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SubjectRe: [PATCH] 64bit unaligned access on 32bit kernel
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.
-
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