Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932357AbdLOOOu (ORCPT ); Fri, 15 Dec 2017 09:14:50 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:60192 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932129AbdLOOOq (ORCPT ); Fri, 15 Dec 2017 09:14:46 -0500 To: Arnaldo Carvalho de Melo , Linux Kernel Mailing List , Ingo Molnar , Peter Zijlstra Cc: Martin Schwidefsky , Heiko Carstens From: Thomas-Mich Richter Subject: Linux 4.15.0-rc3 perf probe/uprobe issue with address randomization Organization: IBM LTC Date: Fri, 15 Dec 2017 15:14:37 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Language: en-IE Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 x-cbid: 17121514-0020-0000-0000-000003E05994 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17121514-0021-0000-0000-00004271641C Message-Id: <8402bed0-bb40-53dc-faf8-bd26f6997de5@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-12-15_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1712150200 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1424 Lines: 40 During debugging of perf probe tool I discovered an issue with uprobes and address randomization. To set a uprobe on a function named inet_pton in libc library, you obtain the address of the symbol inet_pton using command nm and then use the following command to set the uprobe: # echo "p:probe_libc/inet_pton /usr/lib64/libc-2.26.so:0x142060" > /sys/kernel/debug/tracing/uprobe_events 0x142060 is the address of inet_pton on my system. This works nicely and the uprobe is usable. The issue is with the output: # cat /sys/kernel/debug/tracing/uprobe_events p:probe_libc/inet_pton /usr/lib64/libc-2.26.so:0x000000002d0f8952 # The displayed address 0x000000002d0f8952 is wrong, probably randomized and post processing of this output with the perf probe tool fails due to this random address: # linux/tools/perf/perf probe -l Failed to find debug information for address 2d0f8952 probe_libc:inet_pton (on 0x2d0f8952 in /usr/lib64/libc-2.26.so) # So how to fix this (if at all)? Is replacing %p by %llx in line 612 of file kernel/trace/trace_uprobe.c seq_printf(m, "0x%p", (void *)tu->offset) an option? Or is this broken by design and intention? Thanks for hints and suggestions. -- Thomas Richter, Dept 3303, IBM LTC Boeblingen Germany -- Vorsitzende des Aufsichtsrats: Martina Koederitz Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294