[wasm] test deserialization when header is invalid

src/snapshot/code-serializer.cc

Index: src/snapshot/code-serializer.cc
diff --git a/src/snapshot/code-serializer.cc b/src/snapshot/code-serializer.cc
index 9712d79e19ed27c214112d4476bd9d256ddb3347..e0e0eb61609564d11bd2721ea17f093315cfb597 100644
--- a/src/snapshot/code-serializer.cc
+++ b/src/snapshot/code-serializer.cc
@@ -415,5 +415,14 @@ const SerializedCodeData SerializedCodeData::FromCachedData(
   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