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=-7.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_AGENT_NEOMUTT 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 E6197C31E44 for ; Wed, 12 Jun 2019 03:05:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BEE1F20874 for ; Wed, 12 Jun 2019 03:05:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406364AbfFLDFT (ORCPT ); Tue, 11 Jun 2019 23:05:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49286 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404957AbfFLDFT (ORCPT ); Tue, 11 Jun 2019 23:05:19 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 50A2C8553D; Wed, 12 Jun 2019 03:05:08 +0000 (UTC) Received: from treble (ovpn-120-37.rdu2.redhat.com [10.10.120.37]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3AB7D7DFCA; Wed, 12 Jun 2019 03:05:03 +0000 (UTC) Date: Tue, 11 Jun 2019 22:05:01 -0500 From: Josh Poimboeuf To: Peter Zijlstra Cc: Kairui Song , Alexei Starovoitov , Song Liu , lkml , Kernel Team , Alexei Starovoitov , Daniel Borkmann , "bpf@vger.kernel.org" , Steven Rostedt Subject: Re: Getting empty callchain from perf_callchain_kernel() Message-ID: <20190612030501.7tbsjy353g7l74ej@treble> References: <20190522140233.GC16275@worktop.programming.kicks-ass.net> <20190522174517.pbdopvookggen3d7@treble> <20190522234635.a47bettklcf5gt7c@treble> <20190523133253.tad6ywzzexks6hrp@treble> <20190523152413.m2pbnamihu3s2c5s@treble> <20190524085319.GE2589@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190524085319.GE2589@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Wed, 12 Jun 2019 03:05:18 +0000 (UTC) Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Fri, May 24, 2019 at 10:53:19AM +0200, Peter Zijlstra wrote: > > For ORC, I'm thinking we may be able to just require that all generated > > code (BPF and others) always use frame pointers. Then when ORC doesn't > > recognize a code address, it could try using the frame pointer as a > > fallback. > > Yes, this seems like a sensible approach. We'd also have to audit the > ftrace and kprobe trampolines, IIRC they only do framepointer setup for > CONFIG_FRAME_POINTER currently, which should be easy to fix (after the > patches I have to fix the FP generation in the first place: > > https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=x86/wip Right now, ftrace has a special hook in the ORC unwinder (orc_ftrace_find). It would be great if we could get rid of that in favor of the "always use frame pointers" approach. I'll hold off on doing the kpatch/kprobe trampoline conversions in my patches since it would conflict with yours. Though, hm, because of pt_regs I guess ORC would need to be able to decode an encoded frame pointer? I was hoping we could leave those encoded frame pointers behind in CONFIG_FRAME_POINTER-land forever... Here are my latest BPF unwinder patches in case anybody wants a sneak peek: https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/log/?h=bpf-orc-fix -- Josh