【Android 逆向】ART 函数抽取加壳 ( ART 下的函数抽取恢复时机 | 禁用 dex2oat 机制源码分析 )（一）

OatFileAssistant::ResultOfAttemptToUpdate OatFileAssistant::GenerateOatFileNoChecks(
      OatFileAssistant::OatFileInfo& info, CompilerFilter::Filter filter, std::string* error_msg) {
  CHECK(error_msg != nullptr);
  Runtime* runtime = Runtime::Current();
  // 判断 Dex2Oat 当前是否可用 , 如果不可用 , 直接返回 
  if (!runtime->IsDex2OatEnabled()) {
    *error_msg = "Generation of oat file for dex location " + dex_location_
      + " not attempted because dex2oat is disabled.";
    return kUpdateNotAttempted;
  }
  if (info.Filename() == nullptr) {
    *error_msg = "Generation of oat file for dex location " + dex_location_
      + " not attempted because the oat file name could not be determined.";
    return kUpdateNotAttempted;
  }
  const std::string& oat_file_name = *info.Filename();
  const std::string& vdex_file_name = GetVdexFilename(oat_file_name);
  // dex2oat忽略丢失的dex文件，不报告错误。
  // 请在此处明确检查，以便正确检测错误。
  // TODO:为什么dex2oat会这样做？
  struct stat dex_path_stat;
  if (TEMP_FAILURE_RETRY(stat(dex_location_.c_str(), &dex_path_stat)) != 0) {
    *error_msg = "Could not access dex location " + dex_location_ + ":" + strerror(errno);
    return kUpdateNotAttempted;
  }
  // 如果这是odex位置，我们需要创建odex文件布局 (../oat/isa/..)
  if (!info.IsOatLocation()) {
    if (!PrepareOdexDirectories(dex_location_, oat_file_name, isa_, error_msg)) {
      return kUpdateNotAttempted;
    }
  }
  // 设置oat和vdex文件的权限。
  // 当组和其他人传播时，用户总是被读取和写入
  // 原始dex文件的读取权限。
  mode_t file_mode = S_IRUSR | S_IWUSR |
      (dex_path_stat.st_mode & S_IRGRP) |
      (dex_path_stat.st_mode & S_IROTH);
  std::unique_ptr<File> vdex_file(OS::CreateEmptyFile(vdex_file_name.c_str()));
  if (vdex_file.get() == nullptr) {
    *error_msg = "Generation of oat file " + oat_file_name
      + " not attempted because the vdex file " + vdex_file_name
      + " could not be opened.";
    return kUpdateNotAttempted;
  }
  if (fchmod(vdex_file->Fd(), file_mode) != 0) {
    *error_msg = "Generation of oat file " + oat_file_name
      + " not attempted because the vdex file " + vdex_file_name
      + " could not be made world readable.";
    return kUpdateNotAttempted;
  }
  std::unique_ptr<File> oat_file(OS::CreateEmptyFile(oat_file_name.c_str()));
  if (oat_file.get() == nullptr) {
    *error_msg = "Generation of oat file " + oat_file_name
      + " not attempted because the oat file could not be created.";
    return kUpdateNotAttempted;
  }
  if (fchmod(oat_file->Fd(), file_mode) != 0) {
    *error_msg = "Generation of oat file " + oat_file_name
      + " not attempted because the oat file could not be made world readable.";
    oat_file->Erase();
    return kUpdateNotAttempted;
  }
  std::vector<std::string> args;
  args.push_back("--dex-file=" + dex_location_);
  args.push_back("--output-vdex-fd=" + std::to_string(vdex_file->Fd()));
  args.push_back("--oat-fd=" + std::to_string(oat_file->Fd()));
  args.push_back("--oat-location=" + oat_file_name);
  args.push_back("--compiler-filter=" + CompilerFilter::NameOfFilter(filter));
  // ★ 核心跳转 
  if (!Dex2Oat(args, error_msg)) {
    // 手动删除oat和vdex文件。这样可以确保没有垃圾
    // 如果进程意外死亡，则剩余。
    vdex_file->Erase();
    unlink(vdex_file_name.c_str());
    oat_file->Erase();
    unlink(oat_file_name.c_str());
    return kUpdateFailed;
  }
  if (vdex_file->FlushCloseOrErase() != 0) {
    *error_msg = "Unable to close vdex file " + vdex_file_name;
    unlink(vdex_file_name.c_str());
    return kUpdateFailed;
  }
  if (oat_file->FlushCloseOrErase() != 0) {
    *error_msg = "Unable to close oat file " + oat_file_name;
    unlink(oat_file_name.c_str());
    return kUpdateFailed;
  }
  // 标记 odex 件已更改，我们应该尝试重新加载。
  info.Reset();
  return kUpdateSucceeded;
}