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* 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <stdint.h>
#include "base/memory_tool.h"
#include <cstddef>
#include <memory>
#include <ostream>
#include <set>
#include <stack>
#include <string>
#include "art_method.h"
#include "base/bit_utils.h"
#include "base/dchecked_vector.h"
#include "base/enums.h"
#include "base/unix_file/fd_file.h"
#include "base/hash_map.h"
#include "base/hash_set.h"
#include "base/length_prefixed_array.h"
#include "base/macros.h"
#include "base/mem_map.h"
#include "base/os.h"
#include "base/safe_map.h"
#include "base/utils.h"
#include "class_table.h"
#include "gc/accounting/space_bitmap.h"
#include "image.h"
#include "intern_table.h"
#include "lock_word.h"
#include "mirror/dex_cache.h"
#include "oat_file.h"
#include "obj_ptr.h"
namespace art {
namespace gc {
namespace accounting {
template <size_t kAlignment> class SpaceBitmap;
using ContinuousSpaceBitmap = SpaceBitmap<kObjectAlignment>;
} // namespace accounting
namespace space {
class ImageSpace;
} // namespace space
} // namespace gc
namespace mirror {
class ClassLoader;
} // namespace mirror
class ClassLoaderVisitor;
class CompilerOptions;
template<class T> class Handle;
class ImTable;
class ImtConflictTable;
class TimingLogger;
namespace linker {
// Write a Space built during compilation for use during execution.
class ImageWriter final {
ImageWriter(const CompilerOptions& compiler_options,
uintptr_t image_begin,
ImageHeader::StorageMode image_storage_mode,
const std::vector<std::string>& oat_filenames,
const HashMap<const DexFile*, size_t>& dex_file_oat_index_map,
jobject class_loader,
const HashSet<std::string>* dirty_image_objects);
* Modifies the heap and collects information about objects and code so that
* they can be written to the boot or app image later.
* First, unneeded classes are removed from the managed heap. Next, we
* remove cached values and calculate necessary metadata for later in the
* process. Optionally some debugging information is collected and used to
* verify the state of the heap at this point. Next, metadata from earlier
* is used to calculate offsets of references to strings to speed up string
* interning when the image is loaded. Lastly, we allocate enough memory to
* fit all image data minus the bitmap and relocation sections.
* This function should only be called when all objects to be included in the
* image have been initialized and all native methods have been generated. In
* addition, no other thread should be modifying the heap.
bool PrepareImageAddressSpace(TimingLogger* timings);
bool IsImageAddressSpaceReady() const {
for (const ImageInfo& image_info : image_infos_) {
if (image_info.image_roots_address_ == 0u) {
return false;
return true;
ObjPtr<mirror::ClassLoader> GetAppClassLoader() const REQUIRES_SHARED(Locks::mutator_lock_);
template <typename T>
T* GetImageAddress(T* object) const REQUIRES_SHARED(Locks::mutator_lock_) {
if (object == nullptr || IsInBootImage(object)) {
return object;
} else {
size_t oat_index = GetOatIndex(object);
const ImageInfo& image_info = GetImageInfo(oat_index);
return reinterpret_cast<T*>(image_info.image_begin_ + GetImageOffset(object, oat_index));
ArtMethod* GetImageMethodAddress(ArtMethod* method) REQUIRES_SHARED(Locks::mutator_lock_);
const void* GetIntrinsicReferenceAddress(uint32_t intrinsic_data)
size_t GetOatFileOffset(size_t oat_index) const {
return GetImageInfo(oat_index).oat_offset_;
const uint8_t* GetOatFileBegin(size_t oat_index) const {
return GetImageInfo(oat_index).oat_file_begin_;
// If image_fd is not File::kInvalidFd, then we use that for the image file. Otherwise we open
// the names in image_filenames.
// If oat_fd is not File::kInvalidFd, then we use that for the oat file. Otherwise we open
// the names in oat_filenames.
bool Write(int image_fd,
const std::vector<std::string>& image_filenames,
size_t component_count)
uintptr_t GetOatDataBegin(size_t oat_index) {
return reinterpret_cast<uintptr_t>(GetImageInfo(oat_index).oat_data_begin_);
// Get the index of the oat file containing the dex file.
// This "oat_index" is used to retrieve information about the the memory layout
// of the oat file and its associated image file, needed for link-time patching
// of references to the image or across oat files.
size_t GetOatIndexForDexFile(const DexFile* dex_file) const;
// Get the index of the oat file containing the definition of the class.
size_t GetOatIndexForClass(ObjPtr<mirror::Class> klass) const
// Update the oat layout for the given oat file.
// This will make the oat_offset for the next oat file valid.
void UpdateOatFileLayout(size_t oat_index,
size_t oat_loaded_size,
size_t oat_data_offset,
size_t oat_data_size);
// Update information about the oat header, i.e. checksum and trampoline offsets.
void UpdateOatFileHeader(size_t oat_index, const OatHeader& oat_header);
bool AllocMemory();
// Mark the objects defined in this space in the given live bitmap.
void RecordImageAllocations() REQUIRES_SHARED(Locks::mutator_lock_);
// Classify different kinds of bins that objects end up getting packed into during image writing.
// Ordered from dirtiest to cleanest (until ArtMethods).
enum class Bin {
kKnownDirty, // Known dirty objects from --dirty-image-objects list
kMiscDirty, // Dex caches, object locks, etc...
kClassVerified, // Class verified, but initializers haven't been run
// Unknown mix of clean/dirty:
kClassInitialized, // Class initializers have been run
// All classes get their own bins since their fields often dirty
kClassInitializedFinalStatics, // Class initializers have been run, no non-final statics
// Likely-clean:
kString, // [String] Almost always immutable (except for obj header).
// Definitely clean:
kMethodPointerArray, // ART internal vtables and interface method tables, int[]/long[].
// Add more bins here if we add more segregation code.
// Non mirror fields must be below.
// ArtFields should be always clean.
// If the class is initialized, then the ArtMethods are probably clean.
// ArtMethods may be dirty if the class has native methods or a declaring class that isn't
// initialized.
// IMT (clean)
// Conflict tables (clean).
// Runtime methods (always clean, do not have a length prefix array).
// Metadata bin for data that is temporary during image lifetime.
kLast = kMetadata,
// Number of bins which are for mirror objects.
kMirrorCount = kArtField,
friend std::ostream& operator<<(std::ostream& stream, Bin bin);
enum class NativeObjectRelocationType {
friend std::ostream& operator<<(std::ostream& stream, NativeObjectRelocationType type);
enum class StubType {
kLast = kNterpTrampoline,
friend std::ostream& operator<<(std::ostream& stream, StubType stub_type);
static constexpr size_t kBinBits =
MinimumBitsToStore<uint32_t>(static_cast<size_t>(Bin::kMirrorCount) - 1);
// uint32 = typeof(lockword_)
// Subtract read barrier bits since we want these to remain 0, or else it may result in DCHECK
// failures due to invalid read barrier bits during object field reads.
static const size_t kBinShift = BitSizeOf<uint32_t>() - kBinBits - LockWord::kGCStateSize;
// 111000.....0
static const size_t kBinMask = ((static_cast<size_t>(1) << kBinBits) - 1) << kBinShift;
// Number of bins, including non-mirror bins.
static constexpr size_t kNumberOfBins = static_cast<size_t>(Bin::kLast) + 1u;
// Number of stub types.
static constexpr size_t kNumberOfStubTypes = static_cast<size_t>(StubType::kLast) + 1u;
// We use the lock word to store the bin # and bin index of the object in the image.
// The struct size must be exactly sizeof(LockWord), currently 32-bits, since this will end up
// stored in the lock word bit-for-bit when object forwarding addresses are being calculated.
struct BinSlot {
explicit BinSlot(uint32_t lockword);
BinSlot(Bin bin, uint32_t index);
// The bin an object belongs to, i.e. regular, class/verified, class/initialized, etc.
Bin GetBin() const;
// The offset in bytes from the beginning of the bin. Aligned to object size.
uint32_t GetOffset() const;
// Pack into a single uint32_t, for storing into a lock word.
uint32_t Uint32Value() const { return lockword_; }
// Comparison operator for map support
bool operator<(const BinSlot& other) const { return lockword_ < other.lockword_; }
// Must be the same size as LockWord, any larger and we would truncate the data.
uint32_t lockword_;
struct ImageInfo {
ImageInfo(ImageInfo&&) = default;
* Creates ImageSection objects that describe most of the sections of a
* boot or AppImage. The following sections are not included:
* - ImageHeader::kSectionImageBitmap
* In addition, the ImageHeader is not covered here.
* This function will return the total size of the covered sections as well
* as a vector containing the individual ImageSection objects.
std::pair<size_t, std::vector<ImageSection>> CreateImageSections() const;
size_t GetStubOffset(StubType stub_type) const {
DCHECK_LT(static_cast<size_t>(stub_type), kNumberOfStubTypes);
return stub_offsets_[static_cast<size_t>(stub_type)];
void SetStubOffset(StubType stub_type, size_t offset) {
DCHECK_LT(static_cast<size_t>(stub_type), kNumberOfStubTypes);
stub_offsets_[static_cast<size_t>(stub_type)] = offset;
size_t GetBinSlotOffset(Bin bin) const {
DCHECK_LT(static_cast<size_t>(bin), kNumberOfBins);
return bin_slot_offsets_[static_cast<size_t>(bin)];
void IncrementBinSlotSize(Bin bin, size_t size_to_add) {
DCHECK_LT(static_cast<size_t>(bin), kNumberOfBins);
bin_slot_sizes_[static_cast<size_t>(bin)] += size_to_add;
size_t GetBinSlotSize(Bin bin) const {
DCHECK_LT(static_cast<size_t>(bin), kNumberOfBins);
return bin_slot_sizes_[static_cast<size_t>(bin)];
void IncrementBinSlotCount(Bin bin, size_t count_to_add) {
DCHECK_LT(static_cast<size_t>(bin), kNumberOfBins);
bin_slot_count_[static_cast<size_t>(bin)] += count_to_add;
// Calculate the sum total of the bin slot sizes in [0, up_to). Defaults to all bins.
size_t GetBinSizeSum(Bin up_to) const;
MemMap image_; // Memory mapped for generating the image.
// Target begin of this image. Notes: It is not valid to write here, this is the address
// of the target image, not necessarily where image_ is mapped. The address is only valid
// after layouting (otherwise null).
uint8_t* image_begin_ = nullptr;
// Offset to the free space in image_, initially size of image header.
size_t image_end_ = RoundUp(sizeof(ImageHeader), kObjectAlignment);
uint32_t image_roots_address_ = 0; // The image roots address in the image.
size_t image_offset_ = 0; // Offset of this image from the start of the first image.
// Image size is the *address space* covered by this image. As the live bitmap is aligned
// to the page size, the live bitmap will cover more address space than necessary. But live
// bitmaps may not overlap, so an image has a "shadow," which is accounted for in the size.
// The next image may only start at image_begin_ + image_size_ (which is guaranteed to be
// page-aligned).
size_t image_size_ = 0;
// Oat data.
// Offset of the oat file for this image from start of oat files. This is
// valid when the previous oat file has been written.
size_t oat_offset_ = 0;
// Layout of the loaded ELF file containing the oat file, valid after UpdateOatFileLayout().
const uint8_t* oat_file_begin_ = nullptr;
size_t oat_loaded_size_ = 0;
const uint8_t* oat_data_begin_ = nullptr;
size_t oat_size_ = 0; // Size of the corresponding oat data.
// The oat header checksum, valid after UpdateOatFileHeader().
uint32_t oat_checksum_ = 0u;
// Image bitmap which lets us know where the objects inside of the image reside.
gc::accounting::ContinuousSpaceBitmap image_bitmap_;
// The start offsets of the dex cache arrays.
SafeMap<const DexFile*, size_t> dex_cache_array_starts_;
// Offset from oat_data_begin_ to the stubs.
uint32_t stub_offsets_[kNumberOfStubTypes] = {};
// Bin slot tracking for dirty object packing.
size_t bin_slot_sizes_[kNumberOfBins] = {}; // Number of bytes in a bin.
size_t bin_slot_offsets_[kNumberOfBins] = {}; // Number of bytes in previous bins.
size_t bin_slot_count_[kNumberOfBins] = {}; // Number of objects in a bin.
// Cached size of the intern table for when we allocate memory.
size_t intern_table_bytes_ = 0;
// Number of image class table bytes.
size_t class_table_bytes_ = 0;
// Number of object fixup bytes.
size_t object_fixup_bytes_ = 0;
// Number of pointer fixup bytes.
size_t pointer_fixup_bytes_ = 0;
// Number of offsets to string references that will be written to the
// StringFieldOffsets section.
size_t num_string_references_ = 0;
// Offsets into the image that indicate where string references are recorded.
std::vector<AppImageReferenceOffsetInfo> string_reference_offsets_;
// Intern table associated with this image for serialization.
size_t intern_table_size_ = 0;
std::unique_ptr<GcRoot<mirror::String>[]> intern_table_buffer_;
std::optional<InternTable::UnorderedSet> intern_table_;
// Class table associated with this image for serialization.
size_t class_table_size_ = 0;
std::unique_ptr<ClassTable::ClassSet::value_type[]> class_table_buffer_;
std::optional<ClassTable::ClassSet> class_table_;
// Padding offsets to ensure region alignment (if required).
// Objects need to be added from the recorded offset until the end of the region.
std::vector<size_t> padding_offsets_;
// We use the lock word to store the offset of the object in the image.
size_t GetImageOffset(mirror::Object* object, size_t oat_index) const
Bin AssignImageBinSlot(mirror::Object* object, size_t oat_index)
void AssignImageBinSlot(mirror::Object* object, size_t oat_index, Bin bin)
void RecordNativeRelocations(ObjPtr<mirror::Class> klass, size_t oat_index)
void SetImageBinSlot(mirror::Object* object, BinSlot bin_slot)
bool IsImageBinSlotAssigned(mirror::Object* object) const
BinSlot GetImageBinSlot(mirror::Object* object, size_t oat_index) const
void UpdateImageBinSlotOffset(mirror::Object* object, size_t oat_index, size_t new_offset)
// Returns the address in the boot image if we are compiling the app image.
const uint8_t* GetOatAddress(StubType type) const;
const uint8_t* GetOatAddressForOffset(uint32_t offset, const ImageInfo& image_info) const {
// With Quick, code is within the OatFile, as there are all in one
// .o ELF object. But interpret it as signed.
DCHECK_LE(static_cast<int32_t>(offset), static_cast<int32_t>(image_info.oat_size_));
DCHECK(image_info.oat_data_begin_ != nullptr);
return offset == 0u ? nullptr : image_info.oat_data_begin_ + static_cast<int32_t>(offset);
// Returns true if the class was in the original requested image classes list.
bool KeepClass(ObjPtr<mirror::Class> klass) REQUIRES_SHARED(Locks::mutator_lock_);
// Debug aid that list of requested image classes.
void DumpImageClasses();
// Visit all class loaders.
void VisitClassLoaders(ClassLoaderVisitor* visitor) REQUIRES_SHARED(Locks::mutator_lock_);
// Remove unwanted classes from various roots.
void PruneNonImageClasses() REQUIRES_SHARED(Locks::mutator_lock_);
// Find dex caches for pruning or preloading.
std::vector<ObjPtr<mirror::DexCache>> FindDexCaches(Thread* self)
// Verify unwanted classes removed.
void CheckNonImageClassesRemoved() REQUIRES_SHARED(Locks::mutator_lock_);
// Lays out where the image objects will be at runtime.
void CalculateNewObjectOffsets()
void CreateHeader(size_t oat_index, size_t component_count)
ObjPtr<mirror::ObjectArray<mirror::Object>> CollectDexCaches(Thread* self, size_t oat_index) const
ObjPtr<mirror::ObjectArray<mirror::Object>> CreateImageRoots(
size_t oat_index,
Handle<mirror::ObjectArray<mirror::Object>> boot_image_live_objects) const
void CalculateObjectBinSlots(mirror::Object* obj)
// Creates the contiguous image in memory and adjusts pointers.
void CopyAndFixupNativeData(size_t oat_index) REQUIRES_SHARED(Locks::mutator_lock_);
void CopyAndFixupObjects() REQUIRES_SHARED(Locks::mutator_lock_);
void CopyAndFixupObject(mirror::Object* obj) REQUIRES_SHARED(Locks::mutator_lock_);
template <bool kCheckIfDone>
mirror::Object* CopyObject(mirror::Object* obj) REQUIRES_SHARED(Locks::mutator_lock_);
void CopyAndFixupMethodPointerArray(mirror::PointerArray* arr)
void CopyAndFixupMethod(ArtMethod* orig, ArtMethod* copy, size_t oat_index)
void CopyAndFixupImTable(ImTable* orig, ImTable* copy)
void CopyAndFixupImtConflictTable(ImtConflictTable* orig, ImtConflictTable* copy)
* Copies metadata from the heap into a buffer that will be compressed and
* written to the image.
* This function copies the string offset metadata from a local vector to an
* offset inside the image_ field of an ImageInfo struct. The offset into the
* memory pointed to by the image_ field is obtained from the ImageSection
* object for the String Offsets section.
* All data for the image, besides the object bitmap and the relocation data,
* will also be copied into the memory region pointed to by image_.
void CopyMetadata();
void FixupClass(mirror::Class* orig, mirror::Class* copy)
void FixupObject(mirror::Object* orig, mirror::Object* copy)
// Get quick code for non-resolution/imt_conflict/abstract method.
const uint8_t* GetQuickCode(ArtMethod* method, const ImageInfo& image_info)
// Return true if a method is likely to be dirtied at runtime.
bool WillMethodBeDirty(ArtMethod* m) const REQUIRES_SHARED(Locks::mutator_lock_);
// Assign the offset for an ArtMethod.
void AssignMethodOffset(ArtMethod* method,
NativeObjectRelocationType type,
size_t oat_index)
// Return true if imt was newly inserted.
bool TryAssignImTableOffset(ImTable* imt, size_t oat_index) REQUIRES_SHARED(Locks::mutator_lock_);
// Assign the offset for an IMT conflict table. Does nothing if the table already has a native
// relocation.
void TryAssignConflictTableOffset(ImtConflictTable* table, size_t oat_index)
// Return true if klass is loaded by the boot class loader but not in the boot image.
bool IsBootClassLoaderNonImageClass(mirror::Class* klass) REQUIRES_SHARED(Locks::mutator_lock_);
// Return true if `klass` depends on a class defined by the boot class path
// we're compiling against but not present in the boot image spaces. We want
// to prune these classes since we cannot guarantee that they will not be
// already loaded at run time when loading this image. This means that we
// also cannot have any classes which refer to these non image classes.
bool PruneImageClass(ObjPtr<mirror::Class> klass) REQUIRES_SHARED(Locks::mutator_lock_);
// early_exit is true if we had a cyclic dependency anywhere down the chain.
bool PruneImageClassInternal(ObjPtr<mirror::Class> klass,
bool* early_exit,
HashSet<mirror::Object*>* visited)
bool IsMultiImage() const {
return image_infos_.size() > 1;
static Bin BinTypeForNativeRelocationType(NativeObjectRelocationType type);
struct NativeObjectRelocation {
size_t oat_index;
uintptr_t offset;
NativeObjectRelocationType type;
bool IsArtMethodRelocation() const {
return type == NativeObjectRelocationType::kArtMethodClean ||
type == NativeObjectRelocationType::kArtMethodDirty ||
type == NativeObjectRelocationType::kRuntimeMethod;
NativeObjectRelocation GetNativeRelocation(void* obj) REQUIRES_SHARED(Locks::mutator_lock_);
// Location of where the object will be when the image is loaded at runtime.
template <typename T>
T* NativeLocationInImage(T* obj) REQUIRES_SHARED(Locks::mutator_lock_);
ArtField* NativeLocationInImage(ArtField* src_field) REQUIRES_SHARED(Locks::mutator_lock_);
// Return true if `dex_cache` belongs to the image we're writing.
// For a boot image, this is true for all dex caches.
// For an app image, boot class path dex caches are excluded.
bool IsImageDexCache(ObjPtr<mirror::DexCache> dex_cache) const
// Return true if `obj` is inside of a boot image space that we're compiling against.
// (Always false when compiling the boot image.)
ALWAYS_INLINE bool IsInBootImage(const void* obj) const {
return reinterpret_cast<uintptr_t>(obj) - boot_image_begin_ < boot_image_size_;
// Get the index of the oat file associated with the object.
size_t GetOatIndex(mirror::Object* object) const REQUIRES_SHARED(Locks::mutator_lock_);
// The oat index for shared data in multi-image and all data in single-image compilation.
static constexpr size_t GetDefaultOatIndex() {
return 0u;
ImageInfo& GetImageInfo(size_t oat_index) {
return image_infos_[oat_index];
const ImageInfo& GetImageInfo(size_t oat_index) const {
return image_infos_[oat_index];
// Return true if there already exists a native allocation for an object.
bool NativeRelocationAssigned(void* ptr) const;
// Copy a reference and record image relocation.
template <typename DestType>
void CopyAndFixupReference(DestType* dest, ObjPtr<mirror::Object> src)
// Translate a native pointer to the destination value and store in the target location.
template <typename ValueType>
void CopyAndFixupPointer(void** target, ValueType src_value, PointerSize pointer_size)
template <typename ValueType>
void CopyAndFixupPointer(void** target, ValueType src_value)
template <typename ValueType>
void CopyAndFixupPointer(
void* object, MemberOffset offset, ValueType src_value, PointerSize pointer_size)
template <typename ValueType>
void CopyAndFixupPointer(void* object, MemberOffset offset, ValueType src_value)
* Tests an object to see if it will be contained in an AppImage.
* An object reference is considered to be a AppImage String reference iff:
* - It isn't null
* - The referred-object isn't in the boot image
* - The referred-object is a Java String
bool IsInternedAppImageStringReference(ObjPtr<mirror::Object> referred_obj) const
const CompilerOptions& compiler_options_;
// Cached boot image begin and size. This includes heap, native objects and oat files.
const uint32_t boot_image_begin_;
const uint32_t boot_image_size_;
// Beginning target image address for the first image.
uint8_t* global_image_begin_;
// Offset from image_begin_ to where the first object is in image_.
size_t image_objects_offset_begin_;
// Saved hash codes. We use these to restore lockwords which were temporarily used to have
// forwarding addresses as well as copying over hash codes.
HashMap<mirror::Object*, uint32_t> saved_hashcode_map_;
// Oat index map for objects.
HashMap<mirror::Object*, uint32_t> oat_index_map_;
// Size of pointers on the target architecture.
PointerSize target_ptr_size_;
// Image data indexed by the oat file index.
dchecked_vector<ImageInfo> image_infos_;
// ArtField, ArtMethod relocating map. These are allocated as array of structs but we want to
// have one entry per art field for convenience. ArtFields are placed right after the end of the
// image objects (aka sum of bin_slot_sizes_). ArtMethods are placed right after the ArtFields.
HashMap<void*, NativeObjectRelocation> native_object_relocations_;
// Runtime ArtMethods which aren't reachable from any Class but need to be copied into the image.
ArtMethod* image_methods_[ImageHeader::kImageMethodsCount];
// Counters for measurements, used for logging only.
uint64_t dirty_methods_;
uint64_t clean_methods_;
// Prune class memoization table to speed up ContainsBootClassLoaderNonImageClass.
HashMap<mirror::Class*, bool> prune_class_memo_;
// The application class loader. Null for boot image.
jobject app_class_loader_;
// Boot image live objects, null for app image.
mirror::ObjectArray<mirror::Object>* boot_image_live_objects_;
// Which mode the image is stored as, see image.h
const ImageHeader::StorageMode image_storage_mode_;
// The file names of oat files.
const std::vector<std::string>& oat_filenames_;
// Map of dex files to the indexes of oat files that they were compiled into.
const HashMap<const DexFile*, size_t>& dex_file_oat_index_map_;
// Set of objects known to be dirty in the image. Can be nullptr if there are none.
const HashSet<std::string>* dirty_image_objects_;
// Objects are guaranteed to not cross the region size boundary.
size_t region_size_ = 0u;
// Region alignment bytes wasted.
size_t region_alignment_wasted_ = 0u;
class FixupClassVisitor;
class FixupRootVisitor;
class FixupVisitor;
class ImageFileGuard;
class LayoutHelper;
class NativeLocationVisitor;
class PruneClassesVisitor;
class PruneClassLoaderClassesVisitor;
class PruneObjectReferenceVisitor;
// A visitor used by the VerifyNativeGCRootInvariants() function.
class NativeGCRootInvariantVisitor;
std::ostream& operator<<(std::ostream& stream, ImageWriter::Bin bin);
std::ostream& operator<<(std::ostream& stream, ImageWriter::NativeObjectRelocationType type);
std::ostream& operator<<(std::ostream& stream, ImageWriter::StubType stub_type);
} // namespace linker
} // namespace art