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

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Date:   Thu, 9 Jul 2020 07:36:54 -0700
From:   Andi Kleen <andi@...stfloor.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.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

> 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",

I would say something like this.

Consider identifying the final function used at run time and set the
probe directly on that.

I think that's more useful to the user.

-Andi