From: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To: Aakash Hemadri <aakashhemadri123@gmail.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Larry Finger <Larry.Finger@lwfinger.net>,
Phillip Potter <phil@philpotter.co.uk>,
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 [thread overview]
Message-ID: <1777630.LqDDHREl4S@localhost.localdomain> (raw)
In-Reply-To: <YR6S7MfxpXpQFl9d@kroah.com>
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
next prev parent reply other threads:[~2021-08-20 15:10 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-19 8:17 [PATCH v2 0/5] staging: r8188eu: fix sparse warnings Aakash Hemadri
2021-08-19 8:17 ` [PATCH v2 1/5] staging: r8188eu: restricted __be16 degrades to int Aakash Hemadri
2021-08-19 8:17 ` [PATCH v2 2/5] staging: r8188eu: cast to restricted __be32 Aakash Hemadri
2021-08-19 12:58 ` Fabio M. De Francesco
2021-08-19 17:19 ` Greg Kroah-Hartman
2021-08-20 11:40 ` Aakash Hemadri
2021-08-20 21:44 ` Larry Finger
2021-08-21 14:21 ` Aakash Hemadri
2021-08-22 21:30 ` David Laight
2021-08-23 8:26 ` Aakash Hemadri
2021-08-23 14:19 ` Larry Finger
2021-08-19 8:17 ` [PATCH v2 3/5] staging: r8188eu: incorrect type in csum_ipv6_magic Aakash Hemadri
2021-08-20 21:38 ` Larry Finger
2021-08-21 14:19 ` Aakash Hemadri
2021-08-20 21:48 ` Larry Finger
2021-08-19 8:17 ` [PATCH v2 4/5] staging: r8188eu: restricted __be16 degrades to int Aakash Hemadri
2021-08-19 17:20 ` Greg Kroah-Hartman
2021-08-20 15:10 ` Fabio M. De Francesco [this message]
2021-08-21 14:18 ` Aakash Hemadri
2021-08-19 8:17 ` [PATCH v2 5/5] staging: r8188eu: incorrect type in assignment Aakash Hemadri
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