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

Masami Hiramatsu
2014-05-29T11:03:22Z

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@hitachi.com>
> Reported-by: Arnaldo Carvalho de Melo <acme@kernel.org>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Jiri Olsa <jolsa@redhat.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@hitachi.com