Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

38 files changed, 6085 insertions, 0 deletions

diff --git a/memory/replace/dmd/DMD.cpp b/memory/replace/dmd/DMD.cpp
new file mode 100644
index 0000000000..54a154e60e
--- /dev/null
+++ b/memory/replace/dmd/DMD.cpp
@@ -0,0 +1,1884 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <ctype.h>
+#include <errno.h>
+#include <limits.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#if !defined(MOZ_PROFILING)
+#  error "DMD requires MOZ_PROFILING"
+#endif
+
+#ifdef XP_WIN
+#  include <windows.h>
+#  include <process.h>
+#else
+#  include <pthread.h>
+#  include <sys/types.h>
+#  include <unistd.h>
+#endif
+
+#ifdef ANDROID
+#  include <android/log.h>
+#endif
+
+#include "nscore.h"
+
+#include "mozilla/Assertions.h"
+#include "mozilla/FastBernoulliTrial.h"
+#include "mozilla/HashFunctions.h"
+#include "mozilla/HashTable.h"
+#include "mozilla/IntegerPrintfMacros.h"
+#include "mozilla/JSONWriter.h"
+#include "mozilla/Likely.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/PodOperations.h"
+#include "mozilla/StackWalk.h"
+#include "mozilla/ThreadLocal.h"
+
+// CodeAddressService is defined entirely in the header, so this does not make
+// DMD depend on XPCOM's object file.
+#include "CodeAddressService.h"
+
+// replace_malloc.h needs to be included before replace_malloc_bridge.h,
+// which DMD.h includes, so DMD.h needs to be included after replace_malloc.h.
+#include "replace_malloc.h"
+#include "DMD.h"
+
+namespace mozilla {
+namespace dmd {
+
+class DMDBridge : public ReplaceMallocBridge {
+  virtual DMDFuncs* GetDMDFuncs() override;
+};
+
+static DMDBridge* gDMDBridge;
+static DMDFuncs gDMDFuncs;
+
+DMDFuncs* DMDBridge::GetDMDFuncs() { return &gDMDFuncs; }
+
+MOZ_FORMAT_PRINTF(1, 2)
+inline void StatusMsg(const char* aFmt, ...) {
+  va_list ap;
+  va_start(ap, aFmt);
+  gDMDFuncs.StatusMsg(aFmt, ap);
+  va_end(ap);
+}
+
+//---------------------------------------------------------------------------
+// Utilities
+//---------------------------------------------------------------------------
+
+#ifndef DISALLOW_COPY_AND_ASSIGN
+#  define DISALLOW_COPY_AND_ASSIGN(T) \
+    T(const T&);                      \
+    void operator=(const T&)
+#endif
+
+static malloc_table_t gMallocTable;
+
+// This provides infallible allocations (they abort on OOM).  We use it for all
+// of DMD's own allocations, which fall into the following three cases.
+//
+// - Direct allocations (the easy case).
+//
+// - Indirect allocations in mozilla::{Vector,HashSet,HashMap} -- this class
+//   serves as their AllocPolicy.
+//
+// - Other indirect allocations (e.g. MozStackWalk) -- see the comments on
+//   Thread::mBlockIntercepts and in replace_malloc for how these work.
+//
+// It would be nice if we could use the InfallibleAllocPolicy from mozalloc,
+// but DMD cannot use mozalloc.
+//
+class InfallibleAllocPolicy {
+  static void ExitOnFailure(const void* aP);
+
+ public:
+  template <typename T>
+  static T* maybe_pod_malloc(size_t aNumElems) {
+    if (aNumElems & mozilla::tl::MulOverflowMask<sizeof(T)>::value)
+      return nullptr;
+    return (T*)gMallocTable.malloc(aNumElems * sizeof(T));
+  }
+
+  template <typename T>
+  static T* maybe_pod_calloc(size_t aNumElems) {
+    return (T*)gMallocTable.calloc(aNumElems, sizeof(T));
+  }
+
+  template <typename T>
+  static T* maybe_pod_realloc(T* aPtr, size_t aOldSize, size_t aNewSize) {
+    if (aNewSize & mozilla::tl::MulOverflowMask<sizeof(T)>::value)
+      return nullptr;
+    return (T*)gMallocTable.realloc(aPtr, aNewSize * sizeof(T));
+  }
+
+  static void* malloc_(size_t aSize) {
+    void* p = gMallocTable.malloc(aSize);
+    ExitOnFailure(p);
+    return p;
+  }
+
+  template <typename T>
+  static T* pod_malloc(size_t aNumElems) {
+    T* p = maybe_pod_malloc<T>(aNumElems);
+    ExitOnFailure(p);
+    return p;
+  }
+
+  static void* calloc_(size_t aCount, size_t aSize) {
+    void* p = gMallocTable.calloc(aCount, aSize);
+    ExitOnFailure(p);
+    return p;
+  }
+
+  template <typename T>
+  static T* pod_calloc(size_t aNumElems) {
+    T* p = maybe_pod_calloc<T>(aNumElems);
+    ExitOnFailure(p);
+    return p;
+  }
+
+  static void* realloc_(void* aPtr, size_t aNewSize) {
+    void* p = gMallocTable.realloc(aPtr, aNewSize);
+    ExitOnFailure(p);
+    return p;
+  }
+
+  template <typename T>
+  static T* pod_realloc(T* aPtr, size_t aOldSize, size_t aNewSize) {
+    T* p = maybe_pod_realloc(aPtr, aOldSize, aNewSize);
+    ExitOnFailure(p);
+    return p;
+  }
+
+  static void* memalign_(size_t aAlignment, size_t aSize) {
+    void* p = gMallocTable.memalign(aAlignment, aSize);
+    ExitOnFailure(p);
+    return p;
+  }
+
+  template <typename T>
+  static void free_(T* aPtr, size_t aSize = 0) {
+    gMallocTable.free(aPtr);
+  }
+
+  static char* strdup_(const char* aStr) {
+    char* s = (char*)InfallibleAllocPolicy::malloc_(strlen(aStr) + 1);
+    strcpy(s, aStr);
+    return s;
+  }
+
+  template <class T>
+  static T* new_() {
+    void* mem = malloc_(sizeof(T));
+    return new (mem) T;
+  }
+
+  template <class T, typename P1>
+  static T* new_(const P1& aP1) {
+    void* mem = malloc_(sizeof(T));
+    return new (mem) T(aP1);
+  }
+
+  template <class T>
+  static void delete_(T* aPtr) {
+    if (aPtr) {
+      aPtr->~T();
+      InfallibleAllocPolicy::free_(aPtr);
+    }
+  }
+
+  static void reportAllocOverflow() { ExitOnFailure(nullptr); }
+  bool checkSimulatedOOM() const { return true; }
+};
+
+// This is only needed because of the |const void*| vs |void*| arg mismatch.
+static size_t MallocSizeOf(const void* aPtr) {
+  return gMallocTable.malloc_usable_size(const_cast<void*>(aPtr));
+}
+
+void DMDFuncs::StatusMsg(const char* aFmt, va_list aAp) {
+#ifdef ANDROID
+  __android_log_vprint(ANDROID_LOG_INFO, "DMD", aFmt, aAp);
+#else
+  // The +64 is easily enough for the "DMD[<pid>] " prefix and the NUL.
+  size_t size = strlen(aFmt) + 64;
+  char* fmt = (char*)InfallibleAllocPolicy::malloc_(size);
+  snprintf(fmt, size, "DMD[%d] %s", getpid(), aFmt);
+  vfprintf(stderr, fmt, aAp);
+  InfallibleAllocPolicy::free_(fmt);
+#endif
+}
+
+/* static */
+void InfallibleAllocPolicy::ExitOnFailure(const void* aP) {
+  if (!aP) {
+    MOZ_CRASH("DMD out of memory; aborting");
+  }
+}
+
+static double Percent(size_t part, size_t whole) {
+  return (whole == 0) ? 0 : 100 * (double)part / whole;
+}
+
+// Commifies the number.
+static char* Show(size_t n, char* buf, size_t buflen) {
+  int nc = 0, i = 0, lasti = buflen - 2;
+  buf[lasti + 1] = '\0';
+  if (n == 0) {
+    buf[lasti - i] = '0';
+    i++;
+  } else {
+    while (n > 0) {
+      if (((i - nc) % 3) == 0 && i != 0) {
+        buf[lasti - i] = ',';
+        i++;
+        nc++;
+      }
+      buf[lasti - i] = static_cast<char>((n % 10) + '0');
+      i++;
+      n /= 10;
+    }
+  }
+  int firstCharIndex = lasti - i + 1;
+
+  MOZ_ASSERT(firstCharIndex >= 0);
+  return &buf[firstCharIndex];
+}
+
+//---------------------------------------------------------------------------
+// Options (Part 1)
+//---------------------------------------------------------------------------
+
+class Options {
+  template <typename T>
+  struct NumOption {
+    const T mDefault;
+    const T mMax;
+    T mActual;
+    NumOption(T aDefault, T aMax)
+        : mDefault(aDefault), mMax(aMax), mActual(aDefault) {}
+  };
+
+  // DMD has several modes. These modes affect what data is recorded and
+  // written to the output file, and the written data affects the
+  // post-processing that dmd.py can do.
+  //
+  // Users specify the mode as soon as DMD starts. This leads to minimal memory
+  // usage and log file size. It has the disadvantage that is inflexible -- if
+  // you want to change modes you have to re-run DMD. But in practice changing
+  // modes seems to be rare, so it's not much of a problem.
+  //
+  // An alternative possibility would be to always record and output *all* the
+  // information needed for all modes. This would let you choose the mode when
+  // running dmd.py, and so you could do multiple kinds of profiling on a
+  // single DMD run. But if you are only interested in one of the simpler
+  // modes, you'd pay the price of (a) increased memory usage and (b) *very*
+  // large log files.
+  //
+  // Finally, another alternative possibility would be to do mode selection
+  // partly at DMD startup or recording, and then partly in dmd.py. This would
+  // give some extra flexibility at moderate memory and file size cost. But
+  // certain mode pairs wouldn't work, which would be confusing.
+  //
+  enum class Mode {
+    // For each live block, this mode outputs: size (usable and slop) and
+    // (possibly) and allocation stack. This mode is good for live heap
+    // profiling.
+    Live,
+
+    // Like "Live", but for each live block it also outputs: zero or more
+    // report stacks. This mode is good for identifying where memory reporters
+    // should be added. This is the default mode.
+    DarkMatter,
+
+    // Like "Live", but also outputs the same data for dead blocks. This mode
+    // does cumulative heap profiling, which is good for identifying where large
+    // amounts of short-lived allocations ("heap churn") occur.
+    Cumulative,
+
+    // Like "Live", but this mode also outputs for each live block the address
+    // of the block and the values contained in the blocks. This mode is useful
+    // for investigating leaks, by helping to figure out which blocks refer to
+    // other blocks. This mode force-enables full stacks coverage.
+    Scan
+  };
+
+  // With full stacks, every heap block gets a stack trace recorded for it.
+  // This is complete but slow.
+  //
+  // With partial stacks, not all heap blocks will get a stack trace recorded.
+  // A Bernoulli trial (see mfbt/FastBernoulliTrial.h for details) is performed
+  // for each heap block to decide if it gets one. Because bigger heap blocks
+  // are more likely to get a stack trace, even though most heap *blocks* won't
+  // get a stack trace, most heap *bytes* will.
+  enum class Stacks { Full, Partial };
+
+  char* mDMDEnvVar;  // a saved copy, for later printing
+
+  Mode mMode;
+  Stacks mStacks;
+  bool mShowDumpStats;
+
+  void BadArg(const char* aArg);
+  static const char* ValueIfMatch(const char* aArg, const char* aOptionName);
+  static bool GetLong(const char* aArg, const char* aOptionName, long aMin,
+                      long aMax, long* aValue);
+  static bool GetBool(const char* aArg, const char* aOptionName, bool* aValue);
+
+ public:
+  explicit Options(const char* aDMDEnvVar);
+
+  bool IsLiveMode() const { return mMode == Mode::Live; }
+  bool IsDarkMatterMode() const { return mMode == Mode::DarkMatter; }
+  bool IsCumulativeMode() const { return mMode == Mode::Cumulative; }
+  bool IsScanMode() const { return mMode == Mode::Scan; }
+
+  const char* ModeString() const;
+
+  const char* DMDEnvVar() const { return mDMDEnvVar; }
+
+  bool DoFullStacks() const { return mStacks == Stacks::Full; }
+  size_t ShowDumpStats() const { return mShowDumpStats; }
+};
+
+static Options* gOptions;
+
+//---------------------------------------------------------------------------
+// The global lock
+//---------------------------------------------------------------------------
+
+// MutexBase implements the platform-specific parts of a mutex.
+
+#ifdef XP_WIN
+
+class MutexBase {
+  CRITICAL_SECTION mCS;
+
+  DISALLOW_COPY_AND_ASSIGN(MutexBase);
+
+ public:
+  MutexBase() { InitializeCriticalSection(&mCS); }
+  ~MutexBase() { DeleteCriticalSection(&mCS); }
+
+  void Lock() { EnterCriticalSection(&mCS); }
+  void Unlock() { LeaveCriticalSection(&mCS); }
+};
+
+#else
+
+class MutexBase {
+  pthread_mutex_t mMutex;
+
+  MutexBase(const MutexBase&) = delete;
+
+  const MutexBase& operator=(const MutexBase&) = delete;
+
+ public:
+  MutexBase() { pthread_mutex_init(&mMutex, nullptr); }
+
+  void Lock() { pthread_mutex_lock(&mMutex); }
+  void Unlock() { pthread_mutex_unlock(&mMutex); }
+};
+
+#endif
+
+class Mutex : private MutexBase {
+  bool mIsLocked;
+
+  Mutex(const Mutex&) = delete;
+
+  const Mutex& operator=(const Mutex&) = delete;
+
+ public:
+  Mutex() : mIsLocked(false) {}
+
+  void Lock() {
+    MutexBase::Lock();
+    MOZ_ASSERT(!mIsLocked);
+    mIsLocked = true;
+  }
+
+  void Unlock() {
+    MOZ_ASSERT(mIsLocked);
+    mIsLocked = false;
+    MutexBase::Unlock();
+  }
+
+  bool IsLocked() { return mIsLocked; }
+};
+
+// This lock must be held while manipulating global state such as
+// gStackTraceTable, gLiveBlockTable, gDeadBlockTable. Note that gOptions is
+// *not* protected by this lock because it is only written to by Options(),
+// which is only invoked at start-up and in ResetEverything(), which is only
+// used by SmokeDMD.cpp.
+static Mutex* gStateLock = nullptr;
+
+class AutoLockState {
+  AutoLockState(const AutoLockState&) = delete;
+
+  const AutoLockState& operator=(const AutoLockState&) = delete;
+
+ public:
+  AutoLockState() { gStateLock->Lock(); }
+  ~AutoLockState() { gStateLock->Unlock(); }
+};
+
+class AutoUnlockState {
+  AutoUnlockState(const AutoUnlockState&) = delete;
+
+  const AutoUnlockState& operator=(const AutoUnlockState&) = delete;
+
+ public:
+  AutoUnlockState() { gStateLock->Unlock(); }
+  ~AutoUnlockState() { gStateLock->Lock(); }
+};
+
+//---------------------------------------------------------------------------
+// Per-thread blocking of intercepts
+//---------------------------------------------------------------------------
+
+// On MacOS, the first __thread/thread_local access calls malloc, which leads
+// to an infinite loop. So we use pthread-based TLS instead, which somehow
+// doesn't have this problem.
+#if !defined(XP_DARWIN)
+#  define DMD_THREAD_LOCAL(T) MOZ_THREAD_LOCAL(T)
+#else
+#  define DMD_THREAD_LOCAL(T) \
+    detail::ThreadLocal<T, detail::ThreadLocalKeyStorage>
+#endif
+
+class Thread {
+  // Required for allocation via InfallibleAllocPolicy::new_.
+  friend class InfallibleAllocPolicy;
+
+  // When true, this blocks intercepts, which allows malloc interception
+  // functions to themselves call malloc.  (Nb: for direct calls to malloc we
+  // can just use InfallibleAllocPolicy::{malloc_,new_}, but we sometimes
+  // indirectly call vanilla malloc via functions like MozStackWalk.)
+  bool mBlockIntercepts;
+
+  Thread() : mBlockIntercepts(false) {}
+
+  Thread(const Thread&) = delete;
+
+  const Thread& operator=(const Thread&) = delete;
+
+  static DMD_THREAD_LOCAL(Thread*) tlsThread;
+
+ public:
+  static void Init() {
+    if (!tlsThread.init()) {
+      MOZ_CRASH();
+    }
+  }
+
+  static Thread* Fetch() {
+    Thread* t = tlsThread.get();
+    if (MOZ_UNLIKELY(!t)) {
+      // This memory is never freed, even if the thread dies. It's a leak, but
+      // only a tiny one.
+      t = InfallibleAllocPolicy::new_<Thread>();
+      tlsThread.set(t);
+    }
+
+    return t;
+  }
+
+  bool BlockIntercepts() {
+    MOZ_ASSERT(!mBlockIntercepts);
+    return mBlockIntercepts = true;
+  }
+
+  bool UnblockIntercepts() {
+    MOZ_ASSERT(mBlockIntercepts);
+    return mBlockIntercepts = false;
+  }
+
+  bool InterceptsAreBlocked() const { return mBlockIntercepts; }
+};
+
+DMD_THREAD_LOCAL(Thread*) Thread::tlsThread;
+
+// An object of this class must be created (on the stack) before running any
+// code that might allocate.
+class AutoBlockIntercepts {
+  Thread* const mT;
+
+  AutoBlockIntercepts(const AutoBlockIntercepts&) = delete;
+
+  const AutoBlockIntercepts& operator=(const AutoBlockIntercepts&) = delete;
+
+ public:
+  explicit AutoBlockIntercepts(Thread* aT) : mT(aT) { mT->BlockIntercepts(); }
+  ~AutoBlockIntercepts() {
+    MOZ_ASSERT(mT->InterceptsAreBlocked());
+    mT->UnblockIntercepts();
+  }
+};
+
+//---------------------------------------------------------------------------
+// Location service
+//---------------------------------------------------------------------------
+
+struct DescribeCodeAddressLock {
+  static void Unlock() { gStateLock->Unlock(); }
+  static void Lock() { gStateLock->Lock(); }
+  static bool IsLocked() { return gStateLock->IsLocked(); }
+};
+
+typedef CodeAddressService<InfallibleAllocPolicy, DescribeCodeAddressLock>
+    CodeAddressService;
+
+//---------------------------------------------------------------------------
+// Stack traces
+//---------------------------------------------------------------------------
+
+class StackTrace {
+ public:
+  static const uint32_t MaxFrames = 24;
+
+ private:
+  uint32_t mLength;             // The number of PCs.
+  const void* mPcs[MaxFrames];  // The PCs themselves.
+
+ public:
+  StackTrace() : mLength(0) {}
+  StackTrace(const StackTrace& aOther) : mLength(aOther.mLength) {
+    PodCopy(mPcs, aOther.mPcs, mLength);
+  }
+
+  uint32_t Length() const { return mLength; }
+  const void* Pc(uint32_t i) const {
+    MOZ_ASSERT(i < mLength);
+    return mPcs[i];
+  }
+
+  uint32_t Size() const { return mLength * sizeof(mPcs[0]); }
+
+  // The stack trace returned by this function is interned in gStackTraceTable,
+  // and so is immortal and unmovable.
+  static const StackTrace* Get(Thread* aT);
+
+  // Hash policy.
+
+  typedef StackTrace* Lookup;
+
+  static mozilla::HashNumber hash(const StackTrace* const& aSt) {
+    return mozilla::HashBytes(aSt->mPcs, aSt->Size());
+  }
+
+  static bool match(const StackTrace* const& aA, const StackTrace* const& aB) {
+    return aA->mLength == aB->mLength &&
+           memcmp(aA->mPcs, aB->mPcs, aA->Size()) == 0;
+  }
+
+ private:
+  static void StackWalkCallback(uint32_t aFrameNumber, void* aPc, void* aSp,
+                                void* aClosure) {
+    StackTrace* st = (StackTrace*)aClosure;
+    MOZ_ASSERT(st->mLength < MaxFrames);
+    st->mPcs[st->mLength] = aPc;
+    st->mLength++;
+    MOZ_ASSERT(st->mLength == aFrameNumber);
+  }
+};
+
+typedef mozilla::HashSet<StackTrace*, StackTrace, InfallibleAllocPolicy>
+    StackTraceTable;
+static StackTraceTable* gStackTraceTable = nullptr;
+
+typedef mozilla::HashSet<const StackTrace*,
+                         mozilla::DefaultHasher<const StackTrace*>,
+                         InfallibleAllocPolicy>
+    StackTraceSet;
+
+typedef mozilla::HashSet<const void*, mozilla::DefaultHasher<const void*>,
+                         InfallibleAllocPolicy>
+    PointerSet;
+typedef mozilla::HashMap<const void*, uint32_t,
+                         mozilla::DefaultHasher<const void*>,
+                         InfallibleAllocPolicy>
+    PointerIdMap;
+
+// We won't GC the stack trace table until it this many elements.
+static uint32_t gGCStackTraceTableWhenSizeExceeds = 4 * 1024;
+
+/* static */ const StackTrace* StackTrace::Get(Thread* aT) {
+  MOZ_ASSERT(gStateLock->IsLocked());
+  MOZ_ASSERT(aT->InterceptsAreBlocked());
+
+  // On Windows, MozStackWalk can acquire a lock from the shared library
+  // loader.  Another thread might call malloc while holding that lock (when
+  // loading a shared library).  So we can't be in gStateLock during the call
+  // to MozStackWalk.  For details, see
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=374829#c8
+  // On Linux, something similar can happen;  see bug 824340.
+  // So let's just release it on all platforms.
+  StackTrace tmp;
+  {
+    AutoUnlockState unlock;
+    // In each of the following cases, skipFrames is chosen so that the
+    // first frame in each stack trace is a replace_* function (or as close as
+    // possible, given the vagaries of inlining on different platforms).
+#if defined(XP_WIN) && defined(_M_IX86)
+    // This avoids MozStackWalk(), which causes unusably slow startup on Win32
+    // when it is called during static initialization (see bug 1241684).
+    //
+    // This code is cribbed from the Gecko Profiler, which also uses
+    // FramePointerStackWalk() on Win32: REGISTERS_SYNC_POPULATE() for the
+    // frame pointer, and GetStackTop() for the stack end.
+    CONTEXT context;
+    RtlCaptureContext(&context);
+    void** fp = reinterpret_cast<void**>(context.Ebp);
+
+    PNT_TIB pTib = reinterpret_cast<PNT_TIB>(NtCurrentTeb());
+    void* stackEnd = static_cast<void*>(pTib->StackBase);
+    FramePointerStackWalk(StackWalkCallback, MaxFrames, &tmp, fp, stackEnd);
+#elif defined(XP_MACOSX)
+    // This avoids MozStackWalk(), which has become unusably slow on Mac due to
+    // changes in libunwind.
+    //
+    // This code is cribbed from the Gecko Profiler, which also uses
+    // FramePointerStackWalk() on Mac: REGISTERS_SYNC_POPULATE() for the frame
+    // pointer, and GetStackTop() for the stack end.
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wframe-address"
+    void** fp = reinterpret_cast<void**>(__builtin_frame_address(1));
+#  pragma GCC diagnostic pop
+    void* stackEnd = pthread_get_stackaddr_np(pthread_self());
+    FramePointerStackWalk(StackWalkCallback, MaxFrames, &tmp, fp, stackEnd);
+#else
+    MozStackWalk(StackWalkCallback, nullptr, MaxFrames, &tmp);
+#endif
+  }
+
+  StackTraceTable::AddPtr p = gStackTraceTable->lookupForAdd(&tmp);
+  if (!p) {
+    StackTrace* stnew = InfallibleAllocPolicy::new_<StackTrace>(tmp);
+    MOZ_ALWAYS_TRUE(gStackTraceTable->add(p, stnew));
+  }
+  return *p;
+}
+
+//---------------------------------------------------------------------------
+// Heap blocks
+//---------------------------------------------------------------------------
+
+// This class combines a 2-byte-aligned pointer (i.e. one whose bottom bit
+// is zero) with a 1-bit tag.
+//
+// |T| is the pointer type, e.g. |int*|, not the pointed-to type.  This makes
+// is easier to have const pointers, e.g. |TaggedPtr<const int*>|.
+template <typename T>
+class TaggedPtr {
+  union {
+    T mPtr;
+    uintptr_t mUint;
+  };
+
+  static const uintptr_t kTagMask = uintptr_t(0x1);
+  static const uintptr_t kPtrMask = ~kTagMask;
+
+  static bool IsTwoByteAligned(T aPtr) {
+    return (uintptr_t(aPtr) & kTagMask) == 0;
+  }
+
+ public:
+  TaggedPtr() : mPtr(nullptr) {}
+
+  TaggedPtr(T aPtr, bool aBool) : mPtr(aPtr) {
+    MOZ_ASSERT(IsTwoByteAligned(aPtr));
+    uintptr_t tag = uintptr_t(aBool);
+    MOZ_ASSERT(tag <= kTagMask);
+    mUint |= (tag & kTagMask);
+  }
+
+  void Set(T aPtr, bool aBool) {
+    MOZ_ASSERT(IsTwoByteAligned(aPtr));
+    mPtr = aPtr;
+    uintptr_t tag = uintptr_t(aBool);
+    MOZ_ASSERT(tag <= kTagMask);
+    mUint |= (tag & kTagMask);
+  }
+
+  T Ptr() const { return reinterpret_cast<T>(mUint & kPtrMask); }
+
+  bool Tag() const { return bool(mUint & kTagMask); }
+};
+
+// A live heap block. Stores both basic data and data about reports, if we're
+// in DarkMatter mode.
+class LiveBlock {
+  const void* mPtr;
+  const size_t mReqSize;  // size requested
+
+  // The stack trace where this block was allocated, or nullptr if we didn't
+  // record one.
+  const StackTrace* const mAllocStackTrace;
+
+  // This array has two elements because we record at most two reports of a
+  // block.
+  // - Ptr: |mReportStackTrace| - stack trace where this block was reported.
+  //   nullptr if not reported.
+  // - Tag bit 0: |mReportedOnAlloc| - was the block reported immediately on
+  //   allocation?  If so, DMD must not clear the report at the end of
+  //   Analyze(). Only relevant if |mReportStackTrace| is non-nullptr.
+  //
+  // |mPtr| is used as the key in LiveBlockTable, so it's ok for this member
+  // to be |mutable|.
+  //
+  // Only used in DarkMatter mode.
+  mutable TaggedPtr<const StackTrace*> mReportStackTrace_mReportedOnAlloc[2];
+
+ public:
+  LiveBlock(const void* aPtr, size_t aReqSize,
+            const StackTrace* aAllocStackTrace)
+      : mPtr(aPtr), mReqSize(aReqSize), mAllocStackTrace(aAllocStackTrace) {}
+
+  const void* Address() const { return mPtr; }
+
+  size_t ReqSize() const { return mReqSize; }
+
+  size_t SlopSize() const { return MallocSizeOf(mPtr) - mReqSize; }
+
+  const StackTrace* AllocStackTrace() const { return mAllocStackTrace; }
+
+  const StackTrace* ReportStackTrace1() const {
+    MOZ_ASSERT(gOptions->IsDarkMatterMode());
+    return mReportStackTrace_mReportedOnAlloc[0].Ptr();
+  }
+
+  const StackTrace* ReportStackTrace2() const {
+    MOZ_ASSERT(gOptions->IsDarkMatterMode());
+    return mReportStackTrace_mReportedOnAlloc[1].Ptr();
+  }
+
+  bool ReportedOnAlloc1() const {
+    MOZ_ASSERT(gOptions->IsDarkMatterMode());
+    return mReportStackTrace_mReportedOnAlloc[0].Tag();
+  }
+
+  bool ReportedOnAlloc2() const {
+    MOZ_ASSERT(gOptions->IsDarkMatterMode());
+    return mReportStackTrace_mReportedOnAlloc[1].Tag();
+  }
+
+  void AddStackTracesToTable(StackTraceSet& aStackTraces) const {
+    if (AllocStackTrace()) {
+      MOZ_ALWAYS_TRUE(aStackTraces.put(AllocStackTrace()));
+    }
+    if (gOptions->IsDarkMatterMode()) {
+      if (ReportStackTrace1()) {
+        MOZ_ALWAYS_TRUE(aStackTraces.put(ReportStackTrace1()));
+      }
+      if (ReportStackTrace2()) {
+        MOZ_ALWAYS_TRUE(aStackTraces.put(ReportStackTrace2()));
+      }
+    }
+  }
+
+  uint32_t NumReports() const {
+    MOZ_ASSERT(gOptions->IsDarkMatterMode());
+    if (ReportStackTrace2()) {
+      MOZ_ASSERT(ReportStackTrace1());
+      return 2;
+    }
+    if (ReportStackTrace1()) {
+      return 1;
+    }
+    return 0;
+  }
+
+  // This is |const| thanks to the |mutable| fields above.
+  void Report(Thread* aT, bool aReportedOnAlloc) const {
+    MOZ_ASSERT(gOptions->IsDarkMatterMode());
+    // We don't bother recording reports after the 2nd one.
+    uint32_t numReports = NumReports();
+    if (numReports < 2) {
+      mReportStackTrace_mReportedOnAlloc[numReports].Set(StackTrace::Get(aT),
+                                                         aReportedOnAlloc);
+    }
+  }
+
+  void UnreportIfNotReportedOnAlloc() const {
+    MOZ_ASSERT(gOptions->IsDarkMatterMode());
+    if (!ReportedOnAlloc1() && !ReportedOnAlloc2()) {
+      mReportStackTrace_mReportedOnAlloc[0].Set(nullptr, 0);
+      mReportStackTrace_mReportedOnAlloc[1].Set(nullptr, 0);
+
+    } else if (!ReportedOnAlloc1() && ReportedOnAlloc2()) {
+      // Shift the 2nd report down to the 1st one.
+      mReportStackTrace_mReportedOnAlloc[0] =
+          mReportStackTrace_mReportedOnAlloc[1];
+      mReportStackTrace_mReportedOnAlloc[1].Set(nullptr, 0);
+
+    } else if (ReportedOnAlloc1() && !ReportedOnAlloc2()) {
+      mReportStackTrace_mReportedOnAlloc[1].Set(nullptr, 0);
+    }
+  }
+
+  // Hash policy.
+
+  typedef const void* Lookup;
+
+  static mozilla::HashNumber hash(const void* const& aPtr) {
+    return mozilla::HashGeneric(aPtr);
+  }
+
+  static bool match(const LiveBlock& aB, const void* const& aPtr) {
+    return aB.mPtr == aPtr;
+  }
+};
+
+// A table of live blocks where the lookup key is the block address.
+typedef mozilla::HashSet<LiveBlock, LiveBlock, InfallibleAllocPolicy>
+    LiveBlockTable;
+static LiveBlockTable* gLiveBlockTable = nullptr;
+
+class AggregatedLiveBlockHashPolicy {
+ public:
+  typedef const LiveBlock* const Lookup;
+
+  static mozilla::HashNumber hash(const LiveBlock* const& aB) {
+    return gOptions->IsDarkMatterMode()
+               ? mozilla::HashGeneric(
+                     aB->ReqSize(), aB->SlopSize(), aB->AllocStackTrace(),
+                     aB->ReportedOnAlloc1(), aB->ReportedOnAlloc2())
+               : mozilla::HashGeneric(aB->ReqSize(), aB->SlopSize(),
+                                      aB->AllocStackTrace());
+  }
+
+  static bool match(const LiveBlock* const& aA, const LiveBlock* const& aB) {
+    return gOptions->IsDarkMatterMode()
+               ? aA->ReqSize() == aB->ReqSize() &&
+                     aA->SlopSize() == aB->SlopSize() &&
+                     aA->AllocStackTrace() == aB->AllocStackTrace() &&
+                     aA->ReportStackTrace1() == aB->ReportStackTrace1() &&
+                     aA->ReportStackTrace2() == aB->ReportStackTrace2()
+               : aA->ReqSize() == aB->ReqSize() &&
+                     aA->SlopSize() == aB->SlopSize() &&
+                     aA->AllocStackTrace() == aB->AllocStackTrace();
+  }
+};
+
+// A table of live blocks where the lookup key is everything but the block
+// address. For aggregating similar live blocks at output time.
+typedef mozilla::HashMap<const LiveBlock*, size_t,
+                         AggregatedLiveBlockHashPolicy, InfallibleAllocPolicy>
+    AggregatedLiveBlockTable;
+
+// A freed heap block.
+class DeadBlock {
+  const size_t mReqSize;   // size requested
+  const size_t mSlopSize;  // slop above size requested
+
+  // The stack trace where this block was allocated.
+  const StackTrace* const mAllocStackTrace;
+
+ public:
+  DeadBlock() : mReqSize(0), mSlopSize(0), mAllocStackTrace(nullptr) {}
+
+  explicit DeadBlock(const LiveBlock& aLb)
+      : mReqSize(aLb.ReqSize()),
+        mSlopSize(aLb.SlopSize()),
+        mAllocStackTrace(aLb.AllocStackTrace()) {}
+
+  ~DeadBlock() = default;
+
+  size_t ReqSize() const { return mReqSize; }
+  size_t SlopSize() const { return mSlopSize; }
+
+  const StackTrace* AllocStackTrace() const { return mAllocStackTrace; }
+
+  void AddStackTracesToTable(StackTraceSet& aStackTraces) const {
+    if (AllocStackTrace()) {
+      MOZ_ALWAYS_TRUE(aStackTraces.put(AllocStackTrace()));
+    }
+  }
+
+  // Hash policy.
+
+  typedef DeadBlock Lookup;
+
+  static mozilla::HashNumber hash(const DeadBlock& aB) {
+    return mozilla::HashGeneric(aB.ReqSize(), aB.SlopSize(),
+                                aB.AllocStackTrace());
+  }
+
+  static bool match(const DeadBlock& aA, const DeadBlock& aB) {
+    return aA.ReqSize() == aB.ReqSize() && aA.SlopSize() == aB.SlopSize() &&
+           aA.AllocStackTrace() == aB.AllocStackTrace();
+  }
+};
+
+// For each unique DeadBlock value we store a count of how many actual dead
+// blocks have that value.
+typedef mozilla::HashMap<DeadBlock, size_t, DeadBlock, InfallibleAllocPolicy>
+    DeadBlockTable;
+static DeadBlockTable* gDeadBlockTable = nullptr;
+
+// Add the dead block to the dead block table, if that's appropriate.
+void MaybeAddToDeadBlockTable(const DeadBlock& aDb) {
+  if (gOptions->IsCumulativeMode() && aDb.AllocStackTrace()) {
+    AutoLockState lock;
+    if (DeadBlockTable::AddPtr p = gDeadBlockTable->lookupForAdd(aDb)) {
+      p->value() += 1;
+    } else {
+      MOZ_ALWAYS_TRUE(gDeadBlockTable->add(p, aDb, 1));
+    }
+  }
+}
+
+// Add a pointer to each live stack trace into the given StackTraceSet.  (A
+// stack trace is live if it's used by one of the live blocks.)
+static void GatherUsedStackTraces(StackTraceSet& aStackTraces) {
+  MOZ_ASSERT(gStateLock->IsLocked());
+  MOZ_ASSERT(Thread::Fetch()->InterceptsAreBlocked());
+
+  aStackTraces.clear();
+  MOZ_ALWAYS_TRUE(aStackTraces.reserve(512));
+
+  for (auto iter = gLiveBlockTable->iter(); !iter.done(); iter.next()) {
+    iter.get().AddStackTracesToTable(aStackTraces);
+  }
+
+  for (auto iter = gDeadBlockTable->iter(); !iter.done(); iter.next()) {
+    iter.get().key().AddStackTracesToTable(aStackTraces);
+  }
+}
+
+// Delete stack traces that we aren't using, and compact our hashtable.
+static void GCStackTraces() {
+  MOZ_ASSERT(gStateLock->IsLocked());
+  MOZ_ASSERT(Thread::Fetch()->InterceptsAreBlocked());
+
+  StackTraceSet usedStackTraces;
+  GatherUsedStackTraces(usedStackTraces);
+
+  // Delete all unused stack traces from gStackTraceTable.  The ModIterator
+  // destructor will automatically rehash and compact the table.
+  for (auto iter = gStackTraceTable->modIter(); !iter.done(); iter.next()) {
+    StackTrace* const& st = iter.get();
+    if (!usedStackTraces.has(st)) {
+      iter.remove();
+      InfallibleAllocPolicy::delete_(st);
+    }
+  }
+
+  // Schedule a GC when we have twice as many stack traces as we had right after
+  // this GC finished.
+  gGCStackTraceTableWhenSizeExceeds = 2 * gStackTraceTable->count();
+}
+
+//---------------------------------------------------------------------------
+// malloc/free callbacks
+//---------------------------------------------------------------------------
+
+static FastBernoulliTrial* gBernoulli;
+
+// In testing, a probability of 0.003 resulted in ~25% of heap blocks getting
+// a stack trace and ~80% of heap bytes getting a stack trace. (This is
+// possible because big heap blocks are more likely to get a stack trace.)
+//
+// We deliberately choose not to give the user control over this probability
+// (other than effectively setting it to 1 via --stacks=full) because it's
+// quite inscrutable and generally the user just wants "faster and imprecise"
+// or "slower and precise".
+//
+// The random number seeds are arbitrary and were obtained from random.org. If
+// you change them you'll need to change the tests as well, because their
+// expected output is based on the particular sequence of trial results that we
+// get with these seeds.
+static void ResetBernoulli() {
+  new (gBernoulli)
+      FastBernoulliTrial(0.003, 0x8e26eeee166bc8ca, 0x56820f304a9c9ae0);
+}
+
+static void AllocCallback(void* aPtr, size_t aReqSize, Thread* aT) {
+  if (!aPtr) {
+    return;
+  }
+
+  AutoLockState lock;
+  AutoBlockIntercepts block(aT);
+
+  size_t actualSize = gMallocTable.malloc_usable_size(aPtr);
+
+  // We may or may not record the allocation stack trace, depending on the
+  // options and the outcome of a Bernoulli trial.
+  bool getTrace = gOptions->DoFullStacks() || gBernoulli->trial(actualSize);
+  LiveBlock b(aPtr, aReqSize, getTrace ? StackTrace::Get(aT) : nullptr);
+  LiveBlockTable::AddPtr p = gLiveBlockTable->lookupForAdd(aPtr);
+  if (!p) {
+    // Most common case: there wasn't a record already.
+    MOZ_ALWAYS_TRUE(gLiveBlockTable->add(p, b));
+  } else {
+    // Edge-case: there was a record for the same address. We'll assume the
+    // allocator is not giving out a pointer to an existing allocation, so
+    // this means the previously recorded allocation was freed while we were
+    // blocking interceptions. This can happen while processing the data in
+    // e.g. AnalyzeImpl.
+    if (gOptions->IsCumulativeMode()) {
+      // Copy it out so it can be added to the dead block list later.
+      DeadBlock db(*p);
+      MaybeAddToDeadBlockTable(db);
+    }
+    gLiveBlockTable->remove(p);
+    MOZ_ALWAYS_TRUE(gLiveBlockTable->putNew(aPtr, b));
+  }
+}
+
+static void FreeCallback(void* aPtr, Thread* aT, DeadBlock* aDeadBlock) {
+  if (!aPtr) {
+    return;
+  }
+
+  AutoLockState lock;
+  AutoBlockIntercepts block(aT);
+
+  if (LiveBlockTable::Ptr lb = gLiveBlockTable->lookup(aPtr)) {
+    if (gOptions->IsCumulativeMode()) {
+      // Copy it out so it can be added to the dead block list later.
+      new (aDeadBlock) DeadBlock(*lb);
+    }
+    gLiveBlockTable->remove(lb);
+  } else {
+    // We have no record of the block. It must be a bogus pointer, or one that
+    // DMD wasn't able to see allocated. This should be extremely rare.
+  }
+
+  if (gStackTraceTable->count() > gGCStackTraceTableWhenSizeExceeds) {
+    GCStackTraces();
+  }
+}
+
+//---------------------------------------------------------------------------
+// malloc/free interception
+//---------------------------------------------------------------------------
+
+static bool Init(malloc_table_t* aMallocTable);
+
+}  // namespace dmd
+}  // namespace mozilla
+
+static void* replace_malloc(size_t aSize) {
+  using namespace mozilla::dmd;
+
+  Thread* t = Thread::Fetch();
+  if (t->InterceptsAreBlocked()) {
+    // Intercepts are blocked, which means this must be a call to malloc
+    // triggered indirectly by DMD (e.g. via MozStackWalk).  Be infallible.
+    return InfallibleAllocPolicy::malloc_(aSize);
+  }
+
+  // This must be a call to malloc from outside DMD.  Intercept it.
+  void* ptr = gMallocTable.malloc(aSize);
+  AllocCallback(ptr, aSize, t);
+  return ptr;
+}
+
+static void* replace_calloc(size_t aCount, size_t aSize) {
+  using namespace mozilla::dmd;
+
+  Thread* t = Thread::Fetch();
+  if (t->InterceptsAreBlocked()) {
+    return InfallibleAllocPolicy::calloc_(aCount, aSize);
+  }
+
+  // |aCount * aSize| could overflow, but if that happens then
+  // |gMallocTable.calloc()| will return nullptr and |AllocCallback()| will
+  // return immediately without using the overflowed value.
+  void* ptr = gMallocTable.calloc(aCount, aSize);
+  AllocCallback(ptr, aCount * aSize, t);
+  return ptr;
+}
+
+static void* replace_realloc(void* aOldPtr, size_t aSize) {
+  using namespace mozilla::dmd;
+
+  Thread* t = Thread::Fetch();
+  if (t->InterceptsAreBlocked()) {
+    return InfallibleAllocPolicy::realloc_(aOldPtr, aSize);
+  }
+
+  // If |aOldPtr| is nullptr, the call is equivalent to |malloc(aSize)|.
+  if (!aOldPtr) {
+    return replace_malloc(aSize);
+  }
+
+  // Be very careful here!  Must remove the block from the table before doing
+  // the realloc to avoid races, just like in replace_free().
+  // Nb: This does an unnecessary hashtable remove+add if the block doesn't
+  // move, but doing better isn't worth the effort.
+  DeadBlock db;
+  FreeCallback(aOldPtr, t, &db);
+  void* ptr = gMallocTable.realloc(aOldPtr, aSize);
+  if (ptr) {
+    AllocCallback(ptr, aSize, t);
+    MaybeAddToDeadBlockTable(db);
+  } else {
+    // If realloc fails, we undo the prior operations by re-inserting the old
+    // pointer into the live block table. We don't have to do anything with the
+    // dead block list because the dead block hasn't yet been inserted. The
+    // block will end up looking like it was allocated for the first time here,
+    // which is untrue, and the slop bytes will be zero, which may be untrue.
+    // But this case is rare and doing better isn't worth the effort.
+    AllocCallback(aOldPtr, gMallocTable.malloc_usable_size(aOldPtr), t);
+  }
+  return ptr;
+}
+
+static void* replace_memalign(size_t aAlignment, size_t aSize) {
+  using namespace mozilla::dmd;
+
+  Thread* t = Thread::Fetch();
+  if (t->InterceptsAreBlocked()) {
+    return InfallibleAllocPolicy::memalign_(aAlignment, aSize);
+  }
+
+  void* ptr = gMallocTable.memalign(aAlignment, aSize);
+  AllocCallback(ptr, aSize, t);
+  return ptr;
+}
+
+static void replace_free(void* aPtr) {
+  using namespace mozilla::dmd;
+
+  Thread* t = Thread::Fetch();
+  if (t->InterceptsAreBlocked()) {
+    return InfallibleAllocPolicy::free_(aPtr);
+  }
+
+  // Do the actual free after updating the table.  Otherwise, another thread
+  // could call malloc and get the freed block and update the table, and then
+  // our update here would remove the newly-malloc'd block.
+  DeadBlock db;
+  FreeCallback(aPtr, t, &db);
+  MaybeAddToDeadBlockTable(db);
+  gMallocTable.free(aPtr);
+}
+
+void replace_init(malloc_table_t* aMallocTable, ReplaceMallocBridge** aBridge) {
+  if (mozilla::dmd::Init(aMallocTable)) {
+#define MALLOC_FUNCS MALLOC_FUNCS_MALLOC_BASE
+#define MALLOC_DECL(name, ...) aMallocTable->name = replace_##name;
+#include "malloc_decls.h"
+    *aBridge = mozilla::dmd::gDMDBridge;
+  }
+}
+
+namespace mozilla {
+namespace dmd {
+
+//---------------------------------------------------------------------------
+// Options (Part 2)
+//---------------------------------------------------------------------------
+
+// Given an |aOptionName| like "foo", succeed if |aArg| has the form "foo=blah"
+// (where "blah" is non-empty) and return the pointer to "blah".  |aArg| can
+// have leading space chars (but not other whitespace).
+const char* Options::ValueIfMatch(const char* aArg, const char* aOptionName) {
+  MOZ_ASSERT(!isspace(*aArg));  // any leading whitespace should not remain
+  size_t optionLen = strlen(aOptionName);
+  if (strncmp(aArg, aOptionName, optionLen) == 0 && aArg[optionLen] == '=' &&
+      aArg[optionLen + 1]) {
+    return aArg + optionLen + 1;
+  }
+  return nullptr;
+}
+
+// Extracts a |long| value for an option from an argument.  It must be within
+// the range |aMin..aMax| (inclusive).
+bool Options::GetLong(const char* aArg, const char* aOptionName, long aMin,
+                      long aMax, long* aValue) {
+  if (const char* optionValue = ValueIfMatch(aArg, aOptionName)) {
+    char* endPtr;
+    *aValue = strtol(optionValue, &endPtr, /* base */ 10);
+    if (!*endPtr && aMin <= *aValue && *aValue <= aMax && *aValue != LONG_MIN &&
+        *aValue != LONG_MAX) {
+      return true;
+    }
+  }
+  return false;
+}
+
+// Extracts a |bool| value for an option -- encoded as "yes" or "no" -- from an
+// argument.
+bool Options::GetBool(const char* aArg, const char* aOptionName, bool* aValue) {
+  if (const char* optionValue = ValueIfMatch(aArg, aOptionName)) {
+    if (strcmp(optionValue, "yes") == 0) {
+      *aValue = true;
+      return true;
+    }
+    if (strcmp(optionValue, "no") == 0) {
+      *aValue = false;
+      return true;
+    }
+  }
+  return false;
+}
+
+Options::Options(const char* aDMDEnvVar)
+    : mDMDEnvVar(aDMDEnvVar ? InfallibleAllocPolicy::strdup_(aDMDEnvVar)
+                            : nullptr),
+      mMode(Mode::DarkMatter),
+      mStacks(Stacks::Partial),
+      mShowDumpStats(false) {
+  char* e = mDMDEnvVar;
+  if (e && strcmp(e, "1") != 0) {
+    bool isEnd = false;
+    while (!isEnd) {
+      // Consume leading whitespace.
+      while (isspace(*e)) {
+        e++;
+      }
+
+      // Save the start of the arg.
+      const char* arg = e;
+
+      // Find the first char after the arg, and temporarily change it to '\0'
+      // to isolate the arg.
+      while (!isspace(*e) && *e != '\0') {
+        e++;
+      }
+      char replacedChar = *e;
+      isEnd = replacedChar == '\0';
+      *e = '\0';
+
+      // Handle arg
+      bool myBool;
+      if (strcmp(arg, "--mode=live") == 0) {
+        mMode = Mode::Live;
+      } else if (strcmp(arg, "--mode=dark-matter") == 0) {
+        mMode = Mode::DarkMatter;
+      } else if (strcmp(arg, "--mode=cumulative") == 0) {
+        mMode = Mode::Cumulative;
+      } else if (strcmp(arg, "--mode=scan") == 0) {
+        mMode = Mode::Scan;
+
+      } else if (strcmp(arg, "--stacks=full") == 0) {
+        mStacks = Stacks::Full;
+      } else if (strcmp(arg, "--stacks=partial") == 0) {
+        mStacks = Stacks::Partial;
+
+      } else if (GetBool(arg, "--show-dump-stats", &myBool)) {
+        mShowDumpStats = myBool;
+
+      } else if (strcmp(arg, "") == 0) {
+        // This can only happen if there is trailing whitespace.  Ignore.
+        MOZ_ASSERT(isEnd);
+
+      } else {
+        BadArg(arg);
+      }
+
+      // Undo the temporary isolation.
+      *e = replacedChar;
+    }
+  }
+
+  if (mMode == Mode::Scan) {
+    mStacks = Stacks::Full;
+  }
+}
+
+void Options::BadArg(const char* aArg) {
+  StatusMsg("\n");
+  StatusMsg("Bad entry in the $DMD environment variable: '%s'.\n", aArg);
+  StatusMsg("See the output of |mach help run| for the allowed options.\n");
+  exit(1);
+}
+
+const char* Options::ModeString() const {
+  switch (mMode) {
+    case Mode::Live:
+      return "live";
+    case Mode::DarkMatter:
+      return "dark-matter";
+    case Mode::Cumulative:
+      return "cumulative";
+    case Mode::Scan:
+      return "scan";
+    default:
+      MOZ_ASSERT(false);
+      return "(unknown DMD mode)";
+  }
+}
+
+//---------------------------------------------------------------------------
+// DMD start-up
+//---------------------------------------------------------------------------
+
+#ifndef XP_WIN
+static void prefork() {
+  if (gStateLock) {
+    gStateLock->Lock();
+  }
+}
+
+static void postfork() {
+  if (gStateLock) {
+    gStateLock->Unlock();
+  }
+}
+#endif
+
+// WARNING: this function runs *very* early -- before all static initializers
+// have run.  For this reason, non-scalar globals such as gStateLock and
+// gStackTraceTable are allocated dynamically (so we can guarantee their
+// construction in this function) rather than statically.
+static bool Init(malloc_table_t* aMallocTable) {
+  // DMD is controlled by the |DMD| environment variable.
+  const char* e = getenv("DMD");
+
+  if (!e) {
+    return false;
+  }
+  // Initialize the function table first, because StatusMsg uses
+  // InfallibleAllocPolicy::malloc_, which uses it.
+  gMallocTable = *aMallocTable;
+
+  StatusMsg("$DMD = '%s'\n", e);
+
+  gDMDBridge = InfallibleAllocPolicy::new_<DMDBridge>();
+
+#ifndef XP_WIN
+  // Avoid deadlocks when forking by acquiring our state lock prior to forking
+  // and releasing it after forking. See |LogAlloc|'s |replace_init| for
+  // in-depth details.
+  //
+  // Note: This must run after attempting an allocation so as to give the
+  // system malloc a chance to insert its own atfork handler.
+  pthread_atfork(prefork, postfork, postfork);
+#endif
+  // Parse $DMD env var.
+  gOptions = InfallibleAllocPolicy::new_<Options>(e);
+
+  gStateLock = InfallibleAllocPolicy::new_<Mutex>();
+
+  gBernoulli = (FastBernoulliTrial*)InfallibleAllocPolicy::malloc_(
+      sizeof(FastBernoulliTrial));
+  ResetBernoulli();
+
+  Thread::Init();
+
+  {
+    AutoLockState lock;
+
+    gStackTraceTable = InfallibleAllocPolicy::new_<StackTraceTable>(8192);
+    gLiveBlockTable = InfallibleAllocPolicy::new_<LiveBlockTable>(8192);
+
+    // Create this even if the mode isn't Cumulative (albeit with a small
+    // size), in case the mode is changed later on (as is done by SmokeDMD.cpp,
+    // for example).
+    size_t tableSize = gOptions->IsCumulativeMode() ? 8192 : 4;
+    gDeadBlockTable = InfallibleAllocPolicy::new_<DeadBlockTable>(tableSize);
+  }
+
+  return true;
+}
+
+//---------------------------------------------------------------------------
+// Block reporting and unreporting
+//---------------------------------------------------------------------------
+
+static void ReportHelper(const void* aPtr, bool aReportedOnAlloc) {
+  if (!gOptions->IsDarkMatterMode() || !aPtr) {
+    return;
+  }
+
+  Thread* t = Thread::Fetch();
+
+  AutoBlockIntercepts block(t);
+  AutoLockState lock;
+
+  if (LiveBlockTable::Ptr p = gLiveBlockTable->lookup(aPtr)) {
+    p->Report(t, aReportedOnAlloc);
+  } else {
+    // We have no record of the block. It must be a bogus pointer. This should
+    // be extremely rare because Report() is almost always called in
+    // conjunction with a malloc_size_of-style function. Print a message so
+    // that we get some feedback.
+    StatusMsg("Unknown pointer %p\n", aPtr);
+  }
+}
+
+void DMDFuncs::Report(const void* aPtr) {
+  ReportHelper(aPtr, /* onAlloc */ false);
+}
+
+void DMDFuncs::ReportOnAlloc(const void* aPtr) {
+  ReportHelper(aPtr, /* onAlloc */ true);
+}
+
+//---------------------------------------------------------------------------
+// DMD output
+//---------------------------------------------------------------------------
+
+// The version number of the output format. Increment this if you make
+// backwards-incompatible changes to the format. See DMD.h for the version
+// history.
+static const int kOutputVersionNumber = 5;
+
+// Note that, unlike most SizeOf* functions, this function does not take a
+// |mozilla::MallocSizeOf| argument.  That's because those arguments are
+// primarily to aid DMD track heap blocks... but DMD deliberately doesn't track
+// heap blocks it allocated for itself!
+//
+// SizeOfInternal should be called while you're holding the state lock and
+// while intercepts are blocked; SizeOf acquires the lock and blocks
+// intercepts.
+
+static void SizeOfInternal(Sizes* aSizes) {
+  MOZ_ASSERT(gStateLock->IsLocked());
+  MOZ_ASSERT(Thread::Fetch()->InterceptsAreBlocked());
+
+  aSizes->Clear();
+
+  StackTraceSet usedStackTraces;
+  GatherUsedStackTraces(usedStackTraces);
+
+  for (auto iter = gStackTraceTable->iter(); !iter.done(); iter.next()) {
+    StackTrace* const& st = iter.get();
+
+    if (usedStackTraces.has(st)) {
+      aSizes->mStackTracesUsed += MallocSizeOf(st);
+    } else {
+      aSizes->mStackTracesUnused += MallocSizeOf(st);
+    }
+  }
+
+  aSizes->mStackTraceTable =
+      gStackTraceTable->shallowSizeOfIncludingThis(MallocSizeOf);
+
+  aSizes->mLiveBlockTable =
+      gLiveBlockTable->shallowSizeOfIncludingThis(MallocSizeOf);
+
+  aSizes->mDeadBlockTable =
+      gDeadBlockTable->shallowSizeOfIncludingThis(MallocSizeOf);
+}
+
+void DMDFuncs::SizeOf(Sizes* aSizes) {
+  aSizes->Clear();
+
+  AutoBlockIntercepts block(Thread::Fetch());
+  AutoLockState lock;
+  SizeOfInternal(aSizes);
+}
+
+void DMDFuncs::ClearReports() {
+  if (!gOptions->IsDarkMatterMode()) {
+    return;
+  }
+
+  AutoLockState lock;
+
+  // Unreport all blocks that were marked reported by a memory reporter.  This
+  // excludes those that were reported on allocation, because they need to keep
+  // their reported marking.
+  for (auto iter = gLiveBlockTable->iter(); !iter.done(); iter.next()) {
+    iter.get().UnreportIfNotReportedOnAlloc();
+  }
+}
+
+class ToIdStringConverter final {
+ public:
+  ToIdStringConverter() : mIdMap(512), mNextId(0) {}
+
+  // Converts a pointer to a unique ID. Reuses the existing ID for the pointer
+  // if it's been seen before.
+  const char* ToIdString(const void* aPtr) {
+    uint32_t id;
+    PointerIdMap::AddPtr p = mIdMap.lookupForAdd(aPtr);
+    if (!p) {
+      id = mNextId++;
+      MOZ_ALWAYS_TRUE(mIdMap.add(p, aPtr, id));
+    } else {
+      id = p->value();
+    }
+    return Base32(id);
+  }
+
+  size_t sizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const {
+    return mIdMap.shallowSizeOfExcludingThis(aMallocSizeOf);
+  }
+
+ private:
+  // This function converts an integer to base-32. We use base-32 values for
+  // indexing into the traceTable and the frameTable, for the following reasons.
+  //
+  // - Base-32 gives more compact indices than base-16.
+  //
+  // - 32 is a power-of-two, which makes the necessary div/mod calculations
+  //   fast.
+  //
+  // - We can (and do) choose non-numeric digits for base-32. When
+  //   inspecting/debugging the JSON output, non-numeric indices are easier to
+  //   search for than numeric indices.
+  //
+  char* Base32(uint32_t aN) {
+    static const char digits[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdef";
+
+    char* b = mIdBuf + kIdBufLen - 1;
+    *b = '\0';
+    do {
+      b--;
+      if (b == mIdBuf) {
+        MOZ_CRASH("Base32 buffer too small");
+      }
+      *b = digits[aN % 32];
+      aN /= 32;
+    } while (aN);
+
+    return b;
+  }
+
+  PointerIdMap mIdMap;
+  uint32_t mNextId;
+
+  // |mIdBuf| must have space for at least eight chars, which is the space
+  // needed to hold 'Dffffff' (including the terminating null char), which is
+  // the base-32 representation of 0xffffffff.
+  static const size_t kIdBufLen = 16;
+  char mIdBuf[kIdBufLen];
+};
+
+// Helper class for converting a pointer value to a string.
+class ToStringConverter {
+ public:
+  const char* ToPtrString(const void* aPtr) {
+    snprintf(kPtrBuf, sizeof(kPtrBuf) - 1, "%" PRIxPTR, (uintptr_t)aPtr);
+    return kPtrBuf;
+  }
+
+ private:
+  char kPtrBuf[32];
+};
+
+static void WriteBlockContents(JSONWriter& aWriter, const LiveBlock& aBlock) {
+  size_t numWords = aBlock.ReqSize() / sizeof(uintptr_t*);
+  if (numWords == 0) {
+    return;
+  }
+
+  aWriter.StartArrayProperty("contents", aWriter.SingleLineStyle);
+  {
+    const uintptr_t** block = (const uintptr_t**)aBlock.Address();
+    ToStringConverter sc;
+    for (size_t i = 0; i < numWords; ++i) {
+      aWriter.StringElement(MakeStringSpan(sc.ToPtrString(block[i])));
+    }
+  }
+  aWriter.EndArray();
+}
+
+static void AnalyzeImpl(UniquePtr<JSONWriteFunc> aWriter) {
+  // Some blocks may have been allocated while creating |aWriter|. Those blocks
+  // will be freed at the end of this function when |write| is destroyed. The
+  // allocations will have occurred while intercepts were not blocked, so the
+  // frees better be as well, otherwise we'll get assertion failures.
+  // Therefore, this declaration must precede the AutoBlockIntercepts
+  // declaration, to ensure that |write| is destroyed *after* intercepts are
+  // unblocked.
+  JSONWriter writer(std::move(aWriter));
+
+  AutoBlockIntercepts block(Thread::Fetch());
+  AutoLockState lock;
+
+  // Allocate this on the heap instead of the stack because it's fairly large.
+  auto locService = InfallibleAllocPolicy::new_<CodeAddressService>();
+
+  StackTraceSet usedStackTraces(512);
+  PointerSet usedPcs(512);
+
+  size_t iscSize;
+
+  static int analysisCount = 1;
+  StatusMsg("Dump %d {\n", analysisCount++);
+
+  writer.Start();
+  {
+    writer.IntProperty("version", kOutputVersionNumber);
+
+    writer.StartObjectProperty("invocation");
+    {
+      const char* var = gOptions->DMDEnvVar();
+      if (var) {
+        writer.StringProperty("dmdEnvVar", MakeStringSpan(var));
+      } else {
+        writer.NullProperty("dmdEnvVar");
+      }
+
+      writer.StringProperty("mode", MakeStringSpan(gOptions->ModeString()));
+    }
+    writer.EndObject();
+
+    StatusMsg("  Constructing the heap block list...\n");
+
+    ToIdStringConverter isc;
+    ToStringConverter sc;
+
+    writer.StartArrayProperty("blockList");
+    {
+      // Lambda that writes out a live block.
+      auto writeLiveBlock = [&](const LiveBlock& aB, size_t aNum) {
+        aB.AddStackTracesToTable(usedStackTraces);
+
+        MOZ_ASSERT_IF(gOptions->IsScanMode(), aNum == 1);
+
+        writer.StartObjectElement(writer.SingleLineStyle);
+        {
+          if (gOptions->IsScanMode()) {
+            writer.StringProperty("addr",
+                                  MakeStringSpan(sc.ToPtrString(aB.Address())));
+            WriteBlockContents(writer, aB);
+          }
+          writer.IntProperty("req", aB.ReqSize());
+          if (aB.SlopSize() > 0) {
+            writer.IntProperty("slop", aB.SlopSize());
+          }
+
+          if (aB.AllocStackTrace()) {
+            writer.StringProperty(
+                "alloc", MakeStringSpan(isc.ToIdString(aB.AllocStackTrace())));
+          }
+
+          if (gOptions->IsDarkMatterMode() && aB.NumReports() > 0) {
+            writer.StartArrayProperty("reps");
+            {
+              if (aB.ReportStackTrace1()) {
+                writer.StringElement(
+                    MakeStringSpan(isc.ToIdString(aB.ReportStackTrace1())));
+              }
+              if (aB.ReportStackTrace2()) {
+                writer.StringElement(
+                    MakeStringSpan(isc.ToIdString(aB.ReportStackTrace2())));
+              }
+            }
+            writer.EndArray();
+          }
+
+          if (aNum > 1) {
+            writer.IntProperty("num", aNum);
+          }
+        }
+        writer.EndObject();
+      };
+
+      // Live blocks.
+      if (!gOptions->IsScanMode()) {
+        // At this point we typically have many LiveBlocks that differ only in
+        // their address. Aggregate them to reduce the size of the output file.
+        AggregatedLiveBlockTable agg(8192);
+        for (auto iter = gLiveBlockTable->iter(); !iter.done(); iter.next()) {
+          const LiveBlock& b = iter.get();
+          b.AddStackTracesToTable(usedStackTraces);
+
+          if (AggregatedLiveBlockTable::AddPtr p = agg.lookupForAdd(&b)) {
+            p->value() += 1;
+          } else {
+            MOZ_ALWAYS_TRUE(agg.add(p, &b, 1));
+          }
+        }
+
+        // Now iterate over the aggregated table.
+        for (auto iter = agg.iter(); !iter.done(); iter.next()) {
+          const LiveBlock& b = *iter.get().key();
+          size_t num = iter.get().value();
+          writeLiveBlock(b, num);
+        }
+
+      } else {
+        // In scan mode we cannot aggregate because we print each live block's
+        // address and contents.
+        for (auto iter = gLiveBlockTable->iter(); !iter.done(); iter.next()) {
+          const LiveBlock& b = iter.get();
+          b.AddStackTracesToTable(usedStackTraces);
+
+          writeLiveBlock(b, 1);
+        }
+      }
+
+      // Dead blocks.
+      for (auto iter = gDeadBlockTable->iter(); !iter.done(); iter.next()) {
+        const DeadBlock& b = iter.get().key();
+        b.AddStackTracesToTable(usedStackTraces);
+
+        size_t num = iter.get().value();
+        MOZ_ASSERT(num > 0);
+
+        writer.StartObjectElement(writer.SingleLineStyle);
+        {
+          writer.IntProperty("req", b.ReqSize());
+          if (b.SlopSize() > 0) {
+            writer.IntProperty("slop", b.SlopSize());
+          }
+          if (b.AllocStackTrace()) {
+            writer.StringProperty(
+                "alloc", MakeStringSpan(isc.ToIdString(b.AllocStackTrace())));
+          }
+
+          if (num > 1) {
+            writer.IntProperty("num", num);
+          }
+        }
+        writer.EndObject();
+      }
+    }
+    writer.EndArray();
+
+    StatusMsg("  Constructing the stack trace table...\n");
+
+    writer.StartObjectProperty("traceTable");
+    {
+      for (auto iter = usedStackTraces.iter(); !iter.done(); iter.next()) {
+        const StackTrace* const st = iter.get();
+        writer.StartArrayProperty(MakeStringSpan(isc.ToIdString(st)),
+                                  writer.SingleLineStyle);
+        {
+          for (uint32_t i = 0; i < st->Length(); i++) {
+            const void* pc = st->Pc(i);
+            writer.StringElement(MakeStringSpan(isc.ToIdString(pc)));
+            MOZ_ALWAYS_TRUE(usedPcs.put(pc));
+          }
+        }
+        writer.EndArray();
+      }
+    }
+    writer.EndObject();
+
+    StatusMsg("  Constructing the stack frame table...\n");
+
+    writer.StartObjectProperty("frameTable");
+    {
+      static const size_t locBufLen = 1024;
+      char locBuf[locBufLen];
+
+      for (auto iter = usedPcs.iter(); !iter.done(); iter.next()) {
+        const void* const pc = iter.get();
+
+        // Use 0 for the frame number. See the JSON format description comment
+        // in DMD.h to understand why.
+        locService->GetLocation(0, pc, locBuf, locBufLen);
+        writer.StringProperty(MakeStringSpan(isc.ToIdString(pc)),
+                              MakeStringSpan(locBuf));
+      }
+    }
+    writer.EndObject();
+
+    iscSize = isc.sizeOfExcludingThis(MallocSizeOf);
+  }
+  writer.End();
+
+  if (gOptions->ShowDumpStats()) {
+    Sizes sizes;
+    SizeOfInternal(&sizes);
+
+    static const size_t kBufLen = 64;
+    char buf1[kBufLen];
+    char buf2[kBufLen];
+    char buf3[kBufLen];
+
+    StatusMsg("  Execution measurements {\n");
+
+    StatusMsg("    Data structures that persist after Dump() ends {\n");
+
+    StatusMsg("      Used stack traces:    %10s bytes\n",
+              Show(sizes.mStackTracesUsed, buf1, kBufLen));
+
+    StatusMsg("      Unused stack traces:  %10s bytes\n",
+              Show(sizes.mStackTracesUnused, buf1, kBufLen));
+
+    StatusMsg("      Stack trace table:    %10s bytes (%s entries, %s used)\n",
+              Show(sizes.mStackTraceTable, buf1, kBufLen),
+              Show(gStackTraceTable->capacity(), buf2, kBufLen),
+              Show(gStackTraceTable->count(), buf3, kBufLen));
+
+    StatusMsg("      Live block table:     %10s bytes (%s entries, %s used)\n",
+              Show(sizes.mLiveBlockTable, buf1, kBufLen),
+              Show(gLiveBlockTable->capacity(), buf2, kBufLen),
+              Show(gLiveBlockTable->count(), buf3, kBufLen));
+
+    StatusMsg("      Dead block table:     %10s bytes (%s entries, %s used)\n",
+              Show(sizes.mDeadBlockTable, buf1, kBufLen),
+              Show(gDeadBlockTable->capacity(), buf2, kBufLen),
+              Show(gDeadBlockTable->count(), buf3, kBufLen));
+
+    StatusMsg("    }\n");
+    StatusMsg("    Data structures that are destroyed after Dump() ends {\n");
+
+    StatusMsg(
+        "      Location service:      %10s bytes\n",
+        Show(locService->SizeOfIncludingThis(MallocSizeOf), buf1, kBufLen));
+    StatusMsg("      Used stack traces set: %10s bytes\n",
+              Show(usedStackTraces.shallowSizeOfExcludingThis(MallocSizeOf),
+                   buf1, kBufLen));
+    StatusMsg(
+        "      Used PCs set:          %10s bytes\n",
+        Show(usedPcs.shallowSizeOfExcludingThis(MallocSizeOf), buf1, kBufLen));
+    StatusMsg("      Pointer ID map:        %10s bytes\n",
+              Show(iscSize, buf1, kBufLen));
+
+    StatusMsg("    }\n");
+    StatusMsg("    Counts {\n");
+
+    size_t hits = locService->NumCacheHits();
+    size_t misses = locService->NumCacheMisses();
+    size_t requests = hits + misses;
+    StatusMsg("      Location service:    %10s requests\n",
+              Show(requests, buf1, kBufLen));
+
+    size_t count = locService->CacheCount();
+    size_t capacity = locService->CacheCapacity();
+    StatusMsg(
+        "      Location service cache:  "
+        "%4.1f%% hit rate, %.1f%% occupancy at end\n",
+        Percent(hits, requests), Percent(count, capacity));
+
+    StatusMsg("    }\n");
+    StatusMsg("  }\n");
+  }
+
+  InfallibleAllocPolicy::delete_(locService);
+
+  StatusMsg("}\n");
+}
+
+void DMDFuncs::Analyze(UniquePtr<JSONWriteFunc> aWriter) {
+  AnalyzeImpl(std::move(aWriter));
+  ClearReports();
+}
+
+//---------------------------------------------------------------------------
+// Testing
+//---------------------------------------------------------------------------
+
+void DMDFuncs::ResetEverything(const char* aOptions) {
+  AutoLockState lock;
+
+  // Reset options.
+  InfallibleAllocPolicy::delete_(gOptions);
+  gOptions = InfallibleAllocPolicy::new_<Options>(aOptions);
+
+  // Clear all existing blocks.
+  gLiveBlockTable->clear();
+  gDeadBlockTable->clear();
+
+  // Reset gBernoulli to a deterministic state. (Its current state depends on
+  // all previous trials.)
+  ResetBernoulli();
+}
+
+}  // namespace dmd
+}  // namespace mozilla
diff --git a/memory/replace/dmd/DMD.h b/memory/replace/dmd/DMD.h
new file mode 100644
index 0000000000..c057047800
--- /dev/null
+++ b/memory/replace/dmd/DMD.h
@@ -0,0 +1,291 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef DMD_h___
+#define DMD_h___
+
+#include <stdarg.h>
+#include <string.h>
+
+#include <utility>
+
+#include "mozilla/DebugOnly.h"
+#include "mozilla/Types.h"
+#include "mozilla/UniquePtr.h"
+#include "replace_malloc_bridge.h"
+
+namespace mozilla {
+
+class JSONWriteFunc;
+
+namespace dmd {
+
+struct Sizes {
+  size_t mStackTracesUsed;
+  size_t mStackTracesUnused;
+  size_t mStackTraceTable;
+  size_t mLiveBlockTable;
+  size_t mDeadBlockTable;
+
+  Sizes() { Clear(); }
+  void Clear() { memset(this, 0, sizeof(Sizes)); }
+};
+
+// See further below for a description of each method. The DMDFuncs class
+// should contain a virtual method for each of them (except IsRunning,
+// which can be inferred from the DMDFuncs singleton existing).
+struct DMDFuncs {
+  virtual void Report(const void*);
+
+  virtual void ReportOnAlloc(const void*);
+
+  virtual void ClearReports();
+
+  virtual void Analyze(UniquePtr<JSONWriteFunc>);
+
+  virtual void SizeOf(Sizes*);
+
+  virtual void StatusMsg(const char*, va_list) MOZ_FORMAT_PRINTF(2, 0);
+
+  virtual void ResetEverything(const char*);
+
+#ifndef REPLACE_MALLOC_IMPL
+  // We deliberately don't use ReplaceMalloc::GetDMDFuncs here, because if we
+  // did, the following would happen.
+  // - The code footprint of each call to Get() larger as GetDMDFuncs ends
+  //   up inlined.
+  // - When no replace-malloc library is loaded, the number of instructions
+  //   executed is equivalent, but don't necessarily fit in the same cache
+  //   line.
+  // - When a non-DMD replace-malloc library is loaded, the overhead is
+  //   higher because there is first a check for the replace malloc bridge
+  //   and then for the DMDFuncs singleton.
+  // Initializing the DMDFuncs singleton on the first access makes the
+  // overhead even worse. Either Get() is inlined and massive, or it isn't
+  // and a simple value check becomes a function call.
+  static DMDFuncs* Get() { return sSingleton.Get(); }
+
+ private:
+  // Wrapper class keeping a pointer to the DMD functions. It is statically
+  // initialized because it needs to be set early enough.
+  // Debug builds also check that it's never accessed before the static
+  // initialization actually occured, which could be the case if some other
+  // static initializer ended up calling into DMD.
+  class Singleton {
+   public:
+    Singleton()
+        : mValue(ReplaceMalloc::GetDMDFuncs())
+#  ifdef DEBUG
+          ,
+          mInitialized(true)
+#  endif
+    {
+    }
+
+    DMDFuncs* Get() {
+      MOZ_ASSERT(mInitialized);
+      return mValue;
+    }
+
+   private:
+    DMDFuncs* mValue;
+#  ifdef DEBUG
+    bool mInitialized;
+#  endif
+  };
+
+  // This singleton pointer must be defined on the program side. In Gecko,
+  // this is done in xpcom/base/nsMemoryInfoDumper.cpp.
+  static /* DMDFuncs:: */ Singleton sSingleton;
+#endif
+};
+
+#ifndef REPLACE_MALLOC_IMPL
+// Mark a heap block as reported by a memory reporter.
+inline void Report(const void* aPtr) {
+  DMDFuncs* funcs = DMDFuncs::Get();
+  if (funcs) {
+    funcs->Report(aPtr);
+  }
+}
+
+// Mark a heap block as reported immediately on allocation.
+inline void ReportOnAlloc(const void* aPtr) {
+  DMDFuncs* funcs = DMDFuncs::Get();
+  if (funcs) {
+    funcs->ReportOnAlloc(aPtr);
+  }
+}
+
+// Clears existing reportedness data from any prior runs of the memory
+// reporters.  The following sequence should be used.
+// - ClearReports()
+// - run the memory reporters
+// - Analyze()
+// This sequence avoids spurious twice-reported warnings.
+inline void ClearReports() {
+  DMDFuncs* funcs = DMDFuncs::Get();
+  if (funcs) {
+    funcs->ClearReports();
+  }
+}
+
+// Determines which heap blocks have been reported, and dumps JSON output
+// (via |aWriter|) describing the heap.
+//
+// The following sample output contains comments that explain the format and
+// design choices. The output files can be quite large, so a number of
+// decisions were made to minimize size, such as using short property names and
+// omitting properties whenever possible.
+//
+// {
+//   // The version number of the format, which will be incremented each time
+//   // backwards-incompatible changes are made. A mandatory integer.
+//   //
+//   // Version history:
+//   // - 1: Bug 1044709
+//   // - 2: Bug 1094552
+//   // - 3: Bug 1100851
+//   // - 4: Bug 1121830
+//   // - 5: Bug 1253512
+//   "version": 5,
+//
+//   // Information about how DMD was invoked. A mandatory object.
+//   "invocation": {
+//     // The contents of the $DMD environment variable. A string, or |null| if
+//     // $DMD is undefined.
+//     "dmdEnvVar": "--mode=dark-matter",
+//
+//     // The profiling mode. A mandatory string taking one of the following
+//     // values: "live", "dark-matter", "cumulative", "scan".
+//     "mode": "dark-matter",
+//   },
+//
+//   // Details of all analyzed heap blocks. A mandatory array.
+//   "blockList": [
+//     // An example of a heap block.
+//     {
+//       // Requested size, in bytes. This is a mandatory integer.
+//       "req": 3584,
+//
+//       // Requested slop size, in bytes. This is mandatory if it is non-zero,
+//       // but omitted otherwise.
+//       "slop": 512,
+//
+//       // The stack trace at which the block was allocated. An optional
+//       // string that indexes into the "traceTable" object. If omitted, no
+//       // allocation stack trace was recorded for the block.
+//       "alloc": "A",
+//
+//       // One or more stack traces at which this heap block was reported by a
+//       // memory reporter. An optional array that will only be present in
+//       // "dark-matter" mode. The elements are strings that index into
+//       // the "traceTable" object.
+//       "reps": ["B"]
+//
+//       // The number of heap blocks with exactly the above properties. This
+//       // is mandatory if it is greater than one, but omitted otherwise.
+//       // (Blocks with identical properties don't have to be aggregated via
+//       // this property, but it can greatly reduce output file size.)
+//       "num": 5,
+//
+//       // The address of the block. This is mandatory in "scan" mode, but
+//       // omitted otherwise.
+//       "addr": "4e4e4e4e",
+//
+//       // The contents of the block, read one word at a time. This is
+//       // mandatory in "scan" mode for blocks at least one word long, but
+//       // omitted otherwise.
+//       "contents": ["0", "6", "7f7f7f7f", "0"]
+//     }
+//   ],
+//
+//   // The stack traces referenced by elements of the "blockList" array. This
+//   // could be an array, but making it an object makes it easier to see
+//   // which stacks correspond to which references in the "blockList" array.
+//   "traceTable": {
+//     // Each property corresponds to a stack trace mentioned in the "blocks"
+//     // object. Each element is an index into the "frameTable" object.
+//     "A": ["D", "E"],
+//     "B": ["F", "G"]
+//   },
+//
+//   // The stack frames referenced by the "traceTable" object. The
+//   // descriptions can be quite long, so they are stored separately from the
+//   // "traceTable" object so that each one only has to be written once.
+//   // This could also be an array, but again, making it an object makes it
+//   // easier to see which frames correspond to which references in the
+//   // "traceTable" object.
+//   "frameTable": {
+//     // Each property key is a frame key mentioned in the "traceTable" object.
+//     // Each property value is a string containing a frame description. Each
+//     // frame description must be in a format recognized by `fix_stacks.py`,
+//     // which requires a frame number at the start. Because each stack frame
+//     // description in this table can be shared between multiple stack
+//     // traces, we use a dummy value of #00. The proper frame number can be
+//     // reconstructed later by scripts that output stack traces in a
+//     // conventional non-shared format.
+//     "D": "#00: foo (Foo.cpp:123)",
+//     "E": "#00: bar (Bar.cpp:234)",
+//     "F": "#00: baz (Baz.cpp:345)",
+//     "G": "#00: quux (Quux.cpp:456)"
+//   }
+// }
+//
+// Implementation note: normally, this function wouldn't be templated, but in
+// that case, the function is compiled, which makes the destructor for the
+// UniquePtr fire up, and that needs JSONWriteFunc to be fully defined. That,
+// in turn, requires to include JSONWriter.h, which includes
+// double-conversion.h, which ends up breaking various things built with
+// -Werror for various reasons.
+//
+template <typename JSONWriteFunc>
+inline void Analyze(UniquePtr<JSONWriteFunc> aWriteFunc) {
+  DMDFuncs* funcs = DMDFuncs::Get();
+  if (funcs) {
+    funcs->Analyze(std::move(aWriteFunc));
+  }
+}
+
+// Gets the size of various data structures.  Used to implement a memory
+// reporter for DMD.
+inline void SizeOf(Sizes* aSizes) {
+  DMDFuncs* funcs = DMDFuncs::Get();
+  if (funcs) {
+    funcs->SizeOf(aSizes);
+  }
+}
+
+// Prints a status message prefixed with "DMD[<pid>]". Use sparingly.
+MOZ_FORMAT_PRINTF(1, 2)
+inline void StatusMsg(const char* aFmt, ...) {
+  DMDFuncs* funcs = DMDFuncs::Get();
+  if (funcs) {
+    va_list ap;
+    va_start(ap, aFmt);
+    funcs->StatusMsg(aFmt, ap);
+    va_end(ap);
+  }
+}
+
+// Indicates whether or not DMD is running.
+inline bool IsRunning() { return !!DMDFuncs::Get(); }
+
+// Resets all DMD options and then sets new ones according to those specified
+// in |aOptions|. Also clears all recorded data about allocations. Only used
+// for testing purposes.
+inline void ResetEverything(const char* aOptions) {
+  DMDFuncs* funcs = DMDFuncs::Get();
+  if (funcs) {
+    funcs->ResetEverything(aOptions);
+  }
+}
+#endif
+
+}  // namespace dmd
+}  // namespace mozilla
+
+#endif /* DMD_h___ */
diff --git a/memory/replace/dmd/README b/memory/replace/dmd/README
new file mode 100644
index 0000000000..537893358a
--- /dev/null
+++ b/memory/replace/dmd/README
@@ -0,0 +1,3 @@
+This is DMD.  See
+https://firefox-source-docs.mozilla.org/performance/memory/dmd.html for
+details on how to use it.
diff --git a/memory/replace/dmd/block_analyzer.py b/memory/replace/dmd/block_analyzer.py
new file mode 100644
index 0000000000..1f907b38a7
--- /dev/null
+++ b/memory/replace/dmd/block_analyzer.py
@@ -0,0 +1,292 @@
+#!/usr/bin/env python3
+
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# From a scan mode DMD log, extract some information about a
+# particular block, such as its allocation stack or which other blocks
+# contain pointers to it. This can be useful when investigating leaks
+# caused by unknown references to refcounted objects.
+
+import argparse
+import gzip
+import json
+import re
+import sys
+
+# The DMD output version this script handles.
+outputVersion = 5
+
+# If --ignore-alloc-fns is specified, stack frames containing functions that
+# match these strings will be removed from the *start* of stack traces. (Once
+# we hit a non-matching frame, any subsequent frames won't be removed even if
+# they do match.)
+allocatorFns = [
+    "malloc (",
+    "replace_malloc",
+    "replace_calloc",
+    "replace_realloc",
+    "replace_memalign",
+    "replace_posix_memalign",
+    "malloc_zone_malloc",
+    "moz_xmalloc",
+    "moz_xcalloc",
+    "moz_xrealloc",
+    "operator new(",
+    "operator new[](",
+    "g_malloc",
+    "g_slice_alloc",
+    "callocCanGC",
+    "reallocCanGC",
+    "vpx_malloc",
+    "vpx_calloc",
+    "vpx_realloc",
+    "vpx_memalign",
+    "js_malloc",
+    "js_calloc",
+    "js_realloc",
+    "pod_malloc",
+    "pod_calloc",
+    "pod_realloc",
+    "nsTArrayInfallibleAllocator::Malloc",
+    "Allocator<ReplaceMallocBase>::malloc(",
+    "mozilla::dmd::StackTrace::Get(",
+    "mozilla::dmd::AllocCallback(",
+    "mozilla::dom::DOMArena::Allocate(",
+    # This one necessary to fully filter some sequences of allocation functions
+    # that happen in practice. Note that ??? entries that follow non-allocation
+    # functions won't be stripped, as explained above.
+    "???",
+]
+
+####
+
+# Command line arguments
+
+
+def range_1_24(string):
+    value = int(string)
+    if value < 1 or value > 24:
+        msg = "{:s} is not in the range 1..24".format(string)
+        raise argparse.ArgumentTypeError(msg)
+    return value
+
+
+parser = argparse.ArgumentParser(
+    description="Analyze the heap graph to find out things about an object. \
+By default this prints out information about blocks that point to the given block."
+)
+
+parser.add_argument("dmd_log_file_name", help="clamped DMD log file name")
+
+parser.add_argument("block", help="address of the block of interest")
+
+parser.add_argument(
+    "--info",
+    dest="info",
+    action="store_true",
+    default=False,
+    help="Print out information about the block.",
+)
+
+parser.add_argument(
+    "-sfl",
+    "--max-stack-frame-length",
+    type=int,
+    default=300,
+    help="Maximum number of characters to print from each stack frame",
+)
+
+parser.add_argument(
+    "-a",
+    "--ignore-alloc-fns",
+    action="store_true",
+    help="ignore allocation functions at the start of traces",
+)
+
+parser.add_argument(
+    "-f",
+    "--max-frames",
+    type=range_1_24,
+    default=8,
+    help="maximum number of frames to consider in each trace",
+)
+
+parser.add_argument(
+    "-c",
+    "--chain-reports",
+    action="store_true",
+    help="if only one block is found to hold onto the object, report "
+    "the next one, too",
+)
+
+
+####
+
+
+class BlockData:
+    def __init__(self, json_block):
+        self.addr = json_block["addr"]
+
+        if "contents" in json_block:
+            contents = json_block["contents"]
+        else:
+            contents = []
+        self.contents = []
+        for c in contents:
+            self.contents.append(int(c, 16))
+
+        self.req_size = json_block["req"]
+
+        self.alloc_stack = json_block["alloc"]
+
+
+def print_trace_segment(args, stacks, block):
+    (traceTable, frameTable) = stacks
+
+    for l in traceTable[block.alloc_stack]:
+        # The 5: is to remove the bogus leading "#00: " from the stack frame.
+        print("  " + frameTable[l][5 : args.max_stack_frame_length])
+
+
+def show_referrers(args, blocks, stacks, block):
+    visited = set([])
+
+    anyFound = False
+
+    while True:
+        referrers = {}
+
+        for b, data in blocks.items():
+            which_edge = 0
+            for e in data.contents:
+                if e == block:
+                    # 8 is the number of bytes per word on a 64-bit system.
+                    # XXX This means that this output will be wrong for logs from 32-bit systems!
+                    referrers.setdefault(b, []).append(8 * which_edge)
+                    anyFound = True
+                which_edge += 1
+
+        for r in referrers:
+            sys.stdout.write(
+                "0x{} size = {} bytes".format(blocks[r].addr, blocks[r].req_size)
+            )
+            plural = "s" if len(referrers[r]) > 1 else ""
+            print(
+                " at byte offset"
+                + plural
+                + " "
+                + (", ".join(str(x) for x in referrers[r]))
+            )
+            print_trace_segment(args, stacks, blocks[r])
+            print("")
+
+        if args.chain_reports:
+            if len(referrers) == 0:
+                sys.stdout.write("Found no more referrers.\n")
+                break
+            if len(referrers) > 1:
+                sys.stdout.write("Found too many referrers.\n")
+                break
+
+            sys.stdout.write("Chaining to next referrer.\n\n")
+            for r in referrers:
+                block = r
+            if block in visited:
+                sys.stdout.write("Found a loop.\n")
+                break
+            visited.add(block)
+        else:
+            break
+
+    if not anyFound:
+        print("No referrers found.")
+
+
+def show_block_info(args, blocks, stacks, block):
+    b = blocks[block]
+    sys.stdout.write("block: 0x{}\n".format(b.addr))
+    sys.stdout.write("requested size: {} bytes\n".format(b.req_size))
+    sys.stdout.write("\n")
+    sys.stdout.write("block contents: ")
+    for c in b.contents:
+        v = "0" if c == 0 else blocks[c].addr
+        sys.stdout.write("0x{} ".format(v))
+    sys.stdout.write("\n\n")
+    sys.stdout.write("allocation stack:\n")
+    print_trace_segment(args, stacks, b)
+    return
+
+
+def cleanupTraceTable(args, frameTable, traceTable):
+    # Remove allocation functions at the start of traces.
+    if args.ignore_alloc_fns:
+        # Build a regexp that matches every function in allocatorFns.
+        escapedAllocatorFns = map(re.escape, allocatorFns)
+        fn_re = re.compile("|".join(escapedAllocatorFns))
+
+        # Remove allocator fns from each stack trace.
+        for traceKey, frameKeys in traceTable.items():
+            numSkippedFrames = 0
+            for frameKey in frameKeys:
+                frameDesc = frameTable[frameKey]
+                if re.search(fn_re, frameDesc):
+                    numSkippedFrames += 1
+                else:
+                    break
+            if numSkippedFrames > 0:
+                traceTable[traceKey] = frameKeys[numSkippedFrames:]
+
+    # Trim the number of frames.
+    for traceKey, frameKeys in traceTable.items():
+        if len(frameKeys) > args.max_frames:
+            traceTable[traceKey] = frameKeys[: args.max_frames]
+
+
+def loadGraph(options):
+    # Handle gzipped input if necessary.
+    isZipped = options.dmd_log_file_name.endswith(".gz")
+    opener = gzip.open if isZipped else open
+
+    with opener(options.dmd_log_file_name, "rb") as f:
+        j = json.load(f)
+
+    if j["version"] != outputVersion:
+        raise Exception("'version' property isn't '{:d}'".format(outputVersion))
+
+    block_list = j["blockList"]
+    blocks = {}
+
+    for json_block in block_list:
+        blocks[int(json_block["addr"], 16)] = BlockData(json_block)
+
+    traceTable = j["traceTable"]
+    frameTable = j["frameTable"]
+
+    cleanupTraceTable(options, frameTable, traceTable)
+
+    return (blocks, (traceTable, frameTable))
+
+
+def analyzeLogs():
+    options = parser.parse_args()
+
+    (blocks, stacks) = loadGraph(options)
+
+    block = int(options.block, 16)
+
+    if block not in blocks:
+        print("Object " + options.block + " not found in traces.")
+        print("It could still be the target of some nodes.")
+        return
+
+    if options.info:
+        show_block_info(options, blocks, stacks, block)
+        return
+
+    show_referrers(options, blocks, stacks, block)
+
+
+if __name__ == "__main__":
+    analyzeLogs()
diff --git a/memory/replace/dmd/dmd.py b/memory/replace/dmd/dmd.py
new file mode 100755
index 0000000000..3e20d8d6bd
--- /dev/null
+++ b/memory/replace/dmd/dmd.py
@@ -0,0 +1,1028 @@
+#! /usr/bin/env python3
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+"""This script analyzes a JSON file emitted by DMD."""
+
+import argparse
+import collections
+import gzip
+import io
+import json
+import os
+import platform
+import re
+import shutil
+import sys
+import tempfile
+from bisect import bisect_right
+from functools import cmp_to_key
+from typing import Callable
+
+# The DMD output version this script handles.
+outputVersion = 5
+
+# If --ignore-alloc-fns is specified, stack frames containing functions that
+# match these strings will be removed from the *start* of stack traces. (Once
+# we hit a non-matching frame, any subsequent frames won't be removed even if
+# they do match.)
+allocatorFns = [
+    # Matches malloc, replace_malloc, moz_xmalloc, vpx_malloc, js_malloc,
+    # pod_malloc, malloc_zone_*, g_malloc.
+    "malloc",
+    # Matches calloc, replace_calloc, moz_xcalloc, vpx_calloc, js_calloc,
+    # pod_calloc, malloc_zone_calloc, pod_callocCanGC.
+    "calloc",
+    # Matches realloc, replace_realloc, moz_xrealloc, vpx_realloc, js_realloc,
+    # pod_realloc, pod_reallocCanGC.
+    "realloc",
+    # Matches memalign, posix_memalign, replace_memalign, replace_posix_memalign,
+    # moz_xmemalign, vpx_memalign, malloc_zone_memalign.
+    "memalign",
+    "operator new(",
+    "operator new[](",
+    "g_slice_alloc",
+    # This one is necessary to fully filter some sequences of allocation
+    # functions that happen in practice. Note that ??? entries that follow
+    # non-allocation functions won't be stripped, as explained above.
+    "???",
+    # Match DMD internals.
+    "mozilla::dmd::AllocCallback",
+    "mozilla::dmd::StackTrace::Get",
+]
+
+
+def cmp(a, b):
+    return (a > b) - (a < b)
+
+
+class Record(object):
+    """A record is an aggregation of heap blocks that have identical stack
+    traces. It can also be used to represent the difference between two
+    records."""
+
+    def __init__(self):
+        self.numBlocks = 0
+        self.reqSize = 0
+        self.slopSize = 0
+        self.usableSize = 0
+        self.allocatedAtDesc = None
+        self.reportedAtDescs = []
+        self.usableSizes = collections.defaultdict(int)
+
+    def isZero(self, args):
+        return (
+            self.numBlocks == 0
+            and self.reqSize == 0
+            and self.slopSize == 0
+            and self.usableSize == 0
+            and len(self.usableSizes) == 0
+        )
+
+    def negate(self):
+        self.numBlocks = -self.numBlocks
+        self.reqSize = -self.reqSize
+        self.slopSize = -self.slopSize
+        self.usableSize = -self.usableSize
+
+        negatedUsableSizes = collections.defaultdict(int)
+        for usableSize, count in self.usableSizes.items():
+            negatedUsableSizes[-usableSize] = count
+        self.usableSizes = negatedUsableSizes
+
+    def subtract(self, r):
+        # We should only be calling this on records with matching stack traces.
+        # Check this.
+        assert self.allocatedAtDesc == r.allocatedAtDesc
+        assert self.reportedAtDescs == r.reportedAtDescs
+
+        self.numBlocks -= r.numBlocks
+        self.reqSize -= r.reqSize
+        self.slopSize -= r.slopSize
+        self.usableSize -= r.usableSize
+
+        usableSizes1 = self.usableSizes
+        usableSizes2 = r.usableSizes
+        usableSizes3 = collections.defaultdict(int)
+        for usableSize in usableSizes1:
+            counts1 = usableSizes1[usableSize]
+            if usableSize in usableSizes2:
+                counts2 = usableSizes2[usableSize]
+                del usableSizes2[usableSize]
+                counts3 = counts1 - counts2
+                if counts3 != 0:
+                    if counts3 < 0:
+                        usableSize = -usableSize
+                        counts3 = -counts3
+                    usableSizes3[usableSize] = counts3
+            else:
+                usableSizes3[usableSize] = counts1
+
+        for usableSize in usableSizes2:
+            usableSizes3[-usableSize] = usableSizes2[usableSize]
+
+        self.usableSizes = usableSizes3
+
+    @staticmethod
+    def cmpByUsableSize(r1, r2):
+        # Sort by usable size, then by req size.
+        return cmp(abs(r1.usableSize), abs(r2.usableSize)) or Record.cmpByReqSize(
+            r1, r2
+        )
+
+    @staticmethod
+    def cmpByReqSize(r1, r2):
+        # Sort by req size.
+        return cmp(abs(r1.reqSize), abs(r2.reqSize))
+
+    @staticmethod
+    def cmpBySlopSize(r1, r2):
+        # Sort by slop size.
+        return cmp(abs(r1.slopSize), abs(r2.slopSize))
+
+    @staticmethod
+    def cmpByNumBlocks(r1, r2):
+        # Sort by block counts, then by usable size.
+        return cmp(abs(r1.numBlocks), abs(r2.numBlocks)) or Record.cmpByUsableSize(
+            r1, r2
+        )
+
+
+sortByChoices = {
+    "usable": Record.cmpByUsableSize,  # the default
+    "req": Record.cmpByReqSize,
+    "slop": Record.cmpBySlopSize,
+    "num-blocks": Record.cmpByNumBlocks,
+}
+
+
+def parseCommandLine():
+    # 24 is the maximum number of frames that DMD will produce.
+    def range_1_24(string):
+        value = int(string)
+        if value < 1 or value > 24:
+            msg = "{:s} is not in the range 1..24".format(string)
+            raise argparse.ArgumentTypeError(msg)
+        return value
+
+    description = """
+Analyze heap data produced by DMD.
+If one file is specified, analyze it; if two files are specified, analyze the
+difference.
+Input files can be gzipped.
+Write to stdout unless -o/--output is specified.
+Stack traces are fixed to show function names, filenames and line numbers
+unless --no-fix-stacks is specified; stack fixing modifies the original file
+and may take some time. If specified, the BREAKPAD_SYMBOLS_PATH environment
+variable is used to find breakpad symbols for stack fixing.
+"""
+    p = argparse.ArgumentParser(description=description)
+
+    p.add_argument(
+        "-o",
+        "--output",
+        type=argparse.FileType("w"),
+        help="output file; stdout if unspecified",
+    )
+
+    p.add_argument(
+        "-f",
+        "--max-frames",
+        type=range_1_24,
+        default=8,
+        help="maximum number of frames to consider in each trace",
+    )
+
+    p.add_argument(
+        "-s",
+        "--sort-by",
+        choices=sortByChoices.keys(),
+        default="usable",
+        help="sort the records by a particular metric",
+    )
+
+    p.add_argument(
+        "-a",
+        "--ignore-alloc-fns",
+        action="store_true",
+        help="ignore allocation functions at the start of traces",
+    )
+
+    p.add_argument("--no-fix-stacks", action="store_true", help="do not fix stacks")
+
+    p.add_argument(
+        "--clamp-contents",
+        action="store_true",
+        help="for a scan mode log, clamp addresses to the start of live blocks, "
+        "or zero if not in one",
+    )
+
+    p.add_argument(
+        "--print-clamp-stats",
+        action="store_true",
+        help="print information about the results of pointer clamping; mostly "
+        "useful for debugging clamping",
+    )
+
+    p.add_argument(
+        "--filter-stacks-for-testing",
+        action="store_true",
+        help="filter stack traces; only useful for testing purposes",
+    )
+
+    p.add_argument(
+        "--filter",
+        default=[],
+        action="append",
+        help="Only print entries that have a stack that matches the filter. "
+        "A filter may be negated by prefixing it with `!`. "
+        "If multiple filters are specified, all of them must match.",
+    )
+
+    p.add_argument("input_file", help="a file produced by DMD")
+
+    p.add_argument(
+        "input_file2",
+        nargs="?",
+        help="a file produced by DMD; if present, it is diff'd with input_file",
+    )
+
+    return p.parse_args(sys.argv[1:])
+
+
+# Fix stacks if necessary: first write the output to a tempfile, then replace
+# the original file with it.
+def fixStackTraces(inputFilename, isZipped, opener):
+    # This append() call is needed to make the import statements work when this
+    # script is installed as a symlink.
+    sys.path.append(os.path.dirname(__file__))
+
+    bpsyms = os.environ.get("BREAKPAD_SYMBOLS_PATH", None)
+    sysname = platform.system()
+    if bpsyms and os.path.exists(bpsyms):
+        import fix_stacks as fixModule
+
+        def fix(line):
+            return fixModule.fixSymbols(line, jsonMode=True, breakpadSymsDir=bpsyms)
+
+    elif sysname in ("Linux", "Darwin", "Windows"):
+        import fix_stacks as fixModule
+
+        def fix(line):
+            return fixModule.fixSymbols(line, jsonMode=True)
+
+    else:
+        return
+
+    # Fix stacks, writing output to a temporary file, and then overwrite the
+    # original file.
+    tmpFile = tempfile.NamedTemporaryFile(delete=False)
+
+    # If the input is gzipped, then the output (written initially to |tmpFile|)
+    # should be gzipped as well.
+    #
+    # And we want to set its pre-gzipped filename to '' rather than the name of
+    # the temporary file, so that programs like the Unix 'file' utility don't
+    # say that it was called 'tmp6ozTxE' (or something like that) before it was
+    # zipped. So that explains the |filename=''| parameter.
+    #
+    # But setting the filename like that clobbers |tmpFile.name|, so we must
+    # get that now in order to move |tmpFile| at the end.
+    tmpFilename = tmpFile.name
+    if isZipped:
+        tmpFile = gzip.GzipFile(filename="", fileobj=tmpFile, mode="wb")
+
+    with opener(inputFilename, "rb") as inputFile:
+        for line in inputFile:
+            tmpFile.write(fix(line))
+
+    tmpFile.close()
+
+    shutil.move(tmpFilename, inputFilename)
+
+
+def getDigestFromFile(args, inputFile):
+    # Handle gzipped input if necessary.
+    isZipped = inputFile.endswith(".gz")
+    opener = gzip.open if isZipped else open
+
+    # Fix stack traces unless otherwise instructed.
+    if not args.no_fix_stacks:
+        fixStackTraces(inputFile, isZipped, opener)
+
+    if args.clamp_contents:
+        clampBlockList(args, inputFile, isZipped, opener)
+
+    with opener(inputFile, "rb") as f:
+        j = json.load(f)
+
+    if j["version"] != outputVersion:
+        raise Exception("'version' property isn't '{:d}'".format(outputVersion))
+
+    # Extract the main parts of the JSON object.
+    invocation = j["invocation"]
+    dmdEnvVar = invocation["dmdEnvVar"]
+    mode = invocation["mode"]
+    blockList = j["blockList"]
+    traceTable = j["traceTable"]
+    frameTable = j["frameTable"]
+
+    # Insert the necessary entries for unrecorded stack traces. Note that 'ut'
+    # and 'uf' will not overlap with any keys produced by DMD's
+    # ToIdStringConverter::Base32() function.
+    unrecordedTraceID = "ut"
+    unrecordedFrameID = "uf"
+    traceTable[unrecordedTraceID] = [unrecordedFrameID]
+    frameTable[
+        unrecordedFrameID
+    ] = "#00: (no stack trace recorded due to --stacks=partial)"
+
+    # For the purposes of this script, 'scan' behaves like 'live'.
+    if mode == "scan":
+        mode = "live"
+
+    if mode not in ["live", "dark-matter", "cumulative"]:
+        raise Exception("bad 'mode' property: '{:s}'".format(mode))
+
+    # Remove allocation functions at the start of traces.
+    if args.ignore_alloc_fns:
+        # Build a regexp that matches every function in allocatorFns.
+        escapedAllocatorFns = map(re.escape, allocatorFns)
+        fn_re = re.compile("|".join(escapedAllocatorFns))
+
+        # Remove allocator fns from each stack trace.
+        for traceKey, frameKeys in traceTable.items():
+            numSkippedFrames = 0
+            for frameKey in frameKeys:
+                frameDesc = frameTable[frameKey]
+                if re.search(fn_re, frameDesc):
+                    numSkippedFrames += 1
+                else:
+                    break
+            if numSkippedFrames > 0:
+                traceTable[traceKey] = frameKeys[numSkippedFrames:]
+
+    # Trim the number of frames.
+    for traceKey, frameKeys in traceTable.items():
+        if len(frameKeys) > args.max_frames:
+            del frameKeys[args.max_frames :]
+
+    def buildTraceDescription(traceTable, frameTable, traceKey):
+        frameKeys = traceTable[traceKey]
+        fmt = "    #{:02d}{:}"
+
+        if args.filter_stacks_for_testing:
+            # This option is used by `test_dmd.js`, which runs the code in
+            # `SmokeDMD.cpp`. When running that test, there is too much
+            # variation in the stack traces across different machines and
+            # platforms to do exact output matching. However, every stack trace
+            # should have at least three frames that contain `DMD` (in one of
+            # `DMD.cpp`, `SmokeDMD.cpp`, `SmokeDMD`, or `SmokeDMD.exe`). Some
+            # example frames from automation (where `..` indicates excised path
+            # segments):
+            #
+            # Linux debug, with stack fixing using breakpad syms:
+            # `#01: replace_realloc(void*, unsigned long) [../dmd/DMD.cpp:1110]`
+            #
+            # Linux opt, with native stack fixing:
+            # `#02: TestFull(char const*, int, char const*, int) (../dmd/test/SmokeDMD.cpp:165)`
+            #
+            # Mac opt, with native stack fixing:
+            # `#03: RunTests() (../build/tests/bin/SmokeDMD + 0x21f9)`
+            #
+            # Windows opt, with native stack fixing failing due to a missing PDB:
+            # `#04: ??? (..\\build\\tests\\bin\\SmokeDMD.exe + 0x1c58)`
+            #
+            # If we see three such frames, we replace the entire stack trace
+            # with a single, predictable frame. This imprecise matching will at
+            # least detect if stack fixing fails completely.
+            dmd_frame_matches = 0
+            for frameKey in frameKeys:
+                frameDesc = frameTable[frameKey]
+                if "DMD" in frameDesc:
+                    dmd_frame_matches += 1
+                    if dmd_frame_matches >= 3:
+                        return [fmt.format(1, ": ... DMD.cpp ...")]
+
+        # The frame number is always '#00' (see DMD.h for why), so we have to
+        # replace that with the correct frame number.
+        desc = []
+        for n, frameKey in enumerate(traceTable[traceKey], start=1):
+            desc.append(fmt.format(n, frameTable[frameKey][3:]))
+        return desc
+
+    # Aggregate blocks into records. All sufficiently similar blocks go into a
+    # single record.
+
+    if mode in ["live", "cumulative"]:
+        liveOrCumulativeRecords = collections.defaultdict(Record)
+    elif mode == "dark-matter":
+        unreportedRecords = collections.defaultdict(Record)
+        onceReportedRecords = collections.defaultdict(Record)
+        twiceReportedRecords = collections.defaultdict(Record)
+
+    heapUsableSize = 0
+    heapBlocks = 0
+
+    recordKeyPartCache = {}
+
+    for block in blockList:
+        # For each block we compute a |recordKey|, and all blocks with the same
+        # |recordKey| are aggregated into a single record. The |recordKey| is
+        # derived from the block's 'alloc' and 'reps' (if present) stack
+        # traces.
+        #
+        # We use frame descriptions (e.g. "#00: foo (X.cpp:99)") when comparing
+        # traces for equality. We can't use trace keys or frame keys because
+        # they're not comparable across different DMD runs (which is relevant
+        # when doing diffs).
+        #
+        # Using frame descriptions also fits in with the stack trimming done
+        # for --max-frames, which requires that stack traces with common
+        # beginnings but different endings to be considered equivalent. E.g. if
+        # we have distinct traces T1:[A:D1,B:D2,C:D3] and T2:[X:D1,Y:D2,Z:D4]
+        # and we trim the final frame of each they should be considered
+        # equivalent because the untrimmed frame descriptions (D1 and D2)
+        # match.
+        #
+        # Having said all that, during a single invocation of dmd.py on a
+        # single DMD file, for a single frameKey value the record key will
+        # always be the same, and we might encounter it 1000s of times. So we
+        # cache prior results for speed.
+        def makeRecordKeyPart(traceKey):
+            if traceKey in recordKeyPartCache:
+                return recordKeyPartCache[traceKey]
+
+            recordKeyPart = str(
+                list(map(lambda frameKey: frameTable[frameKey], traceTable[traceKey]))
+            )
+            recordKeyPartCache[traceKey] = recordKeyPart
+            return recordKeyPart
+
+        allocatedAtTraceKey = block.get("alloc", unrecordedTraceID)
+        if mode in ["live", "cumulative"]:
+            recordKey = makeRecordKeyPart(allocatedAtTraceKey)
+            records = liveOrCumulativeRecords
+        elif mode == "dark-matter":
+            recordKey = makeRecordKeyPart(allocatedAtTraceKey)
+            if "reps" in block:
+                reportedAtTraceKeys = block["reps"]
+                for reportedAtTraceKey in reportedAtTraceKeys:
+                    recordKey += makeRecordKeyPart(reportedAtTraceKey)
+                if len(reportedAtTraceKeys) == 1:
+                    records = onceReportedRecords
+                else:
+                    records = twiceReportedRecords
+            else:
+                records = unreportedRecords
+
+        record = records[recordKey]
+
+        if "req" not in block:
+            raise Exception("'req' property missing in block'")
+
+        reqSize = block["req"]
+        slopSize = block.get("slop", 0)
+
+        if "num" in block:
+            num = block["num"]
+        else:
+            num = 1
+
+        usableSize = reqSize + slopSize
+        heapUsableSize += num * usableSize
+        heapBlocks += num
+
+        record.numBlocks += num
+        record.reqSize += num * reqSize
+        record.slopSize += num * slopSize
+        record.usableSize += num * usableSize
+        if record.allocatedAtDesc is None:
+            record.allocatedAtDesc = buildTraceDescription(
+                traceTable, frameTable, allocatedAtTraceKey
+            )
+
+        if mode in ["live", "cumulative"]:
+            pass
+        elif mode == "dark-matter":
+            if "reps" in block and record.reportedAtDescs == []:
+
+                def f(k):
+                    return buildTraceDescription(traceTable, frameTable, k)
+
+                record.reportedAtDescs = list(map(f, reportedAtTraceKeys))
+        record.usableSizes[usableSize] += num
+
+    # All the processed data for a single DMD file is called a "digest".
+    digest = {}
+    digest["dmdEnvVar"] = dmdEnvVar
+    digest["mode"] = mode
+    digest["heapUsableSize"] = heapUsableSize
+    digest["heapBlocks"] = heapBlocks
+    if mode in ["live", "cumulative"]:
+        digest["liveOrCumulativeRecords"] = liveOrCumulativeRecords
+    elif mode == "dark-matter":
+        digest["unreportedRecords"] = unreportedRecords
+        digest["onceReportedRecords"] = onceReportedRecords
+        digest["twiceReportedRecords"] = twiceReportedRecords
+    return digest
+
+
+def diffRecords(args, records1, records2):
+    records3 = {}
+
+    # Process records1.
+    for k in records1:
+        r1 = records1[k]
+        if k in records2:
+            # This record is present in both records1 and records2.
+            r2 = records2[k]
+            del records2[k]
+            r2.subtract(r1)
+            if not r2.isZero(args):
+                records3[k] = r2
+        else:
+            # This record is present only in records1.
+            r1.negate()
+            records3[k] = r1
+
+    for k in records2:
+        # This record is present only in records2.
+        records3[k] = records2[k]
+
+    return records3
+
+
+def diffDigests(args, d1, d2):
+    if d1["mode"] != d2["mode"]:
+        raise Exception("the input files have different 'mode' properties")
+
+    d3 = {}
+    d3["dmdEnvVar"] = (d1["dmdEnvVar"], d2["dmdEnvVar"])
+    d3["mode"] = d1["mode"]
+    d3["heapUsableSize"] = d2["heapUsableSize"] - d1["heapUsableSize"]
+    d3["heapBlocks"] = d2["heapBlocks"] - d1["heapBlocks"]
+    if d1["mode"] in ["live", "cumulative"]:
+        d3["liveOrCumulativeRecords"] = diffRecords(
+            args, d1["liveOrCumulativeRecords"], d2["liveOrCumulativeRecords"]
+        )
+    elif d1["mode"] == "dark-matter":
+        d3["unreportedRecords"] = diffRecords(
+            args, d1["unreportedRecords"], d2["unreportedRecords"]
+        )
+        d3["onceReportedRecords"] = diffRecords(
+            args, d1["onceReportedRecords"], d2["onceReportedRecords"]
+        )
+        d3["twiceReportedRecords"] = diffRecords(
+            args, d1["twiceReportedRecords"], d2["twiceReportedRecords"]
+        )
+    return d3
+
+
+def printDigest(args, digest):
+    dmdEnvVar = digest["dmdEnvVar"]
+    mode = digest["mode"]
+    heapUsableSize = digest["heapUsableSize"]
+    heapBlocks = digest["heapBlocks"]
+    if mode in ["live", "cumulative"]:
+        liveOrCumulativeRecords = digest["liveOrCumulativeRecords"]
+    elif mode == "dark-matter":
+        unreportedRecords = digest["unreportedRecords"]
+        onceReportedRecords = digest["onceReportedRecords"]
+        twiceReportedRecords = digest["twiceReportedRecords"]
+
+    separator = "#" + "-" * 65 + "\n"
+
+    def number(n):
+        """Format a number with comma as a separator."""
+        return "{:,d}".format(n)
+
+    def perc(m, n):
+        return 0 if n == 0 else (100 * m / n)
+
+    def plural(n):
+        return "" if n == 1 else "s"
+
+    # Prints to stdout, or to file if -o/--output was specified.
+    def out(*arguments, **kwargs):
+        print(*arguments, file=args.output, **kwargs)
+
+    def printStack(traceDesc):
+        for frameDesc in traceDesc:
+            out(frameDesc)
+
+    def printRecords(recordKind, records, heapUsableSize):
+        RecordKind = recordKind.capitalize()
+        out(separator)
+        numRecords = len(records)
+        cmpRecords = sortByChoices[args.sort_by]
+        sortedRecords = sorted(
+            records.values(), key=cmp_to_key(cmpRecords), reverse=True
+        )
+        kindBlocks = 0
+        kindUsableSize = 0
+        maxRecord = 1000
+
+        def is_match(rec: Record, key: str):
+            return any(key in desc for desc in rec.allocatedAtDesc)
+
+        for arg in args.filter:
+            key: str
+            cond: Callable[[Record], bool]
+            if arg.startswith("\\"):
+                # just in case you really need to start a filter with '!' (or '\')
+                key = arg[1:]
+                cond = is_match
+            elif arg.startswith("!"):
+                key = arg[1:]
+
+                def cond(rec, key):
+                    return not is_match(rec, key)  # noqa: E731
+
+            else:
+                key = arg
+                cond = is_match
+            sortedRecords = [rec for rec in sortedRecords if cond(rec, key)]
+
+        # First iteration: get totals, etc.
+        for record in sortedRecords:
+            kindBlocks += record.numBlocks
+            kindUsableSize += record.usableSize
+
+        # Second iteration: print.
+        if numRecords == 0:
+            out("# no {:} heap blocks\n".format(recordKind))
+
+        kindCumulativeUsableSize = 0
+        for i, record in enumerate(sortedRecords, start=1):
+            # Stop printing at the |maxRecord|th record.
+            if i == maxRecord:
+                out(
+                    "# {:}: stopping after {:,d} heap block records\n".format(
+                        RecordKind, i
+                    )
+                )
+                break
+
+            kindCumulativeUsableSize += record.usableSize
+
+            out(RecordKind + " {")
+            out(
+                "  {:} block{:} in heap block record {:,d} of {:,d}".format(
+                    number(record.numBlocks), plural(record.numBlocks), i, numRecords
+                )
+            )
+            out(
+                "  {:} bytes ({:} requested / {:} slop)".format(
+                    number(record.usableSize),
+                    number(record.reqSize),
+                    number(record.slopSize),
+                )
+            )
+
+            usableSizes = sorted(
+                record.usableSizes.items(), key=lambda x: abs(x[0]), reverse=True
+            )
+            hasSingleBlock = len(usableSizes) == 1 and usableSizes[0][1] == 1
+
+            if not hasSingleBlock:
+                out("  Individual block sizes: ", end="")
+                if len(usableSizes) == 0:
+                    out("(no change)", end="")
+                else:
+                    isFirst = True
+                    for usableSize, count in usableSizes:
+                        if not isFirst:
+                            out("; ", end="")
+                        out("{:}".format(number(usableSize)), end="")
+                        if count > 1:
+                            out(" x {:,d}".format(count), end="")
+                        isFirst = False
+                out()
+
+            out(
+                "  {:4.2f}% of the heap ({:4.2f}% cumulative)".format(
+                    perc(record.usableSize, heapUsableSize),
+                    perc(kindCumulativeUsableSize, heapUsableSize),
+                )
+            )
+            if mode in ["live", "cumulative"]:
+                pass
+            elif mode == "dark-matter":
+                out(
+                    "  {:4.2f}% of {:} ({:4.2f}% cumulative)".format(
+                        perc(record.usableSize, kindUsableSize),
+                        recordKind,
+                        perc(kindCumulativeUsableSize, kindUsableSize),
+                    )
+                )
+            out("  Allocated at {")
+            printStack(record.allocatedAtDesc)
+            out("  }")
+            if mode in ["live", "cumulative"]:
+                pass
+            elif mode == "dark-matter":
+                for n, reportedAtDesc in enumerate(record.reportedAtDescs):
+                    again = "again " if n > 0 else ""
+                    out("  Reported {:}at {{".format(again))
+                    printStack(reportedAtDesc)
+                    out("  }")
+            out("}\n")
+
+        return (kindUsableSize, kindBlocks)
+
+    def printInvocation(n, dmdEnvVar, mode):
+        out("Invocation{:} {{".format(n))
+        if dmdEnvVar is None:
+            out("  $DMD is undefined")
+        else:
+            out("  $DMD = '" + dmdEnvVar + "'")
+        out("  Mode = '" + mode + "'")
+        out("}\n")
+
+    # Print command line. Strip dirs so the output is deterministic, which is
+    # needed for testing.
+    out(separator, end="")
+    out("# " + " ".join(map(os.path.basename, sys.argv)) + "\n")
+
+    # Print invocation(s).
+    if type(dmdEnvVar) is not tuple:
+        printInvocation("", dmdEnvVar, mode)
+    else:
+        printInvocation(" 1", dmdEnvVar[0], mode)
+        printInvocation(" 2", dmdEnvVar[1], mode)
+
+    # Print records.
+    if mode in ["live", "cumulative"]:
+        liveOrCumulativeUsableSize, liveOrCumulativeBlocks = printRecords(
+            mode, liveOrCumulativeRecords, heapUsableSize
+        )
+    elif mode == "dark-matter":
+        twiceReportedUsableSize, twiceReportedBlocks = printRecords(
+            "twice-reported", twiceReportedRecords, heapUsableSize
+        )
+
+        unreportedUsableSize, unreportedBlocks = printRecords(
+            "unreported", unreportedRecords, heapUsableSize
+        )
+
+        onceReportedUsableSize, onceReportedBlocks = printRecords(
+            "once-reported", onceReportedRecords, heapUsableSize
+        )
+
+    # Print summary.
+    out(separator)
+    out("Summary {")
+    if mode in ["live", "cumulative"]:
+        out(
+            "  Total: {:} bytes in {:} blocks".format(
+                number(liveOrCumulativeUsableSize), number(liveOrCumulativeBlocks)
+            )
+        )
+    elif mode == "dark-matter":
+        fmt = "  {:15} {:>12} bytes ({:6.2f}%) in {:>7} blocks ({:6.2f}%)"
+        out(fmt.format("Total:", number(heapUsableSize), 100, number(heapBlocks), 100))
+        out(
+            fmt.format(
+                "Unreported:",
+                number(unreportedUsableSize),
+                perc(unreportedUsableSize, heapUsableSize),
+                number(unreportedBlocks),
+                perc(unreportedBlocks, heapBlocks),
+            )
+        )
+        out(
+            fmt.format(
+                "Once-reported:",
+                number(onceReportedUsableSize),
+                perc(onceReportedUsableSize, heapUsableSize),
+                number(onceReportedBlocks),
+                perc(onceReportedBlocks, heapBlocks),
+            )
+        )
+        out(
+            fmt.format(
+                "Twice-reported:",
+                number(twiceReportedUsableSize),
+                perc(twiceReportedUsableSize, heapUsableSize),
+                number(twiceReportedBlocks),
+                perc(twiceReportedBlocks, heapBlocks),
+            )
+        )
+    out("}\n")
+
+
+#############################
+# Pretty printer for DMD JSON
+#############################
+
+
+def prettyPrintDmdJson(out, j):
+    out.write("{\n")
+
+    out.write(' "version": {0},\n'.format(j["version"]))
+    out.write(' "invocation": ')
+    json.dump(j["invocation"], out, sort_keys=True)
+    out.write(",\n")
+
+    out.write(' "blockList": [')
+    first = True
+    for b in j["blockList"]:
+        out.write("" if first else ",")
+        out.write("\n  ")
+        json.dump(b, out, sort_keys=True)
+        first = False
+    out.write("\n ],\n")
+
+    out.write(' "traceTable": {')
+    first = True
+    for k, l in j["traceTable"].items():
+        out.write("" if first else ",")
+        out.write('\n  "{0}": {1}'.format(k, json.dumps(l)))
+        first = False
+    out.write("\n },\n")
+
+    out.write(' "frameTable": {')
+    first = True
+    for k, v in j["frameTable"].items():
+        out.write("" if first else ",")
+        out.write('\n  "{0}": {1}'.format(k, json.dumps(v)))
+        first = False
+    out.write("\n }\n")
+
+    out.write("}\n")
+
+
+##################################################################
+# Code for clamping addresses using conservative pointer analysis.
+##################################################################
+
+
+# Start is the address of the first byte of the block, while end is
+# the address of the first byte after the final byte in the block.
+class AddrRange:
+    def __init__(self, block, length):
+        self.block = block
+        self.start = int(block, 16)
+        self.length = length
+        self.end = self.start + self.length
+
+        assert self.start > 0
+        assert length >= 0
+
+
+class ClampStats:
+    def __init__(self):
+        # Number of pointers already pointing to the start of a block.
+        self.startBlockPtr = 0
+
+        # Number of pointers pointing to the middle of a block. These
+        # are clamped to the start of the block they point into.
+        self.midBlockPtr = 0
+
+        # Number of null pointers.
+        self.nullPtr = 0
+
+        # Number of non-null pointers that didn't point into the middle
+        # of any blocks. These are clamped to null.
+        self.nonNullNonBlockPtr = 0
+
+    def clampedBlockAddr(self, sameAddress):
+        if sameAddress:
+            self.startBlockPtr += 1
+        else:
+            self.midBlockPtr += 1
+
+    def nullAddr(self):
+        self.nullPtr += 1
+
+    def clampedNonBlockAddr(self):
+        self.nonNullNonBlockPtr += 1
+
+    def log(self):
+        sys.stderr.write("Results:\n")
+        sys.stderr.write(
+            "  Number of pointers already pointing to start of blocks: "
+            + str(self.startBlockPtr)
+            + "\n"
+        )
+        sys.stderr.write(
+            "  Number of pointers clamped to start of blocks: "
+            + str(self.midBlockPtr)
+            + "\n"
+        )
+        sys.stderr.write(
+            "  Number of non-null pointers not pointing into blocks "
+            "clamped to null: " + str(self.nonNullNonBlockPtr) + "\n"
+        )
+        sys.stderr.write("  Number of null pointers: " + str(self.nullPtr) + "\n")
+
+
+# Search the block ranges array for a block that address points into.
+# The search is carried out in an array of starting addresses for each blocks
+# because it is faster.
+def clampAddress(blockRanges, blockStarts, clampStats, address):
+    i = bisect_right(blockStarts, address)
+
+    # Any addresses completely out of the range should have been eliminated already.
+    assert i > 0
+    r = blockRanges[i - 1]
+    assert r.start <= address
+
+    if address >= r.end:
+        assert address < blockRanges[i].start
+        clampStats.clampedNonBlockAddr()
+        return "0"
+
+    clampStats.clampedBlockAddr(r.start == address)
+    return r.block
+
+
+def clampBlockList(args, inputFileName, isZipped, opener):
+    # XXX This isn't very efficient because we end up reading and writing
+    # the file multiple times.
+    with opener(inputFileName, "rb") as f:
+        j = json.load(f)
+
+    if j["version"] != outputVersion:
+        raise Exception("'version' property isn't '{:d}'".format(outputVersion))
+
+    # Check that the invocation is reasonable for contents clamping.
+    invocation = j["invocation"]
+    if invocation["mode"] != "scan":
+        raise Exception("Log was taken in mode " + invocation["mode"] + " not scan")
+
+    sys.stderr.write("Creating block range list.\n")
+    blockList = j["blockList"]
+    blockRanges = []
+    for block in blockList:
+        blockRanges.append(AddrRange(block["addr"], block["req"]))
+    blockRanges.sort(key=lambda r: r.start)
+
+    # Make sure there are no overlapping blocks.
+    prevRange = blockRanges[0]
+    for currRange in blockRanges[1:]:
+        assert prevRange.end <= currRange.start
+        prevRange = currRange
+
+    sys.stderr.write("Clamping block contents.\n")
+    clampStats = ClampStats()
+    firstAddr = blockRanges[0].start
+    lastAddr = blockRanges[-1].end
+
+    blockStarts = []
+    for r in blockRanges:
+        blockStarts.append(r.start)
+
+    for block in blockList:
+        # Small blocks don't have any contents.
+        if "contents" not in block:
+            continue
+
+        cont = block["contents"]
+        for i in range(len(cont)):
+            address = int(cont[i], 16)
+
+            if address == 0:
+                clampStats.nullAddr()
+                continue
+
+            # If the address is before the first block or after the last
+            # block then it can't be within a block.
+            if address < firstAddr or address >= lastAddr:
+                clampStats.clampedNonBlockAddr()
+                cont[i] = "0"
+                continue
+
+            cont[i] = clampAddress(blockRanges, blockStarts, clampStats, address)
+
+        # Remove any trailing nulls.
+        while len(cont) and cont[-1] == "0":
+            cont.pop()
+
+    if args.print_clamp_stats:
+        clampStats.log()
+
+    sys.stderr.write("Saving file.\n")
+    tmpFile = tempfile.NamedTemporaryFile(delete=False)
+    tmpFilename = tmpFile.name
+    if isZipped:
+        tmpFile = gzip.GzipFile(filename="", fileobj=tmpFile, mode="wb")
+    prettyPrintDmdJson(io.TextIOWrapper(tmpFile, encoding="utf-8"), j)
+    tmpFile.close()
+    shutil.move(tmpFilename, inputFileName)
+
+
+def main():
+    args = parseCommandLine()
+    digest = getDigestFromFile(args, args.input_file)
+    if args.input_file2:
+        digest2 = getDigestFromFile(args, args.input_file2)
+        digest = diffDigests(args, digest, digest2)
+    printDigest(args, digest)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/memory/replace/dmd/moz.build b/memory/replace/dmd/moz.build
new file mode 100644
index 0000000000..6f3121df48
--- /dev/null
+++ b/memory/replace/dmd/moz.build
@@ -0,0 +1,37 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+EXPORTS += [
+    "DMD.h",
+]
+
+UNIFIED_SOURCES += [
+    "DMD.cpp",
+]
+
+if not CONFIG["MOZ_REPLACE_MALLOC_STATIC"]:
+    UNIFIED_SOURCES += [
+        "/mfbt/HashFunctions.cpp",
+        "/mfbt/JSONWriter.cpp",
+        "/mfbt/Poison.cpp",
+        "/mozglue/misc/StackWalk.cpp",
+    ]
+    if CONFIG["OS_ARCH"] == "WINNT":
+        OS_LIBS += [
+            "dbghelp",
+        ]
+
+ReplaceMalloc("dmd")
+
+DEFINES["MOZ_NO_MOZALLOC"] = True
+DEFINES["IMPL_MFBT"] = True
+
+if CONFIG["MOZ_OPTIMIZE"]:
+    DEFINES["MOZ_OPTIMIZE"] = True
+
+DisableStlWrapping()
+
+TEST_DIRS += ["test"]
diff --git a/memory/replace/dmd/test/SmokeDMD.cpp b/memory/replace/dmd/test/SmokeDMD.cpp
new file mode 100644
index 0000000000..c72e92a543
--- /dev/null
+++ b/memory/replace/dmd/test/SmokeDMD.cpp
@@ -0,0 +1,378 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// This program is used by the DMD xpcshell test. It is run under DMD and
+// produces some output. The xpcshell test then post-processes and checks this
+// output.
+//
+// Note that this file does not have "Test" or "test" in its name, because that
+// will cause the build system to not record breakpad symbols for it, which
+// will stop the post-processing (which includes stack fixing) from working
+// correctly.
+
+// This is required on some systems such as Fedora to allow
+// building with -O0 together with --warnings-as-errors due to
+// a check in /usr/include/features.h
+#undef _FORTIFY_SOURCE
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/JSONWriter.h"
+#include "mozilla/Sprintf.h"
+#include "mozilla/UniquePtr.h"
+#include "DMD.h"
+
+using mozilla::MakeUnique;
+using namespace mozilla::dmd;
+
+DMDFuncs::Singleton DMDFuncs::sSingleton;
+
+class FpWriteFunc final : public mozilla::JSONWriteFunc {
+ public:
+  explicit FpWriteFunc(const char* aFilename) {
+    mFp = fopen(aFilename, "w");
+    if (!mFp) {
+      fprintf(stderr, "SmokeDMD: can't create %s file: %s\n", aFilename,
+              strerror(errno));
+      exit(1);
+    }
+  }
+
+  ~FpWriteFunc() { fclose(mFp); }
+
+  void Write(const mozilla::Span<const char>& aStr) final {
+    for (const char c : aStr) {
+      fputc(c, mFp);
+    }
+  }
+
+ private:
+  FILE* mFp;
+};
+
+// This stops otherwise-unused variables from being optimized away.
+static void UseItOrLoseIt(void* aPtr, int aSeven) {
+  char buf[64];
+  int n = SprintfLiteral(buf, "%p\n", aPtr);
+  if (n == 20 + aSeven) {
+    fprintf(stderr, "well, that is surprising");
+  }
+}
+
+// This function checks that heap blocks that have the same stack trace but
+// different (or no) reporters get aggregated separately.
+void Foo(int aSeven) {
+  char* a[6];
+  for (int i = 0; i < aSeven - 1; i++) {
+    a[i] = (char*)malloc(128 - 16 * i);
+    UseItOrLoseIt(a[i], aSeven);
+  }
+
+  // Oddly, some versions of clang will cause identical stack traces to be
+  // generated for adjacent calls to Report(), which breaks the test. Inserting
+  // the UseItOrLoseIt() calls in between is enough to prevent this.
+
+  Report(a[2]);  // reported
+
+  UseItOrLoseIt(a[2], aSeven);
+
+  for (int i = 0; i < aSeven - 5; i++) {
+    Report(a[i]);  // reported
+    UseItOrLoseIt(a[i], aSeven);
+  }
+
+  UseItOrLoseIt(a[2], aSeven);
+
+  Report(a[3]);  // reported
+
+  // a[4], a[5] unreported
+}
+
+void TestEmpty(const char* aTestName, const char* aMode) {
+  char filename[128];
+  SprintfLiteral(filename, "complete-%s-%s.json", aTestName, aMode);
+  auto f = MakeUnique<FpWriteFunc>(filename);
+
+  char options[128];
+  SprintfLiteral(options, "--mode=%s --stacks=full", aMode);
+  ResetEverything(options);
+
+  // Zero for everything.
+  Analyze(std::move(f));
+}
+
+void TestFull(const char* aTestName, int aNum, const char* aMode, int aSeven) {
+  char filename[128];
+  SprintfLiteral(filename, "complete-%s%d-%s.json", aTestName, aNum, aMode);
+  auto f = MakeUnique<FpWriteFunc>(filename);
+
+  // The --show-dump-stats=yes is there just to give that option some basic
+  // testing, e.g. ensure it doesn't crash. It's hard to test much beyond that.
+  char options[128];
+  SprintfLiteral(options, "--mode=%s --stacks=full --show-dump-stats=yes",
+                 aMode);
+  ResetEverything(options);
+
+  // Analyze 1: 1 freed, 9 out of 10 unreported.
+  // Analyze 2: still present and unreported.
+  int i;
+  char* a = nullptr;
+  for (i = 0; i < aSeven + 3; i++) {
+    a = (char*)malloc(100);
+    UseItOrLoseIt(a, aSeven);
+  }
+  free(a);
+
+  // A no-op.
+  free(nullptr);
+
+  // Note: 16 bytes is the smallest requested size that gives consistent
+  // behaviour across all platforms with jemalloc.
+  // Analyze 1: reported.
+  // Analyze 2: thrice-reported.
+  char* a2 = (char*)malloc(16);
+  Report(a2);
+
+  // Analyze 1: reported.
+  // Analyze 2: reportedness carries over, due to ReportOnAlloc.
+  char* b = (char*)malloc(10);
+  ReportOnAlloc(b);
+
+  // ReportOnAlloc, then freed.
+  // Analyze 1: freed, irrelevant.
+  // Analyze 2: freed, irrelevant.
+  char* b2 = (char*)malloc(16);
+  ReportOnAlloc(b2);
+  free(b2);
+
+  // Analyze 1: reported 4 times.
+  // Analyze 2: freed, irrelevant.
+  char* c = (char*)calloc(10, 3);
+  Report(c);
+  for (int i = 0; i < aSeven - 4; i++) {
+    Report(c);
+  }
+
+  // Analyze 1: ignored.
+  // Analyze 2: irrelevant.
+  Report((void*)(intptr_t)i);
+
+  // jemalloc rounds this up to 8192.
+  // Analyze 1: reported.
+  // Analyze 2: freed.
+  char* e = (char*)malloc(4096);
+  e = (char*)realloc(e, 7169);
+  Report(e);
+
+  // First realloc is like malloc;  second realloc is shrinking.
+  // Analyze 1: reported.
+  // Analyze 2: re-reported.
+  char* e2 = (char*)realloc(nullptr, 1024);
+  e2 = (char*)realloc(e2, 512);
+  Report(e2);
+
+  // First realloc is like malloc;  second realloc creates a min-sized block.
+  // XXX: on Windows, second realloc frees the block.
+  // Analyze 1: reported.
+  // Analyze 2: freed, irrelevant.
+  char* e3 = (char*)realloc(nullptr, 1023);
+  // e3 = (char*) realloc(e3, 0);
+  MOZ_ASSERT(e3);
+  Report(e3);
+
+  // Analyze 1: freed, irrelevant.
+  // Analyze 2: freed, irrelevant.
+  char* f1 = (char*)malloc(64);
+  UseItOrLoseIt(f1, aSeven);
+  free(f1);
+
+  // Analyze 1: ignored.
+  // Analyze 2: irrelevant.
+  Report((void*)(intptr_t)0x0);
+
+  // Analyze 1: mixture of reported and unreported.
+  // Analyze 2: all unreported.
+  Foo(aSeven);
+
+  // Analyze 1: twice-reported.
+  // Analyze 2: twice-reported.
+  char* g1 = (char*)malloc(77);
+  ReportOnAlloc(g1);
+  ReportOnAlloc(g1);
+
+  // Analyze 1: mixture of reported and unreported.
+  // Analyze 2: all unreported.
+  // Nb: this Foo() call is deliberately not adjacent to the previous one. See
+  // the comment about adjacent calls in Foo() for more details.
+  Foo(aSeven);
+
+  // Analyze 1: twice-reported.
+  // Analyze 2: once-reported.
+  char* g2 = (char*)malloc(78);
+  Report(g2);
+  ReportOnAlloc(g2);
+
+  // Analyze 1: twice-reported.
+  // Analyze 2: once-reported.
+  char* g3 = (char*)malloc(79);
+  ReportOnAlloc(g3);
+  Report(g3);
+
+  // All the odd-ball ones.
+  // Analyze 1: all unreported.
+  // Analyze 2: all freed, irrelevant.
+  // XXX: no memalign on Mac
+  // void* w = memalign(64, 65);           // rounds up to 128
+  // UseItOrLoseIt(w, aSeven);
+
+  // XXX: posix_memalign doesn't work on B2G
+  // void* x;
+  // posix_memalign(&y, 128, 129);         // rounds up to 256
+  // UseItOrLoseIt(x, aSeven);
+
+  // XXX: valloc doesn't work on Windows.
+  // void* y = valloc(1);                  // rounds up to 4096
+  // UseItOrLoseIt(y, aSeven);
+
+  // XXX: C11 only
+  // void* z = aligned_alloc(64, 256);
+  // UseItOrLoseIt(z, aSeven);
+
+  if (aNum == 1) {
+    // Analyze 1.
+    Analyze(std::move(f));
+  }
+
+  ClearReports();
+
+  //---------
+
+  Report(a2);
+  Report(a2);
+  free(c);
+  free(e);
+  Report(e2);
+  free(e3);
+  // free(w);
+  // free(x);
+  // free(y);
+  // free(z);
+
+  // Do some allocations that will only show up in cumulative mode.
+  for (int i = 0; i < 100; i++) {
+    void* v = malloc(128);
+    UseItOrLoseIt(v, aSeven);
+    free(v);
+  }
+
+  if (aNum == 2) {
+    // Analyze 2.
+    Analyze(std::move(f));
+  }
+}
+
+void TestPartial(const char* aTestName, const char* aMode, int aSeven) {
+  char filename[128];
+  SprintfLiteral(filename, "complete-%s-%s.json", aTestName, aMode);
+  auto f = MakeUnique<FpWriteFunc>(filename);
+
+  char options[128];
+  SprintfLiteral(options, "--mode=%s", aMode);
+  ResetEverything(options);
+
+  int kTenThousand = aSeven + 9993;
+  char* s;
+
+  // The output of this function is deterministic but it relies on the
+  // probability and seeds given to the FastBernoulliTrial instance in
+  // ResetBernoulli(). If they change, the output will change too.
+
+  // Expected fraction with stacks: (1 - (1 - 0.003) ** 16) = 0.0469.
+  // So we expect about 0.0469 * 10000 == 469.
+  // We actually get 511.
+  for (int i = 0; i < kTenThousand; i++) {
+    s = (char*)malloc(16);
+    UseItOrLoseIt(s, aSeven);
+  }
+
+  // Expected fraction with stacks: (1 - (1 - 0.003) ** 128) = 0.3193.
+  // So we expect about 0.3193 * 10000 == 3193.
+  // We actually get 3136.
+  for (int i = 0; i < kTenThousand; i++) {
+    s = (char*)malloc(128);
+    UseItOrLoseIt(s, aSeven);
+  }
+
+  // Expected fraction with stacks: (1 - (1 - 0.003) ** 1024) = 0.9539.
+  // So we expect about 0.9539 * 10000 == 9539.
+  // We actually get 9531.
+  for (int i = 0; i < kTenThousand; i++) {
+    s = (char*)malloc(1024);
+    UseItOrLoseIt(s, aSeven);
+  }
+
+  Analyze(std::move(f));
+}
+
+void TestScan(int aSeven) {
+  auto f = MakeUnique<FpWriteFunc>("basic-scan.json");
+
+  ResetEverything("--mode=scan");
+
+  uintptr_t* p = (uintptr_t*)malloc(6 * sizeof(uintptr_t));
+  UseItOrLoseIt(p, aSeven);
+
+  // Hard-coded values checked by scan-test.py
+  p[0] = 0x123;                         // outside a block, small value
+  p[1] = 0x0;                           // null
+  p[2] = (uintptr_t)((uint8_t*)p - 1);  // pointer outside a block, but nearby
+  p[3] = (uintptr_t)p;                  // pointer to start of a block
+  p[4] = (uintptr_t)((uint8_t*)p + 1);  // pointer into a block
+  p[5] = 0x0;                           // trailing null
+
+  Analyze(std::move(f));
+}
+
+void RunTests() {
+  // This test relies on the compiler not doing various optimizations, such as
+  // eliding unused malloc() calls or unrolling loops with fixed iteration
+  // counts. So we compile it with -O0 (or equivalent), which probably prevents
+  // that. We also use the following variable for various loop iteration
+  // counts, just in case compilers might unroll very small loops even with
+  // -O0.
+  int seven = 7;
+
+  // Make sure that DMD is actually running; it is initialized on the first
+  // allocation.
+  int* x = (int*)malloc(100);
+  UseItOrLoseIt(x, seven);
+  MOZ_RELEASE_ASSERT(IsRunning());
+
+  // Please keep this in sync with run_test in test_dmd.js.
+
+  TestEmpty("empty", "live");
+  TestEmpty("empty", "dark-matter");
+  TestEmpty("empty", "cumulative");
+
+  TestFull("full", 1, "live", seven);
+  TestFull("full", 1, "dark-matter", seven);
+
+  TestFull("full", 2, "dark-matter", seven);
+  TestFull("full", 2, "cumulative", seven);
+
+  TestPartial("partial", "live", seven);
+
+  TestScan(seven);
+}
+
+int main() {
+  RunTests();
+
+  return 0;
+}
diff --git a/memory/replace/dmd/test/basic-scan-32-expected.txt b/memory/replace/dmd/test/basic-scan-32-expected.txt
new file mode 100644
index 0000000000..9f6f4db325
--- /dev/null
+++ b/memory/replace/dmd/test/basic-scan-32-expected.txt
@@ -0,0 +1,25 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o basic-scan-32-actual.txt --clamp-contents basic-scan.json
+
+Invocation {
+  $DMD = '--mode=scan'
+  Mode = 'live'
+}
+
+#-----------------------------------------------------------------
+
+Live {
+  1 block in heap block record 1 of 1
+  32 bytes (24 requested / 8 slop)
+  100.00% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: 32 bytes in 1 blocks
+}
+
diff --git a/memory/replace/dmd/test/basic-scan-64-expected.txt b/memory/replace/dmd/test/basic-scan-64-expected.txt
new file mode 100644
index 0000000000..59effc07b7
--- /dev/null
+++ b/memory/replace/dmd/test/basic-scan-64-expected.txt
@@ -0,0 +1,25 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o basic-scan-64-actual.txt --clamp-contents basic-scan.json
+
+Invocation {
+  $DMD = '--mode=scan'
+  Mode = 'live'
+}
+
+#-----------------------------------------------------------------
+
+Live {
+  1 block in heap block record 1 of 1
+  48 bytes (48 requested / 0 slop)
+  100.00% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: 48 bytes in 1 blocks
+}
+
diff --git a/memory/replace/dmd/test/complete-empty-cumulative-expected.txt b/memory/replace/dmd/test/complete-empty-cumulative-expected.txt
new file mode 100644
index 0000000000..2486015d0b
--- /dev/null
+++ b/memory/replace/dmd/test/complete-empty-cumulative-expected.txt
@@ -0,0 +1,18 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o complete-empty-cumulative-actual.txt complete-empty-cumulative.json
+
+Invocation {
+  $DMD = '--mode=cumulative --stacks=full'
+  Mode = 'cumulative'
+}
+
+#-----------------------------------------------------------------
+
+# no cumulative heap blocks
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: 0 bytes in 0 blocks
+}
+
diff --git a/memory/replace/dmd/test/complete-empty-dark-matter-expected.txt b/memory/replace/dmd/test/complete-empty-dark-matter-expected.txt
new file mode 100644
index 0000000000..0020cddde3
--- /dev/null
+++ b/memory/replace/dmd/test/complete-empty-dark-matter-expected.txt
@@ -0,0 +1,29 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o complete-empty-dark-matter-actual.txt complete-empty-dark-matter.json
+
+Invocation {
+  $DMD = '--mode=dark-matter --stacks=full'
+  Mode = 'dark-matter'
+}
+
+#-----------------------------------------------------------------
+
+# no twice-reported heap blocks
+
+#-----------------------------------------------------------------
+
+# no unreported heap blocks
+
+#-----------------------------------------------------------------
+
+# no once-reported heap blocks
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total:                     0 bytes (100.00%) in       0 blocks (100.00%)
+  Unreported:                0 bytes (  0.00%) in       0 blocks (  0.00%)
+  Once-reported:             0 bytes (  0.00%) in       0 blocks (  0.00%)
+  Twice-reported:            0 bytes (  0.00%) in       0 blocks (  0.00%)
+}
+
diff --git a/memory/replace/dmd/test/complete-empty-live-expected.txt b/memory/replace/dmd/test/complete-empty-live-expected.txt
new file mode 100644
index 0000000000..d0d1721965
--- /dev/null
+++ b/memory/replace/dmd/test/complete-empty-live-expected.txt
@@ -0,0 +1,18 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o complete-empty-live-actual.txt complete-empty-live.json
+
+Invocation {
+  $DMD = '--mode=live --stacks=full'
+  Mode = 'live'
+}
+
+#-----------------------------------------------------------------
+
+# no live heap blocks
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: 0 bytes in 0 blocks
+}
+
diff --git a/memory/replace/dmd/test/complete-full1-dark-matter-expected.txt b/memory/replace/dmd/test/complete-full1-dark-matter-expected.txt
new file mode 100644
index 0000000000..2c7d6b6343
--- /dev/null
+++ b/memory/replace/dmd/test/complete-full1-dark-matter-expected.txt
@@ -0,0 +1,265 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o complete-full1-dark-matter-actual.txt complete-full1-dark-matter.json
+
+Invocation {
+  $DMD = '--mode=dark-matter --stacks=full --show-dump-stats=yes'
+  Mode = 'dark-matter'
+}
+
+#-----------------------------------------------------------------
+
+Twice-reported {
+  1 block in heap block record 1 of 4
+  80 bytes (79 requested / 1 slop)
+  0.66% of the heap (0.66% cumulative)
+  29.41% of twice-reported (29.41% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+  Reported again at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Twice-reported {
+  1 block in heap block record 2 of 4
+  80 bytes (78 requested / 2 slop)
+  0.66% of the heap (1.32% cumulative)
+  29.41% of twice-reported (58.82% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+  Reported again at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Twice-reported {
+  1 block in heap block record 3 of 4
+  80 bytes (77 requested / 3 slop)
+  0.66% of the heap (1.98% cumulative)
+  29.41% of twice-reported (88.24% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+  Reported again at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Twice-reported {
+  1 block in heap block record 4 of 4
+  32 bytes (30 requested / 2 slop)
+  0.26% of the heap (2.25% cumulative)
+  11.76% of twice-reported (100.00% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+  Reported again at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+#-----------------------------------------------------------------
+
+Unreported {
+  9 blocks in heap block record 1 of 3
+  1,008 bytes (900 requested / 108 slop)
+  Individual block sizes: 112 x 9
+  8.33% of the heap (8.33% cumulative)
+  81.82% of unreported (81.82% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Unreported {
+  2 blocks in heap block record 2 of 3
+  112 bytes (112 requested / 0 slop)
+  Individual block sizes: 64; 48
+  0.93% of the heap (9.26% cumulative)
+  9.09% of unreported (90.91% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Unreported {
+  2 blocks in heap block record 3 of 3
+  112 bytes (112 requested / 0 slop)
+  Individual block sizes: 64; 48
+  0.93% of the heap (10.19% cumulative)
+  9.09% of unreported (100.00% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+#-----------------------------------------------------------------
+
+Once-reported {
+  1 block in heap block record 1 of 11
+  8,192 bytes (7,169 requested / 1,023 slop)
+  67.72% of the heap (67.72% cumulative)
+  77.34% of once-reported (77.34% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Once-reported {
+  1 block in heap block record 2 of 11
+  1,024 bytes (1,023 requested / 1 slop)
+  8.47% of the heap (76.19% cumulative)
+  9.67% of once-reported (87.01% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Once-reported {
+  1 block in heap block record 3 of 11
+  512 bytes (512 requested / 0 slop)
+  4.23% of the heap (80.42% cumulative)
+  4.83% of once-reported (91.84% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Once-reported {
+  2 blocks in heap block record 4 of 11
+  240 bytes (240 requested / 0 slop)
+  Individual block sizes: 128; 112
+  1.98% of the heap (82.41% cumulative)
+  2.27% of once-reported (94.11% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Once-reported {
+  2 blocks in heap block record 5 of 11
+  240 bytes (240 requested / 0 slop)
+  Individual block sizes: 128; 112
+  1.98% of the heap (84.39% cumulative)
+  2.27% of once-reported (96.37% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Once-reported {
+  1 block in heap block record 6 of 11
+  96 bytes (96 requested / 0 slop)
+  0.79% of the heap (85.19% cumulative)
+  0.91% of once-reported (97.28% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Once-reported {
+  1 block in heap block record 7 of 11
+  96 bytes (96 requested / 0 slop)
+  0.79% of the heap (85.98% cumulative)
+  0.91% of once-reported (98.19% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Once-reported {
+  1 block in heap block record 8 of 11
+  80 bytes (80 requested / 0 slop)
+  0.66% of the heap (86.64% cumulative)
+  0.76% of once-reported (98.94% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Once-reported {
+  1 block in heap block record 9 of 11
+  80 bytes (80 requested / 0 slop)
+  0.66% of the heap (87.30% cumulative)
+  0.76% of once-reported (99.70% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Once-reported {
+  1 block in heap block record 10 of 11
+  16 bytes (16 requested / 0 slop)
+  0.13% of the heap (87.43% cumulative)
+  0.15% of once-reported (99.85% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Once-reported {
+  1 block in heap block record 11 of 11
+  16 bytes (10 requested / 6 slop)
+  0.13% of the heap (87.57% cumulative)
+  0.15% of once-reported (100.00% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total:                12,096 bytes (100.00%) in      30 blocks (100.00%)
+  Unreported:            1,232 bytes ( 10.19%) in      13 blocks ( 43.33%)
+  Once-reported:        10,592 bytes ( 87.57%) in      13 blocks ( 43.33%)
+  Twice-reported:          272 bytes (  2.25%) in       4 blocks ( 13.33%)
+}
+
diff --git a/memory/replace/dmd/test/complete-full1-live-expected.txt b/memory/replace/dmd/test/complete-full1-live-expected.txt
new file mode 100644
index 0000000000..eaa1883e1f
--- /dev/null
+++ b/memory/replace/dmd/test/complete-full1-live-expected.txt
@@ -0,0 +1,127 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o complete-full1-live-actual.txt complete-full1-live.json
+
+Invocation {
+  $DMD = '--mode=live --stacks=full --show-dump-stats=yes'
+  Mode = 'live'
+}
+
+#-----------------------------------------------------------------
+
+Live {
+  1 block in heap block record 1 of 12
+  8,192 bytes (7,169 requested / 1,023 slop)
+  67.72% of the heap (67.72% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Live {
+  1 block in heap block record 2 of 12
+  1,024 bytes (1,023 requested / 1 slop)
+  8.47% of the heap (76.19% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Live {
+  9 blocks in heap block record 3 of 12
+  1,008 bytes (900 requested / 108 slop)
+  Individual block sizes: 112 x 9
+  8.33% of the heap (84.52% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Live {
+  6 blocks in heap block record 4 of 12
+  528 bytes (528 requested / 0 slop)
+  Individual block sizes: 128; 112; 96; 80; 64; 48
+  4.37% of the heap (88.89% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Live {
+  6 blocks in heap block record 5 of 12
+  528 bytes (528 requested / 0 slop)
+  Individual block sizes: 128; 112; 96; 80; 64; 48
+  4.37% of the heap (93.25% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Live {
+  1 block in heap block record 6 of 12
+  512 bytes (512 requested / 0 slop)
+  4.23% of the heap (97.49% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Live {
+  1 block in heap block record 7 of 12
+  80 bytes (79 requested / 1 slop)
+  0.66% of the heap (98.15% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Live {
+  1 block in heap block record 8 of 12
+  80 bytes (78 requested / 2 slop)
+  0.66% of the heap (98.81% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Live {
+  1 block in heap block record 9 of 12
+  80 bytes (77 requested / 3 slop)
+  0.66% of the heap (99.47% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Live {
+  1 block in heap block record 10 of 12
+  32 bytes (30 requested / 2 slop)
+  0.26% of the heap (99.74% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Live {
+  1 block in heap block record 11 of 12
+  16 bytes (16 requested / 0 slop)
+  0.13% of the heap (99.87% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Live {
+  1 block in heap block record 12 of 12
+  16 bytes (10 requested / 6 slop)
+  0.13% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: 12,096 bytes in 30 blocks
+}
+
diff --git a/memory/replace/dmd/test/complete-full2-cumulative-expected.txt b/memory/replace/dmd/test/complete-full2-cumulative-expected.txt
new file mode 100644
index 0000000000..5a225b9b8e
--- /dev/null
+++ b/memory/replace/dmd/test/complete-full2-cumulative-expected.txt
@@ -0,0 +1,173 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o complete-full2-cumulative-actual.txt complete-full2-cumulative.json
+
+Invocation {
+  $DMD = '--mode=cumulative --stacks=full --show-dump-stats=yes'
+  Mode = 'cumulative'
+}
+
+#-----------------------------------------------------------------
+
+Cumulative {
+  100 blocks in heap block record 1 of 17
+  12,800 bytes (12,800 requested / 0 slop)
+  Individual block sizes: 128 x 100
+  42.37% of the heap (42.37% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  1 block in heap block record 2 of 17
+  8,192 bytes (7,169 requested / 1,023 slop)
+  27.12% of the heap (69.49% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  1 block in heap block record 3 of 17
+  4,096 bytes (4,096 requested / 0 slop)
+  13.56% of the heap (83.05% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  10 blocks in heap block record 4 of 17
+  1,120 bytes (1,000 requested / 120 slop)
+  Individual block sizes: 112 x 10
+  3.71% of the heap (86.76% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  1 block in heap block record 5 of 17
+  1,024 bytes (1,024 requested / 0 slop)
+  3.39% of the heap (90.15% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  1 block in heap block record 6 of 17
+  1,024 bytes (1,023 requested / 1 slop)
+  3.39% of the heap (93.54% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  6 blocks in heap block record 7 of 17
+  528 bytes (528 requested / 0 slop)
+  Individual block sizes: 128; 112; 96; 80; 64; 48
+  1.75% of the heap (95.29% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  6 blocks in heap block record 8 of 17
+  528 bytes (528 requested / 0 slop)
+  Individual block sizes: 128; 112; 96; 80; 64; 48
+  1.75% of the heap (97.03% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  1 block in heap block record 9 of 17
+  512 bytes (512 requested / 0 slop)
+  1.69% of the heap (98.73% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  1 block in heap block record 10 of 17
+  80 bytes (79 requested / 1 slop)
+  0.26% of the heap (98.99% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  1 block in heap block record 11 of 17
+  80 bytes (78 requested / 2 slop)
+  0.26% of the heap (99.26% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  1 block in heap block record 12 of 17
+  80 bytes (77 requested / 3 slop)
+  0.26% of the heap (99.52% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  1 block in heap block record 13 of 17
+  64 bytes (64 requested / 0 slop)
+  0.21% of the heap (99.74% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  1 block in heap block record 14 of 17
+  32 bytes (30 requested / 2 slop)
+  0.11% of the heap (99.84% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  1 block in heap block record 15 of 17
+  16 bytes (16 requested / 0 slop)
+  0.05% of the heap (99.89% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  1 block in heap block record 16 of 17
+  16 bytes (16 requested / 0 slop)
+  0.05% of the heap (99.95% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Cumulative {
+  1 block in heap block record 17 of 17
+  16 bytes (10 requested / 6 slop)
+  0.05% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: 30,208 bytes in 135 blocks
+}
+
diff --git a/memory/replace/dmd/test/complete-full2-dark-matter-expected.txt b/memory/replace/dmd/test/complete-full2-dark-matter-expected.txt
new file mode 100644
index 0000000000..5f9585a8c6
--- /dev/null
+++ b/memory/replace/dmd/test/complete-full2-dark-matter-expected.txt
@@ -0,0 +1,140 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o complete-full2-dark-matter-actual.txt complete-full2-dark-matter.json
+
+Invocation {
+  $DMD = '--mode=dark-matter --stacks=full --show-dump-stats=yes'
+  Mode = 'dark-matter'
+}
+
+#-----------------------------------------------------------------
+
+Twice-reported {
+  1 block in heap block record 1 of 2
+  80 bytes (77 requested / 3 slop)
+  2.81% of the heap (2.81% cumulative)
+  83.33% of twice-reported (83.33% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+  Reported again at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Twice-reported {
+  1 block in heap block record 2 of 2
+  16 bytes (16 requested / 0 slop)
+  0.56% of the heap (3.37% cumulative)
+  16.67% of twice-reported (100.00% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+  Reported again at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+#-----------------------------------------------------------------
+
+Unreported {
+  9 blocks in heap block record 1 of 3
+  1,008 bytes (900 requested / 108 slop)
+  Individual block sizes: 112 x 9
+  35.39% of the heap (35.39% cumulative)
+  48.84% of unreported (48.84% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Unreported {
+  6 blocks in heap block record 2 of 3
+  528 bytes (528 requested / 0 slop)
+  Individual block sizes: 128; 112; 96; 80; 64; 48
+  18.54% of the heap (53.93% cumulative)
+  25.58% of unreported (74.42% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Unreported {
+  6 blocks in heap block record 3 of 3
+  528 bytes (528 requested / 0 slop)
+  Individual block sizes: 128; 112; 96; 80; 64; 48
+  18.54% of the heap (72.47% cumulative)
+  25.58% of unreported (100.00% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+#-----------------------------------------------------------------
+
+Once-reported {
+  1 block in heap block record 1 of 4
+  512 bytes (512 requested / 0 slop)
+  17.98% of the heap (17.98% cumulative)
+  74.42% of once-reported (74.42% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Once-reported {
+  1 block in heap block record 2 of 4
+  80 bytes (79 requested / 1 slop)
+  2.81% of the heap (20.79% cumulative)
+  11.63% of once-reported (86.05% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Once-reported {
+  1 block in heap block record 3 of 4
+  80 bytes (78 requested / 2 slop)
+  2.81% of the heap (23.60% cumulative)
+  11.63% of once-reported (97.67% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Once-reported {
+  1 block in heap block record 4 of 4
+  16 bytes (10 requested / 6 slop)
+  0.56% of the heap (24.16% cumulative)
+  2.33% of once-reported (100.00% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+  Reported at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total:                 2,848 bytes (100.00%) in      27 blocks (100.00%)
+  Unreported:            2,064 bytes ( 72.47%) in      21 blocks ( 77.78%)
+  Once-reported:           688 bytes ( 24.16%) in       4 blocks ( 14.81%)
+  Twice-reported:           96 bytes (  3.37%) in       2 blocks (  7.41%)
+}
+
diff --git a/memory/replace/dmd/test/complete-partial-live-expected.txt b/memory/replace/dmd/test/complete-partial-live-expected.txt
new file mode 100644
index 0000000000..e7f27b0ee6
--- /dev/null
+++ b/memory/replace/dmd/test/complete-partial-live-expected.txt
@@ -0,0 +1,56 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o complete-partial-live-actual.txt complete-partial-live.json
+
+Invocation {
+  $DMD = '--mode=live'
+  Mode = 'live'
+}
+
+#-----------------------------------------------------------------
+
+Live {
+  9,531 blocks in heap block record 1 of 4
+  9,759,744 bytes (9,759,744 requested / 0 slop)
+  Individual block sizes: 1,024 x 9,531
+  83.56% of the heap (83.56% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Live {
+  16,822 blocks in heap block record 2 of 4
+  1,510,672 bytes (1,510,672 requested / 0 slop)
+  Individual block sizes: 1,024 x 469; 128 x 6,864; 16 x 9,489
+  12.93% of the heap (96.49% cumulative)
+  Allocated at {
+    #01: (no stack trace recorded due to --stacks=partial)
+  }
+}
+
+Live {
+  3,136 blocks in heap block record 3 of 4
+  401,408 bytes (401,408 requested / 0 slop)
+  Individual block sizes: 128 x 3,136
+  3.44% of the heap (99.93% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+Live {
+  511 blocks in heap block record 4 of 4
+  8,176 bytes (8,176 requested / 0 slop)
+  Individual block sizes: 16 x 511
+  0.07% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: ... DMD.cpp ...
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: 11,680,000 bytes in 30,000 blocks
+}
+
diff --git a/memory/replace/dmd/test/moz.build b/memory/replace/dmd/test/moz.build
new file mode 100644
index 0000000000..77e4fa12a0
--- /dev/null
+++ b/memory/replace/dmd/test/moz.build
@@ -0,0 +1,26 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+GeckoSimplePrograms(
+    [
+        "SmokeDMD",
+    ],
+    linkage=None,
+)
+
+# See the comment at the top of SmokeDMD.cpp:RunTests().
+if CONFIG["CC_TYPE"] == "clang-cl":
+    CXXFLAGS += ["-Od", "-clang:-fno-lto"]
+else:
+    CXXFLAGS += ["-O0", "-fno-lto"]
+
+DEFINES["MOZ_NO_MOZALLOC"] = True
+
+DisableStlWrapping()
+
+XPCSHELL_TESTS_MANIFESTS += [
+    "xpcshell.toml",
+]
diff --git a/memory/replace/dmd/test/scan-test.py b/memory/replace/dmd/test/scan-test.py
new file mode 100644
index 0000000000..c282b02693
--- /dev/null
+++ b/memory/replace/dmd/test/scan-test.py
@@ -0,0 +1,102 @@
+#! /usr/bin/env python
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+"""Testing for the JSON file emitted by DMD heap scan mode when running SmokeDMD."""
+
+import argparse
+import gzip
+import json
+import sys
+
+# The DMD output version this script handles.
+outputVersion = 5
+
+
+def parseCommandLine():
+    description = """
+Ensure that DMD heap scan mode creates the correct output when run with SmokeDMD.
+This is only for testing. Input files can be gzipped.
+"""
+    p = argparse.ArgumentParser(description=description)
+
+    p.add_argument(
+        "--clamp-contents",
+        action="store_true",
+        help="expect that the contents of the JSON input file have had "
+        "their addresses clamped",
+    )
+
+    p.add_argument("input_file", help="a file produced by DMD")
+
+    return p.parse_args(sys.argv[1:])
+
+
+def checkScanContents(contents, expected):
+    if len(contents) != len(expected):
+        raise Exception(
+            "Expected "
+            + str(len(expected))
+            + " things in contents but found "
+            + str(len(contents))
+        )
+
+    for i in range(len(expected)):
+        if contents[i] != expected[i]:
+            raise Exception(
+                "Expected to find "
+                + expected[i]
+                + " at offset "
+                + str(i)
+                + " but found "
+                + contents[i]
+            )
+
+
+def main():
+    args = parseCommandLine()
+
+    # Handle gzipped input if necessary.
+    isZipped = args.input_file.endswith(".gz")
+    opener = gzip.open if isZipped else open
+
+    with opener(args.input_file, "rb") as f:
+        j = json.load(f)
+
+    if j["version"] != outputVersion:
+        raise Exception("'version' property isn't '{:d}'".format(outputVersion))
+
+    invocation = j["invocation"]
+
+    mode = invocation["mode"]
+    if mode != "scan":
+        raise Exception("bad 'mode' property: '{:s}'".format(mode))
+
+    blockList = j["blockList"]
+
+    if len(blockList) != 1:
+        raise Exception("Expected only one block")
+
+    b = blockList[0]
+
+    # The expected values are based on hard-coded values in SmokeDMD.cpp.
+    if args.clamp_contents:
+        expected = ["0", "0", "0", b["addr"], b["addr"]]
+    else:
+        addr = int(b["addr"], 16)
+        expected = [
+            "123",
+            "0",
+            str(format(addr - 1, "x")),
+            b["addr"],
+            str(format(addr + 1, "x")),
+            "0",
+        ]
+
+    checkScanContents(b["contents"], expected)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/memory/replace/dmd/test/script-diff-dark-matter-expected.txt b/memory/replace/dmd/test/script-diff-dark-matter-expected.txt
new file mode 100644
index 0000000000..b1fc28bac5
--- /dev/null
+++ b/memory/replace/dmd/test/script-diff-dark-matter-expected.txt
@@ -0,0 +1,127 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o script-diff-dark-matter-actual.txt script-diff-dark-matter1.json script-diff-dark-matter2.json
+
+Invocation 1 {
+  $DMD = '--mode=dark-matter'
+  Mode = 'dark-matter'
+}
+
+Invocation 2 {
+  $DMD = '1'
+  Mode = 'dark-matter'
+}
+
+#-----------------------------------------------------------------
+
+Twice-reported {
+  -1 blocks in heap block record 1 of 1
+  -1,088 bytes (-1,064 requested / -24 slop)
+  Individual block sizes: -1,024; -127; 63
+  15.46% of the heap (15.46% cumulative)
+  100.00% of twice-reported (100.00% cumulative)
+  Allocated at {
+    #01: F (F.cpp:99)
+  }
+  Reported at {
+    #01: R1 (R1.cpp:99)
+  }
+  Reported again at {
+    #01: R2 (R2.cpp:99)
+  }
+}
+
+#-----------------------------------------------------------------
+
+Unreported {
+  4 blocks in heap block record 1 of 5
+  16,384 bytes (16,384 requested / 0 slop)
+  Individual block sizes: 4,096 x 4
+  -232.76% of the heap (-232.76% cumulative)
+  371.01% of unreported (371.01% cumulative)
+  Allocated at {
+    #01: E (E.cpp:99)
+  }
+}
+
+Unreported {
+  7 blocks in heap block record 2 of 5
+  -11,968 bytes (-12,016 requested / 48 slop)
+  Individual block sizes: -15,360; 2,048; 512 x 2; 128; -127; 64 x 4; 63
+  170.02% of the heap (-62.74% cumulative)
+  -271.01% of unreported (100.00% cumulative)
+  Allocated at {
+    #01: F (F.cpp:99)
+  }
+}
+
+Unreported {
+  0 blocks in heap block record 3 of 5
+  0 bytes (-384 requested / 384 slop)
+  Individual block sizes: (no change)
+  -0.00% of the heap (-62.74% cumulative)
+  0.00% of unreported (100.00% cumulative)
+  Allocated at {
+    #01: C (C.cpp:99)
+  }
+}
+
+Unreported {
+  -2 blocks in heap block record 4 of 5
+  0 bytes (0 requested / 0 slop)
+  Individual block sizes: 8,192 x 2; -4,096 x 4
+  -0.00% of the heap (-62.74% cumulative)
+  0.00% of unreported (100.00% cumulative)
+  Allocated at {
+    #01: B (B.cpp:99)
+  }
+}
+
+Unreported {
+  0 blocks in heap block record 5 of 5
+  0 bytes (0 requested / 0 slop)
+  Individual block sizes: 20,480; -16,384; -8,192; 4,096
+  -0.00% of the heap (-62.74% cumulative)
+  0.00% of unreported (100.00% cumulative)
+  Allocated at {
+    #01: (no stack trace recorded due to --stacks=partial)
+  }
+}
+
+#-----------------------------------------------------------------
+
+Once-reported {
+  -3 blocks in heap block record 1 of 2
+  -10,240 bytes (-10,192 requested / -48 slop)
+  Individual block sizes: -4,096 x 2; -2,048
+  145.48% of the heap (145.48% cumulative)
+  98.77% of once-reported (98.77% cumulative)
+  Allocated at {
+    #01: D (D.cpp:99)
+  }
+  Reported at {
+    #01: R1 (R1.cpp:99)
+  }
+}
+
+Once-reported {
+  -1 blocks in heap block record 2 of 2
+  -127 bytes (-151 requested / 24 slop)
+  1.80% of the heap (147.28% cumulative)
+  1.23% of once-reported (100.00% cumulative)
+  Allocated at {
+    #01: F (F.cpp:99)
+  }
+  Reported at {
+    #01: R1 (R1.cpp:99)
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total:                -7,039 bytes (100.00%) in       4 blocks (100.00%)
+  Unreported:            4,416 bytes (-62.74%) in       9 blocks (225.00%)
+  Once-reported:       -10,367 bytes (147.28%) in      -4 blocks (-100.00%)
+  Twice-reported:       -1,088 bytes ( 15.46%) in      -1 blocks (-25.00%)
+}
+
diff --git a/memory/replace/dmd/test/script-diff-dark-matter1.json b/memory/replace/dmd/test/script-diff-dark-matter1.json
new file mode 100644
index 0000000000..1175394150
--- /dev/null
+++ b/memory/replace/dmd/test/script-diff-dark-matter1.json
@@ -0,0 +1,51 @@
+{
+  "version": 5,
+  "invocation": {
+    "dmdEnvVar": "--mode=dark-matter",
+    "mode": "dark-matter"
+  },
+  "blockList": [
+    { "req": 4096, "alloc": "A", "num": 4 },
+
+    { "req": 4096, "alloc": "B", "num": 3 },
+    { "req": 4096, "alloc": "B" },
+
+    { "req": 4096, "alloc": "C", "num": 2 },
+    { "req": 4096, "alloc": "C", "num": 2 },
+
+    { "req": 4096, "alloc": "D", "reps": ["R1"], "num": 2 },
+    { "req": 2000, "slop": 48, "alloc": "D", "reps": ["R1"] },
+
+    { "req": 15360, "alloc": "F" },
+    { "req": 512, "alloc": "F", "num": 2 },
+    { "req": 127, "alloc": "F" },
+    { "req": 1024, "alloc": "F", "reps": ["R1"] },
+    { "req": 127, "alloc": "F", "reps": ["R1"] },
+    { "req": 1000, "slop": 24, "alloc": "F", "reps": ["R1", "R2"] },
+    { "req": 127, "alloc": "F", "reps": ["R1", "R2"] },
+
+    { "req": 4096 },
+    { "req": 8192 },
+    { "req": 16384 }
+  ],
+  "traceTable": {
+    "A": ["AA"],
+    "B": ["BB"],
+    "C": ["CC"],
+    "D": ["DD"],
+    "E": ["EE"],
+    "F": ["FF"],
+    "R1": ["RR1"],
+    "R2": ["RR2"]
+  },
+  "frameTable": {
+    "AA": "#00: A (A.cpp:99)",
+    "BB": "#00: B (B.cpp:99)",
+    "CC": "#00: C (C.cpp:99)",
+    "DD": "#00: D (D.cpp:99)",
+    "EE": "#00: E (E.cpp:99)",
+    "FF": "#00: F (F.cpp:99)",
+    "RR1": "#00: R1 (R1.cpp:99)",
+    "RR2": "#00: R2 (R2.cpp:99)"
+  }
+}
diff --git a/memory/replace/dmd/test/script-diff-dark-matter2.json b/memory/replace/dmd/test/script-diff-dark-matter2.json
new file mode 100644
index 0000000000..2c3061223f
--- /dev/null
+++ b/memory/replace/dmd/test/script-diff-dark-matter2.json
@@ -0,0 +1,51 @@
+{
+  "version": 5,
+  "invocation": {
+    "dmdEnvVar": "1",
+    "mode": "dark-matter"
+  },
+  "blockList": [
+    { "req": 4096, "alloc": "A", "num": 4 },
+
+    { "req": 8192, "alloc": "B" },
+    { "req": 8192, "alloc": "B" },
+
+    { "req": 4000, "slop": 96, "alloc": "C", "num": 4 },
+
+    { "req": 4096, "alloc": "E", "num": 4 },
+
+    { "req": 2000, "slop": 48, "alloc": "F" },
+    { "req": 1000, "slop": 24, "alloc": "F", "reps": ["R1"] },
+    { "req": 512, "alloc": "F" },
+    { "req": 512, "alloc": "F" },
+    { "req": 512, "alloc": "F" },
+    { "req": 512, "alloc": "F" },
+    { "req": 128, "alloc": "F" },
+    { "req": 63, "alloc": "F", "reps": ["R1", "R2"] },
+    { "req": 64, "alloc": "F", "num": 4 },
+    { "req": 63, "alloc": "F" },
+
+    { "req": 4096, "num": 2 },
+    { "req": 20480 }
+  ],
+  "traceTable": {
+    "A": ["AA"],
+    "B": ["BB"],
+    "C": ["CC"],
+    "D": ["DD"],
+    "E": ["EE"],
+    "F": ["FF"],
+    "R1": ["RR1"],
+    "R2": ["RR2"]
+  },
+  "frameTable": {
+    "AA": "#00: A (A.cpp:99)",
+    "BB": "#00: B (B.cpp:99)",
+    "CC": "#00: C (C.cpp:99)",
+    "DD": "#00: D (D.cpp:99)",
+    "EE": "#00: E (E.cpp:99)",
+    "FF": "#00: F (F.cpp:99)",
+    "RR1": "#00: R1 (R1.cpp:99)",
+    "RR2": "#00: R2 (R2.cpp:99)"
+  }
+}
diff --git a/memory/replace/dmd/test/script-diff-live-expected.txt b/memory/replace/dmd/test/script-diff-live-expected.txt
new file mode 100644
index 0000000000..20208c0768
--- /dev/null
+++ b/memory/replace/dmd/test/script-diff-live-expected.txt
@@ -0,0 +1,81 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o script-diff-live-actual.txt script-diff-live1.json script-diff-live2.json
+
+Invocation 1 {
+  $DMD = '--mode=live'
+  Mode = 'live'
+}
+
+Invocation 2 {
+  $DMD = '--mode=live --stacks=partial'
+  Mode = 'live'
+}
+
+#-----------------------------------------------------------------
+
+Live {
+  4 blocks in heap block record 1 of 6
+  16,384 bytes (16,384 requested / 0 slop)
+  Individual block sizes: 4,096 x 4
+  -232.76% of the heap (-232.76% cumulative)
+  Allocated at {
+    #01: E (E.cpp:99)
+  }
+}
+
+Live {
+  5 blocks in heap block record 2 of 6
+  -13,183 bytes (-13,231 requested / 48 slop)
+  Individual block sizes: -15,360; 2,048; -1,024; 512 x 2; 128; -127 x 3; 64 x 4; 63 x 2
+  187.29% of the heap (-45.48% cumulative)
+  Allocated at {
+    #01: F (F.cpp:99)
+  }
+}
+
+Live {
+  -3 blocks in heap block record 3 of 6
+  -10,240 bytes (-10,192 requested / -48 slop)
+  Individual block sizes: -4,096 x 2; -2,048
+  145.48% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: D (D.cpp:99)
+  }
+}
+
+Live {
+  0 blocks in heap block record 4 of 6
+  0 bytes (-384 requested / 384 slop)
+  Individual block sizes: (no change)
+  -0.00% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: C (C.cpp:99)
+  }
+}
+
+Live {
+  -2 blocks in heap block record 5 of 6
+  0 bytes (0 requested / 0 slop)
+  Individual block sizes: 8,192 x 2; -4,096 x 4
+  -0.00% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: B (B.cpp:99)
+  }
+}
+
+Live {
+  0 blocks in heap block record 6 of 6
+  0 bytes (0 requested / 0 slop)
+  Individual block sizes: 20,480; -16,384; -8,192; 4,096
+  -0.00% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: (no stack trace recorded due to --stacks=partial)
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: -7,039 bytes in 4 blocks
+}
+
diff --git a/memory/replace/dmd/test/script-diff-live1.json b/memory/replace/dmd/test/script-diff-live1.json
new file mode 100644
index 0000000000..1296b9ea09
--- /dev/null
+++ b/memory/replace/dmd/test/script-diff-live1.json
@@ -0,0 +1,51 @@
+{
+  "version": 5,
+  "invocation": {
+    "dmdEnvVar": "--mode=live",
+    "mode": "live"
+  },
+  "blockList": [
+    { "req": 4096, "alloc": "A", "num": 4 },
+
+    { "req": 4096, "alloc": "B", "num": 4 },
+
+    { "req": 4096, "alloc": "C", "num": 4 },
+
+    { "req": 4096, "alloc": "D" },
+    { "req": 4096, "alloc": "D" },
+    { "req": 2000, "slop": 48, "alloc": "D" },
+
+    { "req": 15360, "alloc": "F" },
+    { "req": 512, "alloc": "F" },
+    { "req": 512, "alloc": "F" },
+    { "req": 127, "alloc": "F" },
+    { "req": 1024, "alloc": "F" },
+    { "req": 127, "alloc": "F" },
+    { "req": 1000, "slop": 24, "alloc": "F" },
+    { "req": 127, "alloc": "F" },
+
+    { "req": 4096 },
+    { "req": 8192 },
+    { "req": 16384 }
+  ],
+  "traceTable": {
+    "A": ["AA"],
+    "B": ["BB"],
+    "C": ["CC"],
+    "D": ["DD"],
+    "E": ["EE"],
+    "F": ["FF"],
+    "R1": ["RR1"],
+    "R2": ["RR2"]
+  },
+  "frameTable": {
+    "AA": "#00: A (A.cpp:99)",
+    "BB": "#00: B (B.cpp:99)",
+    "CC": "#00: C (C.cpp:99)",
+    "DD": "#00: D (D.cpp:99)",
+    "EE": "#00: E (E.cpp:99)",
+    "FF": "#00: F (F.cpp:99)",
+    "RR1": "#00: R1 (R1.cpp:99)",
+    "RR2": "#00: R2 (R2.cpp:99)"
+  }
+}
diff --git a/memory/replace/dmd/test/script-diff-live2.json b/memory/replace/dmd/test/script-diff-live2.json
new file mode 100644
index 0000000000..723ea5ff35
--- /dev/null
+++ b/memory/replace/dmd/test/script-diff-live2.json
@@ -0,0 +1,53 @@
+{
+  "version": 5,
+  "invocation": {
+    "dmdEnvVar": "--mode=live --stacks=partial",
+    "mode": "live"
+  },
+  "blockList": [
+    { "req": 4096, "alloc": "A", "num": 3 },
+    { "req": 4096, "alloc": "A" },
+
+    { "req": 8192, "alloc": "B" },
+    { "req": 8192, "alloc": "B" },
+
+    { "req": 4000, "slop": 96, "alloc": "C", "num": 4 },
+
+    { "req": 4096, "alloc": "E" },
+    { "req": 4096, "alloc": "E" },
+    { "req": 4096, "alloc": "E" },
+    { "req": 4096, "alloc": "E" },
+
+    { "req": 2000, "slop": 48, "alloc": "F" },
+    { "req": 1000, "slop": 24, "alloc": "F" },
+    { "req": 512, "alloc": "F", "num": 4 },
+    { "req": 128, "alloc": "F" },
+    { "req": 63, "alloc": "F" },
+    { "req": 64, "alloc": "F", "num": 4 },
+    { "req": 63, "alloc": "F" },
+
+    { "req": 4096 },
+    { "req": 4096 },
+    { "req": 20480 }
+  ],
+  "traceTable": {
+    "A": ["AA"],
+    "B": ["BB"],
+    "C": ["CC"],
+    "D": ["DD"],
+    "E": ["EE"],
+    "F": ["FF"],
+    "R1": ["RR1"],
+    "R2": ["RR2"]
+  },
+  "frameTable": {
+    "AA": "#00: A (A.cpp:99)",
+    "BB": "#00: B (B.cpp:99)",
+    "CC": "#00: C (C.cpp:99)",
+    "DD": "#00: D (D.cpp:99)",
+    "EE": "#00: E (E.cpp:99)",
+    "FF": "#00: F (F.cpp:99)",
+    "RR1": "#00: R1 (R1.cpp:99)",
+    "RR2": "#00: R2 (R2.cpp:99)"
+  }
+}
diff --git a/memory/replace/dmd/test/script-ignore-alloc-fns-expected.txt b/memory/replace/dmd/test/script-ignore-alloc-fns-expected.txt
new file mode 100644
index 0000000000..9428ef45fb
--- /dev/null
+++ b/memory/replace/dmd/test/script-ignore-alloc-fns-expected.txt
@@ -0,0 +1,72 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o script-ignore-alloc-fns-actual.txt --ignore-alloc-fns script-ignore-alloc-fns.json
+
+Invocation {
+  $DMD = '1'
+  Mode = 'dark-matter'
+}
+
+#-----------------------------------------------------------------
+
+# no twice-reported heap blocks
+
+#-----------------------------------------------------------------
+
+Unreported {
+  1 block in heap block record 1 of 4
+  1,048,576 bytes (1,048,576 requested / 0 slop)
+  93.22% of the heap (93.22% cumulative)
+  93.22% of unreported (93.22% cumulative)
+  Allocated at {
+    #01: A (A.cpp:99)
+  }
+}
+
+Unreported {
+  1 block in heap block record 2 of 4
+  65,536 bytes (65,536 requested / 0 slop)
+  5.83% of the heap (99.05% cumulative)
+  5.83% of unreported (99.05% cumulative)
+  Allocated at {
+    #01: js::jit::JitRuntime::initialize(JSContext*) (Ion.cpp:301)
+  }
+}
+
+Unreported {
+  1 block in heap block record 3 of 4
+  8,192 bytes (8,000 requested / 192 slop)
+  0.73% of the heap (99.78% cumulative)
+  0.73% of unreported (99.78% cumulative)
+  Allocated at {
+    #01: mozilla::Vector::growStorageBy(unsigned long) (Vector.h:802)
+    #02: D (D.cpp:99)
+  }
+}
+
+Unreported {
+  1 block in heap block record 4 of 4
+  2,500 bytes (2,500 requested / 0 slop)
+  0.22% of the heap (100.00% cumulative)
+  0.22% of unreported (100.00% cumulative)
+  Allocated at {
+    #01: g_type_create_instance (/usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0)
+    #02: not_an_alloc_function_so_alloc_functions_below_here_will_not_be_stripped (blah)
+    #03: replace_posix_memalign (replace_malloc.h:120)
+    #04: ??? (/lib/x86_64-linux-gnu/libglib-2.0.so.0)
+    #05: another_non_alloc_function (blah)
+  }
+}
+
+#-----------------------------------------------------------------
+
+# no once-reported heap blocks
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total:             1,124,804 bytes (100.00%) in       4 blocks (100.00%)
+  Unreported:        1,124,804 bytes (100.00%) in       4 blocks (100.00%)
+  Once-reported:             0 bytes (  0.00%) in       0 blocks (  0.00%)
+  Twice-reported:            0 bytes (  0.00%) in       0 blocks (  0.00%)
+}
+
diff --git a/memory/replace/dmd/test/script-ignore-alloc-fns.json b/memory/replace/dmd/test/script-ignore-alloc-fns.json
new file mode 100644
index 0000000000..a6c7c8419a
--- /dev/null
+++ b/memory/replace/dmd/test/script-ignore-alloc-fns.json
@@ -0,0 +1,45 @@
+{
+  "version": 5,
+  "invocation": {
+    "dmdEnvVar": "1",
+    "mode": "dark-matter"
+  },
+  "blockList": [
+    { "req": 1048576, "alloc": "A" },
+    { "req": 65536, "alloc": "B" },
+    { "req": 8000, "slop": 192, "alloc": "C" },
+    { "req": 2500, "alloc": "D" }
+  ],
+  "traceTable": {
+    "A": ["AA", "AB", "AC", "AD"],
+    "B": ["BA", "BB", "BC"],
+    "C": ["CA", "CB", "CC", "CD"],
+    "D": ["DA", "DB", "DD", "DD", "DE", "DF", "DG", "DH", "DI", "DJ"]
+  },
+  "frameTable": {
+    "AA": "#00: replace_malloc (DMD.cpp:1106)",
+    "AB": "#00: moz_xmalloc (mozalloc.cpp:68)",
+    "AC": "#00: operator new(unsigned long) (mozalloc.h:208)",
+    "AD": "#00: A (A.cpp:99)",
+
+    "BA": "#00: replace_calloc (DMD.cpp:1125)",
+    "BB": "#00: js_calloc(unsigned long) (Utility.h:107)",
+    "BC": "#06: js::jit::JitRuntime::initialize(JSContext*) (Ion.cpp:301)",
+
+    "CA": "#00: replace_realloc (DMD.cpp:1153)",
+    "CB": "#00: bool* mozilla::MallocAllocPolicy::pod_realloc<bool>(bool*, unsigned long, unsigned long) (AllocPolicy.h:74)",
+    "CC": "#00: mozilla::Vector::growStorageBy(unsigned long) (Vector.h:802)",
+    "CD": "#00: D (D.cpp:99)",
+
+    "DA": "#00: replace_memalign (DMD.cpp:1181)",
+    "DB": "#00: replace_posix_memalign (replace_malloc.h:120)",
+    "DC": "#00: ??? (/lib/x86_64-linux-gnu/libglib-2.0.so.0)",
+    "DD": "#00: g_slice_alloc (/lib/x86_64-linux-gnu/libglib-2.0.so.0)",
+    "DE": "#00: g_slice_alloc0 (/lib/x86_64-linux-gnu/libglib-2.0.so.0)",
+    "DF": "#00: g_type_create_instance (/usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0)",
+    "DG": "#00: not_an_alloc_function_so_alloc_functions_below_here_will_not_be_stripped (blah)",
+    "DH": "#00: replace_posix_memalign (replace_malloc.h:120)",
+    "DI": "#00: ??? (/lib/x86_64-linux-gnu/libglib-2.0.so.0)",
+    "DJ": "#00: another_non_alloc_function (blah)"
+  }
+}
diff --git a/memory/replace/dmd/test/script-max-frames-1-expected.txt b/memory/replace/dmd/test/script-max-frames-1-expected.txt
new file mode 100644
index 0000000000..65a00762bb
--- /dev/null
+++ b/memory/replace/dmd/test/script-max-frames-1-expected.txt
@@ -0,0 +1,26 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o script-max-frames-1-actual.txt --max-frames=1 script-max-frames.json
+
+Invocation {
+  $DMD = '--mode=live --stacks=full'
+  Mode = 'live'
+}
+
+#-----------------------------------------------------------------
+
+Live {
+  4 blocks in heap block record 1 of 1
+  4,416 bytes (4,404 requested / 12 slop)
+  Individual block sizes: 4,096; 128; 112; 80
+  100.00% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: E (E.cpp:99)
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: 4,416 bytes in 4 blocks
+}
+
diff --git a/memory/replace/dmd/test/script-max-frames-3-expected.txt b/memory/replace/dmd/test/script-max-frames-3-expected.txt
new file mode 100644
index 0000000000..5df4914738
--- /dev/null
+++ b/memory/replace/dmd/test/script-max-frames-3-expected.txt
@@ -0,0 +1,48 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o script-max-frames-3-actual.txt --max-frames=3 --no-fix-stacks script-max-frames.json
+
+Invocation {
+  $DMD = '--mode=live --stacks=full'
+  Mode = 'live'
+}
+
+#-----------------------------------------------------------------
+
+Live {
+  2 blocks in heap block record 1 of 3
+  4,224 bytes (4,224 requested / 0 slop)
+  Individual block sizes: 4,096; 128
+  95.65% of the heap (95.65% cumulative)
+  Allocated at {
+    #01: E (E.cpp:99)
+    #02: F (F.cpp:99)
+    #03: G (G.cpp:99)
+  }
+}
+
+Live {
+  1 block in heap block record 2 of 3
+  112 bytes (100 requested / 12 slop)
+  2.54% of the heap (98.19% cumulative)
+  Allocated at {
+    #01: E (E.cpp:99)
+    #02: X (X.cpp:99)
+    #03: Y (Y.cpp:99)
+  }
+}
+
+Live {
+  1 block in heap block record 3 of 3
+  80 bytes (80 requested / 0 slop)
+  1.81% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: E (E.cpp:99)
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: 4,416 bytes in 4 blocks
+}
+
diff --git a/memory/replace/dmd/test/script-max-frames-8-expected.txt b/memory/replace/dmd/test/script-max-frames-8-expected.txt
new file mode 100644
index 0000000000..174992d5b8
--- /dev/null
+++ b/memory/replace/dmd/test/script-max-frames-8-expected.txt
@@ -0,0 +1,69 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o script-max-frames-8-actual.txt script-max-frames.json
+
+Invocation {
+  $DMD = '--mode=live --stacks=full'
+  Mode = 'live'
+}
+
+#-----------------------------------------------------------------
+
+Live {
+  1 block in heap block record 1 of 4
+  4,096 bytes (4,096 requested / 0 slop)
+  92.75% of the heap (92.75% cumulative)
+  Allocated at {
+    #01: E (E.cpp:99)
+    #02: F (F.cpp:99)
+    #03: G (G.cpp:99)
+    #04: H (H.cpp:99)
+    #05: I (I.cpp:99)
+    #06: J (J.cpp:99)
+    #07: K (K.cpp:99)
+    #08: L (L.cpp:99)
+  }
+}
+
+Live {
+  1 block in heap block record 2 of 4
+  128 bytes (128 requested / 0 slop)
+  2.90% of the heap (95.65% cumulative)
+  Allocated at {
+    #01: E (E.cpp:99)
+    #02: F (F.cpp:99)
+    #03: G (G.cpp:99)
+    #04: R (R.cpp:99)
+    #05: S (S.cpp:99)
+    #06: T (T.cpp:99)
+    #07: U (U.cpp:99)
+    #08: V (V.cpp:99)
+  }
+}
+
+Live {
+  1 block in heap block record 3 of 4
+  112 bytes (100 requested / 12 slop)
+  2.54% of the heap (98.19% cumulative)
+  Allocated at {
+    #01: E (E.cpp:99)
+    #02: X (X.cpp:99)
+    #03: Y (Y.cpp:99)
+    #04: Z (Z.cpp:99)
+  }
+}
+
+Live {
+  1 block in heap block record 4 of 4
+  80 bytes (80 requested / 0 slop)
+  1.81% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: E (E.cpp:99)
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: 4,416 bytes in 4 blocks
+}
+
diff --git a/memory/replace/dmd/test/script-max-frames.json b/memory/replace/dmd/test/script-max-frames.json
new file mode 100644
index 0000000000..6de17a88c3
--- /dev/null
+++ b/memory/replace/dmd/test/script-max-frames.json
@@ -0,0 +1,43 @@
+{
+  "version": 5,
+  "invocation": {
+    "dmdEnvVar": "--mode=live --stacks=full",
+    "mode": "live"
+  },
+  "blockList": [
+    { "req": 4096, "alloc": "A" },
+    { "req": 128, "alloc": "B" },
+    { "req": 100, "slop": 12, "alloc": "C" },
+    { "req": 80, "alloc": "D" }
+  ],
+  "traceTable": {
+    "A": ["E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P"],
+    "B": ["E", "F", "G", "R", "S", "T", "U", "V"],
+    "C": ["E", "X", "Y", "Z"],
+    "D": ["E"]
+  },
+  "frameTable": {
+    "E": "#00: E (E.cpp:99)",
+    "F": "#00: F (F.cpp:99)",
+    "G": "#00: G (G.cpp:99)",
+    "H": "#00: H (H.cpp:99)",
+    "I": "#00: I (I.cpp:99)",
+    "J": "#00: J (J.cpp:99)",
+    "K": "#00: K (K.cpp:99)",
+    "L": "#00: L (L.cpp:99)",
+    "M": "#00: M (M.cpp:99)",
+    "N": "#00: N (N.cpp:99)",
+    "O": "#00: O (O.cpp:99)",
+    "P": "#00: P (P.cpp:99)",
+    "Q": "#00: Q (Q.cpp:99)",
+    "R": "#00: R (R.cpp:99)",
+    "S": "#00: S (S.cpp:99)",
+    "T": "#00: T (T.cpp:99)",
+    "U": "#00: U (U.cpp:99)",
+    "V": "#00: V (V.cpp:99)",
+    "W": "#00: W (W.cpp:99)",
+    "X": "#00: X (X.cpp:99)",
+    "Y": "#00: Y (Y.cpp:99)",
+    "Z": "#00: Z (Z.cpp:99)"
+  }
+}
diff --git a/memory/replace/dmd/test/script-sort-by-num-blocks-expected.txt b/memory/replace/dmd/test/script-sort-by-num-blocks-expected.txt
new file mode 100644
index 0000000000..8de03d953b
--- /dev/null
+++ b/memory/replace/dmd/test/script-sort-by-num-blocks-expected.txt
@@ -0,0 +1,46 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o script-sort-by-num-blocks-actual.txt --sort-by=num-blocks script-sort-by.json.gz
+
+Invocation {
+  $DMD = '--mode=live'
+  Mode = 'live'
+}
+
+#-----------------------------------------------------------------
+
+Live {
+  8 blocks in heap block record 1 of 3
+  16,384 bytes (8,200 requested / 8,184 slop)
+  Individual block sizes: 2,048 x 8
+  33.32% of the heap (33.32% cumulative)
+  Allocated at {
+    #01: C (C.cpp:99)
+  }
+}
+
+Live {
+  5 blocks in heap block record 2 of 3
+  16,400 bytes (12,016 requested / 4,384 slop)
+  Individual block sizes: 4,096 x 4; 16
+  33.35% of the heap (66.67% cumulative)
+  Allocated at {
+    #01: B (B.cpp:99)
+  }
+}
+
+Live {
+  5 blocks in heap block record 3 of 3
+  16,392 bytes (16,392 requested / 0 slop)
+  Individual block sizes: 4,096 x 4; 8
+  33.33% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: A (A.cpp:99)
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: 49,176 bytes in 18 blocks
+}
+
diff --git a/memory/replace/dmd/test/script-sort-by-req-expected.txt b/memory/replace/dmd/test/script-sort-by-req-expected.txt
new file mode 100644
index 0000000000..3ab21ba8f7
--- /dev/null
+++ b/memory/replace/dmd/test/script-sort-by-req-expected.txt
@@ -0,0 +1,46 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o script-sort-by-req-actual.txt --sort-by=req --no-fix-stacks script-sort-by.json.gz
+
+Invocation {
+  $DMD = '--mode=live'
+  Mode = 'live'
+}
+
+#-----------------------------------------------------------------
+
+Live {
+  5 blocks in heap block record 1 of 3
+  16,392 bytes (16,392 requested / 0 slop)
+  Individual block sizes: 4,096 x 4; 8
+  33.33% of the heap (33.33% cumulative)
+  Allocated at {
+    #01: A (A.cpp:99)
+  }
+}
+
+Live {
+  5 blocks in heap block record 2 of 3
+  16,400 bytes (12,016 requested / 4,384 slop)
+  Individual block sizes: 4,096 x 4; 16
+  33.35% of the heap (66.68% cumulative)
+  Allocated at {
+    #01: B (B.cpp:99)
+  }
+}
+
+Live {
+  8 blocks in heap block record 3 of 3
+  16,384 bytes (8,200 requested / 8,184 slop)
+  Individual block sizes: 2,048 x 8
+  33.32% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: C (C.cpp:99)
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: 49,176 bytes in 18 blocks
+}
+
diff --git a/memory/replace/dmd/test/script-sort-by-slop-expected.txt b/memory/replace/dmd/test/script-sort-by-slop-expected.txt
new file mode 100644
index 0000000000..c325c7ed40
--- /dev/null
+++ b/memory/replace/dmd/test/script-sort-by-slop-expected.txt
@@ -0,0 +1,46 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o script-sort-by-slop-actual.txt --sort-by=slop script-sort-by.json.gz
+
+Invocation {
+  $DMD = '--mode=live'
+  Mode = 'live'
+}
+
+#-----------------------------------------------------------------
+
+Live {
+  8 blocks in heap block record 1 of 3
+  16,384 bytes (8,200 requested / 8,184 slop)
+  Individual block sizes: 2,048 x 8
+  33.32% of the heap (33.32% cumulative)
+  Allocated at {
+    #01: C (C.cpp:99)
+  }
+}
+
+Live {
+  5 blocks in heap block record 2 of 3
+  16,400 bytes (12,016 requested / 4,384 slop)
+  Individual block sizes: 4,096 x 4; 16
+  33.35% of the heap (66.67% cumulative)
+  Allocated at {
+    #01: B (B.cpp:99)
+  }
+}
+
+Live {
+  5 blocks in heap block record 3 of 3
+  16,392 bytes (16,392 requested / 0 slop)
+  Individual block sizes: 4,096 x 4; 8
+  33.33% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: A (A.cpp:99)
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: 49,176 bytes in 18 blocks
+}
+
diff --git a/memory/replace/dmd/test/script-sort-by-usable-expected.txt b/memory/replace/dmd/test/script-sort-by-usable-expected.txt
new file mode 100644
index 0000000000..8239a4759e
--- /dev/null
+++ b/memory/replace/dmd/test/script-sort-by-usable-expected.txt
@@ -0,0 +1,46 @@
+#-----------------------------------------------------------------
+# dmd.py --filter-stacks-for-testing -o script-sort-by-usable-actual.txt --sort-by=usable script-sort-by.json.gz
+
+Invocation {
+  $DMD = '--mode=live'
+  Mode = 'live'
+}
+
+#-----------------------------------------------------------------
+
+Live {
+  5 blocks in heap block record 1 of 3
+  16,400 bytes (12,016 requested / 4,384 slop)
+  Individual block sizes: 4,096 x 4; 16
+  33.35% of the heap (33.35% cumulative)
+  Allocated at {
+    #01: B (B.cpp:99)
+  }
+}
+
+Live {
+  5 blocks in heap block record 2 of 3
+  16,392 bytes (16,392 requested / 0 slop)
+  Individual block sizes: 4,096 x 4; 8
+  33.33% of the heap (66.68% cumulative)
+  Allocated at {
+    #01: A (A.cpp:99)
+  }
+}
+
+Live {
+  8 blocks in heap block record 3 of 3
+  16,384 bytes (8,200 requested / 8,184 slop)
+  Individual block sizes: 2,048 x 8
+  33.32% of the heap (100.00% cumulative)
+  Allocated at {
+    #01: C (C.cpp:99)
+  }
+}
+
+#-----------------------------------------------------------------
+
+Summary {
+  Total: 49,176 bytes in 18 blocks
+}
+
diff --git a/memory/replace/dmd/test/script-sort-by.json.gz b/memory/replace/dmd/test/script-sort-by.json.gz
new file mode 100644
index 0000000000..f665c945c2
--- /dev/null
+++ b/memory/replace/dmd/test/script-sort-by.json.gz
diff --git a/memory/replace/dmd/test/test_dmd.js b/memory/replace/dmd/test/test_dmd.js
new file mode 100644
index 0000000000..e092c79a02
--- /dev/null
+++ b/memory/replace/dmd/test/test_dmd.js
@@ -0,0 +1,232 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*-*/
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+const { FileUtils } = ChromeUtils.importESModule(
+  "resource://gre/modules/FileUtils.sys.mjs"
+);
+
+// The xpcshell test harness sets PYTHON so we can read it here.
+var gPythonName = Services.env.get("PYTHON");
+
+const gCwd = Services.dirsvc.get("CurWorkD", Ci.nsIFile);
+
+function getRelativeFile(...components) {
+  return new FileUtils.File(PathUtils.join(gCwd.path, ...components));
+}
+
+// If we're testing locally, the executable file is in "CurProcD". Otherwise,
+// it is in another location that we have to find.
+function getExecutable(aFilename) {
+  let file = new FileUtils.File(
+    PathUtils.join(Services.dirsvc.get("CurProcD", Ci.nsIFile).path, aFilename)
+  );
+  if (!file.exists()) {
+    file = gCwd.clone();
+    while (file.path.includes("xpcshell")) {
+      file = file.parent;
+    }
+    file.append("bin");
+    file.append(aFilename);
+  }
+  return file;
+}
+
+var gIsWindows = Services.appinfo.OS === "WINNT";
+var gDmdTestFile = getExecutable("SmokeDMD" + (gIsWindows ? ".exe" : ""));
+
+var gDmdScriptFile = getExecutable("dmd.py");
+
+var gScanTestFile = getRelativeFile("scan-test.py");
+
+function readFile(aFile) {
+  let fstream = Cc["@mozilla.org/network/file-input-stream;1"].createInstance(
+    Ci.nsIFileInputStream
+  );
+  let cstream = Cc["@mozilla.org/intl/converter-input-stream;1"].createInstance(
+    Ci.nsIConverterInputStream
+  );
+  fstream.init(aFile, -1, 0, 0);
+  cstream.init(fstream, "UTF-8", 0, 0);
+
+  let data = "";
+  let str = {};
+  let read = 0;
+  do {
+    // Read as much as we can and put it in str.value.
+    read = cstream.readString(0xffffffff, str);
+    data += str.value;
+  } while (read != 0);
+
+  cstream.close(); // this closes fstream
+  return data.replace(/\r/g, ""); // normalize line endings
+}
+
+function runProcess(aExeFile, aArgs) {
+  let process = Cc["@mozilla.org/process/util;1"].createInstance(Ci.nsIProcess);
+  process.init(aExeFile);
+  process.run(/* blocking = */ true, aArgs, aArgs.length);
+  return process.exitValue;
+}
+
+function test(aPrefix, aArgs) {
+  // DMD writes the JSON files to CurWorkD, so we do likewise here with
+  // |actualFile| for consistency. It is removed once we've finished.
+  let expectedFile = getRelativeFile(`${aPrefix}-expected.txt`);
+  let actualFile = getRelativeFile(`${aPrefix}-actual.txt`);
+
+  // Run dmd.py on the JSON file, producing |actualFile|.
+
+  let args = [
+    gDmdScriptFile.path,
+    "--filter-stacks-for-testing",
+    "-o",
+    actualFile.path,
+  ].concat(aArgs);
+
+  runProcess(new FileUtils.File(gPythonName), args);
+
+  // Compare |expectedFile| with |actualFile|. We produce nice diffs with
+  // /usr/bin/diff on systems that have it (Mac and Linux). Otherwise (Windows)
+  // we do a string compare of the file contents and then print them both if
+  // they don't match.
+
+  let success;
+  try {
+    let rv = runProcess(new FileUtils.File("/usr/bin/diff"), [
+      "-u",
+      expectedFile.path,
+      actualFile.path,
+    ]);
+    success = rv == 0;
+  } catch (e) {
+    let expectedData = readFile(expectedFile);
+    let actualData = readFile(actualFile);
+    success = expectedData === actualData;
+    if (!success) {
+      expectedData = expectedData.split("\n");
+      actualData = actualData.split("\n");
+      for (let i = 0; i < expectedData.length; i++) {
+        print("EXPECTED:" + expectedData[i]);
+      }
+      for (let i = 0; i < actualData.length; i++) {
+        print("  ACTUAL:" + actualData[i]);
+      }
+    }
+  }
+
+  ok(success, aPrefix);
+
+  actualFile.remove(true);
+}
+
+// Run scan-test.py on the JSON file and see if it succeeds.
+function scanTest(aJsonFilePath, aExtraArgs) {
+  let args = [gScanTestFile.path, aJsonFilePath].concat(aExtraArgs);
+
+  return runProcess(new FileUtils.File(gPythonName), args) == 0;
+}
+
+function run_test() {
+  let jsonFile, jsonFile2;
+
+  // These tests do complete end-to-end testing of DMD, i.e. both the C++ code
+  // that generates the JSON output, and the script that post-processes that
+  // output.
+  //
+  // Run these synchronously, because test() updates the complete*.json files
+  // in-place (to fix stacks) when it runs dmd.py, and that's not safe to do
+  // asynchronously.
+
+  Services.env.set("DMD", "1");
+
+  runProcess(gDmdTestFile, []);
+
+  function test2(aTestName, aMode) {
+    let name = "complete-" + aTestName + "-" + aMode;
+    jsonFile = getRelativeFile(`${name}.json`);
+    test(name, [jsonFile.path]);
+    jsonFile.remove(true);
+  }
+
+  // Please keep this in sync with RunTests() in SmokeDMD.cpp.
+
+  test2("empty", "live");
+  test2("empty", "dark-matter");
+  test2("empty", "cumulative");
+
+  test2("full1", "live");
+  test2("full1", "dark-matter");
+
+  test2("full2", "dark-matter");
+  test2("full2", "cumulative");
+
+  test2("partial", "live");
+
+  // Heap scan testing.
+  jsonFile = getRelativeFile("basic-scan.json");
+  ok(scanTest(jsonFile.path), "Basic scan test");
+
+  let is64Bit = Services.appinfo.is64Bit;
+  let basicScanFileName = "basic-scan-" + (is64Bit ? "64" : "32");
+  test(basicScanFileName, ["--clamp-contents", jsonFile.path]);
+  ok(
+    scanTest(jsonFile.path, ["--clamp-contents"]),
+    "Scan with address clamping"
+  );
+
+  // Run the generic test a second time to ensure that the first time produced
+  // valid JSON output. "--clamp-contents" is passed in so we don't have to have
+  // more variants of the files.
+  test(basicScanFileName, ["--clamp-contents", jsonFile.path]);
+  jsonFile.remove(true);
+
+  // These tests only test the post-processing script. They use hand-written
+  // JSON files as input. Ideally the JSON files would contain comments
+  // explaining how they work, but JSON doesn't allow comments, so I've put
+  // explanations here.
+
+  // This just tests that stack traces of various lengths are truncated
+  // appropriately. The number of records in the output is different for each
+  // of the tested values.
+  jsonFile = getRelativeFile("script-max-frames.json");
+  test("script-max-frames-8", [jsonFile.path]); // --max-frames=8 is the default
+  test("script-max-frames-3", [
+    "--max-frames=3",
+    "--no-fix-stacks",
+    jsonFile.path,
+  ]);
+  test("script-max-frames-1", ["--max-frames=1", jsonFile.path]);
+
+  // This file has three records that are shown in a different order for each
+  // of the different sort values. It also tests the handling of gzipped JSON
+  // files.
+  jsonFile = getRelativeFile("script-sort-by.json.gz");
+  test("script-sort-by-usable", ["--sort-by=usable", jsonFile.path]);
+  test("script-sort-by-req", [
+    "--sort-by=req",
+    "--no-fix-stacks",
+    jsonFile.path,
+  ]);
+  test("script-sort-by-slop", ["--sort-by=slop", jsonFile.path]);
+  test("script-sort-by-num-blocks", ["--sort-by=num-blocks", jsonFile.path]);
+
+  // This file has several real stack traces taken from Firefox execution, each
+  // of which tests a different allocator function (or functions).
+  jsonFile = getRelativeFile("script-ignore-alloc-fns.json");
+  test("script-ignore-alloc-fns", ["--ignore-alloc-fns", jsonFile.path]);
+
+  // This tests "live"-mode diffs.
+  jsonFile = getRelativeFile("script-diff-live1.json");
+  jsonFile2 = getRelativeFile("script-diff-live2.json");
+  test("script-diff-live", [jsonFile.path, jsonFile2.path]);
+
+  // This tests "dark-matter"-mode diffs.
+  jsonFile = getRelativeFile("script-diff-dark-matter1.json");
+  jsonFile2 = getRelativeFile("script-diff-dark-matter2.json");
+  test("script-diff-dark-matter", [jsonFile.path, jsonFile2.path]);
+}
diff --git a/memory/replace/dmd/test/xpcshell.toml b/memory/replace/dmd/test/xpcshell.toml
new file mode 100644
index 0000000000..ef05a8ec26
--- /dev/null
+++ b/memory/replace/dmd/test/xpcshell.toml
@@ -0,0 +1,35 @@
+[DEFAULT]
+support-files = [
+  "basic-scan-32-expected.txt",
+  "basic-scan-64-expected.txt",
+  "complete-empty-live-expected.txt",
+  "complete-empty-dark-matter-expected.txt",
+  "complete-empty-cumulative-expected.txt",
+  "complete-full1-live-expected.txt",
+  "complete-full1-dark-matter-expected.txt",
+  "complete-full2-dark-matter-expected.txt",
+  "complete-full2-cumulative-expected.txt",
+  "complete-partial-live-expected.txt",
+  "scan-test.py",
+  "script-max-frames.json",
+  "script-max-frames-8-expected.txt",
+  "script-max-frames-3-expected.txt",
+  "script-max-frames-1-expected.txt",
+  "script-sort-by.json.gz",
+  "script-sort-by-usable-expected.txt",
+  "script-sort-by-req-expected.txt",
+  "script-sort-by-slop-expected.txt",
+  "script-sort-by-num-blocks-expected.txt",
+  "script-ignore-alloc-fns.json",
+  "script-ignore-alloc-fns-expected.txt",
+  "script-diff-live1.json",
+  "script-diff-live2.json",
+  "script-diff-live-expected.txt",
+  "script-diff-dark-matter1.json",
+  "script-diff-dark-matter2.json",
+  "script-diff-dark-matter-expected.txt",
+]
+
+["test_dmd.js"]
+dmd = true
+skip-if = ["!(os=='linux' || os=='mac' || (os=='win' && !pgo))"]