linux-kernel - Re: [PATCH] qeth: don't rely on signedness of char

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Message-ID: <1449489755.18521.7.camel@BR9GV9YG.de.ibm.com>
Date:	Mon, 07 Dec 2015 13:02:35 +0100
From:	Ursula Braun <ubraun@...ux.vnet.ibm.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Ursula Braun <ursula.braun@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] qeth: don't rely on signedness of char

Rasmus,

I do not see a need for your first patch proposal. Our code works fine
in our environment.

But I will pickup your second part to remove the explicit setting of the
0-termination. Thanks!

Regards, Ursula

On Sat, 2015-12-05 at 22:32 +0100, Rasmus Villemoes wrote:
> AFAICT, char is unsigned on s390. Relying on that is a little
> subtle. The problem here is that if char happens to be signed and
> e.g. card->info.mcl_level[2] contains the value -16, the formatted
> output will be "fffffff0", thus overflowing card->info.mcl_level
> (which has size 5). To help future readers, simply do an explicit mask
> so that the value passed to sprintf is in 0-255. If char is indeed
> unsigned, gcc should be able to elide the masking.
> 
> In any case, the subsequent 0-termination is redundant, since sprintf
> has done that.
> 
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
>  drivers/s390/net/qeth_core_main.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
> index 31ac53fa5cee..84bc4b862fbb 100644
> --- a/drivers/s390/net/qeth_core_main.c
> +++ b/drivers/s390/net/qeth_core_main.c
> @@ -2682,10 +2682,8 @@ void qeth_print_status_message(struct qeth_card *card)
>  		 * */
>  		if (!card->info.mcl_level[0]) {
>  			sprintf(card->info.mcl_level, "%02x%02x",
> -				card->info.mcl_level[2],
> -				card->info.mcl_level[3]);
> -
> -			card->info.mcl_level[QETH_MCL_LENGTH] = 0;
> +				card->info.mcl_level[2] & 0xff,
> +				card->info.mcl_level[3] & 0xff);
>  			break;
>  		}
>  		/* fallthrough */


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