Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755074Ab2B0VFL (ORCPT ); Mon, 27 Feb 2012 16:05:11 -0500 Received: from mail-qy0-f174.google.com ([209.85.216.174]:37941 "EHLO mail-qy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754265Ab2B0VFJ (ORCPT ); Mon, 27 Feb 2012 16:05:09 -0500 Authentication-Results: mr.google.com; spf=pass (google.com: domain of peter.maydell@linaro.org designates 10.224.185.207 as permitted sender) smtp.mail=peter.maydell@linaro.org MIME-Version: 1.0 In-Reply-To: <1330360043.8557.302.camel@zakaz.uk.xensource.com> References: <1330019314-20865-1-git-send-email-stefano.stabellini@eu.citrix.com> <1330360043.8557.302.camel@zakaz.uk.xensource.com> Date: Mon, 27 Feb 2012 21:05:08 +0000 Message-ID: Subject: Re: [PATCH-WIP 01/13] xen/arm: use r12 to pass the hypercall number to the hypervisor From: Peter Maydell To: Ian Campbell Cc: Stefano Stabellini , "xen-devel@lists.xensource.com" , "linaro-dev@lists.linaro.org" , "kvm@vger.kernel.org" , "arnd@arndb.de" , "catalin.marinas@arm.com" , "linux-kernel@vger.kernel.org" , David Vrabel , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 793 Lines: 19 On 27 February 2012 16:27, Ian Campbell wrote: > R12 is not accessible from the 16 bit "T1" Thumb encoding of mov > immediate (which can only target r0..r7). > > Since we support only ARMv7+ there are "T2" and "T3" encodings available > which do allow direct mov of an immediate into R12, but are 32 bit Thumb > instructions. > > Should we use r7 instead to maximise instruction density for Thumb code? r7 is (used by gcc as) the Thumb frame pointer; I don't know if this makes it worth avoiding in this context. -- PMM -- 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/