linux-kernel - Re: [PATCH -tip 4/5] [BUGFIX] perf probe: Fix the order of searching scopes for variables

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Date:	Sun, 10 Jul 2011 14:05:56 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, yrl.pp-manager.tt@...achi.com,
	Masami Hiramatsu <masami.hiramatsu@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH -tip 4/5] [BUGFIX] perf probe: Fix the order of searching
 scopes for variables

On Sun, Jul 10, 2011 at 1:00 PM, Masami Hiramatsu
<masami.hiramatsu.pt@...achi.com> wrote:
> Fix variable searching routine to search from inner scope
> to outer scope.

Admittedly, I don't really know this code at all. However, the
changelog is somewhat vague. Why do we need this change? What problem
does it fix? Why does the order in which we iterate 'scopes' matter?

> Signed-off-by: Masami Hiramatsu <masami.hiramatsu@...il.com>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
> ---
>
>  tools/perf/util/probe-finder.c |   14 +++++++-------
>  1 files changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index 222ba66..cf7d48d 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -1135,7 +1135,7 @@ static int find_variable(Dwarf_Die *sp_die, struct probe_finder *pf)
>  {
>        Dwarf_Die vr_die, *scopes;
>        char buf[32], *ptr;
> -       int ret, nscopes;
> +       int ret, nscopes, i;
>
>        if (!is_c_varname(pf->pvar->var)) {
>                /* Copy raw parameters */
> @@ -1179,11 +1179,11 @@ static int find_variable(Dwarf_Die *sp_die, struct probe_finder *pf)
>                /* Search upper class */
>                nscopes = dwarf_getscopes_die(sp_die, &scopes);
>                ret = -ENOENT;
> -               while (nscopes-- > 1) {
> +               for (i = 1; i < nscopes; i++) { /* scopes[0] is sp_die */
>                        pr_debug("Searching variables in %s\n",
> -                                dwarf_diename(&scopes[nscopes]));
> +                                dwarf_diename(&scopes[i]));
>                        /* We should check this scope, so give dummy address */
> -                       if (die_find_variable_at(&scopes[nscopes],
> +                       if (die_find_variable_at(&scopes[i],
>                                                 pf->pvar->var, 0,
>                                                 &vr_die)) {
>                                ret = convert_variable(&vr_die, pf);
> @@ -1693,7 +1693,7 @@ static int add_available_vars(Dwarf_Die *sp_die, struct probe_finder *pf)
>                        container_of(pf, struct available_var_finder, pf);
>        struct variable_list *vl;
>        Dwarf_Die die_mem, *scopes = NULL;
> -       int ret, nscopes;
> +       int ret, nscopes, i;
>
>        /* Check number of tevs */
>        if (af->nvls == af->max_vls) {
> @@ -1723,8 +1723,8 @@ static int add_available_vars(Dwarf_Die *sp_die, struct probe_finder *pf)
>        /* Don't need to search child DIE for externs. */
>        af->child = false;
>        nscopes = dwarf_getscopes_die(sp_die, &scopes);
> -       while (nscopes-- > 1)
> -               die_find_child(&scopes[nscopes], collect_variables_cb,
> +       for (i = 1; i < nscopes; i++)   /* scopes[0] is sp_die */
> +               die_find_child(&scopes[i], collect_variables_cb,
>                               (void *)af, &die_mem);
>        if (scopes)
>                free(scopes);
>
> --
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