text: //===- yaml2elf - Convert YAML to a ELF 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 ELF component of yaml2obj.
  ///
  //===----------------------------------------------------------------------===//
  
  #include "llvm/ADT/ArrayRef.h"
  #include "llvm/ADT/StringSet.h"
  #include "llvm/BinaryFormat/ELF.h"
  #include "llvm/MC/StringTableBuilder.h"
  #include "llvm/Object/ELFObjectFile.h"
  #include "llvm/ObjectYAML/ELFYAML.h"
  #include "llvm/ObjectYAML/yaml2obj.h"
  #include "llvm/Support/EndianStream.h"
  #include "llvm/Support/LEB128.h"
  #include "llvm/Support/MemoryBuffer.h"
  #include "llvm/Support/WithColor.h"
  #include "llvm/Support/YAMLTraits.h"
  #include "llvm/Support/raw_ostream.h"
  
  using namespace llvm;
  
  // This class is used to build up a contiguous binary blob while keeping
  // track of an offset in the output (which notionally begins at
  // `InitialOffset`).
  namespace {
  class ContiguousBlobAccumulator {
    const uint64_t InitialOffset;
    SmallVector<char, 128> Buf;
    raw_svector_ostream OS;
  
    /// \returns The new offset.
    uint64_t padToAlignment(unsigned Align) {
      if (Align == 0)
        Align = 1;
      uint64_t CurrentOffset = InitialOffset + OS.tell();
      uint64_t AlignedOffset = alignTo(CurrentOffset, Align);
      OS.write_zeros(AlignedOffset - CurrentOffset);
      return AlignedOffset; // == CurrentOffset;
    }
  
  public:
    ContiguousBlobAccumulator(uint64_t InitialOffset_)
        : InitialOffset(InitialOffset_), Buf(), OS(Buf) {}
    template <class Integer>
    raw_ostream &getOSAndAlignedOffset(Integer &Offset, unsigned Align) {
      Offset = padToAlignment(Align);
      return OS;
    }
    void writeBlobToStream(raw_ostream &Out) { Out << OS.str(); }
  };
  
  // Used to keep track of section and symbol names, so that in the YAML file
  // sections and symbols can be referenced by name instead of by index.
  class NameToIdxMap {
    StringMap<unsigned> Map;
  
  public:
    /// \Returns false if name is already present in the map.
    bool addName(StringRef Name, unsigned Ndx) {
      return Map.insert({Name, Ndx}).second;
    }
    /// \Returns false if name is not present in the map.
    bool lookup(StringRef Name, unsigned &Idx) const {
      auto I = Map.find(Name);
      if (I == Map.end())
        return false;
      Idx = I->getValue();
      return true;
    }
    /// Asserts if name is not present in the map.
    unsigned get(StringRef Name) const {
      unsigned Idx;
      if (lookup(Name, Idx))
        return Idx;
      assert(false && "Expected section not found in index");
      return 0;
    }
    unsigned size() const { return Map.size(); }
  };
  
  /// "Single point of truth" for the ELF file construction.
  /// TODO: This class still has a ways to go before it is truly a "single
  /// point of truth".
  template <class ELFT> class ELFState {
    typedef typename ELFT::Ehdr Elf_Ehdr;
    typedef typename ELFT::Phdr Elf_Phdr;
    typedef typename ELFT::Shdr Elf_Shdr;
    typedef typename ELFT::Sym Elf_Sym;
    typedef typename ELFT::Rel Elf_Rel;
    typedef typename ELFT::Rela Elf_Rela;
    typedef typename ELFT::Relr Elf_Relr;
    typedef typename ELFT::Dyn Elf_Dyn;
  
    enum class SymtabType { Static, Dynamic };
  
    /// The future ".strtab" section.
    StringTableBuilder DotStrtab{StringTableBuilder::ELF};
  
    /// The future ".shstrtab" section.
    StringTableBuilder DotShStrtab{StringTableBuilder::ELF};
  
    /// The future ".dynstr" section.
    StringTableBuilder DotDynstr{StringTableBuilder::ELF};
  
    NameToIdxMap SN2I;
    NameToIdxMap SymN2I;
    NameToIdxMap DynSymN2I;
    ELFYAML::Object &Doc;
  
    bool HasError = false;
    yaml::ErrorHandler ErrHandler;
    void reportError(const Twine &Msg);
  
    std::vector<Elf_Sym> toELFSymbols(ArrayRef<ELFYAML::Symbol> Symbols,
                                      const StringTableBuilder &Strtab);
    unsigned toSectionIndex(StringRef S, StringRef LocSec, StringRef LocSym = "");
    unsigned toSymbolIndex(StringRef S, StringRef LocSec, bool IsDynamic);
  
    void buildSectionIndex();
    void buildSymbolIndexes();
    void initProgramHeaders(std::vector<Elf_Phdr> &PHeaders);
    bool initImplicitHeader(ContiguousBlobAccumulator &CBA, Elf_Shdr &Header,
                            StringRef SecName, ELFYAML::Section *YAMLSec);
    void initSectionHeaders(std::vector<Elf_Shdr> &SHeaders,
                            ContiguousBlobAccumulator &CBA);
    void initSymtabSectionHeader(Elf_Shdr &SHeader, SymtabType STType,
                                 ContiguousBlobAccumulator &CBA,
                                 ELFYAML::Section *YAMLSec);
    void initStrtabSectionHeader(Elf_Shdr &SHeader, StringRef Name,
                                 StringTableBuilder &STB,
                                 ContiguousBlobAccumulator &CBA,
                                 ELFYAML::Section *YAMLSec);
    void setProgramHeaderLayout(std::vector<Elf_Phdr> &PHeaders,
                                std::vector<Elf_Shdr> &SHeaders);
    void finalizeStrings();
    void writeELFHeader(ContiguousBlobAccumulator &CBA, raw_ostream &OS);
    void writeSectionContent(Elf_Shdr &SHeader,
                             const ELFYAML::RawContentSection &Section,
                             ContiguousBlobAccumulator &CBA);
    void writeSectionContent(Elf_Shdr &SHeader,
                             const ELFYAML::RelocationSection &Section,
                             ContiguousBlobAccumulator &CBA);
    void writeSectionContent(Elf_Shdr &SHeader, const ELFYAML::Group &Group,
                             ContiguousBlobAccumulator &CBA);
    void writeSectionContent(Elf_Shdr &SHeader,
                             const ELFYAML::SymtabShndxSection &Shndx,
                             ContiguousBlobAccumulator &CBA);
    void writeSectionContent(Elf_Shdr &SHeader,
                             const ELFYAML::SymverSection &Section,
                             ContiguousBlobAccumulator &CBA);
    void writeSectionContent(Elf_Shdr &SHeader,
                             const ELFYAML::VerneedSection &Section,
                             ContiguousBlobAccumulator &CBA);
    void writeSectionContent(Elf_Shdr &SHeader,
                             const ELFYAML::VerdefSection &Section,
                             ContiguousBlobAccumulator &CBA);
    void writeSectionContent(Elf_Shdr &SHeader,
                             const ELFYAML::MipsABIFlags &Section,
                             ContiguousBlobAccumulator &CBA);
    void writeSectionContent(Elf_Shdr &SHeader,
                             const ELFYAML::DynamicSection &Section,
                             ContiguousBlobAccumulator &CBA);
    void writeSectionContent(Elf_Shdr &SHeader,
                             const ELFYAML::StackSizesSection &Section,
                             ContiguousBlobAccumulator &CBA);
    void writeSectionContent(Elf_Shdr &SHeader,
                             const ELFYAML::HashSection &Section,
                             ContiguousBlobAccumulator &CBA);
    void writeSectionContent(Elf_Shdr &SHeader,
                             const ELFYAML::AddrsigSection &Section,
                             ContiguousBlobAccumulator &CBA);
  
    ELFState(ELFYAML::Object &D, yaml::ErrorHandler EH);
  
  public:
    static bool writeELF(raw_ostream &OS, ELFYAML::Object &Doc,
                         yaml::ErrorHandler EH);
  };
  } // end anonymous namespace
  
  template <class T> static size_t arrayDataSize(ArrayRef<T> A) {
    return A.size() * sizeof(T);
  }
  
  template <class T> static void writeArrayData(raw_ostream &OS, ArrayRef<T> A) {
    OS.write((const char *)A.data(), arrayDataSize(A));
  }
  
  template <class T> static void zero(T &Obj) { memset(&Obj, 0, sizeof(Obj)); }
  
  template <class ELFT>
  ELFState<ELFT>::ELFState(ELFYAML::Object &D, yaml::ErrorHandler EH)
      : Doc(D), ErrHandler(EH) {
    StringSet<> DocSections;
    for (std::unique_ptr<ELFYAML::Section> &D : Doc.Sections) {
      if (!D->Name.empty())
        DocSections.insert(D->Name);
  
      // Some sections wants to link to .symtab by default.
      // That means we want to create the symbol table for them.
      if (D->Type == llvm::ELF::SHT_REL || D->Type == llvm::ELF::SHT_RELA)
        if (!Doc.Symbols && D->Link.empty())
          Doc.Symbols.emplace();
    }
  
    // Insert SHT_NULL section implicitly when it is not defined in YAML.
    if (Doc.Sections.empty() || Doc.Sections.front()->Type != ELF::SHT_NULL)
      Doc.Sections.insert(
          Doc.Sections.begin(),
          std::make_unique<ELFYAML::Section>(
              ELFYAML::Section::SectionKind::RawContent, /*IsImplicit=*/true));
  
    std::vector<StringRef> ImplicitSections;
    if (Doc.Symbols)
      ImplicitSections.push_back(".symtab");
    ImplicitSections.insert(ImplicitSections.end(), {".strtab", ".shstrtab"});
  
    if (!Doc.DynamicSymbols.empty())
      ImplicitSections.insert(ImplicitSections.end(), {".dynsym", ".dynstr"});
  
    // Insert placeholders for implicit sections that are not
    // defined explicitly in YAML.
    for (StringRef SecName : ImplicitSections) {
      if (DocSections.count(SecName))
        continue;
  
      std::unique_ptr<ELFYAML::Section> Sec = std::make_unique<ELFYAML::Section>(
          ELFYAML::Section::SectionKind::RawContent, true /*IsImplicit*/);
      Sec->Name = SecName;
      Doc.Sections.push_back(std::move(Sec));
    }
  }
  
  template <class ELFT>
  void ELFState<ELFT>::writeELFHeader(ContiguousBlobAccumulator &CBA, raw_ostream &OS) {
    using namespace llvm::ELF;
  
    Elf_Ehdr Header;
    zero(Header);
    Header.e_ident[EI_MAG0] = 0x7f;
    Header.e_ident[EI_MAG1] = 'E';
    Header.e_ident[EI_MAG2] = 'L';
    Header.e_ident[EI_MAG3] = 'F';
    Header.e_ident[EI_CLASS] = ELFT::Is64Bits ? ELFCLASS64 : ELFCLASS32;
    Header.e_ident[EI_DATA] = Doc.Header.Data;
    Header.e_ident[EI_VERSION] = EV_CURRENT;
    Header.e_ident[EI_OSABI] = Doc.Header.OSABI;
    Header.e_ident[EI_ABIVERSION] = Doc.Header.ABIVersion;
    Header.e_type = Doc.Header.Type;
    Header.e_machine = Doc.Header.Machine;
    Header.e_version = EV_CURRENT;
    Header.e_entry = Doc.Header.Entry;
    Header.e_phoff = Doc.ProgramHeaders.size() ? sizeof(Header) : 0;
    Header.e_flags = Doc.Header.Flags;
    Header.e_ehsize = sizeof(Elf_Ehdr);
    Header.e_phentsize = Doc.ProgramHeaders.size() ? sizeof(Elf_Phdr) : 0;
    Header.e_phnum = Doc.ProgramHeaders.size();
  
    Header.e_shentsize =
        Doc.Header.SHEntSize ? (uint16_t)*Doc.Header.SHEntSize : sizeof(Elf_Shdr);
    // Immediately following the ELF header and program headers.
    // Align the start of the section header and write the ELF header.
    uint64_t SHOff;
    CBA.getOSAndAlignedOffset(SHOff, sizeof(typename ELFT::uint));
    Header.e_shoff =
        Doc.Header.SHOff ? typename ELFT::uint(*Doc.Header.SHOff) : SHOff;
    Header.e_shnum =
        Doc.Header.SHNum ? (uint16_t)*Doc.Header.SHNum : Doc.Sections.size();
    Header.e_shstrndx = Doc.Header.SHStrNdx ? (uint16_t)*Doc.Header.SHStrNdx
                                            : SN2I.get(".shstrtab");
  
    OS.write((const char *)&Header, sizeof(Header));
  }
  
  template <class ELFT>
  void ELFState<ELFT>::initProgramHeaders(std::vector<Elf_Phdr> &PHeaders) {
    for (const auto &YamlPhdr : Doc.ProgramHeaders) {
      Elf_Phdr Phdr;
      Phdr.p_type = YamlPhdr.Type;
      Phdr.p_flags = YamlPhdr.Flags;
      Phdr.p_vaddr = YamlPhdr.VAddr;
      Phdr.p_paddr = YamlPhdr.PAddr;
      PHeaders.push_back(Phdr);
    }
  }
  
  template <class ELFT>
  unsigned ELFState<ELFT>::toSectionIndex(StringRef S, StringRef LocSec,
                                          StringRef LocSym) {
    unsigned Index;
    if (SN2I.lookup(S, Index) || to_integer(S, Index))
      return Index;
  
    assert(LocSec.empty() || LocSym.empty());
    if (!LocSym.empty())
      reportError("unknown section referenced: '" + S + "' by YAML symbol '" +
                  LocSym + "'");
    else
      reportError("unknown section referenced: '" + S + "' by YAML section '" +
                  LocSec + "'");
    return 0;
  }
  
  template <class ELFT>
  unsigned ELFState<ELFT>::toSymbolIndex(StringRef S, StringRef LocSec,
                                         bool IsDynamic) {
    const NameToIdxMap &SymMap = IsDynamic ? DynSymN2I : SymN2I;
    unsigned Index;
    // Here we try to look up S in the symbol table. If it is not there,
    // treat its value as a symbol index.
    if (!SymMap.lookup(S, Index) && !to_integer(S, Index)) {
      reportError("unknown symbol referenced: '" + S + "' by YAML section '" +
                  LocSec + "'");
      return 0;
    }
    return Index;
  }
  
  template <class ELFT>
  bool ELFState<ELFT>::initImplicitHeader(ContiguousBlobAccumulator &CBA,
                                          Elf_Shdr &Header, StringRef SecName,
                                          ELFYAML::Section *YAMLSec) {
    // Check if the header was already initialized.
    if (Header.sh_offset)
      return false;
  
    if (SecName == ".symtab")
      initSymtabSectionHeader(Header, SymtabType::Static, CBA, YAMLSec);
    else if (SecName == ".strtab")
      initStrtabSectionHeader(Header, SecName, DotStrtab, CBA, YAMLSec);
    else if (SecName == ".shstrtab")
      initStrtabSectionHeader(Header, SecName, DotShStrtab, CBA, YAMLSec);
    else if (SecName == ".dynsym")
      initSymtabSectionHeader(Header, SymtabType::Dynamic, CBA, YAMLSec);
    else if (SecName == ".dynstr")
      initStrtabSectionHeader(Header, SecName, DotDynstr, CBA, YAMLSec);
    else
      return false;
  
    // Override the fields if requested.
    if (YAMLSec) {
      if (YAMLSec->ShName)
        Header.sh_name = *YAMLSec->ShName;
      if (YAMLSec->ShOffset)
        Header.sh_offset = *YAMLSec->ShOffset;
      if (YAMLSec->ShSize)
        Header.sh_size = *YAMLSec->ShSize;
    }
  
    return true;
  }
  
  StringRef llvm::ELFYAML::dropUniqueSuffix(StringRef S) {
    size_t SuffixPos = S.rfind(" [");
    if (SuffixPos == StringRef::npos)
      return S;
    return S.substr(0, SuffixPos);
  }
  
  template <class ELFT>
  void ELFState<ELFT>::initSectionHeaders(std::vector<Elf_Shdr> &SHeaders,
                                          ContiguousBlobAccumulator &CBA) {
    // Ensure SHN_UNDEF entry is present. An all-zero section header is a
    // valid SHN_UNDEF entry since SHT_NULL == 0.
    SHeaders.resize(Doc.Sections.size());
  
    for (size_t I = 0; I < Doc.Sections.size(); ++I) {
      ELFYAML::Section *Sec = Doc.Sections[I].get();
      if (I == 0 && Sec->IsImplicit)
        continue;
  
      // We have a few sections like string or symbol tables that are usually
      // added implicitly to the end. However, if they are explicitly specified
      // in the YAML, we need to write them here. This ensures the file offset
      // remains correct.
      Elf_Shdr &SHeader = SHeaders[I];
      if (initImplicitHeader(CBA, SHeader, Sec->Name,
                             Sec->IsImplicit ? nullptr : Sec))
        continue;
  
      assert(Sec && "It can't be null unless it is an implicit section. But all "
                    "implicit sections should already have been handled above.");
  
      SHeader.sh_name =
          DotShStrtab.getOffset(ELFYAML::dropUniqueSuffix(Sec->Name));
      SHeader.sh_type = Sec->Type;
      if (Sec->Flags)
        SHeader.sh_flags = *Sec->Flags;
      SHeader.sh_addr = Sec->Address;
      SHeader.sh_addralign = Sec->AddressAlign;
  
      if (!Sec->Link.empty())
        SHeader.sh_link = toSectionIndex(Sec->Link, Sec->Name);
  
      if (I == 0) {
        if (auto RawSec = dyn_cast<ELFYAML::RawContentSection>(Sec)) {
          // We do not write any content for special SHN_UNDEF section.
          if (RawSec->Size)
            SHeader.sh_size = *RawSec->Size;
          if (RawSec->Info)
            SHeader.sh_info = *RawSec->Info;
        }
        if (Sec->EntSize)
          SHeader.sh_entsize = *Sec->EntSize;
      } else if (auto S = dyn_cast<ELFYAML::RawContentSection>(Sec)) {
        writeSectionContent(SHeader, *S, CBA);
      } else if (auto S = dyn_cast<ELFYAML::SymtabShndxSection>(Sec)) {
        writeSectionContent(SHeader, *S, CBA);
      } else if (auto S = dyn_cast<ELFYAML::RelocationSection>(Sec)) {
        writeSectionContent(SHeader, *S, CBA);
      } else if (auto S = dyn_cast<ELFYAML::Group>(Sec)) {
        writeSectionContent(SHeader, *S, CBA);
      } else if (auto S = dyn_cast<ELFYAML::MipsABIFlags>(Sec)) {
        writeSectionContent(SHeader, *S, CBA);
      } else if (auto S = dyn_cast<ELFYAML::NoBitsSection>(Sec)) {
        SHeader.sh_entsize = 0;
        SHeader.sh_size = S->Size;
        // SHT_NOBITS section does not have content
        // so just to setup the section offset.
        CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
      } else if (auto S = dyn_cast<ELFYAML::DynamicSection>(Sec)) {
        writeSectionContent(SHeader, *S, CBA);
      } else if (auto S = dyn_cast<ELFYAML::SymverSection>(Sec)) {
        writeSectionContent(SHeader, *S, CBA);
      } else if (auto S = dyn_cast<ELFYAML::VerneedSection>(Sec)) {
        writeSectionContent(SHeader, *S, CBA);
      } else if (auto S = dyn_cast<ELFYAML::VerdefSection>(Sec)) {
        writeSectionContent(SHeader, *S, CBA);
      } else if (auto S = dyn_cast<ELFYAML::StackSizesSection>(Sec)) {
        writeSectionContent(SHeader, *S, CBA);
      } else if (auto S = dyn_cast<ELFYAML::HashSection>(Sec)) {
        writeSectionContent(SHeader, *S, CBA);
      } else if (auto S = dyn_cast<ELFYAML::AddrsigSection>(Sec)) {
        writeSectionContent(SHeader, *S, CBA);
      } else {
        llvm_unreachable("Unknown section type");
      }
  
      // Override the fields if requested.
      if (Sec) {
        if (Sec->ShName)
          SHeader.sh_name = *Sec->ShName;
        if (Sec->ShOffset)
          SHeader.sh_offset = *Sec->ShOffset;
        if (Sec->ShSize)
          SHeader.sh_size = *Sec->ShSize;
      }
    }
  }
  
  static size_t findFirstNonGlobal(ArrayRef<ELFYAML::Symbol> Symbols) {
    for (size_t I = 0; I < Symbols.size(); ++I)
      if (Symbols[I].Binding.value != ELF::STB_LOCAL)
        return I;
    return Symbols.size();
  }
  
  static uint64_t writeContent(raw_ostream &OS,
                               const Optional<yaml::BinaryRef> &Content,
                               const Optional<llvm::yaml::Hex64> &Size) {
    size_t ContentSize = 0;
    if (Content) {
      Content->writeAsBinary(OS);
      ContentSize = Content->binary_size();
    }
  
    if (!Size)
      return ContentSize;
  
    OS.write_zeros(*Size - ContentSize);
    return *Size;
  }
  
  template <class ELFT>
  std::vector<typename ELFT::Sym>
  ELFState<ELFT>::toELFSymbols(ArrayRef<ELFYAML::Symbol> Symbols,
                               const StringTableBuilder &Strtab) {
    std::vector<Elf_Sym> Ret;
    Ret.resize(Symbols.size() + 1);
  
    size_t I = 0;
    for (const auto &Sym : Symbols) {
      Elf_Sym &Symbol = Ret[++I];
  
      // If NameIndex, which contains the name offset, is explicitly specified, we
      // use it. This is useful for preparing broken objects. Otherwise, we add
      // the specified Name to the string table builder to get its offset.
      if (Sym.NameIndex)
        Symbol.st_name = *Sym.NameIndex;
      else if (!Sym.Name.empty())
        Symbol.st_name = Strtab.getOffset(ELFYAML::dropUniqueSuffix(Sym.Name));
  
      Symbol.setBindingAndType(Sym.Binding, Sym.Type);
      if (!Sym.Section.empty())
        Symbol.st_shndx = toSectionIndex(Sym.Section, "", Sym.Name);
      else if (Sym.Index)
        Symbol.st_shndx = *Sym.Index;
  
      Symbol.st_value = Sym.Value;
      Symbol.st_other = Sym.Other ? *Sym.Other : 0;
      Symbol.st_size = Sym.Size;
    }
  
    return Ret;
  }
  
  template <class ELFT>
  void ELFState<ELFT>::initSymtabSectionHeader(Elf_Shdr &SHeader,
                                               SymtabType STType,
                                               ContiguousBlobAccumulator &CBA,
                                               ELFYAML::Section *YAMLSec) {
  
    bool IsStatic = STType == SymtabType::Static;
    ArrayRef<ELFYAML::Symbol> Symbols;
    if (IsStatic && Doc.Symbols)
      Symbols = *Doc.Symbols;
    else if (!IsStatic)
      Symbols = Doc.DynamicSymbols;
  
    ELFYAML::RawContentSection *RawSec =
        dyn_cast_or_null<ELFYAML::RawContentSection>(YAMLSec);
    if (RawSec && !Symbols.empty() && (RawSec->Content || RawSec->Size)) {
      if (RawSec->Content)
        reportError("cannot specify both `Content` and " +
                    (IsStatic ? Twine("`Symbols`") : Twine("`DynamicSymbols`")) +
                    " for symbol table section '" + RawSec->Name + "'");
      if (RawSec->Size)
        reportError("cannot specify both `Size` and " +
                    (IsStatic ? Twine("`Symbols`") : Twine("`DynamicSymbols`")) +
                    " for symbol table section '" + RawSec->Name + "'");
      return;
    }
  
    zero(SHeader);
    SHeader.sh_name = DotShStrtab.getOffset(IsStatic ? ".symtab" : ".dynsym");
  
    if (YAMLSec)
      SHeader.sh_type = YAMLSec->Type;
    else
      SHeader.sh_type = IsStatic ? ELF::SHT_SYMTAB : ELF::SHT_DYNSYM;
  
    if (RawSec && !RawSec->Link.empty()) {
      // If the Link field is explicitly defined in the document,
      // we should use it.
      SHeader.sh_link = toSectionIndex(RawSec->Link, RawSec->Name);
    } else {
      // When we describe the .dynsym section in the document explicitly, it is
      // allowed to omit the "DynamicSymbols" tag. In this case .dynstr is not
      // added implicitly and we should be able to leave the Link zeroed if
      // .dynstr is not defined.
      unsigned Link = 0;
      if (IsStatic)
        Link = SN2I.get(".strtab");
      else
        SN2I.lookup(".dynstr", Link);
      SHeader.sh_link = Link;
    }
  
    if (YAMLSec && YAMLSec->Flags)
      SHeader.sh_flags = *YAMLSec->Flags;
    else if (!IsStatic)
      SHeader.sh_flags = ELF::SHF_ALLOC;
  
    // If the symbol table section is explicitly described in the YAML
    // then we should set the fields requested.
    SHeader.sh_info = (RawSec && RawSec->Info) ? (unsigned)(*RawSec->Info)
                                               : findFirstNonGlobal(Symbols) + 1;
    SHeader.sh_entsize = (YAMLSec && YAMLSec->EntSize)
                             ? (uint64_t)(*YAMLSec->EntSize)
                             : sizeof(Elf_Sym);
    SHeader.sh_addralign = YAMLSec ? (uint64_t)YAMLSec->AddressAlign : 8;
    SHeader.sh_addr = YAMLSec ? (uint64_t)YAMLSec->Address : 0;
  
    auto &OS = CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
    if (RawSec && (RawSec->Content || RawSec->Size)) {
      assert(Symbols.empty());
      SHeader.sh_size = writeContent(OS, RawSec->Content, RawSec->Size);
      return;
    }
  
    std::vector<Elf_Sym> Syms =
        toELFSymbols(Symbols, IsStatic ? DotStrtab : DotDynstr);
    writeArrayData(OS, makeArrayRef(Syms));
    SHeader.sh_size = arrayDataSize(makeArrayRef(Syms));
  }
  
  template <class ELFT>
  void ELFState<ELFT>::initStrtabSectionHeader(Elf_Shdr &SHeader, StringRef Name,
                                               StringTableBuilder &STB,
                                               ContiguousBlobAccumulator &CBA,
                                               ELFYAML::Section *YAMLSec) {
    zero(SHeader);
    SHeader.sh_name = DotShStrtab.getOffset(Name);
    SHeader.sh_type = YAMLSec ? YAMLSec->Type : ELF::SHT_STRTAB;
    SHeader.sh_addralign = YAMLSec ? (uint64_t)YAMLSec->AddressAlign : 1;
  
    ELFYAML::RawContentSection *RawSec =
        dyn_cast_or_null<ELFYAML::RawContentSection>(YAMLSec);
  
    auto &OS = CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
    if (RawSec && (RawSec->Content || RawSec->Size)) {
      SHeader.sh_size = writeContent(OS, RawSec->Content, RawSec->Size);
    } else {
      STB.write(OS);
      SHeader.sh_size = STB.getSize();
    }
  
    if (YAMLSec && YAMLSec->EntSize)
      SHeader.sh_entsize = *YAMLSec->EntSize;
  
    if (RawSec && RawSec->Info)
      SHeader.sh_info = *RawSec->Info;
  
    if (YAMLSec && YAMLSec->Flags)
      SHeader.sh_flags = *YAMLSec->Flags;
    else if (Name == ".dynstr")
      SHeader.sh_flags = ELF::SHF_ALLOC;
  
    // If the section is explicitly described in the YAML
    // then we want to use its section address.
    if (YAMLSec)
      SHeader.sh_addr = YAMLSec->Address;
  }
  
  template <class ELFT> void ELFState<ELFT>::reportError(const Twine &Msg) {
    ErrHandler(Msg);
    HasError = true;
  }
  
  template <class ELFT>
  void ELFState<ELFT>::setProgramHeaderLayout(std::vector<Elf_Phdr> &PHeaders,
                                              std::vector<Elf_Shdr> &SHeaders) {
    uint32_t PhdrIdx = 0;
    for (auto &YamlPhdr : Doc.ProgramHeaders) {
      Elf_Phdr &PHeader = PHeaders[PhdrIdx++];
  
      std::vector<Elf_Shdr *> Sections;
      for (const ELFYAML::SectionName &SecName : YamlPhdr.Sections) {
        unsigned Index;
        if (!SN2I.lookup(SecName.Section, Index)) {
          reportError("unknown section referenced: '" + SecName.Section +
                      "' by program header");
          continue;
        }
        Sections.push_back(&SHeaders[Index]);
      }
  
      if (YamlPhdr.Offset) {
        PHeader.p_offset = *YamlPhdr.Offset;
      } else {
        if (YamlPhdr.Sections.size())
          PHeader.p_offset = UINT32_MAX;
        else
          PHeader.p_offset = 0;
  
        // Find the minimum offset for the program header.
        for (Elf_Shdr *SHeader : Sections)
          PHeader.p_offset = std::min(PHeader.p_offset, SHeader->sh_offset);
      }
  
      // Find the maximum offset of the end of a section in order to set p_filesz
      // and p_memsz. When setting p_filesz, trailing SHT_NOBITS sections are not
      // counted.
      uint64_t FileOffset = PHeader.p_offset, MemOffset = PHeader.p_offset;
      for (Elf_Shdr *SHeader : Sections) {
        uint64_t End = SHeader->sh_offset + SHeader->sh_size;
        MemOffset = std::max(MemOffset, End);
  
        if (SHeader->sh_type != llvm::ELF::SHT_NOBITS)
          FileOffset = std::max(FileOffset, End);
      }
  
      // Set the file size and the memory size if not set explicitly.
      PHeader.p_filesz = YamlPhdr.FileSize ? uint64_t(*YamlPhdr.FileSize)
                                           : FileOffset - PHeader.p_offset;
      PHeader.p_memsz = YamlPhdr.MemSize ? uint64_t(*YamlPhdr.MemSize)
                                         : MemOffset - PHeader.p_offset;
  
      if (YamlPhdr.Align) {
        PHeader.p_align = *YamlPhdr.Align;
      } else {
        // Set the alignment of the segment to be the maximum alignment of the
        // sections so that by default the segment has a valid and sensible
        // alignment.
        PHeader.p_align = 1;
        for (Elf_Shdr *SHeader : Sections)
          PHeader.p_align = std::max(PHeader.p_align, SHeader->sh_addralign);
      }
    }
  }
  
  template <class ELFT>
  void ELFState<ELFT>::writeSectionContent(
      Elf_Shdr &SHeader, const ELFYAML::RawContentSection &Section,
      ContiguousBlobAccumulator &CBA) {
    raw_ostream &OS =
        CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
    SHeader.sh_size = writeContent(OS, Section.Content, Section.Size);
  
    if (Section.EntSize)
      SHeader.sh_entsize = *Section.EntSize;
    else if (Section.Type == llvm::ELF::SHT_RELR)
      SHeader.sh_entsize = sizeof(Elf_Relr);
    else
      SHeader.sh_entsize = 0;
  
    if (Section.Info)
      SHeader.sh_info = *Section.Info;
  }
  
  static bool isMips64EL(const ELFYAML::Object &Doc) {
    return Doc.Header.Machine == ELFYAML::ELF_EM(llvm::ELF::EM_MIPS) &&
           Doc.Header.Class == ELFYAML::ELF_ELFCLASS(ELF::ELFCLASS64) &&
           Doc.Header.Data == ELFYAML::ELF_ELFDATA(ELF::ELFDATA2LSB);
  }
  
  template <class ELFT>
  void ELFState<ELFT>::writeSectionContent(
      Elf_Shdr &SHeader, const ELFYAML::RelocationSection &Section,
      ContiguousBlobAccumulator &CBA) {
    assert((Section.Type == llvm::ELF::SHT_REL ||
            Section.Type == llvm::ELF::SHT_RELA) &&
           "Section type is not SHT_REL nor SHT_RELA");
  
    bool IsRela = Section.Type == llvm::ELF::SHT_RELA;
    SHeader.sh_entsize = IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
    SHeader.sh_size = SHeader.sh_entsize * Section.Relocations.size();
  
    // For relocation section set link to .symtab by default.
    if (Section.Link.empty())
      SHeader.sh_link = SN2I.get(".symtab");
  
    if (!Section.RelocatableSec.empty())
      SHeader.sh_info = toSectionIndex(Section.RelocatableSec, Section.Name);
  
    auto &OS = CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
    for (const auto &Rel : Section.Relocations) {
      unsigned SymIdx = Rel.Symbol ? toSymbolIndex(*Rel.Symbol, Section.Name,
                                                   Section.Link == ".dynsym")
                                   : 0;
      if (IsRela) {
        Elf_Rela REntry;
        zero(REntry);
        REntry.r_offset = Rel.Offset;
        REntry.r_addend = Rel.Addend;
        REntry.setSymbolAndType(SymIdx, Rel.Type, isMips64EL(Doc));
        OS.write((const char *)&REntry, sizeof(REntry));
      } else {
        Elf_Rel REntry;
        zero(REntry);
        REntry.r_offset = Rel.Offset;
        REntry.setSymbolAndType(SymIdx, Rel.Type, isMips64EL(Doc));
        OS.write((const char *)&REntry, sizeof(REntry));
      }
    }
  }
  
  template <class ELFT>
  void ELFState<ELFT>::writeSectionContent(
      Elf_Shdr &SHeader, const ELFYAML::SymtabShndxSection &Shndx,
      ContiguousBlobAccumulator &CBA) {
    raw_ostream &OS =
        CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
  
    for (uint32_t E : Shndx.Entries)
      support::endian::write<uint32_t>(OS, E, ELFT::TargetEndianness);
  
    SHeader.sh_entsize = Shndx.EntSize ? (uint64_t)*Shndx.EntSize : 4;
    SHeader.sh_size = Shndx.Entries.size() * SHeader.sh_entsize;
  }
  
  template <class ELFT>
  void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                           const ELFYAML::Group &Section,
                                           ContiguousBlobAccumulator &CBA) {
    assert(Section.Type == llvm::ELF::SHT_GROUP &&
           "Section type is not SHT_GROUP");
  
    SHeader.sh_entsize = 4;
    SHeader.sh_size = SHeader.sh_entsize * Section.Members.size();
    SHeader.sh_info =
        toSymbolIndex(Section.Signature, Section.Name, /*IsDynamic=*/false);
  
    raw_ostream &OS =
        CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
  
    for (const ELFYAML::SectionOrType &Member : Section.Members) {
      unsigned int SectionIndex = 0;
      if (Member.sectionNameOrType == "GRP_COMDAT")
        SectionIndex = llvm::ELF::GRP_COMDAT;
      else
        SectionIndex = toSectionIndex(Member.sectionNameOrType, Section.Name);
      support::endian::write<uint32_t>(OS, SectionIndex, ELFT::TargetEndianness);
    }
  }
  
  template <class ELFT>
  void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                           const ELFYAML::SymverSection &Section,
                                           ContiguousBlobAccumulator &CBA) {
    raw_ostream &OS =
        CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
    for (uint16_t Version : Section.Entries)
      support::endian::write<uint16_t>(OS, Version, ELFT::TargetEndianness);
  
    SHeader.sh_entsize = Section.EntSize ? (uint64_t)*Section.EntSize : 2;
    SHeader.sh_size = Section.Entries.size() * SHeader.sh_entsize;
  }
  
  template <class ELFT>
  void ELFState<ELFT>::writeSectionContent(
      Elf_Shdr &SHeader, const ELFYAML::StackSizesSection &Section,
      ContiguousBlobAccumulator &CBA) {
    using uintX_t = typename ELFT::uint;
    raw_ostream &OS =
        CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
  
    if (Section.Content || Section.Size) {
      SHeader.sh_size = writeContent(OS, Section.Content, Section.Size);
      return;
    }
  
    for (const ELFYAML::StackSizeEntry &E : *Section.Entries) {
      support::endian::write<uintX_t>(OS, E.Address, ELFT::TargetEndianness);
      SHeader.sh_size += sizeof(uintX_t) + encodeULEB128(E.Size, OS);
    }
  }
  
  template <class ELFT>
  void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                           const ELFYAML::HashSection &Section,
                                           ContiguousBlobAccumulator &CBA) {
    raw_ostream &OS =
        CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
  
    unsigned Link = 0;
    if (Section.Link.empty() && SN2I.lookup(".dynsym", Link))
      SHeader.sh_link = Link;
  
    if (Section.Content || Section.Size) {
      SHeader.sh_size = writeContent(OS, Section.Content, Section.Size);
      return;
    }
  
    support::endian::write<uint32_t>(OS, Section.Bucket->size(),
                                     ELFT::TargetEndianness);
    support::endian::write<uint32_t>(OS, Section.Chain->size(),
                                     ELFT::TargetEndianness);
    for (uint32_t Val : *Section.Bucket)
      support::endian::write<uint32_t>(OS, Val, ELFT::TargetEndianness);
    for (uint32_t Val : *Section.Chain)
      support::endian::write<uint32_t>(OS, Val, ELFT::TargetEndianness);
  
    SHeader.sh_size = (2 + Section.Bucket->size() + Section.Chain->size()) * 4;
  }
  
  template <class ELFT>
  void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                           const ELFYAML::VerdefSection &Section,
                                           ContiguousBlobAccumulator &CBA) {
    typedef typename ELFT::Verdef Elf_Verdef;
    typedef typename ELFT::Verdaux Elf_Verdaux;
    raw_ostream &OS =
        CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
  
    uint64_t AuxCnt = 0;
    for (size_t I = 0; I < Section.Entries.size(); ++I) {
      const ELFYAML::VerdefEntry &E = Section.Entries[I];
  
      Elf_Verdef VerDef;
      VerDef.vd_version = E.Version;
      VerDef.vd_flags = E.Flags;
      VerDef.vd_ndx = E.VersionNdx;
      VerDef.vd_hash = E.Hash;
      VerDef.vd_aux = sizeof(Elf_Verdef);
      VerDef.vd_cnt = E.VerNames.size();
      if (I == Section.Entries.size() - 1)
        VerDef.vd_next = 0;
      else
        VerDef.vd_next =
            sizeof(Elf_Verdef) + E.VerNames.size() * sizeof(Elf_Verdaux);
      OS.write((const char *)&VerDef, sizeof(Elf_Verdef));
  
      for (size_t J = 0; J < E.VerNames.size(); ++J, ++AuxCnt) {
        Elf_Verdaux VernAux;
        VernAux.vda_name = DotDynstr.getOffset(E.VerNames[J]);
        if (J == E.VerNames.size() - 1)
          VernAux.vda_next = 0;
        else
          VernAux.vda_next = sizeof(Elf_Verdaux);
        OS.write((const char *)&VernAux, sizeof(Elf_Verdaux));
      }
    }
  
    SHeader.sh_size = Section.Entries.size() * sizeof(Elf_Verdef) +
                      AuxCnt * sizeof(Elf_Verdaux);
    SHeader.sh_info = Section.Info;
  }
  
  template <class ELFT>
  void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                           const ELFYAML::VerneedSection &Section,
                                           ContiguousBlobAccumulator &CBA) {
    typedef typename ELFT::Verneed Elf_Verneed;
    typedef typename ELFT::Vernaux Elf_Vernaux;
  
    auto &OS = CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
  
    uint64_t AuxCnt = 0;
    for (size_t I = 0; I < Section.VerneedV.size(); ++I) {
      const ELFYAML::VerneedEntry &VE = Section.VerneedV[I];
  
      Elf_Verneed VerNeed;
      VerNeed.vn_version = VE.Version;
      VerNeed.vn_file = DotDynstr.getOffset(VE.File);
      if (I == Section.VerneedV.size() - 1)
        VerNeed.vn_next = 0;
      else
        VerNeed.vn_next =
            sizeof(Elf_Verneed) + VE.AuxV.size() * sizeof(Elf_Vernaux);
      VerNeed.vn_cnt = VE.AuxV.size();
      VerNeed.vn_aux = sizeof(Elf_Verneed);
      OS.write((const char *)&VerNeed, sizeof(Elf_Verneed));
  
      for (size_t J = 0; J < VE.AuxV.size(); ++J, ++AuxCnt) {
        const ELFYAML::VernauxEntry &VAuxE = VE.AuxV[J];
  
        Elf_Vernaux VernAux;
        VernAux.vna_hash = VAuxE.Hash;
        VernAux.vna_flags = VAuxE.Flags;
        VernAux.vna_other = VAuxE.Other;
        VernAux.vna_name = DotDynstr.getOffset(VAuxE.Name);
        if (J == VE.AuxV.size() - 1)
          VernAux.vna_next = 0;
        else
          VernAux.vna_next = sizeof(Elf_Vernaux);
        OS.write((const char *)&VernAux, sizeof(Elf_Vernaux));
      }
    }
  
    SHeader.sh_size = Section.VerneedV.size() * sizeof(Elf_Verneed) +
                      AuxCnt * sizeof(Elf_Vernaux);
    SHeader.sh_info = Section.Info;
  }
  
  template <class ELFT>
  void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                           const ELFYAML::MipsABIFlags &Section,
                                           ContiguousBlobAccumulator &CBA) {
    assert(Section.Type == llvm::ELF::SHT_MIPS_ABIFLAGS &&
           "Section type is not SHT_MIPS_ABIFLAGS");
  
    object::Elf_Mips_ABIFlags<ELFT> Flags;
    zero(Flags);
    SHeader.sh_entsize = sizeof(Flags);
    SHeader.sh_size = SHeader.sh_entsize;
  
    auto &OS = CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
    Flags.version = Section.Version;
    Flags.isa_level = Section.ISALevel;
    Flags.isa_rev = Section.ISARevision;
    Flags.gpr_size = Section.GPRSize;
    Flags.cpr1_size = Section.CPR1Size;
    Flags.cpr2_size = Section.CPR2Size;
    Flags.fp_abi = Section.FpABI;
    Flags.isa_ext = Section.ISAExtension;
    Flags.ases = Section.ASEs;
    Flags.flags1 = Section.Flags1;
    Flags.flags2 = Section.Flags2;
    OS.write((const char *)&Flags, sizeof(Flags));
  }
  
  template <class ELFT>
  void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                           const ELFYAML::DynamicSection &Section,
                                           ContiguousBlobAccumulator &CBA) {
    typedef typename ELFT::uint uintX_t;
  
    assert(Section.Type == llvm::ELF::SHT_DYNAMIC &&
           "Section type is not SHT_DYNAMIC");
  
    if (!Section.Entries.empty() && Section.Content)
      reportError("cannot specify both raw content and explicit entries "
                  "for dynamic section '" +
                  Section.Name + "'");
  
    if (Section.Content)
      SHeader.sh_size = Section.Content->binary_size();
    else
      SHeader.sh_size = 2 * sizeof(uintX_t) * Section.Entries.size();
    if (Section.EntSize)
      SHeader.sh_entsize = *Section.EntSize;
    else
      SHeader.sh_entsize = sizeof(Elf_Dyn);
  
    raw_ostream &OS =
        CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
    for (const ELFYAML::DynamicEntry &DE : Section.Entries) {
      support::endian::write<uintX_t>(OS, DE.Tag, ELFT::TargetEndianness);
      support::endian::write<uintX_t>(OS, DE.Val, ELFT::TargetEndianness);
    }
    if (Section.Content)
      Section.Content->writeAsBinary(OS);
  }
  
  template <class ELFT>
  void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                           const ELFYAML::AddrsigSection &Section,
                                           ContiguousBlobAccumulator &CBA) {
    raw_ostream &OS =
        CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
  
    unsigned Link = 0;
    if (Section.Link.empty() && SN2I.lookup(".symtab", Link))
      SHeader.sh_link = Link;
  
    if (Section.Content || Section.Size) {
      SHeader.sh_size = writeContent(OS, Section.Content, Section.Size);
      return;
    }
  
    for (const ELFYAML::AddrsigSymbol &Sym : *Section.Symbols) {
      uint64_t Val =
          Sym.Name ? toSymbolIndex(*Sym.Name, Section.Name, /*IsDynamic=*/false)
                   : (uint32_t)*Sym.Index;
      SHeader.sh_size += encodeULEB128(Val, OS);
    }
  }
  
  template <class ELFT> void ELFState<ELFT>::buildSectionIndex() {
    for (unsigned I = 0, E = Doc.Sections.size(); I != E; ++I) {
      StringRef Name = Doc.Sections[I]->Name;
      if (Name.empty())
        continue;
  
      DotShStrtab.add(ELFYAML::dropUniqueSuffix(Name));
      if (!SN2I.addName(Name, I))
        reportError("repeated section name: '" + Name +
                    "' at YAML section number " + Twine(I));
    }
  
    DotShStrtab.finalize();
  }
  
  template <class ELFT> void ELFState<ELFT>::buildSymbolIndexes() {
    auto Build = [this](ArrayRef<ELFYAML::Symbol> V, NameToIdxMap &Map) {
      for (size_t I = 0, S = V.size(); I < S; ++I) {
        const ELFYAML::Symbol &Sym = V[I];
        if (!Sym.Name.empty() && !Map.addName(Sym.Name, I + 1))
          reportError("repeated symbol name: '" + Sym.Name + "'");
      }
    };
  
    if (Doc.Symbols)
      Build(*Doc.Symbols, SymN2I);
    Build(Doc.DynamicSymbols, DynSymN2I);
  }
  
  template <class ELFT> void ELFState<ELFT>::finalizeStrings() {
    // Add the regular symbol names to .strtab section.
    if (Doc.Symbols)
      for (const ELFYAML::Symbol &Sym : *Doc.Symbols)
        DotStrtab.add(ELFYAML::dropUniqueSuffix(Sym.Name));
    DotStrtab.finalize();
  
    // Add the dynamic symbol names to .dynstr section.
    for (const ELFYAML::Symbol &Sym : Doc.DynamicSymbols)
      DotDynstr.add(ELFYAML::dropUniqueSuffix(Sym.Name));
  
    // SHT_GNU_verdef and SHT_GNU_verneed sections might also
    // add strings to .dynstr section.
    for (const std::unique_ptr<ELFYAML::Section> &Sec : Doc.Sections) {
      if (auto VerNeed = dyn_cast<ELFYAML::VerneedSection>(Sec.get())) {
        for (const ELFYAML::VerneedEntry &VE : VerNeed->VerneedV) {
          DotDynstr.add(VE.File);
          for (const ELFYAML::VernauxEntry &Aux : VE.AuxV)
            DotDynstr.add(Aux.Name);
        }
      } else if (auto VerDef = dyn_cast<ELFYAML::VerdefSection>(Sec.get())) {
        for (const ELFYAML::VerdefEntry &E : VerDef->Entries)
          for (StringRef Name : E.VerNames)
            DotDynstr.add(Name);
      }
    }
  
    DotDynstr.finalize();
  }
  
  template <class ELFT>
  bool ELFState<ELFT>::writeELF(raw_ostream &OS, ELFYAML::Object &Doc,
                                yaml::ErrorHandler EH) {
    ELFState<ELFT> State(Doc, EH);
  
    // Finalize .strtab and .dynstr sections. We do that early because want to
    // finalize the string table builders before writing the content of the
    // sections that might want to use them.
    State.finalizeStrings();
  
    State.buildSectionIndex();
    State.buildSymbolIndexes();
  
    std::vector<Elf_Phdr> PHeaders;
    State.initProgramHeaders(PHeaders);
  
    // XXX: This offset is tightly coupled with the order that we write
    // things to `OS`.
    const size_t SectionContentBeginOffset =
        sizeof(Elf_Ehdr) + sizeof(Elf_Phdr) * Doc.ProgramHeaders.size();
    ContiguousBlobAccumulator CBA(SectionContentBeginOffset);
  
    std::vector<Elf_Shdr> SHeaders;
    State.initSectionHeaders(SHeaders, CBA);
  
    // Now we can decide segment offsets
    State.setProgramHeaderLayout(PHeaders, SHeaders);
  
    if (State.HasError)
      return false;
  
    State.writeELFHeader(CBA, OS);
    writeArrayData(OS, makeArrayRef(PHeaders));
    CBA.writeBlobToStream(OS);
    writeArrayData(OS, makeArrayRef(SHeaders));
    return true;
  }
  
  namespace llvm {
  namespace yaml {
  
  bool yaml2elf(llvm::ELFYAML::Object &Doc, raw_ostream &Out, ErrorHandler EH) {
    bool IsLE = Doc.Header.Data == ELFYAML::ELF_ELFDATA(ELF::ELFDATA2LSB);
    bool Is64Bit = Doc.Header.Class == ELFYAML::ELF_ELFCLASS(ELF::ELFCLASS64);
    if (Is64Bit) {
      if (IsLE)
        return ELFState<object::ELF64LE>::writeELF(Out, Doc, EH);
      return ELFState<object::ELF64BE>::writeELF(Out, Doc, EH);
    }
    if (IsLE)
      return ELFState<object::ELF32LE>::writeELF(Out, Doc, EH);
    return ELFState<object::ELF32BE>::writeELF(Out, Doc, EH);
  }
  
  } // namespace yaml
  } // namespace llvm
  