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Thu, 24 Sep 2020 14:47:54 +0100 From: David Laight To: 'YiFei Zhu' , "containers@lists.linux-foundation.org" 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-Language: en-US Cc: Andrea Arcangeli , Giuseppe Scrivano , Valentin Rothberg , Kees Cook , Jann Horn , YiFei Zhu , Tobin Feldman-Fitzthum , "linux-kernel@vger.kernel.org" , Andy Lutomirski , Hubertus Franke , Jack Chen , Dimitrios Skarlatos , Josep Torrellas , Will Drewry , "bpf@vger.kernel.org" , Tianyin Xu X-BeenThere: containers@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux Containers List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: containers-bounces@lists.linux-foundation.org Sender: "Containers" 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) _______________________________________________ Containers mailing list Containers@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/containers