Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765369AbcLTSdT (ORCPT ); Tue, 20 Dec 2016 13:33:19 -0500 Received: from terminus.zytor.com ([198.137.202.10]:60780 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1765302AbcLTSdR (ORCPT ); Tue, 20 Dec 2016 13:33:17 -0500 User-Agent: K-9 Mail for Android In-Reply-To: <20161220115109.GB289@x4> References: <20161215124513.GA289@x4> <20161220100056.GA289@x4> <2966d559-2cea-fd95-76d4-df34192a9b88@zytor.com> <20161220115109.GB289@x4> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Subject: Re: [tip:x86/urgent] x86/tools: Fix gcc-7 warning in relocs.c From: hpa@zytor.com Date: Tue, 20 Dec 2016 10:32:58 -0800 To: Markus Trippelsdorf CC: tglx@linutronix.de, linux-kernel@vger.kernel.org, mingo@kernel.org, linux-tip-commits@vger.kernel.org Message-ID: <20577F06-9AE8-4760-9F38-45711025D6FB@zytor.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1436 Lines: 36 On December 20, 2016 3:51:09 AM PST, Markus Trippelsdorf wrote: >On 2016.12.20 at 03:10 -0800, H. Peter Anvin wrote: >> On 12/20/16 02:00, Markus Trippelsdorf wrote: >> > On 2016.12.20 at 01:30 -0800, H. Peter Anvin wrote: >> >> I'd strongly prefer a non-data-dependent solution, specifically >adding >> >> at the top of sort_relocs(): >> >> >> >> if (!r->count) >> >> return; >> >> >> >> However, by my reading of the C and POSIX standards, this is a gcc >> >> error: qsort() should do nothing if the count is zero. >> > >> > No, it is invoking undefined behavior. >> >> > Notice the nonnull attribute in /usr/include/stdlib.h: >> > >> > 739 /* Sort NMEMB elements of BASE, of SIZE bytes each, >> > 740 using COMPAR to perform the comparisons. */ >> > 741 extern void qsort (void *__base, size_t __nmemb, size_t __size, >> > 742 __compar_fn_t __compar) __nonnull ((1, 4)); >> > >> > But feel free to revert my patch and add your solution. >> >> Well, s/gcc/glibc/ then. >> >> > The qsort() function shall sort an array of nel objects, >the >> > initial element of which is pointed to by base > >NULL does not point to any object, therefore it is UB. That seems, quite frankly, like a pretty idiotic lawyerism. Why would a pointer that by spec is never referenced not be able to be null? -- Sent from my Android device with K-9 Mail. Please excuse my brevity.