Only mark checksummed memory as initialized for MSAN.

src/snapshot/serialize.cc

 // Copyright 2012 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/v8.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/base/platform/platform.h"
 #include "src/bootstrapper.h"
@@ skipping 2110 matching lines @@
       to_skip = 0;  // This instruction includes skip.
     } else {
       // We always end up here if we are outputting the code of a code object.
       sink_->Put(kVariableRawData, "VariableRawData");
       sink_->PutInt(bytes_to_output, "length");
     }
 
     if (is_code_object_) object_start = PrepareCode();
 
     const char* description = is_code_object_ ? "Code" : "Byte";
-#ifdef MEMORY_SANITIZER
-    // Object sizes are usually rounded up with uninitialized padding space.
-    MSAN_MEMORY_IS_INITIALIZED(object_start + base, bytes_to_output);
-#endif  // MEMORY_SANITIZER
     sink_->PutRaw(object_start + base, bytes_to_output, description);
   }
   if (to_skip != 0 && return_skip == kIgnoringReturn) {
     sink_->Put(kSkip, "Skip");
     sink_->PutInt(to_skip, "SkipDistance");
     to_skip = 0;
   }
   return to_skip;
 }
 
@@ skipping 366 matching lines @@
   const byte* payload = data_ + kHeaderSize + reservations_size;
   int length = GetHeaderValue(kPayloadLengthOffset);
   DCHECK_EQ(data_ + size_, payload + length);
   return Vector<const byte>(payload, length);
 }
 
 
 class Checksum {
  public:
   explicit Checksum(Vector<const byte> payload) {
+#ifdef MEMORY_SANITIZER
+    // Computing the checksum includes padding bytes for objects like strings.
+    // Mark every object as initialized in the code serializer.
+    MSAN_MEMORY_IS_INITIALIZED(payload.start(), payload.length());
+#endif  // MEMORY_SANITIZER
     // Fletcher's checksum. Modified to reduce 64-bit sums to 32-bit.
     uintptr_t a = 1;
     uintptr_t b = 0;
     const uintptr_t* cur = reinterpret_cast<const uintptr_t*>(payload.start());
     DCHECK(IsAligned(payload.length(), kIntptrSize));
     const uintptr_t* end = cur + payload.length() / kIntptrSize;
     while (cur < end) {
       // Unsigned overflow expected and intended.
       a += *cur++;
       b += a;
@@ skipping 146 matching lines @@
   SerializedCodeData* scd = new SerializedCodeData(cached_data);
   SanityCheckResult r = scd->SanityCheck(isolate, source);
   if (r == CHECK_SUCCESS) return scd;
   cached_data->Reject();
   source->GetIsolate()->counters()->code_cache_reject_reason()->AddSample(r);
   delete scd;
   return NULL;
 }
 }  // namespace internal
 }  // namespace v8