linux-kernel - Re: [PATCH -tip/urgent ] [BUGFIX] perf/probe: Fix a segfault if asked for variable it doesn't find

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Message-ID: <538713F1.6000801@hitachi.com>
Date:	Thu, 29 May 2014 20:03:13 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH -tip/urgent ] [BUGFIX] perf/probe: Fix a segfault if asked
 for variable it doesn't find

Arnaldo, this fixes the SEGV bug which you reported.

But I've found that perf probe sometimes loses the location of variables
with recent DWARF implementation. I need to check and fix that too.

Anyway, this patch should be applied for fixing critical bug.

Thank you,

(2014/05/29 19:52), Masami Hiramatsu wrote:
> Fix a segfault bug by asking for variable it doesn't find.
> Since the convert_variable() didn't handle error code returned
> from convert_variable_location(), it just passed an incomplete
> variable field and then a segfault was occured when formatting
> the field.
> 
> This fixes that bug by handling success code correctly in
> convert_variable(). Other callers of convert_variable_location()
> are correctly checking the return code.
> 
> This bug was introduced by following commit. But another hidden
> erroneous error handling has been there previuosly (-ENOMEM case).
> 
>  commit 3d918a12a1b3088ac16ff37fa52760639d6e2403
> 
> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Reported-by: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Jiri Olsa <jolsa@...hat.com>
> ---
>  tools/perf/util/probe-finder.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index 5627621..9d8eb26 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -511,12 +511,12 @@ static int convert_variable(Dwarf_Die *vr_die, struct probe_finder *pf)
>  
>  	ret = convert_variable_location(vr_die, pf->addr, pf->fb_ops,
>  					&pf->sp_die, pf->tvar);
> -	if (ret == -ENOENT)
> +	if (ret == -ENOENT || ret == -EINVAL)
>  		pr_err("Failed to find the location of %s at this address.\n"
>  		       " Perhaps, it has been optimized out.\n", pf->pvar->var);
>  	else if (ret == -ENOTSUP)
>  		pr_err("Sorry, we don't support this variable location yet.\n");
> -	else if (pf->pvar->field) {
> +	else if (ret == 0 && pf->pvar->field) {
>  		ret = convert_variable_fields(vr_die, pf->pvar->var,
>  					      pf->pvar->field, &pf->tvar->ref,
>  					      &die_mem);
> 
> 
> 
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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