C++ MCSymbol类代码示例

void XCoreAsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
  // Check to see if this is a special global used by LLVM, if so, emit it.
  if (!GV->hasInitializer() ||
      EmitSpecialLLVMGlobal(GV))
    return;

  const DataLayout *TD = TM.getDataLayout();
  OutStreamer.SwitchSection(getObjFileLowering().SectionForGlobal(GV, Mang,TM));

  
  MCSymbol *GVSym = getSymbol(GV);
  const Constant *C = GV->getInitializer();
  unsigned Align = (unsigned)TD->getPreferredTypeAlignmentShift(C->getType());
  
  // Mark the start of the global
  getTargetStreamer().emitCCTopData(GVSym->getName());

  switch (GV->getLinkage()) {
  case GlobalValue::AppendingLinkage:
    report_fatal_error("AppendingLinkage is not supported by this target!");
  case GlobalValue::LinkOnceAnyLinkage:
  case GlobalValue::LinkOnceODRLinkage:
  case GlobalValue::WeakAnyLinkage:
  case GlobalValue::WeakODRLinkage:
  case GlobalValue::ExternalLinkage:
    emitArrayBound(GVSym, GV);
    OutStreamer.EmitSymbolAttribute(GVSym, MCSA_Global);

    // TODO Use COMDAT groups for LinkOnceLinkage
    if (GV->hasWeakLinkage() || GV->hasLinkOnceLinkage())
      OutStreamer.EmitSymbolAttribute(GVSym, MCSA_Weak);
    // FALL THROUGH
  case GlobalValue::InternalLinkage:
  case GlobalValue::PrivateLinkage:
    break;
  default:
    llvm_unreachable("Unknown linkage type!");
  }

  EmitAlignment(Align > 2 ? Align : 2, GV);
  
  if (GV->isThreadLocal()) {
    report_fatal_error("TLS is not supported by this target!");
  }
  unsigned Size = TD->getTypeAllocSize(C->getType());
  if (MAI->hasDotTypeDotSizeDirective()) {
    OutStreamer.EmitSymbolAttribute(GVSym, MCSA_ELF_TypeObject);
    OutStreamer.EmitELFSize(GVSym, MCConstantExpr::Create(Size, OutContext));
  }
  OutStreamer.EmitLabel(GVSym);
  
  EmitGlobalConstant(C);
  // The ABI requires that unsigned scalar types smaller than 32 bits
  // are padded to 32 bits.
  if (Size < 4)
    OutStreamer.EmitZeros(4 - Size);
  
  // Mark the end of the global
  getTargetStreamer().emitCCBottomData(GVSym->getName());
}

/// Emit extern decls for functions imported from other modules, and emit
/// global declarations for function defined in this module and which are
/// available to other modules.
///
void PIC16AsmPrinter::EmitFunctionDecls(Module &M) {
 // Emit declarations for external functions.
  O <<"\n"<<MAI->getCommentString() << "Function Declarations - BEGIN." <<"\n";
  for (Module::iterator I = M.begin(), E = M.end(); I != E; I++) {
    if (I->isIntrinsic() || I->getName() == "@abort")
      continue;
    
    if (!I->isDeclaration() && !I->hasExternalLinkage())
      continue;

    MCSymbol *Sym = Mang->getSymbol(I);
    
    // Do not emit memcpy, memset, and memmove here.
    // Calls to these routines can be generated in two ways,
    // 1. User calling the standard lib function
    // 2. Codegen generating these calls for llvm intrinsics.
    // In the first case a prototype is alread availale, while in
    // second case the call is via and externalsym and the prototype is missing.
    // So declarations for these are currently always getting printing by
    // tracking both kind of references in printInstrunction.
    if (I->isDeclaration() && PAN::isMemIntrinsic(Sym->getName())) continue;

    const char *directive = I->isDeclaration() ? MAI->getExternDirective() :
                                                 MAI->getGlobalDirective();
      
    O << directive << Sym->getName() << "\n";
    O << directive << PAN::getRetvalLabel(Sym->getName()) << "\n";
    O << directive << PAN::getArgsLabel(Sym->getName()) << "\n";
  }

  O << MAI->getCommentString() << "Function Declarations - END." <<"\n";
}

uint64_t MachObjectWriter::getSymbolAddress(const MCSymbol &S,
                                            const MCAsmLayout &Layout) const {
  // If this is a variable, then recursively evaluate now.
  if (S.isVariable()) {
    if (const MCConstantExpr *C =
          dyn_cast<const MCConstantExpr>(S.getVariableValue()))
      return C->getValue();

    MCValue Target;
    if (!S.getVariableValue()->evaluateAsRelocatable(Target, &Layout, nullptr))
      report_fatal_error("unable to evaluate offset for variable '" +
                         S.getName() + "'");

    // Verify that any used symbols are defined.
    if (Target.getSymA() && Target.getSymA()->getSymbol().isUndefined())
      report_fatal_error("unable to evaluate offset to undefined symbol '" +
                         Target.getSymA()->getSymbol().getName() + "'");
    if (Target.getSymB() && Target.getSymB()->getSymbol().isUndefined())
      report_fatal_error("unable to evaluate offset to undefined symbol '" +
                         Target.getSymB()->getSymbol().getName() + "'");

    uint64_t Address = Target.getConstant();
    if (Target.getSymA())
      Address += getSymbolAddress(Target.getSymA()->getSymbol(), Layout);
    if (Target.getSymB())
      Address += getSymbolAddress(Target.getSymB()->getSymbol(), Layout);
    return Address;
  }

  return getSectionAddress(S.getFragment()->getParent()) +
         Layout.getSymbolOffset(S);
}

const MCSection *TargetLoweringObjectFileCOFF::
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()) {
    const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
    unsigned Characteristics = getCOFFSectionFlags(Kind);

    Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
    MCSymbol *Sym = TM.getSymbol(GV, Mang);
    return getContext().getCOFFSection(Name, Characteristics,
                                       Kind, Sym->getName(),
                                       COFF::IMAGE_COMDAT_SELECT_ANY);
  }

  if (Kind.isText())
    return TextSection;

  if (Kind.isThreadLocal())
    return TLSDataSection;

  if (Kind.isReadOnly())
    return ReadOnlySection;

  if (Kind.isBSS())
    return BSSSection;

  return DataSection;
}

void TargetLoweringObjectFileELF::emitPersonalityValue(MCStreamer &Streamer,
                                                       const TargetMachine &TM,
                                                       const MCSymbol *Sym) const {
  SmallString<64> NameData("DW.ref.");
  NameData += Sym->getName();
  MCSymbol *Label = getContext().GetOrCreateSymbol(NameData);
  Streamer.EmitSymbolAttribute(Label, MCSA_Hidden);
  Streamer.EmitSymbolAttribute(Label, MCSA_Weak);
  StringRef Prefix = ".data.";
  NameData.insert(NameData.begin(), Prefix.begin(), Prefix.end());
  unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE | ELF::SHF_GROUP;
  const MCSection *Sec = getContext().getELFSection(NameData,
                                                    ELF::SHT_PROGBITS,
                                                    Flags,
                                                    SectionKind::getDataRel(),
                                                    0, Label->getName());
  unsigned Size = TM.getDataLayout()->getPointerSize(0);
  Streamer.SwitchSection(Sec);
  Streamer.EmitValueToAlignment(TM.getDataLayout()->getPointerABIAlignment(0));
  Streamer.EmitSymbolAttribute(Label, MCSA_ELF_TypeObject);
  const MCExpr *E = MCConstantExpr::Create(Size, getContext());
  Streamer.EmitELFSize(Label, E);
  Streamer.EmitLabel(Label);

  Streamer.EmitSymbolValue(Sym, Size);
}

/// parseDirectiveIndirectSymbol
///  ::= .indirect_symbol identifier
bool DarwinAsmParser::parseDirectiveIndirectSymbol(StringRef, SMLoc Loc) {
  const MCSectionMachO *Current = static_cast<const MCSectionMachO*>(
                                       getStreamer().getCurrentSection().first);
  MachO::SectionType SectionType = Current->getType();
  if (SectionType != MachO::S_NON_LAZY_SYMBOL_POINTERS &&
      SectionType != MachO::S_LAZY_SYMBOL_POINTERS &&
      SectionType != MachO::S_SYMBOL_STUBS)
    return Error(Loc, "indirect symbol not in a symbol pointer or stub "
                      "section");

  StringRef Name;
  if (getParser().parseIdentifier(Name))
    return TokError("expected identifier in .indirect_symbol directive");

  MCSymbol *Sym = getContext().getOrCreateSymbol(Name);

  // Assembler local symbols don't make any sense here. Complain loudly.
  if (Sym->isTemporary())
    return TokError("non-local symbol required in directive");

  if (!getStreamer().EmitSymbolAttribute(Sym, MCSA_IndirectSymbol))
    return TokError("unable to emit indirect symbol attribute for: " + Name);

  if (getLexer().isNot(AsmToken::EndOfStatement))
    return TokError("unexpected token in '.indirect_symbol' directive");

  Lex();

  return false;
}

MCSectionCOFF *MCContext::getCOFFSection(StringRef Section,
                                         unsigned Characteristics,
                                         SectionKind Kind,
                                         StringRef COMDATSymName, int Selection,
                                         const char *BeginSymName) {
  MCSymbol *COMDATSymbol = nullptr;
  if (!COMDATSymName.empty()) {
    COMDATSymbol = getOrCreateSymbol(COMDATSymName);
    COMDATSymName = COMDATSymbol->getName();
  }

  // Do the lookup, if we have a hit, return it.
  COFFSectionKey T{Section, COMDATSymName, Selection};
  auto IterBool = COFFUniquingMap.insert(std::make_pair(T, nullptr));
  auto Iter = IterBool.first;
  if (!IterBool.second)
    return Iter->second;

  MCSymbol *Begin = nullptr;
  if (BeginSymName)
    Begin = createTempSymbol(BeginSymName, false);

  StringRef CachedName = Iter->first.SectionName;
  MCSectionCOFF *Result = new (COFFAllocator.Allocate()) MCSectionCOFF(
      CachedName, Characteristics, COMDATSymbol, Selection, Kind, Begin);

  Iter->second = Result;
  return Result;
}

static bool canUseLocalRelocation(const MCSectionMachO &Section,
                                  const MCSymbol &Symbol, unsigned Log2Size) {
  // Debug info sections can use local relocations.
  if (Section.hasAttribute(MachO::S_ATTR_DEBUG))
    return true;

  // Otherwise, only pointer sized relocations are supported.
  if (Log2Size != 3)
    return false;

  // But only if they don't point to a few forbidden sections.
  if (!Symbol.isInSection())
    return true;
  const MCSectionMachO &RefSec = cast<MCSectionMachO>(Symbol.getSection());
  if (RefSec.getType() == MachO::S_CSTRING_LITERALS)
    return false;

  if (RefSec.getSegmentName() == "__DATA" &&
      RefSec.getSectionName() == "__objc_classrefs")
    return false;

  // FIXME: ld64 currently handles internal pointer-sized relocations
  // incorrectly (applying the addend twice). We should be able to return true
  // unconditionally by this point when that's fixed.
  return false;
}

MCSection *TargetLoweringObjectFileCOFF::getSectionForJumpTable(
    const Function &F, const TargetMachine &TM) const {
  // If the function can be removed, produce a unique section so that
  // the table doesn't prevent the removal.
  const Comdat *C = F.getComdat();
  bool EmitUniqueSection = TM.getFunctionSections() || C;
  if (!EmitUniqueSection)
    return ReadOnlySection;

  // FIXME: we should produce a symbol for F instead.
  if (F.hasPrivateLinkage())
    return ReadOnlySection;

  MCSymbol *Sym = TM.getSymbol(&F);
  StringRef COMDATSymName = Sym->getName();

  SectionKind Kind = SectionKind::getReadOnly();
  const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
  unsigned Characteristics = getCOFFSectionFlags(Kind, TM);
  Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
  unsigned UniqueID = NextUniqueID++;

  return getContext().getCOFFSection(Name, Characteristics, Kind, COMDATSymName,
                                     COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE, UniqueID);
}

const MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
    const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
    const TargetMachine &TM) const {
  int Selection = 0;
  unsigned Characteristics = getCOFFSectionFlags(Kind);
  StringRef Name = GV->getSection();
  StringRef COMDATSymName = "";
  if ((GV->isWeakForLinker() || GV->hasComdat()) && !Kind.isCommon()) {
    Selection = getSelectionForCOFF(GV);
    const GlobalValue *ComdatGV;
    if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
      ComdatGV = getComdatGVForCOFF(GV);
    else
      ComdatGV = GV;

    if (!ComdatGV->hasPrivateLinkage()) {
      MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
      COMDATSymName = Sym->getName();
      Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
    } else {
      Selection = 0;
    }
  }
  return getContext().getCOFFSection(Name,
                                     Characteristics,
                                     Kind,
                                     COMDATSymName,
                                     Selection);
}

static bool getSymbolOffsetImpl(const MCAsmLayout &Layout, const MCSymbol &S,
                                bool ReportError, uint64_t &Val) {
  if (!S.isVariable())
    return getLabelOffset(Layout, S, ReportError, Val);

  // If SD is a variable, evaluate it.
  MCValue Target;
  if (!S.getVariableValue()->evaluateAsValue(Target, Layout))
    report_fatal_error("unable to evaluate offset for variable '" +
                       S.getName() + "'");

  uint64_t Offset = Target.getConstant();

  const MCSymbolRefExpr *A = Target.getSymA();
  if (A) {
    uint64_t ValA;
    if (!getLabelOffset(Layout, A->getSymbol(), ReportError, ValA))
      return false;
    Offset += ValA;
  }

  const MCSymbolRefExpr *B = Target.getSymB();
  if (B) {
    uint64_t ValB;
    if (!getLabelOffset(Layout, B->getSymbol(), ReportError, ValB))
      return false;
    Offset -= ValB;
  }

  Val = Offset;
  return true;
}

const MCSection *TargetLoweringObjectFileCOFF::
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()) {
    const char *Prefix = getCOFFSectionPrefixForUniqueGlobal(Kind);
    SmallString<128> Name(Prefix, Prefix+strlen(Prefix));
    MCSymbol *Sym = Mang->getSymbol(GV);
    Name.append(Sym->getName().begin() + 1, Sym->getName().end());

    unsigned Characteristics = getCOFFSectionFlags(Kind);

    Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;

    return getContext().getCOFFSection(Name.str(), Characteristics,
                          COFF::IMAGE_COMDAT_SELECT_ANY, Kind);
  }

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

  if (Kind.isThreadLocal())
    return getTLSDataSection();

  return getDataSection();
}

void TargetLoweringObjectFileELF::emitPersonalityValue(MCStreamer &Streamer,
                                                       const TargetMachine &TM,
                                                       const MCSymbol *Sym) const {
  SmallString<64> NameData("DW.ref.");
  // @LOCALMOD-BEGIN
  // The dwarf section label should not include the version suffix.
  // Strip it off here.
  StringRef Name = Sym->getName();
  size_t atpos = Name.find("@");
  if (atpos != StringRef::npos)
    Name = Name.substr(0, atpos);
  // @LOCALMOD-END
  NameData += Name; // @LOCALMOD
  MCSymbol *Label = getContext().GetOrCreateSymbol(NameData);
  Streamer.EmitSymbolAttribute(Label, MCSA_Hidden);
  Streamer.EmitSymbolAttribute(Label, MCSA_Weak);
  StringRef Prefix = ".data.";
  NameData.insert(NameData.begin(), Prefix.begin(), Prefix.end());
  unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE | ELF::SHF_GROUP;
  const MCSection *Sec = getContext().getELFSection(NameData,
                                                    ELF::SHT_PROGBITS,
                                                    Flags,
                                                    SectionKind::getDataRel(),
                                                    0, Label->getName());
  unsigned Size = TM.getDataLayout()->getPointerSize();
  Streamer.SwitchSection(Sec);
  Streamer.EmitValueToAlignment(TM.getDataLayout()->getPointerABIAlignment());
  Streamer.EmitSymbolAttribute(Label, MCSA_ELF_TypeObject);
  const MCExpr *E = MCConstantExpr::Create(Size, getContext());
  Streamer.EmitELFSize(Label, E);
  Streamer.EmitLabel(Label);

  Streamer.EmitSymbolValue(Sym, Size);
}

static bool canUseLocalRelocation(const MCSectionMachO &Section,
                                  const MCSymbol &Symbol, unsigned Log2Size) {
    // Debug info sections can use local relocations.
    if (Section.hasAttribute(MachO::S_ATTR_DEBUG))
        return true;

    // Otherwise, only pointer sized relocations are supported.
    if (Log2Size != 3)
        return false;

    // But only if they don't point to a few forbidden sections.
    if (!Symbol.isInSection())
        return true;
    const MCSectionMachO &RefSec = cast<MCSectionMachO>(Symbol.getSection());
    if (RefSec.getType() == MachO::S_CSTRING_LITERALS)
        return false;

    if (RefSec.getSegmentName() == "__DATA" &&
            RefSec.getSectionName() == "__cfstring")
        return false;

    if (RefSec.getSegmentName() == "__DATA" &&
            RefSec.getSectionName() == "__objc_classrefs")
        return false;

    return true;
}

void Cse523AsmPrinter::EmitStartOfAsmFile(Module &M) {
    if (Subtarget->isTargetMacho())
        OutStreamer.SwitchSection(getObjFileLowering().getTextSection());

    if (Subtarget->isTargetCOFF()) {
        // Emit an absolute @feat.00 symbol.  This appears to be some kind of
        // compiler features bitfield read by link.exe.
        if (!Subtarget->is64Bit()) {
            MCSymbol *S = MMI->getContext().GetOrCreateSymbol(StringRef("@feat.00"));
            OutStreamer.BeginCOFFSymbolDef(S);
            OutStreamer.EmitCOFFSymbolStorageClass(COFF::IMAGE_SYM_CLASS_STATIC);
            OutStreamer.EmitCOFFSymbolType(COFF::IMAGE_SYM_DTYPE_NULL);
            OutStreamer.EndCOFFSymbolDef();
            // According to the PE-COFF spec, the LSB of this value marks the object
            // for "registered SEH".  This means that all SEH handler entry points
            // must be registered in .sxdata.  Use of any unregistered handlers will
            // cause the process to terminate immediately.  LLVM does not know how to
            // register any SEH handlers, so its object files should be safe.
            S->setAbsolute();
            OutStreamer.EmitSymbolAttribute(S, MCSA_Global);
            OutStreamer.EmitAssignment(
                    S, MCConstantExpr::Create(int64_t(1), MMI->getContext()));
        }
    }
}