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

Masami Hiramatsu
2015-03-03T02:39:12Z

(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@kernel.org>
>
> Humm, not working for me, after the patch:
>
> [root@ssdandy ~]# 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@ssdandy ~]#
>
> And then the one asking for 'bytes' to be collectd fails.
>
> After processing the other patches I'll try to debug this...
>
> [root@ssdandy ~]# cat /etc/redhat-release
> Red Hat Enterprise Linux Server release 7.0 (Maipo)
> [root@ssdandy ~]# 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@ssdandy ~]#
> [acme@ssdandy 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@hitachi.com