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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 */
#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"
/* Returns the replace-malloc bridge if there is one to be returned. */
MFBT_API ReplaceMallocBridge* get_bridge();
/* 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;
#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; }
/* 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;
const int mVersion;
/* 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) {
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 /* __cplusplus */
#endif /* replace_malloc_bridge_h */