imgdiag/imgdiag.cc

/*
 * Copyright (C) 2014 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 <stdio.h>
#include <stdlib.h>

#include <fstream>
#include <functional>
#include <iostream>
#include <string>
#include <vector>
#include <set>
#include <map>
#include <unordered_set>

#include "android-base/stringprintf.h"

#include "art_field-inl.h"
#include "art_method-inl.h"
#include "base/unix_file/fd_file.h"
#include "gc/space/image_space.h"
#include "gc/heap.h"
#include "mirror/class-inl.h"
#include "mirror/object-inl.h"
#include "image.h"
#include "scoped_thread_state_change-inl.h"
#include "os.h"

#include "cmdline.h"
#include "backtrace/BacktraceMap.h"

#include <sys/stat.h>
#include <sys/types.h>
#include <signal.h>

namespace art {

using android::base::StringPrintf;

class ImgDiagDumper {
 public:
  explicit ImgDiagDumper(std::ostream* os,
                         const ImageHeader& image_header,
                         const std::string& image_location,
                         pid_t image_diff_pid,
                         pid_t zygote_diff_pid)
      : os_(os),
        image_header_(image_header),
        image_location_(image_location),
        image_diff_pid_(image_diff_pid),
        zygote_diff_pid_(zygote_diff_pid),
        zygote_pid_only_(false) {}

  bool Init() {
    std::ostream& os = *os_;

    if (image_diff_pid_ < 0 && zygote_diff_pid_ < 0) {
      os << "Either --image-diff-pid or --zygote-diff-pid (or both) must be specified.\n";
      return false;
    }

    // To avoid the combinations of command-line argument use cases:
    // If the user invoked with only --zygote-diff-pid, shuffle that to
    // image_diff_pid_, invalidate zygote_diff_pid_, and remember that
    // image_diff_pid_ is now special.
    if (image_diff_pid_ < 0) {
      image_diff_pid_ = zygote_diff_pid_;
      zygote_diff_pid_ = -1;
      zygote_pid_only_ = true;
    }

    {
      struct stat sts;
      std::string proc_pid_str =
          StringPrintf("/proc/%ld", static_cast<long>(image_diff_pid_));  // NOLINT [runtime/int]
      if (stat(proc_pid_str.c_str(), &sts) == -1) {
        os << "Process does not exist";
        return false;
      }
    }

    // Open /proc/$pid/maps to view memory maps
    auto tmp_proc_maps = std::unique_ptr<BacktraceMap>(BacktraceMap::Create(image_diff_pid_));
    if (tmp_proc_maps == nullptr) {
      os << "Could not read backtrace maps";
      return false;
    }

    bool found_boot_map = false;
    // Find the memory map only for boot.art
    for (const backtrace_map_t& map : *tmp_proc_maps) {
      if (EndsWith(map.name, GetImageLocationBaseName())) {
        if ((map.flags & PROT_WRITE) != 0) {
          boot_map_ = map;
          found_boot_map = true;
          break;
        }
        // In actuality there's more than 1 map, but the second one is read-only.
        // The one we care about is the write-able map.
        // The readonly maps are guaranteed to be identical, so its not interesting to compare
        // them.
      }
    }

    if (!found_boot_map) {
      os << "Could not find map for " << GetImageLocationBaseName();
      return false;
    }
    // Sanity check boot_map_.
    CHECK(boot_map_.end >= boot_map_.start);
    boot_map_size_ = boot_map_.end - boot_map_.start;

    pointer_size_ = InstructionSetPointerSize(Runtime::Current()->GetInstructionSet());

    // Open /proc/<image_diff_pid_>/mem and read as remote_contents_.
    std::string image_file_name =
        StringPrintf("/proc/%ld/mem", static_cast<long>(image_diff_pid_));  // NOLINT [runtime/int]
    auto image_map_file = std::unique_ptr<File>(OS::OpenFileForReading(image_file_name.c_str()));
    if (image_map_file == nullptr) {
      os << "Failed to open " << image_file_name << " for reading";
      return false;
    }
    std::vector<uint8_t> tmp_remote_contents(boot_map_size_);
    if (!image_map_file->PreadFully(&tmp_remote_contents[0], boot_map_size_, boot_map_.start)) {
      os << "Could not fully read file " << image_file_name;
      return false;
    }

    // If zygote_diff_pid_ != -1, open /proc/<zygote_diff_pid_>/mem and read as zygote_contents_.
    std::vector<uint8_t> tmp_zygote_contents;
    if (zygote_diff_pid_ != -1) {
      std::string zygote_file_name =
          StringPrintf("/proc/%ld/mem", static_cast<long>(zygote_diff_pid_));  // NOLINT [runtime/int]
      std::unique_ptr<File> zygote_map_file(OS::OpenFileForReading(zygote_file_name.c_str()));
      if (zygote_map_file == nullptr) {
        os << "Failed to open " << zygote_file_name << " for reading";
        return false;
      }
      // The boot map should be at the same address.
      tmp_zygote_contents.reserve(boot_map_size_);
      if (!zygote_map_file->PreadFully(&tmp_zygote_contents[0], boot_map_size_, boot_map_.start)) {
        LOG(WARNING) << "Could not fully read zygote file " << zygote_file_name;
        return false;
      }
    }

    // Open /proc/<image_diff_pid_>/pagemap.
    std::string pagemap_file_name = StringPrintf(
        "/proc/%ld/pagemap", static_cast<long>(image_diff_pid_));  // NOLINT [runtime/int]
    auto tmp_pagemap_file =
        std::unique_ptr<File>(OS::OpenFileForReading(pagemap_file_name.c_str()));
    if (tmp_pagemap_file == nullptr) {
      os << "Failed to open " << pagemap_file_name << " for reading: " << strerror(errno);
      return false;
    }

    // Not truly clean, mmap-ing boot.art again would be more pristine, but close enough
    const char* clean_pagemap_file_name = "/proc/self/pagemap";
    auto tmp_clean_pagemap_file = std::unique_ptr<File>(
        OS::OpenFileForReading(clean_pagemap_file_name));
    if (tmp_clean_pagemap_file == nullptr) {
      os << "Failed to open " << clean_pagemap_file_name << " for reading: " << strerror(errno);
      return false;
    }

    auto tmp_kpageflags_file = std::unique_ptr<File>(OS::OpenFileForReading("/proc/kpageflags"));
    if (tmp_kpageflags_file == nullptr) {
      os << "Failed to open /proc/kpageflags for reading: " << strerror(errno);
      return false;
    }

    auto tmp_kpagecount_file = std::unique_ptr<File>(OS::OpenFileForReading("/proc/kpagecount"));
    if (tmp_kpagecount_file == nullptr) {
      os << "Failed to open /proc/kpagecount for reading:" << strerror(errno);
      return false;
    }

    // Commit the mappings, etc., to the object state.
    proc_maps_ = std::move(tmp_proc_maps);
    remote_contents_ = std::move(tmp_remote_contents);
    zygote_contents_ = std::move(tmp_zygote_contents);
    pagemap_file_ = std::move(*tmp_pagemap_file.release());
    clean_pagemap_file_ = std::move(*tmp_clean_pagemap_file.release());
    kpageflags_file_ = std::move(*tmp_kpageflags_file.release());
    kpagecount_file_ = std::move(*tmp_kpagecount_file.release());

    return true;
  }

  bool Dump() REQUIRES_SHARED(Locks::mutator_lock_) {
    std::ostream& os = *os_;
    os << "IMAGE LOCATION: " << image_location_ << "\n\n";

    os << "MAGIC: " << image_header_.GetMagic() << "\n\n";

    os << "IMAGE BEGIN: " << reinterpret_cast<void*>(image_header_.GetImageBegin()) << "\n\n";

    PrintPidLine("IMAGE", image_diff_pid_);
    os << "\n\n";
    PrintPidLine("ZYGOTE", zygote_diff_pid_);
    bool ret = true;
    if (image_diff_pid_ >= 0 || zygote_diff_pid_ >= 0) {
      ret = DumpImageDiff();
      os << "\n\n";
    }

    os << std::flush;

    return ret;
  }

 private:
  bool DumpImageDiff()
      REQUIRES_SHARED(Locks::mutator_lock_) {
    return DumpImageDiffMap();
  }

  bool ComputeDirtyBytes(const uint8_t* image_begin,
                         size_t* dirty_pages /*out*/,
                         size_t* different_pages /*out*/,
                         size_t* different_bytes /*out*/,
                         size_t* different_int32s /*out*/,
                         size_t* private_pages /*out*/,
                         size_t* private_dirty_pages /*out*/,
                         std::set<size_t>* dirty_page_set_local) {
    std::ostream& os = *os_;

    size_t virtual_page_idx = 0;   // Virtual page number (for an absolute memory address)
    size_t page_idx = 0;           // Page index relative to 0
    size_t previous_page_idx = 0;  // Previous page index relative to 0


    // Iterate through one page at a time. Boot map begin/end already implicitly aligned.
    for (uintptr_t begin = boot_map_.start; begin != boot_map_.end; begin += kPageSize) {
      ptrdiff_t offset = begin - boot_map_.start;

      // We treat the image header as part of the memory map for now
      // If we wanted to change this, we could pass base=start+sizeof(ImageHeader)
      // But it might still be interesting to see if any of the ImageHeader data mutated
      const uint8_t* local_ptr = reinterpret_cast<const uint8_t*>(&image_header_) + offset;
      uint8_t* remote_ptr = &remote_contents_[offset];

      if (memcmp(local_ptr, remote_ptr, kPageSize) != 0) {
        ++*different_pages;

        // Count the number of 32-bit integers that are different.
        for (size_t i = 0; i < kPageSize / sizeof(uint32_t); ++i) {
          uint32_t* remote_ptr_int32 = reinterpret_cast<uint32_t*>(remote_ptr);
          const uint32_t* local_ptr_int32 = reinterpret_cast<const uint32_t*>(local_ptr);

          if (remote_ptr_int32[i] != local_ptr_int32[i]) {
            ++*different_int32s;
          }
        }
      }
    }

    // Iterate through one byte at a time.
    ptrdiff_t page_off_begin = image_header_.GetImageBegin() - image_begin;
    for (uintptr_t begin = boot_map_.start; begin != boot_map_.end; ++begin) {
      previous_page_idx = page_idx;
      ptrdiff_t offset = begin - boot_map_.start;

      // We treat the image header as part of the memory map for now
      // If we wanted to change this, we could pass base=start+sizeof(ImageHeader)
      // But it might still be interesting to see if any of the ImageHeader data mutated
      const uint8_t* local_ptr = reinterpret_cast<const uint8_t*>(&image_header_) + offset;
      uint8_t* remote_ptr = &remote_contents_[offset];

      virtual_page_idx = reinterpret_cast<uintptr_t>(local_ptr) / kPageSize;

      // Calculate the page index, relative to the 0th page where the image begins
      page_idx = (offset + page_off_begin) / kPageSize;
      if (*local_ptr != *remote_ptr) {
        // Track number of bytes that are different
        ++*different_bytes;
      }

      // Independently count the # of dirty pages on the remote side
      size_t remote_virtual_page_idx = begin / kPageSize;
      if (previous_page_idx != page_idx) {
        uint64_t page_count = 0xC0FFEE;
        // TODO: virtual_page_idx needs to be from the same process
        std::string error_msg;
        int dirtiness = (IsPageDirty(&pagemap_file_,           // Image-diff-pid procmap
                                     &clean_pagemap_file_,     // Self procmap
                                     &kpageflags_file_,
                                     &kpagecount_file_,
                                     remote_virtual_page_idx,  // potentially "dirty" page
                                     virtual_page_idx,         // true "clean" page
                                     &page_count,
                                     &error_msg));
        if (dirtiness < 0) {
          os << error_msg;
          return false;
        } else if (dirtiness > 0) {
          ++*dirty_pages;
          dirty_page_set_local->insert(dirty_page_set_local->end(), virtual_page_idx);
        }

        bool is_dirty = dirtiness > 0;
        bool is_private = page_count == 1;

        if (page_count == 1) {
          ++*private_pages;
        }

        if (is_dirty && is_private) {
          ++*private_dirty_pages;
        }
      }
    }
    return true;
  }

  bool ObjectIsOnDirtyPage(const uint8_t* item,
                           size_t size,
                           const std::set<size_t>& dirty_page_set_local) {
    size_t page_off = 0;
    size_t current_page_idx;
    uintptr_t object_address = reinterpret_cast<uintptr_t>(item);
    // Iterate every page this object belongs to
    do {
      current_page_idx = object_address / kPageSize + page_off;

      if (dirty_page_set_local.find(current_page_idx) != dirty_page_set_local.end()) {
        // This object is on a dirty page
        return true;
      }

      page_off++;
    } while ((current_page_idx * kPageSize) < RoundUp(object_address + size, kObjectAlignment));

    return false;
  }

  static std::string PrettyFieldValue(ArtField* field, mirror::Object* obj)
      REQUIRES_SHARED(Locks::mutator_lock_) {
    std::ostringstream oss;
    switch (field->GetTypeAsPrimitiveType()) {
      case Primitive::kPrimNot: {
        oss << obj->GetFieldObject<mirror::Object, kVerifyNone, kWithoutReadBarrier>(
            field->GetOffset());
        break;
      }
      case Primitive::kPrimBoolean: {
        oss << static_cast<bool>(obj->GetFieldBoolean<kVerifyNone>(field->GetOffset()));
        break;
      }
      case Primitive::kPrimByte: {
        oss << static_cast<int32_t>(obj->GetFieldByte<kVerifyNone>(field->GetOffset()));
        break;
      }
      case Primitive::kPrimChar: {
        oss << obj->GetFieldChar<kVerifyNone>(field->GetOffset());
        break;
      }
      case Primitive::kPrimShort: {
        oss << obj->GetFieldShort<kVerifyNone>(field->GetOffset());
        break;
      }
      case Primitive::kPrimInt: {
        oss << obj->GetField32<kVerifyNone>(field->GetOffset());
        break;
      }
      case Primitive::kPrimLong: {
        oss << obj->GetField64<kVerifyNone>(field->GetOffset());
        break;
      }
      case Primitive::kPrimFloat: {
        oss << obj->GetField32<kVerifyNone>(field->GetOffset());
        break;
      }
      case Primitive::kPrimDouble: {
        oss << obj->GetField64<kVerifyNone>(field->GetOffset());
        break;
      }
      case Primitive::kPrimVoid: {
        oss << "void";
        break;
      }
    }
    return oss.str();
  }

  // Aggregate and detail class data from an image diff.
  struct ClassData {
    size_t dirty_object_count = 0;

    // Track only the byte-per-byte dirtiness (in bytes)
    size_t dirty_object_byte_count = 0;

    // Track the object-by-object dirtiness (in bytes)
    size_t dirty_object_size_in_bytes = 0;

    size_t clean_object_count = 0;

    std::string descriptor;

    size_t false_dirty_byte_count = 0;
    size_t false_dirty_object_count = 0;
    std::vector<const uint8_t*> false_dirty_objects;

    // Remote pointers to dirty objects
    std::vector<const uint8_t*> dirty_objects;
  };

  void DiffObjectContents(mirror::Object* obj,
                          uint8_t* remote_bytes,
                          std::ostream& os) REQUIRES_SHARED(Locks::mutator_lock_) {
    const char* tabs = "    ";
    // Attempt to find fields for all dirty bytes.
    mirror::Class* klass = obj->GetClass();
    if (obj->IsClass()) {
      os << tabs << "Class " << mirror::Class::PrettyClass(obj->AsClass()) << " " << obj << "\n";
    } else {
      os << tabs << "Instance of " << mirror::Class::PrettyClass(klass) << " " << obj << "\n";
    }

    std::unordered_set<ArtField*> dirty_instance_fields;
    std::unordered_set<ArtField*> dirty_static_fields;
    const uint8_t* obj_bytes = reinterpret_cast<const uint8_t*>(obj);
    mirror::Object* remote_obj = reinterpret_cast<mirror::Object*>(remote_bytes);
    for (size_t i = 0, count = obj->SizeOf(); i < count; ++i) {
      if (obj_bytes[i] != remote_bytes[i]) {
        ArtField* field = ArtField::FindInstanceFieldWithOffset</*exact*/false>(klass, i);
        if (field != nullptr) {
          dirty_instance_fields.insert(field);
        } else if (obj->IsClass()) {
          field = ArtField::FindStaticFieldWithOffset</*exact*/false>(obj->AsClass(), i);
          if (field != nullptr) {
            dirty_static_fields.insert(field);
          }
        }
        if (field == nullptr) {
          if (klass->IsArrayClass()) {
            mirror::Class* component_type = klass->GetComponentType();
            Primitive::Type primitive_type = component_type->GetPrimitiveType();
            size_t component_size = Primitive::ComponentSize(primitive_type);
            size_t data_offset = mirror::Array::DataOffset(component_size).Uint32Value();
            if (i >= data_offset) {
              os << tabs << "Dirty array element " << (i - data_offset) / component_size << "\n";
              // Skip to next element to prevent spam.
              i += component_size - 1;
              continue;
            }
          }
          os << tabs << "No field for byte offset " << i << "\n";
        }
      }
    }
    // Dump different fields. TODO: Dump field contents.
    if (!dirty_instance_fields.empty()) {
      os << tabs << "Dirty instance fields " << dirty_instance_fields.size() << "\n";
      for (ArtField* field : dirty_instance_fields) {
        os << tabs << ArtField::PrettyField(field)
           << " original=" << PrettyFieldValue(field, obj)
           << " remote=" << PrettyFieldValue(field, remote_obj) << "\n";
      }
    }
    if (!dirty_static_fields.empty()) {
      os << tabs << "Dirty static fields " << dirty_static_fields.size() << "\n";
      for (ArtField* field : dirty_static_fields) {
        os << tabs << ArtField::PrettyField(field)
           << " original=" << PrettyFieldValue(field, obj)
           << " remote=" << PrettyFieldValue(field, remote_obj) << "\n";
      }
    }
    os << "\n";
  }

  struct ObjectRegionData {
    // Count of objects that are different.
    size_t different_objects = 0;

    // Local objects that are dirty (differ in at least one byte).
    size_t dirty_object_bytes = 0;
    std::vector<const uint8_t*>* dirty_objects;

    // Local objects that are clean, but located on dirty pages.
    size_t false_dirty_object_bytes = 0;
    std::vector<const uint8_t*> false_dirty_objects;

    // Image dirty objects
    // If zygote_pid_only_ == true, these are shared dirty objects in the zygote.
    // If zygote_pid_only_ == false, these are private dirty objects in the application.
    std::set<const uint8_t*> image_dirty_objects;

    // Zygote dirty objects (probably private dirty).
    // We only add objects here if they differed in both the image and the zygote, so
    // they are probably private dirty.
    std::set<const uint8_t*> zygote_dirty_objects;

    std::map<off_t /* field offset */, size_t /* count */>* field_dirty_count;
  };

  void ComputeObjectDirty(const uint8_t* current,
                          const uint8_t* current_remote,
                          const uint8_t* current_zygote,
                          ClassData* obj_class_data,
                          size_t obj_size,
                          const std::set<size_t>& dirty_page_set_local,
                          ObjectRegionData* region_data /*out*/) {
    bool different_image_object = memcmp(current, current_remote, obj_size) != 0;
    if (different_image_object) {
      bool different_zygote_object = false;
      if (!zygote_contents_.empty()) {
        different_zygote_object = memcmp(current, current_zygote, obj_size) != 0;
      }
      if (different_zygote_object) {
        // Different from zygote.
        region_data->zygote_dirty_objects.insert(current);
      } else {
        // Just different from image.
        region_data->image_dirty_objects.insert(current);
      }

      ++region_data->different_objects;
      region_data->dirty_object_bytes += obj_size;

      ++obj_class_data->dirty_object_count;

      // Go byte-by-byte and figure out what exactly got dirtied
      size_t dirty_byte_count_per_object = 0;
      for (size_t i = 0; i < obj_size; ++i) {
        if (current[i] != current_remote[i]) {
          dirty_byte_count_per_object++;
        }
      }
      obj_class_data->dirty_object_byte_count += dirty_byte_count_per_object;
      obj_class_data->dirty_object_size_in_bytes += obj_size;
      obj_class_data->dirty_objects.push_back(current_remote);
    } else {
      ++obj_class_data->clean_object_count;
    }

    if (different_image_object) {
      if (region_data->dirty_objects != nullptr) {
        // print the fields that are dirty
        for (size_t i = 0; i < obj_size; ++i) {
          if (current[i] != current_remote[i]) {
            size_t dirty_count = 0;
            if (region_data->field_dirty_count->find(i) != region_data->field_dirty_count->end()) {
              dirty_count = (*region_data->field_dirty_count)[i];
            }
            (*region_data->field_dirty_count)[i] = dirty_count + 1;
          }
        }

        region_data->dirty_objects->push_back(current);
      }
      /*
       * TODO: Resurrect this stuff in the client when we add ArtMethod iterator.
      } else {
        std::string descriptor = GetClassDescriptor(klass);
        if (strcmp(descriptor.c_str(), "Ljava/lang/reflect/ArtMethod;") == 0) {
          // this is an ArtMethod
          ArtMethod* art_method = reinterpret_cast<ArtMethod*>(remote_obj);

          // print the fields that are dirty
          for (size_t i = 0; i < obj_size; ++i) {
            if (current[i] != current_remote[i]) {
              art_method_field_dirty_count[i]++;
            }
          }

          art_method_dirty_objects.push_back(art_method);
        }
      }
      */
    } else if (ObjectIsOnDirtyPage(current, obj_size, dirty_page_set_local)) {
      // This object was either never mutated or got mutated back to the same value.
      // TODO: Do I want to distinguish a "different" vs a "dirty" page here?
      region_data->false_dirty_objects.push_back(current);
      obj_class_data->false_dirty_objects.push_back(current);
      region_data->false_dirty_object_bytes += obj_size;
      obj_class_data->false_dirty_byte_count += obj_size;
      obj_class_data->false_dirty_object_count += 1;
    }
  }

  // Look at /proc/$pid/mem and only diff the things from there
  bool DumpImageDiffMap()
    REQUIRES_SHARED(Locks::mutator_lock_) {
    std::ostream& os = *os_;
    std::string error_msg;

    // Walk the bytes and diff against our boot image
    os << "\nObserving boot image header at address "
       << reinterpret_cast<const void*>(&image_header_)
       << "\n\n";

    const uint8_t* image_begin_unaligned = image_header_.GetImageBegin();
    const uint8_t* image_mirror_end_unaligned = image_begin_unaligned +
        image_header_.GetImageSection(ImageHeader::kSectionObjects).Size();
    const uint8_t* image_end_unaligned = image_begin_unaligned + image_header_.GetImageSize();

    // Adjust range to nearest page
    const uint8_t* image_begin = AlignDown(image_begin_unaligned, kPageSize);
    const uint8_t* image_end = AlignUp(image_end_unaligned, kPageSize);

    if (reinterpret_cast<uintptr_t>(image_begin) > boot_map_.start ||
        reinterpret_cast<uintptr_t>(image_end) < boot_map_.end) {
      // Sanity check that we aren't trying to read a completely different boot image
      os << "Remote boot map is out of range of local boot map: " <<
        "local begin " << reinterpret_cast<const void*>(image_begin) <<
        ", local end " << reinterpret_cast<const void*>(image_end) <<
        ", remote begin " << reinterpret_cast<const void*>(boot_map_.start) <<
        ", remote end " << reinterpret_cast<const void*>(boot_map_.end);
      return false;
      // If we wanted even more validation we could map the ImageHeader from the file
    }

    size_t dirty_pages = 0;
    size_t different_pages = 0;
    size_t different_bytes = 0;
    size_t different_int32s = 0;
    size_t private_pages = 0;
    size_t private_dirty_pages = 0;

    // Set of the local virtual page indices that are dirty
    std::set<size_t> dirty_page_set_local;

    if (!ComputeDirtyBytes(image_begin,
                           &dirty_pages,
                           &different_pages,
                           &different_bytes,
                           &different_int32s,
                           &private_pages,
                           &private_dirty_pages,
                           &dirty_page_set_local)) {
      return false;
    }

    std::map<mirror::Class*, ClassData> class_data;

    // Walk each object in the remote image space and compare it against ours
    std::map<off_t /* field offset */, int /* count */> art_method_field_dirty_count;
    std::vector<ArtMethod*> art_method_dirty_objects;

    std::map<off_t /* field offset */, size_t /* count */> class_field_dirty_count;
    std::vector<const uint8_t*> class_dirty_objects;


    // Look up remote classes by their descriptor
    std::map<std::string, mirror::Class*> remote_class_map;
    // Look up local classes by their descriptor
    std::map<std::string, mirror::Class*> local_class_map;

    const uint8_t* begin_image_ptr = image_begin_unaligned;
    const uint8_t* end_image_ptr = image_mirror_end_unaligned;

    ObjectRegionData region_data;

    const uint8_t* current = begin_image_ptr + RoundUp(sizeof(ImageHeader), kObjectAlignment);
    while (reinterpret_cast<uintptr_t>(current) < reinterpret_cast<uintptr_t>(end_image_ptr)) {
      CHECK_ALIGNED(current, kObjectAlignment);
      mirror::Object* obj = reinterpret_cast<mirror::Object*>(const_cast<uint8_t*>(current));

      // Sanity check that we are reading a real object
      CHECK(obj->GetClass() != nullptr) << "Image object at address " << obj << " has null class";
      if (kUseBakerReadBarrier) {
        obj->AssertReadBarrierState();
      }

      mirror::Class* klass = obj->GetClass();
      size_t obj_size = obj->SizeOf();
      ClassData& obj_class_data = class_data[klass];

      // Check against the other object and see if they are different
      ptrdiff_t offset = current - begin_image_ptr;
      const uint8_t* current_remote = &remote_contents_[offset];
      const uint8_t* current_zygote =
          zygote_contents_.empty() ? nullptr : &zygote_contents_[offset];

      if (klass->IsClassClass()) {
        region_data.field_dirty_count = &class_field_dirty_count;
        region_data.dirty_objects = &class_dirty_objects;
      } else {
        region_data.field_dirty_count = nullptr;
        region_data.dirty_objects = nullptr;
      }


      ComputeObjectDirty(current,
                         current_remote,
                         current_zygote,
                         &obj_class_data,
                         obj_size,
                         dirty_page_set_local,
                         &region_data);

      // Object specific stuff.
      std::string descriptor = GetClassDescriptor(klass);
      if (strcmp(descriptor.c_str(), "Ljava/lang/Class;") == 0) {
        local_class_map[descriptor] = reinterpret_cast<mirror::Class*>(obj);
        mirror::Object* remote_obj = reinterpret_cast<mirror::Object*>(
            const_cast<uint8_t*>(current_remote));
        remote_class_map[descriptor] = reinterpret_cast<mirror::Class*>(remote_obj);
      }

      // Unconditionally store the class descriptor in case we need it later
      obj_class_data.descriptor = descriptor;

      current += RoundUp(obj_size, kObjectAlignment);
    }

    // Looking at only dirty pages, figure out how many of those bytes belong to dirty objects.
    float true_dirtied_percent = region_data.dirty_object_bytes * 1.0f / (dirty_pages * kPageSize);
    size_t false_dirty_pages = dirty_pages - different_pages;

    os << "Mapping at [" << reinterpret_cast<void*>(boot_map_.start) << ", "
       << reinterpret_cast<void*>(boot_map_.end) << ") had: \n  "
       << different_bytes << " differing bytes, \n  "
       << different_int32s << " differing int32s, \n  "
       << region_data.different_objects << " different objects, \n  "
       << region_data.dirty_object_bytes << " different object [bytes], \n  "
       << region_data.false_dirty_objects.size() << " false dirty objects,\n  "
       << region_data.false_dirty_object_bytes << " false dirty object [bytes], \n  "
       << true_dirtied_percent << " different objects-vs-total in a dirty page;\n  "
       << different_pages << " different pages; \n  "
       << dirty_pages << " pages are dirty; \n  "
       << false_dirty_pages << " pages are false dirty; \n  "
       << private_pages << " pages are private; \n  "
       << private_dirty_pages << " pages are Private_Dirty\n  "
       << "";

    // vector of pairs (int count, Class*)
    auto dirty_object_class_values = SortByValueDesc<mirror::Class*, int, ClassData>(
        class_data, [](const ClassData& d) { return d.dirty_object_count; });
    auto clean_object_class_values = SortByValueDesc<mirror::Class*, int, ClassData>(
        class_data, [](const ClassData& d) { return d.clean_object_count; });

    if (!region_data.zygote_dirty_objects.empty()) {
      // We only reach this point if both pids were specified.  Furthermore,
      // objects are only displayed here if they differed in both the image
      // and the zygote, so they are probably private dirty.
      CHECK(image_diff_pid_ > 0 && zygote_diff_pid_ > 0);
      os << "\n" << "  Zygote dirty objects (probably shared dirty): "
         << region_data.zygote_dirty_objects.size() << "\n";
      for (const uint8_t* obj_bytes : region_data.zygote_dirty_objects) {
        auto obj = const_cast<mirror::Object*>(reinterpret_cast<const mirror::Object*>(obj_bytes));
        ptrdiff_t offset = obj_bytes - begin_image_ptr;
        uint8_t* remote_bytes = &zygote_contents_[offset];
        DiffObjectContents(obj, remote_bytes, os);
      }
    }
    os << "\n";
    if (zygote_pid_only_) {
      // image_diff_pid_ is the zygote process.
      os << "  Zygote shared dirty objects: ";
    } else {
      // image_diff_pid_ is actually the image (application) process.
      if (zygote_diff_pid_ > 0) {
        os << "  Application dirty objects (private dirty): ";
      } else {
        os << "  Application dirty objects (unknown whether private or shared dirty): ";
      }
    }
    os << region_data.image_dirty_objects.size() << "\n";
    for (const uint8_t* obj_bytes : region_data.image_dirty_objects) {
      auto obj = const_cast<mirror::Object*>(reinterpret_cast<const mirror::Object*>(obj_bytes));
      ptrdiff_t offset = obj_bytes - begin_image_ptr;
      uint8_t* remote_bytes = &remote_contents_[offset];
      DiffObjectContents(obj, remote_bytes, os);
    }

    os << "\n" << "  Dirty object count by class:\n";
    for (const auto& vk_pair : dirty_object_class_values) {
      int dirty_object_count = vk_pair.first;
      mirror::Class* klass = vk_pair.second;
      int object_sizes = class_data[klass].dirty_object_size_in_bytes;
      float avg_dirty_bytes_per_class =
          class_data[klass].dirty_object_byte_count * 1.0f / object_sizes;
      float avg_object_size = object_sizes * 1.0f / dirty_object_count;
      const std::string& descriptor = class_data[klass].descriptor;
      os << "    " << mirror::Class::PrettyClass(klass) << " ("
         << "objects: " << dirty_object_count << ", "
         << "avg dirty bytes: " << avg_dirty_bytes_per_class << ", "
         << "avg object size: " << avg_object_size << ", "
         << "class descriptor: '" << descriptor << "'"
         << ")\n";

      constexpr size_t kMaxAddressPrint = 5;
      if (strcmp(descriptor.c_str(), "Ljava/lang/reflect/ArtMethod;") == 0) {
        os << "      sample object addresses: ";
        for (size_t i = 0; i < art_method_dirty_objects.size() && i < kMaxAddressPrint; ++i) {
          auto art_method = art_method_dirty_objects[i];

          os << reinterpret_cast<void*>(art_method) << ", ";
        }
        os << "\n";

        os << "      dirty byte +offset:count list = ";
        auto art_method_field_dirty_count_sorted =
            SortByValueDesc<off_t, int, int>(art_method_field_dirty_count);
        for (auto pair : art_method_field_dirty_count_sorted) {
          off_t offset = pair.second;
          int count = pair.first;

          os << "+" << offset << ":" << count << ", ";
        }

        os << "\n";

        os << "      field contents:\n";
        const auto& dirty_objects_list = class_data[klass].dirty_objects;
        for (const uint8_t* uobj : dirty_objects_list) {
          auto obj = const_cast<mirror::Object*>(reinterpret_cast<const mirror::Object*>(uobj));
          // remote method
          auto art_method = reinterpret_cast<ArtMethod*>(obj);

          // remote class
          mirror::Class* remote_declaring_class =
            FixUpRemotePointer(art_method->GetDeclaringClass(), remote_contents_, boot_map_);

          // local class
          mirror::Class* declaring_class =
            RemoteContentsPointerToLocal(remote_declaring_class, remote_contents_, image_header_);

          os << "        " << reinterpret_cast<void*>(obj) << " ";
          os << "  entryPointFromJni: "
             << reinterpret_cast<const void*>(
                    art_method->GetDataPtrSize(pointer_size_)) << ", ";
          os << "  entryPointFromQuickCompiledCode: "
             << reinterpret_cast<const void*>(
                    art_method->GetEntryPointFromQuickCompiledCodePtrSize(pointer_size_))
             << ", ";
          os << "  isNative? " << (art_method->IsNative() ? "yes" : "no") << ", ";
          os << "  class_status (local): " << declaring_class->GetStatus();
          os << "  class_status (remote): " << remote_declaring_class->GetStatus();
          os << "\n";
        }
      }
      if (strcmp(descriptor.c_str(), "Ljava/lang/Class;") == 0) {
        os << "       sample object addresses: ";
        for (size_t i = 0; i < class_dirty_objects.size() && i < kMaxAddressPrint; ++i) {
          auto class_ptr = class_dirty_objects[i];

          os << reinterpret_cast<const void*>(class_ptr) << ", ";
        }
        os << "\n";

        os << "       dirty byte +offset:count list = ";
        auto class_field_dirty_count_sorted =
            SortByValueDesc<off_t, int, size_t>(class_field_dirty_count);
        for (auto pair : class_field_dirty_count_sorted) {
          off_t offset = pair.second;
          int count = pair.first;

          os << "+" << offset << ":" << count << ", ";
        }
        os << "\n";

        os << "      field contents:\n";
        // TODO: templatize this to avoid the awful casts down to uint8_t* and back.
        const auto& dirty_objects_list = class_data[klass].dirty_objects;
        for (const uint8_t* uobj : dirty_objects_list) {
          auto obj = const_cast<mirror::Object*>(reinterpret_cast<const mirror::Object*>(uobj));
          // remote class object
          auto remote_klass = reinterpret_cast<mirror::Class*>(obj);

          // local class object
          auto local_klass = RemoteContentsPointerToLocal(remote_klass,
                                                          remote_contents_,
                                                          image_header_);

          os << "        " << reinterpret_cast<const void*>(obj) << " ";
          os << "  class_status (remote): " << remote_klass->GetStatus() << ", ";
          os << "  class_status (local): " << local_klass->GetStatus();
          os << "\n";
        }
      }
    }

    auto false_dirty_object_class_values = SortByValueDesc<mirror::Class*, int, ClassData>(
        class_data, [](const ClassData& d) { return d.false_dirty_object_count; });

    os << "\n" << "  False-dirty object count by class:\n";
    for (const auto& vk_pair : false_dirty_object_class_values) {
      int object_count = vk_pair.first;
      mirror::Class* klass = vk_pair.second;
      int object_sizes = class_data[klass].false_dirty_byte_count;
      float avg_object_size = object_sizes * 1.0f / object_count;
      const std::string& descriptor = class_data[klass].descriptor;
      os << "    " << mirror::Class::PrettyClass(klass) << " ("
         << "objects: " << object_count << ", "
         << "avg object size: " << avg_object_size << ", "
         << "total bytes: " << object_sizes << ", "
         << "class descriptor: '" << descriptor << "'"
         << ")\n";

      if (strcmp(descriptor.c_str(), "Ljava/lang/reflect/ArtMethod;") == 0) {
        // TODO: templatize this to avoid the awful casts down to uint8_t* and back.
        auto& art_method_false_dirty_objects = class_data[klass].false_dirty_objects;

        os << "      field contents:\n";
        for (const uint8_t* uobj : art_method_false_dirty_objects) {
          auto obj = const_cast<mirror::Object*>(reinterpret_cast<const mirror::Object*>(uobj));
          // local method
          auto art_method = reinterpret_cast<ArtMethod*>(obj);

          // local class
          mirror::Class* declaring_class = art_method->GetDeclaringClass();

          os << "        " << reinterpret_cast<const void*>(obj) << " ";
          os << "  entryPointFromJni: "
             << reinterpret_cast<const void*>(
                    art_method->GetDataPtrSize(pointer_size_)) << ", ";
          os << "  entryPointFromQuickCompiledCode: "
             << reinterpret_cast<const void*>(
                    art_method->GetEntryPointFromQuickCompiledCodePtrSize(pointer_size_))
             << ", ";
          os << "  isNative? " << (art_method->IsNative() ? "yes" : "no") << ", ";
          os << "  class_status (local): " << declaring_class->GetStatus();
          os << "\n";
        }
      }
    }

    os << "\n" << "  Clean object count by class:\n";
    for (const auto& vk_pair : clean_object_class_values) {
      os << "    " << mirror::Class::PrettyClass(vk_pair.second) << " (" << vk_pair.first << ")\n";
    }

    return true;
  }

  // Fixup a remote pointer that we read from a foreign boot.art to point to our own memory.
  // Returned pointer will point to inside of remote_contents.
  template <typename T>
  static T* FixUpRemotePointer(T* remote_ptr,
                               std::vector<uint8_t>& remote_contents,
                               const backtrace_map_t& boot_map) {
    if (remote_ptr == nullptr) {
      return nullptr;
    }

    uintptr_t remote = reinterpret_cast<uintptr_t>(remote_ptr);

    CHECK_LE(boot_map.start, remote);
    CHECK_GT(boot_map.end, remote);

    off_t boot_offset = remote - boot_map.start;

    return reinterpret_cast<T*>(&remote_contents[boot_offset]);
  }

  template <typename T>
  static T* RemoteContentsPointerToLocal(T* remote_ptr,
                                         std::vector<uint8_t>& remote_contents,
                                         const ImageHeader& image_header) {
    if (remote_ptr == nullptr) {
      return nullptr;
    }

    uint8_t* remote = reinterpret_cast<uint8_t*>(remote_ptr);
    ptrdiff_t boot_offset = remote - &remote_contents[0];

    const uint8_t* local_ptr = reinterpret_cast<const uint8_t*>(&image_header) + boot_offset;

    return reinterpret_cast<T*>(const_cast<uint8_t*>(local_ptr));
  }

  static std::string GetClassDescriptor(mirror::Class* klass)
    REQUIRES_SHARED(Locks::mutator_lock_) {
    CHECK(klass != nullptr);

    std::string descriptor;
    const char* descriptor_str = klass->GetDescriptor(&descriptor);

    return std::string(descriptor_str);
  }

  template <typename K, typename V, typename D>
  static std::vector<std::pair<V, K>> SortByValueDesc(
      const std::map<K, D> map,
      std::function<V(const D&)> value_mapper = [](const D& d) { return static_cast<V>(d); }) {
    // Store value->key so that we can use the default sort from pair which
    // sorts by value first and then key
    std::vector<std::pair<V, K>> value_key_vector;

    for (const auto& kv_pair : map) {
      value_key_vector.push_back(std::make_pair(value_mapper(kv_pair.second), kv_pair.first));
    }

    // Sort in reverse (descending order)
    std::sort(value_key_vector.rbegin(), value_key_vector.rend());
    return value_key_vector;
  }

  static bool GetPageFrameNumber(File* page_map_file,
                                size_t virtual_page_index,
                                uint64_t* page_frame_number,
                                std::string* error_msg) {
    CHECK(page_map_file != nullptr);
    CHECK(page_frame_number != nullptr);
    CHECK(error_msg != nullptr);

    constexpr size_t kPageMapEntrySize = sizeof(uint64_t);
    constexpr uint64_t kPageFrameNumberMask = (1ULL << 55) - 1;  // bits 0-54 [in /proc/$pid/pagemap]
    constexpr uint64_t kPageSoftDirtyMask = (1ULL << 55);  // bit 55 [in /proc/$pid/pagemap]

    uint64_t page_map_entry = 0;

    // Read 64-bit entry from /proc/$pid/pagemap to get the physical page frame number
    if (!page_map_file->PreadFully(&page_map_entry, kPageMapEntrySize,
                                  virtual_page_index * kPageMapEntrySize)) {
      *error_msg = StringPrintf("Failed to read the virtual page index entry from %s",
                                page_map_file->GetPath().c_str());
      return false;
    }

    // TODO: seems useless, remove this.
    bool soft_dirty = (page_map_entry & kPageSoftDirtyMask) != 0;
    if ((false)) {
      LOG(VERBOSE) << soft_dirty;  // Suppress unused warning
      UNREACHABLE();
    }

    *page_frame_number = page_map_entry & kPageFrameNumberMask;

    return true;
  }

  static int IsPageDirty(File* page_map_file,
                         File* clean_pagemap_file,
                         File* kpageflags_file,
                         File* kpagecount_file,
                         size_t virtual_page_idx,
                         size_t clean_virtual_page_idx,
                         // Out parameters:
                         uint64_t* page_count, std::string* error_msg) {
    CHECK(page_map_file != nullptr);
    CHECK(clean_pagemap_file != nullptr);
    CHECK_NE(page_map_file, clean_pagemap_file);
    CHECK(kpageflags_file != nullptr);
    CHECK(kpagecount_file != nullptr);
    CHECK(page_count != nullptr);
    CHECK(error_msg != nullptr);

    // Constants are from https://www.kernel.org/doc/Documentation/vm/pagemap.txt

    constexpr size_t kPageFlagsEntrySize = sizeof(uint64_t);
    constexpr size_t kPageCountEntrySize = sizeof(uint64_t);
    constexpr uint64_t kPageFlagsDirtyMask = (1ULL << 4);  // in /proc/kpageflags
    constexpr uint64_t kPageFlagsNoPageMask = (1ULL << 20);  // in /proc/kpageflags
    constexpr uint64_t kPageFlagsMmapMask = (1ULL << 11);  // in /proc/kpageflags

    uint64_t page_frame_number = 0;
    if (!GetPageFrameNumber(page_map_file, virtual_page_idx, &page_frame_number, error_msg)) {
      return -1;
    }

    uint64_t page_frame_number_clean = 0;
    if (!GetPageFrameNumber(clean_pagemap_file, clean_virtual_page_idx, &page_frame_number_clean,
                            error_msg)) {
      return -1;
    }

    // Read 64-bit entry from /proc/kpageflags to get the dirty bit for a page
    uint64_t kpage_flags_entry = 0;
    if (!kpageflags_file->PreadFully(&kpage_flags_entry,
                                     kPageFlagsEntrySize,
                                     page_frame_number * kPageFlagsEntrySize)) {
      *error_msg = StringPrintf("Failed to read the page flags from %s",
                                kpageflags_file->GetPath().c_str());
      return -1;
    }

    // Read 64-bit entyry from /proc/kpagecount to get mapping counts for a page
    if (!kpagecount_file->PreadFully(page_count /*out*/,
                                     kPageCountEntrySize,
                                     page_frame_number * kPageCountEntrySize)) {
      *error_msg = StringPrintf("Failed to read the page count from %s",
                                kpagecount_file->GetPath().c_str());
      return -1;
    }

    // There must be a page frame at the requested address.
    CHECK_EQ(kpage_flags_entry & kPageFlagsNoPageMask, 0u);
    // The page frame must be memory mapped
    CHECK_NE(kpage_flags_entry & kPageFlagsMmapMask, 0u);

    // Page is dirty, i.e. has diverged from file, if the 4th bit is set to 1
    bool flags_dirty = (kpage_flags_entry & kPageFlagsDirtyMask) != 0;

    // page_frame_number_clean must come from the *same* process
    // but a *different* mmap than page_frame_number
    if (flags_dirty) {
      CHECK_NE(page_frame_number, page_frame_number_clean);
    }

    return page_frame_number != page_frame_number_clean;
  }

  void PrintPidLine(const std::string& kind, pid_t pid) {
    if (pid < 0) {
      *os_ << kind << " DIFF PID: disabled\n\n";
    } else {
      *os_ << kind << " DIFF PID (" << pid << "): ";
    }
  }

  static bool EndsWith(const std::string& str, const std::string& suffix) {
    return str.size() >= suffix.size() &&
           str.compare(str.size() - suffix.size(), suffix.size(), suffix) == 0;
  }

  // Return suffix of the file path after the last /. (e.g. /foo/bar -> bar, bar -> bar)
  static std::string BaseName(const std::string& str) {
    size_t idx = str.rfind('/');
    if (idx == std::string::npos) {
      return str;
    }

    return str.substr(idx + 1);
  }

  // Return the image location, stripped of any directories, e.g. "boot.art" or "core.art"
  std::string GetImageLocationBaseName() const {
    return BaseName(std::string(image_location_));
  }

  std::ostream* os_;
  const ImageHeader& image_header_;
  const std::string image_location_;
  pid_t image_diff_pid_;  // Dump image diff against boot.art if pid is non-negative
  pid_t zygote_diff_pid_;  // Dump image diff against zygote boot.art if pid is non-negative
  bool zygote_pid_only_;  // The user only specified a pid for the zygote.

  // Pointer size constant for object fields, etc.
  PointerSize pointer_size_;
  // BacktraceMap used for finding the memory mapping of the image file.
  std::unique_ptr<BacktraceMap> proc_maps_;
  // Boot image mapping.
  backtrace_map_t boot_map_{};  // NOLINT
  // The size of the boot image mapping.
  size_t boot_map_size_;
  // The contents of /proc/<image_diff_pid_>/maps.
  std::vector<uint8_t> remote_contents_;
  // The contents of /proc/<zygote_diff_pid_>/maps.
  std::vector<uint8_t> zygote_contents_;
  // A File for reading /proc/<zygote_diff_pid_>/maps.
  File pagemap_file_;
  // A File for reading /proc/self/pagemap.
  File clean_pagemap_file_;
  // A File for reading /proc/kpageflags.
  File kpageflags_file_;
  // A File for reading /proc/kpagecount.
  File kpagecount_file_;

  DISALLOW_COPY_AND_ASSIGN(ImgDiagDumper);
};

static int DumpImage(Runtime* runtime,
                     std::ostream* os,
                     pid_t image_diff_pid,
                     pid_t zygote_diff_pid) {
  ScopedObjectAccess soa(Thread::Current());
  gc::Heap* heap = runtime->GetHeap();
  std::vector<gc::space::ImageSpace*> image_spaces = heap->GetBootImageSpaces();
  CHECK(!image_spaces.empty());
  for (gc::space::ImageSpace* image_space : image_spaces) {
    const ImageHeader& image_header = image_space->GetImageHeader();
    if (!image_header.IsValid()) {
      fprintf(stderr, "Invalid image header %s\n", image_space->GetImageLocation().c_str());
      return EXIT_FAILURE;
    }

    ImgDiagDumper img_diag_dumper(os,
                                  image_header,
                                  image_space->GetImageLocation(),
                                  image_diff_pid,
                                  zygote_diff_pid);
    if (!img_diag_dumper.Init()) {
      return EXIT_FAILURE;
    }
    if (!img_diag_dumper.Dump()) {
      return EXIT_FAILURE;
    }
  }
  return EXIT_SUCCESS;
}

struct ImgDiagArgs : public CmdlineArgs {
 protected:
  using Base = CmdlineArgs;

  virtual ParseStatus ParseCustom(const StringPiece& option,
                                  std::string* error_msg) OVERRIDE {
    {
      ParseStatus base_parse = Base::ParseCustom(option, error_msg);
      if (base_parse != kParseUnknownArgument) {
        return base_parse;
      }
    }

    if (option.starts_with("--image-diff-pid=")) {
      const char* image_diff_pid = option.substr(strlen("--image-diff-pid=")).data();

      if (!ParseInt(image_diff_pid, &image_diff_pid_)) {
        *error_msg = "Image diff pid out of range";
        return kParseError;
      }
    } else if (option.starts_with("--zygote-diff-pid=")) {
      const char* zygote_diff_pid = option.substr(strlen("--zygote-diff-pid=")).data();

      if (!ParseInt(zygote_diff_pid, &zygote_diff_pid_)) {
        *error_msg = "Zygote diff pid out of range";
        return kParseError;
      }
    } else {
      return kParseUnknownArgument;
    }

    return kParseOk;
  }

  virtual ParseStatus ParseChecks(std::string* error_msg) OVERRIDE {
    // Perform the parent checks.
    ParseStatus parent_checks = Base::ParseChecks(error_msg);
    if (parent_checks != kParseOk) {
      return parent_checks;
    }

    // Perform our own checks.

    if (kill(image_diff_pid_,
             /*sig*/0) != 0) {  // No signal is sent, perform error-checking only.
      // Check if the pid exists before proceeding.
      if (errno == ESRCH) {
        *error_msg = "Process specified does not exist";
      } else {
        *error_msg = StringPrintf("Failed to check process status: %s", strerror(errno));
      }
      return kParseError;
    } else if (instruction_set_ != kRuntimeISA) {
      // Don't allow different ISAs since the images are ISA-specific.
      // Right now the code assumes both the runtime ISA and the remote ISA are identical.
      *error_msg = "Must use the default runtime ISA; changing ISA is not supported.";
      return kParseError;
    }

    return kParseOk;
  }

  virtual std::string GetUsage() const {
    std::string usage;

    usage +=
        "Usage: imgdiag [options] ...\n"
        "    Example: imgdiag --image-diff-pid=$(pidof dex2oat)\n"
        "    Example: adb shell imgdiag --image-diff-pid=$(pid zygote)\n"
        "\n";

    usage += Base::GetUsage();

    usage +=  // Optional.
        "  --image-diff-pid=<pid>: provide the PID of a process whose boot.art you want to diff.\n"
        "      Example: --image-diff-pid=$(pid zygote)\n"
        "  --zygote-diff-pid=<pid>: provide the PID of the zygote whose boot.art you want to diff "
        "against.\n"
        "      Example: --zygote-diff-pid=$(pid zygote)\n"
        "\n";

    return usage;
  }

 public:
  pid_t image_diff_pid_ = -1;
  pid_t zygote_diff_pid_ = -1;
};

struct ImgDiagMain : public CmdlineMain<ImgDiagArgs> {
  virtual bool ExecuteWithRuntime(Runtime* runtime) {
    CHECK(args_ != nullptr);

    return DumpImage(runtime,
                     args_->os_,
                     args_->image_diff_pid_,
                     args_->zygote_diff_pid_) == EXIT_SUCCESS;
  }
};

}  // namespace art

int main(int argc, char** argv) {
  art::ImgDiagMain main;
  return main.Main(argc, argv);
}