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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 984D9C43144 for ; Fri, 29 Jun 2018 02:55:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 27E80279A2 for ; Fri, 29 Jun 2018 02:55:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 27E80279A2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967662AbeF2Czm (ORCPT ); Thu, 28 Jun 2018 22:55:42 -0400 Received: from ozlabs.org ([203.11.71.1]:39223 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966362AbeF2Czl (ORCPT ); Thu, 28 Jun 2018 22:55:41 -0400 Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPSA id 41H1VM6ClLz9s01; Fri, 29 Jun 2018 12:55:39 +1000 (AEST) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au From: Michael Ellerman To: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , malat@debian.org, aneesh.kumar@linux.vnet.ibm.com Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH] powerpc/mm: fix always true/false warning in slice.c In-Reply-To: <63b696ab7be8b941fa1e1589f28260320d12a32a.1529589640.git.christophe.leroy@c-s.fr> References: <63b696ab7be8b941fa1e1589f28260320d12a32a.1529589640.git.christophe.leroy@c-s.fr> Date: Fri, 29 Jun 2018 12:55:39 +1000 Message-ID: <871scqwbbo.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christophe Leroy writes: > This patch fixes the following warnings (obtained with make W=1). > > arch/powerpc/mm/slice.c: In function 'slice_range_to_mask': > arch/powerpc/mm/slice.c:73:12: error: comparison is always true due to limited range of data type [-Werror=type-limits] > if (start < SLICE_LOW_TOP) { Presumably only on 32-bit ? > diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c > index 9530c6db406a..17c57760e06c 100644 > --- a/arch/powerpc/mm/slice.c > +++ b/arch/powerpc/mm/slice.c > @@ -79,7 +86,7 @@ static void slice_range_to_mask(unsigned long start, unsigned long len, > - (1u << GET_LOW_SLICE_INDEX(start)); > } > > - if ((start + len) > SLICE_LOW_TOP) { > + if (!slice_addr_is_low(end)) { > unsigned long start_index = GET_HIGH_SLICE_INDEX(start); > unsigned long align_end = ALIGN(end, (1UL << SLICE_HIGH_SHIFT)); > unsigned long count = GET_HIGH_SLICE_INDEX(align_end) - start_index; This worries me. By casting before the comparison in the helper you squash the compiler warning, but the code is still broken if (start + len) overflows. Presumably that "never happens", but it just seems fishy. The other similar check in that file does: if (SLICE_NUM_HIGH && ((start + len) > SLICE_LOW_TOP)) { Where SLICE_NUM_HIGH == 0 on 32-bit. Could we fix the less than comparisons with SLICE_LOW_TOP with something similar, eg: if (!SLICE_NUM_HIGH || start < SLICE_LOW_TOP) { ie. limit them to the 64-bit code? cheers