Messages in this thread | | | From | "Fabio M. De Francesco" <> | Subject | Re: [PATCH v2 4/5] staging: r8188eu: restricted __be16 degrades to int | Date | Fri, 20 Aug 2021 17:10:30 +0200 |
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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 <aakashhemadri123@gmail.com> > > --- > > 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
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