Killbits is the one I&#x27;ve heard most commonly - as the talk says, most modern processors have a bunch because it&#x27;s impossible to test every possible edge case a priori.<p>(Good recent examples include the AMD lockup bug that Matt Dillon found, and the nasty counter-example of the Intel Quark segfault bug, which can&#x27;t be worked around so easily because the Quark doesn&#x27;t have killbits. &quot;Oops.&quot;)