Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261547AbTHaB2F (ORCPT ); Sat, 30 Aug 2003 21:28:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262319AbTHaB2F (ORCPT ); Sat, 30 Aug 2003 21:28:05 -0400 Received: from aneto.able.es ([212.97.163.22]:34947 "EHLO aneto.able.es") by vger.kernel.org with ESMTP id S261547AbTHaB2B (ORCPT ); Sat, 30 Aug 2003 21:28:01 -0400 Date: Sun, 31 Aug 2003 03:27:59 +0200 From: "J.A. Magallon" To: Lista Linux-Kernel Subject: Re: [2.4] gcc3 warns about type-punned pointers ? Message-ID: <20030831012759.GA3276@werewolf.able.es> References: <20030828223511.GA23528@werewolf.able.es> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Disposition: inline Content-Transfer-Encoding: 7BIT X-Mailer: Balsa 2.0.14 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1989 Lines: 72 On 08.29, J.A. Magallon wrote: > Hi all... > > gcc3 gives this warning when using the __set_64bit_var function: > > /usr/src/linux/include/asm/system.h:190: warning: dereferencing type-punned pointer will break strict-aliasing rules > > Is it a potential problem ? > > This seems to cure it: > > --- linux-2.4.22-jam1m/include/asm-i386/system.h.orig 2003-08-29 00:26:41.000000000 +0200 > +++ linux-2.4.22-jam1m/include/asm-i386/system.h 2003-08-29 00:26:55.000000000 +0200 > @@ -181,8 +181,8 @@ > { > __set_64bit(ptr,(unsigned int)(value), (unsigned int)((value)>>32ULL)); > } > -#define ll_low(x) *(((unsigned int*)&(x))+0) > -#define ll_high(x) *(((unsigned int*)&(x))+1) > +#define ll_low(x) *(((unsigned int*)(void*)&(x))+0) > +#define ll_high(x) *(((unsigned int*)(void*)&(x))+1) > How about something like this: typedef unsigned long long u64; typedef unsigned long u32; typedef unsigned short u16; typedef unsigned char u8; union u64_split { u64 ll; u32 l[2]; u16 w[4]; u8 b[8]; }; void f() { u64 a; int l = ((union u64_split)a).l[0]; int h = ((union u64_split)a).l[1]; } The clean way todo it without pointer arithmetic... And with a modern gcc (anonymous structs): union u64_split { u64 x; struct { u32 l32,h32; }; struct { u16 ll16,lh16,hl16,hh16; }; }; So you just write: int l = ((union u64_split)a).l32; u16 word = ((union u64_split)a).ll16; I think it is better with structs, to take care of endianness if needed. -- J.A. Magallon \ Software is like sex: werewolf.able.es \ It's better when it's free Mandrake Linux release 9.2 (Cooker) for i586 Linux 2.4.22-jam1m (gcc 3.3.1 (Mandrake Linux 9.2 3.3.1-1mdk)) - 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/