From: Ben Pfaff <blp@nicira.com>
Date: Thu, 20 Nov 2008 18:10:59 +0000 (-0800)
Subject: Prevent accidentally passing an integer value to IP_ARGS.
X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=be4da39131b5f6f2dd2632c4b4b41f0155532459;p=openvswitch

Prevent accidentally passing an integer value to IP_ARGS.
---

diff --git a/lib/packets.h b/lib/packets.h
index bad36712..09ee05dc 100644
--- a/lib/packets.h
+++ b/lib/packets.h
@@ -160,9 +160,13 @@ struct vlan_eth_header {
 } __attribute__((packed));
 BUILD_ASSERT_DECL(VLAN_ETH_HEADER_LEN == sizeof(struct vlan_eth_header));
 
+/* The "(void) (ip)[0]" below has no effect on the value, since it's the first
+ * argument of a comma expression, but it makes sure that 'ip' is a pointer.
+ * This is useful since a common mistake is to pass an integer instead of a
+ * pointer to IP_ARGS. */
 #define IP_FMT "%"PRIu8".%"PRIu8".%"PRIu8".%"PRIu8
 #define IP_ARGS(ip)                             \
-        ((uint8_t *) ip)[0],                    \
+        ((void) (ip)[0], ((uint8_t *) ip)[0]),  \
         ((uint8_t *) ip)[1],                    \
         ((uint8_t *) ip)[2],                    \
         ((uint8_t *) ip)[3]