title: Questions on libc's pointer encryption
body: <p><code>glibc</code> and <code>eglibc</code> have a <code>PTR_MANGLE</code>, which encrypts pointers in writable memory (more correctly, 'XOR' rather than 'encrypt').</p>
  
  <p>I'm not finding much reading on the feature. <code>man -k PTR_MANGLE</code> returns no hits, and Google is returning some superficial chatter. One of the few definitive articles is Drepper's <a href="http://udrepper.livejournal.com/13393.html" rel="noreferrer">Pointer Encryption</a> on Live Journal.</p>
  
  <p>Is there any in-depth documentation on it? Can it be extended into the user space process, or is it limited to the runtime library? If so, what is the compiler switch or option to enable the feature? Can the feature be disabled in the runtime?</p>