Return-path: Received: from bu3sch.de ([62.75.166.246]:42198 "EHLO vs166246.vserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757080AbYILPZp (ORCPT ); Fri, 12 Sep 2008 11:25:45 -0400 From: Michael Buesch To: Larry Finger Subject: Re: I need help with a sparse warning Date: Fri, 12 Sep 2008 17:25:06 +0200 Cc: Steven Noonan , LKML , wireless References: <48C9D040.8010107@lwfinger.net> <48C9DACE.5040308@lwfinger.net> In-Reply-To: <48C9DACE.5040308@lwfinger.net> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Message-Id: <200809121725.06870.mb@bu3sch.de> (sfid-20080912_172604_390217_90AA5C01) Sender: linux-wireless-owner@vger.kernel.org List-ID: On Friday 12 September 2008, Larry Finger wrote: > Steven Noonan wrote: > > On Thu, Sep 11, 2008 at 7:13 PM, Larry Finger wrote: > >> In file drivers/net/wireless/p54/p54common.c, the statement > >> > >> priv->rx_mtu = (size_t) le16_to_cpu((__le16)bootrec->data[10]); > >> > >> generates the sparse warning > >> > >> .../p54common.c:185:29: warning: cast to restricted __le16 > >> > >> where bootrec->data is u32, and priv->rx_mtu is u16. > >> > > > > (Whoops, didn't CC the mailing lists. Sorry about the double-message, Larry.) > > > > If priv->rx_mtu is u16, I'm surprised it doesn't get noisy about the > > size_t cast. Unless the machine it's being compiled on is 16-bit, that > > should throw a truncation warning, because size_t should be a 32-bit > > integer on 32-bit machines (typically). > > > > I think if you change the (__le16) cast to (__le16 __force) it will > > stop warning you about that particular issue. > > This one gets rid of the sparse warning. > > priv->rx_mtu = le16_to_cpu((__le16 __force) > bootrec->data[10]); I think you should rather fix the type of bootrec->data. If it is u32, but the data in fact is __le16, please fix the struct instead of adding dangerous casts. Note that this is especially dangerous, because you cast between different typesizes and endianesses at the same time.