ARMELFStreamer.cpp

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//===- lib/MC/ARMELFStreamer.cpp - ELF Object Output for ARM --------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file assembles .s files and emits ARM ELF .o object files. Different
// from generic ELF streamer in emitting mapping symbols ($a, $t and $d) to
// delimit regions of data and code.
//
//===----------------------------------------------------------------------===//

#include "ARMBuildAttrs.h"
#include "ARMFPUName.h"
#include "ARMRegisterInfo.h"
#include "ARMUnwindOp.h"
#include "ARMUnwindOpAsm.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCELF.h"
#include "llvm/MC/MCELFStreamer.h"
#include "llvm/MC/MCELFSymbolFlags.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCInstPrinter.h"
#include "llvm/MC/MCObjectStreamer.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ELF.h"
#include "llvm/Support/FormattedStream.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>

using namespace llvm;

static std::string GetAEABIUnwindPersonalityName(unsigned Index) {
  assert(Index < NUM_PERSONALITY_INDEX && "Invalid personality index");
  return (Twine("__aeabi_unwind_cpp_pr") + Twine(Index)).str();
}

static const char *GetFPUName(unsigned ID) {
  switch (ID) {
  default:
    llvm_unreachable("Unknown FPU kind");
    break;
#define ARM_FPU_NAME(NAME, ID) case ARM::ID: return NAME;
#include "ARMFPUName.def"
  }
  return NULL;
}

namespace {

class ARMELFStreamer;

class ARMTargetAsmStreamer : public ARMTargetStreamer {
  formatted_raw_ostream &OS;
  MCInstPrinter &InstPrinter;

  virtual void emitFnStart();
  virtual void emitFnEnd();
  virtual void emitCantUnwind();
  virtual void emitPersonality(const MCSymbol *Personality);
  virtual void emitHandlerData();
  virtual void emitSetFP(unsigned FpReg, unsigned SpReg, int64_t Offset = 0);
  virtual void emitPad(int64_t Offset);
  virtual void emitRegSave(const SmallVectorImpl<unsigned> &RegList,
                           bool isVector);

  virtual void switchVendor(StringRef Vendor);
  virtual void emitAttribute(unsigned Attribute, unsigned Value);
  virtual void emitTextAttribute(unsigned Attribute, StringRef String);
  virtual void emitFPU(unsigned FPU);
  virtual void finishAttributeSection();

public:
  ARMTargetAsmStreamer(formatted_raw_ostream &OS, MCInstPrinter &InstPrinter);
};

ARMTargetAsmStreamer::ARMTargetAsmStreamer(formatted_raw_ostream &OS,
                                           MCInstPrinter &InstPrinter)
    : OS(OS), InstPrinter(InstPrinter) {}
void ARMTargetAsmStreamer::emitFnStart() { OS << "\t.fnstart\n"; }
void ARMTargetAsmStreamer::emitFnEnd() { OS << "\t.fnend\n"; }
void ARMTargetAsmStreamer::emitCantUnwind() { OS << "\t.cantunwind\n"; }
void ARMTargetAsmStreamer::emitPersonality(const MCSymbol *Personality) {
  OS << "\t.personality " << Personality->getName() << '\n';
}
void ARMTargetAsmStreamer::emitHandlerData() { OS << "\t.handlerdata\n"; }
void ARMTargetAsmStreamer::emitSetFP(unsigned FpReg, unsigned SpReg,
                                     int64_t Offset) {
  OS << "\t.setfp\t";
  InstPrinter.printRegName(OS, FpReg);
  OS << ", ";
  InstPrinter.printRegName(OS, SpReg);
  if (Offset)
    OS << ", #" << Offset;
  OS << '\n';
}
void ARMTargetAsmStreamer::emitPad(int64_t Offset) {
  OS << "\t.pad\t#" << Offset << '\n';
}
void ARMTargetAsmStreamer::emitRegSave(const SmallVectorImpl<unsigned> &RegList,
                                       bool isVector) {
  assert(RegList.size() && "RegList should not be empty");
  if (isVector)
    OS << "\t.vsave\t{";
  else
    OS << "\t.save\t{";

  InstPrinter.printRegName(OS, RegList[0]);

  for (unsigned i = 1, e = RegList.size(); i != e; ++i) {
    OS << ", ";
    InstPrinter.printRegName(OS, RegList[i]);
  }

  OS << "}\n";
}
void ARMTargetAsmStreamer::switchVendor(StringRef Vendor) {
}
void ARMTargetAsmStreamer::emitAttribute(unsigned Attribute, unsigned Value) {
  OS << "\t.eabi_attribute\t" << Attribute << ", " << Twine(Value) << "\n";
}
void ARMTargetAsmStreamer::emitTextAttribute(unsigned Attribute,
                                             StringRef String) {
  switch (Attribute) {
  default: llvm_unreachable("Unsupported Text attribute in ASM Mode");
  case ARMBuildAttrs::CPU_name:
    OS << "\t.cpu\t" << String.lower() << "\n";
    break;
  }
}
void ARMTargetAsmStreamer::emitFPU(unsigned FPU) {
  OS << "\t.fpu\t" << GetFPUName(FPU) << "\n";
}
void ARMTargetAsmStreamer::finishAttributeSection() {
}

class ARMTargetELFStreamer : public ARMTargetStreamer {
private:
  // This structure holds all attributes, accounting for
  // their string/numeric value, so we can later emmit them
  // in declaration order, keeping all in the same vector
  struct AttributeItem {
    enum {
      HiddenAttribute = 0,
      NumericAttribute,
      TextAttribute
    } Type;
    unsigned Tag;
    unsigned IntValue;
    StringRef StringValue;

    static bool LessTag(const AttributeItem &LHS, const AttributeItem &RHS) {
      return (LHS.Tag < RHS.Tag);
    }
  };

  StringRef CurrentVendor;
  unsigned FPU;
  SmallVector<AttributeItem, 64> Contents;

  const MCSection *AttributeSection;

  // FIXME: this should be in a more generic place, but
  // getULEBSize() is in MCAsmInfo and will be moved to MCDwarf
  static size_t getULEBSize(int Value) {
    size_t Size = 0;
    do {
      Value >>= 7;
      Size += sizeof(int8_t); // Is this really necessary?
    } while (Value);
    return Size;
  }

  AttributeItem *getAttributeItem(unsigned Attribute) {
    for (size_t i = 0; i < Contents.size(); ++i)
      if (Contents[i].Tag == Attribute)
        return &Contents[i];
    return 0;
  }

  void setAttributeItem(unsigned Attribute, unsigned Value,
                        bool OverwriteExisting) {
    // Look for existing attribute item
    if (AttributeItem *Item = getAttributeItem(Attribute)) {
      if (!OverwriteExisting)
        return;
      Item->IntValue = Value;
      return;
    }

    // Create new attribute item
    AttributeItem Item = {
      AttributeItem::NumericAttribute,
      Attribute,
      Value,
      StringRef("")
    };
    Contents.push_back(Item);
  }

  void setAttributeItem(unsigned Attribute, StringRef Value,
                        bool OverwriteExisting) {
    // Look for existing attribute item
    if (AttributeItem *Item = getAttributeItem(Attribute)) {
      if (!OverwriteExisting)
        return;
      Item->StringValue = Value;
      return;
    }

    // Create new attribute item
    AttributeItem Item = {
      AttributeItem::TextAttribute,
      Attribute,
      0,
      Value
    };
    Contents.push_back(Item);
  }

  void emitFPUDefaultAttributes();

  ARMELFStreamer &getStreamer();

  virtual void emitFnStart();
  virtual void emitFnEnd();
  virtual void emitCantUnwind();
  virtual void emitPersonality(const MCSymbol *Personality);
  virtual void emitHandlerData();
  virtual void emitSetFP(unsigned FpReg, unsigned SpReg, int64_t Offset = 0);
  virtual void emitPad(int64_t Offset);
  virtual void emitRegSave(const SmallVectorImpl<unsigned> &RegList,
                           bool isVector);

  virtual void switchVendor(StringRef Vendor);
  virtual void emitAttribute(unsigned Attribute, unsigned Value);
  virtual void emitTextAttribute(unsigned Attribute, StringRef String);
  virtual void emitFPU(unsigned FPU);
  virtual void finishAttributeSection();

  size_t calculateContentSize() const;

public:
  ARMTargetELFStreamer()
    : ARMTargetStreamer(), CurrentVendor("aeabi"), FPU(ARM::INVALID_FPU),
      AttributeSection(0) {
  }
};

/// Extend the generic ELFStreamer class so that it can emit mapping symbols at
/// the appropriate points in the object files. These symbols are defined in the
/// ARM ELF ABI: infocenter.arm.com/help/topic/com.arm.../IHI0044D_aaelf.pdf.
///
/// In brief: $a, $t or $d should be emitted at the start of each contiguous
/// region of ARM code, Thumb code or data in a section. In practice, this
/// emission does not rely on explicit assembler directives but on inherent
/// properties of the directives doing the emission (e.g. ".byte" is data, "add
/// r0, r0, r0" an instruction).
///
/// As a result this system is orthogonal to the DataRegion infrastructure used
/// by MachO. Beware!
class ARMELFStreamer : public MCELFStreamer {
public:
  friend class ARMTargetELFStreamer;

  ARMELFStreamer(MCContext &Context, MCTargetStreamer *TargetStreamer,
                 MCAsmBackend &TAB, raw_ostream &OS, MCCodeEmitter *Emitter,
                 bool IsThumb)
      : MCELFStreamer(Context, TargetStreamer, TAB, OS, Emitter),
        IsThumb(IsThumb), MappingSymbolCounter(0), LastEMS(EMS_None) {
    Reset();
  }

  ~ARMELFStreamer() {}

  virtual void FinishImpl();

  // ARM exception handling directives
  void emitFnStart();
  void emitFnEnd();
  void emitCantUnwind();
  void emitPersonality(const MCSymbol *Per);
  void emitHandlerData();
  void emitSetFP(unsigned NewFpReg, unsigned NewSpReg, int64_t Offset = 0);
  void emitPad(int64_t Offset);
  void emitRegSave(const SmallVectorImpl<unsigned> &RegList, bool isVector);

  virtual void ChangeSection(const MCSection *Section,
                             const MCExpr *Subsection) {
    // We have to keep track of the mapping symbol state of any sections we
    // use. Each one should start off as EMS_None, which is provided as the
    // default constructor by DenseMap::lookup.
    LastMappingSymbols[getPreviousSection().first] = LastEMS;
    LastEMS = LastMappingSymbols.lookup(Section);

    MCELFStreamer::ChangeSection(Section, Subsection);
  }

  /// This function is the one used to emit instruction data into the ELF
  /// streamer. We override it to add the appropriate mapping symbol if
  /// necessary.
  virtual void EmitInstruction(const MCInst& Inst) {
    if (IsThumb)
      EmitThumbMappingSymbol();
    else
      EmitARMMappingSymbol();

    MCELFStreamer::EmitInstruction(Inst);
  }

  /// This is one of the functions used to emit data into an ELF section, so the
  /// ARM streamer overrides it to add the appropriate mapping symbol ($d) if
  /// necessary.
  virtual void EmitBytes(StringRef Data) {
    EmitDataMappingSymbol();
    MCELFStreamer::EmitBytes(Data);
  }

  /// This is one of the functions used to emit data into an ELF section, so the
  /// ARM streamer overrides it to add the appropriate mapping symbol ($d) if
  /// necessary.
  virtual void EmitValueImpl(const MCExpr *Value, unsigned Size) {
    EmitDataMappingSymbol();
    MCELFStreamer::EmitValueImpl(Value, Size);
  }

  virtual void EmitAssemblerFlag(MCAssemblerFlag Flag) {
    MCELFStreamer::EmitAssemblerFlag(Flag);

    switch (Flag) {
    case MCAF_SyntaxUnified:
      return; // no-op here.
    case MCAF_Code16:
      IsThumb = true;
      return; // Change to Thumb mode
    case MCAF_Code32:
      IsThumb = false;
      return; // Change to ARM mode
    case MCAF_Code64:
      return;
    case MCAF_SubsectionsViaSymbols:
      return;
    }
  }

private:
  enum ElfMappingSymbol {
    EMS_None,
    EMS_ARM,
    EMS_Thumb,
    EMS_Data
  };

  void EmitDataMappingSymbol() {
    if (LastEMS == EMS_Data) return;
    EmitMappingSymbol("$d");
    LastEMS = EMS_Data;
  }

  void EmitThumbMappingSymbol() {
    if (LastEMS == EMS_Thumb) return;
    EmitMappingSymbol("$t");
    LastEMS = EMS_Thumb;
  }

  void EmitARMMappingSymbol() {
    if (LastEMS == EMS_ARM) return;
    EmitMappingSymbol("$a");
    LastEMS = EMS_ARM;
  }

  void EmitMappingSymbol(StringRef Name) {
    MCSymbol *Start = getContext().CreateTempSymbol();
    EmitLabel(Start);

    MCSymbol *Symbol =
      getContext().GetOrCreateSymbol(Name + "." +
                                     Twine(MappingSymbolCounter++));

    MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
    MCELF::SetType(SD, ELF::STT_NOTYPE);
    MCELF::SetBinding(SD, ELF::STB_LOCAL);
    SD.setExternal(false);
    AssignSection(Symbol, getCurrentSection().first);

    const MCExpr *Value = MCSymbolRefExpr::Create(Start, getContext());
    Symbol->setVariableValue(Value);
  }

  void EmitThumbFunc(MCSymbol *Func) {
    // FIXME: Anything needed here to flag the function as thumb?

    getAssembler().setIsThumbFunc(Func);

    MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Func);
    SD.setFlags(SD.getFlags() | ELF_Other_ThumbFunc);
  }

  // Helper functions for ARM exception handling directives
  void Reset();

  void EmitPersonalityFixup(StringRef Name);
  void FlushPendingOffset();
  void FlushUnwindOpcodes(bool NoHandlerData);

  void SwitchToEHSection(const char *Prefix, unsigned Type, unsigned Flags,
                         SectionKind Kind, const MCSymbol &Fn);
  void SwitchToExTabSection(const MCSymbol &FnStart);
  void SwitchToExIdxSection(const MCSymbol &FnStart);

  bool IsThumb;
  int64_t MappingSymbolCounter;

  DenseMap<const MCSection *, ElfMappingSymbol> LastMappingSymbols;
  ElfMappingSymbol LastEMS;

  // ARM Exception Handling Frame Information
  MCSymbol *ExTab;
  MCSymbol *FnStart;
  const MCSymbol *Personality;
  unsigned PersonalityIndex;
  unsigned FPReg; // Frame pointer register
  int64_t FPOffset; // Offset: (final frame pointer) - (initial $sp)
  int64_t SPOffset; // Offset: (final $sp) - (initial $sp)
  int64_t PendingOffset; // Offset: (final $sp) - (emitted $sp)
  bool UsedFP;
  bool CantUnwind;
  SmallVector<uint8_t, 64> Opcodes;
  UnwindOpcodeAssembler UnwindOpAsm;
};
} // end anonymous namespace

ARMELFStreamer &ARMTargetELFStreamer::getStreamer() {
  ARMELFStreamer *S = static_cast<ARMELFStreamer *>(Streamer);
  return *S;
}

void ARMTargetELFStreamer::emitFnStart() { getStreamer().emitFnStart(); }
void ARMTargetELFStreamer::emitFnEnd() { getStreamer().emitFnEnd(); }
void ARMTargetELFStreamer::emitCantUnwind() { getStreamer().emitCantUnwind(); }
void ARMTargetELFStreamer::emitPersonality(const MCSymbol *Personality) {
  getStreamer().emitPersonality(Personality);
}
void ARMTargetELFStreamer::emitHandlerData() {
  getStreamer().emitHandlerData();
}
void ARMTargetELFStreamer::emitSetFP(unsigned FpReg, unsigned SpReg,
                                     int64_t Offset) {
  getStreamer().emitSetFP(FpReg, SpReg, Offset);
}
void ARMTargetELFStreamer::emitPad(int64_t Offset) {
  getStreamer().emitPad(Offset);
}
void ARMTargetELFStreamer::emitRegSave(const SmallVectorImpl<unsigned> &RegList,
                                       bool isVector) {
  getStreamer().emitRegSave(RegList, isVector);
}
void ARMTargetELFStreamer::switchVendor(StringRef Vendor) {
  assert(!Vendor.empty() && "Vendor cannot be empty.");

  if (CurrentVendor == Vendor)
    return;

  if (!CurrentVendor.empty())
    finishAttributeSection();

  assert(Contents.empty() &&
         ".ARM.attributes should be flushed before changing vendor");
  CurrentVendor = Vendor;

}
void ARMTargetELFStreamer::emitAttribute(unsigned Attribute, unsigned Value) {
  setAttributeItem(Attribute, Value, /* OverwriteExisting= */ true);
}
void ARMTargetELFStreamer::emitTextAttribute(unsigned Attribute,
                                             StringRef Value) {
  setAttributeItem(Attribute, Value, /* OverwriteExisting= */ true);
}
void ARMTargetELFStreamer::emitFPU(unsigned Value) {
  FPU = Value;
}
void ARMTargetELFStreamer::emitFPUDefaultAttributes() {
  switch (FPU) {
  case ARM::VFP:
  case ARM::VFPV2:
    setAttributeItem(ARMBuildAttrs::VFP_arch,
                     ARMBuildAttrs::AllowFPv2,
                     /* OverwriteExisting= */ false);
    break;

  case ARM::VFPV3:
    setAttributeItem(ARMBuildAttrs::VFP_arch,
                     ARMBuildAttrs::AllowFPv3A,
                     /* OverwriteExisting= */ false);
    break;

  case ARM::VFPV3_D16:
    setAttributeItem(ARMBuildAttrs::VFP_arch,
                     ARMBuildAttrs::AllowFPv3B,
                     /* OverwriteExisting= */ false);
    break;

  case ARM::VFPV4:
    setAttributeItem(ARMBuildAttrs::VFP_arch,
                     ARMBuildAttrs::AllowFPv4A,
                     /* OverwriteExisting= */ false);
    break;

  case ARM::VFPV4_D16:
    setAttributeItem(ARMBuildAttrs::VFP_arch,
                     ARMBuildAttrs::AllowFPv4B,
                     /* OverwriteExisting= */ false);
    break;

  case ARM::FP_ARMV8:
    setAttributeItem(ARMBuildAttrs::VFP_arch,
                     ARMBuildAttrs::AllowFPARMv8A,
                     /* OverwriteExisting= */ false);
    break;

  case ARM::NEON:
    setAttributeItem(ARMBuildAttrs::VFP_arch,
                     ARMBuildAttrs::AllowFPv3A,
                     /* OverwriteExisting= */ false);
    setAttributeItem(ARMBuildAttrs::Advanced_SIMD_arch,
                     ARMBuildAttrs::AllowNeon,
                     /* OverwriteExisting= */ false);
    break;

  case ARM::NEON_VFPV4:
    setAttributeItem(ARMBuildAttrs::VFP_arch,
                     ARMBuildAttrs::AllowFPv4A,
                     /* OverwriteExisting= */ false);
    setAttributeItem(ARMBuildAttrs::Advanced_SIMD_arch,
                     ARMBuildAttrs::AllowNeon2,
                     /* OverwriteExisting= */ false);
    break;

  case ARM::NEON_FP_ARMV8:
  case ARM::CRYPTO_NEON_FP_ARMV8:
    setAttributeItem(ARMBuildAttrs::VFP_arch,
                     ARMBuildAttrs::AllowFPARMv8A,
                     /* OverwriteExisting= */ false);
    setAttributeItem(ARMBuildAttrs::Advanced_SIMD_arch,
                     ARMBuildAttrs::AllowNeonARMv8,
                     /* OverwriteExisting= */ false);
    break;

  default:
    report_fatal_error("Unknown FPU: " + Twine(FPU));
    break;
  }
}
size_t ARMTargetELFStreamer::calculateContentSize() const {
  size_t Result = 0;
  for (size_t i = 0; i < Contents.size(); ++i) {
    AttributeItem item = Contents[i];
    switch (item.Type) {
    case AttributeItem::HiddenAttribute:
      break;
    case AttributeItem::NumericAttribute:
      Result += getULEBSize(item.Tag);
      Result += getULEBSize(item.IntValue);
      break;
    case AttributeItem::TextAttribute:
      Result += getULEBSize(item.Tag);
      Result += item.StringValue.size() + 1; // string + '\0'
      break;
    }
  }
  return Result;
}
void ARMTargetELFStreamer::finishAttributeSection() {
  // <format-version>
  // [ <section-length> "vendor-name"
  // [ <file-tag> <size> <attribute>*
  //   | <section-tag> <size> <section-number>* 0 <attribute>*
  //   | <symbol-tag> <size> <symbol-number>* 0 <attribute>*
  //   ]+
  // ]*

  if (FPU != ARM::INVALID_FPU)
    emitFPUDefaultAttributes();

  if (Contents.empty())
    return;

  std::sort(Contents.begin(), Contents.end(), AttributeItem::LessTag);

  ARMELFStreamer &Streamer = getStreamer();

  // Switch to .ARM.attributes section
  if (AttributeSection) {
    Streamer.SwitchSection(AttributeSection);
  } else {
    AttributeSection =
      Streamer.getContext().getELFSection(".ARM.attributes",
                                          ELF::SHT_ARM_ATTRIBUTES,
                                          0,
                                          SectionKind::getMetadata());
    Streamer.SwitchSection(AttributeSection);

    // Format version
    Streamer.EmitIntValue(0x41, 1);
  }

  // Vendor size + Vendor name + '\0'
  const size_t VendorHeaderSize = 4 + CurrentVendor.size() + 1;

  // Tag + Tag Size
  const size_t TagHeaderSize = 1 + 4;

  const size_t ContentsSize = calculateContentSize();

  Streamer.EmitIntValue(VendorHeaderSize + TagHeaderSize + ContentsSize, 4);
  Streamer.EmitBytes(CurrentVendor);
  Streamer.EmitIntValue(0, 1); // '\0'

  Streamer.EmitIntValue(ARMBuildAttrs::File, 1);
  Streamer.EmitIntValue(TagHeaderSize + ContentsSize, 4);

  // Size should have been accounted for already, now
  // emit each field as its type (ULEB or String)
  for (size_t i = 0; i < Contents.size(); ++i) {
    AttributeItem item = Contents[i];
    Streamer.EmitULEB128IntValue(item.Tag);
    switch (item.Type) {
    default: llvm_unreachable("Invalid attribute type");
    case AttributeItem::NumericAttribute:
      Streamer.EmitULEB128IntValue(item.IntValue);
      break;
    case AttributeItem::TextAttribute:
      Streamer.EmitBytes(item.StringValue.upper());
      Streamer.EmitIntValue(0, 1); // '\0'
      break;
    }
  }

  Contents.clear();
  FPU = ARM::INVALID_FPU;
}

void ARMELFStreamer::FinishImpl() {
  MCTargetStreamer &TS = getTargetStreamer();
  ARMTargetStreamer &ATS = static_cast<ARMTargetStreamer &>(TS);
  ATS.finishAttributeSection();

  MCELFStreamer::FinishImpl();
}

inline void ARMELFStreamer::SwitchToEHSection(const char *Prefix,
                                              unsigned Type,
                                              unsigned Flags,
                                              SectionKind Kind,
                                              const MCSymbol &Fn) {
  const MCSectionELF &FnSection =
    static_cast<const MCSectionELF &>(Fn.getSection());

  // Create the name for new section
  StringRef FnSecName(FnSection.getSectionName());
  SmallString<128> EHSecName(Prefix);
  if (FnSecName != ".text") {
    EHSecName += FnSecName;
  }

  // Get .ARM.extab or .ARM.exidx section
  const MCSectionELF *EHSection = NULL;
  if (const MCSymbol *Group = FnSection.getGroup()) {
    EHSection = getContext().getELFSection(
      EHSecName, Type, Flags | ELF::SHF_GROUP, Kind,
      FnSection.getEntrySize(), Group->getName());
  } else {
    EHSection = getContext().getELFSection(EHSecName, Type, Flags, Kind);
  }
  assert(EHSection && "Failed to get the required EH section");

  // Switch to .ARM.extab or .ARM.exidx section
  SwitchSection(EHSection);
  EmitCodeAlignment(4, 0);
}

inline void ARMELFStreamer::SwitchToExTabSection(const MCSymbol &FnStart) {
  SwitchToEHSection(".ARM.extab",
                    ELF::SHT_PROGBITS,
                    ELF::SHF_ALLOC,
                    SectionKind::getDataRel(),
                    FnStart);
}

inline void ARMELFStreamer::SwitchToExIdxSection(const MCSymbol &FnStart) {
  SwitchToEHSection(".ARM.exidx",
                    ELF::SHT_ARM_EXIDX,
                    ELF::SHF_ALLOC | ELF::SHF_LINK_ORDER,
                    SectionKind::getDataRel(),
                    FnStart);
}

void ARMELFStreamer::Reset() {
  ExTab = NULL;
  FnStart = NULL;
  Personality = NULL;
  PersonalityIndex = NUM_PERSONALITY_INDEX;
  FPReg = ARM::SP;
  FPOffset = 0;
  SPOffset = 0;
  PendingOffset = 0;
  UsedFP = false;
  CantUnwind = false;

  Opcodes.clear();
  UnwindOpAsm.Reset();
}

void ARMELFStreamer::emitFnStart() {
  assert(FnStart == 0);
  FnStart = getContext().CreateTempSymbol();
  EmitLabel(FnStart);
}

void ARMELFStreamer::emitFnEnd() {
  assert(FnStart && ".fnstart must preceeds .fnend");

  // Emit unwind opcodes if there is no .handlerdata directive
  if (!ExTab && !CantUnwind)
    FlushUnwindOpcodes(true);

  // Emit the exception index table entry
  SwitchToExIdxSection(*FnStart);

  if (PersonalityIndex < NUM_PERSONALITY_INDEX)
    EmitPersonalityFixup(GetAEABIUnwindPersonalityName(PersonalityIndex));

  const MCSymbolRefExpr *FnStartRef =
    MCSymbolRefExpr::Create(FnStart,
                            MCSymbolRefExpr::VK_ARM_PREL31,
                            getContext());

  EmitValue(FnStartRef, 4);

  if (CantUnwind) {
    EmitIntValue(EXIDX_CANTUNWIND, 4);
  } else if (ExTab) {
    // Emit a reference to the unwind opcodes in the ".ARM.extab" section.
    const MCSymbolRefExpr *ExTabEntryRef =
      MCSymbolRefExpr::Create(ExTab,
                              MCSymbolRefExpr::VK_ARM_PREL31,
                              getContext());
    EmitValue(ExTabEntryRef, 4);
  } else {
    // For the __aeabi_unwind_cpp_pr0, we have to emit the unwind opcodes in
    // the second word of exception index table entry.  The size of the unwind
    // opcodes should always be 4 bytes.
    assert(PersonalityIndex == AEABI_UNWIND_CPP_PR0 &&
           "Compact model must use __aeabi_cpp_unwind_pr0 as personality");
    assert(Opcodes.size() == 4u &&
           "Unwind opcode size for __aeabi_cpp_unwind_pr0 must be equal to 4");
    EmitBytes(StringRef(reinterpret_cast<const char*>(Opcodes.data()),
                        Opcodes.size()));
  }

  // Switch to the section containing FnStart
  SwitchSection(&FnStart->getSection());

  // Clean exception handling frame information
  Reset();
}

void ARMELFStreamer::emitCantUnwind() { CantUnwind = true; }

// Add the R_ARM_NONE fixup at the same position
void ARMELFStreamer::EmitPersonalityFixup(StringRef Name) {
  const MCSymbol *PersonalitySym = getContext().GetOrCreateSymbol(Name);

  const MCSymbolRefExpr *PersonalityRef = MCSymbolRefExpr::Create(
      PersonalitySym, MCSymbolRefExpr::VK_ARM_NONE, getContext());

  AddValueSymbols(PersonalityRef);
  MCDataFragment *DF = getOrCreateDataFragment();
  DF->getFixups().push_back(MCFixup::Create(DF->getContents().size(),
                                            PersonalityRef,
                                            MCFixup::getKindForSize(4, false)));
}

void ARMELFStreamer::FlushPendingOffset() {
  if (PendingOffset != 0) {
    UnwindOpAsm.EmitSPOffset(-PendingOffset);
    PendingOffset = 0;
  }
}

void ARMELFStreamer::FlushUnwindOpcodes(bool NoHandlerData) {
  // Emit the unwind opcode to restore $sp.
  if (UsedFP) {
    const MCRegisterInfo *MRI = getContext().getRegisterInfo();
    int64_t LastRegSaveSPOffset = SPOffset - PendingOffset;
    UnwindOpAsm.EmitSPOffset(LastRegSaveSPOffset - FPOffset);
    UnwindOpAsm.EmitSetSP(MRI->getEncodingValue(FPReg));
  } else {
    FlushPendingOffset();
  }

  // Finalize the unwind opcode sequence
  UnwindOpAsm.Finalize(PersonalityIndex, Opcodes);

  // For compact model 0, we have to emit the unwind opcodes in the .ARM.exidx
  // section.  Thus, we don't have to create an entry in the .ARM.extab
  // section.
  if (NoHandlerData && PersonalityIndex == AEABI_UNWIND_CPP_PR0)
    return;

  // Switch to .ARM.extab section.
  SwitchToExTabSection(*FnStart);

  // Create .ARM.extab label for offset in .ARM.exidx
  assert(!ExTab);
  ExTab = getContext().CreateTempSymbol();
  EmitLabel(ExTab);

  // Emit personality
  if (Personality) {
    const MCSymbolRefExpr *PersonalityRef =
      MCSymbolRefExpr::Create(Personality,
                              MCSymbolRefExpr::VK_ARM_PREL31,
                              getContext());

    EmitValue(PersonalityRef, 4);
  }

  // Emit unwind opcodes
  EmitBytes(StringRef(reinterpret_cast<const char *>(Opcodes.data()),
                      Opcodes.size()));

  // According to ARM EHABI section 9.2, if the __aeabi_unwind_cpp_pr1() or
  // __aeabi_unwind_cpp_pr2() is used, then the handler data must be emitted
  // after the unwind opcodes.  The handler data consists of several 32-bit
  // words, and should be terminated by zero.
  //
  // In case that the .handlerdata directive is not specified by the
  // programmer, we should emit zero to terminate the handler data.
  if (NoHandlerData && !Personality)
    EmitIntValue(0, 4);
}

void ARMELFStreamer::emitHandlerData() { FlushUnwindOpcodes(false); }

void ARMELFStreamer::emitPersonality(const MCSymbol *Per) {
  Personality = Per;
  UnwindOpAsm.setPersonality(Per);
}

void ARMELFStreamer::emitSetFP(unsigned NewFPReg, unsigned NewSPReg,
                               int64_t Offset) {
  assert((NewSPReg == ARM::SP || NewSPReg == FPReg) &&
         "the operand of .setfp directive should be either $sp or $fp");

  UsedFP = true;
  FPReg = NewFPReg;

  if (NewSPReg == ARM::SP)
    FPOffset = SPOffset + Offset;
  else
    FPOffset += Offset;
}

void ARMELFStreamer::emitPad(int64_t Offset) {
  // Track the change of the $sp offset
  SPOffset -= Offset;

  // To squash multiple .pad directives, we should delay the unwind opcode
  // until the .save, .vsave, .handlerdata, or .fnend directives.
  PendingOffset -= Offset;
}

void ARMELFStreamer::emitRegSave(const SmallVectorImpl<unsigned> &RegList,
                                 bool IsVector) {
  // Collect the registers in the register list
  unsigned Count = 0;
  uint32_t Mask = 0;
  const MCRegisterInfo *MRI = getContext().getRegisterInfo();
  for (size_t i = 0; i < RegList.size(); ++i) {
    unsigned Reg = MRI->getEncodingValue(RegList[i]);
    assert(Reg < (IsVector ? 32U : 16U) && "Register out of range");
    unsigned Bit = (1u << Reg);
    if ((Mask & Bit) == 0) {
      Mask |= Bit;
      ++Count;
    }
  }

  // Track the change the $sp offset: For the .save directive, the
  // corresponding push instruction will decrease the $sp by (4 * Count).
  // For the .vsave directive, the corresponding vpush instruction will
  // decrease $sp by (8 * Count).
  SPOffset -= Count * (IsVector ? 8 : 4);

  // Emit the opcode
  FlushPendingOffset();
  if (IsVector)
    UnwindOpAsm.EmitVFPRegSave(Mask);
  else
    UnwindOpAsm.EmitRegSave(Mask);
}

namespace llvm {

MCStreamer *createMCAsmStreamer(MCContext &Ctx, formatted_raw_ostream &OS,
                                bool isVerboseAsm, bool useLoc, bool useCFI,
                                bool useDwarfDirectory,
                                MCInstPrinter *InstPrint, MCCodeEmitter *CE,
                                MCAsmBackend *TAB, bool ShowInst) {
  ARMTargetAsmStreamer *S = new ARMTargetAsmStreamer(OS, *InstPrint);

  return llvm::createAsmStreamer(Ctx, S, OS, isVerboseAsm, useLoc, useCFI,
                                 useDwarfDirectory, InstPrint, CE, TAB,
                                 ShowInst);
}

  MCELFStreamer* createARMELFStreamer(MCContext &Context, MCAsmBackend &TAB,
                                      raw_ostream &OS, MCCodeEmitter *Emitter,
                                      bool RelaxAll, bool NoExecStack,
                                      bool IsThumb) {
    ARMTargetELFStreamer *TS = new ARMTargetELFStreamer();
    ARMELFStreamer *S =
        new ARMELFStreamer(Context, TS, TAB, OS, Emitter, IsThumb);
    // FIXME: This should eventually end up somewhere else where more
    // intelligent flag decisions can be made. For now we are just maintaining
    // the status quo for ARM and setting EF_ARM_EABI_VER5 as the default.
    S->getAssembler().setELFHeaderEFlags(ELF::EF_ARM_EABI_VER5);

    if (RelaxAll)
      S->getAssembler().setRelaxAll(true);
    if (NoExecStack)
      S->getAssembler().setNoExecStack(true);
    return S;
  }

}