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[79.22.100.164]) by smtp.gmail.com with ESMTPSA id de12sm3769728edb.37.2021.08.20.08.10.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Aug 2021 08:10:31 -0700 (PDT) From: "Fabio M. De Francesco" To: Aakash Hemadri , Greg Kroah-Hartman Cc: Larry Finger , Phillip Potter , linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 4/5] staging: r8188eu: restricted __be16 degrades to int Date: Fri, 20 Aug 2021 17:10:30 +0200 Message-ID: <1777630.LqDDHREl4S@localhost.localdomain> In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thursday, August 19, 2021 7:20:44 PM CEST Greg Kroah-Hartman wrote: > On Thu, Aug 19, 2021 at 01:47:56PM +0530, Aakash Hemadri wrote: > > Fix sparse warning: > > > rtw_br_ext.c:839:70: warning: restricted __be16 degrades to integer > > > rtw_br_ext.c:845:70: warning: invalid assignment: |= > > > rtw_br_ext.c:845:70: left side has type unsigned short > > > rtw_br_ext.c:845:70: right side has type restricted __be16 > > > > dhcp->flag is u16, remove htons() as __be16 degrades. > > Um, are you sure? > > > > > Signed-off-by: Aakash Hemadri > > --- > > drivers/staging/r8188eu/core/rtw_br_ext.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/staging/r8188eu/core/rtw_br_ext.c b/drivers/staging/r8188eu/core/rtw_br_ext.c > > index d4acf02ca64f..14b2935cab98 100644 > > --- a/drivers/staging/r8188eu/core/rtw_br_ext.c > > +++ b/drivers/staging/r8188eu/core/rtw_br_ext.c > > @@ -674,13 +674,13 @@ void dhcp_flag_bcast(struct adapter *priv, struct sk_buff *skb) > > u32 cookie = dhcph->cookie; > > > > if (cookie == DHCP_MAGIC) { /* match magic word */ > > - if (!(dhcph->flags & htons(BROADCAST_FLAG))) { > > + if (!(dhcph->flags & BROADCAST_FLAG)) { > > So you now just ignore the fact that the code used to properly check > BROADCAST_FLAG being in big endian mode, and now you assume it is native > endian? > > Why is this ok? Did you test this? > > thanks, > > greg k-h > Aakash, Building on the objections you had from Greg I suggest that, before attempting anew to address problems like these, you get a better understanding of the topics of native and network endianness and of the API that (conditionally) swap bytes in a variable between little endian and big endian representation. To start with, please note that the following code leads to tests for "v.vub[0] == 0xDD" which is true on little endian architectures while "v.vub[0] == 0xAA" is true on big endian ones... union { u32 vud; u8 vub[4]; } v; v.vud = 0xAABBCCDD; Also note that API like cpu_to_be32(), htonl(), be32_to_cpu(), ntohl, and the likes are used to (conditionally) swap bytes (i.e., change the arrangement of the bytes in a multi-bytes variable). Casts have very different purposes and usage patterns and, above all, they cannot magically change the endianness of a variable. Regards, Fabio