llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldImpl.h - toolchain/llvm-project - Gitiles

 //===-- RuntimeDyldImpl.h - Run-time dynamic linker for MC-JIT --*- C++ -*-===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 //
 // Interface for the implementations of runtime dynamic linker facilities.
 //
 //===----------------------------------------------------------------------===//

 #ifndef LLVM_LIB_EXECUTIONENGINE_RUNTIMEDYLD_RUNTIMEDYLDIMPL_H
 #define LLVM_LIB_EXECUTIONENGINE_RUNTIMEDYLD_RUNTIMEDYLDIMPL_H

 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/ExecutionEngine/RTDyldMemoryManager.h"
 #include "llvm/ExecutionEngine/RuntimeDyld.h"
 #include "llvm/ExecutionEngine/RuntimeDyldChecker.h"
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/Mutex.h"
 #include "llvm/Support/SwapByteOrder.h"
 #include <map>
 #include <system_error>
 #include <unordered_map>

 using namespace llvm;
 using namespace llvm::object;

 namespace llvm {

 class Twine;

 #define UNIMPLEMENTED_RELOC(RelType) \
   case RelType: \
     return make_error<RuntimeDyldError>("Unimplemented relocation: " #RelType)

 /// SectionEntry - represents a section emitted into memory by the dynamic
 /// linker.
 class SectionEntry {
   /// Name - section name.
   std::string Name;

   /// Address - address in the linker's memory where the section resides.
   uint8_t *Address;

   /// Size - section size. Doesn't include the stubs.
   size_t Size;

   /// LoadAddress - the address of the section in the target process's memory.
   /// Used for situations in which JIT-ed code is being executed in the address
   /// space of a separate process.  If the code executes in the same address
   /// space where it was JIT-ed, this just equals Address.
   uint64_t LoadAddress;

   /// StubOffset - used for architectures with stub functions for far
   /// relocations (like ARM).
   uintptr_t StubOffset;

   /// The total amount of space allocated for this section.  This includes the
   /// section size and the maximum amount of space that the stubs can occupy.
   size_t AllocationSize;

   /// ObjAddress - address of the section in the in-memory object file.  Used
   /// for calculating relocations in some object formats (like MachO).
   uintptr_t ObjAddress;

 public:
   SectionEntry(StringRef name, uint8_t *address, size_t size,
                size_t allocationSize, uintptr_t objAddress)
       : Name(name), Address(address), Size(size),
         LoadAddress(reinterpret_cast<uintptr_t>(address)), StubOffset(size),
         AllocationSize(allocationSize), ObjAddress(objAddress) {
     // AllocationSize is used only in asserts, prevent an "unused private field"
     // warning:
     (void)AllocationSize;
   }

   StringRef getName() const { return Name; }

   uint8_t *getAddress() const { return Address; }

   /// Return the address of this section with an offset.
   uint8_t *getAddressWithOffset(unsigned OffsetBytes) const {
     assert(OffsetBytes <= AllocationSize && "Offset out of bounds!");
     return Address + OffsetBytes;
   }

   size_t getSize() const { return Size; }

   uint64_t getLoadAddress() const { return LoadAddress; }
   void setLoadAddress(uint64_t LA) { LoadAddress = LA; }

   /// Return the load address of this section with an offset.
   uint64_t getLoadAddressWithOffset(unsigned OffsetBytes) const {
     assert(OffsetBytes <= AllocationSize && "Offset out of bounds!");
     return LoadAddress + OffsetBytes;
   }

   uintptr_t getStubOffset() const { return StubOffset; }

   void advanceStubOffset(unsigned StubSize) {
     StubOffset += StubSize;
     assert(StubOffset <= AllocationSize && "Not enough space allocated!");
   }

   uintptr_t getObjAddress() const { return ObjAddress; }
 };

 /// RelocationEntry - used to represent relocations internally in the dynamic
 /// linker.
 class RelocationEntry {
 public:
   /// SectionID - the section this relocation points to.
   unsigned SectionID;

   /// Offset - offset into the section.
   uint64_t Offset;

   /// RelType - relocation type.
   uint32_t RelType;

   /// Addend - the relocation addend encoded in the instruction itself.  Also
   /// used to make a relocation section relative instead of symbol relative.
   int64_t Addend;

   struct SectionPair {
       uint32_t SectionA;
       uint32_t SectionB;
   };

   /// SymOffset - Section offset of the relocation entry's symbol (used for GOT
   /// lookup).
   union {
     uint64_t SymOffset;
     SectionPair Sections;
   };

   /// True if this is a PCRel relocation (MachO specific).
   bool IsPCRel;

   /// The size of this relocation (MachO specific).
   unsigned Size;

   // ARM (MachO and COFF) specific.
   bool IsTargetThumbFunc = false;

   RelocationEntry(unsigned id, uint64_t offset, uint32_t type, int64_t addend)
       : SectionID(id), Offset(offset), RelType(type), Addend(addend),
         SymOffset(0), IsPCRel(false), Size(0), IsTargetThumbFunc(false) {}

   RelocationEntry(unsigned id, uint64_t offset, uint32_t type, int64_t addend,
                   uint64_t symoffset)
       : SectionID(id), Offset(offset), RelType(type), Addend(addend),
         SymOffset(symoffset), IsPCRel(false), Size(0),
         IsTargetThumbFunc(false) {}

   RelocationEntry(unsigned id, uint64_t offset, uint32_t type, int64_t addend,
                   bool IsPCRel, unsigned Size)
       : SectionID(id), Offset(offset), RelType(type), Addend(addend),
         SymOffset(0), IsPCRel(IsPCRel), Size(Size), IsTargetThumbFunc(false) {}

   RelocationEntry(unsigned id, uint64_t offset, uint32_t type, int64_t addend,
                   unsigned SectionA, uint64_t SectionAOffset, unsigned SectionB,
                   uint64_t SectionBOffset, bool IsPCRel, unsigned Size)
       : SectionID(id), Offset(offset), RelType(type),
         Addend(SectionAOffset - SectionBOffset + addend), IsPCRel(IsPCRel),
         Size(Size), IsTargetThumbFunc(false) {
     Sections.SectionA = SectionA;
     Sections.SectionB = SectionB;
   }

   RelocationEntry(unsigned id, uint64_t offset, uint32_t type, int64_t addend,
                   unsigned SectionA, uint64_t SectionAOffset, unsigned SectionB,
                   uint64_t SectionBOffset, bool IsPCRel, unsigned Size,
                   bool IsTargetThumbFunc)
       : SectionID(id), Offset(offset), RelType(type),
         Addend(SectionAOffset - SectionBOffset + addend), IsPCRel(IsPCRel),
         Size(Size), IsTargetThumbFunc(IsTargetThumbFunc) {
     Sections.SectionA = SectionA;
     Sections.SectionB = SectionB;
   }
 };

 class RelocationValueRef {
 public:
   unsigned SectionID;
   uint64_t Offset;
   int64_t Addend;
   const char *SymbolName;
   bool IsStubThumb = false;
   RelocationValueRef() : SectionID(0), Offset(0), Addend(0),
                          SymbolName(nullptr) {}

   inline bool operator==(const RelocationValueRef &Other) const {
     return SectionID == Other.SectionID && Offset == Other.Offset &&
            Addend == Other.Addend && SymbolName == Other.SymbolName &&
            IsStubThumb == Other.IsStubThumb;
   }
   inline bool operator<(const RelocationValueRef &Other) const {
     if (SectionID != Other.SectionID)
       return SectionID < Other.SectionID;
     if (Offset != Other.Offset)
       return Offset < Other.Offset;
     if (Addend != Other.Addend)
       return Addend < Other.Addend;
     if (IsStubThumb != Other.IsStubThumb)
       return IsStubThumb < Other.IsStubThumb;
     return SymbolName < Other.SymbolName;
   }
 };

 /// Symbol info for RuntimeDyld.
 class SymbolTableEntry {
 public:
   SymbolTableEntry() = default;

   SymbolTableEntry(unsigned SectionID, uint64_t Offset, JITSymbolFlags Flags)
       : Offset(Offset), SectionID(SectionID), Flags(Flags) {}

   unsigned getSectionID() const { return SectionID; }
   uint64_t getOffset() const { return Offset; }
   void setOffset(uint64_t NewOffset) { Offset = NewOffset; }

   JITSymbolFlags getFlags() const { return Flags; }

 private:
   uint64_t Offset = 0;
   unsigned SectionID = 0;
   JITSymbolFlags Flags = JITSymbolFlags::None;
 };

 typedef StringMap<SymbolTableEntry> RTDyldSymbolTable;

 class RuntimeDyldImpl {
   friend class RuntimeDyld::LoadedObjectInfo;
 protected:
   static const unsigned AbsoluteSymbolSection = ~0U;

   // The MemoryManager to load objects into.
   RuntimeDyld::MemoryManager &MemMgr;

   // The symbol resolver to use for external symbols.
   JITSymbolResolver &Resolver;

   // A list of all sections emitted by the dynamic linker.  These sections are
   // referenced in the code by means of their index in this list - SectionID.
   typedef SmallVector<SectionEntry, 64> SectionList;
   SectionList Sections;

   typedef unsigned SID; // Type for SectionIDs
 #define RTDYLD_INVALID_SECTION_ID ((RuntimeDyldImpl::SID)(-1))

   // Keep a map of sections from object file to the SectionID which
   // references it.
   typedef std::map<SectionRef, unsigned> ObjSectionToIDMap;

   // A global symbol table for symbols from all loaded modules.
   RTDyldSymbolTable GlobalSymbolTable;

   // Keep a map of common symbols to their info pairs
   typedef std::vector<SymbolRef> CommonSymbolList;

   // For each symbol, keep a list of relocations based on it. Anytime
   // its address is reassigned (the JIT re-compiled the function, e.g.),
   // the relocations get re-resolved.
   // The symbol (or section) the relocation is sourced from is the Key
   // in the relocation list where it's stored.
   typedef SmallVector<RelocationEntry, 64> RelocationList;
   // Relocations to sections already loaded. Indexed by SectionID which is the
   // source of the address. The target where the address will be written is
   // SectionID/Offset in the relocation itself.
   std::unordered_map<unsigned, RelocationList> Relocations;

   // Relocations to external symbols that are not yet resolved.  Symbols are
   // external when they aren't found in the global symbol table of all loaded
   // modules.  This map is indexed by symbol name.
   StringMap<RelocationList> ExternalSymbolRelocations;


   typedef std::map<RelocationValueRef, uintptr_t> StubMap;

   Triple::ArchType Arch;
   bool IsTargetLittleEndian;
   bool IsMipsO32ABI;
   bool IsMipsN32ABI;
   bool IsMipsN64ABI;

   // True if all sections should be passed to the memory manager, false if only
   // sections containing relocations should be. Defaults to 'false'.
   bool ProcessAllSections;

   // This mutex prevents simultaneously loading objects from two different
   // threads.  This keeps us from having to protect individual data structures
   // and guarantees that section allocation requests to the memory manager
   // won't be interleaved between modules.  It is also used in mapSectionAddress
   // and resolveRelocations to protect write access to internal data structures.
   //
   // loadObject may be called on the same thread during the handling of of
   // processRelocations, and that's OK.  The handling of the relocation lists
   // is written in such a way as to work correctly if new elements are added to
   // the end of the list while the list is being processed.
   sys::Mutex lock;

   using NotifyStubEmittedFunction =
     RuntimeDyld::NotifyStubEmittedFunction;
   NotifyStubEmittedFunction NotifyStubEmitted;

   virtual unsigned getMaxStubSize() const = 0;
   virtual unsigned getStubAlignment() = 0;

   bool HasError;
   std::string ErrorStr;

   void writeInt16BE(uint8_t *Addr, uint16_t Value) {
     if (IsTargetLittleEndian)
       sys::swapByteOrder(Value);
     *Addr       = (Value >> 8) & 0xFF;
     *(Addr + 1) = Value & 0xFF;
   }

   void writeInt32BE(uint8_t *Addr, uint32_t Value) {
     if (IsTargetLittleEndian)
       sys::swapByteOrder(Value);
     *Addr       = (Value >> 24) & 0xFF;
     *(Addr + 1) = (Value >> 16) & 0xFF;
     *(Addr + 2) = (Value >> 8) & 0xFF;
     *(Addr + 3) = Value & 0xFF;
   }

   void writeInt64BE(uint8_t *Addr, uint64_t Value) {
     if (IsTargetLittleEndian)
       sys::swapByteOrder(Value);
     *Addr       = (Value >> 56) & 0xFF;
     *(Addr + 1) = (Value >> 48) & 0xFF;
     *(Addr + 2) = (Value >> 40) & 0xFF;
     *(Addr + 3) = (Value >> 32) & 0xFF;
     *(Addr + 4) = (Value >> 24) & 0xFF;
     *(Addr + 5) = (Value >> 16) & 0xFF;
     *(Addr + 6) = (Value >> 8) & 0xFF;
     *(Addr + 7) = Value & 0xFF;
   }

   virtual void setMipsABI(const ObjectFile &Obj) {
     IsMipsO32ABI = false;
     IsMipsN32ABI = false;
     IsMipsN64ABI = false;
   }

   /// Endian-aware read Read the least significant Size bytes from Src.
   uint64_t readBytesUnaligned(uint8_t *Src, unsigned Size) const;

   /// Endian-aware write. Write the least significant Size bytes from Value to
   /// Dst.
   void writeBytesUnaligned(uint64_t Value, uint8_t *Dst, unsigned Size) const;

   /// Generate JITSymbolFlags from a libObject symbol.
   virtual Expected<JITSymbolFlags> getJITSymbolFlags(const SymbolRef &Sym);

   /// Modify the given target address based on the given symbol flags.
   /// This can be used by subclasses to tweak addresses based on symbol flags,
   /// For example: the MachO/ARM target uses it to set the low bit if the target
   /// is a thumb symbol.
   virtual uint64_t modifyAddressBasedOnFlags(uint64_t Addr,
                                              JITSymbolFlags Flags) const {
     return Addr;
   }

   /// Given the common symbols discovered in the object file, emit a
   /// new section for them and update the symbol mappings in the object and
   /// symbol table.
   Error emitCommonSymbols(const ObjectFile &Obj,
                           CommonSymbolList &CommonSymbols, uint64_t CommonSize,
                           uint32_t CommonAlign);

   /// Emits section data from the object file to the MemoryManager.
   /// \param IsCode if it's true then allocateCodeSection() will be
   ///        used for emits, else allocateDataSection() will be used.
   /// \return SectionID.
   Expected<unsigned> emitSection(const ObjectFile &Obj,
                                  const SectionRef &Section,
                                  bool IsCode);

   /// Find Section in LocalSections. If the secton is not found - emit
   ///        it and store in LocalSections.
   /// \param IsCode if it's true then allocateCodeSection() will be
   ///        used for emmits, else allocateDataSection() will be used.
   /// \return SectionID.
   Expected<unsigned> findOrEmitSection(const ObjectFile &Obj,
                                        const SectionRef &Section, bool IsCode,
                                        ObjSectionToIDMap &LocalSections);

   // Add a relocation entry that uses the given section.
   void addRelocationForSection(const RelocationEntry &RE, unsigned SectionID);

   // Add a relocation entry that uses the given symbol.  This symbol may
   // be found in the global symbol table, or it may be external.
   void addRelocationForSymbol(const RelocationEntry &RE, StringRef SymbolName);

   /// Emits long jump instruction to Addr.
   /// \return Pointer to the memory area for emitting target address.
   uint8_t *createStubFunction(uint8_t *Addr, unsigned AbiVariant = 0);

   /// Resolves relocations from Relocs list with address from Value.
   void resolveRelocationList(const RelocationList &Relocs, uint64_t Value);

   /// A object file specific relocation resolver
   /// \param RE The relocation to be resolved
   /// \param Value Target symbol address to apply the relocation action
   virtual void resolveRelocation(const RelocationEntry &RE, uint64_t Value) = 0;

   /// Parses one or more object file relocations (some object files use
   ///        relocation pairs) and stores it to Relocations or SymbolRelocations
   ///        (this depends on the object file type).
   /// \return Iterator to the next relocation that needs to be parsed.
   virtual Expected<relocation_iterator>
   processRelocationRef(unsigned SectionID, relocation_iterator RelI,
                        const ObjectFile &Obj, ObjSectionToIDMap &ObjSectionToID,
                        StubMap &Stubs) = 0;

   void applyExternalSymbolRelocations(
       const StringMap<JITEvaluatedSymbol> ExternalSymbolMap);

   /// Resolve relocations to external symbols.
   Error resolveExternalSymbols();

   // Compute an upper bound of the memory that is required to load all
   // sections
   Error computeTotalAllocSize(const ObjectFile &Obj,
                               uint64_t &CodeSize, uint32_t &CodeAlign,
                               uint64_t &RODataSize, uint32_t &RODataAlign,
                               uint64_t &RWDataSize, uint32_t &RWDataAlign);

   // Compute GOT size
   unsigned computeGOTSize(const ObjectFile &Obj);

   // Compute the stub buffer size required for a section
   unsigned computeSectionStubBufSize(const ObjectFile &Obj,
                                      const SectionRef &Section);

   // Implementation of the generic part of the loadObject algorithm.
   Expected<ObjSectionToIDMap> loadObjectImpl(const object::ObjectFile &Obj);

   // Return size of Global Offset Table (GOT) entry
   virtual size_t getGOTEntrySize() { return 0; }

   // Return true if the relocation R may require allocating a GOT entry.
   virtual bool relocationNeedsGot(const RelocationRef &R) const {
     return false;
   }

   // Return true if the relocation R may require allocating a stub.
   virtual bool relocationNeedsStub(const RelocationRef &R) const {
     return true;    // Conservative answer
   }

 public:
   RuntimeDyldImpl(RuntimeDyld::MemoryManager &MemMgr,
                   JITSymbolResolver &Resolver)
     : MemMgr(MemMgr), Resolver(Resolver),
       ProcessAllSections(false), HasError(false) {
   }

   virtual ~RuntimeDyldImpl();

   void setProcessAllSections(bool ProcessAllSections) {
     this->ProcessAllSections = ProcessAllSections;
   }

   virtual std::unique_ptr<RuntimeDyld::LoadedObjectInfo>
   loadObject(const object::ObjectFile &Obj) = 0;

   uint64_t getSectionLoadAddress(unsigned SectionID) const {
     return Sections[SectionID].getLoadAddress();
   }

   uint8_t *getSectionAddress(unsigned SectionID) const {
     return Sections[SectionID].getAddress();
   }

   StringRef getSectionContent(unsigned SectionID) const {
     return StringRef(reinterpret_cast<char *>(Sections[SectionID].getAddress()),
                      Sections[SectionID].getStubOffset() + getMaxStubSize());
   }

   uint8_t* getSymbolLocalAddress(StringRef Name) const {
     // FIXME: Just look up as a function for now. Overly simple of course.
     // Work in progress.
     RTDyldSymbolTable::const_iterator pos = GlobalSymbolTable.find(Name);
     if (pos == GlobalSymbolTable.end())
       return nullptr;
     const auto &SymInfo = pos->second;
     // Absolute symbols do not have a local address.
     if (SymInfo.getSectionID() == AbsoluteSymbolSection)
       return nullptr;
     return getSectionAddress(SymInfo.getSectionID()) + SymInfo.getOffset();
   }

   unsigned getSymbolSectionID(StringRef Name) const {
     auto GSTItr = GlobalSymbolTable.find(Name);
     if (GSTItr == GlobalSymbolTable.end())
       return ~0U;
     return GSTItr->second.getSectionID();
   }

   JITEvaluatedSymbol getSymbol(StringRef Name) const {
     // FIXME: Just look up as a function for now. Overly simple of course.
     // Work in progress.
     RTDyldSymbolTable::const_iterator pos = GlobalSymbolTable.find(Name);
     if (pos == GlobalSymbolTable.end())
       return nullptr;
     const auto &SymEntry = pos->second;
     uint64_t SectionAddr = 0;
     if (SymEntry.getSectionID() != AbsoluteSymbolSection)
       SectionAddr = getSectionLoadAddress(SymEntry.getSectionID());
     uint64_t TargetAddr = SectionAddr + SymEntry.getOffset();

     // FIXME: Have getSymbol should return the actual address and the client
     //        modify it based on the flags. This will require clients to be
     //        aware of the target architecture, which we should build
     //        infrastructure for.
     TargetAddr = modifyAddressBasedOnFlags(TargetAddr, SymEntry.getFlags());
     return JITEvaluatedSymbol(TargetAddr, SymEntry.getFlags());
   }

   std::map<StringRef, JITEvaluatedSymbol> getSymbolTable() const {
     std::map<StringRef, JITEvaluatedSymbol> Result;

     for (auto &KV : GlobalSymbolTable) {
       auto SectionID = KV.second.getSectionID();
       uint64_t SectionAddr = 0;
       if (SectionID != AbsoluteSymbolSection)
         SectionAddr = getSectionLoadAddress(SectionID);
       Result[KV.first()] =
         JITEvaluatedSymbol(SectionAddr + KV.second.getOffset(), KV.second.getFlags());
     }

     return Result;
   }

   void resolveRelocations();

   void resolveLocalRelocations();

   static void finalizeAsync(std::unique_ptr<RuntimeDyldImpl> This,
                             unique_function<void(Error)> OnEmitted,
                             std::unique_ptr<MemoryBuffer> UnderlyingBuffer);

   void reassignSectionAddress(unsigned SectionID, uint64_t Addr);

   void mapSectionAddress(const void *LocalAddress, uint64_t TargetAddress);

   // Is the linker in an error state?
   bool hasError() { return HasError; }

   // Mark the error condition as handled and continue.
   void clearError() { HasError = false; }

   // Get the error message.
   StringRef getErrorString() { return ErrorStr; }

   virtual bool isCompatibleFile(const ObjectFile &Obj) const = 0;

   void setNotifyStubEmitted(NotifyStubEmittedFunction NotifyStubEmitted) {
     this->NotifyStubEmitted = std::move(NotifyStubEmitted);
   }

   virtual void registerEHFrames();

   void deregisterEHFrames();

   virtual Error finalizeLoad(const ObjectFile &ObjImg,
                              ObjSectionToIDMap &SectionMap) {
     return Error::success();
   }
 };

 } // end namespace llvm

 #endif
	//===-- RuntimeDyldImpl.h - Run-time dynamic linker for MC-JIT --- C++ --===//
	//
	// 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
	//
	//===----------------------------------------------------------------------===//
	//
	// Interface for the implementations of runtime dynamic linker facilities.
	//
	//===----------------------------------------------------------------------===//

	#ifndef LLVM_LIB_EXECUTIONENGINE_RUNTIMEDYLD_RUNTIMEDYLDIMPL_H
	#define LLVM_LIB_EXECUTIONENGINE_RUNTIMEDYLD_RUNTIMEDYLDIMPL_H

	#include "llvm/ADT/SmallVector.h"
	#include "llvm/ADT/StringMap.h"
	#include "llvm/ADT/Triple.h"
	#include "llvm/ExecutionEngine/RTDyldMemoryManager.h"
	#include "llvm/ExecutionEngine/RuntimeDyld.h"
	#include "llvm/ExecutionEngine/RuntimeDyldChecker.h"
	#include "llvm/Object/ObjectFile.h"
	#include "llvm/Support/Debug.h"
	#include "llvm/Support/ErrorHandling.h"
	#include "llvm/Support/Format.h"
	#include "llvm/Support/Host.h"
	#include "llvm/Support/Mutex.h"
	#include "llvm/Support/SwapByteOrder.h"
	#include <map>
	#include <system_error>
	#include <unordered_map>

	using namespace llvm;
	using namespace llvm::object;

	namespace llvm {

	class Twine;

	#define UNIMPLEMENTED_RELOC(RelType) \
	case RelType: \
	return make_error<RuntimeDyldError>("Unimplemented relocation: " #RelType)

	/// SectionEntry - represents a section emitted into memory by the dynamic
	/// linker.
	class SectionEntry {
	/// Name - section name.
	std::string Name;

	/// Address - address in the linker's memory where the section resides.
	uint8_t *Address;

	/// Size - section size. Doesn't include the stubs.
	size_t Size;

	/// LoadAddress - the address of the section in the target process's memory.
	/// Used for situations in which JIT-ed code is being executed in the address
	/// space of a separate process. If the code executes in the same address
	/// space where it was JIT-ed, this just equals Address.
	uint64_t LoadAddress;

	/// StubOffset - used for architectures with stub functions for far
	/// relocations (like ARM).
	uintptr_t StubOffset;

	/// The total amount of space allocated for this section. This includes the
	/// section size and the maximum amount of space that the stubs can occupy.
	size_t AllocationSize;

	/// ObjAddress - address of the section in the in-memory object file. Used
	/// for calculating relocations in some object formats (like MachO).
	uintptr_t ObjAddress;

	public:
	SectionEntry(StringRef name, uint8_t *address, size_t size,
	size_t allocationSize, uintptr_t objAddress)
	: Name(name), Address(address), Size(size),
	LoadAddress(reinterpret_cast<uintptr_t>(address)), StubOffset(size),
	AllocationSize(allocationSize), ObjAddress(objAddress) {
	// AllocationSize is used only in asserts, prevent an "unused private field"
	// warning:
	(void)AllocationSize;
	}

	StringRef getName() const { return Name; }

	uint8_t *getAddress() const { return Address; }

	/// Return the address of this section with an offset.
	uint8_t *getAddressWithOffset(unsigned OffsetBytes) const {
	assert(OffsetBytes <= AllocationSize && "Offset out of bounds!");
	return Address + OffsetBytes;
	}

	size_t getSize() const { return Size; }

	uint64_t getLoadAddress() const { return LoadAddress; }
	void setLoadAddress(uint64_t LA) { LoadAddress = LA; }

	/// Return the load address of this section with an offset.
	uint64_t getLoadAddressWithOffset(unsigned OffsetBytes) const {
	assert(OffsetBytes <= AllocationSize && "Offset out of bounds!");
	return LoadAddress + OffsetBytes;
	}

	uintptr_t getStubOffset() const { return StubOffset; }

	void advanceStubOffset(unsigned StubSize) {
	StubOffset += StubSize;
	assert(StubOffset <= AllocationSize && "Not enough space allocated!");
	}

	uintptr_t getObjAddress() const { return ObjAddress; }
	};

	/// RelocationEntry - used to represent relocations internally in the dynamic
	/// linker.
	class RelocationEntry {
	public:
	/// SectionID - the section this relocation points to.
	unsigned SectionID;

	/// Offset - offset into the section.
	uint64_t Offset;

	/// RelType - relocation type.
	uint32_t RelType;

	/// Addend - the relocation addend encoded in the instruction itself. Also
	/// used to make a relocation section relative instead of symbol relative.
	int64_t Addend;

	struct SectionPair {
	uint32_t SectionA;
	uint32_t SectionB;
	};

	/// SymOffset - Section offset of the relocation entry's symbol (used for GOT
	/// lookup).
	union {
	uint64_t SymOffset;
	SectionPair Sections;
	};

	/// True if this is a PCRel relocation (MachO specific).
	bool IsPCRel;

	/// The size of this relocation (MachO specific).
	unsigned Size;

	// ARM (MachO and COFF) specific.
	bool IsTargetThumbFunc = false;

	RelocationEntry(unsigned id, uint64_t offset, uint32_t type, int64_t addend)
	: SectionID(id), Offset(offset), RelType(type), Addend(addend),
	SymOffset(0), IsPCRel(false), Size(0), IsTargetThumbFunc(false) {}

	RelocationEntry(unsigned id, uint64_t offset, uint32_t type, int64_t addend,
	uint64_t symoffset)
	: SectionID(id), Offset(offset), RelType(type), Addend(addend),
	SymOffset(symoffset), IsPCRel(false), Size(0),
	IsTargetThumbFunc(false) {}

	RelocationEntry(unsigned id, uint64_t offset, uint32_t type, int64_t addend,
	bool IsPCRel, unsigned Size)
	: SectionID(id), Offset(offset), RelType(type), Addend(addend),
	SymOffset(0), IsPCRel(IsPCRel), Size(Size), IsTargetThumbFunc(false) {}

	RelocationEntry(unsigned id, uint64_t offset, uint32_t type, int64_t addend,
	unsigned SectionA, uint64_t SectionAOffset, unsigned SectionB,
	uint64_t SectionBOffset, bool IsPCRel, unsigned Size)
	: SectionID(id), Offset(offset), RelType(type),
	Addend(SectionAOffset - SectionBOffset + addend), IsPCRel(IsPCRel),
	Size(Size), IsTargetThumbFunc(false) {
	Sections.SectionA = SectionA;
	Sections.SectionB = SectionB;
	}

	RelocationEntry(unsigned id, uint64_t offset, uint32_t type, int64_t addend,
	unsigned SectionA, uint64_t SectionAOffset, unsigned SectionB,
	uint64_t SectionBOffset, bool IsPCRel, unsigned Size,
	bool IsTargetThumbFunc)
	: SectionID(id), Offset(offset), RelType(type),
	Addend(SectionAOffset - SectionBOffset + addend), IsPCRel(IsPCRel),
	Size(Size), IsTargetThumbFunc(IsTargetThumbFunc) {
	Sections.SectionA = SectionA;
	Sections.SectionB = SectionB;
	}
	};

	class RelocationValueRef {
	public:
	unsigned SectionID;
	uint64_t Offset;
	int64_t Addend;
	const char *SymbolName;
	bool IsStubThumb = false;
	RelocationValueRef() : SectionID(0), Offset(0), Addend(0),
	SymbolName(nullptr) {}

	inline bool operator==(const RelocationValueRef &Other) const {
	return SectionID == Other.SectionID && Offset == Other.Offset &&
	Addend == Other.Addend && SymbolName == Other.SymbolName &&
	IsStubThumb == Other.IsStubThumb;
	}
	inline bool operator<(const RelocationValueRef &Other) const {
	if (SectionID != Other.SectionID)
	return SectionID < Other.SectionID;
	if (Offset != Other.Offset)
	return Offset < Other.Offset;
	if (Addend != Other.Addend)
	return Addend < Other.Addend;
	if (IsStubThumb != Other.IsStubThumb)
	return IsStubThumb < Other.IsStubThumb;
	return SymbolName < Other.SymbolName;
	}
	};

	/// Symbol info for RuntimeDyld.
	class SymbolTableEntry {
	public:
	SymbolTableEntry() = default;

	SymbolTableEntry(unsigned SectionID, uint64_t Offset, JITSymbolFlags Flags)
	: Offset(Offset), SectionID(SectionID), Flags(Flags) {}

	unsigned getSectionID() const { return SectionID; }
	uint64_t getOffset() const { return Offset; }
	void setOffset(uint64_t NewOffset) { Offset = NewOffset; }

	JITSymbolFlags getFlags() const { return Flags; }

	private:
	uint64_t Offset = 0;
	unsigned SectionID = 0;
	JITSymbolFlags Flags = JITSymbolFlags::None;
	};

	typedef StringMap<SymbolTableEntry> RTDyldSymbolTable;

	class RuntimeDyldImpl {
	friend class RuntimeDyld::LoadedObjectInfo;
	protected:
	static const unsigned AbsoluteSymbolSection = ~0U;

	// The MemoryManager to load objects into.
	RuntimeDyld::MemoryManager &MemMgr;

	// The symbol resolver to use for external symbols.
	JITSymbolResolver &Resolver;

	// A list of all sections emitted by the dynamic linker. These sections are
	// referenced in the code by means of their index in this list - SectionID.
	typedef SmallVector<SectionEntry, 64> SectionList;
	SectionList Sections;

	typedef unsigned SID; // Type for SectionIDs
	#define RTDYLD_INVALID_SECTION_ID ((RuntimeDyldImpl::SID)(-1))

	// Keep a map of sections from object file to the SectionID which
	// references it.
	typedef std::map<SectionRef, unsigned> ObjSectionToIDMap;

	// A global symbol table for symbols from all loaded modules.
	RTDyldSymbolTable GlobalSymbolTable;

	// Keep a map of common symbols to their info pairs
	typedef std::vector<SymbolRef> CommonSymbolList;

	// For each symbol, keep a list of relocations based on it. Anytime
	// its address is reassigned (the JIT re-compiled the function, e.g.),
	// the relocations get re-resolved.
	// The symbol (or section) the relocation is sourced from is the Key
	// in the relocation list where it's stored.
	typedef SmallVector<RelocationEntry, 64> RelocationList;
	// Relocations to sections already loaded. Indexed by SectionID which is the
	// source of the address. The target where the address will be written is
	// SectionID/Offset in the relocation itself.
	std::unordered_map<unsigned, RelocationList> Relocations;

	// Relocations to external symbols that are not yet resolved. Symbols are
	// external when they aren't found in the global symbol table of all loaded
	// modules. This map is indexed by symbol name.
	StringMap<RelocationList> ExternalSymbolRelocations;


	typedef std::map<RelocationValueRef, uintptr_t> StubMap;

	Triple::ArchType Arch;
	bool IsTargetLittleEndian;
	bool IsMipsO32ABI;
	bool IsMipsN32ABI;
	bool IsMipsN64ABI;

	// True if all sections should be passed to the memory manager, false if only
	// sections containing relocations should be. Defaults to 'false'.
	bool ProcessAllSections;

	// This mutex prevents simultaneously loading objects from two different
	// threads. This keeps us from having to protect individual data structures
	// and guarantees that section allocation requests to the memory manager
	// won't be interleaved between modules. It is also used in mapSectionAddress
	// and resolveRelocations to protect write access to internal data structures.
	//
	// loadObject may be called on the same thread during the handling of of
	// processRelocations, and that's OK. The handling of the relocation lists
	// is written in such a way as to work correctly if new elements are added to
	// the end of the list while the list is being processed.
	sys::Mutex lock;

	using NotifyStubEmittedFunction =
	RuntimeDyld::NotifyStubEmittedFunction;
	NotifyStubEmittedFunction NotifyStubEmitted;

	virtual unsigned getMaxStubSize() const = 0;
	virtual unsigned getStubAlignment() = 0;

	bool HasError;
	std::string ErrorStr;

	void writeInt16BE(uint8_t *Addr, uint16_t Value) {
	if (IsTargetLittleEndian)
	sys::swapByteOrder(Value);
	*Addr = (Value >> 8) & 0xFF;
	*(Addr + 1) = Value & 0xFF;
	}

	void writeInt32BE(uint8_t *Addr, uint32_t Value) {
	if (IsTargetLittleEndian)
	sys::swapByteOrder(Value);
	*Addr = (Value >> 24) & 0xFF;
	*(Addr + 1) = (Value >> 16) & 0xFF;
	*(Addr + 2) = (Value >> 8) & 0xFF;
	*(Addr + 3) = Value & 0xFF;
	}

	void writeInt64BE(uint8_t *Addr, uint64_t Value) {
	if (IsTargetLittleEndian)
	sys::swapByteOrder(Value);
	*Addr = (Value >> 56) & 0xFF;
	*(Addr + 1) = (Value >> 48) & 0xFF;
	*(Addr + 2) = (Value >> 40) & 0xFF;
	*(Addr + 3) = (Value >> 32) & 0xFF;
	*(Addr + 4) = (Value >> 24) & 0xFF;
	*(Addr + 5) = (Value >> 16) & 0xFF;
	*(Addr + 6) = (Value >> 8) & 0xFF;
	*(Addr + 7) = Value & 0xFF;
	}

	virtual void setMipsABI(const ObjectFile &Obj) {
	IsMipsO32ABI = false;
	IsMipsN32ABI = false;
	IsMipsN64ABI = false;
	}

	/// Endian-aware read Read the least significant Size bytes from Src.
	uint64_t readBytesUnaligned(uint8_t *Src, unsigned Size) const;

	/// Endian-aware write. Write the least significant Size bytes from Value to
	/// Dst.
	void writeBytesUnaligned(uint64_t Value, uint8_t *Dst, unsigned Size) const;

	/// Generate JITSymbolFlags from a libObject symbol.
	virtual Expected<JITSymbolFlags> getJITSymbolFlags(const SymbolRef &Sym);

	/// Modify the given target address based on the given symbol flags.
	/// This can be used by subclasses to tweak addresses based on symbol flags,
	/// For example: the MachO/ARM target uses it to set the low bit if the target
	/// is a thumb symbol.
	virtual uint64_t modifyAddressBasedOnFlags(uint64_t Addr,
	JITSymbolFlags Flags) const {
	return Addr;
	}

	/// Given the common symbols discovered in the object file, emit a
	/// new section for them and update the symbol mappings in the object and
	/// symbol table.
	Error emitCommonSymbols(const ObjectFile &Obj,
	CommonSymbolList &CommonSymbols, uint64_t CommonSize,
	uint32_t CommonAlign);

	/// Emits section data from the object file to the MemoryManager.
	/// \param IsCode if it's true then allocateCodeSection() will be
	/// used for emits, else allocateDataSection() will be used.
	/// \return SectionID.
	Expected<unsigned> emitSection(const ObjectFile &Obj,
	const SectionRef &Section,
	bool IsCode);

	/// Find Section in LocalSections. If the secton is not found - emit
	/// it and store in LocalSections.
	/// \param IsCode if it's true then allocateCodeSection() will be
	/// used for emmits, else allocateDataSection() will be used.
	/// \return SectionID.
	Expected<unsigned> findOrEmitSection(const ObjectFile &Obj,
	const SectionRef &Section, bool IsCode,
	ObjSectionToIDMap &LocalSections);

	// Add a relocation entry that uses the given section.
	void addRelocationForSection(const RelocationEntry &RE, unsigned SectionID);

	// Add a relocation entry that uses the given symbol. This symbol may
	// be found in the global symbol table, or it may be external.
	void addRelocationForSymbol(const RelocationEntry &RE, StringRef SymbolName);

	/// Emits long jump instruction to Addr.
	/// \return Pointer to the memory area for emitting target address.
	uint8_t createStubFunction(uint8_t Addr, unsigned AbiVariant = 0);

	/// Resolves relocations from Relocs list with address from Value.
	void resolveRelocationList(const RelocationList &Relocs, uint64_t Value);

	/// A object file specific relocation resolver
	/// \param RE The relocation to be resolved
	/// \param Value Target symbol address to apply the relocation action
	virtual void resolveRelocation(const RelocationEntry &RE, uint64_t Value) = 0;

	/// Parses one or more object file relocations (some object files use
	/// relocation pairs) and stores it to Relocations or SymbolRelocations
	/// (this depends on the object file type).
	/// \return Iterator to the next relocation that needs to be parsed.
	virtual Expected<relocation_iterator>
	processRelocationRef(unsigned SectionID, relocation_iterator RelI,
	const ObjectFile &Obj, ObjSectionToIDMap &ObjSectionToID,
	StubMap &Stubs) = 0;

	void applyExternalSymbolRelocations(
	const StringMap<JITEvaluatedSymbol> ExternalSymbolMap);

	/// Resolve relocations to external symbols.
	Error resolveExternalSymbols();

	// Compute an upper bound of the memory that is required to load all
	// sections
	Error computeTotalAllocSize(const ObjectFile &Obj,
	uint64_t &CodeSize, uint32_t &CodeAlign,
	uint64_t &RODataSize, uint32_t &RODataAlign,
	uint64_t &RWDataSize, uint32_t &RWDataAlign);

	// Compute GOT size
	unsigned computeGOTSize(const ObjectFile &Obj);

	// Compute the stub buffer size required for a section
	unsigned computeSectionStubBufSize(const ObjectFile &Obj,
	const SectionRef &Section);

	// Implementation of the generic part of the loadObject algorithm.
	Expected<ObjSectionToIDMap> loadObjectImpl(const object::ObjectFile &Obj);

	// Return size of Global Offset Table (GOT) entry
	virtual size_t getGOTEntrySize() { return 0; }

	// Return true if the relocation R may require allocating a GOT entry.
	virtual bool relocationNeedsGot(const RelocationRef &R) const {
	return false;
	}

	// Return true if the relocation R may require allocating a stub.
	virtual bool relocationNeedsStub(const RelocationRef &R) const {
	return true; // Conservative answer
	}

	public:
	RuntimeDyldImpl(RuntimeDyld::MemoryManager &MemMgr,
	JITSymbolResolver &Resolver)
	: MemMgr(MemMgr), Resolver(Resolver),
	ProcessAllSections(false), HasError(false) {
	}

	virtual ~RuntimeDyldImpl();

	void setProcessAllSections(bool ProcessAllSections) {
	this->ProcessAllSections = ProcessAllSections;
	}

	virtual std::unique_ptr<RuntimeDyld::LoadedObjectInfo>
	loadObject(const object::ObjectFile &Obj) = 0;

	uint64_t getSectionLoadAddress(unsigned SectionID) const {
	return Sections[SectionID].getLoadAddress();
	}

	uint8_t *getSectionAddress(unsigned SectionID) const {
	return Sections[SectionID].getAddress();
	}

	StringRef getSectionContent(unsigned SectionID) const {
	return StringRef(reinterpret_cast<char *>(Sections[SectionID].getAddress()),
	Sections[SectionID].getStubOffset() + getMaxStubSize());
	}

	uint8_t* getSymbolLocalAddress(StringRef Name) const {
	// FIXME: Just look up as a function for now. Overly simple of course.
	// Work in progress.
	RTDyldSymbolTable::const_iterator pos = GlobalSymbolTable.find(Name);
	if (pos == GlobalSymbolTable.end())
	return nullptr;
	const auto &SymInfo = pos->second;
	// Absolute symbols do not have a local address.
	if (SymInfo.getSectionID() == AbsoluteSymbolSection)
	return nullptr;
	return getSectionAddress(SymInfo.getSectionID()) + SymInfo.getOffset();
	}

	unsigned getSymbolSectionID(StringRef Name) const {
	auto GSTItr = GlobalSymbolTable.find(Name);
	if (GSTItr == GlobalSymbolTable.end())
	return ~0U;
	return GSTItr->second.getSectionID();
	}

	JITEvaluatedSymbol getSymbol(StringRef Name) const {
	// FIXME: Just look up as a function for now. Overly simple of course.
	// Work in progress.
	RTDyldSymbolTable::const_iterator pos = GlobalSymbolTable.find(Name);
	if (pos == GlobalSymbolTable.end())
	return nullptr;
	const auto &SymEntry = pos->second;
	uint64_t SectionAddr = 0;
	if (SymEntry.getSectionID() != AbsoluteSymbolSection)
	SectionAddr = getSectionLoadAddress(SymEntry.getSectionID());
	uint64_t TargetAddr = SectionAddr + SymEntry.getOffset();

	// FIXME: Have getSymbol should return the actual address and the client
	// modify it based on the flags. This will require clients to be
	// aware of the target architecture, which we should build
	// infrastructure for.
	TargetAddr = modifyAddressBasedOnFlags(TargetAddr, SymEntry.getFlags());
	return JITEvaluatedSymbol(TargetAddr, SymEntry.getFlags());
	}

	std::map<StringRef, JITEvaluatedSymbol> getSymbolTable() const {
	std::map<StringRef, JITEvaluatedSymbol> Result;

	for (auto &KV : GlobalSymbolTable) {
	auto SectionID = KV.second.getSectionID();
	uint64_t SectionAddr = 0;
	if (SectionID != AbsoluteSymbolSection)
	SectionAddr = getSectionLoadAddress(SectionID);
	Result[KV.first()] =
	JITEvaluatedSymbol(SectionAddr + KV.second.getOffset(), KV.second.getFlags());
	}

	return Result;
	}

	void resolveRelocations();

	void resolveLocalRelocations();

	static void finalizeAsync(std::unique_ptr<RuntimeDyldImpl> This,
	unique_function<void(Error)> OnEmitted,
	std::unique_ptr<MemoryBuffer> UnderlyingBuffer);

	void reassignSectionAddress(unsigned SectionID, uint64_t Addr);

	void mapSectionAddress(const void *LocalAddress, uint64_t TargetAddress);

	// Is the linker in an error state?
	bool hasError() { return HasError; }

	// Mark the error condition as handled and continue.
	void clearError() { HasError = false; }

	// Get the error message.
	StringRef getErrorString() { return ErrorStr; }

	virtual bool isCompatibleFile(const ObjectFile &Obj) const = 0;

	void setNotifyStubEmitted(NotifyStubEmittedFunction NotifyStubEmitted) {
	this->NotifyStubEmitted = std::move(NotifyStubEmitted);
	}

	virtual void registerEHFrames();

	void deregisterEHFrames();

	virtual Error finalizeLoad(const ObjectFile &ObjImg,
	ObjSectionToIDMap &SectionMap) {
	return Error::success();
	}
	};

	} // end namespace llvm

	#endif