linux-kernel - Re: [PATCH 4/4] perf-probe: Warn if the target function is GNU Indirect function

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Date:   Fri, 10 Jul 2020 21:14:22 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
        Andi Kleen <andi@...stfloor.org>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 4/4] perf-probe: Warn if the target function is GNU
 Indirect function

On Fri, 10 Jul 2020 16:45:12 +0530
Srikar Dronamraju <srikar@...ux.vnet.ibm.com> wrote:

> * Masami Hiramatsu <mhiramat@...nel.org> [2020-07-09 17:07:31]:
> 
> > Reported-by: Andi Kleen <andi@...stfloor.org>
> > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> > ---
> >  tools/perf/util/probe-event.c |    5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> > index 1e95a336862c..671176d39569 100644
> > --- a/tools/perf/util/probe-event.c
> > +++ b/tools/perf/util/probe-event.c
> > @@ -379,6 +379,11 @@ static int find_alternative_probe_point(struct debuginfo *dinfo,
> >  			address = sym->start;
> >  		else
> >  			address = map->unmap_ip(map, sym->start) - map->reloc;
> > +		if (sym->type == STT_GNU_IFUNC) {
> > +			pr_warning("Warning: The probe address (0x%lx) is in a GNU indirect function.\n"
> > +				"This may not work as you expected unless you intend to probe the indirect function.\n",
> > +				(unsigned long)address);
> > +		}
> 
> Are these GNU indirect functions possible in kernel? If not we could move
> this warning under if (uprobes)

OK, I'll move it under if (uprobes).

> 
> Also instead of printing the address, can we print the pp->function?

Hmm, OK. But it may not help user because the pp->function will the name
specified by user...

Thank you,


-- 
Masami Hiramatsu <mhiramat@...nel.org>