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

src/platform-cygwin.cc

 // Copyright 2006-2011 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 191 matching lines @@
   virtual void* memory() { return memory_; }
   virtual int size() { return size_; }
  private:
   FILE* file_;
   void* memory_;
   int size_;
 };
 
 
 OS::MemoryMappedFile* OS::MemoryMappedFile::open(const char* name) {
-  FILE* file = fopen(name, "w+");
+  FILE* file = fopen(name, "a+");
   if (file == NULL) return NULL;
 
   fseek(file, 0, SEEK_END);
   int size = ftell(file);
 
   void* memory =
       mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, fileno(file), 0);
   return new PosixMemoryMappedFile(file, memory, size);
 }
 
@@ skipping 513 matching lines @@
   // Release the thread handles
   CloseHandle(data_->sampler_thread_);
   CloseHandle(data_->profiled_thread_);
 }
 
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal