From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754278AbcFTODk (ORCPT ); Mon, 20 Jun 2016 10:03:40 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:50201 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751970AbcFTODV (ORCPT ); Mon, 20 Jun 2016 10:03:21 -0400 X-IBM-Helo: d23dlp01.au.ibm.com X-IBM-MailFrom: maddy@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] tools/perf: Fix the mask in regs_dump__printf and To: Jiri Olsa , "Wangnan (F)" References: <1466412241-27502-1-git-send-email-maddy@linux.vnet.ibm.com> <20160620091818.GC27702@krava> <5767B6FD.4080708@huawei.com> <20160620094003.GA32172@krava> Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Yury Norov , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Jiri Olsa , Adrian Hunter , Kan Liang , Michael Ellerman From: Madhavan Srinivasan Date: Mon, 20 Jun 2016 15:22:57 +0530 User-Agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <20160620094003.GA32172@krava> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16062009-0008-0000-0000-0000009B3B04 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16062009-0009-0000-0000-0000077FF3B6 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-06-20_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1606200115 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Monday 20 June 2016 03:10 PM, Jiri Olsa wrote: > On Mon, Jun 20, 2016 at 05:27:25PM +0800, Wangnan (F) wrote: >> >> 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. Also in find_first_bit(). >> >> 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. > i see, could you please put this into comment in the code? > > also we could have common function for that, to keep it on > one place only, like bitmap_from_u64 or so Sure will do. > > thanks, > jirka >