compiler/image_writer.cc

/*
 * Copyright (C) 2011 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 "image_writer.h"

#include <sys/stat.h>

#include <memory>
#include <numeric>
#include <vector>

#include "art_field-inl.h"
#include "art_method-inl.h"
#include "base/logging.h"
#include "base/unix_file/fd_file.h"
#include "class_linker-inl.h"
#include "compiled_method.h"
#include "dex_file-inl.h"
#include "driver/compiler_driver.h"
#include "elf_file.h"
#include "elf_utils.h"
#include "elf_writer.h"
#include "gc/accounting/card_table-inl.h"
#include "gc/accounting/heap_bitmap.h"
#include "gc/accounting/space_bitmap-inl.h"
#include "gc/heap.h"
#include "gc/space/large_object_space.h"
#include "gc/space/space-inl.h"
#include "globals.h"
#include "image.h"
#include "intern_table.h"
#include "linear_alloc.h"
#include "lock_word.h"
#include "mirror/abstract_method.h"
#include "mirror/array-inl.h"
#include "mirror/class-inl.h"
#include "mirror/class_loader.h"
#include "mirror/dex_cache-inl.h"
#include "mirror/method.h"
#include "mirror/object-inl.h"
#include "mirror/object_array-inl.h"
#include "mirror/string-inl.h"
#include "oat.h"
#include "oat_file.h"
#include "runtime.h"
#include "scoped_thread_state_change.h"
#include "handle_scope-inl.h"
#include "utils/dex_cache_arrays_layout-inl.h"

using ::art::mirror::Class;
using ::art::mirror::DexCache;
using ::art::mirror::Object;
using ::art::mirror::ObjectArray;
using ::art::mirror::String;

namespace art {

// Separate objects into multiple bins to optimize dirty memory use.
static constexpr bool kBinObjects = true;

static void CheckNoDexObjectsCallback(Object* obj, void* arg ATTRIBUTE_UNUSED)
    SHARED_REQUIRES(Locks::mutator_lock_) {
  Class* klass = obj->GetClass();
  CHECK_NE(PrettyClass(klass), "com.android.dex.Dex");
}

static void CheckNoDexObjects() {
  ScopedObjectAccess soa(Thread::Current());
  Runtime::Current()->GetHeap()->VisitObjects(CheckNoDexObjectsCallback, nullptr);
}

bool ImageWriter::PrepareImageAddressSpace() {
  target_ptr_size_ = InstructionSetPointerSize(compiler_driver_.GetInstructionSet());
  {
    Thread::Current()->TransitionFromSuspendedToRunnable();
    PruneNonImageClasses();  // Remove junk
    ComputeLazyFieldsForImageClasses();  // Add useful information

    Thread::Current()->TransitionFromRunnableToSuspended(kNative);
  }
  gc::Heap* heap = Runtime::Current()->GetHeap();
  heap->CollectGarbage(false);  // Remove garbage.

  // Dex caches must not have their dex fields set in the image. These are memory buffers of mapped
  // dex files.
  //
  // We may open them in the unstarted-runtime code for class metadata. Their fields should all be
  // reset in PruneNonImageClasses and the objects reclaimed in the GC. Make sure that's actually
  // true.
  if (kIsDebugBuild) {
    CheckNoDexObjects();
  }

  if (kIsDebugBuild) {
    ScopedObjectAccess soa(Thread::Current());
    CheckNonImageClassesRemoved();
  }

  Thread::Current()->TransitionFromSuspendedToRunnable();
  CalculateNewObjectOffsets();
  Thread::Current()->TransitionFromRunnableToSuspended(kNative);

  // This needs to happen after CalculateNewObjectOffsets since it relies on intern_table_bytes_ and
  // bin size sums being calculated.
  if (!AllocMemory()) {
    return false;
  }

  return true;
}

bool ImageWriter::Write(const std::string& image_filename,
                        const std::string& oat_filename,
                        const std::string& oat_location) {
  CHECK(!image_filename.empty());

  ClassLinker* class_linker = Runtime::Current()->GetClassLinker();

  std::unique_ptr<File> oat_file(OS::OpenFileReadWrite(oat_filename.c_str()));
  if (oat_file.get() == nullptr) {
    PLOG(ERROR) << "Failed to open oat file " << oat_filename << " for " << oat_location;
    return false;
  }
  std::string error_msg;
  oat_file_ = OatFile::OpenReadable(oat_file.get(), oat_location, nullptr, &error_msg);
  if (oat_file_ == nullptr) {
    PLOG(ERROR) << "Failed to open writable oat file " << oat_filename << " for " << oat_location
        << ": " << error_msg;
    oat_file->Erase();
    return false;
  }
  CHECK_EQ(class_linker->RegisterOatFile(oat_file_), oat_file_);

  interpreter_to_interpreter_bridge_offset_ =
      oat_file_->GetOatHeader().GetInterpreterToInterpreterBridgeOffset();
  interpreter_to_compiled_code_bridge_offset_ =
      oat_file_->GetOatHeader().GetInterpreterToCompiledCodeBridgeOffset();

  jni_dlsym_lookup_offset_ = oat_file_->GetOatHeader().GetJniDlsymLookupOffset();

  quick_generic_jni_trampoline_offset_ =
      oat_file_->GetOatHeader().GetQuickGenericJniTrampolineOffset();
  quick_imt_conflict_trampoline_offset_ =
      oat_file_->GetOatHeader().GetQuickImtConflictTrampolineOffset();
  quick_resolution_trampoline_offset_ =
      oat_file_->GetOatHeader().GetQuickResolutionTrampolineOffset();
  quick_to_interpreter_bridge_offset_ =
      oat_file_->GetOatHeader().GetQuickToInterpreterBridgeOffset();

  size_t oat_loaded_size = 0;
  size_t oat_data_offset = 0;
  ElfWriter::GetOatElfInformation(oat_file.get(), &oat_loaded_size, &oat_data_offset);

  Thread::Current()->TransitionFromSuspendedToRunnable();

  CreateHeader(oat_loaded_size, oat_data_offset);
  CopyAndFixupNativeData();
  // TODO: heap validation can't handle these fix up passes.
  Runtime::Current()->GetHeap()->DisableObjectValidation();
  CopyAndFixupObjects();
  Thread::Current()->TransitionFromRunnableToSuspended(kNative);

  SetOatChecksumFromElfFile(oat_file.get());

  if (oat_file->FlushCloseOrErase() != 0) {
    LOG(ERROR) << "Failed to flush and close oat file " << oat_filename << " for " << oat_location;
    return false;
  }

  std::unique_ptr<File> image_file(OS::CreateEmptyFile(image_filename.c_str()));
  ImageHeader* image_header = reinterpret_cast<ImageHeader*>(image_->Begin());
  if (image_file.get() == nullptr) {
    LOG(ERROR) << "Failed to open image file " << image_filename;
    return false;
  }
  if (fchmod(image_file->Fd(), 0644) != 0) {
    PLOG(ERROR) << "Failed to make image file world readable: " << image_filename;
    image_file->Erase();
    return EXIT_FAILURE;
  }

  // Write out the image + fields + methods.
  const auto write_count = image_header->GetImageSize();
  if (!image_file->WriteFully(image_->Begin(), write_count)) {
    PLOG(ERROR) << "Failed to write image file " << image_filename;
    image_file->Erase();
    return false;
  }

  // Write out the image bitmap at the page aligned start of the image end.
  const ImageSection& bitmap_section = image_header->GetImageSection(ImageHeader::kSectionImageBitmap);
  CHECK_ALIGNED(bitmap_section.Offset(), kPageSize);
  if (!image_file->Write(reinterpret_cast<char*>(image_bitmap_->Begin()),
                         bitmap_section.Size(), bitmap_section.Offset())) {
    PLOG(ERROR) << "Failed to write image file " << image_filename;
    image_file->Erase();
    return false;
  }

  CHECK_EQ(bitmap_section.End(), static_cast<size_t>(image_file->GetLength()));
  if (image_file->FlushCloseOrErase() != 0) {
    PLOG(ERROR) << "Failed to flush and close image file " << image_filename;
    return false;
  }
  return true;
}

void ImageWriter::SetImageOffset(mirror::Object* object, size_t offset) {
  DCHECK(object != nullptr);
  DCHECK_NE(offset, 0U);

  // The object is already deflated from when we set the bin slot. Just overwrite the lock word.
  object->SetLockWord(LockWord::FromForwardingAddress(offset), false);
  DCHECK_EQ(object->GetLockWord(false).ReadBarrierState(), 0u);
  DCHECK(IsImageOffsetAssigned(object));
}

void ImageWriter::UpdateImageOffset(mirror::Object* obj, uintptr_t offset) {
  DCHECK(IsImageOffsetAssigned(obj)) << obj << " " << offset;
  obj->SetLockWord(LockWord::FromForwardingAddress(offset), false);
  DCHECK_EQ(obj->GetLockWord(false).ReadBarrierState(), 0u);
}

void ImageWriter::AssignImageOffset(mirror::Object* object, ImageWriter::BinSlot bin_slot) {
  DCHECK(object != nullptr);
  DCHECK_NE(image_objects_offset_begin_, 0u);

  size_t bin_slot_offset = bin_slot_offsets_[bin_slot.GetBin()];
  size_t new_offset = bin_slot_offset + bin_slot.GetIndex();
  DCHECK_ALIGNED(new_offset, kObjectAlignment);

  SetImageOffset(object, new_offset);
  DCHECK_LT(new_offset, image_end_);
}

bool ImageWriter::IsImageOffsetAssigned(mirror::Object* object) const {
  // Will also return true if the bin slot was assigned since we are reusing the lock word.
  DCHECK(object != nullptr);
  return object->GetLockWord(false).GetState() == LockWord::kForwardingAddress;
}

size_t ImageWriter::GetImageOffset(mirror::Object* object) const {
  DCHECK(object != nullptr);
  DCHECK(IsImageOffsetAssigned(object));
  LockWord lock_word = object->GetLockWord(false);
  size_t offset = lock_word.ForwardingAddress();
  DCHECK_LT(offset, image_end_);
  return offset;
}

void ImageWriter::SetImageBinSlot(mirror::Object* object, BinSlot bin_slot) {
  DCHECK(object != nullptr);
  DCHECK(!IsImageOffsetAssigned(object));
  DCHECK(!IsImageBinSlotAssigned(object));

  // Before we stomp over the lock word, save the hash code for later.
  Monitor::Deflate(Thread::Current(), object);;
  LockWord lw(object->GetLockWord(false));
  switch (lw.GetState()) {
    case LockWord::kFatLocked: {
      LOG(FATAL) << "Fat locked object " << object << " found during object copy";
      break;
    }
    case LockWord::kThinLocked: {
      LOG(FATAL) << "Thin locked object " << object << " found during object copy";
      break;
    }
    case LockWord::kUnlocked:
      // No hash, don't need to save it.
      break;
    case LockWord::kHashCode:
      DCHECK(saved_hashcode_map_.find(object) == saved_hashcode_map_.end());
      saved_hashcode_map_.emplace(object, lw.GetHashCode());
      break;
    default:
      LOG(FATAL) << "Unreachable.";
      UNREACHABLE();
  }
  object->SetLockWord(LockWord::FromForwardingAddress(bin_slot.Uint32Value()), false);
  DCHECK_EQ(object->GetLockWord(false).ReadBarrierState(), 0u);
  DCHECK(IsImageBinSlotAssigned(object));
}

void ImageWriter::PrepareDexCacheArraySlots() {
  ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
  Thread* const self = Thread::Current();
  ReaderMutexLock mu(self, *class_linker->DexLock());
  uint32_t size = 0u;
  for (jobject weak_root : class_linker->GetDexCaches()) {
    mirror::DexCache* dex_cache =
        down_cast<mirror::DexCache*>(self->DecodeJObject(weak_root));
    if (dex_cache == nullptr) {
      continue;
    }
    const DexFile* dex_file = dex_cache->GetDexFile();
    dex_cache_array_starts_.Put(dex_file, size);
    DexCacheArraysLayout layout(target_ptr_size_, dex_file);
    DCHECK(layout.Valid());
    auto types_size = layout.TypesSize(dex_file->NumTypeIds());
    auto methods_size = layout.MethodsSize(dex_file->NumMethodIds());
    auto fields_size = layout.FieldsSize(dex_file->NumFieldIds());
    auto strings_size = layout.StringsSize(dex_file->NumStringIds());
    dex_cache_array_indexes_.Put(
        dex_cache->GetResolvedTypes(),
        DexCacheArrayLocation {size + layout.TypesOffset(), types_size, kBinRegular});
    dex_cache_array_indexes_.Put(
        dex_cache->GetResolvedMethods(),
        DexCacheArrayLocation {size + layout.MethodsOffset(), methods_size, kBinArtMethodClean});
    AddMethodPointerArray(dex_cache->GetResolvedMethods());
    dex_cache_array_indexes_.Put(
        dex_cache->GetResolvedFields(),
        DexCacheArrayLocation {size + layout.FieldsOffset(), fields_size, kBinArtField});
    pointer_arrays_.emplace(dex_cache->GetResolvedFields(), kBinArtField);
    dex_cache_array_indexes_.Put(
        dex_cache->GetStrings(),
        DexCacheArrayLocation {size + layout.StringsOffset(), strings_size, kBinRegular});
    size += layout.Size();
    CHECK_EQ(layout.Size(), types_size + methods_size + fields_size + strings_size);
  }
  // Set the slot size early to avoid DCHECK() failures in IsImageBinSlotAssigned()
  // when AssignImageBinSlot() assigns their indexes out or order.
  bin_slot_sizes_[kBinDexCacheArray] = size;
}

void ImageWriter::AddMethodPointerArray(mirror::PointerArray* arr) {
  DCHECK(arr != nullptr);
  if (kIsDebugBuild) {
    for (size_t i = 0, len = arr->GetLength(); i < len; i++) {
      auto* method = arr->GetElementPtrSize<ArtMethod*>(i, target_ptr_size_);
      if (method != nullptr && !method->IsRuntimeMethod()) {
        auto* klass = method->GetDeclaringClass();
        CHECK(klass == nullptr || IsImageClass(klass)) << PrettyClass(klass)
            << " should be an image class";
      }
    }
  }
  // kBinArtMethodClean picked arbitrarily, just required to differentiate between ArtFields and
  // ArtMethods.
  pointer_arrays_.emplace(arr, kBinArtMethodClean);
}

void ImageWriter::AssignImageBinSlot(mirror::Object* object) {
  DCHECK(object != nullptr);
  size_t object_size = object->SizeOf();

  // The magic happens here. We segregate objects into different bins based
  // on how likely they are to get dirty at runtime.
  //
  // Likely-to-dirty objects get packed together into the same bin so that
  // at runtime their page dirtiness ratio (how many dirty objects a page has) is
  // maximized.
  //
  // This means more pages will stay either clean or shared dirty (with zygote) and
  // the app will use less of its own (private) memory.
  Bin bin = kBinRegular;
  size_t current_offset = 0u;

  if (kBinObjects) {
    //
    // Changing the bin of an object is purely a memory-use tuning.
    // It has no change on runtime correctness.
    //
    // Memory analysis has determined that the following types of objects get dirtied
    // the most:
    //
    // * Dex cache arrays are stored in a special bin. The arrays for each dex cache have
    //   a fixed layout which helps improve generated code (using PC-relative addressing),
    //   so we pre-calculate their offsets separately in PrepareDexCacheArraySlots().
    //   Since these arrays are huge, most pages do not overlap other objects and it's not
    //   really important where they are for the clean/dirty separation. Due to their
    //   special PC-relative addressing, we arbitrarily keep them at the beginning.
    // * Class'es which are verified [their clinit runs only at runtime]
    //   - classes in general [because their static fields get overwritten]
    //   - initialized classes with all-final statics are unlikely to be ever dirty,
    //     so bin them separately
    // * Art Methods that are:
    //   - native [their native entry point is not looked up until runtime]
    //   - have declaring classes that aren't initialized
    //            [their interpreter/quick entry points are trampolines until the class
    //             becomes initialized]
    //
    // We also assume the following objects get dirtied either never or extremely rarely:
    //  * Strings (they are immutable)
    //  * Art methods that aren't native and have initialized declared classes
    //
    // We assume that "regular" bin objects are highly unlikely to become dirtied,
    // so packing them together will not result in a noticeably tighter dirty-to-clean ratio.
    //
    if (object->IsClass()) {
      bin = kBinClassVerified;
      mirror::Class* klass = object->AsClass();

      // Add non-embedded vtable to the pointer array table if there is one.
      auto* vtable = klass->GetVTable();
      if (vtable != nullptr) {
        AddMethodPointerArray(vtable);
      }
      auto* iftable = klass->GetIfTable();
      if (iftable != nullptr) {
        for (int32_t i = 0; i < klass->GetIfTableCount(); ++i) {
          if (iftable->GetMethodArrayCount(i) > 0) {
            AddMethodPointerArray(iftable->GetMethodArray(i));
          }
        }
      }

      if (klass->GetStatus() == Class::kStatusInitialized) {
        bin = kBinClassInitialized;

        // If the class's static fields are all final, put it into a separate bin
        // since it's very likely it will stay clean.
        uint32_t num_static_fields = klass->NumStaticFields();
        if (num_static_fields == 0) {
          bin = kBinClassInitializedFinalStatics;
        } else {
          // Maybe all the statics are final?
          bool all_final = true;
          for (uint32_t i = 0; i < num_static_fields; ++i) {
            ArtField* field = klass->GetStaticField(i);
            if (!field->IsFinal()) {
              all_final = false;
              break;
            }
          }

          if (all_final) {
            bin = kBinClassInitializedFinalStatics;
          }
        }
      }
    } else if (object->GetClass<kVerifyNone>()->IsStringClass()) {
      bin = kBinString;  // Strings are almost always immutable (except for object header).
    } else if (object->IsArrayInstance()) {
      mirror::Class* klass = object->GetClass<kVerifyNone>();
      if (klass->IsObjectArrayClass() || klass->IsIntArrayClass() || klass->IsLongArrayClass()) {
        auto it = dex_cache_array_indexes_.find(object);
        if (it != dex_cache_array_indexes_.end()) {
          bin = kBinDexCacheArray;
          // Use prepared offset defined by the DexCacheLayout.
          current_offset = it->second.offset_;
          // Override incase of cross compilation.
          object_size = it->second.length_;
        }  // else bin = kBinRegular
      }
    }  // else bin = kBinRegular
  }

  size_t offset_delta = RoundUp(object_size, kObjectAlignment);  // 64-bit alignment
  if (bin != kBinDexCacheArray) {
    DCHECK(dex_cache_array_indexes_.find(object) == dex_cache_array_indexes_.end()) << object;
    current_offset = bin_slot_sizes_[bin];  // How many bytes the current bin is at (aligned).
    // Move the current bin size up to accomodate the object we just assigned a bin slot.
    bin_slot_sizes_[bin] += offset_delta;
  }

  BinSlot new_bin_slot(bin, current_offset);
  SetImageBinSlot(object, new_bin_slot);

  ++bin_slot_count_[bin];

  // Grow the image closer to the end by the object we just assigned.
  image_end_ += offset_delta;
}

bool ImageWriter::WillMethodBeDirty(ArtMethod* m) const {
  if (m->IsNative()) {
    return true;
  }
  mirror::Class* declaring_class = m->GetDeclaringClass();
  // Initialized is highly unlikely to dirty since there's no entry points to mutate.
  return declaring_class == nullptr || declaring_class->GetStatus() != Class::kStatusInitialized;
}

bool ImageWriter::IsImageBinSlotAssigned(mirror::Object* object) const {
  DCHECK(object != nullptr);

  // We always stash the bin slot into a lockword, in the 'forwarding address' state.
  // If it's in some other state, then we haven't yet assigned an image bin slot.
  if (object->GetLockWord(false).GetState() != LockWord::kForwardingAddress) {
    return false;
  } else if (kIsDebugBuild) {
    LockWord lock_word = object->GetLockWord(false);
    size_t offset = lock_word.ForwardingAddress();
    BinSlot bin_slot(offset);
    DCHECK_LT(bin_slot.GetIndex(), bin_slot_sizes_[bin_slot.GetBin()])
      << "bin slot offset should not exceed the size of that bin";
  }
  return true;
}

ImageWriter::BinSlot ImageWriter::GetImageBinSlot(mirror::Object* object) const {
  DCHECK(object != nullptr);
  DCHECK(IsImageBinSlotAssigned(object));

  LockWord lock_word = object->GetLockWord(false);
  size_t offset = lock_word.ForwardingAddress();  // TODO: ForwardingAddress should be uint32_t
  DCHECK_LE(offset, std::numeric_limits<uint32_t>::max());

  BinSlot bin_slot(static_cast<uint32_t>(offset));
  DCHECK_LT(bin_slot.GetIndex(), bin_slot_sizes_[bin_slot.GetBin()]);

  return bin_slot;
}

bool ImageWriter::AllocMemory() {
  const size_t length = RoundUp(image_objects_offset_begin_ + GetBinSizeSum() + intern_table_bytes_,
                                kPageSize);
  std::string error_msg;
  image_.reset(MemMap::MapAnonymous("image writer image", nullptr, length, PROT_READ | PROT_WRITE,
                                    false, false, &error_msg));
  if (UNLIKELY(image_.get() == nullptr)) {
    LOG(ERROR) << "Failed to allocate memory for image file generation: " << error_msg;
    return false;
  }

  // Create the image bitmap, only needs to cover mirror object section which is up to image_end_.
  CHECK_LE(image_end_, length);
  image_bitmap_.reset(gc::accounting::ContinuousSpaceBitmap::Create(
      "image bitmap", image_->Begin(), RoundUp(image_end_, kPageSize)));
  if (image_bitmap_.get() == nullptr) {
    LOG(ERROR) << "Failed to allocate memory for image bitmap";
    return false;
  }
  return true;
}

class ComputeLazyFieldsForClassesVisitor : public ClassVisitor {
 public:
  bool Visit(Class* c) OVERRIDE SHARED_REQUIRES(Locks::mutator_lock_) {
    StackHandleScope<1> hs(Thread::Current());
    mirror::Class::ComputeName(hs.NewHandle(c));
    return true;
  }
};

void ImageWriter::ComputeLazyFieldsForImageClasses() {
  ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
  ComputeLazyFieldsForClassesVisitor visitor;
  class_linker->VisitClassesWithoutClassesLock(&visitor);
}

bool ImageWriter::IsImageClass(Class* klass) {
  if (klass == nullptr) {
    return false;
  }
  std::string temp;
  return compiler_driver_.IsImageClass(klass->GetDescriptor(&temp));
}

class NonImageClassesVisitor : public ClassVisitor {
 public:
  explicit NonImageClassesVisitor(ImageWriter* image_writer) : image_writer_(image_writer) {}

  bool Visit(Class* klass) OVERRIDE SHARED_REQUIRES(Locks::mutator_lock_) {
    if (!image_writer_->IsImageClass(klass)) {
      std::string temp;
      non_image_classes_.insert(klass->GetDescriptor(&temp));
    }
    return true;
  }

  std::set<std::string> non_image_classes_;
  ImageWriter* const image_writer_;
};

void ImageWriter::PruneNonImageClasses() {
  if (compiler_driver_.GetImageClasses() == nullptr) {
    return;
  }
  Runtime* runtime = Runtime::Current();
  ClassLinker* class_linker = runtime->GetClassLinker();
  Thread* self = Thread::Current();

  // Make a list of classes we would like to prune.
  NonImageClassesVisitor visitor(this);
  class_linker->VisitClasses(&visitor);

  // Remove the undesired classes from the class roots.
  for (const std::string& it : visitor.non_image_classes_) {
    bool result = class_linker->RemoveClass(it.c_str(), nullptr);
    DCHECK(result);
  }

  // Clear references to removed classes from the DexCaches.
  const ArtMethod* resolution_method = runtime->GetResolutionMethod();

  ScopedAssertNoThreadSuspension sa(self, __FUNCTION__);
  ReaderMutexLock mu(self, *Locks::classlinker_classes_lock_);  // For ClassInClassTable
  ReaderMutexLock mu2(self, *class_linker->DexLock());
  for (jobject weak_root : class_linker->GetDexCaches()) {
    mirror::DexCache* dex_cache = down_cast<mirror::DexCache*>(self->DecodeJObject(weak_root));
    if (dex_cache == nullptr) {
      continue;
    }
    for (size_t i = 0; i < dex_cache->NumResolvedTypes(); i++) {
      Class* klass = dex_cache->GetResolvedType(i);
      if (klass != nullptr && !IsImageClass(klass)) {
        dex_cache->SetResolvedType(i, nullptr);
      }
    }
    auto* resolved_methods = down_cast<mirror::PointerArray*>(dex_cache->GetResolvedMethods());
    for (size_t i = 0, len = resolved_methods->GetLength(); i < len; i++) {
      auto* method = resolved_methods->GetElementPtrSize<ArtMethod*>(i, target_ptr_size_);
      if (method != nullptr) {
        auto* declaring_class = method->GetDeclaringClass();
        // Miranda methods may be held live by a class which was not an image class but have a
        // declaring class which is an image class. Set it to the resolution method to be safe and
        // prevent dangling pointers.
        if (method->IsMiranda() || !IsImageClass(declaring_class)) {
          resolved_methods->SetElementPtrSize(i, resolution_method, target_ptr_size_);
        } else {
          // Check that the class is still in the classes table.
          DCHECK(class_linker->ClassInClassTable(declaring_class)) << "Class "
              << PrettyClass(declaring_class) << " not in class linker table";
        }
      }
    }
    for (size_t i = 0; i < dex_cache->NumResolvedFields(); i++) {
      ArtField* field = dex_cache->GetResolvedField(i, target_ptr_size_);
      if (field != nullptr && !IsImageClass(field->GetDeclaringClass())) {
        dex_cache->SetResolvedField(i, nullptr, target_ptr_size_);
      }
    }
    // Clean the dex field. It might have been populated during the initialization phase, but
    // contains data only valid during a real run.
    dex_cache->SetFieldObject<false>(mirror::DexCache::DexOffset(), nullptr);
  }

  // Drop the array class cache in the ClassLinker, as these are roots holding those classes live.
  class_linker->DropFindArrayClassCache();
}

void ImageWriter::CheckNonImageClassesRemoved() {
  if (compiler_driver_.GetImageClasses() != nullptr) {
    gc::Heap* heap = Runtime::Current()->GetHeap();
    heap->VisitObjects(CheckNonImageClassesRemovedCallback, this);
  }
}

void ImageWriter::CheckNonImageClassesRemovedCallback(Object* obj, void* arg) {
  ImageWriter* image_writer = reinterpret_cast<ImageWriter*>(arg);
  if (obj->IsClass()) {
    Class* klass = obj->AsClass();
    if (!image_writer->IsImageClass(klass)) {
      image_writer->DumpImageClasses();
      std::string temp;
      CHECK(image_writer->IsImageClass(klass)) << klass->GetDescriptor(&temp)
                                               << " " << PrettyDescriptor(klass);
    }
  }
}

void ImageWriter::DumpImageClasses() {
  auto image_classes = compiler_driver_.GetImageClasses();
  CHECK(image_classes != nullptr);
  for (const std::string& image_class : *image_classes) {
    LOG(INFO) << " " << image_class;
  }
}

void ImageWriter::CalculateObjectBinSlots(Object* obj) {
  DCHECK(obj != nullptr);
  // if it is a string, we want to intern it if its not interned.
  if (obj->GetClass()->IsStringClass()) {
    // we must be an interned string that was forward referenced and already assigned
    if (IsImageBinSlotAssigned(obj)) {
      DCHECK_EQ(obj, obj->AsString()->Intern());
      return;
    }
    // InternImageString allows us to intern while holding the heap bitmap lock. This is safe since
    // we are guaranteed to not have GC during image writing.
    mirror::String* const interned = Runtime::Current()->GetInternTable()->InternStrongImageString(
        obj->AsString());
    if (obj != interned) {
      if (!IsImageBinSlotAssigned(interned)) {
        // interned obj is after us, allocate its location early
        AssignImageBinSlot(interned);
      }
      // point those looking for this object to the interned version.
      SetImageBinSlot(obj, GetImageBinSlot(interned));
      return;
    }
    // else (obj == interned), nothing to do but fall through to the normal case
  }

  AssignImageBinSlot(obj);
}

ObjectArray<Object>* ImageWriter::CreateImageRoots() const {
  Runtime* runtime = Runtime::Current();
  ClassLinker* class_linker = runtime->GetClassLinker();
  Thread* self = Thread::Current();
  StackHandleScope<3> hs(self);
  Handle<Class> object_array_class(hs.NewHandle(
      class_linker->FindSystemClass(self, "[Ljava/lang/Object;")));

  // build an Object[] of all the DexCaches used in the source_space_.
  // Since we can't hold the dex lock when allocating the dex_caches
  // ObjectArray, we lock the dex lock twice, first to get the number
  // of dex caches first and then lock it again to copy the dex
  // caches. We check that the number of dex caches does not change.
  size_t dex_cache_count;
  {
    ReaderMutexLock mu(self, *class_linker->DexLock());
    dex_cache_count = class_linker->GetDexCacheCount();
  }
  Handle<ObjectArray<Object>> dex_caches(
      hs.NewHandle(ObjectArray<Object>::Alloc(self, object_array_class.Get(),
                                              dex_cache_count)));
  CHECK(dex_caches.Get() != nullptr) << "Failed to allocate a dex cache array.";
  {
    ReaderMutexLock mu(self, *class_linker->DexLock());
    CHECK_EQ(dex_cache_count, class_linker->GetDexCacheCount())
        << "The number of dex caches changed.";
    size_t i = 0;
    for (jobject weak_root : class_linker->GetDexCaches()) {
      mirror::DexCache* dex_cache =
          down_cast<mirror::DexCache*>(self->DecodeJObject(weak_root));
      dex_caches->Set<false>(i, dex_cache);
      ++i;
    }
  }

  // build an Object[] of the roots needed to restore the runtime
  auto image_roots(hs.NewHandle(
      ObjectArray<Object>::Alloc(self, object_array_class.Get(), ImageHeader::kImageRootsMax)));
  image_roots->Set<false>(ImageHeader::kDexCaches, dex_caches.Get());
  image_roots->Set<false>(ImageHeader::kClassRoots, class_linker->GetClassRoots());
  for (int i = 0; i < ImageHeader::kImageRootsMax; i++) {
    CHECK(image_roots->Get(i) != nullptr);
  }
  return image_roots.Get();
}

// Walk instance fields of the given Class. Separate function to allow recursion on the super
// class.
void ImageWriter::WalkInstanceFields(mirror::Object* obj, mirror::Class* klass) {
  // Visit fields of parent classes first.
  StackHandleScope<1> hs(Thread::Current());
  Handle<mirror::Class> h_class(hs.NewHandle(klass));
  mirror::Class* super = h_class->GetSuperClass();
  if (super != nullptr) {
    WalkInstanceFields(obj, super);
  }
  //
  size_t num_reference_fields = h_class->NumReferenceInstanceFields();
  MemberOffset field_offset = h_class->GetFirstReferenceInstanceFieldOffset();
  for (size_t i = 0; i < num_reference_fields; ++i) {
    mirror::Object* value = obj->GetFieldObject<mirror::Object>(field_offset);
    if (value != nullptr) {
      WalkFieldsInOrder(value);
    }
    field_offset = MemberOffset(field_offset.Uint32Value() +
                                sizeof(mirror::HeapReference<mirror::Object>));
  }
}

// For an unvisited object, visit it then all its children found via fields.
void ImageWriter::WalkFieldsInOrder(mirror::Object* obj) {
  // Use our own visitor routine (instead of GC visitor) to get better locality between
  // an object and its fields
  if (!IsImageBinSlotAssigned(obj)) {
    // Walk instance fields of all objects
    StackHandleScope<2> hs(Thread::Current());
    Handle<mirror::Object> h_obj(hs.NewHandle(obj));
    Handle<mirror::Class> klass(hs.NewHandle(obj->GetClass()));
    // visit the object itself.
    CalculateObjectBinSlots(h_obj.Get());
    WalkInstanceFields(h_obj.Get(), klass.Get());
    // Walk static fields of a Class.
    if (h_obj->IsClass()) {
      size_t num_reference_static_fields = klass->NumReferenceStaticFields();
      MemberOffset field_offset = klass->GetFirstReferenceStaticFieldOffset(target_ptr_size_);
      for (size_t i = 0; i < num_reference_static_fields; ++i) {
        mirror::Object* value = h_obj->GetFieldObject<mirror::Object>(field_offset);
        if (value != nullptr) {
          WalkFieldsInOrder(value);
        }
        field_offset = MemberOffset(field_offset.Uint32Value() +
                                    sizeof(mirror::HeapReference<mirror::Object>));
      }
      // Visit and assign offsets for fields and field arrays.
      auto* as_klass = h_obj->AsClass();
      LengthPrefixedArray<ArtField>* fields[] = {
          as_klass->GetSFieldsPtr(), as_klass->GetIFieldsPtr(),
      };
      for (LengthPrefixedArray<ArtField>* cur_fields : fields) {
        // Total array length including header.
        if (cur_fields != nullptr) {
          const size_t header_size = LengthPrefixedArray<ArtField>::ComputeSize(0);
          // Forward the entire array at once.
          auto it = native_object_relocations_.find(cur_fields);
          CHECK(it == native_object_relocations_.end()) << "Field array " << cur_fields
                                                  << " already forwarded";
          size_t& offset = bin_slot_sizes_[kBinArtField];
          native_object_relocations_.emplace(
              cur_fields, NativeObjectRelocation {
                  offset, kNativeObjectRelocationTypeArtFieldArray });
          offset += header_size;
          // Forward individual fields so that we can quickly find where they belong.
          for (size_t i = 0, count = cur_fields->Length(); i < count; ++i) {
            // Need to forward arrays separate of fields.
            ArtField* field = &cur_fields->At(i);
            auto it2 = native_object_relocations_.find(field);
            CHECK(it2 == native_object_relocations_.end()) << "Field at index=" << i
                << " already assigned " << PrettyField(field) << " static=" << field->IsStatic();
            native_object_relocations_.emplace(
                field, NativeObjectRelocation {offset, kNativeObjectRelocationTypeArtField });
            offset += sizeof(ArtField);
          }
        }
      }
      // Visit and assign offsets for methods.
      LengthPrefixedArray<ArtMethod>* method_arrays[] = {
          as_klass->GetDirectMethodsPtr(), as_klass->GetVirtualMethodsPtr(),
      };
      for (LengthPrefixedArray<ArtMethod>* array : method_arrays) {
        if (array == nullptr) {
          continue;
        }
        bool any_dirty = false;
        size_t count = 0;
        const size_t method_alignment = ArtMethod::Alignment(target_ptr_size_);
        const size_t method_size = ArtMethod::Size(target_ptr_size_);
        auto iteration_range =
            MakeIterationRangeFromLengthPrefixedArray(array, method_size, method_alignment);
        for (auto& m : iteration_range) {
          any_dirty = any_dirty || WillMethodBeDirty(&m);
          ++count;
        }
        NativeObjectRelocationType type = any_dirty ? kNativeObjectRelocationTypeArtMethodDirty :
            kNativeObjectRelocationTypeArtMethodClean;
        Bin bin_type = BinTypeForNativeRelocationType(type);
        // Forward the entire array at once, but header first.
        const size_t header_size = LengthPrefixedArray<ArtMethod>::ComputeSize(0,
                                                                               method_size,
                                                                               method_alignment);
        auto it = native_object_relocations_.find(array);
        CHECK(it == native_object_relocations_.end()) << "Method array " << array
            << " already forwarded";
        size_t& offset = bin_slot_sizes_[bin_type];
        native_object_relocations_.emplace(array, NativeObjectRelocation { offset,
            any_dirty ? kNativeObjectRelocationTypeArtMethodArrayDirty :
                kNativeObjectRelocationTypeArtMethodArrayClean });
        offset += header_size;
        for (auto& m : iteration_range) {
          AssignMethodOffset(&m, type);
        }
        (any_dirty ? dirty_methods_ : clean_methods_) += count;
      }
    } else if (h_obj->IsObjectArray()) {
      // Walk elements of an object array.
      int32_t length = h_obj->AsObjectArray<mirror::Object>()->GetLength();
      for (int32_t i = 0; i < length; i++) {
        mirror::ObjectArray<mirror::Object>* obj_array = h_obj->AsObjectArray<mirror::Object>();
        mirror::Object* value = obj_array->Get(i);
        if (value != nullptr) {
          WalkFieldsInOrder(value);
        }
      }
    }
  }
}

void ImageWriter::AssignMethodOffset(ArtMethod* method, NativeObjectRelocationType type) {
  auto it = native_object_relocations_.find(method);
  CHECK(it == native_object_relocations_.end()) << "Method " << method << " already assigned "
      << PrettyMethod(method);
  size_t& offset = bin_slot_sizes_[BinTypeForNativeRelocationType(type)];
  native_object_relocations_.emplace(method, NativeObjectRelocation { offset, type });
  offset += ArtMethod::Size(target_ptr_size_);
}

void ImageWriter::WalkFieldsCallback(mirror::Object* obj, void* arg) {
  ImageWriter* writer = reinterpret_cast<ImageWriter*>(arg);
  DCHECK(writer != nullptr);
  writer->WalkFieldsInOrder(obj);
}

void ImageWriter::UnbinObjectsIntoOffsetCallback(mirror::Object* obj, void* arg) {
  ImageWriter* writer = reinterpret_cast<ImageWriter*>(arg);
  DCHECK(writer != nullptr);
  writer->UnbinObjectsIntoOffset(obj);
}

void ImageWriter::UnbinObjectsIntoOffset(mirror::Object* obj) {
  CHECK(obj != nullptr);

  // We know the bin slot, and the total bin sizes for all objects by now,
  // so calculate the object's final image offset.

  DCHECK(IsImageBinSlotAssigned(obj));
  BinSlot bin_slot = GetImageBinSlot(obj);
  // Change the lockword from a bin slot into an offset
  AssignImageOffset(obj, bin_slot);
}

void ImageWriter::CalculateNewObjectOffsets() {
  Thread* const self = Thread::Current();
  StackHandleScope<1> hs(self);
  Handle<ObjectArray<Object>> image_roots(hs.NewHandle(CreateImageRoots()));

  auto* runtime = Runtime::Current();
  auto* heap = runtime->GetHeap();
  DCHECK_EQ(0U, image_end_);

  // Leave space for the header, but do not write it yet, we need to
  // know where image_roots is going to end up
  image_end_ += RoundUp(sizeof(ImageHeader), kObjectAlignment);  // 64-bit-alignment

  image_objects_offset_begin_ = image_end_;
  // Prepare bin slots for dex cache arrays.
  PrepareDexCacheArraySlots();
  // Clear any pre-existing monitors which may have been in the monitor words, assign bin slots.
  heap->VisitObjects(WalkFieldsCallback, this);
  // Write the image runtime methods.
  image_methods_[ImageHeader::kResolutionMethod] = runtime->GetResolutionMethod();
  image_methods_[ImageHeader::kImtConflictMethod] = runtime->GetImtConflictMethod();
  image_methods_[ImageHeader::kImtUnimplementedMethod] = runtime->GetImtUnimplementedMethod();
  image_methods_[ImageHeader::kCalleeSaveMethod] = runtime->GetCalleeSaveMethod(Runtime::kSaveAll);
  image_methods_[ImageHeader::kRefsOnlySaveMethod] =
      runtime->GetCalleeSaveMethod(Runtime::kRefsOnly);
  image_methods_[ImageHeader::kRefsAndArgsSaveMethod] =
      runtime->GetCalleeSaveMethod(Runtime::kRefsAndArgs);

  // Add room for fake length prefixed array.
  const auto image_method_type = kNativeObjectRelocationTypeArtMethodArrayClean;
  auto it = native_object_relocations_.find(&image_method_array_);
  CHECK(it == native_object_relocations_.end());
  size_t& offset = bin_slot_sizes_[BinTypeForNativeRelocationType(image_method_type)];
  native_object_relocations_.emplace(&image_method_array_,
                                     NativeObjectRelocation { offset, image_method_type });
  size_t method_alignment = ArtMethod::Alignment(target_ptr_size_);
  const size_t array_size = LengthPrefixedArray<ArtMethod>::ComputeSize(
      0, ArtMethod::Size(target_ptr_size_), method_alignment);
  CHECK_ALIGNED_PARAM(array_size, method_alignment);
  offset += array_size;
  for (auto* m : image_methods_) {
    CHECK(m != nullptr);
    CHECK(m->IsRuntimeMethod());
    AssignMethodOffset(m, kNativeObjectRelocationTypeArtMethodClean);
  }

  // Calculate bin slot offsets.
  size_t bin_offset = image_objects_offset_begin_;
  for (size_t i = 0; i != kBinSize; ++i) {
    bin_slot_offsets_[i] = bin_offset;
    bin_offset += bin_slot_sizes_[i];
    if (i == kBinArtField) {
      static_assert(kBinArtField + 1 == kBinArtMethodClean, "Methods follow fields.");
      static_assert(alignof(ArtField) == 4u, "ArtField alignment is 4.");
      DCHECK_ALIGNED(bin_offset, 4u);
      DCHECK(method_alignment == 4u || method_alignment == 8u);
      bin_offset = RoundUp(bin_offset, method_alignment);
    }
  }
  // NOTE: There may be additional padding between the bin slots and the intern table.

  DCHECK_EQ(image_end_, GetBinSizeSum(kBinMirrorCount) + image_objects_offset_begin_);

  // Transform each object's bin slot into an offset which will be used to do the final copy.
  heap->VisitObjects(UnbinObjectsIntoOffsetCallback, this);

  DCHECK_EQ(image_end_, GetBinSizeSum(kBinMirrorCount) + image_objects_offset_begin_);

  image_roots_address_ = PointerToLowMemUInt32(GetImageAddress(image_roots.Get()));

  // Update the native relocations by adding their bin sums.
  for (auto& pair : native_object_relocations_) {
    NativeObjectRelocation& relocation = pair.second;
    Bin bin_type = BinTypeForNativeRelocationType(relocation.type);
    relocation.offset += bin_slot_offsets_[bin_type];
  }

  // Calculate how big the intern table will be after being serialized.
  auto* const intern_table = Runtime::Current()->GetInternTable();
  CHECK_EQ(intern_table->WeakSize(), 0u) << " should have strong interned all the strings";
  intern_table_bytes_ = intern_table->WriteToMemory(nullptr);

  // Note that image_end_ is left at end of used mirror object section.
}

void ImageWriter::CreateHeader(size_t oat_loaded_size, size_t oat_data_offset) {
  CHECK_NE(0U, oat_loaded_size);
  const uint8_t* oat_file_begin = GetOatFileBegin();
  const uint8_t* oat_file_end = oat_file_begin + oat_loaded_size;
  oat_data_begin_ = oat_file_begin + oat_data_offset;
  const uint8_t* oat_data_end = oat_data_begin_ + oat_file_->Size();

  // Create the image sections.
  ImageSection sections[ImageHeader::kSectionCount];
  // Objects section
  auto* objects_section = &sections[ImageHeader::kSectionObjects];
  *objects_section = ImageSection(0u, image_end_);
  size_t cur_pos = objects_section->End();
  // Add field section.
  auto* field_section = &sections[ImageHeader::kSectionArtFields];
  *field_section = ImageSection(cur_pos, bin_slot_sizes_[kBinArtField]);
  CHECK_EQ(bin_slot_offsets_[kBinArtField], field_section->Offset());
  cur_pos = field_section->End();
  // Round up to the alignment the required by the method section.
  cur_pos = RoundUp(cur_pos, ArtMethod::Alignment(target_ptr_size_));
  // Add method section.
  auto* methods_section = &sections[ImageHeader::kSectionArtMethods];
  *methods_section = ImageSection(cur_pos, bin_slot_sizes_[kBinArtMethodClean] +
                                  bin_slot_sizes_[kBinArtMethodDirty]);
  CHECK_EQ(bin_slot_offsets_[kBinArtMethodClean], methods_section->Offset());
  cur_pos = methods_section->End();
  // Round up to the alignment the string table expects. See HashSet::WriteToMemory.
  cur_pos = RoundUp(cur_pos, sizeof(uint64_t));
  // Calculate the size of the interned strings.
  auto* interned_strings_section = &sections[ImageHeader::kSectionInternedStrings];
  *interned_strings_section = ImageSection(cur_pos, intern_table_bytes_);
  cur_pos = interned_strings_section->End();
  // Finally bitmap section.
  const size_t bitmap_bytes = image_bitmap_->Size();
  auto* bitmap_section = &sections[ImageHeader::kSectionImageBitmap];
  *bitmap_section = ImageSection(RoundUp(cur_pos, kPageSize), RoundUp(bitmap_bytes, kPageSize));
  cur_pos = bitmap_section->End();
  if (kIsDebugBuild) {
    size_t idx = 0;
    for (const ImageSection& section : sections) {
      LOG(INFO) << static_cast<ImageHeader::ImageSections>(idx) << " " << section;
      ++idx;
    }
    LOG(INFO) << "Methods: clean=" << clean_methods_ << " dirty=" << dirty_methods_;
  }
  const size_t image_end = static_cast<uint32_t>(interned_strings_section->End());
  CHECK_EQ(AlignUp(image_begin_ + image_end, kPageSize), oat_file_begin) <<
      "Oat file should be right after the image.";
  // Create the header.
  new (image_->Begin()) ImageHeader(
      PointerToLowMemUInt32(image_begin_), image_end,
      sections, image_roots_address_, oat_file_->GetOatHeader().GetChecksum(),
      PointerToLowMemUInt32(oat_file_begin), PointerToLowMemUInt32(oat_data_begin_),
      PointerToLowMemUInt32(oat_data_end), PointerToLowMemUInt32(oat_file_end), target_ptr_size_,
      compile_pic_);
}

ArtMethod* ImageWriter::GetImageMethodAddress(ArtMethod* method) {
  auto it = native_object_relocations_.find(method);
  CHECK(it != native_object_relocations_.end()) << PrettyMethod(method) << " @ " << method;
  CHECK_GE(it->second.offset, image_end_) << "ArtMethods should be after Objects";
  return reinterpret_cast<ArtMethod*>(image_begin_ + it->second.offset);
}

class FixupRootVisitor : public RootVisitor {
 public:
  explicit FixupRootVisitor(ImageWriter* image_writer) : image_writer_(image_writer) {
  }

  void VisitRoots(mirror::Object*** roots, size_t count, const RootInfo& info ATTRIBUTE_UNUSED)
      OVERRIDE SHARED_REQUIRES(Locks::mutator_lock_) {
    for (size_t i = 0; i < count; ++i) {
      *roots[i] = ImageAddress(*roots[i]);
    }
  }

  void VisitRoots(mirror::CompressedReference<mirror::Object>** roots, size_t count,
                  const RootInfo& info ATTRIBUTE_UNUSED)
      OVERRIDE SHARED_REQUIRES(Locks::mutator_lock_) {
    for (size_t i = 0; i < count; ++i) {
      roots[i]->Assign(ImageAddress(roots[i]->AsMirrorPtr()));
    }
  }

 private:
  ImageWriter* const image_writer_;

  mirror::Object* ImageAddress(mirror::Object* obj) SHARED_REQUIRES(Locks::mutator_lock_) {
    const size_t offset = image_writer_->GetImageOffset(obj);
    auto* const dest = reinterpret_cast<Object*>(image_writer_->image_begin_ + offset);
    VLOG(compiler) << "Update root from " << obj << " to " << dest;
    return dest;
  }
};

void ImageWriter::CopyAndFixupNativeData() {
  // Copy ArtFields and methods to their locations and update the array for convenience.
  for (auto& pair : native_object_relocations_) {
    NativeObjectRelocation& relocation = pair.second;
    auto* dest = image_->Begin() + relocation.offset;
    DCHECK_GE(dest, image_->Begin() + image_end_);
    switch (relocation.type) {
      case kNativeObjectRelocationTypeArtField: {
        memcpy(dest, pair.first, sizeof(ArtField));
        reinterpret_cast<ArtField*>(dest)->SetDeclaringClass(
            GetImageAddress(reinterpret_cast<ArtField*>(pair.first)->GetDeclaringClass()));
        break;
      }
      case kNativeObjectRelocationTypeArtMethodClean:
      case kNativeObjectRelocationTypeArtMethodDirty: {
        CopyAndFixupMethod(reinterpret_cast<ArtMethod*>(pair.first),
                           reinterpret_cast<ArtMethod*>(dest));
        break;
      }
      // For arrays, copy just the header since the elements will get copied by their corresponding
      // relocations.
      case kNativeObjectRelocationTypeArtFieldArray: {
        memcpy(dest, pair.first, LengthPrefixedArray<ArtField>::ComputeSize(0));
        break;
      }
      case kNativeObjectRelocationTypeArtMethodArrayClean:
      case kNativeObjectRelocationTypeArtMethodArrayDirty: {
        memcpy(dest, pair.first, LengthPrefixedArray<ArtMethod>::ComputeSize(
            0,
            ArtMethod::Size(target_ptr_size_),
            ArtMethod::Alignment(target_ptr_size_)));
        break;
      }
    }
  }
  // Fixup the image method roots.
  auto* image_header = reinterpret_cast<ImageHeader*>(image_->Begin());
  const ImageSection& methods_section = image_header->GetMethodsSection();
  for (size_t i = 0; i < ImageHeader::kImageMethodsCount; ++i) {
    auto* m = image_methods_[i];
    CHECK(m != nullptr);
    auto it = native_object_relocations_.find(m);
    CHECK(it != native_object_relocations_.end()) << "No fowarding for " << PrettyMethod(m);
    NativeObjectRelocation& relocation = it->second;
    CHECK(methods_section.Contains(relocation.offset)) << relocation.offset << " not in "
        << methods_section;
    CHECK(relocation.IsArtMethodRelocation()) << relocation.type;
    auto* dest = reinterpret_cast<ArtMethod*>(image_begin_ + it->second.offset);
    image_header->SetImageMethod(static_cast<ImageHeader::ImageMethod>(i), dest);
  }
  // Write the intern table into the image.
  const ImageSection& intern_table_section = image_header->GetImageSection(
      ImageHeader::kSectionInternedStrings);
  InternTable* const intern_table = Runtime::Current()->GetInternTable();
  uint8_t* const memory_ptr = image_->Begin() + intern_table_section.Offset();
  const size_t intern_table_bytes = intern_table->WriteToMemory(memory_ptr);
  // Fixup the pointers in the newly written intern table to contain image addresses.
  InternTable temp_table;
  // Note that we require that ReadFromMemory does not make an internal copy of the elements so that
  // the VisitRoots() will update the memory directly rather than the copies.
  // This also relies on visit roots not doing any verification which could fail after we update
  // the roots to be the image addresses.
  temp_table.ReadFromMemory(memory_ptr);
  CHECK_EQ(temp_table.Size(), intern_table->Size());
  FixupRootVisitor visitor(this);
  temp_table.VisitRoots(&visitor, kVisitRootFlagAllRoots);
  CHECK_EQ(intern_table_bytes, intern_table_bytes_);
}

void ImageWriter::CopyAndFixupObjects() {
  gc::Heap* heap = Runtime::Current()->GetHeap();
  heap->VisitObjects(CopyAndFixupObjectsCallback, this);
  // Fix up the object previously had hash codes.
  for (const auto& hash_pair : saved_hashcode_map_) {
    Object* obj = hash_pair.first;
    DCHECK_EQ(obj->GetLockWord<kVerifyNone>(false).ReadBarrierState(), 0U);
    obj->SetLockWord<kVerifyNone>(LockWord::FromHashCode(hash_pair.second, 0U), false);
  }
  saved_hashcode_map_.clear();
}

void ImageWriter::CopyAndFixupObjectsCallback(Object* obj, void* arg) {
  DCHECK(obj != nullptr);
  DCHECK(arg != nullptr);
  reinterpret_cast<ImageWriter*>(arg)->CopyAndFixupObject(obj);
}

void ImageWriter::FixupPointerArray(mirror::Object* dst, mirror::PointerArray* arr,
                                    mirror::Class* klass, Bin array_type) {
  CHECK(klass->IsArrayClass());
  CHECK(arr->IsIntArray() || arr->IsLongArray()) << PrettyClass(klass) << " " << arr;
  // Fixup int and long pointers for the ArtMethod or ArtField arrays.
  const size_t num_elements = arr->GetLength();
  dst->SetClass(GetImageAddress(arr->GetClass()));
  auto* dest_array = down_cast<mirror::PointerArray*>(dst);
  for (size_t i = 0, count = num_elements; i < count; ++i) {
    auto* elem = arr->GetElementPtrSize<void*>(i, target_ptr_size_);
    if (elem != nullptr) {
      auto it = native_object_relocations_.find(elem);
      if (it == native_object_relocations_.end()) {
        if (it->second.IsArtMethodRelocation()) {
          auto* method = reinterpret_cast<ArtMethod*>(elem);
          LOG(FATAL) << "No relocation entry for ArtMethod " << PrettyMethod(method) << " @ "
              << method << " idx=" << i << "/" << num_elements << " with declaring class "
              << PrettyClass(method->GetDeclaringClass());
        } else {
          CHECK_EQ(array_type, kBinArtField);
          auto* field = reinterpret_cast<ArtField*>(elem);
          LOG(FATAL) << "No relocation entry for ArtField " << PrettyField(field) << " @ "
              << field << " idx=" << i << "/" << num_elements << " with declaring class "
              << PrettyClass(field->GetDeclaringClass());
        }
      } else {
        elem = image_begin_ + it->second.offset;
      }
    }
    dest_array->SetElementPtrSize<false, true>(i, elem, target_ptr_size_);
  }
}

void ImageWriter::CopyAndFixupObject(Object* obj) {
  size_t offset = GetImageOffset(obj);
  auto* dst = reinterpret_cast<Object*>(image_->Begin() + offset);
  DCHECK_LT(offset, image_end_);
  const auto* src = reinterpret_cast<const uint8_t*>(obj);

  image_bitmap_->Set(dst);  // Mark the obj as live.

  const size_t n = obj->SizeOf();
  DCHECK_LE(offset + n, image_->Size());
  memcpy(dst, src, n);

  // Write in a hash code of objects which have inflated monitors or a hash code in their monitor
  // word.
  const auto it = saved_hashcode_map_.find(obj);
  dst->SetLockWord(it != saved_hashcode_map_.end() ?
      LockWord::FromHashCode(it->second, 0u) : LockWord::Default(), false);
  FixupObject(obj, dst);
}

// Rewrite all the references in the copied object to point to their image address equivalent
class FixupVisitor {
 public:
  FixupVisitor(ImageWriter* image_writer, Object* copy) : image_writer_(image_writer), copy_(copy) {
  }

  // Ignore class roots since we don't have a way to map them to the destination. These are handled
  // with other logic.
  void VisitRootIfNonNull(mirror::CompressedReference<mirror::Object>* root ATTRIBUTE_UNUSED)
      const {}
  void VisitRoot(mirror::CompressedReference<mirror::Object>* root ATTRIBUTE_UNUSED) const {}


  void operator()(Object* obj, MemberOffset offset, bool is_static ATTRIBUTE_UNUSED) const
      REQUIRES(Locks::mutator_lock_, Locks::heap_bitmap_lock_) {
    Object* ref = obj->GetFieldObject<Object, kVerifyNone>(offset);
    // Use SetFieldObjectWithoutWriteBarrier to avoid card marking since we are writing to the
    // image.
    copy_->SetFieldObjectWithoutWriteBarrier<false, true, kVerifyNone>(
        offset, image_writer_->GetImageAddress(ref));
  }

  // java.lang.ref.Reference visitor.
  void operator()(mirror::Class* klass ATTRIBUTE_UNUSED, mirror::Reference* ref) const
      SHARED_REQUIRES(Locks::mutator_lock_) REQUIRES(Locks::heap_bitmap_lock_) {
    copy_->SetFieldObjectWithoutWriteBarrier<false, true, kVerifyNone>(
        mirror::Reference::ReferentOffset(), image_writer_->GetImageAddress(ref->GetReferent()));
  }

 protected:
  ImageWriter* const image_writer_;
  mirror::Object* const copy_;
};

class FixupClassVisitor FINAL : public FixupVisitor {
 public:
  FixupClassVisitor(ImageWriter* image_writer, Object* copy) : FixupVisitor(image_writer, copy) {
  }

  void operator()(Object* obj, MemberOffset offset, bool is_static ATTRIBUTE_UNUSED) const
      REQUIRES(Locks::mutator_lock_, Locks::heap_bitmap_lock_) {
    DCHECK(obj->IsClass());
    FixupVisitor::operator()(obj, offset, /*is_static*/false);
  }

  void operator()(mirror::Class* klass ATTRIBUTE_UNUSED,
                  mirror::Reference* ref ATTRIBUTE_UNUSED) const
      SHARED_REQUIRES(Locks::mutator_lock_) REQUIRES(Locks::heap_bitmap_lock_) {
    LOG(FATAL) << "Reference not expected here.";
  }
};

void* ImageWriter::NativeLocationInImage(void* obj) {
  if (obj == nullptr) {
    return nullptr;
  }
  auto it = native_object_relocations_.find(obj);
  CHECK(it != native_object_relocations_.end()) << obj;
  const NativeObjectRelocation& relocation = it->second;
  return reinterpret_cast<void*>(image_begin_ + relocation.offset);
}

void ImageWriter::FixupClass(mirror::Class* orig, mirror::Class* copy) {
  // Update the field arrays.
  copy->SetSFieldsPtrUnchecked(reinterpret_cast<LengthPrefixedArray<ArtField>*>(
      NativeLocationInImage(orig->GetSFieldsPtr())));
  copy->SetIFieldsPtrUnchecked(reinterpret_cast<LengthPrefixedArray<ArtField>*>(
      NativeLocationInImage(orig->GetIFieldsPtr())));
  // Update direct and virtual method arrays.
  copy->SetDirectMethodsPtrUnchecked(reinterpret_cast<LengthPrefixedArray<ArtMethod>*>(
      NativeLocationInImage(orig->GetDirectMethodsPtr())));
  copy->SetVirtualMethodsPtr(reinterpret_cast<LengthPrefixedArray<ArtMethod>*>(
      NativeLocationInImage(orig->GetVirtualMethodsPtr())));
  // Fix up embedded tables.
  if (orig->ShouldHaveEmbeddedImtAndVTable()) {
    for (int32_t i = 0; i < orig->GetEmbeddedVTableLength(); ++i) {
      auto it = native_object_relocations_.find(orig->GetEmbeddedVTableEntry(i, target_ptr_size_));
      CHECK(it != native_object_relocations_.end()) << PrettyClass(orig);
      copy->SetEmbeddedVTableEntryUnchecked(
          i, reinterpret_cast<ArtMethod*>(image_begin_ + it->second.offset), target_ptr_size_);
    }
    for (size_t i = 0; i < mirror::Class::kImtSize; ++i) {
      auto it = native_object_relocations_.find(orig->GetEmbeddedImTableEntry(i, target_ptr_size_));
      CHECK(it != native_object_relocations_.end()) << PrettyClass(orig);
      copy->SetEmbeddedImTableEntry(
          i, reinterpret_cast<ArtMethod*>(image_begin_ + it->second.offset), target_ptr_size_);
    }
  }
  FixupClassVisitor visitor(this, copy);
  static_cast<mirror::Object*>(orig)->VisitReferences(visitor, visitor);
}

void ImageWriter::FixupObject(Object* orig, Object* copy) {
  DCHECK(orig != nullptr);
  DCHECK(copy != nullptr);
  if (kUseBakerOrBrooksReadBarrier) {
    orig->AssertReadBarrierPointer();
    if (kUseBrooksReadBarrier) {
      // Note the address 'copy' isn't the same as the image address of 'orig'.
      copy->SetReadBarrierPointer(GetImageAddress(orig));
      DCHECK_EQ(copy->GetReadBarrierPointer(), GetImageAddress(orig));
    }
  }
  auto* klass = orig->GetClass();
  if (klass->IsIntArrayClass() || klass->IsLongArrayClass()) {
    // Is this a native dex cache array?
    auto it = pointer_arrays_.find(down_cast<mirror::PointerArray*>(orig));
    if (it != pointer_arrays_.end()) {
      // Should only need to fixup every pointer array exactly once.
      FixupPointerArray(copy, down_cast<mirror::PointerArray*>(orig), klass, it->second);
      pointer_arrays_.erase(it);
      return;
    }
    CHECK(dex_cache_array_indexes_.find(orig) == dex_cache_array_indexes_.end())
        << "Should have been pointer array.";
  }
  if (orig->IsClass()) {
    FixupClass(orig->AsClass<kVerifyNone>(), down_cast<mirror::Class*>(copy));
  } else {
    if (klass == mirror::Method::StaticClass() || klass == mirror::Constructor::StaticClass()) {
      // Need to go update the ArtMethod.
      auto* dest = down_cast<mirror::AbstractMethod*>(copy);
      auto* src = down_cast<mirror::AbstractMethod*>(orig);
      ArtMethod* src_method = src->GetArtMethod();
      auto it = native_object_relocations_.find(src_method);
      CHECK(it != native_object_relocations_.end())
          << "Missing relocation for AbstractMethod.artMethod " << PrettyMethod(src_method);
      dest->SetArtMethod(
          reinterpret_cast<ArtMethod*>(image_begin_ + it->second.offset));
    } else if (!klass->IsArrayClass() && klass->IsSubClass(down_cast<mirror::Class*>(
        Thread::Current()->DecodeJObject(WellKnownClasses::java_lang_ClassLoader)))) {
      // If src is a ClassLoader, set the class table to null so that it gets recreated by the
      // ClassLoader.
      down_cast<mirror::ClassLoader*>(copy)->SetClassTable(nullptr);
    }
    FixupVisitor visitor(this, copy);
    orig->VisitReferences(visitor, visitor);
  }
}

const uint8_t* ImageWriter::GetQuickCode(ArtMethod* method, bool* quick_is_interpreted) {
  DCHECK(!method->IsResolutionMethod() && !method->IsImtConflictMethod() &&
         !method->IsImtUnimplementedMethod() && !method->IsAbstract()) << PrettyMethod(method);

  // Use original code if it exists. Otherwise, set the code pointer to the resolution
  // trampoline.

  // Quick entrypoint:
  uint32_t quick_oat_code_offset = PointerToLowMemUInt32(
      method->GetEntryPointFromQuickCompiledCodePtrSize(target_ptr_size_));
  const uint8_t* quick_code = GetOatAddress(quick_oat_code_offset);
  *quick_is_interpreted = false;
  if (quick_code != nullptr && (!method->IsStatic() || method->IsConstructor() ||
      method->GetDeclaringClass()->IsInitialized())) {
    // We have code for a non-static or initialized method, just use the code.
    DCHECK_GE(quick_code, oat_data_begin_);
  } else if (quick_code == nullptr && method->IsNative() &&
      (!method->IsStatic() || method->GetDeclaringClass()->IsInitialized())) {
    // Non-static or initialized native method missing compiled code, use generic JNI version.
    quick_code = GetOatAddress(quick_generic_jni_trampoline_offset_);
    DCHECK_GE(quick_code, oat_data_begin_);
  } else if (quick_code == nullptr && !method->IsNative()) {
    // We don't have code at all for a non-native method, use the interpreter.
    quick_code = GetOatAddress(quick_to_interpreter_bridge_offset_);
    *quick_is_interpreted = true;
    DCHECK_GE(quick_code, oat_data_begin_);
  } else {
    CHECK(!method->GetDeclaringClass()->IsInitialized());
    // We have code for a static method, but need to go through the resolution stub for class
    // initialization.
    quick_code = GetOatAddress(quick_resolution_trampoline_offset_);
    DCHECK_GE(quick_code, oat_data_begin_);
  }
  return quick_code;
}

const uint8_t* ImageWriter::GetQuickEntryPoint(ArtMethod* method) {
  // Calculate the quick entry point following the same logic as FixupMethod() below.
  // The resolution method has a special trampoline to call.
  Runtime* runtime = Runtime::Current();
  if (UNLIKELY(method == runtime->GetResolutionMethod())) {
    return GetOatAddress(quick_resolution_trampoline_offset_);
  } else if (UNLIKELY(method == runtime->GetImtConflictMethod() ||
                      method == runtime->GetImtUnimplementedMethod())) {
    return GetOatAddress(quick_imt_conflict_trampoline_offset_);
  } else {
    // We assume all methods have code. If they don't currently then we set them to the use the
    // resolution trampoline. Abstract methods never have code and so we need to make sure their
    // use results in an AbstractMethodError. We use the interpreter to achieve this.
    if (UNLIKELY(method->IsAbstract())) {
      return GetOatAddress(quick_to_interpreter_bridge_offset_);
    } else {
      bool quick_is_interpreted;
      return GetQuickCode(method, &quick_is_interpreted);
    }
  }
}

void ImageWriter::CopyAndFixupMethod(ArtMethod* orig, ArtMethod* copy) {
  memcpy(copy, orig, ArtMethod::Size(target_ptr_size_));

  copy->SetDeclaringClass(GetImageAddress(orig->GetDeclaringClassUnchecked()));
  copy->SetDexCacheResolvedMethods(GetImageAddress(orig->GetDexCacheResolvedMethods()));
  copy->SetDexCacheResolvedTypes(GetImageAddress(orig->GetDexCacheResolvedTypes()));

  // OatWriter replaces the code_ with an offset value. Here we re-adjust to a pointer relative to
  // oat_begin_

  // The resolution method has a special trampoline to call.
  Runtime* runtime = Runtime::Current();
  if (UNLIKELY(orig == runtime->GetResolutionMethod())) {
    copy->SetEntryPointFromQuickCompiledCodePtrSize(
        GetOatAddress(quick_resolution_trampoline_offset_), target_ptr_size_);
  } else if (UNLIKELY(orig == runtime->GetImtConflictMethod() ||
                      orig == runtime->GetImtUnimplementedMethod())) {
    copy->SetEntryPointFromQuickCompiledCodePtrSize(
        GetOatAddress(quick_imt_conflict_trampoline_offset_), target_ptr_size_);
  } else if (UNLIKELY(orig->IsRuntimeMethod())) {
    bool found_one = false;
    for (size_t i = 0; i < static_cast<size_t>(Runtime::kLastCalleeSaveType); ++i) {
      auto idx = static_cast<Runtime::CalleeSaveType>(i);
      if (runtime->HasCalleeSaveMethod(idx) && runtime->GetCalleeSaveMethod(idx) == orig) {
        found_one = true;
        break;
      }
    }
    CHECK(found_one) << "Expected to find callee save method but got " << PrettyMethod(orig);
    CHECK(copy->IsRuntimeMethod());
  } else {
    // We assume all methods have code. If they don't currently then we set them to the use the
    // resolution trampoline. Abstract methods never have code and so we need to make sure their
    // use results in an AbstractMethodError. We use the interpreter to achieve this.
    if (UNLIKELY(orig->IsAbstract())) {
      copy->SetEntryPointFromQuickCompiledCodePtrSize(
          GetOatAddress(quick_to_interpreter_bridge_offset_), target_ptr_size_);
    } else {
      bool quick_is_interpreted;
      const uint8_t* quick_code = GetQuickCode(orig, &quick_is_interpreted);
      copy->SetEntryPointFromQuickCompiledCodePtrSize(quick_code, target_ptr_size_);

      // JNI entrypoint:
      if (orig->IsNative()) {
        // The native method's pointer is set to a stub to lookup via dlsym.
        // Note this is not the code_ pointer, that is handled above.
        copy->SetEntryPointFromJniPtrSize(
            GetOatAddress(jni_dlsym_lookup_offset_), target_ptr_size_);
      }
    }
  }
}

static OatHeader* GetOatHeaderFromElf(ElfFile* elf) {
  uint64_t data_sec_offset;
  bool has_data_sec = elf->GetSectionOffsetAndSize(".rodata", &data_sec_offset, nullptr);
  if (!has_data_sec) {
    return nullptr;
  }
  return reinterpret_cast<OatHeader*>(elf->Begin() + data_sec_offset);
}

void ImageWriter::SetOatChecksumFromElfFile(File* elf_file) {
  std::string error_msg;
  std::unique_ptr<ElfFile> elf(ElfFile::Open(elf_file, PROT_READ|PROT_WRITE,
                                             MAP_SHARED, &error_msg));
  if (elf.get() == nullptr) {
    LOG(FATAL) << "Unable open oat file: " << error_msg;
    return;
  }
  OatHeader* oat_header = GetOatHeaderFromElf(elf.get());
  CHECK(oat_header != nullptr);
  CHECK(oat_header->IsValid());

  ImageHeader* image_header = reinterpret_cast<ImageHeader*>(image_->Begin());
  image_header->SetOatChecksum(oat_header->GetChecksum());
}

size_t ImageWriter::GetBinSizeSum(ImageWriter::Bin up_to) const {
  DCHECK_LE(up_to, kBinSize);
  return std::accumulate(&bin_slot_sizes_[0], &bin_slot_sizes_[up_to], /*init*/0);
}

ImageWriter::BinSlot::BinSlot(uint32_t lockword) : lockword_(lockword) {
  // These values may need to get updated if more bins are added to the enum Bin
  static_assert(kBinBits == 3, "wrong number of bin bits");
  static_assert(kBinShift == 27, "wrong number of shift");
  static_assert(sizeof(BinSlot) == sizeof(LockWord), "BinSlot/LockWord must have equal sizes");

  DCHECK_LT(GetBin(), kBinSize);
  DCHECK_ALIGNED(GetIndex(), kObjectAlignment);
}

ImageWriter::BinSlot::BinSlot(Bin bin, uint32_t index)
    : BinSlot(index | (static_cast<uint32_t>(bin) << kBinShift)) {
  DCHECK_EQ(index, GetIndex());
}

ImageWriter::Bin ImageWriter::BinSlot::GetBin() const {
  return static_cast<Bin>((lockword_ & kBinMask) >> kBinShift);
}

uint32_t ImageWriter::BinSlot::GetIndex() const {
  return lockword_ & ~kBinMask;
}

uint8_t* ImageWriter::GetOatFileBegin() const {
  DCHECK_GT(intern_table_bytes_, 0u);
  return image_begin_ + RoundUp(
      image_end_ + bin_slot_sizes_[kBinArtField] + bin_slot_sizes_[kBinArtMethodDirty] +
      bin_slot_sizes_[kBinArtMethodClean] + intern_table_bytes_, kPageSize);
}

ImageWriter::Bin ImageWriter::BinTypeForNativeRelocationType(NativeObjectRelocationType type) {
  switch (type) {
    case kNativeObjectRelocationTypeArtField:
    case kNativeObjectRelocationTypeArtFieldArray:
      return kBinArtField;
    case kNativeObjectRelocationTypeArtMethodClean:
    case kNativeObjectRelocationTypeArtMethodArrayClean:
      return kBinArtMethodClean;
    case kNativeObjectRelocationTypeArtMethodDirty:
    case kNativeObjectRelocationTypeArtMethodArrayDirty:
      return kBinArtMethodDirty;
  }
  UNREACHABLE();
}

}  // namespace art