linux-kernel - Re: [PATCH 2/2] perf ppc64le: Fix probe location when using DWARF

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Message-Id: <57AC7BE3.7060808@linux.vnet.ibm.com>
Date:	Thu, 11 Aug 2016 18:51:39 +0530
From:	Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Anton Blanchard <anton@...ba.org>, linux-kernel@...r.kernel.org,
	peterz@...radead.org, mingo@...hat.com,
	alexander.shishkin@...ux.intel.com, bsingharora@...il.com,
	naveen.n.rao@...ux.vnet.ibm.com, ananth@...ibm.com,
	mhiramat@...nel.org, wangnan0@...wei.com, namhyung@...nel.org,
	Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>,
	Hemant Kumar <hemant@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/2] perf ppc64le: Fix probe location when using DWARF



On Thursday 11 August 2016 05:20 PM, Arnaldo Carvalho de Melo wrote:
> Em Thu, Aug 11, 2016 at 10:01:04AM +0530, Ravi Bangoria escreveu:
>>
>> On Thursday 11 August 2016 05:24 AM, Anton Blanchard wrote:
>>> Hi,
>>>
>>>> Powerpc has Global Entry Point and Local Entry Point for functions.
>>>> LEP catches call from both the GEP and the LEP. Symbol table of ELF
>>>> contains GEP and Offset from which we can calculate LEP, but debuginfo
>>>> does not have LEP info.
>>>>
>>>> Currently, perf prioritize symbol table over dwarf to probe on LEP
>>>> for ppc64le. But when user tries to probe with function parameter,
>>>> we fall back to using dwarf(i.e. GEP) and when function called via
>>>> LEP, probe will never hit.
>>> This patch causes a build failure for me on ppc64le:
>>>
>>> libperf.a(libperf-in.o): In function `arch__post_process_probe_trace_events':
>>>
>>> tools/perf/arch/powerpc/util/sym-handling.c:109: undefined reference to `get_target_map'
>> Thanks Anton. Sorry, I should have caught that.
>>
>> @Arnaldo, Can you please pick this up. I've prepared this on top of
>> acme/perf/core.
>>
>>
>>  From 89c977ae9c3ae35c78b16cddabcf2b01d3cf5cc8 Mon Sep 17 00:00:00 2001
>> From: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
>> Date: Wed, 10 Aug 2016 23:13:45 -0500
>> Subject: [PATCH] perf ppc64le: Fix build failure when no dwarf support
>>
>> Fix perf build failure on ppc64le because of Commit 99e608b5954c ("perf
>> probe ppc64le: Fix probe location when using DWARF")
> Can you please provide a better explanation? I had to look at the patch
> to understand what it was fixing, and then the patch adds LIBELF_SUPPORT
> ifdefs while the patch description, talks about DWARF.

Yes. Explanation could have been better. Apologies for that.

arch__post_process_probe_trace_events() calls get_target_map() to prepare
symbol table. get_target_map() is defined inside util/probe-event.c.

probe-event.c will only get included in perf binary if CONFIG_LIBELF is set.
Hence arch__post_process_probe_trace_events() needs to be defined inside
#ifdef HAVE_LIBELF_SUPPORT to solve compilation error.

Please let me know if any doubts.

Thanks,
Ravi

> Anyway, Anton, does this fix the problem for you?
>
> - Arnaldo
>
>> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
>> ---
>>   tools/perf/arch/powerpc/util/sym-handling.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/tools/perf/arch/powerpc/util/sym-handling.c
>> b/tools/perf/arch/powerpc/util/sym-handling.c
>> index 8d4dc97..c27a51a 100644
>> --- a/tools/perf/arch/powerpc/util/sym-handling.c
>> +++ b/tools/perf/arch/powerpc/util/sym-handling.c
>> @@ -97,6 +97,7 @@ void arch__fix_tev_from_maps(struct perf_probe_event *pev,
>>          }
>>   }
>>
>> +#ifdef HAVE_LIBELF_SUPPORT
>>   void arch__post_process_probe_trace_events(struct perf_probe_event *pev,
>>                                             int ntevs)
>>   {
>> @@ -118,5 +119,6 @@ void arch__post_process_probe_trace_events(struct
>> perf_probe_event *pev,
>>                  }
>>          }
>>   }
>> +#endif
>>
>>   #endif
>> -- 
>> 2.7.4