linux-kernel - Re: [PATCH -tip 2/4] perf probe: Fix to use symtab only if no debuginfo

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Date:	Mon, 26 Apr 2010 09:48:15 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, lkml <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <efault@....de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>
Subject: Re: [PATCH -tip 2/4] perf probe: Fix to use symtab only if no
	debuginfo

Em Wed, Apr 21, 2010 at 03:56:24PM -0400, Masami Hiramatsu escreveu:
> Fix perf probe to use symtab only if there is no debuginfo,
> because debuginfo has more precise information than symtab.

"more precise"? Wouldn't it be "more expressive", i.e. with more
information (parameter list with types, return type, location of
parameters, etc), because what is common to both have the same value,
i.e. the function address and size.

> If we can't find a function in debuginfo, we never find it
> in symtab.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
> Reported-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Mike Galbraith <efault@....de>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> ---
> 
>  tools/perf/util/probe-event.c |   17 +++++++++--------
>  1 files changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 4fb4803..5d3baec 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -180,15 +180,16 @@ static int try_to_find_kprobe_trace_events(struct perf_probe_event *pev,
>  		return -ENOENT;
>  	}
>  	/* Error path : ntevs < 0 */
> -	if (need_dwarf) {
> -		if (ntevs == -EBADF)
> -			pr_warning("No dwarf info found in the vmlinux - "
> -				"please rebuild with CONFIG_DEBUG_INFO=y.\n");
> -		return ntevs;
> +	pr_debug("An error occurred in debuginfo analysis (%d).\n", ntevs);
> +	if (ntevs == -EBADF) {
> +		pr_warning("Warning: No dwarf info found in the vmlinux - "
> +			"please rebuild kernel with CONFIG_DEBUG_INFO=y.\n");
> +		if (!need_dwarf) {
> +			pr_debug("Trying to use symbols.\nn");
> +			return 0;
> +		}
>  	}
> -	pr_debug("An error occurred in debuginfo analysis."
> -		 " Try to use symbols.\n");
> -	return 0;
> +	return ntevs;
>  }
>  
>  #define LINEBUF_SIZE 256
> 
> 
> -- 
> Masami Hiramatsu
> e-mail: mhiramat@...hat.com
--
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