Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934453AbeAKUKL (ORCPT + 1 other); Thu, 11 Jan 2018 15:10:11 -0500 Received: from mga07.intel.com ([134.134.136.100]:63365 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932419AbeAKUKK (ORCPT ); Thu, 11 Jan 2018 15:10:10 -0500 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,346,1511856000"; d="scan'208";a="26440805" Date: Thu, 11 Jan 2018 12:10:01 -0800 From: Andi Kleen To: Konrad Rzeszutek Wilk Cc: Andi Kleen , tglx@linutronix.de, x86@kernel.org, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, dwmw@amazon.co.uk, pjt@google.com, luto@kernel.org, peterz@infradead.org, thomas.lendacky@amd.com, tim.c.chen@linux.intel.com, gregkh@linux-foundation.org, dave.hansen@intel.com, jikos@kernel.org Subject: Re: [PATCH v1 2/8] x86/entry/clearregs: Add infrastructure to clear registers Message-ID: <20180111201001.GN6718@tassilo.jf.intel.com> References: <20180110010328.22163-1-andi@firstfloor.org> <20180110010328.22163-3-andi@firstfloor.org> <20180111195839.GC29272@char.us.oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180111195839.GC29272@char.us.oracle.com> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: > > + .macro CLEAR_ALL_REGS > > + CLEAR_R8_TO_R15 > > + xorl %eax, %eax > > + xorl %ebx, %ebx > > How come you use xorl vs xorq? 64bit always zero extends 32->64, and xorl is one byte shorter because it doesn't need a REX prefix. -Andi