Adding upstream version 110.0.1.upstream/110.0.1upstream

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

1 files changed, 2129 insertions, 0 deletions

diff --git a/js/src/vm/ArrayBufferObject.cpp b/js/src/vm/ArrayBufferObject.cpp
new file mode 100644
index 0000000000..485fcee33f
--- /dev/null
+++ b/js/src/vm/ArrayBufferObject.cpp
@@ -0,0 +1,2129 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "vm/ArrayBufferObject-inl.h"
+#include "vm/ArrayBufferObject.h"
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/Likely.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/TaggedAnonymousMemory.h"
+
+#include <algorithm>  // std::max, std::min
+#include <memory>     // std::uninitialized_copy_n
+#include <string.h>
+#if !defined(XP_WIN) && !defined(__wasi__)
+#  include <sys/mman.h>
+#endif
+#include <tuple>  // std::tuple
+#include <type_traits>
+#ifdef MOZ_VALGRIND
+#  include <valgrind/memcheck.h>
+#endif
+
+#include "jsnum.h"
+#include "jstypes.h"
+
+#include "gc/Barrier.h"
+#include "gc/Memory.h"
+#include "js/ArrayBuffer.h"
+#include "js/Conversions.h"
+#include "js/experimental/TypedData.h"  // JS_IsArrayBufferViewObject
+#include "js/friend/ErrorMessages.h"    // js::GetErrorMessage, JSMSG_*
+#include "js/MemoryMetrics.h"
+#include "js/PropertySpec.h"
+#include "js/SharedArrayBuffer.h"
+#include "js/Wrapper.h"
+#include "util/WindowsWrapper.h"
+#include "vm/GlobalObject.h"
+#include "vm/JSContext.h"
+#include "vm/JSObject.h"
+#include "vm/SharedArrayObject.h"
+#include "vm/Warnings.h"  // js::WarnNumberASCII
+#include "wasm/WasmConstants.h"
+#include "wasm/WasmLog.h"
+#include "wasm/WasmModuleTypes.h"
+#include "wasm/WasmProcess.h"
+
+#include "gc/GCContext-inl.h"
+#include "gc/Marking-inl.h"
+#include "vm/NativeObject-inl.h"
+#include "vm/Realm-inl.h"  // js::AutoRealm
+
+using JS::ToInt32;
+
+using js::wasm::IndexType;
+using js::wasm::Pages;
+using mozilla::Atomic;
+using mozilla::CheckedInt;
+using mozilla::DebugOnly;
+using mozilla::Maybe;
+using mozilla::Nothing;
+using mozilla::Some;
+
+using namespace js;
+
+// If there are too many wasm memory buffers (typically 6GB each) live we run up
+// against system resource exhaustion (address space or number of memory map
+// descriptors), see bug 1068684, bug 1073934, bug 1517412, bug 1502733 for
+// details.  The limiting case seems to be Android on ARM64, where the
+// per-process address space is limited to 4TB (39 bits) by the organization of
+// the page tables.  An earlier problem was Windows Vista Home 64-bit, where the
+// per-process address space is limited to 8TB (40 bits).
+//
+// Thus we track the number of live objects if we are using large mappings, and
+// set a limit of the number of live buffer objects per process. We trigger GC
+// work when we approach the limit and we throw an OOM error if the per-process
+// limit is exceeded. The limit (MaximumLiveMappedBuffers) is specific to
+// architecture, OS, and OS configuration.
+//
+// Since the MaximumLiveMappedBuffers limit is not generally accounted for by
+// any existing GC-trigger heuristics, we need an extra heuristic for triggering
+// GCs when the caller is allocating memories rapidly without other garbage.
+// Thus, once the live buffer count crosses the threshold
+// StartTriggeringAtLiveBufferCount, we start triggering GCs every
+// AllocatedBuffersPerTrigger allocations.  Once we reach
+// StartSyncFullGCAtLiveBufferCount live buffers, we perform expensive
+// non-incremental full GCs as a last-ditch effort to avoid unnecessary failure.
+// Once we reach MaximumLiveMappedBuffers, we perform further full GCs before
+// giving up.
+
+#if defined(JS_CODEGEN_ARM64) && defined(ANDROID)
+// With 6GB mappings, the hard limit is 84 buffers.  75 cuts it close.
+static const int32_t MaximumLiveMappedBuffers = 75;
+#elif defined(MOZ_TSAN) || defined(MOZ_ASAN)
+// ASAN and TSAN use a ton of vmem for bookkeeping leaving a lot less for the
+// program so use a lower limit.
+static const int32_t MaximumLiveMappedBuffers = 500;
+#else
+static const int32_t MaximumLiveMappedBuffers = 1000;
+#endif
+
+// StartTriggeringAtLiveBufferCount + AllocatedBuffersPerTrigger must be well
+// below StartSyncFullGCAtLiveBufferCount in order to provide enough time for
+// incremental GC to do its job.
+
+#if defined(JS_CODEGEN_ARM64) && defined(ANDROID)
+static const int32_t StartTriggeringAtLiveBufferCount = 15;
+static const int32_t StartSyncFullGCAtLiveBufferCount =
+    MaximumLiveMappedBuffers - 15;
+static const int32_t AllocatedBuffersPerTrigger = 15;
+#else
+static const int32_t StartTriggeringAtLiveBufferCount = 100;
+static const int32_t StartSyncFullGCAtLiveBufferCount =
+    MaximumLiveMappedBuffers - 100;
+static const int32_t AllocatedBuffersPerTrigger = 100;
+#endif
+
+static Atomic<int32_t, mozilla::ReleaseAcquire> liveBufferCount(0);
+static Atomic<int32_t, mozilla::ReleaseAcquire> allocatedSinceLastTrigger(0);
+
+int32_t js::LiveMappedBufferCount() { return liveBufferCount; }
+
+[[nodiscard]] static bool CheckArrayBufferTooLarge(JSContext* cx,
+                                                   uint64_t nbytes) {
+  // Refuse to allocate too large buffers.
+  if (MOZ_UNLIKELY(nbytes > ArrayBufferObject::MaxByteLength)) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_BAD_ARRAY_LENGTH);
+    return false;
+  }
+
+  return true;
+}
+
+void* js::MapBufferMemory(wasm::IndexType t, size_t mappedSize,
+                          size_t initialCommittedSize) {
+  MOZ_ASSERT(mappedSize % gc::SystemPageSize() == 0);
+  MOZ_ASSERT(initialCommittedSize % gc::SystemPageSize() == 0);
+  MOZ_ASSERT(initialCommittedSize <= mappedSize);
+
+  auto decrement = mozilla::MakeScopeExit([&] { liveBufferCount--; });
+  // Testing just IsHugeMemoryEnabled() here will overestimate the number of
+  // live buffers, as asm.js buffers are not huge.  This is OK in practice.
+  if (wasm::IsHugeMemoryEnabled(t)) {
+    liveBufferCount++;
+  } else {
+    decrement.release();
+  }
+
+  // Test >= to guard against the case where multiple extant runtimes
+  // race to allocate.
+  if (liveBufferCount >= MaximumLiveMappedBuffers) {
+    if (OnLargeAllocationFailure) {
+      OnLargeAllocationFailure();
+    }
+    if (liveBufferCount >= MaximumLiveMappedBuffers) {
+      return nullptr;
+    }
+  }
+
+#ifdef XP_WIN
+  void* data = VirtualAlloc(nullptr, mappedSize, MEM_RESERVE, PAGE_NOACCESS);
+  if (!data) {
+    return nullptr;
+  }
+
+  if (!VirtualAlloc(data, initialCommittedSize, MEM_COMMIT, PAGE_READWRITE)) {
+    VirtualFree(data, 0, MEM_RELEASE);
+    return nullptr;
+  }
+#elif defined(__wasi__)
+  void* data = nullptr;
+  if (int err = posix_memalign(&data, gc::SystemPageSize(), mappedSize)) {
+    MOZ_ASSERT(err == ENOMEM);
+    return nullptr;
+  }
+  MOZ_ASSERT(data);
+  memset(data, 0, mappedSize);
+#else   // !XP_WIN && !__wasi__
+  void* data =
+      MozTaggedAnonymousMmap(nullptr, mappedSize, PROT_NONE,
+                             MAP_PRIVATE | MAP_ANON, -1, 0, "wasm-reserved");
+  if (data == MAP_FAILED) {
+    return nullptr;
+  }
+
+  // Note we will waste a page on zero-sized memories here
+  if (mprotect(data, initialCommittedSize, PROT_READ | PROT_WRITE)) {
+    munmap(data, mappedSize);
+    return nullptr;
+  }
+#endif  // !XP_WIN && !__wasi__
+
+#if defined(MOZ_VALGRIND) && \
+    defined(VALGRIND_DISABLE_ADDR_ERROR_REPORTING_IN_RANGE)
+  VALGRIND_DISABLE_ADDR_ERROR_REPORTING_IN_RANGE(
+      (unsigned char*)data + initialCommittedSize,
+      mappedSize - initialCommittedSize);
+#endif
+
+  decrement.release();
+  return data;
+}
+
+bool js::CommitBufferMemory(void* dataEnd, size_t delta) {
+  MOZ_ASSERT(delta);
+  MOZ_ASSERT(delta % gc::SystemPageSize() == 0);
+
+#ifdef XP_WIN
+  if (!VirtualAlloc(dataEnd, delta, MEM_COMMIT, PAGE_READWRITE)) {
+    return false;
+  }
+#elif defined(__wasi__)
+  // posix_memalign'd memory is already committed
+  return true;
+#else
+  if (mprotect(dataEnd, delta, PROT_READ | PROT_WRITE)) {
+    return false;
+  }
+#endif  // XP_WIN
+
+#if defined(MOZ_VALGRIND) && \
+    defined(VALGRIND_DISABLE_ADDR_ERROR_REPORTING_IN_RANGE)
+  VALGRIND_ENABLE_ADDR_ERROR_REPORTING_IN_RANGE((unsigned char*)dataEnd, delta);
+#endif
+
+  return true;
+}
+
+bool js::ExtendBufferMapping(void* dataPointer, size_t mappedSize,
+                             size_t newMappedSize) {
+  MOZ_ASSERT(mappedSize % gc::SystemPageSize() == 0);
+  MOZ_ASSERT(newMappedSize % gc::SystemPageSize() == 0);
+  MOZ_ASSERT(newMappedSize >= mappedSize);
+
+#ifdef XP_WIN
+  void* mappedEnd = (char*)dataPointer + mappedSize;
+  uint32_t delta = newMappedSize - mappedSize;
+  if (!VirtualAlloc(mappedEnd, delta, MEM_RESERVE, PAGE_NOACCESS)) {
+    return false;
+  }
+  return true;
+#elif defined(__wasi__)
+  return false;
+#elif defined(XP_LINUX)
+  // Note this will not move memory (no MREMAP_MAYMOVE specified)
+  if (MAP_FAILED == mremap(dataPointer, mappedSize, newMappedSize, 0)) {
+    return false;
+  }
+  return true;
+#else
+  // No mechanism for remapping on MacOS and other Unices. Luckily
+  // shouldn't need it here as most of these are 64-bit.
+  return false;
+#endif
+}
+
+void js::UnmapBufferMemory(wasm::IndexType t, void* base, size_t mappedSize) {
+  MOZ_ASSERT(mappedSize % gc::SystemPageSize() == 0);
+
+#ifdef XP_WIN
+  VirtualFree(base, 0, MEM_RELEASE);
+#elif defined(__wasi__)
+  free(base);
+#else
+  munmap(base, mappedSize);
+#endif  // XP_WIN
+
+#if defined(MOZ_VALGRIND) && \
+    defined(VALGRIND_ENABLE_ADDR_ERROR_REPORTING_IN_RANGE)
+  VALGRIND_ENABLE_ADDR_ERROR_REPORTING_IN_RANGE((unsigned char*)base,
+                                                mappedSize);
+#endif
+
+  if (wasm::IsHugeMemoryEnabled(t)) {
+    // Decrement the buffer counter at the end -- otherwise, a race condition
+    // could enable the creation of unlimited buffers.
+    //
+    // Also see comment in MapBufferMemory about overestimation due to the
+    // imprecision of the above guard.
+    --liveBufferCount;
+  }
+}
+
+/*
+ * ArrayBufferObject
+ *
+ * This class holds the underlying raw buffer that the TypedArrayObject classes
+ * access.  It can be created explicitly and passed to a TypedArrayObject, or
+ * can be created implicitly by constructing a TypedArrayObject with a size.
+ */
+
+/*
+ * ArrayBufferObject (base)
+ */
+
+static const JSClassOps ArrayBufferObjectClassOps = {
+    nullptr,                      // addProperty
+    nullptr,                      // delProperty
+    nullptr,                      // enumerate
+    nullptr,                      // newEnumerate
+    nullptr,                      // resolve
+    nullptr,                      // mayResolve
+    ArrayBufferObject::finalize,  // finalize
+    nullptr,                      // call
+    nullptr,                      // construct
+    nullptr,                      // trace
+};
+
+static const JSFunctionSpec arraybuffer_functions[] = {
+    JS_FN("isView", ArrayBufferObject::fun_isView, 1, 0), JS_FS_END};
+
+static const JSPropertySpec arraybuffer_properties[] = {
+    JS_SELF_HOSTED_SYM_GET(species, "$ArrayBufferSpecies", 0), JS_PS_END};
+
+static const JSFunctionSpec arraybuffer_proto_functions[] = {
+    JS_SELF_HOSTED_FN("slice", "ArrayBufferSlice", 2, 0), JS_FS_END};
+
+static const JSPropertySpec arraybuffer_proto_properties[] = {
+    JS_PSG("byteLength", ArrayBufferObject::byteLengthGetter, 0),
+    JS_STRING_SYM_PS(toStringTag, "ArrayBuffer", JSPROP_READONLY), JS_PS_END};
+
+static const ClassSpec ArrayBufferObjectClassSpec = {
+    GenericCreateConstructor<ArrayBufferObject::class_constructor, 1,
+                             gc::AllocKind::FUNCTION>,
+    GenericCreatePrototype<ArrayBufferObject>,
+    arraybuffer_functions,
+    arraybuffer_properties,
+    arraybuffer_proto_functions,
+    arraybuffer_proto_properties};
+
+static const ClassExtension ArrayBufferObjectClassExtension = {
+    ArrayBufferObject::objectMoved,  // objectMovedOp
+};
+
+const JSClass ArrayBufferObject::class_ = {
+    "ArrayBuffer",
+    JSCLASS_DELAY_METADATA_BUILDER |
+        JSCLASS_HAS_RESERVED_SLOTS(RESERVED_SLOTS) |
+        JSCLASS_HAS_CACHED_PROTO(JSProto_ArrayBuffer) |
+        JSCLASS_BACKGROUND_FINALIZE,
+    &ArrayBufferObjectClassOps, &ArrayBufferObjectClassSpec,
+    &ArrayBufferObjectClassExtension};
+
+const JSClass ArrayBufferObject::protoClass_ = {
+    "ArrayBuffer.prototype", JSCLASS_HAS_CACHED_PROTO(JSProto_ArrayBuffer),
+    JS_NULL_CLASS_OPS, &ArrayBufferObjectClassSpec};
+
+static bool IsArrayBuffer(HandleValue v) {
+  return v.isObject() && v.toObject().is<ArrayBufferObject>();
+}
+
+MOZ_ALWAYS_INLINE bool ArrayBufferObject::byteLengthGetterImpl(
+    JSContext* cx, const CallArgs& args) {
+  MOZ_ASSERT(IsArrayBuffer(args.thisv()));
+  auto* buffer = &args.thisv().toObject().as<ArrayBufferObject>();
+  args.rval().setNumber(buffer->byteLength());
+  return true;
+}
+
+bool ArrayBufferObject::byteLengthGetter(JSContext* cx, unsigned argc,
+                                         Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsArrayBuffer, byteLengthGetterImpl>(cx, args);
+}
+
+/*
+ * ArrayBuffer.isView(obj); ES6 (Dec 2013 draft) 24.1.3.1
+ */
+bool ArrayBufferObject::fun_isView(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  args.rval().setBoolean(args.get(0).isObject() &&
+                         JS_IsArrayBufferViewObject(&args.get(0).toObject()));
+  return true;
+}
+
+// ES2017 draft 24.1.2.1
+bool ArrayBufferObject::class_constructor(JSContext* cx, unsigned argc,
+                                          Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  // Step 1.
+  if (!ThrowIfNotConstructing(cx, args, "ArrayBuffer")) {
+    return false;
+  }
+
+  // Step 2.
+  uint64_t byteLength;
+  if (!ToIndex(cx, args.get(0), &byteLength)) {
+    return false;
+  }
+
+  // Step 3 (Inlined 24.1.1.1 AllocateArrayBuffer).
+  // 24.1.1.1, step 1 (Inlined 9.1.14 OrdinaryCreateFromConstructor).
+  RootedObject proto(cx);
+  if (!GetPrototypeFromBuiltinConstructor(cx, args, JSProto_ArrayBuffer,
+                                          &proto)) {
+    return false;
+  }
+
+  // 24.1.1.1, step 3 (Inlined 6.2.6.1 CreateByteDataBlock, step 2).
+  if (!CheckArrayBufferTooLarge(cx, byteLength)) {
+    return false;
+  }
+
+  // 24.1.1.1, steps 1 and 4-6.
+  JSObject* bufobj = createZeroed(cx, byteLength, proto);
+  if (!bufobj) {
+    return false;
+  }
+  args.rval().setObject(*bufobj);
+  return true;
+}
+
+using ArrayBufferContents = UniquePtr<uint8_t[], JS::FreePolicy>;
+
+static ArrayBufferContents AllocateUninitializedArrayBufferContents(
+    JSContext* cx, size_t nbytes) {
+  // First attempt a normal allocation.
+  uint8_t* p =
+      cx->maybe_pod_arena_malloc<uint8_t>(js::ArrayBufferContentsArena, nbytes);
+  if (MOZ_UNLIKELY(!p)) {
+    // Otherwise attempt a large allocation, calling the
+    // large-allocation-failure callback if necessary.
+    p = static_cast<uint8_t*>(cx->runtime()->onOutOfMemoryCanGC(
+        js::AllocFunction::Malloc, js::ArrayBufferContentsArena, nbytes));
+    if (!p) {
+      ReportOutOfMemory(cx);
+    }
+  }
+
+  return ArrayBufferContents(p);
+}
+
+static ArrayBufferContents AllocateArrayBufferContents(JSContext* cx,
+                                                       size_t nbytes) {
+  // First attempt a normal allocation.
+  uint8_t* p =
+      cx->maybe_pod_arena_calloc<uint8_t>(js::ArrayBufferContentsArena, nbytes);
+  if (MOZ_UNLIKELY(!p)) {
+    // Otherwise attempt a large allocation, calling the
+    // large-allocation-failure callback if necessary.
+    p = static_cast<uint8_t*>(cx->runtime()->onOutOfMemoryCanGC(
+        js::AllocFunction::Calloc, js::ArrayBufferContentsArena, nbytes));
+    if (!p) {
+      ReportOutOfMemory(cx);
+    }
+  }
+
+  return ArrayBufferContents(p);
+}
+
+static ArrayBufferContents NewCopiedBufferContents(
+    JSContext* cx, Handle<ArrayBufferObject*> buffer) {
+  ArrayBufferContents dataCopy =
+      AllocateUninitializedArrayBufferContents(cx, buffer->byteLength());
+  if (dataCopy) {
+    if (auto count = buffer->byteLength()) {
+      memcpy(dataCopy.get(), buffer->dataPointer(), count);
+    }
+  }
+  return dataCopy;
+}
+
+/* static */
+void ArrayBufferObject::detach(JSContext* cx,
+                               Handle<ArrayBufferObject*> buffer) {
+  cx->check(buffer);
+  MOZ_ASSERT(!buffer->isPreparedForAsmJS());
+
+  // Update all views of the buffer to account for the buffer having been
+  // detached, and clear the buffer's data and list of views.
+  //
+  // Typed object buffers are not exposed and cannot be detached.
+
+  auto& innerViews = ObjectRealm::get(buffer).innerViews.get();
+  if (InnerViewTable::ViewVector* views =
+          innerViews.maybeViewsUnbarriered(buffer)) {
+    for (size_t i = 0; i < views->length(); i++) {
+      JSObject* view = (*views)[i];
+      view->as<ArrayBufferViewObject>().notifyBufferDetached();
+    }
+    innerViews.removeViews(buffer);
+  }
+  if (JSObject* view = buffer->firstView()) {
+    view->as<ArrayBufferViewObject>().notifyBufferDetached();
+    buffer->setFirstView(nullptr);
+  }
+
+  if (buffer->dataPointer()) {
+    buffer->releaseData(cx->gcContext());
+    buffer->setDataPointer(BufferContents::createNoData());
+  }
+
+  buffer->setByteLength(0);
+  buffer->setIsDetached();
+}
+
+/* clang-format off */
+/*
+ * [SMDOC] WASM Linear Memory structure
+ *
+ * Wasm Raw Buf Linear Memory Structure
+ *
+ * The linear heap in Wasm is an mmaped array buffer. Several constants manage
+ * its lifetime:
+ *
+ *  - byteLength - the wasm-visible current length of the buffer in
+ *    bytes. Accesses in the range [0, byteLength] succeed. May only increase.
+ *
+ *  - boundsCheckLimit - the size against which we perform bounds checks.  The
+ *    value of this depends on the bounds checking strategy chosen for the array
+ *    buffer and the specific bounds checking semantics.  For asm.js code and
+ *    for wasm code running with explicit bounds checking, it is the always the
+ *    same as the byteLength.  For wasm code using the huge-memory trick, it is
+ *    always wasm::GuardSize smaller than mappedSize.
+ *
+ *    See also "Linear memory addresses and bounds checking" in
+ *    wasm/WasmMemory.cpp.
+ *
+ *    See also WasmMemoryObject::boundsCheckLimit().
+ *
+ *  - sourceMaxSize - the optional declared limit on how far byteLength can grow
+ *    in pages. This is the unmodified maximum size from the source module or
+ *    JS-API invocation. This may not be representable in byte lengths, nor
+ *    feasible for a module to actually grow to due to implementation limits.
+ *    It is used for correct linking checks and js-types reflection.
+ *
+ *  - clampedMaxSize - the maximum size on how far the byteLength can grow in
+ *    pages. This value respects implementation limits and is always
+ *    representable as a byte length. Every memory has a clampedMaxSize, even if
+ *    no maximum was specified in source. When a memory has no sourceMaxSize,
+ *    the clampedMaxSize will be the maximum amount of memory that can be grown
+ *    to while still respecting implementation limits.
+ *
+ *  - mappedSize - the actual mmapped size. Access in the range [0, mappedSize]
+ *    will either succeed, or be handled by the wasm signal handlers. If
+ *    sourceMaxSize is present at initialization, then we attempt to map the
+ *    whole clampedMaxSize. Otherwise we only map the region needed for the
+ *    initial size.
+ *
+ * The below diagram shows the layout of the wasm heap. The wasm-visible portion
+ * of the heap starts at 0. There is one extra page prior to the start of the
+ * wasm heap which contains the WasmArrayRawBuffer struct at its end (i.e. right
+ * before the start of the WASM heap).
+ *
+ *  WasmArrayRawBuffer
+ *      \    ArrayBufferObject::dataPointer()
+ *       \  /
+ *        \ |
+ *  ______|_|______________________________________________________
+ * |______|_|______________|___________________|___________________|
+ *          0          byteLength          clampedMaxSize     mappedSize
+ *
+ * \_______________________/
+ *          COMMITED
+ *                          \_____________________________________/
+ *                                           SLOP
+ * \______________________________________________________________/
+ *                         MAPPED
+ *
+ * Invariants on byteLength, clampedMaxSize, and mappedSize:
+ *  - byteLength only increases
+ *  - 0 <= byteLength <= clampedMaxSize <= mappedSize
+ *  - if sourceMaxSize is not specified, mappedSize may grow.
+ *    It is otherwise constant.
+ *  - initialLength <= clampedMaxSize <= sourceMaxSize (if present)
+ *  - clampedMaxSize <= wasm::MaxMemoryPages()
+ *
+ * Invariants on boundsCheckLimit:
+ *  - for wasm code with the huge-memory trick,
+ *      clampedMaxSize <= boundsCheckLimit <= mappedSize
+ *  - for asm.js code or wasm with explicit bounds checking,
+ *      byteLength == boundsCheckLimit <= clampedMaxSize
+ *  - on ARM, boundsCheckLimit must be a valid ARM immediate.
+ *  - if sourceMaxSize is not specified, boundsCheckLimit may grow as
+ *    mappedSize grows. They are otherwise constant.
+
+ * NOTE: For asm.js on 32-bit platforms and on all platforms when running with
+ * explicit bounds checking, we guarantee that
+ *
+ *   byteLength == maxSize == boundsCheckLimit == mappedSize
+ *
+ * That is, signal handlers will not be invoked.
+ *
+ * The region between byteLength and mappedSize is the SLOP - an area where we use
+ * signal handlers to catch things that slip by bounds checks. Logically it has
+ * two parts:
+ *
+ *  - from byteLength to boundsCheckLimit - this part of the SLOP serves to catch
+ *    accesses to memory we have reserved but not yet grown into. This allows us
+ *    to grow memory up to max (when present) without having to patch/update the
+ *    bounds checks.
+ *
+ *  - from boundsCheckLimit to mappedSize - this part of the SLOP allows us to
+ *    bounds check against base pointers and fold some constant offsets inside
+ *    loads. This enables better Bounds Check Elimination.  See "Linear memory
+ *    addresses and bounds checking" in wasm/WasmMemory.cpp.
+ *
+ */
+/* clang-format on */
+
+[[nodiscard]] bool WasmArrayRawBuffer::growToPagesInPlace(Pages newPages) {
+  size_t newSize = newPages.byteLength();
+  size_t oldSize = byteLength();
+
+  MOZ_ASSERT(newSize >= oldSize);
+  MOZ_ASSERT(newPages <= clampedMaxPages());
+  MOZ_ASSERT(newSize <= mappedSize());
+
+  size_t delta = newSize - oldSize;
+  MOZ_ASSERT(delta % wasm::PageSize == 0);
+
+  uint8_t* dataEnd = dataPointer() + oldSize;
+  MOZ_ASSERT(uintptr_t(dataEnd) % gc::SystemPageSize() == 0);
+
+  if (delta && !CommitBufferMemory(dataEnd, delta)) {
+    return false;
+  }
+
+  length_ = newSize;
+
+  return true;
+}
+
+bool WasmArrayRawBuffer::extendMappedSize(Pages maxPages) {
+  size_t newMappedSize = wasm::ComputeMappedSize(maxPages);
+  MOZ_ASSERT(mappedSize_ <= newMappedSize);
+  if (mappedSize_ == newMappedSize) {
+    return true;
+  }
+
+  if (!ExtendBufferMapping(dataPointer(), mappedSize_, newMappedSize)) {
+    return false;
+  }
+
+  mappedSize_ = newMappedSize;
+  return true;
+}
+
+void WasmArrayRawBuffer::tryGrowMaxPagesInPlace(Pages deltaMaxPages) {
+  Pages newMaxPages = clampedMaxPages_;
+
+  DebugOnly<bool> valid = newMaxPages.checkedIncrement(deltaMaxPages);
+  // Caller must ensure increment does not overflow or increase over the
+  // specified maximum pages.
+  MOZ_ASSERT(valid);
+  MOZ_ASSERT_IF(sourceMaxPages_.isSome(), newMaxPages <= *sourceMaxPages_);
+
+  if (!extendMappedSize(newMaxPages)) {
+    return;
+  }
+  clampedMaxPages_ = newMaxPages;
+}
+
+/* static */
+WasmArrayRawBuffer* WasmArrayRawBuffer::AllocateWasm(
+    IndexType indexType, Pages initialPages, Pages clampedMaxPages,
+    const Maybe<Pages>& sourceMaxPages, const Maybe<size_t>& mapped) {
+  // Prior code has asserted that initial pages is within our implementation
+  // limits (wasm::MaxMemoryPages) and we can assume it is a valid size_t.
+  MOZ_ASSERT(initialPages.hasByteLength());
+  size_t numBytes = initialPages.byteLength();
+
+  // If there is a specified maximum, attempt to map the whole range for
+  // clampedMaxPages. Or else map only what's required for initialPages.
+  Pages initialMappedPages =
+      sourceMaxPages.isSome() ? clampedMaxPages : initialPages;
+
+  // Use an override mapped size, or else compute the mapped size from
+  // initialMappedPages.
+  size_t mappedSize =
+      mapped.isSome() ? *mapped : wasm::ComputeMappedSize(initialMappedPages);
+
+  MOZ_RELEASE_ASSERT(mappedSize <= SIZE_MAX - gc::SystemPageSize());
+  MOZ_RELEASE_ASSERT(numBytes <= SIZE_MAX - gc::SystemPageSize());
+  MOZ_RELEASE_ASSERT(initialPages <= clampedMaxPages);
+  MOZ_ASSERT(numBytes % gc::SystemPageSize() == 0);
+  MOZ_ASSERT(mappedSize % gc::SystemPageSize() == 0);
+
+  uint64_t mappedSizeWithHeader = mappedSize + gc::SystemPageSize();
+  uint64_t numBytesWithHeader = numBytes + gc::SystemPageSize();
+
+  void* data = MapBufferMemory(indexType, (size_t)mappedSizeWithHeader,
+                               (size_t)numBytesWithHeader);
+  if (!data) {
+    return nullptr;
+  }
+
+  uint8_t* base = reinterpret_cast<uint8_t*>(data) + gc::SystemPageSize();
+  uint8_t* header = base - sizeof(WasmArrayRawBuffer);
+
+  auto rawBuf = new (header) WasmArrayRawBuffer(
+      indexType, base, clampedMaxPages, sourceMaxPages, mappedSize, numBytes);
+  return rawBuf;
+}
+
+/* static */
+void WasmArrayRawBuffer::Release(void* mem) {
+  WasmArrayRawBuffer* header =
+      (WasmArrayRawBuffer*)((uint8_t*)mem - sizeof(WasmArrayRawBuffer));
+
+  MOZ_RELEASE_ASSERT(header->mappedSize() <= SIZE_MAX - gc::SystemPageSize());
+  size_t mappedSizeWithHeader = header->mappedSize() + gc::SystemPageSize();
+
+  static_assert(std::is_trivially_destructible_v<WasmArrayRawBuffer>,
+                "no need to call the destructor");
+
+  UnmapBufferMemory(header->indexType(), header->basePointer(),
+                    mappedSizeWithHeader);
+}
+
+WasmArrayRawBuffer* ArrayBufferObject::BufferContents::wasmBuffer() const {
+  MOZ_RELEASE_ASSERT(kind_ == WASM);
+  return (WasmArrayRawBuffer*)(data_ - sizeof(WasmArrayRawBuffer));
+}
+
+template <typename ObjT, typename RawbufT>
+static bool CreateSpecificWasmBuffer(
+    JSContext* cx, const wasm::MemoryDesc& memory,
+    MutableHandleArrayBufferObjectMaybeShared maybeSharedObject) {
+  bool useHugeMemory = wasm::IsHugeMemoryEnabled(memory.indexType());
+  Pages initialPages = memory.initialPages();
+  Maybe<Pages> sourceMaxPages = memory.maximumPages();
+  Pages clampedMaxPages = wasm::ClampedMaxPages(
+      memory.indexType(), initialPages, sourceMaxPages, useHugeMemory);
+
+  Maybe<size_t> mappedSize;
+#ifdef WASM_SUPPORTS_HUGE_MEMORY
+  // Override the mapped size if we are using huge memory. If we are not, then
+  // it will be calculated by the raw buffer we are using.
+  if (useHugeMemory) {
+    mappedSize = Some(wasm::HugeMappedSize);
+  }
+#endif
+
+  RawbufT* buffer =
+      RawbufT::AllocateWasm(memory.limits.indexType, initialPages,
+                            clampedMaxPages, sourceMaxPages, mappedSize);
+  if (!buffer) {
+    if (useHugeMemory) {
+      WarnNumberASCII(cx, JSMSG_WASM_HUGE_MEMORY_FAILED);
+      if (cx->isExceptionPending()) {
+        cx->clearPendingException();
+      }
+
+      ReportOutOfMemory(cx);
+      return false;
+    }
+
+    // If we fail, and have a sourceMaxPages, try to reserve the biggest
+    // chunk in the range [initialPages, clampedMaxPages) using log backoff.
+    if (!sourceMaxPages) {
+      wasm::Log(cx, "new Memory({initial=%" PRIu64 " pages}) failed",
+                initialPages.value());
+      ReportOutOfMemory(cx);
+      return false;
+    }
+
+    uint64_t cur = clampedMaxPages.value() / 2;
+    for (; Pages(cur) > initialPages; cur /= 2) {
+      buffer = RawbufT::AllocateWasm(memory.limits.indexType, initialPages,
+                                     Pages(cur), sourceMaxPages, mappedSize);
+      if (buffer) {
+        break;
+      }
+    }
+
+    if (!buffer) {
+      wasm::Log(cx, "new Memory({initial=%" PRIu64 " pages}) failed",
+                initialPages.value());
+      ReportOutOfMemory(cx);
+      return false;
+    }
+
+    // Try to grow our chunk as much as possible.
+    for (size_t d = cur / 2; d >= 1; d /= 2) {
+      buffer->tryGrowMaxPagesInPlace(Pages(d));
+    }
+  }
+
+  // ObjT::createFromNewRawBuffer assumes ownership of |buffer| even in case
+  // of failure.
+  RootedArrayBufferObjectMaybeShared object(
+      cx, ObjT::createFromNewRawBuffer(cx, buffer, initialPages.byteLength()));
+  if (!object) {
+    return false;
+  }
+
+  maybeSharedObject.set(object);
+
+  // See MaximumLiveMappedBuffers comment above.
+  if (liveBufferCount > StartSyncFullGCAtLiveBufferCount) {
+    JS::PrepareForFullGC(cx);
+    JS::NonIncrementalGC(cx, JS::GCOptions::Normal,
+                         JS::GCReason::TOO_MUCH_WASM_MEMORY);
+    allocatedSinceLastTrigger = 0;
+  } else if (liveBufferCount > StartTriggeringAtLiveBufferCount) {
+    allocatedSinceLastTrigger++;
+    if (allocatedSinceLastTrigger > AllocatedBuffersPerTrigger) {
+      (void)cx->runtime()->gc.triggerGC(JS::GCReason::TOO_MUCH_WASM_MEMORY);
+      allocatedSinceLastTrigger = 0;
+    }
+  } else {
+    allocatedSinceLastTrigger = 0;
+  }
+
+  // Log the result with details on the memory allocation
+  if (sourceMaxPages) {
+    if (useHugeMemory) {
+      wasm::Log(cx,
+                "new Memory({initial:%" PRIu64 " pages, maximum:%" PRIu64
+                " pages}) succeeded",
+                initialPages.value(), sourceMaxPages->value());
+    } else {
+      wasm::Log(cx,
+                "new Memory({initial:%" PRIu64 " pages, maximum:%" PRIu64
+                " pages}) succeeded "
+                "with internal maximum of %" PRIu64 " pages",
+                initialPages.value(), sourceMaxPages->value(),
+                object->wasmClampedMaxPages().value());
+    }
+  } else {
+    wasm::Log(cx, "new Memory({initial:%" PRIu64 " pages}) succeeded",
+              initialPages.value());
+  }
+
+  return true;
+}
+
+bool js::CreateWasmBuffer(JSContext* cx, const wasm::MemoryDesc& memory,
+                          MutableHandleArrayBufferObjectMaybeShared buffer) {
+  MOZ_RELEASE_ASSERT(memory.initialPages() <=
+                     wasm::MaxMemoryPages(memory.indexType()));
+  MOZ_RELEASE_ASSERT(cx->wasm().haveSignalHandlers);
+
+  if (memory.isShared()) {
+    if (!cx->realm()->creationOptions().getSharedMemoryAndAtomicsEnabled()) {
+      JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                JSMSG_WASM_NO_SHMEM_LINK);
+      return false;
+    }
+    return CreateSpecificWasmBuffer<SharedArrayBufferObject,
+                                    WasmSharedArrayRawBuffer>(cx, memory,
+                                                              buffer);
+  }
+  return CreateSpecificWasmBuffer<ArrayBufferObject, WasmArrayRawBuffer>(
+      cx, memory, buffer);
+}
+
+bool ArrayBufferObject::prepareForAsmJS() {
+  MOZ_ASSERT(byteLength() % wasm::PageSize == 0,
+             "prior size checking should have guaranteed page-size multiple");
+  MOZ_ASSERT(byteLength() > 0,
+             "prior size checking should have excluded empty buffers");
+
+  switch (bufferKind()) {
+    case MALLOCED:
+    case MAPPED:
+    case EXTERNAL:
+      // It's okay if this uselessly sets the flag a second time.
+      setIsPreparedForAsmJS();
+      return true;
+
+    case INLINE_DATA:
+      static_assert(wasm::PageSize > MaxInlineBytes,
+                    "inline data must be too small to be a page size multiple");
+      MOZ_ASSERT_UNREACHABLE(
+          "inline-data buffers should be implicitly excluded by size checks");
+      return false;
+
+    case NO_DATA:
+      MOZ_ASSERT_UNREACHABLE(
+          "size checking should have excluded detached or empty buffers");
+      return false;
+
+    // asm.js code and associated buffers are potentially long-lived.  Yet a
+    // buffer of user-owned data *must* be detached by the user before the
+    // user-owned data is disposed.  No caller wants to use a user-owned
+    // ArrayBuffer with asm.js, so just don't support this and avoid a mess of
+    // complexity.
+    case USER_OWNED:
+    // wasm buffers can be detached at any time.
+    case WASM:
+      MOZ_ASSERT(!isPreparedForAsmJS());
+      return false;
+
+    case BAD1:
+      MOZ_ASSERT_UNREACHABLE("invalid bufferKind() encountered");
+      return false;
+  }
+
+  MOZ_ASSERT_UNREACHABLE("non-exhaustive kind-handling switch?");
+  return false;
+}
+
+ArrayBufferObject::BufferContents ArrayBufferObject::createMappedContents(
+    int fd, size_t offset, size_t length) {
+  void* data =
+      gc::AllocateMappedContent(fd, offset, length, ARRAY_BUFFER_ALIGNMENT);
+  return BufferContents::createMapped(data);
+}
+
+uint8_t* ArrayBufferObject::inlineDataPointer() const {
+  return static_cast<uint8_t*>(fixedData(JSCLASS_RESERVED_SLOTS(&class_)));
+}
+
+uint8_t* ArrayBufferObject::dataPointer() const {
+  return static_cast<uint8_t*>(getFixedSlot(DATA_SLOT).toPrivate());
+}
+
+SharedMem<uint8_t*> ArrayBufferObject::dataPointerShared() const {
+  return SharedMem<uint8_t*>::unshared(getFixedSlot(DATA_SLOT).toPrivate());
+}
+
+ArrayBufferObject::FreeInfo* ArrayBufferObject::freeInfo() const {
+  MOZ_ASSERT(isExternal());
+  return reinterpret_cast<FreeInfo*>(inlineDataPointer());
+}
+
+void ArrayBufferObject::releaseData(JS::GCContext* gcx) {
+  switch (bufferKind()) {
+    case INLINE_DATA:
+      // Inline data doesn't require releasing.
+      break;
+    case MALLOCED:
+      gcx->free_(this, dataPointer(), byteLength(),
+                 MemoryUse::ArrayBufferContents);
+      break;
+    case NO_DATA:
+      // There's nothing to release if there's no data.
+      MOZ_ASSERT(dataPointer() == nullptr);
+      break;
+    case USER_OWNED:
+      // User-owned data is released by, well, the user.
+      break;
+    case MAPPED:
+      gc::DeallocateMappedContent(dataPointer(), byteLength());
+      gcx->removeCellMemory(this, associatedBytes(),
+                            MemoryUse::ArrayBufferContents);
+      break;
+    case WASM:
+      WasmArrayRawBuffer::Release(dataPointer());
+      gcx->removeCellMemory(this, byteLength(), MemoryUse::ArrayBufferContents);
+      break;
+    case EXTERNAL:
+      if (freeInfo()->freeFunc) {
+        // The analyzer can't know for sure whether the embedder-supplied
+        // free function will GC. We give the analyzer a hint here.
+        // (Doing a GC in the free function is considered a programmer
+        // error.)
+        JS::AutoSuppressGCAnalysis nogc;
+        freeInfo()->freeFunc(dataPointer(), freeInfo()->freeUserData);
+      }
+      break;
+    case BAD1:
+      MOZ_CRASH("invalid BufferKind encountered");
+      break;
+  }
+}
+
+void ArrayBufferObject::setDataPointer(BufferContents contents) {
+  setFixedSlot(DATA_SLOT, PrivateValue(contents.data()));
+  setFlags((flags() & ~KIND_MASK) | contents.kind());
+
+  if (isExternal()) {
+    auto info = freeInfo();
+    info->freeFunc = contents.freeFunc();
+    info->freeUserData = contents.freeUserData();
+  }
+}
+
+size_t ArrayBufferObject::byteLength() const {
+  return size_t(getFixedSlot(BYTE_LENGTH_SLOT).toPrivate());
+}
+
+inline size_t ArrayBufferObject::associatedBytes() const {
+  if (bufferKind() == MALLOCED) {
+    return byteLength();
+  }
+  if (bufferKind() == MAPPED) {
+    return RoundUp(byteLength(), js::gc::SystemPageSize());
+  }
+  MOZ_CRASH("Unexpected buffer kind");
+}
+
+void ArrayBufferObject::setByteLength(size_t length) {
+  MOZ_ASSERT(length <= ArrayBufferObject::MaxByteLength);
+  setFixedSlot(BYTE_LENGTH_SLOT, PrivateValue(length));
+}
+
+size_t ArrayBufferObject::wasmMappedSize() const {
+  if (isWasm()) {
+    return contents().wasmBuffer()->mappedSize();
+  }
+  return byteLength();
+}
+
+IndexType ArrayBufferObject::wasmIndexType() const {
+  if (isWasm()) {
+    return contents().wasmBuffer()->indexType();
+  }
+  MOZ_ASSERT(isPreparedForAsmJS());
+  return wasm::IndexType::I32;
+}
+
+Pages ArrayBufferObject::wasmPages() const {
+  if (isWasm()) {
+    return contents().wasmBuffer()->pages();
+  }
+  MOZ_ASSERT(isPreparedForAsmJS());
+  return Pages::fromByteLengthExact(byteLength());
+}
+
+Pages ArrayBufferObject::wasmClampedMaxPages() const {
+  if (isWasm()) {
+    return contents().wasmBuffer()->clampedMaxPages();
+  }
+  MOZ_ASSERT(isPreparedForAsmJS());
+  return Pages::fromByteLengthExact(byteLength());
+}
+
+Maybe<Pages> ArrayBufferObject::wasmSourceMaxPages() const {
+  if (isWasm()) {
+    return contents().wasmBuffer()->sourceMaxPages();
+  }
+  MOZ_ASSERT(isPreparedForAsmJS());
+  return Some<Pages>(Pages::fromByteLengthExact(byteLength()));
+}
+
+size_t js::WasmArrayBufferMappedSize(const ArrayBufferObjectMaybeShared* buf) {
+  if (buf->is<ArrayBufferObject>()) {
+    return buf->as<ArrayBufferObject>().wasmMappedSize();
+  }
+  return buf->as<SharedArrayBufferObject>().wasmMappedSize();
+}
+
+IndexType js::WasmArrayBufferIndexType(
+    const ArrayBufferObjectMaybeShared* buf) {
+  if (buf->is<ArrayBufferObject>()) {
+    return buf->as<ArrayBufferObject>().wasmIndexType();
+  }
+  return buf->as<SharedArrayBufferObject>().wasmIndexType();
+}
+Pages js::WasmArrayBufferPages(const ArrayBufferObjectMaybeShared* buf) {
+  if (buf->is<ArrayBufferObject>()) {
+    return buf->as<ArrayBufferObject>().wasmPages();
+  }
+  return buf->as<SharedArrayBufferObject>().volatileWasmPages();
+}
+Pages js::WasmArrayBufferClampedMaxPages(
+    const ArrayBufferObjectMaybeShared* buf) {
+  if (buf->is<ArrayBufferObject>()) {
+    return buf->as<ArrayBufferObject>().wasmClampedMaxPages();
+  }
+  return buf->as<SharedArrayBufferObject>().wasmClampedMaxPages();
+}
+Maybe<Pages> js::WasmArrayBufferSourceMaxPages(
+    const ArrayBufferObjectMaybeShared* buf) {
+  if (buf->is<ArrayBufferObject>()) {
+    return buf->as<ArrayBufferObject>().wasmSourceMaxPages();
+  }
+  return Some(buf->as<SharedArrayBufferObject>().wasmSourceMaxPages());
+}
+
+static void CheckStealPreconditions(Handle<ArrayBufferObject*> buffer,
+                                    JSContext* cx) {
+  cx->check(buffer);
+
+  MOZ_ASSERT(!buffer->isDetached(), "can't steal from a detached buffer");
+  MOZ_ASSERT(!buffer->isPreparedForAsmJS(),
+             "asm.js-prepared buffers don't have detachable/stealable data");
+}
+
+/* static */
+bool ArrayBufferObject::wasmGrowToPagesInPlace(
+    wasm::IndexType t, Pages newPages, HandleArrayBufferObject oldBuf,
+    MutableHandleArrayBufferObject newBuf, JSContext* cx) {
+  CheckStealPreconditions(oldBuf, cx);
+
+  MOZ_ASSERT(oldBuf->isWasm());
+
+  // Check that the new pages is within our allowable range. This will
+  // simultaneously check against the maximum specified in source and our
+  // implementation limits.
+  if (newPages > oldBuf->wasmClampedMaxPages()) {
+    return false;
+  }
+  MOZ_ASSERT(newPages <= wasm::MaxMemoryPages(t) &&
+             newPages.byteLength() <= ArrayBufferObject::MaxByteLength);
+
+  // We have checked against the clamped maximum and so we know we can convert
+  // to byte lengths now.
+  size_t newSize = newPages.byteLength();
+
+  // On failure, do not throw and ensure that the original buffer is
+  // unmodified and valid. After WasmArrayRawBuffer::growToPagesInPlace(), the
+  // wasm-visible length of the buffer has been increased so it must be the
+  // last fallible operation.
+
+  newBuf.set(ArrayBufferObject::createEmpty(cx));
+  if (!newBuf) {
+    cx->clearPendingException();
+    return false;
+  }
+
+  MOZ_ASSERT(newBuf->isNoData());
+
+  if (!oldBuf->contents().wasmBuffer()->growToPagesInPlace(newPages)) {
+    return false;
+  }
+
+  // Extract the grown contents from |oldBuf|.
+  BufferContents oldContents = oldBuf->contents();
+
+  // Overwrite |oldBuf|'s data pointer *without* releasing old data.
+  oldBuf->setDataPointer(BufferContents::createNoData());
+
+  // Detach |oldBuf| now that doing so won't release |oldContents|.
+  RemoveCellMemory(oldBuf, oldBuf->byteLength(),
+                   MemoryUse::ArrayBufferContents);
+  ArrayBufferObject::detach(cx, oldBuf);
+
+  // Set |newBuf|'s contents to |oldBuf|'s original contents.
+  newBuf->initialize(newSize, oldContents);
+  AddCellMemory(newBuf, newSize, MemoryUse::ArrayBufferContents);
+
+  return true;
+}
+
+/* static */
+bool ArrayBufferObject::wasmMovingGrowToPages(
+    IndexType t, Pages newPages, HandleArrayBufferObject oldBuf,
+    MutableHandleArrayBufferObject newBuf, JSContext* cx) {
+  // On failure, do not throw and ensure that the original buffer is
+  // unmodified and valid.
+
+  // Check that the new pages is within our allowable range. This will
+  // simultaneously check against the maximum specified in source and our
+  // implementation limits.
+  if (newPages > oldBuf->wasmClampedMaxPages()) {
+    return false;
+  }
+  MOZ_ASSERT(newPages <= wasm::MaxMemoryPages(t) &&
+             newPages.byteLength() < ArrayBufferObject::MaxByteLength);
+
+  // We have checked against the clamped maximum and so we know we can convert
+  // to byte lengths now.
+  size_t newSize = newPages.byteLength();
+
+  if (wasm::ComputeMappedSize(newPages) <= oldBuf->wasmMappedSize() ||
+      oldBuf->contents().wasmBuffer()->extendMappedSize(newPages)) {
+    return wasmGrowToPagesInPlace(t, newPages, oldBuf, newBuf, cx);
+  }
+
+  newBuf.set(ArrayBufferObject::createEmpty(cx));
+  if (!newBuf) {
+    cx->clearPendingException();
+    return false;
+  }
+
+  Pages clampedMaxPages =
+      wasm::ClampedMaxPages(t, newPages, Nothing(), /* hugeMemory */ false);
+  WasmArrayRawBuffer* newRawBuf = WasmArrayRawBuffer::AllocateWasm(
+      oldBuf->wasmIndexType(), newPages, clampedMaxPages, Nothing(), Nothing());
+  if (!newRawBuf) {
+    return false;
+  }
+
+  AddCellMemory(newBuf, newSize, MemoryUse::ArrayBufferContents);
+
+  BufferContents contents =
+      BufferContents::createWasm(newRawBuf->dataPointer());
+  newBuf->initialize(newSize, contents);
+
+  memcpy(newBuf->dataPointer(), oldBuf->dataPointer(), oldBuf->byteLength());
+  ArrayBufferObject::detach(cx, oldBuf);
+  return true;
+}
+
+uint32_t ArrayBufferObject::flags() const {
+  return uint32_t(getFixedSlot(FLAGS_SLOT).toInt32());
+}
+
+void ArrayBufferObject::setFlags(uint32_t flags) {
+  setFixedSlot(FLAGS_SLOT, Int32Value(flags));
+}
+
+static inline js::gc::AllocKind GetArrayBufferGCObjectKind(size_t numSlots) {
+  if (numSlots <= 4) {
+    return js::gc::AllocKind::ARRAYBUFFER4;
+  }
+  if (numSlots <= 8) {
+    return js::gc::AllocKind::ARRAYBUFFER8;
+  }
+  if (numSlots <= 12) {
+    return js::gc::AllocKind::ARRAYBUFFER12;
+  }
+  return js::gc::AllocKind::ARRAYBUFFER16;
+}
+
+static ArrayBufferObject* NewArrayBufferObject(JSContext* cx,
+                                               HandleObject proto_,
+                                               gc::AllocKind allocKind) {
+  MOZ_ASSERT(allocKind == gc::AllocKind::ARRAYBUFFER4 ||
+             allocKind == gc::AllocKind::ARRAYBUFFER8 ||
+             allocKind == gc::AllocKind::ARRAYBUFFER12 ||
+             allocKind == gc::AllocKind::ARRAYBUFFER16);
+
+  RootedObject proto(cx, proto_);
+  if (!proto) {
+    proto = GlobalObject::getOrCreatePrototype(cx, JSProto_ArrayBuffer);
+    if (!proto) {
+      return nullptr;
+    }
+  }
+
+  const JSClass* clasp = &ArrayBufferObject::class_;
+
+  // Array buffers can store data inline so we only use fixed slots to cover the
+  // reserved slots, ignoring the AllocKind.
+  MOZ_ASSERT(ClassCanHaveFixedData(clasp));
+  constexpr size_t nfixed = ArrayBufferObject::RESERVED_SLOTS;
+  static_assert(nfixed <= NativeObject::MAX_FIXED_SLOTS);
+
+  Rooted<SharedShape*> shape(
+      cx,
+      SharedShape::getInitialShape(cx, clasp, cx->realm(), AsTaggedProto(proto),
+                                   nfixed, ObjectFlags()));
+  if (!shape) {
+    return nullptr;
+  }
+
+  // Array buffers can't be nursery allocated but can be background-finalized.
+  MOZ_ASSERT(IsBackgroundFinalized(allocKind));
+  MOZ_ASSERT(!CanNurseryAllocateFinalizedClass(clasp));
+  constexpr gc::InitialHeap heap = gc::TenuredHeap;
+
+  NativeObject* obj = NativeObject::create(cx, allocKind, heap, shape);
+  if (!obj) {
+    return nullptr;
+  }
+
+  return &obj->as<ArrayBufferObject>();
+}
+
+// Creates a new ArrayBufferObject with %ArrayBuffer.prototype% as proto and no
+// space for inline data.
+static ArrayBufferObject* NewArrayBufferObject(JSContext* cx) {
+  static_assert(ArrayBufferObject::RESERVED_SLOTS == 4);
+  return NewArrayBufferObject(cx, nullptr, gc::AllocKind::ARRAYBUFFER4);
+}
+
+ArrayBufferObject* ArrayBufferObject::createForContents(
+    JSContext* cx, size_t nbytes, BufferContents contents) {
+  MOZ_ASSERT(contents);
+  MOZ_ASSERT(contents.kind() != INLINE_DATA);
+  MOZ_ASSERT(contents.kind() != NO_DATA);
+  MOZ_ASSERT(contents.kind() != WASM);
+
+  // 24.1.1.1, step 3 (Inlined 6.2.6.1 CreateByteDataBlock, step 2).
+  if (!CheckArrayBufferTooLarge(cx, nbytes)) {
+    return nullptr;
+  }
+
+  // Some |contents| kinds need to store extra data in the ArrayBuffer beyond a
+  // data pointer.  If needed for the particular kind, add extra fixed slots to
+  // the ArrayBuffer for use as raw storage to store such information.
+  constexpr size_t reservedSlots = ArrayBufferObject::RESERVED_SLOTS;
+
+  size_t nAllocated = 0;
+  size_t nslots = reservedSlots;
+  if (contents.kind() == USER_OWNED) {
+    // No accounting to do in this case.
+  } else if (contents.kind() == EXTERNAL) {
+    // Store the FreeInfo in the inline data slots so that we
+    // don't use up slots for it in non-refcounted array buffers.
+    size_t freeInfoSlots = HowMany(sizeof(FreeInfo), sizeof(Value));
+    MOZ_ASSERT(reservedSlots + freeInfoSlots <= NativeObject::MAX_FIXED_SLOTS,
+               "FreeInfo must fit in inline slots");
+    nslots += freeInfoSlots;
+  } else {
+    // The ABO is taking ownership, so account the bytes against the zone.
+    nAllocated = nbytes;
+    if (contents.kind() == MAPPED) {
+      nAllocated = RoundUp(nbytes, js::gc::SystemPageSize());
+    } else {
+      MOZ_ASSERT(contents.kind() == MALLOCED,
+                 "should have handled all possible callers' kinds");
+    }
+  }
+
+  gc::AllocKind allocKind = GetArrayBufferGCObjectKind(nslots);
+
+  AutoSetNewObjectMetadata metadata(cx);
+  Rooted<ArrayBufferObject*> buffer(
+      cx, NewArrayBufferObject(cx, nullptr, allocKind));
+  if (!buffer) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(!gc::IsInsideNursery(buffer),
+             "ArrayBufferObject has a finalizer that must be called to not "
+             "leak in some cases, so it can't be nursery-allocated");
+
+  buffer->initialize(nbytes, contents);
+
+  if (contents.kind() == MAPPED || contents.kind() == MALLOCED) {
+    AddCellMemory(buffer, nAllocated, MemoryUse::ArrayBufferContents);
+  }
+
+  return buffer;
+}
+
+template <ArrayBufferObject::FillContents FillType>
+/* static */ std::tuple<ArrayBufferObject*, uint8_t*>
+ArrayBufferObject::createBufferAndData(
+    JSContext* cx, size_t nbytes, AutoSetNewObjectMetadata&,
+    JS::Handle<JSObject*> proto /* = nullptr */) {
+  MOZ_ASSERT(nbytes <= ArrayBufferObject::MaxByteLength,
+             "caller must validate the byte count it passes");
+
+  // Try fitting the data inline with the object by repurposing fixed-slot
+  // storage.  Add extra fixed slots if necessary to accomplish this, but don't
+  // exceed the maximum number of fixed slots!
+  size_t nslots = ArrayBufferObject::RESERVED_SLOTS;
+  ArrayBufferContents data;
+  if (nbytes <= MaxInlineBytes) {
+    int newSlots = HowMany(nbytes, sizeof(Value));
+    MOZ_ASSERT(int(nbytes) <= newSlots * int(sizeof(Value)));
+
+    nslots += newSlots;
+  } else {
+    data = FillType == FillContents::Uninitialized
+               ? AllocateUninitializedArrayBufferContents(cx, nbytes)
+               : AllocateArrayBufferContents(cx, nbytes);
+    if (!data) {
+      return {nullptr, nullptr};
+    }
+  }
+
+  gc::AllocKind allocKind = GetArrayBufferGCObjectKind(nslots);
+
+  ArrayBufferObject* buffer = NewArrayBufferObject(cx, proto, allocKind);
+  if (!buffer) {
+    return {nullptr, nullptr};
+  }
+
+  MOZ_ASSERT(!gc::IsInsideNursery(buffer),
+             "ArrayBufferObject has a finalizer that must be called to not "
+             "leak in some cases, so it can't be nursery-allocated");
+
+  uint8_t* toFill;
+  if (data) {
+    toFill = data.release();
+    buffer->initialize(nbytes, BufferContents::createMalloced(toFill));
+    AddCellMemory(buffer, nbytes, MemoryUse::ArrayBufferContents);
+  } else {
+    toFill = static_cast<uint8_t*>(buffer->initializeToInlineData(nbytes));
+    if constexpr (FillType == FillContents::Zero) {
+      memset(toFill, 0, nbytes);
+    }
+  }
+
+  return {buffer, toFill};
+}
+
+/* static */ ArrayBufferObject* ArrayBufferObject::copy(
+    JSContext* cx, JS::Handle<ArrayBufferObject*> unwrappedArrayBuffer) {
+  if (unwrappedArrayBuffer->isDetached()) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_TYPED_ARRAY_DETACHED);
+    return nullptr;
+  }
+
+  size_t nbytes = unwrappedArrayBuffer->byteLength();
+
+  AutoSetNewObjectMetadata metadata(cx);
+  auto [buffer, toFill] = createBufferAndData<FillContents::Uninitialized>(
+      cx, nbytes, metadata, nullptr);
+  if (!buffer) {
+    return nullptr;
+  }
+
+  std::uninitialized_copy_n(unwrappedArrayBuffer->dataPointer(), nbytes,
+                            toFill);
+  return buffer;
+}
+
+ArrayBufferObject* ArrayBufferObject::createZeroed(
+    JSContext* cx, size_t nbytes, HandleObject proto /* = nullptr */) {
+  // 24.1.1.1, step 3 (Inlined 6.2.6.1 CreateByteDataBlock, step 2).
+  if (!CheckArrayBufferTooLarge(cx, nbytes)) {
+    return nullptr;
+  }
+
+  AutoSetNewObjectMetadata metadata(cx);
+  auto [buffer, toFill] =
+      createBufferAndData<FillContents::Zero>(cx, nbytes, metadata, proto);
+  (void)toFill;
+  return buffer;
+}
+
+ArrayBufferObject* ArrayBufferObject::createEmpty(JSContext* cx) {
+  AutoSetNewObjectMetadata metadata(cx);
+  ArrayBufferObject* obj = NewArrayBufferObject(cx);
+  if (!obj) {
+    return nullptr;
+  }
+
+  obj->initialize(0, BufferContents::createNoData());
+  return obj;
+}
+
+ArrayBufferObject* ArrayBufferObject::createFromNewRawBuffer(
+    JSContext* cx, WasmArrayRawBuffer* rawBuffer, size_t initialSize) {
+  AutoSetNewObjectMetadata metadata(cx);
+  ArrayBufferObject* buffer = NewArrayBufferObject(cx);
+  if (!buffer) {
+    WasmArrayRawBuffer::Release(rawBuffer->dataPointer());
+    return nullptr;
+  }
+
+  MOZ_ASSERT(initialSize == rawBuffer->byteLength());
+
+  buffer->setByteLength(initialSize);
+  buffer->setFlags(0);
+  buffer->setFirstView(nullptr);
+
+  auto contents = BufferContents::createWasm(rawBuffer->dataPointer());
+  buffer->setDataPointer(contents);
+
+  AddCellMemory(buffer, initialSize, MemoryUse::ArrayBufferContents);
+
+  return buffer;
+}
+
+/* static */ uint8_t* ArrayBufferObject::stealMallocedContents(
+    JSContext* cx, Handle<ArrayBufferObject*> buffer) {
+  CheckStealPreconditions(buffer, cx);
+
+  switch (buffer->bufferKind()) {
+    case MALLOCED: {
+      uint8_t* stolenData = buffer->dataPointer();
+      MOZ_ASSERT(stolenData);
+
+      RemoveCellMemory(buffer, buffer->byteLength(),
+                       MemoryUse::ArrayBufferContents);
+
+      // Overwrite the old data pointer *without* releasing the contents
+      // being stolen.
+      buffer->setDataPointer(BufferContents::createNoData());
+
+      // Detach |buffer| now that doing so won't free |stolenData|.
+      ArrayBufferObject::detach(cx, buffer);
+      return stolenData;
+    }
+
+    case INLINE_DATA:
+    case NO_DATA:
+    case USER_OWNED:
+    case MAPPED:
+    case EXTERNAL: {
+      // We can't use these data types directly.  Make a copy to return.
+      ArrayBufferContents copiedData = NewCopiedBufferContents(cx, buffer);
+      if (!copiedData) {
+        return nullptr;
+      }
+
+      // Detach |buffer|.  This immediately releases the currently owned
+      // contents, freeing or unmapping data in the MAPPED and EXTERNAL cases.
+      ArrayBufferObject::detach(cx, buffer);
+      return copiedData.release();
+    }
+
+    case WASM:
+      MOZ_ASSERT_UNREACHABLE(
+          "wasm buffers aren't stealable except by a "
+          "memory.grow operation that shouldn't call this "
+          "function");
+      return nullptr;
+
+    case BAD1:
+      MOZ_ASSERT_UNREACHABLE("bad kind when stealing malloc'd data");
+      return nullptr;
+  }
+
+  MOZ_ASSERT_UNREACHABLE("garbage kind computed");
+  return nullptr;
+}
+
+/* static */ ArrayBufferObject::BufferContents
+ArrayBufferObject::extractStructuredCloneContents(
+    JSContext* cx, Handle<ArrayBufferObject*> buffer) {
+  CheckStealPreconditions(buffer, cx);
+
+  BufferContents contents = buffer->contents();
+
+  switch (contents.kind()) {
+    case INLINE_DATA:
+    case NO_DATA:
+    case USER_OWNED: {
+      ArrayBufferContents copiedData = NewCopiedBufferContents(cx, buffer);
+      if (!copiedData) {
+        return BufferContents::createFailed();
+      }
+
+      ArrayBufferObject::detach(cx, buffer);
+      return BufferContents::createMalloced(copiedData.release());
+    }
+
+    case MALLOCED:
+    case MAPPED: {
+      MOZ_ASSERT(contents);
+
+      RemoveCellMemory(buffer, buffer->associatedBytes(),
+                       MemoryUse::ArrayBufferContents);
+
+      // Overwrite the old data pointer *without* releasing old data.
+      buffer->setDataPointer(BufferContents::createNoData());
+
+      // Detach |buffer| now that doing so won't release |oldContents|.
+      ArrayBufferObject::detach(cx, buffer);
+      return contents;
+    }
+
+    case WASM:
+      JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                JSMSG_WASM_NO_TRANSFER);
+      return BufferContents::createFailed();
+
+    case EXTERNAL:
+      MOZ_ASSERT_UNREACHABLE(
+          "external ArrayBuffer shouldn't have passed the "
+          "structured-clone preflighting");
+      break;
+
+    case BAD1:
+      MOZ_ASSERT_UNREACHABLE("bad kind when stealing malloc'd data");
+      break;
+  }
+
+  MOZ_ASSERT_UNREACHABLE("garbage kind computed");
+  return BufferContents::createFailed();
+}
+
+/* static */
+void ArrayBufferObject::addSizeOfExcludingThis(
+    JSObject* obj, mozilla::MallocSizeOf mallocSizeOf, JS::ClassInfo* info,
+    JS::RuntimeSizes* runtimeSizes) {
+  auto& buffer = obj->as<ArrayBufferObject>();
+  switch (buffer.bufferKind()) {
+    case INLINE_DATA:
+      // Inline data's size should be reported by this object's size-class
+      // reporting.
+      break;
+    case MALLOCED:
+      if (buffer.isPreparedForAsmJS()) {
+        info->objectsMallocHeapElementsAsmJS +=
+            mallocSizeOf(buffer.dataPointer());
+      } else {
+        info->objectsMallocHeapElementsNormal +=
+            mallocSizeOf(buffer.dataPointer());
+      }
+      break;
+    case NO_DATA:
+      // No data is no memory.
+      MOZ_ASSERT(buffer.dataPointer() == nullptr);
+      break;
+    case USER_OWNED:
+      // User-owned data should be accounted for by the user.
+      break;
+    case EXTERNAL:
+      // External data will be accounted for by the owner of the buffer,
+      // not this view.
+      break;
+    case MAPPED:
+      info->objectsNonHeapElementsNormal += buffer.byteLength();
+      break;
+    case WASM:
+      if (!buffer.isDetached()) {
+        info->objectsNonHeapElementsWasm += buffer.byteLength();
+        if (runtimeSizes) {
+          MOZ_ASSERT(buffer.wasmMappedSize() >= buffer.byteLength());
+          runtimeSizes->wasmGuardPages +=
+              buffer.wasmMappedSize() - buffer.byteLength();
+        }
+      }
+      break;
+    case BAD1:
+      MOZ_CRASH("bad bufferKind()");
+  }
+}
+
+/* static */
+void ArrayBufferObject::finalize(JS::GCContext* gcx, JSObject* obj) {
+  obj->as<ArrayBufferObject>().releaseData(gcx);
+}
+
+/* static */
+void ArrayBufferObject::copyData(Handle<ArrayBufferObject*> toBuffer,
+                                 size_t toIndex,
+                                 Handle<ArrayBufferObject*> fromBuffer,
+                                 size_t fromIndex, size_t count) {
+  MOZ_ASSERT(toBuffer->byteLength() >= count);
+  MOZ_ASSERT(toBuffer->byteLength() >= toIndex + count);
+  MOZ_ASSERT(fromBuffer->byteLength() >= fromIndex);
+  MOZ_ASSERT(fromBuffer->byteLength() >= fromIndex + count);
+
+  memcpy(toBuffer->dataPointer() + toIndex,
+         fromBuffer->dataPointer() + fromIndex, count);
+}
+
+/* static */
+size_t ArrayBufferObject::objectMoved(JSObject* obj, JSObject* old) {
+  ArrayBufferObject& dst = obj->as<ArrayBufferObject>();
+  const ArrayBufferObject& src = old->as<ArrayBufferObject>();
+
+  // Fix up possible inline data pointer.
+  if (src.hasInlineData()) {
+    dst.setFixedSlot(DATA_SLOT, PrivateValue(dst.inlineDataPointer()));
+  }
+
+  return 0;
+}
+
+JSObject* ArrayBufferObject::firstView() {
+  return getFixedSlot(FIRST_VIEW_SLOT).isObject()
+             ? &getFixedSlot(FIRST_VIEW_SLOT).toObject()
+             : nullptr;
+}
+
+void ArrayBufferObject::setFirstView(ArrayBufferViewObject* view) {
+  setFixedSlot(FIRST_VIEW_SLOT, ObjectOrNullValue(view));
+}
+
+bool ArrayBufferObject::addView(JSContext* cx, ArrayBufferViewObject* view) {
+  if (!firstView()) {
+    setFirstView(view);
+    return true;
+  }
+
+  return ObjectRealm::get(this).innerViews.get().addView(cx, this, view);
+}
+
+/*
+ * InnerViewTable
+ */
+
+constexpr size_t VIEW_LIST_MAX_LENGTH = 500;
+
+bool InnerViewTable::addView(JSContext* cx, ArrayBufferObject* buffer,
+                             JSObject* view) {
+  // ArrayBufferObject entries are only added when there are multiple views.
+  MOZ_ASSERT(buffer->firstView());
+
+  Map::AddPtr p = map.lookupForAdd(buffer);
+
+  MOZ_ASSERT(!gc::IsInsideNursery(buffer));
+  bool addToNursery = nurseryKeysValid && gc::IsInsideNursery(view);
+
+  if (p) {
+    ViewVector& views = p->value();
+    MOZ_ASSERT(!views.empty());
+
+    if (addToNursery) {
+      // Only add the entry to |nurseryKeys| if it isn't already there.
+      if (views.length() >= VIEW_LIST_MAX_LENGTH) {
+        // To avoid quadratic blowup, skip the loop below if we end up
+        // adding enormous numbers of views for the same object.
+        nurseryKeysValid = false;
+      } else {
+        for (size_t i = 0; i < views.length(); i++) {
+          if (gc::IsInsideNursery(views[i])) {
+            addToNursery = false;
+            break;
+          }
+        }
+      }
+    }
+
+    if (!views.append(view)) {
+      ReportOutOfMemory(cx);
+      return false;
+    }
+  } else {
+    if (!map.add(p, buffer, ViewVector(cx->zone()))) {
+      ReportOutOfMemory(cx);
+      return false;
+    }
+    // ViewVector has one inline element, so the first insertion is
+    // guaranteed to succeed.
+    MOZ_ALWAYS_TRUE(p->value().append(view));
+  }
+
+  if (addToNursery && !nurseryKeys.append(buffer)) {
+    nurseryKeysValid = false;
+  }
+
+  return true;
+}
+
+InnerViewTable::ViewVector* InnerViewTable::maybeViewsUnbarriered(
+    ArrayBufferObject* buffer) {
+  Map::Ptr p = map.lookup(buffer);
+  if (p) {
+    return &p->value();
+  }
+  return nullptr;
+}
+
+void InnerViewTable::removeViews(ArrayBufferObject* buffer) {
+  Map::Ptr p = map.lookup(buffer);
+  MOZ_ASSERT(p);
+
+  map.remove(p);
+}
+
+bool InnerViewTable::traceWeak(JSTracer* trc) { return map.traceWeak(trc); }
+
+void InnerViewTable::sweepAfterMinorGC(JSTracer* trc) {
+  MOZ_ASSERT(needsSweepAfterMinorGC());
+
+  if (nurseryKeysValid) {
+    for (size_t i = 0; i < nurseryKeys.length(); i++) {
+      JSObject* buffer = MaybeForwarded(nurseryKeys[i]);
+      Map::Ptr p = map.lookup(buffer);
+      if (p &&
+          !Map::EntryGCPolicy::traceWeak(trc, &p->mutableKey(), &p->value())) {
+        map.remove(p);
+      }
+    }
+  } else {
+    // Do the required sweeping by looking at every map entry.
+    map.traceWeak(trc);
+  }
+
+  nurseryKeys.clear();
+  nurseryKeysValid = true;
+}
+
+size_t InnerViewTable::sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) {
+  size_t vectorSize = 0;
+  for (Map::Enum e(map); !e.empty(); e.popFront()) {
+    vectorSize += e.front().value().sizeOfExcludingThis(mallocSizeOf);
+  }
+
+  return vectorSize + map.shallowSizeOfExcludingThis(mallocSizeOf) +
+         nurseryKeys.sizeOfExcludingThis(mallocSizeOf);
+}
+
+template <>
+bool JSObject::is<js::ArrayBufferObjectMaybeShared>() const {
+  return is<ArrayBufferObject>() || is<SharedArrayBufferObject>();
+}
+
+JS_PUBLIC_API size_t JS::GetArrayBufferByteLength(JSObject* obj) {
+  ArrayBufferObject* aobj = obj->maybeUnwrapAs<ArrayBufferObject>();
+  return aobj ? aobj->byteLength() : 0;
+}
+
+JS_PUBLIC_API uint8_t* JS::GetArrayBufferData(JSObject* obj,
+                                              bool* isSharedMemory,
+                                              const JS::AutoRequireNoGC&) {
+  ArrayBufferObject* aobj = obj->maybeUnwrapIf<ArrayBufferObject>();
+  if (!aobj) {
+    return nullptr;
+  }
+  *isSharedMemory = false;
+  return aobj->dataPointer();
+}
+
+static ArrayBufferObject* UnwrapOrReportArrayBuffer(
+    JSContext* cx, JS::Handle<JSObject*> maybeArrayBuffer) {
+  JSObject* obj = CheckedUnwrapStatic(maybeArrayBuffer);
+  if (!obj) {
+    ReportAccessDenied(cx);
+    return nullptr;
+  }
+
+  if (!obj->is<ArrayBufferObject>()) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_ARRAYBUFFER_REQUIRED);
+    return nullptr;
+  }
+
+  return &obj->as<ArrayBufferObject>();
+}
+
+JS_PUBLIC_API bool JS::DetachArrayBuffer(JSContext* cx, HandleObject obj) {
+  AssertHeapIsIdle();
+  CHECK_THREAD(cx);
+  cx->check(obj);
+
+  Rooted<ArrayBufferObject*> unwrappedBuffer(
+      cx, UnwrapOrReportArrayBuffer(cx, obj));
+  if (!unwrappedBuffer) {
+    return false;
+  }
+
+  if (unwrappedBuffer->isWasm() || unwrappedBuffer->isPreparedForAsmJS()) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_WASM_NO_TRANSFER);
+    return false;
+  }
+
+  AutoRealm ar(cx, unwrappedBuffer);
+  ArrayBufferObject::detach(cx, unwrappedBuffer);
+  return true;
+}
+
+JS_PUBLIC_API bool JS::HasDefinedArrayBufferDetachKey(JSContext* cx,
+                                                      HandleObject obj,
+                                                      bool* isDefined) {
+  Rooted<ArrayBufferObject*> unwrappedBuffer(
+      cx, UnwrapOrReportArrayBuffer(cx, obj));
+  if (!unwrappedBuffer) {
+    return false;
+  }
+
+  if (unwrappedBuffer->isWasm() || unwrappedBuffer->isPreparedForAsmJS()) {
+    *isDefined = true;
+  }
+
+  return true;
+}
+
+JS_PUBLIC_API bool JS::IsDetachedArrayBufferObject(JSObject* obj) {
+  ArrayBufferObject* aobj = obj->maybeUnwrapIf<ArrayBufferObject>();
+  if (!aobj) {
+    return false;
+  }
+
+  return aobj->isDetached();
+}
+
+JS_PUBLIC_API JSObject* JS::NewArrayBuffer(JSContext* cx, size_t nbytes) {
+  AssertHeapIsIdle();
+  CHECK_THREAD(cx);
+
+  return ArrayBufferObject::createZeroed(cx, nbytes);
+}
+
+JS_PUBLIC_API JSObject* JS::NewArrayBufferWithContents(JSContext* cx,
+                                                       size_t nbytes,
+                                                       void* data) {
+  AssertHeapIsIdle();
+  CHECK_THREAD(cx);
+  MOZ_ASSERT_IF(!data, nbytes == 0);
+
+  if (!data) {
+    // Don't pass nulled contents to |createForContents|.
+    return ArrayBufferObject::createZeroed(cx, 0);
+  }
+
+  using BufferContents = ArrayBufferObject::BufferContents;
+
+  BufferContents contents = BufferContents::createMalloced(data);
+  return ArrayBufferObject::createForContents(cx, nbytes, contents);
+}
+
+JS_PUBLIC_API JSObject* JS::CopyArrayBuffer(JSContext* cx,
+                                            Handle<JSObject*> arrayBuffer) {
+  AssertHeapIsIdle();
+  CHECK_THREAD(cx);
+
+  MOZ_ASSERT(arrayBuffer != nullptr);
+
+  Rooted<ArrayBufferObject*> unwrappedSource(
+      cx, UnwrapOrReportArrayBuffer(cx, arrayBuffer));
+  if (!unwrappedSource) {
+    return nullptr;
+  }
+
+  return ArrayBufferObject::copy(cx, unwrappedSource);
+}
+
+JS_PUBLIC_API JSObject* JS::NewExternalArrayBuffer(
+    JSContext* cx, size_t nbytes, void* data,
+    JS::BufferContentsFreeFunc freeFunc, void* freeUserData) {
+  AssertHeapIsIdle();
+  CHECK_THREAD(cx);
+
+  MOZ_ASSERT(data);
+
+  using BufferContents = ArrayBufferObject::BufferContents;
+
+  BufferContents contents =
+      BufferContents::createExternal(data, freeFunc, freeUserData);
+  return ArrayBufferObject::createForContents(cx, nbytes, contents);
+}
+
+JS_PUBLIC_API JSObject* JS::NewArrayBufferWithUserOwnedContents(JSContext* cx,
+                                                                size_t nbytes,
+                                                                void* data) {
+  AssertHeapIsIdle();
+  CHECK_THREAD(cx);
+
+  MOZ_ASSERT(data);
+
+  using BufferContents = ArrayBufferObject::BufferContents;
+
+  BufferContents contents = BufferContents::createUserOwned(data);
+  return ArrayBufferObject::createForContents(cx, nbytes, contents);
+}
+
+JS_PUBLIC_API bool JS::IsArrayBufferObject(JSObject* obj) {
+  return obj->canUnwrapAs<ArrayBufferObject>();
+}
+
+JS_PUBLIC_API bool JS::ArrayBufferHasData(JSObject* obj) {
+  return !obj->unwrapAs<ArrayBufferObject>().isDetached();
+}
+
+JS_PUBLIC_API JSObject* JS::UnwrapArrayBuffer(JSObject* obj) {
+  return obj->maybeUnwrapIf<ArrayBufferObject>();
+}
+
+JS_PUBLIC_API JSObject* JS::UnwrapSharedArrayBuffer(JSObject* obj) {
+  return obj->maybeUnwrapIf<SharedArrayBufferObject>();
+}
+
+JS_PUBLIC_API void* JS::StealArrayBufferContents(JSContext* cx,
+                                                 HandleObject obj) {
+  AssertHeapIsIdle();
+  CHECK_THREAD(cx);
+  cx->check(obj);
+
+  Rooted<ArrayBufferObject*> unwrappedBuffer(
+      cx, UnwrapOrReportArrayBuffer(cx, obj));
+  if (!unwrappedBuffer) {
+    return nullptr;
+  }
+
+  if (unwrappedBuffer->isDetached()) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_TYPED_ARRAY_DETACHED);
+    return nullptr;
+  }
+
+  if (unwrappedBuffer->isWasm() || unwrappedBuffer->isPreparedForAsmJS()) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_WASM_NO_TRANSFER);
+    return nullptr;
+  }
+
+  AutoRealm ar(cx, unwrappedBuffer);
+  return ArrayBufferObject::stealMallocedContents(cx, unwrappedBuffer);
+}
+
+JS_PUBLIC_API JSObject* JS::NewMappedArrayBufferWithContents(JSContext* cx,
+                                                             size_t nbytes,
+                                                             void* data) {
+  AssertHeapIsIdle();
+  CHECK_THREAD(cx);
+
+  MOZ_ASSERT(data);
+
+  using BufferContents = ArrayBufferObject::BufferContents;
+
+  BufferContents contents = BufferContents::createMapped(data);
+  return ArrayBufferObject::createForContents(cx, nbytes, contents);
+}
+
+JS_PUBLIC_API void* JS::CreateMappedArrayBufferContents(int fd, size_t offset,
+                                                        size_t length) {
+  return ArrayBufferObject::createMappedContents(fd, offset, length).data();
+}
+
+JS_PUBLIC_API void JS::ReleaseMappedArrayBufferContents(void* contents,
+                                                        size_t length) {
+  gc::DeallocateMappedContent(contents, length);
+}
+
+JS_PUBLIC_API bool JS::IsMappedArrayBufferObject(JSObject* obj) {
+  ArrayBufferObject* aobj = obj->maybeUnwrapIf<ArrayBufferObject>();
+  if (!aobj) {
+    return false;
+  }
+
+  return aobj->isMapped();
+}
+
+JS_PUBLIC_API JSObject* JS::GetObjectAsArrayBuffer(JSObject* obj,
+                                                   size_t* length,
+                                                   uint8_t** data) {
+  ArrayBufferObject* aobj = obj->maybeUnwrapIf<ArrayBufferObject>();
+  if (!aobj) {
+    return nullptr;
+  }
+
+  *length = aobj->byteLength();
+  *data = aobj->dataPointer();
+
+  return aobj;
+}
+
+JS_PUBLIC_API void JS::GetArrayBufferLengthAndData(JSObject* obj,
+                                                   size_t* length,
+                                                   bool* isSharedMemory,
+                                                   uint8_t** data) {
+  auto& aobj = obj->as<ArrayBufferObject>();
+  *length = aobj.byteLength();
+  *data = aobj.dataPointer();
+  *isSharedMemory = false;
+}
+
+const JSClass* const JS::ArrayBuffer::UnsharedClass =
+    &ArrayBufferObject::class_;
+const JSClass* const JS::ArrayBuffer::SharedClass =
+    &SharedArrayBufferObject::class_;
+
+/* static */ JS::ArrayBuffer JS::ArrayBuffer::create(JSContext* cx,
+                                                     size_t nbytes) {
+  AssertHeapIsIdle();
+  CHECK_THREAD(cx);
+  return JS::ArrayBuffer(ArrayBufferObject::createZeroed(cx, nbytes));
+}
+
+uint8_t* JS::ArrayBuffer::getLengthAndData(size_t* length, bool* isSharedMemory,
+                                           const JS::AutoRequireNoGC& nogc) {
+  auto* buffer = obj->maybeUnwrapAs<ArrayBufferObjectMaybeShared>();
+  if (!buffer) {
+    return nullptr;
+  }
+  *length = buffer->byteLength();
+  if (buffer->is<SharedArrayBufferObject>()) {
+    *isSharedMemory = true;
+    return buffer->dataPointerEither().unwrap();
+  }
+  *isSharedMemory = false;
+  return buffer->as<ArrayBufferObject>().dataPointer();
+};
+
+JS::ArrayBuffer JS::ArrayBuffer::unwrap(JSObject* maybeWrapped) {
+  if (!maybeWrapped) {
+    return JS::ArrayBuffer(nullptr);
+  }
+  auto* ab = maybeWrapped->maybeUnwrapIf<ArrayBufferObjectMaybeShared>();
+  return fromObject(ab);
+}
+
+bool JS::ArrayBufferCopyData(JSContext* cx, Handle<JSObject*> toBlock,
+                             size_t toIndex, Handle<JSObject*> fromBlock,
+                             size_t fromIndex, size_t count) {
+  Rooted<ArrayBufferObjectMaybeShared*> unwrappedToBlock(
+      cx, toBlock->maybeUnwrapIf<ArrayBufferObjectMaybeShared>());
+  if (!unwrappedToBlock) {
+    ReportAccessDenied(cx);
+    return false;
+  }
+
+  Rooted<ArrayBufferObjectMaybeShared*> unwrappedFromBlock(
+      cx, fromBlock->maybeUnwrapIf<ArrayBufferObjectMaybeShared>());
+  if (!unwrappedFromBlock) {
+    ReportAccessDenied(cx);
+    return false;
+  }
+
+  // Verify that lengths still make sense and throw otherwise.
+  if (toIndex + count < toIndex ||      // size_t overflow
+      fromIndex + count < fromIndex ||  // size_t overflow
+      toIndex + count > unwrappedToBlock->byteLength() ||
+      fromIndex + count > unwrappedFromBlock->byteLength()) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_ARRAYBUFFER_COPY_RANGE);
+    return false;
+  }
+
+  // If both are array buffers, can use ArrayBufferCopyData
+  if (unwrappedToBlock->is<ArrayBufferObject>() &&
+      unwrappedFromBlock->is<ArrayBufferObject>()) {
+    Rooted<ArrayBufferObject*> toArray(
+        cx, &unwrappedToBlock->as<ArrayBufferObject>());
+    Rooted<ArrayBufferObject*> fromArray(
+        cx, &unwrappedFromBlock->as<ArrayBufferObject>());
+    ArrayBufferObject::copyData(toArray, toIndex, fromArray, fromIndex, count);
+    return true;
+  }
+
+  Rooted<ArrayBufferObjectMaybeShared*> toArray(
+      cx, &unwrappedToBlock->as<ArrayBufferObjectMaybeShared>());
+  Rooted<ArrayBufferObjectMaybeShared*> fromArray(
+      cx, &unwrappedFromBlock->as<ArrayBufferObjectMaybeShared>());
+  SharedArrayBufferObject::copyData(toArray, toIndex, fromArray, fromIndex,
+                                    count);
+
+  return true;
+}
+
+// https://tc39.es/ecma262/#sec-clonearraybuffer
+// We only support the case where cloneConstructor is %ArrayBuffer%. Note,
+// this means that cloning a SharedArrayBuffer will produce an ArrayBuffer
+JSObject* JS::ArrayBufferClone(JSContext* cx, Handle<JSObject*> srcBuffer,
+                               size_t srcByteOffset, size_t srcLength) {
+  MOZ_ASSERT(srcBuffer->is<ArrayBufferObjectMaybeShared>());
+
+  // 2. (reordered) If IsDetachedBuffer(srcBuffer) is true, throw a TypeError
+  // exception.
+  if (IsDetachedArrayBufferObject(srcBuffer)) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_TYPED_ARRAY_DETACHED);
+    return nullptr;
+  }
+
+  // 1. Let targetBuffer be ? AllocateArrayBuffer(cloneConstructor, srcLength).
+  JS::RootedObject targetBuffer(cx, JS::NewArrayBuffer(cx, srcLength));
+  if (!targetBuffer) {
+    return nullptr;
+  }
+
+  // 3. Let srcBlock be srcBuffer.[[ArrayBufferData]].
+  // 4. Let targetBlock be targetBuffer.[[ArrayBufferData]].
+  // 5. Perform CopyDataBlockBytes(targetBlock, 0, srcBlock, srcByteOffset,
+  // srcLength).
+  if (!ArrayBufferCopyData(cx, targetBuffer, 0, srcBuffer, srcByteOffset,
+                           srcLength)) {
+    return nullptr;
+  }
+
+  // 6. Return targetBuffer.
+  return targetBuffer;
+}