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 C5ADCC433F5 for ; Tue, 10 May 2022 09:10:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238474AbiEJJOT (ORCPT ); Tue, 10 May 2022 05:14:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37074 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238442AbiEJJOP (ORCPT ); Tue, 10 May 2022 05:14:15 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 447942555BB for ; Tue, 10 May 2022 02:10:18 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 688AD614E1 for ; Tue, 10 May 2022 09:10:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 267ACC385A6; Tue, 10 May 2022 09:10:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1652173817; bh=GXpVDYbkF84LLdJ5bx4YwYoSn9Krmcs/u8uVEyFBHiY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=oLb653JNx2KBVbvxGYK7oIFvppbFBTPIYSJD85hFi0sCGzZ1akOP6cPOLeqVNVLjf GLBNMceSMifw+ciRgtuIiZn0keibYMP1pMVYnR8HY4fjLkGHijzfBfdPgUWwDBn4b9 0/3/bvyL6OXPJgxD5cn7/81QNgOSCuEXc+ceYs8g7dGbVfE04bi2zMd2Gs7DGNDWkc 6fYkMlfUr9ckP7s1qG1kHlkcT3c+wVO5K2B5vS7zwIL2kAlgi2mu6phelLWTwM6mVZ uVvdtlvolPNog6AqZ+S11H1LQsVrxO5YHSTo/n0do/5r45zuhHxbk4qC+56zWo55qN 58h8zSW774MTg== Date: Tue, 10 May 2022 18:10:12 +0900 From: Masami Hiramatsu To: Steven Rostedt 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, Jiri Olsa Subject: Re: [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically allocated trampolines Message-Id: <20220510181012.d5cba23a2547f14d14f016b9@kernel.org> In-Reply-To: <20220509142203.6c4f2913@gandalf.local.home> 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> <20220509142203.6c4f2913@gandalf.local.home> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; 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 Hi Steve, On Mon, 9 May 2022 14:22:03 -0400 Steven Rostedt wrote: > 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. Hmm, I thought the ftrace_get_regs() is the all-or-nothing interface, or is there any way to get the arguments from fregs? > 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. If it can provide a partial (subset of) pt_regs, that could be good for me too, since at least kprobe-events on ftrace can check the traced register is in the subset or not and reject it if it doesn't saved. Thank you, -- Masami Hiramatsu