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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DB7B3C4363D for ; Thu, 24 Sep 2020 13:49:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9ADA3206F7 for ; Thu, 24 Sep 2020 13:49:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728105AbgIXNtC convert rfc822-to-8bit (ORCPT ); Thu, 24 Sep 2020 09:49:02 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:54917 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728104AbgIXNtC (ORCPT ); Thu, 24 Sep 2020 09:49:02 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-275-AmPfbs06OlSmLB8NwMzbeQ-1; Thu, 24 Sep 2020 14:47:55 +0100 X-MC-Unique: AmPfbs06OlSmLB8NwMzbeQ-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Thu, 24 Sep 2020 14:47:54 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Thu, 24 Sep 2020 14:47:54 +0100 From: David Laight To: 'YiFei Zhu' , "containers@lists.linux-foundation.org" CC: YiFei Zhu , "bpf@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Aleksa Sarai , "Andrea Arcangeli" , Andy Lutomirski , Dimitrios Skarlatos , Giuseppe Scrivano , Hubertus Franke , Jack Chen , Jann Horn , Josep Torrellas , Kees Cook , Tianyin Xu , Tobin Feldman-Fitzthum , Tycho Andersen , Valentin Rothberg , Will Drewry Subject: RE: [PATCH v2 seccomp 2/6] asm/syscall.h: Add syscall_arches[] array Thread-Topic: [PATCH v2 seccomp 2/6] asm/syscall.h: Add syscall_arches[] array Thread-Index: AQHWknD17ZW/yCPmvkCTJZb3HlQhMal3ymow Date: Thu, 24 Sep 2020 13:47:54 +0000 Message-ID: <7042ba3307b34ce3b95e5fede823514e@AcuMS.aculab.com> References: <20bbc8ed4b9f2c83d0f67f37955eb2d789268525.1600951211.git.yifeifz2@illinois.edu> In-Reply-To: <20bbc8ed4b9f2c83d0f67f37955eb2d789268525.1600951211.git.yifeifz2@illinois.edu> 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-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org From: YiFei Zhu > Sent: 24 September 2020 13:44 > > Seccomp cache emulator needs to know all the architecture numbers > that syscall_get_arch() could return for the kernel build in order > to generate a cache for all of them. > > The array is declared in header as static __maybe_unused const > to maximize compiler optimiation opportunities such as loop > unrolling. I doubt the compiler will do what you want. Looking at it, in most cases there are one or two entries. I think only MIPS has three. So a static inline function that contains a list of conditionals will generate better code that any kind of array lookup. For x86-64 you end up with something like: #ifdef CONFIG_IA32_EMULATION if (sd->arch == AUDIT_ARCH_I386) return xxx; #endif return yyy; Probably saves you having multiple arrays that need to be kept carefully in step. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)