From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH 01/23] all: syscall wrappers: add documentation Date: Fri, 27 May 2016 10:42:59 +0200 Message-ID: <13240365.okADkKsTBJ@wuerfel> References: <6293194.tGy03QJ9ME@wuerfel> <20160527003753.GA14247@yury-N73SV> <20160527060357.GB3820@osiris> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: <20160527060357.GB3820@osiris> Sender: linux-doc-owner@vger.kernel.org To: Heiko Carstens Cc: Yury Norov , Catalin Marinas , 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 List-Id: linux-arch.vger.kernel.org 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. Tile is very similar to arm64 because it also uses the generic system call table, which I think is a good argument to keep them in sync. Arnd From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.kundenserver.de ([212.227.126.187]:52962 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932456AbcE0Inm (ORCPT ); Fri, 27 May 2016 04:43:42 -0400 From: Arnd Bergmann Subject: Re: [PATCH 01/23] all: syscall wrappers: add documentation Date: Fri, 27 May 2016 10:42:59 +0200 Message-ID: <13240365.okADkKsTBJ@wuerfel> In-Reply-To: <20160527060357.GB3820@osiris> References: <6293194.tGy03QJ9ME@wuerfel> <20160527003753.GA14247@yury-N73SV> <20160527060357.GB3820@osiris> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-arch-owner@vger.kernel.org List-ID: To: Heiko Carstens Cc: Yury Norov , Catalin Marinas , 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 Message-ID: <20160527084259.DGmO_TbSNsBVC8su4pOT793rEuDvJJnb7Krh_aUvnZI@z> 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. Tile is very similar to arm64 because it also uses the generic system call table, which I think is a good argument to keep them in sync. Arnd