From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750783AbWFGEIp (ORCPT ); Wed, 7 Jun 2006 00:08:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750810AbWFGEIp (ORCPT ); Wed, 7 Jun 2006 00:08:45 -0400 Received: from hera.kernel.org ([140.211.167.34]:23961 "EHLO hera.kernel.org") by vger.kernel.org with ESMTP id S1750783AbWFGEIo (ORCPT ); Wed, 7 Jun 2006 00:08:44 -0400 To: linux-kernel@vger.kernel.org From: "H. Peter Anvin" Subject: Re: AMD64: 64 bit kernel 32 bit userland - some pending questions Date: Tue, 6 Jun 2006 21:08:26 -0700 (PDT) Organization: Mostly alphabetical, except Q, with we do not fancy Message-ID: References: <787b0d920606062011j21083e80v659228a7565ecfab@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Trace: terminus.zytor.com 1149653306 22752 127.0.0.1 (7 Jun 2006 04:08:26 GMT) X-Complaints-To: news@terminus.zytor.com NNTP-Posting-Date: Wed, 7 Jun 2006 04:08:26 +0000 (UTC) X-Newsreader: trn 4.0-test76 (Apr 2, 2001) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Followup to: <787b0d920606062011j21083e80v659228a7565ecfab@mail.gmail.com> By author: "Albert Cahalan" In newsgroup: linux.dev.kernel > > The bigger problem is that 32-bit code has fewer CPU registers. > (nobody has done an ILP32 ABI for long mode) This is slow. > The issue isn't the ABI, the issue is that the processor doesn't support it, since some of the opcodes mean different things in 16-, 32- and 64-bit mode. The opcodes which access the high half of the register sets (REX prefixes) in 64-bit mode are INC and DEC instructions in 16- and 32-bit mode. AMD was apparently considering adding a "REX32" mode at some point, but rather predictably noone was interested enough to make it worthwhile. -hpa