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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7D782C433F5 for ; Fri, 22 Oct 2021 18:52:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6333C610FF for ; Fri, 22 Oct 2021 18:52:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231308AbhJVSyR (ORCPT ); Fri, 22 Oct 2021 14:54:17 -0400 Received: from foss.arm.com ([217.140.110.172]:57856 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229463AbhJVSyQ (ORCPT ); Fri, 22 Oct 2021 14:54:16 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A9AE61063; Fri, 22 Oct 2021 11:51:58 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.73.6]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3D4D83F73D; Fri, 22 Oct 2021 11:51:56 -0700 (PDT) Date: Fri, 22 Oct 2021 19:51:48 +0100 From: Mark Rutland To: madvenka@linux.microsoft.com Cc: broonie@kernel.org, jpoimboe@redhat.com, ardb@kernel.org, nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v10 04/11] arm64: Make return_address() use arch_stack_walk() Message-ID: <20211022185148.GA91654@C02TD0UTHF1T.local> References: <20211015025847.17694-1-madvenka@linux.microsoft.com> <20211015025847.17694-5-madvenka@linux.microsoft.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211015025847.17694-5-madvenka@linux.microsoft.com> Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Thu, Oct 14, 2021 at 09:58:40PM -0500, madvenka@linux.microsoft.com wrote: > From: "Madhavan T. Venkataraman" > > Currently, return_address() in ARM64 code walks the stack using > start_backtrace() and walk_stackframe(). Make it use arch_stack_walk() > instead. This makes maintenance easier. > > Signed-off-by: Madhavan T. Venkataraman > --- > arch/arm64/kernel/return_address.c | 6 +----- > 1 file changed, 1 insertion(+), 5 deletions(-) > > diff --git a/arch/arm64/kernel/return_address.c b/arch/arm64/kernel/return_address.c > index a6d18755652f..92a0f4d434e4 100644 > --- a/arch/arm64/kernel/return_address.c > +++ b/arch/arm64/kernel/return_address.c > @@ -35,15 +35,11 @@ NOKPROBE_SYMBOL(save_return_addr); > void *return_address(unsigned int level) > { > struct return_address_data data; > - struct stackframe frame; > > data.level = level + 2; > data.addr = NULL; > > - start_backtrace(&frame, > - (unsigned long)__builtin_frame_address(0), > - (unsigned long)return_address); > - walk_stackframe(current, &frame, save_return_addr, &data); > + arch_stack_walk(save_return_addr, &data, current, NULL); This looks equivalent to me. Previously the arguments to start_backtrace() meant that walk_stackframe would report return_address(), then the caller of return_address(), and so on. As arch_stack_walk() starts from its immediate caller (i.e. return_address()), that should result in the same trace. It would be nice if we could note something to that effect in the commit message. I had a play with ftrace, which uses return_address(), and that all looks sound. > > if (!data.level) > return data.addr; The end of this function currently does: if (!data.level) return data.addr; else return NULL; ... but since we initialize data.addr to NULL, and save_return_addr() only writes to data.addr when called at the correct level, we can simplify that to: return data.addr; Regardles of that cleanup: Reviewed-by: Mark Rutland Tested-by: Mark Rutland I'll continue reviewing the series next week. Thanks, Mark.