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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 05700C433F5 for ; Mon, 9 May 2022 18:22:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240133AbiEIS0X (ORCPT ); Mon, 9 May 2022 14:26:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38908 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240214AbiEIS0F (ORCPT ); Mon, 9 May 2022 14:26:05 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 62D2250E32 for ; Mon, 9 May 2022 11:22:09 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 247D3B818E4 for ; Mon, 9 May 2022 18:22:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 92DCBC385B2; Mon, 9 May 2022 18:22:05 +0000 (UTC) Date: Mon, 9 May 2022 14:22:03 -0400 From: Steven Rostedt To: Masami Hiramatsu Cc: Mark Rutland , Wang ShaoBo , cj.chengjian@huawei.com, huawei.libin@huawei.com, xiexiuqi@huawei.com, liwei391@huawei.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will@kernel.org, zengshun.wu@outlook.com Subject: Re: [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically allocated trampolines Message-ID: <20220509142203.6c4f2913@gandalf.local.home> In-Reply-To: <20220505121538.04773ac98e2a8ba17f675d39@kernel.org> References: <20220421100639.03c0d123@gandalf.local.home> <20220421114201.21228eeb@gandalf.local.home> <20220421130648.56b21951@gandalf.local.home> <20220422114541.34d71ad9@gandalf.local.home> <20220426174749.b5372c5769af7bf901649a05@kernel.org> <20220505121538.04773ac98e2a8ba17f675d39@kernel.org> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 5 May 2022 12:15:38 +0900 Masami Hiramatsu wrote: > OK. But my interest is that the ftrace on arm64 can provide a limited > access to registers via pt_regs or not. I don't mind the contained values > so much because in the most case, 'users' will (most likely) access to the > ARGs via BPF or tracefs (and we can just warn users if they try to access > the registers which is not saved.) But if the arm64 ftrace only provides > a special data structure, arch-independent code must have 2 different access > code. That is inefficient. That is my concern. > IOW, I'm interested in interface abstraction. Note, ftrace now has a ftrace_regs structure that is passed to the callbacks for the function tracer. It then has an arch dependent helper function ftrace_get_regs(fregs), that returns a pt_regs from the fregs only if the fregs has a full pt_regs to return. If not, it returns NULL. This was suggested by both Peter Zijlstra and Thomas Gleixner when I introduced FTRACE_WITH_ARGS, where all functions can now get the arguments from fregs, but not the full pt_regs. If a ftrace_ops has the REGS flag set (using ftrace_regs_caller), the ftrace_get_regs(fregs) will return the pt_regs, or it will return NULL if ftrace_regs_caller was not used. This way the same parameter can provide full pt_regs or a subset, and have an generic interface to tell the difference. -- Steve