From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yury Norov Subject: Re: [PATCH 01/23] all: syscall wrappers: add documentation Date: Wed, 25 May 2016 23:03:27 +0300 Message-ID: <20160525200327.GA22395@yury-N73SV> References: <1464048292-30136-1-git-send-email-ynorov@caviumnetworks.com> <1464048292-30136-2-git-send-email-ynorov@caviumnetworks.com> <20160525.123017.1597296248000772613.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Return-path: Content-Disposition: inline In-Reply-To: <20160525.123017.1597296248000772613.davem@davemloft.net> Sender: linux-doc-owner@vger.kernel.org List-Archive: List-Post: To: David Miller Cc: arnd@arndb.de, catalin.marinas@arm.com, 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, heiko.carstens@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: On Wed, May 25, 2016 at 12:30:17PM -0700, David Miller wrote: > From: Yury Norov > Date: Tue, 24 May 2016 03:04:30 +0300 > > > +To clear that top halves, automatic wrappers are introduced. They clear all > > +required registers before passing control to regular syscall handler. > > Why have one of these for every single compat system call, rather than > simply clearing the top half of all of these registers unconditionally > in the 32-bit system call trap before the system call is invoked? > > That's what we do on sparc64. > > And with that, you only need wrappers for the case where there needs > to be proper sign extention of a 32-bit signed argument. It was discussed as one of possible solutions. The downside of it is that we cannot pass 64-bit types (like off_t) in single register. The other downside is that we clear top halves for every single syscall, and it looks excessive. So, from spark64 and s390 approaches we choosed second.