From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965306AbXBOOeu (ORCPT ); Thu, 15 Feb 2007 09:34:50 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965322AbXBOOeu (ORCPT ); Thu, 15 Feb 2007 09:34:50 -0500 Received: from ftp.linux-mips.org ([194.74.144.162]:41413 "EHLO ftp.linux-mips.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965306AbXBOOet (ORCPT ); Thu, 15 Feb 2007 09:34:49 -0500 Date: Thu, 15 Feb 2007 14:34:41 +0000 From: Ralf Baechle To: Andrew Morton Cc: Atsushi Nemoto , linux-mips@linux-mips.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Optimize generic get_unaligned / put_unaligned implementations. Message-ID: <20070215143441.GA18155@linux-mips.org> References: <20050830104056.GA4710@linux-mips.org> <20060306.203218.69025300.nemoto@toshiba-tops.co.jp> <20060306170552.0aab29c5.akpm@osdl.org> <20070214214226.GA17899@linux-mips.org> <20070214203903.8d013170.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070214203903.8d013170.akpm@linux-foundation.org> User-Agent: Mutt/1.4.2.2i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 14, 2007 at 08:39:03PM -0800, Andrew Morton wrote: > Can someone please tell us how this magic works? (And it does appear to > work). > > It seems to assuming that the compiler will assume that members of packed > structures can have arbitrary alignment, even if that alignment is obvious. > > Which makes sense, but I'd like to see chapter-and-verse from the spec or > from the gcc docs so we can rely upon it working on all architectures and > compilers from now until ever more. > > IOW: your changlogging sucks ;) It was my entry for the next edition of the C Puzzle Book ;-) The whole union thing was only needed to get rid of a warning but Marcel's solution does the same thing by attaching the packed keyword to the entire structure instead, so this patch is now using his macros but using __packed instead. Ralf Signed-off-by: Ralf Baechle diff --git a/include/asm-generic/unaligned.h b/include/asm-generic/unaligned.h index 09ec447..60d94fc 100644 --- a/include/asm-generic/unaligned.h +++ b/include/asm-generic/unaligned.h @@ -1,122 +1,27 @@ -#ifndef _ASM_GENERIC_UNALIGNED_H_ -#define _ASM_GENERIC_UNALIGNED_H_ - -/* - * For the benefit of those who are trying to port Linux to another - * architecture, here are some C-language equivalents. - * - * This is based almost entirely upon Richard Henderson's - * asm-alpha/unaligned.h implementation. Some comments were - * taken from David Mosberger's asm-ia64/unaligned.h header. - */ - -#include - -/* - * The main single-value unaligned transfer routines. - */ -#define get_unaligned(ptr) \ - __get_unaligned((ptr), sizeof(*(ptr))) -#define put_unaligned(x,ptr) \ - __put_unaligned((__u64)(x), (ptr), sizeof(*(ptr))) - /* - * This function doesn't actually exist. The idea is that when - * someone uses the macros below with an unsupported size (datatype), - * the linker will alert us to the problem via an unresolved reference - * error. + * This file is subject to the terms and conditions of the GNU General Public + * License. See the file "COPYING" in the main directory of this archive + * for more details. */ -extern void bad_unaligned_access_length(void) __attribute__((noreturn)); - -struct __una_u64 { __u64 x __attribute__((packed)); }; -struct __una_u32 { __u32 x __attribute__((packed)); }; -struct __una_u16 { __u16 x __attribute__((packed)); }; - -/* - * Elemental unaligned loads - */ - -static inline __u64 __uldq(const __u64 *addr) -{ - const struct __una_u64 *ptr = (const struct __una_u64 *) addr; - return ptr->x; -} - -static inline __u32 __uldl(const __u32 *addr) -{ - const struct __una_u32 *ptr = (const struct __una_u32 *) addr; - return ptr->x; -} - -static inline __u16 __uldw(const __u16 *addr) -{ - const struct __una_u16 *ptr = (const struct __una_u16 *) addr; - return ptr->x; -} - -/* - * Elemental unaligned stores - */ - -static inline void __ustq(__u64 val, __u64 *addr) -{ - struct __una_u64 *ptr = (struct __una_u64 *) addr; - ptr->x = val; -} - -static inline void __ustl(__u32 val, __u32 *addr) -{ - struct __una_u32 *ptr = (struct __una_u32 *) addr; - ptr->x = val; -} +#ifndef __ASM_GENERIC_UNALIGNED_H +#define __ASM_GENERIC_UNALIGNED_H -static inline void __ustw(__u16 val, __u16 *addr) -{ - struct __una_u16 *ptr = (struct __una_u16 *) addr; - ptr->x = val; -} +#include -#define __get_unaligned(ptr, size) ({ \ - const void *__gu_p = ptr; \ - __u64 val; \ - switch (size) { \ - case 1: \ - val = *(const __u8 *)__gu_p; \ - break; \ - case 2: \ - val = __uldw(__gu_p); \ - break; \ - case 4: \ - val = __uldl(__gu_p); \ - break; \ - case 8: \ - val = __uldq(__gu_p); \ - break; \ - default: \ - bad_unaligned_access_length(); \ - }; \ - (__typeof__(*(ptr)))val; \ +#define get_unaligned(ptr) \ +({ \ + struct __packed { \ + typeof(*(ptr)) __v; \ + } *__p = (void *) (ptr); \ + __p->__v; \ }) -#define __put_unaligned(val, ptr, size) \ -do { \ - void *__gu_p = ptr; \ - switch (size) { \ - case 1: \ - *(__u8 *)__gu_p = val; \ - break; \ - case 2: \ - __ustw(val, __gu_p); \ - break; \ - case 4: \ - __ustl(val, __gu_p); \ - break; \ - case 8: \ - __ustq(val, __gu_p); \ - break; \ - default: \ - bad_unaligned_access_length(); \ - }; \ +#define put_unaligned(val, ptr) \ +do { \ + struct __packed { \ + typeof(*(ptr)) __v; \ + } *__p = (void *) (ptr); \ + __p->__v = (val); \ } while(0) -#endif /* _ASM_GENERIC_UNALIGNED_H */ +#endif /* __ASM_GENERIC_UNALIGNED_H */