linux-kernel - [PATCH 3.16 291/294] net: ti: cpmac: Fix compiler warning due to type confusion

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Message-ID: <lsq.1510009382.149087557@decadent.org.uk>
Date:   Mon, 06 Nov 2017 23:03:02 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "David S. Miller" <davem@...emloft.net>,
        "Paul Burton" <paul.burton@...tec.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Arnd Bergmann" <arnd@...db.de>
Subject: [PATCH 3.16 291/294] net: ti: cpmac: Fix compiler warning due to
 type confusion

3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Paul Burton <paul.burton@...tec.com>

commit 2f5281ba2a8feaf6f0aee93356f350855bb530fc upstream.

cpmac_start_xmit() used the max() macro on skb->len (an unsigned int)
and ETH_ZLEN (a signed int literal). This led to the following compiler
warning:

  In file included from include/linux/list.h:8:0,
                   from include/linux/module.h:9,
                   from drivers/net/ethernet/ti/cpmac.c:19:
  drivers/net/ethernet/ti/cpmac.c: In function 'cpmac_start_xmit':
  include/linux/kernel.h:748:17: warning: comparison of distinct pointer
  types lacks a cast
    (void) (&_max1 == &_max2);  \
                   ^
  drivers/net/ethernet/ti/cpmac.c:560:8: note: in expansion of macro 'max'
    len = max(skb->len, ETH_ZLEN);
          ^

On top of this, it assigned the result of the max() macro to a signed
integer whilst all further uses of it result in it being cast to varying
widths of unsigned integer.

Fix this up by using max_t to ensure the comparison is performed as
unsigned integers, and for consistency change the type of the len
variable to unsigned int.

Signed-off-by: Paul Burton <paul.burton@...tec.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Cc: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/net/ethernet/ti/cpmac.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/net/ethernet/ti/cpmac.c
+++ b/drivers/net/ethernet/ti/cpmac.c
@@ -543,7 +543,8 @@ fatal_error:
 
 static int cpmac_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
-	int queue, len;
+	int queue;
+	unsigned int len;
 	struct cpmac_desc *desc;
 	struct cpmac_priv *priv = netdev_priv(dev);
 
@@ -553,7 +554,7 @@ static int cpmac_start_xmit(struct sk_bu
 	if (unlikely(skb_padto(skb, ETH_ZLEN)))
 		return NETDEV_TX_OK;
 
-	len = max(skb->len, ETH_ZLEN);
+	len = max_t(unsigned int, skb->len, ETH_ZLEN);
 	queue = skb_get_queue_mapping(skb);
 	netif_stop_subqueue(dev, queue);