[serializer] add test case for unknown external references.

src/snapshot/serializer-common.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/serializer-common.h"
 
 #include "src/external-reference-table.h"
 #include "src/ic/stub-cache.h"
 #include "src/list-inl.h"
 
+#if defined(DEBUG) && defined(V8_OS_LINUX)
+#include <execinfo.h>
+#endif  // DEBUG && V8_OS_LINUX
+
 namespace v8 {
 namespace internal {
 
 ExternalReferenceEncoder::ExternalReferenceEncoder(Isolate* isolate) {
   map_ = isolate->external_reference_map();
   if (map_ != NULL) return;
   map_ = new base::HashMap();
   ExternalReferenceTable* table = ExternalReferenceTable::instance(isolate);
   for (int i = 0; i < table->size(); ++i) {
     Address addr = table->address(i);
     if (addr == ExternalReferenceTable::NotAvailable()) continue;
     // We expect no duplicate external references entries in the table.
     // AccessorRefTable getter may have duplicates, indicated by an empty string
     // as name.
     DCHECK(table->name(i)[0] == '\0' ||
            map_->Lookup(addr, Hash(addr)) == nullptr);
     map_->LookupOrInsert(addr, Hash(addr))->value = reinterpret_cast<void*>(i);
   }
   isolate->set_external_reference_map(map_);
 }
 
 uint32_t ExternalReferenceEncoder::Encode(Address address) const {
   DCHECK_NOT_NULL(address);
   base::HashMap::Entry* entry =
       const_cast<base::HashMap*>(map_)->Lookup(address, Hash(address));
-  DCHECK_NOT_NULL(entry);
+  if (entry == nullptr) {
+    void* function_addr = address;
+    v8::base::OS::PrintError("Unknown external reference %p.\n", function_addr);
+#if defined(DEBUG) && defined(V8_OS_LINUX)
+    v8::base::OS::PrintError("%s\n", backtrace_symbols(&function_addr, 1)[0]);
+#endif  // DEBUG && V8_OS_LINUX
+    v8::base::OS::Abort();
+  }
   return static_cast<uint32_t>(reinterpret_cast<intptr_t>(entry->value));
 }
 
 const char* ExternalReferenceEncoder::NameOfAddress(Isolate* isolate,
                                                     Address address) const {
   base::HashMap::Entry* entry =
       const_cast<base::HashMap*>(map_)->Lookup(address, Hash(address));
   if (entry == NULL) return "<unknown>";
   uint32_t i = static_cast<uint32_t>(reinterpret_cast<intptr_t>(entry->value));
   return ExternalReferenceTable::instance(isolate)->name(i);
@@ skipping 24 matching lines @@
     if (cache->at(i)->IsUndefined(isolate)) break;
   }
 }
 
 bool SerializerDeserializer::CanBeDeferred(HeapObject* o) {
   return !o->IsString() && !o->IsScript();
 }
 
 }  // namespace internal
 }  // namespace v8