linux-kernel - Re: [PATCH 1/4] perf-probe: Avoid setting probes on same address on same event

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Date:   Fri, 10 Jul 2020 16:48:47 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
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>, linux-kernel@...r.kernel.org,
        Andi Kleen <andi@...stfloor.org>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/4] perf-probe: Avoid setting probes on same address on
 same event

* Masami Hiramatsu <mhiramat@...nel.org> [2020-07-09 17:07:01]:

> There is a case that the several same-name symbols points
> same address. In that case, perf probe returns an error.
> 
> E.g.
> 
> With this patch;
> 
>   # perf probe -x /lib64/libc-2.30.so -a "memcpy arg1=%di"
>   Failed to find the location of the '%di' variable at this address.
>    Perhaps it has been optimized out.
>    Use -V with the --range option to show '%di' location range.
>   Added new events:
>     probe_libc:memcpy    (on memcpy in /usr/lib64/libc-2.30.so with arg1=%di)
>     probe_libc:memcpy    (on memcpy in /usr/lib64/libc-2.30.so with arg1=%di)
> 
>   You can now use it in all perf tools, such as:
> 
>   	perf record -e probe_libc:memcpy -aR sleep 1
> 
> 
> Reported-by: Andi Kleen <andi@...stfloor.org>
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>

One small nit:

> ---
>  tools/perf/util/probe-event.c |    9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index df713a5d1e26..1e95a336862c 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -2968,6 +2968,15 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
>  	for (j = 0; j < num_matched_functions; j++) {
>  		sym = syms[j];
> 
> +		/* There can be duplicated symbols in the map */
> +		for (i = 0; i < j; i++)
> +			if (sym->start == syms[i]->start) {
> +				pr_debug("find duplicated symbol %s @ %lx\n", sym->name, sym->start);
	
Would "Found" sound better than "find"?

> +				break;
> +			}
> +		if (i != j)
> +			continue;
> +

Reviewed-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>


>  		tev = (*tevs) + ret;
>  		tp = &tev->point;
>  		if (ret == num_matched_functions) {
> 

-- 
Thanks and Regards
Srikar Dronamraju