From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 47A66C4321D for ; Tue, 21 Aug 2018 06:21:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0381E21774 for ; Tue, 21 Aug 2018 06:21:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0381E21774 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.ibm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726615AbeHUJjp (ORCPT ); Tue, 21 Aug 2018 05:39:45 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:50900 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726175AbeHUJjp (ORCPT ); Tue, 21 Aug 2018 05:39:45 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w7L6IldV053509 for ; Tue, 21 Aug 2018 02:20:59 -0400 Received: from e06smtp05.uk.ibm.com (e06smtp05.uk.ibm.com [195.75.94.101]) by mx0b-001b2d01.pphosted.com with ESMTP id 2m0daxg4h5-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 21 Aug 2018 02:20:59 -0400 Received: from localhost by e06smtp05.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 21 Aug 2018 07:20:51 +0100 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w7L6Kou937093414 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Tue, 21 Aug 2018 06:20:50 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 451ECA4053; Tue, 21 Aug 2018 09:20:51 +0100 (BST) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CA68AA4040; Tue, 21 Aug 2018 09:20:45 +0100 (BST) Received: from [9.195.41.244] (unknown [9.195.41.244]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 21 Aug 2018 09:20:45 +0100 (BST) From: Ravi Bangoria Subject: Re: [PATCH v9 0/4] Uprobes: Support SDT markers having reference count (semaphore) To: Song Liu Cc: Srikar Dronamraju , Oleg Nesterov , Steven Rostedt , mhiramat@kernel.org, Peter Zijlstra , mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, open list , ananth@linux.vnet.ibm.com, Alexis Berlemont , naveen.n.rao@linux.vnet.ibm.com, linux-arm-kernel@lists.infradead.org, linux-mips@linux-mips.org, linux@armlinux.org.uk, ralf@linux-mips.org, paul.burton@mips.com, Ravi Bangoria References: <20180820044250.11659-1-ravi.bangoria@linux.ibm.com> <2e997c62-371c-1d9d-97ab-65726f588ab5@linux.ibm.com> Date: Tue, 21 Aug 2018 11:50:43 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <2e997c62-371c-1d9d-97ab-65726f588ab5@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 18082106-0020-0000-0000-000002B97F43 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18082106-0021-0000-0000-00002106CDF0 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-08-21_03:,, 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 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1808210066 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Song, On 08/21/2018 10:53 AM, Ravi Bangoria wrote: > Hi Song, > >> However, if I start a.out AFTER enabling the uprobe, there is something wrong: >> >> root@virt-test:~# ~/a.out >> 11 >> semaphore 0 <<< this should be non-zero, as the uprobe is already enabled In this testcase, semaphore variable is stored into .bss: $ nm test | grep semaphore 0000000010010c5e B semaphore $ readelf -SW ./test | grep "data\|bss" [22] .data PROGBITS 0000000010010c58 000c58 000004 00 WA 0 0 1 [23] .bss NOBITS 0000000010010c5c 000c5c 000004 00 WA 0 0 2 I'm not so sure but I guess .bss data initialization happens after calling uprobe_mmap() and thus you are seeing semaphore as 0. To verify this, if I force to save semaphore into data section by assigning non-zero value to it: volatile short semaphore = 1 $ nm test | grep semaphore 0000000010010c5c D semaphore $ readelf -SW ./test | grep "data\|bss" [22] .data PROGBITS 0000000010010c58 000c58 000006 00 WA 0 0 2 [23] .bss NOBITS 0000000010010c5e 000c5e 000002 00 WA 0 0 1 increment/decrement works fine. Ravi