From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752890Ab1AYMpp (ORCPT ); Tue, 25 Jan 2011 07:45:45 -0500 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:36854 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752476Ab1AYMpo (ORCPT ); Tue, 25 Jan 2011 07:45:44 -0500 Date: Tue, 25 Jan 2011 12:45:24 +0000 From: Russell King - ARM Linux To: Dave Martin Cc: Santosh Shilimkar , sen wang , David Brown , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: questions about arm trustzone Message-ID: <20110125124524.GJ11507@n2100.arm.linux.org.uk> References: <8yad3nlh18e.fsf@huya.qualcomm.com> <20110125102652.GB11507@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 25, 2011 at 12:24:13PM +0000, Dave Martin wrote: > Avoiding this complexity is one of the motivations for using r7 for > the syscall number with CONFIG_EABI (instead of using the SVC comment > field). Your history is not entirely correct. I had the kernel side of Thumb userspace support in place long before EABI came along. Thumb doesn't have a large enough comment field to store the Linux syscall number, so to get around that problem, I decided to use r7 for the syscall number. You'll find 2.4 kernels support Thumb instructions in userspace. As part of the EABI switch for ARM mode - which created an incompatible SWI interface anyway, we decided that we could reduce data cache pollution by eliminating the read of the SWI instruction, so we adopted the r7 method for ARM EABI mode. From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@arm.linux.org.uk (Russell King - ARM Linux) Date: Tue, 25 Jan 2011 12:45:24 +0000 Subject: questions about arm trustzone In-Reply-To: References: <8yad3nlh18e.fsf@huya.qualcomm.com> <20110125102652.GB11507@n2100.arm.linux.org.uk> Message-ID: <20110125124524.GJ11507@n2100.arm.linux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Jan 25, 2011 at 12:24:13PM +0000, Dave Martin wrote: > Avoiding this complexity is one of the motivations for using r7 for > the syscall number with CONFIG_EABI (instead of using the SVC comment > field). Your history is not entirely correct. I had the kernel side of Thumb userspace support in place long before EABI came along. Thumb doesn't have a large enough comment field to store the Linux syscall number, so to get around that problem, I decided to use r7 for the syscall number. You'll find 2.4 kernels support Thumb instructions in userspace. As part of the EABI switch for ARM mode - which created an incompatible SWI interface anyway, we decided that we could reduce data cache pollution by eliminating the read of the SWI instruction, so we adopted the r7 method for ARM EABI mode.