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

Masami Hiramatsu
2017-01-10T14:17:19Z

On Tue, 10 Jan 2017 10:18:35 -0300
Arnaldo Carvalho de Melo <acme@kernel.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@jouet ~]# 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@jouet ~]# 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@intel/e1000e/80003es2lan.c in e1000e)
> [root@jouet ~]#
>
> 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@jouet ~]#
>
> - 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@mm/mmap.c)
> > probe:chv_prepare_pll (on intel_plane_atomic_get_property+16@drm/i915/intel_atomic_plane.c in i915)
> > probe_perf:alias_lookup (on alias_lookup@util/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@mm/mmap.c)
> > probe:chv_prepare_pll (on chv_prepare_pll@gpu/drm/i915/intel_display.c in i915)
> > probe_perf:alias_lookup (on alias_lookup@util/alias.c in /home/mhiramat/ksrc/linux/tools/perf/perf)
> >
> > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.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@kernel.org>