Return probes

[Perry Cheng]

The systemtap script below fails but works if the return probe is omitted. 
  In general, I have not been able to get return probes to work regardless 
of what the return probe body is and ultimately I boiled it down to the 
following.  Once this scripts starts running, I can get it to crash by 
starting some processes (fork causes page fault for copy-on-write) by 
logging into the machine a few times.  I am using a  very recent version 
of stap  (version 0.5.13 built 2007-02-12) running on a 2.6.16 kernel 
modified with real-time enhancements (specifically 2.6.16-rtj12.11smp). Is 
there a known problem with return probes and are there workarounds?

probe kernel.function("__handle_mm_fault")
{
        doZero()
}

probe kernel.function("__handle_mm_fault").return
{
        doZero()
}

function doZero()
{
}



Perry