From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 83793 invoked by alias); 16 Dec 2015 11:55:34 -0000 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 Received: (qmail 83785 invoked by uid 89); 16 Dec 2015 11:55:33 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.8 required=5.0 tests=AWL,BAYES_00,SPF_HELO_PASS,T_RP_MATCHES_RCVD autolearn=ham version=3.3.2 X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-GCM-SHA384 encrypted) ESMTPS; Wed, 16 Dec 2015 11:55:32 +0000 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (Postfix) with ESMTPS id 0413396BD; Wed, 16 Dec 2015 11:55:31 +0000 (UTC) Received: from localhost (vpn-53-229.rdu2.redhat.com [10.10.53.229]) by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id tBGBtTIx003354; Wed, 16 Dec 2015 06:55:30 -0500 Date: Wed, 16 Dec 2015 11:55:00 -0000 From: Pratyush Anand To: William Cohen Cc: David Long , systemtap@sourceware.org Subject: Re: Recent aarch64 kprobes and uprobes patch systemtap testing Message-ID: <20151216115528.GB316@dhcppc13.redhat.com> References: <5669DF98.3030601@redhat.com> <5669EABE.7040507@linaro.org> <566B3949.2090900@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <566B3949.2090900@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-IsSubscribed: yes X-SW-Source: 2015-q4/txt/msg00289.txt.bz2 On 11/12/2015:03:59:53 PM, William Cohen wrote: > On 12/10/2015 04:12 PM, David Long wrote: > > On 12/10/2015 03:24 PM, William Cohen wrote: > > >> The fslatency-nd and fsslower-nd tests need further investigation: > >> > >> PASS: ./systemtap.examples/lwtools/fslatency-nd build > >> meta taglines 'test_installcheck: stap fslatency-nd.stp 1 1' tag 'test_installcheck' value 'stap fslatency-nd.stp 1 1' > >> attempting command stap fslatency-nd.stp 1 1 > >> OUT ERROR: read fault [man error::fault] at 0x0000000000000034 (addr) near operator '@cast' at fslatency-nd.stp:66:15 > >> Tracing FS sync reads and writes... Output every 1 secs. > >> WARNING: Number of errors: 1, skipped probes: 1 > >> WARNING: /root/systemtap_write/install/bin/staprun exited with status: 1 > >> Pass 5: run failed. [man error::pass5] > >> child process exited abnormally > >> RC 1 > >> FAIL: ./systemtap.examples/lwtools/fslatency-nd run > >> > >> PASS: ./systemtap.examples/lwtools/fsslower-nd build > >> meta taglines 'test_installcheck: stap fsslower-nd.stp -c "sleep 1"' tag 'test_installcheck' value 'stap fsslower-nd.stp -c "sleep 1"' > >> attempting command stap fsslower-nd.stp -c "sleep 1" > >> OUT ERROR: read fault [man error::fault] at 0x0000000000000034 (addr) near operator '@cast' at fsslower-nd.stp:68:15 > >> Tracing FS sync reads and writes slower than 10 ms... Hit Ctrl-C to end. > >> TIME PID COMM FUNC SIZE LAT(ms) > >> WARNING: Number of errors: 1, skipped probes: 1 > >> WARNING: /root/systemtap_write/install/bin/staprun exited with status: 1 > >> Pass 5: run failed. [man error::pass5] > >> child process exited abnormally > >> RC 1 > >> FAIL: ./systemtap.examples/lwtools/fsslower-nd run > > > > > Cool. Wish I could make sense of systemtap error messages. > > > > At Will Deacon's suggested I tested probing the instruction in __copy_to_user that can cause a captured kernel exception when an application passes in a bad buffer address. Unfortunately the result was a hang. So copy_to/from user is going to have to be blacklisted for now, unless there turns out to be a simple fix. I'm worried there might be other places in the kernel where an otherwise probeable instruction might be expected to generate an exception. > > > > -dl > > > > > > > > Hi Dave and Pratyush, > > I did some more experimentation with the fslatency-nd and fsslow-nd tests to see what is going on. The problem seems to be related to the return probes. I have a small reproducer attached which runs fine on x86_64 machine. However on aarch64 it has the bogus read because some of the argument registers have changed value > > # ../install/bin/stap ./aarch64_retkprobe_issue2.stp > ERROR: read fault [man error::fault] at 0x0000000000000034 (addr) near operator '@cast' at ./aarch64_retkprobe_issue2.stp:13:7 > pc : [] lr : [] pstate: 80000145 > sp : fffffe00bad7be30 > x29: fffffe00bad7be30 x28: fffffe00bad78000 > x27: fffffe0000912000 x26: 000000000000003f > x25: 000000000000011d x24: 0000000000000015 > x23: 0000000080000000 x22: 000003fff82b9760 > x21: fffffe00bad7bec8 x20: 0000000000002004 > x19: fffffe01b716e100 x18: 000003fff82b8160 > x17: 000003ff849bf0a0 x16: fffffe000021f4a0 > x15: 0000000000000004 x14: 000003fff82bb910 > x13: 0000000000000001 x12: 000003ff7d75f200 > x11: 00000000003d0f00 x10: 000003ff849b7af4 > x9 : 0000000000000028 x8 : 0000000000000020 > x7 : fffffe00bc5c3600 x6 : 0000000000000000 > x5 : 0000000000000000 x4 : 0000000000000000 > x3 : fffffe00bad7bec8 x2 : 0000000000002004 > x1 : 000003fff82b9760 x0 : fffffe01b716e100 > > pc : [] lr : [] pstate: 60000145 > sp : fffffe00bad7be30 > x29: fffffe00bad7be30 x28: fffffe00bad78000 > x27: fffffe0000912000 x26: 000000000000003f > x25: 000000000000011d x24: 0000000000000015 > x23: 0000000080000000 x22: 000003fff82b9760 > x21: fffffe00bad7bec8 x20: 0000000000002004 > x19: fffffe01b716e100 x18: 000003fff82b8160 > x17: 000003ff849bf0a0 x16: fffffe000021f4a0 > x15: 0000000000000004 x14: 000003fff82bb910 > x13: 0000000000000001 x12: 000003ff7d75f200 > x11: 00000000003d0f00 x10: 000003ff849b7af4 > x9 : 0000000000000028 x8 : 0000000000000020 > x7 : fffffe00bc5c3600 x6 : 000003fff82b976c > x5 : 000003fff82b976c x4 : 0000000000000000 > x3 : 0000000000000000 x2 : 0000000000000000 > x1 : 0000000000000000 x0 : 000000000000000c Although I am not sure, but this is what it seems to me: First argument (file) is in x0, and which is 0xC in case of kretprobe. But, can x0 really be considered as 1st arg in case of kretprobe? I think, x0 should have return value of __vfs_read() in case of kretprobe. So, 0xC could be the number of bytes read. With perf I see: # perf probe -k vmlinux __vfs_read_exit=__vfs_read%return file Semantic error :You can't specify local variable for kretprobe. So, I am not sure what mechanism systemtap uses to get local variable in case of kretprobe. Moreover, on x86 I see that loop exits after the 1st print_regs() only. So it means there was valid file->f_op->read() for the 1st file itself. If I comment "kprobe.function("__vfs_read")", then there is no print at all. It means, we are not hitting a case on x86 when callback was called for kretprobe and we had nonzero 1st argument. ~Pratyush