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From: Andrew Morton <akpm@osdl.org>
To: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Cc: ralf@linux-mips.org, linux-mips@linux-mips.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] 64bit unaligned access on 32bit kernel
Date: Mon, 6 Mar 2006 17:05:52 -0800	[thread overview]
Message-ID: <20060306170552.0aab29c5.akpm@osdl.org> (raw)
In-Reply-To: <20060306.203218.69025300.nemoto@toshiba-tops.co.jp>

Atsushi Nemoto <anemo@mba.ocn.ne.jp> wrote:
>
> >>>>> On Tue, 30 Aug 2005 11:40:56 +0100, Ralf Baechle <ralf@linux-mips.org> said:
> > I've rewriten Atushi's fix for the 64-bit put_unaligned on 32-bit
> > systems bug to generate more efficient code.
> 
> > This case has buzilla URL http://bugzilla.kernel.org/show_bug.cgi?id=5138.
> 
> > Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
> ...
> >  #define __get_unaligned(ptr, size) ({		\
> >  	const void *__gu_p = ptr;		\
> > -	unsigned long val;			\
> > +	__typeof__(*(ptr)) val;			\
> >  	switch (size) {				\
> >  	case 1:					\
> >  		val = *(const __u8 *)__gu_p;	\
> 
> It looks gcc 4.x strike back.  If the 'ptr' is a const, this code
> cause "assignment of read-only variable" error on gcc 4.x.  Let's step
> a back, or do you have any other good idea?
> 
> 
> Use __u64 instead of __typeof__(*(ptr)) for temporary variable to get
> rid of errors on gcc 4.x.
> 
> Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
> 
> diff --git a/include/asm-generic/unaligned.h b/include/asm-generic/unaligned.h
> index 4dc8ddb..09ec447 100644
> --- a/include/asm-generic/unaligned.h
> +++ b/include/asm-generic/unaligned.h
> @@ -78,7 +78,7 @@ static inline void __ustw(__u16 val, __u
>  
>  #define __get_unaligned(ptr, size) ({		\
>  	const void *__gu_p = ptr;		\
> -	__typeof__(*(ptr)) val;			\
> +	__u64 val;				\
>  	switch (size) {				\
>  	case 1:					\
>  		val = *(const __u8 *)__gu_p;	\
> @@ -95,7 +95,7 @@ static inline void __ustw(__u16 val, __u
>  	default:				\
>  		bad_unaligned_access_length();	\
>  	};					\
> -	val;					\
> +	(__typeof__(*(ptr)))val;		\
>  })
>  
>  #define __put_unaligned(val, ptr, size)		\

I worry about what impact that change might have on code generation. 
Hopefully none, if gcc is good enough.

But I cannot think of a better fix.

       reply	other threads:[~2006-03-07  1:07 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20050830104056.GA4710@linux-mips.org>
     [not found] ` <20060306.203218.69025300.nemoto@toshiba-tops.co.jp>
2006-03-07  1:05   ` Andrew Morton [this message]
2006-03-07  2:03     ` Atsushi Nemoto
2006-03-07 18:09     ` Ralf Baechle
2006-03-08  4:58       ` Atsushi Nemoto
2006-03-08  5:12         ` Andrew Morton
2007-02-14 21:42     ` [PATCH] Optimize generic get_unaligned / put_unaligned implementations Ralf Baechle
2007-02-15  4:39       ` Andrew Morton
2007-02-15  8:35         ` Marcel Holtmann
2007-02-15 14:34         ` Ralf Baechle
2007-02-15 21:53           ` Andrew Morton
2007-02-15 22:18             ` Ralf Baechle
2007-02-15 23:05               ` Jeremy Fitzhardinge
2007-02-15 23:38               ` Andrew Morton
2007-02-16  0:13                 ` Jeremy Fitzhardinge
2007-02-16  0:43                 ` Ralf Baechle
2007-02-16  1:27                   ` Andrew Morton
2007-02-16  1:59                     ` Ralf Baechle
2007-02-20 13:50                     ` Pavel Machek

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