runtime/verifier/verifier_deps.cc

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "verifier_deps.h"

#include <cstring>

#include "base/stl_util.h"
#include "compiler_callbacks.h"
#include "leb128.h"
#include "mirror/class-inl.h"
#include "obj_ptr-inl.h"
#include "runtime.h"

namespace art {
namespace verifier {

VerifierDeps::VerifierDeps(const std::vector<const DexFile*>& dex_files) {
  for (const DexFile* dex_file : dex_files) {
    DCHECK(GetDexFileDeps(*dex_file) == nullptr);
    std::unique_ptr<DexFileDeps> deps(new DexFileDeps());
    dex_deps_.emplace(dex_file, std::move(deps));
  }
}

void VerifierDeps::MergeWith(const VerifierDeps& other,
                             const std::vector<const DexFile*>& dex_files) {
  DCHECK(dex_deps_.size() == other.dex_deps_.size());
  for (const DexFile* dex_file : dex_files) {
    DexFileDeps* my_deps = GetDexFileDeps(*dex_file);
    const DexFileDeps& other_deps = *other.GetDexFileDeps(*dex_file);
    // We currently collect extra strings only on the main `VerifierDeps`,
    // which should be the one passed as `this` in this method.
    DCHECK(other_deps.strings_.empty());
    MergeSets(my_deps->assignable_types_, other_deps.assignable_types_);
    MergeSets(my_deps->unassignable_types_, other_deps.unassignable_types_);
    MergeSets(my_deps->classes_, other_deps.classes_);
    MergeSets(my_deps->fields_, other_deps.fields_);
    MergeSets(my_deps->direct_methods_, other_deps.direct_methods_);
    MergeSets(my_deps->virtual_methods_, other_deps.virtual_methods_);
    MergeSets(my_deps->interface_methods_, other_deps.interface_methods_);
    for (dex::TypeIndex entry : other_deps.unverified_classes_) {
      my_deps->unverified_classes_.push_back(entry);
    }
  }
}

VerifierDeps::DexFileDeps* VerifierDeps::GetDexFileDeps(const DexFile& dex_file) {
  auto it = dex_deps_.find(&dex_file);
  return (it == dex_deps_.end()) ? nullptr : it->second.get();
}

const VerifierDeps::DexFileDeps* VerifierDeps::GetDexFileDeps(const DexFile& dex_file) const {
  auto it = dex_deps_.find(&dex_file);
  return (it == dex_deps_.end()) ? nullptr : it->second.get();
}

template <typename T>
uint16_t VerifierDeps::GetAccessFlags(T* element) {
  static_assert(kAccJavaFlagsMask == 0xFFFF, "Unexpected value of a constant");
  if (element == nullptr) {
    return VerifierDeps::kUnresolvedMarker;
  } else {
    uint16_t access_flags = Low16Bits(element->GetAccessFlags());
    CHECK_NE(access_flags, VerifierDeps::kUnresolvedMarker);
    return access_flags;
  }
}

dex::StringIndex VerifierDeps::GetClassDescriptorStringId(const DexFile& dex_file,
                                                          ObjPtr<mirror::Class> klass) {
  DCHECK(klass != nullptr);
  ObjPtr<mirror::DexCache> dex_cache = klass->GetDexCache();
  // Array and proxy classes do not have a dex cache.
  if (!klass->IsArrayClass() && !klass->IsProxyClass()) {
    DCHECK(dex_cache != nullptr) << klass->PrettyClass();
    if (dex_cache->GetDexFile() == &dex_file) {
      // FindStringId is slow, try to go through the class def if we have one.
      const DexFile::ClassDef* class_def = klass->GetClassDef();
      DCHECK(class_def != nullptr) << klass->PrettyClass();
      const DexFile::TypeId& type_id = dex_file.GetTypeId(class_def->class_idx_);
      if (kIsDebugBuild) {
        std::string temp;
        CHECK_EQ(GetIdFromString(dex_file, klass->GetDescriptor(&temp)), type_id.descriptor_idx_);
      }
      return type_id.descriptor_idx_;
    }
  }
  std::string temp;
  return GetIdFromString(dex_file, klass->GetDescriptor(&temp));
}

// Try to find the string descriptor of the class. type_idx is a best guess of a matching string id.
static dex::StringIndex TryGetClassDescriptorStringId(const DexFile& dex_file,
                                                      dex::TypeIndex type_idx,
                                                      ObjPtr<mirror::Class> klass)
    REQUIRES_SHARED(Locks::mutator_lock_) {
  if (!klass->IsArrayClass()) {
    const DexFile::TypeId& type_id = dex_file.GetTypeId(type_idx);
    const DexFile& klass_dex = klass->GetDexFile();
    const DexFile::TypeId& klass_type_id = klass_dex.GetTypeId(klass->GetClassDef()->class_idx_);
    if (strcmp(dex_file.GetTypeDescriptor(type_id),
               klass_dex.GetTypeDescriptor(klass_type_id)) == 0) {
      return type_id.descriptor_idx_;
    }
  }
  return dex::StringIndex::Invalid();
}

dex::StringIndex VerifierDeps::GetMethodDeclaringClassStringId(const DexFile& dex_file,
                                                               uint32_t dex_method_index,
                                                               ArtMethod* method) {
  static_assert(kAccJavaFlagsMask == 0xFFFF, "Unexpected value of a constant");
  if (method == nullptr) {
    return dex::StringIndex(VerifierDeps::kUnresolvedMarker);
  }
  const dex::StringIndex string_id = TryGetClassDescriptorStringId(
      dex_file,
      dex_file.GetMethodId(dex_method_index).class_idx_,
      method->GetDeclaringClass());
  if (string_id.IsValid()) {
    // Got lucky using the original dex file, return based on the input dex file.
    DCHECK_EQ(GetClassDescriptorStringId(dex_file, method->GetDeclaringClass()), string_id);
    return string_id;
  }
  return GetClassDescriptorStringId(dex_file, method->GetDeclaringClass());
}

dex::StringIndex VerifierDeps::GetFieldDeclaringClassStringId(const DexFile& dex_file,
                                                              uint32_t dex_field_idx,
                                                              ArtField* field) {
  static_assert(kAccJavaFlagsMask == 0xFFFF, "Unexpected value of a constant");
  if (field == nullptr) {
    return dex::StringIndex(VerifierDeps::kUnresolvedMarker);
  }
  const dex::StringIndex string_id = TryGetClassDescriptorStringId(
      dex_file,
      dex_file.GetFieldId(dex_field_idx).class_idx_,
      field->GetDeclaringClass());
  if (string_id.IsValid()) {
    // Got lucky using the original dex file, return based on the input dex file.
    DCHECK_EQ(GetClassDescriptorStringId(dex_file, field->GetDeclaringClass()), string_id);
    return string_id;
  }
  return GetClassDescriptorStringId(dex_file, field->GetDeclaringClass());
}

static inline VerifierDeps* GetMainVerifierDeps() {
  // The main VerifierDeps is the one set in the compiler callbacks, which at the
  // end of verification will have all the per-thread VerifierDeps merged into it.
  CompilerCallbacks* callbacks = Runtime::Current()->GetCompilerCallbacks();
  if (callbacks == nullptr) {
    return nullptr;
  }
  return callbacks->GetVerifierDeps();
}

static inline VerifierDeps* GetThreadLocalVerifierDeps() {
  // During AOT, each thread has its own VerifierDeps, to avoid lock contention. At the end
  // of full verification, these VerifierDeps will be merged into the main one.
  if (!Runtime::Current()->IsAotCompiler()) {
    return nullptr;
  }
  return Thread::Current()->GetVerifierDeps();
}

static bool FindExistingStringId(const std::vector<std::string>& strings,
                                 const std::string& str,
                                 uint32_t* found_id) {
  uint32_t num_extra_ids = strings.size();
  for (size_t i = 0; i < num_extra_ids; ++i) {
    if (strings[i] == str) {
      *found_id = i;
      return true;
    }
  }
  return false;
}

dex::StringIndex VerifierDeps::GetIdFromString(const DexFile& dex_file, const std::string& str) {
  const DexFile::StringId* string_id = dex_file.FindStringId(str.c_str());
  if (string_id != nullptr) {
    // String is in the DEX file. Return its ID.
    return dex_file.GetIndexForStringId(*string_id);
  }

  // String is not in the DEX file. Assign a new ID to it which is higher than
  // the number of strings in the DEX file.

  // We use the main `VerifierDeps` for adding new strings to simplify
  // synchronization/merging of these entries between threads.
  VerifierDeps* singleton = GetMainVerifierDeps();
  DexFileDeps* deps = singleton->GetDexFileDeps(dex_file);
  DCHECK(deps != nullptr);

  uint32_t num_ids_in_dex = dex_file.NumStringIds();
  uint32_t found_id;

  {
    ReaderMutexLock mu(Thread::Current(), *Locks::verifier_deps_lock_);
    if (FindExistingStringId(deps->strings_, str, &found_id)) {
      return dex::StringIndex(num_ids_in_dex + found_id);
    }
  }
  {
    WriterMutexLock mu(Thread::Current(), *Locks::verifier_deps_lock_);
    if (FindExistingStringId(deps->strings_, str, &found_id)) {
      return dex::StringIndex(num_ids_in_dex + found_id);
    }
    deps->strings_.push_back(str);
    dex::StringIndex new_id(num_ids_in_dex + deps->strings_.size() - 1);
    CHECK_GE(new_id.index_, num_ids_in_dex);  // check for overflows
    DCHECK_EQ(str, singleton->GetStringFromId(dex_file, new_id));
    return new_id;
  }
}

std::string VerifierDeps::GetStringFromId(const DexFile& dex_file, dex::StringIndex string_id)
    const {
  uint32_t num_ids_in_dex = dex_file.NumStringIds();
  if (string_id.index_ < num_ids_in_dex) {
    return std::string(dex_file.StringDataByIdx(string_id));
  } else {
    const DexFileDeps* deps = GetDexFileDeps(dex_file);
    DCHECK(deps != nullptr);
    string_id.index_ -= num_ids_in_dex;
    CHECK_LT(string_id.index_, deps->strings_.size());
    return deps->strings_[string_id.index_];
  }
}

bool VerifierDeps::IsInClassPath(ObjPtr<mirror::Class> klass) const {
  DCHECK(klass != nullptr);

  ObjPtr<mirror::DexCache> dex_cache = klass->GetDexCache();
  if (dex_cache == nullptr) {
    // This is a synthesized class, in this case always an array. They are not
    // defined in the compiled DEX files and therefore are part of the classpath.
    // We could avoid recording dependencies on arrays with component types in
    // the compiled DEX files but we choose to record them anyway so as to
    // record the access flags VM sets for array classes.
    DCHECK(klass->IsArrayClass()) << klass->PrettyDescriptor();
    return true;
  }

  const DexFile* dex_file = dex_cache->GetDexFile();
  DCHECK(dex_file != nullptr);

  // Test if the `dex_deps_` contains an entry for `dex_file`. If not, the dex
  // file was not registered as being compiled and we assume `klass` is in the
  // classpath.
  return (GetDexFileDeps(*dex_file) == nullptr);
}

void VerifierDeps::AddClassResolution(const DexFile& dex_file,
                                      dex::TypeIndex type_idx,
                                      mirror::Class* klass) {
  DexFileDeps* dex_deps = GetDexFileDeps(dex_file);
  if (dex_deps == nullptr) {
    // This invocation is from verification of a dex file which is not being compiled.
    return;
  }

  if (klass != nullptr && !IsInClassPath(klass)) {
    // Class resolved into one of the DEX files which are being compiled.
    // This is not a classpath dependency.
    return;
  }

  dex_deps->classes_.emplace(ClassResolution(type_idx, GetAccessFlags(klass)));
}

void VerifierDeps::AddFieldResolution(const DexFile& dex_file,
                                      uint32_t field_idx,
                                      ArtField* field) {
  DexFileDeps* dex_deps = GetDexFileDeps(dex_file);
  if (dex_deps == nullptr) {
    // This invocation is from verification of a dex file which is not being compiled.
    return;
  }

  if (field != nullptr && !IsInClassPath(field->GetDeclaringClass())) {
    // Field resolved into one of the DEX files which are being compiled.
    // This is not a classpath dependency.
    return;
  }

  dex_deps->fields_.emplace(FieldResolution(field_idx,
                                            GetAccessFlags(field),
                                            GetFieldDeclaringClassStringId(dex_file,
                                                                           field_idx,
                                                                           field)));
}

void VerifierDeps::AddMethodResolution(const DexFile& dex_file,
                                       uint32_t method_idx,
                                       MethodResolutionKind resolution_kind,
                                       ArtMethod* method) {
  DexFileDeps* dex_deps = GetDexFileDeps(dex_file);
  if (dex_deps == nullptr) {
    // This invocation is from verification of a dex file which is not being compiled.
    return;
  }

  if (method != nullptr && !IsInClassPath(method->GetDeclaringClass())) {
    // Method resolved into one of the DEX files which are being compiled.
    // This is not a classpath dependency.
    return;
  }

  MethodResolution method_tuple(method_idx,
                                GetAccessFlags(method),
                                GetMethodDeclaringClassStringId(dex_file, method_idx, method));
  if (resolution_kind == kDirectMethodResolution) {
    dex_deps->direct_methods_.emplace(method_tuple);
  } else if (resolution_kind == kVirtualMethodResolution) {
    dex_deps->virtual_methods_.emplace(method_tuple);
  } else {
    DCHECK_EQ(resolution_kind, kInterfaceMethodResolution);
    dex_deps->interface_methods_.emplace(method_tuple);
  }
}

void VerifierDeps::AddAssignability(const DexFile& dex_file,
                                    mirror::Class* destination,
                                    mirror::Class* source,
                                    bool is_strict,
                                    bool is_assignable) {
  // Test that the method is only called on reference types.
  // Note that concurrent verification of `destination` and `source` may have
  // set their status to erroneous. However, the tests performed below rely
  // merely on no issues with linking (valid access flags, superclass and
  // implemented interfaces). If the class at any point reached the IsResolved
  // status, the requirement holds. This is guaranteed by RegTypeCache::ResolveClass.
  DCHECK(destination != nullptr && !destination->IsPrimitive());
  DCHECK(source != nullptr && !source->IsPrimitive());

  if (destination == source ||
      destination->IsObjectClass() ||
      (!is_strict && destination->IsInterface())) {
    // Cases when `destination` is trivially assignable from `source`.
    DCHECK(is_assignable);
    return;
  }

  DCHECK_EQ(is_assignable, destination->IsAssignableFrom(source));

  if (destination->IsArrayClass() && source->IsArrayClass()) {
    // Both types are arrays. Break down to component types and add recursively.
    // This helps filter out destinations from compiled DEX files (see below)
    // and deduplicate entries with the same canonical component type.
    mirror::Class* destination_component = destination->GetComponentType();
    mirror::Class* source_component = source->GetComponentType();

    // Only perform the optimization if both types are resolved which guarantees
    // that they linked successfully, as required at the top of this method.
    if (destination_component->IsResolved() && source_component->IsResolved()) {
      AddAssignability(dex_file,
                       destination_component,
                       source_component,
                       /* is_strict */ true,
                       is_assignable);
      return;
    }
  }

  DexFileDeps* dex_deps = GetDexFileDeps(dex_file);
  if (dex_deps == nullptr) {
    // This invocation is from verification of a DEX file which is not being compiled.
    return;
  }

  if (!IsInClassPath(destination) && !IsInClassPath(source)) {
    // Both `destination` and `source` are defined in the compiled DEX files.
    // No need to record a dependency.
    return;
  }

  // Get string IDs for both descriptors and store in the appropriate set.
  dex::StringIndex destination_id = GetClassDescriptorStringId(dex_file, destination);
  dex::StringIndex source_id = GetClassDescriptorStringId(dex_file, source);

  if (is_assignable) {
    dex_deps->assignable_types_.emplace(TypeAssignability(destination_id, source_id));
  } else {
    dex_deps->unassignable_types_.emplace(TypeAssignability(destination_id, source_id));
  }
}

void VerifierDeps::MaybeRecordVerificationStatus(const DexFile& dex_file,
                                                 dex::TypeIndex type_idx,
                                                 MethodVerifier::FailureKind failure_kind) {
  if (failure_kind == MethodVerifier::kNoFailure) {
    // We only record classes that did not fully verify at compile time.
    return;
  }

  VerifierDeps* thread_deps = GetThreadLocalVerifierDeps();
  if (thread_deps != nullptr) {
    DexFileDeps* dex_deps = thread_deps->GetDexFileDeps(dex_file);
    dex_deps->unverified_classes_.push_back(type_idx);
  }
}

void VerifierDeps::MaybeRecordClassResolution(const DexFile& dex_file,
                                              dex::TypeIndex type_idx,
                                              mirror::Class* klass) {
  VerifierDeps* thread_deps = GetThreadLocalVerifierDeps();
  if (thread_deps != nullptr) {
    thread_deps->AddClassResolution(dex_file, type_idx, klass);
  }
}

void VerifierDeps::MaybeRecordFieldResolution(const DexFile& dex_file,
                                              uint32_t field_idx,
                                              ArtField* field) {
  VerifierDeps* thread_deps = GetThreadLocalVerifierDeps();
  if (thread_deps != nullptr) {
    thread_deps->AddFieldResolution(dex_file, field_idx, field);
  }
}

void VerifierDeps::MaybeRecordMethodResolution(const DexFile& dex_file,
                                               uint32_t method_idx,
                                               MethodResolutionKind resolution_kind,
                                               ArtMethod* method) {
  VerifierDeps* thread_deps = GetThreadLocalVerifierDeps();
  if (thread_deps != nullptr) {
    thread_deps->AddMethodResolution(dex_file, method_idx, resolution_kind, method);
  }
}

void VerifierDeps::MaybeRecordAssignability(const DexFile& dex_file,
                                            mirror::Class* destination,
                                            mirror::Class* source,
                                            bool is_strict,
                                            bool is_assignable) {
  VerifierDeps* thread_deps = GetThreadLocalVerifierDeps();
  if (thread_deps != nullptr) {
    thread_deps->AddAssignability(dex_file, destination, source, is_strict, is_assignable);
  }
}

namespace {

static inline uint32_t DecodeUint32WithOverflowCheck(const uint8_t** in, const uint8_t* end) {
  CHECK_LT(*in, end);
  return DecodeUnsignedLeb128(in);
}

template<typename T> inline uint32_t Encode(T in);

template<> inline uint32_t Encode<uint16_t>(uint16_t in) {
  return in;
}
template<> inline uint32_t Encode<uint32_t>(uint32_t in) {
  return in;
}
template<> inline uint32_t Encode<dex::TypeIndex>(dex::TypeIndex in) {
  return in.index_;
}
template<> inline uint32_t Encode<dex::StringIndex>(dex::StringIndex in) {
  return in.index_;
}

template<typename T> inline T Decode(uint32_t in);

template<> inline uint16_t Decode<uint16_t>(uint32_t in) {
  return dchecked_integral_cast<uint16_t>(in);
}
template<> inline uint32_t Decode<uint32_t>(uint32_t in) {
  return in;
}
template<> inline dex::TypeIndex Decode<dex::TypeIndex>(uint32_t in) {
  return dex::TypeIndex(in);
}
template<> inline dex::StringIndex Decode<dex::StringIndex>(uint32_t in) {
  return dex::StringIndex(in);
}

template<typename T1, typename T2>
static inline void EncodeTuple(std::vector<uint8_t>* out, const std::tuple<T1, T2>& t) {
  EncodeUnsignedLeb128(out, Encode(std::get<0>(t)));
  EncodeUnsignedLeb128(out, Encode(std::get<1>(t)));
}

template<typename T1, typename T2>
static inline void DecodeTuple(const uint8_t** in, const uint8_t* end, std::tuple<T1, T2>* t) {
  T1 v1 = Decode<T1>(DecodeUint32WithOverflowCheck(in, end));
  T2 v2 = Decode<T2>(DecodeUint32WithOverflowCheck(in, end));
  *t = std::make_tuple(v1, v2);
}

template<typename T1, typename T2, typename T3>
static inline void EncodeTuple(std::vector<uint8_t>* out, const std::tuple<T1, T2, T3>& t) {
  EncodeUnsignedLeb128(out, Encode(std::get<0>(t)));
  EncodeUnsignedLeb128(out, Encode(std::get<1>(t)));
  EncodeUnsignedLeb128(out, Encode(std::get<2>(t)));
}

template<typename T1, typename T2, typename T3>
static inline void DecodeTuple(const uint8_t** in, const uint8_t* end, std::tuple<T1, T2, T3>* t) {
  T1 v1 = Decode<T1>(DecodeUint32WithOverflowCheck(in, end));
  T2 v2 = Decode<T2>(DecodeUint32WithOverflowCheck(in, end));
  T3 v3 = Decode<T3>(DecodeUint32WithOverflowCheck(in, end));
  *t = std::make_tuple(v1, v2, v3);
}

template<typename T>
static inline void EncodeSet(std::vector<uint8_t>* out, const std::set<T>& set) {
  EncodeUnsignedLeb128(out, set.size());
  for (const T& entry : set) {
    EncodeTuple(out, entry);
  }
}

template <typename T>
static inline void EncodeUint16Vector(std::vector<uint8_t>* out,
                                      const std::vector<T>& vector) {
  EncodeUnsignedLeb128(out, vector.size());
  for (const T& entry : vector) {
    EncodeUnsignedLeb128(out, Encode(entry));
  }
}

template<typename T>
static inline void DecodeSet(const uint8_t** in, const uint8_t* end, std::set<T>* set) {
  DCHECK(set->empty());
  size_t num_entries = DecodeUint32WithOverflowCheck(in, end);
  for (size_t i = 0; i < num_entries; ++i) {
    T tuple;
    DecodeTuple(in, end, &tuple);
    set->emplace(tuple);
  }
}

template<typename T>
static inline void DecodeUint16Vector(const uint8_t** in,
                                      const uint8_t* end,
                                      std::vector<T>* vector) {
  DCHECK(vector->empty());
  size_t num_entries = DecodeUint32WithOverflowCheck(in, end);
  vector->reserve(num_entries);
  for (size_t i = 0; i < num_entries; ++i) {
    vector->push_back(
        Decode<T>(dchecked_integral_cast<uint16_t>(DecodeUint32WithOverflowCheck(in, end))));
  }
}

static inline void EncodeStringVector(std::vector<uint8_t>* out,
                                      const std::vector<std::string>& strings) {
  EncodeUnsignedLeb128(out, strings.size());
  for (const std::string& str : strings) {
    const uint8_t* data = reinterpret_cast<const uint8_t*>(str.c_str());
    size_t length = str.length() + 1;
    out->insert(out->end(), data, data + length);
    DCHECK_EQ(0u, out->back());
  }
}

static inline void DecodeStringVector(const uint8_t** in,
                                      const uint8_t* end,
                                      std::vector<std::string>* strings) {
  DCHECK(strings->empty());
  size_t num_strings = DecodeUint32WithOverflowCheck(in, end);
  strings->reserve(num_strings);
  for (size_t i = 0; i < num_strings; ++i) {
    CHECK_LT(*in, end);
    const char* string_start = reinterpret_cast<const char*>(*in);
    strings->emplace_back(std::string(string_start));
    *in += strings->back().length() + 1;
  }
}

}  // namespace

void VerifierDeps::Encode(const std::vector<const DexFile*>& dex_files,
                          std::vector<uint8_t>* buffer) const {
  for (const DexFile* dex_file : dex_files) {
    const DexFileDeps& deps = *GetDexFileDeps(*dex_file);
    EncodeStringVector(buffer, deps.strings_);
    EncodeSet(buffer, deps.assignable_types_);
    EncodeSet(buffer, deps.unassignable_types_);
    EncodeSet(buffer, deps.classes_);
    EncodeSet(buffer, deps.fields_);
    EncodeSet(buffer, deps.direct_methods_);
    EncodeSet(buffer, deps.virtual_methods_);
    EncodeSet(buffer, deps.interface_methods_);
    EncodeUint16Vector(buffer, deps.unverified_classes_);
  }
}

VerifierDeps::VerifierDeps(const std::vector<const DexFile*>& dex_files,
                           ArrayRef<const uint8_t> data)
    : VerifierDeps(dex_files) {
  if (data.empty()) {
    // Return eagerly, as the first thing we expect from VerifierDeps data is
    // the number of created strings, even if there is no dependency.
    // Currently, only the boot image does not have any VerifierDeps data.
    return;
  }
  const uint8_t* data_start = data.data();
  const uint8_t* data_end = data_start + data.size();
  for (const DexFile* dex_file : dex_files) {
    DexFileDeps* deps = GetDexFileDeps(*dex_file);
    DecodeStringVector(&data_start, data_end, &deps->strings_);
    DecodeSet(&data_start, data_end, &deps->assignable_types_);
    DecodeSet(&data_start, data_end, &deps->unassignable_types_);
    DecodeSet(&data_start, data_end, &deps->classes_);
    DecodeSet(&data_start, data_end, &deps->fields_);
    DecodeSet(&data_start, data_end, &deps->direct_methods_);
    DecodeSet(&data_start, data_end, &deps->virtual_methods_);
    DecodeSet(&data_start, data_end, &deps->interface_methods_);
    DecodeUint16Vector(&data_start, data_end, &deps->unverified_classes_);
  }
  CHECK_LE(data_start, data_end);
}

bool VerifierDeps::Equals(const VerifierDeps& rhs) const {
  if (dex_deps_.size() != rhs.dex_deps_.size()) {
    return false;
  }

  auto lhs_it = dex_deps_.begin();
  auto rhs_it = rhs.dex_deps_.begin();

  for (; (lhs_it != dex_deps_.end()) && (rhs_it != rhs.dex_deps_.end()); lhs_it++, rhs_it++) {
    const DexFile* lhs_dex_file = lhs_it->first;
    const DexFile* rhs_dex_file = rhs_it->first;
    if (lhs_dex_file != rhs_dex_file) {
      return false;
    }

    DexFileDeps* lhs_deps = lhs_it->second.get();
    DexFileDeps* rhs_deps = rhs_it->second.get();
    if (!lhs_deps->Equals(*rhs_deps)) {
      return false;
    }
  }

  DCHECK((lhs_it == dex_deps_.end()) && (rhs_it == rhs.dex_deps_.end()));
  return true;
}

bool VerifierDeps::DexFileDeps::Equals(const VerifierDeps::DexFileDeps& rhs) const {
  return (strings_ == rhs.strings_) &&
         (assignable_types_ == rhs.assignable_types_) &&
         (unassignable_types_ == rhs.unassignable_types_) &&
         (classes_ == rhs.classes_) &&
         (fields_ == rhs.fields_) &&
         (direct_methods_ == rhs.direct_methods_) &&
         (virtual_methods_ == rhs.virtual_methods_) &&
         (interface_methods_ == rhs.interface_methods_) &&
         (unverified_classes_ == rhs.unverified_classes_);
}

void VerifierDeps::Dump(VariableIndentationOutputStream* vios) const {
  for (const auto& dep : dex_deps_) {
    const DexFile& dex_file = *dep.first;
    vios->Stream()
        << "Dependencies of "
        << dex_file.GetLocation()
        << ":\n";

    ScopedIndentation indent(vios);

    for (const std::string& str : dep.second->strings_) {
      vios->Stream() << "Extra string: " << str << "\n";
    }

    for (const TypeAssignability& entry : dep.second->assignable_types_) {
      vios->Stream()
        << GetStringFromId(dex_file, entry.GetSource())
        << " must be assignable to "
        << GetStringFromId(dex_file, entry.GetDestination())
        << "\n";
    }

    for (const TypeAssignability& entry : dep.second->unassignable_types_) {
      vios->Stream()
        << GetStringFromId(dex_file, entry.GetSource())
        << " must not be assignable to "
        << GetStringFromId(dex_file, entry.GetDestination())
        << "\n";
    }

    for (const ClassResolution& entry : dep.second->classes_) {
      vios->Stream()
          << dex_file.StringByTypeIdx(entry.GetDexTypeIndex())
          << (entry.IsResolved() ? " must be resolved " : "must not be resolved ")
          << " with access flags " << std::hex << entry.GetAccessFlags() << std::dec
          << "\n";
    }

    for (const FieldResolution& entry : dep.second->fields_) {
      const DexFile::FieldId& field_id = dex_file.GetFieldId(entry.GetDexFieldIndex());
      vios->Stream()
          << dex_file.GetFieldDeclaringClassDescriptor(field_id) << "->"
          << dex_file.GetFieldName(field_id) << ":"
          << dex_file.GetFieldTypeDescriptor(field_id)
          << " is expected to be ";
      if (!entry.IsResolved()) {
        vios->Stream() << "unresolved\n";
      } else {
        vios->Stream()
          << "in class "
          << GetStringFromId(dex_file, entry.GetDeclaringClassIndex())
          << ", and have the access flags " << std::hex << entry.GetAccessFlags() << std::dec
          << "\n";
      }
    }

    for (const auto& entry :
            { std::make_pair(kDirectMethodResolution, dep.second->direct_methods_),
              std::make_pair(kVirtualMethodResolution, dep.second->virtual_methods_),
              std::make_pair(kInterfaceMethodResolution, dep.second->interface_methods_) }) {
      for (const MethodResolution& method : entry.second) {
        const DexFile::MethodId& method_id = dex_file.GetMethodId(method.GetDexMethodIndex());
        vios->Stream()
            << dex_file.GetMethodDeclaringClassDescriptor(method_id) << "->"
            << dex_file.GetMethodName(method_id)
            << dex_file.GetMethodSignature(method_id).ToString()
            << " is expected to be ";
        if (!method.IsResolved()) {
          vios->Stream() << "unresolved\n";
        } else {
          vios->Stream()
            << "in class "
            << GetStringFromId(dex_file, method.GetDeclaringClassIndex())
            << ", have the access flags " << std::hex << method.GetAccessFlags() << std::dec
            << ", and be of kind " << entry.first
            << "\n";
        }
      }
    }

    for (dex::TypeIndex type_index : dep.second->unverified_classes_) {
      vios->Stream()
          << dex_file.StringByTypeIdx(type_index)
          << " is expected to be verified at runtime\n";
    }
  }
}

bool VerifierDeps::ValidateDependencies(Handle<mirror::ClassLoader> class_loader,
                                        Thread* self) const {
  for (const auto& entry : dex_deps_) {
    if (!VerifyDexFile(class_loader, *entry.first, *entry.second, self)) {
      return false;
    }
  }
  return true;
}

// TODO: share that helper with other parts of the compiler that have
// the same lookup pattern.
static mirror::Class* FindClassAndClearException(ClassLinker* class_linker,
                                                 Thread* self,
                                                 const char* name,
                                                 Handle<mirror::ClassLoader> class_loader)
    REQUIRES_SHARED(Locks::mutator_lock_) {
  mirror::Class* result = class_linker->FindClass(self, name, class_loader);
  if (result == nullptr) {
    DCHECK(self->IsExceptionPending());
    self->ClearException();
  }
  return result;
}

bool VerifierDeps::VerifyAssignability(Handle<mirror::ClassLoader> class_loader,
                                       const DexFile& dex_file,
                                       const std::set<TypeAssignability>& assignables,
                                       bool expected_assignability,
                                       Thread* self) const {
  StackHandleScope<2> hs(self);
  ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
  MutableHandle<mirror::Class> source(hs.NewHandle<mirror::Class>(nullptr));
  MutableHandle<mirror::Class> destination(hs.NewHandle<mirror::Class>(nullptr));

  for (const auto& entry : assignables) {
    const std::string& destination_desc = GetStringFromId(dex_file, entry.GetDestination());
    destination.Assign(
        FindClassAndClearException(class_linker, self, destination_desc.c_str(), class_loader));
    const std::string& source_desc = GetStringFromId(dex_file, entry.GetSource());
    source.Assign(
        FindClassAndClearException(class_linker, self, source_desc.c_str(), class_loader));

    if (destination.Get() == nullptr) {
      LOG(INFO) << "VerifiersDeps: Could not resolve class " << destination_desc;
      return false;
    }

    if (source.Get() == nullptr) {
      LOG(INFO) << "VerifierDeps: Could not resolve class " << source_desc;
      return false;
    }

    DCHECK(destination->IsResolved() && source->IsResolved());
    if (destination->IsAssignableFrom(source.Get()) != expected_assignability) {
      LOG(INFO) << "VerifierDeps: Class "
                << destination_desc
                << (expected_assignability ? " not " : " ")
                << "assignable from "
                << source_desc;
      return false;
    }
  }
  return true;
}

bool VerifierDeps::VerifyClasses(Handle<mirror::ClassLoader> class_loader,
                                 const DexFile& dex_file,
                                 const std::set<ClassResolution>& classes,
                                 Thread* self) const {
  StackHandleScope<1> hs(self);
  ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
  MutableHandle<mirror::Class> cls(hs.NewHandle<mirror::Class>(nullptr));
  for (const auto& entry : classes) {
    const char* descriptor = dex_file.StringByTypeIdx(entry.GetDexTypeIndex());
    cls.Assign(FindClassAndClearException(class_linker, self, descriptor, class_loader));

    if (entry.IsResolved()) {
      if (cls.Get() == nullptr) {
        LOG(INFO) << "VerifierDeps: Could not resolve class " << descriptor;
        return false;
      } else if (entry.GetAccessFlags() != GetAccessFlags(cls.Get())) {
        LOG(INFO) << "VerifierDeps: Unexpected access flags on class "
                  << descriptor
                  << std::hex
                  << " (expected="
                  << entry.GetAccessFlags()
                  << ", actual="
                  << GetAccessFlags(cls.Get()) << ")"
                  << std::dec;
        return false;
      }
    } else if (cls.Get() != nullptr) {
      LOG(INFO) << "VerifierDeps: Unexpected successful resolution of class " << descriptor;
      return false;
    }
  }
  return true;
}

static std::string GetFieldDescription(const DexFile& dex_file, uint32_t index) {
  const DexFile::FieldId& field_id = dex_file.GetFieldId(index);
  return std::string(dex_file.GetFieldDeclaringClassDescriptor(field_id))
      + "->"
      + dex_file.GetFieldName(field_id)
      + ":"
      + dex_file.GetFieldTypeDescriptor(field_id);
}

bool VerifierDeps::VerifyFields(Handle<mirror::ClassLoader> class_loader,
                                const DexFile& dex_file,
                                const std::set<FieldResolution>& fields,
                                Thread* self) const {
  // Check recorded fields are resolved the same way, have the same recorded class,
  // and have the same recorded flags.
  ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
  StackHandleScope<1> hs(self);
  Handle<mirror::DexCache> dex_cache(
      hs.NewHandle(class_linker->FindDexCache(self, dex_file, /* allow_failure */ false)));
  for (const auto& entry : fields) {
    ArtField* field = class_linker->ResolveFieldJLS(
        dex_file, entry.GetDexFieldIndex(), dex_cache, class_loader);

    if (field == nullptr) {
      DCHECK(self->IsExceptionPending());
      self->ClearException();
    }

    if (entry.IsResolved()) {
      std::string expected_decl_klass = GetStringFromId(dex_file, entry.GetDeclaringClassIndex());
      std::string temp;
      if (field == nullptr) {
        LOG(INFO) << "VerifierDeps: Could not resolve field "
                  << GetFieldDescription(dex_file, entry.GetDexFieldIndex());
        return false;
      } else if (expected_decl_klass != field->GetDeclaringClass()->GetDescriptor(&temp)) {
        LOG(INFO) << "VerifierDeps: Unexpected declaring class for field resolution "
                  << GetFieldDescription(dex_file, entry.GetDexFieldIndex())
                  << " (expected=" << expected_decl_klass
                  << ", actual=" << field->GetDeclaringClass()->GetDescriptor(&temp) << ")";
        return false;
      } else if (entry.GetAccessFlags() != GetAccessFlags(field)) {
        LOG(INFO) << "VerifierDeps: Unexpected access flags for resolved field "
                  << GetFieldDescription(dex_file, entry.GetDexFieldIndex())
                  << std::hex << " (expected=" << entry.GetAccessFlags()
                  << ", actual=" << GetAccessFlags(field) << ")" << std::dec;
        return false;
      }
    } else if (field != nullptr) {
      LOG(INFO) << "VerifierDeps: Unexpected successful resolution of field "
                << GetFieldDescription(dex_file, entry.GetDexFieldIndex());
      return false;
    }
  }
  return true;
}

static std::string GetMethodDescription(const DexFile& dex_file, uint32_t index) {
  const DexFile::MethodId& method_id = dex_file.GetMethodId(index);
  return std::string(dex_file.GetMethodDeclaringClassDescriptor(method_id))
      + "->"
      + dex_file.GetMethodName(method_id)
      + dex_file.GetMethodSignature(method_id).ToString();
}

bool VerifierDeps::VerifyMethods(Handle<mirror::ClassLoader> class_loader,
                                 const DexFile& dex_file,
                                 const std::set<MethodResolution>& methods,
                                 MethodResolutionKind kind,
                                 Thread* self) const {
  ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
  PointerSize pointer_size = class_linker->GetImagePointerSize();

  for (const auto& entry : methods) {
    const DexFile::MethodId& method_id = dex_file.GetMethodId(entry.GetDexMethodIndex());

    const char* name = dex_file.GetMethodName(method_id);
    const Signature signature = dex_file.GetMethodSignature(method_id);
    const char* descriptor = dex_file.GetMethodDeclaringClassDescriptor(method_id);

    mirror::Class* cls = FindClassAndClearException(class_linker, self, descriptor, class_loader);
    if (cls == nullptr) {
      LOG(INFO) << "VerifierDeps: Could not resolve class " << descriptor;
      return false;
    }
    DCHECK(cls->IsResolved());
    ArtMethod* method = nullptr;
    if (kind == kDirectMethodResolution) {
      method = cls->FindDirectMethod(name, signature, pointer_size);
    } else if (kind == kVirtualMethodResolution) {
      method = cls->FindVirtualMethod(name, signature, pointer_size);
    } else {
      DCHECK_EQ(kind, kInterfaceMethodResolution);
      method = cls->FindInterfaceMethod(name, signature, pointer_size);
    }

    if (entry.IsResolved()) {
      std::string temp;
      std::string expected_decl_klass = GetStringFromId(dex_file, entry.GetDeclaringClassIndex());
      if (method == nullptr) {
        LOG(INFO) << "VerifierDeps: Could not resolve "
                  << kind
                  << " method "
                  << GetMethodDescription(dex_file, entry.GetDexMethodIndex());
        return false;
      } else if (expected_decl_klass != method->GetDeclaringClass()->GetDescriptor(&temp)) {
        LOG(INFO) << "VerifierDeps: Unexpected declaring class for "
                  << kind
                  << " method resolution "
                  << GetMethodDescription(dex_file, entry.GetDexMethodIndex())
                  << " (expected="
                  << expected_decl_klass
                  << ", actual="
                  << method->GetDeclaringClass()->GetDescriptor(&temp)
                  << ")";
        return false;
      } else if (entry.GetAccessFlags() != GetAccessFlags(method)) {
        LOG(INFO) << "VerifierDeps: Unexpected access flags for resolved "
                  << kind
                  << " method resolution "
                  << GetMethodDescription(dex_file, entry.GetDexMethodIndex())
                  << std::hex
                  << " (expected="
                  << entry.GetAccessFlags()
                  << ", actual="
                  << GetAccessFlags(method) << ")"
                  << std::dec;
        return false;
      }
    } else if (method != nullptr) {
      LOG(INFO) << "VerifierDeps: Unexpected successful resolution of "
                << kind
                << " method "
                << GetMethodDescription(dex_file, entry.GetDexMethodIndex());
      return false;
    }
  }
  return true;
}

bool VerifierDeps::VerifyDexFile(Handle<mirror::ClassLoader> class_loader,
                                 const DexFile& dex_file,
                                 const DexFileDeps& deps,
                                 Thread* self) const {
  bool result = VerifyAssignability(
      class_loader, dex_file, deps.assignable_types_, /* expected_assignability */ true, self);
  result = result && VerifyAssignability(
      class_loader, dex_file, deps.unassignable_types_, /* expected_assignability */ false, self);

  result = result && VerifyClasses(class_loader, dex_file, deps.classes_, self);
  result = result && VerifyFields(class_loader, dex_file, deps.fields_, self);

  result = result && VerifyMethods(
      class_loader, dex_file, deps.direct_methods_, kDirectMethodResolution, self);
  result = result && VerifyMethods(
      class_loader, dex_file, deps.virtual_methods_, kVirtualMethodResolution, self);
  result = result && VerifyMethods(
      class_loader, dex_file, deps.interface_methods_, kInterfaceMethodResolution, self);

  return result;
}

}  // namespace verifier
}  // namespace art