From mboxrd@z Thu Jan 1 00:00:00 1970 From: ynorov@caviumnetworks.com (Yury Norov) Date: Wed, 25 May 2016 23:03:27 +0300 Subject: [PATCH 01/23] all: syscall wrappers: add documentation In-Reply-To: <20160525.123017.1597296248000772613.davem@davemloft.net> 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> Message-ID: <20160525200327.GA22395@yury-N73SV> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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.