert>
44#include <cstddef>
45#include <cstdint>
46#include <cstring>
47#include <ctime>
48#include <memory>
49#include <string>
50#include <vector>
51
52using namespace llvm;
53using llvm::support::endian::write32le;
54
55#define DEBUG_TYPE "WinCOFFObjectWriter"
56
57namespace {
58
59using name = SmallString<COFF::NameSize>;
60
61enum AuxiliaryType {
62  ATWeakExternal,
63  ATFile,
64  ATSectionDefinition
65};
66
67struct AuxSymbol {
68  AuxiliaryType AuxType;
69  COFF::Auxiliary Aux;
70};
71
72class COFFSection;
73
74class COFFSymbol {
75public:
76  COFF::symbol Data = {};
77
78  using AuxiliarySymbols = SmallVector<AuxSymbol, 1>;
79
80  name Name;
81  int Index;
82  AuxiliarySymbols Aux;
83  COFFSymbol *Other = nullptr;
84  COFFSection *Section = nullptr;
85  int Relocations = 0;
86  const MCSymbol *MC = nullptr;
87
88  COFFSymbol(StringRef Name) : Name(Name) {}
89
90  void set_name_offset(uint32_t Offset);
91
92  int64_t getIndex() const { return Index; }
93  void setIndex(int Value) {
94    Index = Value;
95    if (MC)
96      MC->setIndex(static_cast<uint32_t>(Value));
97  }
98};
99
100// This class contains staging data for a COFF relocation entry.
101struct COFFRelocation {
102  COFF::relocation Data;
103  COFFSymbol *Symb = nullptr;
104
105  COFFRelocation() = default;
106
107  static size_t size() { return COFF::RelocationSize; }
108};
109
110using relocations = std::vector<COFFRelocation>;
111
112class COFFSection {
113public:
114  COFF::section Header = {};
115
116  std::string Name;
117  int Number;
118  MCSectionCOFF const *MCSection = nullptr;
119  COFFSymbol *Symbol = nullptr;
120  relocations Relocations;
121
122  COFFSection(StringRef Name) : Name(std::string(Name)) {}
123};
124
125class WinCOFFObjectWriter : public MCObjectWriter {
126public:
127  support::endian::Writer W;
128
129  using symbols = std::vector<std::unique_ptr<COFFSymbol>>;
130  using sections = std::vector<std::unique_ptr<COFFSection>>;
131
132  using symbol_map = DenseMap<MCSymbol const *, COFFSymbol *>;
133  using section_map = DenseMap<MCSection const *, COFFSection *>;
134
135  using symbol_list = DenseSet<COFFSymbol *>;
136
137  std::unique_ptr<MCWinCOFFObjectTargetWriter> TargetObjectWriter;
138
139  // Root level file contents.
140  COFF::header Header = {};
141  sections Sections;
142  symbols Symbols;
143  StringTableBuilder Strings{StringTableBuilder::WinCOFF};
144
145  // Maps used during object file creation.
146  section_map SectionMap;
147  symbol_map SymbolMap;
148
149  symbol_list WeakDefaults;
150
151  bool UseBigObj;
152
153  bool EmitAddrsigSection = false;
154  MCSectionCOFF *AddrsigSection;
155  std::vector<const MCSymbol *> AddrsigSyms;
156
157  MCSectionCOFF *CGProfileSection = nullptr;
158
159  WinCOFFObjectWriter(std::unique_ptr<MCWinCOFFObjectTargetWriter> MOTW,
160                      raw_pwrite_stream &OS);
161
162  void reset() override {
163    memset(&Header, 0, sizeof(Header));
164    Header.Machine = TargetObjectWriter->getMachine();
165    Sections.clear();
166    Symbols.clear();
167    Strings.clear();
168    SectionMap.clear();
169    SymbolMap.clear();
170    MCObjectWriter::reset();
171  }
172
173  COFFSymbol *createSymbol(StringRef Name);
174  COFFSymbol *GetOrCreateCOFFSymbol(const MCSymbol *Symbol);
175  COFFSection *createSection(StringRef Name);
176
177  void defineSection(MCSectionCOFF const &Sec);
178
179  COFFSymbol *getLinkedSymbol(const MCSymbol &Symbol);
180  void DefineSymbol(const MCSymbol &Symbol, MCAssembler &Assembler,
181                    const MCAsmLayout &Layout);
182
183  void SetSymbolName(COFFSymbol &S);
184  void SetSectionName(COFFSection &S);
185
186  bool IsPhysicalSection(COFFSection *S);
187
188  // Entity writing methods.
189
190  void WriteFileHeader(const COFF::header &Header);
191  void WriteSymbol(const COFFSymbol &S);
192  void WriteAuxiliarySymbols(const COFFSymbol::AuxiliarySymbols &S);
193  void writeSectionHeaders();
194  void WriteRelocation(const COFF::relocation &R);
195  uint32_t writeSectionContents(MCAssembler &Asm, const MCAsmLayout &Layout,
196                                const MCSection &MCSec);
197  void writeSection(MCAssembler &Asm, const MCAsmLayout &Layout,
198                    const COFFSection &Sec, const MCSection &MCSec);
199
200  // MCObjectWriter interface implementation.
201
202  void executePostLayoutBinding(MCAssembler &Asm,
203                                const MCAsmLayout &Layout) override;
204
205  bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
206                                              const MCSymbol &SymA,
207                                              const MCFragment &FB, bool InSet,
208                                              bool IsPCRel) const override;
209
210  void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
211                        const MCFragment *Fragment, const MCFixup &Fixup,
212                        MCValue Target, uint64_t &FixedValue) override;
213
214  void createFileSymbols(MCAssembler &Asm);
215  void setWeakDefaultNames();
216  void assignSectionNumbers();
217  void assignFileOffsets(MCAssembler &Asm, const MCAsmLayout &Layout);
218
219  void emitAddrsigSection() override { EmitAddrsigSection = true; }
220  void addAddrsigSymbol(const MCSymbol *Sym) override {
221    AddrsigSyms.push_back(Sym);
222  }
223
224  uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
225};
226
227} // end anonymous namespace
228
229//------------------------------------------------------------------------------
230// Symbol class implementation
231
232// In the case that the name does not fit within 8 bytes, the offset
233// into the string table is stored in the last 4 bytes instead, leaving
234// the first 4 bytes as 0.
235void COFFSymbol::set_name_offset(uint32_t Offset) {
236  write32le(Data.Name + 0, 0);
237  write32le(Data.Name + 4, Offset);
238}
239
240//------------------------------------------------------------------------------
241// WinCOFFObjectWriter class implementation
242
243WinCOFFObjectWriter::WinCOFFObjectWriter(
244    std::unique_ptr<MCWinCOFFObjectTargetWriter> MOTW, raw_pwrite_stream &OS)
245    : W(OS, support::little), TargetObjectWriter(std::move(MOTW)) {
246  Header.Machine = TargetObjectWriter->getMachine();
247}
248
249COFFSymbol *WinCOFFObjectWriter::createSymbol(StringRef Name) {
250  Symbols.push_back(std::make_unique<COFFSymbol>(Name));
251  return Symbols.back().get();
252}
253
254COFFSymbol *WinCOFFObjectWriter::GetOrCreateCOFFSymbol(const MCSymbol *Symbol) {
255  COFFSymbol *&Ret = SymbolMap[Symbol];
256  if (!Ret)
257    Ret = createSymbol(Symbol->getName());
258  return Ret;
259}
260
261COFFSection *WinCOFFObjectWriter::createSection(StringRef Name) {
262  Sections.emplace_back(std::make_unique<COFFSection>(Name));
263  return Sections.back().get();
264}
265
266static uint32_t getAlignment(const MCSectionCOFF &Sec) {
267  switch (Sec.getAlignment()) {
268  case 1:
269    return COFF::IMAGE_SCN_ALIGN_1BYTES;
270  case 2:
271    return COFF::IMAGE_SCN_ALIGN_2BYTES;
272  case 4:
273    return COFF::IMAGE_SCN_ALIGN_4BYTES;
274  case 8:
275    return COFF::IMAGE_SCN_ALIGN_8BYTES;
276  case 16:
277    return COFF::IMAGE_SCN_ALIGN_16BYTES;
278  case 32:
279    return COFF::IMAGE_SCN_ALIGN_32BYTES;
280  case 64:
281    return COFF::IMAGE_SCN_ALIGN_64BYTES;
282  case 128:
283    return COFF::IMAGE_SCN_ALIGN_128BYTES;
284  case 256:
285    return COFF::IMAGE_SCN_ALIGN_256BYTES;
286  case 512:
287    return COFF::IMAGE_SCN_ALIGN_512BYTES;
288  case 1024:
289    return COFF::IMAGE_SCN_ALIGN_1024BYTES;
290  case 2048:
291    return COFF::IMAGE_SCN_ALIGN_2048BYTES;
292  case 4096:
293    return COFF::IMAGE_SCN_ALIGN_4096BYTES;
294  case 8192:
295    return COFF::IMAGE_SCN_ALIGN_8192BYTES;
296  }
297  llvm_unreachable("unsupported section alignment");
298}
299
300/// This function takes a section data object from the assembler
301/// and creates the associated COFF section staging object.
302void WinCOFFObjectWriter::defineSection(const MCSectionCOFF &MCSec) {
303  COFFSection *Section = createSection(MCSec.getName());
304  COFFSymbol *Symbol = createSymbol(MCSec.getName());
305  Section->Symbol = Symbol;
306  Symbol->Section = Section;
307  Symbol->Data.StorageClass = COFF::IMAGE_SYM_CLASS_STATIC;
308
309  // Create a COMDAT symbol if needed.
310  if (MCSec.getSelection() != COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE) {
311    if (const MCSymbol *S = MCSec.getCOMDATSymbol()) {
312      COFFSymbol *COMDATSymbol = GetOrCreateCOFFSymbol(S);
313      if (COMDATSymbol->Section)
314        report_fatal_error("two sections have the same comdat");
315      COMDATSymbol->Section = Section;
316    }
317  }
318
319  // In this case the auxiliary symbol is a Section Definition.
320  Symbol->Aux.resize(1);
321  Symbol->Aux[0] = {};
322  Symbol->Aux[0].AuxType = ATSectionDefinition;
323  Symbol->Aux[0].Aux.SectionDefinition.Selection = MCSec.getSelection();
324
325  // Set section alignment.
326  Section->Header.Characteristics = MCSec.getCharacteristics();
327  Section->Header.Characteristics |= getAlignment(MCSec);
328
329  // Bind internal COFF section to MC section.
330  Section->MCSection = &MCSec;
331  SectionMap[&MCSec] = Section;
332}
333
334static uint64_t getSymbolValue(const MCSymbol &Symbol,
335                               const MCAsmLayout &Layout) {
336  if (Symbol.isCommon() && Symbol.isExternal())
337    return Symbol.getCommonSize();
338
339  uint64_t Res;
340  if (!Layout.getSymbolOffset(Symbol, Res))
341    return 0;
342
343  return Res;
344}
345
346COFFSymbol *WinCOFFObjectWriter::getLinkedSymbol(const MCSymbol &Symbol) {
347  if (!Symbol.isVariable())
348    return nullptr;
349
350  const MCSymbolRefExpr *SymRef =
351      dyn_cast<MCSymbolRefExpr>(Symbol.getVariableValue());
352  if (!SymRef)
353    return nullptr;
354
355  const MCSymbol &Aliasee = SymRef->getSymbol();
356  if (!Aliasee.isUndefined())
357    return nullptr;
358  return GetOrCreateCOFFSymbol(&Aliasee);
359}
360
361/// This function takes a symbol data object from the assembler
362/// and creates the associated COFF symbol staging object.
363void WinCOFFObjectWriter::DefineSymbol(const MCSymbol &MCSym,
364                                       MCAssembler &Assembler,
365                                       const MCAsmLayout &Layout) {
366  COFFSymbol *Sym = GetOrCreateCOFFSymbol(&MCSym);
367  const MCSymbol *Base = Layout.getBaseSymbol(MCSym);
368  COFFSection *Sec = nullptr;
369  if (Base && Base->getFragment()) {
370    Sec = SectionMap[Base->getFragment()->getParent()];
371    if (Sym->Section && Sym->Section != Sec)
372      report_fatal_error("conflicting sections for symbol");
373  }
374
375  COFFSymbol *Local = nullptr;
376  if (cast<MCSymbolCOFF>(MCSym).isWeakExternal()) {
377    Sym->Data.StorageClass = COFF::IMAGE_SYM_CLASS_WEAK_EXTERNAL;
378    Sym->Section = nullptr;
379
380    COFFSymbol *WeakDefault = getLinkedSymbol(MCSym);
381    if (!WeakDefault) {
382      std::string WeakName = (".weak." + MCSym.getName() + ".default").str();
383      WeakDefault = createSymbol(WeakName);
384      if (!Sec)
385        WeakDefault->Data.SectionNumber = COFF::IMAGE_SYM_ABSOLUTE;
386      else
387        WeakDefault->Section = Sec;
388      WeakDefaults.insert(WeakDefault);
389      Local = WeakDefault;
390    }
391
392    Sym->Other = WeakDefault;
393
394    // Setup the Weak External auxiliary symbol.
395    Sym->Aux.resize(1);
396    memset(&Sym->Aux[0], 0, sizeof(Sym->Aux[0]));
397    Sym->Aux[0].AuxType = ATWeakExternal;
398    Sym->Aux[0].Aux.WeakExternal.TagIndex = 0;
399    Sym->Aux[0].Aux.WeakExternal.Characteristics =
400        COFF::IMAGE_WEAK_EXTERN_SEARCH_ALIAS;
401  } else {
402    if (!Base)
403      Sym->Data.SectionNumber = COFF::IMAGE_SYM_ABSOLUTE;
404    else
405      Sym->Section = Sec;
406    Local = Sym;
407  }
408
409  if (Local) {
410    Local->Data.Value = getSymbolValue(MCSym, Layout);
411
412    const MCSymbolCOFF &SymbolCOFF = cast<MCSymbolCOFF>(MCSym);
413    Local->Data.Type = SymbolCOFF.getType();
414    Local->Data.StorageClass = SymbolCOFF.getClass();
415
416    // If no storage class was specified in the streamer, define it here.
417    if (Local->Data.StorageClass == COFF::IMAGE_SYM_CLASS_NULL) {
418      bool IsExternal = MCSym.isExternal() ||
419                        (!MCSym.getFragment() && !MCSym.isVariable());
420
421      Local->Data.StorageClass = IsExternal ? COFF::IMAGE_SYM_CLASS_EXTERNAL
422                                            : COFF::IMAGE_SYM_CLASS_STATIC;
423    }
424  }
425
426  Sym->MC = &MCSym;
427}
428
429// Maximum offsets for different string table entry encodings.
430enum : unsigned { Max7DecimalOffset = 9999999U };
431enum : uint64_t { MaxBase64Offset = 0xFFFFFFFFFULL }; // 64^6, including 0
432
433// Encode a string table entry offset in base 64, padded to 6 chars, and
434// prefixed with a double slash: '//AAAAAA', '//AAAAAB', ...
435// Buffer must be at least 8 bytes large. No terminating null appended.
436static void encodeBase64StringEntry(char *Buffer, uint64_t Value) {
437  assert(Value > Max7DecimalOffset && Value <= MaxBase64Offset &&
438         "Illegal section name encoding for value");
439
440  static const char Alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
441                                 "abcdefghijklmnopqrstuvwxyz"
442                                 "0123456789+/";
443
444  Buffer[0] = '/';
445  Buffer[1] = '/';
446
447  char *Ptr = Buffer + 7;
448  for (unsigned i = 0; i < 6; ++i) {
449    unsigned Rem = Value % 64;
450    Value /= 64;
451    *(Ptr--) = Alphabet[Rem];
452  }
453}
454
455void WinCOFFObjectWriter::SetSectionName(COFFSection &S) {
456  if (S.Name.size() <= COFF::NameSize) {
457    std::memcpy(S.Header.Name, S.Name.c_str(), S.Name.size());
458    return;
459  }
460
461  uint64_t StringTableEntry = Strings.getOffset(S.Name);
462  if (StringTableEntry <= Max7DecimalOffset) {
463    SmallVector<char, COFF::NameSize> Buffer;
464    Twine('/').concat(Twine(StringTableEntry)).toVector(Buffer);
465    assert(Buffer.size() <= COFF::NameSize && Buffer.size() >= 2);
466    std::memcpy(S.Header.Name, Buffer.data(), Buffer.size());
467    return;
468  }
469  if (StringTableEntry <= MaxBase64Offset) {
470    // Starting with 10,000,000, offsets are encoded as base64.
471    encodeBase64StringEntry(S.Header.Name, StringTableEntry);
472    return;
473  }
474  report_fatal_error("COFF string table is greater than 64 GB.");
475}
476
477void WinCOFFObjectWriter::SetSymbolName(COFFSymbol &S) {
478  if (S.Name.size() > COFF::NameSize)
479    S.set_name_offset(Strings.getOffset(S.Name));
480  else
481    std::memcpy(S.Data.Name, S.Name.c_str(), S.Name.size());
482}
483
484bool WinCOFFObjectWriter::IsPhysicalSection(COFFSection *S) {
485  return (S->Header.Characteristics & COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA) ==
486         0;
487}
488
489//------------------------------------------------------------------------------
490// entity writing methods
491
492void WinCOFFObjectWriter::WriteFileHeader(const COFF::header &Header) {
493  if (UseBigObj) {
494    W.write<uint16_t>(COFF::IMAGE_FILE_MACHINE_UNKNOWN);
495    W.write<uint16_t>(0xFFFF);
496    W.write<uint16_t>(COFF::BigObjHeader::MinBigObjectVersion);
497    W.write<uint16_t>(Header.Machine);
498    W.write<uint32_t>(Header.TimeDateStamp);
499    W.OS.write(COFF::BigObjMagic, sizeof(COFF::BigObjMagic));
500    W.write<uint32_t>(0);
501    W.write<uint32_t>(0);
502    W.write<uint32_t>(0);
503    W.write<uint32_t>(0);
504    W.write<uint32_t>(Header.NumberOfSections);
505    W.write<uint32_t>(Header.PointerToSymbolTable);
506    W.write<uint32_t>(Header.NumberOfSymbols);
507  } else {
508    W.write<uint16_t>(Header.Machine);
509    W.write<uint16_t>(static_cast<int16_t>(Header.NumberOfSections));
510    W.write<uint32_t>(Header.TimeDateStamp);
511    W.write<uint32_t>(Header.PointerToSymbolTable);
512    W.write<uint32_t>(Header.NumberOfSymbols);
513    W.write<uint16_t>(Header.SizeOfOptionalHeader);
514    W.write<uint16_t>(Header.Characteristics);
515  }
516}
517
518void WinCOFFObjectWriter::WriteSymbol(const COFFSymbol &S) {
519  W.OS.write(S.Data.Name, COFF::NameSize);
520  W.write<uint32_t>(S.Data.Value);
521  if (UseBigObj)
522    W.write<uint32_t>(S.Data.SectionNumber);
523  else
524    W.write<uint16_t>(static_cast<int16_t>(S.Data.SectionNumber));
525  W.write<uint16_t>(S.Data.Type);
526  W.OS << char(S.Data.StorageClass);
527  W.OS << char(S.Data.NumberOfAuxSymbols);
528  WriteAuxiliarySymbols(S.Aux);
529}
530
531void WinCOFFObjectWriter::WriteAuxiliarySymbols(
532    const COFFSymbol::AuxiliarySymbols &S) {
533  for (const AuxSymbol &i : S) {
534    switch (i.AuxType) {
535    case ATWeakExternal:
536      W.write<uint32_t>(i.Aux.WeakExternal.TagIndex);
537      W.write<uint32_t>(i.Aux.WeakExternal.Characteristics);
538      W.OS.write_zeros(sizeof(i.Aux.WeakExternal.unused));
539      if (UseBigObj)
540        W.OS.write_zeros(COFF::Symbol32Size - COFF::Symbol16Size);
541      break;
542    case ATFile:
543      W.OS.write(reinterpret_cast<const char *>(&i.Aux),
544                        UseBigObj ? COFF::Symbol32Size : COFF::Symbol16Size);
545      break;
546    case ATSectionDefinition:
547      W.write<uint32_t>(i.Aux.SectionDefinition.Length);
548      W.write<uint16_t>(i.Aux.SectionDefinition.NumberOfRelocations);
549      W.write<uint16_t>(i.Aux.SectionDefinition.NumberOfLinenumbers);
550      W.write<uint32_t>(i.Aux.SectionDefinition.CheckSum);
551      W.write<uint16_t>(static_cast<int16_t>(i.Aux.SectionDefinition.Number));
552      W.OS << char(i.Aux.SectionDefinition.Selection);
553      W.OS.write_zeros(sizeof(i.Aux.SectionDefinition.unused));
554      W.write<uint16_t>(static_cast<int16_t>(i.Aux.SectionDefinition.Number >> 16));
555      if (UseBigObj)
556        W.OS.write_zeros(COFF::Symbol32Size - COFF::Symbol16Size);
557      break;
558    }
559  }
560}
561
562// Write the section header.
563void WinCOFFObjectWriter::writeSectionHeaders() {
564  // Section numbers must be monotonically increasing in the section
565  // header, but our Sections array is not sorted by section number,
566  // so make a copy of Sections and sort it.
567  std::vector<COFFSection *> Arr;
568  for (auto &Section : Sections)
569    Arr.push_back(Section.get());
570  llvm::sort(Arr, [](const COFFSection *A, const COFFSection *B) {
571    return A->Number < B->Number;
572  });
573
574  for (auto &Section : Arr) {
575    if (Section->Number == -1)
576      continue;
577
578    COFF::section &S = Section->Header;
579    if (Section->Relocations.size() >= 0xffff)
580      S.Characteristics |= COFF::IMAGE_SCN_LNK_NRELOC_OVFL;
581    W.OS.write(S.Name, COFF::NameSize);
582    W.write<uint32_t>(S.VirtualSize);
583    W.write<uint32_t>(S.VirtualAddress);
584    W.write<uint32_t>(S.SizeOfRawData);
585    W.write<uint32_t>(S.PointerToRawData);
586    W.write<uint32_t>(S.PointerToRelocations);
587    W.write<uint32_t>(S.PointerToLineNumbers);
588    W.write<uint16_t>(S.NumberOfRelocations);
589    W.write<uint16_t>(S.NumberOfLineNumbers);
590    W.write<uint32_t>(S.Characteristics);
591  }
592}
593
594void WinCOFFObjectWriter::WriteRelocation(const COFF::relocation &R) {
595  W.write<uint32_t>(R.VirtualAddress);
596  W.write<uint32_t>(R.SymbolTableIndex);
597  W.write<uint16_t>(R.Type);
598}
599
600// Write MCSec's contents. What this function does is essentially
601// "Asm.writeSectionData(&MCSec, Layout)", but it's a bit complicated
602// because it needs to compute a CRC.
603uint32_t WinCOFFObjectWriter::writeSectionContents(MCAssembler &Asm,
604                                                   const MCAsmLayout &Layout,
605                                                   const MCSection &MCSec) {
606  // Save the contents of the section to a temporary buffer, we need this
607  // to CRC the data before we dump it into the object file.
608  SmallVector<char, 128> Buf;
609  raw_svector_ostream VecOS(Buf);
610  Asm.writeSectionData(VecOS, &MCSec, Layout);
611
612  // Write the section contents to the object file.
613  W.OS << Buf;
614
615  // Calculate our CRC with an initial value of '0', this is not how
616  // JamCRC is specified but it aligns with the expected output.
617  JamCRC JC(/*Init=*/0);
618  JC.update(makeArrayRef(reinterpret_cast<uint8_t*>(Buf.data()), Buf.size()));
619  return JC.getCRC();
620}
621
622void WinCOFFObjectWriter::writeSection(MCAssembler &Asm,
623                                       const MCAsmLayout &Layout,
624                                       const COFFSection &Sec,
625                                       const MCSection &MCSec) {
626  if (Sec.Number == -1)
627    return;
628
629  // Write the section contents.
630  if (Sec.Header.PointerToRawData != 0) {
631    assert(W.OS.tell() == Sec.Header.PointerToRawData &&
632           "Section::PointerToRawData is insane!");
633
634    uint32_t CRC = writeSectionContents(Asm, Layout, MCSec);
635
636    // Update the section definition auxiliary symbol to record the CRC.
637    COFFSection *Sec = SectionMap[&MCSec];
638    COFFSymbol::AuxiliarySymbols &AuxSyms = Sec->Symbol->Aux;
639    assert(AuxSyms.size() == 1 && AuxSyms[0].AuxType == ATSectionDefinition);
640    AuxSymbol &SecDef = AuxSyms[0];
641    SecDef.Aux.SectionDefinition.CheckSum = CRC;
642  }
643
644  // Write relocations for this section.
645  if (Sec.Relocations.empty()) {
646    assert(Sec.Header.PointerToRelocations == 0 &&
647           "Section::PointerToRelocations is insane!");
648    return;
649  }
650
651  assert(W.OS.tell() == Sec.Header.PointerToRelocations &&
652         "Section::PointerToRelocations is insane!");
653
654  if (Sec.Relocations.size() >= 0xffff) {
655    // In case of overflow, write actual relocation count as first
656    // relocation. Including the synthetic reloc itself (+ 1).
657    COFF::relocation R;
658    R.VirtualAddress = Sec.Relocations.size() + 1;
659    R.SymbolTableIndex = 0;
660    R.Type = 0;
661    WriteRelocation(R);
662  }
663
664  for (const auto &Relocation : Sec.Relocations)
665    WriteRelocation(Relocation.Data);
666}
667
668////////////////////////////////////////////////////////////////////////////////
669// MCObjectWriter interface implementations
670
671void WinCOFFObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
672                                                   const MCAsmLayout &Layout) {
673  if (EmitAddrsigSection) {
674    AddrsigSection = Asm.getContext().getCOFFSection(
675        ".llvm_addrsig", COFF::IMAGE_SCN_LNK_REMOVE,
676        SectionKind::getMetadata());
677    Asm.registerSection(*AddrsigSection);
678  }
679
680  if (!Asm.CGProfile.empty()) {
681    CGProfileSection = Asm.getContext().getCOFFSection(
682        ".llvm.call-graph-profile", COFF::IMAGE_SCN_LNK_REMOVE,
683        SectionKind::getMetadata());
684    Asm.registerSection(*CGProfileSection);
685  }
686
687  // "Define" each section & symbol. This creates section & symbol
688  // entries in the staging area.
689  for (const auto &Section : Asm)
690    defineSection(static_cast<const MCSectionCOFF &>(Section));
691
692  for (const MCSymbol &Symbol : Asm.symbols())
693    if (!Symbol.isTemporary())
694      DefineSymbol(Symbol, Asm, Layout);
695}
696
697bool WinCOFFObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
698    const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
699    bool InSet, bool IsPCRel) const {
700  // Don't drop relocations between functions, even if they are in the same text
701  // section. Multiple Visual C++ linker features depend on having the
702  // relocations present. The /INCREMENTAL flag will cause these relocations to
703  // point to thunks, and the /GUARD:CF flag assumes that it can use relocations
704  // to approximate the set of all address taken functions. LLD's implementation
705  // of /GUARD:CF also relies on the existance of these relocations.
706  uint16_t Type = cast<MCSymbolCOFF>(SymA).getType();
707  if ((Type >> COFF::SCT_COMPLEX_TYPE_SHIFT) == COFF::IMAGE_SYM_DTYPE_FUNCTION)
708    return false;
709  return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
710                                                                InSet, IsPCRel);
711}
712
713void WinCOFFObjectWriter::recordRelocation(MCAssembler &Asm,
714                                           const MCAsmLayout &Layout,
715                                           const MCFragment *Fragment,
716                                           const MCFixup &Fixup, MCValue Target,
717                                           uint64_t &FixedValue) {
718  assert(Target.getSymA() && "Relocation must reference a symbol!");
719
720  const MCSymbol &A = Target.getSymA()->getSymbol();
721  if (!A.isRegistered()) {
722    Asm.getContext().reportError(Fixup.getLoc(),
723                                      Twine("symbol '") + A.getName() +
724                                          "' can not be undefined");
725    return;
726  }
727  if (A.isTemporary() && A.isUndefined()) {
728    Asm.getContext().reportError(Fixup.getLoc(),
729                                      Twine("assembler label '") + A.getName() +
730                                          "' can not be undefined");
731    return;
732  }
733
734  MCSection *MCSec = Fragment->getParent();
735
736  // Mark this symbol as requiring an entry in the symbol table.
737  assert(SectionMap.find(MCSec) != SectionMap.end() &&
738         "Section must already have been defined in executePostLayoutBinding!");
739
740  COFFSection *Sec = SectionMap[MCSec];
741  const MCSymbolRefExpr *SymB = Target.getSymB();
742
743  if (SymB) {
744    const MCSymbol *B = &SymB->getSymbol();
745    if (!B->getFragment()) {
746      Asm.getContext().reportError(
747          Fixup.getLoc(),
748          Twine("symbol '") + B->getName() +
749              "' can not be undefined in a subtraction expression");
750      return;
751    }
752
753    // Offset of the symbol in the section
754    int64_t OffsetOfB = Layout.getSymbolOffset(*B);
755
756    // Offset of the relocation in the section
757    int64_t OffsetOfRelocation =
758        Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
759
760    FixedValue = (OffsetOfRelocation - OffsetOfB) + Target.getConstant();
761  } else {
762    FixedValue = Target.getConstant();
763  }
764
765  COFFRelocation Reloc;
766
767  Reloc.Data.SymbolTableIndex = 0;
768  Reloc.Data.VirtualAddress = Layout.getFragmentOffset(Fragment);
769
770  // Turn relocations for temporary symbols into section relocations.
771  if (A.isTemporary()) {
772    MCSection *TargetSection = &A.getSection();
773    assert(
774        SectionMap.find(TargetSection) != SectionMap.end() &&
775        "Section must already have been defined in executePostLayoutBinding!");
776    Reloc.Symb = SectionMap[TargetSection]->Symbol;
777    FixedValue += Layout.getSymbolOffset(A);
778  } else {
779    assert(
780        SymbolMap.find(&A) != SymbolMap.end() &&
781        "Symbol must already have been defined in executePostLayoutBinding!");
782    Reloc.Symb = SymbolMap[&A];
783  }
784
785  ++Reloc.Symb->Relocations;
786
787  Reloc.Data.VirtualAddress += Fixup.getOffset();
788  Reloc.Data.Type = TargetObjectWriter->getRelocType(
789      Asm.getContext(), Target, Fixup, SymB, Asm.getBackend());
790
791  // FIXME: Can anyone explain what this does other than adjust for the size
792  // of the offset?
793  if ((Header.Machine == COFF::IMAGE_FILE_MACHINE_AMD64 &&
794       Reloc.Data.Type == COFF::IMAGE_REL_AMD64_REL32) ||
795      (Header.Machine == COFF::IMAGE_FILE_MACHINE_I386 &&
796       Reloc.Data.Type == COFF::IMAGE_REL_I386_REL32))
797    FixedValue += 4;
798
799  if (Header.Machine == COFF::IMAGE_FILE_MACHINE_ARMNT) {
800    switch (Reloc.Data.Type) {
801    case COFF::IMAGE_REL_ARM_ABSOLUTE:
802    case COFF::IMAGE_REL_ARM_ADDR32:
803    case COFF::IMAGE_REL_ARM_ADDR32NB:
804    case COFF::IMAGE_REL_ARM_TOKEN:
805    case COFF::IMAGE_REL_ARM_SECTION:
806    case COFF::IMAGE_REL_ARM_SECREL:
807      break;
808    case COFF::IMAGE_REL_ARM_BRANCH11:
809    case COFF::IMAGE_REL_ARM_BLX11:
810    // IMAGE_REL_ARM_BRANCH11 and IMAGE_REL_ARM_BLX11 are only used for
811    // pre-ARMv7, which implicitly rules it out of ARMNT (it would be valid
812    // for Windows CE).
813    case COFF::IMAGE_REL_ARM_BRANCH24:
814    case COFF::IMAGE_REL_ARM_BLX24:
815    case COFF::IMAGE_REL_ARM_MOV32A:
816      // IMAGE_REL_ARM_BRANCH24, IMAGE_REL_ARM_BLX24, IMAGE_REL_ARM_MOV32A are
817      // only used for ARM mode code, which is documented as being unsupported
818      // by Windows on ARM.  Empirical proof indicates that masm is able to
819      // generate the relocations however the rest of the MSVC toolchain is
820      // unable to handle it.
821      llvm_unreachable("unsupported relocation");
822      break;
823    case COFF::IMAGE_REL_ARM_MOV32T:
824      break;
825    case COFF::IMAGE_REL_ARM_BRANCH20T:
826    case COFF::IMAGE_REL_ARM_BRANCH24T:
827    case COFF::IMAGE_REL_ARM_BLX23T:
828      // IMAGE_REL_BRANCH20T, IMAGE_REL_ARM_BRANCH24T, IMAGE_REL_ARM_BLX23T all
829      // perform a 4 byte adjustment to the relocation.  Relative branches are
830      // offset by 4 on ARM, however, because there is no RELA relocations, all
831      // branches are offset by 4.
832      FixedValue = FixedValue + 4;
833      break;
834    }
835  }
836
837  // The fixed value never makes sense for section indices, ignore it.
838  if (Fixup.getKind() == FK_SecRel_2)
839    FixedValue = 0;
840
841  if (TargetObjectWriter->recordRelocation(Fixup))
842    Sec->Relocations.push_back(Reloc);
843}
844
845static std::time_t getTime() {
846  std::time_t Now = time(nullptr);
847  if (Now < 0 || !isUInt<32>(Now))
848    return UINT32_MAX;
849  return Now;
850}
851
852// Create .file symbols.
853void WinCOFFObjectWriter::createFileSymbols(MCAssembler &Asm) {
854  for (const std::string &Name : Asm.getFileNames()) {
855    // round up to calculate the number of auxiliary symbols required
856    unsigned SymbolSize = UseBigObj ? COFF::Symbol32Size : COFF::Symbol16Size;
857    unsigned Count = (Name.size() + SymbolSize - 1) / SymbolSize;
858
859    COFFSymbol *File = createSymbol(".file");
860    File->Data.SectionNumber = COFF::IMAGE_SYM_DEBUG;
861    File->Data.StorageClass = COFF::IMAGE_SYM_CLASS_FILE;
862    File->Aux.resize(Count);
863
864    unsigned Offset = 0;
865    unsigned Length = Name.size();
866    for (auto &Aux : File->Aux) {
867      Aux.AuxType = ATFile;
868
869      if (Length > SymbolSize) {
870        memcpy(&Aux.Aux, Name.c_str() + Offset, SymbolSize);
871        Length = Length - SymbolSize;
872      } else {
873        memcpy(&Aux.Aux, Name.c_str() + Offset, Length);
874        memset((char *)&Aux.Aux + Length, 0, SymbolSize - Length);
875        break;
876      }
877
878      Offset += SymbolSize;
879    }
880  }
881}
882
883void WinCOFFObjectWriter::setWeakDefaultNames() {
884  if (WeakDefaults.empty())
885    return;
886
887  // If multiple object files use a weak symbol (either with a regular
888  // defined default, or an absolute zero symbol as default), the defaults
889  // cause duplicate definitions unless their names are made unique. Look
890  // for a defined extern symbol, that isn't comdat - that should be unique
891  // unless there are other duplicate definitions. And if none is found,
892  // allow picking a comdat symbol, as that's still better than nothing.
893
894  COFFSymbol *Unique = nullptr;
895  for (bool AllowComdat : {false, true}) {
896    for (auto &Sym : Symbols) {
897      // Don't include the names of the defaults themselves
898      if (WeakDefaults.count(Sym.get()))
899        continue;
900      // Only consider external symbols
901      if (Sym->Data.StorageClass != COFF::IMAGE_SYM_CLASS_EXTERNAL)
902        continue;
903      // Only consider symbols defined in a section or that are absolute
904      if (!Sym->Section && Sym->Data.SectionNumber != COFF::IMAGE_SYM_ABSOLUTE)
905        continue;
906      if (!AllowComdat && Sym->Section &&
907          Sym->Section->Header.Characteristics & COFF::IMAGE_SCN_LNK_COMDAT)
908        continue;
909      Unique = Sym.get();
910      break;
911    }
912    if (Unique)
913      break;
914  }
915  // If we didn't find any unique symbol to use for the names, just skip this.
916  if (!Unique)
917    return;
918  for (auto *Sym : WeakDefaults) {
919    Sym->Name.append(".");
920    Sym->Name.append(Unique->Name);
921  }
922}
923
924static bool isAssociative(const COFFSection &Section) {
925  return Section.Symbol->Aux[0].Aux.SectionDefinition.Selection ==
926         COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
927}
928
929void WinCOFFObjectWriter::assignSectionNumbers() {
930  size_t I = 1;
931  auto Assign = [&](COFFSection &Section) {
932    Section.Number = I;
933    Section.Symbol->Data.SectionNumber = I;
934    Section.Symbol->Aux[0].Aux.SectionDefinition.Number = I;
935    ++I;
936  };
937
938  // Although it is not explicitly requested by the Microsoft COFF spec,
939  // we should avoid emitting forward associative section references,
940  // because MSVC link.exe as of 2017 cannot handle that.
941  for (const std::unique_ptr<COFFSection> &Section : Sections)
942    if (!isAssociative(*Section))
943      Assign(*Section);
944  for (const std::unique_ptr<COFFSection> &Section : Sections)
945    if (isAssociative(*Section))
946      Assign(*Section);
947}
948
949// Assign file offsets to COFF object file structures.
950void WinCOFFObjectWriter::assignFileOffsets(MCAssembler &Asm,
951                                            const MCAsmLayout &Layout) {
952  unsigned Offset = W.OS.tell();
953
954  Offset += UseBigObj ? COFF::Header32Size : COFF::Header16Size;
955  Offset += COFF::SectionSize * Header.NumberOfSections;
956
957  for (const auto &Section : Asm) {
958    COFFSection *Sec = SectionMap[&Section];
959
960    if (Sec->Number == -1)
961      continue;
962
963    Sec->Header.SizeOfRawData = Layout.getSectionAddressSize(&Section);
964
965    if (IsPhysicalSection(Sec)) {
966      Sec->Header.PointerToRawData = Offset;
967      Offset += Sec->Header.SizeOfRawData;
968    }
969
970    if (!Sec->Relocations.empty()) {
971      bool RelocationsOverflow = Sec->Relocations.size() >= 0xffff;
972
973      if (RelocationsOverflow) {
974        // Signal overflow by setting NumberOfRelocations to max value. Actual
975        // size is found in reloc #0. Microsoft tools understand this.
976        Sec->Header.NumberOfRelocations = 0xffff;
977      } else {
978        Sec->Header.NumberOfRelocations = Sec->Relocations.size();
979      }
980      Sec->Header.PointerToRelocations = Offset;
981
982      if (RelocationsOverflow) {
983        // Reloc #0 will contain actual count, so make room for it.
984        Offset += COFF::RelocationSize;
985      }
986
987      Offset += COFF::RelocationSize * Sec->Relocations.size();
988
989      for (auto &Relocation : Sec->Relocations) {
990        assert(Relocation.Symb->getIndex() != -1);
991        Relocation.Data.SymbolTableIndex = Relocation.Symb->getIndex();
992      }
993    }
994
995    assert(Sec->Symbol->Aux.size() == 1 &&
996           "Section's symbol must have one aux!");
997    AuxSymbol &Aux = Sec->Symbol->Aux[0];
998    assert(Aux.AuxType == ATSectionDefinition &&
999           "Section's symbol's aux symbol must be a Section Definition!");
1000    Aux.Aux.SectionDefinition.Length = Sec->Header.SizeOfRawData;
1001    Aux.Aux.SectionDefinition.NumberOfRelocations =
1002        Sec->Header.NumberOfRelocations;
1003    Aux.Aux.SectionDefinition.NumberOfLinenumbers =
1004        Sec->Header.NumberOfLineNumbers;
1005  }
1006
1007  Header.PointerToSymbolTable = Offset;
1008}
1009
1010uint64_t WinCOFFObjectWriter::writeObject(MCAssembler &Asm,
1011                                          const MCAsmLayout &Layout) {
1012  uint64_t StartOffset = W.OS.tell();
1013
1014  if (Sections.size() > INT32_MAX)
1015    report_fatal_error(
1016        "PE COFF object files can't have more than 2147483647 sections");
1017
1018  UseBigObj = Sections.size() > COFF::MaxNumberOfSections16;
1019  Header.NumberOfSections = Sections.size();
1020  Header.NumberOfSymbols = 0;
1021
1022  setWeakDefaultNames();
1023  assignSectionNumbers();
1024  createFileSymbols(Asm);
1025
1026  for (auto &Symbol : Symbols) {
1027    // Update section number & offset for symbols that have them.
1028    if (Symbol->Section)
1029      Symbol->Data.SectionNumber = Symbol->Section->Number;
1030    Symbol->setIndex(Header.NumberOfSymbols++);
1031    // Update auxiliary symbol info.
1032    Symbol->Data.NumberOfAuxSymbols = Symbol->Aux.size();
1033    Header.NumberOfSymbols += Symbol->Data.NumberOfAuxSymbols;
1034  }
1035
1036  // Build string table.
1037  for (const auto &S : Sections)
1038    if (S->Name.size() > COFF::NameSize)
1039      Strings.add(S->Name);
1040  for (const auto &S : Symbols)
1041    if (S->Name.size() > COFF::NameSize)
1042      Strings.add(S->Name);
1043  Strings.finalize();
1044
1045  // Set names.
1046  for (const auto &S : Sections)
1047    SetSectionName(*S);
1048  for (auto &S : Symbols)
1049    SetSymbolName(*S);
1050
1051  // Fixup weak external references.
1052  for (auto &Symbol : Symbols) {
1053    if (Symbol->Other) {
1054      assert(Symbol->getIndex() != -1);
1055      assert(Symbol->Aux.size() == 1 && "Symbol must contain one aux symbol!");
1056      assert(Symbol->Aux[0].AuxType == ATWeakExternal &&
1057             "Symbol's aux symbol must be a Weak External!");
1058      Symbol->Aux[0].Aux.WeakExternal.TagIndex = Symbol->Other->getIndex();
1059    }
1060  }
1061
1062  // Fixup associative COMDAT sections.
1063  for (auto &Section : Sections) {
1064    if (Section->Symbol->Aux[0].Aux.SectionDefinition.Selection !=
1065        COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
1066      continue;
1067
1068    const MCSectionCOFF &MCSec = *Section->MCSection;
1069    const MCSymbol *AssocMCSym = MCSec.getCOMDATSymbol();
1070    assert(AssocMCSym);
1071
1072    // It's an error to try to associate with an undefined symbol or a symbol
1073    // without a section.
1074    if (!AssocMCSym->isInSection()) {
1075      Asm.getContext().reportError(
1076          SMLoc(), Twine("cannot make section ") + MCSec.getName() +
1077                       Twine(" associative with sectionless symbol ") +
1078                       AssocMCSym->getName());
1079      continue;
1080    }
1081
1082    const auto *AssocMCSec = cast<MCSectionCOFF>(&AssocMCSym->getSection());
1083    assert(SectionMap.count(AssocMCSec));
1084    COFFSection *AssocSec = SectionMap[AssocMCSec];
1085
1086    // Skip this section if the associated section is unused.
1087    if (AssocSec->Number == -1)
1088      continue;
1089
1090    Section->Symbol->Aux[0].Aux.SectionDefinition.Number = AssocSec->Number;
1091  }
1092
1093  // Create the contents of the .llvm_addrsig section.
1094  if (EmitAddrsigSection) {
1095    auto Frag = new MCDataFragment(AddrsigSection);
1096    Frag->setLayoutOrder(0);
1097    raw_svector_ostream OS(Frag->getContents());
1098    for (const MCSymbol *S : AddrsigSyms) {
1099      if (!S->isTemporary()) {
1100        encodeULEB128(S->getIndex(), OS);
1101        continue;
1102      }
1103
1104      MCSection *TargetSection = &S->getSection();
1105      assert(SectionMap.find(TargetSection) != SectionMap.end() &&
1106             "Section must already have been defined in "
1107             "executePostLayoutBinding!");
1108      encodeULEB128(SectionMap[TargetSection]->Symbol->getIndex(), OS);
1109    }
1110  }
1111
1112  // Create the contents of the .llvm.call-graph-profile section.
1113  if (CGProfileSection) {
1114    auto *Frag = new MCDataFragment(CGProfileSection);
1115    Frag->setLayoutOrder(0);
1116    raw_svector_ostream OS(Frag->getContents());
1117    for (const MCAssembler::CGProfileEntry &CGPE : Asm.CGProfile) {
1118      uint32_t FromIndex = CGPE.From->getSymbol().getIndex();
1119      uint32_t ToIndex = CGPE.To->getSymbol().getIndex();
1120      support::endian::write(OS, FromIndex, W.Endian);
1121      support::endian::write(OS, ToIndex, W.Endian);
1122      support::endian::write(OS, CGPE.Count, W.Endian);
1123    }
1124  }
1125
1126  assignFileOffsets(Asm, Layout);
1127
1128  // MS LINK expects to be able to use this timestamp to implement their
1129  // /INCREMENTAL feature.
1130  if (Asm.isIncrementalLinkerCompatible()) {
1131    Header.TimeDateStamp = getTime();
1132  } else {
1133    // Have deterministic output if /INCREMENTAL isn't needed. Also matches GNU.
1134    Header.TimeDateStamp = 0;
1135  }
1136
1137  // Write it all to disk...
1138  WriteFileHeader(Header);
1139  writeSectionHeaders();
1140
1141  // Write section contents.
1142  sections::iterator I = Sections.begin();
1143  sections::iterator IE = Sections.end();
1144  MCAssembler::iterator J = Asm.begin();
1145  MCAssembler::iterator JE = Asm.end();
1146  for (; I != IE && J != JE; ++I, ++J)
1147    writeSection(Asm, Layout, **I, *J);
1148
1149  assert(W.OS.tell() == Header.PointerToSymbolTable &&
1150         "Header::PointerToSymbolTable is insane!");
1151
1152  // Write a symbol table.
1153  for (auto &Symbol : Symbols)
1154    if (Symbol->getIndex() != -1)
1155      WriteSymbol(*Symbol);
1156
1157  // Write a string table, which completes the entire COFF file.
1158  Strings.write(W.OS);
1159
1160  return W.OS.tell() - StartOffset;
1161}
1162
1163MCWinCOFFObjectTargetWriter::MCWinCOFFObjectTargetWriter(unsigned Machine_)
1164    : Machine(Machine_) {}
1165
1166// Pin the vtable to this file.
1167void MCWinCOFFObjectTargetWriter::anchor() {}
1168
1169//------------------------------------------------------------------------------
1170// WinCOFFObjectWriter factory function
1171
1172std::unique_ptr<MCObjectWriter> llvm::createWinCOFFObjectWriter(
1173    std::unique_ptr<MCWinCOFFObjectTargetWriter> MOTW, raw_pwrite_stream &OS) {
1174  return std::make_unique<WinCOFFObjectWriter>(std::move(MOTW), OS);
1175}
1176