From: Namhyung Kim <namhyung@kernel.org>
To: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
Ingo Molnar <mingo@kernel.org>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
David Ahern <dsahern@gmail.com>,
lkml <linux-kernel@vger.kernel.org>,
"Steven Rostedt \(Red Hat\)" <rostedt@goodmis.org>,
Oleg Nesterov <oleg@redhat.com>,
"David A. Long" <dave.long@linaro.org>,
systemtap@sourceware.org, yrl.pp-manager.tt@hitachi.com
Subject: Re: [PATCH -tip 3/3] perf-probe: Use the actual address as a hint for uprobes
Date: Tue, 24 Dec 2013 07:54:00 -0000 [thread overview]
Message-ID: <87y53afzv3.fsf@sejong.aot.lge.com> (raw)
In-Reply-To: <52B81562.5000607@hitachi.com> (Masami Hiramatsu's message of "Mon, 23 Dec 2013 19:50:10 +0900")
Hi Masami,
On Mon, 23 Dec 2013 19:50:10 +0900, Masami Hiramatsu wrote:
> (2013/12/23 16:46), Namhyung Kim wrote:
>> On Mon, 23 Dec 2013 06:54:38 +0900, Masami Hiramatsu wrote:
>>> (2013/12/21 3:03), Arnaldo Carvalho de Melo wrote:
>>>> Em Fri, Dec 20, 2013 at 10:03:02AM +0000, Masami Hiramatsu escreveu:
>>> BTW, I'm not sure why debuginfo and nm shows symbol address + 0x400000,
>>> and why the perf's map/symbol can remove this offset. Could you tell me
>>> how it works?
>>> If I can get the offset (0x400000) from binary, I don't need this kind
>>> of ugly hacks...
>>
>> AFAIK the actual symbol address is what nm (and debuginfo) shows. But
>> perf adjusts symbol address to have a relative address from the start of
>> mapping (i.e. file offset) like below:
>>
>> sym.st_value -= shdr.sh_addr - shdr.sh_offset;
>
> Thanks! this is what I really need!
>
>> This way, we can handle mmap and symbol address almost uniformly
>> (i.e. ip = map->start + symbol->address). But this requires the mmap
>> event during perf record. For perf probe, we might need to synthesize
>> mapping info from the section/segment header since it doesn't have the
>> mmap event. Currently, the dso__new_map() just creates a map starts
>> from 0.
>
> I think the uprobe requires only the relative address, doesn't that?
Yes, but fetching arguments is little different than a normal relative
address, I think.
An offset of an argument bases on the mapping address of text segment.
This fits naturally for a shared library case - base address is 0. So
we can use the symbol address (st_value) directly. But for executables,
the base address of text segment is 0x400000 on x86-64 and data symbol
is on 0x6XXXXX typically. So in this case the offset given to uprobe
should be "@+0x2XXXXX" (st_value - text_base).
Thanks,
Namhyung
next prev parent reply other threads:[~2013-12-24 7:54 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-20 10:08 [PATCH -tip 0/3] perf-probe: Dwarf support " Masami Hiramatsu
2013-12-20 10:08 ` [PATCH -tip 1/3] [CLEANUP] perf-probe: Expand given path to absolute path Masami Hiramatsu
2013-12-20 18:00 ` Arnaldo Carvalho de Melo
2013-12-22 21:35 ` Masami Hiramatsu
2013-12-23 14:28 ` Arnaldo Carvalho de Melo
2013-12-24 6:51 ` Masami Hiramatsu
2013-12-23 6:17 ` Namhyung Kim
2013-12-23 10:46 ` Masami Hiramatsu
2013-12-20 10:08 ` [PATCH -tip 2/3] perf-probe: Support dwarf on uprobe events Masami Hiramatsu
2013-12-20 18:02 ` Arnaldo Carvalho de Melo
2013-12-22 21:39 ` Masami Hiramatsu
2013-12-23 14:34 ` Arnaldo Carvalho de Melo
2013-12-24 1:03 ` Masami Hiramatsu
2013-12-20 10:08 ` [PATCH -tip 3/3] perf-probe: Use the actual address as a hint for uprobes Masami Hiramatsu
2013-12-20 18:04 ` Arnaldo Carvalho de Melo
2013-12-22 21:54 ` Masami Hiramatsu
2013-12-23 7:46 ` Namhyung Kim
2013-12-23 10:50 ` Masami Hiramatsu
2013-12-24 7:54 ` Namhyung Kim [this message]
2013-12-24 8:28 ` Masami Hiramatsu
2013-12-24 8:46 ` Namhyung Kim
2013-12-24 15:03 ` Masami Hiramatsu
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