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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;
+
+
+/* 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.
+ */
+#define MALLOC_DECL(name, return_type, ...) \
+  return_type (*name ## _hook)(return_type, __VA_ARGS__);
+#define MALLOC_DECL_VOID(name, ...) \
+  void (*name ## _hook)(__VA_ARGS__);
+
+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;
+
+MOZ_END_EXTERN_C
+
+#ifdef __cplusplus
+
+namespace mozilla {
+namespace dmd {
+struct DMDFuncs;
+} // namespace dmd
+
+/* 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(3) {}
+
+  /* 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; }
+
+#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;
+  }
+};
+#endif
+
+#endif /* __cplusplus */
+
+#endif /* replace_malloc_bridge_h */