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=-7.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_MUTT 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 55E1EC43219 for ; Mon, 29 Apr 2019 08:40:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2E0BF20449 for ; Mon, 29 Apr 2019 08:40:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727660AbfD2Ikd (ORCPT ); Mon, 29 Apr 2019 04:40:33 -0400 Received: from smtp2200-217.mail.aliyun.com ([121.197.200.217]:34164 "EHLO smtp2200-217.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727517AbfD2Ikd (ORCPT ); Mon, 29 Apr 2019 04:40:33 -0400 X-Alimail-AntiSpam: AC=CONTINUE;BC=0.07727315|-1;CH=green;DM=CONTINUE|CONTINUE|true|0.115371-0.00976564-0.874864;FP=0|0|0|0|0|-1|-1|-1;HT=e01a16367;MF=han_mao@c-sky.com;NM=1;PH=DS;RN=4;RT=4;SR=0;TI=SMTPD_---.ERaYIfo_1556527229; Received: from localhost(mailfrom:han_mao@c-sky.com fp:SMTPD_---.ERaYIfo_1556527229) by smtp.aliyun-inc.com(10.147.41.178); Mon, 29 Apr 2019 16:40:29 +0800 Date: Mon, 29 Apr 2019 16:39:40 +0800 From: Mao Han To: Palmer Dabbelt Cc: linux-riscv@lists.infradead.org, guoren@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] riscv: Add perf callchain support Message-ID: <20190429083940.GA22718@vmh-VirtualBox> References: <195185ea63240ed396026505d96d1f6449963482.1554961908.git.han_mao@c-sky.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 25, 2019 at 02:11:00PM -0700, Palmer Dabbelt wrote: > On Thu, 11 Apr 2019 00:53:48 PDT (-0700), han_mao@c-sky.com wrote: > >+ if (!kstack_end((void *)frame->fp) && > >+ !((unsigned long)frame->fp & 0x3) && > >+ ((unsigned long)frame->fp >= TASK_SIZE)) { > >+ frame->ra = ((struct stackframe *)frame->fp - 1)->ra; > >+ frame->fp = ((struct stackframe *)frame->fp - 1)->fp; > > It looks like this depends on having a frame pointer? In that case, shouldn't > we add some Kconfig logic to make CONFIG_PERF_EVENTS select > -fno-omit-frame-pointer? Frame pointers aren't enabled by default on RISC-V > and therefor are unlikely to exist at all. > Yes, frame pointer is required for kernel backtrace, -fno-omit-frame-pointer should be added if frame pointer is not enabled by default on RISC-V. When I testing the callchain support with buildroot chunk git://git.busybox.net/buildroot cbf1d861fadb491eee6e3686019d8f67d7f4ad85 both kernel and user program have fp without adding any extra option, so I thought frame pointer was enabled by default. ffffffe0000009ee : ffffffe0000009ee: 711d addi sp,sp,-96 ffffffe0000009f0: ec86 sd ra,88(sp) ffffffe0000009f2: e8a2 sd s0,80(sp) ffffffe0000009f4: e4a6 sd s1,72(sp) void test_3(void) { 10498: fe010113 addi sp,sp,-32 1049c: 00113c23 sd ra,24(sp) 104a0: 00813823 sd s0,16(sp) 104a4: 02010413 addi s0,sp,32 > >+ /* make sure CONFIG_FUNCTION_GRAPH_TRACER is turned on */ > > Should that also be mandated by a Kconfig? > Yes, it is required for ftrace_graph_ret_addr support. It's already default for ARCH_RV64I in Kconfig. > >+/* > >+ * This will be called when the target is in user mode > >+ * This function will only be called when we use > >+ * "PERF_SAMPLE_CALLCHAIN" in > >+ * kernel/events/core.c:perf_prepare_sample() > >+ * > >+ * How to trigger perf_callchain_[user/kernel] : > >+ * $ perf record -e cpu-clock --call-graph fp ./program > >+ * $ perf report --call-graph > >+ * > >+ * On RISC-V platform, the program being sampled and the C library > >+ * need to be compiled with * -mbacktrace, otherwise the user > > What is "-mbacktrace"? I don't remember that ever being a RISC-V GCC option, > and my compiler doesn't undersand it. It understands "-fbacktrace" but that > doesn't produce a frame pointer. > It's a csky specific option, I forget to modify the comment. So it should be -fno-omit-frame-pointer here. Thanks, Mao Han