From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 94725 invoked by alias); 24 Jan 2018 19:01:37 -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 94708 invoked by uid 89); 24 Jan 2018 19:01:37 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.4 required=5.0 tests=BAYES_00,KAM_NUMSUBJECT,KAM_SHORT,SPF_HELO_PASS,T_RP_MATCHES_RCVD autolearn=no version=3.3.2 spammy=circulation, anticipate, Systemtap 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 ESMTP; Wed, 24 Jan 2018 19:01:35 +0000 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C9404A1F6F; Wed, 24 Jan 2018 19:01:34 +0000 (UTC) Received: from redhat.com (ovpn-116-136.phx2.redhat.com [10.3.116.136]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9AC715C544; Wed, 24 Jan 2018 19:01:34 +0000 (UTC) Received: from [127.0.0.1] (helo=vm-rhel7) by redhat.com with esmtps (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.89) (envelope-from ) id 1eeQIf-00013f-DU; Wed, 24 Jan 2018 14:01:33 -0500 From: fche@redhat.com (Frank Ch. Eigler) To: Avi Kivity Cc: systemtap@sourceware.org Subject: Re: Systemtap kernel backtraces not working on 4.14.14 Date: Wed, 24 Jan 2018 19:01:00 -0000 References: <4e07a614-b734-8d91-b18d-d6313981c191@scylladb.com> Message-ID: <87a7x3f5df.fsf@redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-SW-Source: 2018-q1/txt/msg00010.txt.bz2 avi wrote: > I have a centos installation with 4.14.14 installed [...] > =C2=A0 at:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 8483=C2=A0=C2=A0 to: rcu_s= ched > =C2=A00xffffffffa0335150 : 0xffffffffa0335150 > [stap_fc3e91a0b756c0a804d73b3d051959b6__1891+0xd150/0x0] > =C2=A00xffffffffa0336476 : 0xffffffffa0336476 > [...] Ouch. > Is there something in the kernel configuration I need to turn on > (.config taken from elrepo's -ml kernel)? Or a missing dependency > while building systemtap?=20 Shouldn't be the case. > Maybe systemtap can't cope with retpolines? systemtap's backtrace engine uses dwarf unwind information. In principle, retpolines should be representable properly, but in practice, there may be some problems with some compilers [1] or some kernel-side asm .cfi annotations. I don't currently anticipate systemtap having to change, but these tools do need to produce correct output. [1] https://gcc.gnu.org/ml/gcc/2018-01/msg00160.html As your kernel seems to be hand-built, and we don't have retpoline kernels already in circulation, so it'll be tricky to reproduce the problem here. Running stap with -DDEBUG_UNWIND=3D3 would let us see its point of view. Try also backtracing from other probe points to see how systemic the problem is. It may also help to let us get hold of your kernel & its build vitals (esp. gcc version). - FChE