palemoon27/js/src/vm/ArrayBufferObject.cpp

/* -*- 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/. */

#include "vm/ArrayBufferObject.h"

#include "mozilla/Alignment.h"
#include "mozilla/FloatingPoint.h"
#include "mozilla/PodOperations.h"
#include "mozilla/TaggedAnonymousMemory.h"

#include <string.h>
#ifndef XP_WIN
# include <sys/mman.h>
#endif

#ifdef MOZ_VALGRIND
# include <valgrind/memcheck.h>
#endif

#include "jsapi.h"
#include "jsarray.h"
#include "jscntxt.h"
#include "jscpucfg.h"
#include "jsfriendapi.h"
#include "jsnum.h"
#include "jsobj.h"
#include "jstypes.h"
#include "jsutil.h"
#ifdef XP_WIN
# include "jswin.h"
#endif
#include "jswrapper.h"

#include "asmjs/Wasm.h"
#include "gc/Barrier.h"
#include "gc/Marking.h"
#include "gc/Memory.h"
#include "js/Conversions.h"
#include "js/MemoryMetrics.h"
#include "vm/GlobalObject.h"
#include "vm/Interpreter.h"
#include "vm/SharedArrayObject.h"
#include "vm/WrapperObject.h"

#include "jsatominlines.h"

#include "vm/NativeObject-inl.h"
#include "vm/Shape-inl.h"

using JS::ToInt32;

using mozilla::DebugOnly;

using namespace js;
using namespace js::gc;

/*
 * Convert |v| to an array index for an array of length |length| per
 * the Typed Array Specification section 7.0, |subarray|. If successful,
 * the output value is in the range [0, length].
 */
bool
js::ToClampedIndex(JSContext* cx, HandleValue v, uint32_t length, uint32_t* out)
{
    int32_t result;
    if (!ToInt32(cx, v, &result))
        return false;
    if (result < 0) {
        result += length;
        if (result < 0)
            result = 0;
    } else if (uint32_t(result) > length) {
        result = length;
    }
    *out = uint32_t(result);
    return true;
}

/*
 * ArrayBufferObject
 *
 * This class holds the underlying raw buffer that the TypedArrayObject classes
 * access.  It can be created explicitly and passed to a TypedArrayObject, or
 * can be created implicitly by constructing a TypedArrayObject with a size.
 */

/*
 * ArrayBufferObject (base)
 */

const Class ArrayBufferObject::protoClass = {
    "ArrayBufferPrototype",
    JSCLASS_HAS_CACHED_PROTO(JSProto_ArrayBuffer)
};

const ClassOps ArrayBufferObject::classOps_ = {
    nullptr,        /* addProperty */
    nullptr,        /* delProperty */
    nullptr,        /* getProperty */
    nullptr,        /* setProperty */
    nullptr,        /* enumerate */
    nullptr,        /* resolve */
    nullptr,        /* mayResolve */
    ArrayBufferObject::finalize,
    nullptr,        /* call        */
    nullptr,        /* hasInstance */
    nullptr,        /* construct   */
    ArrayBufferObject::trace,
};

static const ClassExtension ArrayBufferObjectClassExtension = {
    nullptr,    /* weakmapKeyDelegateOp */
    ArrayBufferObject::objectMoved
};

const Class ArrayBufferObject::class_ = {
    "ArrayBuffer",
    JSCLASS_DELAY_METADATA_BUILDER |
    JSCLASS_HAS_RESERVED_SLOTS(RESERVED_SLOTS) |
    JSCLASS_HAS_CACHED_PROTO(JSProto_ArrayBuffer) |
    JSCLASS_BACKGROUND_FINALIZE,
    &ArrayBufferObject::classOps_,
    JS_NULL_CLASS_SPEC,
    &ArrayBufferObjectClassExtension
};

const JSFunctionSpec ArrayBufferObject::jsfuncs[] = {
    JS_SELF_HOSTED_FN("slice", "ArrayBufferSlice", 2,0),
    JS_FS_END
};

const JSFunctionSpec ArrayBufferObject::jsstaticfuncs[] = {
    JS_FN("isView", ArrayBufferObject::fun_isView, 1, 0),
    JS_SELF_HOSTED_FN("slice", "ArrayBufferStaticSlice", 3,0),
    JS_FS_END
};

const JSPropertySpec ArrayBufferObject::jsstaticprops[] = {
    JS_SELF_HOSTED_SYM_GET(species, "ArrayBufferSpecies", 0),
    JS_PS_END
};

bool
js::IsArrayBuffer(HandleValue v)
{
    return v.isObject() && v.toObject().is<ArrayBufferObject>();
}

bool
js::IsArrayBuffer(HandleObject obj)
{
    return obj->is<ArrayBufferObject>();
}

bool
js::IsArrayBuffer(JSObject* obj)
{
    return obj->is<ArrayBufferObject>();
}

ArrayBufferObject&
js::AsArrayBuffer(HandleObject obj)
{
    MOZ_ASSERT(IsArrayBuffer(obj));
    return obj->as<ArrayBufferObject>();
}

ArrayBufferObject&
js::AsArrayBuffer(JSObject* obj)
{
    MOZ_ASSERT(IsArrayBuffer(obj));
    return obj->as<ArrayBufferObject>();
}

MOZ_ALWAYS_INLINE bool
ArrayBufferObject::byteLengthGetterImpl(JSContext* cx, const CallArgs& args)
{
    MOZ_ASSERT(IsArrayBuffer(args.thisv()));
    args.rval().setInt32(args.thisv().toObject().as<ArrayBufferObject>().byteLength());
    return true;
}

bool
ArrayBufferObject::byteLengthGetter(JSContext* cx, unsigned argc, Value* vp)
{
    CallArgs args = CallArgsFromVp(argc, vp);
    return CallNonGenericMethod<IsArrayBuffer, byteLengthGetterImpl>(cx, args);
}

/*
 * ArrayBuffer.isView(obj); ES6 (Dec 2013 draft) 24.1.3.1
 */
bool
ArrayBufferObject::fun_isView(JSContext* cx, unsigned argc, Value* vp)
{
    CallArgs args = CallArgsFromVp(argc, vp);
    args.rval().setBoolean(args.get(0).isObject() &&
                           JS_IsArrayBufferViewObject(&args.get(0).toObject()));
    return true;
}

/*
 * new ArrayBuffer(byteLength)
 */
bool
ArrayBufferObject::class_constructor(JSContext* cx, unsigned argc, Value* vp)
{
    CallArgs args = CallArgsFromVp(argc, vp);

    if (!ThrowIfNotConstructing(cx, args, "ArrayBuffer"))
        return false;

    int32_t nbytes = 0;
    if (argc > 0 && !ToInt32(cx, args[0], &nbytes))
        return false;

    if (nbytes < 0) {
        /*
         * We're just not going to support arrays that are bigger than what will fit
         * as an integer value; if someone actually ever complains (validly), then we
         * can fix.
         */
        JS_ReportErrorNumber(cx, GetErrorMessage, nullptr, JSMSG_BAD_ARRAY_LENGTH);
        return false;
    }

    RootedObject proto(cx);
    RootedObject newTarget(cx, &args.newTarget().toObject());
    if (!GetPrototypeFromConstructor(cx, newTarget, &proto))
        return false;

    JSObject* bufobj = create(cx, uint32_t(nbytes), proto);
    if (!bufobj)
        return false;
    args.rval().setObject(*bufobj);
    return true;
}

static ArrayBufferObject::BufferContents
AllocateArrayBufferContents(JSContext* cx, uint32_t nbytes)
{
    uint8_t* p = cx->runtime()->pod_callocCanGC<uint8_t>(nbytes);
    if (!p)
        ReportOutOfMemory(cx);

    return ArrayBufferObject::BufferContents::create<ArrayBufferObject::PLAIN>(p);
}

static void
NoteViewBufferWasDetached(ArrayBufferViewObject* view,
                          ArrayBufferObject::BufferContents newContents,
                          JSContext* cx)
{
    view->notifyBufferDetached(newContents.data());

    // Notify compiled jit code that the base pointer has moved.
    MarkObjectStateChange(cx, view);
}

/* static */ bool
ArrayBufferObject::detach(JSContext* cx, Handle<ArrayBufferObject*> buffer,
                          BufferContents newContents)
{
    if (buffer->isWasm()) {
        JS_ReportErrorNumber(cx, GetErrorMessage, nullptr, JSMSG_OUT_OF_MEMORY);
        return false;
    }

    // When detaching buffers where we don't know all views, the new data must
    // match the old data. All missing views are typed objects, which do not
    // expect their data to ever change.
    MOZ_ASSERT_IF(buffer->forInlineTypedObject(),
                  newContents.data() == buffer->dataPointer());

    // When detaching a buffer with typed object views, any jitcode accessing
    // such views must be deoptimized so that detachment checks are performed.
    // This is done by setting a compartment-wide flag indicating that buffers
    // with typed object views have been detached.
    if (buffer->hasTypedObjectViews()) {
        // Make sure the global object's group has been instantiated, so the
        // flag change will be observed.
        AutoEnterOOMUnsafeRegion oomUnsafe;
        if (!cx->global()->getGroup(cx))
            oomUnsafe.crash("ArrayBufferObject::detach");
        MarkObjectGroupFlags(cx, cx->global(), OBJECT_FLAG_TYPED_OBJECT_HAS_DETACHED_BUFFER);
        cx->compartment()->detachedTypedObjects = 1;
    }

    // Update all views of the buffer to account for the buffer having been
    // detached, and clear the buffer's data and list of views.

    if (InnerViewTable::ViewVector* views = cx->compartment()->innerViews.maybeViewsUnbarriered(buffer)) {
        for (size_t i = 0; i < views->length(); i++)
            NoteViewBufferWasDetached((*views)[i], newContents, cx);
        cx->compartment()->innerViews.removeViews(buffer);
    }
    if (buffer->firstView()) {
        if (buffer->forInlineTypedObject()) {
            // The buffer points to inline data in its first view, so to keep
            // this pointer alive we don't clear out the first view.
            MOZ_ASSERT(buffer->firstView()->is<InlineTransparentTypedObject>());
        } else {
            NoteViewBufferWasDetached(buffer->firstView(), newContents, cx);
            buffer->setFirstView(nullptr);
        }
    }

    if (newContents.data() != buffer->dataPointer())
        buffer->setNewOwnedData(cx->runtime()->defaultFreeOp(), newContents);

    buffer->setByteLength(0);
    buffer->setIsDetached();
    return true;
}

void
ArrayBufferObject::setNewOwnedData(FreeOp* fop, BufferContents newContents)
{
    if (ownsData()) {
        MOZ_ASSERT(newContents.data() != dataPointer());
        releaseData(fop);
    }

    setDataPointer(newContents, OwnsData);
}

// This is called *only* from changeContents(), below.
// By construction, every view parameter will be mapping unshared memory (an ArrayBuffer).
// Hence no reason to worry about shared memory here.

void
ArrayBufferObject::changeViewContents(JSContext* cx, ArrayBufferViewObject* view,
                                      uint8_t* oldDataPointer, BufferContents newContents)
{
    MOZ_ASSERT(!view->isSharedMemory());

    // Watch out for NULL data pointers in views. This means that the view
    // is not fully initialized (in which case it'll be initialized later
    // with the correct pointer).
    uint8_t* viewDataPointer = view->dataPointerUnshared();
    if (viewDataPointer) {
        MOZ_ASSERT(newContents);
        ptrdiff_t offset = viewDataPointer - oldDataPointer;
        viewDataPointer = static_cast<uint8_t*>(newContents.data()) + offset;
        view->setDataPointerUnshared(viewDataPointer);
    }

    // Notify compiled jit code that the base pointer has moved.
    MarkObjectStateChange(cx, view);
}

// BufferContents is specific to ArrayBuffer, hence it will not represent shared memory.

void
ArrayBufferObject::changeContents(JSContext* cx, BufferContents newContents)
{
    MOZ_ASSERT(!forInlineTypedObject());

    // Change buffer contents.
    uint8_t* oldDataPointer = dataPointer();
    setNewOwnedData(cx->runtime()->defaultFreeOp(), newContents);

    // Update all views.
    if (InnerViewTable::ViewVector* views = cx->compartment()->innerViews.maybeViewsUnbarriered(this)) {
        for (size_t i = 0; i < views->length(); i++)
            changeViewContents(cx, (*views)[i], oldDataPointer, newContents);
    }
    if (firstView())
        changeViewContents(cx, firstView(), oldDataPointer, newContents);
}

#ifdef ASMJS_MAY_USE_SIGNAL_HANDLERS_FOR_OOB
# ifdef XP_WIN
static void*
AllocateWasmMappedMemory(uint32_t numBytes)
{
    MOZ_ASSERT(numBytes % wasm::PageSize == 0);

    void* data = VirtualAlloc(nullptr, wasm::MappedSize, MEM_RESERVE, PAGE_NOACCESS);
    if (!data)
        return nullptr;

    if (numBytes && !VirtualAlloc(data, numBytes, MEM_COMMIT, PAGE_READWRITE)) {
        VirtualFree(data, 0, MEM_RELEASE);
        return nullptr;
    }

    MemProfiler::SampleNative(data, numBytes);

    return data;
}

static void
ReleaseWasmMappedMemory(void* base)
{
    VirtualFree(base, 0, MEM_RELEASE);
    MemProfiler::RemoveNative(base);
}
# else  // XP_WIN
static void*
AllocateWasmMappedMemory(uint32_t numBytes)
{
    void* data = MozTaggedAnonymousMmap(nullptr, wasm::MappedSize, PROT_NONE,
                                        MAP_PRIVATE | MAP_ANON, -1, 0, "wasm-reserved");
    if (data == MAP_FAILED)
        return nullptr;

    if (numBytes && mprotect(data, numBytes, PROT_READ | PROT_WRITE)) {
        munmap(data, wasm::MappedSize);
        return nullptr;
    }

    MemProfiler::SampleNative(data, numBytes);

#  if defined(MOZ_VALGRIND) && defined(VALGRIND_DISABLE_ADDR_ERROR_REPORTING_IN_RANGE)
    VALGRIND_DISABLE_ADDR_ERROR_REPORTING_IN_RANGE((unsigned char*)data + numBytes,
                                                   wasm::MappedSize - numBytes);
#  endif

    return data;
}

static void
ReleaseWasmMappedMemory(void* base)
{
    munmap(base, wasm::MappedSize);
    MemProfiler::RemoveNative(base);

#  if defined(MOZ_VALGRIND) && defined(VALGRIND_ENABLE_ADDR_ERROR_REPORTING_IN_RANGE)
    VALGRIND_ENABLE_ADDR_ERROR_REPORTING_IN_RANGE(base, wasm::MappedSize);
#  endif
}
# endif  // !XP_WIN
#endif  // ASMJS_MAY_USE_SIGNAL_HANDLERS_FOR_OOB

/* static */ ArrayBufferObject*
ArrayBufferObject::createForWasm(JSContext* cx, uint32_t numBytes, bool signalsForOOB)
{
    MOZ_ASSERT(numBytes % wasm::PageSize == 0);

    if (signalsForOOB) {
#ifdef ASMJS_MAY_USE_SIGNAL_HANDLERS_FOR_OOB
        void* data = AllocateWasmMappedMemory(numBytes);
        if (!data) {
            ReportOutOfMemory(cx);
            return nullptr;
        }

        BufferContents contents = BufferContents::create<WASM_MAPPED>(data);
        ArrayBufferObject* buffer = ArrayBufferObject::create(cx, numBytes, contents);
        if (!buffer) {
            ReleaseWasmMappedMemory(data);
            return nullptr;
        }

        return buffer;
#else
        MOZ_CRASH("shouldn't be using signal handlers for out-of-bounds");
#endif
    }

    auto buffer = ArrayBufferObject::create(cx, numBytes);
    if (!buffer)
        return nullptr;

    buffer->setIsWasmMalloced();
    return buffer;
}

/* static */ bool
ArrayBufferObject::prepareForAsmJS(JSContext* cx, Handle<ArrayBufferObject*> buffer, bool signalsForOOB)
{
    MOZ_ASSERT(buffer->byteLength() % wasm::PageSize == 0);

    if (signalsForOOB) {
#ifdef ASMJS_MAY_USE_SIGNAL_HANDLERS_FOR_OOB
        if (buffer->isWasmMapped())
            return true;

        // This can't happen except via the shell toggling signals.enabled.
        if (buffer->isWasmMalloced()) {
            JS_ReportError(cx, "can't access same buffer with and without signals enabled");
            return false;
        }

        if (buffer->forInlineTypedObject()) {
            JS_ReportError(cx, "ArrayBuffer can't be used by asm.js");
            return false;
        }

        void* data = AllocateWasmMappedMemory(buffer->byteLength());
        if (!data) {
            ReportOutOfMemory(cx);
            return false;
        }

        // Copy over the current contents of the typed array.
        memcpy(data, buffer->dataPointer(), buffer->byteLength());

        // Swap the new elements into the ArrayBufferObject. Mark the
        // ArrayBufferObject so we don't do this again.
        BufferContents newContents = BufferContents::create<WASM_MAPPED>(data);
        buffer->changeContents(cx, newContents);
        MOZ_ASSERT(data == buffer->dataPointer());
        return true;
#else
        MOZ_CRASH("shouldn't be using signal handlers for out-of-bounds");
#endif  // ASMJS_MAY_USE_SIGNAL_HANDLERS_FOR_OOB
    }

    if (buffer->forInlineTypedObject()) {
        JS_ReportError(cx, "ArrayBuffer can't be used by asm.js");
        return false;
    }

    if (!buffer->ownsData()) {
        BufferContents contents = AllocateArrayBufferContents(cx, buffer->byteLength());
        if (!contents)
            return false;
        memcpy(contents.data(), buffer->dataPointer(), buffer->byteLength());
        buffer->changeContents(cx, contents);
    }

    buffer->setIsWasmMalloced();
    return true;
}

ArrayBufferObject::BufferContents
ArrayBufferObject::createMappedContents(int fd, size_t offset, size_t length)
{
    void* data = AllocateMappedContent(fd, offset, length, ARRAY_BUFFER_ALIGNMENT);
    MemProfiler::SampleNative(data, length);
    return BufferContents::create<MAPPED>(data);
}

uint8_t*
ArrayBufferObject::inlineDataPointer() const
{
    return static_cast<uint8_t*>(fixedData(JSCLASS_RESERVED_SLOTS(&class_)));
}

uint8_t*
ArrayBufferObject::dataPointer() const
{
    return static_cast<uint8_t*>(getSlot(DATA_SLOT).toPrivate());
}

SharedMem<uint8_t*>
ArrayBufferObject::dataPointerShared() const
{
    return SharedMem<uint8_t*>::unshared(getSlot(DATA_SLOT).toPrivate());
}

void
ArrayBufferObject::releaseData(FreeOp* fop)
{
    MOZ_ASSERT(ownsData());

    switch (bufferKind()) {
      case PLAIN:
      case WASM_MALLOCED:
        fop->free_(dataPointer());
        break;
      case MAPPED:
        MemProfiler::RemoveNative(dataPointer());
        DeallocateMappedContent(dataPointer(), byteLength());
        break;
      case WASM_MAPPED:
#ifdef ASMJS_MAY_USE_SIGNAL_HANDLERS_FOR_OOB
        ReleaseWasmMappedMemory(dataPointer());
#else
        MOZ_CRASH("shouldn't have wasm mapped ArrayBuffer");
#endif
        break;
    }
}

void
ArrayBufferObject::setDataPointer(BufferContents contents, OwnsState ownsData)
{
    setSlot(DATA_SLOT, PrivateValue(contents.data()));
    setOwnsData(ownsData);
    setFlags((flags() & ~KIND_MASK) | contents.kind());
}

uint32_t
ArrayBufferObject::byteLength() const
{
    return getSlot(BYTE_LENGTH_SLOT).toInt32();
}

void
ArrayBufferObject::setByteLength(uint32_t length)
{
    MOZ_ASSERT(length <= INT32_MAX);
    setSlot(BYTE_LENGTH_SLOT, Int32Value(length));
}

uint32_t
ArrayBufferObject::flags() const
{
    return uint32_t(getSlot(FLAGS_SLOT).toInt32());
}

void
ArrayBufferObject::setFlags(uint32_t flags)
{
    setSlot(FLAGS_SLOT, Int32Value(flags));
}

ArrayBufferObject*
ArrayBufferObject::create(JSContext* cx, uint32_t nbytes, BufferContents contents,
                          OwnsState ownsState /* = OwnsData */,
                          HandleObject proto /* = nullptr */,
                          NewObjectKind newKind /* = GenericObject */)
{
    MOZ_ASSERT_IF(contents.kind() == MAPPED, contents);

    // If we need to allocate data, try to use a larger object size class so
    // that the array buffer's data can be allocated inline with the object.
    // The extra space will be left unused by the object's fixed slots and
    // available for the buffer's data, see NewObject().
    size_t reservedSlots = JSCLASS_RESERVED_SLOTS(&class_);

    size_t nslots = reservedSlots;
    bool allocated = false;
    if (contents) {
        if (ownsState == OwnsData) {
            // The ABO is taking ownership, so account the bytes against the zone.
            size_t nAllocated = nbytes;
            if (contents.kind() == MAPPED)
                nAllocated = JS_ROUNDUP(nbytes, js::gc::SystemPageSize());
            cx->zone()->updateMallocCounter(nAllocated);
        }
    } else {
        MOZ_ASSERT(ownsState == OwnsData);
        size_t usableSlots = NativeObject::MAX_FIXED_SLOTS - reservedSlots;
        if (nbytes <= usableSlots * sizeof(Value)) {
            int newSlots = (nbytes - 1) / sizeof(Value) + 1;
            MOZ_ASSERT(int(nbytes) <= newSlots * int(sizeof(Value)));
            nslots = reservedSlots + newSlots;
            contents = BufferContents::createPlain(nullptr);
        } else {
            contents = AllocateArrayBufferContents(cx, nbytes);
            if (!contents)
                return nullptr;
            allocated = true;
        }
    }

    MOZ_ASSERT(!(class_.flags & JSCLASS_HAS_PRIVATE));
    gc::AllocKind allocKind = GetGCObjectKind(nslots);

    AutoSetNewObjectMetadata metadata(cx);
    Rooted<ArrayBufferObject*> obj(cx,
        NewObjectWithClassProto<ArrayBufferObject>(cx, proto, allocKind, newKind));
    if (!obj) {
        if (allocated)
            js_free(contents.data());
        return nullptr;
    }

    MOZ_ASSERT(obj->getClass() == &class_);
    MOZ_ASSERT(!gc::IsInsideNursery(obj));

    if (!contents) {
        void* data = obj->inlineDataPointer();
        memset(data, 0, nbytes);
        obj->initialize(nbytes, BufferContents::createPlain(data), DoesntOwnData);
    } else {
        obj->initialize(nbytes, contents, ownsState);
    }

    return obj;
}

ArrayBufferObject*
ArrayBufferObject::create(JSContext* cx, uint32_t nbytes,
                          HandleObject proto /* = nullptr */,
                          NewObjectKind newKind /* = GenericObject */)
{
    return create(cx, nbytes, BufferContents::createPlain(nullptr),
                  OwnsState::OwnsData, proto);
}

bool
ArrayBufferObject::createDataViewForThisImpl(JSContext* cx, const CallArgs& args)
{
    MOZ_ASSERT(IsArrayBuffer(args.thisv()));

    /*
     * This method is only called for |DataView(alienBuf, ...)| which calls
     * this as |createDataViewForThis.call(alienBuf, byteOffset, byteLength,
     *                                     DataView.prototype)|,
     * ergo there must be exactly 3 arguments.
     */
    MOZ_ASSERT(args.length() == 3);

    uint32_t byteOffset = args[0].toPrivateUint32();
    uint32_t byteLength = args[1].toPrivateUint32();
    Rooted<ArrayBufferObject*> buffer(cx, &args.thisv().toObject().as<ArrayBufferObject>());

    /*
     * Pop off the passed-along prototype and delegate to normal DataViewObject
     * construction.
     */
    JSObject* obj = DataViewObject::create(cx, byteOffset, byteLength, buffer, &args[2].toObject());
    if (!obj)
        return false;
    args.rval().setObject(*obj);
    return true;
}

bool
ArrayBufferObject::createDataViewForThis(JSContext* cx, unsigned argc, Value* vp)
{
    CallArgs args = CallArgsFromVp(argc, vp);
    return CallNonGenericMethod<IsArrayBuffer, createDataViewForThisImpl>(cx, args);
}

/* static */ ArrayBufferObject::BufferContents
ArrayBufferObject::stealContents(JSContext* cx, Handle<ArrayBufferObject*> buffer,
                                 bool hasStealableContents)
{
    MOZ_ASSERT_IF(hasStealableContents, buffer->hasStealableContents());
    assertSameCompartment(cx, buffer);

    BufferContents oldContents(buffer->dataPointer(), buffer->bufferKind());
    BufferContents newContents = AllocateArrayBufferContents(cx, buffer->byteLength());
    if (!newContents)
        return BufferContents::createPlain(nullptr);

    if (hasStealableContents) {
        // Return the old contents and give the detached buffer a pointer to
        // freshly allocated memory that we will never write to and should
        // never get committed.
        buffer->setOwnsData(DoesntOwnData);
        if (!ArrayBufferObject::detach(cx, buffer, newContents)) {
            js_free(newContents.data());
            return BufferContents::createPlain(nullptr);
        }
        return oldContents;
    }

    // Create a new chunk of memory to return since we cannot steal the
    // existing contents away from the buffer.
    memcpy(newContents.data(), oldContents.data(), buffer->byteLength());
    if (!ArrayBufferObject::detach(cx, buffer, oldContents)) {
        js_free(newContents.data());
        return BufferContents::createPlain(nullptr);
    }
    return newContents;
}

/* static */ void
ArrayBufferObject::addSizeOfExcludingThis(JSObject* obj, mozilla::MallocSizeOf mallocSizeOf,
                                          JS::ClassInfo* info)
{
    ArrayBufferObject& buffer = AsArrayBuffer(obj);

    if (!buffer.ownsData())
        return;

    switch (buffer.bufferKind()) {
      case PLAIN:
        info->objectsMallocHeapElementsNormal += mallocSizeOf(buffer.dataPointer());
        break;
      case MAPPED:
        info->objectsNonHeapElementsNormal += buffer.byteLength();
        break;
      case WASM_MALLOCED:
        info->objectsMallocHeapElementsAsmJS += mallocSizeOf(buffer.dataPointer());
        break;
      case WASM_MAPPED:
        info->objectsNonHeapElementsAsmJS += buffer.byteLength();
        break;
    }
}

/* static */ void
ArrayBufferObject::finalize(FreeOp* fop, JSObject* obj)
{
    ArrayBufferObject& buffer = obj->as<ArrayBufferObject>();

    if (buffer.ownsData())
        buffer.releaseData(fop);
}

/* static */ void
ArrayBufferObject::copyData(Handle<ArrayBufferObject*> toBuffer,
                            Handle<ArrayBufferObject*> fromBuffer,
                            uint32_t fromIndex, uint32_t count)
{
    MOZ_ASSERT(toBuffer->byteLength() >= count);
    MOZ_ASSERT(fromBuffer->byteLength() >= fromIndex);
    MOZ_ASSERT(fromBuffer->byteLength() >= fromIndex + count);

    memcpy(toBuffer->dataPointer(), fromBuffer->dataPointer() + fromIndex, count);
}

/* static */ void
ArrayBufferObject::trace(JSTracer* trc, JSObject* obj)
{
    // If this buffer is associated with an inline typed object,
    // fix up the data pointer if the typed object was moved.
    ArrayBufferObject& buf = obj->as<ArrayBufferObject>();

    if (!buf.forInlineTypedObject())
        return;

    JSObject* view = MaybeForwarded(buf.firstView());
    MOZ_ASSERT(view && view->is<InlineTransparentTypedObject>());

    TraceManuallyBarrieredEdge(trc, &view, "array buffer inline typed object owner");
    buf.setSlot(DATA_SLOT, PrivateValue(view->as<InlineTransparentTypedObject>().inlineTypedMem()));
}

/* static */ void
ArrayBufferObject::objectMoved(JSObject* obj, const JSObject* old)
{
    ArrayBufferObject& dst = obj->as<ArrayBufferObject>();
    const ArrayBufferObject& src = old->as<ArrayBufferObject>();

    // Fix up possible inline data pointer.
    if (src.hasInlineData())
        dst.setSlot(DATA_SLOT, PrivateValue(dst.inlineDataPointer()));
}

ArrayBufferViewObject*
ArrayBufferObject::firstView()
{
    return getSlot(FIRST_VIEW_SLOT).isObject()
        ? static_cast<ArrayBufferViewObject*>(&getSlot(FIRST_VIEW_SLOT).toObject())
        : nullptr;
}

void
ArrayBufferObject::setFirstView(ArrayBufferViewObject* view)
{
    setSlot(FIRST_VIEW_SLOT, ObjectOrNullValue(view));
}

bool
ArrayBufferObject::addView(JSContext* cx, JSObject* viewArg)
{
    // Note: we don't pass in an ArrayBufferViewObject as the argument due to
    // tricky inheritance in the various view classes. View classes do not
    // inherit from ArrayBufferViewObject so won't be upcast automatically.
    MOZ_ASSERT(viewArg->is<ArrayBufferViewObject>() || viewArg->is<TypedObject>());
    ArrayBufferViewObject* view = static_cast<ArrayBufferViewObject*>(viewArg);

    if (!firstView()) {
        setFirstView(view);
        return true;
    }
    return cx->compartment()->innerViews.addView(cx, this, view);
}

/*
 * InnerViewTable
 */

static size_t VIEW_LIST_MAX_LENGTH = 500;

bool
InnerViewTable::addView(JSContext* cx, ArrayBufferObject* buffer, ArrayBufferViewObject* view)
{
    // ArrayBufferObject entries are only added when there are multiple views.
    MOZ_ASSERT(buffer->firstView());

    if (!map.initialized() && !map.init()) {
        ReportOutOfMemory(cx);
        return false;
    }

    Map::AddPtr p = map.lookupForAdd(buffer);

    MOZ_ASSERT(!gc::IsInsideNursery(buffer));
    bool addToNursery = nurseryKeysValid && gc::IsInsideNursery(view);

    if (p) {
        ViewVector& views = p->value();
        MOZ_ASSERT(!views.empty());

        if (addToNursery) {
            // Only add the entry to |nurseryKeys| if it isn't already there.
            if (views.length() >= VIEW_LIST_MAX_LENGTH) {
                // To avoid quadratic blowup, skip the loop below if we end up
                // adding enormous numbers of views for the same object.
                nurseryKeysValid = false;
            } else {
                for (size_t i = 0; i < views.length(); i++) {
                    if (gc::IsInsideNursery(views[i])) {
                        addToNursery = false;
                        break;
                    }
                }
            }
        }

        if (!views.append(view)) {
            ReportOutOfMemory(cx);
            return false;
        }
    } else {
        if (!map.add(p, buffer, ViewVector())) {
            ReportOutOfMemory(cx);
            return false;
        }
        // ViewVector has one inline element, so the first insertion is
        // guaranteed to succeed.
        MOZ_ALWAYS_TRUE(p->value().append(view));
    }

    if (addToNursery && !nurseryKeys.append(buffer))
        nurseryKeysValid = false;

    return true;
}

InnerViewTable::ViewVector*
InnerViewTable::maybeViewsUnbarriered(ArrayBufferObject* buffer)
{
    if (!map.initialized())
        return nullptr;

    Map::Ptr p = map.lookup(buffer);
    if (p)
        return &p->value();
    return nullptr;
}

void
InnerViewTable::removeViews(ArrayBufferObject* buffer)
{
    Map::Ptr p = map.lookup(buffer);
    MOZ_ASSERT(p);

    map.remove(p);
}

/* static */ bool
InnerViewTable::sweepEntry(JSObject** pkey, ViewVector& views)
{
    if (IsAboutToBeFinalizedUnbarriered(pkey))
        return true;

    MOZ_ASSERT(!views.empty());
    for (size_t i = 0; i < views.length(); i++) {
        if (IsAboutToBeFinalizedUnbarriered(&views[i])) {
            views[i--] = views.back();
            views.popBack();
        }
    }

    return views.empty();
}

void
InnerViewTable::sweep()
{
    MOZ_ASSERT(nurseryKeys.empty());
    map.sweep();
}

void
InnerViewTable::sweepAfterMinorGC()
{
    MOZ_ASSERT(needsSweepAfterMinorGC());

    if (nurseryKeysValid) {
        for (size_t i = 0; i < nurseryKeys.length(); i++) {
            JSObject* buffer = MaybeForwarded(nurseryKeys[i]);
            Map::Ptr p = map.lookup(buffer);
            if (!p)
                continue;

            if (sweepEntry(&p->mutableKey(), p->value()))
                map.remove(buffer);
        }
        nurseryKeys.clear();
    } else {
        // Do the required sweeping by looking at every map entry.
        nurseryKeys.clear();
        sweep();

        nurseryKeysValid = true;
    }
}

size_t
InnerViewTable::sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf)
{
    if (!map.initialized())
        return 0;

    size_t vectorSize = 0;
    for (Map::Enum e(map); !e.empty(); e.popFront())
        vectorSize += e.front().value().sizeOfExcludingThis(mallocSizeOf);

    return vectorSize
         + map.sizeOfExcludingThis(mallocSizeOf)
         + nurseryKeys.sizeOfExcludingThis(mallocSizeOf);
}

/*
 * ArrayBufferViewObject
 */

/*
 * This method is used to trace TypedArrayObjects and DataViewObjects. We need
 * a custom tracer to move the object's data pointer if its owner was moved and
 * stores its data inline.
 */
/* static */ void
ArrayBufferViewObject::trace(JSTracer* trc, JSObject* objArg)
{
    NativeObject* obj = &objArg->as<NativeObject>();
    HeapSlot& bufSlot = obj->getFixedSlotRef(TypedArrayObject::BUFFER_SLOT);
    TraceEdge(trc, &bufSlot, "typedarray.buffer");

    // Update obj's data pointer if it moved.
    if (bufSlot.isObject()) {
        if (IsArrayBuffer(&bufSlot.toObject())) {
            ArrayBufferObject& buf = AsArrayBuffer(MaybeForwarded(&bufSlot.toObject()));
            uint32_t offset = uint32_t(obj->getFixedSlot(TypedArrayObject::BYTEOFFSET_SLOT).toInt32());
            MOZ_ASSERT(buf.dataPointer() != nullptr);
            MOZ_ASSERT(offset <= INT32_MAX);

            if (buf.forInlineTypedObject()) {
                // The data is inline with an InlineTypedObject associated with the
                // buffer. Get a new address for the typed object if it moved.
                JSObject* view = buf.firstView();

                // Mark the object to move it into the tenured space.
                TraceManuallyBarrieredEdge(trc, &view, "typed array nursery owner");
                MOZ_ASSERT(view->is<InlineTypedObject>());
                MOZ_ASSERT(view != obj);

                void* srcData = obj->getPrivate();
                void* dstData = view->as<InlineTypedObject>().inlineTypedMem() + offset;
                obj->setPrivateUnbarriered(dstData);

                // We can't use a direct forwarding pointer here, as there might
                // not be enough bytes available, and other views might have data
                // pointers whose forwarding pointers would overlap this one.
                trc->runtime()->gc.nursery.maybeSetForwardingPointer(trc, srcData, dstData,
                                                                     /* direct = */ false);
            } else {
                // The data may or may not be inline with the buffer. The buffer
                // can only move during a compacting GC, in which case its
                // objectMoved hook has already updated the buffer's data pointer.
                obj->initPrivate(buf.dataPointer() + offset);
            }
        }
    }
}

template <>
bool
JSObject::is<js::ArrayBufferViewObject>() const
{
    return is<DataViewObject>() || is<TypedArrayObject>();
}

template <>
bool
JSObject::is<js::ArrayBufferObjectMaybeShared>() const
{
    return is<ArrayBufferObject>() || is<SharedArrayBufferObject>();
}

void
ArrayBufferViewObject::notifyBufferDetached(void* newData)
{
    MOZ_ASSERT(newData != nullptr);
    if (is<DataViewObject>()) {
        as<DataViewObject>().notifyBufferDetached(newData);
    } else if (is<TypedArrayObject>()) {
        if (as<TypedArrayObject>().isSharedMemory())
            return;
        as<TypedArrayObject>().notifyBufferDetached(newData);
    } else {
        as<OutlineTypedObject>().notifyBufferDetached(newData);
    }
}

uint8_t*
ArrayBufferViewObject::dataPointerUnshared()
{
    if (is<DataViewObject>())
        return static_cast<uint8_t*>(as<DataViewObject>().dataPointer());
    if (is<TypedArrayObject>()) {
        MOZ_ASSERT(!as<TypedArrayObject>().isSharedMemory());
        return static_cast<uint8_t*>(as<TypedArrayObject>().viewDataUnshared());
    }
    return as<TypedObject>().typedMem();
}

#ifdef DEBUG
bool
ArrayBufferViewObject::isSharedMemory()
{
    if (is<TypedArrayObject>())
        return as<TypedArrayObject>().isSharedMemory();
    return false;
}
#endif

void
ArrayBufferViewObject::setDataPointerUnshared(uint8_t* data)
{
    if (is<DataViewObject>()) {
        as<DataViewObject>().setPrivate(data);
    } else if (is<TypedArrayObject>()) {
        MOZ_ASSERT(!as<TypedArrayObject>().isSharedMemory());
        as<TypedArrayObject>().setPrivate(data);
    } else if (is<OutlineTypedObject>()) {
        as<OutlineTypedObject>().setData(data);
    } else {
        MOZ_CRASH();
    }
}

/* static */ ArrayBufferObjectMaybeShared*
ArrayBufferViewObject::bufferObject(JSContext* cx, Handle<ArrayBufferViewObject*> thisObject)
{
    if (thisObject->is<TypedArrayObject>()) {
        Rooted<TypedArrayObject*> typedArray(cx, &thisObject->as<TypedArrayObject>());
        if (!TypedArrayObject::ensureHasBuffer(cx, typedArray))
            return nullptr;
        return thisObject->as<TypedArrayObject>().bufferEither();
    }
    MOZ_ASSERT(thisObject->is<DataViewObject>());
    return &thisObject->as<DataViewObject>().arrayBuffer();
}

/* JS Friend API */

JS_FRIEND_API(bool)
JS_IsArrayBufferViewObject(JSObject* obj)
{
    obj = CheckedUnwrap(obj);
    return obj && obj->is<ArrayBufferViewObject>();
}

JS_FRIEND_API(JSObject*)
js::UnwrapArrayBufferView(JSObject* obj)
{
    if (JSObject* unwrapped = CheckedUnwrap(obj))
        return unwrapped->is<ArrayBufferViewObject>() ? unwrapped : nullptr;
    return nullptr;
}

JS_FRIEND_API(uint32_t)
JS_GetArrayBufferByteLength(JSObject* obj)
{
    obj = CheckedUnwrap(obj);
    return obj ? AsArrayBuffer(obj).byteLength() : 0;
}

JS_FRIEND_API(uint8_t*)
JS_GetArrayBufferData(JSObject* obj, bool* isSharedMemory, const JS::AutoCheckCannotGC&)
{
    obj = CheckedUnwrap(obj);
    if (!obj)
        return nullptr;
    if (!IsArrayBuffer(obj))
        return nullptr;
    *isSharedMemory = false;
    return AsArrayBuffer(obj).dataPointer();
}

JS_FRIEND_API(bool)
JS_DetachArrayBuffer(JSContext* cx, HandleObject obj,
                     DetachDataDisposition changeData)
{
    if (!obj->is<ArrayBufferObject>()) {
        JS_ReportError(cx, "ArrayBuffer object required");
        return false;
    }

    Rooted<ArrayBufferObject*> buffer(cx, &obj->as<ArrayBufferObject>());

    if (changeData == ChangeData && buffer->hasStealableContents()) {
        ArrayBufferObject::BufferContents newContents =
            AllocateArrayBufferContents(cx, buffer->byteLength());
        if (!newContents)
            return false;
        if (!ArrayBufferObject::detach(cx, buffer, newContents)) {
            js_free(newContents.data());
            return false;
        }
    } else {
        if (!ArrayBufferObject::detach(cx, buffer, buffer->contents()))
            return false;
    }

    return true;
}

JS_FRIEND_API(bool)
JS_IsDetachedArrayBufferObject(JSObject* obj)
{
    obj = CheckedUnwrap(obj);
    if (!obj)
        return false;

    return obj->is<ArrayBufferObject>() && obj->as<ArrayBufferObject>().isDetached();
}

JS_FRIEND_API(JSObject*)
JS_NewArrayBuffer(JSContext* cx, uint32_t nbytes)
{
    MOZ_ASSERT(nbytes <= INT32_MAX);
    return ArrayBufferObject::create(cx, nbytes);
}

JS_PUBLIC_API(JSObject*)
JS_NewArrayBufferWithContents(JSContext* cx, size_t nbytes, void* data)
{
    MOZ_ASSERT_IF(!data, nbytes == 0);
    ArrayBufferObject::BufferContents contents =
        ArrayBufferObject::BufferContents::create<ArrayBufferObject::PLAIN>(data);
    return ArrayBufferObject::create(cx, nbytes, contents, ArrayBufferObject::OwnsData,
                                     /* proto = */ nullptr, TenuredObject);
}

JS_FRIEND_API(bool)
JS_IsArrayBufferObject(JSObject* obj)
{
    obj = CheckedUnwrap(obj);
    return obj && obj->is<ArrayBufferObject>();
}

JS_FRIEND_API(bool)
JS_ArrayBufferHasData(JSObject* obj)
{
    return CheckedUnwrap(obj)->as<ArrayBufferObject>().hasData();
}

JS_FRIEND_API(JSObject*)
js::UnwrapArrayBuffer(JSObject* obj)
{
    if (JSObject* unwrapped = CheckedUnwrap(obj))
        return unwrapped->is<ArrayBufferObject>() ? unwrapped : nullptr;
    return nullptr;
}

JS_FRIEND_API(JSObject*)
js::UnwrapSharedArrayBuffer(JSObject* obj)
{
    if (JSObject* unwrapped = CheckedUnwrap(obj))
        return unwrapped->is<SharedArrayBufferObject>() ? unwrapped : nullptr;
    return nullptr;
}

JS_PUBLIC_API(void*)
JS_StealArrayBufferContents(JSContext* cx, HandleObject objArg)
{
    JSObject* obj = CheckedUnwrap(objArg);
    if (!obj)
        return nullptr;

    if (!obj->is<ArrayBufferObject>()) {
        JS_ReportErrorNumber(cx, GetErrorMessage, nullptr, JSMSG_TYPED_ARRAY_BAD_ARGS);
        return nullptr;
    }

    Rooted<ArrayBufferObject*> buffer(cx, &obj->as<ArrayBufferObject>());
    if (buffer->isDetached()) {
        JS_ReportErrorNumber(cx, GetErrorMessage, nullptr, JSMSG_TYPED_ARRAY_DETACHED);
        return nullptr;
    }

    // The caller assumes that a plain malloc'd buffer is returned.
    // hasStealableContents is true for mapped buffers, so we must additionally
    // require that the buffer is plain. In the future, we could consider
    // returning something that handles releasing the memory.
    bool hasStealableContents = buffer->hasStealableContents() && buffer->hasMallocedContents();

    return ArrayBufferObject::stealContents(cx, buffer, hasStealableContents).data();
}

JS_PUBLIC_API(JSObject*)
JS_NewMappedArrayBufferWithContents(JSContext* cx, size_t nbytes, void* data)
{
    MOZ_ASSERT(data);
    ArrayBufferObject::BufferContents contents =
        ArrayBufferObject::BufferContents::create<ArrayBufferObject::MAPPED>(data);
    return ArrayBufferObject::create(cx, nbytes, contents, ArrayBufferObject::OwnsData,
                                     /* proto = */ nullptr, TenuredObject);
}

JS_PUBLIC_API(void*)
JS_CreateMappedArrayBufferContents(int fd, size_t offset, size_t length)
{
    return ArrayBufferObject::createMappedContents(fd, offset, length).data();
}

JS_PUBLIC_API(void)
JS_ReleaseMappedArrayBufferContents(void* contents, size_t length)
{
    MemProfiler::RemoveNative(contents);
    DeallocateMappedContent(contents, length);
}

JS_FRIEND_API(bool)
JS_IsMappedArrayBufferObject(JSObject* obj)
{
    obj = CheckedUnwrap(obj);
    if (!obj)
        return false;

    return obj->is<ArrayBufferObject>() && obj->as<ArrayBufferObject>().isMapped();
}

JS_FRIEND_API(void*)
JS_GetArrayBufferViewData(JSObject* obj, bool* isSharedMemory, const JS::AutoCheckCannotGC&)
{
    obj = CheckedUnwrap(obj);
    if (!obj)
        return nullptr;
    if (obj->is<DataViewObject>()) {
        *isSharedMemory = false;
        return obj->as<DataViewObject>().dataPointer();
    }
    TypedArrayObject& ta = obj->as<TypedArrayObject>();
    *isSharedMemory = ta.isSharedMemory();
    return ta.viewDataEither().unwrap(/*safe - caller sees isShared flag*/);
}

JS_FRIEND_API(JSObject*)
JS_GetArrayBufferViewBuffer(JSContext* cx, HandleObject objArg, bool* isSharedMemory)
{
    JSObject* obj = CheckedUnwrap(objArg);
    if (!obj)
        return nullptr;
    MOZ_ASSERT(obj->is<ArrayBufferViewObject>());

    Rooted<ArrayBufferViewObject*> viewObject(cx, static_cast<ArrayBufferViewObject*>(obj));
    ArrayBufferObjectMaybeShared* buffer = ArrayBufferViewObject::bufferObject(cx, viewObject);
    *isSharedMemory = buffer->is<SharedArrayBufferObject>();
    return buffer;
}

JS_FRIEND_API(uint32_t)
JS_GetArrayBufferViewByteLength(JSObject* obj)
{
    obj = CheckedUnwrap(obj);
    if (!obj)
        return 0;
    return obj->is<DataViewObject>()
           ? obj->as<DataViewObject>().byteLength()
           : obj->as<TypedArrayObject>().byteLength();
}

JS_FRIEND_API(JSObject*)
JS_GetObjectAsArrayBufferView(JSObject* obj, uint32_t* length, bool* isSharedMemory, uint8_t** data)
{
    if (!(obj = CheckedUnwrap(obj)))
        return nullptr;
    if (!(obj->is<ArrayBufferViewObject>()))
        return nullptr;

    js::GetArrayBufferViewLengthAndData(obj, length, isSharedMemory, data);
    return obj;
}

JS_FRIEND_API(void)
js::GetArrayBufferViewLengthAndData(JSObject* obj, uint32_t* length, bool* isSharedMemory, uint8_t** data)
{
    MOZ_ASSERT(obj->is<ArrayBufferViewObject>());

    *length = obj->is<DataViewObject>()
              ? obj->as<DataViewObject>().byteLength()
              : obj->as<TypedArrayObject>().byteLength();

    if (obj->is<DataViewObject>()) {
        *isSharedMemory = false;
        *data = static_cast<uint8_t*>(obj->as<DataViewObject>().dataPointer());
    }
    else {
        TypedArrayObject& ta = obj->as<TypedArrayObject>();
        *isSharedMemory = ta.isSharedMemory();
        *data = static_cast<uint8_t*>(ta.viewDataEither().unwrap(/*safe - caller sees isShared flag*/));
    }
}

JS_FRIEND_API(JSObject*)
JS_GetObjectAsArrayBuffer(JSObject* obj, uint32_t* length, uint8_t** data)
{
    if (!(obj = CheckedUnwrap(obj)))
        return nullptr;
    if (!IsArrayBuffer(obj))
        return nullptr;

    *length = AsArrayBuffer(obj).byteLength();
    *data = AsArrayBuffer(obj).dataPointer();

    return obj;
}

JS_FRIEND_API(void)
js::GetArrayBufferLengthAndData(JSObject* obj, uint32_t* length, bool* isSharedMemory, uint8_t** data)
{
    MOZ_ASSERT(IsArrayBuffer(obj));
    *length = AsArrayBuffer(obj).byteLength();
    *data = AsArrayBuffer(obj).dataPointer();
    *isSharedMemory = false;
}

JSObject*
js::InitArrayBufferClass(JSContext* cx, HandleObject obj)
{
    Rooted<GlobalObject*> global(cx, cx->compartment()->maybeGlobal());
    if (global->isStandardClassResolved(JSProto_ArrayBuffer))
        return &global->getPrototype(JSProto_ArrayBuffer).toObject();

    RootedNativeObject arrayBufferProto(cx, global->createBlankPrototype(cx, &ArrayBufferObject::protoClass));
    if (!arrayBufferProto)
        return nullptr;

    RootedFunction ctor(cx, global->createConstructor(cx, ArrayBufferObject::class_constructor,
                                                      cx->names().ArrayBuffer, 1));
    if (!ctor)
        return nullptr;

    if (!LinkConstructorAndPrototype(cx, ctor, arrayBufferProto))
        return nullptr;

    RootedId byteLengthId(cx, NameToId(cx->names().byteLength));
    RootedAtom atom(cx, IdToFunctionName(cx, byteLengthId, "get"));
    if (!atom)
        return nullptr;
    unsigned attrs = JSPROP_SHARED | JSPROP_GETTER;
    JSObject* getter =
        NewNativeFunction(cx, ArrayBufferObject::byteLengthGetter, 0, atom);
    if (!getter)
        return nullptr;

    if (!NativeDefineProperty(cx, arrayBufferProto, byteLengthId, UndefinedHandleValue,
                              JS_DATA_TO_FUNC_PTR(GetterOp, getter), nullptr, attrs))
        return nullptr;

    if (!JS_DefineFunctions(cx, ctor, ArrayBufferObject::jsstaticfuncs))
        return nullptr;

    if (!JS_DefineProperties(cx, ctor, ArrayBufferObject::jsstaticprops))
        return nullptr;

    if (!JS_DefineFunctions(cx, arrayBufferProto, ArrayBufferObject::jsfuncs))
        return nullptr;

    if (!GlobalObject::initBuiltinConstructor(cx, global, JSProto_ArrayBuffer,
                                              ctor, arrayBufferProto))
    {
        return nullptr;
    }

    return arrayBufferProto;
}