linux-kernel - Re: [PATCH] asm-generic/bitops/fls64.h

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Message-Id: <1210677433.22341.1252875863@webmail.messagingengine.com>
Date:	Tue, 13 May 2008 13:17:13 +0200
From:	"Alexander van Heukelum" <heukelum@...tmail.fm>
To:	nickolay@...tei.ru, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] asm-generic/bitops/fls64.h

> bugfix in fls64 on a big endian systems(against 2.6.25).
> 
> Signed-off-by: Nickolay Vinogradov <nickolay@...tei.ru>
> 
> --
> 
> diff --git a/include/asm-generic/bitops/fls64.h 
> b/include/asm-generic/bitops/fls64.h
> index 1b6b17c..2eedb6f 100644
> --- a/include/asm-generic/bitops/fls64.h
> +++ b/include/asm-generic/bitops/fls64.h
> @@ -8,7 +8,7 @@ static inline int fls64(__u64 x)
>          __u32 h = x >> 32;
>          if (h)
>                  return fls(h) + 32;
> -       return fls(x);
> +       return fls((__u32)x);
>   }

Hi Nickolay,

The change is ok, I guess, but the cast should be a no-op (fls
takes an int, which is always 32 bit in linux). What is the problem
you are seeing? Does fls64() return a wrong value in some cases? If
so, what cpu? Which values?

Why would this be a bug on big endian systems only? There is no
pointer magic involved, so the compiler should take care of the
casts in a correct way.

Maybe you see a compiler warning? Which compiler version?

(also note that current (development) kernels now have separate
versions for 32-bit and 64-bit environments.)

Greetings,
    Alexander

>   #endif /* _ASM_GENERIC_BITOPS_FLS64_H_ */
> 
> -- 
> Nickolay Vinogradov
> Protei Research and Development Center
> St.Petersburg, 194044, Russia
> Tel.: +7 812 449 47 27
> --
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> 
-- 
  Alexander van Heukelum
  heukelum@...tmail.fm

-- 
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