From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 3060 invoked by alias); 16 Nov 2011 19:05:18 -0000 Received: (qmail 3030 invoked by uid 22791); 16 Nov 2011 19:05:15 -0000 X-SWARE-Spam-Status: No, hits=-6.9 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD,SPF_HELO_PASS X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Wed, 16 Nov 2011 19:04:58 +0000 Received: from int-mx12.intmail.prod.int.phx2.redhat.com (int-mx12.intmail.prod.int.phx2.redhat.com [10.5.11.25]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id pAGJ4UK0015616 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Wed, 16 Nov 2011 14:04:56 -0500 Received: from t510.usersys.redhat.com (vpn-10-80.rdu.redhat.com [10.11.10.80]) by int-mx12.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id pAGHdYxt014191 (version=TLSv1/SSLv3 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO); Wed, 16 Nov 2011 12:39:34 -0500 Message-ID: <4EC3F556.4010902@redhat.com> Date: Wed, 16 Nov 2011 19:05:00 -0000 From: David Smith User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:7.0.1) Gecko/20110930 Thunderbird/7.0.1 MIME-Version: 1.0 To: Josh Stone CC: systemtap@sourceware.org, Srikar Dronamraju Subject: Re: Initial stap support for inode-based uprobes References: <4DD5DEAA.3050908@redhat.com> In-Reply-To: <4DD5DEAA.3050908@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-IsSubscribed: yes Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org X-SW-Source: 2011-q4/txt/msg00185.txt.bz2 I just got through running the systemtap testsuite on 2 different configurations: 1) stock f16 kernel and HEAD systemtap # of expected passes 3096 # of unexpected failures 63 # of unexpected successes 8 # of expected failures 259 # of untested testcases 61 # of unsupported tests 4 2) f16 kernel with the new inode-based uprobes built-in and systemtap with a merged dsmith/task_finder2 and jistone/inode-uprobes branches # of expected passes 2638 # of unexpected failures 329 # of unexpected successes 9 # of expected failures 251 # of untested testcases 70 # of unsupported tests 4 That isn't too bad for a first stab. Here's the link to the diff in dejazilla: I haven't had time to do a full analysis of the results, but the problems Josh listed in his original email (included below) are still there. > * Return probes. This hasn't yet been added to the new uprobes. > > * Process filtering. AFAICS, the current uprobes implementation sets > the breakpoint in all processes that map the particular inode. There is > a filtering mechanism, but that seems only to decide whether to call the > handler each time. You'll still take the bp/sstep overhead. Also, on > stap's side, we previously had the ability to limit process probes to > the -x/-c target and children, which I haven't tried here yet. > > * Runtime build-id verification. Right now I'm just mapping the path to > inode*, without checking that the build-id is what we expected. I'm not > sure we even could at the systemtap-init point. Even if we did, the > file may still get modified without changing the inode, and I don't > think this uprobes gives us any way to notice or decide whether we like > the new form. > > * SDT semaphore. In the current form, we have no hook on individual > processes, so we can't modify the semaphores in applications that are > actively gating their markers. We'll probably need something like > PR10994 to achieve this, which isn't really about uprobes per-se, but > rather about living without utrace. > > * Argument access. If you try $args, it will fail with a missing symbol > 'task_user_regset_view'. I haven't looked closely at this yet. > > * Probe IP. For many probe handlers, we try to set the pt_regs IP to > the actual breakpoint IP, but in this case we don't happen to even know > the virtualized address. Uprobes itself uses uprobes_get_bkpt_addr() in > some instances, but that's not exposed for our use. -- David Smith dsmith@redhat.com Red Hat http://www.redhat.com 256.217.0141 (direct) 256.837.0057 (fax)