Add a new imgdiag tool to diff boot.art/core.art against a process

Analyze the dirty memory pages of a running process per-object,
this allows is to to fine-tune the dirty object binning algorithm in
image writer.

Also:
* Factor out oatdump command line parsing code into cmdline.h
* Factor out common build rules for building variations of binaries
* Add a gtest for imgdiag

Bug: 17611661
Change-Id: I3ac852a0d223af66f6d59ae5dbc3df101475e3d0

3 files changed, 1117 insertions, 0 deletions

diff --git a/imgdiag/Android.mk b/imgdiag/Android.mk
new file mode 100644
index 0000000..d5d7c22
--- /dev/null
+++ b/imgdiag/Android.mk
@@ -0,0 +1,28 @@
+#
+# 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.
+#
+
+LOCAL_PATH := $(call my-dir)
+
+include art/build/Android.executable.mk
+
+IMGDIAG_SRC_FILES := \
+	imgdiag.cc
+
+# Note that this tool needs to be built for both 32-bit and 64-bit since it requires
+# that the image it's analyzing be the same ISA as the runtime ISA.
+
+# Build variants {target,host} x {debug,ndebug} x {32,64}
+$(eval $(call build-art-multi-executable,imgdiag,$(IMGDIAG_SRC_FILES),libart-compiler libbacktrace,libcutils,libziparchive-host,art/compiler,both))
diff --git a/imgdiag/imgdiag.cc b/imgdiag/imgdiag.cc
new file mode 100644
index 0000000..9b57ecb
--- /dev/null
+++ b/imgdiag/imgdiag.cc
@@ -0,0 +1,951 @@
+/*
+ * 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 <iostream>
+#include <string>
+#include <vector>
+#include <set>
+#include <map>
+
+#include "base/unix_file/fd_file.h"
+#include "base/stringprintf.h"
+#include "gc/space/image_space.h"
+#include "gc/heap.h"
+#include "mirror/class-inl.h"
+#include "mirror/object-inl.h"
+#include "mirror/art_method-inl.h"
+#include "image.h"
+#include "scoped_thread_state_change.h"
+#include "os.h"
+#include "gc_map.h"
+
+#include "cmdline.h"
+#include "backtrace/BacktraceMap.h"
+
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <signal.h>
+
+namespace art {
+
+class ImgDiagDumper {
+ public:
+  explicit ImgDiagDumper(std::ostream* os,
+                       const ImageHeader& image_header,
+                       const char* image_location,
+                       pid_t image_diff_pid)
+      : os_(os),
+        image_header_(image_header),
+        image_location_(image_location),
+        image_diff_pid_(image_diff_pid) {}
+
+  bool Dump() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
+    std::ostream& os = *os_;
+    os << "MAGIC: " << image_header_.GetMagic() << "\n\n";
+
+    os << "IMAGE BEGIN: " << reinterpret_cast<void*>(image_header_.GetImageBegin()) << "\n\n";
+
+    bool ret = true;
+    if (image_diff_pid_ >= 0) {
+      os << "IMAGE DIFF PID (" << image_diff_pid_ << "): ";
+      ret = DumpImageDiff(image_diff_pid_);
+      os << "\n\n";
+    } else {
+      os << "IMAGE DIFF PID: disabled\n\n";
+    }
+
+    os << std::flush;
+
+    return ret;
+  }
+
+ private:
+  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);
+  }
+
+  bool DumpImageDiff(pid_t image_diff_pid) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
+    std::ostream& os = *os_;
+
+    {
+      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/$pid/maps to view memory maps
+    auto proc_maps = std::unique_ptr<BacktraceMap>(BacktraceMap::Create(image_diff_pid));
+    if (proc_maps == nullptr) {
+      os << "Could not read backtrace maps";
+      return false;
+    }
+
+    bool found_boot_map = false;
+    backtrace_map_t boot_map = backtrace_map_t();
+    // Find the memory map only for boot.art
+    for (const backtrace_map_t& map : *proc_maps) {
+      if (EndsWith(map.name, GetImageLocationBaseName())) {
+        if ((map.flags & PROT_WRITE) != 0) {
+          boot_map = map;
+          found_boot_map = true;
+          break;
+        }
+        // In actuality there's more than 1 map, but the second one is read-only.
+        // The one we care about is the write-able map.
+        // The readonly maps are guaranteed to be identical, so its not interesting to compare
+        // them.
+      }
+    }
+
+    if (!found_boot_map) {
+      os << "Could not find map for " << GetImageLocationBaseName();
+      return false;
+    }
+
+    // Future idea: diff against zygote so we can ignore the shared dirty pages.
+    return DumpImageDiffMap(image_diff_pid, boot_map);
+  }
+
+    // Look at /proc/$pid/mem and only diff the things from there
+  bool DumpImageDiffMap(pid_t image_diff_pid, const backtrace_map_t& boot_map)
+    SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
+    std::ostream& os = *os_;
+    const size_t pointer_size = InstructionSetPointerSize(
+        Runtime::Current()->GetInstructionSet());
+
+    std::string file_name = StringPrintf("/proc/%ld/mem", static_cast<long>(image_diff_pid));  // NOLINT [runtime/int]
+
+    size_t boot_map_size = boot_map.end - boot_map.start;
+
+    // Open /proc/$pid/mem as a file
+    auto map_file = std::unique_ptr<File>(OS::OpenFileForReading(file_name.c_str()));
+    if (map_file == nullptr) {
+      os << "Failed to open " << file_name << " for reading";
+      return false;
+    }
+
+    // Memory-map /proc/$pid/mem subset from the boot map
+    CHECK(boot_map.end >= boot_map.start);
+
+    std::string error_msg;
+
+    // Walk the bytes and diff against our boot image
+    const ImageHeader& boot_image_header = GetBootImageHeader();
+
+    os << "\nObserving boot image header at address "
+       << reinterpret_cast<const void*>(&boot_image_header)
+       << "\n\n";
+
+    const uint8_t* image_begin_unaligned = boot_image_header.GetImageBegin();
+    const uint8_t* image_end_unaligned = image_begin_unaligned + boot_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);
+
+    ptrdiff_t page_off_begin = boot_image_header.GetImageBegin() - image_begin;
+
+    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
+    }
+
+    std::vector<uint8_t> remote_contents(boot_map_size);
+    if (!map_file->PreadFully(&remote_contents[0], boot_map_size, boot_map.start)) {
+      os << "Could not fully read file " << file_name;
+      return false;
+    }
+
+    std::string page_map_file_name = StringPrintf("/proc/%ld/pagemap",
+                                                  static_cast<long>(image_diff_pid));  // NOLINT [runtime/int]
+    auto page_map_file = std::unique_ptr<File>(OS::OpenFileForReading(page_map_file_name.c_str()));
+    if (page_map_file == nullptr) {
+      os << "Failed to open " << page_map_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_page_map_file_name = "/proc/self/pagemap";
+    auto clean_page_map_file = std::unique_ptr<File>(
+        OS::OpenFileForReading(clean_page_map_file_name));
+    if (clean_page_map_file == nullptr) {
+      os << "Failed to open " << clean_page_map_file_name << " for reading: " << strerror(errno);
+      return false;
+    }
+
+    auto kpage_flags_file = std::unique_ptr<File>(OS::OpenFileForReading("/proc/kpageflags"));
+    if (kpage_flags_file == nullptr) {
+      os << "Failed to open /proc/kpageflags for reading: " << strerror(errno);
+      return false;
+    }
+
+    auto kpage_count_file = std::unique_ptr<File>(OS::OpenFileForReading("/proc/kpagecount"));
+    if (kpage_count_file == nullptr) {
+      os << "Failed to open /proc/kpagecount for reading:" << strerror(errno);
+      return false;
+    }
+
+    std::set<size_t> dirty_page_set_remote;  // Set of the remote virtual page indices that are dirty
+    std::set<size_t> dirty_page_set_local;   // Set of the local virtual page indices that are dirty
+
+    size_t different_int32s = 0;
+    size_t different_bytes = 0;
+    size_t different_pages = 0;
+    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
+    size_t dirty_pages = 0;
+    size_t private_pages = 0;
+    size_t private_dirty_pages = 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*>(&boot_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.
+    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*>(&boot_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
+        int dirtiness = (IsPageDirty(page_map_file.get(),        // Image-diff-pid procmap
+                                     clean_page_map_file.get(),  // Self procmap
+                                     kpage_flags_file.get(),
+                                     kpage_count_file.get(),
+                                     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_remote.insert(dirty_page_set_remote.end(), remote_virtual_page_idx);
+          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++;
+        }
+      }
+    }
+
+    // Walk each object in the remote image space and compare it against ours
+    size_t different_objects = 0;
+    std::map<mirror::Class*, int /*count*/> dirty_object_class_map;
+    // Track only the byte-per-byte dirtiness (in bytes)
+    std::map<mirror::Class*, int /*byte_count*/> dirty_object_byte_count;
+    // Track the object-by-object dirtiness (in bytes)
+    std::map<mirror::Class*, int /*byte_count*/> dirty_object_size_in_bytes;
+    std::map<mirror::Class*, int /*count*/> clean_object_class_map;
+
+    std::map<mirror::Class*, std::string> class_to_descriptor_map;
+
+    std::map<off_t /* field offset */, int /* count */> art_method_field_dirty_count;
+    std::vector<mirror::ArtMethod*> art_method_dirty_objects;
+
+    std::map<off_t /* field offset */, int /* count */> class_field_dirty_count;
+    std::vector<mirror::Class*> class_dirty_objects;
+
+    // List of local objects that are clean, but located on dirty pages.
+    std::vector<mirror::Object*> false_dirty_objects;
+    std::map<mirror::Class*, int /*byte_count*/> false_dirty_byte_count;
+    std::map<mirror::Class*, int /*object_count*/> false_dirty_object_count;
+    std::map<mirror::Class*, std::vector<mirror::Object*>> false_dirty_objects_map;
+    size_t false_dirty_object_bytes = 0;
+
+    // Remote pointers to dirty objects
+    std::map<mirror::Class*, std::vector<mirror::Object*>> dirty_objects_by_class;
+    // 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;
+
+    size_t dirty_object_bytes = 0;
+    {
+      const uint8_t* begin_image_ptr = image_begin_unaligned;
+      const uint8_t* end_image_ptr = image_end_unaligned;
+
+      const uint8_t* current = begin_image_ptr + RoundUp(sizeof(ImageHeader), kObjectAlignment);
+      while (reinterpret_cast<const uintptr_t>(current)
+             < reinterpret_cast<const 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 (kUseBakerOrBrooksReadBarrier) {
+          obj->AssertReadBarrierPointer();
+        }
+
+        // Iterate every page this object belongs to
+        bool on_dirty_page = false;
+        size_t page_off = 0;
+        size_t current_page_idx;
+        uintptr_t object_address;
+        do {
+          object_address = reinterpret_cast<uintptr_t>(current);
+          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
+            on_dirty_page = true;
+          }
+
+          page_off++;
+        } while ((current_page_idx * kPageSize) <
+                 RoundUp(object_address + obj->SizeOf(), kObjectAlignment));
+
+        mirror::Class* klass = obj->GetClass();
+
+        bool different_object = false;
+
+        // 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];
+        mirror::Object* remote_obj = reinterpret_cast<mirror::Object*>(
+            const_cast<uint8_t*>(current_remote));
+        if (memcmp(current, current_remote, obj->SizeOf()) != 0) {
+          different_objects++;
+          dirty_object_bytes += obj->SizeOf();
+
+          ++dirty_object_class_map[klass];
+
+          // 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->SizeOf(); ++i) {
+            if (current[i] != current_remote[i]) {
+              dirty_byte_count_per_object++;
+            }
+          }
+          dirty_object_byte_count[klass] += dirty_byte_count_per_object;
+          dirty_object_size_in_bytes[klass] += obj->SizeOf();
+
+          different_object = true;
+
+          dirty_objects_by_class[klass].push_back(remote_obj);
+        } else {
+          ++clean_object_class_map[klass];
+        }
+
+        std::string descriptor = GetClassDescriptor(klass);
+        if (different_object) {
+          if (strcmp(descriptor.c_str(), "Ljava/lang/Class;") == 0) {
+            // this is a "Class"
+            mirror::Class* obj_as_class  = reinterpret_cast<mirror::Class*>(remote_obj);
+
+            // print the fields that are dirty
+            for (size_t i = 0; i < obj->SizeOf(); ++i) {
+              if (current[i] != current_remote[i]) {
+                class_field_dirty_count[i]++;
+              }
+            }
+
+            class_dirty_objects.push_back(obj_as_class);
+          } else if (strcmp(descriptor.c_str(), "Ljava/lang/reflect/ArtMethod;") == 0) {
+            // this is an ArtMethod
+            mirror::ArtMethod* art_method = reinterpret_cast<mirror::ArtMethod*>(remote_obj);
+
+            // print the fields that are dirty
+            for (size_t i = 0; i < obj->SizeOf(); ++i) {
+              if (current[i] != current_remote[i]) {
+                art_method_field_dirty_count[i]++;
+              }
+            }
+
+            art_method_dirty_objects.push_back(art_method);
+          }
+        } else if (on_dirty_page) {
+          // 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?
+          false_dirty_objects.push_back(obj);
+          false_dirty_objects_map[klass].push_back(obj);
+          false_dirty_object_bytes += obj->SizeOf();
+          false_dirty_byte_count[obj->GetClass()] += obj->SizeOf();
+          false_dirty_object_count[obj->GetClass()] += 1;
+        }
+
+        if (strcmp(descriptor.c_str(), "Ljava/lang/Class;") == 0) {
+          local_class_map[descriptor] = reinterpret_cast<mirror::Class*>(obj);
+          remote_class_map[descriptor] = reinterpret_cast<mirror::Class*>(remote_obj);
+        }
+
+        // Unconditionally store the class descriptor in case we need it later
+        class_to_descriptor_map[klass] = descriptor;
+        current += RoundUp(obj->SizeOf(), kObjectAlignment);
+      }
+    }
+
+    // Looking at only dirty pages, figure out how many of those bytes belong to dirty objects.
+    float true_dirtied_percent = 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  "
+       << different_objects << " different objects, \n  "
+       << dirty_object_bytes << " different object [bytes], \n  "
+       << false_dirty_objects.size() << " false dirty objects,\n  "
+       << 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(dirty_object_class_map);
+    auto clean_object_class_values = SortByValueDesc(clean_object_class_map);
+
+    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 = dirty_object_size_in_bytes[klass];
+      float avg_dirty_bytes_per_class = dirty_object_byte_count[klass] * 1.0f / object_sizes;
+      float avg_object_size = object_sizes * 1.0f / dirty_object_count;
+      const std::string& descriptor = class_to_descriptor_map[klass];
+      os << "    " << 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(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 = dirty_objects_by_class[klass];
+        for (mirror::Object* obj : dirty_objects_list) {
+          // remote method
+          auto art_method = reinterpret_cast<mirror::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,
+                                         boot_image_header);
+
+          os << "        " << reinterpret_cast<void*>(obj) << " ";
+          os << "  entryPointFromJni: "
+             << reinterpret_cast<const void*>(
+                    art_method->GetEntryPointFromJniPtrSize(pointer_size)) << ", ";
+          os << "  entryPointFromInterpreter: "
+             << reinterpret_cast<const void*>(
+                    art_method->GetEntryPointFromInterpreterPtrSize<kVerifyNone>(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<void*>(class_ptr) << ", ";
+        }
+        os << "\n";
+
+        os << "       dirty byte +offset:count list = ";
+        auto class_field_dirty_count_sorted = SortByValueDesc(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";
+        const auto& dirty_objects_list = dirty_objects_by_class[klass];
+        for (mirror::Object* obj : dirty_objects_list) {
+          // remote class object
+          auto remote_klass = reinterpret_cast<mirror::Class*>(obj);
+
+          // local class object
+          auto local_klass = RemoteContentsPointerToLocal(remote_klass,
+                                                          remote_contents,
+                                                          boot_image_header);
+
+          os << "        " << reinterpret_cast<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(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 = false_dirty_byte_count[klass];
+      float avg_object_size = object_sizes * 1.0f / object_count;
+      const std::string& descriptor = class_to_descriptor_map[klass];
+      os << "    " << 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) {
+        auto& art_method_false_dirty_objects = false_dirty_objects_map[klass];
+
+        os << "      field contents:\n";
+        for (mirror::Object* obj : art_method_false_dirty_objects) {
+          // local method
+          auto art_method = reinterpret_cast<mirror::ArtMethod*>(obj);
+
+          // local class
+          mirror::Class* declaring_class = art_method->GetDeclaringClass();
+
+          os << "        " << reinterpret_cast<void*>(obj) << " ";
+          os << "  entryPointFromJni: "
+             << reinterpret_cast<const void*>(
+                    art_method->GetEntryPointFromJniPtrSize(pointer_size)) << ", ";
+          os << "  entryPointFromInterpreter: "
+             << reinterpret_cast<const void*>(
+                    art_method->GetEntryPointFromInterpreterPtrSize<kVerifyNone>(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 << "    " << 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)
+    SHARED_LOCKS_REQUIRED(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>
+  static std::vector<std::pair<V, K>> SortByValueDesc(const std::map<K, V> map) {
+    // 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(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_page_map_file,
+                         File* kpage_flags_file,
+                         File* kpage_count_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_page_map_file != nullptr);
+    CHECK_NE(page_map_file, clean_page_map_file);
+    CHECK(kpage_flags_file != nullptr);
+    CHECK(kpage_count_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_page_map_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 (!kpage_flags_file->PreadFully(&kpage_flags_entry,
+                                     kPageFlagsEntrySize,
+                                     page_frame_number * kPageFlagsEntrySize)) {
+      *error_msg = StringPrintf("Failed to read the page flags from %s",
+                                kpage_flags_file->GetPath().c_str());
+      return -1;
+    }
+
+    // Read 64-bit entyry from /proc/kpagecount to get mapping counts for a page
+    if (!kpage_count_file->PreadFully(page_count /*out*/,
+                                     kPageCountEntrySize,
+                                     page_frame_number * kPageCountEntrySize)) {
+      *error_msg = StringPrintf("Failed to read the page count from %s",
+                                kpage_count_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;
+  }
+
+  static const ImageHeader& GetBootImageHeader() {
+    gc::Heap* heap = Runtime::Current()->GetHeap();
+    gc::space::ImageSpace* image_space = heap->GetImageSpace();
+    CHECK(image_space != nullptr);
+    const ImageHeader& image_header = image_space->GetImageHeader();
+    return image_header;
+  }
+
+ private:
+  // 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 char* image_location_;
+  pid_t image_diff_pid_;  // Dump image diff against boot.art if pid is non-negative
+
+  DISALLOW_COPY_AND_ASSIGN(ImgDiagDumper);
+};
+
+static int DumpImage(Runtime* runtime, const char* image_location,
+                     std::ostream* os, pid_t image_diff_pid) {
+  ScopedObjectAccess soa(Thread::Current());
+  gc::Heap* heap = runtime->GetHeap();
+  gc::space::ImageSpace* image_space = heap->GetImageSpace();
+  CHECK(image_space != nullptr);
+  const ImageHeader& image_header = image_space->GetImageHeader();
+  if (!image_header.IsValid()) {
+    fprintf(stderr, "Invalid image header %s\n", image_location);
+    return EXIT_FAILURE;
+  }
+
+  ImgDiagDumper img_diag_dumper(os, image_header, image_location, image_diff_pid);
+
+  bool success = img_diag_dumper.Dump();
+  return (success) ? EXIT_SUCCESS : EXIT_FAILURE;
+}
+
+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 {
+      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"
+        "\n";
+
+    return usage;
+  }
+
+ public:
+  pid_t image_diff_pid_ = -1;
+};
+
+struct ImgDiagMain : public CmdlineMain<ImgDiagArgs> {
+  virtual bool ExecuteWithRuntime(Runtime* runtime) {
+    CHECK(args_ != nullptr);
+
+    return DumpImage(runtime,
+                     args_->boot_image_location_,
+                     args_->os_,
+                     args_->image_diff_pid_) == EXIT_SUCCESS;
+  }
+};
+
+}  // namespace art
+
+int main(int argc, char** argv) {
+  art::ImgDiagMain main;
+  return main.Main(argc, argv);
+}
diff --git a/imgdiag/imgdiag_test.cc b/imgdiag/imgdiag_test.cc
new file mode 100644
index 0000000..1ac7930
--- /dev/null
+++ b/imgdiag/imgdiag_test.cc
@@ -0,0 +1,138 @@
+/*
+ * 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 <string>
+#include <vector>
+#include <sstream>
+
+#include "common_runtime_test.h"
+
+#include "runtime/os.h"
+#include "runtime/arch/instruction_set.h"
+#include "runtime/utils.h"
+#include "runtime/gc/space/image_space.h"
+#include "runtime/gc/heap.h"
+#include "base/stringprintf.h"
+
+#include <sys/types.h>
+#include <unistd.h>
+
+namespace art {
+
+static const char* kImgDiagDiffPid = "--image-diff-pid";
+static const char* kImgDiagBootImage = "--boot-image";
+static const char* kImgDiagBinaryName = "imgdiag";
+
+class ImgDiagTest : public CommonRuntimeTest {
+ protected:
+  virtual void SetUp() {
+    CommonRuntimeTest::SetUp();
+
+    // We loaded the runtime with an explicit image. Therefore the image space must exist.
+    gc::space::ImageSpace* image_space = Runtime::Current()->GetHeap()->GetImageSpace();
+    ASSERT_TRUE(image_space != nullptr);
+    boot_image_location_ = image_space->GetImageLocation();
+  }
+
+  virtual void SetUpRuntimeOptions(RuntimeOptions* options) OVERRIDE {
+    // Needs to live until CommonRuntimeTest::SetUp finishes, since we pass it a cstring.
+    runtime_args_image_ = StringPrintf("-Ximage:%s", GetCoreArtLocation().c_str());
+    options->push_back(std::make_pair(runtime_args_image_, nullptr));
+  }
+
+  // Path to the imgdiag(d?)[32|64] binary.
+  std::string GetImgDiagFilePath() {
+    std::string root = GetTestAndroidRoot();
+
+    root += "/bin/";
+    root += kImgDiagBinaryName;
+
+    if (kIsDebugBuild) {
+      root += "d";
+    }
+
+    std::string root32 = root + "32";
+    // If we have both a 32-bit and a 64-bit build, the 32-bit file will have a 32 suffix.
+    if (OS::FileExists(root32.c_str()) && !Is64BitInstructionSet(kRuntimeISA)) {
+      return root32;
+    // Only a single build exists, so the filename never has an extra suffix.
+    } else {
+      return root;
+    }
+  }
+
+  // Run imgdiag with a custom boot image location.
+  bool Exec(pid_t image_diff_pid, const std::string& boot_image, std::string* error_msg) {
+    // Invoke 'img_diag' against the current process.
+    // This should succeed because we have a runtime and so it should
+    // be able to map in the boot.art and do a diff for it.
+    std::string file_path = GetImgDiagFilePath();
+    EXPECT_TRUE(OS::FileExists(file_path.c_str())) << file_path << " should be a valid file path";
+
+    // Run imgdiag --image-diff-pid=$image_diff_pid and wait until it's done with a 0 exit code.
+    std::string diff_pid_args;
+    {
+      std::stringstream diff_pid_args_ss;
+      diff_pid_args_ss << kImgDiagDiffPid << "=" << image_diff_pid;
+      diff_pid_args = diff_pid_args_ss.str();
+    }
+    std::string boot_image_args;
+    {
+      boot_image_args = boot_image_args + kImgDiagBootImage + "=" + boot_image;
+    }
+
+    std::vector<std::string> exec_argv = { file_path, diff_pid_args, boot_image_args };
+
+    return ::art::Exec(exec_argv, error_msg);
+  }
+
+  // Run imgdiag with the default boot image location.
+  bool ExecDefaultBootImage(pid_t image_diff_pid, std::string* error_msg) {
+    return Exec(image_diff_pid, boot_image_location_, error_msg);
+  }
+
+ private:
+  std::string runtime_args_image_;
+  std::string boot_image_location_;
+};
+
+#if defined (ART_TARGET)
+TEST_F(ImgDiagTest, ImageDiffPidSelf) {
+#else
+// Can't run this test on the host, it will fail when trying to open /proc/kpagestats
+// because it's root read-only.
+TEST_F(ImgDiagTest, DISABLED_ImageDiffPidSelf) {
+#endif
+  // Invoke 'img_diag' against the current process.
+  // This should succeed because we have a runtime and so it should
+  // be able to map in the boot.art and do a diff for it.
+
+  // Run imgdiag --image-diff-pid=$(self pid) and wait until it's done with a 0 exit code.
+  std::string error_msg;
+  ASSERT_TRUE(ExecDefaultBootImage(getpid(), &error_msg)) << "Failed to execute -- because: "
+                                                          << error_msg;
+}
+
+TEST_F(ImgDiagTest, ImageDiffBadPid) {
+  // Invoke 'img_diag' against a non-existing process. This should fail.
+
+  // Run imgdiag --image-diff-pid=some_bad_pid and wait until it's done with a 0 exit code.
+  std::string error_msg;
+  ASSERT_FALSE(ExecDefaultBootImage(-12345, &error_msg)) << "Incorrectly executed";
+  UNUSED(error_msg);
+}
+
+}  // namespace art