Dex2Oat源码流程(1)——Android6.0

痛定思痛。 2022-06-13 02:14 283阅读 0赞

当framework层的PackageManagerService需要执行安装请求时，需要对目标APK文件进行处理，而这个过程归根到底是对dex文件的处理，Android将dex文件转化为虚拟机可以直接执行的oat文件，这个转化过程是在art/dex2oat/dex2oat.cc([http://androidxref.com/6.0.0\_r1/xref/art/dex2oat/dex2oat.cc][http_androidxref.com_6.0.0_r1_xref_art_dex2oat_dex2oat.cc])中完成的。

## main() ##

从dex2oat.cc的执行入口main函数开始跟踪，可以很容易看出dex2oat的逻辑：

int main(int argc, char** argv) {
      int result = art::dex2oat(argc, argv);
      // Everything was done, do an explicit exit here to avoid running Runtime destructors that take
      // time (bug 10645725) unless we're a debug build or running on valgrind. Note: The Dex2Oat class
      // should not destruct the runtime in this case.
      if (!art::kIsDebugBuild && (RUNNING_ON_VALGRIND == 0)) {
        exit(result);
      }
      return result;
    }

## dex2oat() ##

main函数中，调用了art命名空间下的dex2oat函数，在dex2oat()函数中，

1.  arm上的workaround由b13564922()完成，这个与dex2oat的主要线程无关，可以暂时忽略。
2.  构造Dex2oat对象——Dex2Oat dex2oat(&timings);
3.  处理命令行参数，将dex文件名文件路径等参数传入函数中——dex2oat.ParseArgs(argc, argv);
4.  判断对于dex文件是否有写的权限——dex2oat.OpenFile()
5.  打印命令行参数——LOG(INFO) << CommandLine();
6.  判断dex2oat编译环境是否启动成功——dex2oat.Setup()
7.  根据是否image分别调用CompileImage(dex2oat)或CompileApp(dex2oat)的处理

static int dex2oat(int argc, char** argv) {
      b13564922();
    
      TimingLogger timings("compiler", false, false);
    
      Dex2Oat dex2oat(&timings);
    
      // Parse arguments. Argument mistakes will lead to exit(EXIT_FAILURE) in UsageError.
      dex2oat.ParseArgs(argc, argv);
    
      // Check early that the result of compilation can be written
      if (!dex2oat.OpenFile()) {
        return EXIT_FAILURE;
      }
    
      // Print the complete line when any of the following is true:
      //   1) Debug build
      //   2) Compiling an image
      //   3) Compiling with --host
      //   4) Compiling on the host (not a target build)
      // Otherwise, print a stripped command line.
      if (kIsDebugBuild || dex2oat.IsImage() || dex2oat.IsHost() || !kIsTargetBuild) {
        LOG(INFO) << CommandLine();
      } else {
        LOG(INFO) << StrippedCommandLine();
      }
    
      if (!dex2oat.Setup()) {
        dex2oat.EraseOatFile();
        return EXIT_FAILURE;
      }
    
      if (dex2oat.IsImage()) {
        return CompileImage(dex2oat);
      } else {
        return CompileApp(dex2oat);
      }
    }
    }  // namespace art

## CompileApp()&&CompileImage() ##

这两个函数可以一起分析，从他们的代码中可以看出，代码基本上一样。  
dex2oat.Compile()的代码如下所示：

static int CompileImage(Dex2Oat& dex2oat) {
      dex2oat.Compile();
    
      // Create the boot.oat.
      if (!dex2oat.CreateOatFile()) {
        dex2oat.EraseOatFile();
        return EXIT_FAILURE;
      }
    
      // Flush and close the boot.oat. We always expect the output file by name, and it will be
      // re-opened from the unstripped name.
      if (!dex2oat.FlushCloseOatFile()) {
        return EXIT_FAILURE;
      }
    
      // Creates the boot.art and patches the boot.oat.
      if (!dex2oat.HandleImage()) {
        return EXIT_FAILURE;
      }
    
      // When given --host, finish early without stripping.
      if (dex2oat.IsHost()) {
        dex2oat.DumpTiming();
        return EXIT_SUCCESS;
      }
    
      // Copy unstripped to stripped location, if necessary.
      if (!dex2oat.CopyUnstrippedToStripped()) {
        return EXIT_FAILURE;
      }
    
      // FlushClose again, as stripping might have re-opened the oat file.
      if (!dex2oat.FlushCloseOatFile()) {
        return EXIT_FAILURE;
      }
    
      dex2oat.DumpTiming();
      return EXIT_SUCCESS;
    }

CompileApp()的代码如下所示：

static int CompileApp(Dex2Oat& dex2oat) {
      dex2oat.Compile();
    
      // Create the app oat.
      if (!dex2oat.CreateOatFile()) {
        dex2oat.EraseOatFile();
        return EXIT_FAILURE;
      }
    
      // Do not close the oat file here. We might haven gotten the output file by file descriptor,
      // which we would lose.
      if (!dex2oat.FlushOatFile()) {
        return EXIT_FAILURE;
      }
    
      // When given --host, finish early without stripping.
      if (dex2oat.IsHost()) {
        if (!dex2oat.FlushCloseOatFile()) {
          return EXIT_FAILURE;
        }
    
        dex2oat.DumpTiming();
        return EXIT_SUCCESS;
      }
    
      // Copy unstripped to stripped location, if necessary. This will implicitly flush & close the
      // unstripped version. If this is given, we expect to be able to open writable files by name.
      if (!dex2oat.CopyUnstrippedToStripped()) {
        return EXIT_FAILURE;
      }
    
      // Flush and close the file.
      if (!dex2oat.FlushCloseOatFile()) {
        return EXIT_FAILURE;
      }
    
      dex2oat.DumpTiming();
      return EXIT_SUCCESS;
    }

可以看出他们有一个共同的特点，就是都先调用了dex2oat.Compile()函数。

## Compile() ##

在这一步，创建compiler driver，编译所有的dex文件。dex2oat.Compile()的代码如下所示：

// Create and invoke the compiler driver. This will compile all the dex files.
      void Compile() {
        TimingLogger::ScopedTiming t("dex2oat Compile", timings_);
        compiler_phases_timings_.reset(new CumulativeLogger("compilation times"));
    
        // Handle and ClassLoader creation needs to come after Runtime::Create
        jobject class_loader = nullptr;
        Thread* self = Thread::Current();
        if (!boot_image_option_.empty()) {
          ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
          OpenClassPathFiles(runtime_->GetClassPathString(), dex_files_, &class_path_files_);
          ScopedObjectAccess soa(self);
    
          // Classpath: first the class-path given.
          std::vector<const DexFile*> class_path_files;
          for (auto& class_path_file : class_path_files_) {
            class_path_files.push_back(class_path_file.get());
          }
    
          // Store the classpath we have right now.
          key_value_store_->Put(OatHeader::kClassPathKey,
                                OatFile::EncodeDexFileDependencies(class_path_files));
    
          // Then the dex files we'll compile. Thus we'll resolve the class-path first.
          class_path_files.insert(class_path_files.end(), dex_files_.begin(), dex_files_.end());
    
          class_loader = class_linker->CreatePathClassLoader(self, class_path_files);
        }
    
        driver_.reset(new CompilerDriver(compiler_options_.get(),
                                         verification_results_.get(),
                                         &method_inliner_map_,
                                         compiler_kind_,
                                         instruction_set_,
                                         instruction_set_features_.get(),
                                         image_,
                                         image_classes_.release(),
                                         compiled_classes_.release(),
                                         nullptr,
                                         thread_count_,
                                         dump_stats_,
                                         dump_passes_,
                                         dump_cfg_file_name_,
                                         compiler_phases_timings_.get(),
                                         swap_fd_,
                                         profile_file_));
    
        driver_->CompileAll(class_loader, dex_files_, timings_);
      }

这一步的操作由driver\_这个对象完成的，而这个对象在Dex2Oat类中由CompilerDriver 创建的——CompilerDriver\* driver\_;之后调用driver\_的ComileAll()函数来完成编译过程。

[http_androidxref.com_6.0.0_r1_xref_art_dex2oat_dex2oat.cc]: http://androidxref.com/6.0.0_r1/xref/art/dex2oat/dex2oat.cc