linux-kernel - Re: [PATCH] perf probe: Fix bug in perf probe with global variables

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Message-ID: <553C37A6.3090206@hitachi.com>
Date:	Sun, 26 Apr 2015 09:56:06 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	He Kuang <hekuang@...wei.com>
CC:	acme@...nel.org, a.p.zijlstra@...llo.nl, mingo@...hat.com,
	paulus@...ba.org, wangnan0@...wei.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf probe: Fix bug in perf probe with global variables

(2015/04/25 17:08), He Kuang wrote:
> There are missing curly braces which causes find_variable() return wrong
> value when probing with global variables.
> 
> This problem can be reproduced as following:
> 
>   $ perf probe -v --add='generic_perform_write global_variable_for_test'
>   ...
>   Try to find probe point from debuginfo.
>   Probe point found: generic_perform_write+0
>   Searching 'global_variable_for_test' variable in context.
>   An error occurred in debuginfo analysis (-2).
>     Error: Failed to add events. Reason: No such file or directory (Code: -2)
> 
> After this patch:
> 
>   $ perf probe -v --add='generic_perform_write global_variable_for_test'
>   ...
>   Converting variable global_variable_for_test into trace event.
>   global_variable_for_test type is int.
>   Found 1 probe_trace_events.
>   Opening /sys/kernel/debug/tracing/kprobe_events write=1
>   Added new event:
>   Writing event: p:probe/generic_perform_write _stext+1237464
>   global_variable_for_test=@...bal_variable_for_test+0:s32
>     probe:generic_perform_write (on generic_perform_write with
>     global_variable_for_test)
> 
>   You can now use it in all perf tools, such as:
> 
>       perf record -e probe:generic_perform_write -aR sleep 1

Oops, that's my fault! :(

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

Thank you!!

> 
> Signed-off-by: He Kuang <hekuang@...wei.com>
> ---
>  tools/perf/util/probe-finder.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index 44554c3..1c3cc07 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -578,10 +578,12 @@ static int find_variable(Dwarf_Die *sc_die, struct probe_finder *pf)
>  	/* Search child die for local variables and parameters. */
>  	if (!die_find_variable_at(sc_die, pf->pvar->var, pf->addr, &vr_die)) {
>  		/* Search again in global variables */
> -		if (!die_find_variable_at(&pf->cu_die, pf->pvar->var, 0, &vr_die))
> +		if (!die_find_variable_at(&pf->cu_die, pf->pvar->var,
> +						0, &vr_die)) {
>  			pr_warning("Failed to find '%s' in this function.\n",
>  				   pf->pvar->var);
>  			ret = -ENOENT;
> +		}
>  	}
>  	if (ret >= 0)
>  		ret = convert_variable(&vr_die, pf);
> 


-- 
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@...achi.com


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