From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752837AbcFTJa4 (ORCPT <rfc822;w@1wt.eu>);
	Mon, 20 Jun 2016 05:30:56 -0400
Received: from szxga01-in.huawei.com ([58.251.152.64]:63424 "EHLO
	szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751599AbcFTJ3O (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 20 Jun 2016 05:29:14 -0400
Subject: Re: [PATCH v2] tools/perf: Fix the mask in regs_dump__printf and
To: Jiri Olsa <jolsa@redhat.com>,
        Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
References: <1466412241-27502-1-git-send-email-maddy@linux.vnet.ibm.com>
 <20160620091818.GC27702@krava>
CC: <linux-kernel@vger.kernel.org>, <linuxppc-dev@lists.ozlabs.org>,
        "Yury Norov" <ynorov@caviumnetworks.com>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>, Adrian Hunter <adrian.hunter@intel.com>,
        Kan Liang <kan.liang@intel.com>, Michael Ellerman <mpe@ellerman.id.au>
From: "Wangnan (F)" <wangnan0@huawei.com>
Message-ID: <5767B6FD.4080708@huawei.com>
Date: Mon, 20 Jun 2016 17:27:25 +0800
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101
 Thunderbird/38.5.0
MIME-Version: 1.0
In-Reply-To: <20160620091818.GC27702@krava>
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Transfer-Encoding: 7bit
X-Originating-IP: [10.111.66.109]
X-CFilter-Loop: Reflected
X-Mirapoint-Virus-RAPID-Raw: score=unknown(0),
	refid=str=0001.0A090205.5767B713.0018,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0,
	ip=0.0.0.0,
	so=2013-06-18 04:22:30,
	dmn=2013-03-21 17:37:32
X-Mirapoint-Loop-Id: 05bfb07b7e632d5386ac31568504cc18
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org



On 2016/6/20 17:18, Jiri Olsa wrote:
> On Mon, Jun 20, 2016 at 02:14:01PM +0530, Madhavan Srinivasan wrote:
>> When decoding the perf_regs mask in regs_dump__printf(),
>> we loop through the mask using find_first_bit and find_next_bit functions.
>> "mask" is of type "u64", but sent as a "unsigned long *" to
>> lib functions along with sizeof(). While the exisitng code works fine in
>> most of the case, the logic is broken when using a 32bit perf on a
>> 64bit kernel (Big Endian). We end up reading the wrong word of the u64
>> first in the lib functions.
> hum, I still don't see why this happens.. why do we read the
> wrong word in this case?

If you read a u64 using (u32 *)(&val)[0] and (u32 *)(&val)[1]
you can get wrong value. This is what _find_next_bit() is doing.

In a big endian environment where 'unsigned long' is 32 bits
long, "(u32 *)(&val)[0]" gets upper 32 bits, but without this patch
perf assumes it gets lower 32 bits. The root cause is wrongly convert
u64 value to bitmap.


Thank you.