diff -r 000000000000 -r 6474c204b198 js/public/RootingAPI.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/public/RootingAPI.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,1251 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * 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 js_RootingAPI_h
+#define js_RootingAPI_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/GuardObjects.h"
+#include "mozilla/LinkedList.h"
+#include "mozilla/NullPtr.h"
+#include "mozilla/TypeTraits.h"
+
+#include "jspubtd.h"
+
+#include "js/TypeDecls.h"
+#include "js/Utility.h"
+
+/*
+ * Moving GC Stack Rooting
+ *
+ * A moving GC may change the physical location of GC allocated things, even
+ * when they are rooted, updating all pointers to the thing to refer to its new
+ * location. The GC must therefore know about all live pointers to a thing,
+ * not just one of them, in order to behave correctly.
+ *
+ * The |Rooted| and |Handle| classes below are used to root stack locations
+ * whose value may be held live across a call that can trigger GC. For a
+ * code fragment such as:
+ *
+ * JSObject *obj = NewObject(cx);
+ * DoSomething(cx);
+ * ... = obj->lastProperty();
+ *
+ * If |DoSomething()| can trigger a GC, the stack location of |obj| must be
+ * rooted to ensure that the GC does not move the JSObject referred to by
+ * |obj| without updating |obj|'s location itself. This rooting must happen
+ * regardless of whether there are other roots which ensure that the object
+ * itself will not be collected.
+ *
+ * If |DoSomething()| cannot trigger a GC, and the same holds for all other
+ * calls made between |obj|'s definitions and its last uses, then no rooting
+ * is required.
+ *
+ * SpiderMonkey can trigger a GC at almost any time and in ways that are not
+ * always clear. For example, the following innocuous-looking actions can
+ * cause a GC: allocation of any new GC thing; JSObject::hasProperty;
+ * JS_ReportError and friends; and ToNumber, among many others. The following
+ * dangerous-looking actions cannot trigger a GC: js_malloc, cx->malloc_,
+ * rt->malloc_, and friends and JS_ReportOutOfMemory.
+ *
+ * The following family of three classes will exactly root a stack location.
+ * Incorrect usage of these classes will result in a compile error in almost
+ * all cases. Therefore, it is very hard to be incorrectly rooted if you use
+ * these classes exclusively. These classes are all templated on the type T of
+ * the value being rooted.
+ *
+ * - Rooted<T> declares a variable of type T, whose value is always rooted.
+ *   Rooted<T> may be automatically coerced to a Handle<T>, below. Rooted<T>
+ *   should be used whenever a local variable's value may be held live across a
+ *   call which can trigger a GC.
+ *
+ * - Handle<T> is a const reference to a Rooted<T>. Functions which take GC
+ *   things or values as arguments and need to root those arguments should
+ *   generally use handles for those arguments and avoid any explicit rooting.
+ *   This has two benefits. First, when several such functions call each other
+ *   then redundant rooting of multiple copies of the GC thing can be avoided.
+ *   Second, if the caller does not pass a rooted value a compile error will be
+ *   generated, which is quicker and easier to fix than when relying on a
+ *   separate rooting analysis.
+ *
+ * - MutableHandle<T> is a non-const reference to Rooted<T>. It is used in the
+ *   same way as Handle<T> and includes a |set(const T &v)| method to allow
+ *   updating the value of the referenced Rooted<T>. A MutableHandle<T> can be
+ *   created from a Rooted<T> by using |Rooted<T>::operator&()|.
+ *
+ * In some cases the small performance overhead of exact rooting (measured to
+ * be a few nanoseconds on desktop) is too much. In these cases, try the
+ * following:
+ *
+ * - Move all Rooted<T> above inner loops: this allows you to re-use the root
+ *   on each iteration of the loop.
+ *
+ * - Pass Handle<T> through your hot call stack to avoid re-rooting costs at
+ *   every invocation.
+ *
+ * The following diagram explains the list of supported, implicit type
+ * conversions between classes of this family:
+ *
+ *  Rooted<T> ----> Handle<T>
+ *     |               ^
+ *     |               |
+ *     |               |
+ *     +---> MutableHandle<T>
+ *     (via &)
+ *
+ * All of these types have an implicit conversion to raw pointers.
+ */
+
+namespace js {
+
+class ScriptSourceObject;
+
+template <typename T>
+struct GCMethods {};
+
+template <typename T>
+class RootedBase {};
+
+template <typename T>
+class HandleBase {};
+
+template <typename T>
+class MutableHandleBase {};
+
+template <typename T>
+class HeapBase {};
+
+/*
+ * js::NullPtr acts like a nullptr pointer in contexts that require a Handle.
+ *
+ * Handle provides an implicit constructor for js::NullPtr so that, given:
+ *   foo(Handle<JSObject*> h);
+ * callers can simply write:
+ *   foo(js::NullPtr());
+ * which avoids creating a Rooted<JSObject*> just to pass nullptr.
+ *
+ * This is the SpiderMonkey internal variant. js::NullPtr should be used in
+ * preference to JS::NullPtr to avoid the GOT access required for JS_PUBLIC_API
+ * symbols.
+ */
+struct NullPtr
+{
+    static void * const constNullValue;
+};
+
+namespace gc {
+struct Cell;
+template<typename T>
+struct PersistentRootedMarker;
+} /* namespace gc */
+
+} /* namespace js */
+
+namespace JS {
+
+template <typename T> class Rooted;
+template <typename T> class PersistentRooted;
+
+/* This is exposing internal state of the GC for inlining purposes. */
+JS_FRIEND_API(bool) isGCEnabled();
+
+/*
+ * JS::NullPtr acts like a nullptr pointer in contexts that require a Handle.
+ *
+ * Handle provides an implicit constructor for JS::NullPtr so that, given:
+ *   foo(Handle<JSObject*> h);
+ * callers can simply write:
+ *   foo(JS::NullPtr());
+ * which avoids creating a Rooted<JSObject*> just to pass nullptr.
+ */
+struct JS_PUBLIC_API(NullPtr)
+{
+    static void * const constNullValue;
+};
+
+/*
+ * The Heap<T> class is a heap-stored reference to a JS GC thing. All members of
+ * heap classes that refer to GC things should use Heap<T> (or possibly
+ * TenuredHeap<T>, described below).
+ *
+ * Heap<T> is an abstraction that hides some of the complexity required to
+ * maintain GC invariants for the contained reference. It uses operator
+ * overloading to provide a normal pointer interface, but notifies the GC every
+ * time the value it contains is updated. This is necessary for generational GC,
+ * which keeps track of all pointers into the nursery.
+ *
+ * Heap<T> instances must be traced when their containing object is traced to
+ * keep the pointed-to GC thing alive.
+ *
+ * Heap<T> objects should only be used on the heap. GC references stored on the
+ * C/C++ stack must use Rooted/Handle/MutableHandle instead.
+ *
+ * Type T must be one of: JS::Value, jsid, JSObject*, JSString*, JSScript*
+ */
+template <typename T>
+class Heap : public js::HeapBase<T>
+{
+  public:
+    Heap() {
+        static_assert(sizeof(T) == sizeof(Heap<T>),
+                      "Heap<T> must be binary compatible with T.");
+        init(js::GCMethods<T>::initial());
+    }
+    explicit Heap(T p) { init(p); }
+
+    /*
+     * For Heap, move semantics are equivalent to copy semantics. In C++, a
+     * copy constructor taking const-ref is the way to get a single function
+     * that will be used for both lvalue and rvalue copies, so we can simply
+     * omit the rvalue variant.
+     */
+    explicit Heap(const Heap<T> &p) { init(p.ptr); }
+
+    ~Heap() {
+        if (js::GCMethods<T>::needsPostBarrier(ptr))
+            relocate();
+    }
+
+    bool operator==(const Heap<T> &other) { return ptr == other.ptr; }
+    bool operator!=(const Heap<T> &other) { return ptr != other.ptr; }
+
+    bool operator==(const T &other) const { return ptr == other; }
+    bool operator!=(const T &other) const { return ptr != other; }
+
+    operator T() const { return ptr; }
+    T operator->() const { return ptr; }
+    const T *address() const { return &ptr; }
+    const T &get() const { return ptr; }
+
+    T *unsafeGet() { return &ptr; }
+
+    Heap<T> &operator=(T p) {
+        set(p);
+        return *this;
+    }
+
+    Heap<T> &operator=(const Heap<T>& other) {
+        set(other.get());
+        return *this;
+    }
+
+    void set(T newPtr) {
+        MOZ_ASSERT(!js::GCMethods<T>::poisoned(newPtr));
+        if (js::GCMethods<T>::needsPostBarrier(newPtr)) {
+            ptr = newPtr;
+            post();
+        } else if (js::GCMethods<T>::needsPostBarrier(ptr)) {
+            relocate();  /* Called before overwriting ptr. */
+            ptr = newPtr;
+        } else {
+            ptr = newPtr;
+        }
+    }
+
+    /*
+     * Set the pointer to a value which will cause a crash if it is
+     * dereferenced.
+     */
+    void setToCrashOnTouch() {
+        ptr = reinterpret_cast<T>(crashOnTouchPointer);
+    }
+
+    bool isSetToCrashOnTouch() {
+        return ptr == crashOnTouchPointer;
+    }
+
+  private:
+    void init(T newPtr) {
+        MOZ_ASSERT(!js::GCMethods<T>::poisoned(newPtr));
+        ptr = newPtr;
+        if (js::GCMethods<T>::needsPostBarrier(ptr))
+            post();
+    }
+
+    void post() {
+#ifdef JSGC_GENERATIONAL
+        MOZ_ASSERT(js::GCMethods<T>::needsPostBarrier(ptr));
+        js::GCMethods<T>::postBarrier(&ptr);
+#endif
+    }
+
+    void relocate() {
+#ifdef JSGC_GENERATIONAL
+        js::GCMethods<T>::relocate(&ptr);
+#endif
+    }
+
+    enum {
+        crashOnTouchPointer = 1
+    };
+
+    T ptr;
+};
+
+#ifdef JS_DEBUG
+/*
+ * For generational GC, assert that an object is in the tenured generation as
+ * opposed to being in the nursery.
+ */
+extern JS_FRIEND_API(void)
+AssertGCThingMustBeTenured(JSObject* obj);
+#else
+inline void
+AssertGCThingMustBeTenured(JSObject *obj) {}
+#endif
+
+/*
+ * The TenuredHeap<T> class is similar to the Heap<T> class above in that it
+ * encapsulates the GC concerns of an on-heap reference to a JS object. However,
+ * it has two important differences:
+ *
+ *  1) Pointers which are statically known to only reference "tenured" objects
+ *     can avoid the extra overhead of SpiderMonkey's write barriers.
+ *
+ *  2) Objects in the "tenured" heap have stronger alignment restrictions than
+ *     those in the "nursery", so it is possible to store flags in the lower
+ *     bits of pointers known to be tenured. TenuredHeap wraps a normal tagged
+ *     pointer with a nice API for accessing the flag bits and adds various
+ *     assertions to ensure that it is not mis-used.
+ *
+ * GC things are said to be "tenured" when they are located in the long-lived
+ * heap: e.g. they have gained tenure as an object by surviving past at least
+ * one GC. For performance, SpiderMonkey allocates some things which are known
+ * to normally be long lived directly into the tenured generation; for example,
+ * global objects. Additionally, SpiderMonkey does not visit individual objects
+ * when deleting non-tenured objects, so object with finalizers are also always
+ * tenured; for instance, this includes most DOM objects.
+ *
+ * The considerations to keep in mind when using a TenuredHeap<T> vs a normal
+ * Heap<T> are:
+ *
+ *  - It is invalid for a TenuredHeap<T> to refer to a non-tenured thing.
+ *  - It is however valid for a Heap<T> to refer to a tenured thing.
+ *  - It is not possible to store flag bits in a Heap<T>.
+ */
+template <typename T>
+class TenuredHeap : public js::HeapBase<T>
+{
+  public:
+    TenuredHeap() : bits(0) {
+        static_assert(sizeof(T) == sizeof(TenuredHeap<T>),
+                      "TenuredHeap<T> must be binary compatible with T.");
+    }
+    explicit TenuredHeap(T p) : bits(0) { setPtr(p); }
+    explicit TenuredHeap(const TenuredHeap<T> &p) : bits(0) { setPtr(p.getPtr()); }
+
+    bool operator==(const TenuredHeap<T> &other) { return bits == other.bits; }
+    bool operator!=(const TenuredHeap<T> &other) { return bits != other.bits; }
+
+    void setPtr(T newPtr) {
+        MOZ_ASSERT((reinterpret_cast<uintptr_t>(newPtr) & flagsMask) == 0);
+        MOZ_ASSERT(!js::GCMethods<T>::poisoned(newPtr));
+        if (newPtr)
+            AssertGCThingMustBeTenured(newPtr);
+        bits = (bits & flagsMask) | reinterpret_cast<uintptr_t>(newPtr);
+    }
+
+    void setFlags(uintptr_t flagsToSet) {
+        MOZ_ASSERT((flagsToSet & ~flagsMask) == 0);
+        bits |= flagsToSet;
+    }
+
+    void unsetFlags(uintptr_t flagsToUnset) {
+        MOZ_ASSERT((flagsToUnset & ~flagsMask) == 0);
+        bits &= ~flagsToUnset;
+    }
+
+    bool hasFlag(uintptr_t flag) const {
+        MOZ_ASSERT((flag & ~flagsMask) == 0);
+        return (bits & flag) != 0;
+    }
+
+    T getPtr() const { return reinterpret_cast<T>(bits & ~flagsMask); }
+    uintptr_t getFlags() const { return bits & flagsMask; }
+
+    operator T() const { return getPtr(); }
+    T operator->() const { return getPtr(); }
+
+    TenuredHeap<T> &operator=(T p) {
+        setPtr(p);
+        return *this;
+    }
+
+    TenuredHeap<T> &operator=(const TenuredHeap<T>& other) {
+        bits = other.bits;
+        return *this;
+    }
+
+  private:
+    enum {
+        maskBits = 3,
+        flagsMask = (1 << maskBits) - 1,
+    };
+
+    uintptr_t bits;
+};
+
+/*
+ * Reference to a T that has been rooted elsewhere. This is most useful
+ * as a parameter type, which guarantees that the T lvalue is properly
+ * rooted. See "Move GC Stack Rooting" above.
+ *
+ * If you want to add additional methods to Handle for a specific
+ * specialization, define a HandleBase<T> specialization containing them.
+ */
+template <typename T>
+class MOZ_NONHEAP_CLASS Handle : public js::HandleBase<T>
+{
+    friend class JS::MutableHandle<T>;
+
+  public:
+    /* Creates a handle from a handle of a type convertible to T. */
+    template <typename S>
+    Handle(Handle<S> handle,
+           typename mozilla::EnableIf<mozilla::IsConvertible<S, T>::value, int>::Type dummy = 0)
+    {
+        static_assert(sizeof(Handle<T>) == sizeof(T *),
+                      "Handle must be binary compatible with T*.");
+        ptr = reinterpret_cast<const T *>(handle.address());
+    }
+
+    /* Create a handle for a nullptr pointer. */
+    Handle(js::NullPtr) {
+        static_assert(mozilla::IsPointer<T>::value,
+                      "js::NullPtr overload not valid for non-pointer types");
+        ptr = reinterpret_cast<const T *>(&js::NullPtr::constNullValue);
+    }
+
+    /* Create a handle for a nullptr pointer. */
+    Handle(JS::NullPtr) {
+        static_assert(mozilla::IsPointer<T>::value,
+                      "JS::NullPtr overload not valid for non-pointer types");
+        ptr = reinterpret_cast<const T *>(&JS::NullPtr::constNullValue);
+    }
+
+    Handle(MutableHandle<T> handle) {
+        ptr = handle.address();
+    }
+
+    /*
+     * Take care when calling this method!
+     *
+     * This creates a Handle from the raw location of a T.
+     *
+     * It should be called only if the following conditions hold:
+     *
+     *  1) the location of the T is guaranteed to be marked (for some reason
+     *     other than being a Rooted), e.g., if it is guaranteed to be reachable
+     *     from an implicit root.
+     *
+     *  2) the contents of the location are immutable, or at least cannot change
+     *     for the lifetime of the handle, as its users may not expect its value
+     *     to change underneath them.
+     */
+    static MOZ_CONSTEXPR Handle fromMarkedLocation(const T *p) {
+        return Handle(p, DeliberatelyChoosingThisOverload,
+                      ImUsingThisOnlyInFromFromMarkedLocation);
+    }
+
+    /*
+     * Construct a handle from an explicitly rooted location. This is the
+     * normal way to create a handle, and normally happens implicitly.
+     */
+    template <typename S>
+    inline
+    Handle(const Rooted<S> &root,
+           typename mozilla::EnableIf<mozilla::IsConvertible<S, T>::value, int>::Type dummy = 0);
+
+    template <typename S>
+    inline
+    Handle(const PersistentRooted<S> &root,
+           typename mozilla::EnableIf<mozilla::IsConvertible<S, T>::value, int>::Type dummy = 0);
+
+    /* Construct a read only handle from a mutable handle. */
+    template <typename S>
+    inline
+    Handle(MutableHandle<S> &root,
+           typename mozilla::EnableIf<mozilla::IsConvertible<S, T>::value, int>::Type dummy = 0);
+
+    const T *address() const { return ptr; }
+    const T& get() const { return *ptr; }
+
+    /*
+     * Return a reference so passing a Handle<T> to something that
+     * takes a |const T&| is not a GC hazard.
+     */
+    operator const T&() const { return get(); }
+    T operator->() const { return get(); }
+
+    bool operator!=(const T &other) const { return *ptr != other; }
+    bool operator==(const T &other) const { return *ptr == other; }
+
+    /* Change this handle to point to the same rooted location RHS does. */
+    void repoint(const Handle &rhs) { ptr = rhs.address(); }
+
+  private:
+    Handle() {}
+
+    enum Disambiguator { DeliberatelyChoosingThisOverload = 42 };
+    enum CallerIdentity { ImUsingThisOnlyInFromFromMarkedLocation = 17 };
+    MOZ_CONSTEXPR Handle(const T *p, Disambiguator, CallerIdentity) : ptr(p) {}
+
+    const T *ptr;
+
+    template <typename S> void operator=(S) MOZ_DELETE;
+    void operator=(Handle) MOZ_DELETE;
+};
+
+/*
+ * Similar to a handle, but the underlying storage can be changed. This is
+ * useful for outparams.
+ *
+ * If you want to add additional methods to MutableHandle for a specific
+ * specialization, define a MutableHandleBase<T> specialization containing
+ * them.
+ */
+template <typename T>
+class MOZ_STACK_CLASS MutableHandle : public js::MutableHandleBase<T>
+{
+  public:
+    inline MutableHandle(Rooted<T> *root);
+    inline MutableHandle(PersistentRooted<T> *root);
+
+  private:
+    // Disallow true nullptr and emulated nullptr (gcc 4.4/4.5, __null, appears
+    // as int/long [32/64-bit]) for overloading purposes.
+    template<typename N>
+    MutableHandle(N,
+                  typename mozilla::EnableIf<mozilla::IsNullPointer<N>::value ||
+                                             mozilla::IsSame<N, int>::value ||
+                                             mozilla::IsSame<N, long>::value,
+                                             int>::Type dummy = 0)
+    MOZ_DELETE;
+
+  public:
+    void set(T v) {
+        MOZ_ASSERT(!js::GCMethods<T>::poisoned(v));
+        *ptr = v;
+    }
+
+    /*
+     * This may be called only if the location of the T is guaranteed
+     * to be marked (for some reason other than being a Rooted),
+     * e.g., if it is guaranteed to be reachable from an implicit root.
+     *
+     * Create a MutableHandle from a raw location of a T.
+     */
+    static MutableHandle fromMarkedLocation(T *p) {
+        MutableHandle h;
+        h.ptr = p;
+        return h;
+    }
+
+    T *address() const { return ptr; }
+    const T& get() const { return *ptr; }
+
+    /*
+     * Return a reference so passing a MutableHandle<T> to something that takes
+     * a |const T&| is not a GC hazard.
+     */
+    operator const T&() const { return get(); }
+    T operator->() const { return get(); }
+
+  private:
+    MutableHandle() {}
+
+    T *ptr;
+
+    template <typename S> void operator=(S v) MOZ_DELETE;
+    void operator=(MutableHandle other) MOZ_DELETE;
+};
+
+#ifdef JSGC_GENERATIONAL
+JS_FRIEND_API(void) HeapCellPostBarrier(js::gc::Cell **cellp);
+JS_FRIEND_API(void) HeapCellRelocate(js::gc::Cell **cellp);
+#endif
+
+} /* namespace JS */
+
+namespace js {
+
+/*
+ * InternalHandle is a handle to an internal pointer into a gcthing. Use
+ * InternalHandle when you have a pointer to a direct field of a gcthing, or
+ * when you need a parameter type for something that *may* be a pointer to a
+ * direct field of a gcthing.
+ */
+template <typename T>
+class InternalHandle {};
+
+template <typename T>
+class InternalHandle<T*>
+{
+    void * const *holder;
+    size_t offset;
+
+  public:
+    /*
+     * Create an InternalHandle using a Handle to the gcthing containing the
+     * field in question, and a pointer to the field.
+     */
+    template<typename H>
+    InternalHandle(const JS::Handle<H> &handle, T *field)
+      : holder((void**)handle.address()), offset(uintptr_t(field) - uintptr_t(handle.get()))
+    {}
+
+    /*
+     * Create an InternalHandle to a field within a Rooted<>.
+     */
+    template<typename R>
+    InternalHandle(const JS::Rooted<R> &root, T *field)
+      : holder((void**)root.address()), offset(uintptr_t(field) - uintptr_t(root.get()))
+    {}
+
+    InternalHandle(const InternalHandle<T*>& other)
+      : holder(other.holder), offset(other.offset) {}
+
+    T *get() const { return reinterpret_cast<T*>(uintptr_t(*holder) + offset); }
+
+    const T &operator*() const { return *get(); }
+    T *operator->() const { return get(); }
+
+    static InternalHandle<T*> fromMarkedLocation(T *fieldPtr) {
+        return InternalHandle(fieldPtr);
+    }
+
+  private:
+    /*
+     * Create an InternalHandle to something that is not a pointer to a
+     * gcthing, and so does not need to be rooted in the first place. Use these
+     * InternalHandles to pass pointers into functions that also need to accept
+     * regular InternalHandles to gcthing fields.
+     *
+     * Make this private to prevent accidental misuse; this is only for
+     * fromMarkedLocation().
+     */
+    InternalHandle(T *field)
+      : holder(reinterpret_cast<void * const *>(&js::NullPtr::constNullValue)),
+        offset(uintptr_t(field))
+    {}
+
+    void operator=(InternalHandle<T*> other) MOZ_DELETE;
+};
+
+/*
+ * By default, pointers should use the inheritance hierarchy to find their
+ * ThingRootKind. Some pointer types are explicitly set in jspubtd.h so that
+ * Rooted<T> may be used without the class definition being available.
+ */
+template <typename T>
+struct RootKind<T *>
+{
+    static ThingRootKind rootKind() { return T::rootKind(); }
+};
+
+template <typename T>
+struct GCMethods<T *>
+{
+    static T *initial() { return nullptr; }
+    static ThingRootKind kind() { return RootKind<T *>::rootKind(); }
+    static bool poisoned(T *v) { return JS::IsPoisonedPtr(v); }
+    static bool needsPostBarrier(T *v) { return false; }
+#ifdef JSGC_GENERATIONAL
+    static void postBarrier(T **vp) {}
+    static void relocate(T **vp) {}
+#endif
+};
+
+template <>
+struct GCMethods<JSObject *>
+{
+    static JSObject *initial() { return nullptr; }
+    static ThingRootKind kind() { return RootKind<JSObject *>::rootKind(); }
+    static bool poisoned(JSObject *v) { return JS::IsPoisonedPtr(v); }
+    static bool needsPostBarrier(JSObject *v) { return v; }
+#ifdef JSGC_GENERATIONAL
+    static void postBarrier(JSObject **vp) {
+        JS::HeapCellPostBarrier(reinterpret_cast<js::gc::Cell **>(vp));
+    }
+    static void relocate(JSObject **vp) {
+        JS::HeapCellRelocate(reinterpret_cast<js::gc::Cell **>(vp));
+    }
+#endif
+};
+
+template <>
+struct GCMethods<JSFunction *>
+{
+    static JSFunction *initial() { return nullptr; }
+    static ThingRootKind kind() { return RootKind<JSObject *>::rootKind(); }
+    static bool poisoned(JSFunction *v) { return JS::IsPoisonedPtr(v); }
+    static bool needsPostBarrier(JSFunction *v) { return v; }
+#ifdef JSGC_GENERATIONAL
+    static void postBarrier(JSFunction **vp) {
+        JS::HeapCellPostBarrier(reinterpret_cast<js::gc::Cell **>(vp));
+    }
+    static void relocate(JSFunction **vp) {
+        JS::HeapCellRelocate(reinterpret_cast<js::gc::Cell **>(vp));
+    }
+#endif
+};
+
+#ifdef JS_DEBUG
+/* This helper allows us to assert that Rooted<T> is scoped within a request. */
+extern JS_PUBLIC_API(bool)
+IsInRequest(JSContext *cx);
+#endif
+
+} /* namespace js */
+
+namespace JS {
+
+/*
+ * Local variable of type T whose value is always rooted. This is typically
+ * used for local variables, or for non-rooted values being passed to a
+ * function that requires a handle, e.g. Foo(Root<T>(cx, x)).
+ *
+ * If you want to add additional methods to Rooted for a specific
+ * specialization, define a RootedBase<T> specialization containing them.
+ */
+template <typename T>
+class MOZ_STACK_CLASS Rooted : public js::RootedBase<T>
+{
+    /* Note: CX is a subclass of either ContextFriendFields or PerThreadDataFriendFields. */
+    template <typename CX>
+    void init(CX *cx) {
+#ifdef JSGC_TRACK_EXACT_ROOTS
+        js::ThingRootKind kind = js::GCMethods<T>::kind();
+        this->stack = &cx->thingGCRooters[kind];
+        this->prev = *stack;
+        *stack = reinterpret_cast<Rooted<void*>*>(this);
+
+        MOZ_ASSERT(!js::GCMethods<T>::poisoned(ptr));
+#endif
+    }
+
+  public:
+    Rooted(JSContext *cx
+           MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+      : ptr(js::GCMethods<T>::initial())
+    {
+        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+#ifdef JS_DEBUG
+        MOZ_ASSERT(js::IsInRequest(cx));
+#endif
+        init(js::ContextFriendFields::get(cx));
+    }
+
+    Rooted(JSContext *cx, T initial
+           MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+      : ptr(initial)
+    {
+        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+#ifdef JS_DEBUG
+        MOZ_ASSERT(js::IsInRequest(cx));
+#endif
+        init(js::ContextFriendFields::get(cx));
+    }
+
+    Rooted(js::ContextFriendFields *cx
+           MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+      : ptr(js::GCMethods<T>::initial())
+    {
+        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+        init(cx);
+    }
+
+    Rooted(js::ContextFriendFields *cx, T initial
+           MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+      : ptr(initial)
+    {
+        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+        init(cx);
+    }
+
+    Rooted(js::PerThreadDataFriendFields *pt
+           MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+      : ptr(js::GCMethods<T>::initial())
+    {
+        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+        init(pt);
+    }
+
+    Rooted(js::PerThreadDataFriendFields *pt, T initial
+           MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+      : ptr(initial)
+    {
+        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+        init(pt);
+    }
+
+    Rooted(JSRuntime *rt
+           MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+      : ptr(js::GCMethods<T>::initial())
+    {
+        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+        init(js::PerThreadDataFriendFields::getMainThread(rt));
+    }
+
+    Rooted(JSRuntime *rt, T initial
+           MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+      : ptr(initial)
+    {
+        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+        init(js::PerThreadDataFriendFields::getMainThread(rt));
+    }
+
+    // Note that we need to let the compiler generate the default destructor in
+    // non-exact-rooting builds because of a bug in the instrumented PGO builds
+    // using MSVC, see bug 915735 for more details.
+#ifdef JSGC_TRACK_EXACT_ROOTS
+    ~Rooted() {
+        MOZ_ASSERT(*stack == reinterpret_cast<Rooted<void*>*>(this));
+        *stack = prev;
+    }
+#endif
+
+#ifdef JSGC_TRACK_EXACT_ROOTS
+    Rooted<T> *previous() { return prev; }
+#endif
+
+    /*
+     * Important: Return a reference here so passing a Rooted<T> to
+     * something that takes a |const T&| is not a GC hazard.
+     */
+    operator const T&() const { return ptr; }
+    T operator->() const { return ptr; }
+    T *address() { return &ptr; }
+    const T *address() const { return &ptr; }
+    T &get() { return ptr; }
+    const T &get() const { return ptr; }
+
+    T &operator=(T value) {
+        MOZ_ASSERT(!js::GCMethods<T>::poisoned(value));
+        ptr = value;
+        return ptr;
+    }
+
+    T &operator=(const Rooted &value) {
+        ptr = value;
+        return ptr;
+    }
+
+    void set(T value) {
+        MOZ_ASSERT(!js::GCMethods<T>::poisoned(value));
+        ptr = value;
+    }
+
+    bool operator!=(const T &other) const { return ptr != other; }
+    bool operator==(const T &other) const { return ptr == other; }
+
+  private:
+#ifdef JSGC_TRACK_EXACT_ROOTS
+    Rooted<void*> **stack, *prev;
+#endif
+
+    /*
+     * |ptr| must be the last field in Rooted because the analysis treats all
+     * Rooted as Rooted<void*> during the analysis. See bug 829372.
+     */
+    T ptr;
+
+    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+
+    Rooted(const Rooted &) MOZ_DELETE;
+};
+
+} /* namespace JS */
+
+namespace js {
+
+/*
+ * Augment the generic Rooted<T> interface when T = JSObject* with
+ * class-querying and downcasting operations.
+ *
+ * Given a Rooted<JSObject*> obj, one can view
+ *   Handle<StringObject*> h = obj.as<StringObject*>();
+ * as an optimization of
+ *   Rooted<StringObject*> rooted(cx, &obj->as<StringObject*>());
+ *   Handle<StringObject*> h = rooted;
+ */
+template <>
+class RootedBase<JSObject*>
+{
+  public:
+    template <class U>
+    JS::Handle<U*> as() const;
+};
+
+
+/*
+ * RootedGeneric<T> allows a class to instantiate its own Rooted type by
+ * including the following two methods:
+ *
+ *    static inline js::ThingRootKind rootKind() { return js::THING_ROOT_CUSTOM; }
+ *    void trace(JSTracer *trc);
+ *
+ * The trace() method must trace all of the class's fields.
+ *
+ * Implementation:
+ *
+ * RootedGeneric<T> works by placing a pointer to its 'rooter' field into the
+ * usual list of rooters when it is instantiated. When marking, it backs up
+ * from this pointer to find a vtable containing a type-appropriate trace()
+ * method.
+ */
+template <typename GCType>
+class JS_PUBLIC_API(RootedGeneric)
+{
+  public:
+    JS::Rooted<GCType> rooter;
+
+    RootedGeneric(js::ContextFriendFields *cx)
+        : rooter(cx)
+    {
+    }
+
+    RootedGeneric(js::ContextFriendFields *cx, const GCType &initial)
+        : rooter(cx, initial)
+    {
+    }
+
+    virtual inline void trace(JSTracer *trc);
+
+    operator const GCType&() const { return rooter.get(); }
+    GCType operator->() const { return rooter.get(); }
+};
+
+template <typename GCType>
+inline void RootedGeneric<GCType>::trace(JSTracer *trc)
+{
+    rooter->trace(trc);
+}
+
+// We will instantiate RootedGeneric<void*> in RootMarking.cpp, and MSVC will
+// notice that void*s have no trace() method defined on them and complain (even
+// though it's never called.) MSVC's complaint is not unreasonable, so
+// specialize for void*.
+template <>
+inline void RootedGeneric<void*>::trace(JSTracer *trc)
+{
+    MOZ_ASSUME_UNREACHABLE("RootedGeneric<void*>::trace()");
+}
+
+/* Interface substitute for Rooted<T> which does not root the variable's memory. */
+template <typename T>
+class FakeRooted : public RootedBase<T>
+{
+  public:
+    template <typename CX>
+    FakeRooted(CX *cx
+               MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+      : ptr(GCMethods<T>::initial())
+    {
+        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+    }
+
+    template <typename CX>
+    FakeRooted(CX *cx, T initial
+               MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+      : ptr(initial)
+    {
+        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+    }
+
+    operator T() const { return ptr; }
+    T operator->() const { return ptr; }
+    T *address() { return &ptr; }
+    const T *address() const { return &ptr; }
+    T &get() { return ptr; }
+    const T &get() const { return ptr; }
+
+    FakeRooted<T> &operator=(T value) {
+        MOZ_ASSERT(!GCMethods<T>::poisoned(value));
+        ptr = value;
+        return *this;
+    }
+
+    FakeRooted<T> &operator=(const FakeRooted<T> &other) {
+        MOZ_ASSERT(!GCMethods<T>::poisoned(other.ptr));
+        ptr = other.ptr;
+        return *this;
+    }
+
+    bool operator!=(const T &other) const { return ptr != other; }
+    bool operator==(const T &other) const { return ptr == other; }
+
+  private:
+    T ptr;
+
+    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+
+    FakeRooted(const FakeRooted &) MOZ_DELETE;
+};
+
+/* Interface substitute for MutableHandle<T> which is not required to point to rooted memory. */
+template <typename T>
+class FakeMutableHandle : public js::MutableHandleBase<T>
+{
+  public:
+    FakeMutableHandle(T *t) {
+        ptr = t;
+    }
+
+    FakeMutableHandle(FakeRooted<T> *root) {
+        ptr = root->address();
+    }
+
+    void set(T v) {
+        MOZ_ASSERT(!js::GCMethods<T>::poisoned(v));
+        *ptr = v;
+    }
+
+    T *address() const { return ptr; }
+    T get() const { return *ptr; }
+
+    operator T() const { return get(); }
+    T operator->() const { return get(); }
+
+  private:
+    FakeMutableHandle() {}
+
+    T *ptr;
+
+    template <typename S>
+    void operator=(S v) MOZ_DELETE;
+
+    void operator=(const FakeMutableHandle<T>& other) MOZ_DELETE;
+};
+
+/*
+ * Types for a variable that either should or shouldn't be rooted, depending on
+ * the template parameter allowGC. Used for implementing functions that can
+ * operate on either rooted or unrooted data.
+ *
+ * The toHandle() and toMutableHandle() functions are for calling functions
+ * which require handle types and are only called in the CanGC case. These
+ * allow the calling code to type check.
+ */
+enum AllowGC {
+    NoGC = 0,
+    CanGC = 1
+};
+template <typename T, AllowGC allowGC>
+class MaybeRooted
+{
+};
+
+template <typename T> class MaybeRooted<T, CanGC>
+{
+  public:
+    typedef JS::Handle<T> HandleType;
+    typedef JS::Rooted<T> RootType;
+    typedef JS::MutableHandle<T> MutableHandleType;
+
+    static inline JS::Handle<T> toHandle(HandleType v) {
+        return v;
+    }
+
+    static inline JS::MutableHandle<T> toMutableHandle(MutableHandleType v) {
+        return v;
+    }
+};
+
+template <typename T> class MaybeRooted<T, NoGC>
+{
+  public:
+    typedef T HandleType;
+    typedef FakeRooted<T> RootType;
+    typedef FakeMutableHandle<T> MutableHandleType;
+
+    static inline JS::Handle<T> toHandle(HandleType v) {
+        MOZ_ASSUME_UNREACHABLE("Bad conversion");
+    }
+
+    static inline JS::MutableHandle<T> toMutableHandle(MutableHandleType v) {
+        MOZ_ASSUME_UNREACHABLE("Bad conversion");
+    }
+};
+
+} /* namespace js */
+
+namespace JS {
+
+template <typename T> template <typename S>
+inline
+Handle<T>::Handle(const Rooted<S> &root,
+                  typename mozilla::EnableIf<mozilla::IsConvertible<S, T>::value, int>::Type dummy)
+{
+    ptr = reinterpret_cast<const T *>(root.address());
+}
+
+template <typename T> template <typename S>
+inline
+Handle<T>::Handle(const PersistentRooted<S> &root,
+                  typename mozilla::EnableIf<mozilla::IsConvertible<S, T>::value, int>::Type dummy)
+{
+    ptr = reinterpret_cast<const T *>(root.address());
+}
+
+template <typename T> template <typename S>
+inline
+Handle<T>::Handle(MutableHandle<S> &root,
+                  typename mozilla::EnableIf<mozilla::IsConvertible<S, T>::value, int>::Type dummy)
+{
+    ptr = reinterpret_cast<const T *>(root.address());
+}
+
+template <typename T>
+inline
+MutableHandle<T>::MutableHandle(Rooted<T> *root)
+{
+    static_assert(sizeof(MutableHandle<T>) == sizeof(T *),
+                  "MutableHandle must be binary compatible with T*.");
+    ptr = root->address();
+}
+
+template <typename T>
+inline
+MutableHandle<T>::MutableHandle(PersistentRooted<T> *root)
+{
+    static_assert(sizeof(MutableHandle<T>) == sizeof(T *),
+                  "MutableHandle must be binary compatible with T*.");
+    ptr = root->address();
+}
+
+/*
+ * A copyable, assignable global GC root type with arbitrary lifetime, an
+ * infallible constructor, and automatic unrooting on destruction.
+ *
+ * These roots can be used in heap-allocated data structures, so they are not
+ * associated with any particular JSContext or stack. They are registered with
+ * the JSRuntime itself, without locking, so they require a full JSContext to be
+ * constructed, not one of its more restricted superclasses.
+ *
+ * Note that you must not use an PersistentRooted in an object owned by a JS
+ * object:
+ *
+ * Whenever one object whose lifetime is decided by the GC refers to another
+ * such object, that edge must be traced only if the owning JS object is traced.
+ * This applies not only to JS objects (which obviously are managed by the GC)
+ * but also to C++ objects owned by JS objects.
+ *
+ * If you put a PersistentRooted in such a C++ object, that is almost certainly
+ * a leak. When a GC begins, the referent of the PersistentRooted is treated as
+ * live, unconditionally (because a PersistentRooted is a *root*), even if the
+ * JS object that owns it is unreachable. If there is any path from that
+ * referent back to the JS object, then the C++ object containing the
+ * PersistentRooted will not be destructed, and the whole blob of objects will
+ * not be freed, even if there are no references to them from the outside.
+ *
+ * In the context of Firefox, this is a severe restriction: almost everything in
+ * Firefox is owned by some JS object or another, so using PersistentRooted in
+ * such objects would introduce leaks. For these kinds of edges, Heap<T> or
+ * TenuredHeap<T> would be better types. It's up to the implementor of the type
+ * containing Heap<T> or TenuredHeap<T> members to make sure their referents get
+ * marked when the object itself is marked.
+ */
+template<typename T>
+class PersistentRooted : private mozilla::LinkedListElement<PersistentRooted<T> > {
+    friend class mozilla::LinkedList<PersistentRooted>;
+    friend class mozilla::LinkedListElement<PersistentRooted>;
+
+    friend class js::gc::PersistentRootedMarker<T>;
+
+    void registerWithRuntime(JSRuntime *rt) {
+        JS::shadow::Runtime *srt = JS::shadow::Runtime::asShadowRuntime(rt);
+        srt->getPersistentRootedList<T>().insertBack(this);
+    }
+
+  public:
+    PersistentRooted(JSContext *cx) : ptr(js::GCMethods<T>::initial())
+    {
+        registerWithRuntime(js::GetRuntime(cx));
+    }
+
+    PersistentRooted(JSContext *cx, T initial) : ptr(initial)
+    {
+        registerWithRuntime(js::GetRuntime(cx));
+    }
+
+    PersistentRooted(JSRuntime *rt) : ptr(js::GCMethods<T>::initial())
+    {
+        registerWithRuntime(rt);
+    }
+
+    PersistentRooted(JSRuntime *rt, T initial) : ptr(initial)
+    {
+        registerWithRuntime(rt);
+    }
+
+    PersistentRooted(PersistentRooted &rhs) : ptr(rhs.ptr)
+    {
+        /*
+         * Copy construction takes advantage of the fact that the original
+         * is already inserted, and simply adds itself to whatever list the
+         * original was on - no JSRuntime pointer needed.
+         */
+        rhs.setNext(this);
+    }
+
+    /*
+     * Important: Return a reference here so passing a Rooted<T> to
+     * something that takes a |const T&| is not a GC hazard.
+     */
+    operator const T&() const { return ptr; }
+    T operator->() const { return ptr; }
+    T *address() { return &ptr; }
+    const T *address() const { return &ptr; }
+    T &get() { return ptr; }
+    const T &get() const { return ptr; }
+
+    T &operator=(T value) {
+        MOZ_ASSERT(!js::GCMethods<T>::poisoned(value));
+        ptr = value;
+        return ptr;
+    }
+
+    T &operator=(const PersistentRooted &value) {
+        ptr = value;
+        return ptr;
+    }
+
+    void set(T value) {
+        MOZ_ASSERT(!js::GCMethods<T>::poisoned(value));
+        ptr = value;
+    }
+
+    bool operator!=(const T &other) const { return ptr != other; }
+    bool operator==(const T &other) const { return ptr == other; }
+
+  private:
+    T ptr;
+};
+
+} /* namespace JS */
+
+namespace js {
+
+/* Base class for automatic read-only object rooting during compilation. */
+class CompilerRootNode
+{
+  protected:
+    CompilerRootNode(js::gc::Cell *ptr) : next(nullptr), ptr_(ptr) {}
+
+  public:
+    void **address() { return (void **)&ptr_; }
+
+  public:
+    CompilerRootNode *next;
+
+  protected:
+    js::gc::Cell *ptr_;
+};
+
+}  /* namespace js */
+
+#endif  /* js_RootingAPI_h */