[求助]在Android P ART源码中，ClassLinker::DefineClass调用了Runtime::Current()->GetRuntimeCallbacks()->ClassPreDefine函数。。。。-Android安全-看雪论坛-安全社区|非营利性质技术交流社区

[求助]在Android P ART源码中，ClassLinker::DefineClass调用了Runtime::Current()->GetRuntimeCallbacks()->ClassPreDefine函数。。。。

发表于: 2018-11-28 22:16 3245

[求助]在Android P ART源码中，ClassLinker::DefineClass调用了Runtime::Current()->GetRuntimeCallbacks()->ClassPreDefine函数。。。。

倔强石头

2018-11-28 22:16

3245

在Android P ART源码中，ClassLinker::DefineClass调用了Runtime::Current()->GetRuntimeCallbacks()->ClassPreDefine函数

ObjPtr<mirror::Class> ClassLinker::DefineClass(Thread* self,
                                               const char* descriptor,
                                               size_t hash,
                                               Handle<mirror::ClassLoader> class_loader,
                                               const DexFile& dex_file,
                                               const DexFile::ClassDef& dex_class_def) {
  StackHandleScope<3> hs(self);
  auto klass = hs.NewHandle<mirror::Class>(nullptr);

.......
  // Get the real dex file. This will return the input if there aren't any callbacks or they do
  // nothing.
  DexFile const* new_dex_file = nullptr;   //
  DexFile::ClassDef const* new_class_def = nullptr   //
  // TODO We should ideally figure out some way to move this after we get a lock on the klass so it
  // will only be called once.
  /*ClassPreDefine会根据dex_file、dex_class_def生成新的new_dex_file，new_class_def
   */
  Runtime::Current()->GetRuntimeCallbacks()->ClassPreDefine(descriptor,
                                                            klass,
                                                            class_loader,
                                                            dex_file,
                                                            dex_class_def,
                                                            &new_dex_file,
                                                            &new_class_def);
  .......
}

RuntimeCallbacks中对应的是

void RuntimeCallbacks::ClassPreDefine(const char* descriptor,
                                      Handle<mirror::Class> temp_class,
                                      Handle<mirror::ClassLoader> loader,
                                      const DexFile& initial_dex_file,
                                      const DexFile::ClassDef& initial_class_def,
                                      /*out*/DexFile const** final_dex_file,
                                      /*out*/DexFile::ClassDef const** final_class_def) {
  DexFile const* current_dex_file = &initial_dex_file;
  DexFile::ClassDef const* current_class_def = &initial_class_def;
  for (ClassLoadCallback* cb : class_callbacks_) {
    DexFile const* new_dex_file = nullptr;
    DexFile::ClassDef const* new_class_def = nullptr;
	//ClassLoadCallback为 ClassCallback或DbgClassLoadCallback，
    cb->ClassPreDefine(descriptor,
                       temp_class,
                       loader,
                       *current_dex_file,
                       *current_class_def,
                       &new_dex_file,
                       &new_class_def);
    if ((new_dex_file != nullptr && new_dex_file != current_dex_file) ||
        (new_class_def != nullptr && new_class_def != current_class_def)) {
      DCHECK(new_dex_file != nullptr && new_class_def != nullptr);
      current_dex_file = new_dex_file;
      current_class_def = new_class_def;
    }
  }
  *final_dex_file = current_dex_file;
  *final_class_def = current_class_def;
}

而ClassCallback的ClassPreDefine方法中

struct ClassCallback : public art::ClassLoadCallback {
  void ClassPreDefine(const char* descriptor,
                      art::Handle<art::mirror::Class> klass,
                      art::Handle<art::mirror::ClassLoader> class_loader,
                      const art::DexFile& initial_dex_file,
                      const art::DexFile::ClassDef& initial_class_def ATTRIBUTE_UNUSED,
                      /*out*/art::DexFile const** final_dex_file,
                      /*out*/art::DexFile::ClassDef const** final_class_def)
      OVERRIDE REQUIRES_SHARED(art::Locks::mutator_lock_) {
 ....................
*final_class_def = &dex_file->GetClassDef(0);//返回GetClassDef(0)？？？？？？？？？？？？？？？
      *final_dex_file = dex_file.release();//返回DexFile
.....................
}
}

final_class_def = &dex_file->GetClassDef(0)返回的永远是第1个ClassDef，这样的话不是与最初传入的initial_class_def类型完全不一样了吗？

ClassLinker::DefineClass 后面还怎么利用new_class_def来加载类？除非class_callbacks_为null,但是在ti_class.cc是将ClassCallback 对象加入 class_callbacks_中。哪位坛友能帮忙指点一下？万分感谢~~

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最后于 2018-11-29 11:44 被倔强石头编辑，原因：

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