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diff --git a/memory/build/replace_malloc_bridge.h b/memory/build/replace_malloc_bridge.h
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+/* -*- 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/. */
+
+#ifndef replace_malloc_bridge_h
+#define replace_malloc_bridge_h
+
+// The replace-malloc bridge allows bidirectional method calls between
+// a program and the replace-malloc library that has been loaded for it.
+// In Firefox, this is used to allow method calls between code in libxul
+// and code in the replace-malloc library, without libxul needing to link
+// against that library or vice-versa.
+//
+// Subsystems can add methods for their own need. Replace-malloc libraries
+// can decide to implement those methods or not.
+//
+// Replace-malloc libraries can provide such a bridge by implementing
+// a ReplaceMallocBridge-derived class, and a replace_get_bridge function
+// returning an instance of that class. The default methods in
+// ReplaceMallocBridge are expected to return values that callers would
+// understand as "the bridge doesn't implement this method", so that a
+// replace-malloc library doesn't have to implement all methods.
+//
+// The ReplaceMallocBridge class contains definitions for methods for
+// all replace-malloc libraries. Each library picks the methods it wants
+// to reply to in its ReplaceMallocBridge-derived class instance.
+// All methods of ReplaceMallocBridge must be virtual. Similarly,
+// anything passed as an argument to those methods must be plain data, or
+// an instance of a class with only virtual methods.
+//
+// Binary compatibility is expected to be maintained, such that a newer
+// Firefox can be used with an old replace-malloc library, or an old
+// Firefox can be used with a newer replace-malloc library. As such, only
+// new virtual methods should be added to ReplaceMallocBridge, and
+// each change should have a corresponding bump of the mVersion value.
+// At the same time, each virtual method should have a corresponding
+// wrapper calling the virtual method on the instance from
+// ReplaceMallocBridge::Get(), giving it the version the virtual method
+// was added.
+//
+// Parts that are not relevant to the replace-malloc library end of the
+// bridge are hidden when REPLACE_MALLOC_IMPL is not defined, which is
+// the case when including replace_malloc.h.
+
+struct ReplaceMallocBridge;
+
+#include "mozilla/Types.h"
+
+MOZ_BEGIN_EXTERN_C
+
+#ifndef REPLACE_MALLOC_IMPL
+// Returns the replace-malloc bridge if there is one to be returned.
+MFBT_API ReplaceMallocBridge* get_bridge();
+#endif
+
+// Table of malloc functions.
+//   e.g. void* (*malloc)(size_t), etc.
+
+#define MALLOC_DECL(name, return_type, ...) \
+  typedef return_type(name##_impl_t)(__VA_ARGS__);
+
+#include "malloc_decls.h"
+
+#define MALLOC_DECL(name, return_type, ...) name##_impl_t* name;
+
+typedef struct {
+#include "malloc_decls.h"
+} malloc_table_t;
+
+MOZ_END_EXTERN_C
+
+#ifdef __cplusplus
+
+// Table of malloc hook functions.
+// Those functions are called with the arguments and results of malloc
+// functions after they are called.
+//   e.g. void* (*malloc_hook)(void*, size_t), etc.
+// They can either return the result they're given, or alter it before
+// returning it.
+// The hooks corresponding to functions, like free(void*), that return no
+// value, don't take an extra argument.
+// The table must at least contain a pointer for malloc_hook and free_hook
+// functions. They will be used as fallback if no pointer is given for
+// other allocation functions, like calloc_hook.
+namespace mozilla {
+namespace detail {
+template <typename R, typename... Args>
+struct AllocHookType {
+  using Type = R (*)(R, Args...);
+};
+
+template <typename... Args>
+struct AllocHookType<void, Args...> {
+  using Type = void (*)(Args...);
+};
+
+}  // namespace detail
+}  // namespace mozilla
+
+#  define MALLOC_DECL(name, return_type, ...)                                 \
+    typename mozilla::detail::AllocHookType<return_type, ##__VA_ARGS__>::Type \
+        name##_hook;
+
+typedef struct {
+#  include "malloc_decls.h"
+  // Like free_hook, but called before realloc_hook. free_hook is called
+  // instead of not given.
+  void (*realloc_hook_before)(void* aPtr);
+} malloc_hook_table_t;
+
+namespace mozilla {
+namespace dmd {
+struct DMDFuncs;
+}  // namespace dmd
+
+namespace phc {
+class AddrInfo;
+}  // namespace phc
+
+// Callbacks to register debug file handles for Poison IO interpose.
+// See Mozilla(|Un)RegisterDebugHandle in xpcom/build/PoisonIOInterposer.h
+struct DebugFdRegistry {
+  virtual void RegisterHandle(intptr_t aFd);
+
+  virtual void UnRegisterHandle(intptr_t aFd);
+};
+
+}  // namespace mozilla
+
+struct ReplaceMallocBridge {
+  ReplaceMallocBridge() : mVersion(4) {}
+
+  // This method was added in version 1 of the bridge.
+  virtual mozilla::dmd::DMDFuncs* GetDMDFuncs() { return nullptr; }
+
+  // Send a DebugFdRegistry instance to the replace-malloc library so that
+  // it can register/unregister file descriptors whenever needed. The
+  // instance is valid until the process dies.
+  // This method was added in version 2 of the bridge.
+  virtual void InitDebugFd(mozilla::DebugFdRegistry&) {}
+
+  // Register a list of malloc functions and hook functions to the
+  // replace-malloc library so that it can choose to dispatch to them
+  // when needed. The details of what is dispatched when is left to the
+  // replace-malloc library.
+  // Passing a nullptr for either table will unregister a previously
+  // registered table under the same name.
+  // Returns nullptr if registration failed.
+  // If registration succeeded, a table of "pure" malloc functions is
+  // returned. Those "pure" malloc functions won't call hooks.
+  // /!\ Do not rely on registration/unregistration to be instantaneous.
+  // Functions from a previously registered table may still be called for
+  // a brief time after RegisterHook returns.
+  // This method was added in version 3 of the bridge.
+  virtual const malloc_table_t* RegisterHook(
+      const char* aName, const malloc_table_t* aTable,
+      const malloc_hook_table_t* aHookTable) {
+    return nullptr;
+  }
+
+  // If this is a PHC-handled address, return true, and if an AddrInfo is
+  // provided, fill in all of its fields. Otherwise, return false and leave
+  // AddrInfo unchanged.
+  // This method was added in version 4 of the bridge.
+  virtual bool IsPHCAllocation(const void*, mozilla::phc::AddrInfo*) {
+    return false;
+  }
+
+  // Disable PHC allocations on the current thread. Only useful for tests. Note
+  // that PHC deallocations will still occur as needed.
+  // This method was added in version 4 of the bridge.
+  virtual void DisablePHCOnCurrentThread() {}
+
+  // Re-enable PHC allocations on the current thread. Only useful for tests.
+  // This method was added in version 4 of the bridge.
+  virtual void ReenablePHCOnCurrentThread() {}
+
+  // Test whether PHC allocations are enabled on the current thread. Only
+  // useful for tests.
+  // This method was added in version 4 of the bridge.
+  virtual bool IsPHCEnabledOnCurrentThread() { return false; }
+
+#  ifndef REPLACE_MALLOC_IMPL
+  // Returns the replace-malloc bridge if its version is at least the
+  // requested one.
+  static ReplaceMallocBridge* Get(int aMinimumVersion) {
+    static ReplaceMallocBridge* sSingleton = get_bridge();
+    return (sSingleton && sSingleton->mVersion >= aMinimumVersion) ? sSingleton
+                                                                   : nullptr;
+  }
+#  endif
+
+ protected:
+  const int mVersion;
+};
+
+#  ifndef REPLACE_MALLOC_IMPL
+// Class containing wrappers for calls to ReplaceMallocBridge methods.
+// Those wrappers need to be static methods in a class because compilers
+// complain about unused static global functions, and linkers complain
+// about multiple definitions of non-static global functions.
+// Using a separate class from ReplaceMallocBridge allows the function
+// names to be identical.
+struct ReplaceMalloc {
+  // Don't call this method from performance critical code. Use
+  // mozilla::dmd::DMDFuncs::Get() instead, it has less overhead.
+  static mozilla::dmd::DMDFuncs* GetDMDFuncs() {
+    auto singleton = ReplaceMallocBridge::Get(/* minimumVersion */ 1);
+    return singleton ? singleton->GetDMDFuncs() : nullptr;
+  }
+
+  static void InitDebugFd(mozilla::DebugFdRegistry& aRegistry) {
+    auto singleton = ReplaceMallocBridge::Get(/* minimumVersion */ 2);
+    if (singleton) {
+      singleton->InitDebugFd(aRegistry);
+    }
+  }
+
+  static const malloc_table_t* RegisterHook(
+      const char* aName, const malloc_table_t* aTable,
+      const malloc_hook_table_t* aHookTable) {
+    auto singleton = ReplaceMallocBridge::Get(/* minimumVersion */ 3);
+    return singleton ? singleton->RegisterHook(aName, aTable, aHookTable)
+                     : nullptr;
+  }
+
+  static bool IsPHCAllocation(const void* aPtr, mozilla::phc::AddrInfo* aOut) {
+    auto singleton = ReplaceMallocBridge::Get(/* minimumVersion */ 4);
+    return singleton ? singleton->IsPHCAllocation(aPtr, aOut) : false;
+  }
+
+  static void DisablePHCOnCurrentThread() {
+    auto singleton = ReplaceMallocBridge::Get(/* minimumVersion */ 4);
+    if (singleton) {
+      singleton->DisablePHCOnCurrentThread();
+    }
+  }
+
+  static void ReenablePHCOnCurrentThread() {
+    auto singleton = ReplaceMallocBridge::Get(/* minimumVersion */ 4);
+    if (singleton) {
+      singleton->ReenablePHCOnCurrentThread();
+    }
+  }
+
+  static bool IsPHCEnabledOnCurrentThread() {
+    auto singleton = ReplaceMallocBridge::Get(/* minimumVersion */ 4);
+    return singleton ? singleton->IsPHCEnabledOnCurrentThread() : false;
+  }
+};
+#  endif
+
+#endif  // __cplusplus
+
+#endif  // replace_malloc_bridge_h