Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753334AbbBMShy (ORCPT ); Fri, 13 Feb 2015 13:37:54 -0500 Received: from 216-12-86-13.cv.mvl.ntelos.net ([216.12.86.13]:37076 "EHLO brightrain.aerifal.cx" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751263AbbBMShx (ORCPT ); Fri, 13 Feb 2015 13:37:53 -0500 Date: Fri, 13 Feb 2015 13:37:07 -0500 From: Rich Felker To: Catalin Marinas Cc: "libc-alpha@sourceware.org" , "arnd@arndb.de" , "pinskia@gmail.com" , "musl@lists.openwall.com" , "linux-kernel@vger.kernel.org" , Andrew Pinski , Marcus Shawcroft , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCHv3 00/24] ILP32 support in ARM64 Message-ID: <20150213183706.GF23507@brightrain.aerifal.cx> References: <20141002155217.GH32147@e104818-lin.cambridge.arm.com> <20150210181302.GA23886@brightrain.aerifal.cx> <20150211173919.GF9058@e104818-lin.cambridge.arm.com> <20150211192118.GC23507@brightrain.aerifal.cx> <20150212181735.GF25491@e104818-lin.cambridge.arm.com> <501530245.495972.1423767564997.JavaMail.open-xchange@oxbaltgw04.schlund.de> <20150213133355.GD3508@e104818-lin.cambridge.arm.com> <20150213163013.GE23507@brightrain.aerifal.cx> <20150213173345.GA26217@e104818-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150213173345.GA26217@e104818-lin.cambridge.arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2159 Lines: 40 On Fri, Feb 13, 2015 at 05:33:46PM +0000, Catalin Marinas wrote: > > > > The data structure definition is a little bit fragile, as it depends on > > > > user space not using the __BIT_ENDIAN symbol in a conflicting way. So > > > > far we have managed to keep that outside of general purpose headers, but > > > > it should at least blow up in an obvious way if it does, rather than > > > > breaking silently. > > > > > > > > I still think it's more practical to keep the zeroing in user space though. > > > > In that case, we keep defining __kernel_timespec64 with a 'typedef long > > > > long __kernel_snseconds_t', and it's up to the libc to either use > > > > __kernel_timespec64 as its timespec, or to define a C11-compliant > > > > timespec itself and zero out the bits before passing the data to the kernel. > > > > > > The problem with doing this in user space is syscall(2). If we don't > > > allow it, then it's fine to do the padding in libc. > > > > It's already the case that callers have to tiptoe around syscall(2) > > usage on a per-arch basis for silly things like the convention for > > passing 64-bit arguments on 32-bit archs, different arg orders to work > > around 64-bit alignment and issues with too many args, and various > > legacy issues. So I think manual use of syscall(2) is a less-critical > > issue, though of course from a libc perspective I would very much like > > for the kernel to handle it right. > > I think there is another problem with sign-extending tv_nsec in libc. > The prototype for functions like clock_settime(2) take a const struct > timespec *. There isn't anything to prevent such structure being in a > read-only section, even though it is unlikely. So libc would have to > duplicate the structure rather than just sign-extending tv_nsec in > place. Yes, we already have to do this for x32 in musl. I'd rather not have to do the same for aarch64-ILP32. Rich -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/