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=-8.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,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 76C77C4363A for ; Fri, 23 Oct 2020 18:00:46 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E4F7D22201 for ; Fri, 23 Oct 2020 18:00:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="UjHQA+Pn" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E4F7D22201 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=JarB8xSvvKQTvGKFlwWX7iGyvrzi4z9wquhaopLhy5c=; b=UjHQA+Pn4xfBBvZad9RkauzJq JgioA5Uj9VxNsX298TQyuRBWJ6I4yZyQqmzFxD0JtmuTeN3h8TmrzJAbI9SCIWcdpMJG1oFIUekX7 p3a7igXiK9f+lpCczcBNsnmijA1wLRQFU4fem/5RwDKVIrIVmO7oWsThwRFtrs5z2V3W85lk/QT5f TnSeZ1O3D1i5l54HZog89gONrr0B0hGFOOAMXEWH73w1a2W/X7vswXmyR5gWk+IM6S1oPSktKUr6M +ZhhDR4a7klbqdianQHWyfg9GY6LpSKs1wWnDLWUEtmUqMId5uV86yk6V+Sw4ae78T/viK3oMzdmW okI+V+BsA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kW1LT-0005Qr-Uo; Fri, 23 Oct 2020 17:59:19 +0000 Received: from [2002:c35c:fd02::1] (helo=ZenIV.linux.org.uk) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kW1LP-0005PH-Sm for linux-arm-kernel@lists.infradead.org; Fri, 23 Oct 2020 17:59:18 +0000 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kW1L7-00749v-U5; Fri, 23 Oct 2020 17:58:58 +0000 Date: Fri, 23 Oct 2020 18:58:57 +0100 From: Al Viro To: David Hildenbrand Subject: Re: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c" Message-ID: <20201023175857.GA3576660@ZenIV.linux.org.uk> References: <5fd6003b-55a6-2c3c-9a28-8fd3a575ca78@redhat.com> <20201022104805.GA1503673@kroah.com> <20201022121849.GA1664412@kroah.com> <98d9df88-b7ef-fdfb-7d90-2fa7a9d7bab5@redhat.com> <20201022125759.GA1685526@kroah.com> <20201022135036.GA1787470@kroah.com> <134f162d711d466ebbd88906fae35b33@AcuMS.aculab.com> <935f7168-c2f5-dd14-7124-412b284693a2@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <935f7168-c2f5-dd14-7124-412b284693a2@redhat.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201023_135915_967114_18F3148B X-CRM114-Status: GOOD ( 17.54 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "linux-aio@kvack.org" , "linux-mips@vger.kernel.org" , David Howells , "linux-mm@kvack.org" , "keyrings@vger.kernel.org" , "sparclinux@vger.kernel.org" , Christoph Hellwig , "linux-arch@vger.kernel.org" , "linux-s390@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "kernel-team@android.com" , Arnd Bergmann , "linux-block@vger.kernel.org" , "io-uring@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Jens Axboe , "linux-parisc@vger.kernel.org" , 'Greg KH' , Nick Desaulniers , "linux-kernel@vger.kernel.org" , "linux-security-module@vger.kernel.org" , David Laight , "netdev@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , Andrew Morton , "linuxppc-dev@lists.ozlabs.org" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Oct 23, 2020 at 03:09:30PM +0200, David Hildenbrand wrote: > Now, I am not a compiler expert, but as I already cited, at least on > x86-64 clang expects that the high bits were cleared by the caller - in > contrast to gcc. I suspect it's the same on arm64, but again, I am no > compiler expert. > > If what I said and cites for x86-64 is correct, if the function expects > an "unsigned int", it will happily use 64bit operations without further > checks where valid when assuming high bits are zero. That's why even > converting everything to "unsigned int" as proposed by me won't work on > clang - it assumes high bits are zero (as indicated by Nick). > > As I am neither a compiler experts (did I mention that already? ;) ) nor > an arm64 experts, I can't tell if this is a compiler BUG or not. On arm64 when callee expects a 32bit argument, the caller is *not* responsible for clearing the upper half of 64bit register used to pass the value - it only needs to store the actual value into the lower half. The callee must consider the contents of the upper half of that register as undefined. See AAPCS64 (e.g. https://github.com/ARM-software/abi-aa/blob/master/aapcs64/aapcs64.rst#parameter-passing-rules ); AFAICS, the relevant bit is "Unlike in the 32-bit AAPCS, named integral values must be narrowed by the callee rather than the caller." _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel