Bug: OS::MemoryMappedFile::open() should not truncate a pre-existing file.

src/platform-win32.cc

 // Copyright 2006-2008 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 920 matching lines @@
   HANDLE file_;
   HANDLE file_mapping_;
   void* memory_;
   int size_;
 };
 
 
 OS::MemoryMappedFile* OS::MemoryMappedFile::open(const char* name) {
   // Open a physical file
   HANDLE file = CreateFileA(name, GENERIC_READ | GENERIC_WRITE,
-      FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, 0, NULL);
+      FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_ALWAYS, 0, NULL);
   if (file == NULL) return NULL;
 
   int size = static_cast<int>(GetFileSize(file, NULL));
 
   // Create a file mapping for the physical file
   HANDLE file_mapping = CreateFileMapping(file, NULL,
       PAGE_READWRITE, 0, static_cast<DWORD>(size), NULL);
   if (file_mapping == NULL) return NULL;
 
   // Map a view of the file into memory
@@ skipping 1013 matching lines @@
 
   // Release the thread handles
   CloseHandle(data_->sampler_thread_);
   CloseHandle(data_->profiled_thread_);
 }
 
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal