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 9F48CC63798 for ; Thu, 19 Nov 2020 14:59:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 41D93246A5 for ; Thu, 19 Nov 2020 14:59:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728072AbgKSO74 (ORCPT ); Thu, 19 Nov 2020 09:59:56 -0500 Received: from mail.kernel.org ([198.145.29.99]:59088 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726641AbgKSO74 (ORCPT ); Thu, 19 Nov 2020 09:59:56 -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 EDAB624695; Thu, 19 Nov 2020 14:59:52 +0000 (UTC) Date: Thu, 19 Nov 2020 09:59:51 -0500 From: Steven Rostedt To: Segher Boessenkool Cc: Peter Zijlstra , Florian Weimer , Nick Desaulniers , 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: <20201119095951.30269233@gandalf.local.home> In-Reply-To: <20201119143735.GU2672@gate.crashing.org> References: <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> <20201118135823.3f0d24b7@gandalf.local.home> <20201118191127.GM2672@gate.crashing.org> <20201119083648.GE3121392@hirez.programming.kicks-ass.net> <20201119143735.GU2672@gate.crashing.org> 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 Thu, 19 Nov 2020 08:37:35 -0600 Segher Boessenkool wrote: > > Note that we have a fairly extensive tradition of defining away UB with > > language extentions, -fno-strict-overflow, -fno-strict-aliasing, > > These are options to make a large swath of not correct C programs > compile (and often work) anyway. This is useful because there are so > many such programs, because a) people did not lint; and/or b) the > problem never was obvious with some other (or older) compiler; and/or > c) people do not care about writing portable C and prefer writing in > their own non-C dialect. Note, this is not about your average C program. This is about the Linux kernel, which already does a lot of tricks in C. There's a lot of code in assembly that gets called from C (and vise versa). We modify code on the fly (which tracepoints use two methods of that - with asm-goto/jump-labels and static functions). As for your point c), I'm not sure what you mean about portable C (stuck to a single compiler, or stuck to a single architecture?). Linux obviously supports multiple architectures (more than any other OS), but it is pretty stuck to gcc as a compiler (with LLVM just starting to work too). We are fine with being stuck to a compiler if it gives us what we want. -- Steve