[wasm] test deserialization when header is invalid

src/snapshot/code-serializer.cc

 // Copyright 2016 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.
 
 #include "src/snapshot/code-serializer.h"
 
 #include <memory>
 
 #include "src/code-stubs.h"
 #include "src/log.h"
@@ skipping 397 matching lines @@
   DisallowHeapAllocation no_gc;
   SerializedCodeData scd(cached_data);
   *rejection_result = scd.SanityCheck(isolate, expected_source_hash);
   if (*rejection_result != CHECK_SUCCESS) {
     cached_data->Reject();
     return SerializedCodeData(nullptr, 0);
   }
   return scd;
 }
 
+void SerializedCodeData::InvalidateVersionForTest(byte* buffer,

[Yang, 2016/10/13 06:52:59]

I'm not really happy with introducing test APIs. Can we either extend
SerializedCodeData in test-run-wasm-module.cc to include a test method, or
simply flip some bits in the first bytes in the serialized data?

[Mircea Trofin, 2016/10/13 16:09:10]

The former is more complicated, because the field definitions
(kVersionHashOffset, etc) are private. I'd rather make those public, together
with the general-purpose SetHeaderValueInBuffer static method I just added.
Feels more appropriate for the scope of the change.

Simply flipping the bits - directly - was what I originally did, but received
pushback in the previous review :)

+                                                  size_t buffer_size) {
+  DCHECK_GE(buffer_size, static_cast<size_t>(kVersionHashOffset + kInt32Size));
+  uint32_t expected_version_hash = Version::Hash();
+  uint32_t invalid_version_hash = expected_version_hash + 1;
+  SerializedData::SetHeaderValueInBuffer(buffer, kVersionHashOffset,
+                                         invalid_version_hash);
+}
+
 }  // namespace internal
 }  // namespace v8