In src/share/vm/utilities/ostream.hpp there is a comparison that implicitly casts a size_t (GCLogFileSize) to a jlong (_bytes_written). On 32-bit platforms this will likely not work as expected if GCLogFileSize is set to a large (unsigned) number.

  bool should_rotate(bool force) {
    return force ||
             ((GCLogFileSize != 0) && ((size_t)_bytes_written >= GCLogFileSize));
  }