netdev - Re: [Patch net] mlx5: fixup checksum for ethernet padding

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Date:   Fri, 30 Nov 2018 05:51:05 +0800
From:   kbuild test robot <lkp@...el.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     kbuild-all@...org, netdev@...r.kernel.org,
        Cong Wang <xiyou.wangcong@...il.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [Patch net] mlx5: fixup checksum for ethernet padding

Hi Cong,

I love your patch! Perhaps something to improve:

[auto build test WARNING on net/master]

url:    https://github.com/0day-ci/linux/commits/Cong-Wang/mlx5-fixup-checksum-for-ethernet-padding/20181130-014928
config: ia64-allmodconfig (attached as .config)
compiler: ia64-linux-gcc (GCC) 8.1.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=8.1.0 make.cross ARCH=ia64 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   drivers/net/ethernet/mellanox/mlx5/core/en_rx.c: In function 'mlx5e_csum_padding':
>> drivers/net/ethernet/mellanox/mlx5/core/en_rx.c:740:6: warning: 'pad_offset' may be used uninitialized in this function [-Wmaybe-uninitialized]
     u32 pad_offset, pad_len;
         ^~~~~~~~~~

vim +/pad_offset +740 drivers/net/ethernet/mellanox/mlx5/core/en_rx.c

   734	
   735	static void mlx5e_csum_padding(struct sk_buff *skb, int network_depth,
   736				       __be16 proto, bool has_fcs)
   737	{
   738		u32 frame_len = has_fcs ? skb->len - ETH_FCS_LEN : skb->len;
   739		void *ip_p = skb->data + network_depth;
 > 740		u32 pad_offset, pad_len;
   741		void *pad;
   742	
   743		if (likely(frame_len > ETH_ZLEN))
   744			return;
   745	
   746		if (proto == htons(ETH_P_IP)) {
   747			struct iphdr *ipv4 = ip_p;
   748	
   749			pad_offset =  network_depth + be16_to_cpu(ipv4->tot_len);
   750		} else if (proto == htons(ETH_P_IPV6)) {
   751			struct ipv6hdr *ipv6 = ip_p;
   752	
   753			pad_offset = network_depth + sizeof(struct ipv6hdr) +
   754				     be16_to_cpu(ipv6->payload_len);
   755		}
   756	
   757		pad = skb->data + pad_offset;
   758		pad_len = frame_len - pad_offset;
   759	
   760		skb->csum = csum_block_add(skb->csum, csum_partial(pad, pad_len, 0),
   761					   pad_offset);
   762	}
   763	

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