title: Why libc enter address always change in redhat 7
body: <p>I use <code>backtrace()</code> and <code>backtrace_symbols()</code> to get some information.
  outputs looks like:</p>
  
  <p>./a.out</p>
  
  <pre><code>....
      (_Z8fun+0x1d( [0x400bb3]
      /lib64/libpthread.so.0 (+0x7dc5) [**0x7f2cb2b99dc5**]
      /lib64/libc.so.6(clone+0x6d) [**0x7fc20a61cd**]
  ...
  </code></pre>
  
  <p>In redhat 7, the bolder addrs is always change between times,
  while in redhat 6, the addrs looks fixed.</p>