From: He Kuang <hekuang@huawei.com>
To: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
hekuang <hekuang@zoho.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: <a.p.zijlstra@chello.nl>, <mingo@redhat.com>,
<namhyung@kernel.org>, <wangnan0@huawei.com>,
<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] perf probe: Fix failure to probe events on arm
Date: Wed, 17 Jun 2015 17:43:42 +0800 [thread overview]
Message-ID: <5581414E.2070903@huawei.com> (raw)
In-Reply-To: <5581355B.3010906@hitachi.com>
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@huawei.com>
>>>> ---
>>>> 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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>>
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>> the body of a message to majordomo@vger.kernel.org
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>> Please read the FAQ at http://www.tux.org/lkml/
>>
>
>
next prev parent reply other threads:[~2015-06-17 9:44 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-15 8:06 [PATCH] perf probe: Fix failure to probe events on arm He Kuang
2015-06-15 14:49 ` Arnaldo Carvalho de Melo
2015-06-16 6:05 ` Masami Hiramatsu
2015-06-16 13:39 ` Arnaldo Carvalho de Melo
2015-06-16 15:26 ` hekuang
2015-06-17 8:52 ` Masami Hiramatsu
2015-06-17 9:43 ` He Kuang [this message]
2015-06-17 11:18 ` Masami Hiramatsu
2015-06-18 2:49 ` [PATCH v2] " He Kuang
2015-06-19 21:08 ` Arnaldo Carvalho de Melo
2015-06-23 3:07 ` Masami Hiramatsu
2015-06-23 3:07 ` Masami Hiramatsu
2015-06-25 7:57 ` [tip:perf/core] " tip-bot for He Kuang
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