From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751906AbcE0KuP (ORCPT ); Fri, 27 May 2016 06:50:15 -0400 Received: from mout.kundenserver.de ([217.72.192.75]:53511 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750698AbcE0KuN (ORCPT ); Fri, 27 May 2016 06:50:13 -0400 From: Arnd Bergmann To: Catalin Marinas Cc: Heiko Carstens , Yury Norov , David Miller , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, libc-alpha@sourceware.org, schwidefsky@de.ibm.com, pinskia@gmail.com, broonie@kernel.org, joseph@codesourcery.com, christoph.muellner@theobroma-systems.com, bamvor.zhangjian@huawei.com, szabolcs.nagy@arm.com, klimov.linux@gmail.com, Nathan_Lynch@mentor.com, agraf@suse.de, Prasun.Kapoor@caviumnetworks.com, kilobyte@angband.pl, geert@linux-m68k.org, philipp.tomsich@theobroma-systems.com Subject: Re: [PATCH 01/23] all: syscall wrappers: add documentation Date: Fri, 27 May 2016 12:49:11 +0200 Message-ID: <5422652.7gdoDlB8u0@wuerfel> User-Agent: KMail/5.1.3 (Linux/4.4.0-22-generic; KDE/5.18.0; x86_64; ; ) In-Reply-To: <20160527093052.GB7865@e104818-lin.cambridge.arm.com> References: <6293194.tGy03QJ9ME@wuerfel> <13240365.okADkKsTBJ@wuerfel> <20160527093052.GB7865@e104818-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Provags-ID: V03:K0:mi/XtiUjn7mQa950H7XNqgIvsvrUJgj/Okte1eKz/EDuhrjSybh WNLOLPc6Zy+UmKGZ7vHTCMj0EoRTAWx28yCCZBIVsZawVAOltuWFIZ81vtHkyBB3Oqvew0K s4yPNBY/F+dAAxcEyEbKStuXjcTUnFzji+8aIo219ErbSOpjDBQPWOMQ1dAJ/QIHIDB67SE PwDor067QhGrQwfFmk+dg== X-UI-Out-Filterresults: notjunk:1;V01:K0:m7Edizn9Gzg=:akqlwLQbNvC0VzFkDMj22+ b4q8cXe8+tgnZyjL2nAMrKsutbdV/c2tPhWX0dxvvpJEvpj5TvfSQ8pMUDSzkyYjCbUZr4gxJ a2pnq3TwhYyr/9b3pHklSkFB5SunE65pKaqeCyFYxY7Cs4bEoURE5rRSwhu3E7q4w+sLlM09Y vdrOIVvoQiC3bblb9z3Ce6eyoSWFN6gtlDONehJKzAlpRyURVqcBS8CpOcUfKQTTORFsNBofY KfLNuLPySCvbkhyaokYrNLKwxpcSFhGjkL6vkd8FVg+sSPzrZDPIrwicH3B3XVZ/rRtucQW2j 5CYSxJzCdbyuzbzJCYO5YICwSzCrkpZkkwKzzAxjMLNZdX9ginEqrkK+wTj+7ARjszh7R62lP 9kwzkZZun2g24Uj4QOZ5CQw5yShOTsNJtPlYgZRGYtGtHxrLhWvo8FYdIMRhzyCoSOHDdIjXD mjHlLDYxapzh48SIcj9lRMEUMihX1nSqizw9DQNWi+VnYG2WzhFzebLAHd6EOzEW2jUKYBWvb hjI/Ev1Dli/Xwg0VALzOwpJcYOCGlG7ypzmv8Y5K7ZFr0d2cV6w/YP1VwMa5RqOTkf8bua7H8 7zsy+gbnNfAyGc0CltsNv5/ZHl7CSM6JtpuPYEdC8MzkM4BEiFSoUtCQnjj4NsKY8MWWbJRW2 0j4J+mjUhMcAKWiOi1FA/DgmkFhKHxmteg3umXU8ZYEivlMi7dYmvaIfznDybdeiMajh3FFEe NTff/FczGjsyqANW Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday, May 27, 2016 10:30:52 AM CEST Catalin Marinas wrote: > On Fri, May 27, 2016 at 10:42:59AM +0200, Arnd Bergmann wrote: > > On Friday, May 27, 2016 8:03:57 AM CEST Heiko Carstens wrote: > > > > > > > Cost wise, this seems like it all cancels out in the end, but what > > > > > > > do I know? > > > > > > > > > > > > I think you know something, and I also think Heiko and other s390 guys > > > > > > know something as well. So I'd like to listen their arguments here. > > > > > > If it comes to 64 bit arguments for compat system calls: s390 also has an > > > x32-like ABI extension which allows user space to use full 64 bit > > > registers. As far as I know hardly anybody ever made use of that. > > > > > > However even if that would be widely used, to me it wouldn't make sense to > > > add new compat system calls which allow 64 bit arguments, simply because > > > something like > > > > > > c = (u32)a | (u64)b << 32; > > > > > > can be done with a single 1-cycle instruction. It's just not worth the > > > extra effort to maintain additional system call variants. > > > > For reference, both tile and mips also have separate 32-bit ABIs that are > > only used on 64-bit kernels (aside from the normal 32-bit ABI). Tile > > does it like s390 and passes 64-bit arguments as pairs, while MIPS > > and x86 and pass them as single registers. > > AFAIK, x32 also requires that the upper half of a 64-bit reg is zeroed > by the user when a 32-bit value is passed. We could require the same on > AArch64/ILP32 but I'm a bit uneasy on trusting a multitude of C > libraries on this. It's not about trusting a C library, it's about ensuring malicious code cannot pass argumentst that the kernel code assumes will never happen. Arnd