Re: [PATCH] perf probe: Fix failure to probe events on arm
From: He Kuang
Date: Wed Jun 17 2015 - 05:44:33 EST
hi, Masami
On 2015/6/17 16:52, Masami Hiramatsu wrote:
On 2015/06/17 0:26, hekuang wrote:
hi, Arnaldo
On 06/15/2015 10:49 PM, Arnaldo Carvalho de Melo wrote:
Em Mon, Jun 15, 2015 at 08:06:53AM +0000, He Kuang escreveu:
Fix failure to probe events on arm, problem is introduced by commit
5a51fcd1f30c ("perf probe: Skip kernel symbols which is out of
.text"). For some architectures, label '_etext' is not in the .text
section(in .notes section for arm/arm64). Label out of .text section is
not loaded as symbols and we got a zero value when look up its address,
which causes all events be wrongly skiped.
This patch uses kernel map->end when failed to get the address of
'_etext' and fixes the problem.
Masami, can't we always use map->end then? Can you please take a look at
this patch and ack/nack it?
- Arnaldo
I think _etext is more accurate than kernel map->end, because
__map_groups__fixup_end() is called at the end of
dso__load_sym(), which fixes map->end to next_map->start.
Comparative result as this:
etext_addr=ffffffff819a1b85, map->end=ffffffff81ff1000.
So if possible, we should use _etext.
Hmm, this seems to have another problem. If etext_addr != map->end,
we can't relay on that. Is there any good way to get the ".text"
address range from symbol map? Until we find it, I'd rather like to
skip checking text address range on arm, because it looks meaningless :(
OK. Maybe I thought using kernel map->end(always > _etext) is a way to
skip checking .text range on arm ..
Thank you,
Thanks.
Problem can be reproduced on arm as following:
# perf probe --add='generic_perform_write'
generic_perform_write+0 is out of .text, skip it.
Probe point 'generic_perform_write' not found.
Error: Failed to add events. Reason: No such file or directory (Code: -2)
After this patch:
# perf probe --add='generic_perform_write'
Added new event:
probe:generic_perform_write (on generic_perform_write)
You can now use it in all perf tools, such as:
perf record -e probe:generic_perform_write -aR sleep 1
Signed-off-by: He Kuang <hekuang@xxxxxxxxxx>
---
tools/perf/util/probe-event.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index daa24a2..ee26961 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -575,8 +575,22 @@ static int post_process_probe_trace_events(struct probe_trace_event *tevs,
pr_warning("Relocated base symbol is not found!\n");
return -EINVAL;
}
- /* Get the address of _etext for checking non-probable text symbol */
+ /* Get the address of _etext for checking non-probable text symbol,
+ for some architectures (e.g. arm, arm64), _etext is out of .text
+ section and not loaded as symbols, use kernel map->end instead.
+ */
etext_addr = kernel_get_symbol_address_by_name("_etext", false);
+ if (etext_addr == 0) {
+ struct map *map;
+
+ map = kernel_get_module_map(NULL);
+ if (!map) {
+ pr_err("Failed to get a map for kernel\n");
+ return -EINVAL;
+ }
+
+ etext_addr = map->end;
+ }
for (i = 0; i < ntevs; i++) {
if (tevs[i].point.address && !tevs[i].point.retprobe) {
--
1.8.5.2
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