From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jiri Benc <jbenc@redhat.com>
Date: Fri, 11 Nov 2016 13:05:09 +0000
Subject: Re: [bug report] vxlan: keep flags and vni in network byte order
Message-Id: <20161111140509.288e2fd4@griffin>
List-Id: <kernel-janitors.vger.kernel.org>
References: <20161111124941.GA3991@mwanda>
In-Reply-To: <20161111124941.GA3991@mwanda>
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To: kernel-janitors@vger.kernel.org

On Fri, 11 Nov 2016 15:49:41 +0300, Dan Carpenter wrote:
> Hello Jiri Benc,
> 
> The patch 54bfd872bf16: "vxlan: keep flags and vni in network byte
> order" from Feb 16, 2016, leads to the following static checker
> warning:
> 
> 	./include/net/vxlan.h:340 vxlan_vni()
> 	warn: potential shift truncation.  '0xffffff00 << 8'
> 
> include/net/vxlan.h
>    335  static inline __be32 vxlan_vni(__be32 vni_field)
>    336  {
>    337  #if defined(__BIG_ENDIAN)
>    338          return (__force __be32)((__force u32)vni_field >> 8);
>    339  #else
>    340          return (__force __be32)((__force u32)(vni_field & VXLAN_VNI_MASK) << 8);
> 
> Are you sure this is correct?  VXLAN_VNI_MASK already has an << 8 shift
> so this feels like maybe it is a double shift.

The static checker clearly can't understand endian conversion macros.
VXLAN_VNI_MASK is:

cpu_to_be32(VXLAN_VID_MASK << 8)

Thus on little endian, it becomes 0x00ffffff.

 Jiri