Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752459AbdCDViR (ORCPT ); Sat, 4 Mar 2017 16:38:17 -0500 Received: from mail-pf0-f195.google.com ([209.85.192.195]:35571 "EHLO mail-pf0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752234AbdCDViK (ORCPT ); Sat, 4 Mar 2017 16:38:10 -0500 Date: Sun, 5 Mar 2017 06:38:05 +0900 From: Stafford Horne To: "H. Peter Anvin" Cc: Russell King - ARM Linux , Jiri Slaby , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, Richard Henderson , Ivan Kokshaysky , Matt Turner , Vineet Gupta , Catalin Marinas , Will Deacon , Richard Kuo , Tony Luck , Fenghua Yu , Michal Simek , Ralf Baechle , Jonas Bonn , Stefan Kristiansson , "James E.J. Bottomley" , Helge Deller , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Martin Schwidefsky , Heiko Carstens , Yoshinori Sato , Rich Felker , "David S. Miller" , Chris Metcalf , Thomas Gleixner , Ingo Molnar , Chris Zankel , Max Filippov , Arnd Bergmann , x86@kernel.org, linux-alpha@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, linux-mips@linux-mips.org, openrisc@lists.librecores.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org Subject: Re: [PATCH 1/3] futex: remove duplicated code Message-ID: <20170304213805.GA2449@lianli.shorne-pla.net> References: <20170303122712.13353-1-jslaby@suse.cz> <20170304130550.GT21222@n2100.armlinux.org.uk> <3994975e-89a5-d2b5-60be-a8633ddc3733@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3994975e-89a5-d2b5-60be-a8633ddc3733@zytor.com> User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1959 Lines: 69 On Sat, Mar 04, 2017 at 11:15:17AM -0800, H. Peter Anvin wrote: > On 03/04/17 05:05, Russell King - ARM Linux wrote: > >> > >> +static int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr) > >> +{ > >> + int op = (encoded_op >> 28) & 7; > >> + int cmp = (encoded_op >> 24) & 15; > >> + int oparg = (encoded_op << 8) >> 20; > >> + int cmparg = (encoded_op << 20) >> 20; > > > > Hmm. oparg and cmparg look like they're doing these shifts to get sign > > extension of the 12-bit values by assuming that "int" is 32-bit - > > probably worth a comment, or for safety, they should be "s32" so it's > > not dependent on the bit-width of "int". > > > > For readability, perhaps we should make sign- and zero-extension an > explicit facility? There is some of this in already here, 32 and 64 bit versions: include/linux/bitops.h Do we really need zero extension? It seems the same. Example implementation from bitops.h static inline __s32 sign_extend32(__u32 value, int index) { __u8 shift = 31 - index; return (__s32)(value << shift) >> shift; } > /* > * Truncate an integer x to n bits, using sign- or > * zero-extension, respectively. > */ > static inline __const_func__ s32 sex32(s32 x, int n) > { > return (x << (32-n)) >> (32-n); > } > > static inline __const_func__ s64 sex64(s64 x, int n) > { > return (x << (64-n)) >> (64-n); > } > > #define sex(x,y) \ > ((__typeof__(x)) \ > (((__builtin_constant_p(y) && ((y) <= 32)) || \ > (sizeof(x) <= sizeof(s32))) \ > ? sex32((x),(y)) : sex64((x),(y)))) > > static inline __const_func__ u32 zex32(u32 x, int n) > { > return (x << (32-n)) >> (32-n); > } > > static inline __const_func__ u64 zex64(u64 x, int n) > { > return (x << (64-n)) >> (64-n); > } > > #define zex(x,y) \ > ((__typeof__(x)) \ > (((__builtin_constant_p(y) && ((y) <= 32)) || \ > (sizeof(x) <= sizeof(u32))) \ > ? zex32((x),(y)) : zex64((x),(y)))) >