runtime/hprof/hprof.cc

/*
 * Copyright (C) 2008 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.
 */

/*
 * Preparation and completion of hprof data generation.  The output is
 * written into two files and then combined.  This is necessary because
 * we generate some of the data (strings and classes) while we dump the
 * heap, and some analysis tools require that the class and string data
 * appear first.
 */

#include "hprof.h"

#include <cutils/open_memstream.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <sys/time.h>
#include <sys/uio.h>
#include <time.h>
#include <time.h>
#include <unistd.h>

#include <set>

#include "art_field-inl.h"
#include "base/logging.h"
#include "base/stringprintf.h"
#include "base/time_utils.h"
#include "base/unix_file/fd_file.h"
#include "class_linker.h"
#include "common_throws.h"
#include "debugger.h"
#include "dex_file-inl.h"
#include "gc_root.h"
#include "gc/accounting/heap_bitmap.h"
#include "gc/allocation_record.h"
#include "gc/heap.h"
#include "gc/space/space.h"
#include "globals.h"
#include "jdwp/jdwp.h"
#include "jdwp/jdwp_priv.h"
#include "mirror/class.h"
#include "mirror/class-inl.h"
#include "mirror/object-inl.h"
#include "os.h"
#include "safe_map.h"
#include "scoped_thread_state_change.h"
#include "thread_list.h"

namespace art {

namespace hprof {

static constexpr bool kDirectStream = true;

static constexpr uint32_t kHprofTime = 0;
static constexpr uint32_t kHprofNullThread = 0;

static constexpr size_t kMaxObjectsPerSegment = 128;
static constexpr size_t kMaxBytesPerSegment = 4096;

// The static field-name for the synthetic object generated to account for class static overhead.
static constexpr const char* kClassOverheadName = "$classOverhead";

enum HprofTag {
  HPROF_TAG_STRING = 0x01,
  HPROF_TAG_LOAD_CLASS = 0x02,
  HPROF_TAG_UNLOAD_CLASS = 0x03,
  HPROF_TAG_STACK_FRAME = 0x04,
  HPROF_TAG_STACK_TRACE = 0x05,
  HPROF_TAG_ALLOC_SITES = 0x06,
  HPROF_TAG_HEAP_SUMMARY = 0x07,
  HPROF_TAG_START_THREAD = 0x0A,
  HPROF_TAG_END_THREAD = 0x0B,
  HPROF_TAG_HEAP_DUMP = 0x0C,
  HPROF_TAG_HEAP_DUMP_SEGMENT = 0x1C,
  HPROF_TAG_HEAP_DUMP_END = 0x2C,
  HPROF_TAG_CPU_SAMPLES = 0x0D,
  HPROF_TAG_CONTROL_SETTINGS = 0x0E,
};

// Values for the first byte of HEAP_DUMP and HEAP_DUMP_SEGMENT records:
enum HprofHeapTag {
  // Traditional.
  HPROF_ROOT_UNKNOWN = 0xFF,
  HPROF_ROOT_JNI_GLOBAL = 0x01,
  HPROF_ROOT_JNI_LOCAL = 0x02,
  HPROF_ROOT_JAVA_FRAME = 0x03,
  HPROF_ROOT_NATIVE_STACK = 0x04,
  HPROF_ROOT_STICKY_CLASS = 0x05,
  HPROF_ROOT_THREAD_BLOCK = 0x06,
  HPROF_ROOT_MONITOR_USED = 0x07,
  HPROF_ROOT_THREAD_OBJECT = 0x08,
  HPROF_CLASS_DUMP = 0x20,
  HPROF_INSTANCE_DUMP = 0x21,
  HPROF_OBJECT_ARRAY_DUMP = 0x22,
  HPROF_PRIMITIVE_ARRAY_DUMP = 0x23,

  // Android.
  HPROF_HEAP_DUMP_INFO = 0xfe,
  HPROF_ROOT_INTERNED_STRING = 0x89,
  HPROF_ROOT_FINALIZING = 0x8a,  // Obsolete.
  HPROF_ROOT_DEBUGGER = 0x8b,
  HPROF_ROOT_REFERENCE_CLEANUP = 0x8c,  // Obsolete.
  HPROF_ROOT_VM_INTERNAL = 0x8d,
  HPROF_ROOT_JNI_MONITOR = 0x8e,
  HPROF_UNREACHABLE = 0x90,  // Obsolete.
  HPROF_PRIMITIVE_ARRAY_NODATA_DUMP = 0xc3,  // Obsolete.
};

enum HprofHeapId {
  HPROF_HEAP_DEFAULT = 0,
  HPROF_HEAP_ZYGOTE = 'Z',
  HPROF_HEAP_APP = 'A',
  HPROF_HEAP_IMAGE = 'I',
};

enum HprofBasicType {
  hprof_basic_object = 2,
  hprof_basic_boolean = 4,
  hprof_basic_char = 5,
  hprof_basic_float = 6,
  hprof_basic_double = 7,
  hprof_basic_byte = 8,
  hprof_basic_short = 9,
  hprof_basic_int = 10,
  hprof_basic_long = 11,
};

typedef uint32_t HprofStringId;
typedef uint32_t HprofClassObjectId;
typedef uint32_t HprofClassSerialNumber;
typedef uint32_t HprofStackTraceSerialNumber;
typedef uint32_t HprofStackFrameId;
static constexpr HprofStackTraceSerialNumber kHprofNullStackTrace = 0;

class EndianOutput {
 public:
  EndianOutput() : length_(0), sum_length_(0), max_length_(0), started_(false) {}
  virtual ~EndianOutput() {}

  void StartNewRecord(uint8_t tag, uint32_t time) {
    if (length_ > 0) {
      EndRecord();
    }
    DCHECK_EQ(length_, 0U);
    AddU1(tag);
    AddU4(time);
    AddU4(0xdeaddead);  // Length, replaced on flush.
    started_ = true;
  }

  void EndRecord() {
    // Replace length in header.
    if (started_) {
      UpdateU4(sizeof(uint8_t) + sizeof(uint32_t),
               length_ - sizeof(uint8_t) - 2 * sizeof(uint32_t));
    }

    HandleEndRecord();

    sum_length_ += length_;
    max_length_ = std::max(max_length_, length_);
    length_ = 0;
    started_ = false;
  }

  void AddU1(uint8_t value) {
    AddU1List(&value, 1);
  }
  void AddU2(uint16_t value) {
    AddU2List(&value, 1);
  }
  void AddU4(uint32_t value) {
    AddU4List(&value, 1);
  }

  void AddU8(uint64_t value) {
    AddU8List(&value, 1);
  }

  void AddObjectId(const mirror::Object* value) {
    AddU4(PointerToLowMemUInt32(value));
  }

  void AddStackTraceSerialNumber(HprofStackTraceSerialNumber value) {
    AddU4(value);
  }

  // The ID for the synthetic object generated to account for class static overhead.
  void AddClassStaticsId(const mirror::Class* value) {
    AddU4(1 | PointerToLowMemUInt32(value));
  }

  void AddJniGlobalRefId(jobject value) {
    AddU4(PointerToLowMemUInt32(value));
  }

  void AddClassId(HprofClassObjectId value) {
    AddU4(value);
  }

  void AddStringId(HprofStringId value) {
    AddU4(value);
  }

  void AddU1List(const uint8_t* values, size_t count) {
    HandleU1List(values, count);
    length_ += count;
  }
  void AddU2List(const uint16_t* values, size_t count) {
    HandleU2List(values, count);
    length_ += count * sizeof(uint16_t);
  }
  void AddU4List(const uint32_t* values, size_t count) {
    HandleU4List(values, count);
    length_ += count * sizeof(uint32_t);
  }
  virtual void UpdateU4(size_t offset, uint32_t new_value ATTRIBUTE_UNUSED) {
    DCHECK_LE(offset, length_ - 4);
  }
  void AddU8List(const uint64_t* values, size_t count) {
    HandleU8List(values, count);
    length_ += count * sizeof(uint64_t);
  }

  void AddIdList(mirror::ObjectArray<mirror::Object>* values)
      SHARED_REQUIRES(Locks::mutator_lock_) {
    const int32_t length = values->GetLength();
    for (int32_t i = 0; i < length; ++i) {
      AddObjectId(values->GetWithoutChecks(i));
    }
  }

  void AddUtf8String(const char* str) {
    // The terminating NUL character is NOT written.
    AddU1List((const uint8_t*)str, strlen(str));
  }

  size_t Length() const {
    return length_;
  }

  size_t SumLength() const {
    return sum_length_;
  }

  size_t MaxLength() const {
    return max_length_;
  }

 protected:
  virtual void HandleU1List(const uint8_t* values ATTRIBUTE_UNUSED,
                            size_t count ATTRIBUTE_UNUSED) {
  }
  virtual void HandleU2List(const uint16_t* values ATTRIBUTE_UNUSED,
                            size_t count ATTRIBUTE_UNUSED) {
  }
  virtual void HandleU4List(const uint32_t* values ATTRIBUTE_UNUSED,
                            size_t count ATTRIBUTE_UNUSED) {
  }
  virtual void HandleU8List(const uint64_t* values ATTRIBUTE_UNUSED,
                            size_t count ATTRIBUTE_UNUSED) {
  }
  virtual void HandleEndRecord() {
  }

  size_t length_;      // Current record size.
  size_t sum_length_;  // Size of all data.
  size_t max_length_;  // Maximum seen length.
  bool started_;       // Was StartRecord called?
};

// This keeps things buffered until flushed.
class EndianOutputBuffered : public EndianOutput {
 public:
  explicit EndianOutputBuffered(size_t reserve_size) {
    buffer_.reserve(reserve_size);
  }
  virtual ~EndianOutputBuffered() {}

  void UpdateU4(size_t offset, uint32_t new_value) OVERRIDE {
    DCHECK_LE(offset, length_ - 4);
    buffer_[offset + 0] = static_cast<uint8_t>((new_value >> 24) & 0xFF);
    buffer_[offset + 1] = static_cast<uint8_t>((new_value >> 16) & 0xFF);
    buffer_[offset + 2] = static_cast<uint8_t>((new_value >> 8)  & 0xFF);
    buffer_[offset + 3] = static_cast<uint8_t>((new_value >> 0)  & 0xFF);
  }

 protected:
  void HandleU1List(const uint8_t* values, size_t count) OVERRIDE {
    DCHECK_EQ(length_, buffer_.size());
    buffer_.insert(buffer_.end(), values, values + count);
  }

  void HandleU2List(const uint16_t* values, size_t count) OVERRIDE {
    DCHECK_EQ(length_, buffer_.size());
    for (size_t i = 0; i < count; ++i) {
      uint16_t value = *values;
      buffer_.push_back(static_cast<uint8_t>((value >> 8) & 0xFF));
      buffer_.push_back(static_cast<uint8_t>((value >> 0) & 0xFF));
      values++;
    }
  }

  void HandleU4List(const uint32_t* values, size_t count) OVERRIDE {
    DCHECK_EQ(length_, buffer_.size());
    for (size_t i = 0; i < count; ++i) {
      uint32_t value = *values;
      buffer_.push_back(static_cast<uint8_t>((value >> 24) & 0xFF));
      buffer_.push_back(static_cast<uint8_t>((value >> 16) & 0xFF));
      buffer_.push_back(static_cast<uint8_t>((value >> 8)  & 0xFF));
      buffer_.push_back(static_cast<uint8_t>((value >> 0)  & 0xFF));
      values++;
    }
  }

  void HandleU8List(const uint64_t* values, size_t count) OVERRIDE {
    DCHECK_EQ(length_, buffer_.size());
    for (size_t i = 0; i < count; ++i) {
      uint64_t value = *values;
      buffer_.push_back(static_cast<uint8_t>((value >> 56) & 0xFF));
      buffer_.push_back(static_cast<uint8_t>((value >> 48) & 0xFF));
      buffer_.push_back(static_cast<uint8_t>((value >> 40) & 0xFF));
      buffer_.push_back(static_cast<uint8_t>((value >> 32) & 0xFF));
      buffer_.push_back(static_cast<uint8_t>((value >> 24) & 0xFF));
      buffer_.push_back(static_cast<uint8_t>((value >> 16) & 0xFF));
      buffer_.push_back(static_cast<uint8_t>((value >> 8)  & 0xFF));
      buffer_.push_back(static_cast<uint8_t>((value >> 0)  & 0xFF));
      values++;
    }
  }

  void HandleEndRecord() OVERRIDE {
    DCHECK_EQ(buffer_.size(), length_);
    if (kIsDebugBuild && started_) {
      uint32_t stored_length =
          static_cast<uint32_t>(buffer_[5]) << 24 |
          static_cast<uint32_t>(buffer_[6]) << 16 |
          static_cast<uint32_t>(buffer_[7]) << 8 |
          static_cast<uint32_t>(buffer_[8]);
      DCHECK_EQ(stored_length, length_ - sizeof(uint8_t) - 2 * sizeof(uint32_t));
    }
    HandleFlush(buffer_.data(), length_);
    buffer_.clear();
  }

  virtual void HandleFlush(const uint8_t* buffer ATTRIBUTE_UNUSED, size_t length ATTRIBUTE_UNUSED) {
  }

  std::vector<uint8_t> buffer_;
};

class FileEndianOutput FINAL : public EndianOutputBuffered {
 public:
  FileEndianOutput(File* fp, size_t reserved_size)
      : EndianOutputBuffered(reserved_size), fp_(fp), errors_(false) {
    DCHECK(fp != nullptr);
  }
  ~FileEndianOutput() {
  }

  bool Errors() {
    return errors_;
  }

 protected:
  void HandleFlush(const uint8_t* buffer, size_t length) OVERRIDE {
    if (!errors_) {
      errors_ = !fp_->WriteFully(buffer, length);
    }
  }

 private:
  File* fp_;
  bool errors_;
};

class NetStateEndianOutput FINAL : public EndianOutputBuffered {
 public:
  NetStateEndianOutput(JDWP::JdwpNetStateBase* net_state, size_t reserved_size)
      : EndianOutputBuffered(reserved_size), net_state_(net_state) {
    DCHECK(net_state != nullptr);
  }
  ~NetStateEndianOutput() {}

 protected:
  void HandleFlush(const uint8_t* buffer, size_t length) OVERRIDE {
    std::vector<iovec> iov;
    iov.push_back(iovec());
    iov[0].iov_base = const_cast<void*>(reinterpret_cast<const void*>(buffer));
    iov[0].iov_len = length;
    net_state_->WriteBufferedPacketLocked(iov);
  }

 private:
  JDWP::JdwpNetStateBase* net_state_;
};

#define __ output_->

class Hprof : public SingleRootVisitor {
 public:
  Hprof(const char* output_filename, int fd, bool direct_to_ddms)
      : filename_(output_filename),
        fd_(fd),
        direct_to_ddms_(direct_to_ddms) {
    LOG(INFO) << "hprof: heap dump \"" << filename_ << "\" starting...";
  }

  void Dump()
    REQUIRES(Locks::mutator_lock_)
    REQUIRES(!Locks::heap_bitmap_lock_, !Locks::alloc_tracker_lock_) {
    {
      MutexLock mu(Thread::Current(), *Locks::alloc_tracker_lock_);
      if (Runtime::Current()->GetHeap()->IsAllocTrackingEnabled()) {
        PopulateAllocationTrackingTraces();
      }
    }

    // First pass to measure the size of the dump.
    size_t overall_size;
    size_t max_length;
    {
      EndianOutput count_output;
      output_ = &count_output;
      ProcessHeap(false);
      overall_size = count_output.SumLength();
      max_length = count_output.MaxLength();
      output_ = nullptr;
    }

    bool okay;
    if (direct_to_ddms_) {
      if (kDirectStream) {
        okay = DumpToDdmsDirect(overall_size, max_length, CHUNK_TYPE("HPDS"));
      } else {
        okay = DumpToDdmsBuffered(overall_size, max_length);
      }
    } else {
      okay = DumpToFile(overall_size, max_length);
    }

    if (okay) {
      const uint64_t duration = NanoTime() - start_ns_;
      LOG(INFO) << "hprof: heap dump completed (" << PrettySize(RoundUp(overall_size, KB))
                << ") in " << PrettyDuration(duration)
                << " objects " << total_objects_
                << " objects with stack traces " << total_objects_with_stack_trace_;
    }
  }

 private:
  static void VisitObjectCallback(mirror::Object* obj, void* arg)
      SHARED_REQUIRES(Locks::mutator_lock_) {
    DCHECK(obj != nullptr);
    DCHECK(arg != nullptr);
    reinterpret_cast<Hprof*>(arg)->DumpHeapObject(obj);
  }

  void DumpHeapObject(mirror::Object* obj)
      SHARED_REQUIRES(Locks::mutator_lock_);

  void DumpHeapClass(mirror::Class* klass)
      SHARED_REQUIRES(Locks::mutator_lock_);

  void DumpHeapArray(mirror::Array* obj, mirror::Class* klass)
      SHARED_REQUIRES(Locks::mutator_lock_);

  void DumpHeapInstanceObject(mirror::Object* obj, mirror::Class* klass)
      SHARED_REQUIRES(Locks::mutator_lock_);

  void ProcessHeap(bool header_first)
      REQUIRES(Locks::mutator_lock_) {
    // Reset current heap and object count.
    current_heap_ = HPROF_HEAP_DEFAULT;
    objects_in_segment_ = 0;

    if (header_first) {
      ProcessHeader(true);
      ProcessBody();
    } else {
      ProcessBody();
      ProcessHeader(false);
    }
  }

  void ProcessBody() REQUIRES(Locks::mutator_lock_) {
    Runtime* const runtime = Runtime::Current();
    // Walk the roots and the heap.
    output_->StartNewRecord(HPROF_TAG_HEAP_DUMP_SEGMENT, kHprofTime);

    runtime->VisitRoots(this);
    runtime->VisitImageRoots(this);
    runtime->GetHeap()->VisitObjectsPaused(VisitObjectCallback, this);

    output_->StartNewRecord(HPROF_TAG_HEAP_DUMP_END, kHprofTime);
    output_->EndRecord();
  }

  void ProcessHeader(bool string_first) REQUIRES(Locks::mutator_lock_) {
    // Write the header.
    WriteFixedHeader();
    // Write the string and class tables, and any stack traces, to the header.
    // (jhat requires that these appear before any of the data in the body that refers to them.)
    // jhat also requires the string table appear before class table and stack traces.
    // However, WriteStackTraces() can modify the string table, so it's necessary to call
    // WriteStringTable() last in the first pass, to compute the correct length of the output.
    if (string_first) {
      WriteStringTable();
    }
    WriteClassTable();
    WriteStackTraces();
    if (!string_first) {
      WriteStringTable();
    }
    output_->EndRecord();
  }

  void WriteClassTable() SHARED_REQUIRES(Locks::mutator_lock_) {
    for (const auto& p : classes_) {
      mirror::Class* c = p.first;
      HprofClassSerialNumber sn = p.second;
      CHECK(c != nullptr);
      output_->StartNewRecord(HPROF_TAG_LOAD_CLASS, kHprofTime);
      // LOAD CLASS format:
      // U4: class serial number (always > 0)
      // ID: class object ID. We use the address of the class object structure as its ID.
      // U4: stack trace serial number
      // ID: class name string ID
      __ AddU4(sn);
      __ AddObjectId(c);
      __ AddStackTraceSerialNumber(LookupStackTraceSerialNumber(c));
      __ AddStringId(LookupClassNameId(c));
    }
  }

  void WriteStringTable() {
    for (const std::pair<std::string, HprofStringId>& p : strings_) {
      const std::string& string = p.first;
      const size_t id = p.second;

      output_->StartNewRecord(HPROF_TAG_STRING, kHprofTime);

      // STRING format:
      // ID:  ID for this string
      // U1*: UTF8 characters for string (NOT null terminated)
      //      (the record format encodes the length)
      __ AddU4(id);
      __ AddUtf8String(string.c_str());
    }
  }

  void StartNewHeapDumpSegment() {
    // This flushes the old segment and starts a new one.
    output_->StartNewRecord(HPROF_TAG_HEAP_DUMP_SEGMENT, kHprofTime);
    objects_in_segment_ = 0;
    // Starting a new HEAP_DUMP resets the heap to default.
    current_heap_ = HPROF_HEAP_DEFAULT;
  }

  void CheckHeapSegmentConstraints() {
    if (objects_in_segment_ >= kMaxObjectsPerSegment || output_->Length() >= kMaxBytesPerSegment) {
      StartNewHeapDumpSegment();
    }
  }

  void VisitRoot(mirror::Object* obj, const RootInfo& root_info)
      OVERRIDE SHARED_REQUIRES(Locks::mutator_lock_);
  void MarkRootObject(const mirror::Object* obj, jobject jni_obj, HprofHeapTag heap_tag,
                      uint32_t thread_serial);

  HprofClassObjectId LookupClassId(mirror::Class* c) SHARED_REQUIRES(Locks::mutator_lock_) {
    if (c != nullptr) {
      auto it = classes_.find(c);
      if (it == classes_.end()) {
        // first time to see this class
        HprofClassSerialNumber sn = next_class_serial_number_++;
        classes_.Put(c, sn);
        // Make sure that we've assigned a string ID for this class' name
        LookupClassNameId(c);
      }
    }
    return PointerToLowMemUInt32(c);
  }

  HprofStackTraceSerialNumber LookupStackTraceSerialNumber(const mirror::Object* obj)
      SHARED_REQUIRES(Locks::mutator_lock_) {
    auto r = allocation_records_.find(obj);
    if (r == allocation_records_.end()) {
      return kHprofNullStackTrace;
    } else {
      const gc::AllocRecordStackTrace* trace = r->second;
      auto result = traces_.find(trace);
      CHECK(result != traces_.end());
      return result->second;
    }
  }

  HprofStringId LookupStringId(mirror::String* string) SHARED_REQUIRES(Locks::mutator_lock_) {
    return LookupStringId(string->ToModifiedUtf8());
  }

  HprofStringId LookupStringId(const char* string) {
    return LookupStringId(std::string(string));
  }

  HprofStringId LookupStringId(const std::string& string) {
    auto it = strings_.find(string);
    if (it != strings_.end()) {
      return it->second;
    }
    HprofStringId id = next_string_id_++;
    strings_.Put(string, id);
    return id;
  }

  HprofStringId LookupClassNameId(mirror::Class* c) SHARED_REQUIRES(Locks::mutator_lock_) {
    return LookupStringId(PrettyDescriptor(c));
  }

  void WriteFixedHeader() {
    // Write the file header.
    // U1: NUL-terminated magic string.
    const char magic[] = "JAVA PROFILE 1.0.3";
    __ AddU1List(reinterpret_cast<const uint8_t*>(magic), sizeof(magic));

    // U4: size of identifiers.  We're using addresses as IDs and our heap references are stored
    // as uint32_t.
    // Note of warning: hprof-conv hard-codes the size of identifiers to 4.
    static_assert(sizeof(mirror::HeapReference<mirror::Object>) == sizeof(uint32_t),
                  "Unexpected HeapReference size");
    __ AddU4(sizeof(uint32_t));

    // The current time, in milliseconds since 0:00 GMT, 1/1/70.
    timeval now;
    const uint64_t nowMs = (gettimeofday(&now, nullptr) < 0) ? 0 :
        (uint64_t)now.tv_sec * 1000 + now.tv_usec / 1000;
    // TODO: It seems it would be correct to use U8.
    // U4: high word of the 64-bit time.
    __ AddU4(static_cast<uint32_t>(nowMs >> 32));
    // U4: low word of the 64-bit time.
    __ AddU4(static_cast<uint32_t>(nowMs & 0xFFFFFFFF));
  }

  void WriteStackTraces() SHARED_REQUIRES(Locks::mutator_lock_) {
    // Write a dummy stack trace record so the analysis tools don't freak out.
    output_->StartNewRecord(HPROF_TAG_STACK_TRACE, kHprofTime);
    __ AddStackTraceSerialNumber(kHprofNullStackTrace);
    __ AddU4(kHprofNullThread);
    __ AddU4(0);    // no frames

    // TODO: jhat complains "WARNING: Stack trace not found for serial # -1", but no trace should
    // have -1 as its serial number (as long as HprofStackTraceSerialNumber doesn't overflow).
    for (const auto& it : traces_) {
      const gc::AllocRecordStackTrace* trace = it.first;
      HprofStackTraceSerialNumber trace_sn = it.second;
      size_t depth = trace->GetDepth();

      // First write stack frames of the trace
      for (size_t i = 0; i < depth; ++i) {
        const gc::AllocRecordStackTraceElement* frame = &trace->GetStackElement(i);
        ArtMethod* method = frame->GetMethod();
        CHECK(method != nullptr);
        output_->StartNewRecord(HPROF_TAG_STACK_FRAME, kHprofTime);
        // STACK FRAME format:
        // ID: stack frame ID. We use the address of the AllocRecordStackTraceElement object as its ID.
        // ID: method name string ID
        // ID: method signature string ID
        // ID: source file name string ID
        // U4: class serial number
        // U4: >0, line number; 0, no line information available; -1, unknown location
        auto frame_result = frames_.find(frame);
        CHECK(frame_result != frames_.end());
        __ AddU4(frame_result->second);
        __ AddStringId(LookupStringId(method->GetName()));
        __ AddStringId(LookupStringId(method->GetSignature().ToString()));
        const char* source_file = method->GetDeclaringClassSourceFile();
        if (source_file == nullptr) {
          source_file = "";
        }
        __ AddStringId(LookupStringId(source_file));
        auto class_result = classes_.find(method->GetDeclaringClass());
        CHECK(class_result != classes_.end());
        __ AddU4(class_result->second);
        __ AddU4(frame->ComputeLineNumber());
      }

      // Then write the trace itself
      output_->StartNewRecord(HPROF_TAG_STACK_TRACE, kHprofTime);
      // STACK TRACE format:
      // U4: stack trace serial number. We use the address of the AllocRecordStackTrace object as its serial number.
      // U4: thread serial number. We use Thread::GetTid().
      // U4: number of frames
      // [ID]*: series of stack frame ID's
      __ AddStackTraceSerialNumber(trace_sn);
      __ AddU4(trace->GetTid());
      __ AddU4(depth);
      for (size_t i = 0; i < depth; ++i) {
        const gc::AllocRecordStackTraceElement* frame = &trace->GetStackElement(i);
        auto frame_result = frames_.find(frame);
        CHECK(frame_result != frames_.end());
        __ AddU4(frame_result->second);
      }
    }
  }

  bool DumpToDdmsBuffered(size_t overall_size ATTRIBUTE_UNUSED, size_t max_length ATTRIBUTE_UNUSED)
      REQUIRES(Locks::mutator_lock_) {
    LOG(FATAL) << "Unimplemented";
    UNREACHABLE();
    //        // Send the data off to DDMS.
    //        iovec iov[2];
    //        iov[0].iov_base = header_data_ptr_;
    //        iov[0].iov_len = header_data_size_;
    //        iov[1].iov_base = body_data_ptr_;
    //        iov[1].iov_len = body_data_size_;
    //        Dbg::DdmSendChunkV(CHUNK_TYPE("HPDS"), iov, 2);
  }

  bool DumpToFile(size_t overall_size, size_t max_length)
      REQUIRES(Locks::mutator_lock_) {
    // Where exactly are we writing to?
    int out_fd;
    if (fd_ >= 0) {
      out_fd = dup(fd_);
      if (out_fd < 0) {
        ThrowRuntimeException("Couldn't dump heap; dup(%d) failed: %s", fd_, strerror(errno));
        return false;
      }
    } else {
      out_fd = open(filename_.c_str(), O_WRONLY|O_CREAT|O_TRUNC, 0644);
      if (out_fd < 0) {
        ThrowRuntimeException("Couldn't dump heap; open(\"%s\") failed: %s", filename_.c_str(),
                              strerror(errno));
        return false;
      }
    }

    std::unique_ptr<File> file(new File(out_fd, filename_, true));
    bool okay;
    {
      FileEndianOutput file_output(file.get(), max_length);
      output_ = &file_output;
      ProcessHeap(true);
      okay = !file_output.Errors();

      if (okay) {
        // Check for expected size. Output is expected to be less-or-equal than first phase, see
        // b/23521263.
        DCHECK_LE(file_output.SumLength(), overall_size);
      }
      output_ = nullptr;
    }

    if (okay) {
      okay = file->FlushCloseOrErase() == 0;
    } else {
      file->Erase();
    }
    if (!okay) {
      std::string msg(StringPrintf("Couldn't dump heap; writing \"%s\" failed: %s",
                                   filename_.c_str(), strerror(errno)));
      ThrowRuntimeException("%s", msg.c_str());
      LOG(ERROR) << msg;
    }

    return okay;
  }

  bool DumpToDdmsDirect(size_t overall_size, size_t max_length, uint32_t chunk_type)
      REQUIRES(Locks::mutator_lock_) {
    CHECK(direct_to_ddms_);
    JDWP::JdwpState* state = Dbg::GetJdwpState();
    CHECK(state != nullptr);
    JDWP::JdwpNetStateBase* net_state = state->netState;
    CHECK(net_state != nullptr);

    // Hold the socket lock for the whole time since we want this to be atomic.
    MutexLock mu(Thread::Current(), *net_state->GetSocketLock());

    // Prepare the Ddms chunk.
    constexpr size_t kChunkHeaderSize = kJDWPHeaderLen + 8;
    uint8_t chunk_header[kChunkHeaderSize] = { 0 };
    state->SetupChunkHeader(chunk_type, overall_size, kChunkHeaderSize, chunk_header);

    // Prepare the output and send the chunk header.
    NetStateEndianOutput net_output(net_state, max_length);
    output_ = &net_output;
    net_output.AddU1List(chunk_header, kChunkHeaderSize);

    // Write the dump.
    ProcessHeap(true);

    // Check for expected size. See DumpToFile for comment.
    DCHECK_LE(net_output.SumLength(), overall_size + kChunkHeaderSize);
    output_ = nullptr;

    return true;
  }

  void PopulateAllocationTrackingTraces()
      REQUIRES(Locks::mutator_lock_, Locks::alloc_tracker_lock_) {
    gc::AllocRecordObjectMap* records = Runtime::Current()->GetHeap()->GetAllocationRecords();
    CHECK(records != nullptr);
    HprofStackTraceSerialNumber next_trace_sn = kHprofNullStackTrace + 1;
    HprofStackFrameId next_frame_id = 0;
    size_t count = 0;

    for (auto it = records->Begin(), end = records->End(); it != end; ++it) {
      const mirror::Object* obj = it->first.Read();
      if (obj == nullptr) {
        continue;
      }
      ++count;
      const gc::AllocRecordStackTrace* trace = it->second.GetStackTrace();

      // Copy the pair into a real hash map to speed up look up.
      auto records_result = allocation_records_.emplace(obj, trace);
      // The insertion should always succeed, i.e. no duplicate object pointers in "records"
      CHECK(records_result.second);

      // Generate serial numbers for traces, and IDs for frames.
      auto traces_result = traces_.find(trace);
      if (traces_result == traces_.end()) {
        traces_.emplace(trace, next_trace_sn++);
        // only check frames if the trace is newly discovered
        for (size_t i = 0, depth = trace->GetDepth(); i < depth; ++i) {
          const gc::AllocRecordStackTraceElement* frame = &trace->GetStackElement(i);
          auto frames_result = frames_.find(frame);
          if (frames_result == frames_.end()) {
            frames_.emplace(frame, next_frame_id++);
          }
        }
      }
    }
    CHECK_EQ(traces_.size(), next_trace_sn - kHprofNullStackTrace - 1);
    CHECK_EQ(frames_.size(), next_frame_id);
    total_objects_with_stack_trace_ = count;
  }

  // If direct_to_ddms_ is set, "filename_" and "fd" will be ignored.
  // Otherwise, "filename_" must be valid, though if "fd" >= 0 it will
  // only be used for debug messages.
  std::string filename_;
  int fd_;
  bool direct_to_ddms_;

  uint64_t start_ns_ = NanoTime();

  EndianOutput* output_ = nullptr;

  HprofHeapId current_heap_ = HPROF_HEAP_DEFAULT;  // Which heap we're currently dumping.
  size_t objects_in_segment_ = 0;

  size_t total_objects_ = 0u;
  size_t total_objects_with_stack_trace_ = 0u;

  HprofStringId next_string_id_ = 0x400000;
  SafeMap<std::string, HprofStringId> strings_;
  HprofClassSerialNumber next_class_serial_number_ = 1;
  SafeMap<mirror::Class*, HprofClassSerialNumber> classes_;

  std::unordered_map<const gc::AllocRecordStackTrace*, HprofStackTraceSerialNumber,
                     gc::HashAllocRecordTypesPtr<gc::AllocRecordStackTrace>,
                     gc::EqAllocRecordTypesPtr<gc::AllocRecordStackTrace>> traces_;
  std::unordered_map<const gc::AllocRecordStackTraceElement*, HprofStackFrameId,
                     gc::HashAllocRecordTypesPtr<gc::AllocRecordStackTraceElement>,
                     gc::EqAllocRecordTypesPtr<gc::AllocRecordStackTraceElement>> frames_;
  std::unordered_map<const mirror::Object*, const gc::AllocRecordStackTrace*> allocation_records_;

  friend class GcRootVisitor;
  DISALLOW_COPY_AND_ASSIGN(Hprof);
};

static HprofBasicType SignatureToBasicTypeAndSize(const char* sig, size_t* size_out) {
  char c = sig[0];
  HprofBasicType ret;
  size_t size;

  switch (c) {
    case '[':
    case 'L':
      ret = hprof_basic_object;
      size = 4;
      break;
    case 'Z':
      ret = hprof_basic_boolean;
      size = 1;
      break;
    case 'C':
      ret = hprof_basic_char;
      size = 2;
      break;
    case 'F':
      ret = hprof_basic_float;
      size = 4;
      break;
    case 'D':
      ret = hprof_basic_double;
      size = 8;
      break;
    case 'B':
      ret = hprof_basic_byte;
      size = 1;
      break;
    case 'S':
      ret = hprof_basic_short;
      size = 2;
      break;
    case 'I':
      ret = hprof_basic_int;
      size = 4;
      break;
    case 'J':
      ret = hprof_basic_long;
      size = 8;
      break;
    default:
      LOG(FATAL) << "UNREACHABLE";
      UNREACHABLE();
  }

  if (size_out != nullptr) {
    *size_out = size;
  }

  return ret;
}

// Always called when marking objects, but only does
// something when ctx->gc_scan_state_ is non-zero, which is usually
// only true when marking the root set or unreachable
// objects.  Used to add rootset references to obj.
void Hprof::MarkRootObject(const mirror::Object* obj, jobject jni_obj, HprofHeapTag heap_tag,
                           uint32_t thread_serial) {
  if (heap_tag == 0) {
    return;
  }

  CheckHeapSegmentConstraints();

  switch (heap_tag) {
    // ID: object ID
    case HPROF_ROOT_UNKNOWN:
    case HPROF_ROOT_STICKY_CLASS:
    case HPROF_ROOT_MONITOR_USED:
    case HPROF_ROOT_INTERNED_STRING:
    case HPROF_ROOT_DEBUGGER:
    case HPROF_ROOT_VM_INTERNAL:
      __ AddU1(heap_tag);
      __ AddObjectId(obj);
      break;

      // ID: object ID
      // ID: JNI global ref ID
    case HPROF_ROOT_JNI_GLOBAL:
      __ AddU1(heap_tag);
      __ AddObjectId(obj);
      __ AddJniGlobalRefId(jni_obj);
      break;

      // ID: object ID
      // U4: thread serial number
      // U4: frame number in stack trace (-1 for empty)
    case HPROF_ROOT_JNI_LOCAL:
    case HPROF_ROOT_JNI_MONITOR:
    case HPROF_ROOT_JAVA_FRAME:
      __ AddU1(heap_tag);
      __ AddObjectId(obj);
      __ AddU4(thread_serial);
      __ AddU4((uint32_t)-1);
      break;

      // ID: object ID
      // U4: thread serial number
    case HPROF_ROOT_NATIVE_STACK:
    case HPROF_ROOT_THREAD_BLOCK:
      __ AddU1(heap_tag);
      __ AddObjectId(obj);
      __ AddU4(thread_serial);
      break;

      // ID: thread object ID
      // U4: thread serial number
      // U4: stack trace serial number
    case HPROF_ROOT_THREAD_OBJECT:
      __ AddU1(heap_tag);
      __ AddObjectId(obj);
      __ AddU4(thread_serial);
      __ AddU4((uint32_t)-1);    // xxx
      break;

    case HPROF_CLASS_DUMP:
    case HPROF_INSTANCE_DUMP:
    case HPROF_OBJECT_ARRAY_DUMP:
    case HPROF_PRIMITIVE_ARRAY_DUMP:
    case HPROF_HEAP_DUMP_INFO:
    case HPROF_PRIMITIVE_ARRAY_NODATA_DUMP:
      // Ignored.
      break;

    case HPROF_ROOT_FINALIZING:
    case HPROF_ROOT_REFERENCE_CLEANUP:
    case HPROF_UNREACHABLE:
      LOG(FATAL) << "obsolete tag " << static_cast<int>(heap_tag);
      break;
  }

  ++objects_in_segment_;
}

// Use for visiting the GcRoots held live by ArtFields, ArtMethods, and ClassLoaders.
class GcRootVisitor {
 public:
  explicit GcRootVisitor(Hprof* hprof) : hprof_(hprof) {}

  void operator()(mirror::Object* obj ATTRIBUTE_UNUSED,
                  MemberOffset offset ATTRIBUTE_UNUSED,
                  bool is_static ATTRIBUTE_UNUSED) const {}

  // Note that these don't have read barriers. Its OK however since the GC is guaranteed to not be
  // running during the hprof dumping process.
  void VisitRootIfNonNull(mirror::CompressedReference<mirror::Object>* root) const
      SHARED_REQUIRES(Locks::mutator_lock_) {
    if (!root->IsNull()) {
      VisitRoot(root);
    }
  }

  void VisitRoot(mirror::CompressedReference<mirror::Object>* root) const
      SHARED_REQUIRES(Locks::mutator_lock_) {
    mirror::Object* obj = root->AsMirrorPtr();
    // The two cases are either classes or dex cache arrays. If it is a dex cache array, then use
    // VM internal. Otherwise the object is a declaring class of an ArtField or ArtMethod or a
    // class from a ClassLoader.
    hprof_->VisitRoot(obj, RootInfo(obj->IsClass() ? kRootStickyClass : kRootVMInternal));
  }


 private:
  Hprof* const hprof_;
};

void Hprof::DumpHeapObject(mirror::Object* obj) {
  // Ignore classes that are retired.
  if (obj->IsClass() && obj->AsClass()->IsRetired()) {
    return;
  }

  ++total_objects_;

  GcRootVisitor visitor(this);
  obj->VisitReferences(visitor, VoidFunctor());

  gc::Heap* const heap = Runtime::Current()->GetHeap();
  const gc::space::ContinuousSpace* const space = heap->FindContinuousSpaceFromObject(obj, true);
  HprofHeapId heap_type = HPROF_HEAP_APP;
  if (space != nullptr) {
    if (space->IsZygoteSpace()) {
      heap_type = HPROF_HEAP_ZYGOTE;
    } else if (space->IsImageSpace()) {
      heap_type = HPROF_HEAP_IMAGE;
    }
  } else {
    const auto* los = heap->GetLargeObjectsSpace();
    if (los->Contains(obj) && los->IsZygoteLargeObject(Thread::Current(), obj)) {
      heap_type = HPROF_HEAP_ZYGOTE;
    }
  }
  CheckHeapSegmentConstraints();

  if (heap_type != current_heap_) {
    HprofStringId nameId;

    // This object is in a different heap than the current one.
    // Emit a HEAP_DUMP_INFO tag to change heaps.
    __ AddU1(HPROF_HEAP_DUMP_INFO);
    __ AddU4(static_cast<uint32_t>(heap_type));   // uint32_t: heap type
    switch (heap_type) {
    case HPROF_HEAP_APP:
      nameId = LookupStringId("app");
      break;
    case HPROF_HEAP_ZYGOTE:
      nameId = LookupStringId("zygote");
      break;
    case HPROF_HEAP_IMAGE:
      nameId = LookupStringId("image");
      break;
    default:
      // Internal error
      LOG(ERROR) << "Unexpected desiredHeap";
      nameId = LookupStringId("<ILLEGAL>");
      break;
    }
    __ AddStringId(nameId);
    current_heap_ = heap_type;
  }

  mirror::Class* c = obj->GetClass();
  if (c == nullptr) {
    // This object will bother HprofReader, because it has a null
    // class, so just don't dump it. It could be
    // gDvm.unlinkedJavaLangClass or it could be an object just
    // allocated which hasn't been initialized yet.
  } else {
    if (obj->IsClass()) {
      DumpHeapClass(obj->AsClass());
    } else if (c->IsArrayClass()) {
      DumpHeapArray(obj->AsArray(), c);
    } else {
      DumpHeapInstanceObject(obj, c);
    }
  }

  ++objects_in_segment_;
}

void Hprof::DumpHeapClass(mirror::Class* klass) {
  if (!klass->IsLoaded() && !klass->IsErroneous()) {
    // Class is allocated but not yet loaded: we cannot access its fields or super class.
    return;
  }
  const size_t num_static_fields = klass->NumStaticFields();
  // Total class size including embedded IMT, embedded vtable, and static fields.
  const size_t class_size = klass->GetClassSize();
  // Class size excluding static fields (relies on reference fields being the first static fields).
  const size_t class_size_without_overhead = sizeof(mirror::Class);
  CHECK_LE(class_size_without_overhead, class_size);
  const size_t overhead_size = class_size - class_size_without_overhead;

  if (overhead_size != 0) {
    // Create a byte array to reflect the allocation of the
    // StaticField array at the end of this class.
    __ AddU1(HPROF_PRIMITIVE_ARRAY_DUMP);
    __ AddClassStaticsId(klass);
    __ AddStackTraceSerialNumber(LookupStackTraceSerialNumber(klass));
    __ AddU4(overhead_size);
    __ AddU1(hprof_basic_byte);
    for (size_t i = 0; i < overhead_size; ++i) {
      __ AddU1(0);
    }
  }

  __ AddU1(HPROF_CLASS_DUMP);
  __ AddClassId(LookupClassId(klass));
  __ AddStackTraceSerialNumber(LookupStackTraceSerialNumber(klass));
  __ AddClassId(LookupClassId(klass->GetSuperClass()));
  __ AddObjectId(klass->GetClassLoader());
  __ AddObjectId(nullptr);    // no signer
  __ AddObjectId(nullptr);    // no prot domain
  __ AddObjectId(nullptr);    // reserved
  __ AddObjectId(nullptr);    // reserved
  if (klass->IsClassClass()) {
    // ClassObjects have their static fields appended, so aren't all the same size.
    // But they're at least this size.
    __ AddU4(class_size_without_overhead);  // instance size
  } else if (klass->IsStringClass()) {
    // Strings are variable length with character data at the end like arrays.
    // This outputs the size of an empty string.
    __ AddU4(sizeof(mirror::String));
  } else if (klass->IsArrayClass() || klass->IsPrimitive()) {
    __ AddU4(0);
  } else {
    __ AddU4(klass->GetObjectSize());  // instance size
  }

  __ AddU2(0);  // empty const pool

  // Static fields
  if (overhead_size == 0) {
    __ AddU2(static_cast<uint16_t>(0));
  } else {
    __ AddU2(static_cast<uint16_t>(num_static_fields + 1));
    __ AddStringId(LookupStringId(kClassOverheadName));
    __ AddU1(hprof_basic_object);
    __ AddClassStaticsId(klass);

    for (size_t i = 0; i < num_static_fields; ++i) {
      ArtField* f = klass->GetStaticField(i);

      size_t size;
      HprofBasicType t = SignatureToBasicTypeAndSize(f->GetTypeDescriptor(), &size);
      __ AddStringId(LookupStringId(f->GetName()));
      __ AddU1(t);
      switch (t) {
        case hprof_basic_byte:
          __ AddU1(f->GetByte(klass));
          break;
        case hprof_basic_boolean:
          __ AddU1(f->GetBoolean(klass));
          break;
        case hprof_basic_char:
          __ AddU2(f->GetChar(klass));
          break;
        case hprof_basic_short:
          __ AddU2(f->GetShort(klass));
          break;
        case hprof_basic_float:
        case hprof_basic_int:
        case hprof_basic_object:
          __ AddU4(f->Get32(klass));
          break;
        case hprof_basic_double:
        case hprof_basic_long:
          __ AddU8(f->Get64(klass));
          break;
        default:
          LOG(FATAL) << "Unexpected size " << size;
          UNREACHABLE();
      }
    }
  }

  // Instance fields for this class (no superclass fields)
  int iFieldCount = klass->NumInstanceFields();
  if (klass->IsStringClass()) {
    __ AddU2((uint16_t)iFieldCount + 1);
  } else {
    __ AddU2((uint16_t)iFieldCount);
  }
  for (int i = 0; i < iFieldCount; ++i) {
    ArtField* f = klass->GetInstanceField(i);
    __ AddStringId(LookupStringId(f->GetName()));
    HprofBasicType t = SignatureToBasicTypeAndSize(f->GetTypeDescriptor(), nullptr);
    __ AddU1(t);
  }
  // Add native value character array for strings.
  if (klass->IsStringClass()) {
    __ AddStringId(LookupStringId("value"));
    __ AddU1(hprof_basic_object);
  }
}

void Hprof::DumpHeapArray(mirror::Array* obj, mirror::Class* klass) {
  uint32_t length = obj->GetLength();

  if (obj->IsObjectArray()) {
    // obj is an object array.
    __ AddU1(HPROF_OBJECT_ARRAY_DUMP);

    __ AddObjectId(obj);
    __ AddStackTraceSerialNumber(LookupStackTraceSerialNumber(obj));
    __ AddU4(length);
    __ AddClassId(LookupClassId(klass));

    // Dump the elements, which are always objects or null.
    __ AddIdList(obj->AsObjectArray<mirror::Object>());
  } else {
    size_t size;
    HprofBasicType t = SignatureToBasicTypeAndSize(
        Primitive::Descriptor(klass->GetComponentType()->GetPrimitiveType()), &size);

    // obj is a primitive array.
    __ AddU1(HPROF_PRIMITIVE_ARRAY_DUMP);

    __ AddObjectId(obj);
    __ AddStackTraceSerialNumber(LookupStackTraceSerialNumber(obj));
    __ AddU4(length);
    __ AddU1(t);

    // Dump the raw, packed element values.
    if (size == 1) {
      __ AddU1List(reinterpret_cast<const uint8_t*>(obj->GetRawData(sizeof(uint8_t), 0)), length);
    } else if (size == 2) {
      __ AddU2List(reinterpret_cast<const uint16_t*>(obj->GetRawData(sizeof(uint16_t), 0)), length);
    } else if (size == 4) {
      __ AddU4List(reinterpret_cast<const uint32_t*>(obj->GetRawData(sizeof(uint32_t), 0)), length);
    } else if (size == 8) {
      __ AddU8List(reinterpret_cast<const uint64_t*>(obj->GetRawData(sizeof(uint64_t), 0)), length);
    }
  }
}

void Hprof::DumpHeapInstanceObject(mirror::Object* obj, mirror::Class* klass) {
  // obj is an instance object.
  __ AddU1(HPROF_INSTANCE_DUMP);
  __ AddObjectId(obj);
  __ AddStackTraceSerialNumber(LookupStackTraceSerialNumber(obj));
  __ AddClassId(LookupClassId(klass));

  // Reserve some space for the length of the instance data, which we won't
  // know until we're done writing it.
  size_t size_patch_offset = output_->Length();
  __ AddU4(0x77777777);

  // What we will use for the string value if the object is a string.
  mirror::Object* string_value = nullptr;

  // Write the instance data;  fields for this class, followed by super class fields, and so on.
  do {
    const size_t instance_fields = klass->NumInstanceFields();
    for (size_t i = 0; i < instance_fields; ++i) {
      ArtField* f = klass->GetInstanceField(i);
      size_t size;
      HprofBasicType t = SignatureToBasicTypeAndSize(f->GetTypeDescriptor(), &size);
      switch (t) {
      case hprof_basic_byte:
        __ AddU1(f->GetByte(obj));
        break;
      case hprof_basic_boolean:
        __ AddU1(f->GetBoolean(obj));
        break;
      case hprof_basic_char:
        __ AddU2(f->GetChar(obj));
        break;
      case hprof_basic_short:
        __ AddU2(f->GetShort(obj));
        break;
      case hprof_basic_float:
      case hprof_basic_int:
      case hprof_basic_object:
        __ AddU4(f->Get32(obj));
        break;
      case hprof_basic_double:
      case hprof_basic_long:
        __ AddU8(f->Get64(obj));
        break;
      }
    }
    // Add value field for String if necessary.
    if (klass->IsStringClass()) {
      mirror::String* s = obj->AsString();
      if (s->GetLength() == 0) {
        // If string is empty, use an object-aligned address within the string for the value.
        string_value = reinterpret_cast<mirror::Object*>(
            reinterpret_cast<uintptr_t>(s) + kObjectAlignment);
      } else {
        string_value = reinterpret_cast<mirror::Object*>(s->GetValue());
      }
      __ AddObjectId(string_value);
    }

    klass = klass->GetSuperClass();
  } while (klass != nullptr);

  // Patch the instance field length.
  __ UpdateU4(size_patch_offset, output_->Length() - (size_patch_offset + 4));

  // Output native value character array for strings.
  CHECK_EQ(obj->IsString(), string_value != nullptr);
  if (string_value != nullptr) {
    mirror::String* s = obj->AsString();
    __ AddU1(HPROF_PRIMITIVE_ARRAY_DUMP);
    __ AddObjectId(string_value);
    __ AddStackTraceSerialNumber(LookupStackTraceSerialNumber(obj));
    __ AddU4(s->GetLength());
    __ AddU1(hprof_basic_char);
    __ AddU2List(s->GetValue(), s->GetLength());
  }
}

void Hprof::VisitRoot(mirror::Object* obj, const RootInfo& info) {
  static const HprofHeapTag xlate[] = {
    HPROF_ROOT_UNKNOWN,
    HPROF_ROOT_JNI_GLOBAL,
    HPROF_ROOT_JNI_LOCAL,
    HPROF_ROOT_JAVA_FRAME,
    HPROF_ROOT_NATIVE_STACK,
    HPROF_ROOT_STICKY_CLASS,
    HPROF_ROOT_THREAD_BLOCK,
    HPROF_ROOT_MONITOR_USED,
    HPROF_ROOT_THREAD_OBJECT,
    HPROF_ROOT_INTERNED_STRING,
    HPROF_ROOT_FINALIZING,
    HPROF_ROOT_DEBUGGER,
    HPROF_ROOT_REFERENCE_CLEANUP,
    HPROF_ROOT_VM_INTERNAL,
    HPROF_ROOT_JNI_MONITOR,
  };
  CHECK_LT(info.GetType(), sizeof(xlate) / sizeof(HprofHeapTag));
  if (obj == nullptr) {
    return;
  }
  MarkRootObject(obj, 0, xlate[info.GetType()], info.GetThreadId());
}

// If "direct_to_ddms" is true, the other arguments are ignored, and data is
// sent directly to DDMS.
// If "fd" is >= 0, the output will be written to that file descriptor.
// Otherwise, "filename" is used to create an output file.
void DumpHeap(const char* filename, int fd, bool direct_to_ddms) {
  CHECK(filename != nullptr);

  Thread* self = Thread::Current();
  gc::Heap* heap = Runtime::Current()->GetHeap();
  if (heap->IsGcConcurrentAndMoving()) {
    // Need to take a heap dump while GC isn't running. See the
    // comment in Heap::VisitObjects().
    heap->IncrementDisableMovingGC(self);
  }
  {
    ScopedSuspendAll ssa(__FUNCTION__, true /* long suspend */);
    Hprof hprof(filename, fd, direct_to_ddms);
    hprof.Dump();
  }
  if (heap->IsGcConcurrentAndMoving()) {
    heap->DecrementDisableMovingGC(self);
  }
}

}  // namespace hprof
}  // namespace art