lib/CodeGen/TargetLoweringObjectFileImpl.cpp

//===-- llvm/CodeGen/TargetLoweringObjectFileImpl.cpp - Object File Info --===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements classes used to handle lowerings specific to common
// object file formats.
//
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
#include "llvm/CodeGen/MachineModuleInfoImpls.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Target/Mangler.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Support/Dwarf.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringExtras.h"
using namespace llvm;
using namespace dwarf;

//===----------------------------------------------------------------------===//
//                                  ELF
//===----------------------------------------------------------------------===//
typedef StringMap<const MCSectionELF*> ELFUniqueMapTy;

TargetLoweringObjectFileELF::~TargetLoweringObjectFileELF() {
  // If we have the section uniquing map, free it.
  delete (ELFUniqueMapTy*)UniquingMap;
}

const MCSection *TargetLoweringObjectFileELF::
getELFSection(StringRef Section, unsigned Type, unsigned Flags,
              SectionKind Kind, bool IsExplicit) const {
  if (UniquingMap == 0)
    UniquingMap = new ELFUniqueMapTy();
  ELFUniqueMapTy &Map = *(ELFUniqueMapTy*)UniquingMap;

  // Do the lookup, if we have a hit, return it.
  const MCSectionELF *&Entry = Map[Section];
  if (Entry) return Entry;

  return Entry = MCSectionELF::Create(Section, Type, Flags, Kind, IsExplicit,
                                      getContext());
}

void TargetLoweringObjectFileELF::Initialize(MCContext &Ctx,
                                             const TargetMachine &TM) {
  if (UniquingMap != 0)
    ((ELFUniqueMapTy*)UniquingMap)->clear();
  TargetLoweringObjectFile::Initialize(Ctx, TM);

  BSSSection =
    getELFSection(".bss", MCSectionELF::SHT_NOBITS,
                  MCSectionELF::SHF_WRITE | MCSectionELF::SHF_ALLOC,
                  SectionKind::getBSS());

  TextSection =
    getELFSection(".text", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_EXECINSTR | MCSectionELF::SHF_ALLOC,
                  SectionKind::getText());

  DataSection =
    getELFSection(".data", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_WRITE | MCSectionELF::SHF_ALLOC,
                  SectionKind::getDataRel());

  ReadOnlySection =
    getELFSection(".rodata", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_ALLOC,
                  SectionKind::getReadOnly());

  TLSDataSection =
    getELFSection(".tdata", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_TLS |
                  MCSectionELF::SHF_WRITE, SectionKind::getThreadData());

  TLSBSSSection =
    getELFSection(".tbss", MCSectionELF::SHT_NOBITS,
                  MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_TLS |
                  MCSectionELF::SHF_WRITE, SectionKind::getThreadBSS());

  DataRelSection =
    getELFSection(".data.rel", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_WRITE,
                  SectionKind::getDataRel());

  DataRelLocalSection =
    getELFSection(".data.rel.local", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_WRITE,
                  SectionKind::getDataRelLocal());

  DataRelROSection =
    getELFSection(".data.rel.ro", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_WRITE,
                  SectionKind::getReadOnlyWithRel());

  DataRelROLocalSection =
    getELFSection(".data.rel.ro.local", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_WRITE,
                  SectionKind::getReadOnlyWithRelLocal());

  MergeableConst4Section =
    getELFSection(".rodata.cst4", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_MERGE,
                  SectionKind::getMergeableConst4());

  MergeableConst8Section =
    getELFSection(".rodata.cst8", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_MERGE,
                  SectionKind::getMergeableConst8());

  MergeableConst16Section =
    getELFSection(".rodata.cst16", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_MERGE,
                  SectionKind::getMergeableConst16());

  StaticCtorSection =
    getELFSection(".ctors", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_WRITE,
                  SectionKind::getDataRel());

  StaticDtorSection =
    getELFSection(".dtors", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_WRITE,
                  SectionKind::getDataRel());

  // Exception Handling Sections.

  // FIXME: We're emitting LSDA info into a readonly section on ELF, even though
  // it contains relocatable pointers.  In PIC mode, this is probably a big
  // runtime hit for C++ apps.  Either the contents of the LSDA need to be
  // adjusted or this should be a data section.
  LSDASection =
    getELFSection(".gcc_except_table", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_ALLOC, SectionKind::getReadOnly());
  EHFrameSection =
    getELFSection(".eh_frame", MCSectionELF::SHT_PROGBITS,
                  MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_WRITE,
                  SectionKind::getDataRel());

  // Debug Info Sections.
  DwarfAbbrevSection =
    getELFSection(".debug_abbrev", MCSectionELF::SHT_PROGBITS, 0,
                  SectionKind::getMetadata());
  DwarfInfoSection =
    getELFSection(".debug_info", MCSectionELF::SHT_PROGBITS, 0,
                  SectionKind::getMetadata());
  DwarfLineSection =
    getELFSection(".debug_line", MCSectionELF::SHT_PROGBITS, 0,
                  SectionKind::getMetadata());
  DwarfFrameSection =
    getELFSection(".debug_frame", MCSectionELF::SHT_PROGBITS, 0,
                  SectionKind::getMetadata());
  DwarfPubNamesSection =
    getELFSection(".debug_pubnames", MCSectionELF::SHT_PROGBITS, 0,
                  SectionKind::getMetadata());
  DwarfPubTypesSection =
    getELFSection(".debug_pubtypes", MCSectionELF::SHT_PROGBITS, 0,
                  SectionKind::getMetadata());
  DwarfStrSection =
    getELFSection(".debug_str", MCSectionELF::SHT_PROGBITS, 0,
                  SectionKind::getMetadata());
  DwarfLocSection =
    getELFSection(".debug_loc", MCSectionELF::SHT_PROGBITS, 0,
                  SectionKind::getMetadata());
  DwarfARangesSection =
    getELFSection(".debug_aranges", MCSectionELF::SHT_PROGBITS, 0,
                  SectionKind::getMetadata());
  DwarfRangesSection =
    getELFSection(".debug_ranges", MCSectionELF::SHT_PROGBITS, 0,
                  SectionKind::getMetadata());
  DwarfMacroInfoSection =
    getELFSection(".debug_macinfo", MCSectionELF::SHT_PROGBITS, 0,
                  SectionKind::getMetadata());
}


static SectionKind
getELFKindForNamedSection(StringRef Name, SectionKind K) {
  if (Name.empty() || Name[0] != '.') return K;

  // Some lame default implementation based on some magic section names.
  if (Name == ".bss" ||
      Name.startswith(".bss.") ||
      Name.startswith(".gnu.linkonce.b.") ||
      Name.startswith(".llvm.linkonce.b.") ||
      Name == ".sbss" ||
      Name.startswith(".sbss.") ||
      Name.startswith(".gnu.linkonce.sb.") ||
      Name.startswith(".llvm.linkonce.sb."))
    return SectionKind::getBSS();

  if (Name == ".tdata" ||
      Name.startswith(".tdata.") ||
      Name.startswith(".gnu.linkonce.td.") ||
      Name.startswith(".llvm.linkonce.td."))
    return SectionKind::getThreadData();

  if (Name == ".tbss" ||
      Name.startswith(".tbss.") ||
      Name.startswith(".gnu.linkonce.tb.") ||
      Name.startswith(".llvm.linkonce.tb."))
    return SectionKind::getThreadBSS();

  return K;
}


static unsigned getELFSectionType(StringRef Name, SectionKind K) {

  if (Name == ".init_array")
    return MCSectionELF::SHT_INIT_ARRAY;

  if (Name == ".fini_array")
    return MCSectionELF::SHT_FINI_ARRAY;

  if (Name == ".preinit_array")
    return MCSectionELF::SHT_PREINIT_ARRAY;

  if (K.isBSS() || K.isThreadBSS())
    return MCSectionELF::SHT_NOBITS;

  return MCSectionELF::SHT_PROGBITS;
}


static unsigned
getELFSectionFlags(SectionKind K) {
  unsigned Flags = 0;

  if (!K.isMetadata())
    Flags |= MCSectionELF::SHF_ALLOC;

  if (K.isText())
    Flags |= MCSectionELF::SHF_EXECINSTR;

  if (K.isWriteable())
    Flags |= MCSectionELF::SHF_WRITE;

  if (K.isThreadLocal())
    Flags |= MCSectionELF::SHF_TLS;

  // K.isMergeableConst() is left out to honour PR4650
  if (K.isMergeableCString() || K.isMergeableConst4() ||
      K.isMergeableConst8() || K.isMergeableConst16())
    Flags |= MCSectionELF::SHF_MERGE;

  if (K.isMergeableCString())
    Flags |= MCSectionELF::SHF_STRINGS;

  return Flags;
}


const MCSection *TargetLoweringObjectFileELF::
getExplicitSectionGlobal(const GlobalValue *GV, SectionKind Kind,
                         Mangler *Mang, const TargetMachine &TM) const {
  StringRef SectionName = GV->getSection();

  // Infer section flags from the section name if we can.
  Kind = getELFKindForNamedSection(SectionName, Kind);

  return getELFSection(SectionName,
                       getELFSectionType(SectionName, Kind),
                       getELFSectionFlags(Kind), Kind, true);
}

static const char *getSectionPrefixForUniqueGlobal(SectionKind Kind) {
  if (Kind.isText())                 return ".gnu.linkonce.t.";
  if (Kind.isReadOnly())             return ".gnu.linkonce.r.";

  if (Kind.isThreadData())           return ".gnu.linkonce.td.";
  if (Kind.isThreadBSS())            return ".gnu.linkonce.tb.";

  if (Kind.isDataNoRel())            return ".gnu.linkonce.d.";
  if (Kind.isDataRelLocal())         return ".gnu.linkonce.d.rel.local.";
  if (Kind.isDataRel())              return ".gnu.linkonce.d.rel.";
  if (Kind.isReadOnlyWithRelLocal()) return ".gnu.linkonce.d.rel.ro.local.";

  assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
  return ".gnu.linkonce.d.rel.ro.";
}

const MCSection *TargetLoweringObjectFileELF::
SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
                       Mangler *Mang, const TargetMachine &TM) const {

  // If this global is linkonce/weak and the target handles this by emitting it
  // into a 'uniqued' section name, create and return the section now.
  if (GV->isWeakForLinker() && !Kind.isCommon() && !Kind.isBSS()) {
    const char *Prefix = getSectionPrefixForUniqueGlobal(Kind);
    SmallString<128> Name;
    Name.append(Prefix, Prefix+strlen(Prefix));
    Mang->getNameWithPrefix(Name, GV, false);
    return getELFSection(Name.str(), getELFSectionType(Name.str(), Kind),
                         getELFSectionFlags(Kind), Kind);
  }

  if (Kind.isText()) return TextSection;

  if (Kind.isMergeable1ByteCString() ||
      Kind.isMergeable2ByteCString() ||
      Kind.isMergeable4ByteCString()) {

    // We also need alignment here.
    // FIXME: this is getting the alignment of the character, not the
    // alignment of the global!
    unsigned Align =
      TM.getTargetData()->getPreferredAlignment(cast<GlobalVariable>(GV));

    const char *SizeSpec = ".rodata.str1.";
    if (Kind.isMergeable2ByteCString())
      SizeSpec = ".rodata.str2.";
    else if (Kind.isMergeable4ByteCString())
      SizeSpec = ".rodata.str4.";
    else
      assert(Kind.isMergeable1ByteCString() && "unknown string width");


    std::string Name = SizeSpec + utostr(Align);
    return getELFSection(Name, MCSectionELF::SHT_PROGBITS,
                         MCSectionELF::SHF_ALLOC |
                         MCSectionELF::SHF_MERGE |
                         MCSectionELF::SHF_STRINGS,
                         Kind);
  }

  if (Kind.isMergeableConst()) {
    if (Kind.isMergeableConst4() && MergeableConst4Section)
      return MergeableConst4Section;
    if (Kind.isMergeableConst8() && MergeableConst8Section)
      return MergeableConst8Section;
    if (Kind.isMergeableConst16() && MergeableConst16Section)
      return MergeableConst16Section;
    return ReadOnlySection;  // .const
  }

  if (Kind.isReadOnly())             return ReadOnlySection;

  if (Kind.isThreadData())           return TLSDataSection;
  if (Kind.isThreadBSS())            return TLSBSSSection;

  // Note: we claim that common symbols are put in BSSSection, but they are
  // really emitted with the magic .comm directive, which creates a symbol table
  // entry but not a section.
  if (Kind.isBSS() || Kind.isCommon()) return BSSSection;

  if (Kind.isDataNoRel())            return DataSection;
  if (Kind.isDataRelLocal())         return DataRelLocalSection;
  if (Kind.isDataRel())              return DataRelSection;
  if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;

  assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
  return DataRelROSection;
}

/// getSectionForConstant - Given a mergeable constant with the
/// specified size and relocation information, return a section that it
/// should be placed in.
const MCSection *TargetLoweringObjectFileELF::
getSectionForConstant(SectionKind Kind) const {
  if (Kind.isMergeableConst4() && MergeableConst4Section)
    return MergeableConst4Section;
  if (Kind.isMergeableConst8() && MergeableConst8Section)
    return MergeableConst8Section;
  if (Kind.isMergeableConst16() && MergeableConst16Section)
    return MergeableConst16Section;
  if (Kind.isReadOnly())
    return ReadOnlySection;

  if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
  assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
  return DataRelROSection;
}

const MCExpr *TargetLoweringObjectFileELF::
getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
                               MachineModuleInfo *MMI,
                               unsigned Encoding, MCStreamer &Streamer) const {

  if (Encoding & dwarf::DW_EH_PE_indirect) {
    MachineModuleInfoELF &ELFMMI = MMI->getObjFileInfo<MachineModuleInfoELF>();

    SmallString<128> Name;
    Mang->getNameWithPrefix(Name, GV, true);
    Name += ".DW.stub";

    // Add information about the stub reference to ELFMMI so that the stub
    // gets emitted by the asmprinter.
    MCSymbol *Sym = getContext().GetOrCreateTemporarySymbol(Name.str());
    MachineModuleInfoImpl::StubValueTy &StubSym = ELFMMI.getGVStubEntry(Sym);
    if (StubSym.getPointer() == 0) {
      Name.clear();
      Mang->getNameWithPrefix(Name, GV, false);

      if (GV->hasPrivateLinkage())
        StubSym = MachineModuleInfoImpl::
          StubValueTy(getContext().GetOrCreateTemporarySymbol(Name.str()),
                      false);
      else
        StubSym = MachineModuleInfoImpl::
          StubValueTy(getContext().GetOrCreateSymbol(Name.str()),
                      !GV->hasInternalLinkage());
    }

    return TargetLoweringObjectFile::
      getExprForDwarfReference(Sym, Mang, MMI,
                               Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
  }

  return TargetLoweringObjectFile::
    getExprForDwarfGlobalReference(GV, Mang, MMI, Encoding, Streamer);
}

//===----------------------------------------------------------------------===//
//                                 MachO
//===----------------------------------------------------------------------===//

typedef StringMap<const MCSectionMachO*> MachOUniqueMapTy;

TargetLoweringObjectFileMachO::~TargetLoweringObjectFileMachO() {
  // If we have the MachO uniquing map, free it.
  delete (MachOUniqueMapTy*)UniquingMap;
}


const MCSectionMachO *TargetLoweringObjectFileMachO::
getMachOSection(StringRef Segment, StringRef Section,
                unsigned TypeAndAttributes,
                unsigned Reserved2, SectionKind Kind) const {
  // We unique sections by their segment/section pair.  The returned section
  // may not have the same flags as the requested section, if so this should be
  // diagnosed by the client as an error.

  // Create the map if it doesn't already exist.
  if (UniquingMap == 0)
    UniquingMap = new MachOUniqueMapTy();
  MachOUniqueMapTy &Map = *(MachOUniqueMapTy*)UniquingMap;

  // Form the name to look up.
  SmallString<64> Name;
  Name += Segment;
  Name.push_back(',');
  Name += Section;

  // Do the lookup, if we have a hit, return it.
  const MCSectionMachO *&Entry = Map[Name.str()];
  if (Entry) return Entry;

  // Otherwise, return a new section.
  return Entry = MCSectionMachO::Create(Segment, Section, TypeAndAttributes,
                                        Reserved2, Kind, getContext());
}


void TargetLoweringObjectFileMachO::Initialize(MCContext &Ctx,
                                               const TargetMachine &TM) {
  // _foo.eh symbols are currently always exported so that the linker knows
  // about them.  This is not necessary on 10.6 and later, but it
  // doesn't hurt anything.
  // FIXME: I need to get this from Triple.
  IsFunctionEHSymbolGlobal = true;
  IsFunctionEHFrameSymbolPrivate = false;
  SupportsWeakOmittedEHFrame = false;
  
  if (UniquingMap != 0)
    ((MachOUniqueMapTy*)UniquingMap)->clear();
  TargetLoweringObjectFile::Initialize(Ctx, TM);

  TextSection // .text
    = getMachOSection("__TEXT", "__text",
                      MCSectionMachO::S_ATTR_PURE_INSTRUCTIONS,
                      SectionKind::getText());
  DataSection // .data
    = getMachOSection("__DATA", "__data", 0, SectionKind::getDataRel());

  CStringSection // .cstring
    = getMachOSection("__TEXT", "__cstring", MCSectionMachO::S_CSTRING_LITERALS,
                      SectionKind::getMergeable1ByteCString());
  UStringSection
    = getMachOSection("__TEXT","__ustring", 0,
                      SectionKind::getMergeable2ByteCString());
  FourByteConstantSection // .literal4
    = getMachOSection("__TEXT", "__literal4", MCSectionMachO::S_4BYTE_LITERALS,
                      SectionKind::getMergeableConst4());
  EightByteConstantSection // .literal8
    = getMachOSection("__TEXT", "__literal8", MCSectionMachO::S_8BYTE_LITERALS,
                      SectionKind::getMergeableConst8());

  // ld_classic doesn't support .literal16 in 32-bit mode, and ld64 falls back
  // to using it in -static mode.
  SixteenByteConstantSection = 0;
  if (TM.getRelocationModel() != Reloc::Static &&
      TM.getTargetData()->getPointerSize() == 32)
    SixteenByteConstantSection =   // .literal16
      getMachOSection("__TEXT", "__literal16",MCSectionMachO::S_16BYTE_LITERALS,
                      SectionKind::getMergeableConst16());

  ReadOnlySection  // .const
    = getMachOSection("__TEXT", "__const", 0, SectionKind::getReadOnly());

  TextCoalSection
    = getMachOSection("__TEXT", "__textcoal_nt",
                      MCSectionMachO::S_COALESCED |
                      MCSectionMachO::S_ATTR_PURE_INSTRUCTIONS,
                      SectionKind::getText());
  ConstTextCoalSection
    = getMachOSection("__TEXT", "__const_coal", MCSectionMachO::S_COALESCED,
                      SectionKind::getText());
  ConstDataCoalSection
    = getMachOSection("__DATA","__const_coal", MCSectionMachO::S_COALESCED,
                      SectionKind::getText());
  ConstDataSection  // .const_data
    = getMachOSection("__DATA", "__const", 0,
                      SectionKind::getReadOnlyWithRel());
  DataCoalSection
    = getMachOSection("__DATA","__datacoal_nt", MCSectionMachO::S_COALESCED,
                      SectionKind::getDataRel());
  DataCommonSection
    = getMachOSection("__DATA","__common", MCSectionMachO::S_ZEROFILL,
                      SectionKind::getBSS());
  DataBSSSection
    = getMachOSection("__DATA","__bss", MCSectionMachO::S_ZEROFILL,
                    SectionKind::getBSS());
  

  LazySymbolPointerSection
    = getMachOSection("__DATA", "__la_symbol_ptr",
                      MCSectionMachO::S_LAZY_SYMBOL_POINTERS,
                      SectionKind::getMetadata());
  NonLazySymbolPointerSection
    = getMachOSection("__DATA", "__nl_symbol_ptr",
                      MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS,
                      SectionKind::getMetadata());

  if (TM.getRelocationModel() == Reloc::Static) {
    StaticCtorSection
      = getMachOSection("__TEXT", "__constructor", 0,SectionKind::getDataRel());
    StaticDtorSection
      = getMachOSection("__TEXT", "__destructor", 0, SectionKind::getDataRel());
  } else {
    StaticCtorSection
      = getMachOSection("__DATA", "__mod_init_func",
                        MCSectionMachO::S_MOD_INIT_FUNC_POINTERS,
                        SectionKind::getDataRel());
    StaticDtorSection
      = getMachOSection("__DATA", "__mod_term_func",
                        MCSectionMachO::S_MOD_TERM_FUNC_POINTERS,
                        SectionKind::getDataRel());
  }

  // Exception Handling.
  LSDASection = getMachOSection("__DATA", "__gcc_except_tab", 0,
                                SectionKind::getDataRel());
  EHFrameSection =
    getMachOSection("__TEXT", "__eh_frame",
                    MCSectionMachO::S_COALESCED |
                    MCSectionMachO::S_ATTR_NO_TOC |
                    MCSectionMachO::S_ATTR_STRIP_STATIC_SYMS |
                    MCSectionMachO::S_ATTR_LIVE_SUPPORT,
                    SectionKind::getReadOnly());

  // Debug Information.
  DwarfAbbrevSection =
    getMachOSection("__DWARF", "__debug_abbrev", MCSectionMachO::S_ATTR_DEBUG,
                    SectionKind::getMetadata());
  DwarfInfoSection =
    getMachOSection("__DWARF", "__debug_info", MCSectionMachO::S_ATTR_DEBUG,
                    SectionKind::getMetadata());
  DwarfLineSection =
    getMachOSection("__DWARF", "__debug_line", MCSectionMachO::S_ATTR_DEBUG,
                    SectionKind::getMetadata());
  DwarfFrameSection =
    getMachOSection("__DWARF", "__debug_frame", MCSectionMachO::S_ATTR_DEBUG,
                    SectionKind::getMetadata());
  DwarfPubNamesSection =
    getMachOSection("__DWARF", "__debug_pubnames", MCSectionMachO::S_ATTR_DEBUG,
                    SectionKind::getMetadata());
  DwarfPubTypesSection =
    getMachOSection("__DWARF", "__debug_pubtypes", MCSectionMachO::S_ATTR_DEBUG,
                    SectionKind::getMetadata());
  DwarfStrSection =
    getMachOSection("__DWARF", "__debug_str", MCSectionMachO::S_ATTR_DEBUG,
                    SectionKind::getMetadata());
  DwarfLocSection =
    getMachOSection("__DWARF", "__debug_loc", MCSectionMachO::S_ATTR_DEBUG,
                    SectionKind::getMetadata());
  DwarfARangesSection =
    getMachOSection("__DWARF", "__debug_aranges", MCSectionMachO::S_ATTR_DEBUG,
                    SectionKind::getMetadata());
  DwarfRangesSection =
    getMachOSection("__DWARF", "__debug_ranges", MCSectionMachO::S_ATTR_DEBUG,
                    SectionKind::getMetadata());
  DwarfMacroInfoSection =
    getMachOSection("__DWARF", "__debug_macinfo", MCSectionMachO::S_ATTR_DEBUG,
                    SectionKind::getMetadata());
  DwarfDebugInlineSection =
    getMachOSection("__DWARF", "__debug_inlined", MCSectionMachO::S_ATTR_DEBUG,
                    SectionKind::getMetadata());
}

const MCSection *TargetLoweringObjectFileMachO::
getExplicitSectionGlobal(const GlobalValue *GV, SectionKind Kind,
                         Mangler *Mang, const TargetMachine &TM) const {
  // Parse the section specifier and create it if valid.
  StringRef Segment, Section;
  unsigned TAA, StubSize;
  std::string ErrorCode =
    MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
                                          TAA, StubSize);
  if (!ErrorCode.empty()) {
    // If invalid, report the error with llvm_report_error.
    llvm_report_error("Global variable '" + GV->getNameStr() +
                      "' has an invalid section specifier '" + GV->getSection()+
                      "': " + ErrorCode + ".");
    // Fall back to dropping it into the data section.
    return DataSection;
  }

  // Get the section.
  const MCSectionMachO *S =
    getMachOSection(Segment, Section, TAA, StubSize, Kind);

  // Okay, now that we got the section, verify that the TAA & StubSize agree.
  // If the user declared multiple globals with different section flags, we need
  // to reject it here.
  if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
    // If invalid, report the error with llvm_report_error.
    llvm_report_error("Global variable '" + GV->getNameStr() +
                      "' section type or attributes does not match previous"
                      " section specifier");
  }

  return S;
}

const MCSection *TargetLoweringObjectFileMachO::
SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
                       Mangler *Mang, const TargetMachine &TM) const {
  assert(!Kind.isThreadLocal() && "Darwin doesn't support TLS");

  if (Kind.isText())
    return GV->isWeakForLinker() ? TextCoalSection : TextSection;

  // If this is weak/linkonce, put this in a coalescable section, either in text
  // or data depending on if it is writable.
  if (GV->isWeakForLinker()) {
    if (Kind.isReadOnly())
      return ConstTextCoalSection;
    return DataCoalSection;
  }

  // FIXME: Alignment check should be handled by section classifier.
  if (Kind.isMergeable1ByteCString() &&
      TM.getTargetData()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
    return CStringSection;
      
  // Do not put 16-bit arrays in the UString section if they have an
  // externally visible label, this runs into issues with certain linker
  // versions.
  if (Kind.isMergeable2ByteCString() && !GV->hasExternalLinkage() &&
      TM.getTargetData()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
    return UStringSection;

  if (Kind.isMergeableConst()) {
    if (Kind.isMergeableConst4())
      return FourByteConstantSection;
    if (Kind.isMergeableConst8())
      return EightByteConstantSection;
    if (Kind.isMergeableConst16() && SixteenByteConstantSection)
      return SixteenByteConstantSection;
  }

  // Otherwise, if it is readonly, but not something we can specially optimize,
  // just drop it in .const.
  if (Kind.isReadOnly())
    return ReadOnlySection;

  // If this is marked const, put it into a const section.  But if the dynamic
  // linker needs to write to it, put it in the data segment.
  if (Kind.isReadOnlyWithRel())
    return ConstDataSection;

  // Put zero initialized globals with strong external linkage in the
  // DATA, __common section with the .zerofill directive.
  if (Kind.isBSSExtern())
    return DataCommonSection;

  // Put zero initialized globals with local linkage in __DATA,__bss directive
  // with the .zerofill directive (aka .lcomm).
  if (Kind.isBSSLocal())
    return DataBSSSection;
  
  // Otherwise, just drop the variable in the normal data section.
  return DataSection;
}

const MCSection *
TargetLoweringObjectFileMachO::getSectionForConstant(SectionKind Kind) const {
  // If this constant requires a relocation, we have to put it in the data
  // segment, not in the text segment.
  if (Kind.isDataRel() || Kind.isReadOnlyWithRel())
    return ConstDataSection;

  if (Kind.isMergeableConst4())
    return FourByteConstantSection;
  if (Kind.isMergeableConst8())
    return EightByteConstantSection;
  if (Kind.isMergeableConst16() && SixteenByteConstantSection)
    return SixteenByteConstantSection;
  return ReadOnlySection;  // .const
}

/// shouldEmitUsedDirectiveFor - This hook allows targets to selectively decide
/// not to emit the UsedDirective for some symbols in llvm.used.
// FIXME: REMOVE this (rdar://7071300)
bool TargetLoweringObjectFileMachO::
shouldEmitUsedDirectiveFor(const GlobalValue *GV, Mangler *Mang) const {
  /// On Darwin, internally linked data beginning with "L" or "l" does not have
  /// the directive emitted (this occurs in ObjC metadata).
  if (!GV) return false;

  // Check whether the mangled name has the "Private" or "LinkerPrivate" prefix.
  if (GV->hasLocalLinkage() && !isa<Function>(GV)) {
    // FIXME: ObjC metadata is currently emitted as internal symbols that have
    // \1L and \0l prefixes on them.  Fix them to be Private/LinkerPrivate and
    // this horrible hack can go away.
    SmallString<64> Name;
    Mang->getNameWithPrefix(Name, GV, false);
    if (Name[0] == 'L' || Name[0] == 'l')
      return false;
  }

  return true;
}

const MCExpr *TargetLoweringObjectFileMachO::
getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
                               MachineModuleInfo *MMI, unsigned Encoding,
                               MCStreamer &Streamer) const {
  // The mach-o version of this method defaults to returning a stub reference.

  if (Encoding & DW_EH_PE_indirect) {
    MachineModuleInfoMachO &MachOMMI =
      MMI->getObjFileInfo<MachineModuleInfoMachO>();

    SmallString<128> Name;
    Mang->getNameWithPrefix(Name, GV, true);
    Name += "$non_lazy_ptr";

    // Add information about the stub reference to MachOMMI so that the stub
    // gets emitted by the asmprinter.
    MCSymbol *Sym = getContext().GetOrCreateTemporarySymbol(Name.str());
    MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(Sym);
    if (StubSym.getPointer() == 0) {
      Name.clear();
      Mang->getNameWithPrefix(Name, GV, false);

      if (GV->hasPrivateLinkage())
        StubSym = MachineModuleInfoImpl::
          StubValueTy(getContext().GetOrCreateTemporarySymbol(Name.str()),
                      false);
      else
        StubSym = MachineModuleInfoImpl::
          StubValueTy(getContext().GetOrCreateSymbol(Name.str()),
                      !GV->hasInternalLinkage());
    }

    return TargetLoweringObjectFile::
      getExprForDwarfReference(Sym, Mang, MMI,
                               Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
  }

  return TargetLoweringObjectFile::
    getExprForDwarfGlobalReference(GV, Mang, MMI, Encoding, Streamer);
}

unsigned TargetLoweringObjectFileMachO::getPersonalityEncoding() const {
  return DW_EH_PE_indirect | DW_EH_PE_pcrel | DW_EH_PE_sdata4;
}

unsigned TargetLoweringObjectFileMachO::getLSDAEncoding() const {
  return DW_EH_PE_pcrel;
}

unsigned TargetLoweringObjectFileMachO::getFDEEncoding() const {
  return DW_EH_PE_pcrel;
}

unsigned TargetLoweringObjectFileMachO::getTTypeEncoding() const {
  return DW_EH_PE_absptr;
}

//===----------------------------------------------------------------------===//
//                                  COFF
//===----------------------------------------------------------------------===//

typedef StringMap<const MCSectionCOFF*> COFFUniqueMapTy;

TargetLoweringObjectFileCOFF::~TargetLoweringObjectFileCOFF() {
  delete (COFFUniqueMapTy*)UniquingMap;
}


const MCSection *TargetLoweringObjectFileCOFF::
getCOFFSection(StringRef Name, bool isDirective, SectionKind Kind) const {
  // Create the map if it doesn't already exist.
  if (UniquingMap == 0)
    UniquingMap = new MachOUniqueMapTy();
  COFFUniqueMapTy &Map = *(COFFUniqueMapTy*)UniquingMap;

  // Do the lookup, if we have a hit, return it.
  const MCSectionCOFF *&Entry = Map[Name];
  if (Entry) return Entry;

  return Entry = MCSectionCOFF::Create(Name, isDirective, Kind, getContext());
}

void TargetLoweringObjectFileCOFF::Initialize(MCContext &Ctx,
                                              const TargetMachine &TM) {
  if (UniquingMap != 0)
    ((COFFUniqueMapTy*)UniquingMap)->clear();
  TargetLoweringObjectFile::Initialize(Ctx, TM);
  TextSection = getCOFFSection("\t.text", true, SectionKind::getText());
  DataSection = getCOFFSection("\t.data", true, SectionKind::getDataRel());
  StaticCtorSection =
    getCOFFSection(".ctors", false, SectionKind::getDataRel());
  StaticDtorSection =
    getCOFFSection(".dtors", false, SectionKind::getDataRel());

  // FIXME: We're emitting LSDA info into a readonly section on COFF, even
  // though it contains relocatable pointers.  In PIC mode, this is probably a
  // big runtime hit for C++ apps.  Either the contents of the LSDA need to be
  // adjusted or this should be a data section.
  LSDASection =
    getCOFFSection(".gcc_except_table", false, SectionKind::getReadOnly());
  EHFrameSection =
    getCOFFSection(".eh_frame", false, SectionKind::getDataRel());

  // Debug info.
  // FIXME: Don't use 'directive' mode here.
  DwarfAbbrevSection =
    getCOFFSection("\t.section\t.debug_abbrev,\"dr\"",
                   true, SectionKind::getMetadata());
  DwarfInfoSection =
    getCOFFSection("\t.section\t.debug_info,\"dr\"",
                   true, SectionKind::getMetadata());
  DwarfLineSection =
    getCOFFSection("\t.section\t.debug_line,\"dr\"",
                   true, SectionKind::getMetadata());
  DwarfFrameSection =
    getCOFFSection("\t.section\t.debug_frame,\"dr\"",
                   true, SectionKind::getMetadata());
  DwarfPubNamesSection =
    getCOFFSection("\t.section\t.debug_pubnames,\"dr\"",
                   true, SectionKind::getMetadata());
  DwarfPubTypesSection =
    getCOFFSection("\t.section\t.debug_pubtypes,\"dr\"",
                   true, SectionKind::getMetadata());
  DwarfStrSection =
    getCOFFSection("\t.section\t.debug_str,\"dr\"",
                   true, SectionKind::getMetadata());
  DwarfLocSection =
    getCOFFSection("\t.section\t.debug_loc,\"dr\"",
                   true, SectionKind::getMetadata());
  DwarfARangesSection =
    getCOFFSection("\t.section\t.debug_aranges,\"dr\"",
                   true, SectionKind::getMetadata());
  DwarfRangesSection =
    getCOFFSection("\t.section\t.debug_ranges,\"dr\"",
                   true, SectionKind::getMetadata());
  DwarfMacroInfoSection =
    getCOFFSection("\t.section\t.debug_macinfo,\"dr\"",
                   true, SectionKind::getMetadata());
}

const MCSection *TargetLoweringObjectFileCOFF::
getExplicitSectionGlobal(const GlobalValue *GV, SectionKind Kind,
                         Mangler *Mang, const TargetMachine &TM) const {
  return getCOFFSection(GV->getSection(), false, Kind);
}

static const char *getCOFFSectionPrefixForUniqueGlobal(SectionKind Kind) {
  if (Kind.isText())
    return ".text$linkonce";
  if (Kind.isWriteable())
    return ".data$linkonce";
  return ".rdata$linkonce";
}


const MCSection *TargetLoweringObjectFileCOFF::
SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
                       Mangler *Mang, const TargetMachine &TM) const {
  assert(!Kind.isThreadLocal() && "Doesn't support TLS");

  // If this global is linkonce/weak and the target handles this by emitting it
  // into a 'uniqued' section name, create and return the section now.
  if (GV->isWeakForLinker()) {
    const char *Prefix = getCOFFSectionPrefixForUniqueGlobal(Kind);
    SmallString<128> Name(Prefix, Prefix+strlen(Prefix));
    Mang->getNameWithPrefix(Name, GV, false);
    return getCOFFSection(Name.str(), false, Kind);
  }

  if (Kind.isText())
    return getTextSection();

  return getDataSection();
}