From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752541AbdCDXjY (ORCPT ); Sat, 4 Mar 2017 18:39:24 -0500 Received: from mail-pg0-f68.google.com ([74.125.83.68]:33316 "EHLO mail-pg0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752450AbdCDXjW (ORCPT ); Sat, 4 Mar 2017 18:39:22 -0500 Date: Sun, 5 Mar 2017 08:39:19 +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 , DavidS.Miller@zytor.com Subject: Re: [PATCH 1/3] futex: remove duplicated code Message-ID: <20170304233919.GB2449@lianli.shorne-pla.net> References: <20170303122712.13353-1-jslaby@suse.cz> <20170304130550.GT21222@n2100.armlinux.org.uk> <3994975e-89a5-d2b5-60be-a8633ddc3733@zytor.com> <20170304213805.GA2449@lianli.shorne-pla.net> <201703042308.v24N8wvh012716@mail.zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201703042308.v24N8wvh012716@mail.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 On Sat, Mar 04, 2017 at 03:08:50PM -0800, H. Peter Anvin wrote: > ,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 > From: hpa@zytor.com > Message-ID: > > On March 4, 2017 1:38:05 PM PST, Stafford Horne wrote: > >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)))) > >> > > Also, i strongly believe that making it syntactically cumbersome encodes people to open-code it which is bad... Right, I missed the signed vs unsigned bit. And it is cumbersome, this would be better > -- > Sent from my Android device with K-9 Mail. Please excuse my brevity.