path: root/js/src/wasm/WasmGcObject.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: set ts=8 sts=2 et sw=2 tw=80:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "wasm/WasmGcObject.h"

#include "mozilla/ArrayUtils.h"
#include "mozilla/Casting.h"
#include "mozilla/CheckedInt.h"

#include <algorithm>

#include "gc/Marking.h"
#include "js/CharacterEncoding.h"
#include "js/friend/ErrorMessages.h"  // js::GetErrorMessage, JSMSG_*
#include "js/PropertySpec.h"
#include "js/ScalarType.h"  // js::Scalar::Type
#include "js/Vector.h"
#include "util/StringBuffer.h"
#include "vm/GlobalObject.h"
#include "vm/JSFunction.h"
#include "vm/JSObject.h"
#include "vm/PlainObject.h"  // js::PlainObject
#include "vm/Realm.h"
#include "vm/SelfHosting.h"
#include "vm/StringType.h"
#include "vm/TypedArrayObject.h"
#include "vm/Uint8Clamped.h"

#include "gc/GCContext-inl.h"
#include "gc/Marking-inl.h"
#include "gc/Nursery-inl.h"
#include "gc/StoreBuffer-inl.h"
#include "vm/JSAtom-inl.h"
#include "vm/JSObject-inl.h"
#include "vm/NativeObject-inl.h"
#include "vm/Shape-inl.h"

using mozilla::AssertedCast;
using mozilla::CheckedUint32;
using mozilla::IsPowerOfTwo;
using mozilla::PodCopy;
using mozilla::PointerRangeSize;

using namespace js;
using namespace wasm;

// [SMDOC] Management of OOL storage areas for Wasm{Array,Struct}Object.
//
// WasmArrayObject always has its payload data stored in a block the C++-heap,
// which is pointed to from the WasmArrayObject.  The same is true for
// WasmStructObject in the case where the fields cannot fit in the object
// itself.  These C++ blocks are in some places referred to as "trailer blocks".
//
// The presence of trailer blocks complicates the use of generational GC (that
// is, Nursery allocation) of Wasm{Array,Struct}Object.  In particular:
//
// (1) For objects which do not get tenured at minor collection, there must be
//     a way to free the associated trailer, but there is no way to visit
//     non-tenured blocks during minor collection.
//
// (2) Even if (1) were solved, calling js_malloc/js_free for every object
//     creation-death cycle is expensive, possibly around 400 machine
//     instructions, and we expressly want to avoid that in a generational GC
//     scenario.
//
// The following scheme is therefore employed.
//
// (a) gc::Nursery maintains a pool of available C++-heap-allocated blocks --
//     a js::MallocedBlockCache -- and the intention is that trailers are
//     allocated from this pool and freed back into it whenever possible.
//
// (b) WasmArrayObject::createArray and WasmStructObject::createStructOOL
//     always request trailer allocation from the nursery's cache (a).  If the
//     cache cannot honour the request directly it will allocate directly from
//     js_malloc; we hope this happens only infrequently.
//
// (c) The allocated block is returned as a js::PointerAndUint7, a pair that
//     holds the trailer block pointer and an auxiliary tag that the
//     js::MallocedBlockCache needs to see when the block is freed.
//
//     The raw trailer block pointer (a `void*`) is stored in the
//     Wasm{Array,Struct}Object OOL data field.  These objects are not aware
//     of and do not interact with js::PointerAndUint7, and nor does any
//     JIT-generated code.
//
// (d) Still in WasmArrayObject::createArray and
//     WasmStructObject::createStructOOL, if the object was allocated in the
//     nursery, then the resulting js::PointerAndUint7 is "registered" with
//     the nursery by handing it to Nursery::registerTrailer.
//
// (e) When a minor collection happens (Nursery::doCollection), we are
//     notified of objects that are moved by calls to the ::obj_moved methods
//     in this file.  For those objects that have been tenured, the raw
//     trailer pointer is "deregistered" with the nursery by handing it to
//     Nursery::deregisterTrailer.
//
// (f) Still during minor collection: The nursery now knows both the set of
//     trailer blocks added, and those removed because the corresponding
//     object has been tenured.  The difference between these two sets (that
//     is, `added - removed`) is the set of trailer blocks corresponding to
//     blocks that didn't get tenured.  That set is computed and freed (back
//     to the nursery's js::MallocedBlockCache) by
//     :Nursery::freeTrailerBlocks.
//
// (g) At the end of minor collection, the added and removed sets are made
//     empty, and the cycle begins again.
//
// (h) Also at the end of minor collection, a call to
//     `mallocedBlockCache_.preen` hands a few blocks in the cache back to
//     js_free.  This mechanism exists so as to ensure that unused blocks do
//     not remain in the cache indefinitely.
//
// (i) For objects that got tenured, we are eventually notified of their death
//     by a call to the ::obj_finalize methods below.  At that point we hand
//     their block pointers to js_free.
//
// (j) When the nursery is eventually destroyed, all blocks in its block cache
//     are handed to js_free.  Hence, at process exit, provided all nurseries
//     are first collected and then their destructors run, no C++ heap blocks
//     are leaked.
//
// As a result of this scheme, trailer blocks associated with what we hope is
// the frequent case -- objects that are allocated but never make it out of
// the nursery -- are cycled through the nursery's block cache.
//
// Trailers associated with tenured blocks cannot participate though; they are
// always returned to js_free.  It would be possible to enable them to
// participate by changing their owning object's OOL data pointer to be a
// js::PointerAndUint7 rather than a raw `void*`, so that then the blocks
// could be released to the cache in the ::obj_finalize methods.  This would
// however require changes in the generated code for array element and OOL
// struct element accesses.
//
// Here's a short summary of the trailer block life cycle:
//
// * allocated:
//
//   - in WasmArrayObject::createArray / WasmStructObject::createStructOOL
//
//   - by calling the nursery's MallocBlockCache alloc method
//
// * deallocated:
//
//   - for non-tenured objects, in the collector itself,
//     in Nursery::doCollection calling Nursery::freeTrailerBlocks,
//     releasing to the nursery's block cache
//
//   - for tenured objects, in the ::obj_finalize methods, releasing directly
//     to js_free
//
// If this seems confusing ("why is it ok to allocate from the cache but
// release to js_free?"), remember that the cache holds blocks previously
// obtained from js_malloc but which are *not* currently in use.  Hence it is
// fine to give them back to js_free; that just makes the cache a bit emptier
// but has no effect on correctness.

//=========================================================================
// WasmGcObject

bool WasmGcObject::lookupProperty(JSContext* cx, Handle<WasmGcObject*> object,
                                  jsid id, PropOffset* offset,
                                  FieldType* type) {
  switch (kind()) {
    case wasm::TypeDefKind::Struct: {
      const auto& structType = typeDef().structType();
      uint32_t index;
      if (!IdIsIndex(id, &index)) {
        return false;
      }
      if (index >= structType.fields_.length()) {
        return false;
      }
      const StructField& field = structType.fields_[index];
      offset->set(field.offset);
      *type = field.type;
      return true;
    }
    case wasm::TypeDefKind::Array: {
      const auto& arrayType = typeDef().arrayType();

      // Special case for property 'length' that loads the length field at the
      // beginning of the data buffer
      if (id.isString() &&
          id.toString() == cx->runtime()->commonNames->length) {
        STATIC_ASSERT_WASMARRAYELEMENTS_NUMELEMENTS_IS_U32;
        *type = FieldType::I32;
        offset->set(UINT32_MAX);
        return true;
      }

      // Normal case of indexed properties for loading array elements
      uint32_t index;
      if (!IdIsIndex(id, &index)) {
        return false;
      }
      uint32_t numElements = object->as<WasmArrayObject>().numElements_;
      if (index >= numElements) {
        return false;
      }
      uint64_t scaledIndex =
          uint64_t(index) * uint64_t(arrayType.elementType_.size());
      if (scaledIndex >= uint64_t(UINT32_MAX)) {
        // It's unrepresentable as an WasmGcObject::PropOffset.  Give up.
        return false;
      }
      offset->set(uint32_t(scaledIndex));
      *type = arrayType.elementType_;
      return true;
    }
    default:
      MOZ_ASSERT_UNREACHABLE();
      return false;
  }
}

const ObjectOps WasmGcObject::objectOps_ = {
    WasmGcObject::obj_lookupProperty,            // lookupProperty
    WasmGcObject::obj_defineProperty,            // defineProperty
    WasmGcObject::obj_hasProperty,               // hasProperty
    WasmGcObject::obj_getProperty,               // getProperty
    WasmGcObject::obj_setProperty,               // setProperty
    WasmGcObject::obj_getOwnPropertyDescriptor,  // getOwnPropertyDescriptor
    WasmGcObject::obj_deleteProperty,            // deleteProperty
    nullptr,                                     // getElements
    nullptr,                                     // funToString
};

/* static */
bool WasmGcObject::obj_lookupProperty(JSContext* cx, HandleObject obj,
                                      HandleId id, MutableHandleObject objp,
                                      PropertyResult* propp) {
  Rooted<WasmGcObject*> typedObj(cx, &obj->as<WasmGcObject>());
  if (typedObj->hasProperty(cx, typedObj, id)) {
    propp->setWasmGcProperty();
    objp.set(obj);
    return true;
  }

  RootedObject proto(cx, obj->staticPrototype());
  if (!proto) {
    objp.set(nullptr);
    propp->setNotFound();
    return true;
  }

  return LookupProperty(cx, proto, id, objp, propp);
}

bool WasmGcObject::obj_defineProperty(JSContext* cx, HandleObject obj,
                                      HandleId id,
                                      Handle<PropertyDescriptor> desc,
                                      ObjectOpResult& result) {
  JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
                           JSMSG_OBJECT_NOT_EXTENSIBLE, "WasmGcObject");
  return false;
}

bool WasmGcObject::obj_hasProperty(JSContext* cx, HandleObject obj, HandleId id,
                                   bool* foundp) {
  Rooted<WasmGcObject*> typedObj(cx, &obj->as<WasmGcObject>());
  if (typedObj->hasProperty(cx, typedObj, id)) {
    *foundp = true;
    return true;
  }

  RootedObject proto(cx, obj->staticPrototype());
  if (!proto) {
    *foundp = false;
    return true;
  }

  return HasProperty(cx, proto, id, foundp);
}

bool WasmGcObject::obj_getProperty(JSContext* cx, HandleObject obj,
                                   HandleValue receiver, HandleId id,
                                   MutableHandleValue vp) {
  Rooted<WasmGcObject*> typedObj(cx, &obj->as<WasmGcObject>());

  WasmGcObject::PropOffset offset;
  FieldType type;
  if (typedObj->lookupProperty(cx, typedObj, id, &offset, &type)) {
    return typedObj->loadValue(cx, offset, type, vp);
  }

  RootedObject proto(cx, obj->staticPrototype());
  if (!proto) {
    vp.setUndefined();
    return true;
  }

  return GetProperty(cx, proto, receiver, id, vp);
}

bool WasmGcObject::obj_setProperty(JSContext* cx, HandleObject obj, HandleId id,
                                   HandleValue v, HandleValue receiver,
                                   ObjectOpResult& result) {
  Rooted<WasmGcObject*> typedObj(cx, &obj->as<WasmGcObject>());

  if (typedObj->hasProperty(cx, typedObj, id)) {
    if (!receiver.isObject() || obj != &receiver.toObject()) {
      return SetPropertyByDefining(cx, id, v, receiver, result);
    }

    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
                              JSMSG_TYPEDOBJECT_SETTING_IMMUTABLE);
    return false;
  }

  return SetPropertyOnProto(cx, obj, id, v, receiver, result);
}

bool WasmGcObject::obj_getOwnPropertyDescriptor(
    JSContext* cx, HandleObject obj, HandleId id,
    MutableHandle<mozilla::Maybe<PropertyDescriptor>> desc) {
  Rooted<WasmGcObject*> typedObj(cx, &obj->as<WasmGcObject>());

  WasmGcObject::PropOffset offset;
  FieldType type;
  if (typedObj->lookupProperty(cx, typedObj, id, &offset, &type)) {
    RootedValue value(cx);
    if (!typedObj->loadValue(cx, offset, type, &value)) {
      return false;
    }
    desc.set(mozilla::Some(PropertyDescriptor::Data(
        value,
        {JS::PropertyAttribute::Enumerable, JS::PropertyAttribute::Writable})));
    return true;
  }

  desc.reset();
  return true;
}

bool WasmGcObject::obj_deleteProperty(JSContext* cx, HandleObject obj,
                                      HandleId id, ObjectOpResult& result) {
  Rooted<WasmGcObject*> typedObj(cx, &obj->as<WasmGcObject>());
  if (typedObj->hasProperty(cx, typedObj, id)) {
    return Throw(cx, id, JSMSG_CANT_DELETE);
  }

  RootedObject proto(cx, obj->staticPrototype());
  if (!proto) {
    return result.succeed();
  }

  return DeleteProperty(cx, proto, id, result);
}

/* static */
WasmGcObject* WasmGcObject::create(JSContext* cx,
                                   wasm::TypeDefInstanceData* typeDefData,
                                   js::gc::Heap initialHeap) {
  MOZ_ASSERT(IsWasmGcObjectClass(typeDefData->clasp));
  MOZ_ASSERT(!typeDefData->clasp->isNativeObject());

  debugCheckNewObject(typeDefData->shape, typeDefData->allocKind, initialHeap);

  WasmGcObject* obj =
      cx->newCell<WasmGcObject>(typeDefData->allocKind, initialHeap,
                                typeDefData->clasp, &typeDefData->allocSite);
  if (!obj) {
    return nullptr;
  }

  obj->initShape(typeDefData->shape);
  obj->superTypeVector_ = typeDefData->superTypeVector;

  js::gc::gcprobes::CreateObject(obj);
  probes::CreateObject(cx, obj);

  return obj;
}

bool WasmGcObject::loadValue(JSContext* cx,
                             const WasmGcObject::PropOffset& offset,
                             FieldType type, MutableHandleValue vp) {
  // Temporary hack, (ref T) is not exposable to JS yet but some tests would
  // like to access it so we erase (ref T) with eqref when loading. This is
  // safe as (ref T) <: eqref and we're not in the writing case where we
  // would need to perform a type check.
  if (type.isTypeRef()) {
    type = RefType::fromTypeCode(TypeCode::EqRef, true);
  }

  if (!type.isExposable()) {
    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
                             JSMSG_WASM_BAD_VAL_TYPE);
    return false;
  }

  if (is<WasmStructObject>()) {
    // `offset` is the field offset, without regard to the in/out-line split.
    // That is handled by the call to `fieldOffsetToAddress`.
    WasmStructObject& structObj = as<WasmStructObject>();
    // Ensure no out-of-range access possible
    MOZ_RELEASE_ASSERT(structObj.kind() == TypeDefKind::Struct);
    MOZ_RELEASE_ASSERT(offset.get() + type.size() <=
                       structObj.typeDef().structType().size_);
    return ToJSValue(cx, structObj.fieldOffsetToAddress(type, offset.get()),
                     type, vp);
  }

  MOZ_ASSERT(is<WasmArrayObject>());
  WasmArrayObject& arrayObj = as<WasmArrayObject>();
  if (offset.get() == UINT32_MAX) {
    // This denotes "length"
    uint32_t numElements = arrayObj.numElements_;
    // We can't use `ToJSValue(.., ValType::I32, ..)` here since it will
    // treat the integer as signed, which it isn't.  `vp.set(..)` will
    // coerce correctly to a JS::Value, though.
    vp.set(NumberValue(numElements));
    return true;
  }
  return ToJSValue(cx, arrayObj.data_ + offset.get(), type, vp);
}

bool WasmGcObject::isRuntimeSubtypeOf(
    const wasm::TypeDef* parentTypeDef) const {
  return TypeDef::isSubTypeOf(&typeDef(), parentTypeDef);
}

bool WasmGcObject::obj_newEnumerate(JSContext* cx, HandleObject obj,
                                    MutableHandleIdVector properties,
                                    bool enumerableOnly) {
  MOZ_ASSERT(obj->is<WasmGcObject>());
  Rooted<WasmGcObject*> typedObj(cx, &obj->as<WasmGcObject>());

  size_t indexCount = 0;
  size_t otherCount = 0;
  switch (typedObj->kind()) {
    case wasm::TypeDefKind::Struct: {
      indexCount = typedObj->typeDef().structType().fields_.length();
      break;
    }
    case wasm::TypeDefKind::Array: {
      indexCount = typedObj->as<WasmArrayObject>().numElements_;
      otherCount = 1;
      break;
    }
    default:
      MOZ_ASSERT_UNREACHABLE();
  }

  if (!properties.reserve(indexCount + otherCount)) {
    return false;
  }
  RootedId id(cx);
  for (size_t index = 0; index < indexCount; index++) {
    id = PropertyKey::Int(int32_t(index));
    properties.infallibleAppend(id);
  }

  if (typedObj->kind() == wasm::TypeDefKind::Array) {
    properties.infallibleAppend(NameToId(cx->runtime()->commonNames->length));
  }

  return true;
}

static void WriteValTo(const Val& val, FieldType ty, void* dest) {
  switch (ty.kind()) {
    case FieldType::I8:
      *((uint8_t*)dest) = val.i32();
      break;
    case FieldType::I16:
      *((uint16_t*)dest) = val.i32();
      break;
    case FieldType::I32:
      *((uint32_t*)dest) = val.i32();
      break;
    case FieldType::I64:
      *((uint64_t*)dest) = val.i64();
      break;
    case FieldType::F32:
      *((float*)dest) = val.f32();
      break;
    case FieldType::F64:
      *((double*)dest) = val.f64();
      break;
    case FieldType::V128:
      *((V128*)dest) = val.v128();
      break;
    case FieldType::Ref:
      *((GCPtr<AnyRef>*)dest) = val.ref();
      break;
  }
}

//=========================================================================
// WasmArrayObject

/* static */
gc::AllocKind WasmArrayObject::allocKind() {
  return gc::GetGCObjectKindForBytes(sizeof(WasmArrayObject));
}

/* static */
template <bool ZeroFields>
WasmArrayObject* WasmArrayObject::createArray(
    JSContext* cx, wasm::TypeDefInstanceData* typeDefData,
    js::gc::Heap initialHeap, uint32_t numElements) {
  const TypeDef* typeDef = typeDefData->typeDef;
  STATIC_ASSERT_WASMARRAYELEMENTS_NUMELEMENTS_IS_U32;
  MOZ_ASSERT(typeDef->kind() == wasm::TypeDefKind::Array);

  // Calculate the byte length of the outline storage, being careful to check
  // for overflow.  Note this logic assumes that MaxArrayPayloadBytes is
  // within uint32_t range.
  CheckedUint32 outlineBytes = typeDef->arrayType().elementType_.size();
  outlineBytes *= numElements;
  if (!outlineBytes.isValid() ||
      outlineBytes.value() > uint32_t(MaxArrayPayloadBytes)) {
    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
                             JSMSG_WASM_ARRAY_IMP_LIMIT);
    return nullptr;
  }

  // Allocate the outline data before allocating the object so that we can
  // infallibly initialize the pointer on the array object after it is
  // allocated.
  Nursery& nursery = cx->nursery();
  PointerAndUint7 outlineData(nullptr, 0);
  if (outlineBytes.value() > 0) {
    outlineData = nursery.mallocedBlockCache().alloc(outlineBytes.value());
    if (!outlineData.pointer()) {
      ReportOutOfMemory(cx);
      return nullptr;
    }
  }

  // It's unfortunate that `arrayObj` has to be rooted, since this is a hot
  // path and rooting costs around 15 instructions.  It is the call to
  // registerTrailer that makes it necessary.
  Rooted<WasmArrayObject*> arrayObj(cx);
  arrayObj =
      (WasmArrayObject*)WasmGcObject::create(cx, typeDefData, initialHeap);
  if (!arrayObj) {
    ReportOutOfMemory(cx);
    if (outlineData.pointer()) {
      nursery.mallocedBlockCache().free(outlineData);
    }
    return nullptr;
  }

  arrayObj->numElements_ = numElements;
  arrayObj->data_ = (uint8_t*)outlineData.pointer();
  if (outlineData.pointer()) {
    if constexpr (ZeroFields) {
      memset(outlineData.pointer(), 0, outlineBytes.value());
    }
    if (js::gc::IsInsideNursery(arrayObj)) {
      // We need to register the OOL area with the nursery, so it will be
      // freed after GCing of the nursery if `arrayObj_` doesn't make it into
      // the tenured heap.
      if (!nursery.registerTrailer(outlineData, outlineBytes.value())) {
        nursery.mallocedBlockCache().free(outlineData);
        ReportOutOfMemory(cx);
        return nullptr;
      }
    }
  }

  return arrayObj;
}

template WasmArrayObject* WasmArrayObject::createArray<true>(
    JSContext* cx, wasm::TypeDefInstanceData* typeDefData,
    js::gc::Heap initialHeap, uint32_t numElements);
template WasmArrayObject* WasmArrayObject::createArray<false>(
    JSContext* cx, wasm::TypeDefInstanceData* typeDefData,
    js::gc::Heap initialHeap, uint32_t numElements);

/* static */
void WasmArrayObject::obj_trace(JSTracer* trc, JSObject* object) {
  WasmArrayObject& arrayObj = object->as<WasmArrayObject>();
  uint8_t* data = arrayObj.data_;
  if (!data) {
    MOZ_ASSERT(arrayObj.numElements_ == 0);
    return;
  }

  const auto& typeDef = arrayObj.typeDef();
  const auto& arrayType = typeDef.arrayType();
  if (!arrayType.elementType_.isRefRepr()) {
    return;
  }

  uint32_t numElements = arrayObj.numElements_;
  MOZ_ASSERT(numElements > 0);
  uint32_t elemSize = arrayType.elementType_.size();
  for (uint32_t i = 0; i < numElements; i++) {
    GCPtr<JSObject*>* objectPtr =
        reinterpret_cast<GCPtr<JSObject*>*>(data + i * elemSize);
    TraceNullableEdge(trc, objectPtr, "reference-obj");
  }
}

/* static */
void WasmArrayObject::obj_finalize(JS::GCContext* gcx, JSObject* object) {
  WasmArrayObject& arrayObj = object->as<WasmArrayObject>();
  MOZ_ASSERT((arrayObj.data_ == nullptr) == (arrayObj.numElements_ == 0));
  if (arrayObj.data_) {
    js_free(arrayObj.data_);
    arrayObj.data_ = nullptr;
  }
}

/* static */
size_t WasmArrayObject::obj_moved(JSObject* obj, JSObject* old) {
  MOZ_ASSERT(!IsInsideNursery(obj));
  if (IsInsideNursery(old)) {
    // It's been tenured.
    MOZ_ASSERT(obj->isTenured());
    WasmArrayObject& arrayObj = obj->as<WasmArrayObject>();
    if (arrayObj.data_) {
      Nursery& nursery = obj->runtimeFromMainThread()->gc.nursery();
      nursery.unregisterTrailer(arrayObj.data_);
    }
  }
  return 0;
}

void WasmArrayObject::storeVal(const Val& val, uint32_t itemIndex) {
  const ArrayType& arrayType = typeDef().arrayType();
  size_t elementSize = arrayType.elementType_.size();
  MOZ_ASSERT(itemIndex < numElements_);
  uint8_t* data = data_ + elementSize * itemIndex;
  WriteValTo(val, arrayType.elementType_, data);
}

void WasmArrayObject::fillVal(const Val& val, uint32_t itemIndex,
                              uint32_t len) {
  const ArrayType& arrayType = typeDef().arrayType();
  size_t elementSize = arrayType.elementType_.size();
  uint8_t* data = data_ + elementSize * itemIndex;
  MOZ_ASSERT(itemIndex <= numElements_ && len <= numElements_ - itemIndex);
  for (uint32_t i = 0; i < len; i++) {
    WriteValTo(val, arrayType.elementType_, data);
    data += elementSize;
  }
}

static const JSClassOps WasmArrayObjectClassOps = {
    nullptr, /* addProperty */
    nullptr, /* delProperty */
    nullptr, /* enumerate   */
    WasmGcObject::obj_newEnumerate,
    nullptr,                       /* resolve     */
    nullptr,                       /* mayResolve  */
    WasmArrayObject::obj_finalize, /* finalize    */
    nullptr,                       /* call        */
    nullptr,                       /* construct   */
    WasmArrayObject::obj_trace,
};
static const ClassExtension WasmArrayObjectClassExt = {
    WasmArrayObject::obj_moved /* objectMovedOp */
};
const JSClass WasmArrayObject::class_ = {
    "WasmArrayObject",
    JSClass::NON_NATIVE | JSCLASS_DELAY_METADATA_BUILDER |
        JSCLASS_BACKGROUND_FINALIZE | JSCLASS_SKIP_NURSERY_FINALIZE,
    &WasmArrayObjectClassOps,
    JS_NULL_CLASS_SPEC,
    &WasmArrayObjectClassExt,
    &WasmGcObject::objectOps_};

//=========================================================================
// WasmStructObject

/* static */
const JSClass* js::WasmStructObject::classForTypeDef(
    const wasm::TypeDef* typeDef) {
  MOZ_ASSERT(typeDef->kind() == wasm::TypeDefKind::Struct);
  size_t nbytes = typeDef->structType().size_;
  return nbytes > WasmStructObject_MaxInlineBytes
             ? &WasmStructObject::classOutline_
             : &WasmStructObject::classInline_;
}

/* static */
js::gc::AllocKind js::WasmStructObject::allocKindForTypeDef(
    const wasm::TypeDef* typeDef) {
  MOZ_ASSERT(typeDef->kind() == wasm::TypeDefKind::Struct);
  size_t nbytes = typeDef->structType().size_;

  // `nbytes` is the total required size for all struct fields, including
  // padding.  What we need is the size of resulting WasmStructObject,
  // ignoring any space used for out-of-line data.  First, restrict `nbytes`
  // to cover just the inline data.
  if (nbytes > WasmStructObject_MaxInlineBytes) {
    nbytes = WasmStructObject_MaxInlineBytes;
  }

  // Now convert it to size of the WasmStructObject as a whole.
  nbytes = sizeOfIncludingInlineData(nbytes);

  return gc::GetGCObjectKindForBytes(nbytes);
}

/* static MOZ_NEVER_INLINE */
template <bool ZeroFields>
WasmStructObject* WasmStructObject::createStructOOL(
    JSContext* cx, wasm::TypeDefInstanceData* typeDefData,
    js::gc::Heap initialHeap, uint32_t inlineBytes, uint32_t outlineBytes) {
  // This method is called as the slow path from the (inlineable)
  // WasmStructObject::createStruct.  It handles the case where an object
  // needs OOL storage.  It doesn't handle the non-OOL case at all.

  // Allocate the outline data area before allocating the object so that we can
  // infallibly initialize the outline data area.
  Nursery& nursery = cx->nursery();
  PointerAndUint7 outlineData =
      nursery.mallocedBlockCache().alloc(outlineBytes);
  if (MOZ_UNLIKELY(!outlineData.pointer())) {
    ReportOutOfMemory(cx);
    return nullptr;
  }

  // See corresponding comment in WasmArrayObject::createArray.
  Rooted<WasmStructObject*> structObj(cx);
  structObj =
      (WasmStructObject*)WasmGcObject::create(cx, typeDefData, initialHeap);
  if (MOZ_UNLIKELY(!structObj)) {
    ReportOutOfMemory(cx);
    if (outlineData.pointer()) {
      nursery.mallocedBlockCache().free(outlineData);
    }
    return nullptr;
  }

  // Initialize the outline data fields
  structObj->outlineData_ = (uint8_t*)outlineData.pointer();
  if constexpr (ZeroFields) {
    memset(&(structObj->inlineData_[0]), 0, inlineBytes);
    memset(outlineData.pointer(), 0, outlineBytes);
  }
  if (MOZ_LIKELY(js::gc::IsInsideNursery(structObj))) {
    // See corresponding comment in WasmArrayObject::createArray.
    if (!nursery.registerTrailer(outlineData, outlineBytes)) {
      nursery.mallocedBlockCache().free(outlineData);
      ReportOutOfMemory(cx);
      return nullptr;
    }
  }

  return structObj;
}

template WasmStructObject* WasmStructObject::createStruct<true>(
    JSContext* cx, wasm::TypeDefInstanceData* typeDefData,
    js::gc::Heap initialHeap);
template WasmStructObject* WasmStructObject::createStruct<false>(
    JSContext* cx, wasm::TypeDefInstanceData* typeDefData,
    js::gc::Heap initialHeap);

/* static */
void WasmStructObject::obj_trace(JSTracer* trc, JSObject* object) {
  WasmStructObject& structObj = object->as<WasmStructObject>();

  const auto& structType = structObj.typeDef().structType();
  for (uint32_t offset : structType.inlineTraceOffsets_) {
    GCPtr<JSObject*>* objectPtr =
        reinterpret_cast<GCPtr<JSObject*>*>(&structObj.inlineData_[0] + offset);
    TraceNullableEdge(trc, objectPtr, "reference-obj");
  }
  for (uint32_t offset : structType.outlineTraceOffsets_) {
    GCPtr<JSObject*>* objectPtr =
        reinterpret_cast<GCPtr<JSObject*>*>(structObj.outlineData_ + offset);
    TraceNullableEdge(trc, objectPtr, "reference-obj");
  }
}

/* static */
void WasmStructObject::obj_finalize(JS::GCContext* gcx, JSObject* object) {
  WasmStructObject& structObj = object->as<WasmStructObject>();

  if (structObj.outlineData_) {
    js_free(structObj.outlineData_);
    structObj.outlineData_ = nullptr;
  }
}

/* static */
size_t WasmStructObject::obj_moved(JSObject* obj, JSObject* old) {
  MOZ_ASSERT(!IsInsideNursery(obj));
  if (IsInsideNursery(old)) {
    // It's been tenured.
    MOZ_ASSERT(obj->isTenured());
    WasmStructObject& structObj = obj->as<WasmStructObject>();
    // WasmStructObject::classForTypeDef ensures we only get called for
    // structs with OOL data.  Hence:
    MOZ_ASSERT(structObj.outlineData_);
    Nursery& nursery = obj->runtimeFromMainThread()->gc.nursery();
    nursery.unregisterTrailer(structObj.outlineData_);
  }
  return 0;
}

void WasmStructObject::storeVal(const Val& val, uint32_t fieldIndex) {
  const StructType& structType = typeDef().structType();
  FieldType fieldType = structType.fields_[fieldIndex].type;
  uint32_t fieldOffset = structType.fields_[fieldIndex].offset;

  MOZ_ASSERT(fieldIndex < structType.fields_.length());
  bool areaIsOutline;
  uint32_t areaOffset;
  fieldOffsetToAreaAndOffset(fieldType, fieldOffset, &areaIsOutline,
                             &areaOffset);

  uint8_t* data;
  if (areaIsOutline) {
    data = outlineData_ + areaOffset;
  } else {
    data = inlineData_ + areaOffset;
  }

  WriteValTo(val, fieldType, data);
}

static const JSClassOps WasmStructObjectOutlineClassOps = {
    nullptr, /* addProperty */
    nullptr, /* delProperty */
    nullptr, /* enumerate   */
    WasmGcObject::obj_newEnumerate,
    nullptr,                        /* resolve     */
    nullptr,                        /* mayResolve  */
    WasmStructObject::obj_finalize, /* finalize    */
    nullptr,                        /* call        */
    nullptr,                        /* construct   */
    WasmStructObject::obj_trace,
};
static const ClassExtension WasmStructObjectOutlineClassExt = {
    WasmStructObject::obj_moved /* objectMovedOp */
};
const JSClass WasmStructObject::classOutline_ = {
    "WasmStructObject",
    JSClass::NON_NATIVE | JSCLASS_DELAY_METADATA_BUILDER |
        JSCLASS_BACKGROUND_FINALIZE | JSCLASS_SKIP_NURSERY_FINALIZE,
    &WasmStructObjectOutlineClassOps,
    JS_NULL_CLASS_SPEC,
    &WasmStructObjectOutlineClassExt,
    &WasmGcObject::objectOps_};

// Structs that only have inline data get a different class without a
// finalizer. This class should otherwise be identical to the class for
// structs with outline data.
static const JSClassOps WasmStructObjectInlineClassOps = {
    nullptr, /* addProperty */
    nullptr, /* delProperty */
    nullptr, /* enumerate   */
    WasmGcObject::obj_newEnumerate,
    nullptr, /* resolve     */
    nullptr, /* mayResolve  */
    nullptr, /* finalize    */
    nullptr, /* call        */
    nullptr, /* construct   */
    WasmStructObject::obj_trace,
};
static const ClassExtension WasmStructObjectInlineClassExt = {
    nullptr /* objectMovedOp */
};
const JSClass WasmStructObject::classInline_ = {
    "WasmStructObject",
    JSClass::NON_NATIVE | JSCLASS_DELAY_METADATA_BUILDER,
    &WasmStructObjectInlineClassOps,
    JS_NULL_CLASS_SPEC,
    &WasmStructObjectInlineClassExt,
    &WasmGcObject::objectOps_};