Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756140Ab0LRM7Z (ORCPT ); Sat, 18 Dec 2010 07:59:25 -0500 Received: from mail-px0-f179.google.com ([209.85.212.179]:62238 "EHLO mail-px0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755685Ab0LRM7X convert rfc822-to-8bit (ORCPT ); Sat, 18 Dec 2010 07:59:23 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=pxuKA9ALaNKd4NrMGHiLT8gNC2ryhKGWjZH6xp2ID/NfVB8XbuWb3SPiWVwoLb4Pi0 sB7T6s3J8QeQIRyqckmIhdbAzur6vYqiTR2NE0u3x3ehreS7z9oq/FnMhudHKeB18P19 r4XFPQ/SlZeZ3jgMY56L0J2BoQPMO42HusKpM= MIME-Version: 1.0 In-Reply-To: References: Date: Sat, 18 Dec 2010 12:59:23 +0000 Message-ID: Subject: Re: [PATCH] include/linux/unaligned: Pack the whole struct rather than just the field. From: Will Newton To: Linux Kernel list Cc: Andrew Morton , Arnd Bergmann Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2720 Lines: 71 On Tue, Dec 7, 2010 at 11:12 AM, Will Newton wrote: > On Wed, Dec 1, 2010 at 10:11 PM, Will Newton wrote: >> The current packed struct implementation of unaligned access adds >> the packed attribute only to the field within the unaligned struct >> rather than to the struct as a whole. This is not sufficient to >> enforce proper behaviour on architectures with a default struct >> alignment of more than one byte. >> >> For example, the current implementation of __get_unaligned_cpu16 >> when compiled for arm with gcc -O1 -mstructure-size-boundary=32 >> assumes the struct is on a 4 byte boundary so performs the load >> of the 16bit packed field as if it were on a 4 byte boundary: >> >> __get_unaligned_cpu16: >> ? ? ? ?ldrh ? ?r0, [r0, #0] >> ? ? ? ?bx ? ? ?lr >> >> Moving the packed attribute to the struct rather than the field >> causes the proper unaligned access code to be generated: >> >> __get_unaligned_cpu16: >> ? ? ? ?ldrb ? ?r3, [r0, #0] ? ?@ zero_extendqisi2 >> ? ? ? ?ldrb ? ?r0, [r0, #1] ? ?@ zero_extendqisi2 >> ? ? ? ?orr ? ? r0, r3, r0, asl #8 >> ? ? ? ?bx ? ? ?lr >> >> Signed-off-by: Will Newton > > I don't know of any designated maintainer for this code, but add a > couple of ccs of people who might be interested. > > This change doesn't change any behaviour on current architectures, but > is more correct and may enable other architectures to move to the > packed struct unaligned access implementation and so allow us to move > more architectures to the asm-generic implementation. Ping! Does anyone have any opinions on this? >> --- >> ?include/linux/unaligned/packed_struct.h | ? ?6 +++--- >> ?1 files changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/include/linux/unaligned/packed_struct.h >> b/include/linux/unaligned/packed_struct.h >> index 2498bb9..c9a6abd 100644 >> --- a/include/linux/unaligned/packed_struct.h >> +++ b/include/linux/unaligned/packed_struct.h >> @@ -3,9 +3,9 @@ >> >> ?#include >> >> -struct __una_u16 { u16 x __attribute__((packed)); }; >> -struct __una_u32 { u32 x __attribute__((packed)); }; >> -struct __una_u64 { u64 x __attribute__((packed)); }; >> +struct __una_u16 { u16 x; } __attribute__((packed)); >> +struct __una_u32 { u32 x; } __attribute__((packed)); >> +struct __una_u64 { u64 x; } __attribute__((packed)); >> >> ?static inline u16 __get_unaligned_cpu16(const void *p) >> ?{ >> -- >> 1.7.0.4 >> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/