From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-s390-owner@vger.kernel.org>
Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57888 "EHLO
        lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S2502779AbgJVUJV (ORCPT
        <rfc822;linux-s390@vger.kernel.org>); Thu, 22 Oct 2020 16:09:21 -0400
Date: Thu, 22 Oct 2020 21:09:14 +0100
From: Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move
 rw_copy_check_uvector() into lib/iov_iter.c"
Message-ID: <20201022200914.GY3576660@ZenIV.linux.org.uk>
References: <a1533569-948a-1d5b-e231-5531aa988047@redhat.com>
 <bc0a091865f34700b9df332c6e9dcdfd@AcuMS.aculab.com>
 <5fd6003b-55a6-2c3c-9a28-8fd3a575ca78@redhat.com>
 <20201022132342.GB8781@lst.de>
 <8f1fff0c358b4b669d51cc80098dbba1@AcuMS.aculab.com>
 <CAKwvOdnix6YGFhsmT_mY8ORNPTOsN3HwS33Dr0Ykn-pyJ6e-Bw@mail.gmail.com>
 <CAK8P3a3LjG+ZvmQrkb9zpgov8xBkQQWrkHBPgjfYSqBKGrwT4w@mail.gmail.com>
 <CAKwvOdnhONvrHLAuz_BrAuEpnF5mD9p0YPGJs=NZZ0EZNo7dFQ@mail.gmail.com>
 <20201022192458.GV3576660@ZenIV.linux.org.uk>
 <20201022200629.GX3576660@ZenIV.linux.org.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20201022200629.GX3576660@ZenIV.linux.org.uk>
Sender: Al Viro <viro@ftp.linux.org.uk>
List-ID: <linux-s390.vger.kernel.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>, David Laight <David.Laight@aculab.com>, Christoph Hellwig <hch@lst.de>, David Hildenbrand <david@redhat.com>, Greg KH <gregkh@linuxfoundation.org>, "kernel-team@android.com" <kernel-team@android.com>, Andrew Morton <akpm@linux-foundation.org>, Jens Axboe <axboe@kernel.dk>, David Howells <dhowells@redhat.com>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>, "linux-parisc@vger.kernel.org" <linux-parisc@vger.kernel.org>, "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>, "linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>, "sparclinux@vger.kernel.org" <sparclinux@vger.kernel.org>, "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>, "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>, "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>, "linux-aio@kvack.org" <linux-aio@kvack.org>, "io-uring@vger.kernel.org" <io-uring@vger.kernel.org>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "netdev@vger.kernel.org" <netdev@vger.kernel.org>, "keyrings@vger.kernel.org" <keyrings@vger.kernel.org>, "linux-security-module@vger.kernel.org" <linux-security-module@vger.kernel.org>

On Thu, Oct 22, 2020 at 09:06:29PM +0100, Al Viro wrote:
> On Thu, Oct 22, 2020 at 08:24:58PM +0100, Al Viro wrote:
> 
> > Depending upon the calling conventions, compiler might do truncation in caller or
> > in a callee, but it must be done _somewhere_.
> 
> Unless I'm misreading AAPCS64,
> 	"Unlike in the 32-bit AAPCS, named integral values must be narrowed by the callee
> 	 rather than the caller"
> in 6.4.2 means that callee must not _not_ expect the upper 32 bits of %x0..%x7 to contain

Sorry, artefact of editing - that's

"in 6.4.2 means that callee must _not_ expect the upper 32 bits of %x0..%x7 to contain"

obviously.