Make snapshots reproducible.

src/serialize.cc

 // Copyright 2012 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
@@ skipping 1758 matching lines @@
         return;
       }
     }
   }
   // One of the strings in the natives cache should match the resource.  We
   // can't serialize any other kinds of external strings.
   UNREACHABLE();
 }
 
 
+static Code* CloneCodeObject(HeapObject* code) {
+  Address copy = new byte[code->Size()];
+  OS::MemCopy(copy, code->address(), code->Size());
+  return Code::cast(HeapObject::FromAddress(copy));
+}
+
+
+static void WipeOutCodeHeader(Code* code) {
+  code->set_relocation_info(

[Benedikt Meurer, 2013/11/04 11:25:14]

Nit: Can we do better here?

+      reinterpret_cast<ByteArray*>(Smi::FromInt(0)), SKIP_WRITE_BARRIER);
+  code->set_handler_table(
+      reinterpret_cast<FixedArray*>(Smi::FromInt(0)), SKIP_WRITE_BARRIER);
+  code->set_deoptimization_data(
+      reinterpret_cast<FixedArray*>(Smi::FromInt(0)), SKIP_WRITE_BARRIER);
+  // Do not wipe out e.g. a minor key.
+  if (!code->raw_type_feedback_info()->IsSmi()) {
+    code->InitializeTypeFeedbackInfoNoWriteBarrier(Smi::FromInt(0));
+  }
+}
+
+
+static void WipeOutRelocations(Code* code) {
+  int mode_mask =
+      RelocInfo::kCodeTargetMask |
+      RelocInfo::ModeMask(RelocInfo::EMBEDDED_OBJECT) |
+      RelocInfo::ModeMask(RelocInfo::EXTERNAL_REFERENCE) |
+      RelocInfo::ModeMask(RelocInfo::RUNTIME_ENTRY);
+  for (RelocIterator it(code, mode_mask); !it.done(); it.next()) {
+    it.rinfo()->WipeOut();
+  }
+}
+
+
 int Serializer::ObjectSerializer::OutputRawData(
     Address up_to, Serializer::ObjectSerializer::ReturnSkip return_skip) {
   Address object_start = object_->address();
-  Address base = object_start + bytes_processed_so_far_;
+  int base = bytes_processed_so_far_;
   int up_to_offset = static_cast<int>(up_to - object_start);
   int to_skip = up_to_offset - bytes_processed_so_far_;
   int bytes_to_output = to_skip;
   bytes_processed_so_far_ +=  to_skip;
   // This assert will fail if the reloc info gives us the target_address_address
   // locations in a non-ascending order.  Luckily that doesn't happen.
   ASSERT(to_skip >= 0);
   bool outputting_code = false;
   if (to_skip != 0 && code_object_ && !code_has_been_output_) {
     // Output the code all at once and fix later.
     bytes_to_output = object_->Size() + to_skip - bytes_processed_so_far_;
     outputting_code = true;
     code_has_been_output_ = true;
   }
   if (bytes_to_output != 0 &&
       (!code_object_ || outputting_code)) {
 #define RAW_CASE(index)                                                        \
     if (!outputting_code && bytes_to_output == index * kPointerSize &&         \
         index * kPointerSize == to_skip) {                                     \
       sink_->PutSection(kRawData + index, "RawDataFixed");                     \
       to_skip = 0;  /* This insn already skips. */                             \
     } else  /* NOLINT */
     COMMON_RAW_LENGTHS(RAW_CASE)
 #undef RAW_CASE
     {  /* NOLINT */
       // We always end up here if we are outputting the code of a code object.
       sink_->Put(kRawData, "RawData");
       sink_->PutInt(bytes_to_output, "length");
     }
+
+    // To make snapshots reproducible, we need to wipe out all pointers in code.
+    if (code_object_) {
+      Code* code = CloneCodeObject(object_);
+      WipeOutRelocations(code);
+      // We need to wipe out the header fields *after* wiping out the
+      // relocations, because some of these fields are needed for the latter.
+      WipeOutCodeHeader(code);
+      object_start = code->address();
+    }
+
+    const char* description = code_object_ ? "Code" : "Byte";
     for (int i = 0; i < bytes_to_output; i++) {
-      unsigned int data = base[i];
-      sink_->PutSection(data, "Byte");
+      sink_->PutSection(object_start[base + i], description);
     }
+    if (code_object_) delete[] object_start;
   }
   if (to_skip != 0 && return_skip == kIgnoringReturn) {
     sink_->Put(kSkip, "Skip");
     sink_->PutInt(to_skip, "SkipDistance");
     to_skip = 0;
   }
   return to_skip;
 }
 
 
@@ skipping 38 matching lines @@
 
 bool SnapshotByteSource::AtEOF() {
   if (0u + length_ - position_ > 2 * sizeof(uint32_t)) return false;
   for (int x = position_; x < length_; x++) {
     if (data_[x] != SerializerDeserializer::nop()) return false;
   }
   return true;
 }
 
 } }  // namespace v8::internal