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 8FD41C433EF for ; Tue, 22 Mar 2022 11:39:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231180AbiCVLkm convert rfc822-to-8bit (ORCPT ); Tue, 22 Mar 2022 07:40:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39226 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233062AbiCVLki (ORCPT ); Tue, 22 Mar 2022 07:40:38 -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 ESMTP id 534B513F90 for ; Tue, 22 Mar 2022 04:39:09 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-38-lnX6-H1VMiaQvmmh42a07A-1; Tue, 22 Mar 2022 11:39:06 +0000 X-MC-Unique: lnX6-H1VMiaQvmmh42a07A-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.32; Tue, 22 Mar 2022 11:39:07 +0000 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.033; Tue, 22 Mar 2022 11:39:07 +0000 From: David Laight To: 'Ammar Faizi' , Willy Tarreau CC: "Paul E. McKenney" , Alviro Iskandar Setiawan , Nugraha , "Linux Kernel Mailing List" , GNU/Weeb Mailing List , "x86@kernel.org" , "llvm@lists.linux.dev" Subject: RE: [RFC PATCH v2 3/8] tools/nolibc: i386: Implement syscall with 6 arguments Thread-Topic: [RFC PATCH v2 3/8] tools/nolibc: i386: Implement syscall with 6 arguments Thread-Index: AQHYPdalMvftIu2CIkSH1LImoy2kmazLRP7A Date: Tue, 22 Mar 2022 11:39:06 +0000 Message-ID: <8653f6784a9b4272a59a75a530663567@AcuMS.aculab.com> References: <20220322102115.186179-1-ammarfaizi2@gnuweeb.org> <20220322102115.186179-4-ammarfaizi2@gnuweeb.org> In-Reply-To: <20220322102115.186179-4-ammarfaizi2@gnuweeb.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 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com 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: 22 March 2022 10:21 > On i386, the 6th argument of syscall goes in %ebp. However, both Clang > and GCC cannot use %ebp in the clobber list and in the "r" constraint > without using -fomit-frame-pointer. To make it always available for > any kind of compilation, the below workaround is implemented. > ... > diff --git a/tools/include/nolibc/arch-i386.h b/tools/include/nolibc/arch-i386.h > index 125a691fc631..9f4dc36e6ac2 100644 > --- a/tools/include/nolibc/arch-i386.h > +++ b/tools/include/nolibc/arch-i386.h > @@ -167,6 +167,72 @@ struct sys_stat_struct { > _ret; \ > }) > > + > +/* > + * Both Clang and GCC cannot use %ebp in the clobber list and in the "r" > + * constraint without using -fomit-frame-pointer. To make it always > + * available for any kind of compilation, the below workaround is > + * implemented. > + * > + * For clang (the Assembly statement can't clobber %ebp): > + * 1) Push the 6-th argument. > + * 2) Push %ebp. > + * 3) Load the 6-th argument from 4(%esp) to %ebp. > + * 4) Do the syscall (int $0x80). > + * 5) Pop %ebp (restore the old value of %ebp). > + * 6) Add %esp by 4 (undo the stack pointer). > + * > + * For GCC, fortunately it has a #pragma that can force a specific function > + * to be compiled with -fomit-frame-pointer, so it can use "r"(var) where > + * var is a variable bound to %ebp. > + * > + */ > +#if defined(__clang__) > +static inline long ____do_syscall6(long eax, long ebx, long ecx, long edx, > + long esi, long edi, long ebp) That should probably be: static inline long ____do_syscall6(long nr, long arg1, long arg2, long arg3, long arg4, long arg5, long arg6) and the input constraints changed to match. > +{ > + __asm__ volatile ( > + "pushl %[arg6]\n\t" > + "pushl %%ebp\n\t" > + "movl 4(%%esp), %%ebp\n\t" > + "int $0x80\n\t" > + "popl %%ebp\n\t" > + "addl $4,%%esp\n\t" > + : "=a"(eax) > + : "a"(eax), "b"(ebx), "c"(ecx), "d"(edx), "S"(esi), "D"(edi), Does having "=a" for an output constraint and "a" for an input constraint actually DTRT? There is a special syntax for tying input and output to the same register. Or you could use "+a"(nr_rval) and 'return nr_rval'. David > + [arg6]"m"(ebp) > + : "memory", "cc" > + ); > + return eax; > +} - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)