static std::unique_ptr<const DexFile> Open(const uint8_t* base,
                                             size_t size,
                                             const std::string& location,
                                             uint32_t location_checksum,
                                             const OatDexFile* oat_dex_file,
                                             bool verify,
                                             bool verify_checksum,
                                             std::string* error_msg);//这是OpenDexFilesFromOat里，通过oatfile获得dexfile走这个，看OpenDexFile函数中DexFile::Open的参数可以判断，不清楚的去看下上一篇

  // Opens .dex file that has been memory-mapped by the caller.
  static std::unique_ptr<const DexFile> Open(const std::string& location,
                                             uint32_t location_checkum,
                                             std::unique_ptr<MemMap> mem_map,
                                             bool verify,
                                             bool verify_checksum,
                                             std::string* error_msg);//这是打开已经被调用者memory-mapped过的

  // Opens all .dex files found in the file, guessing the container format based on file extension.
  static bool Open(const char* filename,
                   const std::string& location,
                   bool verify_checksum,
                   std::string* error_msg,
                   std::vector<std::unique_ptr<const DexFile>>* dex_files);//这是OpenDexFilesFromOat里，通过oatfile获得dexfile失败，直接打开源dex走这个，看OpenDexFilesFromOat函数中DexFile::Open的参数可以判断

std::unique_ptr<const DexFile> DexFile::Open(const uint8_t* base,
                                             size_t size,
                                             const std::string& location,
                                             uint32_t location_checksum,
                                             const OatDexFile* oat_dex_file,//这个参数就是上一篇的this，就是oat_dex_file，是从这里面找出dex_file哦，其他2个重载函数都不是从oat_dex_file里找到dex_file，所以肯定没有调用他们
                                             bool verify,
                                             bool verify_checksum,
                                             std::string* error_msg) {
  ScopedTrace trace(std::string("Open dex file from RAM ") + location);
  return OpenCommon(base,
                    size,
                    location,
                    location_checksum,
                    oat_dex_file,
                    verify,
                    verify_checksum,
                    error_msg);
}

std::vector<std::unique_ptr<const DexFile>> OatFileManager::OpenDexFilesFromOat(
    const char* dex_location,
    jobject class_loader,
    jobjectArray dex_elements,
    const OatFile** out_oat_file,
    std::vector<std::string>* error_msgs) {
。。。
 
  // Get the oat file on disk.
  std::unique_ptr<const OatFile> oat_file(oat_file_assistant.GetBestOatFile().release());//这句获得了oat_file，下面LoadDexFiles使用这个oat_file获得dex_files
 
 。。。
    if (accept_oat_file) {
      VLOG(class_linker) << "Registering " << oat_file->GetLocation();
      source_oat_file = RegisterOatFile(std::move(oat_file));//这里把oat_file注册给source_oat_file
      *out_oat_file = source_oat_file;
    }
  }
 
  std::vector<std::unique_ptr<const DexFile>> dex_files;
 
  // Load the dex files from the oat file.
  。。。
      dex_files = oat_file_assistant.LoadDexFiles(*source_oat_file, dex_location);//这里通过加载source_oat_file获得dex_files，最终调用了DexFile::Open，这里的DexFile::Open是一个重载
  。。。
  // Fall back to running out of the original dex file if we couldn't load any
  // dex_files from the oat file.
  if (dex_files.empty()) {
    if (oat_file_assistant.HasOriginalDexFiles()) {
      if (Runtime::Current()->IsDexFileFallbackEnabled()) {
        static constexpr bool kVerifyChecksum = true;
        if (!DexFile::Open(
            dex_location, dex_location, kVerifyChecksum, /*out*/ &error_msg, &dex_files)) {//如果LoadDexFiles上面没有获得dex_files，直接DexFile::Open打开加载原始的dexfile，这里的DexFile::Open是另一个重载
          LOG(WARNING) << error_msg;
          error_msgs->push_back("Failed to open dex files from " + std::string(dex_location)
                                + " because: " + error_msg);
        }
  。。。
 
  return dex_files;
}

bool DexFile::Open(const char* filename,
                   const std::string& location,
                   bool verify_checksum,
                   std::string* error_msg,
                   std::vector<std::unique_ptr<const DexFile>>* dex_files) {
  ScopedTrace trace(std::string("Open dex file ") + std::string(location));
  DCHECK(dex_files != nullptr) << "DexFile::Open: out-param is nullptr";
  uint32_t magic;
  File fd = OpenAndReadMagic(filename, &magic, error_msg);//OpenAndReadMagic也是一个常用脱壳点，如果不是直接打开dex走这个函数，不会在这里被调用
  if (fd.Fd() == -1) {
    DCHECK(!error_msg->empty());
    return false;
  }
  if (IsZipMagic(magic)) {
    return DexFile::OpenZip(fd.Release(), location, verify_checksum, error_msg, dex_files);//如果是Zip，调用DexFile::OpenZip
  }
  if (IsDexMagic(magic)) {
    std::unique_ptr<const DexFile> dex_file(DexFile::OpenFile(fd.Release(),
                                                              location,
                                                              /* verify */ true,
                                                              verify_checksum,
                                                              error_msg));//如果是Dex，调用DexFile::OpenFile
    if (dex_file.get() != nullptr) {
      dex_files->push_back(std::move(dex_file));
      return true;
    } else {
      return false;
    }
  }
  *error_msg = StringPrintf("Expected valid zip or dex file: '%s'", filename);
  return false;
}

bool DexFile::OpenZip(int fd,
                      const std::string& location,
                      bool verify_checksum,
                      std::string* error_msg,
                      std::vector<std::unique_ptr<const DexFile>>* dex_files) {
  ScopedTrace trace("Dex file open Zip " + std::string(location));
  DCHECK(dex_files != nullptr) << "DexFile::OpenZip: out-param is nullptr";
  std::unique_ptr<ZipArchive> zip_archive(ZipArchive::OpenFromFd(fd, location.c_str(), error_msg));
  if (zip_archive.get() == nullptr) {
    DCHECK(!error_msg->empty());
    return false;
  }
  return DexFile::OpenAllDexFilesFromZip(*zip_archive,
                                         location,
                                         verify_checksum,
                                         error_msg,
                                         dex_files);
}

bool DexFile::OpenAllDexFilesFromZip(const ZipArchive& zip_archive,
                                     const std::string& location,
                                     bool verify_checksum,
                                     std::string* error_msg,
                                     std::vector<std::unique_ptr<const DexFile>>* dex_files) {
  ScopedTrace trace("Dex file open from Zip " + std::string(location));
  DCHECK(dex_files != nullptr) << "DexFile::OpenFromZip: out-param is nullptr";
  ZipOpenErrorCode error_code;
  std::unique_ptr<const DexFile> dex_file(OpenOneDexFileFromZip(zip_archive,
                                                                kClassesDex,
                                                                location,
                                                                verify_checksum,
                                                                error_msg,
                                                                &error_code));
  if (dex_file.get() == nullptr) {
    return false;
  } else {
    // Had at least classes.dex.
    dex_files->push_back(std::move(dex_file));

    // Now try some more.

    // We could try to avoid std::string allocations by working on a char array directly. As we
    // do not expect a lot of iterations, this seems too involved and brittle.

    for (size_t i = 1; ; ++i) {
      std::string name = GetMultiDexClassesDexName(i);
      std::string fake_location = GetMultiDexLocation(i, location.c_str());
      std::unique_ptr<const DexFile> next_dex_file(OpenOneDexFileFromZip(zip_archive,
                                                                         name.c_str(),
                                                                         fake_location,
                                                                         verify_checksum,
                                                                         error_msg,
                                                                         &error_code));
      if (next_dex_file.get() == nullptr) {
        if (error_code != ZipOpenErrorCode::kEntryNotFound) {
          LOG(WARNING) << "Zip open failed: " << *error_msg;
        }
        break;
      } else {
        dex_files->push_back(std::move(next_dex_file));
      }

      if (i == kWarnOnManyDexFilesThreshold) {
        LOG(WARNING) << location << " has in excess of " << kWarnOnManyDexFilesThreshold
                     << " dex files. Please consider coalescing and shrinking the number to "
                        " avoid runtime overhead.";
      }

      if (i == std::numeric_limits<size_t>::max()) {
        LOG(ERROR) << "Overflow in number of dex files!";
        break;
      }
    }

    return true;
  }
}

std::unique_ptr<const DexFile> DexFile::OpenOneDexFileFromZip(const ZipArchive& zip_archive,
                                                              const char* entry_name,
                                                              const std::string& location,
                                                              bool verify_checksum,
                                                              std::string* error_msg,
                                                              ZipOpenErrorCode* error_code) {
  ScopedTrace trace("Dex file open from Zip Archive " + std::string(location));
  CHECK(!location.empty());
  std::unique_ptr<ZipEntry> zip_entry(zip_archive.Find(entry_name, error_msg));
  if (zip_entry == nullptr) {
    *error_code = ZipOpenErrorCode::kEntryNotFound;
    return nullptr;
  }
  if (zip_entry->GetUncompressedLength() == 0) {
    *error_msg = StringPrintf("Dex file '%s' has zero length", location.c_str());
    *error_code = ZipOpenErrorCode::kDexFileError;
    return nullptr;
  }

  std::unique_ptr<MemMap> map;
  if (zip_entry->IsUncompressed()) {
    if (!zip_entry->IsAlignedTo(alignof(Header))) {
      // Do not mmap unaligned ZIP entries because
      // doing so would fail dex verification which requires 4 byte alignment.
      LOG(WARNING) << "Can't mmap dex file " << location << "!" << entry_name << " directly; "
                   << "please zipalign to " << alignof(Header) << " bytes. "
                   << "Falling back to extracting file.";
    } else {
      // Map uncompressed files within zip as file-backed to avoid a dirty copy.
      map.reset(zip_entry->MapDirectlyFromFile(location.c_str(), /*out*/error_msg));
      if (map == nullptr) {
        LOG(WARNING) << "Can't mmap dex file " << location << "!" << entry_name << " directly; "
                     << "is your ZIP file corrupted? Falling back to extraction.";
        // Try again with Extraction which still has a chance of recovery.
      }
    }
  }

  if (map == nullptr) {
    // Default path for compressed ZIP entries,
    // and fallback for stored ZIP entries.
    map.reset(zip_entry->ExtractToMemMap(location.c_str(), entry_name, error_msg));
  }

  if (map == nullptr) {
    *error_msg = StringPrintf("Failed to extract '%s' from '%s': %s", entry_name, location.c_str(),
                              error_msg->c_str());
    *error_code = ZipOpenErrorCode::kExtractToMemoryError;
    return nullptr;
  }
  VerifyResult verify_result;
  std::unique_ptr<DexFile> dex_file = OpenCommon(map->Begin(),
                                                 map->Size(),
                                                 location,
                                                 zip_entry->GetCrc32(),
                                                 kNoOatDexFile,
                                                 /* verify */ true,
                                                 verify_checksum,
                                                 error_msg,
                                                 &verify_result);
  if (dex_file == nullptr) {
    if (verify_result == VerifyResult::kVerifyNotAttempted) {
      *error_code = ZipOpenErrorCode::kDexFileError;
    } else {
      *error_code = ZipOpenErrorCode::kVerifyError;
    }
    return nullptr;
  }
  dex_file->mem_map_ = std::move(map);
  if (!dex_file->DisableWrite()) {
    *error_msg = StringPrintf("Failed to make dex file '%s' read only", location.c_str());
    *error_code = ZipOpenErrorCode::kMakeReadOnlyError;
    return nullptr;
  }
  CHECK(dex_file->IsReadOnly()) << location;
  if (verify_result != VerifyResult::kVerifySucceeded) {
    *error_code = ZipOpenErrorCode::kVerifyError;
    return nullptr;
  }
  *error_code = ZipOpenErrorCode::kNoError;
  return dex_file;
}

std::unique_ptr<DexFile> DexFile::OpenCommon(const uint8_t* base,//这里是dex的开始
                                             size_t size,//这里是dex的大小
                                             const std::string& location,//这里是地址
                                             uint32_t location_checksum,
                                             const OatDexFile* oat_dex_file,//如果直接打开文件而不是通过oat文件获得dex，这个参数是kNoOatDexFile，hook打印这个参数就可以判断一些壳是否放弃了oat文件强制以dex解释运行
                                             bool verify,
                                             bool verify_checksum,
                                             std::string* error_msg,
                                             VerifyResult* verify_result) {
  if (verify_result != nullptr) {
    *verify_result = VerifyResult::kVerifyNotAttempted;
  }
  std::unique_ptr<DexFile> dex_file(new DexFile(base,
                                                size,
                                                location,
                                                location_checksum,
                                                oat_dex_file));//这里new了一个dex_file实例，至此dex_file加载结束
  if (dex_file == nullptr) {
    *error_msg = StringPrintf("Failed to open dex file '%s' from memory: %s", location.c_str(),
                              error_msg->c_str());
    return nullptr;
  }
  if (!dex_file->Init(error_msg)) {//init初始化
    dex_file.reset();
    return nullptr;
  }
  if (verify && !DexFileVerifier::Verify(dex_file.get(),
                                         dex_file->Begin(),
                                         dex_file->Size(),
                                         location.c_str(),
                                         verify_checksum,
                                         error_msg)) {//Verify验证
    if (verify_result != nullptr) {
      *verify_result = VerifyResult::kVerifyFailed;
    }
    return nullptr;
  }
  if (verify_result != nullptr) {
    *verify_result = VerifyResult::kVerifySucceeded;
  }
  return dex_file;
}