Em Thu, Oct 30, 2014 at 09:16:36PM -0400, Vince Weaver escreveu: > On Thu, 30 Oct 2014, Peter Zijlstra wrote: > > > So would something simple, like an offset into the struct > > perf_event_attr pointing at the current field we're trying to process > > make sense? Maybe with negative offsets to indicate the syscall > > arguments? > > > > That would narrow down the 'WTF is wrong noaw' a lot I think. But then, > > I've not actually done a lot of userspace the last few years, so maybe > > I'm just dreaming things. > > well, as someone who spends a lot of time in userspace trying to help > people who report probems like 'perf_event_open() returns EINVAL, what's > wrong' I can say pretty much anything will be an improvement. > > What would really help is if we could somehow return the > filename/line-number of whatever source code file that's setting errno. > > Even if perf_event_open() told me that hey, we're getting EOPNOTSUPP due > to the precise_ip parameter (something that happened just yesterday) it's > still a lot of grepping and poking around source files to find out what's > going on. It would be much better if it just told me the issue was at > kernel/events/core.c line 995 or so, but I'm not sure how you could pass > that back to the user, and one could argue it wouldn't help much the > average user without a kernel tree lying around.
But perhaps we can have a mode where we can say to perf to setup function tracing in the sys_perf_event_open() for the perf tool pid, that would output the lines leading to the return ERRNO. Or use 'perf probe' like stuff to insert/enable some kretprobes, both ideas need some prototyping and would require root privilege :-\ - Arnaldo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
