lib/MC/WinCOFFObjectWriter.cpp

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