linux-kernel - Re: [PATCH perf/core 1/4] perf-probe: Fix to show correct locations for events on modules

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Date:   Tue, 10 Jan 2017 23:15:35 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH perf/core 1/4] perf-probe: Fix to show correct locations
 for events on modules

On Tue, 10 Jan 2017 10:18:35 -0300
Arnaldo Carvalho de Melo <acme@...nel.org> wrote:

> Em Sat, Jan 07, 2017 at 02:25:09PM +0900, Masami Hiramatsu escreveu:
> > Fix to show correct locations for events on modules by
> > relocating given address. Currently the relocation is
> > done when we failed to find the address in debuginfo,
> > but for modules it always makes a mistakes.
> 
> Try to provide precise instructions on how to reproduce, for instance,
> here I'm not being able to reproduce:
> 
> [root@...et ~]# perf probe -m i915 chv_prepare_pll
> Added new event:
>   probe:chv_prepare_pll (on chv_prepare_pll in i915)
> 
> You can now use it in all perf tools, such as:
> 
> 	perf record -e probe:chv_prepare_pll -aR sleep 1
> 
> [root@...et ~]# perf probe -l
>   probe:chv_prepare_pll (on chv_prepare_pll in i915)
>   probe:e1000_xmit_frame (on e1000_get_link_up_info_80003es2lan:7@...el/e1000e/80003es2lan.c in e1000e)
> [root@...et ~]#
> 
> So it doesn't seem to "always make mistakes", what are the precise
> conditions to reproduce this problem?

Hmm, OK, I also found same issue. I'll recheck that...

Thank you,

> 
> Running with 'perf probe -vv -m i915 chv_prepare_pll' to get more
> debugging info:
> 
> Failed to get build-id from i915.
> Cache open error: -1
> Open Debuginfo file: /lib/modules/4.9.0+/kernel/drivers/gpu/drm/i915/i915.ko
> Try to find probe point from debuginfo.
> Matched function: chv_prepare_pll [6ce853]
> found inline addr: 0x883a0
> Probe point found: chv_prepare_pll+0
> Found 1 probe_trace_events.
> Opening /sys/kernel/debug/tracing//kprobe_events write=1
> Writing event: p:probe/chv_prepare_pll i915:chv_prepare_pll+0
> Added new event:
>   probe:chv_prepare_pll (on chv_prepare_pll in i915)
> 
> You can now use it in all perf tools, such as:
> 
> 	perf record -e probe:chv_prepare_pll -aR sleep 1
> 
> [root@...et ~]#
> 
> - Arnaldo
>  
> > E.g. without this fix, events on module seems wrong,
> > but other cases (kernel and user space) looks good.
> > 
> >   # perf probe -l
> >     probe:SyS_remap_file_pages (on SyS_remap_file_pages@...mmap.c)
> >     probe:chv_prepare_pll (on intel_plane_atomic_get_property+16@.../i915/intel_atomic_plane.c in i915)
> >     probe_perf:alias_lookup (on alias_lookup@...l/alias.c in /home/mhiramat/ksrc/linux/tools/perf/perf)
> > 
> > With this fix, all cases are OK now.
> > 
> >   # perf probe -l
> >     probe:SyS_remap_file_pages (on SyS_remap_file_pages@...mmap.c)
> >     probe:chv_prepare_pll (on chv_prepare_pll@.../drm/i915/intel_display.c in i915)
> >     probe_perf:alias_lookup (on alias_lookup@...l/alias.c in /home/mhiramat/ksrc/linux/tools/perf/perf)
> > 
> > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> > ---
> >  tools/perf/util/probe-finder.c |   10 +++-------
> >  1 file changed, 3 insertions(+), 7 deletions(-)
> > 
> > diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> > index df4debe..0278fe1 100644
> > --- a/tools/perf/util/probe-finder.c
> > +++ b/tools/perf/util/probe-finder.c
> > @@ -1543,16 +1543,12 @@ int debuginfo__find_probe_point(struct debuginfo *dbg, unsigned long addr,
> >  	Dwarf_Addr _addr = 0, baseaddr = 0;
> >  	const char *fname = NULL, *func = NULL, *basefunc = NULL, *tmp;
> >  	int baseline = 0, lineno = 0, ret = 0;
> > -	bool reloc = false;
> >  
> > -retry:
> > +	/* We always need to relocate the address for aranges */
> > +	if (debuginfo__get_text_offset(dbg, &baseaddr) == 0)
> > +		addr += baseaddr;
> >  	/* Find cu die */
> >  	if (!dwarf_addrdie(dbg->dbg, (Dwarf_Addr)addr, &cudie)) {
> > -		if (!reloc && debuginfo__get_text_offset(dbg, &baseaddr) == 0) {
> > -			addr += baseaddr;
> > -			reloc = true;
> > -			goto retry;
> > -		}
> >  		pr_warning("Failed to find debug information for address %lx\n",
> >  			   addr);
> >  		ret = -EINVAL;


-- 
Masami Hiramatsu <mhiramat@...nel.org>