netdev - Re: [net,2/2] net: i40e: shut up uninitialized variable warnings

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Date:	Sun, 31 Jan 2016 15:59:17 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Vasily Averin <vvs@...tuozzo.com>
Cc:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>, davem@...emloft.net,
	netdev@...r.kernel.org, nhorman@...hat.com, sassmann@...hat.com,
	jogreene@...hat.com
Subject: Re: [net,2/2] net: i40e: shut up uninitialized variable warnings

On Saturday 30 January 2016 18:33:26 Vasily Averin wrote:
> On 26.01.2016 02:58, Jeff Kirsher wrote:
> > From: Arnd Bergmann <arnd@...db.de>
> > 
> > intel/i40e/i40e_txrx.c: In function 'i40e_xmit_frame_ring':
> > intel/i40e/i40e_txrx.c:2367:20: error: 'oiph' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> > intel/i40e/i40e_txrx.c:2317:16: note: 'oiph' was declared here
> > intel/i40e/i40e_txrx.c:2367:17: error: 'oudph' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> > intel/i40e/i40e_txrx.c:2316:17: note: 'oudph' was declared here
> 
> 2364                 if ((tx_ring->flags & I40E_TXR_FLAGS_OUTER_UDP_CSUM) &&
> 2365                     (l4_tunnel == I40E_TXD_CTX_UDP_TUNNELING)        &&
> 2366                     (*cd_tunneling & I40E_TXD_CTX_QW0_EXT_IP_MASK)) {
> 2367                         oudph->check = ~csum_tcpudp_magic(oiph->saddr,
> 2368                                         oiph->daddr,
> 2369                                         (skb->len - skb_transport_offset(skb)),
> 2370                                         IPPROTO_UDP, 0);
> 
> if compiler reports that oudph and oiph can be unitialized here,
> it's not enough just to set them to NULL.
> 
> Do we need probably to check that variables was initialized before access here?
> i.e. add  oudph && oiph into condition?

Sorry, I should not have mentioned my patch when it wasn't meant as
a serious submission. The patch I sent did not have a proper changelog
on it so it failed to explain it.

The reason why my patch works correctly is that the check on "l4_tunnel
== I40E_TXD_CTX_UDP_TUNNELING" means we can only get here if the
two variables have been initialized, and gcc fails to see this.

Jeff mentioned that he already had a patch for this, so I did not follow
up with a real patch.

	Arnd