From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS22989 209.51.188.0/24 X-Spam-Status: No, score=-4.0 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS, SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id 9E7231F910 for ; Thu, 17 Nov 2022 13:31:14 +0000 (UTC) Authentication-Results: dcvr.yhbt.net; dkim=pass (1024-bit key; unprotected) header.d=suse.de header.i=@suse.de header.b="0HJ2Jere"; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b="69Fd7ufm"; dkim-atps=neutral Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oveyS-0000mC-Ha; Thu, 17 Nov 2022 08:30:36 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oveyQ-0000ll-1n; Thu, 17 Nov 2022 08:30:34 -0500 Received: from smtp-out2.suse.de ([2001:67c:2178:6::1d]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1oveyN-00005H-RV; Thu, 17 Nov 2022 08:30:33 -0500 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 15BE01F8E2; Thu, 17 Nov 2022 13:30:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1668691828; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=S9s3euRI52E23U0lyqtXLN5IP0BEP4LaY/n3T/kn7N8=; b=0HJ2JeresGEZ6fwPT+ac5+Li6jdivKakWb05xkxlTyWNz0hh2e0cXLHzoBCv4cc51UAkKV IX1cxZroyhAOC7A80SWnyeH9QKTYlz8IbyPWK2n38WIioNKaM/GMFsMgR9R9Pw6dpL16VO e1rEp7Riurhzm3NEon8tt6UorXglBs4= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1668691828; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=S9s3euRI52E23U0lyqtXLN5IP0BEP4LaY/n3T/kn7N8=; b=69Fd7ufmGkp0bw6pl8PeAreXHg3xyrWs3He5P2p+sI8A0MwibkyaeXOVn0eoizwOb0oe1m dPZGGeOu4Oqm37CQ== Received: from wotan.suse.de (wotan.suse.de [10.160.0.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id B28B92C141; Thu, 17 Nov 2022 13:30:26 +0000 (UTC) Received: by wotan.suse.de (Postfix, from userid 10510) id 8B4B2635A; Thu, 17 Nov 2022 13:30:26 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by wotan.suse.de (Postfix) with ESMTP id 8920C6266; Thu, 17 Nov 2022 13:30:26 +0000 (UTC) Date: Thu, 17 Nov 2022 13:30:26 +0000 (UTC) From: Michael Matz To: Paul Eggert cc: Jonathan Wakely , Aaron Ballman , Zack Weinberg , c-std-porting@lists.linux.dev, autoconf@gnu.org, gcc@gcc.gnu.org, cfe-commits@lists.llvm.org, Gnulib bugs Subject: Re: How can Autoconf help with the transition to stricter compilation defaults? In-Reply-To: <4cfa16b3-e9e0-0ec0-659c-e4aef6090995@cs.ucla.edu> Message-ID: References: <24ed5604-305a-4343-a1b6-a789e4723849@app.fastmail.com> <251923e7-57be-1611-be10-49c3067adf0d@cs.ucla.edu> <7ef0ce03-d908-649a-a6ee-89fea374d2b1@cs.ucla.edu> <9cb106e9-16ff-65ec-6a44-6567c77521dc@cs.ucla.edu> <06a5d2cd-44eb-7404-17f3-ff64dd505427@cs.ucla.edu> <4cfa16b3-e9e0-0ec0-659c-e4aef6090995@cs.ucla.edu> User-Agent: Alpine 2.20 (LSU 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Received-SPF: pass client-ip=2001:67c:2178:6::1d; envelope-from=matz@suse.de; helo=smtp-out2.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: bug-gnulib@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gnulib discussion list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-gnulib-bounces+normalperson=yhbt.net@gnu.org Sender: bug-gnulib-bounces+normalperson=yhbt.net@gnu.org Hello, On Wed, 16 Nov 2022, Paul Eggert wrote: > On 2022-11-16 06:26, Michael Matz wrote: > > char foobar(void); > > int main(void) { > > return &foobar != 0; > > } > > That still has undefined behavior according to draft C23, This is correct (and also holds for the actually working variant later, with a volatile variable). If your argument is then that as both solutions for the link-test problem are relying on undefined behaviour they are equivalent and hence no change is needed, you have a point, but I disagree. In practice one (with the call) will cause more problems than the other (with address taking). > If Clang's threatened pickiness were of some real use elsewhere, it > might be justifiable for default Clang to break Autoconf. But so far we > haven't seen real-world uses that would justify this pickiness for > Autoconf's use of 'char memset_explicit(void);'. Note that both, GCC and clang, already warn (not error out!) about the mismatching decl, even without any headers. So we are in the pickiness era already. I.e. a C file containing just a single line "char printf(void);" will be warned about, by default. There is about nothing that autoconf could do to rectify this, except containing a long list of prototypes for well-known functions, with the associated maintenance hassle. But autoconf _can_ do something about how the decls are used in the link-tests. Ciao, Michael.