From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on gnuweeb.org X-Spam-Level: X-Spam-Status: No, score=-0.7 required=5.0 tests=PDS_BAD_THREAD_QP_64, RCVD_IN_DNSWL_LOW,RCVD_IN_MSPIKE_H5,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) by gnuweeb.org (Postfix) with ESMTPS id B790F7E2BC for ; Sun, 20 Mar 2022 13:10:36 +0000 (UTC) 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-319-oFCxxHf5MgGGf8WvpDCCEg-1; Sun, 20 Mar 2022 13:10:33 +0000 X-MC-Unique: oFCxxHf5MgGGf8WvpDCCEg-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; Sun, 20 Mar 2022 13:10:33 +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; Sun, 20 Mar 2022 13:10:33 +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 v1 3/6] tools/nolibc: i386: Implement syscall with 6 arguments Thread-Topic: [RFC PATCH v1 3/6] tools/nolibc: i386: Implement syscall with 6 arguments Thread-Index: AQHYPD5aHmXDAqFOcUemVcZ8MoFj5azIOuNw Date: Sun, 20 Mar 2022 13:10:33 +0000 Message-ID: <2e335ac54db44f1d8496583d97f9dab0@AcuMS.aculab.com> References: <20220320093750.159991-1-ammarfaizi2@gnuweeb.org> <20220320093750.159991-4-ammarfaizi2@gnuweeb.org> In-Reply-To: <20220320093750.159991-4-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: quoted-printable List-Id: From: Ammar Faizi > Sent: 20 March 2022 09:38 >=20 > In 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. >=20 > For clang (the Assembly statement can't clobber %ebp): > 1) Save the %ebp value to the redzone area -4(%esp). i386 doesn't have a redzone. If you get a signal it will trash -4(%sp) > 2) Load the 6-th argument from memory to %ebp. > 3) Subtract the %esp by 4. > 4) Do the syscall (int $0x80). > 5) Pop %ebp. >=20 > For GCC, fortunately it has a #pragma that can force a specific function > to be compiled with -fomit-frame-pointer, so it can always use "r"(var) > where `var` is a variable bound to %ebp. How is that going to work for an inlined functon? And using xchg is slow - it is always locked. One possibility might be to do: =09push arg6 =09push %ebp =09mov %ebp, 4(%sp) =09int 0x80 =09pop %ebp =09add %esp,4 Although I'm not sure you really want to allocate 4k pages for every malloc() call. Probably better to write a mini 'libc' that uses sbrk() and a best fit scan of a linear free list. =09David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales)