Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2992459AbXBIRuF (ORCPT ); Fri, 9 Feb 2007 12:50:05 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S2992463AbXBIRuE (ORCPT ); Fri, 9 Feb 2007 12:50:04 -0500 Received: from tmailer.gwdg.de ([134.76.10.23]:48466 "EHLO tmailer.gwdg.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2992457AbXBIRuB (ORCPT ); Fri, 9 Feb 2007 12:50:01 -0500 Date: Fri, 9 Feb 2007 18:45:54 +0100 (MET) From: Jan Engelhardt To: "linux-os (Dick Johnson)" cc: Linus Torvalds , David Rientjes , Jeff Garzik , Linux Kernel Mailing List , Andrew Morton Subject: Re: somebody dropped a (warning) bomb In-Reply-To: Message-ID: References: <45CB3B28.60102@garzik.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Spam-Report: Content analysis: 0.0 points, 6.0 required _SUMMARY_ Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1470 Lines: 37 On Feb 9 2007 08:16, linux-os (Dick Johnson) wrote: >On Fri, 9 Feb 2007, Jan Engelhardt wrote: >> On Feb 8 2007 16:42, Linus Torvalds wrote: >>> >> Further, giving again answer to the question whether they generate >> signed or unsigned comparisons: Have you ever seen a computer which >> addresses memory with negative numbers? Since the answer is most likely >> no, signed comparisons would > >Yes, most all do. Indexed memory operands are signed displacements. See >page 2-16, Intel486 Microprocessor Programmer's Reference Manual. This I was referring to "absolute memory", not the offset magic that assembler allows. After all, (reg+relativeOffset) will yield an absolute address. What I was out at: for machines that have more than 2 GB of memory, you don't call the address that is given by 0x80000000U actually "byte -2147483648", but "byte 2147483648". >gets hidden by higher-level languages such as 'C'. It is also non-obvious >when using the AT&T (GNU) assembly language. However, the Intel documentation >shows it clearly: > MOV AL, [EBX+0xFFFFFFFF] ; -1 It can be debated what exactly this is... negative offset or "using overflow to get where we want". Jan -- ft: http://freshmeat.net/p/chaostables/ - 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/