[builtins] Use the byte_length for byte length, not byte_offset.

length != offset.

Bug: chromium:718285
Change-Id: I150af1473cb5180c242f3817b940fa1cf1c49cea
Reviewed-on: https://chromium-review.googlesource.com/497727
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45121}

src/elements.cc

@@ -3149,8 +3149,8 @@ class TypedElementsAccessor
     // TypedArrays.
     uint8_t* source_data = static_cast<uint8_t*>(source_elements->DataPtr());
     uint8_t* dest_data = static_cast<uint8_t*>(destination_elements->DataPtr());
-    size_t source_byte_length = NumberToSize(source->byte_offset());
-    size_t dest_byte_length = NumberToSize(destination->byte_offset());
+    size_t source_byte_length = NumberToSize(source->byte_length());
+    size_t dest_byte_length = NumberToSize(destination->byte_length());
     CHECK(dest_data + dest_byte_length <= source_data ||
           source_data + source_byte_length <= dest_data);
 

test/mjsunit/regress/regress-718285.js

+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+function foo_reference(n) {
+  var array = new Int32Array(n + 1);
+  for (var i = 0; i < n; ++i) {
+    array[i] = i;
+  }
+  var array2 = new Int32Array(array);
+  array2.set(new Uint8Array(array.buffer, 0, n), 1);
+  return array2;
+}
+
+function foo(n) {
+  var array = new Int32Array(n + 1);
+  for (var i = 0; i < n; ++i) {
+    array[i] = i;
+  }
+  array.set(new Uint8Array(array.buffer, 0, n), 1);
+  return array;
+}
+
+function bar_reference(n) {
+  var array = new Int32Array(n + 1);
+  for (var i = 0; i < n; ++i) {
+    array[i] = i;
+  }
+  var array2 = new Int32Array(array);
+  array2.set(new Uint8Array(array.buffer, 34), 0);
+  return array2;
+}
+
+function bar(n) {
+  var array = new Int32Array(n + 1);
+  for (var i = 0; i < n; ++i) {
+    array[i] = i;
+  }
+  array.set(new Uint8Array(array.buffer, 34), 0);
+  return array;
+}
+
+foo(10);
+foo_reference(10);
+bar(10);
+bar_reference(10);