linux-kernel - Re: [PATCH perf/core 2/4] perf-probe: Fix to handle aliased symbols in glibc

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Date:	Tue, 03 Mar 2015 11:39:02 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Naohiro Aota <naota@...sp.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>, namhyung@...nel.org,
	Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH perf/core 2/4] perf-probe: Fix to handle aliased symbols
 in glibc

(2015/03/03 0:46), Arnaldo Carvalho de Melo wrote:
> Em Mon, Mar 02, 2015 at 09:49:53PM +0900, Masami Hiramatsu escreveu:
>> With this patch;
>>   -----
>>   # ./perf probe -x /usr/lib64/libc-2.17.so -V malloc
>>   Available variables at malloc
>>           @<__libc_malloc+0>
>>                   size_t  bytes
>>   # ./perf probe -x /usr/lib64/libc-2.17.so -a "malloc bytes"
>>   Added new event:
>>     probe_libc:malloc    (on malloc in /usr/lib64/libc-2.17.so with bytes)
>>
>>   You can now use it in all perf tools, such as:
>>
>>           perf record -e probe_libc:malloc -aR sleep 1
> 
>> Reported-by: Arnaldo Carvalho de Melo <acme@...nel.org>
> 
> Humm, not working for me, after the patch:
> 
> [root@...andy ~]# perf probe -x /usr/lib64/libc-2.17.so -V malloc
> Available variables at malloc
>         @<__malloc_check_init+96>
>                 (No matched variables)

Could you run it with -v (verbose) option?

> [root@...andy ~]#
> 
> And then the one asking for 'bytes' to be collectd fails.
> 
> After processing the other patches I'll try to debug this...
> 
> [root@...andy ~]# cat /etc/redhat-release 
> Red Hat Enterprise Linux Server release 7.0 (Maipo)
> [root@...andy ~]# rpm -q glibc glibc-debuginfo
> glibc-2.17-55.el7_0.3.x86_64
> glibc-debuginfo-2.17-55.el7_0.1.x86_64
                              ^^^ why is this different from the glibc version??

> [root@...andy ~]#
> [acme@...andy linux]$ readelf -Ws /usr/lib64/libc-2.17.so| grep malloc
[...]
>   4849: 0000000000080050   107 FUNC    LOCAL  DEFAULT   12 __malloc_check_init

__malloc_check_init+96(0x60) becomes 0x80050 + 0x60 = 0x800b0

>   5351: 00000000000800c0   245 FUNC    LOCAL  DEFAULT   12 __malloc
>   1170: 00000000000800c0   245 FUNC    GLOBAL DEFAULT   12 malloc@@GLIBC_2.2.5

that is not 0x800c0, so something goes wrong when translating the address
to probe point. Could you check the patch 1/4 was applied?
Actually there is a bug in the routine which gets the probe point from
address. 1/4 fixes it.

Thank you,

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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