Probe on function entry rather than the end of the prolog (s390x only)

[Stone, Joshua I]

On Thursday, February 08, 2007 3:48 PM, David Wilder wrote:
> I would like to re-open this discussion.
> I have not had a chance to do any targeted testing of the correctness
> of location lists at function entry on the s390x. However, in other
> testing I have not seen any issues related to bad location info at
> the function entry. Setting the probe points at the end of the prolog
> may be problematic on the s390x for another reason. I am told that
> depending on the optimization level, finding the end of the prolog
> may be tricky as the prolog may be interspersed with other code. The
> method used today of finding the prolog by searching for the next
> line of C code after the function entry may not fly. These are
> clearly all bugs/issues with gcc and we should push for solutions
> from the gcc folks. But before that happens I believe the best
> solution for s390x is going to be placing our probe points at the
> function entry (only for s390x). 

If we can figure out in what cases the GCC info is reliable, then moving
probes to function entry will also help avoid this sort of problem:
http://sourceware.org/ml/systemtap/2006-q3/msg00065.html


Josh