Update LLVM to r99115.

11 files changed, 1413 insertions, 1035 deletions

diff --git a/lib/MC/CMakeLists.txt b/lib/MC/CMakeLists.txt
index 4cf71dcabee0..dba0e1435651 100644
--- a/lib/MC/CMakeLists.txt
+++ b/lib/MC/CMakeLists.txt
@@ -12,11 +12,13 @@ add_llvm_library(LLVMMC
   MCInstPrinter.cpp
   MCMachOStreamer.cpp
   MCNullStreamer.cpp
+  MCObjectWriter.cpp
   MCSection.cpp
   MCSectionELF.cpp
   MCSectionMachO.cpp
   MCStreamer.cpp
   MCSymbol.cpp
   MCValue.cpp
+  MachObjectWriter.cpp
   TargetAsmBackend.cpp
   )
diff --git a/lib/MC/MCAsmStreamer.cpp b/lib/MC/MCAsmStreamer.cpp
index 7f3947114fe4..2025463a80be 100644
--- a/lib/MC/MCAsmStreamer.cpp
+++ b/lib/MC/MCAsmStreamer.cpp
@@ -16,6 +16,7 @@
 #include "llvm/MC/MCInstPrinter.h"
 #include "llvm/MC/MCSectionMachO.h"
 #include "llvm/MC/MCSymbol.h"
+#include "llvm/ADT/OwningPtr.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -29,7 +30,7 @@ namespace {
 class MCAsmStreamer : public MCStreamer {
   formatted_raw_ostream &OS;
   const MCAsmInfo &MAI;
-  MCInstPrinter *InstPrinter;
+  OwningPtr<MCInstPrinter> InstPrinter;
   MCCodeEmitter *Emitter;
   
   SmallString<128> CommentToEmit;
diff --git a/lib/MC/MCAssembler.cpp b/lib/MC/MCAssembler.cpp
index 4cf8b7e522b3..beecf7e6b858 100644
--- a/lib/MC/MCAssembler.cpp
+++ b/lib/MC/MCAssembler.cpp
@@ -10,18 +10,16 @@
 #define DEBUG_TYPE "assembler"
 #include "llvm/MC/MCAssembler.h"
 #include "llvm/MC/MCAsmLayout.h"
+#include "llvm/MC/MCCodeEmitter.h"
 #include "llvm/MC/MCExpr.h"
-#include "llvm/MC/MCSectionMachO.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/MC/MCValue.h"
-#include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/OwningPtr.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringExtras.h"
-#include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/ErrorHandling.h"
-#include "llvm/Support/MachO.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Target/TargetRegistry.h"
@@ -33,8 +31,6 @@
 #include <vector>
 using namespace llvm;
 
-class MachObjectWriter;
-
 STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
 
 // FIXME FIXME FIXME: There are number of places in this file where we convert
@@ -42,917 +38,6 @@ STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
 // object file, which may truncate it. We should detect that truncation where
 // invalid and report errors back.
 
-static void WriteFileData(raw_ostream &OS, const MCSectionData &SD,
-                          MachObjectWriter &MOW);
-
-static uint64_t WriteNopData(uint64_t Count, MachObjectWriter &MOW);
-
-/// isVirtualSection - Check if this is a section which does not actually exist
-/// in the object file.
-static bool isVirtualSection(const MCSection &Section) {
-  // FIXME: Lame.
-  const MCSectionMachO &SMO = static_cast<const MCSectionMachO&>(Section);
-  return (SMO.getType() == MCSectionMachO::S_ZEROFILL);
-}
-
-static unsigned getFixupKindLog2Size(unsigned Kind) {
-  switch (Kind) {
-  default: llvm_unreachable("invalid fixup kind!");
-  case X86::reloc_pcrel_1byte:
-  case FK_Data_1: return 0;
-  case FK_Data_2: return 1;
-  case X86::reloc_pcrel_4byte:
-  case X86::reloc_riprel_4byte:
-  case FK_Data_4: return 2;
-  case FK_Data_8: return 3;
-  }
-}
-
-static bool isFixupKindPCRel(unsigned Kind) {
-  switch (Kind) {
-  default:
-    return false;
-  case X86::reloc_pcrel_1byte:
-  case X86::reloc_pcrel_4byte:
-  case X86::reloc_riprel_4byte:
-    return true;
-  }
-}
-
-class MachObjectWriter {
-  // See <mach-o/loader.h>.
-  enum {
-    Header_Magic32 = 0xFEEDFACE,
-    Header_Magic64 = 0xFEEDFACF
-  };
-
-  enum {
-    Header32Size = 28,
-    Header64Size = 32,
-    SegmentLoadCommand32Size = 56,
-    SegmentLoadCommand64Size = 72,
-    Section32Size = 68,
-    Section64Size = 80,
-    SymtabLoadCommandSize = 24,
-    DysymtabLoadCommandSize = 80,
-    Nlist32Size = 12,
-    Nlist64Size = 16,
-    RelocationInfoSize = 8
-  };
-
-  enum HeaderFileType {
-    HFT_Object = 0x1
-  };
-
-  enum HeaderFlags {
-    HF_SubsectionsViaSymbols = 0x2000
-  };
-
-  enum LoadCommandType {
-    LCT_Segment = 0x1,
-    LCT_Symtab = 0x2,
-    LCT_Dysymtab = 0xb,
-    LCT_Segment64 = 0x19
-  };
-
-  // See <mach-o/nlist.h>.
-  enum SymbolTypeType {
-    STT_Undefined = 0x00,
-    STT_Absolute  = 0x02,
-    STT_Section   = 0x0e
-  };
-
-  enum SymbolTypeFlags {
-    // If any of these bits are set, then the entry is a stab entry number (see
-    // <mach-o/stab.h>. Otherwise the other masks apply.
-    STF_StabsEntryMask = 0xe0,
-
-    STF_TypeMask       = 0x0e,
-    STF_External       = 0x01,
-    STF_PrivateExtern  = 0x10
-  };
-
-  /// IndirectSymbolFlags - Flags for encoding special values in the indirect
-  /// symbol entry.
-  enum IndirectSymbolFlags {
-    ISF_Local    = 0x80000000,
-    ISF_Absolute = 0x40000000
-  };
-
-  /// RelocationFlags - Special flags for addresses.
-  enum RelocationFlags {
-    RF_Scattered = 0x80000000
-  };
-
-  enum RelocationInfoType {
-    RIT_Vanilla             = 0,
-    RIT_Pair                = 1,
-    RIT_Difference          = 2,
-    RIT_PreboundLazyPointer = 3,
-    RIT_LocalDifference     = 4
-  };
-
-  /// MachSymbolData - Helper struct for containing some precomputed information
-  /// on symbols.
-  struct MachSymbolData {
-    MCSymbolData *SymbolData;
-    uint64_t StringIndex;
-    uint8_t SectionIndex;
-
-    // Support lexicographic sorting.
-    bool operator<(const MachSymbolData &RHS) const {
-      const std::string &Name = SymbolData->getSymbol().getName();
-      return Name < RHS.SymbolData->getSymbol().getName();
-    }
-  };
-
-  raw_ostream &OS;
-  unsigned Is64Bit : 1;
-  unsigned IsLSB : 1;
-
-public:
-  MachObjectWriter(raw_ostream &_OS, bool _Is64Bit, bool _IsLSB = true)
-    : OS(_OS), Is64Bit(_Is64Bit), IsLSB(_IsLSB) {
-  }
-
-  /// @name Helper Methods
-  /// @{
-
-  void Write8(uint8_t Value) {
-    OS << char(Value);
-  }
-
-  void Write16(uint16_t Value) {
-    if (IsLSB) {
-      Write8(uint8_t(Value >> 0));
-      Write8(uint8_t(Value >> 8));
-    } else {
-      Write8(uint8_t(Value >> 8));
-      Write8(uint8_t(Value >> 0));
-    }
-  }
-
-  void Write32(uint32_t Value) {
-    if (IsLSB) {
-      Write16(uint16_t(Value >> 0));
-      Write16(uint16_t(Value >> 16));
-    } else {
-      Write16(uint16_t(Value >> 16));
-      Write16(uint16_t(Value >> 0));
-    }
-  }
-
-  void Write64(uint64_t Value) {
-    if (IsLSB) {
-      Write32(uint32_t(Value >> 0));
-      Write32(uint32_t(Value >> 32));
-    } else {
-      Write32(uint32_t(Value >> 32));
-      Write32(uint32_t(Value >> 0));
-    }
-  }
-
-  void WriteZeros(unsigned N) {
-    const char Zeros[16] = { 0 };
-
-    for (unsigned i = 0, e = N / 16; i != e; ++i)
-      OS << StringRef(Zeros, 16);
-
-    OS << StringRef(Zeros, N % 16);
-  }
-
-  void WriteString(StringRef Str, unsigned ZeroFillSize = 0) {
-    OS << Str;
-    if (ZeroFillSize)
-      WriteZeros(ZeroFillSize - Str.size());
-  }
-
-  /// @}
-
-  void WriteHeader(unsigned NumLoadCommands, unsigned LoadCommandsSize,
-                   bool SubsectionsViaSymbols) {
-    uint32_t Flags = 0;
-
-    if (SubsectionsViaSymbols)
-      Flags |= HF_SubsectionsViaSymbols;
-
-    // struct mach_header (28 bytes) or
-    // struct mach_header_64 (32 bytes)
-
-    uint64_t Start = OS.tell();
-    (void) Start;
-
-    Write32(Is64Bit ? Header_Magic64 : Header_Magic32);
-
-    // FIXME: Support cputype.
-    Write32(Is64Bit ? MachO::CPUTypeX86_64 : MachO::CPUTypeI386);
-    // FIXME: Support cpusubtype.
-    Write32(MachO::CPUSubType_I386_ALL);
-    Write32(HFT_Object);
-    Write32(NumLoadCommands);    // Object files have a single load command, the
-                                 // segment.
-    Write32(LoadCommandsSize);
-    Write32(Flags);
-    if (Is64Bit)
-      Write32(0); // reserved
-
-    assert(OS.tell() - Start == Is64Bit ? Header64Size : Header32Size);
-  }
-
-  /// WriteSegmentLoadCommand - Write a segment load command.
-  ///
-  /// \arg NumSections - The number of sections in this segment.
-  /// \arg SectionDataSize - The total size of the sections.
-  void WriteSegmentLoadCommand(unsigned NumSections,
-                               uint64_t VMSize,
-                               uint64_t SectionDataStartOffset,
-                               uint64_t SectionDataSize) {
-    // struct segment_command (56 bytes) or
-    // struct segment_command_64 (72 bytes)
-
-    uint64_t Start = OS.tell();
-    (void) Start;
-
-    unsigned SegmentLoadCommandSize = Is64Bit ? SegmentLoadCommand64Size :
-      SegmentLoadCommand32Size;
-    Write32(Is64Bit ? LCT_Segment64 : LCT_Segment);
-    Write32(SegmentLoadCommandSize +
-            NumSections * (Is64Bit ? Section64Size : Section32Size));
-
-    WriteString("", 16);
-    if (Is64Bit) {
-      Write64(0); // vmaddr
-      Write64(VMSize); // vmsize
-      Write64(SectionDataStartOffset); // file offset
-      Write64(SectionDataSize); // file size
-    } else {
-      Write32(0); // vmaddr
-      Write32(VMSize); // vmsize
-      Write32(SectionDataStartOffset); // file offset
-      Write32(SectionDataSize); // file size
-    }
-    Write32(0x7); // maxprot
-    Write32(0x7); // initprot
-    Write32(NumSections);
-    Write32(0); // flags
-
-    assert(OS.tell() - Start == SegmentLoadCommandSize);
-  }
-
-  void WriteSection(const MCSectionData &SD, uint64_t FileOffset,
-                    uint64_t RelocationsStart, unsigned NumRelocations) {
-    // The offset is unused for virtual sections.
-    if (isVirtualSection(SD.getSection())) {
-      assert(SD.getFileSize() == 0 && "Invalid file size!");
-      FileOffset = 0;
-    }
-
-    // struct section (68 bytes) or
-    // struct section_64 (80 bytes)
-
-    uint64_t Start = OS.tell();
-    (void) Start;
-
-    // FIXME: cast<> support!
-    const MCSectionMachO &Section =
-      static_cast<const MCSectionMachO&>(SD.getSection());
-    WriteString(Section.getSectionName(), 16);
-    WriteString(Section.getSegmentName(), 16);
-    if (Is64Bit) {
-      Write64(SD.getAddress()); // address
-      Write64(SD.getSize()); // size
-    } else {
-      Write32(SD.getAddress()); // address
-      Write32(SD.getSize()); // size
-    }
-    Write32(FileOffset);
-
-    unsigned Flags = Section.getTypeAndAttributes();
-    if (SD.hasInstructions())
-      Flags |= MCSectionMachO::S_ATTR_SOME_INSTRUCTIONS;
-
-    assert(isPowerOf2_32(SD.getAlignment()) && "Invalid alignment!");
-    Write32(Log2_32(SD.getAlignment()));
-    Write32(NumRelocations ? RelocationsStart : 0);
-    Write32(NumRelocations);
-    Write32(Flags);
-    Write32(0); // reserved1
-    Write32(Section.getStubSize()); // reserved2
-    if (Is64Bit)
-      Write32(0); // reserved3
-
-    assert(OS.tell() - Start == Is64Bit ? Section64Size : Section32Size);
-  }
-
-  void WriteSymtabLoadCommand(uint32_t SymbolOffset, uint32_t NumSymbols,
-                              uint32_t StringTableOffset,
-                              uint32_t StringTableSize) {
-    // struct symtab_command (24 bytes)
-
-    uint64_t Start = OS.tell();
-    (void) Start;
-
-    Write32(LCT_Symtab);
-    Write32(SymtabLoadCommandSize);
-    Write32(SymbolOffset);
-    Write32(NumSymbols);
-    Write32(StringTableOffset);
-    Write32(StringTableSize);
-
-    assert(OS.tell() - Start == SymtabLoadCommandSize);
-  }
-
-  void WriteDysymtabLoadCommand(uint32_t FirstLocalSymbol,
-                                uint32_t NumLocalSymbols,
-                                uint32_t FirstExternalSymbol,
-                                uint32_t NumExternalSymbols,
-                                uint32_t FirstUndefinedSymbol,
-                                uint32_t NumUndefinedSymbols,
-                                uint32_t IndirectSymbolOffset,
-                                uint32_t NumIndirectSymbols) {
-    // struct dysymtab_command (80 bytes)
-
-    uint64_t Start = OS.tell();
-    (void) Start;
-
-    Write32(LCT_Dysymtab);
-    Write32(DysymtabLoadCommandSize);
-    Write32(FirstLocalSymbol);
-    Write32(NumLocalSymbols);
-    Write32(FirstExternalSymbol);
-    Write32(NumExternalSymbols);
-    Write32(FirstUndefinedSymbol);
-    Write32(NumUndefinedSymbols);
-    Write32(0); // tocoff
-    Write32(0); // ntoc
-    Write32(0); // modtaboff
-    Write32(0); // nmodtab
-    Write32(0); // extrefsymoff
-    Write32(0); // nextrefsyms
-    Write32(IndirectSymbolOffset);
-    Write32(NumIndirectSymbols);
-    Write32(0); // extreloff
-    Write32(0); // nextrel
-    Write32(0); // locreloff
-    Write32(0); // nlocrel
-
-    assert(OS.tell() - Start == DysymtabLoadCommandSize);
-  }
-
-  void WriteNlist(MachSymbolData &MSD) {
-    MCSymbolData &Data = *MSD.SymbolData;
-    const MCSymbol &Symbol = Data.getSymbol();
-    uint8_t Type = 0;
-    uint16_t Flags = Data.getFlags();
-    uint32_t Address = 0;
-
-    // Set the N_TYPE bits. See <mach-o/nlist.h>.
-    //
-    // FIXME: Are the prebound or indirect fields possible here?
-    if (Symbol.isUndefined())
-      Type = STT_Undefined;
-    else if (Symbol.isAbsolute())
-      Type = STT_Absolute;
-    else
-      Type = STT_Section;
-
-    // FIXME: Set STAB bits.
-
-    if (Data.isPrivateExtern())
-      Type |= STF_PrivateExtern;
-
-    // Set external bit.
-    if (Data.isExternal() || Symbol.isUndefined())
-      Type |= STF_External;
-
-    // Compute the symbol address.
-    if (Symbol.isDefined()) {
-      if (Symbol.isAbsolute()) {
-        llvm_unreachable("FIXME: Not yet implemented!");
-      } else {
-        Address = Data.getAddress();
-      }
-    } else if (Data.isCommon()) {
-      // Common symbols are encoded with the size in the address
-      // field, and their alignment in the flags.
-      Address = Data.getCommonSize();
-
-      // Common alignment is packed into the 'desc' bits.
-      if (unsigned Align = Data.getCommonAlignment()) {
-        unsigned Log2Size = Log2_32(Align);
-        assert((1U << Log2Size) == Align && "Invalid 'common' alignment!");
-        if (Log2Size > 15)
-          llvm_report_error("invalid 'common' alignment '" +
-                            Twine(Align) + "'");
-        // FIXME: Keep this mask with the SymbolFlags enumeration.
-        Flags = (Flags & 0xF0FF) | (Log2Size << 8);
-      }
-    }
-
-    // struct nlist (12 bytes)
-
-    Write32(MSD.StringIndex);
-    Write8(Type);
-    Write8(MSD.SectionIndex);
-
-    // The Mach-O streamer uses the lowest 16-bits of the flags for the 'desc'
-    // value.
-    Write16(Flags);
-    if (Is64Bit)
-      Write64(Address);
-    else
-      Write32(Address);
-  }
-
-  struct MachRelocationEntry {
-    uint32_t Word0;
-    uint32_t Word1;
-  };
-  void ComputeScatteredRelocationInfo(MCAssembler &Asm, MCFragment &Fragment,
-                                      MCAsmFixup &Fixup,
-                                      const MCValue &Target,
-                                     std::vector<MachRelocationEntry> &Relocs) {
-    uint32_t Address = Fragment.getOffset() + Fixup.Offset;
-    unsigned IsPCRel = isFixupKindPCRel(Fixup.Kind);
-    unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
-    unsigned Type = RIT_Vanilla;
-
-    // See <reloc.h>.
-    const MCSymbol *A = Target.getSymA();
-    MCSymbolData *A_SD = &Asm.getSymbolData(*A);
-
-    if (!A_SD->getFragment())
-      llvm_report_error("symbol '" + A->getName() +
-                        "' can not be undefined in a subtraction expression");
-
-    uint32_t Value = A_SD->getAddress();
-    uint32_t Value2 = 0;
-
-    if (const MCSymbol *B = Target.getSymB()) {
-      MCSymbolData *B_SD = &Asm.getSymbolData(*B);
-
-      if (!B_SD->getFragment())
-        llvm_report_error("symbol '" + B->getName() +
-                          "' can not be undefined in a subtraction expression");
-
-      // Select the appropriate difference relocation type.
-      //
-      // Note that there is no longer any semantic difference between these two
-      // relocation types from the linkers point of view, this is done solely
-      // for pedantic compatibility with 'as'.
-      Type = A_SD->isExternal() ? RIT_Difference : RIT_LocalDifference;
-      Value2 = B_SD->getAddress();
-    }
-
-    MachRelocationEntry MRE;
-    MRE.Word0 = ((Address   <<  0) |
-                 (Type      << 24) |
-                 (Log2Size  << 28) |
-                 (IsPCRel   << 30) |
-                 RF_Scattered);
-    MRE.Word1 = Value;
-    Relocs.push_back(MRE);
-
-    if (Type == RIT_Difference || Type == RIT_LocalDifference) {
-      MachRelocationEntry MRE;
-      MRE.Word0 = ((0         <<  0) |
-                   (RIT_Pair  << 24) |
-                   (Log2Size  << 28) |
-                   (IsPCRel   << 30) |
-                   RF_Scattered);
-      MRE.Word1 = Value2;
-      Relocs.push_back(MRE);
-    }
-  }
-
-  void ComputeRelocationInfo(MCAssembler &Asm, MCDataFragment &Fragment,
-                             MCAsmFixup &Fixup,
-                             std::vector<MachRelocationEntry> &Relocs) {
-    unsigned IsPCRel = isFixupKindPCRel(Fixup.Kind);
-    unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
-
-    // FIXME: Share layout object.
-    MCAsmLayout Layout(Asm);
-
-    // Evaluate the fixup; if the value was resolved, no relocation is needed.
-    MCValue Target;
-    if (Asm.EvaluateFixup(Layout, Fixup, &Fragment, Target, Fixup.FixedValue))
-      return;
-
-    // If this is a difference or a defined symbol plus an offset, then we need
-    // a scattered relocation entry.
-    uint32_t Offset = Target.getConstant();
-    if (IsPCRel)
-      Offset += 1 << Log2Size;
-    if (Target.getSymB() ||
-        (Target.getSymA() && !Target.getSymA()->isUndefined() &&
-         Offset))
-      return ComputeScatteredRelocationInfo(Asm, Fragment, Fixup, Target,
-                                            Relocs);
-
-    // See <reloc.h>.
-    uint32_t Address = Fragment.getOffset() + Fixup.Offset;
-    uint32_t Value = 0;
-    unsigned Index = 0;
-    unsigned IsExtern = 0;
-    unsigned Type = 0;
-
-    if (Target.isAbsolute()) { // constant
-      // SymbolNum of 0 indicates the absolute section.
-      //
-      // FIXME: Currently, these are never generated (see code below). I cannot
-      // find a case where they are actually emitted.
-      Type = RIT_Vanilla;
-      Value = 0;
-    } else {
-      const MCSymbol *Symbol = Target.getSymA();
-      MCSymbolData *SD = &Asm.getSymbolData(*Symbol);
-
-      if (Symbol->isUndefined()) {
-        IsExtern = 1;
-        Index = SD->getIndex();
-        Value = 0;
-      } else {
-        // The index is the section ordinal.
-        //
-        // FIXME: O(N)
-        Index = 1;
-        MCAssembler::iterator it = Asm.begin(), ie = Asm.end();
-        for (; it != ie; ++it, ++Index)
-          if (&*it == SD->getFragment()->getParent())
-            break;
-        assert(it != ie && "Unable to find section index!");
-        Value = SD->getAddress();
-      }
-
-      Type = RIT_Vanilla;
-    }
-
-    // struct relocation_info (8 bytes)
-    MachRelocationEntry MRE;
-    MRE.Word0 = Address;
-    MRE.Word1 = ((Index     <<  0) |
-                 (IsPCRel   << 24) |
-                 (Log2Size  << 25) |
-                 (IsExtern  << 27) |
-                 (Type      << 28));
-    Relocs.push_back(MRE);
-  }
-
-  void BindIndirectSymbols(MCAssembler &Asm) {
-    // This is the point where 'as' creates actual symbols for indirect symbols
-    // (in the following two passes). It would be easier for us to do this
-    // sooner when we see the attribute, but that makes getting the order in the
-    // symbol table much more complicated than it is worth.
-    //
-    // FIXME: Revisit this when the dust settles.
-
-    // Bind non lazy symbol pointers first.
-    for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
-           ie = Asm.indirect_symbol_end(); it != ie; ++it) {
-      // FIXME: cast<> support!
-      const MCSectionMachO &Section =
-        static_cast<const MCSectionMachO&>(it->SectionData->getSection());
-
-      if (Section.getType() != MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS)
-        continue;
-
-      Asm.getOrCreateSymbolData(*it->Symbol);
-    }
-
-    // Then lazy symbol pointers and symbol stubs.
-    for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
-           ie = Asm.indirect_symbol_end(); it != ie; ++it) {
-      // FIXME: cast<> support!
-      const MCSectionMachO &Section =
-        static_cast<const MCSectionMachO&>(it->SectionData->getSection());
-
-      if (Section.getType() != MCSectionMachO::S_LAZY_SYMBOL_POINTERS &&
-          Section.getType() != MCSectionMachO::S_SYMBOL_STUBS)
-        continue;
-
-      // Set the symbol type to undefined lazy, but only on construction.
-      //
-      // FIXME: Do not hardcode.
-      bool Created;
-      MCSymbolData &Entry = Asm.getOrCreateSymbolData(*it->Symbol, &Created);
-      if (Created)
-        Entry.setFlags(Entry.getFlags() | 0x0001);
-    }
-  }
-
-  /// ComputeSymbolTable - Compute the symbol table data
-  ///
-  /// \param StringTable [out] - The string table data.
-  /// \param StringIndexMap [out] - Map from symbol names to offsets in the
-  /// string table.
-  void ComputeSymbolTable(MCAssembler &Asm, SmallString<256> &StringTable,
-                          std::vector<MachSymbolData> &LocalSymbolData,
-                          std::vector<MachSymbolData> &ExternalSymbolData,
-                          std::vector<MachSymbolData> &UndefinedSymbolData) {
-    // Build section lookup table.
-    DenseMap<const MCSection*, uint8_t> SectionIndexMap;
-    unsigned Index = 1;
-    for (MCAssembler::iterator it = Asm.begin(),
-           ie = Asm.end(); it != ie; ++it, ++Index)
-      SectionIndexMap[&it->getSection()] = Index;
-    assert(Index <= 256 && "Too many sections!");
-
-    // Index 0 is always the empty string.
-    StringMap<uint64_t> StringIndexMap;
-    StringTable += '\x00';
-
-    // Build the symbol arrays and the string table, but only for non-local
-    // symbols.
-    //
-    // The particular order that we collect the symbols and create the string
-    // table, then sort the symbols is chosen to match 'as'. Even though it
-    // doesn't matter for correctness, this is important for letting us diff .o
-    // files.
-    for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
-           ie = Asm.symbol_end(); it != ie; ++it) {
-      const MCSymbol &Symbol = it->getSymbol();
-
-      // Ignore assembler temporaries.
-      if (it->getSymbol().isTemporary() &&
-          (!it->getFragment() ||
-           !Asm.getBackend().doesSectionRequireSymbols(
-             it->getFragment()->getParent()->getSection())))
-        continue;
-
-      if (!it->isExternal() && !Symbol.isUndefined())
-        continue;
-
-      uint64_t &Entry = StringIndexMap[Symbol.getName()];
-      if (!Entry) {
-        Entry = StringTable.size();
-        StringTable += Symbol.getName();
-        StringTable += '\x00';
-      }
-
-      MachSymbolData MSD;
-      MSD.SymbolData = it;
-      MSD.StringIndex = Entry;
-
-      if (Symbol.isUndefined()) {
-        MSD.SectionIndex = 0;
-        UndefinedSymbolData.push_back(MSD);
-      } else if (Symbol.isAbsolute()) {
-        MSD.SectionIndex = 0;
-        ExternalSymbolData.push_back(MSD);
-      } else {
-        MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
-        assert(MSD.SectionIndex && "Invalid section index!");
-        ExternalSymbolData.push_back(MSD);
-      }
-    }
-
-    // Now add the data for local symbols.
-    for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
-           ie = Asm.symbol_end(); it != ie; ++it) {
-      const MCSymbol &Symbol = it->getSymbol();
-
-      // Ignore assembler temporaries.
-      if (it->getSymbol().isTemporary() &&
-          (!it->getFragment() ||
-           !Asm.getBackend().doesSectionRequireSymbols(
-             it->getFragment()->getParent()->getSection())))
-        continue;
-
-      if (it->isExternal() || Symbol.isUndefined())
-        continue;
-
-      uint64_t &Entry = StringIndexMap[Symbol.getName()];
-      if (!Entry) {
-        Entry = StringTable.size();
-        StringTable += Symbol.getName();
-        StringTable += '\x00';
-      }
-
-      MachSymbolData MSD;
-      MSD.SymbolData = it;
-      MSD.StringIndex = Entry;
-
-      if (Symbol.isAbsolute()) {
-        MSD.SectionIndex = 0;
-        LocalSymbolData.push_back(MSD);
-      } else {
-        MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
-        assert(MSD.SectionIndex && "Invalid section index!");
-        LocalSymbolData.push_back(MSD);
-      }
-    }
-
-    // External and undefined symbols are required to be in lexicographic order.
-    std::sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
-    std::sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
-
-    // Set the symbol indices.
-    Index = 0;
-    for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
-      LocalSymbolData[i].SymbolData->setIndex(Index++);
-    for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
-      ExternalSymbolData[i].SymbolData->setIndex(Index++);
-    for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
-      UndefinedSymbolData[i].SymbolData->setIndex(Index++);
-
-    // The string table is padded to a multiple of 4.
-    while (StringTable.size() % 4)
-      StringTable += '\x00';
-  }
-
-  void WriteObject(MCAssembler &Asm) {
-    unsigned NumSections = Asm.size();
-
-    // Create symbol data for any indirect symbols.
-    BindIndirectSymbols(Asm);
-
-    // Compute symbol table information.
-    SmallString<256> StringTable;
-    std::vector<MachSymbolData> LocalSymbolData;
-    std::vector<MachSymbolData> ExternalSymbolData;
-    std::vector<MachSymbolData> UndefinedSymbolData;
-    unsigned NumSymbols = Asm.symbol_size();
-
-    // No symbol table command is written if there are no symbols.
-    if (NumSymbols)
-      ComputeSymbolTable(Asm, StringTable, LocalSymbolData, ExternalSymbolData,
-                         UndefinedSymbolData);
-
-    // The section data starts after the header, the segment load command (and
-    // section headers) and the symbol table.
-    unsigned NumLoadCommands = 1;
-    uint64_t LoadCommandsSize = Is64Bit ?
-      SegmentLoadCommand64Size + NumSections * Section64Size :
-      SegmentLoadCommand32Size + NumSections * Section32Size;
-
-    // Add the symbol table load command sizes, if used.
-    if (NumSymbols) {
-      NumLoadCommands += 2;
-      LoadCommandsSize += SymtabLoadCommandSize + DysymtabLoadCommandSize;
-    }
-
-    // Compute the total size of the section data, as well as its file size and
-    // vm size.
-    uint64_t SectionDataStart = (Is64Bit ? Header64Size : Header32Size)
-      + LoadCommandsSize;
-    uint64_t SectionDataSize = 0;
-    uint64_t SectionDataFileSize = 0;
-    uint64_t VMSize = 0;
-    for (MCAssembler::iterator it = Asm.begin(),
-           ie = Asm.end(); it != ie; ++it) {
-      MCSectionData &SD = *it;
-
-      VMSize = std::max(VMSize, SD.getAddress() + SD.getSize());
-
-      if (isVirtualSection(SD.getSection()))
-        continue;
-
-      SectionDataSize = std::max(SectionDataSize,
-                                 SD.getAddress() + SD.getSize());
-      SectionDataFileSize = std::max(SectionDataFileSize,
-                                     SD.getAddress() + SD.getFileSize());
-    }
-
-    // The section data is padded to 4 bytes.
-    //
-    // FIXME: Is this machine dependent?
-    unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
-    SectionDataFileSize += SectionDataPadding;
-
-    // Write the prolog, starting with the header and load command...
-    WriteHeader(NumLoadCommands, LoadCommandsSize,
-                Asm.getSubsectionsViaSymbols());
-    WriteSegmentLoadCommand(NumSections, VMSize,
-                            SectionDataStart, SectionDataSize);
-
-    // ... and then the section headers.
-    //
-    // We also compute the section relocations while we do this. Note that
-    // computing relocation info will also update the fixup to have the correct
-    // value; this will overwrite the appropriate data in the fragment when it
-    // is written.
-    std::vector<MachRelocationEntry> RelocInfos;
-    uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
-    for (MCAssembler::iterator it = Asm.begin(),
-           ie = Asm.end(); it != ie; ++it) {
-      MCSectionData &SD = *it;
-
-      // The assembler writes relocations in the reverse order they were seen.
-      //
-      // FIXME: It is probably more complicated than this.
-      unsigned NumRelocsStart = RelocInfos.size();
-      for (MCSectionData::reverse_iterator it2 = SD.rbegin(),
-             ie2 = SD.rend(); it2 != ie2; ++it2)
-        if (MCDataFragment *DF = dyn_cast<MCDataFragment>(&*it2))
-          for (unsigned i = 0, e = DF->fixup_size(); i != e; ++i)
-            ComputeRelocationInfo(Asm, *DF, DF->getFixups()[e - i - 1],
-                                  RelocInfos);
-
-      unsigned NumRelocs = RelocInfos.size() - NumRelocsStart;
-      uint64_t SectionStart = SectionDataStart + SD.getAddress();
-      WriteSection(SD, SectionStart, RelocTableEnd, NumRelocs);
-      RelocTableEnd += NumRelocs * RelocationInfoSize;
-    }
-
-    // Write the symbol table load command, if used.
-    if (NumSymbols) {
-      unsigned FirstLocalSymbol = 0;
-      unsigned NumLocalSymbols = LocalSymbolData.size();
-      unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
-      unsigned NumExternalSymbols = ExternalSymbolData.size();
-      unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
-      unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
-      unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
-      unsigned NumSymTabSymbols =
-        NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
-      uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
-      uint64_t IndirectSymbolOffset = 0;
-
-      // If used, the indirect symbols are written after the section data.
-      if (NumIndirectSymbols)
-        IndirectSymbolOffset = RelocTableEnd;
-
-      // The symbol table is written after the indirect symbol data.
-      uint64_t SymbolTableOffset = RelocTableEnd + IndirectSymbolSize;
-
-      // The string table is written after symbol table.
-      uint64_t StringTableOffset =
-        SymbolTableOffset + NumSymTabSymbols * (Is64Bit ? Nlist64Size :
-                                                Nlist32Size);
-      WriteSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
-                             StringTableOffset, StringTable.size());
-
-      WriteDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
-                               FirstExternalSymbol, NumExternalSymbols,
-                               FirstUndefinedSymbol, NumUndefinedSymbols,
-                               IndirectSymbolOffset, NumIndirectSymbols);
-    }
-
-    // Write the actual section data.
-    for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
-      WriteFileData(OS, *it, *this);
-
-    // Write the extra padding.
-    WriteZeros(SectionDataPadding);
-
-    // Write the relocation entries.
-    for (unsigned i = 0, e = RelocInfos.size(); i != e; ++i) {
-      Write32(RelocInfos[i].Word0);
-      Write32(RelocInfos[i].Word1);
-    }
-
-    // Write the symbol table data, if used.
-    if (NumSymbols) {
-      // Write the indirect symbol entries.
-      for (MCAssembler::indirect_symbol_iterator
-             it = Asm.indirect_symbol_begin(),
-             ie = Asm.indirect_symbol_end(); it != ie; ++it) {
-        // Indirect symbols in the non lazy symbol pointer section have some
-        // special handling.
-        const MCSectionMachO &Section =
-          static_cast<const MCSectionMachO&>(it->SectionData->getSection());
-        if (Section.getType() == MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS) {
-          // If this symbol is defined and internal, mark it as such.
-          if (it->Symbol->isDefined() &&
-              !Asm.getSymbolData(*it->Symbol).isExternal()) {
-            uint32_t Flags = ISF_Local;
-            if (it->Symbol->isAbsolute())
-              Flags |= ISF_Absolute;
-            Write32(Flags);
-            continue;
-          }
-        }
-
-        Write32(Asm.getSymbolData(*it->Symbol).getIndex());
-      }
-
-      // FIXME: Check that offsets match computed ones.
-
-      // Write the symbol table entries.
-      for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
-        WriteNlist(LocalSymbolData[i]);
-      for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
-        WriteNlist(ExternalSymbolData[i]);
-      for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
-        WriteNlist(UndefinedSymbolData[i]);
-
-      // Write the string table.
-      OS << StringTable.str();
-    }
-  }
-
-  void ApplyFixup(const MCAsmFixup &Fixup, MCDataFragment &DF) {
-    unsigned Size = 1 << getFixupKindLog2Size(Fixup.Kind);
-
-    // FIXME: Endianness assumption.
-    assert(Fixup.Offset + Size <= DF.getContents().size() &&
-           "Invalid fixup offset!");
-    for (unsigned i = 0; i != Size; ++i)
-      DF.getContents()[Fixup.Offset + i] = uint8_t(Fixup.FixedValue >> (i * 8));
-  }
-};
-
 /* *** */
 
 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
@@ -1008,14 +93,149 @@ MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
 /* *** */
 
 MCAssembler::MCAssembler(MCContext &_Context, TargetAsmBackend &_Backend,
-                         raw_ostream &_OS)
-  : Context(_Context), Backend(_Backend), OS(_OS), SubsectionsViaSymbols(false)
+                         MCCodeEmitter &_Emitter, raw_ostream &_OS)
+  : Context(_Context), Backend(_Backend), Emitter(_Emitter),
+    OS(_OS), SubsectionsViaSymbols(false)
 {
 }
 
 MCAssembler::~MCAssembler() {
 }
 
+static bool isScatteredFixupFullyResolvedSimple(const MCAssembler &Asm,
+                                                const MCAsmFixup &Fixup,
+                                                const MCDataFragment *DF,
+                                                const MCValue Target,
+                                                const MCSection *BaseSection) {
+  // The effective fixup address is
+  //     addr(atom(A)) + offset(A)
+  //   - addr(atom(B)) - offset(B)
+  //   - addr(<base symbol>) + <fixup offset from base symbol>
+  // and the offsets are not relocatable, so the fixup is fully resolved when
+  //  addr(atom(A)) - addr(atom(B)) - addr(<base symbol>)) == 0.
+  //
+  // The simple (Darwin, except on x86_64) way of dealing with this was to
+  // assume that any reference to a temporary symbol *must* be a temporary
+  // symbol in the same atom, unless the sections differ. Therefore, any PCrel
+  // relocation to a temporary symbol (in the same section) is fully
+  // resolved. This also works in conjunction with absolutized .set, which
+  // requires the compiler to use .set to absolutize the differences between
+  // symbols which the compiler knows to be assembly time constants, so we don't
+  // need to worry about consider symbol differences fully resolved.
+
+  // Non-relative fixups are only resolved if constant.
+  if (!BaseSection)
+    return Target.isAbsolute();
+
+  // Otherwise, relative fixups are only resolved if not a difference and the
+  // target is a temporary in the same section.
+  if (Target.isAbsolute() || Target.getSymB())
+    return false;
+
+  const MCSymbol *A = &Target.getSymA()->getSymbol();
+  if (!A->isTemporary() || !A->isInSection() ||
+      &A->getSection() != BaseSection)
+    return false;
+
+  return true;
+}
+
+static bool isScatteredFixupFullyResolved(const MCAssembler &Asm,
+                                          const MCAsmFixup &Fixup,
+                                          const MCDataFragment *DF,
+                                          const MCValue Target,
+                                          const MCSymbolData *BaseSymbol) {
+  // The effective fixup address is
+  //     addr(atom(A)) + offset(A)
+  //   - addr(atom(B)) - offset(B)
+  //   - addr(BaseSymbol) + <fixup offset from base symbol>
+  // and the offsets are not relocatable, so the fixup is fully resolved when
+  //  addr(atom(A)) - addr(atom(B)) - addr(BaseSymbol) == 0.
+  //
+  // Note that "false" is almost always conservatively correct (it means we emit
+  // a relocation which is unnecessary), except when it would force us to emit a
+  // relocation which the target cannot encode.
+
+  const MCSymbolData *A_Base = 0, *B_Base = 0;
+  if (const MCSymbolRefExpr *A = Target.getSymA()) {
+    // Modified symbol references cannot be resolved.
+    if (A->getKind() != MCSymbolRefExpr::VK_None)
+      return false;
+
+    A_Base = Asm.getAtom(&Asm.getSymbolData(A->getSymbol()));
+    if (!A_Base)
+      return false;
+  }
+
+  if (const MCSymbolRefExpr *B = Target.getSymB()) {
+    // Modified symbol references cannot be resolved.
+    if (B->getKind() != MCSymbolRefExpr::VK_None)
+      return false;
+
+    B_Base = Asm.getAtom(&Asm.getSymbolData(B->getSymbol()));
+    if (!B_Base)
+      return false;
+  }
+
+  // If there is no base, A and B have to be the same atom for this fixup to be
+  // fully resolved.
+  if (!BaseSymbol)
+    return A_Base == B_Base;
+
+  // Otherwise, B must be missing and A must be the base.
+  return !B_Base && BaseSymbol == A_Base;
+}
+
+bool MCAssembler::isSymbolLinkerVisible(const MCSymbolData *SD) const {
+  // Non-temporary labels should always be visible to the linker.
+  if (!SD->getSymbol().isTemporary())
+    return true;
+
+  // Absolute temporary labels are never visible.
+  if (!SD->getFragment())
+    return false;
+
+  // Otherwise, check if the section requires symbols even for temporary labels.
+  return getBackend().doesSectionRequireSymbols(
+    SD->getFragment()->getParent()->getSection());
+}
+
+const MCSymbolData *MCAssembler::getAtomForAddress(const MCSectionData *Section,
+                                                   uint64_t Address) const {
+  const MCSymbolData *Best = 0;
+  for (MCAssembler::const_symbol_iterator it = symbol_begin(),
+         ie = symbol_end(); it != ie; ++it) {
+    // Ignore non-linker visible symbols.
+    if (!isSymbolLinkerVisible(it))
+      continue;
+
+    // Ignore symbols not in the same section.
+    if (!it->getFragment() || it->getFragment()->getParent() != Section)
+      continue;
+
+    // Otherwise, find the closest symbol preceding this address (ties are
+    // resolved in favor of the last defined symbol).
+    if (it->getAddress() <= Address &&
+        (!Best || it->getAddress() >= Best->getAddress()))
+      Best = it;
+  }
+
+  return Best;
+}
+
+const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
+  // Linker visible symbols define atoms.
+  if (isSymbolLinkerVisible(SD))
+    return SD;
+
+  // Absolute and undefined symbols have no defining atom.
+  if (!SD->getFragment())
+    return 0;
+
+  // Otherwise, search by address.
+  return getAtomForAddress(SD->getFragment()->getParent(), SD->getAddress());
+}
+
 bool MCAssembler::EvaluateFixup(const MCAsmLayout &Layout, MCAsmFixup &Fixup,
                                 MCDataFragment *DF,
                                 MCValue &Target, uint64_t &Value) const {
@@ -1028,34 +248,47 @@ bool MCAssembler::EvaluateFixup(const MCAsmLayout &Layout, MCAsmFixup &Fixup,
 
   Value = Target.getConstant();
 
-  // FIXME: This "resolved" check isn't quite right. The assumption is that if
-  // we have a PCrel access to a temporary, then that temporary is in the same
-  // atom, and so the value is resolved. We need explicit atom's to implement
-  // this more precisely.
-  bool IsResolved = true, IsPCRel = isFixupKindPCRel(Fixup.Kind);
-  if (const MCSymbol *Symbol = Target.getSymA()) {
-    if (Symbol->isDefined())
-      Value += getSymbolData(*Symbol).getAddress();
+  bool IsPCRel =
+    Emitter.getFixupKindInfo(Fixup.Kind).Flags & MCFixupKindInfo::FKF_IsPCRel;
+  bool IsResolved = true;
+  if (const MCSymbolRefExpr *A = Target.getSymA()) {
+    if (A->getSymbol().isDefined())
+      Value += getSymbolData(A->getSymbol()).getAddress();
     else
       IsResolved = false;
-
-    // With scattered symbols, we assume anything that isn't a PCrel temporary
-    // access can have an arbitrary value.
-    if (getBackend().hasScatteredSymbols() &&
-        (!IsPCRel || !Symbol->isTemporary()))
-      IsResolved = false;
   }
-  if (const MCSymbol *Symbol = Target.getSymB()) {
-    if (Symbol->isDefined())
-      Value -= getSymbolData(*Symbol).getAddress();
+  if (const MCSymbolRefExpr *B = Target.getSymB()) {
+    if (B->getSymbol().isDefined())
+      Value -= getSymbolData(B->getSymbol()).getAddress();
     else
       IsResolved = false;
+  }
 
-    // With scattered symbols, we assume anything that isn't a PCrel temporary
-    // access can have an arbitrary value.
-    if (getBackend().hasScatteredSymbols() &&
-        (!IsPCRel || !Symbol->isTemporary()))
-      IsResolved = false;
+  // If we are using scattered symbols, determine whether this value is actually
+  // resolved; scattering may cause atoms to move.
+  if (IsResolved && getBackend().hasScatteredSymbols()) {
+    if (getBackend().hasReliableSymbolDifference()) {
+      // If this is a PCrel relocation, find the base atom (identified by its
+      // symbol) that the fixup value is relative to.
+      const MCSymbolData *BaseSymbol = 0;
+      if (IsPCRel) {
+        BaseSymbol = getAtomForAddress(
+          DF->getParent(), DF->getAddress() + Fixup.Offset);
+        if (!BaseSymbol)
+          IsResolved = false;
+      }
+
+      if (IsResolved)
+        IsResolved = isScatteredFixupFullyResolved(*this, Fixup, DF, Target,
+                                                   BaseSymbol);
+    } else {
+      const MCSection *BaseSection = 0;
+      if (IsPCRel)
+        BaseSection = &DF->getParent()->getSection();
+
+      IsResolved = isScatteredFixupFullyResolvedSimple(*this, Fixup, DF, Target,
+                                                       BaseSection);
+    }
   }
 
   if (IsPCRel)
@@ -1127,7 +360,7 @@ void MCAssembler::LayoutSection(MCSectionData &SD) {
 
   // Set the section sizes.
   SD.setSize(Address - SD.getAddress());
-  if (isVirtualSection(SD.getSection()))
+  if (getBackend().isVirtualSection(SD.getSection()))
     SD.setFileSize(0);
   else
     SD.setFileSize(Address - SD.getAddress());
@@ -1138,7 +371,7 @@ void MCAssembler::LayoutSection(MCSectionData &SD) {
 /// the \arg Count is more than the maximum optimal nops.
 ///
 /// FIXME this is X86 32-bit specific and should move to a better place.
-static uint64_t WriteNopData(uint64_t Count, MachObjectWriter &MOW) {
+static uint64_t WriteNopData(uint64_t Count, MCObjectWriter *OW) {
   static const uint8_t Nops[16][16] = {
     // nop
     {0x90},
@@ -1186,15 +419,14 @@ static uint64_t WriteNopData(uint64_t Count, MachObjectWriter &MOW) {
     return 0;
 
   for (uint64_t i = 0; i < Count; i++)
-    MOW.Write8 (uint8_t(Nops[Count - 1][i]));
+    OW->Write8(uint8_t(Nops[Count - 1][i]));
 
   return Count;
 }
 
-/// WriteFileData - Write the \arg F data to the output file.
-static void WriteFileData(raw_ostream &OS, const MCFragment &F,
-                          MachObjectWriter &MOW) {
-  uint64_t Start = OS.tell();
+/// WriteFragmentData - Write the \arg F data to the output file.
+static void WriteFragmentData(const MCFragment &F, MCObjectWriter *OW) {
+  uint64_t Start = OW->getStream().tell();
   (void) Start;
 
   ++EmittedFragments;
@@ -1218,7 +450,7 @@ static void WriteFileData(raw_ostream &OS, const MCFragment &F,
     // the Count bytes.  Then if that did not fill any bytes or there are any
     // bytes left to fill use the the Value and ValueSize to fill the rest.
     if (AF.getEmitNops()) {
-      uint64_t NopByteCount = WriteNopData(Count, MOW);
+      uint64_t NopByteCount = WriteNopData(Count, OW);
       Count -= NopByteCount;
     }
 
@@ -1226,26 +458,17 @@ static void WriteFileData(raw_ostream &OS, const MCFragment &F,
       switch (AF.getValueSize()) {
       default:
         assert(0 && "Invalid size!");
-      case 1: MOW.Write8 (uint8_t (AF.getValue())); break;
-      case 2: MOW.Write16(uint16_t(AF.getValue())); break;
-      case 4: MOW.Write32(uint32_t(AF.getValue())); break;
-      case 8: MOW.Write64(uint64_t(AF.getValue())); break;
+      case 1: OW->Write8 (uint8_t (AF.getValue())); break;
+      case 2: OW->Write16(uint16_t(AF.getValue())); break;
+      case 4: OW->Write32(uint32_t(AF.getValue())); break;
+      case 8: OW->Write64(uint64_t(AF.getValue())); break;
       }
     }
     break;
   }
 
   case MCFragment::FT_Data: {
-    MCDataFragment &DF = cast<MCDataFragment>(F);
-
-    // Apply the fixups.
-    //
-    // FIXME: Move elsewhere.
-    for (MCDataFragment::const_fixup_iterator it = DF.fixup_begin(),
-           ie = DF.fixup_end(); it != ie; ++it)
-      MOW.ApplyFixup(*it, DF);
-
-    OS << cast<MCDataFragment>(F).getContents().str();
+    OW->WriteBytes(cast<MCDataFragment>(F).getContents().str());
     break;
   }
 
@@ -1255,10 +478,10 @@ static void WriteFileData(raw_ostream &OS, const MCFragment &F,
       switch (FF.getValueSize()) {
       default:
         assert(0 && "Invalid size!");
-      case 1: MOW.Write8 (uint8_t (FF.getValue())); break;
-      case 2: MOW.Write16(uint16_t(FF.getValue())); break;
-      case 4: MOW.Write32(uint32_t(FF.getValue())); break;
-      case 8: MOW.Write64(uint64_t(FF.getValue())); break;
+      case 1: OW->Write8 (uint8_t (FF.getValue())); break;
+      case 2: OW->Write16(uint16_t(FF.getValue())); break;
+      case 4: OW->Write32(uint32_t(FF.getValue())); break;
+      case 8: OW->Write64(uint64_t(FF.getValue())); break;
       }
     }
     break;
@@ -1268,7 +491,7 @@ static void WriteFileData(raw_ostream &OS, const MCFragment &F,
     MCOrgFragment &OF = cast<MCOrgFragment>(F);
 
     for (uint64_t i = 0, e = OF.getFileSize(); i != e; ++i)
-      MOW.Write8(uint8_t(OF.getValue()));
+      OW->Write8(uint8_t(OF.getValue()));
 
     break;
   }
@@ -1279,30 +502,29 @@ static void WriteFileData(raw_ostream &OS, const MCFragment &F,
   }
   }
 
-  assert(OS.tell() - Start == F.getFileSize());
+  assert(OW->getStream().tell() - Start == F.getFileSize());
 }
 
-/// WriteFileData - Write the \arg SD data to the output file.
-static void WriteFileData(raw_ostream &OS, const MCSectionData &SD,
-                          MachObjectWriter &MOW) {
+void MCAssembler::WriteSectionData(const MCSectionData *SD,
+                                   MCObjectWriter *OW) const {
   // Ignore virtual sections.
-  if (isVirtualSection(SD.getSection())) {
-    assert(SD.getFileSize() == 0);
+  if (getBackend().isVirtualSection(SD->getSection())) {
+    assert(SD->getFileSize() == 0);
     return;
   }
 
-  uint64_t Start = OS.tell();
+  uint64_t Start = OW->getStream().tell();
   (void) Start;
 
-  for (MCSectionData::const_iterator it = SD.begin(),
-         ie = SD.end(); it != ie; ++it)
-    WriteFileData(OS, *it, MOW);
+  for (MCSectionData::const_iterator it = SD->begin(),
+         ie = SD->end(); it != ie; ++it)
+    WriteFragmentData(*it, OW);
 
   // Add section padding.
-  assert(SD.getFileSize() >= SD.getSize() && "Invalid section sizes!");
-  MOW.WriteZeros(SD.getFileSize() - SD.getSize());
+  assert(SD->getFileSize() >= SD->getSize() && "Invalid section sizes!");
+  OW->WriteZeros(SD->getFileSize() - SD->getSize());
 
-  assert(OS.tell() - Start == SD.getFileSize());
+  assert(OW->getStream().tell() - Start == SD->getFileSize());
 }
 
 void MCAssembler::Finish() {
@@ -1318,13 +540,47 @@ void MCAssembler::Finish() {
       llvm::errs() << "assembler backend - post-layout\n--\n";
       dump(); });
 
-  // Write the object file.
-  //
   // FIXME: Factor out MCObjectWriter.
-  bool Is64Bit = StringRef(getBackend().getTarget().getName()) == "x86-64";
-  MachObjectWriter MOW(OS, Is64Bit);
-  MOW.WriteObject(*this);
+  llvm::OwningPtr<MCObjectWriter> Writer(getBackend().createObjectWriter(OS));
+  if (!Writer)
+    llvm_report_error("unable to create object writer!");
+
+  // Allow the object writer a chance to perform post-layout binding (for
+  // example, to set the index fields in the symbol data).
+  Writer->ExecutePostLayoutBinding(*this);
+
+  // Evaluate and apply the fixups, generating relocation entries as necessary.
+  //
+  // FIXME: Share layout object.
+  MCAsmLayout Layout(*this);
+  for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
+    for (MCSectionData::iterator it2 = it->begin(),
+           ie2 = it->end(); it2 != ie2; ++it2) {
+      MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
+      if (!DF)
+        continue;
+
+      for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
+             ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
+        MCAsmFixup &Fixup = *it3;
 
+        // Evaluate the fixup.
+        MCValue Target;
+        uint64_t FixedValue;
+        if (!EvaluateFixup(Layout, Fixup, DF, Target, FixedValue)) {
+          // The fixup was unresolved, we need a relocation. Inform the object
+          // writer of the relocation, and give it an opportunity to adjust the
+          // fixup value if need be.
+          Writer->RecordRelocation(*this, *DF, Fixup, Target, FixedValue);
+        }
+
+        getBackend().ApplyFixup(Fixup, *DF, FixedValue);
+      }
+    }
+  }
+
+  // Write the object file.
+  Writer->WriteObject(*this);
   OS.flush();
 }
 
@@ -1354,7 +610,7 @@ bool MCAssembler::LayoutOnce() {
     MCSectionData &SD = *it;
 
     // Skip virtual sections.
-    if (isVirtualSection(SD.getSection()))
+    if (getBackend().isVirtualSection(SD.getSection()))
       continue;
 
     // Align this section if necessary by adding padding bytes to the previous
@@ -1377,7 +633,7 @@ bool MCAssembler::LayoutOnce() {
   for (iterator it = begin(), ie = end(); it != ie; ++it) {
     MCSectionData &SD = *it;
 
-    if (!isVirtualSection(SD.getSection()))
+    if (!getBackend().isVirtualSection(SD.getSection()))
       continue;
 
     // Align this section if necessary by adding padding bytes to the previous
diff --git a/lib/MC/MCCodeEmitter.cpp b/lib/MC/MCCodeEmitter.cpp
index accb06c8af54..d51323785541 100644
--- a/lib/MC/MCCodeEmitter.cpp
+++ b/lib/MC/MCCodeEmitter.cpp
@@ -19,10 +19,10 @@ MCCodeEmitter::~MCCodeEmitter() {
 
 const MCFixupKindInfo &MCCodeEmitter::getFixupKindInfo(MCFixupKind Kind) const {
   static const MCFixupKindInfo Builtins[] = {
-    { "FK_Data_1", 0, 8 },
-    { "FK_Data_2", 0, 16 },
-    { "FK_Data_4", 0, 32 },
-    { "FK_Data_8", 0, 64 }
+    { "FK_Data_1", 0, 8, 0 },
+    { "FK_Data_2", 0, 16, 0 },
+    { "FK_Data_4", 0, 32, 0 },
+    { "FK_Data_8", 0, 64, 0 }
   };
   
   assert(Kind <= 3 && "Unknown fixup kind");
diff --git a/lib/MC/MCContext.cpp b/lib/MC/MCContext.cpp
index 70c89a2333af..37e828252602 100644
--- a/lib/MC/MCContext.cpp
+++ b/lib/MC/MCContext.cpp
@@ -49,17 +49,6 @@ MCSymbol *MCContext::CreateTempSymbol() {
                                     "tmp" + Twine(NextUniqueID++));
 }
 
-
-MCSymbol *MCContext::GetOrCreateTemporarySymbol(StringRef Name) {
-  // If there is no name, create a new anonymous symbol.
-  // FIXME: Remove this.  This form of the method should always take a name.
-  if (Name.empty())
-    return GetOrCreateTemporarySymbol(Twine(MAI.getPrivateGlobalPrefix()) +
-                                      "tmp" + Twine(NextUniqueID++));
-  
-  return GetOrCreateSymbol(Name, true);
-}
-
 MCSymbol *MCContext::GetOrCreateTemporarySymbol(const Twine &Name) {
   SmallString<128> NameSV;
   Name.toVector(NameSV);
diff --git a/lib/MC/MCExpr.cpp b/lib/MC/MCExpr.cpp
index a2ed20bb28ca..275994431ee0 100644
--- a/lib/MC/MCExpr.cpp
+++ b/lib/MC/MCExpr.cpp
@@ -30,7 +30,7 @@ void MCExpr::print(raw_ostream &OS) const {
   case MCExpr::SymbolRef: {
     const MCSymbolRefExpr &SRE = cast<MCSymbolRefExpr>(*this);
     const MCSymbol &Sym = SRE.getSymbol();
-    
+
     // Parenthesize names that start with $ so that they don't look like
     // absolute names.
     if (Sym.getName()[0] == '$')
@@ -59,14 +59,14 @@ void MCExpr::print(raw_ostream &OS) const {
 
   case MCExpr::Binary: {
     const MCBinaryExpr &BE = cast<MCBinaryExpr>(*this);
-    
+
     // Only print parens around the LHS if it is non-trivial.
     if (isa<MCConstantExpr>(BE.getLHS()) || isa<MCSymbolRefExpr>(BE.getLHS())) {
       OS << *BE.getLHS();
     } else {
       OS << '(' << *BE.getLHS() << ')';
     }
-    
+
     switch (BE.getOpcode()) {
     default: assert(0 && "Invalid opcode!");
     case MCBinaryExpr::Add:
@@ -77,7 +77,7 @@ void MCExpr::print(raw_ostream &OS) const {
           return;
         }
       }
-        
+
       OS <<  '+';
       break;
     case MCBinaryExpr::And:  OS <<  '&'; break;
@@ -98,7 +98,7 @@ void MCExpr::print(raw_ostream &OS) const {
     case MCBinaryExpr::Sub:  OS <<  '-'; break;
     case MCBinaryExpr::Xor:  OS <<  '^'; break;
     }
-    
+
     // Only print parens around the LHS if it is non-trivial.
     if (isa<MCConstantExpr>(BE.getRHS()) || isa<MCSymbolRefExpr>(BE.getRHS())) {
       OS << *BE.getRHS();
@@ -193,7 +193,7 @@ void MCTargetExpr::Anchor() {}
 
 bool MCExpr::EvaluateAsAbsolute(int64_t &Res, const MCAsmLayout *Layout) const {
   MCValue Value;
-  
+
   if (!EvaluateAsRelocatable(Value, Layout) || !Value.isAbsolute())
     return false;
 
@@ -201,16 +201,16 @@ bool MCExpr::EvaluateAsAbsolute(int64_t &Res, const MCAsmLayout *Layout) const {
   return true;
 }
 
-static bool EvaluateSymbolicAdd(const MCValue &LHS, const MCSymbol *RHS_A, 
-                                const MCSymbol *RHS_B, int64_t RHS_Cst,
+static bool EvaluateSymbolicAdd(const MCValue &LHS,const MCSymbolRefExpr *RHS_A,
+                                const MCSymbolRefExpr *RHS_B, int64_t RHS_Cst,
                                 MCValue &Res) {
   // We can't add or subtract two symbols.
   if ((LHS.getSymA() && RHS_A) ||
       (LHS.getSymB() && RHS_B))
     return false;
 
-  const MCSymbol *A = LHS.getSymA() ? LHS.getSymA() : RHS_A;
-  const MCSymbol *B = LHS.getSymB() ? LHS.getSymB() : RHS_B;
+  const MCSymbolRefExpr *A = LHS.getSymA() ? LHS.getSymA() : RHS_A;
+  const MCSymbolRefExpr *B = LHS.getSymB() ? LHS.getSymB() : RHS_B;
   if (B) {
     // If we have a negated symbol, then we must have also have a non-negated
     // symbol in order to encode the expression. We can do this check later to
@@ -228,13 +228,14 @@ bool MCExpr::EvaluateAsRelocatable(MCValue &Res,
   switch (getKind()) {
   case Target:
     return cast<MCTargetExpr>(this)->EvaluateAsRelocatableImpl(Res, Layout);
-      
+
   case Constant:
     Res = MCValue::get(cast<MCConstantExpr>(this)->getValue());
     return true;
 
   case SymbolRef: {
-    const MCSymbol &Sym = cast<MCSymbolRefExpr>(this)->getSymbol();
+    const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(this);
+    const MCSymbol &Sym = SRE->getSymbol();
 
     // Evaluate recursively if this is a variable.
     if (Sym.isVariable()) {
@@ -245,9 +246,12 @@ bool MCExpr::EvaluateAsRelocatable(MCValue &Res,
       // layout object and the target requests it.
       if (Layout && Res.getSymB() &&
           Layout->getAssembler().getBackend().hasAbsolutizedSet() &&
-          Res.getSymA()->isDefined() && Res.getSymB()->isDefined()) {
-        MCSymbolData &A = Layout->getAssembler().getSymbolData(*Res.getSymA());
-        MCSymbolData &B = Layout->getAssembler().getSymbolData(*Res.getSymB());
+          Res.getSymA()->getSymbol().isDefined() &&
+          Res.getSymB()->getSymbol().isDefined()) {
+        MCSymbolData &A =
+          Layout->getAssembler().getSymbolData(Res.getSymA()->getSymbol());
+        MCSymbolData &B =
+          Layout->getAssembler().getSymbolData(Res.getSymB()->getSymbol());
         Res = MCValue::get(+ A.getFragment()->getAddress() + A.getOffset()
                            - B.getFragment()->getAddress() - B.getOffset()
                            + Res.getConstant());
@@ -256,7 +260,7 @@ bool MCExpr::EvaluateAsRelocatable(MCValue &Res,
       return true;
     }
 
-    Res = MCValue::get(&Sym, 0, 0);
+    Res = MCValue::get(SRE, 0, 0);
     return true;
   }
 
@@ -277,13 +281,13 @@ bool MCExpr::EvaluateAsRelocatable(MCValue &Res,
       /// -(a - b + const) ==> (b - a - const)
       if (Value.getSymA() && !Value.getSymB())
         return false;
-      Res = MCValue::get(Value.getSymB(), Value.getSymA(), 
-                         -Value.getConstant()); 
+      Res = MCValue::get(Value.getSymB(), Value.getSymA(),
+                         -Value.getConstant());
       break;
     case MCUnaryExpr::Not:
       if (!Value.isAbsolute())
         return false;
-      Res = MCValue::get(~Value.getConstant()); 
+      Res = MCValue::get(~Value.getConstant());
       break;
     case MCUnaryExpr::Plus:
       Res = Value;
@@ -296,7 +300,7 @@ bool MCExpr::EvaluateAsRelocatable(MCValue &Res,
   case Binary: {
     const MCBinaryExpr *ABE = cast<MCBinaryExpr>(this);
     MCValue LHSValue, RHSValue;
-    
+
     if (!ABE->getLHS()->EvaluateAsRelocatable(LHSValue, Layout) ||
         !ABE->getRHS()->EvaluateAsRelocatable(RHSValue, Layout))
       return false;
diff --git a/lib/MC/MCMachOStreamer.cpp b/lib/MC/MCMachOStreamer.cpp
index 73b1074531d1..9504392bc1bc 100644
--- a/lib/MC/MCMachOStreamer.cpp
+++ b/lib/MC/MCMachOStreamer.cpp
@@ -45,7 +45,6 @@ class MCMachOStreamer : public MCStreamer {
 
 private:
   MCAssembler Assembler;
-  MCCodeEmitter *Emitter;
   MCSectionData *CurSectionData;
 
 private:
@@ -61,7 +60,7 @@ private:
 public:
   MCMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
                   raw_ostream &_OS, MCCodeEmitter *_Emitter)
-    : MCStreamer(Context), Assembler(Context, TAB, _OS), Emitter(_Emitter),
+    : MCStreamer(Context), Assembler(Context, TAB, *_Emitter, _OS),
       CurSectionData(0) {}
   ~MCMachOStreamer() {}
 
@@ -370,15 +369,12 @@ void MCMachOStreamer::EmitInstruction(const MCInst &Inst) {
     if (Inst.getOperand(i).isExpr())
       AddValueSymbols(Inst.getOperand(i).getExpr());
 
-  if (!Emitter)
-    llvm_unreachable("no code emitter available!");
-
   CurSectionData->setHasInstructions(true);
 
   SmallVector<MCFixup, 4> Fixups;
   SmallString<256> Code;
   raw_svector_ostream VecOS(Code);
-  Emitter->EncodeInstruction(Inst, VecOS, Fixups);
+  Assembler.getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
   VecOS.flush();
 
   // Add the fixups and data.
diff --git a/lib/MC/MCObjectWriter.cpp b/lib/MC/MCObjectWriter.cpp
new file mode 100644
index 000000000000..d117e82b8a1f
--- /dev/null
+++ b/lib/MC/MCObjectWriter.cpp
@@ -0,0 +1,15 @@
+//===- lib/MC/MCObjectWriter.cpp - MCObjectWriter implementation ----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCObjectWriter.h"
+
+using namespace llvm;
+
+MCObjectWriter::~MCObjectWriter() {
+}
diff --git a/lib/MC/MCValue.cpp b/lib/MC/MCValue.cpp
index 043a49d80c6c..c6ea16ce7b4d 100644
--- a/lib/MC/MCValue.cpp
+++ b/lib/MC/MCValue.cpp
@@ -8,6 +8,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/MC/MCValue.h"
+#include "llvm/MC/MCExpr.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -19,10 +20,12 @@ void MCValue::print(raw_ostream &OS, const MCAsmInfo *MAI) const {
     return;
   }
 
-  OS << *getSymA();
+  getSymA()->print(OS);
 
-  if (getSymB())
-    OS << " - " << *getSymB();
+  if (getSymB()) {
+    OS << " - ";
+    getSymB()->print(OS);
+  }
 
   if (getConstant())
     OS << " + " << getConstant();
diff --git a/lib/MC/MachObjectWriter.cpp b/lib/MC/MachObjectWriter.cpp
new file mode 100644
index 000000000000..4b08c226d144
--- /dev/null
+++ b/lib/MC/MachObjectWriter.cpp
@@ -0,0 +1,1109 @@
+//===- lib/MC/MachObjectWriter.cpp - Mach-O File Writer -------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MachObjectWriter.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/MC/MCAssembler.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCObjectWriter.h"
+#include "llvm/MC/MCSectionMachO.h"
+#include "llvm/MC/MCSymbol.h"
+#include "llvm/MC/MCValue.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/MachO.h"
+#include "llvm/Target/TargetAsmBackend.h"
+
+// FIXME: Gross.
+#include "../Target/X86/X86FixupKinds.h"
+
+#include <vector>
+using namespace llvm;
+
+static unsigned getFixupKindLog2Size(unsigned Kind) {
+  switch (Kind) {
+  default: llvm_unreachable("invalid fixup kind!");
+  case X86::reloc_pcrel_1byte:
+  case FK_Data_1: return 0;
+  case FK_Data_2: return 1;
+  case X86::reloc_pcrel_4byte:
+  case X86::reloc_riprel_4byte:
+  case X86::reloc_riprel_4byte_movq_load:
+  case FK_Data_4: return 2;
+  case FK_Data_8: return 3;
+  }
+}
+
+static bool isFixupKindPCRel(unsigned Kind) {
+  switch (Kind) {
+  default:
+    return false;
+  case X86::reloc_pcrel_1byte:
+  case X86::reloc_pcrel_4byte:
+  case X86::reloc_riprel_4byte:
+  case X86::reloc_riprel_4byte_movq_load:
+    return true;
+  }
+}
+
+static bool isFixupKindRIPRel(unsigned Kind) {
+  return Kind == X86::reloc_riprel_4byte ||
+    Kind == X86::reloc_riprel_4byte_movq_load;
+}
+
+namespace {
+
+class MachObjectWriterImpl {
+  // See <mach-o/loader.h>.
+  enum {
+    Header_Magic32 = 0xFEEDFACE,
+    Header_Magic64 = 0xFEEDFACF
+  };
+
+  enum {
+    Header32Size = 28,
+    Header64Size = 32,
+    SegmentLoadCommand32Size = 56,
+    SegmentLoadCommand64Size = 72,
+    Section32Size = 68,
+    Section64Size = 80,
+    SymtabLoadCommandSize = 24,
+    DysymtabLoadCommandSize = 80,
+    Nlist32Size = 12,
+    Nlist64Size = 16,
+    RelocationInfoSize = 8
+  };
+
+  enum HeaderFileType {
+    HFT_Object = 0x1
+  };
+
+  enum HeaderFlags {
+    HF_SubsectionsViaSymbols = 0x2000
+  };
+
+  enum LoadCommandType {
+    LCT_Segment = 0x1,
+    LCT_Symtab = 0x2,
+    LCT_Dysymtab = 0xb,
+    LCT_Segment64 = 0x19
+  };
+
+  // See <mach-o/nlist.h>.
+  enum SymbolTypeType {
+    STT_Undefined = 0x00,
+    STT_Absolute  = 0x02,
+    STT_Section   = 0x0e
+  };
+
+  enum SymbolTypeFlags {
+    // If any of these bits are set, then the entry is a stab entry number (see
+    // <mach-o/stab.h>. Otherwise the other masks apply.
+    STF_StabsEntryMask = 0xe0,
+
+    STF_TypeMask       = 0x0e,
+    STF_External       = 0x01,
+    STF_PrivateExtern  = 0x10
+  };
+
+  /// IndirectSymbolFlags - Flags for encoding special values in the indirect
+  /// symbol entry.
+  enum IndirectSymbolFlags {
+    ISF_Local    = 0x80000000,
+    ISF_Absolute = 0x40000000
+  };
+
+  /// RelocationFlags - Special flags for addresses.
+  enum RelocationFlags {
+    RF_Scattered = 0x80000000
+  };
+
+  enum RelocationInfoType {
+    RIT_Vanilla             = 0,
+    RIT_Pair                = 1,
+    RIT_Difference          = 2,
+    RIT_PreboundLazyPointer = 3,
+    RIT_LocalDifference     = 4
+  };
+
+  /// X86_64 uses its own relocation types.
+  enum RelocationInfoTypeX86_64 {
+    RIT_X86_64_Unsigned   = 0,
+    RIT_X86_64_Signed     = 1,
+    RIT_X86_64_Branch     = 2,
+    RIT_X86_64_GOTLoad    = 3,
+    RIT_X86_64_GOT        = 4,
+    RIT_X86_64_Subtractor = 5,
+    RIT_X86_64_Signed1    = 6,
+    RIT_X86_64_Signed2    = 7,
+    RIT_X86_64_Signed4    = 8
+  };
+
+  /// MachSymbolData - Helper struct for containing some precomputed information
+  /// on symbols.
+  struct MachSymbolData {
+    MCSymbolData *SymbolData;
+    uint64_t StringIndex;
+    uint8_t SectionIndex;
+
+    // Support lexicographic sorting.
+    bool operator<(const MachSymbolData &RHS) const {
+      const std::string &Name = SymbolData->getSymbol().getName();
+      return Name < RHS.SymbolData->getSymbol().getName();
+    }
+  };
+
+  /// @name Relocation Data
+  /// @{
+
+  struct MachRelocationEntry {
+    uint32_t Word0;
+    uint32_t Word1;
+  };
+
+  llvm::DenseMap<const MCSectionData*,
+                 std::vector<MachRelocationEntry> > Relocations;
+
+  /// @}
+  /// @name Symbol Table Data
+  /// @{
+
+  SmallString<256> StringTable;
+  std::vector<MachSymbolData> LocalSymbolData;
+  std::vector<MachSymbolData> ExternalSymbolData;
+  std::vector<MachSymbolData> UndefinedSymbolData;
+
+  /// @}
+
+  MachObjectWriter *Writer;
+
+  raw_ostream &OS;
+
+  unsigned Is64Bit : 1;
+
+public:
+  MachObjectWriterImpl(MachObjectWriter *_Writer, bool _Is64Bit)
+    : Writer(_Writer), OS(Writer->getStream()), Is64Bit(_Is64Bit) {
+  }
+
+  void Write8(uint8_t Value) { Writer->Write8(Value); }
+  void Write16(uint16_t Value) { Writer->Write16(Value); }
+  void Write32(uint32_t Value) { Writer->Write32(Value); }
+  void Write64(uint64_t Value) { Writer->Write64(Value); }
+  void WriteZeros(unsigned N) { Writer->WriteZeros(N); }
+  void WriteBytes(StringRef Str, unsigned ZeroFillSize = 0) {
+    Writer->WriteBytes(Str, ZeroFillSize);
+  }
+
+  void WriteHeader(unsigned NumLoadCommands, unsigned LoadCommandsSize,
+                   bool SubsectionsViaSymbols) {
+    uint32_t Flags = 0;
+
+    if (SubsectionsViaSymbols)
+      Flags |= HF_SubsectionsViaSymbols;
+
+    // struct mach_header (28 bytes) or
+    // struct mach_header_64 (32 bytes)
+
+    uint64_t Start = OS.tell();
+    (void) Start;
+
+    Write32(Is64Bit ? Header_Magic64 : Header_Magic32);
+
+    // FIXME: Support cputype.
+    Write32(Is64Bit ? MachO::CPUTypeX86_64 : MachO::CPUTypeI386);
+    // FIXME: Support cpusubtype.
+    Write32(MachO::CPUSubType_I386_ALL);
+    Write32(HFT_Object);
+    Write32(NumLoadCommands);    // Object files have a single load command, the
+                                 // segment.
+    Write32(LoadCommandsSize);
+    Write32(Flags);
+    if (Is64Bit)
+      Write32(0); // reserved
+
+    assert(OS.tell() - Start == Is64Bit ? Header64Size : Header32Size);
+  }
+
+  /// WriteSegmentLoadCommand - Write a segment load command.
+  ///
+  /// \arg NumSections - The number of sections in this segment.
+  /// \arg SectionDataSize - The total size of the sections.
+  void WriteSegmentLoadCommand(unsigned NumSections,
+                               uint64_t VMSize,
+                               uint64_t SectionDataStartOffset,
+                               uint64_t SectionDataSize) {
+    // struct segment_command (56 bytes) or
+    // struct segment_command_64 (72 bytes)
+
+    uint64_t Start = OS.tell();
+    (void) Start;
+
+    unsigned SegmentLoadCommandSize = Is64Bit ? SegmentLoadCommand64Size :
+      SegmentLoadCommand32Size;
+    Write32(Is64Bit ? LCT_Segment64 : LCT_Segment);
+    Write32(SegmentLoadCommandSize +
+            NumSections * (Is64Bit ? Section64Size : Section32Size));
+
+    WriteBytes("", 16);
+    if (Is64Bit) {
+      Write64(0); // vmaddr
+      Write64(VMSize); // vmsize
+      Write64(SectionDataStartOffset); // file offset
+      Write64(SectionDataSize); // file size
+    } else {
+      Write32(0); // vmaddr
+      Write32(VMSize); // vmsize
+      Write32(SectionDataStartOffset); // file offset
+      Write32(SectionDataSize); // file size
+    }
+    Write32(0x7); // maxprot
+    Write32(0x7); // initprot
+    Write32(NumSections);
+    Write32(0); // flags
+
+    assert(OS.tell() - Start == SegmentLoadCommandSize);
+  }
+
+  void WriteSection(const MCAssembler &Asm, const MCSectionData &SD,
+                    uint64_t FileOffset, uint64_t RelocationsStart,
+                    unsigned NumRelocations) {
+    // The offset is unused for virtual sections.
+    if (Asm.getBackend().isVirtualSection(SD.getSection())) {
+      assert(SD.getFileSize() == 0 && "Invalid file size!");
+      FileOffset = 0;
+    }
+
+    // struct section (68 bytes) or
+    // struct section_64 (80 bytes)
+
+    uint64_t Start = OS.tell();
+    (void) Start;
+
+    // FIXME: cast<> support!
+    const MCSectionMachO &Section =
+      static_cast<const MCSectionMachO&>(SD.getSection());
+    WriteBytes(Section.getSectionName(), 16);
+    WriteBytes(Section.getSegmentName(), 16);
+    if (Is64Bit) {
+      Write64(SD.getAddress()); // address
+      Write64(SD.getSize()); // size
+    } else {
+      Write32(SD.getAddress()); // address
+      Write32(SD.getSize()); // size
+    }
+    Write32(FileOffset);
+
+    unsigned Flags = Section.getTypeAndAttributes();
+    if (SD.hasInstructions())
+      Flags |= MCSectionMachO::S_ATTR_SOME_INSTRUCTIONS;
+
+    assert(isPowerOf2_32(SD.getAlignment()) && "Invalid alignment!");
+    Write32(Log2_32(SD.getAlignment()));
+    Write32(NumRelocations ? RelocationsStart : 0);
+    Write32(NumRelocations);
+    Write32(Flags);
+    Write32(0); // reserved1
+    Write32(Section.getStubSize()); // reserved2
+    if (Is64Bit)
+      Write32(0); // reserved3
+
+    assert(OS.tell() - Start == Is64Bit ? Section64Size : Section32Size);
+  }
+
+  void WriteSymtabLoadCommand(uint32_t SymbolOffset, uint32_t NumSymbols,
+                              uint32_t StringTableOffset,
+                              uint32_t StringTableSize) {
+    // struct symtab_command (24 bytes)
+
+    uint64_t Start = OS.tell();
+    (void) Start;
+
+    Write32(LCT_Symtab);
+    Write32(SymtabLoadCommandSize);
+    Write32(SymbolOffset);
+    Write32(NumSymbols);
+    Write32(StringTableOffset);
+    Write32(StringTableSize);
+
+    assert(OS.tell() - Start == SymtabLoadCommandSize);
+  }
+
+  void WriteDysymtabLoadCommand(uint32_t FirstLocalSymbol,
+                                uint32_t NumLocalSymbols,
+                                uint32_t FirstExternalSymbol,
+                                uint32_t NumExternalSymbols,
+                                uint32_t FirstUndefinedSymbol,
+                                uint32_t NumUndefinedSymbols,
+                                uint32_t IndirectSymbolOffset,
+                                uint32_t NumIndirectSymbols) {
+    // struct dysymtab_command (80 bytes)
+
+    uint64_t Start = OS.tell();
+    (void) Start;
+
+    Write32(LCT_Dysymtab);
+    Write32(DysymtabLoadCommandSize);
+    Write32(FirstLocalSymbol);
+    Write32(NumLocalSymbols);
+    Write32(FirstExternalSymbol);
+    Write32(NumExternalSymbols);
+    Write32(FirstUndefinedSymbol);
+    Write32(NumUndefinedSymbols);
+    Write32(0); // tocoff
+    Write32(0); // ntoc
+    Write32(0); // modtaboff
+    Write32(0); // nmodtab
+    Write32(0); // extrefsymoff
+    Write32(0); // nextrefsyms
+    Write32(IndirectSymbolOffset);
+    Write32(NumIndirectSymbols);
+    Write32(0); // extreloff
+    Write32(0); // nextrel
+    Write32(0); // locreloff
+    Write32(0); // nlocrel
+
+    assert(OS.tell() - Start == DysymtabLoadCommandSize);
+  }
+
+  void WriteNlist(MachSymbolData &MSD) {
+    MCSymbolData &Data = *MSD.SymbolData;
+    const MCSymbol &Symbol = Data.getSymbol();
+    uint8_t Type = 0;
+    uint16_t Flags = Data.getFlags();
+    uint32_t Address = 0;
+
+    // Set the N_TYPE bits. See <mach-o/nlist.h>.
+    //
+    // FIXME: Are the prebound or indirect fields possible here?
+    if (Symbol.isUndefined())
+      Type = STT_Undefined;
+    else if (Symbol.isAbsolute())
+      Type = STT_Absolute;
+    else
+      Type = STT_Section;
+
+    // FIXME: Set STAB bits.
+
+    if (Data.isPrivateExtern())
+      Type |= STF_PrivateExtern;
+
+    // Set external bit.
+    if (Data.isExternal() || Symbol.isUndefined())
+      Type |= STF_External;
+
+    // Compute the symbol address.
+    if (Symbol.isDefined()) {
+      if (Symbol.isAbsolute()) {
+        llvm_unreachable("FIXME: Not yet implemented!");
+      } else {
+        Address = Data.getAddress();
+      }
+    } else if (Data.isCommon()) {
+      // Common symbols are encoded with the size in the address
+      // field, and their alignment in the flags.
+      Address = Data.getCommonSize();
+
+      // Common alignment is packed into the 'desc' bits.
+      if (unsigned Align = Data.getCommonAlignment()) {
+        unsigned Log2Size = Log2_32(Align);
+        assert((1U << Log2Size) == Align && "Invalid 'common' alignment!");
+        if (Log2Size > 15)
+          llvm_report_error("invalid 'common' alignment '" +
+                            Twine(Align) + "'");
+        // FIXME: Keep this mask with the SymbolFlags enumeration.
+        Flags = (Flags & 0xF0FF) | (Log2Size << 8);
+      }
+    }
+
+    // struct nlist (12 bytes)
+
+    Write32(MSD.StringIndex);
+    Write8(Type);
+    Write8(MSD.SectionIndex);
+
+    // The Mach-O streamer uses the lowest 16-bits of the flags for the 'desc'
+    // value.
+    Write16(Flags);
+    if (Is64Bit)
+      Write64(Address);
+    else
+      Write32(Address);
+  }
+
+  void RecordX86_64Relocation(const MCAssembler &Asm,
+                              const MCDataFragment &Fragment,
+                              const MCAsmFixup &Fixup, MCValue Target,
+                              uint64_t &FixedValue) {
+    unsigned IsPCRel = isFixupKindPCRel(Fixup.Kind);
+    unsigned IsRIPRel = isFixupKindRIPRel(Fixup.Kind);
+    unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
+
+    // See <reloc.h>.
+    uint32_t Address = Fragment.getOffset() + Fixup.Offset;
+    int64_t Value = 0;
+    unsigned Index = 0;
+    unsigned IsExtern = 0;
+    unsigned Type = 0;
+
+    Value = Target.getConstant();
+
+    if (IsPCRel) {
+      // Compensate for the relocation offset, Darwin x86_64 relocations only
+      // have the addend and appear to have attempted to define it to be the
+      // actual expression addend without the PCrel bias. However, instructions
+      // with data following the relocation are not accomodated for (see comment
+      // below regarding SIGNED{1,2,4}), so it isn't exactly that either.
+      Value += 1 << Log2Size;
+    }
+
+    if (Target.isAbsolute()) { // constant
+      // SymbolNum of 0 indicates the absolute section.
+      Type = RIT_X86_64_Unsigned;
+      Index = 0;
+
+      // FIXME: I believe this is broken, I don't think the linker can
+      // understand it. I think it would require a local relocation, but I'm not
+      // sure if that would work either. The official way to get an absolute
+      // PCrel relocation is to use an absolute symbol (which we don't support
+      // yet).
+      if (IsPCRel) {
+        IsExtern = 1;
+        Type = RIT_X86_64_Branch;
+      }
+    } else if (Target.getSymB()) { // A - B + constant
+      const MCSymbol *A = &Target.getSymA()->getSymbol();
+      MCSymbolData &A_SD = Asm.getSymbolData(*A);
+      const MCSymbolData *A_Base = Asm.getAtom(&A_SD);
+
+      const MCSymbol *B = &Target.getSymB()->getSymbol();
+      MCSymbolData &B_SD = Asm.getSymbolData(*B);
+      const MCSymbolData *B_Base = Asm.getAtom(&B_SD);
+
+      // Neither symbol can be modified.
+      if (Target.getSymA()->getKind() != MCSymbolRefExpr::VK_None ||
+          Target.getSymB()->getKind() != MCSymbolRefExpr::VK_None)
+        llvm_report_error("unsupported relocation of modified symbol");
+
+      // We don't support PCrel relocations of differences. Darwin 'as' doesn't
+      // implement most of these correctly.
+      if (IsPCRel)
+        llvm_report_error("unsupported pc-relative relocation of difference");
+
+      // We don't currently support any situation where one or both of the
+      // symbols would require a local relocation. This is almost certainly
+      // unused and may not be possible to encode correctly.
+      if (!A_Base || !B_Base)
+        llvm_report_error("unsupported local relocations in difference");
+
+      // Darwin 'as' doesn't emit correct relocations for this (it ends up with
+      // a single SIGNED relocation); reject it for now.
+      if (A_Base == B_Base)
+        llvm_report_error("unsupported relocation with identical base");
+
+      Value += A_SD.getAddress() - A_Base->getAddress();
+      Value -= B_SD.getAddress() - B_Base->getAddress();
+
+      Index = A_Base->getIndex();
+      IsExtern = 1;
+      Type = RIT_X86_64_Unsigned;
+
+      MachRelocationEntry MRE;
+      MRE.Word0 = Address;
+      MRE.Word1 = ((Index     <<  0) |
+                   (IsPCRel   << 24) |
+                   (Log2Size  << 25) |
+                   (IsExtern  << 27) |
+                   (Type      << 28));
+      Relocations[Fragment.getParent()].push_back(MRE);
+
+      Index = B_Base->getIndex();
+      IsExtern = 1;
+      Type = RIT_X86_64_Subtractor;
+    } else {
+      const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
+      MCSymbolData &SD = Asm.getSymbolData(*Symbol);
+      const MCSymbolData *Base = Asm.getAtom(&SD);
+
+      // x86_64 almost always uses external relocations, except when there is no
+      // symbol to use as a base address (a local symbol with no preceeding
+      // non-local symbol).
+      if (Base) {
+        Index = Base->getIndex();
+        IsExtern = 1;
+
+        // Add the local offset, if needed.
+        if (Base != &SD)
+          Value += SD.getAddress() - Base->getAddress();
+      } else {
+        // The index is the section ordinal.
+        //
+        // FIXME: O(N)
+        Index = 1;
+        MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
+        for (; it != ie; ++it, ++Index)
+          if (&*it == SD.getFragment()->getParent())
+            break;
+        assert(it != ie && "Unable to find section index!");
+        IsExtern = 0;
+        Value += SD.getAddress();
+
+        if (IsPCRel)
+          Value -= Address + (1 << Log2Size);
+      }
+
+      MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
+      if (IsPCRel) {
+        if (IsRIPRel) {
+          if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
+            // x86_64 distinguishes movq foo@GOTPCREL so that the linker can
+            // rewrite the movq to an leaq at link time if the symbol ends up in
+            // the same linkage unit.
+            if (unsigned(Fixup.Kind) == X86::reloc_riprel_4byte_movq_load)
+              Type = RIT_X86_64_GOTLoad;
+            else
+              Type = RIT_X86_64_GOT;
+          } else if (Modifier != MCSymbolRefExpr::VK_None)
+            llvm_report_error("unsupported symbol modifier in relocation");
+          else
+            Type = RIT_X86_64_Signed;
+        } else {
+          if (Modifier != MCSymbolRefExpr::VK_None)
+            llvm_report_error("unsupported symbol modifier in branch "
+                              "relocation");
+
+          Type = RIT_X86_64_Branch;
+        }
+
+        // The Darwin x86_64 relocation format has a problem where it cannot
+        // encode an address (L<foo> + <constant>) which is outside the atom
+        // containing L<foo>. Generally, this shouldn't occur but it does happen
+        // when we have a RIPrel instruction with data following the relocation
+        // entry (e.g., movb $012, L0(%rip)). Even with the PCrel adjustment
+        // Darwin x86_64 uses, the offset is still negative and the linker has
+        // no way to recognize this.
+        //
+        // To work around this, Darwin uses several special relocation types to
+        // indicate the offsets. However, the specification or implementation of
+        // these seems to also be incomplete; they should adjust the addend as
+        // well based on the actual encoded instruction (the additional bias),
+        // but instead appear to just look at the final offset.
+        if (IsRIPRel) {
+          switch (-(Target.getConstant() + (1 << Log2Size))) {
+          case 1: Type = RIT_X86_64_Signed1; break;
+          case 2: Type = RIT_X86_64_Signed2; break;
+          case 4: Type = RIT_X86_64_Signed4; break;
+          }
+        }
+      } else {
+        if (Modifier == MCSymbolRefExpr::VK_GOT)
+          Type = RIT_X86_64_GOT;
+        else if (Modifier != MCSymbolRefExpr::VK_None)
+          llvm_report_error("unsupported symbol modifier in relocation");
+        else
+          Type = RIT_X86_64_Unsigned;
+      }
+    }
+
+    // x86_64 always writes custom values into the fixups.
+    FixedValue = Value;
+
+    // struct relocation_info (8 bytes)
+    MachRelocationEntry MRE;
+    MRE.Word0 = Address;
+    MRE.Word1 = ((Index     <<  0) |
+                 (IsPCRel   << 24) |
+                 (Log2Size  << 25) |
+                 (IsExtern  << 27) |
+                 (Type      << 28));
+    Relocations[Fragment.getParent()].push_back(MRE);
+  }
+
+  void RecordScatteredRelocation(const MCAssembler &Asm,
+                                 const MCFragment &Fragment,
+                                 const MCAsmFixup &Fixup, MCValue Target,
+                                 uint64_t &FixedValue) {
+    uint32_t Address = Fragment.getOffset() + Fixup.Offset;
+    unsigned IsPCRel = isFixupKindPCRel(Fixup.Kind);
+    unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
+    unsigned Type = RIT_Vanilla;
+
+    // See <reloc.h>.
+    const MCSymbol *A = &Target.getSymA()->getSymbol();
+    MCSymbolData *A_SD = &Asm.getSymbolData(*A);
+
+    if (!A_SD->getFragment())
+      llvm_report_error("symbol '" + A->getName() +
+                        "' can not be undefined in a subtraction expression");
+
+    uint32_t Value = A_SD->getAddress();
+    uint32_t Value2 = 0;
+
+    if (const MCSymbolRefExpr *B = Target.getSymB()) {
+      MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol());
+
+      if (!B_SD->getFragment())
+        llvm_report_error("symbol '" + B->getSymbol().getName() +
+                          "' can not be undefined in a subtraction expression");
+
+      // Select the appropriate difference relocation type.
+      //
+      // Note that there is no longer any semantic difference between these two
+      // relocation types from the linkers point of view, this is done solely
+      // for pedantic compatibility with 'as'.
+      Type = A_SD->isExternal() ? RIT_Difference : RIT_LocalDifference;
+      Value2 = B_SD->getAddress();
+    }
+
+    // Relocations are written out in reverse order, so the PAIR comes first.
+    if (Type == RIT_Difference || Type == RIT_LocalDifference) {
+      MachRelocationEntry MRE;
+      MRE.Word0 = ((0         <<  0) |
+                   (RIT_Pair  << 24) |
+                   (Log2Size  << 28) |
+                   (IsPCRel   << 30) |
+                   RF_Scattered);
+      MRE.Word1 = Value2;
+      Relocations[Fragment.getParent()].push_back(MRE);
+    }
+
+    MachRelocationEntry MRE;
+    MRE.Word0 = ((Address   <<  0) |
+                 (Type      << 24) |
+                 (Log2Size  << 28) |
+                 (IsPCRel   << 30) |
+                 RF_Scattered);
+    MRE.Word1 = Value;
+    Relocations[Fragment.getParent()].push_back(MRE);
+  }
+
+  void RecordRelocation(const MCAssembler &Asm, const MCDataFragment &Fragment,
+                        const MCAsmFixup &Fixup, MCValue Target,
+                        uint64_t &FixedValue) {
+    if (Is64Bit) {
+      RecordX86_64Relocation(Asm, Fragment, Fixup, Target, FixedValue);
+      return;
+    }
+
+    unsigned IsPCRel = isFixupKindPCRel(Fixup.Kind);
+    unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
+
+    // If this is a difference or a defined symbol plus an offset, then we need
+    // a scattered relocation entry.
+    uint32_t Offset = Target.getConstant();
+    if (IsPCRel)
+      Offset += 1 << Log2Size;
+    if (Target.getSymB() ||
+        (Target.getSymA() && !Target.getSymA()->getSymbol().isUndefined() &&
+         Offset)) {
+      RecordScatteredRelocation(Asm, Fragment, Fixup, Target, FixedValue);
+      return;
+    }
+
+    // See <reloc.h>.
+    uint32_t Address = Fragment.getOffset() + Fixup.Offset;
+    uint32_t Value = 0;
+    unsigned Index = 0;
+    unsigned IsExtern = 0;
+    unsigned Type = 0;
+
+    if (Target.isAbsolute()) { // constant
+      // SymbolNum of 0 indicates the absolute section.
+      //
+      // FIXME: Currently, these are never generated (see code below). I cannot
+      // find a case where they are actually emitted.
+      Type = RIT_Vanilla;
+      Value = 0;
+    } else {
+      const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
+      MCSymbolData *SD = &Asm.getSymbolData(*Symbol);
+
+      if (Symbol->isUndefined()) {
+        IsExtern = 1;
+        Index = SD->getIndex();
+        Value = 0;
+      } else {
+        // The index is the section ordinal.
+        //
+        // FIXME: O(N)
+        Index = 1;
+        MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
+        for (; it != ie; ++it, ++Index)
+          if (&*it == SD->getFragment()->getParent())
+            break;
+        assert(it != ie && "Unable to find section index!");
+        Value = SD->getAddress();
+      }
+
+      Type = RIT_Vanilla;
+    }
+
+    // struct relocation_info (8 bytes)
+    MachRelocationEntry MRE;
+    MRE.Word0 = Address;
+    MRE.Word1 = ((Index     <<  0) |
+                 (IsPCRel   << 24) |
+                 (Log2Size  << 25) |
+                 (IsExtern  << 27) |
+                 (Type      << 28));
+    Relocations[Fragment.getParent()].push_back(MRE);
+  }
+
+  void BindIndirectSymbols(MCAssembler &Asm) {
+    // This is the point where 'as' creates actual symbols for indirect symbols
+    // (in the following two passes). It would be easier for us to do this
+    // sooner when we see the attribute, but that makes getting the order in the
+    // symbol table much more complicated than it is worth.
+    //
+    // FIXME: Revisit this when the dust settles.
+
+    // Bind non lazy symbol pointers first.
+    for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
+           ie = Asm.indirect_symbol_end(); it != ie; ++it) {
+      // FIXME: cast<> support!
+      const MCSectionMachO &Section =
+        static_cast<const MCSectionMachO&>(it->SectionData->getSection());
+
+      if (Section.getType() != MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS)
+        continue;
+
+      Asm.getOrCreateSymbolData(*it->Symbol);
+    }
+
+    // Then lazy symbol pointers and symbol stubs.
+    for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
+           ie = Asm.indirect_symbol_end(); it != ie; ++it) {
+      // FIXME: cast<> support!
+      const MCSectionMachO &Section =
+        static_cast<const MCSectionMachO&>(it->SectionData->getSection());
+
+      if (Section.getType() != MCSectionMachO::S_LAZY_SYMBOL_POINTERS &&
+          Section.getType() != MCSectionMachO::S_SYMBOL_STUBS)
+        continue;
+
+      // Set the symbol type to undefined lazy, but only on construction.
+      //
+      // FIXME: Do not hardcode.
+      bool Created;
+      MCSymbolData &Entry = Asm.getOrCreateSymbolData(*it->Symbol, &Created);
+      if (Created)
+        Entry.setFlags(Entry.getFlags() | 0x0001);
+    }
+  }
+
+  /// ComputeSymbolTable - Compute the symbol table data
+  ///
+  /// \param StringTable [out] - The string table data.
+  /// \param StringIndexMap [out] - Map from symbol names to offsets in the
+  /// string table.
+  void ComputeSymbolTable(MCAssembler &Asm, SmallString<256> &StringTable,
+                          std::vector<MachSymbolData> &LocalSymbolData,
+                          std::vector<MachSymbolData> &ExternalSymbolData,
+                          std::vector<MachSymbolData> &UndefinedSymbolData) {
+    // Build section lookup table.
+    DenseMap<const MCSection*, uint8_t> SectionIndexMap;
+    unsigned Index = 1;
+    for (MCAssembler::iterator it = Asm.begin(),
+           ie = Asm.end(); it != ie; ++it, ++Index)
+      SectionIndexMap[&it->getSection()] = Index;
+    assert(Index <= 256 && "Too many sections!");
+
+    // Index 0 is always the empty string.
+    StringMap<uint64_t> StringIndexMap;
+    StringTable += '\x00';
+
+    // Build the symbol arrays and the string table, but only for non-local
+    // symbols.
+    //
+    // The particular order that we collect the symbols and create the string
+    // table, then sort the symbols is chosen to match 'as'. Even though it
+    // doesn't matter for correctness, this is important for letting us diff .o
+    // files.
+    for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
+           ie = Asm.symbol_end(); it != ie; ++it) {
+      const MCSymbol &Symbol = it->getSymbol();
+
+      // Ignore non-linker visible symbols.
+      if (!Asm.isSymbolLinkerVisible(it))
+        continue;
+
+      if (!it->isExternal() && !Symbol.isUndefined())
+        continue;
+
+      uint64_t &Entry = StringIndexMap[Symbol.getName()];
+      if (!Entry) {
+        Entry = StringTable.size();
+        StringTable += Symbol.getName();
+        StringTable += '\x00';
+      }
+
+      MachSymbolData MSD;
+      MSD.SymbolData = it;
+      MSD.StringIndex = Entry;
+
+      if (Symbol.isUndefined()) {
+        MSD.SectionIndex = 0;
+        UndefinedSymbolData.push_back(MSD);
+      } else if (Symbol.isAbsolute()) {
+        MSD.SectionIndex = 0;
+        ExternalSymbolData.push_back(MSD);
+      } else {
+        MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
+        assert(MSD.SectionIndex && "Invalid section index!");
+        ExternalSymbolData.push_back(MSD);
+      }
+    }
+
+    // Now add the data for local symbols.
+    for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
+           ie = Asm.symbol_end(); it != ie; ++it) {
+      const MCSymbol &Symbol = it->getSymbol();
+
+      // Ignore non-linker visible symbols.
+      if (!Asm.isSymbolLinkerVisible(it))
+        continue;
+
+      if (it->isExternal() || Symbol.isUndefined())
+        continue;
+
+      uint64_t &Entry = StringIndexMap[Symbol.getName()];
+      if (!Entry) {
+        Entry = StringTable.size();
+        StringTable += Symbol.getName();
+        StringTable += '\x00';
+      }
+
+      MachSymbolData MSD;
+      MSD.SymbolData = it;
+      MSD.StringIndex = Entry;
+
+      if (Symbol.isAbsolute()) {
+        MSD.SectionIndex = 0;
+        LocalSymbolData.push_back(MSD);
+      } else {
+        MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
+        assert(MSD.SectionIndex && "Invalid section index!");
+        LocalSymbolData.push_back(MSD);
+      }
+    }
+
+    // External and undefined symbols are required to be in lexicographic order.
+    std::sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
+    std::sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
+
+    // Set the symbol indices.
+    Index = 0;
+    for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
+      LocalSymbolData[i].SymbolData->setIndex(Index++);
+    for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
+      ExternalSymbolData[i].SymbolData->setIndex(Index++);
+    for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
+      UndefinedSymbolData[i].SymbolData->setIndex(Index++);
+
+    // The string table is padded to a multiple of 4.
+    while (StringTable.size() % 4)
+      StringTable += '\x00';
+  }
+
+  void ExecutePostLayoutBinding(MCAssembler &Asm) {
+    // Create symbol data for any indirect symbols.
+    BindIndirectSymbols(Asm);
+
+    // Compute symbol table information and bind symbol indices.
+    ComputeSymbolTable(Asm, StringTable, LocalSymbolData, ExternalSymbolData,
+                       UndefinedSymbolData);
+  }
+
+  void WriteObject(const MCAssembler &Asm) {
+    unsigned NumSections = Asm.size();
+
+    // The section data starts after the header, the segment load command (and
+    // section headers) and the symbol table.
+    unsigned NumLoadCommands = 1;
+    uint64_t LoadCommandsSize = Is64Bit ?
+      SegmentLoadCommand64Size + NumSections * Section64Size :
+      SegmentLoadCommand32Size + NumSections * Section32Size;
+
+    // Add the symbol table load command sizes, if used.
+    unsigned NumSymbols = LocalSymbolData.size() + ExternalSymbolData.size() +
+      UndefinedSymbolData.size();
+    if (NumSymbols) {
+      NumLoadCommands += 2;
+      LoadCommandsSize += SymtabLoadCommandSize + DysymtabLoadCommandSize;
+    }
+
+    // Compute the total size of the section data, as well as its file size and
+    // vm size.
+    uint64_t SectionDataStart = (Is64Bit ? Header64Size : Header32Size)
+      + LoadCommandsSize;
+    uint64_t SectionDataSize = 0;
+    uint64_t SectionDataFileSize = 0;
+    uint64_t VMSize = 0;
+    for (MCAssembler::const_iterator it = Asm.begin(),
+           ie = Asm.end(); it != ie; ++it) {
+      const MCSectionData &SD = *it;
+
+      VMSize = std::max(VMSize, SD.getAddress() + SD.getSize());
+
+      if (Asm.getBackend().isVirtualSection(SD.getSection()))
+        continue;
+
+      SectionDataSize = std::max(SectionDataSize,
+                                 SD.getAddress() + SD.getSize());
+      SectionDataFileSize = std::max(SectionDataFileSize,
+                                     SD.getAddress() + SD.getFileSize());
+    }
+
+    // The section data is padded to 4 bytes.
+    //
+    // FIXME: Is this machine dependent?
+    unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
+    SectionDataFileSize += SectionDataPadding;
+
+    // Write the prolog, starting with the header and load command...
+    WriteHeader(NumLoadCommands, LoadCommandsSize,
+                Asm.getSubsectionsViaSymbols());
+    WriteSegmentLoadCommand(NumSections, VMSize,
+                            SectionDataStart, SectionDataSize);
+
+    // ... and then the section headers.
+    uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
+    for (MCAssembler::const_iterator it = Asm.begin(),
+           ie = Asm.end(); it != ie; ++it) {
+      std::vector<MachRelocationEntry> &Relocs = Relocations[it];
+      unsigned NumRelocs = Relocs.size();
+      uint64_t SectionStart = SectionDataStart + it->getAddress();
+      WriteSection(Asm, *it, SectionStart, RelocTableEnd, NumRelocs);
+      RelocTableEnd += NumRelocs * RelocationInfoSize;
+    }
+
+    // Write the symbol table load command, if used.
+    if (NumSymbols) {
+      unsigned FirstLocalSymbol = 0;
+      unsigned NumLocalSymbols = LocalSymbolData.size();
+      unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
+      unsigned NumExternalSymbols = ExternalSymbolData.size();
+      unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
+      unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
+      unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
+      unsigned NumSymTabSymbols =
+        NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
+      uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
+      uint64_t IndirectSymbolOffset = 0;
+
+      // If used, the indirect symbols are written after the section data.
+      if (NumIndirectSymbols)
+        IndirectSymbolOffset = RelocTableEnd;
+
+      // The symbol table is written after the indirect symbol data.
+      uint64_t SymbolTableOffset = RelocTableEnd + IndirectSymbolSize;
+
+      // The string table is written after symbol table.
+      uint64_t StringTableOffset =
+        SymbolTableOffset + NumSymTabSymbols * (Is64Bit ? Nlist64Size :
+                                                Nlist32Size);
+      WriteSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
+                             StringTableOffset, StringTable.size());
+
+      WriteDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
+                               FirstExternalSymbol, NumExternalSymbols,
+                               FirstUndefinedSymbol, NumUndefinedSymbols,
+                               IndirectSymbolOffset, NumIndirectSymbols);
+    }
+
+    // Write the actual section data.
+    for (MCAssembler::const_iterator it = Asm.begin(),
+           ie = Asm.end(); it != ie; ++it)
+      Asm.WriteSectionData(it, Writer);
+
+    // Write the extra padding.
+    WriteZeros(SectionDataPadding);
+
+    // Write the relocation entries.
+    for (MCAssembler::const_iterator it = Asm.begin(),
+           ie = Asm.end(); it != ie; ++it) {
+      // Write the section relocation entries, in reverse order to match 'as'
+      // (approximately, the exact algorithm is more complicated than this).
+      std::vector<MachRelocationEntry> &Relocs = Relocations[it];
+      for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
+        Write32(Relocs[e - i - 1].Word0);
+        Write32(Relocs[e - i - 1].Word1);
+      }
+    }
+
+    // Write the symbol table data, if used.
+    if (NumSymbols) {
+      // Write the indirect symbol entries.
+      for (MCAssembler::const_indirect_symbol_iterator
+             it = Asm.indirect_symbol_begin(),
+             ie = Asm.indirect_symbol_end(); it != ie; ++it) {
+        // Indirect symbols in the non lazy symbol pointer section have some
+        // special handling.
+        const MCSectionMachO &Section =
+          static_cast<const MCSectionMachO&>(it->SectionData->getSection());
+        if (Section.getType() == MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS) {
+          // If this symbol is defined and internal, mark it as such.
+          if (it->Symbol->isDefined() &&
+              !Asm.getSymbolData(*it->Symbol).isExternal()) {
+            uint32_t Flags = ISF_Local;
+            if (it->Symbol->isAbsolute())
+              Flags |= ISF_Absolute;
+            Write32(Flags);
+            continue;
+          }
+        }
+
+        Write32(Asm.getSymbolData(*it->Symbol).getIndex());
+      }
+
+      // FIXME: Check that offsets match computed ones.
+
+      // Write the symbol table entries.
+      for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
+        WriteNlist(LocalSymbolData[i]);
+      for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
+        WriteNlist(ExternalSymbolData[i]);
+      for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
+        WriteNlist(UndefinedSymbolData[i]);
+
+      // Write the string table.
+      OS << StringTable.str();
+    }
+  }
+};
+
+}
+
+MachObjectWriter::MachObjectWriter(raw_ostream &OS,
+                                   bool Is64Bit,
+                                   bool IsLittleEndian)
+  : MCObjectWriter(OS, IsLittleEndian)
+{
+  Impl = new MachObjectWriterImpl(this, Is64Bit);
+}
+
+MachObjectWriter::~MachObjectWriter() {
+  delete (MachObjectWriterImpl*) Impl;
+}
+
+void MachObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
+  ((MachObjectWriterImpl*) Impl)->ExecutePostLayoutBinding(Asm);
+}
+
+void MachObjectWriter::RecordRelocation(const MCAssembler &Asm,
+                                        const MCDataFragment &Fragment,
+                                        const MCAsmFixup &Fixup, MCValue Target,
+                                        uint64_t &FixedValue) {
+  ((MachObjectWriterImpl*) Impl)->RecordRelocation(Asm, Fragment, Fixup,
+                                                   Target, FixedValue);
+}
+
+void MachObjectWriter::WriteObject(const MCAssembler &Asm) {
+  ((MachObjectWriterImpl*) Impl)->WriteObject(Asm);
+}
diff --git a/lib/MC/TargetAsmBackend.cpp b/lib/MC/TargetAsmBackend.cpp
index 918d2727daa6..bbfddbe9e71f 100644
--- a/lib/MC/TargetAsmBackend.cpp
+++ b/lib/MC/TargetAsmBackend.cpp
@@ -11,7 +11,10 @@
 using namespace llvm;
 
 TargetAsmBackend::TargetAsmBackend(const Target &T)
-  : TheTarget(T)
+  : TheTarget(T),
+    HasAbsolutizedSet(false),
+    HasReliableSymbolDifference(false),
+    HasScatteredSymbols(false)
 {
 }