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 10:18:35 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Masami Hiramatsu <mhiramat@...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

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?

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;