Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 5412 insertions, 0 deletions

diff --git a/js/src/wasm/WasmJS.cpp b/js/src/wasm/WasmJS.cpp
new file mode 100644
index 0000000000..6cc9528415
--- /dev/null
+++ b/js/src/wasm/WasmJS.cpp
@@ -0,0 +1,5412 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ *
+ * Copyright 2016 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "wasm/WasmJS.h"
+
+#include "mozilla/CheckedInt.h"
+#include "mozilla/EndianUtils.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/RangedPtr.h"
+
+#include <algorithm>
+#include <cstdint>
+
+#include "jsapi.h"
+#include "jsexn.h"
+
+#include "ds/IdValuePair.h"            // js::IdValuePair
+#include "frontend/FrontendContext.h"  // AutoReportFrontendContext
+#include "gc/GCContext.h"
+#include "jit/AtomicOperations.h"
+#include "jit/FlushICache.h"
+#include "jit/JitContext.h"
+#include "jit/JitOptions.h"
+#include "jit/Simulator.h"
+#include "js/ColumnNumber.h"  // JS::ColumnNumberOneOrigin
+#include "js/ForOfIterator.h"
+#include "js/friend/ErrorMessages.h"  // js::GetErrorMessage, JSMSG_*
+#include "js/Printf.h"
+#include "js/PropertyAndElement.h"  // JS_DefineProperty, JS_GetProperty
+#include "js/PropertySpec.h"        // JS_{PS,FN}{,_END}
+#include "js/Stack.h"               // BuildStackString
+#include "js/StreamConsumer.h"
+#include "util/StringBuffer.h"
+#include "util/Text.h"
+#include "vm/ErrorObject.h"
+#include "vm/FunctionFlags.h"      // js::FunctionFlags
+#include "vm/GlobalObject.h"       // js::GlobalObject
+#include "vm/HelperThreadState.h"  // js::PromiseHelperTask
+#include "vm/Interpreter.h"
+#include "vm/JSFunction.h"
+#include "vm/PlainObject.h"    // js::PlainObject
+#include "vm/PromiseObject.h"  // js::PromiseObject
+#include "vm/SharedArrayObject.h"
+#include "vm/StringType.h"
+#include "vm/Warnings.h"  // js::WarnNumberASCII
+#include "wasm/WasmBaselineCompile.h"
+#include "wasm/WasmBuiltinModule.h"
+#include "wasm/WasmBuiltins.h"
+#include "wasm/WasmCompile.h"
+#include "wasm/WasmDebug.h"
+#include "wasm/WasmFeatures.h"
+#include "wasm/WasmInstance.h"
+#include "wasm/WasmIonCompile.h"
+#include "wasm/WasmMemory.h"
+#include "wasm/WasmModule.h"
+#include "wasm/WasmProcess.h"
+#include "wasm/WasmSignalHandlers.h"
+#include "wasm/WasmStubs.h"
+#include "wasm/WasmValidate.h"
+
+#include "gc/GCContext-inl.h"
+#include "gc/StableCellHasher-inl.h"
+#include "vm/ArrayBufferObject-inl.h"
+#include "vm/JSObject-inl.h"
+#include "vm/NativeObject-inl.h"
+#include "wasm/WasmInstance-inl.h"
+
+/*
+ * [SMDOC] WebAssembly code rules (evolving)
+ *
+ * TlsContext.get() is only to be invoked from functions that have been invoked
+ *   _directly_ by generated code as cold(!) Builtin calls, from code that is
+ *   only used by signal handlers, or from helper functions that have been
+ *   called _directly_ from a simulator.  All other code shall pass in a
+ *   JSContext* to functions that need it, or an Instance* or Instance* since
+ * the context is available through them.
+ *
+ *   Code that uses TlsContext.get() shall annotate each such call with the
+ *   reason why the call is OK.
+ */
+
+using namespace js;
+using namespace js::jit;
+using namespace js::wasm;
+
+using mozilla::CheckedInt;
+using mozilla::Nothing;
+using mozilla::RangedPtr;
+using mozilla::Span;
+
+static bool ThrowCompileOutOfMemory(JSContext* cx) {
+  // Most OOMs during compilation are due to large contiguous allocations,
+  // and future allocations are likely to succeed. Throwing a proper error
+  // object is nicer for users in these circumstances.
+  JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_OUT_OF_MEMORY);
+  return false;
+}
+
+// ============================================================================
+// Imports
+
+static bool ThrowBadImportArg(JSContext* cx) {
+  JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                           JSMSG_WASM_BAD_IMPORT_ARG);
+  return false;
+}
+
+static bool ThrowBadImportType(JSContext* cx, const CacheableName& field,
+                               const char* str) {
+  UniqueChars fieldQuoted = field.toQuotedString(cx);
+  JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                           JSMSG_WASM_BAD_IMPORT_TYPE, fieldQuoted.get(), str);
+  return false;
+}
+
+// For now reject cross-compartment wrappers. These have more complicated realm
+// semantics (we use nonCCWRealm in a few places) and may require unwrapping to
+// test for specific function types.
+static bool IsCallableNonCCW(const Value& v) {
+  return IsCallable(v) && !IsCrossCompartmentWrapper(&v.toObject());
+}
+
+bool js::wasm::GetImports(JSContext* cx, const Module& module,
+                          HandleObject importObj, ImportValues* imports) {
+  if (!module.imports().empty() && !importObj) {
+    return ThrowBadImportArg(cx);
+  }
+
+  const Metadata& metadata = module.metadata();
+
+  BuiltinModuleInstances builtinInstances(cx);
+  RootedValue importModuleValue(cx);
+  RootedObject importModuleObject(cx);
+  RootedValue importFieldValue(cx);
+
+  uint32_t tagIndex = 0;
+  const TagDescVector& tags = metadata.tags;
+  uint32_t globalIndex = 0;
+  const GlobalDescVector& globals = metadata.globals;
+  uint32_t tableIndex = 0;
+  const TableDescVector& tables = metadata.tables;
+  for (const Import& import : module.imports()) {
+    Maybe<BuiltinModuleId> builtinModule = ImportMatchesBuiltinModule(
+        import.module.utf8Bytes(), metadata.builtinModules);
+    if (builtinModule) {
+      MutableHandle<JSObject*> builtinInstance =
+          builtinInstances[*builtinModule];
+      if (!builtinInstance && !wasm::InstantiateBuiltinModule(
+                                  cx, *builtinModule, builtinInstance)) {
+        return false;
+      }
+      importModuleObject = builtinInstance;
+    } else {
+      RootedId moduleName(cx);
+      if (!import.module.toPropertyKey(cx, &moduleName)) {
+        return false;
+      }
+
+      if (!GetProperty(cx, importObj, importObj, moduleName,
+                       &importModuleValue)) {
+        return false;
+      }
+
+      if (!importModuleValue.isObject()) {
+        UniqueChars moduleQuoted = import.module.toQuotedString(cx);
+        JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                                 JSMSG_WASM_BAD_IMPORT_FIELD,
+                                 moduleQuoted.get());
+        return false;
+      }
+
+      importModuleObject = &importModuleValue.toObject();
+    }
+
+    RootedId fieldName(cx);
+    if (!import.field.toPropertyKey(cx, &fieldName)) {
+      return false;
+    }
+
+    if (!GetProperty(cx, importModuleObject, importModuleObject, fieldName,
+                     &importFieldValue)) {
+      return false;
+    }
+
+    switch (import.kind) {
+      case DefinitionKind::Function: {
+        if (!IsCallableNonCCW(importFieldValue)) {
+          return ThrowBadImportType(cx, import.field, "Function");
+        }
+
+        if (!imports->funcs.append(&importFieldValue.toObject())) {
+          return false;
+        }
+
+        break;
+      }
+      case DefinitionKind::Table: {
+        const uint32_t index = tableIndex++;
+        if (!importFieldValue.isObject() ||
+            !importFieldValue.toObject().is<WasmTableObject>()) {
+          return ThrowBadImportType(cx, import.field, "Table");
+        }
+
+        Rooted<WasmTableObject*> obj(
+            cx, &importFieldValue.toObject().as<WasmTableObject>());
+        if (obj->table().elemType() != tables[index].elemType) {
+          JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                                   JSMSG_WASM_BAD_TBL_TYPE_LINK);
+          return false;
+        }
+
+        if (!imports->tables.append(obj)) {
+          return false;
+        }
+        break;
+      }
+      case DefinitionKind::Memory: {
+        if (!importFieldValue.isObject() ||
+            !importFieldValue.toObject().is<WasmMemoryObject>()) {
+          return ThrowBadImportType(cx, import.field, "Memory");
+        }
+
+        if (!imports->memories.append(
+                &importFieldValue.toObject().as<WasmMemoryObject>())) {
+          return false;
+        }
+        break;
+      }
+      case DefinitionKind::Tag: {
+        const uint32_t index = tagIndex++;
+        if (!importFieldValue.isObject() ||
+            !importFieldValue.toObject().is<WasmTagObject>()) {
+          return ThrowBadImportType(cx, import.field, "Tag");
+        }
+
+        Rooted<WasmTagObject*> obj(
+            cx, &importFieldValue.toObject().as<WasmTagObject>());
+
+        // Checks whether the signature of the imported exception object matches
+        // the signature declared in the exception import's TagDesc.
+        if (obj->resultType() != tags[index].type->resultType()) {
+          UniqueChars fieldQuoted = import.field.toQuotedString(cx);
+          UniqueChars moduleQuoted = import.module.toQuotedString(cx);
+          JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                                   JSMSG_WASM_BAD_TAG_SIG, moduleQuoted.get(),
+                                   fieldQuoted.get());
+          return false;
+        }
+
+        if (!imports->tagObjs.append(obj)) {
+          ReportOutOfMemory(cx);
+          return false;
+        }
+        break;
+      }
+      case DefinitionKind::Global: {
+        const uint32_t index = globalIndex++;
+        const GlobalDesc& global = globals[index];
+        MOZ_ASSERT(global.importIndex() == index);
+
+        RootedVal val(cx);
+        if (importFieldValue.isObject() &&
+            importFieldValue.toObject().is<WasmGlobalObject>()) {
+          Rooted<WasmGlobalObject*> obj(
+              cx, &importFieldValue.toObject().as<WasmGlobalObject>());
+
+          if (obj->isMutable() != global.isMutable()) {
+            JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                                     JSMSG_WASM_BAD_GLOB_MUT_LINK);
+            return false;
+          }
+
+          bool matches = global.isMutable()
+                             ? obj->type() == global.type()
+                             : ValType::isSubTypeOf(obj->type(), global.type());
+          if (!matches) {
+            JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                                     JSMSG_WASM_BAD_GLOB_TYPE_LINK);
+            return false;
+          }
+
+          if (imports->globalObjs.length() <= index &&
+              !imports->globalObjs.resize(index + 1)) {
+            ReportOutOfMemory(cx);
+            return false;
+          }
+          imports->globalObjs[index] = obj;
+          val = obj->val();
+        } else {
+          if (!global.type().isRefType()) {
+            if (global.type() == ValType::I64 && !importFieldValue.isBigInt()) {
+              return ThrowBadImportType(cx, import.field, "BigInt");
+            }
+            if (global.type() != ValType::I64 && !importFieldValue.isNumber()) {
+              return ThrowBadImportType(cx, import.field, "Number");
+            }
+          }
+
+          if (global.isMutable()) {
+            JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                                     JSMSG_WASM_BAD_GLOB_MUT_LINK);
+            return false;
+          }
+
+          if (!Val::fromJSValue(cx, global.type(), importFieldValue, &val)) {
+            return false;
+          }
+        }
+
+        if (!imports->globalValues.append(val)) {
+          return false;
+        }
+
+        break;
+      }
+    }
+  }
+
+  MOZ_ASSERT(globalIndex == globals.length() ||
+             !globals[globalIndex].isImport());
+
+  return true;
+}
+
+static bool DescribeScriptedCaller(JSContext* cx, ScriptedCaller* caller,
+                                   const char* introducer) {
+  // Note: JS::DescribeScriptedCaller returns whether a scripted caller was
+  // found, not whether an error was thrown. This wrapper function converts
+  // back to the more ordinary false-if-error form.
+
+  JS::AutoFilename af;
+  if (JS::DescribeScriptedCaller(cx, &af, &caller->line)) {
+    caller->filename =
+        FormatIntroducedFilename(af.get(), caller->line, introducer);
+    if (!caller->filename) {
+      ReportOutOfMemory(cx);
+      return false;
+    }
+  }
+
+  return true;
+}
+
+static SharedCompileArgs InitCompileArgs(JSContext* cx, FeatureOptions options,
+                                         const char* introducer) {
+  ScriptedCaller scriptedCaller;
+  if (!DescribeScriptedCaller(cx, &scriptedCaller, introducer)) {
+    return nullptr;
+  }
+
+  return CompileArgs::buildAndReport(cx, std::move(scriptedCaller), options);
+}
+
+// ============================================================================
+// Testing / Fuzzing support
+
+bool wasm::Eval(JSContext* cx, Handle<TypedArrayObject*> code,
+                HandleObject importObj,
+                MutableHandle<WasmInstanceObject*> instanceObj) {
+  if (!GlobalObject::ensureConstructor(cx, cx->global(), JSProto_WebAssembly)) {
+    return false;
+  }
+
+  MutableBytes bytecode = cx->new_<ShareableBytes>();
+  if (!bytecode) {
+    return false;
+  }
+
+  if (!bytecode->append((uint8_t*)code->dataPointerEither().unwrap(),
+                        code->byteLength().valueOr(0))) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  FeatureOptions options;
+  SharedCompileArgs compileArgs = InitCompileArgs(cx, options, "wasm_eval");
+  if (!compileArgs) {
+    return false;
+  }
+
+  UniqueChars error;
+  UniqueCharsVector warnings;
+  SharedModule module =
+      CompileBuffer(*compileArgs, *bytecode, &error, &warnings, nullptr);
+  if (!module) {
+    if (error) {
+      JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                               JSMSG_WASM_COMPILE_ERROR, error.get());
+      return false;
+    }
+    return ThrowCompileOutOfMemory(cx);
+  }
+
+  Rooted<ImportValues> imports(cx);
+  if (!GetImports(cx, *module, importObj, imports.address())) {
+    return false;
+  }
+
+  return module->instantiate(cx, imports.get(), nullptr, instanceObj);
+}
+
+struct MOZ_STACK_CLASS SerializeListener : JS::OptimizedEncodingListener {
+  // MOZ_STACK_CLASS means these can be nops.
+  MozExternalRefCountType MOZ_XPCOM_ABI AddRef() override { return 0; }
+  MozExternalRefCountType MOZ_XPCOM_ABI Release() override { return 0; }
+
+  DebugOnly<bool> called = false;
+  Bytes* serialized;
+  explicit SerializeListener(Bytes* serialized) : serialized(serialized) {}
+
+  void storeOptimizedEncoding(const uint8_t* bytes, size_t length) override {
+    MOZ_ASSERT(!called);
+    called = true;
+    if (serialized->resizeUninitialized(length)) {
+      memcpy(serialized->begin(), bytes, length);
+    }
+  }
+};
+
+bool wasm::CompileAndSerialize(JSContext* cx, const ShareableBytes& bytecode,
+                               Bytes* serialized) {
+  // The caller must check that code caching is available
+  MOZ_ASSERT(CodeCachingAvailable(cx));
+
+  // Create and manually fill in compile args for code caching
+  MutableCompileArgs compileArgs = js_new<CompileArgs>(ScriptedCaller());
+  if (!compileArgs) {
+    return false;
+  }
+
+  // The caller has ensured CodeCachingAvailable(). Moreover, we want to ensure
+  // we go straight to tier-2 so that we synchronously call
+  // JS::OptimizedEncodingListener::storeOptimizedEncoding().
+  compileArgs->baselineEnabled = false;
+  compileArgs->forceTiering = false;
+
+  // We always pick Ion here, and we depend on CodeCachingAvailable() having
+  // determined that Ion is available, see comments at CodeCachingAvailable().
+  // To do better, we need to pass information about which compiler that should
+  // be used into CompileAndSerialize().
+  compileArgs->ionEnabled = true;
+
+  // Select features that are enabled. This is guaranteed to be consistent with
+  // our compiler selection, as code caching is only available if ion is
+  // available, and ion is only available if it's not disabled by enabled
+  // features.
+  compileArgs->features = FeatureArgs::build(cx, FeatureOptions());
+
+  SerializeListener listener(serialized);
+
+  UniqueChars error;
+  UniqueCharsVector warnings;
+  SharedModule module =
+      CompileBuffer(*compileArgs, bytecode, &error, &warnings, &listener);
+  if (!module) {
+    fprintf(stderr, "Compilation error: %s\n", error ? error.get() : "oom");
+    return false;
+  }
+
+  MOZ_ASSERT(module->code().hasTier(Tier::Serialized));
+  MOZ_ASSERT(listener.called);
+  return !listener.serialized->empty();
+}
+
+bool wasm::DeserializeModule(JSContext* cx, const Bytes& serialized,
+                             MutableHandleObject moduleObj) {
+  MutableModule module =
+      Module::deserialize(serialized.begin(), serialized.length());
+  if (!module) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  moduleObj.set(module->createObject(cx));
+  return !!moduleObj;
+}
+
+// ============================================================================
+// Common functions
+
+// '[EnforceRange] unsigned long' types are coerced with
+//    ConvertToInt(v, 32, 'unsigned')
+// defined in Web IDL Section 3.2.4.9.
+//
+// This just generalizes that to an arbitrary limit that is representable as an
+// integer in double form.
+
+static bool EnforceRange(JSContext* cx, HandleValue v, const char* kind,
+                         const char* noun, uint64_t max, uint64_t* val) {
+  // Step 4.
+  double x;
+  if (!ToNumber(cx, v, &x)) {
+    return false;
+  }
+
+  // Step 5.
+  if (mozilla::IsNegativeZero(x)) {
+    x = 0.0;
+  }
+
+  // Step 6.1.
+  if (!std::isfinite(x)) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_ENFORCE_RANGE, kind, noun);
+    return false;
+  }
+
+  // Step 6.2.
+  x = JS::ToInteger(x);
+
+  // Step 6.3.
+  if (x < 0 || x > double(max)) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_ENFORCE_RANGE, kind, noun);
+    return false;
+  }
+
+  *val = uint64_t(x);
+  MOZ_ASSERT(double(*val) == x);
+  return true;
+}
+
+static bool EnforceRangeU32(JSContext* cx, HandleValue v, const char* kind,
+                            const char* noun, uint32_t* u32) {
+  uint64_t u64 = 0;
+  if (!EnforceRange(cx, v, kind, noun, uint64_t(UINT32_MAX), &u64)) {
+    return false;
+  }
+  *u32 = uint32_t(u64);
+  return true;
+}
+
+static bool EnforceRangeU64(JSContext* cx, HandleValue v, const char* kind,
+                            const char* noun, uint64_t* u64) {
+  // The max is Number.MAX_SAFE_INTEGER
+  return EnforceRange(cx, v, kind, noun, (1LL << 53) - 1, u64);
+}
+
+static bool GetLimit(JSContext* cx, HandleObject obj, const char* name,
+                     const char* noun, const char* msg, uint32_t range,
+                     bool* found, uint64_t* value) {
+  JSAtom* atom = Atomize(cx, name, strlen(name));
+  if (!atom) {
+    return false;
+  }
+  RootedId id(cx, AtomToId(atom));
+
+  RootedValue val(cx);
+  if (!GetProperty(cx, obj, obj, id, &val)) {
+    return false;
+  }
+
+  if (val.isUndefined()) {
+    *found = false;
+    return true;
+  }
+  *found = true;
+  // The range can be greater than 53, but then the logic in EnforceRange has to
+  // change to avoid precision loss.
+  MOZ_ASSERT(range < 54);
+  return EnforceRange(cx, val, noun, msg, (uint64_t(1) << range) - 1, value);
+}
+
+static bool GetLimits(JSContext* cx, HandleObject obj, LimitsKind kind,
+                      Limits* limits) {
+  limits->indexType = IndexType::I32;
+
+  // Memory limits may specify an alternate index type, and we need this to
+  // check the ranges for initial and maximum, so look for the index type first.
+  if (kind == LimitsKind::Memory) {
+#ifdef ENABLE_WASM_MEMORY64
+    // Get the index type field
+    JSAtom* indexTypeAtom = Atomize(cx, "index", strlen("index"));
+    if (!indexTypeAtom) {
+      return false;
+    }
+    RootedId indexTypeId(cx, AtomToId(indexTypeAtom));
+
+    RootedValue indexTypeVal(cx);
+    if (!GetProperty(cx, obj, obj, indexTypeId, &indexTypeVal)) {
+      return false;
+    }
+
+    // The index type has a default value
+    if (!indexTypeVal.isUndefined()) {
+      if (!ToIndexType(cx, indexTypeVal, &limits->indexType)) {
+        return false;
+      }
+
+      if (limits->indexType == IndexType::I64 && !Memory64Available(cx)) {
+        JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                  JSMSG_WASM_NO_MEM64_LINK);
+        return false;
+      }
+    }
+#endif
+  }
+
+  const char* noun = (kind == LimitsKind::Memory ? "Memory" : "Table");
+  // 2^48 is a valid value, so the range goes to 49 bits.  Values above 2^48 are
+  // filtered later, just as values above 2^16 are filtered for mem32.
+  const uint32_t range = limits->indexType == IndexType::I32 ? 32 : 49;
+  uint64_t limit = 0;
+
+  bool haveInitial = false;
+  if (!GetLimit(cx, obj, "initial", noun, "initial size", range, &haveInitial,
+                &limit)) {
+    return false;
+  }
+  if (haveInitial) {
+    limits->initial = limit;
+  }
+
+  bool haveMinimum = false;
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+  if (!GetLimit(cx, obj, "minimum", noun, "initial size", range, &haveMinimum,
+                &limit)) {
+    return false;
+  }
+  if (haveMinimum) {
+    limits->initial = limit;
+  }
+#endif
+
+  if (!(haveInitial || haveMinimum)) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_MISSING_REQUIRED, "initial");
+    return false;
+  }
+  if (haveInitial && haveMinimum) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_SUPPLY_ONLY_ONE, "minimum", "initial");
+    return false;
+  }
+
+  bool haveMaximum = false;
+  if (!GetLimit(cx, obj, "maximum", noun, "maximum size", range, &haveMaximum,
+                &limit)) {
+    return false;
+  }
+  if (haveMaximum) {
+    limits->maximum = Some(limit);
+  }
+
+  limits->shared = Shareable::False;
+
+  // Memory limits may be shared.
+  if (kind == LimitsKind::Memory) {
+    // Get the shared field
+    JSAtom* sharedAtom = Atomize(cx, "shared", strlen("shared"));
+    if (!sharedAtom) {
+      return false;
+    }
+    RootedId sharedId(cx, AtomToId(sharedAtom));
+
+    RootedValue sharedVal(cx);
+    if (!GetProperty(cx, obj, obj, sharedId, &sharedVal)) {
+      return false;
+    }
+
+    // shared's default value is false, which is already the value set above.
+    if (!sharedVal.isUndefined()) {
+      limits->shared =
+          ToBoolean(sharedVal) ? Shareable::True : Shareable::False;
+
+      if (limits->shared == Shareable::True) {
+        if (!haveMaximum) {
+          JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                    JSMSG_WASM_MISSING_MAXIMUM, noun);
+          return false;
+        }
+
+        if (!cx->realm()
+                 ->creationOptions()
+                 .getSharedMemoryAndAtomicsEnabled()) {
+          JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                    JSMSG_WASM_NO_SHMEM_LINK);
+          return false;
+        }
+      }
+    }
+  }
+
+  return true;
+}
+
+static bool CheckLimits(JSContext* cx, uint64_t maximumField, LimitsKind kind,
+                        Limits* limits) {
+  const char* noun = (kind == LimitsKind::Memory ? "Memory" : "Table");
+
+  if (limits->initial > maximumField) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr, JSMSG_WASM_BAD_RANGE,
+                             noun, "initial size");
+    return false;
+  }
+
+  if (limits->maximum.isSome() &&
+      (*limits->maximum > maximumField || limits->initial > *limits->maximum)) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr, JSMSG_WASM_BAD_RANGE,
+                             noun, "maximum size");
+    return false;
+  }
+  return true;
+}
+
+template <class Class, const char* name>
+static JSObject* CreateWasmConstructor(JSContext* cx, JSProtoKey key) {
+  Rooted<JSAtom*> className(cx, Atomize(cx, name, strlen(name)));
+  if (!className) {
+    return nullptr;
+  }
+
+  return NewNativeConstructor(cx, Class::construct, 1, className);
+}
+
+static JSObject* GetWasmConstructorPrototype(JSContext* cx,
+                                             const CallArgs& callArgs,
+                                             JSProtoKey key) {
+  RootedObject proto(cx);
+  if (!GetPrototypeFromBuiltinConstructor(cx, callArgs, key, &proto)) {
+    return nullptr;
+  }
+  if (!proto) {
+    proto = GlobalObject::getOrCreatePrototype(cx, key);
+  }
+  return proto;
+}
+
+[[nodiscard]] static bool ParseValTypes(JSContext* cx, HandleValue src,
+                                        ValTypeVector& dest) {
+  JS::ForOfIterator iterator(cx);
+
+  if (!iterator.init(src, JS::ForOfIterator::ThrowOnNonIterable)) {
+    return false;
+  }
+
+  RootedValue nextParam(cx);
+  while (true) {
+    bool done;
+    if (!iterator.next(&nextParam, &done)) {
+      return false;
+    }
+    if (done) {
+      break;
+    }
+
+    ValType valType;
+    if (!ToValType(cx, nextParam, &valType) || !dest.append(valType)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+static JSString* UTF8CharsToString(JSContext* cx, const char* chars) {
+  return NewStringCopyUTF8Z(cx, JS::ConstUTF8CharsZ(chars, strlen(chars)));
+}
+
+[[nodiscard]] static JSObject* ValTypesToArray(JSContext* cx,
+                                               const ValTypeVector& valTypes) {
+  Rooted<ArrayObject*> arrayObj(cx, NewDenseEmptyArray(cx));
+  if (!arrayObj) {
+    return nullptr;
+  }
+  for (ValType valType : valTypes) {
+    RootedString type(cx,
+                      UTF8CharsToString(cx, ToString(valType, nullptr).get()));
+    if (!type) {
+      return nullptr;
+    }
+    if (!NewbornArrayPush(cx, arrayObj, StringValue(type))) {
+      return nullptr;
+    }
+  }
+  return arrayObj;
+}
+
+static JSObject* FuncTypeToObject(JSContext* cx, const FuncType& type) {
+  Rooted<IdValueVector> props(cx, IdValueVector(cx));
+
+  RootedObject parametersObj(cx, ValTypesToArray(cx, type.args()));
+  if (!parametersObj ||
+      !props.append(IdValuePair(NameToId(cx->names().parameters),
+                                ObjectValue(*parametersObj)))) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  RootedObject resultsObj(cx, ValTypesToArray(cx, type.results()));
+  if (!resultsObj || !props.append(IdValuePair(NameToId(cx->names().results),
+                                               ObjectValue(*resultsObj)))) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  return NewPlainObjectWithUniqueNames(cx, props.begin(), props.length());
+}
+
+static JSObject* TableTypeToObject(JSContext* cx, RefType type,
+                                   uint32_t initial, Maybe<uint32_t> maximum) {
+  Rooted<IdValueVector> props(cx, IdValueVector(cx));
+
+  RootedString elementType(
+      cx, UTF8CharsToString(cx, ToString(type, nullptr).get()));
+  if (!elementType || !props.append(IdValuePair(NameToId(cx->names().element),
+                                                StringValue(elementType)))) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  if (maximum.isSome()) {
+    if (!props.append(IdValuePair(NameToId(cx->names().maximum),
+                                  NumberValue(maximum.value())))) {
+      ReportOutOfMemory(cx);
+      return nullptr;
+    }
+  }
+
+  if (!props.append(
+          IdValuePair(NameToId(cx->names().minimum), NumberValue(initial)))) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  return NewPlainObjectWithUniqueNames(cx, props.begin(), props.length());
+}
+
+static JSObject* MemoryTypeToObject(JSContext* cx, bool shared,
+                                    wasm::IndexType indexType,
+                                    wasm::Pages minPages,
+                                    Maybe<wasm::Pages> maxPages) {
+  Rooted<IdValueVector> props(cx, IdValueVector(cx));
+  if (maxPages) {
+    double maxPagesNum;
+    if (indexType == IndexType::I32) {
+      maxPagesNum = double(mozilla::AssertedCast<uint32_t>(maxPages->value()));
+    } else {
+      // The maximum number of pages is 2^48.
+      maxPagesNum = double(maxPages->value());
+    }
+    if (!props.append(IdValuePair(NameToId(cx->names().maximum),
+                                  NumberValue(maxPagesNum)))) {
+      ReportOutOfMemory(cx);
+      return nullptr;
+    }
+  }
+
+  double minPagesNum;
+  if (indexType == IndexType::I32) {
+    minPagesNum = double(mozilla::AssertedCast<uint32_t>(minPages.value()));
+  } else {
+    minPagesNum = double(minPages.value());
+  }
+  if (!props.append(IdValuePair(NameToId(cx->names().minimum),
+                                NumberValue(minPagesNum)))) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+#  ifdef ENABLE_WASM_MEMORY64
+  RootedString it(
+      cx, JS_NewStringCopyZ(cx, indexType == IndexType::I32 ? "i32" : "i64"));
+  if (!it) {
+    return nullptr;
+  }
+  if (!props.append(
+          IdValuePair(NameToId(cx->names().index), StringValue(it)))) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+#  endif
+
+  if (!props.append(
+          IdValuePair(NameToId(cx->names().shared), BooleanValue(shared)))) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  return NewPlainObjectWithUniqueNames(cx, props.begin(), props.length());
+}
+
+static JSObject* GlobalTypeToObject(JSContext* cx, ValType type,
+                                    bool isMutable) {
+  Rooted<IdValueVector> props(cx, IdValueVector(cx));
+
+  if (!props.append(IdValuePair(NameToId(cx->names().mutable_),
+                                BooleanValue(isMutable)))) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  RootedString valueType(cx,
+                         UTF8CharsToString(cx, ToString(type, nullptr).get()));
+  if (!valueType || !props.append(IdValuePair(NameToId(cx->names().value),
+                                              StringValue(valueType)))) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  return NewPlainObjectWithUniqueNames(cx, props.begin(), props.length());
+}
+
+static JSObject* TagTypeToObject(JSContext* cx,
+                                 const wasm::ValTypeVector& params) {
+  Rooted<IdValueVector> props(cx, IdValueVector(cx));
+
+  RootedObject parametersObj(cx, ValTypesToArray(cx, params));
+  if (!parametersObj ||
+      !props.append(IdValuePair(NameToId(cx->names().parameters),
+                                ObjectValue(*parametersObj)))) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  return NewPlainObjectWithUniqueNames(cx, props.begin(), props.length());
+}
+#endif  // ENABLE_WASM_TYPE_REFLECTIONS
+
+// ============================================================================
+// WebAssembly.Module class and methods
+
+const JSClassOps WasmModuleObject::classOps_ = {
+    nullptr,                     // addProperty
+    nullptr,                     // delProperty
+    nullptr,                     // enumerate
+    nullptr,                     // newEnumerate
+    nullptr,                     // resolve
+    nullptr,                     // mayResolve
+    WasmModuleObject::finalize,  // finalize
+    nullptr,                     // call
+    nullptr,                     // construct
+    nullptr,                     // trace
+};
+
+const JSClass WasmModuleObject::class_ = {
+    "WebAssembly.Module",
+    JSCLASS_DELAY_METADATA_BUILDER |
+        JSCLASS_HAS_RESERVED_SLOTS(WasmModuleObject::RESERVED_SLOTS) |
+        JSCLASS_FOREGROUND_FINALIZE,
+    &WasmModuleObject::classOps_,
+    &WasmModuleObject::classSpec_,
+};
+
+const JSClass& WasmModuleObject::protoClass_ = PlainObject::class_;
+
+static constexpr char WasmModuleName[] = "Module";
+
+const ClassSpec WasmModuleObject::classSpec_ = {
+    CreateWasmConstructor<WasmModuleObject, WasmModuleName>,
+    GenericCreatePrototype<WasmModuleObject>,
+    WasmModuleObject::static_methods,
+    nullptr,
+    WasmModuleObject::methods,
+    WasmModuleObject::properties,
+    nullptr,
+    ClassSpec::DontDefineConstructor};
+
+const JSPropertySpec WasmModuleObject::properties[] = {
+    JS_STRING_SYM_PS(toStringTag, "WebAssembly.Module", JSPROP_READONLY),
+    JS_PS_END};
+
+const JSFunctionSpec WasmModuleObject::methods[] = {JS_FS_END};
+
+const JSFunctionSpec WasmModuleObject::static_methods[] = {
+    JS_FN("imports", WasmModuleObject::imports, 1, JSPROP_ENUMERATE),
+    JS_FN("exports", WasmModuleObject::exports, 1, JSPROP_ENUMERATE),
+    JS_FN("customSections", WasmModuleObject::customSections, 2,
+          JSPROP_ENUMERATE),
+    JS_FS_END};
+
+/* static */
+void WasmModuleObject::finalize(JS::GCContext* gcx, JSObject* obj) {
+  const Module& module = obj->as<WasmModuleObject>().module();
+  obj->zone()->decJitMemory(module.codeLength(module.code().stableTier()));
+  gcx->release(obj, &module, module.gcMallocBytesExcludingCode(),
+               MemoryUse::WasmModule);
+}
+
+static bool IsModuleObject(JSObject* obj, const Module** module) {
+  WasmModuleObject* mobj = obj->maybeUnwrapIf<WasmModuleObject>();
+  if (!mobj) {
+    return false;
+  }
+
+  *module = &mobj->module();
+  return true;
+}
+
+static bool GetModuleArg(JSContext* cx, CallArgs args, uint32_t numRequired,
+                         const char* name, const Module** module) {
+  if (!args.requireAtLeast(cx, name, numRequired)) {
+    return false;
+  }
+
+  if (!args[0].isObject() || !IsModuleObject(&args[0].toObject(), module)) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_MOD_ARG);
+    return false;
+  }
+
+  return true;
+}
+
+struct KindNames {
+  Rooted<PropertyName*> kind;
+  Rooted<PropertyName*> table;
+  Rooted<PropertyName*> memory;
+  Rooted<PropertyName*> tag;
+  Rooted<PropertyName*> type;
+
+  explicit KindNames(JSContext* cx)
+      : kind(cx), table(cx), memory(cx), tag(cx), type(cx) {}
+};
+
+static bool InitKindNames(JSContext* cx, KindNames* names) {
+  JSAtom* kind = Atomize(cx, "kind", strlen("kind"));
+  if (!kind) {
+    return false;
+  }
+  names->kind = kind->asPropertyName();
+
+  JSAtom* table = Atomize(cx, "table", strlen("table"));
+  if (!table) {
+    return false;
+  }
+  names->table = table->asPropertyName();
+
+  JSAtom* memory = Atomize(cx, "memory", strlen("memory"));
+  if (!memory) {
+    return false;
+  }
+  names->memory = memory->asPropertyName();
+
+  JSAtom* tag = Atomize(cx, "tag", strlen("tag"));
+  if (!tag) {
+    return false;
+  }
+  names->tag = tag->asPropertyName();
+
+  JSAtom* type = Atomize(cx, "type", strlen("type"));
+  if (!type) {
+    return false;
+  }
+  names->type = type->asPropertyName();
+
+  return true;
+}
+
+static JSString* KindToString(JSContext* cx, const KindNames& names,
+                              DefinitionKind kind) {
+  switch (kind) {
+    case DefinitionKind::Function:
+      return cx->names().function;
+    case DefinitionKind::Table:
+      return names.table;
+    case DefinitionKind::Memory:
+      return names.memory;
+    case DefinitionKind::Global:
+      return cx->names().global;
+    case DefinitionKind::Tag:
+      return names.tag;
+  }
+
+  MOZ_CRASH("invalid kind");
+}
+
+/* static */
+bool WasmModuleObject::imports(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  const Module* module;
+  if (!GetModuleArg(cx, args, 1, "WebAssembly.Module.imports", &module)) {
+    return false;
+  }
+
+  KindNames names(cx);
+  if (!InitKindNames(cx, &names)) {
+    return false;
+  }
+
+  RootedValueVector elems(cx);
+  if (!elems.reserve(module->imports().length())) {
+    return false;
+  }
+
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+  const Metadata& metadata = module->metadata();
+  const MetadataTier& metadataTier =
+      module->metadata(module->code().stableTier());
+
+  size_t numFuncImport = 0;
+  size_t numMemoryImport = 0;
+  size_t numGlobalImport = 0;
+  size_t numTableImport = 0;
+  size_t numTagImport = 0;
+#endif  // ENABLE_WASM_TYPE_REFLECTIONS
+
+  for (const Import& import : module->imports()) {
+    Rooted<IdValueVector> props(cx, IdValueVector(cx));
+    if (!props.reserve(3)) {
+      return false;
+    }
+
+    JSString* moduleStr = import.module.toAtom(cx);
+    if (!moduleStr) {
+      return false;
+    }
+    props.infallibleAppend(
+        IdValuePair(NameToId(cx->names().module), StringValue(moduleStr)));
+
+    JSString* nameStr = import.field.toAtom(cx);
+    if (!nameStr) {
+      return false;
+    }
+    props.infallibleAppend(
+        IdValuePair(NameToId(cx->names().name), StringValue(nameStr)));
+
+    JSString* kindStr = KindToString(cx, names, import.kind);
+    if (!kindStr) {
+      return false;
+    }
+    props.infallibleAppend(
+        IdValuePair(NameToId(names.kind), StringValue(kindStr)));
+
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+    RootedObject typeObj(cx);
+    switch (import.kind) {
+      case DefinitionKind::Function: {
+        size_t funcIndex = numFuncImport++;
+        const FuncType& funcType =
+            metadata.getFuncImportType(metadataTier.funcImports[funcIndex]);
+        typeObj = FuncTypeToObject(cx, funcType);
+        break;
+      }
+      case DefinitionKind::Table: {
+        size_t tableIndex = numTableImport++;
+        const TableDesc& table = metadata.tables[tableIndex];
+        typeObj = TableTypeToObject(cx, table.elemType, table.initialLength,
+                                    table.maximumLength);
+        break;
+      }
+      case DefinitionKind::Memory: {
+        size_t memoryIndex = numMemoryImport++;
+        const MemoryDesc& memory = metadata.memories[memoryIndex];
+        typeObj =
+            MemoryTypeToObject(cx, memory.isShared(), memory.indexType(),
+                               memory.initialPages(), memory.maximumPages());
+        break;
+      }
+      case DefinitionKind::Global: {
+        size_t globalIndex = numGlobalImport++;
+        const GlobalDesc& global = metadata.globals[globalIndex];
+        typeObj = GlobalTypeToObject(cx, global.type(), global.isMutable());
+        break;
+      }
+      case DefinitionKind::Tag: {
+        size_t tagIndex = numTagImport++;
+        const TagDesc& tag = metadata.tags[tagIndex];
+        typeObj = TagTypeToObject(cx, tag.type->argTypes());
+        break;
+      }
+    }
+
+    if (!typeObj || !props.append(IdValuePair(NameToId(names.type),
+                                              ObjectValue(*typeObj)))) {
+      ReportOutOfMemory(cx);
+      return false;
+    }
+#endif  // ENABLE_WASM_TYPE_REFLECTIONS
+
+    JSObject* obj =
+        NewPlainObjectWithUniqueNames(cx, props.begin(), props.length());
+    if (!obj) {
+      return false;
+    }
+
+    elems.infallibleAppend(ObjectValue(*obj));
+  }
+
+  JSObject* arr = NewDenseCopiedArray(cx, elems.length(), elems.begin());
+  if (!arr) {
+    return false;
+  }
+
+  args.rval().setObject(*arr);
+  return true;
+}
+
+/* static */
+bool WasmModuleObject::exports(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  const Module* module;
+  if (!GetModuleArg(cx, args, 1, "WebAssembly.Module.exports", &module)) {
+    return false;
+  }
+
+  KindNames names(cx);
+  if (!InitKindNames(cx, &names)) {
+    return false;
+  }
+
+  RootedValueVector elems(cx);
+  if (!elems.reserve(module->exports().length())) {
+    return false;
+  }
+
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+  const Metadata& metadata = module->metadata();
+  const MetadataTier& metadataTier =
+      module->metadata(module->code().stableTier());
+#endif  // ENABLE_WASM_TYPE_REFLECTIONS
+
+  for (const Export& exp : module->exports()) {
+    Rooted<IdValueVector> props(cx, IdValueVector(cx));
+    if (!props.reserve(2)) {
+      return false;
+    }
+
+    JSString* nameStr = exp.fieldName().toAtom(cx);
+    if (!nameStr) {
+      return false;
+    }
+    props.infallibleAppend(
+        IdValuePair(NameToId(cx->names().name), StringValue(nameStr)));
+
+    JSString* kindStr = KindToString(cx, names, exp.kind());
+    if (!kindStr) {
+      return false;
+    }
+    props.infallibleAppend(
+        IdValuePair(NameToId(names.kind), StringValue(kindStr)));
+
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+    RootedObject typeObj(cx);
+    switch (exp.kind()) {
+      case DefinitionKind::Function: {
+        const FuncExport& fe = metadataTier.lookupFuncExport(exp.funcIndex());
+        const FuncType& funcType = metadata.getFuncExportType(fe);
+        typeObj = FuncTypeToObject(cx, funcType);
+        break;
+      }
+      case DefinitionKind::Table: {
+        const TableDesc& table = metadata.tables[exp.tableIndex()];
+        typeObj = TableTypeToObject(cx, table.elemType, table.initialLength,
+                                    table.maximumLength);
+        break;
+      }
+      case DefinitionKind::Memory: {
+        const MemoryDesc& memory = metadata.memories[exp.memoryIndex()];
+        typeObj =
+            MemoryTypeToObject(cx, memory.isShared(), memory.indexType(),
+                               memory.initialPages(), memory.maximumPages());
+        break;
+      }
+      case DefinitionKind::Global: {
+        const GlobalDesc& global = metadata.globals[exp.globalIndex()];
+        typeObj = GlobalTypeToObject(cx, global.type(), global.isMutable());
+        break;
+      }
+      case DefinitionKind::Tag: {
+        const TagDesc& tag = metadata.tags[exp.tagIndex()];
+        typeObj = TagTypeToObject(cx, tag.type->argTypes());
+        break;
+      }
+    }
+
+    if (!typeObj || !props.append(IdValuePair(NameToId(names.type),
+                                              ObjectValue(*typeObj)))) {
+      ReportOutOfMemory(cx);
+      return false;
+    }
+#endif  // ENABLE_WASM_TYPE_REFLECTIONS
+
+    JSObject* obj =
+        NewPlainObjectWithUniqueNames(cx, props.begin(), props.length());
+    if (!obj) {
+      return false;
+    }
+
+    elems.infallibleAppend(ObjectValue(*obj));
+  }
+
+  JSObject* arr = NewDenseCopiedArray(cx, elems.length(), elems.begin());
+  if (!arr) {
+    return false;
+  }
+
+  args.rval().setObject(*arr);
+  return true;
+}
+
+/* static */
+bool WasmModuleObject::customSections(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  const Module* module;
+  if (!GetModuleArg(cx, args, 2, "WebAssembly.Module.customSections",
+                    &module)) {
+    return false;
+  }
+
+  Vector<char, 8> name(cx);
+  {
+    RootedString str(cx, ToString(cx, args.get(1)));
+    if (!str) {
+      return false;
+    }
+
+    Rooted<JSLinearString*> linear(cx, str->ensureLinear(cx));
+    if (!linear) {
+      return false;
+    }
+
+    if (!name.initLengthUninitialized(
+            JS::GetDeflatedUTF8StringLength(linear))) {
+      return false;
+    }
+
+    (void)JS::DeflateStringToUTF8Buffer(linear,
+                                        Span(name.begin(), name.length()));
+  }
+
+  RootedValueVector elems(cx);
+  Rooted<ArrayBufferObject*> buf(cx);
+  for (const CustomSection& cs : module->customSections()) {
+    if (name.length() != cs.name.length()) {
+      continue;
+    }
+    if (memcmp(name.begin(), cs.name.begin(), name.length()) != 0) {
+      continue;
+    }
+
+    buf = ArrayBufferObject::createZeroed(cx, cs.payload->length());
+    if (!buf) {
+      return false;
+    }
+
+    memcpy(buf->dataPointer(), cs.payload->begin(), cs.payload->length());
+    if (!elems.append(ObjectValue(*buf))) {
+      return false;
+    }
+  }
+
+  JSObject* arr = NewDenseCopiedArray(cx, elems.length(), elems.begin());
+  if (!arr) {
+    return false;
+  }
+
+  args.rval().setObject(*arr);
+  return true;
+}
+
+/* static */
+WasmModuleObject* WasmModuleObject::create(JSContext* cx, const Module& module,
+                                           HandleObject proto) {
+  AutoSetNewObjectMetadata metadata(cx);
+  auto* obj = NewObjectWithGivenProto<WasmModuleObject>(cx, proto);
+  if (!obj) {
+    return nullptr;
+  }
+
+  // The pipeline state on some architectures may retain stale instructions
+  // even after we invalidate the instruction cache. There is no generally
+  // available method to broadcast this pipeline flush to all threads after
+  // we've compiled new code, so conservatively perform one here when we're
+  // receiving a module that may have been compiled from another thread.
+  //
+  // The cost of this flush is expected to minimal enough to not be worth
+  // optimizing away in the case the module was compiled on this thread.
+  jit::FlushExecutionContext();
+
+  // This accounts for module allocation size (excluding code which is handled
+  // separately - see below). This assumes that the size of associated data
+  // doesn't change for the life of the WasmModuleObject. The size is counted
+  // once per WasmModuleObject referencing a Module.
+  InitReservedSlot(obj, MODULE_SLOT, const_cast<Module*>(&module),
+                   module.gcMallocBytesExcludingCode(), MemoryUse::WasmModule);
+  module.AddRef();
+
+  // Bug 1569888: We account for the first tier here; the second tier, if
+  // different, also needs to be accounted for.
+  cx->zone()->incJitMemory(module.codeLength(module.code().stableTier()));
+  return obj;
+}
+
+static bool GetBufferSource(JSContext* cx, JSObject* obj, unsigned errorNumber,
+                            MutableBytes* bytecode) {
+  *bytecode = cx->new_<ShareableBytes>();
+  if (!*bytecode) {
+    return false;
+  }
+
+  JSObject* unwrapped = CheckedUnwrapStatic(obj);
+
+  SharedMem<uint8_t*> dataPointer;
+  size_t byteLength;
+  if (!unwrapped || !IsBufferSource(unwrapped, &dataPointer, &byteLength)) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr, errorNumber);
+    return false;
+  }
+
+  if (!(*bytecode)->append(dataPointer.unwrap(), byteLength)) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  return true;
+}
+
+static bool ReportCompileWarnings(JSContext* cx,
+                                  const UniqueCharsVector& warnings) {
+  // Avoid spamming the console.
+  size_t numWarnings = std::min<size_t>(warnings.length(), 3);
+
+  for (size_t i = 0; i < numWarnings; i++) {
+    if (!WarnNumberASCII(cx, JSMSG_WASM_COMPILE_WARNING, warnings[i].get())) {
+      return false;
+    }
+  }
+
+  if (warnings.length() > numWarnings) {
+    if (!WarnNumberASCII(cx, JSMSG_WASM_COMPILE_WARNING,
+                         "other warnings suppressed")) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+/* static */
+bool WasmModuleObject::construct(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs callArgs = CallArgsFromVp(argc, vp);
+
+  Log(cx, "sync new Module() started");
+
+  if (!ThrowIfNotConstructing(cx, callArgs, "Module")) {
+    return false;
+  }
+
+  if (!cx->isRuntimeCodeGenEnabled(JS::RuntimeCode::WASM, nullptr)) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_CSP_BLOCKED_WASM, "WebAssembly.Module");
+    return false;
+  }
+
+  if (!callArgs.requireAtLeast(cx, "WebAssembly.Module", 1)) {
+    return false;
+  }
+
+  if (!callArgs[0].isObject()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_BUF_ARG);
+    return false;
+  }
+
+  MutableBytes bytecode;
+  if (!GetBufferSource(cx, &callArgs[0].toObject(), JSMSG_WASM_BAD_BUF_ARG,
+                       &bytecode)) {
+    return false;
+  }
+
+  FeatureOptions options;
+  if (!options.init(cx, callArgs.get(1))) {
+    return false;
+  }
+
+  SharedCompileArgs compileArgs =
+      InitCompileArgs(cx, options, "WebAssembly.Module");
+  if (!compileArgs) {
+    return false;
+  }
+
+  UniqueChars error;
+  UniqueCharsVector warnings;
+  SharedModule module =
+      CompileBuffer(*compileArgs, *bytecode, &error, &warnings, nullptr);
+
+  if (!ReportCompileWarnings(cx, warnings)) {
+    return false;
+  }
+  if (!module) {
+    if (error) {
+      JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                               JSMSG_WASM_COMPILE_ERROR, error.get());
+      return false;
+    }
+    return ThrowCompileOutOfMemory(cx);
+  }
+
+  RootedObject proto(
+      cx, GetWasmConstructorPrototype(cx, callArgs, JSProto_WasmModule));
+  if (!proto) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  RootedObject moduleObj(cx, WasmModuleObject::create(cx, *module, proto));
+  if (!moduleObj) {
+    return false;
+  }
+
+  Log(cx, "sync new Module() succeded");
+
+  callArgs.rval().setObject(*moduleObj);
+  return true;
+}
+
+const Module& WasmModuleObject::module() const {
+  MOZ_ASSERT(is<WasmModuleObject>());
+  return *(const Module*)getReservedSlot(MODULE_SLOT).toPrivate();
+}
+
+// ============================================================================
+// WebAssembly.Instance class and methods
+
+const JSClassOps WasmInstanceObject::classOps_ = {
+    nullptr,                       // addProperty
+    nullptr,                       // delProperty
+    nullptr,                       // enumerate
+    nullptr,                       // newEnumerate
+    nullptr,                       // resolve
+    nullptr,                       // mayResolve
+    WasmInstanceObject::finalize,  // finalize
+    nullptr,                       // call
+    nullptr,                       // construct
+    WasmInstanceObject::trace,     // trace
+};
+
+const JSClass WasmInstanceObject::class_ = {
+    "WebAssembly.Instance",
+    JSCLASS_DELAY_METADATA_BUILDER |
+        JSCLASS_HAS_RESERVED_SLOTS(WasmInstanceObject::RESERVED_SLOTS) |
+        JSCLASS_FOREGROUND_FINALIZE,
+    &WasmInstanceObject::classOps_,
+    &WasmInstanceObject::classSpec_,
+};
+
+const JSClass& WasmInstanceObject::protoClass_ = PlainObject::class_;
+
+static constexpr char WasmInstanceName[] = "Instance";
+
+const ClassSpec WasmInstanceObject::classSpec_ = {
+    CreateWasmConstructor<WasmInstanceObject, WasmInstanceName>,
+    GenericCreatePrototype<WasmInstanceObject>,
+    WasmInstanceObject::static_methods,
+    nullptr,
+    WasmInstanceObject::methods,
+    WasmInstanceObject::properties,
+    nullptr,
+    ClassSpec::DontDefineConstructor};
+
+static bool IsInstance(HandleValue v) {
+  return v.isObject() && v.toObject().is<WasmInstanceObject>();
+}
+
+/* static */
+bool WasmInstanceObject::exportsGetterImpl(JSContext* cx,
+                                           const CallArgs& args) {
+  args.rval().setObject(
+      args.thisv().toObject().as<WasmInstanceObject>().exportsObj());
+  return true;
+}
+
+/* static */
+bool WasmInstanceObject::exportsGetter(JSContext* cx, unsigned argc,
+                                       Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsInstance, exportsGetterImpl>(cx, args);
+}
+
+const JSPropertySpec WasmInstanceObject::properties[] = {
+    JS_PSG("exports", WasmInstanceObject::exportsGetter, JSPROP_ENUMERATE),
+    JS_STRING_SYM_PS(toStringTag, "WebAssembly.Instance", JSPROP_READONLY),
+    JS_PS_END};
+
+const JSFunctionSpec WasmInstanceObject::methods[] = {JS_FS_END};
+
+const JSFunctionSpec WasmInstanceObject::static_methods[] = {JS_FS_END};
+
+bool WasmInstanceObject::isNewborn() const {
+  MOZ_ASSERT(is<WasmInstanceObject>());
+  return getReservedSlot(INSTANCE_SLOT).isUndefined();
+}
+
+// WeakScopeMap maps from function index to js::Scope. This maps is weak
+// to avoid holding scope objects alive. The scopes are normally created
+// during debugging.
+//
+// This is defined here in order to avoid recursive dependency between
+// WasmJS.h and Scope.h.
+using WasmFunctionScopeMap =
+    WeakCache<GCHashMap<uint32_t, WeakHeapPtr<WasmFunctionScope*>,
+                        DefaultHasher<uint32_t>, CellAllocPolicy>>;
+class WasmInstanceObject::UnspecifiedScopeMap {
+ public:
+  WasmFunctionScopeMap& asWasmFunctionScopeMap() {
+    return *(WasmFunctionScopeMap*)this;
+  }
+};
+
+/* static */
+void WasmInstanceObject::finalize(JS::GCContext* gcx, JSObject* obj) {
+  WasmInstanceObject& instance = obj->as<WasmInstanceObject>();
+  gcx->delete_(obj, &instance.exports(), MemoryUse::WasmInstanceExports);
+  gcx->delete_(obj, &instance.scopes().asWasmFunctionScopeMap(),
+               MemoryUse::WasmInstanceScopes);
+  gcx->delete_(obj, &instance.indirectGlobals(),
+               MemoryUse::WasmInstanceGlobals);
+  if (!instance.isNewborn()) {
+    if (instance.instance().debugEnabled()) {
+      instance.instance().debug().finalize(gcx);
+    }
+    Instance::destroy(&instance.instance());
+    gcx->removeCellMemory(obj, sizeof(Instance),
+                          MemoryUse::WasmInstanceInstance);
+  }
+}
+
+/* static */
+void WasmInstanceObject::trace(JSTracer* trc, JSObject* obj) {
+  WasmInstanceObject& instanceObj = obj->as<WasmInstanceObject>();
+  instanceObj.exports().trace(trc);
+  instanceObj.indirectGlobals().trace(trc);
+  if (!instanceObj.isNewborn()) {
+    instanceObj.instance().tracePrivate(trc);
+  }
+}
+
+/* static */
+WasmInstanceObject* WasmInstanceObject::create(
+    JSContext* cx, const SharedCode& code,
+    const DataSegmentVector& dataSegments,
+    const ModuleElemSegmentVector& elemSegments, uint32_t instanceDataLength,
+    Handle<WasmMemoryObjectVector> memories, SharedTableVector&& tables,
+    const JSObjectVector& funcImports, const GlobalDescVector& globals,
+    const ValVector& globalImportValues,
+    const WasmGlobalObjectVector& globalObjs,
+    const WasmTagObjectVector& tagObjs, HandleObject proto,
+    UniqueDebugState maybeDebug) {
+  Rooted<UniquePtr<ExportMap>> exports(cx,
+                                       js::MakeUnique<ExportMap>(cx->zone()));
+  if (!exports) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  UniquePtr<WasmFunctionScopeMap> scopes =
+      js::MakeUnique<WasmFunctionScopeMap>(cx->zone(), cx->zone());
+  if (!scopes) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+  // Note that `scopes` is a WeakCache, auto-linked into a sweep list on the
+  // Zone, and so does not require rooting.
+
+  uint32_t indirectGlobals = 0;
+
+  for (uint32_t i = 0; i < globalObjs.length(); i++) {
+    if (globalObjs[i] && globals[i].isIndirect()) {
+      indirectGlobals++;
+    }
+  }
+
+  Rooted<UniquePtr<GlobalObjectVector>> indirectGlobalObjs(
+      cx, js::MakeUnique<GlobalObjectVector>(cx->zone()));
+  if (!indirectGlobalObjs || !indirectGlobalObjs->resize(indirectGlobals)) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  {
+    uint32_t next = 0;
+    for (uint32_t i = 0; i < globalObjs.length(); i++) {
+      if (globalObjs[i] && globals[i].isIndirect()) {
+        (*indirectGlobalObjs)[next++] = globalObjs[i];
+      }
+    }
+  }
+
+  Instance* instance = nullptr;
+  Rooted<WasmInstanceObject*> obj(cx);
+
+  {
+    // We must delay creating metadata for this object until after all its
+    // slots have been initialized. We must also create the metadata before
+    // calling Instance::init as that may allocate new objects.
+    AutoSetNewObjectMetadata metadata(cx);
+    obj = NewObjectWithGivenProto<WasmInstanceObject>(cx, proto);
+    if (!obj) {
+      return nullptr;
+    }
+
+    MOZ_ASSERT(obj->isTenured(), "assumed by WasmTableObject write barriers");
+
+    // Finalization assumes these slots are always initialized:
+    InitReservedSlot(obj, EXPORTS_SLOT, exports.release(),
+                     MemoryUse::WasmInstanceExports);
+
+    InitReservedSlot(obj, SCOPES_SLOT, scopes.release(),
+                     MemoryUse::WasmInstanceScopes);
+
+    InitReservedSlot(obj, GLOBALS_SLOT, indirectGlobalObjs.release(),
+                     MemoryUse::WasmInstanceGlobals);
+
+    obj->initReservedSlot(INSTANCE_SCOPE_SLOT, UndefinedValue());
+
+    // The INSTANCE_SLOT may not be initialized if Instance allocation fails,
+    // leading to an observable "newborn" state in tracing/finalization.
+    MOZ_ASSERT(obj->isNewborn());
+
+    // Create this just before constructing Instance to avoid rooting hazards.
+    instance = Instance::create(cx, obj, code, instanceDataLength,
+                                std::move(tables), std::move(maybeDebug));
+    if (!instance) {
+      return nullptr;
+    }
+
+    InitReservedSlot(obj, INSTANCE_SLOT, instance,
+                     MemoryUse::WasmInstanceInstance);
+    MOZ_ASSERT(!obj->isNewborn());
+  }
+
+  if (!instance->init(cx, funcImports, globalImportValues, memories, globalObjs,
+                      tagObjs, dataSegments, elemSegments)) {
+    return nullptr;
+  }
+
+  return obj;
+}
+
+void WasmInstanceObject::initExportsObj(JSObject& exportsObj) {
+  MOZ_ASSERT(getReservedSlot(EXPORTS_OBJ_SLOT).isUndefined());
+  setReservedSlot(EXPORTS_OBJ_SLOT, ObjectValue(exportsObj));
+}
+
+static bool GetImportArg(JSContext* cx, HandleValue importArg,
+                         MutableHandleObject importObj) {
+  if (!importArg.isUndefined()) {
+    if (!importArg.isObject()) {
+      return ThrowBadImportArg(cx);
+    }
+    importObj.set(&importArg.toObject());
+  }
+  return true;
+}
+
+/* static */
+bool WasmInstanceObject::construct(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  Log(cx, "sync new Instance() started");
+
+  if (!ThrowIfNotConstructing(cx, args, "Instance")) {
+    return false;
+  }
+
+  if (!args.requireAtLeast(cx, "WebAssembly.Instance", 1)) {
+    return false;
+  }
+
+  const Module* module;
+  if (!args[0].isObject() || !IsModuleObject(&args[0].toObject(), &module)) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_MOD_ARG);
+    return false;
+  }
+
+  RootedObject importObj(cx);
+  if (!GetImportArg(cx, args.get(1), &importObj)) {
+    return false;
+  }
+
+  RootedObject proto(
+      cx, GetWasmConstructorPrototype(cx, args, JSProto_WasmInstance));
+  if (!proto) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  Rooted<ImportValues> imports(cx);
+  if (!GetImports(cx, *module, importObj, imports.address())) {
+    return false;
+  }
+
+  Rooted<WasmInstanceObject*> instanceObj(cx);
+  if (!module->instantiate(cx, imports.get(), proto, &instanceObj)) {
+    return false;
+  }
+
+  Log(cx, "sync new Instance() succeeded");
+
+  args.rval().setObject(*instanceObj);
+  return true;
+}
+
+Instance& WasmInstanceObject::instance() const {
+  MOZ_ASSERT(!isNewborn());
+  return *(Instance*)getReservedSlot(INSTANCE_SLOT).toPrivate();
+}
+
+JSObject& WasmInstanceObject::exportsObj() const {
+  return getReservedSlot(EXPORTS_OBJ_SLOT).toObject();
+}
+
+WasmInstanceObject::ExportMap& WasmInstanceObject::exports() const {
+  return *(ExportMap*)getReservedSlot(EXPORTS_SLOT).toPrivate();
+}
+
+WasmInstanceObject::UnspecifiedScopeMap& WasmInstanceObject::scopes() const {
+  return *(UnspecifiedScopeMap*)(getReservedSlot(SCOPES_SLOT).toPrivate());
+}
+
+WasmInstanceObject::GlobalObjectVector& WasmInstanceObject::indirectGlobals()
+    const {
+  return *(GlobalObjectVector*)getReservedSlot(GLOBALS_SLOT).toPrivate();
+}
+
+static bool WasmCall(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  RootedFunction callee(cx, &args.callee().as<JSFunction>());
+
+  Instance& instance = ExportedFunctionToInstance(callee);
+  uint32_t funcIndex = ExportedFunctionToFuncIndex(callee);
+  return instance.callExport(cx, funcIndex, args);
+}
+
+/*
+ * [SMDOC] Exported wasm functions and the jit-entry stubs
+ *
+ * ## The kinds of exported functions
+ *
+ * There are several kinds of exported wasm functions.  /Explicitly/ exported
+ * functions are:
+ *
+ *  - any wasm function exported via the export section
+ *  - any asm.js export
+ *  - the module start function
+ *
+ * There are also /implicitly/ exported functions, these are the functions whose
+ * indices in the module are referenced outside the code segment, eg, in element
+ * segments and in global initializers.
+ *
+ * ## Wasm functions as JSFunctions
+ *
+ * Any exported function can be manipulated by JS and wasm code, and to both the
+ * exported function is represented as a JSFunction.  To JS, that means that the
+ * function can be called in the same way as any other JSFunction.  To Wasm, it
+ * means that the function is a reference with the same representation as
+ * externref.
+ *
+ * However, the JSFunction object is created only when the function value is
+ * actually exposed to JS the first time.  The creation is performed by
+ * getExportedFunction(), below, as follows:
+ *
+ *  - A function exported via the export section (or from asm.js) is created
+ *    when the export object is created, which happens at instantiation time.
+ *
+ *  - A function implicitly exported via a table is created when the table
+ *    element is read (by JS or wasm) and a function value is needed to
+ *    represent that value.  Functions stored in tables by initializers have a
+ *    special representation that does not require the function object to be
+ *    created, as long as the initializing element segment uses the more
+ *    efficient index encoding instead of the more general expression encoding.
+ *
+ *  - A function implicitly exported via a global initializer is created when
+ *    the global is initialized.
+ *
+ *  - A function referenced from a ref.func instruction in code is created when
+ *    that instruction is executed the first time.
+ *
+ * The JSFunction representing a wasm function never changes: every reference to
+ * the wasm function that exposes the JSFunction gets the same JSFunction.  In
+ * particular, imported functions already have a JSFunction representation (from
+ * JS or from their home module), and will be exposed using that representation.
+ *
+ * The mapping from a wasm function to its JSFunction is instance-specific, and
+ * held in a hashmap in the instance.  If a module is shared across multiple
+ * instances, possibly in multiple threads, each instance will have its own
+ * JSFunction representing the wasm function.
+ *
+ * ## Stubs -- interpreter, eager, lazy, provisional, and absent
+ *
+ * While a Wasm exported function is just a JSFunction, the internal wasm ABI is
+ * neither the C++ ABI nor the JS JIT ABI, so there needs to be an extra step
+ * when C++ or JS JIT code calls wasm code.  For this, execution passes through
+ * a stub that is adapted to both the JS caller and the wasm callee.
+ *
+ * ### Interpreter stubs and jit-entry stubs
+ *
+ * When JS interpreted code calls a wasm function, we end up in
+ * Instance::callExport() to execute the call.  This function must enter wasm,
+ * and to do this it uses a stub that is specific to the wasm function (see
+ * GenerateInterpEntry) that is callable with the C++ interpreter ABI and which
+ * will convert arguments as necessary and enter compiled wasm code.
+ *
+ * The interpreter stub is created eagerly, when the module is compiled.
+ *
+ * However, the interpreter call path is slow, and when JS jitted code calls
+ * wasm we want to do better.  In this case, there is a different, optimized
+ * stub that is to be invoked, and it uses the JIT ABI.  This is the jit-entry
+ * stub for the function.  Jitted code will call a wasm function's jit-entry
+ * stub to invoke the function with the JIT ABI.  The stub will adapt the call
+ * to the wasm ABI.
+ *
+ * Some jit-entry stubs are created eagerly and some are created lazily.
+ *
+ * ### Eager jit-entry stubs
+ *
+ * The explicitly exported functions have stubs created for them eagerly.  Eager
+ * stubs are created with their tier when the module is compiled, see
+ * ModuleGenerator::finishCodeTier(), which calls wasm::GenerateStubs(), which
+ * generates stubs for functions with eager stubs.
+ *
+ * An eager stub for tier-1 is upgraded to tier-2 if the module tiers up, see
+ * below.
+ *
+ * ### Lazy jit-entry stubs
+ *
+ * Stubs are created lazily for all implicitly exported functions.  These
+ * functions may flow out to JS, but will only need a stub if they are ever
+ * called from jitted code.  (That's true for explicitly exported functions too,
+ * but for them the presumption is that they will be called.)
+ *
+ * Lazy stubs are created only when they are needed, and they are /doubly/ lazy,
+ * see getExportedFunction(), below: A function implicitly exported via a table
+ * or global may be manipulated eagerly by host code without actually being
+ * called (maybe ever), so we do not generate a lazy stub when the function
+ * object escapes to JS, but instead delay stub generation until the function is
+ * actually called.
+ *
+ * ### The provisional lazy jit-entry stub
+ *
+ * However, JS baseline compilation needs to have a stub to start with in order
+ * to allow it to attach CacheIR data to the call (or it deoptimizes the call as
+ * a C++ call).  Thus when the JSFunction for the wasm export is retrieved by JS
+ * code, a /provisional/ lazy jit-entry stub is associated with the function.
+ * The stub will invoke the wasm function on the slow interpreter path via
+ * callExport - if the function is ever called - and will cause a fast jit-entry
+ * stub to be created at the time of the call.  The provisional lazy stub is
+ * shared globally, it contains no function-specific or context-specific data.
+ *
+ * Thus, the final lazy jit-entry stubs are eventually created by
+ * Instance::callExport, when a call is routed through it on the slow path for
+ * any of the reasons given above.
+ *
+ * ### Absent jit-entry stubs
+ *
+ * Some functions never get jit-entry stubs.  The predicate canHaveJitEntry()
+ * determines if a wasm function gets a stub, and it will deny this if the
+ * function's signature exposes non-JS-compatible types (such as v128) or if
+ * stub optimization has been disabled by a jit option.  Calls to these
+ * functions will continue to go via callExport and use the slow interpreter
+ * stub.
+ *
+ * ## The jit-entry jump table
+ *
+ * The mapping from the exported function to its jit-entry stub is implemented
+ * by the jit-entry jump table in the JumpTables object (see WasmCode.h).  The
+ * jit-entry jump table entry for a function holds a stub that the jit can call
+ * to perform fast calls.
+ *
+ * While there is a single contiguous jump table, it has two logical sections:
+ * one for eager stubs, and one for lazy stubs.  These sections are initialized
+ * and updated separately, using logic that is specific to each section.
+ *
+ * The value of the table element for an eager stub is a pointer to the stub
+ * code in the current tier.  The pointer is installed just after the creation
+ * of the stub, before any code in the module is executed.  If the module later
+ * tiers up, the eager jit-entry stub for tier-1 code is replaced by one for
+ * tier-2 code, see the next section.
+ *
+ * Initially the value of the jump table element for a lazy stub is null.
+ *
+ * If the function is retrieved by JS (by getExportedFunction()) and is not
+ * barred from having a jit-entry, then the stub is upgraded to the shared
+ * provisional lazy jit-entry stub.  This upgrade happens to be racy if the
+ * module is shared, and so the update is atomic and only happens if the entry
+ * is already null.  Since the provisional lazy stub is shared, this is fine; if
+ * several threads try to upgrade at the same time, it is to the same shared
+ * value.
+ *
+ * If the retrieved function is later invoked (via callExport()), the stub is
+ * upgraded to an actual jit-entry stub for the current code tier, again if the
+ * function is allowed to have a jit-entry.  This is not racy -- though multiple
+ * threads can be trying to create a jit-entry stub at the same time, they do so
+ * under a lock and only the first to take the lock will be allowed to create a
+ * stub, the others will reuse the first-installed stub.
+ *
+ * If the module later tiers up, the lazy jit-entry stub for tier-1 code (if it
+ * exists) is replaced by one for tier-2 code, see the next section.
+ *
+ * (Note, the InterpEntry stub is never stored in the jit-entry table, as it
+ * uses the C++ ABI, not the JIT ABI.  It is accessible through the
+ * FunctionEntry.)
+ *
+ * ### Interaction of the jit-entry jump table and tiering
+ *
+ * (For general info about tiering, see the comment in WasmCompile.cpp.)
+ *
+ * The jit-entry stub, whether eager or lazy, is specific to a code tier - a
+ * stub will invoke the code for its function for the tier.  When we tier up,
+ * new jit-entry stubs must be created that reference tier-2 code, and must then
+ * be patched into the jit-entry table.  The complication here is that, since
+ * the jump table is shared with its code between instances on multiple threads,
+ * tier-1 code is running on other threads and new tier-1 specific jit-entry
+ * stubs may be created concurrently with trying to create the tier-2 stubs on
+ * the thread that performs the tiering-up.  Indeed, there may also be
+ * concurrent attempts to upgrade null jit-entries to the provisional lazy stub.
+ *
+ * Eager stubs:
+ *
+ *  - Eager stubs for tier-2 code are patched in racily by Module::finishTier2()
+ *    along with code pointers for tiering; nothing conflicts with these writes.
+ *
+ * Lazy stubs:
+ *
+ *  - An upgrade from a null entry to a lazy provisional stub is atomic and can
+ *    only happen if the entry is null, and it only happens in
+ *    getExportedFunction().  No lazy provisional stub will be installed if
+ *    there's another stub present.
+ *
+ *  - The lazy tier-appropriate stub is installed by callExport() (really by
+ *    EnsureEntryStubs()) during the first invocation of the exported function
+ *    that reaches callExport().  That invocation must be from within JS, and so
+ *    the jit-entry element can't be null, because a prior getExportedFunction()
+ *    will have ensured that it is not: the lazy provisional stub will have been
+ *    installed.  Hence the installing of the lazy tier-appropriate stub does
+ *    not race with the installing of the lazy provisional stub.
+ *
+ *  - A lazy tier-1 stub is upgraded to a lazy tier-2 stub by
+ *    Module::finishTier2().  The upgrade needs to ensure that all tier-1 stubs
+ *    are upgraded, and that once the upgrade is finished, callExport() will
+ *    only create tier-2 lazy stubs.  (This upgrading does not upgrade lazy
+ *    provisional stubs or absent stubs.)
+ *
+ *    The locking protocol ensuring that all stubs are upgraded properly and
+ *    that the system switches to creating tier-2 stubs is implemented in
+ *    Module::finishTier2() and EnsureEntryStubs():
+ *
+ *    There are two locks, one per code tier.
+ *
+ *    EnsureEntryStubs() is attempting to create a tier-appropriate lazy stub,
+ *    so it takes the lock for the current best tier, checks to see if there is
+ *    a stub, and exits if there is.  If the tier changed racily it takes the
+ *    other lock too, since that is now the lock for the best tier.  Then it
+ *    creates the stub, installs it, and releases the locks.  Thus at most one
+ *    stub per tier can be created at a time.
+ *
+ *    Module::finishTier2() takes both locks (tier-1 before tier-2), thus
+ *    preventing EnsureEntryStubs() from creating stubs while stub upgrading is
+ *    going on, and itself waiting until EnsureEntryStubs() is not active.  Once
+ *    it has both locks, it upgrades all lazy stubs and makes tier-2 the new
+ *    best tier.  Should EnsureEntryStubs subsequently enter, it will find that
+ *    a stub already exists at tier-2 and will exit early.
+ *
+ * (It would seem that the locking protocol could be simplified a little by
+ * having only one lock, hanging off the Code object, or by unconditionally
+ * taking both locks in EnsureEntryStubs().  However, in some cases where we
+ * acquire a lock the Code object is not readily available, so plumbing would
+ * have to be added, and in EnsureEntryStubs(), there are sometimes not two code
+ * tiers.)
+ *
+ * ## Stub lifetimes and serialization
+ *
+ * Eager jit-entry stub code, along with stub code for import functions, is
+ * serialized along with the tier-2 code for the module.
+ *
+ * Lazy stub code and thunks for builtin functions (including the provisional
+ * lazy jit-entry stub) are never serialized.
+ */
+
+/* static */
+bool WasmInstanceObject::getExportedFunction(
+    JSContext* cx, Handle<WasmInstanceObject*> instanceObj, uint32_t funcIndex,
+    MutableHandleFunction fun) {
+  if (ExportMap::Ptr p = instanceObj->exports().lookup(funcIndex)) {
+    fun.set(p->value());
+    return true;
+  }
+
+  const Instance& instance = instanceObj->instance();
+  const FuncExport& funcExport =
+      instance.metadata(instance.code().bestTier()).lookupFuncExport(funcIndex);
+  const TypeDef& funcTypeDef =
+      instance.metadata().getFuncExportTypeDef(funcExport);
+  unsigned numArgs = funcTypeDef.funcType().args().length();
+
+  if (instance.isAsmJS()) {
+    // asm.js needs to act like a normal JS function which means having the
+    // name from the original source and being callable as a constructor.
+    Rooted<JSAtom*> name(cx, instance.getFuncDisplayAtom(cx, funcIndex));
+    if (!name) {
+      return false;
+    }
+    fun.set(NewNativeConstructor(cx, WasmCall, numArgs, name,
+                                 gc::AllocKind::FUNCTION_EXTENDED,
+                                 TenuredObject, FunctionFlags::ASMJS_CTOR));
+    if (!fun) {
+      return false;
+    }
+
+    // asm.js does not support jit entries.
+    fun->setWasmFuncIndex(funcIndex);
+  } else {
+    Rooted<JSAtom*> name(cx, NumberToAtom(cx, funcIndex));
+    if (!name) {
+      return false;
+    }
+    RootedObject proto(cx);
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+    proto = GlobalObject::getOrCreatePrototype(cx, JSProto_WasmFunction);
+    if (!proto) {
+      return false;
+    }
+#endif
+    fun.set(NewFunctionWithProto(
+        cx, WasmCall, numArgs, FunctionFlags::WASM, nullptr, name, proto,
+        gc::AllocKind::FUNCTION_EXTENDED, TenuredObject));
+    if (!fun) {
+      return false;
+    }
+
+    // Some applications eagerly access all table elements which currently
+    // triggers worst-case behavior for lazy stubs, since each will allocate a
+    // separate 4kb code page. Most eagerly-accessed functions are not called,
+    // so use a shared, provisional (and slow) lazy stub as JitEntry and wait
+    // until Instance::callExport() to create the fast entry stubs.
+    if (funcTypeDef.funcType().canHaveJitEntry()) {
+      if (!funcExport.hasEagerStubs()) {
+        if (!EnsureBuiltinThunksInitialized()) {
+          return false;
+        }
+        void* provisionalLazyJitEntryStub = ProvisionalLazyJitEntryStub();
+        MOZ_ASSERT(provisionalLazyJitEntryStub);
+        instance.code().setJitEntryIfNull(funcIndex,
+                                          provisionalLazyJitEntryStub);
+      }
+      fun->setWasmJitEntry(instance.code().getAddressOfJitEntry(funcIndex));
+    } else {
+      fun->setWasmFuncIndex(funcIndex);
+    }
+  }
+
+  fun->setExtendedSlot(FunctionExtended::WASM_INSTANCE_SLOT,
+                       PrivateValue(const_cast<Instance*>(&instance)));
+  fun->setExtendedSlot(FunctionExtended::WASM_STV_SLOT,
+                       PrivateValue((void*)funcTypeDef.superTypeVector()));
+
+  const CodeTier& codeTier =
+      instance.code().codeTier(instance.code().bestTier());
+  const CodeRange& codeRange = codeTier.metadata().codeRange(funcExport);
+
+  fun->setExtendedSlot(FunctionExtended::WASM_FUNC_UNCHECKED_ENTRY_SLOT,
+                       PrivateValue(codeTier.segment().base() +
+                                    codeRange.funcUncheckedCallEntry()));
+
+  if (!instanceObj->exports().putNew(funcIndex, fun)) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  return true;
+}
+
+const CodeRange& WasmInstanceObject::getExportedFunctionCodeRange(
+    JSFunction* fun, Tier tier) {
+  uint32_t funcIndex = ExportedFunctionToFuncIndex(fun);
+  MOZ_ASSERT(exports().lookup(funcIndex)->value() == fun);
+  const MetadataTier& metadata = instance().metadata(tier);
+  return metadata.codeRange(metadata.lookupFuncExport(funcIndex));
+}
+
+/* static */
+WasmInstanceScope* WasmInstanceObject::getScope(
+    JSContext* cx, Handle<WasmInstanceObject*> instanceObj) {
+  if (!instanceObj->getReservedSlot(INSTANCE_SCOPE_SLOT).isUndefined()) {
+    return (WasmInstanceScope*)instanceObj->getReservedSlot(INSTANCE_SCOPE_SLOT)
+        .toGCThing();
+  }
+
+  Rooted<WasmInstanceScope*> instanceScope(
+      cx, WasmInstanceScope::create(cx, instanceObj));
+  if (!instanceScope) {
+    return nullptr;
+  }
+
+  instanceObj->setReservedSlot(INSTANCE_SCOPE_SLOT,
+                               PrivateGCThingValue(instanceScope));
+
+  return instanceScope;
+}
+
+/* static */
+WasmFunctionScope* WasmInstanceObject::getFunctionScope(
+    JSContext* cx, Handle<WasmInstanceObject*> instanceObj,
+    uint32_t funcIndex) {
+  if (auto p =
+          instanceObj->scopes().asWasmFunctionScopeMap().lookup(funcIndex)) {
+    return p->value();
+  }
+
+  Rooted<WasmInstanceScope*> instanceScope(
+      cx, WasmInstanceObject::getScope(cx, instanceObj));
+  if (!instanceScope) {
+    return nullptr;
+  }
+
+  Rooted<WasmFunctionScope*> funcScope(
+      cx, WasmFunctionScope::create(cx, instanceScope, funcIndex));
+  if (!funcScope) {
+    return nullptr;
+  }
+
+  if (!instanceObj->scopes().asWasmFunctionScopeMap().putNew(funcIndex,
+                                                             funcScope)) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  return funcScope;
+}
+
+bool wasm::IsWasmExportedFunction(JSFunction* fun) {
+  return fun->kind() == FunctionFlags::Wasm;
+}
+
+Instance& wasm::ExportedFunctionToInstance(JSFunction* fun) {
+  return fun->wasmInstance();
+}
+
+WasmInstanceObject* wasm::ExportedFunctionToInstanceObject(JSFunction* fun) {
+  return fun->wasmInstance().object();
+}
+
+uint32_t wasm::ExportedFunctionToFuncIndex(JSFunction* fun) {
+  return fun->wasmInstance().code().getFuncIndex(fun);
+}
+
+// ============================================================================
+// WebAssembly.Memory class and methods
+
+const JSClassOps WasmMemoryObject::classOps_ = {
+    nullptr,                     // addProperty
+    nullptr,                     // delProperty
+    nullptr,                     // enumerate
+    nullptr,                     // newEnumerate
+    nullptr,                     // resolve
+    nullptr,                     // mayResolve
+    WasmMemoryObject::finalize,  // finalize
+    nullptr,                     // call
+    nullptr,                     // construct
+    nullptr,                     // trace
+};
+
+const JSClass WasmMemoryObject::class_ = {
+    "WebAssembly.Memory",
+    JSCLASS_DELAY_METADATA_BUILDER |
+        JSCLASS_HAS_RESERVED_SLOTS(WasmMemoryObject::RESERVED_SLOTS) |
+        JSCLASS_FOREGROUND_FINALIZE,
+    &WasmMemoryObject::classOps_, &WasmMemoryObject::classSpec_};
+
+const JSClass& WasmMemoryObject::protoClass_ = PlainObject::class_;
+
+static constexpr char WasmMemoryName[] = "Memory";
+
+static JSObject* CreateWasmMemoryPrototype(JSContext* cx, JSProtoKey key) {
+  RootedObject proto(cx, GlobalObject::createBlankPrototype(
+                             cx, cx->global(), &WasmMemoryObject::protoClass_));
+  if (!proto) {
+    return nullptr;
+  }
+  if (MemoryControlAvailable(cx)) {
+    if (!JS_DefineFunctions(cx, proto,
+                            WasmMemoryObject::memoryControlMethods)) {
+      return nullptr;
+    }
+  }
+  return proto;
+}
+
+const ClassSpec WasmMemoryObject::classSpec_ = {
+    CreateWasmConstructor<WasmMemoryObject, WasmMemoryName>,
+    CreateWasmMemoryPrototype,
+    WasmMemoryObject::static_methods,
+    nullptr,
+    WasmMemoryObject::methods,
+    WasmMemoryObject::properties,
+    nullptr,
+    ClassSpec::DontDefineConstructor};
+
+/* static */
+void WasmMemoryObject::finalize(JS::GCContext* gcx, JSObject* obj) {
+  WasmMemoryObject& memory = obj->as<WasmMemoryObject>();
+  if (memory.hasObservers()) {
+    gcx->delete_(obj, &memory.observers(), MemoryUse::WasmMemoryObservers);
+  }
+}
+
+/* static */
+WasmMemoryObject* WasmMemoryObject::create(
+    JSContext* cx, Handle<ArrayBufferObjectMaybeShared*> buffer, bool isHuge,
+    HandleObject proto) {
+  AutoSetNewObjectMetadata metadata(cx);
+  auto* obj = NewObjectWithGivenProto<WasmMemoryObject>(cx, proto);
+  if (!obj) {
+    return nullptr;
+  }
+
+  obj->initReservedSlot(BUFFER_SLOT, ObjectValue(*buffer));
+  obj->initReservedSlot(ISHUGE_SLOT, BooleanValue(isHuge));
+  MOZ_ASSERT(!obj->hasObservers());
+
+  return obj;
+}
+
+/* static */
+bool WasmMemoryObject::construct(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  if (!ThrowIfNotConstructing(cx, args, "Memory")) {
+    return false;
+  }
+
+  if (!args.requireAtLeast(cx, "WebAssembly.Memory", 1)) {
+    return false;
+  }
+
+  if (!args.get(0).isObject()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_DESC_ARG, "memory");
+    return false;
+  }
+
+  RootedObject obj(cx, &args[0].toObject());
+  Limits limits;
+  if (!GetLimits(cx, obj, LimitsKind::Memory, &limits) ||
+      !CheckLimits(cx, MaxMemoryLimitField(limits.indexType),
+                   LimitsKind::Memory, &limits)) {
+    return false;
+  }
+
+  if (Pages(limits.initial) > MaxMemoryPages(limits.indexType)) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_MEM_IMP_LIMIT);
+    return false;
+  }
+  MemoryDesc memory(limits);
+
+  Rooted<ArrayBufferObjectMaybeShared*> buffer(cx,
+                                               CreateWasmBuffer(cx, memory));
+  if (!buffer) {
+    return false;
+  }
+
+  RootedObject proto(cx,
+                     GetWasmConstructorPrototype(cx, args, JSProto_WasmMemory));
+  if (!proto) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  Rooted<WasmMemoryObject*> memoryObj(
+      cx, WasmMemoryObject::create(
+              cx, buffer, IsHugeMemoryEnabled(limits.indexType), proto));
+  if (!memoryObj) {
+    return false;
+  }
+
+  args.rval().setObject(*memoryObj);
+  return true;
+}
+
+static bool IsMemory(HandleValue v) {
+  return v.isObject() && v.toObject().is<WasmMemoryObject>();
+}
+
+/* static */
+bool WasmMemoryObject::bufferGetterImpl(JSContext* cx, const CallArgs& args) {
+  Rooted<WasmMemoryObject*> memoryObj(
+      cx, &args.thisv().toObject().as<WasmMemoryObject>());
+  Rooted<ArrayBufferObjectMaybeShared*> buffer(cx, &memoryObj->buffer());
+
+  if (memoryObj->isShared()) {
+    size_t memoryLength = memoryObj->volatileMemoryLength();
+    MOZ_ASSERT(memoryLength >= buffer->byteLength());
+
+    if (memoryLength > buffer->byteLength()) {
+      Rooted<SharedArrayBufferObject*> newBuffer(
+          cx, SharedArrayBufferObject::New(
+                  cx, memoryObj->sharedArrayRawBuffer(), memoryLength));
+      if (!newBuffer) {
+        return false;
+      }
+      // OK to addReference after we try to allocate because the memoryObj
+      // keeps the rawBuffer alive.
+      if (!memoryObj->sharedArrayRawBuffer()->addReference()) {
+        JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                  JSMSG_SC_SAB_REFCNT_OFLO);
+        return false;
+      }
+      buffer = newBuffer;
+      memoryObj->setReservedSlot(BUFFER_SLOT, ObjectValue(*newBuffer));
+    }
+  }
+
+  args.rval().setObject(*buffer);
+  return true;
+}
+
+/* static */
+bool WasmMemoryObject::bufferGetter(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsMemory, bufferGetterImpl>(cx, args);
+}
+
+const JSPropertySpec WasmMemoryObject::properties[] = {
+    JS_PSG("buffer", WasmMemoryObject::bufferGetter, JSPROP_ENUMERATE),
+    JS_STRING_SYM_PS(toStringTag, "WebAssembly.Memory", JSPROP_READONLY),
+    JS_PS_END};
+
+/* static */
+bool WasmMemoryObject::growImpl(JSContext* cx, const CallArgs& args) {
+  Rooted<WasmMemoryObject*> memory(
+      cx, &args.thisv().toObject().as<WasmMemoryObject>());
+
+  if (!args.requireAtLeast(cx, "WebAssembly.Memory.grow", 1)) {
+    return false;
+  }
+
+  uint32_t delta;
+  if (!EnforceRangeU32(cx, args.get(0), "Memory", "grow delta", &delta)) {
+    return false;
+  }
+
+  uint32_t ret = grow(memory, delta, cx);
+
+  if (ret == uint32_t(-1)) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr, JSMSG_WASM_BAD_GROW,
+                             "memory");
+    return false;
+  }
+
+  args.rval().setInt32(int32_t(ret));
+  return true;
+}
+
+/* static */
+bool WasmMemoryObject::grow(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsMemory, growImpl>(cx, args);
+}
+
+/* static */
+bool WasmMemoryObject::discardImpl(JSContext* cx, const CallArgs& args) {
+  Rooted<WasmMemoryObject*> memory(
+      cx, &args.thisv().toObject().as<WasmMemoryObject>());
+
+  if (!args.requireAtLeast(cx, "WebAssembly.Memory.discard", 2)) {
+    return false;
+  }
+
+  uint64_t byteOffset;
+  if (!EnforceRangeU64(cx, args.get(0), "Memory", "byte offset", &byteOffset)) {
+    return false;
+  }
+
+  uint64_t byteLen;
+  if (!EnforceRangeU64(cx, args.get(1), "Memory", "length", &byteLen)) {
+    return false;
+  }
+
+  if (byteOffset % wasm::PageSize != 0 || byteLen % wasm::PageSize != 0) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_UNALIGNED_ACCESS);
+    return false;
+  }
+
+  if (!wasm::MemoryBoundsCheck(byteOffset, byteLen,
+                               memory->volatileMemoryLength())) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_OUT_OF_BOUNDS);
+    return false;
+  }
+
+  discard(memory, byteOffset, byteLen, cx);
+
+  args.rval().setUndefined();
+  return true;
+}
+
+/* static */
+bool WasmMemoryObject::discard(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsMemory, discardImpl>(cx, args);
+}
+
+const JSFunctionSpec WasmMemoryObject::methods[] = {
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+    JS_FN("type", WasmMemoryObject::type, 0, JSPROP_ENUMERATE),
+#endif
+    JS_FN("grow", WasmMemoryObject::grow, 1, JSPROP_ENUMERATE), JS_FS_END};
+
+const JSFunctionSpec WasmMemoryObject::memoryControlMethods[] = {
+    JS_FN("discard", WasmMemoryObject::discard, 2, JSPROP_ENUMERATE),
+    JS_FS_END};
+
+const JSFunctionSpec WasmMemoryObject::static_methods[] = {JS_FS_END};
+
+ArrayBufferObjectMaybeShared& WasmMemoryObject::buffer() const {
+  return getReservedSlot(BUFFER_SLOT)
+      .toObject()
+      .as<ArrayBufferObjectMaybeShared>();
+}
+
+WasmSharedArrayRawBuffer* WasmMemoryObject::sharedArrayRawBuffer() const {
+  MOZ_ASSERT(isShared());
+  return buffer().as<SharedArrayBufferObject>().rawWasmBufferObject();
+}
+
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+bool WasmMemoryObject::typeImpl(JSContext* cx, const CallArgs& args) {
+  Rooted<WasmMemoryObject*> memoryObj(
+      cx, &args.thisv().toObject().as<WasmMemoryObject>());
+  RootedObject typeObj(
+      cx, MemoryTypeToObject(cx, memoryObj->isShared(), memoryObj->indexType(),
+                             memoryObj->volatilePages(),
+                             memoryObj->sourceMaxPages()));
+  if (!typeObj) {
+    return false;
+  }
+  args.rval().setObject(*typeObj);
+  return true;
+}
+
+bool WasmMemoryObject::type(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsMemory, typeImpl>(cx, args);
+}
+#endif
+
+size_t WasmMemoryObject::volatileMemoryLength() const {
+  if (isShared()) {
+    return sharedArrayRawBuffer()->volatileByteLength();
+  }
+  return buffer().byteLength();
+}
+
+wasm::Pages WasmMemoryObject::volatilePages() const {
+  if (isShared()) {
+    return sharedArrayRawBuffer()->volatileWasmPages();
+  }
+  return buffer().wasmPages();
+}
+
+wasm::Pages WasmMemoryObject::clampedMaxPages() const {
+  if (isShared()) {
+    return sharedArrayRawBuffer()->wasmClampedMaxPages();
+  }
+  return buffer().wasmClampedMaxPages();
+}
+
+Maybe<wasm::Pages> WasmMemoryObject::sourceMaxPages() const {
+  if (isShared()) {
+    return Some(sharedArrayRawBuffer()->wasmSourceMaxPages());
+  }
+  return buffer().wasmSourceMaxPages();
+}
+
+wasm::IndexType WasmMemoryObject::indexType() const {
+  if (isShared()) {
+    return sharedArrayRawBuffer()->wasmIndexType();
+  }
+  return buffer().wasmIndexType();
+}
+
+bool WasmMemoryObject::isShared() const {
+  return buffer().is<SharedArrayBufferObject>();
+}
+
+bool WasmMemoryObject::hasObservers() const {
+  return !getReservedSlot(OBSERVERS_SLOT).isUndefined();
+}
+
+WasmMemoryObject::InstanceSet& WasmMemoryObject::observers() const {
+  MOZ_ASSERT(hasObservers());
+  return *reinterpret_cast<InstanceSet*>(
+      getReservedSlot(OBSERVERS_SLOT).toPrivate());
+}
+
+WasmMemoryObject::InstanceSet* WasmMemoryObject::getOrCreateObservers(
+    JSContext* cx) {
+  if (!hasObservers()) {
+    auto observers = MakeUnique<InstanceSet>(cx->zone(), cx->zone());
+    if (!observers) {
+      ReportOutOfMemory(cx);
+      return nullptr;
+    }
+
+    InitReservedSlot(this, OBSERVERS_SLOT, observers.release(),
+                     MemoryUse::WasmMemoryObservers);
+  }
+
+  return &observers();
+}
+
+bool WasmMemoryObject::isHuge() const {
+  return getReservedSlot(ISHUGE_SLOT).toBoolean();
+}
+
+bool WasmMemoryObject::movingGrowable() const {
+  return !isHuge() && !buffer().wasmSourceMaxPages();
+}
+
+size_t WasmMemoryObject::boundsCheckLimit() const {
+  if (!buffer().isWasm() || isHuge()) {
+    return buffer().byteLength();
+  }
+  size_t mappedSize = buffer().wasmMappedSize();
+#if !defined(JS_64BIT)
+  // See clamping performed in CreateSpecificWasmBuffer().  On 32-bit systems
+  // we do not want to overflow a uint32_t.  For the other 64-bit compilers,
+  // all constraints are implied by the largest accepted value for a memory's
+  // max field.
+  MOZ_ASSERT(mappedSize < UINT32_MAX);
+#endif
+  MOZ_ASSERT(mappedSize % wasm::PageSize == 0);
+  MOZ_ASSERT(mappedSize >= wasm::GuardSize);
+  MOZ_ASSERT(wasm::IsValidBoundsCheckImmediate(mappedSize - wasm::GuardSize));
+  size_t limit = mappedSize - wasm::GuardSize;
+  MOZ_ASSERT(limit <= MaxMemoryBoundsCheckLimit(indexType()));
+  return limit;
+}
+
+bool WasmMemoryObject::addMovingGrowObserver(JSContext* cx,
+                                             WasmInstanceObject* instance) {
+  MOZ_ASSERT(movingGrowable());
+
+  InstanceSet* observers = getOrCreateObservers(cx);
+  if (!observers) {
+    return false;
+  }
+
+  // A memory can be imported multiple times into an instance, but we only
+  // register the instance as an observer once.
+  if (!observers->put(instance)) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  return true;
+}
+
+/* static */
+uint64_t WasmMemoryObject::growShared(Handle<WasmMemoryObject*> memory,
+                                      uint64_t delta) {
+  WasmSharedArrayRawBuffer* rawBuf = memory->sharedArrayRawBuffer();
+  WasmSharedArrayRawBuffer::Lock lock(rawBuf);
+
+  Pages oldNumPages = rawBuf->volatileWasmPages();
+  Pages newPages = oldNumPages;
+  if (!newPages.checkedIncrement(Pages(delta))) {
+    return uint64_t(int64_t(-1));
+  }
+
+  if (!rawBuf->wasmGrowToPagesInPlace(lock, memory->indexType(), newPages)) {
+    return uint64_t(int64_t(-1));
+  }
+  // New buffer objects will be created lazily in all agents (including in
+  // this agent) by bufferGetterImpl, above, so no more work to do here.
+
+  return oldNumPages.value();
+}
+
+/* static */
+uint64_t WasmMemoryObject::grow(Handle<WasmMemoryObject*> memory,
+                                uint64_t delta, JSContext* cx) {
+  if (memory->isShared()) {
+    return growShared(memory, delta);
+  }
+
+  Rooted<ArrayBufferObject*> oldBuf(cx,
+                                    &memory->buffer().as<ArrayBufferObject>());
+
+#if !defined(JS_64BIT)
+  // TODO (large ArrayBuffer): See more information at the definition of
+  // MaxMemoryBytes().
+  MOZ_ASSERT(MaxMemoryBytes(memory->indexType()) <= UINT32_MAX,
+             "Avoid 32-bit overflows");
+#endif
+
+  Pages oldNumPages = oldBuf->wasmPages();
+  Pages newPages = oldNumPages;
+  if (!newPages.checkedIncrement(Pages(delta))) {
+    return uint64_t(int64_t(-1));
+  }
+
+  ArrayBufferObject* newBuf;
+  if (memory->movingGrowable()) {
+    MOZ_ASSERT(!memory->isHuge());
+    newBuf = ArrayBufferObject::wasmMovingGrowToPages(memory->indexType(),
+                                                      newPages, oldBuf, cx);
+  } else {
+    newBuf = ArrayBufferObject::wasmGrowToPagesInPlace(memory->indexType(),
+                                                       newPages, oldBuf, cx);
+  }
+  if (!newBuf) {
+    return uint64_t(int64_t(-1));
+  }
+
+  memory->setReservedSlot(BUFFER_SLOT, ObjectValue(*newBuf));
+
+  // Only notify moving-grow-observers after the BUFFER_SLOT has been updated
+  // since observers will call buffer().
+  if (memory->hasObservers()) {
+    for (InstanceSet::Range r = memory->observers().all(); !r.empty();
+         r.popFront()) {
+      r.front()->instance().onMovingGrowMemory(memory);
+    }
+  }
+
+  return oldNumPages.value();
+}
+
+/* static */
+void WasmMemoryObject::discard(Handle<WasmMemoryObject*> memory,
+                               uint64_t byteOffset, uint64_t byteLen,
+                               JSContext* cx) {
+  if (memory->isShared()) {
+    Rooted<SharedArrayBufferObject*> buf(
+        cx, &memory->buffer().as<SharedArrayBufferObject>());
+    SharedArrayBufferObject::wasmDiscard(buf, byteOffset, byteLen);
+  } else {
+    Rooted<ArrayBufferObject*> buf(cx,
+                                   &memory->buffer().as<ArrayBufferObject>());
+    ArrayBufferObject::wasmDiscard(buf, byteOffset, byteLen);
+  }
+}
+
+bool js::wasm::IsSharedWasmMemoryObject(JSObject* obj) {
+  WasmMemoryObject* mobj = obj->maybeUnwrapIf<WasmMemoryObject>();
+  return mobj && mobj->isShared();
+}
+
+// ============================================================================
+// WebAssembly.Table class and methods
+
+const JSClassOps WasmTableObject::classOps_ = {
+    nullptr,                    // addProperty
+    nullptr,                    // delProperty
+    nullptr,                    // enumerate
+    nullptr,                    // newEnumerate
+    nullptr,                    // resolve
+    nullptr,                    // mayResolve
+    WasmTableObject::finalize,  // finalize
+    nullptr,                    // call
+    nullptr,                    // construct
+    WasmTableObject::trace,     // trace
+};
+
+const JSClass WasmTableObject::class_ = {
+    "WebAssembly.Table",
+    JSCLASS_DELAY_METADATA_BUILDER |
+        JSCLASS_HAS_RESERVED_SLOTS(WasmTableObject::RESERVED_SLOTS) |
+        JSCLASS_FOREGROUND_FINALIZE,
+    &WasmTableObject::classOps_, &WasmTableObject::classSpec_};
+
+const JSClass& WasmTableObject::protoClass_ = PlainObject::class_;
+
+static constexpr char WasmTableName[] = "Table";
+
+const ClassSpec WasmTableObject::classSpec_ = {
+    CreateWasmConstructor<WasmTableObject, WasmTableName>,
+    GenericCreatePrototype<WasmTableObject>,
+    WasmTableObject::static_methods,
+    nullptr,
+    WasmTableObject::methods,
+    WasmTableObject::properties,
+    nullptr,
+    ClassSpec::DontDefineConstructor};
+
+bool WasmTableObject::isNewborn() const {
+  MOZ_ASSERT(is<WasmTableObject>());
+  return getReservedSlot(TABLE_SLOT).isUndefined();
+}
+
+/* static */
+void WasmTableObject::finalize(JS::GCContext* gcx, JSObject* obj) {
+  WasmTableObject& tableObj = obj->as<WasmTableObject>();
+  if (!tableObj.isNewborn()) {
+    auto& table = tableObj.table();
+    gcx->release(obj, &table, table.gcMallocBytes(), MemoryUse::WasmTableTable);
+  }
+}
+
+/* static */
+void WasmTableObject::trace(JSTracer* trc, JSObject* obj) {
+  WasmTableObject& tableObj = obj->as<WasmTableObject>();
+  if (!tableObj.isNewborn()) {
+    tableObj.table().tracePrivate(trc);
+  }
+}
+
+// Return the JS value to use when a parameter to a function requiring a table
+// value is omitted. An implementation of [1].
+//
+// [1]
+// https://webassembly.github.io/reference-types/js-api/index.html#defaultvalue
+static Value RefTypeDefautValue(wasm::RefType tableType) {
+  return tableType.isExtern() ? UndefinedValue() : NullValue();
+}
+
+static bool CheckRefTypeValue(JSContext* cx, wasm::RefType type,
+                              HandleValue value) {
+  RootedFunction fun(cx);
+  RootedAnyRef any(cx, AnyRef::null());
+
+  return CheckRefType(cx, type, value, &fun, &any);
+}
+
+/* static */
+WasmTableObject* WasmTableObject::create(JSContext* cx, uint32_t initialLength,
+                                         Maybe<uint32_t> maximumLength,
+                                         wasm::RefType tableType,
+                                         HandleObject proto) {
+  AutoSetNewObjectMetadata metadata(cx);
+  Rooted<WasmTableObject*> obj(
+      cx, NewObjectWithGivenProto<WasmTableObject>(cx, proto));
+  if (!obj) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(obj->isNewborn());
+
+  TableDesc td(tableType, initialLength, maximumLength, Nothing(),
+               /*isAsmJS*/ false,
+               /*isImported=*/true, /*isExported=*/true);
+
+  SharedTable table = Table::create(cx, td, obj);
+  if (!table) {
+    return nullptr;
+  }
+
+  size_t size = table->gcMallocBytes();
+  InitReservedSlot(obj, TABLE_SLOT, table.forget().take(), size,
+                   MemoryUse::WasmTableTable);
+
+  MOZ_ASSERT(!obj->isNewborn());
+  return obj;
+}
+
+/* static */
+bool WasmTableObject::construct(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  if (!ThrowIfNotConstructing(cx, args, "Table")) {
+    return false;
+  }
+
+  if (!args.requireAtLeast(cx, "WebAssembly.Table", 1)) {
+    return false;
+  }
+
+  if (!args.get(0).isObject()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_DESC_ARG, "table");
+    return false;
+  }
+
+  RootedObject obj(cx, &args[0].toObject());
+
+  JSAtom* elementAtom = Atomize(cx, "element", strlen("element"));
+  if (!elementAtom) {
+    return false;
+  }
+  RootedId elementId(cx, AtomToId(elementAtom));
+
+  RootedValue elementVal(cx);
+  if (!GetProperty(cx, obj, obj, elementId, &elementVal)) {
+    return false;
+  }
+
+  RefType tableType;
+  if (!ToRefType(cx, elementVal, &tableType)) {
+    return false;
+  }
+
+  Limits limits;
+  if (!GetLimits(cx, obj, LimitsKind::Table, &limits) ||
+      !CheckLimits(cx, MaxTableLimitField, LimitsKind::Table, &limits)) {
+    return false;
+  }
+
+  // Converting limits for a table only supports i32
+  MOZ_ASSERT(limits.indexType == IndexType::I32);
+
+  if (limits.initial > MaxTableLength) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_TABLE_IMP_LIMIT);
+    return false;
+  }
+
+  RootedObject proto(cx,
+                     GetWasmConstructorPrototype(cx, args, JSProto_WasmTable));
+  if (!proto) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  // The rest of the runtime expects table limits to be within a 32-bit range.
+  static_assert(MaxTableLimitField <= UINT32_MAX, "invariant");
+  uint32_t initialLength = uint32_t(limits.initial);
+  Maybe<uint32_t> maximumLength;
+  if (limits.maximum) {
+    maximumLength = Some(uint32_t(*limits.maximum));
+  }
+
+  Rooted<WasmTableObject*> table(
+      cx, WasmTableObject::create(cx, initialLength, maximumLength, tableType,
+                                  proto));
+  if (!table) {
+    return false;
+  }
+
+  // Initialize the table to a default value
+  RootedValue initValue(
+      cx, args.length() < 2 ? RefTypeDefautValue(tableType) : args[1]);
+  if (!CheckRefTypeValue(cx, tableType, initValue)) {
+    return false;
+  }
+
+  // Skip initializing the table if the fill value is null, as that is the
+  // default value.
+  if (!initValue.isNull() &&
+      !table->fillRange(cx, 0, initialLength, initValue)) {
+    return false;
+  }
+#ifdef DEBUG
+  // Assert that null is the default value of a new table.
+  if (initValue.isNull()) {
+    table->table().assertRangeNull(0, initialLength);
+  }
+  if (!tableType.isNullable()) {
+    table->table().assertRangeNotNull(0, initialLength);
+  }
+#endif
+
+  args.rval().setObject(*table);
+  return true;
+}
+
+static bool IsTable(HandleValue v) {
+  return v.isObject() && v.toObject().is<WasmTableObject>();
+}
+
+/* static */
+bool WasmTableObject::lengthGetterImpl(JSContext* cx, const CallArgs& args) {
+  args.rval().setNumber(
+      args.thisv().toObject().as<WasmTableObject>().table().length());
+  return true;
+}
+
+/* static */
+bool WasmTableObject::lengthGetter(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsTable, lengthGetterImpl>(cx, args);
+}
+
+const JSPropertySpec WasmTableObject::properties[] = {
+    JS_PSG("length", WasmTableObject::lengthGetter, JSPROP_ENUMERATE),
+    JS_STRING_SYM_PS(toStringTag, "WebAssembly.Table", JSPROP_READONLY),
+    JS_PS_END};
+
+static bool ToTableIndex(JSContext* cx, HandleValue v, const Table& table,
+                         const char* noun, uint32_t* index) {
+  if (!EnforceRangeU32(cx, v, "Table", noun, index)) {
+    return false;
+  }
+
+  if (*index >= table.length()) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_WASM_BAD_RANGE, "Table", noun);
+    return false;
+  }
+
+  return true;
+}
+
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+/* static */
+bool WasmTableObject::typeImpl(JSContext* cx, const CallArgs& args) {
+  Table& table = args.thisv().toObject().as<WasmTableObject>().table();
+  RootedObject typeObj(cx, TableTypeToObject(cx, table.elemType(),
+                                             table.length(), table.maximum()));
+  if (!typeObj) {
+    return false;
+  }
+  args.rval().setObject(*typeObj);
+  return true;
+}
+
+/* static */
+bool WasmTableObject::type(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsTable, typeImpl>(cx, args);
+}
+#endif
+
+/* static */
+bool WasmTableObject::getImpl(JSContext* cx, const CallArgs& args) {
+  Rooted<WasmTableObject*> tableObj(
+      cx, &args.thisv().toObject().as<WasmTableObject>());
+  const Table& table = tableObj->table();
+
+  if (!args.requireAtLeast(cx, "WebAssembly.Table.get", 1)) {
+    return false;
+  }
+
+  uint32_t index;
+  if (!ToTableIndex(cx, args.get(0), table, "get index", &index)) {
+    return false;
+  }
+
+  return table.getValue(cx, index, args.rval());
+}
+
+/* static */
+bool WasmTableObject::get(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsTable, getImpl>(cx, args);
+}
+
+/* static */
+bool WasmTableObject::setImpl(JSContext* cx, const CallArgs& args) {
+  Rooted<WasmTableObject*> tableObj(
+      cx, &args.thisv().toObject().as<WasmTableObject>());
+  Table& table = tableObj->table();
+
+  if (!args.requireAtLeast(cx, "WebAssembly.Table.set", 1)) {
+    return false;
+  }
+
+  uint32_t index;
+  if (!ToTableIndex(cx, args.get(0), table, "set index", &index)) {
+    return false;
+  }
+
+  RootedValue fillValue(
+      cx, args.length() < 2 ? RefTypeDefautValue(table.elemType()) : args[1]);
+  if (!tableObj->fillRange(cx, index, 1, fillValue)) {
+    return false;
+  }
+
+  args.rval().setUndefined();
+  return true;
+}
+
+/* static */
+bool WasmTableObject::set(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsTable, setImpl>(cx, args);
+}
+
+/* static */
+bool WasmTableObject::growImpl(JSContext* cx, const CallArgs& args) {
+  Rooted<WasmTableObject*> tableObj(
+      cx, &args.thisv().toObject().as<WasmTableObject>());
+  Table& table = tableObj->table();
+
+  if (!args.requireAtLeast(cx, "WebAssembly.Table.grow", 1)) {
+    return false;
+  }
+
+  uint32_t delta;
+  if (!EnforceRangeU32(cx, args.get(0), "Table", "grow delta", &delta)) {
+    return false;
+  }
+
+  RootedValue fillValue(
+      cx, args.length() < 2 ? RefTypeDefautValue(table.elemType()) : args[1]);
+  if (!CheckRefTypeValue(cx, table.elemType(), fillValue)) {
+    return false;
+  }
+
+  uint32_t oldLength = table.grow(delta);
+
+  if (oldLength == uint32_t(-1)) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr, JSMSG_WASM_BAD_GROW,
+                             "table");
+    return false;
+  }
+
+  // Skip filling the grown range of the table if the fill value is null, as
+  // that is the default value.
+  if (!fillValue.isNull() &&
+      !tableObj->fillRange(cx, oldLength, delta, fillValue)) {
+    return false;
+  }
+#ifdef DEBUG
+  // Assert that null is the default value of the grown range.
+  if (fillValue.isNull()) {
+    table.assertRangeNull(oldLength, delta);
+  }
+  if (!table.elemType().isNullable()) {
+    table.assertRangeNotNull(oldLength, delta);
+  }
+#endif
+
+  args.rval().setInt32(int32_t(oldLength));
+  return true;
+}
+
+/* static */
+bool WasmTableObject::grow(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsTable, growImpl>(cx, args);
+}
+
+const JSFunctionSpec WasmTableObject::methods[] = {
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+    JS_FN("type", WasmTableObject::type, 0, JSPROP_ENUMERATE),
+#endif
+    JS_FN("get", WasmTableObject::get, 1, JSPROP_ENUMERATE),
+    JS_FN("set", WasmTableObject::set, 2, JSPROP_ENUMERATE),
+    JS_FN("grow", WasmTableObject::grow, 1, JSPROP_ENUMERATE), JS_FS_END};
+
+const JSFunctionSpec WasmTableObject::static_methods[] = {JS_FS_END};
+
+Table& WasmTableObject::table() const {
+  return *(Table*)getReservedSlot(TABLE_SLOT).toPrivate();
+}
+
+bool WasmTableObject::fillRange(JSContext* cx, uint32_t index, uint32_t length,
+                                HandleValue value) const {
+  Table& tab = table();
+
+  // All consumers are required to either bounds check or statically be in
+  // bounds
+  MOZ_ASSERT(uint64_t(index) + uint64_t(length) <= tab.length());
+
+  RootedFunction fun(cx);
+  RootedAnyRef any(cx, AnyRef::null());
+  if (!CheckRefType(cx, tab.elemType(), value, &fun, &any)) {
+    return false;
+  }
+  switch (tab.repr()) {
+    case TableRepr::Func:
+      MOZ_RELEASE_ASSERT(!tab.isAsmJS());
+      tab.fillFuncRef(index, length, FuncRef::fromJSFunction(fun), cx);
+      break;
+    case TableRepr::Ref:
+      tab.fillAnyRef(index, length, any);
+      break;
+  }
+  return true;
+}
+
+// ============================================================================
+// WebAssembly.global class and methods
+
+const JSClassOps WasmGlobalObject::classOps_ = {
+    nullptr,                     // addProperty
+    nullptr,                     // delProperty
+    nullptr,                     // enumerate
+    nullptr,                     // newEnumerate
+    nullptr,                     // resolve
+    nullptr,                     // mayResolve
+    WasmGlobalObject::finalize,  // finalize
+    nullptr,                     // call
+    nullptr,                     // construct
+    WasmGlobalObject::trace,     // trace
+};
+
+const JSClass WasmGlobalObject::class_ = {
+    "WebAssembly.Global",
+    JSCLASS_HAS_RESERVED_SLOTS(WasmGlobalObject::RESERVED_SLOTS) |
+        JSCLASS_BACKGROUND_FINALIZE,
+    &WasmGlobalObject::classOps_, &WasmGlobalObject::classSpec_};
+
+const JSClass& WasmGlobalObject::protoClass_ = PlainObject::class_;
+
+static constexpr char WasmGlobalName[] = "Global";
+
+const ClassSpec WasmGlobalObject::classSpec_ = {
+    CreateWasmConstructor<WasmGlobalObject, WasmGlobalName>,
+    GenericCreatePrototype<WasmGlobalObject>,
+    WasmGlobalObject::static_methods,
+    nullptr,
+    WasmGlobalObject::methods,
+    WasmGlobalObject::properties,
+    nullptr,
+    ClassSpec::DontDefineConstructor};
+
+/* static */
+void WasmGlobalObject::trace(JSTracer* trc, JSObject* obj) {
+  WasmGlobalObject* global = reinterpret_cast<WasmGlobalObject*>(obj);
+  if (global->isNewborn()) {
+    // This can happen while we're allocating the object, in which case
+    // every single slot of the object is not defined yet. In particular,
+    // there's nothing to trace yet.
+    return;
+  }
+  global->val().get().trace(trc);
+}
+
+/* static */
+void WasmGlobalObject::finalize(JS::GCContext* gcx, JSObject* obj) {
+  WasmGlobalObject* global = reinterpret_cast<WasmGlobalObject*>(obj);
+  if (!global->isNewborn()) {
+    // Release the strong reference to the type definitions this global could
+    // be referencing.
+    global->type().Release();
+    gcx->delete_(obj, &global->val(), MemoryUse::WasmGlobalCell);
+  }
+}
+
+/* static */
+WasmGlobalObject* WasmGlobalObject::create(JSContext* cx, HandleVal value,
+                                           bool isMutable, HandleObject proto) {
+  Rooted<WasmGlobalObject*> obj(
+      cx, NewObjectWithGivenProto<WasmGlobalObject>(cx, proto));
+  if (!obj) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(obj->isNewborn());
+  MOZ_ASSERT(obj->isTenured(), "assumed by global.set post barriers");
+
+  GCPtrVal* val = js_new<GCPtrVal>(Val());
+  if (!val) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+  obj->initReservedSlot(MUTABLE_SLOT, JS::BooleanValue(isMutable));
+  InitReservedSlot(obj, VAL_SLOT, val, MemoryUse::WasmGlobalCell);
+
+  // It's simpler to initialize the cell after the object has been created,
+  // to avoid needing to root the cell before the object creation.
+  obj->val() = value.get();
+  // Acquire a strong reference to a type definition this global could
+  // be referencing.
+  obj->type().AddRef();
+
+  MOZ_ASSERT(!obj->isNewborn());
+
+  return obj;
+}
+
+/* static */
+bool WasmGlobalObject::construct(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  if (!ThrowIfNotConstructing(cx, args, "Global")) {
+    return false;
+  }
+
+  if (!args.requireAtLeast(cx, "WebAssembly.Global", 1)) {
+    return false;
+  }
+
+  if (!args.get(0).isObject()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_DESC_ARG, "global");
+    return false;
+  }
+
+  RootedObject obj(cx, &args[0].toObject());
+
+  // Extract properties in lexicographic order per spec.
+
+  RootedValue mutableVal(cx);
+  if (!JS_GetProperty(cx, obj, "mutable", &mutableVal)) {
+    return false;
+  }
+
+  RootedValue typeVal(cx);
+  if (!JS_GetProperty(cx, obj, "value", &typeVal)) {
+    return false;
+  }
+
+  ValType globalType;
+  if (!ToValType(cx, typeVal, &globalType)) {
+    return false;
+  }
+
+  if (!globalType.isExposable()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_VAL_TYPE);
+    return false;
+  }
+
+  bool isMutable = ToBoolean(mutableVal);
+
+  // Extract the initial value, or provide a suitable default.
+  RootedVal globalVal(cx, globalType);
+
+  // Override with non-undefined value, if provided.
+  RootedValue valueVal(cx);
+  if (globalType.isRefType()) {
+    valueVal.set(args.length() < 2 ? RefTypeDefautValue(globalType.refType())
+                                   : args[1]);
+    if (!Val::fromJSValue(cx, globalType, valueVal, &globalVal)) {
+      return false;
+    }
+  } else {
+    valueVal.set(args.get(1));
+    if (!valueVal.isUndefined() &&
+        !Val::fromJSValue(cx, globalType, valueVal, &globalVal)) {
+      return false;
+    }
+  }
+
+  RootedObject proto(cx,
+                     GetWasmConstructorPrototype(cx, args, JSProto_WasmGlobal));
+  if (!proto) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  WasmGlobalObject* global =
+      WasmGlobalObject::create(cx, globalVal, isMutable, proto);
+  if (!global) {
+    return false;
+  }
+
+  args.rval().setObject(*global);
+  return true;
+}
+
+static bool IsGlobal(HandleValue v) {
+  return v.isObject() && v.toObject().is<WasmGlobalObject>();
+}
+
+/* static */
+bool WasmGlobalObject::valueGetterImpl(JSContext* cx, const CallArgs& args) {
+  const WasmGlobalObject& globalObj =
+      args.thisv().toObject().as<WasmGlobalObject>();
+  if (!globalObj.type().isExposable()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_VAL_TYPE);
+    return false;
+  }
+  return globalObj.val().get().toJSValue(cx, args.rval());
+}
+
+/* static */
+bool WasmGlobalObject::valueGetter(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsGlobal, valueGetterImpl>(cx, args);
+}
+
+/* static */
+bool WasmGlobalObject::valueSetterImpl(JSContext* cx, const CallArgs& args) {
+  if (!args.requireAtLeast(cx, "WebAssembly.Global setter", 1)) {
+    return false;
+  }
+
+  Rooted<WasmGlobalObject*> global(
+      cx, &args.thisv().toObject().as<WasmGlobalObject>());
+  if (!global->isMutable()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_GLOBAL_IMMUTABLE);
+    return false;
+  }
+
+  RootedVal val(cx);
+  if (!Val::fromJSValue(cx, global->type(), args.get(0), &val)) {
+    return false;
+  }
+  global->val() = val.get();
+
+  args.rval().setUndefined();
+  return true;
+}
+
+/* static */
+bool WasmGlobalObject::valueSetter(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsGlobal, valueSetterImpl>(cx, args);
+}
+
+const JSPropertySpec WasmGlobalObject::properties[] = {
+    JS_PSGS("value", WasmGlobalObject::valueGetter,
+            WasmGlobalObject::valueSetter, JSPROP_ENUMERATE),
+    JS_STRING_SYM_PS(toStringTag, "WebAssembly.Global", JSPROP_READONLY),
+    JS_PS_END};
+
+const JSFunctionSpec WasmGlobalObject::methods[] = {
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+    JS_FN("type", WasmGlobalObject::type, 0, JSPROP_ENUMERATE),
+#endif
+    JS_FN("valueOf", WasmGlobalObject::valueGetter, 0, JSPROP_ENUMERATE),
+    JS_FS_END};
+
+const JSFunctionSpec WasmGlobalObject::static_methods[] = {JS_FS_END};
+
+bool WasmGlobalObject::isMutable() const {
+  return getReservedSlot(MUTABLE_SLOT).toBoolean();
+}
+
+ValType WasmGlobalObject::type() const { return val().get().type(); }
+
+GCPtrVal& WasmGlobalObject::val() const {
+  return *reinterpret_cast<GCPtrVal*>(getReservedSlot(VAL_SLOT).toPrivate());
+}
+
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+/* static */
+bool WasmGlobalObject::typeImpl(JSContext* cx, const CallArgs& args) {
+  Rooted<WasmGlobalObject*> global(
+      cx, &args.thisv().toObject().as<WasmGlobalObject>());
+  RootedObject typeObj(
+      cx, GlobalTypeToObject(cx, global->type(), global->isMutable()));
+  if (!typeObj) {
+    return false;
+  }
+  args.rval().setObject(*typeObj);
+  return true;
+}
+
+/* static */
+bool WasmGlobalObject::type(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsGlobal, typeImpl>(cx, args);
+}
+#endif
+
+// ============================================================================
+// WebAssembly.Tag class and methods
+
+const JSClassOps WasmTagObject::classOps_ = {
+    nullptr,                  // addProperty
+    nullptr,                  // delProperty
+    nullptr,                  // enumerate
+    nullptr,                  // newEnumerate
+    nullptr,                  // resolve
+    nullptr,                  // mayResolve
+    WasmTagObject::finalize,  // finalize
+    nullptr,                  // call
+    nullptr,                  // construct
+    nullptr,                  // trace
+};
+
+const JSClass WasmTagObject::class_ = {
+    "WebAssembly.Tag",
+    JSCLASS_HAS_RESERVED_SLOTS(WasmTagObject::RESERVED_SLOTS) |
+        JSCLASS_FOREGROUND_FINALIZE,
+    &WasmTagObject::classOps_, &WasmTagObject::classSpec_};
+
+const JSClass& WasmTagObject::protoClass_ = PlainObject::class_;
+
+static constexpr char WasmTagName[] = "Tag";
+
+const ClassSpec WasmTagObject::classSpec_ = {
+    CreateWasmConstructor<WasmTagObject, WasmTagName>,
+    GenericCreatePrototype<WasmTagObject>,
+    WasmTagObject::static_methods,
+    nullptr,
+    WasmTagObject::methods,
+    WasmTagObject::properties,
+    nullptr,
+    ClassSpec::DontDefineConstructor};
+
+/* static */
+void WasmTagObject::finalize(JS::GCContext* gcx, JSObject* obj) {
+  WasmTagObject& tagObj = obj->as<WasmTagObject>();
+  tagObj.tagType()->Release();
+}
+
+static bool IsTag(HandleValue v) {
+  return v.isObject() && v.toObject().is<WasmTagObject>();
+}
+
+bool WasmTagObject::construct(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  if (!ThrowIfNotConstructing(cx, args, "Tag")) {
+    return false;
+  }
+
+  if (!args.requireAtLeast(cx, "WebAssembly.Tag", 1)) {
+    return false;
+  }
+
+  if (!args.get(0).isObject()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_DESC_ARG, "tag");
+    return false;
+  }
+
+  RootedObject obj(cx, &args[0].toObject());
+  RootedValue paramsVal(cx);
+  if (!JS_GetProperty(cx, obj, "parameters", &paramsVal)) {
+    return false;
+  }
+
+  ValTypeVector params;
+  if (!ParseValTypes(cx, paramsVal, params)) {
+    return false;
+  }
+  wasm::MutableTagType tagType = js_new<wasm::TagType>();
+  if (!tagType || !tagType->initialize(std::move(params))) {
+    return false;
+  }
+
+  RootedObject proto(cx,
+                     GetWasmConstructorPrototype(cx, args, JSProto_WasmTag));
+  if (!proto) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  Rooted<WasmTagObject*> tagObj(cx, WasmTagObject::create(cx, tagType, proto));
+  if (!tagObj) {
+    return false;
+  }
+
+  args.rval().setObject(*tagObj);
+  return true;
+}
+
+/* static */
+WasmTagObject* WasmTagObject::create(JSContext* cx,
+                                     const wasm::SharedTagType& tagType,
+                                     HandleObject proto) {
+  Rooted<WasmTagObject*> obj(cx,
+                             NewObjectWithGivenProto<WasmTagObject>(cx, proto));
+  if (!obj) {
+    return nullptr;
+  }
+
+  tagType.get()->AddRef();
+  obj->initReservedSlot(TYPE_SLOT, PrivateValue((void*)tagType.get()));
+
+  return obj;
+}
+
+const JSPropertySpec WasmTagObject::properties[] = {
+    JS_STRING_SYM_PS(toStringTag, "WebAssembly.Tag", JSPROP_READONLY),
+    JS_PS_END};
+
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+/* static */
+bool WasmTagObject::typeImpl(JSContext* cx, const CallArgs& args) {
+  Rooted<WasmTagObject*> tag(cx, &args.thisv().toObject().as<WasmTagObject>());
+  RootedObject typeObj(cx, TagTypeToObject(cx, tag->valueTypes()));
+  if (!typeObj) {
+    return false;
+  }
+  args.rval().setObject(*typeObj);
+  return true;
+}
+
+/* static  */
+bool WasmTagObject::type(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsTag, typeImpl>(cx, args);
+}
+#endif
+
+const JSFunctionSpec WasmTagObject::methods[] = {
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+    JS_FN("type", WasmTagObject::type, 0, JSPROP_ENUMERATE),
+#endif
+    JS_FS_END};
+
+const JSFunctionSpec WasmTagObject::static_methods[] = {JS_FS_END};
+
+const TagType* WasmTagObject::tagType() const {
+  return (const TagType*)getFixedSlot(TYPE_SLOT).toPrivate();
+};
+
+const wasm::ValTypeVector& WasmTagObject::valueTypes() const {
+  return tagType()->argTypes();
+};
+
+wasm::ResultType WasmTagObject::resultType() const {
+  return wasm::ResultType::Vector(valueTypes());
+}
+
+// ============================================================================
+// WebAssembly.Exception class and methods
+
+const JSClassOps WasmExceptionObject::classOps_ = {
+    nullptr,                        // addProperty
+    nullptr,                        // delProperty
+    nullptr,                        // enumerate
+    nullptr,                        // newEnumerate
+    nullptr,                        // resolve
+    nullptr,                        // mayResolve
+    WasmExceptionObject::finalize,  // finalize
+    nullptr,                        // call
+    nullptr,                        // construct
+    WasmExceptionObject::trace,     // trace
+};
+
+const JSClass WasmExceptionObject::class_ = {
+    "WebAssembly.Exception",
+    JSCLASS_HAS_RESERVED_SLOTS(WasmExceptionObject::RESERVED_SLOTS) |
+        JSCLASS_FOREGROUND_FINALIZE,
+    &WasmExceptionObject::classOps_, &WasmExceptionObject::classSpec_};
+
+const JSClass& WasmExceptionObject::protoClass_ = PlainObject::class_;
+
+static constexpr char WasmExceptionName[] = "Exception";
+
+const ClassSpec WasmExceptionObject::classSpec_ = {
+    CreateWasmConstructor<WasmExceptionObject, WasmExceptionName>,
+    GenericCreatePrototype<WasmExceptionObject>,
+    WasmExceptionObject::static_methods,
+    nullptr,
+    WasmExceptionObject::methods,
+    WasmExceptionObject::properties,
+    nullptr,
+    ClassSpec::DontDefineConstructor};
+
+/* static */
+void WasmExceptionObject::finalize(JS::GCContext* gcx, JSObject* obj) {
+  WasmExceptionObject& exnObj = obj->as<WasmExceptionObject>();
+  if (exnObj.isNewborn()) {
+    return;
+  }
+  gcx->free_(obj, exnObj.typedMem(), exnObj.tagType()->tagSize(),
+             MemoryUse::WasmExceptionData);
+  exnObj.tagType()->Release();
+}
+
+/* static */
+void WasmExceptionObject::trace(JSTracer* trc, JSObject* obj) {
+  WasmExceptionObject& exnObj = obj->as<WasmExceptionObject>();
+  if (exnObj.isNewborn()) {
+    return;
+  }
+
+  wasm::SharedTagType tag = exnObj.tagType();
+  const wasm::ValTypeVector& params = tag->argTypes();
+  const wasm::TagOffsetVector& offsets = tag->argOffsets();
+  uint8_t* typedMem = exnObj.typedMem();
+  for (size_t i = 0; i < params.length(); i++) {
+    ValType paramType = params[i];
+    if (paramType.isRefRepr()) {
+      GCPtr<wasm::AnyRef>* paramPtr =
+          reinterpret_cast<GCPtr<AnyRef>*>(typedMem + offsets[i]);
+      TraceNullableEdge(trc, paramPtr, "wasm exception param");
+    }
+  }
+}
+
+static bool IsException(HandleValue v) {
+  return v.isObject() && v.toObject().is<WasmExceptionObject>();
+}
+
+struct ExceptionOptions {
+  bool traceStack;
+
+  ExceptionOptions() : traceStack(false) {}
+
+  [[nodiscard]] bool init(JSContext* cx, HandleValue val);
+};
+
+bool ExceptionOptions::init(JSContext* cx, HandleValue val) {
+  if (val.isNullOrUndefined()) {
+    return true;
+  }
+
+  if (!val.isObject()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_EXN_OPTIONS);
+    return false;
+  }
+  RootedObject obj(cx, &val.toObject());
+
+  // Get `traceStack` and coerce to boolean
+  RootedValue traceStackVal(cx);
+  if (!JS_GetProperty(cx, obj, "traceStack", &traceStackVal)) {
+    return false;
+  }
+  traceStack = ToBoolean(traceStackVal);
+
+  return true;
+}
+
+bool WasmExceptionObject::construct(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  if (!ThrowIfNotConstructing(cx, args, "Exception")) {
+    return false;
+  }
+
+  if (!args.requireAtLeast(cx, "WebAssembly.Exception", 2)) {
+    return false;
+  }
+
+  if (!IsTag(args[0])) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_EXN_ARG);
+    return false;
+  }
+  Rooted<WasmTagObject*> exnTag(cx, &args[0].toObject().as<WasmTagObject>());
+
+  if (!args.get(1).isObject()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_EXN_PAYLOAD);
+    return false;
+  }
+
+  JS::ForOfIterator iterator(cx);
+  if (!iterator.init(args.get(1), JS::ForOfIterator::ThrowOnNonIterable)) {
+    return false;
+  }
+
+  // Get the optional 'options' parameter
+  ExceptionOptions options;
+  if (!options.init(cx, args.get(2))) {
+    return false;
+  }
+
+  // Trace the stack if requested
+  RootedObject stack(cx);
+  if (options.traceStack && !CaptureStack(cx, &stack)) {
+    return false;
+  }
+
+  RootedObject proto(
+      cx, GetWasmConstructorPrototype(cx, args, JSProto_WasmException));
+  if (!proto) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  Rooted<WasmExceptionObject*> exnObj(
+      cx, WasmExceptionObject::create(cx, exnTag, stack, proto));
+  if (!exnObj) {
+    return false;
+  }
+
+  wasm::SharedTagType tagType = exnObj->tagType();
+  const wasm::ValTypeVector& params = tagType->argTypes();
+  const wasm::TagOffsetVector& offsets = tagType->argOffsets();
+
+  RootedValue nextArg(cx);
+  for (size_t i = 0; i < params.length(); i++) {
+    bool done;
+    if (!iterator.next(&nextArg, &done)) {
+      return false;
+    }
+    if (done) {
+      UniqueChars expected(JS_smprintf("%zu", params.length()));
+      UniqueChars got(JS_smprintf("%zu", i));
+      if (!expected || !got) {
+        ReportOutOfMemory(cx);
+        return false;
+      }
+
+      JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                               JSMSG_WASM_BAD_EXN_PAYLOAD_LEN, expected.get(),
+                               got.get());
+      return false;
+    }
+
+    if (!exnObj->initArg(cx, offsets[i], params[i], nextArg)) {
+      return false;
+    }
+  }
+
+  args.rval().setObject(*exnObj);
+  return true;
+}
+
+/* static */
+WasmExceptionObject* WasmExceptionObject::create(JSContext* cx,
+                                                 Handle<WasmTagObject*> tag,
+                                                 HandleObject stack,
+                                                 HandleObject proto) {
+  Rooted<WasmExceptionObject*> obj(
+      cx, NewObjectWithGivenProto<WasmExceptionObject>(cx, proto));
+  if (!obj) {
+    return nullptr;
+  }
+  const TagType* tagType = tag->tagType();
+
+  // Allocate the data buffer before initializing the object so that an OOM
+  // does not result in a partially constructed object.
+  uint8_t* data = (uint8_t*)js_calloc(tagType->tagSize());
+  if (!data) {
+    ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  MOZ_ASSERT(obj->isNewborn());
+  obj->initFixedSlot(TAG_SLOT, ObjectValue(*tag));
+  tagType->AddRef();
+  obj->initFixedSlot(TYPE_SLOT, PrivateValue((void*)tagType));
+  InitReservedSlot(obj, DATA_SLOT, data, tagType->tagSize(),
+                   MemoryUse::WasmExceptionData);
+  obj->initFixedSlot(STACK_SLOT, ObjectOrNullValue(stack));
+
+  MOZ_ASSERT(!obj->isNewborn());
+
+  return obj;
+}
+
+WasmExceptionObject* WasmExceptionObject::wrapJSValue(JSContext* cx,
+                                                      HandleValue value) {
+  Rooted<WasmNamespaceObject*> wasm(cx, WasmNamespaceObject::getOrCreate(cx));
+  if (!wasm) {
+    return nullptr;
+  }
+
+  Rooted<AnyRef> valueAnyRef(cx);
+  if (!AnyRef::fromJSValue(cx, value, &valueAnyRef)) {
+    return nullptr;
+  }
+
+  Rooted<WasmTagObject*> wrappedJSValueTag(cx, wasm->wrappedJSValueTag());
+  WasmExceptionObject* exn =
+      WasmExceptionObject::create(cx, wrappedJSValueTag, nullptr, nullptr);
+  if (!exn) {
+    return nullptr;
+  }
+  MOZ_ASSERT(exn->isWrappedJSValue());
+
+  exn->initRefArg(WrappedJSValueTagType_ValueOffset, valueAnyRef);
+  return exn;
+}
+
+bool WasmExceptionObject::isNewborn() const {
+  MOZ_ASSERT(is<WasmExceptionObject>());
+  return getReservedSlot(DATA_SLOT).isUndefined();
+}
+
+bool WasmExceptionObject::isWrappedJSValue() const {
+  return tagType() == sWrappedJSValueTagType;
+}
+
+Value WasmExceptionObject::wrappedJSValue() const {
+  MOZ_ASSERT(isWrappedJSValue());
+  return loadRefArg(WrappedJSValueTagType_ValueOffset).toJSValue();
+}
+
+const JSPropertySpec WasmExceptionObject::properties[] = {
+    JS_PSG("stack", WasmExceptionObject::getStack, 0),
+    JS_STRING_SYM_PS(toStringTag, "WebAssembly.Exception", JSPROP_READONLY),
+    JS_PS_END};
+
+/* static */
+bool WasmExceptionObject::isImpl(JSContext* cx, const CallArgs& args) {
+  Rooted<WasmExceptionObject*> exnObj(
+      cx, &args.thisv().toObject().as<WasmExceptionObject>());
+
+  if (!args.requireAtLeast(cx, "WebAssembly.Exception.is", 1)) {
+    return false;
+  }
+
+  if (!IsTag(args[0])) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_EXN_ARG);
+    return false;
+  }
+
+  Rooted<WasmTagObject*> exnTag(cx,
+                                &args.get(0).toObject().as<WasmTagObject>());
+  args.rval().setBoolean(exnTag.get() == &exnObj->tag());
+
+  return true;
+}
+
+/* static  */
+bool WasmExceptionObject::isMethod(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsException, isImpl>(cx, args);
+}
+
+/* static */
+bool WasmExceptionObject::getArgImpl(JSContext* cx, const CallArgs& args) {
+  Rooted<WasmExceptionObject*> exnObj(
+      cx, &args.thisv().toObject().as<WasmExceptionObject>());
+
+  if (!args.requireAtLeast(cx, "WebAssembly.Exception.getArg", 2)) {
+    return false;
+  }
+
+  if (!IsTag(args[0])) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_EXN_ARG);
+    return false;
+  }
+
+  Rooted<WasmTagObject*> exnTag(cx,
+                                &args.get(0).toObject().as<WasmTagObject>());
+  if (exnTag.get() != &exnObj->tag()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_EXN_TAG);
+    return false;
+  }
+
+  uint32_t index;
+  if (!EnforceRangeU32(cx, args.get(1), "Exception", "getArg index", &index)) {
+    return false;
+  }
+
+  const wasm::ValTypeVector& params = exnTag->valueTypes();
+  if (index >= params.length()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr, JSMSG_WASM_BAD_RANGE,
+                             "Exception", "getArg index");
+    return false;
+  }
+
+  uint32_t offset = exnTag->tagType()->argOffsets()[index];
+  RootedValue result(cx);
+  if (!exnObj->loadArg(cx, offset, params[index], &result)) {
+    return false;
+  }
+  args.rval().set(result);
+  return true;
+}
+
+/* static  */
+bool WasmExceptionObject::getArg(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsException, getArgImpl>(cx, args);
+}
+
+/* static */
+bool WasmExceptionObject::getStack_impl(JSContext* cx, const CallArgs& args) {
+  Rooted<WasmExceptionObject*> exnObj(
+      cx, &args.thisv().toObject().as<WasmExceptionObject>());
+  RootedObject savedFrameObj(cx, exnObj->stack());
+  if (!savedFrameObj) {
+    args.rval().setUndefined();
+    return true;
+  }
+  JSPrincipals* principals = exnObj->realm()->principals();
+  RootedString stackString(cx);
+  if (!BuildStackString(cx, principals, savedFrameObj, &stackString)) {
+    return false;
+  }
+  args.rval().setString(stackString);
+  return true;
+}
+
+/* static */
+bool WasmExceptionObject::getStack(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsException, getStack_impl>(cx, args);
+}
+
+JSObject* WasmExceptionObject::stack() const {
+  return getReservedSlot(STACK_SLOT).toObjectOrNull();
+}
+
+uint8_t* WasmExceptionObject::typedMem() const {
+  return (uint8_t*)getReservedSlot(DATA_SLOT).toPrivate();
+}
+
+bool WasmExceptionObject::loadArg(JSContext* cx, size_t offset,
+                                  wasm::ValType type,
+                                  MutableHandleValue vp) const {
+  if (!type.isExposable()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_VAL_TYPE);
+    return false;
+  }
+  return ToJSValue(cx, typedMem() + offset, type, vp);
+}
+
+bool WasmExceptionObject::initArg(JSContext* cx, size_t offset,
+                                  wasm::ValType type, HandleValue value) {
+  if (!type.isExposable()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_VAL_TYPE);
+    return false;
+  }
+
+  // Avoid rooting hazard of `this` being live across `fromJSValue`
+  // which may GC.
+  uint8_t* dest = typedMem() + offset;
+  RootedVal val(cx);
+  if (!Val::fromJSValue(cx, type, value, &val)) {
+    return false;
+  }
+  val.get().writeToHeapLocation(dest);
+  return true;
+}
+
+void WasmExceptionObject::initRefArg(size_t offset, wasm::AnyRef ref) {
+  uint8_t* dest = typedMem() + offset;
+  *((GCPtr<AnyRef>*)dest) = ref;
+}
+
+wasm::AnyRef WasmExceptionObject::loadRefArg(size_t offset) const {
+  uint8_t* src = typedMem() + offset;
+  return *((GCPtr<AnyRef>*)src);
+}
+
+const JSFunctionSpec WasmExceptionObject::methods[] = {
+    JS_FN("is", WasmExceptionObject::isMethod, 1, JSPROP_ENUMERATE),
+    JS_FN("getArg", WasmExceptionObject::getArg, 2, JSPROP_ENUMERATE),
+    JS_FS_END};
+
+const JSFunctionSpec WasmExceptionObject::static_methods[] = {JS_FS_END};
+
+const TagType* WasmExceptionObject::tagType() const {
+  return (const TagType*)getReservedSlot(TYPE_SLOT).toPrivate();
+}
+
+WasmTagObject& WasmExceptionObject::tag() const {
+  return getReservedSlot(TAG_SLOT).toObject().as<WasmTagObject>();
+}
+
+// ============================================================================
+// WebAssembly.Function and methods
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+static JSObject* CreateWasmFunctionPrototype(JSContext* cx, JSProtoKey key) {
+  // WasmFunction's prototype should inherit from JSFunction's prototype.
+  RootedObject jsProto(cx, &cx->global()->getFunctionPrototype());
+  return GlobalObject::createBlankPrototypeInheriting(cx, &PlainObject::class_,
+                                                      jsProto);
+}
+
+[[nodiscard]] static bool IsWasmFunction(HandleValue v) {
+  if (!v.isObject()) {
+    return false;
+  }
+  if (!v.toObject().is<JSFunction>()) {
+    return false;
+  }
+  return v.toObject().as<JSFunction>().isWasm();
+}
+
+bool WasmFunctionTypeImpl(JSContext* cx, const CallArgs& args) {
+  RootedFunction function(cx, &args.thisv().toObject().as<JSFunction>());
+  Rooted<WasmInstanceObject*> instanceObj(
+      cx, ExportedFunctionToInstanceObject(function));
+  uint32_t funcIndex = ExportedFunctionToFuncIndex(function);
+  Instance& instance = instanceObj->instance();
+  const FuncExport& fe =
+      instance.metadata(instance.code().bestTier()).lookupFuncExport(funcIndex);
+  const FuncType& funcType = instance.metadata().getFuncExportType(fe);
+  RootedObject typeObj(cx, FuncTypeToObject(cx, funcType));
+  if (!typeObj) {
+    return false;
+  }
+  args.rval().setObject(*typeObj);
+  return true;
+}
+
+bool WasmFunctionType(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsWasmFunction, WasmFunctionTypeImpl>(cx, args);
+}
+
+static JSFunction* WasmFunctionCreate(JSContext* cx, HandleObject func,
+                                      wasm::ValTypeVector&& params,
+                                      wasm::ValTypeVector&& results,
+                                      HandleObject proto) {
+  MOZ_ASSERT(IsCallableNonCCW(ObjectValue(*func)));
+  MOZ_RELEASE_ASSERT(!func->is<JSFunction>() ||
+                     !IsWasmExportedFunction(&func->as<JSFunction>()));
+
+  // We want to import the function to a wasm module and then export it again so
+  // that it behaves exactly like a normal wasm function and can be used like
+  // one in wasm tables. We synthesize such a module below, instantiate it, and
+  // then return the exported function as the result.
+  FeatureOptions options;
+  ScriptedCaller scriptedCaller;
+  SharedCompileArgs compileArgs =
+      CompileArgs::buildAndReport(cx, std::move(scriptedCaller), options);
+  if (!compileArgs) {
+    return nullptr;
+  }
+
+  ModuleEnvironment moduleEnv(compileArgs->features);
+  CompilerEnvironment compilerEnv(CompileMode::Once, Tier::Optimized,
+                                  DebugEnabled::False);
+  compilerEnv.computeParameters();
+
+  if (!moduleEnv.init()) {
+    return nullptr;
+  }
+
+  FuncType funcType = FuncType(std::move(params), std::move(results));
+  if (!moduleEnv.types->addType(std::move(funcType))) {
+    return nullptr;
+  }
+
+  // Add an (import (func ...))
+  FuncDesc funcDesc = FuncDesc(&(*moduleEnv.types)[0].funcType(), 0);
+  if (!moduleEnv.funcs.append(funcDesc)) {
+    return nullptr;
+  }
+  moduleEnv.numFuncImports = 1;
+
+  // Add an (export (func 0))
+  moduleEnv.declareFuncExported(0, /* eager */ true, /* canRefFunc */ true);
+
+  // We will be looking up and using the function in the future by index so the
+  // name doesn't matter.
+  CacheableName fieldName;
+  if (!moduleEnv.exports.emplaceBack(std::move(fieldName), 0,
+                                     DefinitionKind::Function)) {
+    return nullptr;
+  }
+
+  ModuleGenerator mg(*compileArgs, &moduleEnv, &compilerEnv, nullptr, nullptr,
+                     nullptr);
+  if (!mg.init(nullptr)) {
+    return nullptr;
+  }
+  // We're not compiling any function definitions.
+  if (!mg.finishFuncDefs()) {
+    return nullptr;
+  }
+  SharedBytes shareableBytes = js_new<ShareableBytes>();
+  if (!shareableBytes) {
+    return nullptr;
+  }
+  SharedModule module = mg.finishModule(*shareableBytes);
+  if (!module) {
+    return nullptr;
+  }
+
+  // Instantiate the module.
+  Rooted<ImportValues> imports(cx);
+  if (!imports.get().funcs.append(func)) {
+    return nullptr;
+  }
+  Rooted<WasmInstanceObject*> instance(cx);
+  if (!module->instantiate(cx, imports.get(), nullptr, &instance)) {
+    MOZ_ASSERT(cx->isThrowingOutOfMemory());
+    return nullptr;
+  }
+
+  // Get the exported function which wraps the JS function to return.
+  RootedFunction wasmFunc(cx);
+  if (!instance->getExportedFunction(cx, instance, 0, &wasmFunc)) {
+    return nullptr;
+  }
+  return wasmFunc;
+}
+
+bool WasmFunctionConstruct(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  if (!ThrowIfNotConstructing(cx, args, "WebAssembly.Function")) {
+    return false;
+  }
+
+  if (!args.requireAtLeast(cx, "WebAssembly.Function", 2)) {
+    return false;
+  }
+
+  if (!args[0].isObject()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_DESC_ARG, "function");
+    return false;
+  }
+  RootedObject typeObj(cx, &args[0].toObject());
+
+  // Extract properties in lexicographic order per spec.
+
+  RootedValue parametersVal(cx);
+  if (!JS_GetProperty(cx, typeObj, "parameters", &parametersVal)) {
+    return false;
+  }
+
+  ValTypeVector params;
+  if (!ParseValTypes(cx, parametersVal, params)) {
+    return false;
+  }
+
+  RootedValue resultsVal(cx);
+  if (!JS_GetProperty(cx, typeObj, "results", &resultsVal)) {
+    return false;
+  }
+
+  ValTypeVector results;
+  if (!ParseValTypes(cx, resultsVal, results)) {
+    return false;
+  }
+
+  // Get the target function
+
+  if (!IsCallableNonCCW(args[1]) || IsWasmFunction(args[1])) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_FUNCTION_VALUE);
+    return false;
+  }
+  RootedObject func(cx, &args[1].toObject());
+
+  RootedObject proto(
+      cx, GetWasmConstructorPrototype(cx, args, JSProto_WasmFunction));
+  if (!proto) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  RootedFunction wasmFunc(cx, WasmFunctionCreate(cx, func, std::move(params),
+                                                 std::move(results), proto));
+  if (!wasmFunc) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+  args.rval().setObject(*wasmFunc);
+
+  return true;
+}
+
+static constexpr char WasmFunctionName[] = "Function";
+
+static JSObject* CreateWasmFunctionConstructor(JSContext* cx, JSProtoKey key) {
+  RootedObject proto(cx, &cx->global()->getFunctionConstructor());
+
+  Rooted<JSAtom*> className(
+      cx, Atomize(cx, WasmFunctionName, strlen(WasmFunctionName)));
+  if (!className) {
+    return nullptr;
+  }
+  return NewFunctionWithProto(cx, WasmFunctionConstruct, 1,
+                              FunctionFlags::NATIVE_CTOR, nullptr, className,
+                              proto, gc::AllocKind::FUNCTION, TenuredObject);
+}
+
+const JSFunctionSpec WasmFunctionMethods[] = {
+    JS_FN("type", WasmFunctionType, 0, 0), JS_FS_END};
+
+const ClassSpec WasmFunctionClassSpec = {CreateWasmFunctionConstructor,
+                                         CreateWasmFunctionPrototype,
+                                         nullptr,
+                                         nullptr,
+                                         WasmFunctionMethods,
+                                         nullptr,
+                                         nullptr,
+                                         ClassSpec::DontDefineConstructor};
+
+const JSClass js::WasmFunctionClass = {
+    "WebAssembly.Function", 0, JS_NULL_CLASS_OPS, &WasmFunctionClassSpec};
+
+#endif
+
+// ============================================================================
+// WebAssembly class and static methods
+
+static bool WebAssembly_toSource(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  args.rval().setString(cx->names().WebAssembly);
+  return true;
+}
+
+static bool RejectWithPendingException(JSContext* cx,
+                                       Handle<PromiseObject*> promise) {
+  if (!cx->isExceptionPending()) {
+    return false;
+  }
+
+  RootedValue rejectionValue(cx);
+  if (!GetAndClearException(cx, &rejectionValue)) {
+    return false;
+  }
+
+  return PromiseObject::reject(cx, promise, rejectionValue);
+}
+
+static bool Reject(JSContext* cx, const CompileArgs& args,
+                   Handle<PromiseObject*> promise, const UniqueChars& error) {
+  if (!error) {
+    ThrowCompileOutOfMemory(cx);
+    return RejectWithPendingException(cx, promise);
+  }
+
+  RootedObject stack(cx, promise->allocationSite());
+  RootedString fileName(cx);
+  if (const char* filename = args.scriptedCaller.filename.get()) {
+    fileName =
+        JS_NewStringCopyUTF8N(cx, JS::UTF8Chars(filename, strlen(filename)));
+  } else {
+    fileName = JS_GetEmptyString(cx);
+  }
+  if (!fileName) {
+    return false;
+  }
+
+  uint32_t line = args.scriptedCaller.line;
+
+  // Ideally we'd report a JSMSG_WASM_COMPILE_ERROR here, but there's no easy
+  // way to create an ErrorObject for an arbitrary error code with multiple
+  // replacements.
+  UniqueChars str(JS_smprintf("wasm validation error: %s", error.get()));
+  if (!str) {
+    return false;
+  }
+
+  size_t len = strlen(str.get());
+  RootedString message(cx, NewStringCopyN<CanGC>(cx, str.get(), len));
+  if (!message) {
+    return false;
+  }
+
+  // There's no error |cause| available here.
+  auto cause = JS::NothingHandleValue;
+
+  RootedObject errorObj(
+      cx, ErrorObject::create(cx, JSEXN_WASMCOMPILEERROR, stack, fileName, 0,
+                              line, JS::ColumnNumberOneOrigin(), nullptr,
+                              message, cause));
+  if (!errorObj) {
+    return false;
+  }
+
+  RootedValue rejectionValue(cx, ObjectValue(*errorObj));
+  return PromiseObject::reject(cx, promise, rejectionValue);
+}
+
+static void LogAsync(JSContext* cx, const char* funcName,
+                     const Module& module) {
+  Log(cx, "async %s succeeded%s", funcName,
+      module.loggingDeserialized() ? " (loaded from cache)" : "");
+}
+
+enum class Ret { Pair, Instance };
+
+class AsyncInstantiateTask : public OffThreadPromiseTask {
+  SharedModule module_;
+  PersistentRooted<ImportValues> imports_;
+  Ret ret_;
+
+ public:
+  AsyncInstantiateTask(JSContext* cx, const Module& module, Ret ret,
+                       Handle<PromiseObject*> promise)
+      : OffThreadPromiseTask(cx, promise),
+        module_(&module),
+        imports_(cx),
+        ret_(ret) {}
+
+  ImportValues& imports() { return imports_.get(); }
+
+  bool resolve(JSContext* cx, Handle<PromiseObject*> promise) override {
+    RootedObject instanceProto(
+        cx, &cx->global()->getPrototype(JSProto_WasmInstance));
+
+    Rooted<WasmInstanceObject*> instanceObj(cx);
+    if (!module_->instantiate(cx, imports_.get(), instanceProto,
+                              &instanceObj)) {
+      return RejectWithPendingException(cx, promise);
+    }
+
+    RootedValue resolutionValue(cx);
+    if (ret_ == Ret::Instance) {
+      resolutionValue = ObjectValue(*instanceObj);
+    } else {
+      RootedObject resultObj(cx, JS_NewPlainObject(cx));
+      if (!resultObj) {
+        return RejectWithPendingException(cx, promise);
+      }
+
+      RootedObject moduleProto(cx,
+                               &cx->global()->getPrototype(JSProto_WasmModule));
+      RootedObject moduleObj(
+          cx, WasmModuleObject::create(cx, *module_, moduleProto));
+      if (!moduleObj) {
+        return RejectWithPendingException(cx, promise);
+      }
+
+      RootedValue val(cx, ObjectValue(*moduleObj));
+      if (!JS_DefineProperty(cx, resultObj, "module", val, JSPROP_ENUMERATE)) {
+        return RejectWithPendingException(cx, promise);
+      }
+
+      val = ObjectValue(*instanceObj);
+      if (!JS_DefineProperty(cx, resultObj, "instance", val,
+                             JSPROP_ENUMERATE)) {
+        return RejectWithPendingException(cx, promise);
+      }
+
+      resolutionValue = ObjectValue(*resultObj);
+    }
+
+    if (!PromiseObject::resolve(cx, promise, resolutionValue)) {
+      return RejectWithPendingException(cx, promise);
+    }
+
+    LogAsync(cx, "instantiate", *module_);
+    return true;
+  }
+};
+
+static bool AsyncInstantiate(JSContext* cx, const Module& module,
+                             HandleObject importObj, Ret ret,
+                             Handle<PromiseObject*> promise) {
+  auto task = js::MakeUnique<AsyncInstantiateTask>(cx, module, ret, promise);
+  if (!task || !task->init(cx)) {
+    return false;
+  }
+
+  if (!GetImports(cx, module, importObj, &task->imports())) {
+    return RejectWithPendingException(cx, promise);
+  }
+
+  task.release()->dispatchResolveAndDestroy();
+  return true;
+}
+
+static bool ResolveCompile(JSContext* cx, const Module& module,
+                           Handle<PromiseObject*> promise) {
+  RootedObject proto(cx, &cx->global()->getPrototype(JSProto_WasmModule));
+  RootedObject moduleObj(cx, WasmModuleObject::create(cx, module, proto));
+  if (!moduleObj) {
+    return RejectWithPendingException(cx, promise);
+  }
+
+  RootedValue resolutionValue(cx, ObjectValue(*moduleObj));
+  if (!PromiseObject::resolve(cx, promise, resolutionValue)) {
+    return RejectWithPendingException(cx, promise);
+  }
+
+  LogAsync(cx, "compile", module);
+  return true;
+}
+
+struct CompileBufferTask : PromiseHelperTask {
+  MutableBytes bytecode;
+  SharedCompileArgs compileArgs;
+  UniqueChars error;
+  UniqueCharsVector warnings;
+  SharedModule module;
+  bool instantiate;
+  PersistentRootedObject importObj;
+
+  CompileBufferTask(JSContext* cx, Handle<PromiseObject*> promise,
+                    HandleObject importObj)
+      : PromiseHelperTask(cx, promise),
+        instantiate(true),
+        importObj(cx, importObj) {}
+
+  CompileBufferTask(JSContext* cx, Handle<PromiseObject*> promise)
+      : PromiseHelperTask(cx, promise), instantiate(false) {}
+
+  bool init(JSContext* cx, FeatureOptions options, const char* introducer) {
+    compileArgs = InitCompileArgs(cx, options, introducer);
+    if (!compileArgs) {
+      return false;
+    }
+    return PromiseHelperTask::init(cx);
+  }
+
+  void execute() override {
+    module = CompileBuffer(*compileArgs, *bytecode, &error, &warnings, nullptr);
+  }
+
+  bool resolve(JSContext* cx, Handle<PromiseObject*> promise) override {
+    if (!ReportCompileWarnings(cx, warnings)) {
+      return false;
+    }
+    if (!module) {
+      return Reject(cx, *compileArgs, promise, error);
+    }
+    if (instantiate) {
+      return AsyncInstantiate(cx, *module, importObj, Ret::Pair, promise);
+    }
+    return ResolveCompile(cx, *module, promise);
+  }
+};
+
+static bool RejectWithPendingException(JSContext* cx,
+                                       Handle<PromiseObject*> promise,
+                                       CallArgs& callArgs) {
+  if (!RejectWithPendingException(cx, promise)) {
+    return false;
+  }
+
+  callArgs.rval().setObject(*promise);
+  return true;
+}
+
+static bool EnsurePromiseSupport(JSContext* cx) {
+  if (!cx->runtime()->offThreadPromiseState.ref().initialized()) {
+    JS_ReportErrorASCII(
+        cx, "WebAssembly Promise APIs not supported in this runtime.");
+    return false;
+  }
+  return true;
+}
+
+static bool GetBufferSource(JSContext* cx, CallArgs callArgs, const char* name,
+                            MutableBytes* bytecode) {
+  if (!callArgs.requireAtLeast(cx, name, 1)) {
+    return false;
+  }
+
+  if (!callArgs[0].isObject()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_BUF_ARG);
+    return false;
+  }
+
+  return GetBufferSource(cx, &callArgs[0].toObject(), JSMSG_WASM_BAD_BUF_ARG,
+                         bytecode);
+}
+
+static bool WebAssembly_compile(JSContext* cx, unsigned argc, Value* vp) {
+  if (!EnsurePromiseSupport(cx)) {
+    return false;
+  }
+
+  Log(cx, "async compile() started");
+
+  Rooted<PromiseObject*> promise(cx, PromiseObject::createSkippingExecutor(cx));
+  if (!promise) {
+    return false;
+  }
+
+  CallArgs callArgs = CallArgsFromVp(argc, vp);
+
+  if (!cx->isRuntimeCodeGenEnabled(JS::RuntimeCode::WASM, nullptr)) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_CSP_BLOCKED_WASM, "WebAssembly.compile");
+    return RejectWithPendingException(cx, promise, callArgs);
+  }
+
+  auto task = cx->make_unique<CompileBufferTask>(cx, promise);
+  if (!task) {
+    return false;
+  }
+
+  if (!GetBufferSource(cx, callArgs, "WebAssembly.compile", &task->bytecode)) {
+    return RejectWithPendingException(cx, promise, callArgs);
+  }
+
+  FeatureOptions options;
+  if (!options.init(cx, callArgs.get(1))) {
+    return false;
+  }
+
+  if (!task->init(cx, options, "WebAssembly.compile")) {
+    return false;
+  }
+
+  if (!StartOffThreadPromiseHelperTask(cx, std::move(task))) {
+    return false;
+  }
+
+  callArgs.rval().setObject(*promise);
+  return true;
+}
+
+static bool GetInstantiateArgs(JSContext* cx, CallArgs callArgs,
+                               MutableHandleObject firstArg,
+                               MutableHandleObject importObj,
+                               MutableHandleValue featureOptions) {
+  if (!callArgs.requireAtLeast(cx, "WebAssembly.instantiate", 1)) {
+    return false;
+  }
+
+  if (!callArgs[0].isObject()) {
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_WASM_BAD_BUF_MOD_ARG);
+    return false;
+  }
+
+  firstArg.set(&callArgs[0].toObject());
+
+  if (!GetImportArg(cx, callArgs.get(1), importObj)) {
+    return false;
+  }
+
+  featureOptions.set(callArgs.get(2));
+  return true;
+}
+
+static bool WebAssembly_instantiate(JSContext* cx, unsigned argc, Value* vp) {
+  if (!EnsurePromiseSupport(cx)) {
+    return false;
+  }
+
+  Log(cx, "async instantiate() started");
+
+  Rooted<PromiseObject*> promise(cx, PromiseObject::createSkippingExecutor(cx));
+  if (!promise) {
+    return false;
+  }
+
+  CallArgs callArgs = CallArgsFromVp(argc, vp);
+
+  RootedObject firstArg(cx);
+  RootedObject importObj(cx);
+  RootedValue featureOptions(cx);
+  if (!GetInstantiateArgs(cx, callArgs, &firstArg, &importObj,
+                          &featureOptions)) {
+    return RejectWithPendingException(cx, promise, callArgs);
+  }
+
+  const Module* module;
+  if (IsModuleObject(firstArg, &module)) {
+    if (!AsyncInstantiate(cx, *module, importObj, Ret::Instance, promise)) {
+      return false;
+    }
+  } else {
+    if (!cx->isRuntimeCodeGenEnabled(JS::RuntimeCode::WASM, nullptr)) {
+      JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                JSMSG_CSP_BLOCKED_WASM,
+                                "WebAssembly.instantiate");
+      return RejectWithPendingException(cx, promise, callArgs);
+    }
+
+    FeatureOptions options;
+    if (!options.init(cx, featureOptions)) {
+      return false;
+    }
+
+    auto task = cx->make_unique<CompileBufferTask>(cx, promise, importObj);
+    if (!task || !task->init(cx, options, "WebAssembly.instantiate")) {
+      return false;
+    }
+
+    if (!GetBufferSource(cx, firstArg, JSMSG_WASM_BAD_BUF_MOD_ARG,
+                         &task->bytecode)) {
+      return RejectWithPendingException(cx, promise, callArgs);
+    }
+
+    if (!StartOffThreadPromiseHelperTask(cx, std::move(task))) {
+      return false;
+    }
+  }
+
+  callArgs.rval().setObject(*promise);
+  return true;
+}
+
+static bool WebAssembly_validate(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs callArgs = CallArgsFromVp(argc, vp);
+
+  MutableBytes bytecode;
+  if (!GetBufferSource(cx, callArgs, "WebAssembly.validate", &bytecode)) {
+    return false;
+  }
+
+  FeatureOptions options;
+  UniqueChars error;
+  bool validated = Validate(cx, *bytecode, options, &error);
+
+  // If the reason for validation failure was OOM (signalled by null error
+  // message), report out-of-memory so that validate's return is always
+  // correct.
+  if (!validated && !error) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  if (error) {
+    MOZ_ASSERT(!validated);
+    Log(cx, "validate() failed with: %s", error.get());
+  }
+
+  callArgs.rval().setBoolean(validated);
+  return true;
+}
+
+static bool EnsureStreamSupport(JSContext* cx) {
+  // This should match wasm::StreamingCompilationAvailable().
+
+  if (!EnsurePromiseSupport(cx)) {
+    return false;
+  }
+
+  if (!CanUseExtraThreads()) {
+    JS_ReportErrorASCII(
+        cx, "WebAssembly.compileStreaming not supported with --no-threads");
+    return false;
+  }
+
+  if (!cx->runtime()->consumeStreamCallback) {
+    JS_ReportErrorASCII(cx,
+                        "WebAssembly streaming not supported in this runtime");
+    return false;
+  }
+
+  return true;
+}
+
+// This value is chosen and asserted to be disjoint from any host error code.
+static const size_t StreamOOMCode = 0;
+
+static bool RejectWithStreamErrorNumber(JSContext* cx, size_t errorCode,
+                                        Handle<PromiseObject*> promise) {
+  if (errorCode == StreamOOMCode) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  cx->runtime()->reportStreamErrorCallback(cx, errorCode);
+  return RejectWithPendingException(cx, promise);
+}
+
+class CompileStreamTask : public PromiseHelperTask, public JS::StreamConsumer {
+  // The stream progresses monotonically through these states; the helper
+  // thread wait()s for streamState_ to reach Closed.
+  enum StreamState { Env, Code, Tail, Closed };
+  ExclusiveWaitableData<StreamState> streamState_;
+
+  // Immutable:
+  const bool instantiate_;
+  const PersistentRootedObject importObj_;
+
+  // Immutable after noteResponseURLs() which is called at most once before
+  // first call on stream thread:
+  const MutableCompileArgs compileArgs_;
+
+  // Immutable after Env state:
+  Bytes envBytes_;
+  SectionRange codeSection_;
+
+  // The code section vector is resized once during the Env state and filled
+  // in chunk by chunk during the Code state, updating the end-pointer after
+  // each chunk:
+  Bytes codeBytes_;
+  uint8_t* codeBytesEnd_;
+  ExclusiveBytesPtr exclusiveCodeBytesEnd_;
+
+  // Immutable after Tail state:
+  Bytes tailBytes_;
+  ExclusiveStreamEndData exclusiveStreamEnd_;
+
+  // Written once before Closed state and read in Closed state on main thread:
+  SharedModule module_;
+  Maybe<size_t> streamError_;
+  UniqueChars compileError_;
+  UniqueCharsVector warnings_;
+
+  // Set on stream thread and read racily on helper thread to abort compilation:
+  Atomic<bool> streamFailed_;
+
+  // Called on some thread before consumeChunk(), streamEnd(), streamError()):
+
+  void noteResponseURLs(const char* url, const char* sourceMapUrl) override {
+    if (url) {
+      compileArgs_->scriptedCaller.filename = DuplicateString(url);
+      compileArgs_->scriptedCaller.filenameIsURL = true;
+    }
+    if (sourceMapUrl) {
+      compileArgs_->sourceMapURL = DuplicateString(sourceMapUrl);
+    }
+  }
+
+  // Called on a stream thread:
+
+  // Until StartOffThreadPromiseHelperTask succeeds, we are responsible for
+  // dispatching ourselves back to the JS thread.
+  //
+  // Warning: After this function returns, 'this' can be deleted at any time, so
+  // the caller must immediately return from the stream callback.
+  void setClosedAndDestroyBeforeHelperThreadStarted() {
+    streamState_.lock().get() = Closed;
+    dispatchResolveAndDestroy();
+  }
+
+  // See setClosedAndDestroyBeforeHelperThreadStarted() comment.
+  bool rejectAndDestroyBeforeHelperThreadStarted(size_t errorNumber) {
+    MOZ_ASSERT(streamState_.lock() == Env);
+    MOZ_ASSERT(!streamError_);
+    streamError_ = Some(errorNumber);
+    setClosedAndDestroyBeforeHelperThreadStarted();
+    return false;
+  }
+
+  // Once StartOffThreadPromiseHelperTask succeeds, the helper thread will
+  // dispatchResolveAndDestroy() after execute() returns, but execute()
+  // wait()s for state to be Closed.
+  //
+  // Warning: After this function returns, 'this' can be deleted at any time, so
+  // the caller must immediately return from the stream callback.
+  void setClosedAndDestroyAfterHelperThreadStarted() {
+    auto streamState = streamState_.lock();
+    MOZ_ASSERT(streamState != Closed);
+    streamState.get() = Closed;
+    streamState.notify_one(/* stream closed */);
+  }
+
+  // See setClosedAndDestroyAfterHelperThreadStarted() comment.
+  bool rejectAndDestroyAfterHelperThreadStarted(size_t errorNumber) {
+    MOZ_ASSERT(!streamError_);
+    streamError_ = Some(errorNumber);
+    streamFailed_ = true;
+    exclusiveCodeBytesEnd_.lock().notify_one();
+    exclusiveStreamEnd_.lock().notify_one();
+    setClosedAndDestroyAfterHelperThreadStarted();
+    return false;
+  }
+
+  bool consumeChunk(const uint8_t* begin, size_t length) override {
+    switch (streamState_.lock().get()) {
+      case Env: {
+        if (!envBytes_.append(begin, length)) {
+          return rejectAndDestroyBeforeHelperThreadStarted(StreamOOMCode);
+        }
+
+        if (!StartsCodeSection(envBytes_.begin(), envBytes_.end(),
+                               &codeSection_)) {
+          return true;
+        }
+
+        uint32_t extraBytes = envBytes_.length() - codeSection_.start;
+        if (extraBytes) {
+          envBytes_.shrinkTo(codeSection_.start);
+        }
+
+        if (codeSection_.size > MaxCodeSectionBytes) {
+          return rejectAndDestroyBeforeHelperThreadStarted(StreamOOMCode);
+        }
+
+        if (!codeBytes_.resize(codeSection_.size)) {
+          return rejectAndDestroyBeforeHelperThreadStarted(StreamOOMCode);
+        }
+
+        codeBytesEnd_ = codeBytes_.begin();
+        exclusiveCodeBytesEnd_.lock().get() = codeBytesEnd_;
+
+        if (!StartOffThreadPromiseHelperTask(this)) {
+          return rejectAndDestroyBeforeHelperThreadStarted(StreamOOMCode);
+        }
+
+        // Set the state to Code iff StartOffThreadPromiseHelperTask()
+        // succeeds so that the state tells us whether we are before or
+        // after the helper thread started.
+        streamState_.lock().get() = Code;
+
+        if (extraBytes) {
+          return consumeChunk(begin + length - extraBytes, extraBytes);
+        }
+
+        return true;
+      }
+      case Code: {
+        size_t copyLength =
+            std::min<size_t>(length, codeBytes_.end() - codeBytesEnd_);
+        memcpy(codeBytesEnd_, begin, copyLength);
+        codeBytesEnd_ += copyLength;
+
+        {
+          auto codeStreamEnd = exclusiveCodeBytesEnd_.lock();
+          codeStreamEnd.get() = codeBytesEnd_;
+          codeStreamEnd.notify_one();
+        }
+
+        if (codeBytesEnd_ != codeBytes_.end()) {
+          return true;
+        }
+
+        streamState_.lock().get() = Tail;
+
+        if (uint32_t extraBytes = length - copyLength) {
+          return consumeChunk(begin + copyLength, extraBytes);
+        }
+
+        return true;
+      }
+      case Tail: {
+        if (!tailBytes_.append(begin, length)) {
+          return rejectAndDestroyAfterHelperThreadStarted(StreamOOMCode);
+        }
+
+        return true;
+      }
+      case Closed:
+        MOZ_CRASH("consumeChunk() in Closed state");
+    }
+    MOZ_CRASH("unreachable");
+  }
+
+  void streamEnd(JS::OptimizedEncodingListener* tier2Listener) override {
+    switch (streamState_.lock().get()) {
+      case Env: {
+        SharedBytes bytecode = js_new<ShareableBytes>(std::move(envBytes_));
+        if (!bytecode) {
+          rejectAndDestroyBeforeHelperThreadStarted(StreamOOMCode);
+          return;
+        }
+        module_ = CompileBuffer(*compileArgs_, *bytecode, &compileError_,
+                                &warnings_, nullptr);
+        setClosedAndDestroyBeforeHelperThreadStarted();
+        return;
+      }
+      case Code:
+      case Tail:
+        // Unlock exclusiveStreamEnd_ before locking streamState_.
+        {
+          auto streamEnd = exclusiveStreamEnd_.lock();
+          MOZ_ASSERT(!streamEnd->reached);
+          streamEnd->reached = true;
+          streamEnd->tailBytes = &tailBytes_;
+          streamEnd->tier2Listener = tier2Listener;
+          streamEnd.notify_one();
+        }
+        setClosedAndDestroyAfterHelperThreadStarted();
+        return;
+      case Closed:
+        MOZ_CRASH("streamEnd() in Closed state");
+    }
+  }
+
+  void streamError(size_t errorCode) override {
+    MOZ_ASSERT(errorCode != StreamOOMCode);
+    switch (streamState_.lock().get()) {
+      case Env:
+        rejectAndDestroyBeforeHelperThreadStarted(errorCode);
+        return;
+      case Tail:
+      case Code:
+        rejectAndDestroyAfterHelperThreadStarted(errorCode);
+        return;
+      case Closed:
+        MOZ_CRASH("streamError() in Closed state");
+    }
+  }
+
+  void consumeOptimizedEncoding(const uint8_t* begin, size_t length) override {
+    module_ = Module::deserialize(begin, length);
+
+    MOZ_ASSERT(streamState_.lock().get() == Env);
+    setClosedAndDestroyBeforeHelperThreadStarted();
+  }
+
+  // Called on a helper thread:
+
+  void execute() override {
+    module_ = CompileStreaming(*compileArgs_, envBytes_, codeBytes_,
+                               exclusiveCodeBytesEnd_, exclusiveStreamEnd_,
+                               streamFailed_, &compileError_, &warnings_);
+
+    // When execute() returns, the CompileStreamTask will be dispatched
+    // back to its JS thread to call resolve() and then be destroyed. We
+    // can't let this happen until the stream has been closed lest
+    // consumeChunk() or streamEnd() be called on a dead object.
+    auto streamState = streamState_.lock();
+    while (streamState != Closed) {
+      streamState.wait(/* stream closed */);
+    }
+  }
+
+  // Called on a JS thread after streaming compilation completes/errors:
+
+  bool resolve(JSContext* cx, Handle<PromiseObject*> promise) override {
+    MOZ_ASSERT(streamState_.lock() == Closed);
+
+    if (!ReportCompileWarnings(cx, warnings_)) {
+      return false;
+    }
+    if (module_) {
+      MOZ_ASSERT(!streamFailed_ && !streamError_ && !compileError_);
+      if (instantiate_) {
+        return AsyncInstantiate(cx, *module_, importObj_, Ret::Pair, promise);
+      }
+      return ResolveCompile(cx, *module_, promise);
+    }
+
+    if (streamError_) {
+      return RejectWithStreamErrorNumber(cx, *streamError_, promise);
+    }
+
+    return Reject(cx, *compileArgs_, promise, compileError_);
+  }
+
+ public:
+  CompileStreamTask(JSContext* cx, Handle<PromiseObject*> promise,
+                    CompileArgs& compileArgs, bool instantiate,
+                    HandleObject importObj)
+      : PromiseHelperTask(cx, promise),
+        streamState_(mutexid::WasmStreamStatus, Env),
+        instantiate_(instantiate),
+        importObj_(cx, importObj),
+        compileArgs_(&compileArgs),
+        codeSection_{},
+        codeBytesEnd_(nullptr),
+        exclusiveCodeBytesEnd_(mutexid::WasmCodeBytesEnd, nullptr),
+        exclusiveStreamEnd_(mutexid::WasmStreamEnd),
+        streamFailed_(false) {
+    MOZ_ASSERT_IF(importObj_, instantiate_);
+  }
+};
+
+// A short-lived object that captures the arguments of a
+// WebAssembly.{compileStreaming,instantiateStreaming} while waiting for
+// the Promise<Response> to resolve to a (hopefully) Promise.
+class ResolveResponseClosure : public NativeObject {
+  static const unsigned COMPILE_ARGS_SLOT = 0;
+  static const unsigned PROMISE_OBJ_SLOT = 1;
+  static const unsigned INSTANTIATE_SLOT = 2;
+  static const unsigned IMPORT_OBJ_SLOT = 3;
+  static const JSClassOps classOps_;
+
+  static void finalize(JS::GCContext* gcx, JSObject* obj) {
+    auto& closure = obj->as<ResolveResponseClosure>();
+    gcx->release(obj, &closure.compileArgs(),
+                 MemoryUse::WasmResolveResponseClosure);
+  }
+
+ public:
+  static const unsigned RESERVED_SLOTS = 4;
+  static const JSClass class_;
+
+  static ResolveResponseClosure* create(JSContext* cx, const CompileArgs& args,
+                                        HandleObject promise, bool instantiate,
+                                        HandleObject importObj) {
+    MOZ_ASSERT_IF(importObj, instantiate);
+
+    AutoSetNewObjectMetadata metadata(cx);
+    auto* obj = NewObjectWithGivenProto<ResolveResponseClosure>(cx, nullptr);
+    if (!obj) {
+      return nullptr;
+    }
+
+    args.AddRef();
+    InitReservedSlot(obj, COMPILE_ARGS_SLOT, const_cast<CompileArgs*>(&args),
+                     MemoryUse::WasmResolveResponseClosure);
+    obj->setReservedSlot(PROMISE_OBJ_SLOT, ObjectValue(*promise));
+    obj->setReservedSlot(INSTANTIATE_SLOT, BooleanValue(instantiate));
+    obj->setReservedSlot(IMPORT_OBJ_SLOT, ObjectOrNullValue(importObj));
+    return obj;
+  }
+
+  CompileArgs& compileArgs() const {
+    return *(CompileArgs*)getReservedSlot(COMPILE_ARGS_SLOT).toPrivate();
+  }
+  PromiseObject& promise() const {
+    return getReservedSlot(PROMISE_OBJ_SLOT).toObject().as<PromiseObject>();
+  }
+  bool instantiate() const {
+    return getReservedSlot(INSTANTIATE_SLOT).toBoolean();
+  }
+  JSObject* importObj() const {
+    return getReservedSlot(IMPORT_OBJ_SLOT).toObjectOrNull();
+  }
+};
+
+const JSClassOps ResolveResponseClosure::classOps_ = {
+    nullptr,                           // addProperty
+    nullptr,                           // delProperty
+    nullptr,                           // enumerate
+    nullptr,                           // newEnumerate
+    nullptr,                           // resolve
+    nullptr,                           // mayResolve
+    ResolveResponseClosure::finalize,  // finalize
+    nullptr,                           // call
+    nullptr,                           // construct
+    nullptr,                           // trace
+};
+
+const JSClass ResolveResponseClosure::class_ = {
+    "WebAssembly ResolveResponseClosure",
+    JSCLASS_DELAY_METADATA_BUILDER |
+        JSCLASS_HAS_RESERVED_SLOTS(ResolveResponseClosure::RESERVED_SLOTS) |
+        JSCLASS_FOREGROUND_FINALIZE,
+    &ResolveResponseClosure::classOps_,
+};
+
+static ResolveResponseClosure* ToResolveResponseClosure(CallArgs args) {
+  return &args.callee()
+              .as<JSFunction>()
+              .getExtendedSlot(0)
+              .toObject()
+              .as<ResolveResponseClosure>();
+}
+
+static bool RejectWithErrorNumber(JSContext* cx, uint32_t errorNumber,
+                                  Handle<PromiseObject*> promise) {
+  JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr, errorNumber);
+  return RejectWithPendingException(cx, promise);
+}
+
+static bool ResolveResponse_OnFulfilled(JSContext* cx, unsigned argc,
+                                        Value* vp) {
+  CallArgs callArgs = CallArgsFromVp(argc, vp);
+
+  Rooted<ResolveResponseClosure*> closure(cx,
+                                          ToResolveResponseClosure(callArgs));
+  Rooted<PromiseObject*> promise(cx, &closure->promise());
+  CompileArgs& compileArgs = closure->compileArgs();
+  bool instantiate = closure->instantiate();
+  Rooted<JSObject*> importObj(cx, closure->importObj());
+
+  auto task = cx->make_unique<CompileStreamTask>(cx, promise, compileArgs,
+                                                 instantiate, importObj);
+  if (!task || !task->init(cx)) {
+    return false;
+  }
+
+  if (!callArgs.get(0).isObject()) {
+    return RejectWithErrorNumber(cx, JSMSG_WASM_BAD_RESPONSE_VALUE, promise);
+  }
+
+  RootedObject response(cx, &callArgs.get(0).toObject());
+  if (!cx->runtime()->consumeStreamCallback(cx, response, JS::MimeType::Wasm,
+                                            task.get())) {
+    return RejectWithPendingException(cx, promise);
+  }
+
+  (void)task.release();
+
+  callArgs.rval().setUndefined();
+  return true;
+}
+
+static bool ResolveResponse_OnRejected(JSContext* cx, unsigned argc,
+                                       Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  Rooted<ResolveResponseClosure*> closure(cx, ToResolveResponseClosure(args));
+  Rooted<PromiseObject*> promise(cx, &closure->promise());
+
+  if (!PromiseObject::reject(cx, promise, args.get(0))) {
+    return false;
+  }
+
+  args.rval().setUndefined();
+  return true;
+}
+
+static bool ResolveResponse(JSContext* cx, Handle<Value> responsePromise,
+                            Handle<Value> featureOptions,
+                            Handle<PromiseObject*> resultPromise,
+                            bool instantiate = false,
+                            HandleObject importObj = nullptr) {
+  MOZ_ASSERT_IF(importObj, instantiate);
+
+  const char* introducer = instantiate ? "WebAssembly.instantiateStreaming"
+                                       : "WebAssembly.compileStreaming";
+
+  FeatureOptions options;
+  if (!options.init(cx, featureOptions)) {
+    return false;
+  }
+
+  SharedCompileArgs compileArgs = InitCompileArgs(cx, options, introducer);
+  if (!compileArgs) {
+    return false;
+  }
+
+  RootedObject closure(
+      cx, ResolveResponseClosure::create(cx, *compileArgs, resultPromise,
+                                         instantiate, importObj));
+  if (!closure) {
+    return false;
+  }
+
+  RootedFunction onResolved(
+      cx, NewNativeFunction(cx, ResolveResponse_OnFulfilled, 1, nullptr,
+                            gc::AllocKind::FUNCTION_EXTENDED, GenericObject));
+  if (!onResolved) {
+    return false;
+  }
+
+  RootedFunction onRejected(
+      cx, NewNativeFunction(cx, ResolveResponse_OnRejected, 1, nullptr,
+                            gc::AllocKind::FUNCTION_EXTENDED, GenericObject));
+  if (!onRejected) {
+    return false;
+  }
+
+  onResolved->setExtendedSlot(0, ObjectValue(*closure));
+  onRejected->setExtendedSlot(0, ObjectValue(*closure));
+
+  RootedObject resolve(cx,
+                       PromiseObject::unforgeableResolve(cx, responsePromise));
+  if (!resolve) {
+    return false;
+  }
+
+  return JS::AddPromiseReactions(cx, resolve, onResolved, onRejected);
+}
+
+static bool WebAssembly_compileStreaming(JSContext* cx, unsigned argc,
+                                         Value* vp) {
+  if (!EnsureStreamSupport(cx)) {
+    return false;
+  }
+
+  Log(cx, "async compileStreaming() started");
+
+  Rooted<PromiseObject*> resultPromise(
+      cx, PromiseObject::createSkippingExecutor(cx));
+  if (!resultPromise) {
+    return false;
+  }
+
+  CallArgs callArgs = CallArgsFromVp(argc, vp);
+
+  if (!cx->isRuntimeCodeGenEnabled(JS::RuntimeCode::WASM, nullptr)) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_CSP_BLOCKED_WASM,
+                              "WebAssembly.compileStreaming");
+    return RejectWithPendingException(cx, resultPromise, callArgs);
+  }
+
+  Rooted<Value> responsePromise(cx, callArgs.get(0));
+  Rooted<Value> featureOptions(cx, callArgs.get(1));
+  if (!ResolveResponse(cx, responsePromise, featureOptions, resultPromise)) {
+    return RejectWithPendingException(cx, resultPromise, callArgs);
+  }
+
+  callArgs.rval().setObject(*resultPromise);
+  return true;
+}
+
+static bool WebAssembly_instantiateStreaming(JSContext* cx, unsigned argc,
+                                             Value* vp) {
+  if (!EnsureStreamSupport(cx)) {
+    return false;
+  }
+
+  Log(cx, "async instantiateStreaming() started");
+
+  Rooted<PromiseObject*> resultPromise(
+      cx, PromiseObject::createSkippingExecutor(cx));
+  if (!resultPromise) {
+    return false;
+  }
+
+  CallArgs callArgs = CallArgsFromVp(argc, vp);
+
+  if (!cx->isRuntimeCodeGenEnabled(JS::RuntimeCode::WASM, nullptr)) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_CSP_BLOCKED_WASM,
+                              "WebAssembly.instantiateStreaming");
+    return RejectWithPendingException(cx, resultPromise, callArgs);
+  }
+
+  Rooted<JSObject*> firstArg(cx);
+  Rooted<JSObject*> importObj(cx);
+  Rooted<Value> featureOptions(cx);
+  if (!GetInstantiateArgs(cx, callArgs, &firstArg, &importObj,
+                          &featureOptions)) {
+    return RejectWithPendingException(cx, resultPromise, callArgs);
+  }
+  Rooted<Value> responsePromise(cx, ObjectValue(*firstArg.get()));
+
+  if (!ResolveResponse(cx, responsePromise, featureOptions, resultPromise, true,
+                       importObj)) {
+    return RejectWithPendingException(cx, resultPromise, callArgs);
+  }
+
+  callArgs.rval().setObject(*resultPromise);
+  return true;
+}
+
+#ifdef ENABLE_WASM_MOZ_INTGEMM
+
+static bool WebAssembly_mozIntGemm(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  Rooted<WasmModuleObject*> module(cx);
+  if (!wasm::CompileBuiltinModule(cx, wasm::BuiltinModuleId::IntGemm,
+                                  &module)) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+  args.rval().set(ObjectValue(*module.get()));
+  return true;
+}
+
+static const JSFunctionSpec WebAssembly_mozIntGemm_methods[] = {
+    JS_FN("mozIntGemm", WebAssembly_mozIntGemm, 0, JSPROP_ENUMERATE),
+    JS_FS_END};
+
+#endif  // ENABLE_WASM_MOZ_INTGEMM
+
+static const JSFunctionSpec WebAssembly_static_methods[] = {
+    JS_FN("toSource", WebAssembly_toSource, 0, 0),
+    JS_FN("compile", WebAssembly_compile, 1, JSPROP_ENUMERATE),
+    JS_FN("instantiate", WebAssembly_instantiate, 1, JSPROP_ENUMERATE),
+    JS_FN("validate", WebAssembly_validate, 1, JSPROP_ENUMERATE),
+    JS_FN("compileStreaming", WebAssembly_compileStreaming, 1,
+          JSPROP_ENUMERATE),
+    JS_FN("instantiateStreaming", WebAssembly_instantiateStreaming, 1,
+          JSPROP_ENUMERATE),
+    JS_FS_END};
+
+static const JSPropertySpec WebAssembly_static_properties[] = {
+    JS_STRING_SYM_PS(toStringTag, "WebAssembly", JSPROP_READONLY), JS_PS_END};
+
+static JSObject* CreateWebAssemblyObject(JSContext* cx, JSProtoKey key) {
+  MOZ_RELEASE_ASSERT(HasSupport(cx));
+
+  RootedObject proto(cx, &cx->global()->getObjectPrototype());
+  return NewTenuredObjectWithGivenProto(cx, &WasmNamespaceObject::class_,
+                                        proto);
+}
+
+struct NameAndProtoKey {
+  const char* const name;
+  JSProtoKey key;
+};
+
+static bool WebAssemblyDefineConstructor(JSContext* cx,
+                                         Handle<WasmNamespaceObject*> wasm,
+                                         NameAndProtoKey entry,
+                                         MutableHandleValue ctorValue,
+                                         MutableHandleId id) {
+  JSObject* ctor = GlobalObject::getOrCreateConstructor(cx, entry.key);
+  if (!ctor) {
+    return false;
+  }
+  ctorValue.setObject(*ctor);
+
+  JSAtom* className = Atomize(cx, entry.name, strlen(entry.name));
+  if (!className) {
+    return false;
+  }
+  id.set(AtomToId(className));
+
+  return DefineDataProperty(cx, wasm, id, ctorValue, 0);
+}
+
+static bool WebAssemblyClassFinish(JSContext* cx, HandleObject object,
+                                   HandleObject proto) {
+  Handle<WasmNamespaceObject*> wasm = object.as<WasmNamespaceObject>();
+
+  constexpr NameAndProtoKey entries[] = {
+      {"Module", JSProto_WasmModule},
+      {"Instance", JSProto_WasmInstance},
+      {"Memory", JSProto_WasmMemory},
+      {"Table", JSProto_WasmTable},
+      {"Global", JSProto_WasmGlobal},
+      {"CompileError", GetExceptionProtoKey(JSEXN_WASMCOMPILEERROR)},
+      {"LinkError", GetExceptionProtoKey(JSEXN_WASMLINKERROR)},
+      {"RuntimeError", GetExceptionProtoKey(JSEXN_WASMRUNTIMEERROR)},
+#ifdef ENABLE_WASM_TYPE_REFLECTIONS
+      {"Function", JSProto_WasmFunction},
+#endif
+  };
+  RootedValue ctorValue(cx);
+  RootedId id(cx);
+  for (const auto& entry : entries) {
+    if (!WebAssemblyDefineConstructor(cx, wasm, entry, &ctorValue, &id)) {
+      return false;
+    }
+  }
+
+  if (ExceptionsAvailable(cx)) {
+    constexpr NameAndProtoKey exceptionEntries[] = {
+        {"Tag", JSProto_WasmTag},
+        {"Exception", JSProto_WasmException},
+    };
+    for (const auto& entry : exceptionEntries) {
+      if (!WebAssemblyDefineConstructor(cx, wasm, entry, &ctorValue, &id)) {
+        return false;
+      }
+    }
+  }
+
+  RootedObject tagProto(
+      cx, GlobalObject::getOrCreatePrototype(cx, JSProto_WasmTag));
+  if (!tagProto) {
+    ReportOutOfMemory(cx);
+    return false;
+  }
+
+  SharedTagType wrappedJSValueTagType(sWrappedJSValueTagType);
+  WasmTagObject* wrappedJSValueTagObject =
+      WasmTagObject::create(cx, wrappedJSValueTagType, tagProto);
+  if (!wrappedJSValueTagObject) {
+    return false;
+  }
+
+  wasm->setWrappedJSValueTag(wrappedJSValueTagObject);
+
+#ifdef ENABLE_WASM_MOZ_INTGEMM
+  if (MozIntGemmAvailable(cx) &&
+      !JS_DefineFunctions(cx, wasm, WebAssembly_mozIntGemm_methods)) {
+    return false;
+  }
+#endif
+
+  return true;
+}
+
+WasmNamespaceObject* WasmNamespaceObject::getOrCreate(JSContext* cx) {
+  JSObject* wasm =
+      GlobalObject::getOrCreateConstructor(cx, JSProto_WebAssembly);
+  if (!wasm) {
+    return nullptr;
+  }
+  return &wasm->as<WasmNamespaceObject>();
+}
+
+static const ClassSpec WebAssemblyClassSpec = {
+    CreateWebAssemblyObject,       nullptr, WebAssembly_static_methods,
+    WebAssembly_static_properties, nullptr, nullptr,
+    WebAssemblyClassFinish};
+
+const JSClass js::WasmNamespaceObject::class_ = {
+    "WebAssembly",
+    JSCLASS_HAS_CACHED_PROTO(JSProto_WebAssembly) |
+        JSCLASS_HAS_RESERVED_SLOTS(WasmNamespaceObject::RESERVED_SLOTS),
+    JS_NULL_CLASS_OPS, &WebAssemblyClassSpec};
+
+// Sundry