title: What parts of ARMv4/5/6 code will not work on ARMv7?
body: <p>It is my understanding that ARMv7 processors, such as the Cortex-A9, are mostly backwards-compatible with code for older ARM architecture versions.  However, I've read reports of <a href="https://stackoverflow.com/questions/11268442/cortex-a8-binary-compatibility">segfaults trying to run ARM9 code on a Cortex-A8</a>, for example.</p>
  
  <p>What parts of ARMv4/5/6 (ARM7TDMI/ARM9/ARM11) code will not work on an ARMv7 processor?  What features or architectural characteristics exist in these older ARM architecture versions that can cause a program built for these versions to fail on ARMv7?</p>