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

Arnaldo Carvalho de Melo
2017-01-10T13:18:44Z

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?

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;