Return-path: Received: from sj-iport-5.cisco.com ([171.68.10.87]:24424 "EHLO sj-iport-5.cisco.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754403AbYILCkv (ORCPT ); Thu, 11 Sep 2008 22:40:51 -0400 From: Roland Dreier To: Larry Finger Cc: LKML , wireless Subject: Re: I need help with a sparse warning References: <48C9D040.8010107@lwfinger.net> Date: Thu, 11 Sep 2008 19:39:49 -0700 In-Reply-To: <48C9D040.8010107@lwfinger.net> (Larry Finger's message of "Thu, 11 Sep 2008 21:13:20 -0500") Message-ID: (sfid-20080912_044058_316145_87CAAEA2) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-wireless-owner@vger.kernel.org List-ID: > In file drivers/net/wireless/p54/p54common.c, the statement > > priv->rx_mtu = (size_t) le16_to_cpu((__le16)bootrec->data[10]); [I don't see this code in Linus's tree] > > generates the sparse warning > > .../p54common.c:185:29: warning: cast to restricted __le16 > > where bootrec->data is u32, and priv->rx_mtu is u16. > > What should be done to eliminate this warning? the code in question looks buggy to me. Since bootrec->data[10] is u32, casting it to a 16-bit type is going to take a different 2 bytes out of the 4 bytes depending on the endianness of the system the driver is built for. And I assume you are parsing some fixed-layout thing that the firmware is giving you or something like that. I would guess you want something like: priv->rx_mtu = le16_to_cpu(((__force __le16 *) bootrec->data)[20]); (__force is what shuts up sparse, and as far as I can see, the size_t cast is useless, since the result will be promoted anyway) - R.