usr.sbin/pmcstat: return non-zero if the launched command fails

[arichardson]

Summary

Previously pmcstat would return a success return code even if the process
that it launched crashed or returned a failure code. Returning a non-zero
exit code means that we can more easily detect if a benchmark did not
run as expected even when running it under pmcstat.

While it might make sense to propagate the exit code/signal via pmcstat,
I believe returning EX_IOERR if the child process fails should
be sufficient.

[arichardson]

drop unnecessary line

[emaste]

While it might make sense to propagate the exit code/signal via pmcstat, I believe returning EX_IOERR if the child process fails should be sufficient.

I think it probably does; it looks like that's what ktrace does, for instance. Do you know what Linux perf does?

I don't object if you think this is best; I think returning EX_IOERR is better than EX_OK if the child reports failure anyhow.

[arichardson]

In D36953#839355, @emaste wrote:

While it might make sense to propagate the exit code/signal via pmcstat, I believe returning EX_IOERR if the child process fails should be sufficient.

I think it probably does; it looks like that's what ktrace does, for instance. Do you know what Linux perf does?

I don't object if you think this is best; I think returning EX_IOERR is better than EX_OK if the child reports failure anyhow.

It looks like perf stat passes through the exit code, so I'll do the same here.

[emaste]

@arichardson plans to change this to return the child's exit code