C89 says that the result of shifting an N-bit value by >= N bits is

undefined; we want it to be zero, so we explicitly check for a 32-bit
shift count and clear the netmask in that case.

1 files changed, 9 insertions, 2 deletions

diff --git a/gencode.c b/gencode.c
index d7b704a9..472427b9 100644
--- a/gencode.c
+++ b/gencode.c
@@ -21,7 +21,7 @@
  */
 #ifndef lint
 static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/libpcap/gencode.c,v 1.267 2006-05-18 08:40:52 hannes Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/gencode.c,v 1.268 2006-05-28 20:12:28 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -5019,7 +5019,14 @@ gen_mcode(s1, s2, masklen, q)
 		/* Convert mask len to mask */
 		if (masklen > 32)
 			bpf_error("mask length must be <= 32");
-		m = 0xffffffff << (32 - masklen);
+		if (masklen == 0) {
+			/*
+			 * X << 32 is not guaranteed by C to be 0; it's
+			 * undefined.
+			 */
+			m = 0;
+		} else
+			m = 0xffffffff << (32 - masklen);
 		if ((n & ~m) != 0)
 			bpf_error("non-network bits set in \"%s/%d\"",
 			    s1, masklen);