[async-await] Fix global-buffer-overflow issue when loading flag

Bug: chromium:892858
Change-Id: I97b0b239e3ee0a9073fdbd609fb26271dda64d6d
Reviewed-on: https://chromium-review.googlesource.com/c/1267936
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56432}

src/builtins/builtins-async-gen.cc

@@ -287,8 +287,10 @@ Node* AsyncBuiltinsAssembler::Await(Node* context, Node* generator, Node* value,
   VARIABLE(result, MachineRepresentation::kTagged);
   Label if_old(this), if_new(this), done(this);
 
+  STATIC_ASSERT(sizeof(FLAG_harmony_await_optimization) == 1);
+
   TNode<Word32T> flag_value = UncheckedCast<Word32T>(Load(
-      MachineType::Int32(),
+      MachineType::Uint8(),
       ExternalConstant(
           ExternalReference::address_of_harmony_await_optimization_flag())));
 

test/mjsunit/regress/regress-892858.js

+// Copyright 2018 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+async function foo() {
+  await Promise.resolve(42);
+}
+
+foo();