From mboxrd@z Thu Jan  1 00:00:00 1970
From: Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH net-next] net: can: Fix compiling warning
Date: Mon, 12 Aug 2019 10:19:27 -0700
Message-ID: <201908121001.0AC0A90@keescook>
References: <20190802033643.84243-1-maowenan@huawei.com>
 <0050efdb-af9f-49b9-8d83-f574b3d46a2e@hartkopp.net>
 <20190806135231.GJ1974@kadam>
 <6e1c5aa0-8ed3-eec3-a34d-867ea8f54e9d@hartkopp.net>
 <20190807105042.GK1974@kadam>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Return-path: <linux-kernel-owner@vger.kernel.org>
Content-Disposition: inline
In-Reply-To: <20190807105042.GK1974@kadam>
Sender: linux-kernel-owner@vger.kernel.org
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Oliver Hartkopp <socketcan@hartkopp.net>, Patrick Bellasi <patrick.bellasi@arm.com>, linux-sparse@vger.kernel.org, Mao Wenan <maowenan@huawei.com>, davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org, Ingo Molnar <mingo@kernel.org>
List-Id: linux-sparse@vger.kernel.org

On Wed, Aug 07, 2019 at 01:50:42PM +0300, Dan Carpenter wrote:
> On Tue, Aug 06, 2019 at 06:41:44PM +0200, Oliver Hartkopp wrote:
> > I compiled the code (the original version), but I do not get that "Should it
> > be static?" warning:
> > 
> > user@box:~/net-next$ make C=1
> >   CALL    scripts/checksyscalls.sh
> >   CALL    scripts/atomic/check-atomics.sh
> >   DESCEND  objtool
> >   CHK     include/generated/compile.h
> >   CHECK   net/can/af_can.c
> > ./include/linux/sched.h:609:43: error: bad integer constant expression
> > ./include/linux/sched.h:609:73: error: invalid named zero-width bitfield
> > `value'
> > ./include/linux/sched.h:610:43: error: bad integer constant expression
> > ./include/linux/sched.h:610:67: error: invalid named zero-width bitfield
> > `bucket_id'
> >   CC [M]  net/can/af_can.o
> 
> The sched.h errors suppress Sparse warnings so it's broken/useless now.
> The code looks like this:
> 
> include/linux/sched.h
>    613  struct uclamp_se {
>    614          unsigned int value              : bits_per(SCHED_CAPACITY_SCALE);
>    615          unsigned int bucket_id          : bits_per(UCLAMP_BUCKETS);
>    616          unsigned int active             : 1;
>    617          unsigned int user_defined       : 1;
>    618  };
> 
> bits_per() is zero and Sparse doesn't like zero sized bitfields.

I just noticed these sparse warnings too -- what's happening here? Are
they _supposed_ to be 0-width fields? It doesn't look like it to me:

CONFIG_UCLAMP_BUCKETS_COUNT=5
...
#define UCLAMP_BUCKETS CONFIG_UCLAMP_BUCKETS_COUNT
...
        unsigned int bucket_id          : bits_per(UCLAMP_BUCKETS);

I would expect this to be 3 bits wide. ... Looks like gcc agrees:

struct uclamp_se {
    unsigned int               value:11;             /*     0: 0  4 */
    unsigned int               bucket_id:3;          /*     0:11  4 */
...

So this is a sparse issue?

-- 
Kees Cook