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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 D8E91C54FCB for ; Sat, 25 Apr 2020 18:38:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B3470206ED for ; Sat, 25 Apr 2020 18:38:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726294AbgDYSiP (ORCPT ); Sat, 25 Apr 2020 14:38:15 -0400 Received: from gate.crashing.org ([63.228.1.57]:57374 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726145AbgDYSiO (ORCPT ); Sat, 25 Apr 2020 14:38:14 -0400 Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 03PIb3e7031547; Sat, 25 Apr 2020 13:37:03 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 03PIb15d031546; Sat, 25 Apr 2020 13:37:01 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Sat, 25 Apr 2020 13:37:01 -0500 From: Segher Boessenkool To: Borislav Petkov Cc: Arvind Sankar , Jakub Jelinek , jgross@suse.com, x86@kernel.org, Kees Cook , Peter Zijlstra , linuxppc-dev@lists.ozlabs.org, Michael Matz , Nick Desaulniers , LKML , Sergei Trofimovich , clang-built-linux , Ingo Molnar , Paul Mackerras , Andy Lutomirski , "H. Peter Anvin" , =?iso-8859-1?Q?Fr=E9d=E9ric_Pierret_=28fepitre=29?= , Thomas Gleixner , Martin =?utf-8?B?TGnFoWth?= , boris.ostrovsky@oracle.com Subject: Re: [PATCH] x86: Fix early boot crash on gcc-10, next try Message-ID: <20200425183701.GE17645@gate.crashing.org> References: <20200422192113.GG26846@zn.tnic> <20200422212605.GI26846@zn.tnic> <20200423125300.GC26021@zn.tnic> <20200423161126.GD26021@zn.tnic> <20200425014657.GA2191784@rani.riverdale.lan> <20200425085759.GA24294@zn.tnic> <20200425150440.GA470719@rani.riverdale.lan> <20200425173140.GB24294@zn.tnic> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200425173140.GB24294@zn.tnic> User-Agent: Mutt/1.4.2.3i Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Apr 25, 2020 at 07:31:40PM +0200, Borislav Petkov wrote: > > There's also the one in init/main.c which is used by multiple > > architectures. On x86 at least, the call to arch_call_rest_init at the > > end of start_kernel does not get tail-call optimized by gcc-10, but I > > don't see anything that actually prevents that from happening. We should > > add the asm("") there as well I think, unless the compiler guys see > > something about this function that will always prevent the optimization? > > Hmm, that's what I was afraid of - having to sprinkle this around. Yah, let's > wait for compiler guys to have a look here and then maybe I'll convert that > thing to a macro called > > compiler_prevent_tail_call_opt() > > or so, so that it can be sprinkled around. ;-\ That is a lot more typing then asm(""); but more seriously, you probably should explain why you do not want a tail call *anyway*, and in such a comment you can say that is what the asm is for. I don't see anything that prevents the tailcall in current code either, fwiw. Segher