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 096BDC7EE24 for ; Fri, 2 Jun 2023 15:32:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236645AbjFBPcq (ORCPT ); Fri, 2 Jun 2023 11:32:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46378 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235747AbjFBPcn (ORCPT ); Fri, 2 Jun 2023 11:32:43 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 005ED18C for ; Fri, 2 Jun 2023 08:32:42 -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 847D064D44 for ; Fri, 2 Jun 2023 15:32:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7D0CDC433D2; Fri, 2 Jun 2023 15:32:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1685719961; bh=SVkGyzyW8nD/mzC5YVIz+vKUiiAkmDQMqMj4UnkMOvY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=a4LjYWTpbyhaOCA2bjWfV6TKsAgOy0MeWkpXwXMgRqQrO2fOpIwDxkpGCod6ev4ca 4exLVAQJyOMXp3tiGzfhhJSoawY9lZ7CjmtbafYeUSEgx8zMoe+5cO8WLK7Ld1+U7Q B78Ybw4fArsHemqOhqq/BsAK0D1ZxmWYIek99Kjpv6Ub5LWPtmgP6Kj4SvPdGYoP/5 z8sPMznaMNgOnEiietpuLDNEH+Z/KkQjUj/swTZ8CRoi1YRNSq9ZdVCzqHO8tLSMPR M+s9niZ/npdhaRbYZD+/6nk5+6OugCI/TRittqnyBK+2HgnC6DQkz7rhn8C66EWYMB mxs+26vWyM5ww== Date: Fri, 2 Jun 2023 08:32:39 -0700 From: Josh Poimboeuf To: Peter Zijlstra Cc: Zack Rusin , linux-kernel@vger.kernel.org, Miroslav Benes , x86@kernel.org, VMware Graphics Reviewers , kernel test robot Subject: Re: [PATCH] drm/vmwgfx: Silence RBP clobber warnings Message-ID: <20230602153239.fsug6rgvoxgnrea6@treble> References: <20230602151639.GK620383@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230602151639.GK620383@hirez.programming.kicks-ass.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 02, 2023 at 05:16:39PM +0200, Peter Zijlstra wrote: > On Fri, Jun 02, 2023 at 07:56:34AM -0700, Josh Poimboeuf wrote: > > VMware hypercalls take the RBP register as input. This breaks basic > > frame pointer convention, as RBP should never be clobbered. > > > > So frame pointer unwinding is broken for the instructions surrounding > > the hypercall with the clobbered RBP. There's nothing that can be done > > about that. Just tell objtool to ignore it. > > > > That's a pretty horrific ABI, one that violates the oldest x86 calling > convention in existence. > > VMware folks, shame!! Agreed :-( BTW, please ignore the patch, I'll be sending a v2. I realized (with Peter's prodding on IRC) that reliable ORC unwinding would be broken if the function has a frame pointer. Which can happen if the function needs an aligned stack. -- Josh