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=-5.2 required=3.0 tests=BAYES_00, 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 5C2DEC56202 for ; Wed, 18 Nov 2020 18:58:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1062521D7A for ; Wed, 18 Nov 2020 18:58:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726963AbgKRS6a (ORCPT ); Wed, 18 Nov 2020 13:58:30 -0500 Received: from mail.kernel.org ([198.145.29.99]:58582 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726721AbgKRS62 (ORCPT ); Wed, 18 Nov 2020 13:58:28 -0500 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 900DA20639; Wed, 18 Nov 2020 18:58:25 +0000 (UTC) Date: Wed, 18 Nov 2020 13:58:23 -0500 From: Steven Rostedt To: Florian Weimer Cc: Segher Boessenkool , Nick Desaulniers , Peter Zijlstra , Sami Tolvanen , Mathieu Desnoyers , linux-kernel , Matt Mullins , Ingo Molnar , Alexei Starovoitov , Daniel Borkmann , Dmitry Vyukov , Martin KaFai Lau , Song Liu , Yonghong Song , Andrii Nakryiko , John Fastabend , KP Singh , netdev , bpf , Kees Cook , Josh Poimboeuf , linux-toolchains@vger.kernel.org Subject: Re: violating function pointer signature Message-ID: <20201118135823.3f0d24b7@gandalf.local.home> In-Reply-To: <87o8jutt2h.fsf@mid.deneb.enyo.de> References: <20201116175107.02db396d@gandalf.local.home> <47463878.48157.1605640510560.JavaMail.zimbra@efficios.com> <20201117142145.43194f1a@gandalf.local.home> <375636043.48251.1605642440621.JavaMail.zimbra@efficios.com> <20201117153451.3015c5c9@gandalf.local.home> <20201118132136.GJ3121378@hirez.programming.kicks-ass.net> <20201118121730.12ee645b@gandalf.local.home> <20201118181226.GK2672@gate.crashing.org> <87o8jutt2h.fsf@mid.deneb.enyo.de> X-Mailer: Claws Mail 3.17.3 (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 On Wed, 18 Nov 2020 19:31:50 +0100 Florian Weimer wrote: > * Segher Boessenkool: > > > On Wed, Nov 18, 2020 at 12:17:30PM -0500, Steven Rostedt wrote: > >> I could change the stub from (void) to () if that would be better. > > > > Don't? In a function definition they mean exactly the same thing (and > > the kernel uses (void) everywhere else, which many people find clearer). > > And I think () functions expected a caller-provided parameter save > area on powerpc64le, while (void) functions do not. It does not > matter for an empty function, but GCC prefers to use the parameter > save area instead of setting up a stack frame if it is present. So > you get stack corruption if you call a () function as a (void) > function. (The other way round is fine.) I wonder if we should define on all architectures a void void_stub(void), in assembly, that just does a return, an not worry about gcc messing up the creation of the stub function. On x86_64: GLOBAL(void_stub) retq And so on. -- Steve