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Message-ID: <20160525200327.GA22395@yury-N73SV> Date: Wed, 25 May 2016 23:03:27 +0300 From: Yury Norov <ynorov@...iumnetworks.com> To: David Miller <davem@...emloft.net> CC: <arnd@...db.de>, <catalin.marinas@....com>, <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>, <linux-arch@...r.kernel.org>, <linux-s390@...r.kernel.org>, <libc-alpha@...rceware.org>, <schwidefsky@...ibm.com>, <heiko.carstens@...ibm.com>, <pinskia@...il.com>, <broonie@...nel.org>, <joseph@...esourcery.com>, <christoph.muellner@...obroma-systems.com>, <bamvor.zhangjian@...wei.com>, <szabolcs.nagy@....com>, <klimov.linux@...il.com>, <Nathan_Lynch@...tor.com>, <agraf@...e.de>, <Prasun.Kapoor@...iumnetworks.com>, <kilobyte@...band.pl>, <geert@...ux-m68k.org>, <philipp.tomsich@...obroma-systems.com> Subject: Re: [PATCH 01/23] all: syscall wrappers: add documentation On Wed, May 25, 2016 at 12:30:17PM -0700, David Miller wrote: > From: Yury Norov <ynorov@...iumnetworks.com> > 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.
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