1 files changed, 588 insertions, 0 deletions
diff --git a/js/src/vm/SharedArrayObject.cpp b/js/src/vm/SharedArrayObject.cpp
new file mode 100644
index 0000000000..52d1bdde69
--- /dev/null
+++ b/js/src/vm/SharedArrayObject.cpp
@@ -0,0 +1,588 @@
+/* -*- 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/SharedArrayObject.h"
+
+#include "mozilla/Atomics.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/TaggedAnonymousMemory.h"
+
+#include "gc/GCContext.h"
+#include "gc/Memory.h"
+#include "jit/AtomicOperations.h"
+#include "js/friend/ErrorMessages.h"  // js::GetErrorMessage, JSMSG_*
+#include "js/PropertySpec.h"
+#include "js/SharedArrayBuffer.h"
+#include "util/Memory.h"
+#include "util/WindowsWrapper.h"
+#include "vm/SharedMem.h"
+#include "wasm/WasmConstants.h"
+#include "wasm/WasmMemory.h"
+
+#include "vm/ArrayBufferObject-inl.h"
+#include "vm/JSObject-inl.h"
+#include "vm/NativeObject-inl.h"
+
+using js::wasm::Pages;
+using mozilla::DebugOnly;
+using mozilla::Maybe;
+using mozilla::Nothing;
+using mozilla::Some;
+
+using namespace js;
+using namespace js::jit;
+
+static size_t WasmSharedArrayAccessibleSize(size_t length) {
+  return AlignBytes(length, gc::SystemPageSize());
+}
+
+static size_t NonWasmSharedArrayAllocSize(size_t length) {
+  MOZ_ASSERT(length <= ArrayBufferObject::MaxByteLength);
+  return sizeof(SharedArrayRawBuffer) + length;
+}
+
+// The mapped size for a plain shared array buffer, used only for tracking
+// memory usage. This is incorrect for some WASM cases, and for hypothetical
+// callers of js::SharedArrayBufferObject::createFromNewRawBuffer that do not
+// currently exist, but it's fine as a signal of GC pressure.
+static size_t SharedArrayMappedSize(bool isWasm, size_t length) {
+  // Wasm buffers use MapBufferMemory and allocate a full page for the header.
+  // Non-Wasm buffers use malloc.
+  if (isWasm) {
+    return WasmSharedArrayAccessibleSize(length) + gc::SystemPageSize();
+  }
+  return NonWasmSharedArrayAllocSize(length);
+}
+
+SharedArrayRawBuffer* SharedArrayRawBuffer::Allocate(size_t length) {
+  MOZ_RELEASE_ASSERT(length <= ArrayBufferObject::MaxByteLength);
+
+  size_t allocSize = NonWasmSharedArrayAllocSize(length);
+  uint8_t* p = js_pod_calloc<uint8_t>(allocSize);
+  if (!p) {
+    return nullptr;
+  }
+
+  uint8_t* buffer = p + sizeof(SharedArrayRawBuffer);
+  auto* rawbuf =
+      new (p) SharedArrayRawBuffer(/* isWasm = */ false, buffer, length);
+  MOZ_ASSERT(rawbuf->length_ == length);  // Deallocation needs this
+  return rawbuf;
+}
+
+WasmSharedArrayRawBuffer* WasmSharedArrayRawBuffer::AllocateWasm(
+    wasm::IndexType indexType, Pages initialPages, wasm::Pages clampedMaxPages,
+    const mozilla::Maybe<wasm::Pages>& sourceMaxPages,
+    const mozilla::Maybe<size_t>& mappedSize) {
+  // 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 length = initialPages.byteLength();
+
+  MOZ_RELEASE_ASSERT(length <= ArrayBufferObject::MaxByteLength);
+
+  size_t accessibleSize = WasmSharedArrayAccessibleSize(length);
+  if (accessibleSize < length) {
+    return nullptr;
+  }
+
+  size_t computedMappedSize = mappedSize.isSome()
+                                  ? *mappedSize
+                                  : wasm::ComputeMappedSize(clampedMaxPages);
+  MOZ_ASSERT(accessibleSize <= computedMappedSize);
+
+  uint64_t mappedSizeWithHeader = computedMappedSize + gc::SystemPageSize();
+  uint64_t accessibleSizeWithHeader = accessibleSize + gc::SystemPageSize();
+
+  void* p = MapBufferMemory(indexType, mappedSizeWithHeader,
+                            accessibleSizeWithHeader);
+  if (!p) {
+    return nullptr;
+  }
+
+  uint8_t* buffer = reinterpret_cast<uint8_t*>(p) + gc::SystemPageSize();
+  uint8_t* base = buffer - sizeof(WasmSharedArrayRawBuffer);
+  auto* rawbuf = new (base) WasmSharedArrayRawBuffer(
+      buffer, length, indexType, clampedMaxPages,
+      sourceMaxPages.valueOr(Pages(0)), computedMappedSize);
+  MOZ_ASSERT(rawbuf->length_ == length);  // Deallocation needs this
+  return rawbuf;
+}
+
+void WasmSharedArrayRawBuffer::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(newMaxPages <= sourceMaxPages_);
+
+  size_t newMappedSize = wasm::ComputeMappedSize(newMaxPages);
+  MOZ_ASSERT(mappedSize_ <= newMappedSize);
+  if (mappedSize_ == newMappedSize) {
+    return;
+  }
+
+  if (!ExtendBufferMapping(basePointer(), mappedSize_, newMappedSize)) {
+    return;
+  }
+
+  mappedSize_ = newMappedSize;
+  clampedMaxPages_ = newMaxPages;
+}
+
+bool WasmSharedArrayRawBuffer::wasmGrowToPagesInPlace(const Lock&,
+                                                      wasm::IndexType t,
+                                                      wasm::Pages newPages) {
+  // 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 > clampedMaxPages_) {
+    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 newLength = newPages.byteLength();
+
+  MOZ_ASSERT(newLength >= length_);
+
+  if (newLength == length_) {
+    return true;
+  }
+
+  size_t delta = newLength - length_;
+  MOZ_ASSERT(delta % wasm::PageSize == 0);
+
+  uint8_t* dataEnd = dataPointerShared().unwrap(/* for resize */) + length_;
+  MOZ_ASSERT(uintptr_t(dataEnd) % gc::SystemPageSize() == 0);
+
+  if (!CommitBufferMemory(dataEnd, delta)) {
+    return false;
+  }
+
+  // We rely on CommitBufferMemory (and therefore memmap/VirtualAlloc) to only
+  // return once it has committed memory for all threads. We only update with a
+  // new length once this has occurred.
+  length_ = newLength;
+
+  return true;
+}
+
+void WasmSharedArrayRawBuffer::discard(size_t byteOffset, size_t byteLen) {
+  SharedMem<uint8_t*> memBase = dataPointerShared();
+
+  // The caller is responsible for ensuring these conditions are met; see this
+  // function's comment in SharedArrayObject.h.
+  MOZ_ASSERT(byteOffset % wasm::PageSize == 0);
+  MOZ_ASSERT(byteLen % wasm::PageSize == 0);
+  MOZ_ASSERT(wasm::MemoryBoundsCheck(uint64_t(byteOffset), uint64_t(byteLen),
+                                     volatileByteLength()));
+
+  // Discarding zero bytes "succeeds" with no effect.
+  if (byteLen == 0) {
+    return;
+  }
+
+  SharedMem<uint8_t*> addr = memBase + uintptr_t(byteOffset);
+
+  // On POSIX-ish platforms, we discard memory by overwriting previously-mapped
+  // pages with freshly-mapped pages (which are all zeroed). The operating
+  // system recognizes this and decreases the process RSS, and eventually
+  // collects the abandoned physical pages.
+  //
+  // On Windows, committing over previously-committed pages has no effect. We
+  // could decommit and recommit, but this doesn't work for shared memories
+  // since other threads could access decommitted memory - causing a trap.
+  // Instead, we simply zero memory (memset 0), and then VirtualUnlock(), which
+  // for Historical Reasons immediately removes the pages from the working set.
+  // And then, because the pages were zeroed, Windows will actually reclaim the
+  // memory entirely instead of paging it out to disk. Naturally this behavior
+  // is not officially documented, but a Raymond Chen blog post is basically as
+  // good as MSDN, right?
+  //
+  // https://devblogs.microsoft.com/oldnewthing/20170113-00/?p=95185
+
+#ifdef XP_WIN
+  // Discarding the entire region at once causes us to page the entire region
+  // into the working set, only to throw it out again. This can be actually
+  // disastrous when discarding already-discarded memory. To mitigate this, we
+  // discard a chunk of memory at a time - this comes at a small performance
+  // cost from syscalls and potentially less-optimal memsets.
+  size_t numPages = byteLen / wasm::PageSize;
+  for (size_t i = 0; i < numPages; i++) {
+    AtomicOperations::memsetSafeWhenRacy(addr + (i * wasm::PageSize), 0,
+                                         wasm::PageSize);
+    DebugOnly<bool> result =
+        VirtualUnlock(addr.unwrap() + (i * wasm::PageSize), wasm::PageSize);
+    MOZ_ASSERT(!result);  // this always "fails" when unlocking unlocked
+                          // memory...which is the only case we care about
+  }
+#elif defined(__wasi__)
+  AtomicOperations::memsetSafeWhenRacy(addr, 0, byteLen);
+#else  // !XP_WIN
+  void* data = MozTaggedAnonymousMmap(
+      addr.unwrap(), byteLen, PROT_READ | PROT_WRITE,
+      MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0, "wasm-reserved");
+  if (data == MAP_FAILED) {
+    MOZ_CRASH("failed to discard wasm memory; memory mappings may be broken");
+  }
+#endif
+}
+
+bool SharedArrayRawBuffer::addReference() {
+  MOZ_RELEASE_ASSERT(refcount_ > 0);
+
+  // Be careful never to overflow the refcount field.
+  for (;;) {
+    uint32_t old_refcount = refcount_;
+    uint32_t new_refcount = old_refcount + 1;
+    if (new_refcount == 0) {
+      return false;
+    }
+    if (refcount_.compareExchange(old_refcount, new_refcount)) {
+      return true;
+    }
+  }
+}
+
+void SharedArrayRawBuffer::dropReference() {
+  // Normally if the refcount is zero then the memory will have been unmapped
+  // and this test may just crash, but if the memory has been retained for any
+  // reason we will catch the underflow here.
+  MOZ_RELEASE_ASSERT(refcount_ > 0);
+
+  // Drop the reference to the buffer.
+  uint32_t new_refcount = --refcount_;  // Atomic.
+  if (new_refcount) {
+    return;
+  }
+
+  // This was the final reference, so release the buffer.
+  if (isWasm()) {
+    WasmSharedArrayRawBuffer* wasmBuf = toWasmBuffer();
+    wasm::IndexType indexType = wasmBuf->wasmIndexType();
+    uint8_t* basePointer = wasmBuf->basePointer();
+    size_t mappedSizeWithHeader = wasmBuf->mappedSize() + gc::SystemPageSize();
+    // Call the destructor to destroy the growLock_ Mutex.
+    wasmBuf->~WasmSharedArrayRawBuffer();
+    UnmapBufferMemory(indexType, basePointer, mappedSizeWithHeader);
+  } else {
+    js_delete(this);
+  }
+}
+
+static bool IsSharedArrayBuffer(HandleValue v) {
+  return v.isObject() && v.toObject().is<SharedArrayBufferObject>();
+}
+
+MOZ_ALWAYS_INLINE bool SharedArrayBufferObject::byteLengthGetterImpl(
+    JSContext* cx, const CallArgs& args) {
+  MOZ_ASSERT(IsSharedArrayBuffer(args.thisv()));
+  auto* buffer = &args.thisv().toObject().as<SharedArrayBufferObject>();
+  args.rval().setNumber(buffer->byteLength());
+  return true;
+}
+
+bool SharedArrayBufferObject::byteLengthGetter(JSContext* cx, unsigned argc,
+                                               Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  return CallNonGenericMethod<IsSharedArrayBuffer, byteLengthGetterImpl>(cx,
+                                                                         args);
+}
+
+// ES2017 draft rev 6390c2f1b34b309895d31d8c0512eac8660a0210
+// 24.2.2.1 SharedArrayBuffer( length )
+bool SharedArrayBufferObject::class_constructor(JSContext* cx, unsigned argc,
+                                                Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  // Step 1.
+  if (!ThrowIfNotConstructing(cx, args, "SharedArrayBuffer")) {
+    return false;
+  }
+
+  // Step 2.
+  uint64_t byteLength;
+  if (!ToIndex(cx, args.get(0), &byteLength)) {
+    return false;
+  }
+
+  // Step 3 (Inlined 24.2.1.1 AllocateSharedArrayBuffer).
+  // 24.2.1.1, step 1 (Inlined 9.1.14 OrdinaryCreateFromConstructor).
+  RootedObject proto(cx);
+  if (!GetPrototypeFromBuiltinConstructor(cx, args, JSProto_SharedArrayBuffer,
+                                          &proto)) {
+    return false;
+  }
+
+  // 24.2.1.1, step 3 (Inlined 6.2.7.2 CreateSharedByteDataBlock, step 2).
+  // Refuse to allocate too large buffers.
+  if (byteLength > ArrayBufferObject::MaxByteLength) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_SHARED_ARRAY_BAD_LENGTH);
+    return false;
+  }
+
+  // 24.2.1.1, steps 1 and 4-6.
+  JSObject* bufobj = New(cx, byteLength, proto);
+  if (!bufobj) {
+    return false;
+  }
+  args.rval().setObject(*bufobj);
+  return true;
+}
+
+SharedArrayBufferObject* SharedArrayBufferObject::New(JSContext* cx,
+                                                      size_t length,
+                                                      HandleObject proto) {
+  SharedArrayRawBuffer* buffer = SharedArrayRawBuffer::Allocate(length);
+  if (!buffer) {
+    js::ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  SharedArrayBufferObject* obj = New(cx, buffer, length, proto);
+  if (!obj) {
+    buffer->dropReference();
+    return nullptr;
+  }
+
+  return obj;
+}
+
+SharedArrayBufferObject* SharedArrayBufferObject::New(
+    JSContext* cx, SharedArrayRawBuffer* buffer, size_t length,
+    HandleObject proto) {
+  MOZ_ASSERT(cx->realm()->creationOptions().getSharedMemoryAndAtomicsEnabled());
+
+  AutoSetNewObjectMetadata metadata(cx);
+  Rooted<SharedArrayBufferObject*> obj(
+      cx, NewObjectWithClassProto<SharedArrayBufferObject>(cx, proto));
+  if (!obj) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(obj->getClass() == &class_);
+
+  cx->runtime()->incSABCount();
+
+  if (!obj->acceptRawBuffer(buffer, length)) {
+    js::ReportOutOfMemory(cx);
+    return nullptr;
+  }
+
+  return obj;
+}
+
+bool SharedArrayBufferObject::acceptRawBuffer(SharedArrayRawBuffer* buffer,
+                                              size_t length) {
+  if (!zone()->addSharedMemory(buffer,
+                               SharedArrayMappedSize(buffer->isWasm(), length),
+                               MemoryUse::SharedArrayRawBuffer)) {
+    return false;
+  }
+
+  setFixedSlot(RAWBUF_SLOT, PrivateValue(buffer));
+  setFixedSlot(LENGTH_SLOT, PrivateValue(length));
+  return true;
+}
+
+void SharedArrayBufferObject::dropRawBuffer() {
+  size_t size = SharedArrayMappedSize(isWasm(), byteLength());
+  zoneFromAnyThread()->removeSharedMemory(rawBufferObject(), size,
+                                          MemoryUse::SharedArrayRawBuffer);
+  rawBufferObject()->dropReference();
+  setFixedSlot(RAWBUF_SLOT, UndefinedValue());
+}
+
+SharedArrayRawBuffer* SharedArrayBufferObject::rawBufferObject() const {
+  Value v = getFixedSlot(RAWBUF_SLOT);
+  MOZ_ASSERT(!v.isUndefined());
+  return reinterpret_cast<SharedArrayRawBuffer*>(v.toPrivate());
+}
+
+void SharedArrayBufferObject::Finalize(JS::GCContext* gcx, JSObject* obj) {
+  // Must be foreground finalizable so that we can account for the object.
+  MOZ_ASSERT(gcx->onMainThread());
+  gcx->runtime()->decSABCount();
+
+  SharedArrayBufferObject& buf = obj->as<SharedArrayBufferObject>();
+
+  // Detect the case of failure during SharedArrayBufferObject creation,
+  // which causes a SharedArrayRawBuffer to never be attached.
+  Value v = buf.getFixedSlot(RAWBUF_SLOT);
+  if (!v.isUndefined()) {
+    buf.dropRawBuffer();
+  }
+}
+
+/* static */
+void SharedArrayBufferObject::addSizeOfExcludingThis(
+    JSObject* obj, mozilla::MallocSizeOf mallocSizeOf, JS::ClassInfo* info,
+    JS::RuntimeSizes* runtimeSizes) {
+  // Divide the buffer size by the refcount to get the fraction of the buffer
+  // owned by this thread. It's conceivable that the refcount might change in
+  // the middle of memory reporting, in which case the amount reported for
+  // some threads might be to high (if the refcount goes up) or too low (if
+  // the refcount goes down). But that's unlikely and hard to avoid, so we
+  // just live with the risk.
+  const SharedArrayBufferObject& buf = obj->as<SharedArrayBufferObject>();
+  size_t owned = buf.byteLength() / buf.rawBufferObject()->refcount();
+  if (buf.isWasm()) {
+    info->objectsNonHeapElementsWasmShared += owned;
+    if (runtimeSizes) {
+      size_t ownedGuardPages = (buf.wasmMappedSize() - buf.byteLength()) /
+                               buf.rawBufferObject()->refcount();
+      runtimeSizes->wasmGuardPages += ownedGuardPages;
+    }
+  } else {
+    info->objectsNonHeapElementsShared += owned;
+  }
+}
+
+/* static */
+void SharedArrayBufferObject::copyData(
+    Handle<ArrayBufferObjectMaybeShared*> toBuffer, size_t toIndex,
+    Handle<ArrayBufferObjectMaybeShared*> 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);
+
+  jit::AtomicOperations::memcpySafeWhenRacy(
+      toBuffer->dataPointerEither() + toIndex,
+      fromBuffer->dataPointerEither() + fromIndex, count);
+}
+
+SharedArrayBufferObject* SharedArrayBufferObject::createFromNewRawBuffer(
+    JSContext* cx, WasmSharedArrayRawBuffer* buffer, size_t initialSize) {
+  MOZ_ASSERT(cx->realm()->creationOptions().getSharedMemoryAndAtomicsEnabled());
+
+  AutoSetNewObjectMetadata metadata(cx);
+  SharedArrayBufferObject* obj =
+      NewBuiltinClassInstance<SharedArrayBufferObject>(cx);
+  if (!obj) {
+    buffer->dropReference();
+    return nullptr;
+  }
+
+  cx->runtime()->incSABCount();
+
+  if (!obj->acceptRawBuffer(buffer, initialSize)) {
+    buffer->dropReference();
+    return nullptr;
+  }
+
+  return obj;
+}
+
+/* static */
+void SharedArrayBufferObject::wasmDiscard(HandleSharedArrayBufferObject buf,
+                                          uint64_t byteOffset,
+                                          uint64_t byteLen) {
+  MOZ_ASSERT(buf->isWasm());
+  buf->rawWasmBufferObject()->discard(byteOffset, byteLen);
+}
+
+static const JSClassOps SharedArrayBufferObjectClassOps = {
+    nullptr,                            // addProperty
+    nullptr,                            // delProperty
+    nullptr,                            // enumerate
+    nullptr,                            // newEnumerate
+    nullptr,                            // resolve
+    nullptr,                            // mayResolve
+    SharedArrayBufferObject::Finalize,  // finalize
+    nullptr,                            // call
+    nullptr,                            // construct
+    nullptr,                            // trace
+};
+
+static const JSFunctionSpec sharedarrray_functions[] = {JS_FS_END};
+
+static const JSPropertySpec sharedarrray_properties[] = {
+    JS_SELF_HOSTED_SYM_GET(species, "$SharedArrayBufferSpecies", 0), JS_PS_END};
+
+static const JSFunctionSpec sharedarray_proto_functions[] = {
+    JS_SELF_HOSTED_FN("slice", "SharedArrayBufferSlice", 2, 0), JS_FS_END};
+
+static const JSPropertySpec sharedarray_proto_properties[] = {
+    JS_PSG("byteLength", SharedArrayBufferObject::byteLengthGetter, 0),
+    JS_STRING_SYM_PS(toStringTag, "SharedArrayBuffer", JSPROP_READONLY),
+    JS_PS_END};
+
+static const ClassSpec SharedArrayBufferObjectClassSpec = {
+    GenericCreateConstructor<SharedArrayBufferObject::class_constructor, 1,
+                             gc::AllocKind::FUNCTION>,
+    GenericCreatePrototype<SharedArrayBufferObject>,
+    sharedarrray_functions,
+    sharedarrray_properties,
+    sharedarray_proto_functions,
+    sharedarray_proto_properties};
+
+const JSClass SharedArrayBufferObject::class_ = {
+    "SharedArrayBuffer",
+    JSCLASS_DELAY_METADATA_BUILDER |
+        JSCLASS_HAS_RESERVED_SLOTS(SharedArrayBufferObject::RESERVED_SLOTS) |
+        JSCLASS_HAS_CACHED_PROTO(JSProto_SharedArrayBuffer) |
+        JSCLASS_FOREGROUND_FINALIZE,
+    &SharedArrayBufferObjectClassOps, &SharedArrayBufferObjectClassSpec,
+    JS_NULL_CLASS_EXT};
+
+const JSClass SharedArrayBufferObject::protoClass_ = {
+    "SharedArrayBuffer.prototype",
+    JSCLASS_HAS_CACHED_PROTO(JSProto_SharedArrayBuffer), JS_NULL_CLASS_OPS,
+    &SharedArrayBufferObjectClassSpec};
+
+JS_PUBLIC_API size_t JS::GetSharedArrayBufferByteLength(JSObject* obj) {
+  auto* aobj = obj->maybeUnwrapAs<SharedArrayBufferObject>();
+  return aobj ? aobj->byteLength() : 0;
+}
+
+JS_PUBLIC_API void JS::GetSharedArrayBufferLengthAndData(JSObject* obj,
+                                                         size_t* length,
+                                                         bool* isSharedMemory,
+                                                         uint8_t** data) {
+  MOZ_ASSERT(obj->is<SharedArrayBufferObject>());
+  *length = obj->as<SharedArrayBufferObject>().byteLength();
+  *data = obj->as<SharedArrayBufferObject>().dataPointerShared().unwrap(
+      /*safe - caller knows*/);
+  *isSharedMemory = true;
+}
+
+JS_PUBLIC_API JSObject* JS::NewSharedArrayBuffer(JSContext* cx, size_t nbytes) {
+  MOZ_ASSERT(cx->realm()->creationOptions().getSharedMemoryAndAtomicsEnabled());
+
+  if (nbytes > ArrayBufferObject::MaxByteLength) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_SHARED_ARRAY_BAD_LENGTH);
+    return nullptr;
+  }
+
+  return SharedArrayBufferObject::New(cx, nbytes,
+                                      /* proto = */ nullptr);
+}
+
+JS_PUBLIC_API bool JS::IsSharedArrayBufferObject(JSObject* obj) {
+  return obj->canUnwrapAs<SharedArrayBufferObject>();
+}
+
+JS_PUBLIC_API uint8_t* JS::GetSharedArrayBufferData(
+    JSObject* obj, bool* isSharedMemory, const JS::AutoRequireNoGC&) {
+  auto* aobj = obj->maybeUnwrapAs<SharedArrayBufferObject>();
+  if (!aobj) {
+    return nullptr;
+  }
+  *isSharedMemory = true;
+  return aobj->dataPointerShared().unwrap(/*safe - caller knows*/);
+}
+
+JS_PUBLIC_API bool JS::ContainsSharedArrayBuffer(JSContext* cx) {
+  return cx->runtime()->hasLiveSABs();
+}