Bug 1240984 - Remove dummy ArrayBufferContents backstop, r=Waldo

--HG--
extra : rebase_source : ac3a7e8d21f47f056956c5339c8cc4f9dc3fcd36
extra : intermediate-source : 11de53329deb91bd355f6b3d62b6be32a0f40bd7
extra : source : 694c87cbc37ae55cd49123324f842669baee7760

js/src/jit-test/tests/asm.js/testNeuter.js

@@ -23,10 +23,7 @@ var buffer = new ArrayBuffer(BUF_MIN);
 var {get, set} = asmLink(m, this, null, buffer);
 set(4, 42);
 assertEq(get(4), 42);
-assertThrowsInstanceOf(() => detachArrayBuffer(buffer, "change-data"),
-                       InternalError);
-assertThrowsInstanceOf(() => detachArrayBuffer(buffer, "same-data"),
-                       InternalError);
+assertThrowsInstanceOf(() => detachArrayBuffer(buffer), Error);
 
 var m = asmCompile('stdlib', 'foreign', 'buffer',
                   `"use asm";
@@ -42,8 +39,7 @@ var m = asmCompile('stdlib', 'foreign', 'buffer',
 var buffer = new ArrayBuffer(BUF_MIN);
 function ffi1()
 {
-    assertThrowsInstanceOf(() => detachArrayBuffer(buffer, "change-data"),
-                           InternalError);
+    assertThrowsInstanceOf(() => detachArrayBuffer(buffer), Error);
 }
 
 var inner = asmLink(m, this, {ffi: ffi1}, buffer);

js/src/jsfriendapi.h

@@ -2106,12 +2106,7 @@ enum DetachDataDisposition {
  * Detach an ArrayBuffer, causing all associated views to no longer refer to
  * the ArrayBuffer's original attached memory.
  *
- * The |changeData| argument is a hint to inform internal behavior with respect
- * to the ArrayBuffer's internal pointer to associated data.  |ChangeData|
- * attempts to set the internal pointer to fresh memory of the same size as the
- * original memory; |KeepData| attempts to preserve the original pointer, even
- * while the ArrayBuffer appears observably detached.  There is no guarantee
- * this parameter is respected -- it's only a hint.
+ * The |changeData| argument is obsolete and ignored.
  */
 extern JS_FRIEND_API(bool)
 JS_DetachArrayBuffer(JSContext* cx, JS::HandleObject obj,

js/src/vm/ArrayBufferObject.cpp

@@ -260,16 +260,13 @@ NoteViewBufferWasDetached(ArrayBufferViewObject* view,
     MarkObjectStateChange(cx, view);
 }
 
-/* static */ bool
+/* static */ void
 ArrayBufferObject::detach(JSContext* cx, Handle<ArrayBufferObject*> buffer,
                           BufferContents newContents)
 {
     assertSameCompartment(cx, buffer);
 
-    if (buffer->isWasm()) {
-        JS_ReportErrorNumber(cx, GetErrorMessage, nullptr, JSMSG_OUT_OF_MEMORY);
-        return false;
-    }
+    MOZ_ASSERT(!buffer->isWasm());
 
     // When detaching buffers where we don't know all views, the new data must
     // match the old data. All missing views are typed objects, which do not
@@ -316,7 +313,6 @@ ArrayBufferObject::detach(JSContext* cx, Handle<ArrayBufferObject*> buffer,
 
     buffer->setByteLength(0);
     buffer->setIsDetached();
-    return true;
 }
 
 void
@@ -737,30 +733,27 @@ ArrayBufferObject::stealContents(JSContext* cx, Handle<ArrayBufferObject*> buffe
     assertSameCompartment(cx, buffer);
 
     BufferContents oldContents(buffer->dataPointer(), buffer->bufferKind());
-    BufferContents newContents = AllocateArrayBufferContents(cx, buffer->byteLength());
-    if (!newContents)
-        return BufferContents::createPlain(nullptr);
 
     if (hasStealableContents) {
-        // Return the old contents and give the detached buffer a pointer to
-        // freshly allocated memory that we will never write to and should
-        // never get committed.
-        buffer->setOwnsData(DoesntOwnData);
-        if (!ArrayBufferObject::detach(cx, buffer, newContents)) {
-            js_free(newContents.data());
-            return BufferContents::createPlain(nullptr);
-        }
+        // Return the old contents and reset the detached buffer's data
+        // pointer. This pointer should never be accessed.
+        auto newContents = BufferContents::createPlain(nullptr);
+        buffer->setOwnsData(DoesntOwnData); // Do not free the stolen data.
+        ArrayBufferObject::detach(cx, buffer, newContents);
+        buffer->setOwnsData(DoesntOwnData); // Do not free the nullptr.
         return oldContents;
     }
 
     // Create a new chunk of memory to return since we cannot steal the
     // existing contents away from the buffer.
-    memcpy(newContents.data(), oldContents.data(), buffer->byteLength());
-    if (!ArrayBufferObject::detach(cx, buffer, oldContents)) {
-        js_free(newContents.data());
+    BufferContents contentsCopy = AllocateArrayBufferContents(cx, buffer->byteLength());
+    if (!contentsCopy)
         return BufferContents::createPlain(nullptr);
-    }
-    return newContents;
+
+    if (buffer->byteLength() > 0)
+        memcpy(contentsCopy.data(), oldContents.data(), buffer->byteLength());
+    ArrayBufferObject::detach(cx, buffer, oldContents);
+    return contentsCopy;
 }
 
 /* static */ void
@@ -1035,10 +1028,11 @@ ArrayBufferViewObject::trace(JSTracer* trc, JSObject* objArg)
         if (IsArrayBuffer(&bufSlot.toObject())) {
             ArrayBufferObject& buf = AsArrayBuffer(MaybeForwarded(&bufSlot.toObject()));
             uint32_t offset = uint32_t(obj->getFixedSlot(TypedArrayObject::BYTEOFFSET_SLOT).toInt32());
-            MOZ_ASSERT(buf.dataPointer() != nullptr);
             MOZ_ASSERT(offset <= INT32_MAX);
 
             if (buf.forInlineTypedObject()) {
+                MOZ_ASSERT(buf.dataPointer() != nullptr);
+
                 // The data is inline with an InlineTypedObject associated with the
                 // buffer. Get a new address for the typed object if it moved.
                 JSObject* view = buf.firstView();
@@ -1058,6 +1052,8 @@ ArrayBufferViewObject::trace(JSTracer* trc, JSObject* objArg)
                 trc->runtime()->gc.nursery.maybeSetForwardingPointer(trc, srcData, dstData,
                                                                      /* direct = */ false);
             } else {
+                MOZ_ASSERT_IF(buf.dataPointer() == nullptr, offset == 0);
+
                 // The data may or may not be inline with the buffer. The buffer
                 // can only move during a compacting GC, in which case its
                 // objectMoved hook has already updated the buffer's data pointer.
@@ -1084,7 +1080,6 @@ JSObject::is<js::ArrayBufferObjectMaybeShared>() const
 void
 ArrayBufferViewObject::notifyBufferDetached(JSContext* cx, void* newData)
 {
-    MOZ_ASSERT(newData != nullptr);
     if (is<DataViewObject>()) {
         as<DataViewObject>().notifyBufferDetached(newData);
     } else if (is<TypedArrayObject>()) {
@@ -1193,20 +1188,17 @@ JS_DetachArrayBuffer(JSContext* cx, HandleObject obj,
 
     Rooted<ArrayBufferObject*> buffer(cx, &obj->as<ArrayBufferObject>());
 
-    if (changeData == ChangeData && buffer->hasStealableContents()) {
-        ArrayBufferObject::BufferContents newContents =
-            AllocateArrayBufferContents(cx, buffer->byteLength());
-        if (!newContents)
-            return false;
-        if (!ArrayBufferObject::detach(cx, buffer, newContents)) {
-            js_free(newContents.data());
-            return false;
-        }
-    } else {
-        if (!ArrayBufferObject::detach(cx, buffer, buffer->contents()))
-            return false;
+    if (buffer->isWasm()) {
+        JS_ReportError(cx, "Cannot detach WASM ArrayBuffer");
+        return false;
     }
 
+    ArrayBufferObject::BufferContents newContents =
+        buffer->hasStealableContents() ? ArrayBufferObject::BufferContents::createPlain(nullptr)
+                                       : buffer->contents();
+
+    ArrayBufferObject::detach(cx, buffer, newContents);
+
     return true;
 }
 

js/src/vm/ArrayBufferObject.h

@@ -213,9 +213,6 @@ class ArrayBufferObject : public ArrayBufferObjectMaybeShared
     static bool fun_slice(JSContext* cx, unsigned argc, Value* vp);
 
     static bool fun_isView(JSContext* cx, unsigned argc, Value* vp);
-#ifdef NIGHTLY_BUILD
-    static bool fun_transfer(JSContext* cx, unsigned argc, Value* vp);
-#endif
 
     static bool fun_species(JSContext* cx, unsigned argc, Value* vp);
 
@@ -252,15 +249,7 @@ class ArrayBufferObject : public ArrayBufferObjectMaybeShared
 
     bool hasStealableContents() const {
         // Inline elements strictly adhere to the corresponding buffer.
-        if (!ownsData())
-            return false;
-
-        // Detached contents aren't transferrable because we want a detached
-        // buffer's contents to be backed by zeroed memory equal in length to
-        // the original buffer contents.  Transferring these contents would
-        // allocate new ones based on the current byteLength, which is 0 for a
-        // detached buffer -- not the original byteLength.
-        return !isDetached();
+        return ownsData();
     }
 
     // Return whether the buffer is allocated by js_malloc and should be freed
@@ -286,7 +275,7 @@ class ArrayBufferObject : public ArrayBufferObjectMaybeShared
 
     // Detach this buffer from its original memory.  (This necessarily makes
     // views of this buffer unusable for modifying that original memory.)
-    static MOZ_MUST_USE bool
+    static void
     detach(JSContext* cx, Handle<ArrayBufferObject*> buffer, BufferContents newContents);
 
   private:

js/src/vm/StructuredClone.cpp

@@ -1378,7 +1378,7 @@ JSStructuredCloneWriter::transferOwnership()
             ArrayBufferObject::BufferContents bufContents =
                 ArrayBufferObject::stealContents(context(), arrayBuffer, hasStealableContents);
             if (!bufContents)
-                return false; // Destructor will clean up the already-transferred data.
+                return false; // already transferred data
 
             content = bufContents.data();
             tag = SCTAG_TRANSFER_MAP_ARRAY_BUFFER;