From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S271619AbTGQXKa (ORCPT ); Thu, 17 Jul 2003 19:10:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S271625AbTGQXKa (ORCPT ); Thu, 17 Jul 2003 19:10:30 -0400 Received: from x35.xmailserver.org ([208.129.208.51]:11970 "EHLO x35.xmailserver.org") by vger.kernel.org with ESMTP id S271619AbTGQXK3 (ORCPT ); Thu, 17 Jul 2003 19:10:29 -0400 X-AuthUser: davidel@xmailserver.org Date: Thu, 17 Jul 2003 16:18:06 -0700 (PDT) From: Davide Libenzi X-X-Sender: davide@bigblue.dev.mcafeelabs.com To: "Randy.Dunlap" cc: lkml Subject: Re: asm (lidt) question In-Reply-To: Message-ID: References: <20030717152819.66cfdbaf.rddunlap@osdl.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 17 Jul 2003, Davide Libenzi wrote: > On Thu, 17 Jul 2003, Randy.Dunlap wrote: > > > > > In arch/i386/kernel, inline asm for loading IDT (lidt) is used a few > > times, but with slightly different constraints and output/input > > definitions. Are these OK, equivalent, or what? > > > > [rddunlap@dragon kernel]$ findc lidt > > ./cpu/common.c:484: __asm__ __volatile__("lidt %0": "=m" (idt_descr)); > > ./traps.c:783: __asm__ __volatile__("lidt %0": "=m" (idt_descr)); > > > > vs. > > > > ./reboot.c:186: __asm__ __volatile__ ("lidt %0" : : "m" (real_mode_idt)); > > ./reboot.c:261: __asm__ __volatile__("lidt %0": :"m" (no_idt)); > > ./suspend.c:95: asm volatile ("lidt %0" :: "m" (saved_context.idt_limit)); > > I'd have said no looking at the syntax (input/output), but they indeed > generate the same code (just checked). Randy, I'd say that this : __asm__ __volatile__("lidt %0": "=m" (var)); is better then : __asm__ __volatile__("lidt %0": :"m" (var)); IMHO, since "var" is really an output parameter. - Davide