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 A7553C7EE29 for ; Fri, 9 Jun 2023 09:21:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239033AbjFIJVn convert rfc822-to-8bit (ORCPT ); Fri, 9 Jun 2023 05:21:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43048 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240531AbjFIJVJ (ORCPT ); Fri, 9 Jun 2023 05:21:09 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 29D135FC9 for ; Fri, 9 Jun 2023 02:15:53 -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-311-q9nRy84GPH-DWMN5iDJwaQ-1; Fri, 09 Jun 2023 10:15:08 +0100 X-MC-Unique: q9nRy84GPH-DWMN5iDJwaQ-1 Received: from AcuMS.Aculab.com (10.202.163.4) by AcuMS.aculab.com (10.202.163.4) with Microsoft SMTP Server (TLS) id 15.0.1497.48; Fri, 9 Jun 2023 10:15:05 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.048; Fri, 9 Jun 2023 10:15:05 +0100 From: David Laight To: 'Zhangjin Wu' , "thomas@t-8ch.de" CC: "arnd@arndb.de" , "linux-kernel@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "linux-riscv@lists.infradead.org" , "w@1wt.eu" Subject: RE: [PATCH v2 1/4] tools/nolibc: sys.h: add __syscall() and __sysret() helpers Thread-Topic: [PATCH v2 1/4] tools/nolibc: sys.h: add __syscall() and __sysret() helpers Thread-Index: AQHZmozMSUsfyUxi2UiZnouHjWtcta+CLgRA Date: Fri, 9 Jun 2023 09:15:05 +0000 Message-ID: <13d8756927914b578b076babc8b7f7fb@AcuMS.aculab.com> References: <9edb16b4-0d3f-4355-a7b1-684a28f9b4cb@t-8ch.de> <20230609044230.165494-1-falcon@tinylab.org> In-Reply-To: <20230609044230.165494-1-falcon@tinylab.org> 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: Zhangjin Wu > Sent: 09 June 2023 05:43 > > Hi, Thomas, David, Willy > > > Hi David, > > > > On 2023-06-08 14:35:49+0000, David Laight wrote: > > > From: Zhangjin Wu > > > > Sent: 06 June 2023 09:10 > > > > > > > > most of the library routines share the same code model, let's add two > > > > helpers to simplify the coding and shrink the code lines too. > > > > > > > ... > > > > +/* Syscall return helper, set errno as -ret when ret < 0 */ > > > > +static inline __attribute__((always_inline)) long __sysret(long ret) > > > > +{ > > > > + if (ret < 0) { > > > > + SET_ERRNO(-ret); > > > > + ret = -1; > > > > + } > > > > + return ret; > > > > +} > > > > > > If that right? > > > I thought that that only the first few (1024?) negative values > > > got used as errno values. > > > > > Thanks David, this question did inspire me to think about the syscalls > who returns pointers, we didn't touch them yet: I'm also not sure whether lseek() is expected to return values that would be negative. (I do remember having to patch out some checks (not Linux) in order to use: echo -n xxxx | dd of=/dev/kmem oseek=nnn in order to patch a live kernel!) Technically read() and write() can do longer transfers, but Linux limits them to MAXINT. IIRC both BSD and SYSV allow drivers return all values (except -1) form ioctl(). The check for -4095UL is probably reasonable. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)