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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=no 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 5721BC433FF for ; Wed, 7 Aug 2019 17:21:14 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1CABF22296 for ; Wed, 7 Aug 2019 17:21:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="kj4qtTpD" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1CABF22296 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=qNaqyGFby7dW/GKm5TZlBcdWzQ1KAqxTaByx0ysnOgA=; b=kj4qtTpDTuPI+g aciPm1LOtAfkN89532Zvsgg+nFAa4JwA5fuYdY3G+vNAm2Rx+3RsfIptR8BEgj5i/NYnF8IcideV1 Hl591PmY7z6XuSxfdsRI3MluYQ57zniswLjFuRCigH7ZWaXUIdnEkpZxW9CkM3b//MqwZa86gSNeO MBYHetW3hO4c6K9Q0U3C9w37evsk4ErALWApmjQXxOnYfytAhUtrTr8WFsu29u5eDldfr7Tx1V4G9 AaXI9FaCNJMP+eZtaGPi3mQYKM50/oBr2MAmD8PYMpA6N1axQiZEtxpTAQImvqS6K5uo9VZWW6uCJ mUrgEFxZqfKeB+TEumfA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hvPcY-0004Sp-Qd; Wed, 07 Aug 2019 17:21:06 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hvPcU-0004SA-1L for linux-arm-kernel@lists.infradead.org; Wed, 07 Aug 2019 17:21:03 +0000 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B813E22296; Wed, 7 Aug 2019 17:21:00 +0000 (UTC) Date: Wed, 7 Aug 2019 13:20:58 -0400 From: Steven Rostedt To: Mark Rutland Subject: Re: [PATCH 0/2] tracing/arm: Fix the stack tracer when LR is saved after local storage Message-ID: <20190807132058.37616e8f@gandalf.local.home> In-Reply-To: <20190807170814.GA45351@lakrids.cambridge.arm.com> References: <20190807163401.570339297@goodmis.org> <20190807170814.GA45351@lakrids.cambridge.arm.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190807_102102_101482_F34C727C X-CRM114-Status: GOOD ( 16.04 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jiping Ma , catalin.marinas@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, mingo@redhat.com, Joel Fernandes , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, 7 Aug 2019 18:08:14 +0100 Mark Rutland wrote: > Hi Steve, > > On Wed, Aug 07, 2019 at 12:34:01PM -0400, Steven Rostedt wrote: > > As arm64 saves the link register after a function's local variables are > > stored, it causes the max stack tracer to be off by one in its output > > of which function has the bloated stack frame. > > For reference, it's a bit more complex than that. :/ Yeah, I know it is. ;-) > > Our procedure call standard (the AAPCS) says that the frame record may > be placed anywhere within a stackframe, so we don't have a guarantee as > to where the saved lr will fall w.r.t local variables. Yep. > > Today, GCC happens to create the stack frame by creating the stack > record, so the LR is saved at a lower addresss than the local variables. Which is what breaks the current algorithm (without this update). > > However, I am aware that there are reasons why a compiler may choose to > place the frame record at a different locations, e.g. using pointer > authentication to provide an implicit stack canary, so this could change > in future, or potentially differ across functions. > > Maybe that's a bridge we'll have to cross in future. OK, how about I update the change log and add a comment that states that this can change. But even if it does, it wont break anything but show the wrong stack size, which is usually only important for us kernel developers anyway ;-) Let me send a v2. -- Steve _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel