Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933139Ab2EXPjn (ORCPT ); Thu, 24 May 2012 11:39:43 -0400 Received: from mail-lpp01m010-f46.google.com ([209.85.215.46]:36832 "EHLO mail-lpp01m010-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752761Ab2EXPjm convert rfc822-to-8bit (ORCPT ); Thu, 24 May 2012 11:39:42 -0400 MIME-Version: 1.0 In-Reply-To: <20120523191439.GC6908@n2100.arm.linux.org.uk> References: <20120523185610.GB6908@n2100.arm.linux.org.uk> <20120523191439.GC6908@n2100.arm.linux.org.uk> Date: Thu, 24 May 2012 10:39:38 -0500 Message-ID: Subject: Re: New ARM asm/syscall.h incompatible? (commit bf2c9f9866928df60157bc4f1ab39f93a32c754e) From: Will Drewry To: Russell King - ARM Linux Cc: wade_farnsworth@mentor.com, stevenrwalter@gmail.com, will.deacon@arm.com, Alexander Viro , Olof Johansson , LKML Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1451 Lines: 30 On Wed, May 23, 2012 at 2:14 PM, Russell King - ARM Linux wrote: > On Wed, May 23, 2012 at 02:04:20PM -0500, Will Drewry wrote: >> I'm still curious if it wouldn't make more sense to handle the >> sys_syscall special case prior to any cross-arch (slowpath) code >> involvement rather than truncating the 7th parameter making >> sys_syscall a second class citizen for those cross-arch paths. > > It would mean making sys_syscall an explicit special case in the fast > path of syscall entry, which we really don't want to do. ?It _is_ a > standard syscall, it just happens to have 7 arguments which are > rewritten back to what the syscall actually expects. > > As I say, the alternative would be to explicitly test for the syscall > number in the fast path of system call entry and branch away to deal > with it. ?Adding unnecessary instructions to this fast path for such > a special case when there's already a perfectly reasonable alternative > solution doesn't fill me with any joy. I'd been picturing this as being done exclusively after the slow-path is triggered, in __sys_trace or syscall_trace(), but perhaps I'm missing something that makes that untenable. thanks! will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/