title: x86 assembly: How does the 'subl' command work in AT&T syntax
body: <p><code>%edx</code> has a value of <code>0x3</code>, and <code>%eax</code> has a value of <code>0x100</code>.
  Then we have the instruction: <code>subl %edx, %eax</code>
  What's the result value of <code>%eax</code>?</p>