From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: Re: [PATCH v4] net: mac802154: comparision issue of type cast, finding by EXTRA_CFLAGS=-W Date: Thu, 25 Apr 2013 11:59:06 +0200 Message-ID: <5178FE6A.3050108@redhat.com> References: <5175DFBC.7040000@asianux.com> <5175F7F7.7000703@asianux.com> <51766F74.2090007@asianux.com> <20130425.041044.768895561908042668.davem@davemloft.net> <5178ECA2.6020402@asianux.com> <5178F120.5030500@acn-group.ch> <5178FA0D.8060009@asianux.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: David Miller , Christophe Aeschlimann , sergei.shtylyov@cogentembedded.com, alex.bluesman.smirnov@gmail.com, dbaryshkov@gmail.com, linux-zigbee-devel@lists.sourceforge.net, netdev@vger.kernel.org To: Chen Gang Return-path: Received: from mx1.redhat.com ([209.132.183.28]:47777 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755522Ab3DYJ7Z (ORCPT ); Thu, 25 Apr 2013 05:59:25 -0400 In-Reply-To: <5178FA0D.8060009@asianux.com> Sender: netdev-owner@vger.kernel.org List-ID: On 04/25/2013 11:40 AM, Chen Gang wrote: > Need change ~(u8)0 to 0xff, or in mac802154_wpan_xmit(), "u8 chan" > will never == MAC802154_CHAN_NONE. > > The related warning: > net/mac802154/wpan.c:325:2: warning: comparison is always false > due to limited range of data type [-Wtype-limits] Hm, do you really need to include this huge pile of code below into the commit message? Couldn't you make the commit message simpler resp. more compact, e.g.: Change MAC802154_CHAN_NONE from ~(u8)0 to 0xff, otherwise the comparison in mac802154_wpan_xmit() for ``chan == MAC802154_CHAN_NONE'' will not succeed. This bug can be boiled down to ``u8 foo = 0xff; if (foo == ~(u8)0) [...] else [...]'' where the condition will always take the else branch. .... something like that maybe? > The related unit test: > cc -Wall -O2 -o test test.c > ./test > will output 'different' > > (after use '0xff' instead of '~(u8)0', it will output 'equal') > > -----------------------test code begin-------------------------------- > > #include > > typedef unsigned char u8; > > int main() > { > u8 uc = 0xff; > > if (uc == ~(u8)0) > printf("\nequal\n"); > else > printf("\ndifferent\n"); > > return 0; > } > > -----------------------test code end---------------------------------- > > > Signed-off-by: Chen Gang > --- > net/mac802154/mac802154.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/mac802154/mac802154.h b/net/mac802154/mac802154.h > index a4dcaf1..703c121 100644 > --- a/net/mac802154/mac802154.h > +++ b/net/mac802154/mac802154.h > @@ -90,7 +90,7 @@ struct mac802154_sub_if_data { > > #define MAC802154_MAX_XMIT_ATTEMPTS 3 > > -#define MAC802154_CHAN_NONE (~(u8)0) /* No channel is assigned */ > +#define MAC802154_CHAN_NONE 0xff /* No channel is assigned */ > > extern struct ieee802154_reduced_mlme_ops mac802154_mlme_reduced; > extern struct ieee802154_mlme_ops mac802154_mlme_wpan; >