linux-kernel - Re: [PATCH] perf tool: fix endianness handling of u32 data in samples

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Date:	Thu, 01 Sep 2011 10:41:58 -0600
From:	David Ahern <dsahern@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	mingo@...e.hu, peterz@...radead.org, fweisbec@...il.com,
	paulus@...ba.org, tglx@...utronix.de, anton@...ba.org
Subject: Re: [PATCH] perf tool: fix endianness handling of u32 data in samples



On 09/01/2011 10:19 AM, Arnaldo Carvalho de Melo wrote:
> Em Mon, Aug 29, 2011 at 03:55:24PM -0600, David Ahern escreveu:
>> Currently, analyzing PPC data files on x86 the cpu field is always 0 and
>> the tid and pid are backwards. For example, analyzing a PPC file on PPC
>> the pid/tid fields show:
>>         rsyslogd  1210/1212
>>
>> and analyzing the same PPC file using an x86 perf binary shows:
>>         rsyslogd  1212/1210
>>
>> The problem is that the swap_op method for samples is
>> perf_event__all64_swap which assumes all elements in the sample_data
>> struct are u64s. cpu, tid and pid are u32s and need to be handled
>> individually. Given that the swap is done before the sample is parsed,
>> the simplest solution is to undo the 64-bit swap of those elements when
>> the sample is parsed and do the proper swap.
>>
>> The RAW data field is generic and perf cannot have programmatic knowledge
>> of how to treat that data. Instead a warning is given to the user.
>>
>> Thanks to Anton Blanchard for providing a data file for a mult-CPU
>> PPC system so I could verify the fix for the CPU fields.
>>
>> Signed-off-by: David Ahern <dsahern@...il.com>
> 
> cc1: warnings being treated as errors
> util/evsel.c: In function ‘perf_event__parse_sample’:
> util/evsel.c:379: error: dereferencing pointer ‘p’ does break strict-aliasing rules
> util/evsel.c:375: error: dereferencing pointer ‘p’ does break strict-aliasing rules
> util/evsel.c:375: error: dereferencing pointer ‘p’ does break strict-aliasing rules
> util/evsel.c:371: note: initialized from here
> util/evsel.c:376: error: dereferencing pointer ‘({anonymous})’ does break strict-aliasing rules
> util/evsel.c:376: error: dereferencing pointer ‘({anonymous})’ does break strict-aliasing rules
> util/evsel.c:376: note: initialized from here
> util/evsel.c:380: error: dereferencing pointer ‘({anonymous})’ does break strict-aliasing rules
> util/evsel.c:380: note: initialized from here
> util/evsel.c:414: error: dereferencing pointer ‘p’ does break strict-aliasing rules
> util/evsel.c:412: error: dereferencing pointer ‘p’ does break strict-aliasing rules
> util/evsel.c:408: note: initialized from here
> util/evsel.c:462: error: dereferencing pointer ‘p’ does break strict-aliasing rules
> util/evsel.c:450: error: dereferencing pointer ‘p’ does break strict-aliasing rules
> util/evsel.c:450: error: dereferencing pointer ‘p’ does break strict-aliasing rules
> util/evsel.c:444: note: initialized from here
> util/evsel.c:451: error: dereferencing pointer ‘({anonymous})’ does break strict-aliasing rules
> util/evsel.c:451: error: dereferencing pointer ‘({anonymous})’ does break strict-aliasing rules
> util/evsel.c:451: note: initialized from here

That's no good. It compiles cleanly on Fedora 15-x86 and Fedora 12-ppc.
What version of gcc is this?

David


>     CC /home/acme/git/build/perf//util/symbol.o
> make: *** [/home/acme/git/build/perf//util/evsel.o] Error 1
> make: *** Waiting for unfinished jobs....
> make: Leaving directory `/home/acme/git/linux/tools/perf'
> [acme@...lia linux]$
> 
> [acme@...lia linux]$ uname -a
> Linux emilia.ghostprotocols.net 3.0.3-rt12.14.el6rt.x86_64 #1 SMP PREEMPT RT Wed Aug 31 12:38:53 BRT 2011 x86_64 x86_64 x86_64 GNU/Linux
> [acme@...lia linux]$ cat /etc/redhat-release 
> Red Hat Enterprise Linux release 6.0 Beta (Santiago)
> [acme@...lia linux]$
> 
> - Arnaldo

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