C++ MCSectionData::getSection方法代码示例

void MachObjectWriter::WriteSection(const MCAssembler &Asm,
                                    const MCAsmLayout &Layout,
                                    const MCSectionData &SD,
                                    uint64_t FileOffset,
                                    uint64_t RelocationsStart,
                                    unsigned NumRelocations) {
  uint64_t SectionSize = Layout.getSectionAddressSize(&SD);

  // The offset is unused for virtual sections.
  if (SD.getSection().isVirtualSection()) {
    assert(Layout.getSectionFileSize(&SD) == 0 && "Invalid file size!");
    FileOffset = 0;
  }

  // struct section (68 bytes) or
  // struct section_64 (80 bytes)

  uint64_t Start = OS.tell();
  (void) Start;

  const MCSectionMachO &Section = cast<MCSectionMachO>(SD.getSection());
  WriteBytes(Section.getSectionName(), 16);
  WriteBytes(Section.getSegmentName(), 16);
  if (is64Bit()) {
    Write64(getSectionAddress(&SD)); // address
    Write64(SectionSize); // size
  } else {
    Write32(getSectionAddress(&SD)); // address
    Write32(SectionSize); // 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(IndirectSymBase.lookup(&SD)); // reserved1
  Write32(Section.getStubSize()); // reserved2
  if (is64Bit())
    Write32(0); // reserved3

  assert(OS.tell() - Start == (is64Bit() ? macho::Section64Size :
                               macho::Section32Size));
}

/// This function takes a section data object from the assembler
/// and creates the associated COFF section staging object.
void WinCOFFObjectWriter::DefineSection(MCSectionData const &SectionData) {
  assert(SectionData.getSection().getVariant() == MCSection::SV_COFF
    && "Got non COFF section in the COFF backend!");
  // FIXME: Not sure how to verify this (at least in a debug build).
  MCSectionCOFF const &Sec =
    static_cast<MCSectionCOFF const &>(SectionData.getSection());

  COFFSection *coff_section = createSection(Sec.getSectionName());
  COFFSymbol  *coff_symbol = createSymbol(Sec.getSectionName());

  coff_section->Symbol = coff_symbol;
  coff_symbol->Section = coff_section;
  coff_symbol->Data.StorageClass = COFF::IMAGE_SYM_CLASS_STATIC;

  // In this case the auxiliary symbol is a Section Definition.
  coff_symbol->Aux.resize(1);
  memset(&coff_symbol->Aux[0], 0, sizeof(coff_symbol->Aux[0]));
  coff_symbol->Aux[0].AuxType = ATSectionDefinition;
  coff_symbol->Aux[0].Aux.SectionDefinition.Selection = Sec.getSelection();

  coff_section->Header.Characteristics = Sec.getCharacteristics();

  uint32_t &Characteristics = coff_section->Header.Characteristics;
  switch (SectionData.getAlignment()) {
  case 1:    Characteristics |= COFF::IMAGE_SCN_ALIGN_1BYTES;    break;
  case 2:    Characteristics |= COFF::IMAGE_SCN_ALIGN_2BYTES;    break;
  case 4:    Characteristics |= COFF::IMAGE_SCN_ALIGN_4BYTES;    break;
  case 8:    Characteristics |= COFF::IMAGE_SCN_ALIGN_8BYTES;    break;
  case 16:   Characteristics |= COFF::IMAGE_SCN_ALIGN_16BYTES;   break;
  case 32:   Characteristics |= COFF::IMAGE_SCN_ALIGN_32BYTES;   break;
  case 64:   Characteristics |= COFF::IMAGE_SCN_ALIGN_64BYTES;   break;
  case 128:  Characteristics |= COFF::IMAGE_SCN_ALIGN_128BYTES;  break;
  case 256:  Characteristics |= COFF::IMAGE_SCN_ALIGN_256BYTES;  break;
  case 512:  Characteristics |= COFF::IMAGE_SCN_ALIGN_512BYTES;  break;
  case 1024: Characteristics |= COFF::IMAGE_SCN_ALIGN_1024BYTES; break;
  case 2048: Characteristics |= COFF::IMAGE_SCN_ALIGN_2048BYTES; break;
  case 4096: Characteristics |= COFF::IMAGE_SCN_ALIGN_4096BYTES; break;
  case 8192: Characteristics |= COFF::IMAGE_SCN_ALIGN_8192BYTES; break;
  default:
    llvm_unreachable("unsupported section alignment");
  }

  // Bind internal COFF section to MC section.
  coff_section->MCData = &SectionData;
  SectionMap[&SectionData.getSection()] = coff_section;
}

void MCObjectStreamer::EmitInstruction(const MCInst &Inst,
                                       const MCSubtargetInfo &STI) {
  MCStreamer::EmitInstruction(Inst, STI);

  MCSectionData *SD = getCurrentSectionData();
  SD->getSection().setHasInstructions(true);

  // Now that a machine instruction has been assembled into this section, make
  // a line entry for any .loc directive that has been seen.
  MCLineEntry::Make(this, getCurrentSection().first);

  // If this instruction doesn't need relaxation, just emit it as data.
  MCAssembler &Assembler = getAssembler();
  if (!Assembler.getBackend().mayNeedRelaxation(Inst)) {
    EmitInstToData(Inst, STI);
    return;
  }

  // Otherwise, relax and emit it as data if either:
  // - The RelaxAll flag was passed
  // - Bundling is enabled and this instruction is inside a bundle-locked
  //   group. We want to emit all such instructions into the same data
  //   fragment.
  if (Assembler.getRelaxAll() ||
      (Assembler.isBundlingEnabled() && SD->getSection().isBundleLocked())) {
    MCInst Relaxed;
    getAssembler().getBackend().relaxInstruction(Inst, Relaxed);
    while (getAssembler().getBackend().mayNeedRelaxation(Relaxed))
      getAssembler().getBackend().relaxInstruction(Relaxed, Relaxed);
    EmitInstToData(Relaxed, STI);
    return;
  }

  // Otherwise emit to a separate fragment.
  EmitInstToFragment(Inst, STI);
}