text: //===- yaml2elf - Convert YAML to a ELF object file -----------------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  ///
  /// \file
  /// \brief The ELF component of yaml2obj.
  ///
  //===----------------------------------------------------------------------===//
  
  #include "yaml2obj.h"
  #include "llvm/ADT/ArrayRef.h"
  #include "llvm/Object/ELFObjectFile.h"
  #include "llvm/Object/ELFYAML.h"
  #include "llvm/Support/ELF.h"
  #include "llvm/Support/MemoryBuffer.h"
  #include "llvm/Support/YAMLTraits.h"
  #include "llvm/Support/raw_ostream.h"
  
  using namespace llvm;
  
  // There is similar code in yaml2coff, but with some slight COFF-specific
  // variations like different initial state. Might be able to deduplicate
  // some day, but also want to make sure that the Mach-O use case is served.
  //
  // This class has a deliberately small interface, since a lot of
  // implementation variation is possible.
  //
  // TODO: Use an ordered container with a suffix-based comparison in order
  // to deduplicate suffixes. std::map<> with a custom comparator is likely
  // to be the simplest implementation, but a suffix trie could be more
  // suitable for the job.
  namespace {
  class StringTableBuilder {
    /// \brief Indices of strings currently present in `Buf`.
    StringMap<unsigned> StringIndices;
    /// \brief The contents of the string table as we build it.
    std::string Buf;
  public:
    StringTableBuilder() {
      Buf.push_back('\0');
    }
    /// \returns Index of string in string table.
    unsigned addString(StringRef S) {
      StringMapEntry<unsigned> &Entry = StringIndices.GetOrCreateValue(S);
      unsigned &I = Entry.getValue();
      if (I != 0)
        return I;
      I = Buf.size();
      Buf.append(S.begin(), S.end());
      Buf.push_back('\0');
      return I;
    }
    size_t size() const {
      return Buf.size();
    }
    void writeToStream(raw_ostream &OS) {
      OS.write(Buf.data(), Buf.size());
    }
  };
  } // end anonymous namespace
  
  // 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) {
      uint64_t CurrentOffset = InitialOffset + OS.tell();
      uint64_t AlignedOffset = RoundUpToAlignment(CurrentOffset, Align);
      for (; CurrentOffset != AlignedOffset; ++CurrentOffset)
        OS.write('\0');
      return AlignedOffset; // == CurrentOffset;
    }
  
  public:
    ContiguousBlobAccumulator(uint64_t InitialOffset_)
        : InitialOffset(InitialOffset_), Buf(), OS(Buf) {}
    template <class Integer>
    raw_ostream &getOSAndAlignedOffset(Integer &Offset, unsigned Align = 16) {
      Offset = padToAlignment(Align);
      return OS;
    }
    void writeBlobToStream(raw_ostream &Out) { Out << OS.str(); }
  };
  } // end anonymous namespace
  
  // Used to keep track of section names, so that in the YAML file sections
  // can be referenced by name instead of by index.
  namespace {
  class SectionNameToIdxMap {
    StringMap<int> Map;
  public:
    /// \returns true if name is already present in the map.
    bool addName(StringRef SecName, unsigned i) {
      StringMapEntry<int> &Entry = Map.GetOrCreateValue(SecName, -1);
      if (Entry.getValue() != -1)
        return true;
      Entry.setValue((int)i);
      return false;
    }
    /// \returns true if name is not present in the map
    bool lookupSection(StringRef SecName, unsigned &Idx) const {
      StringMap<int>::const_iterator I = Map.find(SecName);
      if (I == Map.end())
        return true;
      Idx = I->getValue();
      return false;
    }
  };
  } // 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));
  }
  
  /// \brief Create a string table in `SHeader`, which we assume is already
  /// zero'd.
  template <class Elf_Shdr>
  static void createStringTableSectionHeader(Elf_Shdr &SHeader,
                                             StringTableBuilder &STB,
                                             ContiguousBlobAccumulator &CBA) {
    SHeader.sh_type = ELF::SHT_STRTAB;
    STB.writeToStream(CBA.getOSAndAlignedOffset(SHeader.sh_offset));
    SHeader.sh_size = STB.size();
    SHeader.sh_addralign = 1;
  }
  
  namespace {
  /// \brief "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 {
    /// \brief The future ".strtab" section.
    StringTableBuilder DotStrtab;
    /// \brief The section number of the ".strtab" section.
    unsigned DotStrtabSecNo;
    /// \brief The accumulated contents of all sections so far.
    ContiguousBlobAccumulator &SectionContentAccum;
    typedef typename object::ELFFile<ELFT>::Elf_Ehdr Elf_Ehdr;
    /// \brief The ELF file header.
    Elf_Ehdr &Header;
  
    SectionNameToIdxMap &SN2I;
  
  public:
  
    ELFState(Elf_Ehdr &Header_, ContiguousBlobAccumulator &Accum,
             unsigned DotStrtabSecNo_, SectionNameToIdxMap &SN2I_)
        : DotStrtab(), DotStrtabSecNo(DotStrtabSecNo_),
          SectionContentAccum(Accum), Header(Header_), SN2I(SN2I_) {}
  
    unsigned getDotStrTabSecNo() const { return DotStrtabSecNo; }
    StringTableBuilder &getStringTable() { return DotStrtab; }
    ContiguousBlobAccumulator &getSectionContentAccum() {
      return SectionContentAccum;
    }
    SectionNameToIdxMap &getSN2I() { return SN2I; }
  };
  } // end anonymous namespace
  
  // FIXME: At this point it is fairly clear that we need to refactor these
  // static functions into methods of a class sharing some typedefs. These
  // ELF type names are insane.
  template <class ELFT>
  static void
  addSymbols(const std::vector<ELFYAML::Symbol> &Symbols, ELFState<ELFT> &State,
             std::vector<typename object::ELFFile<ELFT>::Elf_Sym> &Syms,
             unsigned SymbolBinding) {
    typedef typename object::ELFFile<ELFT>::Elf_Sym Elf_Sym;
    for (unsigned i = 0, e = Symbols.size(); i != e; ++i) {
      const ELFYAML::Symbol &Sym = Symbols[i];
      Elf_Sym Symbol;
      zero(Symbol);
      if (!Sym.Name.empty())
        Symbol.st_name = State.getStringTable().addString(Sym.Name);
      Symbol.setBindingAndType(SymbolBinding, Sym.Type);
      if (!Sym.Section.empty()) {
        unsigned Index;
        if (State.getSN2I().lookupSection(Sym.Section, Index)) {
          errs() << "error: Unknown section referenced: '" << Sym.Section
                 << "' by YAML symbol " << Sym.Name << ".\n";
          exit(1);
        }
        Symbol.st_shndx = Index;
      } // else Symbol.st_shndex == SHN_UNDEF (== 0), since it was zero'd earlier.
      Symbol.st_value = Sym.Value;
      Symbol.st_size = Sym.Size;
      Syms.push_back(Symbol);
    }
  }
  
  template <class ELFT>
  static void
  handleSymtabSectionHeader(const ELFYAML::LocalGlobalWeakSymbols &Symbols,
                            ELFState<ELFT> &State,
                            typename object::ELFFile<ELFT>::Elf_Shdr &SHeader) {
  
    typedef typename object::ELFFile<ELFT>::Elf_Sym Elf_Sym;
    SHeader.sh_type = ELF::SHT_SYMTAB;
    SHeader.sh_link = State.getDotStrTabSecNo();
    // One greater than symbol table index of the last local symbol.
    SHeader.sh_info = Symbols.Local.size() + 1;
    SHeader.sh_entsize = sizeof(Elf_Sym);
  
    std::vector<Elf_Sym> Syms;
    {
      // Ensure STN_UNDEF is present
      Elf_Sym Sym;
      zero(Sym);
      Syms.push_back(Sym);
    }
    addSymbols(Symbols.Local, State, Syms, ELF::STB_LOCAL);
    addSymbols(Symbols.Global, State, Syms, ELF::STB_GLOBAL);
    addSymbols(Symbols.Weak, State, Syms, ELF::STB_WEAK);
  
    ContiguousBlobAccumulator &CBA = State.getSectionContentAccum();
    writeArrayData(CBA.getOSAndAlignedOffset(SHeader.sh_offset),
                   makeArrayRef(Syms));
    SHeader.sh_size = arrayDataSize(makeArrayRef(Syms));
  }
  
  template <class ELFT>
  static int writeELF(raw_ostream &OS, const ELFYAML::Object &Doc) {
    using namespace llvm::ELF;
    typedef typename object::ELFFile<ELFT>::Elf_Ehdr Elf_Ehdr;
    typedef typename object::ELFFile<ELFT>::Elf_Shdr Elf_Shdr;
  
    const ELFYAML::FileHeader &Hdr = Doc.Header;
  
    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;
    bool IsLittleEndian = ELFT::TargetEndianness == support::little;
    Header.e_ident[EI_DATA] = IsLittleEndian ? ELFDATA2LSB : ELFDATA2MSB;
    Header.e_ident[EI_VERSION] = EV_CURRENT;
    Header.e_ident[EI_OSABI] = Hdr.OSABI;
    Header.e_ident[EI_ABIVERSION] = 0;
    Header.e_type = Hdr.Type;
    Header.e_machine = Hdr.Machine;
    Header.e_version = EV_CURRENT;
    Header.e_entry = Hdr.Entry;
    Header.e_ehsize = sizeof(Elf_Ehdr);
  
    // TODO: Flesh out section header support.
    // TODO: Program headers.
  
    Header.e_shentsize = sizeof(Elf_Shdr);
    // Immediately following the ELF header.
    Header.e_shoff = sizeof(Header);
    const std::vector<ELFYAML::Section> &Sections = Doc.Sections;
    // "+ 4" for
    // - SHT_NULL entry (placed first, i.e. 0'th entry)
    // - symbol table (.symtab) (placed third to last)
    // - string table (.strtab) (placed second to last)
    // - section header string table. (placed last)
    Header.e_shnum = Sections.size() + 4;
    // Place section header string table last.
    Header.e_shstrndx = Header.e_shnum - 1;
    const unsigned DotStrtabSecNo = Header.e_shnum - 2;
  
    // XXX: This offset is tightly coupled with the order that we write
    // things to `OS`.
    const size_t SectionContentBeginOffset =
        Header.e_ehsize + Header.e_shentsize * Header.e_shnum;
    ContiguousBlobAccumulator CBA(SectionContentBeginOffset);
    SectionNameToIdxMap SN2I;
    for (unsigned i = 0, e = Sections.size(); i != e; ++i) {
      StringRef Name = Sections[i].Name;
      if (Name.empty())
        continue;
      // "+ 1" to take into account the SHT_NULL entry.
      if (SN2I.addName(Name, i + 1)) {
        errs() << "error: Repeated section name: '" << Name
               << "' at YAML section number " << i << ".\n";
        return 1;
      }
    }
  
    ELFState<ELFT> State(Header, CBA, DotStrtabSecNo, SN2I);
  
    StringTableBuilder SHStrTab;
    std::vector<Elf_Shdr> SHeaders;
    {
      // Ensure SHN_UNDEF entry is present. An all-zero section header is a
      // valid SHN_UNDEF entry since SHT_NULL == 0.
      Elf_Shdr SHdr;
      zero(SHdr);
      SHeaders.push_back(SHdr);
    }
    for (unsigned i = 0, e = Sections.size(); i != e; ++i) {
      const ELFYAML::Section &Sec = Sections[i];
      Elf_Shdr SHeader;
      zero(SHeader);
      SHeader.sh_name = SHStrTab.addString(Sec.Name);
      SHeader.sh_type = Sec.Type;
      SHeader.sh_flags = Sec.Flags;
      SHeader.sh_addr = Sec.Address;
  
      Sec.Content.writeAsBinary(CBA.getOSAndAlignedOffset(SHeader.sh_offset));
      SHeader.sh_size = Sec.Content.binary_size();
  
      if (!Sec.Link.empty()) {
        unsigned Index;
        if (SN2I.lookupSection(Sec.Link, Index)) {
          errs() << "error: Unknown section referenced: '" << Sec.Link
                 << "' at YAML section number " << i << ".\n";
          return 1;
        }
        SHeader.sh_link = Index;
      }
      SHeader.sh_info = 0;
      SHeader.sh_addralign = Sec.AddressAlign;
      SHeader.sh_entsize = 0;
      SHeaders.push_back(SHeader);
    }
  
    // .symtab section.
    Elf_Shdr SymtabSHeader;
    zero(SymtabSHeader);
    SymtabSHeader.sh_name = SHStrTab.addString(StringRef(".symtab"));
    handleSymtabSectionHeader<ELFT>(Doc.Symbols, State, SymtabSHeader);
    SHeaders.push_back(SymtabSHeader);
  
    // .strtab string table header.
    Elf_Shdr DotStrTabSHeader;
    zero(DotStrTabSHeader);
    DotStrTabSHeader.sh_name = SHStrTab.addString(StringRef(".strtab"));
    createStringTableSectionHeader(DotStrTabSHeader, State.getStringTable(), CBA);
    SHeaders.push_back(DotStrTabSHeader);
  
    // Section header string table header.
    Elf_Shdr SHStrTabSHeader;
    zero(SHStrTabSHeader);
    createStringTableSectionHeader(SHStrTabSHeader, SHStrTab, CBA);
    SHeaders.push_back(SHStrTabSHeader);
  
    OS.write((const char *)&Header, sizeof(Header));
    writeArrayData(OS, makeArrayRef(SHeaders));
    CBA.writeBlobToStream(OS);
    return 0;
  }
  
  static bool is64Bit(const ELFYAML::Object &Doc) {
    return Doc.Header.Class == ELFYAML::ELF_ELFCLASS(ELF::ELFCLASS64);
  }
  
  static bool isLittleEndian(const ELFYAML::Object &Doc) {
    return Doc.Header.Data == ELFYAML::ELF_ELFDATA(ELF::ELFDATA2LSB);
  }
  
  int yaml2elf(llvm::raw_ostream &Out, llvm::MemoryBuffer *Buf) {
    yaml::Input YIn(Buf->getBuffer());
    ELFYAML::Object Doc;
    YIn >> Doc;
    if (YIn.error()) {
      errs() << "yaml2obj: Failed to parse YAML file!\n";
      return 1;
    }
    using object::ELFType;
    typedef ELFType<support::little, 8, true> LE64;
    typedef ELFType<support::big, 8, true> BE64;
    typedef ELFType<support::little, 4, false> LE32;
    typedef ELFType<support::big, 4, false> BE32;
    if (is64Bit(Doc)) {
      if (isLittleEndian(Doc))
        return writeELF<LE64>(outs(), Doc);
      else
        return writeELF<BE64>(outs(), Doc);
    } else {
      if (isLittleEndian(Doc))
        return writeELF<LE32>(outs(), Doc);
      else
        return writeELF<BE32>(outs(), Doc);
    }
  }
  