title: Privileged instructions, adding register values?
body: <p>I finished homework for a graduate course in operating systems. I got a great score and I only missed <em>one</em> tiny point of a question. It asked which were privileged instructions and which were not. I answered all correctly except one: Adding one register value to another</p>
  
  <p>I answered it was privileged but apparently it's not! How can this be? </p>
  
  <p>I figured the user interacts with registers/memory by using systems calls, which in a sense change from user mode system calls to kernel mode routines. Therefore the adding of one register value to another could be called by a non-privileged user, but in the end the kernel is doing the work and is in kernel, privileged mode. Therefore it's privileged? A user can't do it by themselves. Am I wrong? Why?! </p>
  
  <ul>
  <li>Thanks!</li>
  </ul>