示例#1
0
void MachObjectWriter::WriteObject(MCAssembler &Asm,
                                   const MCAsmLayout &Layout) {
  unsigned NumSections = Asm.size();

  // The section data starts after the header, the segment load command (and
  // section headers) and the symbol table.
  unsigned NumLoadCommands = 1;
  uint64_t LoadCommandsSize = is64Bit() ?
    macho::SegmentLoadCommand64Size + NumSections * macho::Section64Size :
    macho::SegmentLoadCommand32Size + NumSections * macho::Section32Size;

  // Add the data-in-code load command size, if used.
  unsigned NumDataRegions = Asm.getDataRegions().size();
  if (NumDataRegions) {
    ++NumLoadCommands;
    LoadCommandsSize += macho::LinkeditLoadCommandSize;
  }

  // Add the symbol table load command sizes, if used.
  unsigned NumSymbols = LocalSymbolData.size() + ExternalSymbolData.size() +
    UndefinedSymbolData.size();
  if (NumSymbols) {
    NumLoadCommands += 2;
    LoadCommandsSize += (macho::SymtabLoadCommandSize +
                         macho::DysymtabLoadCommandSize);
  }

  // Add the linker option load commands sizes.
  const std::vector<std::vector<std::string> > &LinkerOptions =
    Asm.getLinkerOptions();
  for (unsigned i = 0, e = LinkerOptions.size(); i != e; ++i) {
    ++NumLoadCommands;
    LoadCommandsSize += ComputeLinkerOptionsLoadCommandSize(LinkerOptions[i],
                                                            is64Bit());
  }
  
  // Compute the total size of the section data, as well as its file size and vm
  // size.
  uint64_t SectionDataStart = (is64Bit() ? macho::Header64Size :
                               macho::Header32Size) + LoadCommandsSize;
  uint64_t SectionDataSize = 0;
  uint64_t SectionDataFileSize = 0;
  uint64_t VMSize = 0;
  for (MCAssembler::const_iterator it = Asm.begin(),
         ie = Asm.end(); it != ie; ++it) {
    const MCSectionData &SD = *it;
    uint64_t Address = getSectionAddress(&SD);
    uint64_t Size = Layout.getSectionAddressSize(&SD);
    uint64_t FileSize = Layout.getSectionFileSize(&SD);
    FileSize += getPaddingSize(&SD, Layout);

    VMSize = std::max(VMSize, Address + Size);

    if (SD.getSection().isVirtualSection())
      continue;

    SectionDataSize = std::max(SectionDataSize, Address + Size);
    SectionDataFileSize = std::max(SectionDataFileSize, Address + FileSize);
  }

  // The section data is padded to 4 bytes.
  //
  // FIXME: Is this machine dependent?
  unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
  SectionDataFileSize += SectionDataPadding;

  // Write the prolog, starting with the header and load command...
  WriteHeader(NumLoadCommands, LoadCommandsSize,
              Asm.getSubsectionsViaSymbols());
  WriteSegmentLoadCommand(NumSections, VMSize,
                          SectionDataStart, SectionDataSize);

  // ... and then the section headers.
  uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
  for (MCAssembler::const_iterator it = Asm.begin(),
         ie = Asm.end(); it != ie; ++it) {
    std::vector<macho::RelocationEntry> &Relocs = Relocations[it];
    unsigned NumRelocs = Relocs.size();
    uint64_t SectionStart = SectionDataStart + getSectionAddress(it);
    WriteSection(Asm, Layout, *it, SectionStart, RelocTableEnd, NumRelocs);
    RelocTableEnd += NumRelocs * macho::RelocationInfoSize;
  }

  // Write the data-in-code load command, if used.
  uint64_t DataInCodeTableEnd = RelocTableEnd + NumDataRegions * 8;
  if (NumDataRegions) {
    uint64_t DataRegionsOffset = RelocTableEnd;
    uint64_t DataRegionsSize = NumDataRegions * 8;
    WriteLinkeditLoadCommand(macho::LCT_DataInCode, DataRegionsOffset,
                             DataRegionsSize);
  }

  // Write the symbol table load command, if used.
  if (NumSymbols) {
    unsigned FirstLocalSymbol = 0;
    unsigned NumLocalSymbols = LocalSymbolData.size();
    unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
    unsigned NumExternalSymbols = ExternalSymbolData.size();
    unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
    unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
    unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
    unsigned NumSymTabSymbols =
      NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
    uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
    uint64_t IndirectSymbolOffset = 0;

    // If used, the indirect symbols are written after the section data.
    if (NumIndirectSymbols)
      IndirectSymbolOffset = DataInCodeTableEnd;

    // The symbol table is written after the indirect symbol data.
    uint64_t SymbolTableOffset = DataInCodeTableEnd + IndirectSymbolSize;

    // The string table is written after symbol table.
    uint64_t StringTableOffset =
      SymbolTableOffset + NumSymTabSymbols * (is64Bit() ? macho::Nlist64Size :
                                              macho::Nlist32Size);
    WriteSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
                           StringTableOffset, StringTable.size());

    WriteDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
                             FirstExternalSymbol, NumExternalSymbols,
                             FirstUndefinedSymbol, NumUndefinedSymbols,
                             IndirectSymbolOffset, NumIndirectSymbols);
  }

  // Write the linker options load commands.
  for (unsigned i = 0, e = LinkerOptions.size(); i != e; ++i) {
    WriteLinkerOptionsLoadCommand(LinkerOptions[i]);
  }

  // Write the actual section data.
  for (MCAssembler::const_iterator it = Asm.begin(),
         ie = Asm.end(); it != ie; ++it) {
    Asm.writeSectionData(it, Layout);

    uint64_t Pad = getPaddingSize(it, Layout);
    for (unsigned int i = 0; i < Pad; ++i)
      Write8(0);
  }

  // Write the extra padding.
  WriteZeros(SectionDataPadding);

  // Write the relocation entries.
  for (MCAssembler::const_iterator it = Asm.begin(),
         ie = Asm.end(); it != ie; ++it) {
    // Write the section relocation entries, in reverse order to match 'as'
    // (approximately, the exact algorithm is more complicated than this).
    std::vector<macho::RelocationEntry> &Relocs = Relocations[it];
    for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
      Write32(Relocs[e - i - 1].Word0);
      Write32(Relocs[e - i - 1].Word1);
    }
  }

  // Write out the data-in-code region payload, if there is one.
  for (MCAssembler::const_data_region_iterator
         it = Asm.data_region_begin(), ie = Asm.data_region_end();
         it != ie; ++it) {
    const DataRegionData *Data = &(*it);
    uint64_t Start =
      getSymbolAddress(&Layout.getAssembler().getSymbolData(*Data->Start),
                       Layout);
    uint64_t End =
      getSymbolAddress(&Layout.getAssembler().getSymbolData(*Data->End),
                       Layout);
    DEBUG(dbgs() << "data in code region-- kind: " << Data->Kind
                 << "  start: " << Start << "(" << Data->Start->getName() << ")"
                 << "  end: " << End << "(" << Data->End->getName() << ")"
                 << "  size: " << End - Start
                 << "\n");
    Write32(Start);
    Write16(End - Start);
    Write16(Data->Kind);
  }

  // Write the symbol table data, if used.
  if (NumSymbols) {
    // Write the indirect symbol entries.
    for (MCAssembler::const_indirect_symbol_iterator
           it = Asm.indirect_symbol_begin(),
           ie = Asm.indirect_symbol_end(); it != ie; ++it) {
      // Indirect symbols in the non lazy symbol pointer section have some
      // special handling.
      const MCSectionMachO &Section =
        static_cast<const MCSectionMachO&>(it->SectionData->getSection());
      if (Section.getType() == MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS) {
        // If this symbol is defined and internal, mark it as such.
        if (it->Symbol->isDefined() &&
            !Asm.getSymbolData(*it->Symbol).isExternal()) {
          uint32_t Flags = macho::ISF_Local;
          if (it->Symbol->isAbsolute())
            Flags |= macho::ISF_Absolute;
          Write32(Flags);
          continue;
        }
      }

      Write32(Asm.getSymbolData(*it->Symbol).getIndex());
    }

    // FIXME: Check that offsets match computed ones.

    // Write the symbol table entries.
    for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
      WriteNlist(LocalSymbolData[i], Layout);
    for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
      WriteNlist(ExternalSymbolData[i], Layout);
    for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
      WriteNlist(UndefinedSymbolData[i], Layout);

    // Write the string table.
    OS << StringTable.str();
  }
}
示例#2
0
void MachObjectWriter::writeObject(MCAssembler &Asm,
                                   const MCAsmLayout &Layout) {
  // Compute symbol table information and bind symbol indices.
  computeSymbolTable(Asm, LocalSymbolData, ExternalSymbolData,
                     UndefinedSymbolData);

  unsigned NumSections = Asm.size();
  const MCAssembler::VersionMinInfoType &VersionInfo =
    Layout.getAssembler().getVersionMinInfo();

  // The section data starts after the header, the segment load command (and
  // section headers) and the symbol table.
  unsigned NumLoadCommands = 1;
  uint64_t LoadCommandsSize = is64Bit() ?
    sizeof(MachO::segment_command_64) + NumSections * sizeof(MachO::section_64):
    sizeof(MachO::segment_command) + NumSections * sizeof(MachO::section);

  // Add the deployment target version info load command size, if used.
  if (VersionInfo.Major != 0) {
    ++NumLoadCommands;
    LoadCommandsSize += sizeof(MachO::version_min_command);
  }

  // Add the data-in-code load command size, if used.
  unsigned NumDataRegions = Asm.getDataRegions().size();
  if (NumDataRegions) {
    ++NumLoadCommands;
    LoadCommandsSize += sizeof(MachO::linkedit_data_command);
  }

  // Add the loh load command size, if used.
  uint64_t LOHRawSize = Asm.getLOHContainer().getEmitSize(*this, Layout);
  uint64_t LOHSize = alignTo(LOHRawSize, is64Bit() ? 8 : 4);
  if (LOHSize) {
    ++NumLoadCommands;
    LoadCommandsSize += sizeof(MachO::linkedit_data_command);
  }

  // Add the symbol table load command sizes, if used.
  unsigned NumSymbols = LocalSymbolData.size() + ExternalSymbolData.size() +
    UndefinedSymbolData.size();
  if (NumSymbols) {
    NumLoadCommands += 2;
    LoadCommandsSize += (sizeof(MachO::symtab_command) +
                         sizeof(MachO::dysymtab_command));
  }

  // Add the linker option load commands sizes.
  for (const auto &Option : Asm.getLinkerOptions()) {
    ++NumLoadCommands;
    LoadCommandsSize += ComputeLinkerOptionsLoadCommandSize(Option, is64Bit());
  }

  // Compute the total size of the section data, as well as its file size and vm
  // size.
  uint64_t SectionDataStart = (is64Bit() ? sizeof(MachO::mach_header_64) :
                               sizeof(MachO::mach_header)) + LoadCommandsSize;
  uint64_t SectionDataSize = 0;
  uint64_t SectionDataFileSize = 0;
  uint64_t VMSize = 0;
  for (const MCSection &Sec : Asm) {
    uint64_t Address = getSectionAddress(&Sec);
    uint64_t Size = Layout.getSectionAddressSize(&Sec);
    uint64_t FileSize = Layout.getSectionFileSize(&Sec);
    FileSize += getPaddingSize(&Sec, Layout);

    VMSize = std::max(VMSize, Address + Size);

    if (Sec.isVirtualSection())
      continue;

    SectionDataSize = std::max(SectionDataSize, Address + Size);
    SectionDataFileSize = std::max(SectionDataFileSize, Address + FileSize);
  }

  // The section data is padded to 4 bytes.
  //
  // FIXME: Is this machine dependent?
  unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
  SectionDataFileSize += SectionDataPadding;

  // Write the prolog, starting with the header and load command...
  writeHeader(MachO::MH_OBJECT, NumLoadCommands, LoadCommandsSize,
              Asm.getSubsectionsViaSymbols());
  uint32_t Prot =
      MachO::VM_PROT_READ | MachO::VM_PROT_WRITE | MachO::VM_PROT_EXECUTE;
  writeSegmentLoadCommand("", NumSections, 0, VMSize, SectionDataStart,
                          SectionDataSize, Prot, Prot);

  // ... and then the section headers.
  uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
  for (const MCSection &Section : Asm) {
    const auto &Sec = cast<MCSectionMachO>(Section);
    std::vector<RelAndSymbol> &Relocs = Relocations[&Sec];
    unsigned NumRelocs = Relocs.size();
    uint64_t SectionStart = SectionDataStart + getSectionAddress(&Sec);
    unsigned Flags = Sec.getTypeAndAttributes();
    if (Sec.hasInstructions())
      Flags |= MachO::S_ATTR_SOME_INSTRUCTIONS;
    writeSection(Layout, Sec, getSectionAddress(&Sec), SectionStart, Flags,
                 RelocTableEnd, NumRelocs);
    RelocTableEnd += NumRelocs * sizeof(MachO::any_relocation_info);
  }

  // Write out the deployment target information, if it's available.
  if (VersionInfo.Major != 0) {
    assert(VersionInfo.Update < 256 && "unencodable update target version");
    assert(VersionInfo.Minor < 256 && "unencodable minor target version");
    assert(VersionInfo.Major < 65536 && "unencodable major target version");
    uint32_t EncodedVersion = VersionInfo.Update | (VersionInfo.Minor << 8) |
      (VersionInfo.Major << 16);
    MachO::LoadCommandType LCType;
    switch (VersionInfo.Kind) {
    case MCVM_OSXVersionMin:
      LCType = MachO::LC_VERSION_MIN_MACOSX;
      break;
    case MCVM_IOSVersionMin:
      LCType = MachO::LC_VERSION_MIN_IPHONEOS;
      break;
    case MCVM_TvOSVersionMin:
      LCType = MachO::LC_VERSION_MIN_TVOS;
      break;
    case MCVM_WatchOSVersionMin:
      LCType = MachO::LC_VERSION_MIN_WATCHOS;
      break;
    }
    write32(LCType);
    write32(sizeof(MachO::version_min_command));
    write32(EncodedVersion);
    write32(0);         // reserved.
  }

  // Write the data-in-code load command, if used.
  uint64_t DataInCodeTableEnd = RelocTableEnd + NumDataRegions * 8;
  if (NumDataRegions) {
    uint64_t DataRegionsOffset = RelocTableEnd;
    uint64_t DataRegionsSize = NumDataRegions * 8;
    writeLinkeditLoadCommand(MachO::LC_DATA_IN_CODE, DataRegionsOffset,
                             DataRegionsSize);
  }

  // Write the loh load command, if used.
  uint64_t LOHTableEnd = DataInCodeTableEnd + LOHSize;
  if (LOHSize)
    writeLinkeditLoadCommand(MachO::LC_LINKER_OPTIMIZATION_HINT,
                             DataInCodeTableEnd, LOHSize);

  // Write the symbol table load command, if used.
  if (NumSymbols) {
    unsigned FirstLocalSymbol = 0;
    unsigned NumLocalSymbols = LocalSymbolData.size();
    unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
    unsigned NumExternalSymbols = ExternalSymbolData.size();
    unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
    unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
    unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
    unsigned NumSymTabSymbols =
      NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
    uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
    uint64_t IndirectSymbolOffset = 0;

    // If used, the indirect symbols are written after the section data.
    if (NumIndirectSymbols)
      IndirectSymbolOffset = LOHTableEnd;

    // The symbol table is written after the indirect symbol data.
    uint64_t SymbolTableOffset = LOHTableEnd + IndirectSymbolSize;

    // The string table is written after symbol table.
    uint64_t StringTableOffset =
      SymbolTableOffset + NumSymTabSymbols * (is64Bit() ?
                                              sizeof(MachO::nlist_64) :
                                              sizeof(MachO::nlist));
    writeSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
                           StringTableOffset, StringTable.data().size());

    writeDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
                             FirstExternalSymbol, NumExternalSymbols,
                             FirstUndefinedSymbol, NumUndefinedSymbols,
                             IndirectSymbolOffset, NumIndirectSymbols);
  }

  // Write the linker options load commands.
  for (const auto &Option : Asm.getLinkerOptions())
    writeLinkerOptionsLoadCommand(Option);

  // Write the actual section data.
  for (const MCSection &Sec : Asm) {
    Asm.writeSectionData(&Sec, Layout);

    uint64_t Pad = getPaddingSize(&Sec, Layout);
    WriteZeros(Pad);
  }

  // Write the extra padding.
  WriteZeros(SectionDataPadding);

  // Write the relocation entries.
  for (const MCSection &Sec : Asm) {
    // Write the section relocation entries, in reverse order to match 'as'
    // (approximately, the exact algorithm is more complicated than this).
    std::vector<RelAndSymbol> &Relocs = Relocations[&Sec];
    for (const RelAndSymbol &Rel : make_range(Relocs.rbegin(), Relocs.rend())) {
      write32(Rel.MRE.r_word0);
      write32(Rel.MRE.r_word1);
    }
  }

  // Write out the data-in-code region payload, if there is one.
  for (MCAssembler::const_data_region_iterator
         it = Asm.data_region_begin(), ie = Asm.data_region_end();
         it != ie; ++it) {
    const DataRegionData *Data = &(*it);
    uint64_t Start = getSymbolAddress(*Data->Start, Layout);
    uint64_t End = getSymbolAddress(*Data->End, Layout);
    DEBUG(dbgs() << "data in code region-- kind: " << Data->Kind
                 << "  start: " << Start << "(" << Data->Start->getName() << ")"
                 << "  end: " << End << "(" << Data->End->getName() << ")"
                 << "  size: " << End - Start
                 << "\n");
    write32(Start);
    write16(End - Start);
    write16(Data->Kind);
  }

  // Write out the loh commands, if there is one.
  if (LOHSize) {
#ifndef NDEBUG
    unsigned Start = getStream().tell();
#endif
    Asm.getLOHContainer().emit(*this, Layout);
    // Pad to a multiple of the pointer size.
    writeBytes("", OffsetToAlignment(LOHRawSize, is64Bit() ? 8 : 4));
    assert(getStream().tell() - Start == LOHSize);
  }

  // Write the symbol table data, if used.
  if (NumSymbols) {
    // Write the indirect symbol entries.
    for (MCAssembler::const_indirect_symbol_iterator
           it = Asm.indirect_symbol_begin(),
           ie = Asm.indirect_symbol_end(); it != ie; ++it) {
      // Indirect symbols in the non-lazy symbol pointer section have some
      // special handling.
      const MCSectionMachO &Section =
          static_cast<const MCSectionMachO &>(*it->Section);
      if (Section.getType() == MachO::S_NON_LAZY_SYMBOL_POINTERS) {
        // If this symbol is defined and internal, mark it as such.
        if (it->Symbol->isDefined() && !it->Symbol->isExternal()) {
          uint32_t Flags = MachO::INDIRECT_SYMBOL_LOCAL;
          if (it->Symbol->isAbsolute())
            Flags |= MachO::INDIRECT_SYMBOL_ABS;
          write32(Flags);
          continue;
        }
      }

      write32(it->Symbol->getIndex());
    }

    // FIXME: Check that offsets match computed ones.

    // Write the symbol table entries.
    for (auto *SymbolData :
         {&LocalSymbolData, &ExternalSymbolData, &UndefinedSymbolData})
      for (MachSymbolData &Entry : *SymbolData)
        writeNlist(Entry, Layout);

    // Write the string table.
    getStream() << StringTable.data();
  }
}
示例#3
0
void MachObjectWriter::WriteObject(MCAssembler &Asm,
                                   const MCAsmLayout &Layout) {
  unsigned NumSections = Asm.size();
  const MCAssembler::VersionMinInfoType &VersionInfo =
    Layout.getAssembler().getVersionMinInfo();

  // The section data starts after the header, the segment load command (and
  // section headers) and the symbol table.
  unsigned NumLoadCommands = 1;
  uint64_t LoadCommandsSize = is64Bit() ?
    sizeof(MachO::segment_command_64) + NumSections * sizeof(MachO::section_64):
    sizeof(MachO::segment_command) + NumSections * sizeof(MachO::section);

  // Add the deployment target version info load command size, if used.
  if (VersionInfo.Major != 0) {
    ++NumLoadCommands;
    LoadCommandsSize += sizeof(MachO::version_min_command);
  }

  // Add the data-in-code load command size, if used.
  unsigned NumDataRegions = Asm.getDataRegions().size();
  if (NumDataRegions) {
    ++NumLoadCommands;
    LoadCommandsSize += sizeof(MachO::linkedit_data_command);
  }

  // Add the loh load command size, if used.
  uint64_t LOHRawSize = Asm.getLOHContainer().getEmitSize(*this, Layout);
  uint64_t LOHSize = RoundUpToAlignment(LOHRawSize, is64Bit() ? 8 : 4);
  if (LOHSize) {
    ++NumLoadCommands;
    LoadCommandsSize += sizeof(MachO::linkedit_data_command);
  }

  // Add the symbol table load command sizes, if used.
  unsigned NumSymbols = LocalSymbolData.size() + ExternalSymbolData.size() +
    UndefinedSymbolData.size();
  if (NumSymbols) {
    NumLoadCommands += 2;
    LoadCommandsSize += (sizeof(MachO::symtab_command) +
                         sizeof(MachO::dysymtab_command));
  }

  // Add the linker option load commands sizes.
  const std::vector<std::vector<std::string> > &LinkerOptions =
    Asm.getLinkerOptions();
  for (unsigned i = 0, e = LinkerOptions.size(); i != e; ++i) {
    ++NumLoadCommands;
    LoadCommandsSize += ComputeLinkerOptionsLoadCommandSize(LinkerOptions[i],
                                                            is64Bit());
  }
  
  // Compute the total size of the section data, as well as its file size and vm
  // size.
  uint64_t SectionDataStart = (is64Bit() ? sizeof(MachO::mach_header_64) :
                               sizeof(MachO::mach_header)) + LoadCommandsSize;
  uint64_t SectionDataSize = 0;
  uint64_t SectionDataFileSize = 0;
  uint64_t VMSize = 0;
  for (MCAssembler::const_iterator it = Asm.begin(),
         ie = Asm.end(); it != ie; ++it) {
    const MCSectionData &SD = *it;
    uint64_t Address = getSectionAddress(&SD);
    uint64_t Size = Layout.getSectionAddressSize(&SD);
    uint64_t FileSize = Layout.getSectionFileSize(&SD);
    FileSize += getPaddingSize(&SD, Layout);

    VMSize = std::max(VMSize, Address + Size);

    if (SD.getSection().isVirtualSection())
      continue;

    SectionDataSize = std::max(SectionDataSize, Address + Size);
    SectionDataFileSize = std::max(SectionDataFileSize, Address + FileSize);
  }

  // The section data is padded to 4 bytes.
  //
  // FIXME: Is this machine dependent?
  unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
  SectionDataFileSize += SectionDataPadding;

  // Write the prolog, starting with the header and load command...
  WriteHeader(NumLoadCommands, LoadCommandsSize,
              Asm.getSubsectionsViaSymbols());
  WriteSegmentLoadCommand(NumSections, VMSize,
                          SectionDataStart, SectionDataSize);

  // ... and then the section headers.
  uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
  for (MCAssembler::const_iterator it = Asm.begin(),
         ie = Asm.end(); it != ie; ++it) {
    std::vector<MachO::any_relocation_info> &Relocs = Relocations[it];
    unsigned NumRelocs = Relocs.size();
    uint64_t SectionStart = SectionDataStart + getSectionAddress(it);
    WriteSection(Asm, Layout, *it, SectionStart, RelocTableEnd, NumRelocs);
    RelocTableEnd += NumRelocs * sizeof(MachO::any_relocation_info);
  }

  // Write out the deployment target information, if it's available.
  if (VersionInfo.Major != 0) {
    assert(VersionInfo.Update < 256 && "unencodable update target version");
    assert(VersionInfo.Minor < 256 && "unencodable minor target version");
    assert(VersionInfo.Major < 65536 && "unencodable major target version");
    uint32_t EncodedVersion = VersionInfo.Update | (VersionInfo.Minor << 8) |
      (VersionInfo.Major << 16);
    Write32(VersionInfo.Kind == MCVM_OSXVersionMin ? MachO::LC_VERSION_MIN_MACOSX :
            MachO::LC_VERSION_MIN_IPHONEOS);
    Write32(sizeof(MachO::version_min_command));
    Write32(EncodedVersion);
    Write32(0);         // reserved.
  }

  // Write the data-in-code load command, if used.
  uint64_t DataInCodeTableEnd = RelocTableEnd + NumDataRegions * 8;
  if (NumDataRegions) {
    uint64_t DataRegionsOffset = RelocTableEnd;
    uint64_t DataRegionsSize = NumDataRegions * 8;
    WriteLinkeditLoadCommand(MachO::LC_DATA_IN_CODE, DataRegionsOffset,
                             DataRegionsSize);
  }

  // Write the loh load command, if used.
  uint64_t LOHTableEnd = DataInCodeTableEnd + LOHSize;
  if (LOHSize)
    WriteLinkeditLoadCommand(MachO::LC_LINKER_OPTIMIZATION_HINT,
                             DataInCodeTableEnd, LOHSize);

  // Write the symbol table load command, if used.
  if (NumSymbols) {
    unsigned FirstLocalSymbol = 0;
    unsigned NumLocalSymbols = LocalSymbolData.size();
    unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
    unsigned NumExternalSymbols = ExternalSymbolData.size();
    unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
    unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
    unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
    unsigned NumSymTabSymbols =
      NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
    uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
    uint64_t IndirectSymbolOffset = 0;

    // If used, the indirect symbols are written after the section data.
    if (NumIndirectSymbols)
      IndirectSymbolOffset = LOHTableEnd;

    // The symbol table is written after the indirect symbol data.
    uint64_t SymbolTableOffset = LOHTableEnd + IndirectSymbolSize;

    // The string table is written after symbol table.
    uint64_t StringTableOffset =
      SymbolTableOffset + NumSymTabSymbols * (is64Bit() ?
                                              sizeof(MachO::nlist_64) :
                                              sizeof(MachO::nlist));
    WriteSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
                           StringTableOffset, StringTable.data().size());

    WriteDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
                             FirstExternalSymbol, NumExternalSymbols,
                             FirstUndefinedSymbol, NumUndefinedSymbols,
                             IndirectSymbolOffset, NumIndirectSymbols);
  }

  // Write the linker options load commands.
  for (unsigned i = 0, e = LinkerOptions.size(); i != e; ++i) {
    WriteLinkerOptionsLoadCommand(LinkerOptions[i]);
  }

  // Write the actual section data.
  for (MCAssembler::const_iterator it = Asm.begin(),
         ie = Asm.end(); it != ie; ++it) {
    Asm.writeSectionData(it, Layout);

    uint64_t Pad = getPaddingSize(it, Layout);
    for (unsigned int i = 0; i < Pad; ++i)
      Write8(0);
  }

  // Write the extra padding.
  WriteZeros(SectionDataPadding);

  // Write the relocation entries.
  for (MCAssembler::const_iterator it = Asm.begin(),
         ie = Asm.end(); it != ie; ++it) {
    // Write the section relocation entries, in reverse order to match 'as'
    // (approximately, the exact algorithm is more complicated than this).
    std::vector<MachO::any_relocation_info> &Relocs = Relocations[it];
    for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
      Write32(Relocs[e - i - 1].r_word0);
      Write32(Relocs[e - i - 1].r_word1);
    }
  }

  // Write out the data-in-code region payload, if there is one.
  for (MCAssembler::const_data_region_iterator
         it = Asm.data_region_begin(), ie = Asm.data_region_end();
         it != ie; ++it) {
    const DataRegionData *Data = &(*it);
    uint64_t Start =
      getSymbolAddress(&Layout.getAssembler().getSymbolData(*Data->Start),
                       Layout);
    uint64_t End =
      getSymbolAddress(&Layout.getAssembler().getSymbolData(*Data->End),
                       Layout);
    DEBUG(dbgs() << "data in code region-- kind: " << Data->Kind
                 << "  start: " << Start << "(" << Data->Start->getName() << ")"
                 << "  end: " << End << "(" << Data->End->getName() << ")"
                 << "  size: " << End - Start
                 << "\n");
    Write32(Start);
    Write16(End - Start);
    Write16(Data->Kind);
  }

  // Write out the loh commands, if there is one.
  if (LOHSize) {
#ifndef NDEBUG
    unsigned Start = OS.tell();
#endif
    Asm.getLOHContainer().Emit(*this, Layout);
    // Pad to a multiple of the pointer size.
    WriteBytes("", OffsetToAlignment(LOHRawSize, is64Bit() ? 8 : 4));
    assert(OS.tell() - Start == LOHSize);
  }

  // Write the symbol table data, if used.
  if (NumSymbols) {
    // Write the indirect symbol entries.
    for (MCAssembler::const_indirect_symbol_iterator
           it = Asm.indirect_symbol_begin(),
           ie = Asm.indirect_symbol_end(); it != ie; ++it) {
      // Indirect symbols in the non-lazy symbol pointer section have some
      // special handling.
      const MCSectionMachO &Section =
        static_cast<const MCSectionMachO&>(it->SectionData->getSection());
      if (Section.getType() == MachO::S_NON_LAZY_SYMBOL_POINTERS) {
        // If this symbol is defined and internal, mark it as such.
        if (it->Symbol->isDefined() &&
            !Asm.getSymbolData(*it->Symbol).isExternal()) {
          uint32_t Flags = MachO::INDIRECT_SYMBOL_LOCAL;
          if (it->Symbol->isAbsolute())
            Flags |= MachO::INDIRECT_SYMBOL_ABS;
          Write32(Flags);
          continue;
        }
      }

      Write32(Asm.getSymbolData(*it->Symbol).getIndex());
    }

    // FIXME: Check that offsets match computed ones.

    // Write the symbol table entries.
    for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
      WriteNlist(LocalSymbolData[i], Layout);
    for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
      WriteNlist(ExternalSymbolData[i], Layout);
    for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
      WriteNlist(UndefinedSymbolData[i], Layout);

    // Write the string table.
    OS << StringTable.data();
  }
}