From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 973C6CA0FE1 for ; Fri, 1 Sep 2023 14:55:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350081AbjIAOzM convert rfc822-to-8bit (ORCPT ); Fri, 1 Sep 2023 10:55:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60126 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232461AbjIAOzL (ORCPT ); Fri, 1 Sep 2023 10:55:11 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C380DE7E for ; Fri, 1 Sep 2023 07:55:03 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with both STARTTLS and AUTH (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-320-eHemhXGyN5euSxOhUlYG5Q-1; Fri, 01 Sep 2023 15:55:01 +0100 X-MC-Unique: eHemhXGyN5euSxOhUlYG5Q-1 Received: from AcuMS.Aculab.com (10.202.163.6) by AcuMS.aculab.com (10.202.163.6) with Microsoft SMTP Server (TLS) id 15.0.1497.48; Fri, 1 Sep 2023 15:54:57 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.048; Fri, 1 Sep 2023 15:54:57 +0100 From: David Laight To: 'Ammar Faizi' CC: Willy Tarreau , =?iso-8859-1?Q?Thomas_Wei=DFschuh?= , Nicholas Rosenberg , "Alviro Iskandar Setiawan" , Michael William Jonathan , GNU/Weeb Mailing List , "Linux Kernel Mailing List" Subject: RE: [RFC PATCH v1 0/5] nolibc x86-64 string functions Thread-Topic: [RFC PATCH v1 0/5] nolibc x86-64 string functions Thread-Index: AQHZ23UUaWogkrxxpUapKlllYL+KVbAF2IcQgAAa01yAABQxQP//9ZyAgAASV3A= Date: Fri, 1 Sep 2023 14:54:56 +0000 Message-ID: <0d4effd9255143d6a7d90b5b37f01cdb@AcuMS.aculab.com> References: <20230830135726.1939997-1-ammarfaizi2@gnuweeb.org> <5a821292d96a4dbc84c96ccdc6b5b666@AcuMS.aculab.com> In-Reply-To: Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Ammar Faizi > Sent: 01 September 2023 15:42 ... > > > " movq %rdx, %rcx\n" > > > " movq %rdi, %rdx\n" > > > " movq %rdi, %rax\n" > > > > You seem to have confused yourself about whether you are using %eax or %edx. > > What do you mean? They're all 64-bit pointers. %ax, %eax, %rax - what is the difference :-) > What I know is that the %rdx will be clobbered by "subq %rsi, %rdx" > below and the %rax should be return value. That's why I copy the %rdi > twice. memmove() returns the dst pointer. Did I miss something? I'd forgotten about the (stupid) return value. I'm pretty sure it is an accident from the original pdp-11 implementation from the days before C had an explicit 'return' statement. (The pdp-11 I used ran RSX/11M - so had a Fortran compiler not a C one.) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)