SnapshotCreator: start from existing snapshot if we have one

test/cctest/wasm/test-run-wasm-module.cc

 // Copyright 2015 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 <stdlib.h>
 #include <string.h>
 
 #include "src/objects-inl.h"
 #include "src/snapshot/code-serializer.h"
 #include "src/version.h"
@@ skipping 219 matching lines @@
 
     builder->WriteTo(*buffer);
   }
 
   void ClearSerializedData() {
     serialized_bytes_.first = nullptr;
     serialized_bytes_.second = 0;
   }
 
   void InvalidateVersion() {
-    uint32_t* buffer = reinterpret_cast<uint32_t*>(
-        const_cast<uint8_t*>(serialized_bytes_.first));
-    buffer[SerializedCodeData::kVersionHashOffset] = Version::Hash() + 1;
+    uint32_t* slot = reinterpret_cast<uint32_t*>(
+        const_cast<uint8_t*>(serialized_bytes_.first) +
+        SerializedCodeData::kVersionHashOffset);
+    *slot = Version::Hash() + 1;
   }
 
   void InvalidateWireBytes() {
     memset(const_cast<uint8_t*>(wire_bytes_.first), '\0',
            wire_bytes_.second / 2);
   }
 
+  void InvalidateLength() {
+    uint32_t* slot = reinterpret_cast<uint32_t*>(
+        const_cast<uint8_t*>(serialized_bytes_.first) +
+        SerializedCodeData::kPayloadLengthOffset);
+    *slot = 0xfefefefeu;
+  }
+
   v8::MaybeLocal<v8::WasmCompiledModule> Deserialize() {
     ErrorThrower thrower(current_isolate(), "");
     v8::MaybeLocal<v8::WasmCompiledModule> deserialized =
         v8::WasmCompiledModule::DeserializeOrCompile(
             current_isolate_v8(), serialized_bytes(), wire_bytes());
     return deserialized;
   }
 
   void DeserializeAndRun() {
     ErrorThrower thrower(current_isolate(), "");
@@ skipping 139 matching lines @@
   WasmSerializationTest test;
   {
     HandleScope scope(test.current_isolate());
     test.ClearSerializedData();
     test.DeserializeAndRun();
   }
   Cleanup(test.current_isolate());
   Cleanup();
 }
 
+TEST(DeserializeInvalidLength) {
+  WasmSerializationTest test;
+  {
+    HandleScope scope(test.current_isolate());
+    test.InvalidateLength();
+    test.DeserializeAndRun();
+  }
+  Cleanup(test.current_isolate());
+  Cleanup();
+}
+
 TEST(DeserializeWireBytesAndSerializedDataInvalid) {
   WasmSerializationTest test;
   {
     HandleScope scope(test.current_isolate());
     test.InvalidateVersion();
     test.InvalidateWireBytes();
     test.Deserialize();
   }
   Cleanup(test.current_isolate());
   Cleanup();
@@ skipping 529 matching lines @@
     };
 
     testing::CompileInstantiateWasmModuleForTesting(isolate, &thrower, data,
                                                     data + arraysize(data),
                                                     ModuleOrigin::kWasmOrigin);
     // It should not be possible to instantiate this module.
     CHECK(thrower.error());
   }
   Cleanup();
 }