title: gdb: how to set break point at main function or _start, when there's no debug info?
body: <p>In release version, when debugging, sometimes there's no debug information files, in this case, there's no convenient way to <code>b main</code> to start at main function. </p>
  
  <p>So how can I let gdb break at the entry of the program, either the <code>_start</code> entry point or the C style <code>main</code> function?</p>