lib/MC/WinCOFFObjectWriter.cpp

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