C++ MCSectionELF::getAssociatedSymbol方法代码示例

MCSection *TargetLoweringObjectFileELF::SelectSectionForGlobal(
    const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
  unsigned Flags = getELFSectionFlags(Kind);

  // If we have -ffunction-section or -fdata-section then we should emit the
  // global value to a uniqued section specifically for it.
  bool EmitUniqueSection = false;
  if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
    if (Kind.isText())
      EmitUniqueSection = TM.getFunctionSections();
    else
      EmitUniqueSection = TM.getDataSections();
  }
  EmitUniqueSection |= GO->hasComdat();

  const MCSymbolELF *AssociatedSymbol = getAssociatedSymbol(GO, TM);
  if (AssociatedSymbol) {
    EmitUniqueSection = true;
    Flags |= ELF::SHF_LINK_ORDER;
  }

  MCSectionELF *Section = selectELFSectionForGlobal(
      getContext(), GO, Kind, getMangler(), TM, EmitUniqueSection, Flags,
      &NextUniqueID, AssociatedSymbol);
  assert(Section->getAssociatedSymbol() == AssociatedSymbol);
  return Section;
}

MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
    const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
  StringRef SectionName = GO->getSection();

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

  StringRef Group = "";
  unsigned Flags = getELFSectionFlags(Kind);
  if (const Comdat *C = getELFComdat(GO)) {
    Group = C->getName();
    Flags |= ELF::SHF_GROUP;
  }

  // A section can have at most one associated section. Put each global with
  // MD_associated in a unique section.
  unsigned UniqueID = MCContext::GenericSectionID;
  const MCSymbolELF *AssociatedSymbol = getAssociatedSymbol(GO, TM);
  if (AssociatedSymbol) {
    UniqueID = NextUniqueID++;
    Flags |= ELF::SHF_LINK_ORDER;
  }

  MCSectionELF *Section = getContext().getELFSection(
      SectionName, getELFSectionType(SectionName, Kind), Flags,
      /*EntrySize=*/0, Group, UniqueID, AssociatedSymbol);
  // Make sure that we did not get some other section with incompatible sh_link.
  // This should not be possible due to UniqueID code above.
  assert(Section->getAssociatedSymbol() == AssociatedSymbol);
  return Section;
}

MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
    const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
  StringRef SectionName = GO->getSection();

  // Check if '#pragma clang section' name is applicable.
  // Note that pragma directive overrides -ffunction-section, -fdata-section
  // and so section name is exactly as user specified and not uniqued.
  const GlobalVariable *GV = dyn_cast<GlobalVariable>(GO);
  if (GV && GV->hasImplicitSection()) {
    auto Attrs = GV->getAttributes();
    if (Attrs.hasAttribute("bss-section") && Kind.isBSS()) {
      SectionName = Attrs.getAttribute("bss-section").getValueAsString();
    } else if (Attrs.hasAttribute("rodata-section") && Kind.isReadOnly()) {
      SectionName = Attrs.getAttribute("rodata-section").getValueAsString();
    } else if (Attrs.hasAttribute("data-section") && Kind.isData()) {
      SectionName = Attrs.getAttribute("data-section").getValueAsString();
    }
  }
  const Function *F = dyn_cast<Function>(GO);
  if (F && F->hasFnAttribute("implicit-section-name")) {
    SectionName = F->getFnAttribute("implicit-section-name").getValueAsString();
  }

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

  StringRef Group = "";
  unsigned Flags = getELFSectionFlags(Kind);
  if (const Comdat *C = getELFComdat(GO)) {
    Group = C->getName();
    Flags |= ELF::SHF_GROUP;
  }

  // A section can have at most one associated section. Put each global with
  // MD_associated in a unique section.
  unsigned UniqueID = MCContext::GenericSectionID;
  const MCSymbolELF *AssociatedSymbol = getAssociatedSymbol(GO, TM);
  if (AssociatedSymbol) {
    UniqueID = NextUniqueID++;
    Flags |= ELF::SHF_LINK_ORDER;
  }

  MCSectionELF *Section = getContext().getELFSection(
      SectionName, getELFSectionType(SectionName, Kind), Flags,
      /*EntrySize=*/0, Group, UniqueID, AssociatedSymbol);
  // Make sure that we did not get some other section with incompatible sh_link.
  // This should not be possible due to UniqueID code above.
  assert(Section->getAssociatedSymbol() == AssociatedSymbol);
  return Section;
}

void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
                                   uint32_t GroupSymbolIndex, uint64_t Offset,
                                   uint64_t Size, const MCSectionELF &Section) {
  uint64_t sh_link = 0;
  uint64_t sh_info = 0;

  switch(Section.getType()) {
  default:
    // Nothing to do.
    break;

  case ELF::SHT_DYNAMIC:
    llvm_unreachable("SHT_DYNAMIC in a relocatable object");

  case ELF::SHT_REL:
  case ELF::SHT_RELA: {
    sh_link = SymbolTableIndex;
    assert(sh_link && ".symtab not found");
    const MCSection *InfoSection = Section.getAssociatedSection();
    sh_info = SectionIndexMap.lookup(cast<MCSectionELF>(InfoSection));
    break;
  }

  case ELF::SHT_SYMTAB:
  case ELF::SHT_DYNSYM:
    sh_link = StringTableIndex;
    sh_info = LastLocalSymbolIndex;
    break;

  case ELF::SHT_SYMTAB_SHNDX:
    sh_link = SymbolTableIndex;
    break;

  case ELF::SHT_GROUP:
    sh_link = SymbolTableIndex;
    sh_info = GroupSymbolIndex;
    break;
  }

  if (Section.getFlags() & ELF::SHF_LINK_ORDER) {
    const MCSymbol *Sym = Section.getAssociatedSymbol();
    const MCSectionELF *Sec = cast<MCSectionELF>(&Sym->getSection());
    sh_link = SectionIndexMap.lookup(Sec);
  }

  WriteSecHdrEntry(StrTabBuilder.getOffset(Section.getSectionName()),
                   Section.getType(), Section.getFlags(), 0, Offset, Size,
                   sh_link, sh_info, Section.getAlignment(),
                   Section.getEntrySize());
}