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Re: [PATCH] xfsprogs: fix crc32 build on big endian

To: Eric Sandeen <sandeen@xxxxxxxxxx>
Subject: Re: [PATCH] xfsprogs: fix crc32 build on big endian
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Sat, 5 Oct 2013 13:54:59 +1000
Cc: xfs-oss <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <524F7753.8050801@xxxxxxxxxx>
References: <524F7753.8050801@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Fri, Oct 04, 2013 at 09:20:03PM -0500, Eric Sandeen wrote:
> While kernelspace can test #ifdef __LITTLE_ENDIAN, this
> doesn't work in userspace.  __LITTLE_ENDIAN is defined -
> as is __BIG_ENDIAN.
> 
> So we build on all boxes as __LITTLE_ENDIAN, and the
> self-test (thankfully!) fails on big endian boxes.

I'm glad I put that self test into the build now. :)

> Fix this by testing __BYTE_ORDER values.
> 
> And add an else which should never be hit, but just in case...
> 
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
> 
> diff --git a/libxfs/crc32.c b/libxfs/crc32.c
> index 1c0d958..0f847d2 100644
> --- a/libxfs/crc32.c
> +++ b/libxfs/crc32.c
> @@ -63,18 +63,20 @@ typedef __u32     u64;
>  static inline u32
>  crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 
> (*tab)[256])
>  {
> -# ifdef __LITTLE_ENDIAN
> +#if __BYTE_ORDER == __LITTLE_ENDIAN
>  #  define DO_CRC(x) crc = t0[(crc ^ (x)) & 255] ^ (crc >> 8)
>  #  define DO_CRC4 (t3[(q) & 255] ^ t2[(q >> 8) & 255] ^ \
>                  t1[(q >> 16) & 255] ^ t0[(q >> 24) & 255])
>  #  define DO_CRC8 (t7[(q) & 255] ^ t6[(q >> 8) & 255] ^ \
>                  t5[(q >> 16) & 255] ^ t4[(q >> 24) & 255])
> -# else
> +# elif __BYTE_ORDER == __BIG_ENDIAN
>  #  define DO_CRC(x) crc = t0[((crc >> 24) ^ (x)) & 255] ^ (crc << 8)
>  #  define DO_CRC4 (t0[(q) & 255] ^ t1[(q >> 8) & 255] ^ \
>                  t2[(q >> 16) & 255] ^ t3[(q >> 24) & 255])
>  #  define DO_CRC8 (t4[(q) & 255] ^ t5[(q >> 8) & 255] ^ \
>                  t6[(q >> 16) & 255] ^ t7[(q >> 24) & 255])
> +# else
> +#  error What endian are you?
>  # endif
>       const u32 *b;
>       size_t    rem_len;

Looks good - it matches the other endian checks in the code.

Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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