Re: [RFC/PATCH] doc2000: Fix uninitialized variable in doc_ecc_decode()

[Artem Bityutskiy <dedekind1@gmail.com>]

On Thu, 2010-05-27 at 11:45 +1000, Mark Ware wrote:
> The variable 'syn' was being used uninitialized.  Also
> fixed incorrect use of syn[] vs s[].
> 
> Tested on powerpc board with 64MB DOC2000.
> ---
> 
> I am porting from a 2.4.18 kernel to 2.6.32, and I saw random media header
> mismatches causing a failure to detect the DOC device partitions.  Tracing
> through, I saw this variable being used uninitialized and I suspect
> incorrectly also.
> 
> I do not really understand how the ecc/syndrome code works, so I do not
> know if this patch is the correct solution, but it did make my problem
> go away...
> 
> CC: Thomas Gleixner as I believe he may have written this function initially.
> 
>  drivers/mtd/nand/diskonchip.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/nand/diskonchip.c b/drivers/mtd/nand/diskonchip.c
> index a5bf9ff..7da2321 100644
> --- a/drivers/mtd/nand/diskonchip.c
> +++ b/drivers/mtd/nand/diskonchip.c
> @@ -145,6 +145,7 @@ static int doc_ecc_decode(struct rs_control *rs, uint8_t *data, uint8_t *ecc)
>  	uint8_t parity;
>  	uint16_t ds[4], s[5], tmp, errval[8], syn[4];
>  
> +	memset(syn, 0, sizeof(syn));

I also do not know the math of this stuff, but this change is not
needed ...

>  	/* Convert the ecc bytes into words */
>  	ds[0] = ((ecc[4] & 0xff) >> 0) | ((ecc[5] & 0x03) << 8);
>  	ds[1] = ((ecc[5] & 0xfc) >> 2) | ((ecc[2] & 0x0f) << 6);
> @@ -168,9 +169,9 @@ static int doc_ecc_decode(struct rs_control *rs, uint8_t *data, uint8_t *ecc)
>  			s[i] ^= rs->alpha_to[rs_modnn(rs, tmp + (FCR + i) * j)];
>  	}
>  
> -	/* Calc s[i] = s[i] / alpha^(v + i) */
> +	/* Calc syn[i] = s[i] / alpha^(v + i) */
>  	for (i = 0; i < NROOTS; i++) {
> -		if (syn[i])
> +		if (s[i])
>  			syn[i] = rs_modnn(rs, rs->index_of[s[i]] + (NN - FCR - i));
>  	}

... after this change, right?

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)