From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753181Ab2CVRRM (ORCPT ); Thu, 22 Mar 2012 13:17:12 -0400 Received: from mx.scalarmail.ca ([98.158.95.75]:41950 "EHLO ironport-01.sms.scalar.ca" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751124Ab2CVRRI (ORCPT ); Thu, 22 Mar 2012 13:17:08 -0400 Date: Thu, 22 Mar 2012 13:17:02 -0400 From: Nick Bowler To: Jiri Slaby Cc: Phil Carmody , apw@canonical.com, hpa@zytor.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] checkpatch.pl: thou shalt not use () or (...) in function declarations Message-ID: <20120322171702.GA27776@elliptictech.com> References: <1332430038-21057-1-git-send-email-ext-phil.2.carmody@nokia.com> <4F6B51C9.6010904@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4F6B51C9.6010904@suse.cz> Organization: Elliptic Technologies Inc. User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2012-03-22 17:22 +0100, Jiri Slaby wrote: > On 03/22/2012 04:27 PM, Phil Carmody wrote: [...] > > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl > > index a3b9782..3993011 100755 > > --- a/scripts/checkpatch.pl > > +++ b/scripts/checkpatch.pl > > @@ -1881,6 +1881,10 @@ sub process { > > substr($ctx, 0, $name_len + 1, ''); > > $ctx =~ s/\)[^\)]*$//; > > > > + if ($ctx =~ /^\s*(?:\.\.\.)?\s*$/) { > > + # HPA explains why: http://lwn.net/Articles/487493/ > > + ERROR("(...) and () are not sufficiently informative function declarations\n$hereline"); > > + } > > That explanation is not fully correct. C99 explicitly says (6.7.5.3.14): > An identifier list declares only the identifiers of the parameters of > the function. An empty list in a function declarator that is part of a > definition of that function specifies that the function has no > parameters. Nevertheless, an empty identifier list in a declaration is still not the same as a parameter type list with (void). In particular, the empty identifier list *is not a prototype declaration for the function*. That means that arguments passed to the function are not subject to the usual checks/conversions implied by a prototype. Consider: int foo() { return 0; } int main(void) { return foo(1, 2, 3, 4, 5); /* this is syntactically OK; undefined behaviour at runtime. */ } GCC will not normally warn about the above (unless you pass -Wold-style-definition) which warns for all function definitions that lack a prototype. On the other hand, changing it to int foo(void) provides the required prototype for the arguments to be checked, and the above becomes a proper error. > So what you are trying to force here holds only for (forward) > declarations. Not for functions with definitions (bodies). Is > checkpatch capable to differ between those? For the above reasons, non-prototype declarations of any sort should be avoided. No need for checkpatch to distinguish between whether or not there's a function body. Cheers, -- Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)