src/class_linker.cc

// Copyright 2011 Google Inc. All Rights Reserved.
// Author: cshapiro@google.com (Carl Shapiro)

#include "class_linker.h"

#include <vector>
#include <utility>

#include "casts.h"
#include "dex_cache.h"
#include "dex_verifier.h"
#include "heap.h"
#include "logging.h"
#include "monitor.h"
#include "object.h"
#include "dex_file.h"
#include "scoped_ptr.h"
#include "thread.h"
#include "utils.h"

namespace art {

ClassLinker* ClassLinker::Create(std::vector<DexFile*> boot_class_path) {
  scoped_ptr<ClassLinker> class_linker(new ClassLinker);
  class_linker->Init(boot_class_path);
  // TODO: check for failure during initialization
  return class_linker.release();
}

void ClassLinker::Init(std::vector<DexFile*> boot_class_path) {

  // setup boot_class_path_ so that object_array_class_ can be properly initialized
  for (size_t i = 0; i != boot_class_path.size(); ++i) {
    AppendToBootClassPath(boot_class_path[i]);
  }

  // Allocate and partially initialize the Class, Object, Field, Method classes.
  // Initialization will be completed when the definitions are loaded.
  java_lang_Class_ = down_cast<Class*>(Heap::AllocObject(NULL, sizeof(Class)));
  CHECK(java_lang_Class_ != NULL);
  java_lang_Class_->descriptor_ = "Ljava/lang/Class;";
  java_lang_Class_->object_size_ = sizeof(Class);
  java_lang_Class_->klass_ = java_lang_Class_;

  java_lang_Object_ = AllocClass(NULL);
  CHECK(java_lang_Object_ != NULL);
  java_lang_Object_->descriptor_ = "Ljava/lang/Object;";

  java_lang_Class_->super_class_ = java_lang_Object_;

  java_lang_ref_Field_ = AllocClass(NULL);
  CHECK(java_lang_ref_Field_ != NULL);
  java_lang_ref_Field_->descriptor_ = "Ljava/lang/ref/Field;";

  java_lang_ref_Method_ = AllocClass(NULL);
  CHECK(java_lang_ref_Method_ != NULL);
  java_lang_ref_Method_->descriptor_ = "Ljava/lang/Method;";

  java_lang_Cloneable_ = AllocClass(NULL);
  CHECK(java_lang_Cloneable_ != NULL);
  java_lang_Cloneable_->descriptor_ = "Ljava/lang/Cloneable;";

  java_io_Serializable_ = AllocClass(NULL);
  CHECK(java_io_Serializable_ != NULL);
  java_io_Serializable_->descriptor_ = "Ljava/io/Serializable;";

  java_lang_String_ = AllocClass(NULL);
  CHECK(java_lang_String_ != NULL);
  java_lang_String_->descriptor_ = "Ljava/lang/String;";

  // Allocate and initialize the primitive type classes.
  primitive_byte_ = CreatePrimitiveClass("B");
  primitive_char_ = CreatePrimitiveClass("C");
  primitive_double_ = CreatePrimitiveClass("D");
  primitive_float_ = CreatePrimitiveClass("F");
  primitive_int_ = CreatePrimitiveClass("I");
  primitive_long_ = CreatePrimitiveClass("J");
  primitive_short_ = CreatePrimitiveClass("S");
  primitive_boolean_ = CreatePrimitiveClass("Z");
  primitive_void_ = CreatePrimitiveClass("V");

  char_array_class_ = FindSystemClass("[C");
  CHECK(char_array_class_ != NULL);

  object_array_class_ = FindSystemClass("[Ljava/lang/Object;");
  CHECK(object_array_class_ != NULL);
}

DexCache* ClassLinker::AllocDexCache() {
  return down_cast<DexCache*>(Heap::AllocObjectArray(object_array_class_, DexCache::kMax));
}

Class* ClassLinker::AllocClass(DexCache* dex_cache) {
  Class* klass = down_cast<Class*>(Heap::AllocObject(java_lang_Class_));
  klass->dex_cache_ = dex_cache;
  return klass;
}

StaticField* ClassLinker::AllocStaticField() {
  return down_cast<StaticField*>(Heap::AllocObject(java_lang_ref_Field_,
                                                   sizeof(StaticField)));
}

InstanceField* ClassLinker::AllocInstanceField() {
  return down_cast<InstanceField*>(Heap::AllocObject(java_lang_ref_Field_,
                                                     sizeof(InstanceField)));
}

Method* ClassLinker::AllocMethod() {
  return down_cast<Method*>(Heap::AllocObject(java_lang_ref_Method_,
                                              sizeof(Method)));
}

ObjectArray* ClassLinker::AllocObjectArray(size_t length) {
    return Heap::AllocObjectArray(object_array_class_, length);
}

Class* ClassLinker::FindClass(const StringPiece& descriptor,
                              Object* class_loader,
                              const DexFile* dex_file) {
  Thread* self = Thread::Current();
  DCHECK(self != NULL);
  CHECK(!self->IsExceptionPending());
  // Find the class in the loaded classes table.
  Class* klass = LookupClass(descriptor, class_loader);
  if (klass == NULL) {
    // Class is not yet loaded.
    if (descriptor[0] == '[') {
      return CreateArrayClass(descriptor, class_loader, dex_file);
    }
    ClassPathEntry pair;
    if (dex_file == NULL) {
      pair = FindInBootClassPath(descriptor);
    } else {
      pair.first = dex_file;
      pair.second = dex_file->FindClassDef(descriptor);
    }
    if (pair.second == NULL) {
      LG << "Class " << descriptor << " not found";  // TODO: NoClassDefFoundError
      return NULL;
    }
    const DexFile* dex_file = pair.first;
    const DexFile::ClassDef* dex_class_def = pair.second;
    DexCache* dex_cache = FindDexCache(dex_file);
    // Load the class from the dex file.
    if (descriptor == "Ljava/lang/Object;") {
      klass = java_lang_Object_;
      klass->dex_cache_ = dex_cache;
      klass->object_size_ = sizeof(Object);
      char_array_class_->super_class_idx_ = dex_class_def->class_idx_;
    } else if (descriptor == "Ljava/lang/Class;") {
      klass = java_lang_Class_;
      klass->dex_cache_ = dex_cache;
      klass->object_size_ = sizeof(Class);
    } else if (descriptor == "Ljava/lang/ref/Field;") {
      klass = java_lang_ref_Field_;
      klass->dex_cache_ = dex_cache;
      klass->object_size_ = sizeof(Field);
    } else if (descriptor == "Ljava/lang/ref/Method;") {
      klass = java_lang_ref_Method_;
      klass->dex_cache_ = dex_cache;
      klass->object_size_ = sizeof(Method);
    } else if (descriptor == "Ljava/lang/Cloneable;") {
      klass = java_lang_Cloneable_;
      klass->dex_cache_ = dex_cache;
    } else if (descriptor == "Ljava/io/Serializable;") {
      klass = java_io_Serializable_;
      klass->dex_cache_ = dex_cache;
    } else if (descriptor == "Ljava/lang/String;") {
      klass = java_lang_String_;
      klass->dex_cache_ = dex_cache;
      klass->object_size_ = sizeof(String);
    } else {
      klass = AllocClass(dex_cache);
    }
    LoadClass(*dex_file, *dex_class_def, klass);
    // Check for a pending exception during load
    if (self->IsExceptionPending()) {
      // TODO: free native allocations in klass
      return NULL;
    }
    {
      ObjectLock lock(klass);
      klass->clinit_thread_id_ = self->GetId();
      // Add the newly loaded class to the loaded classes table.
      bool success = InsertClass(klass);
      if (!success) {
        // We may fail to insert if we raced with another thread.
        klass->clinit_thread_id_ = 0;
        // TODO: free native allocations in klass
        klass = LookupClass(descriptor, class_loader);
        CHECK(klass != NULL);
      } else {
        // Link the class.
        if (!LinkClass(klass, dex_file)) {
          // Linking failed.
          // TODO: CHECK(self->IsExceptionPending());
          lock.NotifyAll();
          return NULL;
        }
      }
    }
  }
  // Link the class if it has not already been linked.
  if (!klass->IsLinked() && !klass->IsErroneous()) {
    ObjectLock lock(klass);
    // Check for circular dependencies between classes.
    if (!klass->IsLinked() && klass->clinit_thread_id_ == self->GetId()) {
      LG << "Recursive link";  // TODO: ClassCircularityError
      return NULL;
    }
    // Wait for the pending initialization to complete.
    while (!klass->IsLinked() && !klass->IsErroneous()) {
      lock.Wait();
    }
  }
  if (klass->IsErroneous()) {
    LG << "EarlierClassFailure";  // TODO: EarlierClassFailure
    return NULL;
  }
  // Return the loaded class.  No exceptions should be pending.
  CHECK(!self->IsExceptionPending());
  return klass;
}

void ClassLinker::LoadClass(const DexFile& dex_file,
                            const DexFile::ClassDef& dex_class_def,
                            Class* klass) {
  CHECK(klass != NULL);
  CHECK(klass->dex_cache_ != NULL);
  const byte* class_data = dex_file.GetClassData(dex_class_def);
  DexFile::ClassDataHeader header = dex_file.ReadClassDataHeader(&class_data);

  const char* descriptor = dex_file.GetClassDescriptor(dex_class_def);
  CHECK(descriptor != NULL);

  klass->klass_ = java_lang_Class_;
  klass->descriptor_.set(descriptor);
  klass->descriptor_alloc_ = NULL;
  klass->access_flags_ = dex_class_def.access_flags_;
  klass->class_loader_ = NULL;  // TODO
  klass->primitive_type_ = Class::kPrimNot;
  klass->status_ = Class::kStatusIdx;

  klass->super_class_ = NULL;
  klass->super_class_idx_ = dex_class_def.superclass_idx_;

  klass->num_static_fields_ = header.static_fields_size_;
  klass->num_instance_fields_ = header.instance_fields_size_;
  klass->num_direct_methods_ = header.direct_methods_size_;
  klass->num_virtual_methods_ = header.virtual_methods_size_;

  klass->source_file_ = dex_file.dexGetSourceFile(dex_class_def);

  // Load class interfaces.
  LoadInterfaces(dex_file, dex_class_def, klass);

  // Load static fields.
  if (klass->NumStaticFields() != 0) {
    // TODO: allocate on the object heap.
    klass->sfields_ = new StaticField*[klass->NumStaticFields()]();
    uint32_t last_idx = 0;
    for (size_t i = 0; i < klass->NumStaticFields(); ++i) {
      DexFile::Field dex_field;
      dex_file.dexReadClassDataField(&class_data, &dex_field, &last_idx);
      StaticField* sfield = AllocStaticField();
      klass->sfields_[i] = sfield;
      LoadField(dex_file, dex_field, klass, sfield);
    }
  }

  // Load instance fields.
  if (klass->NumInstanceFields() != 0) {
    // TODO: allocate on the object heap.
    klass->ifields_ = new InstanceField*[klass->NumInstanceFields()]();
    uint32_t last_idx = 0;
    for (size_t i = 0; i < klass->NumInstanceFields(); ++i) {
      DexFile::Field dex_field;
      dex_file.dexReadClassDataField(&class_data, &dex_field, &last_idx);
      InstanceField* ifield = AllocInstanceField();
      klass->ifields_[i] = ifield;
      LoadField(dex_file, dex_field, klass, ifield);
    }
  }

  // Load direct methods.
  if (klass->NumDirectMethods() != 0) {
    // TODO: append direct methods to class object
    klass->direct_methods_ = new Method*[klass->NumDirectMethods()]();
    uint32_t last_idx = 0;
    for (size_t i = 0; i < klass->NumDirectMethods(); ++i) {
      DexFile::Method dex_method;
      dex_file.dexReadClassDataMethod(&class_data, &dex_method, &last_idx);
      Method* meth = AllocMethod();
      klass->direct_methods_[i] = meth;
      LoadMethod(dex_file, dex_method, klass, meth);
      // TODO: register maps
    }
  }

  // Load virtual methods.
  if (klass->NumVirtualMethods() != 0) {
    // TODO: append virtual methods to class object
    klass->virtual_methods_ = new Method*[klass->NumVirtualMethods()]();
    uint32_t last_idx = 0;
    for (size_t i = 0; i < klass->NumVirtualMethods(); ++i) {
      DexFile::Method dex_method;
      dex_file.dexReadClassDataMethod(&class_data, &dex_method, &last_idx);
      Method* meth = AllocMethod();
      klass->virtual_methods_[i] = meth;
      LoadMethod(dex_file, dex_method, klass, meth);
      // TODO: register maps
    }
  }
}

void ClassLinker::LoadInterfaces(const DexFile& dex_file,
                                 const DexFile::ClassDef& dex_class_def,
                                 Class* klass) {
  const DexFile::TypeList* list = dex_file.GetInterfacesList(dex_class_def);
  if (list != NULL) {
    klass->interface_count_ = list->Size();
    // TODO: allocate the interfaces array on the object heap.
    klass->interfaces_ = new Class*[list->Size()]();
    for (size_t i = 0; i < list->Size(); ++i) {
      const DexFile::TypeItem& type_item = list->GetTypeItem(i);
      klass->interfaces_[i] = reinterpret_cast<Class*>(type_item.type_idx_);
    }
  }
}

void ClassLinker::LoadField(const DexFile& dex_file,
                            const DexFile::Field& src,
                            Class* klass,
                            Field* dst) {
  const DexFile::FieldId& field_id = dex_file.GetFieldId(src.field_idx_);
  dst->klass_ = klass;
  dst->name_ = dex_file.dexStringById(field_id.name_idx_);
  dst->signature_ = dex_file.dexStringByTypeIdx(field_id.type_idx_);
  dst->access_flags_ = src.access_flags_;
}

void ClassLinker::LoadMethod(const DexFile& dex_file,
                             const DexFile::Method& src,
                             Class* klass,
                             Method* dst) {
  const DexFile::MethodId& method_id = dex_file.GetMethodId(src.method_idx_);
  dst->klass_ = klass;
  dst->name_.set(dex_file.dexStringById(method_id.name_idx_));
  dst->proto_idx_ = method_id.proto_idx_;
  dst->shorty_.set(dex_file.GetShorty(method_id.proto_idx_));
  dst->access_flags_ = src.access_flags_;

  // TODO: check for finalize method

  const DexFile::CodeItem* code_item = dex_file.GetCodeItem(src);
  if (code_item != NULL) {
    dst->num_registers_ = code_item->registers_size_;
    dst->num_ins_ = code_item->ins_size_;
    dst->num_outs_ = code_item->outs_size_;
    dst->insns_ = code_item->insns_;
  } else {
    uint16_t num_args = dst->NumArgRegisters();
    if (!dst->IsStatic()) {
      ++num_args;
    }
    dst->num_registers_ = dst->num_ins_ + num_args;
    // TODO: native methods
  }
}

ClassLinker::ClassPathEntry ClassLinker::FindInBootClassPath(const StringPiece& descriptor) {
  for (size_t i = 0; i != boot_class_path_.size(); ++i) {
    DexFile* dex_file = boot_class_path_[i];
    const DexFile::ClassDef* dex_class_def = dex_file->FindClassDef(descriptor);
    if (dex_class_def != NULL) {
      return ClassPathEntry(dex_file, dex_class_def);
    }
  }
  return ClassPathEntry(NULL, NULL);
}

void ClassLinker::AppendToBootClassPath(DexFile* dex_file) {
  boot_class_path_.push_back(dex_file);
  RegisterDexFile(dex_file);
}

void ClassLinker::RegisterDexFile(DexFile* dex_file) {
  dex_files_.push_back(dex_file);
  DexCache* dex_cache = AllocDexCache();
  CHECK(dex_cache != NULL);
  dex_cache->Init(AllocObjectArray(dex_file->NumStringIds()),
                  AllocObjectArray(dex_file->NumTypeIds()),
                  AllocObjectArray(dex_file->NumMethodIds()),
                  AllocObjectArray(dex_file->NumFieldIds()));
  dex_caches_.push_back(dex_cache);
}

const DexFile* ClassLinker::FindDexFile(const DexCache* dex_cache) const {
  CHECK(dex_cache != NULL);
  for (size_t i = 0; i != dex_caches_.size(); ++i) {
    if (dex_caches_[i] == dex_cache) {
        return dex_files_[i];
    }
  }
  CHECK(false) << "Could not find DexFile";
  return NULL;
}

DexCache* ClassLinker::FindDexCache(const DexFile* dex_file) const {
  CHECK(dex_file != NULL);
  for (size_t i = 0; i != dex_files_.size(); ++i) {
    if (dex_files_[i] == dex_file) {
        return dex_caches_[i];
    }
  }
  CHECK(false) << "Could not find DexCache";
  return NULL;
}

Class* ClassLinker::CreatePrimitiveClass(const StringPiece& descriptor) {
  Class* klass = AllocClass(NULL);
  CHECK(klass != NULL);
  klass->super_class_ = NULL;
  klass->access_flags_ = kAccPublic | kAccFinal | kAccAbstract;
  klass->descriptor_ = descriptor;
  klass->descriptor_alloc_ = NULL;
  klass->status_ = Class::kStatusInitialized;
  bool success = InsertClass(klass);
  CHECK(success);
  return klass;
}

// Create an array class (i.e. the class object for the array, not the
// array itself).  "descriptor" looks like "[C" or "[[[[B" or
// "[Ljava/lang/String;".
//
// If "descriptor" refers to an array of primitives, look up the
// primitive type's internally-generated class object.
//
// "loader" is the class loader of the class that's referring to us.  It's
// used to ensure that we're looking for the element type in the right
// context.  It does NOT become the class loader for the array class; that
// always comes from the base element class.
//
// Returns NULL with an exception raised on failure.
Class* ClassLinker::CreateArrayClass(const StringPiece& descriptor,
                                     Object* class_loader,
                                     const DexFile* dex_file)
{
    CHECK(descriptor[0] == '[');
    DCHECK(java_lang_Class_ != NULL);
    DCHECK(java_lang_Object_ != NULL);

    // Identify the underlying element class and the array dimension depth.
    Class* component_type_ = NULL;
    int array_rank;
    if (descriptor[1] == '[') {
        // array of arrays; keep descriptor and grab stuff from parent
        Class* outer = FindClass(descriptor.substr(1), class_loader, dex_file);
        if (outer != NULL) {
            // want the base class, not "outer", in our component_type_
            component_type_ = outer->component_type_;
            array_rank = outer->array_rank_ + 1;
        } else {
            DCHECK(component_type_ == NULL);  // make sure we fail
        }
    } else {
        array_rank = 1;
        if (descriptor[1] == 'L') {
            // array of objects; strip off "[" and look up descriptor.
            const StringPiece subDescriptor = descriptor.substr(1);
            component_type_ = FindClass(subDescriptor, class_loader, dex_file);
        } else {
            // array of a primitive type
            component_type_ = FindPrimitiveClass(descriptor[1]);
        }
    }

    if (component_type_ == NULL) {
        // failed
        DCHECK(Thread::Current()->IsExceptionPending());
        return NULL;
    }

    // See if the component type is already loaded.  Array classes are
    // always associated with the class loader of their underlying
    // element type -- an array of Strings goes with the loader for
    // java/lang/String -- so we need to look for it there.  (The
    // caller should have checked for the existence of the class
    // before calling here, but they did so with *their* class loader,
    // not the component type's loader.)
    //
    // If we find it, the caller adds "loader" to the class' initiating
    // loader list, which should prevent us from going through this again.
    //
    // This call is unnecessary if "loader" and "component_type_->class_loader_"
    // are the same, because our caller (FindClass) just did the
    // lookup.  (Even if we get this wrong we still have correct behavior,
    // because we effectively do this lookup again when we add the new
    // class to the hash table --- necessary because of possible races with
    // other threads.)
    if (class_loader != component_type_->class_loader_) {
        Class* new_class = LookupClass(descriptor, component_type_->class_loader_);
        if (new_class != NULL) {
            return new_class;
        }
    }

    // Fill out the fields in the Class.
    //
    // It is possible to execute some methods against arrays, because
    // all arrays are subclasses of java_lang_Object_, so we need to set
    // up a vtable.  We can just point at the one in java_lang_Object_.
    //
    // Array classes are simple enough that we don't need to do a full
    // link step.
    Class* new_class = AllocClass(NULL);
    if (new_class == NULL) {
      return NULL;
    }
    new_class->descriptor_alloc_ = new std::string(descriptor.data(),
                                                   descriptor.size());
    new_class->descriptor_.set(new_class->descriptor_alloc_->data(),
                               new_class->descriptor_alloc_->size());
    new_class->super_class_ = java_lang_Object_;
    new_class->vtable_count_ = java_lang_Object_->vtable_count_;
    new_class->vtable_ = java_lang_Object_->vtable_;
    new_class->primitive_type_ = Class::kPrimNot;
    new_class->component_type_ = component_type_;
    new_class->class_loader_ = component_type_->class_loader_;
    new_class->array_rank_ = array_rank;
    new_class->status_ = Class::kStatusInitialized;
    // don't need to set new_class->object_size_


    // All arrays have java/lang/Cloneable and java/io/Serializable as
    // interfaces.  We need to set that up here, so that stuff like
    // "instanceof" works right.
    //
    // Note: The GC could run during the call to FindSystemClass,
    // so we need to make sure the class object is GC-valid while we're in
    // there.  Do this by clearing the interface list so the GC will just
    // think that the entries are null.
    //
    // TODO?
    // We may want to create a single, global copy of "interfaces" and
    // "iftable" somewhere near the start and just point to those (and
    // remember not to free them for arrays).
    new_class->interface_count_ = 2;
    new_class->interfaces_ = new Class*[2];
    memset(new_class->interfaces_, 0, sizeof(Class*) * 2);
    new_class->interfaces_[0] = java_lang_Cloneable_;
    new_class->interfaces_[1] = java_io_Serializable_;

    // We assume that Cloneable/Serializable don't have superinterfaces --
    // normally we'd have to crawl up and explicitly list all of the
    // supers as well.  These interfaces don't have any methods, so we
    // don't have to worry about the ifviPool either.
    new_class->iftable_count_ = 2;
    new_class->iftable_ = new InterfaceEntry[2];
    memset(new_class->iftable_, 0, sizeof(InterfaceEntry) * 2);
    new_class->iftable_[0].SetClass(new_class->interfaces_[0]);
    new_class->iftable_[1].SetClass(new_class->interfaces_[1]);

    // Inherit access flags from the component type.  Arrays can't be
    // used as a superclass or interface, so we want to add "final"
    // and remove "interface".
    //
    // Don't inherit any non-standard flags (e.g., kAccFinal)
    // from component_type_.  We assume that the array class does not
    // override finalize().
    new_class->access_flags_ = ((new_class->component_type_->access_flags_ &
                                 ~kAccInterface) | kAccFinal) & kAccJavaFlagsMask;

    if (InsertClass(new_class)) {
      return new_class;
    }
    // Another thread must have loaded the class after we
    // started but before we finished.  Abandon what we've
    // done.
    //
    // (Yes, this happens.)

    // Grab the winning class.
    Class* other_class = LookupClass(descriptor, component_type_->class_loader_);
    DCHECK(other_class != NULL);
    return other_class;
}

Class* ClassLinker::FindPrimitiveClass(char type) {
  switch (type) {
    case 'B':
      CHECK(primitive_byte_ != NULL);
      return primitive_byte_;
    case 'C':
      CHECK(primitive_char_ != NULL);
      return primitive_char_;
    case 'D':
      CHECK(primitive_double_ != NULL);
      return primitive_double_;
    case 'F':
      CHECK(primitive_float_ != NULL);
      return primitive_float_;
    case 'I':
      CHECK(primitive_int_ != NULL);
      return primitive_int_;
    case 'J':
      CHECK(primitive_long_ != NULL);
      return primitive_long_;
    case 'S':
      CHECK(primitive_short_ != NULL);
      return primitive_short_;
    case 'Z':
      CHECK(primitive_boolean_ != NULL);
      return primitive_boolean_;
    case 'V':
      CHECK(primitive_void_ != NULL);
      return primitive_void_;
    case 'L':
    case '[':
      LOG(ERROR) << "Not a primitive type " << static_cast<int>(type);
    default:
      LOG(ERROR) << "Unknown primitive type " << static_cast<int>(type);
  };
  return NULL;  // Not reachable.
}

bool ClassLinker::InsertClass(Class* klass) {
  // TODO: acquire classes_lock_
  const StringPiece& key = klass->GetDescriptor();
  bool success = classes_.insert(std::make_pair(key, klass)).second;
  // TODO: release classes_lock_
  return success;
}

Class* ClassLinker::LookupClass(const StringPiece& descriptor, Object* class_loader) {
  // TODO: acquire classes_lock_
  Table::iterator it = classes_.find(descriptor);
  // TODO: release classes_lock_
  if (it == classes_.end()) {
    return NULL;
  } else {
    return (*it).second;
  }
}

bool ClassLinker::InitializeClass(Class* klass) {
  CHECK(klass->GetStatus() == Class::kStatusResolved ||
        klass->GetStatus() == Class::kStatusError);

  Thread* self = Thread::Current();

  {
    ObjectLock lock(klass);

    if (klass->GetStatus() < Class::kStatusVerified) {
      if (klass->IsErroneous()) {
        LG << "re-initializing failed class";  // TODO: throw
        return false;
      }

      CHECK(klass->GetStatus() == Class::kStatusResolved);

      klass->status_ = Class::kStatusVerifying;
      if (!DexVerify::VerifyClass(klass)) {
        LG << "Verification failed";  // TODO: ThrowVerifyError
        Object* exception = self->GetException();
        size_t field_offset = OFFSETOF_MEMBER(Class, verify_error_class_);
        klass->SetFieldObject(field_offset, exception->GetClass());
        klass->SetStatus(Class::kStatusError);
        return false;
      }

      klass->SetStatus(Class::kStatusVerified);
    }

    if (klass->status_ == Class::kStatusInitialized) {
      return true;
    }

    while (klass->status_ == Class::kStatusInitializing) {
      // we caught somebody else in the act; was it us?
      if (klass->clinit_thread_id_ == self->GetId()) {
        LG << "recursive <clinit>";
        return true;
      }

      CHECK(!self->IsExceptionPending());

      lock.Wait();  // TODO: check for interruption

      // When we wake up, repeat the test for init-in-progress.  If
      // there's an exception pending (only possible if
      // "interruptShouldThrow" was set), bail out.
      if (self->IsExceptionPending()) {
        CHECK(false);
        LG << "Exception in initialization.";  // TODO: ExceptionInInitializerError
        klass->SetStatus(Class::kStatusError);
        return false;
      }
      if (klass->GetStatus() == Class::kStatusInitializing) {
        continue;
      }
      DCHECK(klass->GetStatus() == Class::kStatusInitialized ||
             klass->GetStatus() == Class::kStatusError);
      if (klass->IsErroneous()) {
        // The caller wants an exception, but it was thrown in a
        // different thread.  Synthesize one here.
        LG << "<clinit> failed";  // TODO: throw UnsatisfiedLinkError
        return false;
      }
      return true;  // otherwise, initialized
    }

    // see if we failed previously
    if (klass->IsErroneous()) {
      // might be wise to unlock before throwing; depends on which class
      // it is that we have locked

      // TODO: throwEarlierClassFailure(klass);
      return false;
    }

    if (!ValidateSuperClassDescriptors(klass)) {
      klass->SetStatus(Class::kStatusError);
      return false;
    }

    DCHECK(klass->status_ < Class::kStatusInitializing);

    klass->clinit_thread_id_ = self->GetId();
    klass->status_ = Class::kStatusInitializing;
  }

  if (!InitializeSuperClass(klass)) {
    return false;
  }

  InitializeStaticFields(klass);

  Method* clinit = klass->FindDirectMethodLocally("<clinit>", "()V");
  if (clinit != NULL) {
  } else {
    // JValue unused;
    // TODO: dvmCallMethod(self, method, NULL, &unused);
    //CHECK(!"unimplemented");
  }

  {
    ObjectLock lock(klass);

    if (self->IsExceptionPending()) {
      klass->SetStatus(Class::kStatusError);
    } else {
      klass->SetStatus(Class::kStatusInitialized);
    }
    lock.NotifyAll();
  }

  return true;
}

bool ClassLinker::ValidateSuperClassDescriptors(const Class* klass) {
  if (klass->IsInterface()) {
    return true;
  }
  // begin with the methods local to the superclass
  if (klass->HasSuperClass() &&
      klass->GetClassLoader() != klass->GetSuperClass()->GetClassLoader()) {
    const Class* super = klass->GetSuperClass();
    for (int i = super->NumVirtualMethods() - 1; i >= 0; --i) {
      const Method* method = klass->GetVirtualMethod(i);
      if (method != super->GetVirtualMethod(i) &&
          !HasSameMethodDescriptorClasses(method, super, klass)) {
        LG << "Classes resolve differently in superclass";
        return false;
      }
    }
  }
  for (size_t i = 0; i < klass->iftable_count_; ++i) {
    const InterfaceEntry* iftable = &klass->iftable_[i];
    Class* interface = iftable->GetClass();
    if (klass->GetClassLoader() != interface->GetClassLoader()) {
      for (size_t j = 0; j < interface->NumVirtualMethods(); ++j) {
        uint32_t vtable_index = iftable->method_index_array_[j];
        const Method* method = klass->GetVirtualMethod(vtable_index);
        if (!HasSameMethodDescriptorClasses(method, interface,
                                            method->GetClass())) {
          LG << "Classes resolve differently in interface";  // TODO: LinkageError
          return false;
        }
      }
    }
  }
  return true;
}

bool ClassLinker::HasSameMethodDescriptorClasses(const Method* method,
                                                 const Class* klass1,
                                                 const Class* klass2) {
  const DexFile* dex_file = FindDexFile(method->GetClass()->GetDexCache());
  const DexFile::ProtoId& proto_id = dex_file->GetProtoId(method->proto_idx_);
  DexFile::ParameterIterator *it;
  for (it = dex_file->GetParameterIterator(proto_id); it->HasNext(); it->Next()) {
    const char* descriptor = it->GetDescriptor();
    if (descriptor == NULL) {
      break;
    }
    if (descriptor[0] == 'L' || descriptor[0] == '[') {
      // Found a non-primitive type.
      if (!HasSameDescriptorClasses(descriptor, klass1, klass2)) {
        return false;
      }
    }
  }
  // Check the return type
  const char* descriptor = dex_file->GetReturnTypeDescriptor(proto_id);
  if (descriptor[0] == 'L' || descriptor[0] == '[') {
    if (HasSameDescriptorClasses(descriptor, klass1, klass2)) {
      return false;
    }
  }
  return true;
}

// Returns true if classes referenced by the descriptor are the
// same classes in klass1 as they are in klass2.
bool ClassLinker::HasSameDescriptorClasses(const char* descriptor,
                                           const Class* klass1,
                                           const Class* klass2) {
  CHECK(descriptor != NULL);
  CHECK(klass1 != NULL);
  CHECK(klass2 != NULL);
#if 0
  Class* found1 = FindClass(descriptor, klass1->GetClassLoader());
  // TODO: found1 == NULL
  Class* found2 = FindClass(descriptor, klass2->GetClassLoader());
  // TODO: found2 == NULL
  // TODO: lookup found1 in initiating loader list
  if (found1 == NULL || found2 == NULL) {
    Thread::Current()->ClearException();
    if (found1 == found2) {
      return true;
    } else {
      return false;
    }
  }
#endif
  return true;
}

bool ClassLinker::HasSameArgumentTypes(const Method* m1, const Method* m2) const {
  const DexFile* dex1 = FindDexFile(m1->GetClass()->GetDexCache());
  const DexFile* dex2 = FindDexFile(m2->GetClass()->GetDexCache());
  const DexFile::ProtoId& proto1 = dex1->GetProtoId(m1->proto_idx_);
  const DexFile::ProtoId& proto2 = dex2->GetProtoId(m2->proto_idx_);

  // TODO: compare ProtoId objects for equality and exit early
  const DexFile::TypeList* type_list1 = dex1->GetProtoParameters(proto1);
  const DexFile::TypeList* type_list2 = dex2->GetProtoParameters(proto2);
  size_t arity1 = (type_list1 == NULL) ? 0 : type_list1->Size();
  size_t arity2 = (type_list2 == NULL) ? 0 : type_list2->Size();
  if (arity1 != arity2) {
    return false;
  }

  for (size_t i = 0; i < arity1; ++i) {
    uint32_t type_idx1 = type_list1->GetTypeItem(i).type_idx_;
    uint32_t type_idx2 = type_list2->GetTypeItem(i).type_idx_;
    const char* type1 = dex1->dexStringByTypeIdx(type_idx1);
    const char* type2 = dex2->dexStringByTypeIdx(type_idx2);
    if (strcmp(type1, type2) != 0) {
      return false;
    }
  }

  return true;
}

bool ClassLinker::HasSameReturnType(const Method* m1, const Method* m2) const {
  const DexFile* dex1 = FindDexFile(m1->GetClass()->GetDexCache());
  const DexFile* dex2 = FindDexFile(m2->GetClass()->GetDexCache());
  const DexFile::ProtoId& proto1 = dex1->GetProtoId(m1->proto_idx_);
  const DexFile::ProtoId& proto2 = dex2->GetProtoId(m2->proto_idx_);
  const char* type1 = dex1->dexStringByTypeIdx(proto1.return_type_idx_);
  const char* type2 = dex2->dexStringByTypeIdx(proto2.return_type_idx_);
  return (strcmp(type1, type2) == 0);
}

bool ClassLinker::InitializeSuperClass(Class* klass) {
  CHECK(klass != NULL);
  // TODO: assert klass lock is acquired
  if (!klass->IsInterface() && klass->HasSuperClass()) {
    Class* super_class = klass->GetSuperClass();
    if (super_class->GetStatus() != Class::kStatusInitialized) {
      CHECK(!super_class->IsInterface());
      klass->MonitorExit();
      bool super_initialized = InitializeClass(super_class);
      klass->MonitorEnter();
      // TODO: check for a pending exception
      if (!super_initialized) {
        klass->SetStatus(Class::kStatusError);
        klass->NotifyAll();
        return false;
      }
    }
  }
  return true;
}

void ClassLinker::InitializeStaticFields(Class* klass) {
  size_t num_static_fields = klass->NumStaticFields();
  if (num_static_fields == 0) {
    return;
  }
  DexCache* dex_cache = klass->GetDexCache();
  if (dex_cache == NULL) {
    return;
  }
  const StringPiece& descriptor = klass->GetDescriptor();
  const DexFile* dex_file = FindDexFile(dex_cache);
  const DexFile::ClassDef* dex_class_def = dex_file->FindClassDef(descriptor);
  CHECK(dex_class_def != NULL);
  const byte* addr = dex_file->GetEncodedArray(*dex_class_def);
  size_t array_size = DecodeUnsignedLeb128(&addr);
  for (size_t i = 0; i < array_size; ++i) {
    StaticField* field = klass->GetStaticField(i);
    JValue value;
    DexFile::ValueType type = dex_file->ReadEncodedValue(&addr, &value);
    switch (type) {
      case DexFile::kByte:
        field->SetByte(value.b);
        break;
      case DexFile::kShort:
        field->SetShort(value.s);
        break;
      case DexFile::kChar:
        field->SetChar(value.c);
        break;
      case DexFile::kInt:
        field->SetInt(value.i);
        break;
      case DexFile::kLong:
        field->SetLong(value.j);
        break;
      case DexFile::kFloat:
        field->SetFloat(value.f);
        break;
      case DexFile::kDouble:
        field->SetDouble(value.d);
        break;
      case DexFile::kString: {
        uint32_t string_idx = value.i;
        String* resolved = ResolveString(klass, string_idx);
        field->SetObject(resolved);
        break;
      }
      case DexFile::kBoolean:
        field->SetBoolean(value.z);
        break;
      case DexFile::kNull:
        field->SetObject(value.l);
        break;
      default:
        LOG(FATAL) << "Unknown type " << static_cast<int>(type);
    }
  }
}

bool ClassLinker::LinkClass(Class* klass, const DexFile* dex_file) {
  CHECK(klass->status_ == Class::kStatusIdx ||
        klass->status_ == Class::kStatusLoaded);
  if (klass->status_ == Class::kStatusIdx) {
    if (!LinkInterfaces(klass, dex_file)) {
      return false;
    }
  }
  if (!LinkSuperClass(klass)) {
    return false;
  }
  if (!LinkMethods(klass)) {
    return false;
  }
  if (!LinkInstanceFields(klass)) {
    return false;
  }
  CreateReferenceOffsets(klass);
  CHECK_EQ(klass->status_, Class::kStatusLoaded);
  klass->status_ = Class::kStatusResolved;
  return true;
}

bool ClassLinker::LinkInterfaces(Class* klass, const DexFile* dex_file) {
  scoped_array<uint32_t> interfaces_idx;
  // TODO: store interfaces_idx in the Class object
  // TODO: move this outside of link interfaces
  if (klass->interface_count_ > 0) {
    size_t length = klass->interface_count_ * sizeof(klass->interfaces_[0]);
    interfaces_idx.reset(new uint32_t[klass->interface_count_]);
    memcpy(interfaces_idx.get(), klass->interfaces_, length);
    memset(klass->interfaces_, 0xFF, length);
  }
  // Mark the class as loaded.
  klass->status_ = Class::kStatusLoaded;
  if (klass->super_class_idx_ != DexFile::kDexNoIndex) {
    Class* super_class = ResolveClass(klass, klass->super_class_idx_, dex_file);
    if (super_class == NULL) {
      LG << "Failed to resolve superclass";
      return false;
    }
    klass->super_class_ = super_class;  // TODO: write barrier
  }
  if (klass->interface_count_ > 0) {
    for (size_t i = 0; i < klass->interface_count_; ++i) {
      uint32_t idx = interfaces_idx[i];
      klass->interfaces_[i] = ResolveClass(klass, idx, dex_file);
      if (klass->interfaces_[i] == NULL) {
        LG << "Failed to resolve interface";
        return false;
      }
      // Verify
      if (!klass->CanAccess(klass->interfaces_[i])) {
        LG << "Inaccessible interface";
        return false;
      }
    }
  }
  return true;
}

bool ClassLinker::LinkSuperClass(Class* klass) {
  CHECK(!klass->IsPrimitive());
  const Class* super = klass->GetSuperClass();
  if (klass->GetDescriptor() == "Ljava/lang/Object;") {
    if (super != NULL) {
      LG << "Superclass must not be defined";  // TODO: ClassFormatError
      return false;
    }
    // TODO: clear finalize attribute
    return true;
  }
  if (super == NULL) {
    LG << "No superclass defined";  // TODO: LinkageError
    return false;
  }
  // Verify
  if (super->IsFinal()) {
    LG << "Superclass is declared final";  // TODO: IncompatibleClassChangeError
    return false;
  }
  if (super->IsInterface()) {
    LG << "Superclass is an interface";  // TODO: IncompatibleClassChangeError
    return false;
  }
  if (!klass->CanAccess(super)) {
    LG << "Superclass is inaccessible";  // TODO: IllegalAccessError
    return false;
  }
  return true;
}

// Populate the class vtable and itable.
bool ClassLinker::LinkMethods(Class* klass) {
  if (klass->IsInterface()) {
    // No vtable.
    size_t count = klass->NumVirtualMethods();
    if (!IsUint(16, count)) {
      LG << "Too many methods on interface";  // TODO: VirtualMachineError
      return false;
    }
    for (size_t i = 0; i < count; ++i) {
      klass->GetVirtualMethod(i)->method_index_ = i;
    }
  } else {
    // Link virtual method tables
    LinkVirtualMethods(klass);

    // Link interface method tables
    LinkInterfaceMethods(klass);

    // Insert stubs.
    LinkAbstractMethods(klass);
  }
  return true;
}

bool ClassLinker::LinkVirtualMethods(Class* klass) {
  uint32_t max_count = klass->NumVirtualMethods();
  if (klass->GetSuperClass() != NULL) {
    max_count += klass->GetSuperClass()->NumVirtualMethods();
  } else {
    CHECK(klass->GetDescriptor() == "Ljava/lang/Object;");
  }
  // TODO: do not assign to the vtable field until it is fully constructed.
  // TODO: make this a vector<Method*> instead?
  klass->vtable_ = new Method*[max_count];
  if (klass->HasSuperClass()) {
    memcpy(klass->vtable_,
           klass->GetSuperClass()->vtable_,
           klass->GetSuperClass()->vtable_count_ * sizeof(Method*));
    size_t actual_count = klass->GetSuperClass()->vtable_count_;
    // See if any of our virtual methods override the superclass.
    for (size_t i = 0; i < klass->NumVirtualMethods(); ++i) {
      Method* local_method = klass->GetVirtualMethod(i);
      size_t j = 0;
      for (; j < klass->GetSuperClass()->vtable_count_; ++j) {
        const Method* super_method = klass->vtable_[j];
        if (HasSameNameAndPrototype(local_method, super_method)) {
          // Verify
          if (super_method->IsFinal()) {
            LG << "Method overrides final method";  // TODO: VirtualMachineError
            return false;
          }
          klass->vtable_[j] = local_method;
          local_method->method_index_ = j;
          break;
        }
      }
      if (j == klass->GetSuperClass()->vtable_count_) {
        // Not overriding, append.
        klass->vtable_[actual_count] = local_method;
        local_method->method_index_ = actual_count;
        actual_count += 1;
      }
    }
    if (!IsUint(16, actual_count)) {
      LG << "Too many methods defined on class";  // TODO: VirtualMachineError
      return false;
    }
    CHECK_LE(actual_count, max_count);
    if (actual_count < max_count) {
      Method** new_vtable = new Method*[actual_count];
      memcpy(new_vtable, klass->vtable_, actual_count * sizeof(Method*));
      delete[] klass->vtable_;
      klass->vtable_ = new_vtable;
      LG << "shrunk vtable: "
         << "was " << max_count << ", "
         << "now " << actual_count;
    }
    klass->vtable_count_ = actual_count;
  } else {
    CHECK(klass->GetDescriptor() == "Ljava/lang/Object;");
    if (!IsUint(16, klass->NumVirtualMethods())) {
      LG << "Too many methods";  // TODO: VirtualMachineError
      return false;
    }
    for (size_t i = 0; i < klass->NumVirtualMethods(); ++i) {
      klass->vtable_[i] = klass->GetVirtualMethod(i);
      klass->GetVirtualMethod(i)->method_index_ = i & 0xFFFF;
    }
    klass->vtable_count_ = klass->NumVirtualMethods();
  }
  return true;
}

bool ClassLinker::LinkInterfaceMethods(Class* klass) {
  int pool_offset = 0;
  int pool_size = 0;
  int miranda_count = 0;
  int miranda_alloc = 0;
  size_t super_ifcount;
  if (klass->HasSuperClass()) {
    super_ifcount = klass->GetSuperClass()->iftable_count_;
  } else {
    super_ifcount = 0;
  }
  size_t ifCount = super_ifcount;
  ifCount += klass->interface_count_;
  for (size_t i = 0; i < klass->interface_count_; i++) {
    ifCount += klass->interfaces_[i]->iftable_count_;
  }
  if (ifCount == 0) {
    DCHECK(klass->iftable_count_ == 0);
    DCHECK(klass->iftable_ == NULL);
    return true;
  }
  klass->iftable_ = new InterfaceEntry[ifCount * sizeof(InterfaceEntry)];
  memset(klass->iftable_, 0x00, sizeof(InterfaceEntry) * ifCount);
  if (super_ifcount != 0) {
    memcpy(klass->iftable_, klass->GetSuperClass()->iftable_,
           sizeof(InterfaceEntry) * super_ifcount);
  }
  // Flatten the interface inheritance hierarchy.
  size_t idx = super_ifcount;
  for (size_t i = 0; i < klass->interface_count_; i++) {
    Class* interf = klass->interfaces_[i];
    DCHECK(interf != NULL);
    if (!interf->IsInterface()) {
      LG << "Class implements non-interface class";  // TODO: IncompatibleClassChangeError
      return false;
    }
    klass->iftable_[idx++].SetClass(interf);
    for (size_t j = 0; j < interf->iftable_count_; j++) {
      klass->iftable_[idx++].SetClass(interf->iftable_[j].GetClass());
    }
  }
  CHECK_EQ(idx, ifCount);
  klass->iftable_count_ = ifCount;
  if (klass->IsInterface() || super_ifcount == ifCount) {
    return true;
  }
  for (size_t i = super_ifcount; i < ifCount; i++) {
    pool_size += klass->iftable_[i].GetClass()->NumVirtualMethods();
  }
  if (pool_size == 0) {
    return true;
  }
  klass->ifvi_pool_count_ = pool_size;
  klass->ifvi_pool_ = new uint32_t[pool_size];
  std::vector<Method*> miranda_list;
  for (size_t i = super_ifcount; i < ifCount; ++i) {
    klass->iftable_[i].method_index_array_ = klass->ifvi_pool_ + pool_offset;
    Class* interface = klass->iftable_[i].GetClass();
    pool_offset += interface->NumVirtualMethods();    // end here
    for (size_t j = 0; j < interface->NumVirtualMethods(); ++j) {
      Method* interface_method = interface->GetVirtualMethod(j);
      int k;  // must be signed
      for (k = klass->vtable_count_ - 1; k >= 0; --k) {
        if (HasSameNameAndPrototype(interface_method, klass->vtable_[k])) {
          if (!klass->vtable_[k]->IsPublic()) {
            LG << "Implementation not public";
            return false;
          }
          klass->iftable_[i].method_index_array_[j] = k;
          break;
        }
      }
      if (k < 0) {
        if (miranda_count == miranda_alloc) {
          miranda_alloc += 8;
          if (miranda_list.empty()) {
            miranda_list.resize(miranda_alloc);
          } else {
            miranda_list.resize(miranda_alloc);
          }
        }
        int mir;
        for (mir = 0; mir < miranda_count; mir++) {
          if (HasSameNameAndPrototype(miranda_list[mir], interface_method)) {
            break;
          }
        }
        // point the interface table at a phantom slot index
        klass->iftable_[i].method_index_array_[j] = klass->vtable_count_ + mir;
        if (mir == miranda_count) {
          miranda_list[miranda_count++] = interface_method;
        }
      }
    }
  }
  if (miranda_count != 0) {
    int oldMethodCount = klass->NumVirtualMethods();
    int newMethodCount = oldMethodCount + miranda_count;
    Method** newVirtualMethods = new Method*[newMethodCount];
    if (klass->virtual_methods_ != NULL) {
      memcpy(newVirtualMethods,
             klass->virtual_methods_,
             klass->NumVirtualMethods() * sizeof(Method*));
    }
    klass->virtual_methods_ = newVirtualMethods;
    klass->num_virtual_methods_ = newMethodCount;

    CHECK(klass->vtable_ != NULL);
    int oldVtableCount = klass->vtable_count_;
    klass->vtable_count_ += miranda_count;

    for (int i = 0; i < miranda_count; i++) {
      Method* meth = AllocMethod();
      memcpy(meth, miranda_list[i], sizeof(Method));
      meth->klass_ = klass;
      meth->access_flags_ |= kAccMiranda;
      meth->method_index_ = 0xFFFF & (oldVtableCount + i);
      klass->virtual_methods_[oldMethodCount+i] = meth;
      klass->vtable_[oldVtableCount + i] = meth;
    }
  }
  return true;
}

void ClassLinker::LinkAbstractMethods(Class* klass) {
  for (size_t i = 0; i < klass->NumVirtualMethods(); ++i) {
    Method* method = klass->GetVirtualMethod(i);
    if (method->IsAbstract()) {
      method->insns_ = reinterpret_cast<uint16_t*>(0xFFFFFFFF);  // TODO: AbstractMethodError
    }
  }
}

bool ClassLinker::LinkInstanceFields(Class* klass) {
  int field_offset;
  if (klass->GetSuperClass() != NULL) {
    field_offset = klass->GetSuperClass()->object_size_;
  } else {
    field_offset = OFFSETOF_MEMBER(DataObject, fields_);
  }
  // Move references to the front.
  klass->num_reference_instance_fields_ = 0;
  size_t i = 0;
  for ( ; i < klass->NumInstanceFields(); i++) {
    InstanceField* pField = klass->GetInstanceField(i);
    char c = pField->GetType();
    if (c != '[' && c != 'L') {
      for (size_t j = klass->NumInstanceFields() - 1; j > i; j--) {
        InstanceField* refField = klass->GetInstanceField(j);
        char rc = refField->GetType();
        if (rc == '[' || rc == 'L') {
          klass->SetInstanceField(i, refField);
          klass->SetInstanceField(j, pField);
          pField = refField;
          c = rc;
          klass->num_reference_instance_fields_++;
          break;
        }
      }
    } else {
      klass->num_reference_instance_fields_++;
    }
    if (c != '[' && c != 'L') {
      break;
    }
    pField->SetOffset(field_offset);
    field_offset += sizeof(uint32_t);
  }

  // Now we want to pack all of the double-wide fields together.  If
  // we're not aligned, though, we want to shuffle one 32-bit field
  // into place.  If we can't find one, we'll have to pad it.
  if (i != klass->NumInstanceFields() && (field_offset & 0x04) != 0) {
    InstanceField* pField = klass->GetInstanceField(i);
    char c = pField->GetType();

    if (c != 'J' && c != 'D') {
      // The field that comes next is 32-bit, so just advance past it.
      DCHECK(c != '[');
      DCHECK(c != 'L');
      pField->SetOffset(field_offset);
      field_offset += sizeof(uint32_t);
      i++;
    } else {
      // Next field is 64-bit, so search for a 32-bit field we can
      // swap into it.
      bool found = false;
      for (size_t j = klass->NumInstanceFields() - 1; j > i; j--) {
        InstanceField* singleField = klass->GetInstanceField(j);
        char rc = singleField->GetType();
        if (rc != 'J' && rc != 'D') {
          klass->SetInstanceField(i, singleField);
          klass->SetInstanceField(j, pField);
          pField = singleField;
          pField->SetOffset(field_offset);
          field_offset += sizeof(uint32_t);
          found = true;
          i++;
          break;
        }
      }
      if (!found) {
        field_offset += sizeof(uint32_t);
      }
    }
  }

  // Alignment is good, shuffle any double-wide fields forward, and
  // finish assigning field offsets to all fields.
  DCHECK(i == klass->NumInstanceFields() || (field_offset & 0x04) == 0);
  for ( ; i < klass->NumInstanceFields(); i++) {
    InstanceField* pField = klass->GetInstanceField(i);
    char c = pField->GetType();
    if (c != 'D' && c != 'J') {
      for (size_t j = klass->NumInstanceFields() - 1; j > i; j--) {
        InstanceField* doubleField = klass->GetInstanceField(j);
        char rc = doubleField->GetType();
        if (rc == 'D' || rc == 'J') {
          klass->SetInstanceField(i, doubleField);
          klass->SetInstanceField(j, pField);
          pField = doubleField;
          c = rc;
          break;
        }
      }
    } else {
      // This is a double-wide field, leave it be.
    }

    pField->SetOffset(field_offset);
    field_offset += sizeof(uint32_t);
    if (c == 'J' || c == 'D')
      field_offset += sizeof(uint32_t);
  }

#ifndef NDEBUG
  // Make sure that all reference fields appear before
  // non-reference fields, and all double-wide fields are aligned.
  bool seen_non_ref = false;
  for (i = 0; i < klass->NumInstanceFields(); i++) {
    InstanceField *pField = klass->GetInstanceField(i);
    char c = pField->GetType();

    if (c == 'D' || c == 'J') {
      DCHECK_EQ(0U, pField->GetOffset() & 0x07);
    }

    if (c != '[' && c != 'L') {
      if (!seen_non_ref) {
        seen_non_ref = true;
        DCHECK_EQ(klass->num_reference_ifields_, i);
      }
    } else {
      DCHECK(!seen_non_ref);
    }
  }
  if (!seen_non_ref) {
    DCHECK(klass->NumInstanceFields(), klass->num_reference_ifields_);
  }
#endif

  klass->object_size_ = field_offset;
  return true;
}

//  Set the bitmap of reference offsets, refOffsets, from the ifields
//  list.
void ClassLinker::CreateReferenceOffsets(Class* klass) {
  uint32_t reference_offsets = 0;
  if (klass->HasSuperClass()) {
    reference_offsets = klass->GetSuperClass()->GetReferenceOffsets();
  }
  // If our superclass overflowed, we don't stand a chance.
  if (reference_offsets != CLASS_WALK_SUPER) {
    // All of the fields that contain object references are guaranteed
    // to be at the beginning of the ifields list.
    for (size_t i = 0; i < klass->NumReferenceInstanceFields(); ++i) {
      // Note that, per the comment on struct InstField, f->byteOffset
      // is the offset from the beginning of obj, not the offset into
      // obj->instanceData.
      const InstanceField* field = klass->GetInstanceField(i);
      size_t byte_offset = field->GetOffset();
      CHECK_GE(byte_offset, CLASS_SMALLEST_OFFSET);
      CHECK_EQ(byte_offset & (CLASS_OFFSET_ALIGNMENT - 1), 0U);
      if (CLASS_CAN_ENCODE_OFFSET(byte_offset)) {
        uint32_t new_bit = CLASS_BIT_FROM_OFFSET(byte_offset);
        CHECK_NE(new_bit, 0U);
        reference_offsets |= new_bit;
      } else {
        reference_offsets = CLASS_WALK_SUPER;
        break;
      }
    }
    klass->SetReferenceOffsets(reference_offsets);
  }
}

Class* ClassLinker::ResolveClass(const Class* referrer,
                                 uint32_t class_idx,
                                 const DexFile* dex_file) {
  DexCache* dex_cache = referrer->GetDexCache();
  Class* resolved = dex_cache->GetResolvedClass(class_idx);
  if (resolved != NULL) {
    return resolved;
  }
  const char* descriptor = dex_file->dexStringByTypeIdx(class_idx);
  if (descriptor[0] != '\0' && descriptor[1] == '\0') {
    resolved = FindPrimitiveClass(descriptor[0]);
  } else {
    resolved = FindClass(descriptor, referrer->GetClassLoader(), dex_file);
  }
  if (resolved != NULL) {
    Class* check = resolved->IsArray() ? resolved->component_type_ : resolved;
    if (referrer->GetDexCache() != check->GetDexCache()) {
      if (check->GetClassLoader() != NULL) {
        LG << "Class resolved by unexpected DEX";  // TODO: IllegalAccessError
        return NULL;
      }
    }
    dex_cache->SetResolvedClass(class_idx, resolved);
  } else {
    DCHECK(Thread::Current()->IsExceptionPending());
  }
  return resolved;
}

Method* ResolveMethod(const Class* referrer, uint32_t method_idx,
                      /*MethodType*/ int method_type) {
  CHECK(false);
  return NULL;
}

String* ClassLinker::ResolveString(const Class* referring,
                                   uint32_t string_idx) {
  const DexFile* dex_file = FindDexFile(referring->GetDexCache());
  const DexFile::StringId& string_id = dex_file->GetStringId(string_idx);
  const char* string_data = dex_file->GetStringData(string_id);
  String* new_string = Heap::AllocStringFromModifiedUtf8(java_lang_String_,
                                                         char_array_class_,
                                                         string_data);
  // TODO: intern the new string
  referring->GetDexCache()->SetResolvedString(string_idx, new_string);
  return new_string;
}

}  // namespace art