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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 288E1C4167D for ; Thu, 14 Apr 2022 15:57:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355860AbiDNP72 (ORCPT ); Thu, 14 Apr 2022 11:59:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58326 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354687AbiDNPlG (ORCPT ); Thu, 14 Apr 2022 11:41:06 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 77B1CDFD5D for ; Thu, 14 Apr 2022 08:21:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=+iRSXHQlt9lmhOSBYrvMuVQHw2ElrWncN2mrge5/yQ4=; b=D4UH8lPRYK29ybcCYqOCJLNd3u Q4+bXU/1kTRxIE7w0/mHcMkrSCPJLapr2iCBsE80oGx3aeLmDbXhfKP6Fkzs31vlY0FP+8YSnLnGA psKONhCK8ST+iduJ2Cti5dc3/6xuzu4tUyrIHXDJUf3AQJwRNtqCqg/sZFQdBxJcqgIJGbD60Bxdi oaS0jyseexJ2bmKgeTcR1u426IWL9UnLdxAAKWVNxQBpyvSlDMHvhbL3rxBlCURpBfsccZHjsU40U p/tYya+kBtsh2ywbDnxGs9FU+WwVs7jWaPh4lOoJ1W1BUap47SGA8TWNcD30kSVuVAPp+UnWSnl0A I59pSpRQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nf1HL-0052yG-BV; Thu, 14 Apr 2022 15:21:03 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 578083002DE; Thu, 14 Apr 2022 17:21:01 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 3B94F2057AAE7; Thu, 14 Apr 2022 17:21:01 +0200 (CEST) Date: Thu, 14 Apr 2022 17:21:01 +0200 From: Peter Zijlstra To: Christophe de Dinechin Cc: trivial@kernel.org, Ben Segall , "Michael S. Tsirkin" , Andrew Morton , Steven Rostedt , Ingo Molnar , Mel Gorman , Dietmar Eggemann , Vincent Guittot , Paolo Bonzini , Daniel Bristot de Oliveira , Jason Wang , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Zhen Lei , Juri Lelli Subject: Re: [PATCH 1/3] sched/headers: Fix compilation error with GCC 12 Message-ID: References: <20220414150855.2407137-1-dinechin@redhat.com> <20220414150855.2407137-2-dinechin@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220414150855.2407137-2-dinechin@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 14, 2022 at 05:08:53PM +0200, Christophe de Dinechin wrote: > With gcc version 12.0.1 20220401 (Red Hat 12.0.1-0) (GCC), the following > errors are reported in sched.h when building after `make defconfig`: > Rewrite the definitions of sched_class_highest and for_class_range to > avoid this error as follows: > > 1/ The sched_class_highest is rewritten to be relative to > __begin_sched_classes, so that GCC sees it as being part of the > __begin_sched_classes array and not a distinct __end_sched_classes > array. > > 2/ The for_class_range macro is modified to replace the comparison with > an out-of-bound pointer __begin_sched_classes - 1 with an equivalent, > but in-bounds comparison. > > In that specific case, I believe that the GCC analysis is correct and > potentially valuable for other arrays, so it makes sense to keep it > enabled. > > Signed-off-by: Christophe de Dinechin > Signed-off-by: Christophe de Dinechin > --- > kernel/sched/sched.h | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 8dccb34eb190..6350fbc7418d 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -2193,11 +2193,18 @@ const struct sched_class name##_sched_class \ > extern struct sched_class __begin_sched_classes[]; > extern struct sched_class __end_sched_classes[]; > > -#define sched_class_highest (__end_sched_classes - 1) > +/* > + * sched_class_highests is really __end_sched_classes - 1, but written in a way > + * that makes it clear that it is within __begin_sched_classes[] and not outside > + * of __end_sched_classes[]. > + */ > +#define sched_class_highest (__begin_sched_classes + \ > + (__end_sched_classes - __begin_sched_classes - 1)) > #define sched_class_lowest (__begin_sched_classes - 1) > > +/* The + 1 below places the pointers within the range of their array */ > #define for_class_range(class, _from, _to) \ > - for (class = (_from); class != (_to); class--) > + for (class = (_from); class + 1 != (_to) + 1; class--) Urgh, so now we get less readable code, just because GCC is being stupid? What's wrong with negative array indexes? memory is memory, stuff works.