linux-kernel - Re: [PATCH 2/3] perf symbol: Implement a very simple ELF symbol parser

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Date:	Mon, 10 Nov 2014 09:09:04 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	David Ahern <dsahern@...il.com>
Subject: Re: [PATCH 2/3] perf symbol: Implement a very simple ELF symbol
 parser

Em Mon, Nov 10, 2014 at 03:36:48PM +0900, Namhyung Kim escreveu:
> Hi Arnaldo,
> 
> On Fri, 7 Nov 2014 12:26:18 -0300, Arnaldo Carvalho de Melo wrote:
> > Em Fri, Nov 07, 2014 at 02:20:05PM +0900, Namhyung Kim escreveu:
> >> It'll be used to show (userspace) symbol names when libelf isn't (or
> >> cannot be) linked.
> >
> > Does this deals with prelink, etc?
> 
> I believe so. :)
> 
> >  
> >>   # Overhead  Command     Shared Object      Symbol
> >>   # ........  ..........  .................  .........................
> >>   #
> >>       37.01%  mem-memcpy  libc-2.17.so       [.] __memcpy_ssse3_back
> 
>   namhyung@...ong:linux$ readelf -WS /lib64/libc-2.17.so | grep prelink
>     [41] .gnu.prelink_undo PROGBITS        0000000000000000 200368 000c30 01      0   0  8
> 
>   namhyung@...ong:linux$ nm /lib64/libc-2.17.so | grep __memcpy_ssse3_back
>   0000003153f46f40 t __memcpy_ssse3_back

Right, in this case most of the samples seems to map to what is expected
for that workload, and the binary was prelinked. Good.

What about binaries that are not prelinked? IIRC there is code in the
full blown ELF symbol-elf.c file to detect that and act accordingly,
from a _very_ quick look I didn't saw it in this minimalistic ELF symtab
reader, hence my question.

- Arnaldo
 
> 
> Thanks,
> Namhyung
> 
> 
> >>       24.25%  perf        ld-2.17.so         [.] _dl_relocate_object
> >>       22.16%  perf        [kernel.kallsyms]  [k] kmem_cache_alloc
> >>       14.29%  mem-memset  libc-2.17.so       [.] __memset_sse2
> >>        2.21%  perf        [kernel.kallsyms]  [k] flush_signal_handlers
> >>        0.07%  perf        [kernel.kallsyms]  [k] intel_pmu_enable_all
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