ImageHeader

ImageHeader size 0x80 = 140个字节

// header of image files written by ImageWriter, read and validated by Space.
class PACKED(4) ImageHeader {
 public:
  ImageHeader() : compile_pic_(0) {}

  ImageHeader(uint32_t image_begin,
              uint32_t image_size_,
              ImageSection* sections,
              uint32_t image_roots,
              uint32_t oat_checksum,
              uint32_t oat_file_begin,
              uint32_t oat_data_begin,
              uint32_t oat_data_end,
              uint32_t oat_file_end,
              uint32_t pointer_size,
              bool compile_pic_);
  static std::string GetOatLocationFromImageLocation(const std::string& image) {
    std::string oat_filename = image;
    if (oat_filename.length() <= 3) {
      oat_filename += ".oat";
    } else {
      oat_filename.replace(oat_filename.length() - 3, 3, "oat");
    }
    return oat_filename;
  }

  enum ImageMethod {
    kResolutionMethod,
    kImtConflictMethod,
    kImtUnimplementedMethod,
    kCalleeSaveMethod,
    kRefsOnlySaveMethod,
    kRefsAndArgsSaveMethod,
    kImageMethodsCount,  // Number of elements in enum.
  };

  enum ImageRoot {
    kDexCaches,
    kClassRoots,
    kImageRootsMax,
  };

  enum ImageSections {
    kSectionObjects,
    kSectionArtFields,
    kSectionArtMethods,
    kSectionInternedStrings,
    kSectionImageBitmap,
    kSectionCount,  // Number of elements in enum.
  };

  void RelocateImage(off_t delta);

 private:
  static const uint8_t kImageMagic[4];
  static const uint8_t kImageVersion[4];

  uint8_t magic_[4];
  uint8_t version_[4];

  // Required base address for mapping the image.
  uint32_t image_begin_;

  // Image size, not page aligned.
  uint32_t image_size_;

  // Checksum of the oat file we link to for load time sanity check.
  uint32_t oat_checksum_;

  // Start address for oat file. Will be before oat_data_begin_ for .so files.
  uint32_t oat_file_begin_;

  // Required oat address expected by image Method::GetCode() pointers.
  uint32_t oat_data_begin_;

  // End of oat data address range for this image file.
  uint32_t oat_data_end_;

  // End of oat file address range. will be after oat_data_end_ for
  // .so files. Used for positioning a following alloc spaces.
  uint32_t oat_file_end_;

  // The total delta that this image has been patched.
  int32_t patch_delta_;

  // Absolute address of an Object[] of objects needed to reinitialize from an image.
  uint32_t image_roots_;

  // Pointer size, this affects the size of the ArtMethods.
  uint32_t pointer_size_;

  // Boolean (0 or 1) to denote if the image was compiled with --compile-pic option
  const uint32_t compile_pic_;

  // Image sections
  ImageSection sections_[kSectionCount];

  // Image methods.
  uint64_t image_methods_[kImageMethodsCount];
};

image_begin_ : image_file映射到内存的绝对地址。是从image_file文件的0位置开始映射的，映射的字节数为image_size_（因为整页映射可能会被修正）

image map

  std::unique_ptr<MemMap> map(MemMap::MapFileAtAddress(
      image_header.GetImageBegin(), image_header.GetImageSize(),
      PROT_READ | PROT_WRITE, MAP_PRIVATE, file->Fd(), 0, false, image_filename, error_msg));

live_bitmap map

  // caoming ImageSection bitmap_section is used to describe live_bitmap
  const auto& bitmap_section = image_header.GetImageSection(ImageHeader::kSectionImageBitmap);

 std::unique_ptr<MemMap> image_map(MemMap::MapFileAtAddress(
      nullptr, bitmap_section.Size(), PROT_READ, MAP_PRIVATE, file->Fd(),
      bitmap_section.Offset(), false, image_filename, error_msg));

 

boot.art@class.dex 文件的加载

oat_checksum_: 与Image文件关联的boot.art@classes.oat文件的检验值。
oat_file_begin_: 与Image文件关联的boot.art@classes.oat文件映射到内存的起始位置。
oat_data_begin_: 与Image文件关联的boot.art@classes.oat文件的OATDATA段映射到内存的起始位置。
oat_data_end_: 与Image文件关联的boot.art@classes.oat文件的OATDATA段映射到内存的结束位置。
oat_file_end_: 与Image文件关联的boot.art@classes.oat文件映射到内存的结束位置。

image_roots_: 一个Object对象地址数组地址，这些Object对象就是在Image Space上分配的对象。