Re: [PATCH] mci: fix wrong sd/mmc/emmc card size computation for arch where char is signed

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Yann,

On 9/14/20 5:27 PM, Yann Sionneau wrote:
> char type can be either signed or unsigned according to C standard.
> If your arch has signed char, this kind of computation will end up wrong
> because of sign extension:
> 
> https://git.pengutronix.de/cgit/barebox/tree/drivers/mci/mci-core.c#n869
> 
> mci->capacity = mci->ext_csd[EXT_CSD_SEC_COUNT] << 0 |
> 		mci->ext_csd[EXT_CSD_SEC_COUNT + 1] << 8 |
> 		mci->ext_csd[EXT_CSD_SEC_COUNT + 2] << 16 |
> 		mci->ext_csd[EXT_CSD_SEC_COUNT + 3] << 24;

Good catch! I wondered why this wasn't noticed before,
so I looked at the OSELAS.Toolchain`s we have on our build
server. Only x86 and MIPS have signed chars by default.

On x86, we usually do EFI, so barebox mci-core is not involved
and MIPS apparently doesn't have any MCI drivers yet.

(Of course, you can compile do -fsigned-char or compile
 your own toolchain with a different default, but I guess
 not many do that)

Thanks for fixing it.

> Turning the ext_csd field into u8 * fixes the issue.

Your Signed-off-by is required.
Please check https://developercertificate.org/

> ---
>  include/mci.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/mci.h b/include/mci.h
> index 96547fb39..f6d845440 100644
> --- a/include/mci.h
> +++ b/include/mci.h
> @@ -456,7 +456,7 @@ struct mci {
>  	uint64_t capacity;	/**< Card's data capacity in bytes */
>  	int ready_for_use;	/** true if already probed */
>  	int dsr_imp;		/**< DSR implementation state from CSD */
> -	char *ext_csd;
> +	u8 *ext_csd;
>  	int probe;
>  	struct param_d *param_boot;
>  	int bootpart;
> 

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