text: //===-- RuntimeDyld.cpp - Run-time dynamic linker for MC-JIT ----*- C++ -*-===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // Implementation of the MC-JIT runtime dynamic linker.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/ExecutionEngine/RuntimeDyld.h"
  #include "RuntimeDyldCheckerImpl.h"
  #include "RuntimeDyldCOFF.h"
  #include "RuntimeDyldELF.h"
  #include "RuntimeDyldImpl.h"
  #include "RuntimeDyldMachO.h"
  #include "llvm/Object/ELFObjectFile.h"
  #include "llvm/Object/COFF.h"
  #include "llvm/Support/MathExtras.h"
  #include "llvm/Support/MutexGuard.h"
  
  using namespace llvm;
  using namespace llvm::object;
  
  #define DEBUG_TYPE "dyld"
  
  // Empty out-of-line virtual destructor as the key function.
  RuntimeDyldImpl::~RuntimeDyldImpl() {}
  
  // Pin LoadedObjectInfo's vtables to this file.
  void RuntimeDyld::LoadedObjectInfo::anchor() {}
  
  namespace llvm {
  
  void RuntimeDyldImpl::registerEHFrames() {}
  
  void RuntimeDyldImpl::deregisterEHFrames() {}
  
  #ifndef NDEBUG
  static void dumpSectionMemory(const SectionEntry &S, StringRef State) {
    dbgs() << "----- Contents of section " << S.Name << " " << State << " -----";
  
    if (S.Address == nullptr) {
      dbgs() << "\n          <section not emitted>\n";
      return;
    }
  
    const unsigned ColsPerRow = 16;
  
    uint8_t *DataAddr = S.Address;
    uint64_t LoadAddr = S.LoadAddress;
  
    unsigned StartPadding = LoadAddr & (ColsPerRow - 1);
    unsigned BytesRemaining = S.Size;
  
    if (StartPadding) {
      dbgs() << "\n" << format("0x%016" PRIx64,
                               LoadAddr & ~(uint64_t)(ColsPerRow - 1)) << ":";
      while (StartPadding--)
        dbgs() << "   ";
    }
  
    while (BytesRemaining > 0) {
      if ((LoadAddr & (ColsPerRow - 1)) == 0)
        dbgs() << "\n" << format("0x%016" PRIx64, LoadAddr) << ":";
  
      dbgs() << " " << format("%02x", *DataAddr);
  
      ++DataAddr;
      ++LoadAddr;
      --BytesRemaining;
    }
  
    dbgs() << "\n";
  }
  #endif
  
  // Resolve the relocations for all symbols we currently know about.
  void RuntimeDyldImpl::resolveRelocations() {
    MutexGuard locked(lock);
  
    // First, resolve relocations associated with external symbols.
    resolveExternalSymbols();
  
    // Just iterate over the sections we have and resolve all the relocations
    // in them. Gross overkill, but it gets the job done.
    for (int i = 0, e = Sections.size(); i != e; ++i) {
      // The Section here (Sections[i]) refers to the section in which the
      // symbol for the relocation is located.  The SectionID in the relocation
      // entry provides the section to which the relocation will be applied.
      uint64_t Addr = Sections[i].LoadAddress;
      DEBUG(dbgs() << "Resolving relocations Section #" << i << "\t"
                   << format("%p", (uintptr_t)Addr) << "\n");
      DEBUG(dumpSectionMemory(Sections[i], "before relocations"));
      resolveRelocationList(Relocations[i], Addr);
      DEBUG(dumpSectionMemory(Sections[i], "after relocations"));
      Relocations.erase(i);
    }
  }
  
  void RuntimeDyldImpl::mapSectionAddress(const void *LocalAddress,
                                          uint64_t TargetAddress) {
    MutexGuard locked(lock);
    for (unsigned i = 0, e = Sections.size(); i != e; ++i) {
      if (Sections[i].Address == LocalAddress) {
        reassignSectionAddress(i, TargetAddress);
        return;
      }
    }
    llvm_unreachable("Attempting to remap address of unknown section!");
  }
  
  static std::error_code getOffset(const SymbolRef &Sym, SectionRef Sec,
                                   uint64_t &Result) {
    ErrorOr<uint64_t> AddressOrErr = Sym.getAddress();
    if (std::error_code EC = AddressOrErr.getError())
      return EC;
    Result = *AddressOrErr - Sec.getAddress();
    return std::error_code();
  }
  
  std::pair<unsigned, unsigned>
  RuntimeDyldImpl::loadObjectImpl(const object::ObjectFile &Obj) {
    MutexGuard locked(lock);
  
    // Grab the first Section ID. We'll use this later to construct the underlying
    // range for the returned LoadedObjectInfo.
    unsigned SectionsAddedBeginIdx = Sections.size();
  
    // Save information about our target
    Arch = (Triple::ArchType)Obj.getArch();
    IsTargetLittleEndian = Obj.isLittleEndian();
    setMipsABI(Obj);
  
    // Compute the memory size required to load all sections to be loaded
    // and pass this information to the memory manager
    if (MemMgr.needsToReserveAllocationSpace()) {
      uint64_t CodeSize = 0, DataSizeRO = 0, DataSizeRW = 0;
      computeTotalAllocSize(Obj, CodeSize, DataSizeRO, DataSizeRW);
      MemMgr.reserveAllocationSpace(CodeSize, DataSizeRO, DataSizeRW);
    }
  
    // Used sections from the object file
    ObjSectionToIDMap LocalSections;
  
    // Common symbols requiring allocation, with their sizes and alignments
    CommonSymbolList CommonSymbols;
  
    // Parse symbols
    DEBUG(dbgs() << "Parse symbols:\n");
    for (symbol_iterator I = Obj.symbol_begin(), E = Obj.symbol_end(); I != E;
         ++I) {
      uint32_t Flags = I->getFlags();
  
      bool IsCommon = Flags & SymbolRef::SF_Common;
      if (IsCommon)
        CommonSymbols.push_back(*I);
      else {
        object::SymbolRef::Type SymType = I->getType();
  
        if (SymType == object::SymbolRef::ST_Function ||
            SymType == object::SymbolRef::ST_Data ||
            SymType == object::SymbolRef::ST_Unknown) {
  
          ErrorOr<StringRef> NameOrErr = I->getName();
          Check(NameOrErr.getError());
          StringRef Name = *NameOrErr;
          section_iterator SI = Obj.section_end();
          Check(I->getSection(SI));
          if (SI == Obj.section_end())
            continue;
          uint64_t SectOffset;
          Check(getOffset(*I, *SI, SectOffset));
          StringRef SectionData;
          Check(SI->getContents(SectionData));
          bool IsCode = SI->isText();
          unsigned SectionID =
              findOrEmitSection(Obj, *SI, IsCode, LocalSections);
          DEBUG(dbgs() << "\tType: " << SymType << " Name: " << Name
                       << " SID: " << SectionID << " Offset: "
                       << format("%p", (uintptr_t)SectOffset)
                       << " flags: " << Flags << "\n");
          JITSymbolFlags RTDyldSymFlags = JITSymbolFlags::None;
          if (Flags & SymbolRef::SF_Weak)
            RTDyldSymFlags |= JITSymbolFlags::Weak;
          if (Flags & SymbolRef::SF_Exported)
            RTDyldSymFlags |= JITSymbolFlags::Exported;
          GlobalSymbolTable[Name] =
            SymbolTableEntry(SectionID, SectOffset, RTDyldSymFlags);
        }
      }
    }
  
    // Allocate common symbols
    emitCommonSymbols(Obj, CommonSymbols);
  
    // Parse and process relocations
    DEBUG(dbgs() << "Parse relocations:\n");
    for (section_iterator SI = Obj.section_begin(), SE = Obj.section_end();
         SI != SE; ++SI) {
      unsigned SectionID = 0;
      StubMap Stubs;
      section_iterator RelocatedSection = SI->getRelocatedSection();
  
      if (RelocatedSection == SE)
        continue;
  
      relocation_iterator I = SI->relocation_begin();
      relocation_iterator E = SI->relocation_end();
  
      if (I == E && !ProcessAllSections)
        continue;
  
      bool IsCode = RelocatedSection->isText();
      SectionID =
          findOrEmitSection(Obj, *RelocatedSection, IsCode, LocalSections);
      DEBUG(dbgs() << "\tSectionID: " << SectionID << "\n");
  
      for (; I != E;)
        I = processRelocationRef(SectionID, I, Obj, LocalSections, Stubs);
  
      // If there is an attached checker, notify it about the stubs for this
      // section so that they can be verified.
      if (Checker)
        Checker->registerStubMap(Obj.getFileName(), SectionID, Stubs);
    }
  
    // Give the subclasses a chance to tie-up any loose ends.
    finalizeLoad(Obj, LocalSections);
  
    unsigned SectionsAddedEndIdx = Sections.size();
  
    return std::make_pair(SectionsAddedBeginIdx, SectionsAddedEndIdx);
  }
  
  // A helper method for computeTotalAllocSize.
  // Computes the memory size required to allocate sections with the given sizes,
  // assuming that all sections are allocated with the given alignment
  static uint64_t
  computeAllocationSizeForSections(std::vector<uint64_t> &SectionSizes,
                                   uint64_t Alignment) {
    uint64_t TotalSize = 0;
    for (size_t Idx = 0, Cnt = SectionSizes.size(); Idx < Cnt; Idx++) {
      uint64_t AlignedSize =
          (SectionSizes[Idx] + Alignment - 1) / Alignment * Alignment;
      TotalSize += AlignedSize;
    }
    return TotalSize;
  }
  
  static bool isRequiredForExecution(const SectionRef Section) {
    const ObjectFile *Obj = Section.getObject();
    if (isa<object::ELFObjectFileBase>(Obj))
      return ELFSectionRef(Section).getFlags() & ELF::SHF_ALLOC;
    if (auto *COFFObj = dyn_cast<object::COFFObjectFile>(Obj)) {
      const coff_section *CoffSection = COFFObj->getCOFFSection(Section);
      // Avoid loading zero-sized COFF sections.
      // In PE files, VirtualSize gives the section size, and SizeOfRawData
      // may be zero for sections with content. In Obj files, SizeOfRawData 
      // gives the section size, and VirtualSize is always zero. Hence
      // the need to check for both cases below.
      bool HasContent = (CoffSection->VirtualSize > 0) 
        || (CoffSection->SizeOfRawData > 0);
      bool IsDiscardable = CoffSection->Characteristics &
        (COFF::IMAGE_SCN_MEM_DISCARDABLE | COFF::IMAGE_SCN_LNK_INFO);
      return HasContent && !IsDiscardable;
    }
    
    assert(isa<MachOObjectFile>(Obj));
    return true;
  }
  
  static bool isReadOnlyData(const SectionRef Section) {
    const ObjectFile *Obj = Section.getObject();
    if (isa<object::ELFObjectFileBase>(Obj))
      return !(ELFSectionRef(Section).getFlags() &
               (ELF::SHF_WRITE | ELF::SHF_EXECINSTR));
    if (auto *COFFObj = dyn_cast<object::COFFObjectFile>(Obj))
      return ((COFFObj->getCOFFSection(Section)->Characteristics &
               (COFF::IMAGE_SCN_CNT_INITIALIZED_DATA
               | COFF::IMAGE_SCN_MEM_READ
               | COFF::IMAGE_SCN_MEM_WRITE))
               ==
               (COFF::IMAGE_SCN_CNT_INITIALIZED_DATA
               | COFF::IMAGE_SCN_MEM_READ));
  
    assert(isa<MachOObjectFile>(Obj));
    return false;
  }
  
  static bool isZeroInit(const SectionRef Section) {
    const ObjectFile *Obj = Section.getObject();
    if (isa<object::ELFObjectFileBase>(Obj))
      return ELFSectionRef(Section).getType() == ELF::SHT_NOBITS;
    if (auto *COFFObj = dyn_cast<object::COFFObjectFile>(Obj))
      return COFFObj->getCOFFSection(Section)->Characteristics &
              COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA;
  
    auto *MachO = cast<MachOObjectFile>(Obj);
    unsigned SectionType = MachO->getSectionType(Section);
    return SectionType == MachO::S_ZEROFILL ||
           SectionType == MachO::S_GB_ZEROFILL;
  }
  
  // Compute an upper bound of the memory size that is required to load all
  // sections
  void RuntimeDyldImpl::computeTotalAllocSize(const ObjectFile &Obj,
                                              uint64_t &CodeSize,
                                              uint64_t &DataSizeRO,
                                              uint64_t &DataSizeRW) {
    // Compute the size of all sections required for execution
    std::vector<uint64_t> CodeSectionSizes;
    std::vector<uint64_t> ROSectionSizes;
    std::vector<uint64_t> RWSectionSizes;
    uint64_t MaxAlignment = sizeof(void *);
  
    // Collect sizes of all sections to be loaded;
    // also determine the max alignment of all sections
    for (section_iterator SI = Obj.section_begin(), SE = Obj.section_end();
         SI != SE; ++SI) {
      const SectionRef &Section = *SI;
  
      bool IsRequired = isRequiredForExecution(Section);
  
      // Consider only the sections that are required to be loaded for execution
      if (IsRequired) {
        StringRef Name;
        uint64_t DataSize = Section.getSize();
        uint64_t Alignment64 = Section.getAlignment();
        bool IsCode = Section.isText();
        bool IsReadOnly = isReadOnlyData(Section);
        Check(Section.getName(Name));
        unsigned Alignment = (unsigned)Alignment64 & 0xffffffffL;
  
        uint64_t StubBufSize = computeSectionStubBufSize(Obj, Section);
        uint64_t SectionSize = DataSize + StubBufSize;
  
        // The .eh_frame section (at least on Linux) needs an extra four bytes
        // padded
        // with zeroes added at the end.  For MachO objects, this section has a
        // slightly different name, so this won't have any effect for MachO
        // objects.
        if (Name == ".eh_frame")
          SectionSize += 4;
  
        if (!SectionSize)
          SectionSize = 1;
  
        if (IsCode) {
          CodeSectionSizes.push_back(SectionSize);
        } else if (IsReadOnly) {
          ROSectionSizes.push_back(SectionSize);
        } else {
          RWSectionSizes.push_back(SectionSize);
        }
  
        // update the max alignment
        if (Alignment > MaxAlignment) {
          MaxAlignment = Alignment;
        }
      }
    }
  
    // Compute the size of all common symbols
    uint64_t CommonSize = 0;
    for (symbol_iterator I = Obj.symbol_begin(), E = Obj.symbol_end(); I != E;
         ++I) {
      uint32_t Flags = I->getFlags();
      if (Flags & SymbolRef::SF_Common) {
        // Add the common symbols to a list.  We'll allocate them all below.
        uint64_t Size = I->getCommonSize();
        CommonSize += Size;
      }
    }
    if (CommonSize != 0) {
      RWSectionSizes.push_back(CommonSize);
    }
  
    // Compute the required allocation space for each different type of sections
    // (code, read-only data, read-write data) assuming that all sections are
    // allocated with the max alignment. Note that we cannot compute with the
    // individual alignments of the sections, because then the required size
    // depends on the order, in which the sections are allocated.
    CodeSize = computeAllocationSizeForSections(CodeSectionSizes, MaxAlignment);
    DataSizeRO = computeAllocationSizeForSections(ROSectionSizes, MaxAlignment);
    DataSizeRW = computeAllocationSizeForSections(RWSectionSizes, MaxAlignment);
  }
  
  // compute stub buffer size for the given section
  unsigned RuntimeDyldImpl::computeSectionStubBufSize(const ObjectFile &Obj,
                                                      const SectionRef &Section) {
    unsigned StubSize = getMaxStubSize();
    if (StubSize == 0) {
      return 0;
    }
    // FIXME: this is an inefficient way to handle this. We should computed the
    // necessary section allocation size in loadObject by walking all the sections
    // once.
    unsigned StubBufSize = 0;
    for (section_iterator SI = Obj.section_begin(), SE = Obj.section_end();
         SI != SE; ++SI) {
      section_iterator RelSecI = SI->getRelocatedSection();
      if (!(RelSecI == Section))
        continue;
  
      for (const RelocationRef &Reloc : SI->relocations()) {
        (void)Reloc;
        StubBufSize += StubSize;
      }
    }
  
    // Get section data size and alignment
    uint64_t DataSize = Section.getSize();
    uint64_t Alignment64 = Section.getAlignment();
  
    // Add stubbuf size alignment
    unsigned Alignment = (unsigned)Alignment64 & 0xffffffffL;
    unsigned StubAlignment = getStubAlignment();
    unsigned EndAlignment = (DataSize | Alignment) & -(DataSize | Alignment);
    if (StubAlignment > EndAlignment)
      StubBufSize += StubAlignment - EndAlignment;
    return StubBufSize;
  }
  
  uint64_t RuntimeDyldImpl::readBytesUnaligned(uint8_t *Src,
                                               unsigned Size) const {
    uint64_t Result = 0;
    if (IsTargetLittleEndian) {
      Src += Size - 1;
      while (Size--)
        Result = (Result << 8) | *Src--;
    } else
      while (Size--)
        Result = (Result << 8) | *Src++;
  
    return Result;
  }
  
  void RuntimeDyldImpl::writeBytesUnaligned(uint64_t Value, uint8_t *Dst,
                                            unsigned Size) const {
    if (IsTargetLittleEndian) {
      while (Size--) {
        *Dst++ = Value & 0xFF;
        Value >>= 8;
      }
    } else {
      Dst += Size - 1;
      while (Size--) {
        *Dst-- = Value & 0xFF;
        Value >>= 8;
      }
    }
  }
  
  void RuntimeDyldImpl::emitCommonSymbols(const ObjectFile &Obj,
                                          CommonSymbolList &CommonSymbols) {
    if (CommonSymbols.empty())
      return;
  
    uint64_t CommonSize = 0;
    CommonSymbolList SymbolsToAllocate;
  
    DEBUG(dbgs() << "Processing common symbols...\n");
  
    for (const auto &Sym : CommonSymbols) {
      ErrorOr<StringRef> NameOrErr = Sym.getName();
      Check(NameOrErr.getError());
      StringRef Name = *NameOrErr;
  
      // Skip common symbols already elsewhere.
      if (GlobalSymbolTable.count(Name) ||
          Resolver.findSymbolInLogicalDylib(Name)) {
        DEBUG(dbgs() << "\tSkipping already emitted common symbol '" << Name
                     << "'\n");
        continue;
      }
  
      uint32_t Align = Sym.getAlignment();
      uint64_t Size = Sym.getCommonSize();
  
      CommonSize += Align + Size;
      SymbolsToAllocate.push_back(Sym);
    }
  
    // Allocate memory for the section
    unsigned SectionID = Sections.size();
    uint8_t *Addr = MemMgr.allocateDataSection(CommonSize, sizeof(void *),
                                               SectionID, StringRef(), false);
    if (!Addr)
      report_fatal_error("Unable to allocate memory for common symbols!");
    uint64_t Offset = 0;
    Sections.push_back(SectionEntry("<common symbols>", Addr, CommonSize, 0));
    memset(Addr, 0, CommonSize);
  
    DEBUG(dbgs() << "emitCommonSection SectionID: " << SectionID << " new addr: "
                 << format("%p", Addr) << " DataSize: " << CommonSize << "\n");
  
    // Assign the address of each symbol
    for (auto &Sym : SymbolsToAllocate) {
      uint32_t Align = Sym.getAlignment();
      uint64_t Size = Sym.getCommonSize();
      ErrorOr<StringRef> NameOrErr = Sym.getName();
      Check(NameOrErr.getError());
      StringRef Name = *NameOrErr;
      if (Align) {
        // This symbol has an alignment requirement.
        uint64_t AlignOffset = OffsetToAlignment((uint64_t)Addr, Align);
        Addr += AlignOffset;
        Offset += AlignOffset;
      }
      uint32_t Flags = Sym.getFlags();
      JITSymbolFlags RTDyldSymFlags = JITSymbolFlags::None;
      if (Flags & SymbolRef::SF_Weak)
        RTDyldSymFlags |= JITSymbolFlags::Weak;
      if (Flags & SymbolRef::SF_Exported)
        RTDyldSymFlags |= JITSymbolFlags::Exported;
      DEBUG(dbgs() << "Allocating common symbol " << Name << " address "
                   << format("%p", Addr) << "\n");
      GlobalSymbolTable[Name] =
        SymbolTableEntry(SectionID, Offset, RTDyldSymFlags);
      Offset += Size;
      Addr += Size;
    }
  }
  
  unsigned RuntimeDyldImpl::emitSection(const ObjectFile &Obj,
                                        const SectionRef &Section, bool IsCode) {
  
    StringRef data;
    uint64_t Alignment64 = Section.getAlignment();
  
    unsigned Alignment = (unsigned)Alignment64 & 0xffffffffL;
    unsigned PaddingSize = 0;
    unsigned StubBufSize = 0;
    StringRef Name;
    bool IsRequired = isRequiredForExecution(Section);
    bool IsVirtual = Section.isVirtual();
    bool IsZeroInit = isZeroInit(Section);
    bool IsReadOnly = isReadOnlyData(Section);
    uint64_t DataSize = Section.getSize();
    Check(Section.getName(Name));
  
    StubBufSize = computeSectionStubBufSize(Obj, Section);
  
    // The .eh_frame section (at least on Linux) needs an extra four bytes padded
    // with zeroes added at the end.  For MachO objects, this section has a
    // slightly different name, so this won't have any effect for MachO objects.
    if (Name == ".eh_frame")
      PaddingSize = 4;
  
    uintptr_t Allocate;
    unsigned SectionID = Sections.size();
    uint8_t *Addr;
    const char *pData = nullptr;
  
    // In either case, set the location of the unrelocated section in memory,
    // since we still process relocations for it even if we're not applying them.
    Check(Section.getContents(data));
    // Virtual sections have no data in the object image, so leave pData = 0
    if (!IsVirtual)
      pData = data.data();
  
    // Some sections, such as debug info, don't need to be loaded for execution.
    // Leave those where they are.
    if (IsRequired) {
      Allocate = DataSize + PaddingSize + StubBufSize;
      if (!Allocate)
        Allocate = 1;
      Addr = IsCode ? MemMgr.allocateCodeSection(Allocate, Alignment, SectionID,
                                                 Name)
                    : MemMgr.allocateDataSection(Allocate, Alignment, SectionID,
                                                 Name, IsReadOnly);
      if (!Addr)
        report_fatal_error("Unable to allocate section memory!");
  
      // Zero-initialize or copy the data from the image
      if (IsZeroInit || IsVirtual)
        memset(Addr, 0, DataSize);
      else
        memcpy(Addr, pData, DataSize);
  
      // Fill in any extra bytes we allocated for padding
      if (PaddingSize != 0) {
        memset(Addr + DataSize, 0, PaddingSize);
        // Update the DataSize variable so that the stub offset is set correctly.
        DataSize += PaddingSize;
      }
  
      DEBUG(dbgs() << "emitSection SectionID: " << SectionID << " Name: " << Name
                   << " obj addr: " << format("%p", pData)
                   << " new addr: " << format("%p", Addr)
                   << " DataSize: " << DataSize << " StubBufSize: " << StubBufSize
                   << " Allocate: " << Allocate << "\n");
    } else {
      // Even if we didn't load the section, we need to record an entry for it
      // to handle later processing (and by 'handle' I mean don't do anything
      // with these sections).
      Allocate = 0;
      Addr = nullptr;
      DEBUG(dbgs() << "emitSection SectionID: " << SectionID << " Name: " << Name
                   << " obj addr: " << format("%p", data.data()) << " new addr: 0"
                   << " DataSize: " << DataSize << " StubBufSize: " << StubBufSize
                   << " Allocate: " << Allocate << "\n");
    }
  
    Sections.push_back(SectionEntry(Name, Addr, DataSize, (uintptr_t)pData));
  
    if (Checker)
      Checker->registerSection(Obj.getFileName(), SectionID);
  
    return SectionID;
  }
  
  unsigned RuntimeDyldImpl::findOrEmitSection(const ObjectFile &Obj,
                                              const SectionRef &Section,
                                              bool IsCode,
                                              ObjSectionToIDMap &LocalSections) {
  
    unsigned SectionID = 0;
    ObjSectionToIDMap::iterator i = LocalSections.find(Section);
    if (i != LocalSections.end())
      SectionID = i->second;
    else {
      SectionID = emitSection(Obj, Section, IsCode);
      LocalSections[Section] = SectionID;
    }
    return SectionID;
  }
  
  void RuntimeDyldImpl::addRelocationForSection(const RelocationEntry &RE,
                                                unsigned SectionID) {
    Relocations[SectionID].push_back(RE);
  }
  
  void RuntimeDyldImpl::addRelocationForSymbol(const RelocationEntry &RE,
                                               StringRef SymbolName) {
    // Relocation by symbol.  If the symbol is found in the global symbol table,
    // create an appropriate section relocation.  Otherwise, add it to
    // ExternalSymbolRelocations.
    RTDyldSymbolTable::const_iterator Loc = GlobalSymbolTable.find(SymbolName);
    if (Loc == GlobalSymbolTable.end()) {
      ExternalSymbolRelocations[SymbolName].push_back(RE);
    } else {
      // Copy the RE since we want to modify its addend.
      RelocationEntry RECopy = RE;
      const auto &SymInfo = Loc->second;
      RECopy.Addend += SymInfo.getOffset();
      Relocations[SymInfo.getSectionID()].push_back(RECopy);
    }
  }
  
  uint8_t *RuntimeDyldImpl::createStubFunction(uint8_t *Addr,
                                               unsigned AbiVariant) {
    if (Arch == Triple::aarch64 || Arch == Triple::aarch64_be) {
      // This stub has to be able to access the full address space,
      // since symbol lookup won't necessarily find a handy, in-range,
      // PLT stub for functions which could be anywhere.
      // Stub can use ip0 (== x16) to calculate address
      writeBytesUnaligned(0xd2e00010, Addr,    4); // movz ip0, #:abs_g3:<addr>
      writeBytesUnaligned(0xf2c00010, Addr+4,  4); // movk ip0, #:abs_g2_nc:<addr>
      writeBytesUnaligned(0xf2a00010, Addr+8,  4); // movk ip0, #:abs_g1_nc:<addr>
      writeBytesUnaligned(0xf2800010, Addr+12, 4); // movk ip0, #:abs_g0_nc:<addr>
      writeBytesUnaligned(0xd61f0200, Addr+16, 4); // br ip0
  
      return Addr;
    } else if (Arch == Triple::arm || Arch == Triple::armeb) {
      // TODO: There is only ARM far stub now. We should add the Thumb stub,
      // and stubs for branches Thumb - ARM and ARM - Thumb.
      writeBytesUnaligned(0xe51ff004, Addr, 4); // ldr pc,<label>
      return Addr + 4;
    } else if (IsMipsO32ABI) {
      // 0:   3c190000        lui     t9,%hi(addr).
      // 4:   27390000        addiu   t9,t9,%lo(addr).
      // 8:   03200008        jr      t9.
      // c:   00000000        nop.
      const unsigned LuiT9Instr = 0x3c190000, AdduiT9Instr = 0x27390000;
      const unsigned JrT9Instr = 0x03200008, NopInstr = 0x0;
  
      writeBytesUnaligned(LuiT9Instr, Addr, 4);
      writeBytesUnaligned(AdduiT9Instr, Addr+4, 4);
      writeBytesUnaligned(JrT9Instr, Addr+8, 4);
      writeBytesUnaligned(NopInstr, Addr+12, 4);
      return Addr;
    } else if (Arch == Triple::ppc64 || Arch == Triple::ppc64le) {
      // Depending on which version of the ELF ABI is in use, we need to
      // generate one of two variants of the stub.  They both start with
      // the same sequence to load the target address into r12.
      writeInt32BE(Addr,    0x3D800000); // lis   r12, highest(addr)
      writeInt32BE(Addr+4,  0x618C0000); // ori   r12, higher(addr)
      writeInt32BE(Addr+8,  0x798C07C6); // sldi  r12, r12, 32
      writeInt32BE(Addr+12, 0x658C0000); // oris  r12, r12, h(addr)
      writeInt32BE(Addr+16, 0x618C0000); // ori   r12, r12, l(addr)
      if (AbiVariant == 2) {
        // PowerPC64 stub ELFv2 ABI: The address points to the function itself.
        // The address is already in r12 as required by the ABI.  Branch to it.
        writeInt32BE(Addr+20, 0xF8410018); // std   r2,  24(r1)
        writeInt32BE(Addr+24, 0x7D8903A6); // mtctr r12
        writeInt32BE(Addr+28, 0x4E800420); // bctr
      } else {
        // PowerPC64 stub ELFv1 ABI: The address points to a function descriptor.
        // Load the function address on r11 and sets it to control register. Also
        // loads the function TOC in r2 and environment pointer to r11.
        writeInt32BE(Addr+20, 0xF8410028); // std   r2,  40(r1)
        writeInt32BE(Addr+24, 0xE96C0000); // ld    r11, 0(r12)
        writeInt32BE(Addr+28, 0xE84C0008); // ld    r2,  0(r12)
        writeInt32BE(Addr+32, 0x7D6903A6); // mtctr r11
        writeInt32BE(Addr+36, 0xE96C0010); // ld    r11, 16(r2)
        writeInt32BE(Addr+40, 0x4E800420); // bctr
      }
      return Addr;
    } else if (Arch == Triple::systemz) {
      writeInt16BE(Addr,    0xC418);     // lgrl %r1,.+8
      writeInt16BE(Addr+2,  0x0000);
      writeInt16BE(Addr+4,  0x0004);
      writeInt16BE(Addr+6,  0x07F1);     // brc 15,%r1
      // 8-byte address stored at Addr + 8
      return Addr;
    } else if (Arch == Triple::x86_64) {
      *Addr      = 0xFF; // jmp
      *(Addr+1)  = 0x25; // rip
      // 32-bit PC-relative address of the GOT entry will be stored at Addr+2
    } else if (Arch == Triple::x86) {
      *Addr      = 0xE9; // 32-bit pc-relative jump.
    }
    return Addr;
  }
  
  // Assign an address to a symbol name and resolve all the relocations
  // associated with it.
  void RuntimeDyldImpl::reassignSectionAddress(unsigned SectionID,
                                               uint64_t Addr) {
    // The address to use for relocation resolution is not
    // the address of the local section buffer. We must be doing
    // a remote execution environment of some sort. Relocations can't
    // be applied until all the sections have been moved.  The client must
    // trigger this with a call to MCJIT::finalize() or
    // RuntimeDyld::resolveRelocations().
    //
    // Addr is a uint64_t because we can't assume the pointer width
    // of the target is the same as that of the host. Just use a generic
    // "big enough" type.
    DEBUG(dbgs() << "Reassigning address for section "
                 << SectionID << " (" << Sections[SectionID].Name << "): "
                 << format("0x%016" PRIx64, Sections[SectionID].LoadAddress) << " -> "
                 << format("0x%016" PRIx64, Addr) << "\n");
    Sections[SectionID].LoadAddress = Addr;
  }
  
  void RuntimeDyldImpl::resolveRelocationList(const RelocationList &Relocs,
                                              uint64_t Value) {
    for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
      const RelocationEntry &RE = Relocs[i];
      // Ignore relocations for sections that were not loaded
      if (Sections[RE.SectionID].Address == nullptr)
        continue;
      resolveRelocation(RE, Value);
    }
  }
  
  void RuntimeDyldImpl::resolveExternalSymbols() {
    while (!ExternalSymbolRelocations.empty()) {
      StringMap<RelocationList>::iterator i = ExternalSymbolRelocations.begin();
  
      StringRef Name = i->first();
      if (Name.size() == 0) {
        // This is an absolute symbol, use an address of zero.
        DEBUG(dbgs() << "Resolving absolute relocations."
                     << "\n");
        RelocationList &Relocs = i->second;
        resolveRelocationList(Relocs, 0);
      } else {
        uint64_t Addr = 0;
        RTDyldSymbolTable::const_iterator Loc = GlobalSymbolTable.find(Name);
        if (Loc == GlobalSymbolTable.end()) {
          // This is an external symbol, try to get its address from the symbol
          // resolver.
          Addr = Resolver.findSymbol(Name.data()).getAddress();
          // The call to getSymbolAddress may have caused additional modules to
          // be loaded, which may have added new entries to the
          // ExternalSymbolRelocations map.  Consquently, we need to update our
          // iterator.  This is also why retrieval of the relocation list
          // associated with this symbol is deferred until below this point.
          // New entries may have been added to the relocation list.
          i = ExternalSymbolRelocations.find(Name);
        } else {
          // We found the symbol in our global table.  It was probably in a
          // Module that we loaded previously.
          const auto &SymInfo = Loc->second;
          Addr = getSectionLoadAddress(SymInfo.getSectionID()) +
                 SymInfo.getOffset();
        }
  
        // FIXME: Implement error handling that doesn't kill the host program!
        if (!Addr)
          report_fatal_error("Program used external function '" + Name +
                             "' which could not be resolved!");
  
        // If Resolver returned UINT64_MAX, the client wants to handle this symbol
        // manually and we shouldn't resolve its relocations.
        if (Addr != UINT64_MAX) {
          DEBUG(dbgs() << "Resolving relocations Name: " << Name << "\t"
                       << format("0x%lx", Addr) << "\n");
          // This list may have been updated when we called getSymbolAddress, so
          // don't change this code to get the list earlier.
          RelocationList &Relocs = i->second;
          resolveRelocationList(Relocs, Addr);
        }
      }
  
      ExternalSymbolRelocations.erase(i);
    }
  }
  
  //===----------------------------------------------------------------------===//
  // RuntimeDyld class implementation
  
  uint64_t RuntimeDyld::LoadedObjectInfo::getSectionLoadAddress(
                                                    StringRef SectionName) const {
    for (unsigned I = BeginIdx; I != EndIdx; ++I)
      if (RTDyld.Sections[I].Name == SectionName)
        return RTDyld.Sections[I].LoadAddress;
  
    return 0;
  }
  
  void RuntimeDyld::MemoryManager::anchor() {}
  void RuntimeDyld::SymbolResolver::anchor() {}
  
  RuntimeDyld::RuntimeDyld(RuntimeDyld::MemoryManager &MemMgr,
                           RuntimeDyld::SymbolResolver &Resolver)
      : MemMgr(MemMgr), Resolver(Resolver) {
    // FIXME: There's a potential issue lurking here if a single instance of
    // RuntimeDyld is used to load multiple objects.  The current implementation
    // associates a single memory manager with a RuntimeDyld instance.  Even
    // though the public class spawns a new 'impl' instance for each load,
    // they share a single memory manager.  This can become a problem when page
    // permissions are applied.
    Dyld = nullptr;
    ProcessAllSections = false;
    Checker = nullptr;
  }
  
  RuntimeDyld::~RuntimeDyld() {}
  
  static std::unique_ptr<RuntimeDyldCOFF>
  createRuntimeDyldCOFF(Triple::ArchType Arch, RuntimeDyld::MemoryManager &MM,
                        RuntimeDyld::SymbolResolver &Resolver,
                        bool ProcessAllSections, RuntimeDyldCheckerImpl *Checker) {
    std::unique_ptr<RuntimeDyldCOFF> Dyld =
      RuntimeDyldCOFF::create(Arch, MM, Resolver);
    Dyld->setProcessAllSections(ProcessAllSections);
    Dyld->setRuntimeDyldChecker(Checker);
    return Dyld;
  }
  
  static std::unique_ptr<RuntimeDyldELF>
  createRuntimeDyldELF(RuntimeDyld::MemoryManager &MM,
                       RuntimeDyld::SymbolResolver &Resolver,
                       bool ProcessAllSections, RuntimeDyldCheckerImpl *Checker) {
    std::unique_ptr<RuntimeDyldELF> Dyld(new RuntimeDyldELF(MM, Resolver));
    Dyld->setProcessAllSections(ProcessAllSections);
    Dyld->setRuntimeDyldChecker(Checker);
    return Dyld;
  }
  
  static std::unique_ptr<RuntimeDyldMachO>
  createRuntimeDyldMachO(Triple::ArchType Arch, RuntimeDyld::MemoryManager &MM,
                         RuntimeDyld::SymbolResolver &Resolver,
                         bool ProcessAllSections,
                         RuntimeDyldCheckerImpl *Checker) {
    std::unique_ptr<RuntimeDyldMachO> Dyld =
      RuntimeDyldMachO::create(Arch, MM, Resolver);
    Dyld->setProcessAllSections(ProcessAllSections);
    Dyld->setRuntimeDyldChecker(Checker);
    return Dyld;
  }
  
  std::unique_ptr<RuntimeDyld::LoadedObjectInfo>
  RuntimeDyld::loadObject(const ObjectFile &Obj) {
    if (!Dyld) {
      if (Obj.isELF())
        Dyld = createRuntimeDyldELF(MemMgr, Resolver, ProcessAllSections, Checker);
      else if (Obj.isMachO())
        Dyld = createRuntimeDyldMachO(
                 static_cast<Triple::ArchType>(Obj.getArch()), MemMgr, Resolver,
                 ProcessAllSections, Checker);
      else if (Obj.isCOFF())
        Dyld = createRuntimeDyldCOFF(
                 static_cast<Triple::ArchType>(Obj.getArch()), MemMgr, Resolver,
                 ProcessAllSections, Checker);
      else
        report_fatal_error("Incompatible object format!");
    }
  
    if (!Dyld->isCompatibleFile(Obj))
      report_fatal_error("Incompatible object format!");
  
    return Dyld->loadObject(Obj);
  }
  
  void *RuntimeDyld::getSymbolLocalAddress(StringRef Name) const {
    if (!Dyld)
      return nullptr;
    return Dyld->getSymbolLocalAddress(Name);
  }
  
  RuntimeDyld::SymbolInfo RuntimeDyld::getSymbol(StringRef Name) const {
    if (!Dyld)
      return nullptr;
    return Dyld->getSymbol(Name);
  }
  
  void RuntimeDyld::resolveRelocations() { Dyld->resolveRelocations(); }
  
  void RuntimeDyld::reassignSectionAddress(unsigned SectionID, uint64_t Addr) {
    Dyld->reassignSectionAddress(SectionID, Addr);
  }
  
  void RuntimeDyld::mapSectionAddress(const void *LocalAddress,
                                      uint64_t TargetAddress) {
    Dyld->mapSectionAddress(LocalAddress, TargetAddress);
  }
  
  bool RuntimeDyld::hasError() { return Dyld->hasError(); }
  
  StringRef RuntimeDyld::getErrorString() { return Dyld->getErrorString(); }
  
  void RuntimeDyld::registerEHFrames() {
    if (Dyld)
      Dyld->registerEHFrames();
  }
  
  void RuntimeDyld::deregisterEHFrames() {
    if (Dyld)
      Dyld->deregisterEHFrames();
  }
  
  } // end namespace llvm
  