Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752233Ab3FEHDY (ORCPT ); Wed, 5 Jun 2013 03:03:24 -0400 Received: from nat28.tlf.novell.com ([130.57.49.28]:45826 "EHLO nat28.tlf.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751682Ab3FEHDX convert rfc822-to-8bit (ORCPT ); Wed, 5 Jun 2013 03:03:23 -0400 Message-Id: <51AEFED002000078000DB542@nat28.tlf.novell.com> X-Mailer: Novell GroupWise Internet Agent 12.0.2 Date: Wed, 05 Jun 2013 08:03:12 +0100 From: "Jan Beulich" To: "Mukesh Rathor" Cc: "xen-devel" , , Subject: Re: [Xen-devel] [PATCH] PVH: vcpu info placement, load selectors, and remove debug printk. References: <1370306612-12984-1-git-send-email-mukesh.rathor@oracle.com> <51ADC0F702000078000DAF5A@nat28.tlf.novell.com> <20130604145304.117ac60f@mantra.us.oracle.com> In-Reply-To: <20130604145304.117ac60f@mantra.us.oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1486 Lines: 47 >>> On 04.06.13 at 23:53, Mukesh Rathor wrote: > Following OK? : > > if (xen_feature(XENFEAT_auto_translated_physmap)) { > switch_to_new_gdt(0); > > asm volatile ( > "pushq %%rax\n" > "leaq 1f(%%rip),%%rax\n" > "pushq %%rax\n" > "lretq\n" > "1:\n" > : : "a" (__KERNEL_CS) : "memory"); > > return; > } While generally the choice of using %%rax instead of %0 here is a matter of taste to some degree, I still don't see why you can't use "r" as the constraint here in the first place. Furthermore, assuming this sits in a function guaranteed to not be inlined, this has a latent bug (and if the assumption isn't right, the bug is real) in that the asm() modifies %rax without telling the compiler. This is how I would have done it: unsigned long dummy; asm volatile ("pushq %0\n" "leaq 1f(%%rip),%0\n" "pushq %0\n" "lretq\n" "1:\n" : "=&r" (dummy) : "0" (__KERNEL_CS)); (also dropping the memory clobber, as I don't see what you need this for). Jan -- 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/