COFFEmitter.cpp

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//===- yaml2coff - Convert YAML to a COFF object file ---------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// The COFF component of yaml2obj.
///
//===----------------------------------------------------------------------===//
 
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/DebugInfo/CodeView/DebugStringTableSubsection.h"
#include "llvm/DebugInfo/CodeView/StringsAndChecksums.h"
#include "llvm/Object/COFF.h"
#include "llvm/ObjectYAML/ObjectYAML.h"
#include "llvm/ObjectYAML/yaml2obj.h"
#include "llvm/Support/BinaryStreamWriter.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/WithColor.h"
#include "llvm/Support/raw_ostream.h"
#include <vector>
 
using namespace llvm;
 
namespace {
 
/// This parses a yaml stream that represents a COFF object file.
/// See docs/yaml2obj for the yaml scheema.
struct COFFParser {
  COFFParser(COFFYAML::Object &Obj, yaml::ErrorHandler EH)
      : Obj(Obj), SectionTableStart(0), SectionTableSize(0), ErrHandler(EH) {
    // A COFF string table always starts with a 4 byte size field. Offsets into
    // it include this size, so allocate it now.
    StringTable.append(4, char(0));
  }
 
  bool useBigObj() const {
    return static_cast<int32_t>(Obj.Sections.size()) >
           COFF::MaxNumberOfSections16;
  }
 
  bool isPE() const { return Obj.OptionalHeader.hasValue(); }
  bool is64Bit() const {
    return Obj.Header.Machine == COFF::IMAGE_FILE_MACHINE_AMD64 ||
           Obj.Header.Machine == COFF::IMAGE_FILE_MACHINE_ARM64;
  }
 
  uint32_t getFileAlignment() const {
    return Obj.OptionalHeader->Header.FileAlignment;
  }
 
  unsigned getHeaderSize() const {
    return useBigObj() ? COFF::Header32Size : COFF::Header16Size;
  }
 
  unsigned getSymbolSize() const {
    return useBigObj() ? COFF::Symbol32Size : COFF::Symbol16Size;
  }
 
  bool parseSections() {
    for (COFFYAML::Section &Sec : Obj.Sections) {
      // If the name is less than 8 bytes, store it in place, otherwise
      // store it in the string table.
      StringRef Name = Sec.Name;
 
      if (Name.size() <= COFF::NameSize) {
        std::copy(Name.begin(), Name.end(), Sec.Header.Name);
      } else {
        // Add string to the string table and format the index for output.
        unsigned Index = getStringIndex(Name);
        std::string str = utostr(Index);
        if (str.size() > 7) {
          ErrHandler("string table got too large");
          return false;
        }
        Sec.Header.Name[0] = '/';
        std::copy(str.begin(), str.end(), Sec.Header.Name + 1);
      }
 
      if (Sec.Alignment) {
        if (Sec.Alignment > 8192) {
          ErrHandler("section alignment is too large");
          return false;
        }
        if (!isPowerOf2_32(Sec.Alignment)) {
          ErrHandler("section alignment is not a power of 2");
          return false;
        }
        Sec.Header.Characteristics |= (Log2_32(Sec.Alignment) + 1) << 20;
      }
    }
    return true;
  }
 
  bool parseSymbols() {
    for (COFFYAML::Symbol &Sym : Obj.Symbols) {
      // If the name is less than 8 bytes, store it in place, otherwise
      // store it in the string table.
      StringRef Name = Sym.Name;
      if (Name.size() <= COFF::NameSize) {
        std::copy(Name.begin(), Name.end(), Sym.Header.Name);
      } else {
        // Add string to the string table and format the index for output.
        unsigned Index = getStringIndex(Name);
        *reinterpret_cast<support::aligned_ulittle32_t *>(Sym.Header.Name + 4) =
            Index;
      }
 
      Sym.Header.Type = Sym.SimpleType;
      Sym.Header.Type |= Sym.ComplexType << COFF::SCT_COMPLEX_TYPE_SHIFT;
    }
    return true;
  }
 
  bool parse() {
    if (!parseSections())
      return false;
    if (!parseSymbols())
      return false;
    return true;
  }
 
  unsigned getStringIndex(StringRef Str) {
    StringMap<unsigned>::iterator i = StringTableMap.find(Str);
    if (i == StringTableMap.end()) {
      unsigned Index = StringTable.size();
      StringTable.append(Str.begin(), Str.end());
      StringTable.push_back(0);
      StringTableMap[Str] = Index;
      return Index;
    }
    return i->second;
  }
 
  COFFYAML::Object &Obj;
 
  codeview::StringsAndChecksums StringsAndChecksums;
  BumpPtrAllocator Allocator;
  StringMap<unsigned> StringTableMap;
  std::string StringTable;
  uint32_t SectionTableStart;
  uint32_t SectionTableSize;
 
  yaml::ErrorHandler ErrHandler;
};
 
enum { DOSStubSize = 128 };
 
} // end anonymous namespace
 
// Take a CP and assign addresses and sizes to everything. Returns false if the
// layout is not valid to do.
static bool layoutOptionalHeader(COFFParser &CP) {
  if (!CP.isPE())
    return true;
  unsigned PEHeaderSize = CP.is64Bit() ? sizeof(object::pe32plus_header)
                                       : sizeof(object::pe32_header);
  CP.Obj.Header.SizeOfOptionalHeader =
      PEHeaderSize + sizeof(object::data_directory) *
                         CP.Obj.OptionalHeader->Header.NumberOfRvaAndSize;
  return true;
}
 
static yaml::BinaryRef
toDebugS(ArrayRef<CodeViewYAML::YAMLDebugSubsection> Subsections,
         const codeview::StringsAndChecksums &SC, BumpPtrAllocator &Allocator) {
  using namespace codeview;
  ExitOnError Err("Error occurred writing .debug$S section");
  auto CVSS =
      Err(CodeViewYAML::toCodeViewSubsectionList(Allocator, Subsections, SC));
 
  std::vector<DebugSubsectionRecordBuilder> Builders;
  uint32_t Size = sizeof(uint32_t);
  for (auto &SS : CVSS) {
    DebugSubsectionRecordBuilder B(SS);
    Size += B.calculateSerializedLength();
    Builders.push_back(std::move(B));
  }
  uint8_t *Buffer = Allocator.Allocate<uint8_t>(Size);
  MutableArrayRef<uint8_t> Output(Buffer, Size);
  BinaryStreamWriter Writer(Output, support::little);
 
  Err(Writer.writeInteger<uint32_t>(COFF::DEBUG_SECTION_MAGIC));
  for (const auto &B : Builders) {
    Err(B.commit(Writer, CodeViewContainer::ObjectFile));
  }
  return {Output};
}
 
// Take a CP and assign addresses and sizes to everything. Returns false if the
// layout is not valid to do.
static bool layoutCOFF(COFFParser &CP) {
  // The section table starts immediately after the header, including the
  // optional header.
  CP.SectionTableStart =
      CP.getHeaderSize() + CP.Obj.Header.SizeOfOptionalHeader;
  if (CP.isPE())
    CP.SectionTableStart += DOSStubSize + sizeof(COFF::PEMagic);
  CP.SectionTableSize = COFF::SectionSize * CP.Obj.Sections.size();
 
  uint32_t CurrentSectionDataOffset =
      CP.SectionTableStart + CP.SectionTableSize;
 
  for (COFFYAML::Section &S : CP.Obj.Sections) {
    // We support specifying exactly one of SectionData or Subsections.  So if
    // there is already some SectionData, then we don't need to do any of this.
    if (S.Name == ".debug$S" && S.SectionData.binary_size() == 0) {
      CodeViewYAML::initializeStringsAndChecksums(S.DebugS,
                                                  CP.StringsAndChecksums);
      if (CP.StringsAndChecksums.hasChecksums() &&
          CP.StringsAndChecksums.hasStrings())
        break;
    }
  }
 
  // Assign each section data address consecutively.
  for (COFFYAML::Section &S : CP.Obj.Sections) {
    if (S.Name == ".debug$S") {
      if (S.SectionData.binary_size() == 0) {
        assert(CP.StringsAndChecksums.hasStrings() &&
               "Object file does not have debug string table!");
 
        S.SectionData =
            toDebugS(S.DebugS, CP.StringsAndChecksums, CP.Allocator);
      }
    } else if (S.Name == ".debug$T") {
      if (S.SectionData.binary_size() == 0)
        S.SectionData = CodeViewYAML::toDebugT(S.DebugT, CP.Allocator, S.Name);
    } else if (S.Name == ".debug$P") {
      if (S.SectionData.binary_size() == 0)
        S.SectionData = CodeViewYAML::toDebugT(S.DebugP, CP.Allocator, S.Name);
    } else if (S.Name == ".debug$H") {
      if (S.DebugH.hasValue() && S.SectionData.binary_size() == 0)
        S.SectionData = CodeViewYAML::toDebugH(*S.DebugH, CP.Allocator);
    }
 
    if (S.SectionData.binary_size() > 0) {
      CurrentSectionDataOffset = alignTo(CurrentSectionDataOffset,
                                         CP.isPE() ? CP.getFileAlignment() : 4);
      S.Header.SizeOfRawData = S.SectionData.binary_size();
      if (CP.isPE())
        S.Header.SizeOfRawData =
            alignTo(S.Header.SizeOfRawData, CP.getFileAlignment());
      S.Header.PointerToRawData = CurrentSectionDataOffset;
      CurrentSectionDataOffset += S.Header.SizeOfRawData;
      if (!S.Relocations.empty()) {
        S.Header.PointerToRelocations = CurrentSectionDataOffset;
        if (S.Header.Characteristics & COFF::IMAGE_SCN_LNK_NRELOC_OVFL) {
          S.Header.NumberOfRelocations = 0xffff;
          CurrentSectionDataOffset += COFF::RelocationSize;
        } else
          S.Header.NumberOfRelocations = S.Relocations.size();
        CurrentSectionDataOffset += S.Relocations.size() * COFF::RelocationSize;
      }
    } else {
      // Leave SizeOfRawData unaltered. For .bss sections in object files, it
      // carries the section size.
      S.Header.PointerToRawData = 0;
    }
  }
 
  uint32_t SymbolTableStart = CurrentSectionDataOffset;
 
  // Calculate number of symbols.
  uint32_t NumberOfSymbols = 0;
  for (std::vector<COFFYAML::Symbol>::iterator i = CP.Obj.Symbols.begin(),
                                               e = CP.Obj.Symbols.end();
       i != e; ++i) {
    uint32_t NumberOfAuxSymbols = 0;
    if (i->FunctionDefinition)
      NumberOfAuxSymbols += 1;
    if (i->bfAndefSymbol)
      NumberOfAuxSymbols += 1;
    if (i->WeakExternal)
      NumberOfAuxSymbols += 1;
    if (!i->File.empty())
      NumberOfAuxSymbols +=
          (i->File.size() + CP.getSymbolSize() - 1) / CP.getSymbolSize();
    if (i->SectionDefinition)
      NumberOfAuxSymbols += 1;
    if (i->CLRToken)
      NumberOfAuxSymbols += 1;
    i->Header.NumberOfAuxSymbols = NumberOfAuxSymbols;
    NumberOfSymbols += 1 + NumberOfAuxSymbols;
  }
 
  // Store all the allocated start addresses in the header.
  CP.Obj.Header.NumberOfSections = CP.Obj.Sections.size();
  CP.Obj.Header.NumberOfSymbols = NumberOfSymbols;
  if (NumberOfSymbols > 0 || CP.StringTable.size() > 4)
    CP.Obj.Header.PointerToSymbolTable = SymbolTableStart;
  else
    CP.Obj.Header.PointerToSymbolTable = 0;
 
  *reinterpret_cast<support::ulittle32_t *>(&CP.StringTable[0]) =
      CP.StringTable.size();
 
  return true;
}
 
template <typename value_type> struct binary_le_impl {
  value_type Value;
  binary_le_impl(value_type V) : Value(V) {}
};
 
template <typename value_type>
raw_ostream &operator<<(raw_ostream &OS,
                        const binary_le_impl<value_type> &BLE) {
  char Buffer[sizeof(BLE.Value)];
  support::endian::write<value_type, support::little, support::unaligned>(
      Buffer, BLE.Value);
  OS.write(Buffer, sizeof(BLE.Value));
  return OS;
}
 
template <typename value_type>
binary_le_impl<value_type> binary_le(value_type V) {
  return binary_le_impl<value_type>(V);
}
 
template <size_t NumBytes> struct zeros_impl {};
 
template <size_t NumBytes>
raw_ostream &operator<<(raw_ostream &OS, const zeros_impl<NumBytes> &) {
  char Buffer[NumBytes];
  memset(Buffer, 0, sizeof(Buffer));
  OS.write(Buffer, sizeof(Buffer));
  return OS;
}
 
template <typename T> zeros_impl<sizeof(T)> zeros(const T &) {
  return zeros_impl<sizeof(T)>();
}
 
template <typename T>
static uint32_t initializeOptionalHeader(COFFParser &CP, uint16_t Magic,
                                         T Header) {
  memset(Header, 0, sizeof(*Header));
  Header->Magic = Magic;
  Header->SectionAlignment = CP.Obj.OptionalHeader->Header.SectionAlignment;
  Header->FileAlignment = CP.Obj.OptionalHeader->Header.FileAlignment;
  uint32_t SizeOfCode = 0, SizeOfInitializedData = 0,
           SizeOfUninitializedData = 0;
  uint32_t SizeOfHeaders = alignTo(CP.SectionTableStart + CP.SectionTableSize,
                                   Header->FileAlignment);
  uint32_t SizeOfImage = alignTo(SizeOfHeaders, Header->SectionAlignment);
  uint32_t BaseOfData = 0;
  for (const COFFYAML::Section &S : CP.Obj.Sections) {
    if (S.Header.Characteristics & COFF::IMAGE_SCN_CNT_CODE)
      SizeOfCode += S.Header.SizeOfRawData;
    if (S.Header.Characteristics & COFF::IMAGE_SCN_CNT_INITIALIZED_DATA)
      SizeOfInitializedData += S.Header.SizeOfRawData;
    if (S.Header.Characteristics & COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA)
      SizeOfUninitializedData += S.Header.SizeOfRawData;
    if (S.Name.equals(".text"))
      Header->BaseOfCode = S.Header.VirtualAddress; // RVA
    else if (S.Name.equals(".data"))
      BaseOfData = S.Header.VirtualAddress; // RVA
    if (S.Header.VirtualAddress)
      SizeOfImage += alignTo(S.Header.VirtualSize, Header->SectionAlignment);
  }
  Header->SizeOfCode = SizeOfCode;
  Header->SizeOfInitializedData = SizeOfInitializedData;
  Header->SizeOfUninitializedData = SizeOfUninitializedData;
  Header->AddressOfEntryPoint =
      CP.Obj.OptionalHeader->Header.AddressOfEntryPoint; // RVA
  Header->ImageBase = CP.Obj.OptionalHeader->Header.ImageBase;
  Header->MajorOperatingSystemVersion =
      CP.Obj.OptionalHeader->Header.MajorOperatingSystemVersion;
  Header->MinorOperatingSystemVersion =
      CP.Obj.OptionalHeader->Header.MinorOperatingSystemVersion;
  Header->MajorImageVersion = CP.Obj.OptionalHeader->Header.MajorImageVersion;
  Header->MinorImageVersion = CP.Obj.OptionalHeader->Header.MinorImageVersion;
  Header->MajorSubsystemVersion =
      CP.Obj.OptionalHeader->Header.MajorSubsystemVersion;
  Header->MinorSubsystemVersion =
      CP.Obj.OptionalHeader->Header.MinorSubsystemVersion;
  Header->SizeOfImage = SizeOfImage;
  Header->SizeOfHeaders = SizeOfHeaders;
  Header->Subsystem = CP.Obj.OptionalHeader->Header.Subsystem;
  Header->DLLCharacteristics = CP.Obj.OptionalHeader->Header.DLLCharacteristics;
  Header->SizeOfStackReserve = CP.Obj.OptionalHeader->Header.SizeOfStackReserve;
  Header->SizeOfStackCommit = CP.Obj.OptionalHeader->Header.SizeOfStackCommit;
  Header->SizeOfHeapReserve = CP.Obj.OptionalHeader->Header.SizeOfHeapReserve;
  Header->SizeOfHeapCommit = CP.Obj.OptionalHeader->Header.SizeOfHeapCommit;
  Header->NumberOfRvaAndSize = CP.Obj.OptionalHeader->Header.NumberOfRvaAndSize;
  return BaseOfData;
}
 
static bool writeCOFF(COFFParser &CP, raw_ostream &OS) {
  if (CP.isPE()) {
    // PE files start with a DOS stub.
    object::dos_header DH;
    memset(&DH, 0, sizeof(DH));
 
    // DOS EXEs start with "MZ" magic.
    DH.Magic[0] = 'M';
    DH.Magic[1] = 'Z';
    // Initializing the AddressOfRelocationTable is strictly optional but
    // mollifies certain tools which expect it to have a value greater than
    // 0x40.
    DH.AddressOfRelocationTable = sizeof(DH);
    // This is the address of the PE signature.
    DH.AddressOfNewExeHeader = DOSStubSize;
 
    // Write out our DOS stub.
    OS.write(reinterpret_cast<char *>(&DH), sizeof(DH));
    // Write padding until we reach the position of where our PE signature
    // should live.
    OS.write_zeros(DOSStubSize - sizeof(DH));
    // Write out the PE signature.
    OS.write(COFF::PEMagic, sizeof(COFF::PEMagic));
  }
  if (CP.useBigObj()) {
    OS << binary_le(static_cast<uint16_t>(COFF::IMAGE_FILE_MACHINE_UNKNOWN))
       << binary_le(static_cast<uint16_t>(0xffff))
       << binary_le(
              static_cast<uint16_t>(COFF::BigObjHeader::MinBigObjectVersion))
       << binary_le(CP.Obj.Header.Machine)
       << binary_le(CP.Obj.Header.TimeDateStamp);
    OS.write(COFF::BigObjMagic, sizeof(COFF::BigObjMagic));
    OS << zeros(uint32_t(0)) << zeros(uint32_t(0)) << zeros(uint32_t(0))
       << zeros(uint32_t(0)) << binary_le(CP.Obj.Header.NumberOfSections)
       << binary_le(CP.Obj.Header.PointerToSymbolTable)
       << binary_le(CP.Obj.Header.NumberOfSymbols);
  } else {
    OS << binary_le(CP.Obj.Header.Machine)
       << binary_le(static_cast<int16_t>(CP.Obj.Header.NumberOfSections))
       << binary_le(CP.Obj.Header.TimeDateStamp)
       << binary_le(CP.Obj.Header.PointerToSymbolTable)
       << binary_le(CP.Obj.Header.NumberOfSymbols)
       << binary_le(CP.Obj.Header.SizeOfOptionalHeader)
       << binary_le(CP.Obj.Header.Characteristics);
  }
  if (CP.isPE()) {
    if (CP.is64Bit()) {
      object::pe32plus_header PEH;
      initializeOptionalHeader(CP, COFF::PE32Header::PE32_PLUS, &PEH);
      OS.write(reinterpret_cast<char *>(&PEH), sizeof(PEH));
    } else {
      object::pe32_header PEH;
      uint32_t BaseOfData =
          initializeOptionalHeader(CP, COFF::PE32Header::PE32, &PEH);
      PEH.BaseOfData = BaseOfData;
      OS.write(reinterpret_cast<char *>(&PEH), sizeof(PEH));
    }
    for (uint32_t I = 0; I < CP.Obj.OptionalHeader->Header.NumberOfRvaAndSize;
         ++I) {
      const Optional<COFF::DataDirectory> *DataDirectories =
          CP.Obj.OptionalHeader->DataDirectories;
      uint32_t NumDataDir = sizeof(CP.Obj.OptionalHeader->DataDirectories) /
                            sizeof(Optional<COFF::DataDirectory>);
      if (I >= NumDataDir || !DataDirectories[I].hasValue()) {
        OS << zeros(uint32_t(0));
        OS << zeros(uint32_t(0));
      } else {
        OS << binary_le(DataDirectories[I]->RelativeVirtualAddress);
        OS << binary_le(DataDirectories[I]->Size);
      }
    }
  }
 
  assert(OS.tell() == CP.SectionTableStart);
  // Output section table.
  for (const COFFYAML::Section &S : CP.Obj.Sections) {
    OS.write(S.Header.Name, COFF::NameSize);
    OS << binary_le(S.Header.VirtualSize)
       << binary_le(S.Header.VirtualAddress)
       << binary_le(S.Header.SizeOfRawData)
       << binary_le(S.Header.PointerToRawData)
       << binary_le(S.Header.PointerToRelocations)
       << binary_le(S.Header.PointerToLineNumbers)
       << binary_le(S.Header.NumberOfRelocations)
       << binary_le(S.Header.NumberOfLineNumbers)
       << binary_le(S.Header.Characteristics);
  }
  assert(OS.tell() == CP.SectionTableStart + CP.SectionTableSize);
 
  unsigned CurSymbol = 0;
  StringMap<unsigned> SymbolTableIndexMap;
  for (const COFFYAML::Symbol &Sym : CP.Obj.Symbols) {
    SymbolTableIndexMap[Sym.Name] = CurSymbol;
    CurSymbol += 1 + Sym.Header.NumberOfAuxSymbols;
  }
 
  // Output section data.
  for (const COFFYAML::Section &S : CP.Obj.Sections) {
    if (S.Header.SizeOfRawData == 0 || S.Header.PointerToRawData == 0)
      continue;
    assert(S.Header.PointerToRawData >= OS.tell());
    OS.write_zeros(S.Header.PointerToRawData - OS.tell());
    S.SectionData.writeAsBinary(OS);
    assert(S.Header.SizeOfRawData >= S.SectionData.binary_size());
    OS.write_zeros(S.Header.SizeOfRawData - S.SectionData.binary_size());
    if (S.Header.Characteristics & COFF::IMAGE_SCN_LNK_NRELOC_OVFL)
      OS << binary_le<uint32_t>(/*VirtualAddress=*/ S.Relocations.size() + 1)
         << binary_le<uint32_t>(/*SymbolTableIndex=*/ 0)
         << binary_le<uint16_t>(/*Type=*/ 0);
    for (const COFFYAML::Relocation &R : S.Relocations) {
      uint32_t SymbolTableIndex;
      if (R.SymbolTableIndex) {
        if (!R.SymbolName.empty())
          WithColor::error()
              << "Both SymbolName and SymbolTableIndex specified\n";
        SymbolTableIndex = *R.SymbolTableIndex;
      } else {
        SymbolTableIndex = SymbolTableIndexMap[R.SymbolName];
      }
      OS << binary_le(R.VirtualAddress) << binary_le(SymbolTableIndex)
         << binary_le(R.Type);
    }
  }
 
  // Output symbol table.
 
  for (std::vector<COFFYAML::Symbol>::const_iterator i = CP.Obj.Symbols.begin(),
                                                     e = CP.Obj.Symbols.end();
       i != e; ++i) {
    OS.write(i->Header.Name, COFF::NameSize);
    OS << binary_le(i->Header.Value);
    if (CP.useBigObj())
      OS << binary_le(i->Header.SectionNumber);
    else
      OS << binary_le(static_cast<int16_t>(i->Header.SectionNumber));
    OS << binary_le(i->Header.Type) << binary_le(i->Header.StorageClass)
       << binary_le(i->Header.NumberOfAuxSymbols);
 
    if (i->FunctionDefinition) {
      OS << binary_le(i->FunctionDefinition->TagIndex)
         << binary_le(i->FunctionDefinition->TotalSize)
         << binary_le(i->FunctionDefinition->PointerToLinenumber)
         << binary_le(i->FunctionDefinition->PointerToNextFunction)
         << zeros(i->FunctionDefinition->unused);
      OS.write_zeros(CP.getSymbolSize() - COFF::Symbol16Size);
    }
    if (i->bfAndefSymbol) {
      OS << zeros(i->bfAndefSymbol->unused1)
         << binary_le(i->bfAndefSymbol->Linenumber)
         << zeros(i->bfAndefSymbol->unused2)
         << binary_le(i->bfAndefSymbol->PointerToNextFunction)
         << zeros(i->bfAndefSymbol->unused3);
      OS.write_zeros(CP.getSymbolSize() - COFF::Symbol16Size);
    }
    if (i->WeakExternal) {
      OS << binary_le(i->WeakExternal->TagIndex)
         << binary_le(i->WeakExternal->Characteristics)
         << zeros(i->WeakExternal->unused);
      OS.write_zeros(CP.getSymbolSize() - COFF::Symbol16Size);
    }
    if (!i->File.empty()) {
      unsigned SymbolSize = CP.getSymbolSize();
      uint32_t NumberOfAuxRecords =
          (i->File.size() + SymbolSize - 1) / SymbolSize;
      uint32_t NumberOfAuxBytes = NumberOfAuxRecords * SymbolSize;
      uint32_t NumZeros = NumberOfAuxBytes - i->File.size();
      OS.write(i->File.data(), i->File.size());
      OS.write_zeros(NumZeros);
    }
    if (i->SectionDefinition) {
      OS << binary_le(i->SectionDefinition->Length)
         << binary_le(i->SectionDefinition->NumberOfRelocations)
         << binary_le(i->SectionDefinition->NumberOfLinenumbers)
         << binary_le(i->SectionDefinition->CheckSum)
         << binary_le(static_cast<int16_t>(i->SectionDefinition->Number))
         << binary_le(i->SectionDefinition->Selection)
         << zeros(i->SectionDefinition->unused)
         << binary_le(static_cast<int16_t>(i->SectionDefinition->Number >> 16));
      OS.write_zeros(CP.getSymbolSize() - COFF::Symbol16Size);
    }
    if (i->CLRToken) {
      OS << binary_le(i->CLRToken->AuxType) << zeros(i->CLRToken->unused1)
         << binary_le(i->CLRToken->SymbolTableIndex)
         << zeros(i->CLRToken->unused2);
      OS.write_zeros(CP.getSymbolSize() - COFF::Symbol16Size);
    }
  }
 
  // Output string table.
  if (CP.Obj.Header.PointerToSymbolTable)
    OS.write(&CP.StringTable[0], CP.StringTable.size());
  return true;
}
 
namespace llvm {
namespace yaml {
 
bool yaml2coff(llvm::COFFYAML::Object &Doc, raw_ostream &Out,
               ErrorHandler ErrHandler) {
  COFFParser CP(Doc, ErrHandler);
  if (!CP.parse()) {
    ErrHandler("failed to parse YAML file");
    return false;
  }
 
  if (!layoutOptionalHeader(CP)) {
    ErrHandler("failed to layout optional header for COFF file");
    return false;
  }
 
  if (!layoutCOFF(CP)) {
    ErrHandler("failed to layout COFF file");
    return false;
  }
  if (!writeCOFF(CP, Out)) {
    ErrHandler("failed to write COFF file");
    return false;
  }
  return true;
}
 
} // namespace yaml
} // namespace llvm