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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9A111CCFA13 for ; Sun, 9 Nov 2025 06:54:24 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EFE1A8E0010; Sun, 9 Nov 2025 01:54:23 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id E62F08E0003; Sun, 9 Nov 2025 01:54:23 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D29B68E0010; Sun, 9 Nov 2025 01:54:23 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id BE3358E0003 for ; Sun, 9 Nov 2025 01:54:23 -0500 (EST) Received: from smtpin20.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 5A2DE1608C6 for ; Sun, 9 Nov 2025 06:54:23 +0000 (UTC) X-FDA: 84090154806.20.2DEB7A3 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf01.hostedemail.com (Postfix) with ESMTP id C50CA40006 for ; Sun, 9 Nov 2025 06:54:21 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=g4DJE34b; spf=pass (imf01.hostedemail.com: domain of rppt@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=rppt@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1762671261; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=XPWeKyzg8BB/Y/rh4nIrXhUKH7lPMvXxfiBvVBDK/oY=; b=HHV68C4wkuRA11yM4Gqkfvx1+r8cyGvIBS4pkgfY/xL+pOQcAkrsaThyaUV4dek5T/GKtg p4FQgzsYUhBHAI2dUtvxK85RSL1RbNO5/gCRy6ye0LDfx5sOBhjp7al4TS2u/efh2mDYUk dN1DiRDiw2xpvFCxQgs4cx5nUzYc6zU= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=g4DJE34b; spf=pass (imf01.hostedemail.com: domain of rppt@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=rppt@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1762671261; a=rsa-sha256; cv=none; b=AVHmkIchc578VBtlipRp0V1GqAC2PxK6uaYJUATrtfibOP/RlZTe1aEfu/Mr4D3kkO8RtY NwsEr+qvc5D7vgMBCPUKz9vMG4SUA6cnzh6U6EY21Oj5NvLebCmR71Oo3nxxULtFFP8WGf COKWjOdqdl1UsCI45UQGaFJpnZjZJIw= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 20B55601B2; Sun, 9 Nov 2025 06:54:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 835B6C16AAE; Sun, 9 Nov 2025 06:54:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762671260; bh=3JS1OgZ14RhHt06MEdgrfvg3N/fs6BGb/Kur+DRi2oE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=g4DJE34bZXgLmGCl+bPOHU3/pMacEfW6fXeyFOj4KAAaKC8vgSxqmhz+nCX5IoYly /q2t44l39jqUTuoxLwsvscAUEzf46VSW+s4sloJSKvEq4sXjoSVDyP2c0IlrEbS7DZ NYyv0G5d11oSBi4aWzo2zt/Y6RJNASmKFpX3FofOhaoM9OdaMpQB6Xj4LgIgNsog65 VYms1n0QIYM83TSiIdy0LQSgaBugIOmbuNFmiJW/9psFhVjbnZwOTrCrqqzjzBZfCX tmyXuwTYZiGPZ3IM++NLq6+haE6uqZmXREDw41mogiaVbRQD5rw8YfKV/k0Hzoz0kL RVSa5hJth48Wg== Date: Sun, 9 Nov 2025 08:54:12 +0200 From: Mike Rapoport To: Andrew Morton , Nathan Chancellor Cc: "David Hildenbrand (Red Hat)" , Ankit Khushwaha , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Shuah Khan , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] selftest/mm: fix pointer comparison in mremap_test Message-ID: References: <20251106104917.39890-1-ankitkhushwaha.linux@gmail.com> <6e07949b-d86f-46d8-a68c-9717cfb26084@kernel.org> <20251107160855.58891ac6df6854a3b608185f@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251107160855.58891ac6df6854a3b608185f@linux-foundation.org> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: C50CA40006 X-Stat-Signature: ynx4w13pcqsmazd7fnq4roi1d66jhwj6 X-Rspam-User: X-HE-Tag: 1762671261-399281 X-HE-Meta: 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 SPFZMZOy HJLori05pqjDOU9z2r38zEhhj29GGnx3i8YCGlFxc5S5lZvLPEgSEfmsSSKyhP3/vXgQ5+ZcY6U1LrEfoeBu4hmk/WLvebxqki4WP2p1lpomhVqOXRsTTkUNiaeN7Due1/S7SKgB1T3WtYi6sm8EdsMdyYBNSoDJI6IrJMa3R54kSCsts/Jz5HzRAkIqVF5o1ITZwdJ4+bBnjaaxQ8j1nCBPqk7oL9uRQ52kP5AWJ/MdA2WdGUXXHKJ4X+gsI2bYRI0U6ZnR0MdoH3v5WH+Ng0P9jbqz8ke/viFk1xlsfAEHeS2SNDnHi5WUOMl1q0b7zraZ6BFn7OE//ho4sak+8cRzobg9But8dQuSzxJOe6UocyyCorUYnejAk+pUkKAvUSHPNpc4O9wmPEDM= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: (added Nathan for clang advice) On Fri, Nov 07, 2025 at 04:08:55PM -0800, Andrew Morton wrote: > On Fri, 7 Nov 2025 10:27:27 +0100 "David Hildenbrand (Red Hat)" wrote: > > > On 06.11.25 13:02, Ankit Khushwaha wrote: > > > On Thu, Nov 06, 2025 at 12:18:57PM +0100, David Hildenbrand (Red Hat) wrote: > > >> On 06.11.25 11:49, Ankit Khushwaha wrote: > > >>> Pointer arthemitic with 'void * addr' and 'unsigned long long dest_alignment' > > >>> triggers following warning: > > >>> > > >>> mremap_test.c:1035:31: warning: pointer comparison always evaluates to > > >>> false [-Wtautological-compare] > > >>> 1035 | if (addr + c.dest_alignment < addr) { > > >>> | ^ > > >>> > > >>> typecasting 'addr' to 'unsigned long long' to fix pointer comparison. > > >> > > >> With which compiler are you seeing this? > > > > > > Hi David, > > > > > > clang version 20.1.8 (Fedora 20.1.8-4.fc42) raised this warning. > > > > > > To reproduce: > > > make -C tools/testing/selftests/mm CC=clang > > > > Thanks, and thanks to Lorenzo for the details. > > > > Acked-by: David Hildenbrand (Red Hat) > > I must say, applying this would be an unhappy life event. > > if (void* + ulong < void*) > > makes perfect sense in a world which permits void* arithmetic (ie, > ours). So what the heck is clang doing?? > > If we do > > void *addr2 = addr + c.dest_alignment; > if (addr2 < addr) > ... > > then which statement warns, and why? -- Sincerely yours, Mike.