linux-kernel - Re: [BUGFIX PATCH 3/6] perf/probe: Fix to probe an inline function which has no entry pc

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Date:   Fri, 25 Oct 2019 11:39:10 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [BUGFIX PATCH 3/6] perf/probe: Fix to probe an inline function
 which has no entry pc

Em Fri, Oct 25, 2019 at 11:35:13AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Fri, Oct 25, 2019 at 05:46:43PM +0900, Masami Hiramatsu escreveu:
> > Fix perf probe to probe an inlne function which has no entry pc
> > or low pc but only has ranges attribute.
> > 
> > This seems very rare case, but I could find a few examples, as
> > same as probe_point_search_cb(), use die_entrypc() to get the
> > entry address in probe_point_inline_cb() too.
> > 
> > Without this patch,
> >   # tools/perf/perf probe -D __amd_put_nb_event_constraints
> >   Failed to get entry address of __amd_put_nb_event_constraints.
> >   Probe point '__amd_put_nb_event_constraints' not found.
> >     Error: Failed to add events.
> > 
> > With this patch,
> >   # tools/perf/perf probe -D __amd_put_nb_event_constraints
> >   p:probe/__amd_put_nb_event_constraints amd_put_event_constraints+43
> 
> Here I got it slightly different:
> 
> Before:
> 
>   [root@...co ~]# perf probe -D __amd_put_nb_event_constraints
>   Failed to get entry address of __amd_put_nb_event_constraints.
>   Probe point '__amd_put_nb_event_constraints' not found.
>     Error: Failed to add events.
>   [root@...co ~]#
> 
> After:
> 
>   [root@...co ~]# perf probe -D __amd_put_nb_event_constraints
>   p:probe/__amd_put_nb_event_constraints _text+33789
>   [root@...co ~]#
> 
> 
> ----
> 
> I'm now checking if this is because I applied patch 4/6 before 3/6

Nope, even then:

[root@...co ~]# perf probe -D __amd_put_nb_event_constraints
p:probe/__amd_put_nb_event_constraints _text+33789
[root@...co ~]# grep __amd_put_nb_event_constraints /proc/kallsyms
[root@...co ~]#

Ok, maybe this may help:

[root@...co ~]# perf probe -v -D __amd_put_nb_event_constraints |& grep vmlinux
Looking at the vmlinux_path (8 entries long)
Using /usr/lib/debug/lib/modules/5.2.18-200.fc30.x86_64/vmlinux for symbols
Open Debuginfo file: /usr/lib/debug/lib/modules/5.2.18-200.fc30.x86_64/vmlinux
[root@...co ~]#

[root@...co ~]# readelf -wi /usr/lib/debug/lib/modules/5.2.18-200.fc30.x86_64/vmlinux | grep __amd_put_nb_event_constraints -B1 -A7
 <1><192640>: Abbrev Number: 123 (DW_TAG_subprogram)
    <192641>   DW_AT_name        : (indirect string, offset: 0x299576): __amd_put_nb_event_constraints
    <192645>   DW_AT_decl_file   : 1
    <192646>   DW_AT_decl_line   : 361
    <192648>   DW_AT_decl_column : 13
    <192649>   DW_AT_prototyped  : 1
    <192649>   DW_AT_inline      : 1	(inlined)
    <19264a>   DW_AT_sibling     : <0x192700>
 <2><19264e>: Abbrev Number: 38 (DW_TAG_formal_parameter)
^C
[root@...co ~]#

Continuing to process the other patches...

- Arnaldo
  
> > Fixes: 4ea42b181434 ("perf: Add perf probe subcommand, a kprobe-event setup helper")
> > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> > ---
> >  tools/perf/util/probe-finder.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> > index 71633f55f045..2fa932bcf960 100644
> > --- a/tools/perf/util/probe-finder.c
> > +++ b/tools/perf/util/probe-finder.c
> > @@ -930,7 +930,7 @@ static int probe_point_inline_cb(Dwarf_Die *in_die, void *data)
> >  		ret = find_probe_point_lazy(in_die, pf);
> >  	else {
> >  		/* Get probe address */
> > -		if (dwarf_entrypc(in_die, &addr) != 0) {
> > +		if (die_entrypc(in_die, &addr) != 0) {
> >  			pr_warning("Failed to get entry address of %s.\n",
> >  				   dwarf_diename(in_die));
> >  			return -ENOENT;
> 
> -- 
> 
> - Arnaldo

-- 

- Arnaldo