static size_t get_dump_directory() {
  const char* dump_path = JfrEmergencyDump::get_dump_path();
  if (*dump_path == '\0') {
    if (os::get_current_directory(_path_buffer, sizeof(_path_buffer)) == NULL) {
      return 0;
    }
  } else {
    strcpy(_path_buffer, dump_path);
  }
  const size_t path_len = strlen(_path_buffer);
  const int result = jio_snprintf(_path_buffer + path_len,
                                  sizeof(_path_buffer),
                                  "%s",
                                  os::file_separator());
  return (result == -1) ? 0 : strlen(_path_buffer);
}

Since the start address of the char buffer passing to jio_snprintf is offset by path_len, the length of the buffer (second arg to jio_snprintf) should be adjusted according.