Index: head/sbin/dhclient/Makefile
===================================================================
--- head/sbin/dhclient/Makefile
+++ head/sbin/dhclient/Makefile
@@ -50,7 +50,8 @@
 CFLAGS+=-DWITH_CASPER
 .endif
 
-WARNS?=	3
+WARNS?=	4
+NO_WCAST_ALIGN=	yes
 
 HAS_TESTS=
 SUBDIR.${MK_TESTS}+= tests
Index: head/sbin/dhclient/clparse.c
===================================================================
--- head/sbin/dhclient/clparse.c
+++ head/sbin/dhclient/clparse.c
@@ -687,7 +687,7 @@
 	u_int8_t	 hunkbuf[1024];
 	unsigned	 hunkix = 0;
 	char		*vendor;
-	char		*fmt;
+	const char	*fmt;
 	struct universe	*universe;
 	struct option	*option;
 	struct iaddr	 ip_addr;
Index: head/sbin/dhclient/conflex.c
===================================================================
--- head/sbin/dhclient/conflex.c
+++ head/sbin/dhclient/conflex.c
@@ -55,7 +55,7 @@
 char *token_line;
 char *prev_line;
 char *cur_line;
-char *tlname;
+const char *tlname;
 int eol_token;
 
 static char line1[81];
@@ -78,7 +78,7 @@
 static int intern(char *, int);
 
 void
-new_parse(char *name)
+new_parse(const char *name)
 {
 	tlname = name;
 	lpos = line = 1;
@@ -264,7 +264,7 @@
 static int
 read_number(int c, FILE *cfile)
 {
-	int	seenx = 0, token = NUMBER;
+	int	seenx = 0, _token = NUMBER;
 	unsigned i = 0;
 
 	tokbuf[i++] = c;
@@ -286,7 +286,7 @@
 	tokbuf[i] = 0;
 	tval = tokbuf;
 
-	return (token);
+	return (_token);
 }
 
 static int
Index: head/sbin/dhclient/dhclient.c
===================================================================
--- head/sbin/dhclient/dhclient.c
+++ head/sbin/dhclient/dhclient.c
@@ -91,7 +91,7 @@
 time_t cur_time;
 time_t default_lease_time = 43200; /* 12 hours... */
 
-char *path_dhclient_conf = _PATH_DHCLIENT_CONF;
+const char *path_dhclient_conf = _PATH_DHCLIENT_CONF;
 char *path_dhclient_db = NULL;
 
 int log_perror = 1;
@@ -131,10 +131,10 @@
 void		 usage(void);
 int		 check_option(struct client_lease *l, int option);
 int		 check_classless_option(unsigned char *data, int len);
-int		 ipv4addrs(char * buf);
+int		 ipv4addrs(const char * buf);
 int		 res_hnok(const char *dn);
 int		 check_search(const char *srch);
-char		*option_as_string(unsigned int code, unsigned char *data, int len);
+const char	*option_as_string(unsigned int code, unsigned char *data, int len);
 int		 fork_privchld(int, int);
 
 #define	ROUNDUP(a) \
@@ -201,26 +201,25 @@
 static void
 disassoc(void *arg)
 {
-	struct interface_info *ifi = arg;
+	struct interface_info *_ifi = arg;
 
 	/*
 	 * Clear existing state.
 	 */
-	if (ifi->client->active != NULL) {
+	if (_ifi->client->active != NULL) {
 		script_init("EXPIRE", NULL);
 		script_write_params("old_",
-		    ifi->client->active);
-		if (ifi->client->alias)
+		    _ifi->client->active);
+		if (_ifi->client->alias)
 			script_write_params("alias_",
-				ifi->client->alias);
+				_ifi->client->alias);
 		script_go();
 	}
-	ifi->client->state = S_INIT;
+	_ifi->client->state = S_INIT;
 }
 
-/* ARGSUSED */
 void
-routehandler(struct protocol *p)
+routehandler(struct protocol *p __unused)
 {
 	char msg[2048], *addr;
 	struct rt_msghdr *rtm;
@@ -230,7 +229,7 @@
 	struct ieee80211_join_event *jev;
 	struct client_lease *l;
 	time_t t = time(NULL);
-	struct sockaddr *sa;
+	struct sockaddr_in *sa;
 	struct iaddr a;
 	ssize_t n;
 	int linkstat;
@@ -254,13 +253,13 @@
 		if (scripttime == 0 || t < scripttime + 10)
 			break;
 
-		sa = get_ifa((char *)(ifam + 1), ifam->ifam_addrs);
+		sa = (struct sockaddr_in*)get_ifa((char *)(ifam + 1), ifam->ifam_addrs);
 		if (sa == NULL)
 			break;
 
 		if ((a.len = sizeof(struct in_addr)) > sizeof(a.iabuf))
 			error("king bula sez: len mismatch");
-		memcpy(a.iabuf, &((struct sockaddr_in *)sa)->sin_addr, a.len);
+		memcpy(a.iabuf, &sa->sin_addr, a.len);
 		if (addr_eq(a, defaddr))
 			break;
 
@@ -271,7 +270,7 @@
 		if (l == NULL)	/* added/deleted addr is not the one we set */
 			break;
 
-		addr = inet_ntoa(((struct sockaddr_in *)sa)->sin_addr);
+		addr = inet_ntoa(sa->sin_addr);
 		if (rtm->rtm_type == RTM_NEWADDR)  {
 			/*
 			 * XXX: If someone other than us adds our address,
@@ -946,7 +945,7 @@
 {
 	struct iaddrlist *ap;
 	void (*handler)(struct packet *);
-	char *type;
+	const char *type;
 
 	switch (packet->packet_type) {
 	case DHCPOFFER:
@@ -984,7 +983,7 @@
 	struct client_lease *lease, *lp;
 	int i;
 	int arp_timeout_needed, stop_selecting;
-	char *name = packet->options[DHO_DHCP_MESSAGE_TYPE].len ?
+	const char *name = packet->options[DHO_DHCP_MESSAGE_TYPE].len ?
 	    "DHCPOFFER" : "BOOTREPLY";
 
 	/* If we're not receptive to an offer right now, or if the offer
@@ -1993,7 +1992,7 @@
 }
 
 void
-script_init(char *reason, struct string_list *medium)
+script_init(const char *reason, struct string_list *medium)
 {
 	size_t		 len, mediumlen = 0;
 	struct imsg_hdr	 hdr;
@@ -2028,7 +2027,7 @@
 }
 
 void
-priv_script_init(char *reason, char *medium)
+priv_script_init(const char *reason, char *medium)
 {
 	struct interface_info *ip = ifi;
 
@@ -2056,7 +2055,7 @@
 }
 
 void
-priv_script_write_params(char *prefix, struct client_lease *lease)
+priv_script_write_params(const char *prefix, struct client_lease *lease)
 {
 	struct interface_info *ip = ifi;
 	u_int8_t dbuf[1500], *dp = NULL;
@@ -2196,7 +2195,7 @@
 }
 
 void
-script_write_params(char *prefix, struct client_lease *lease)
+script_write_params(const char *prefix, struct client_lease *lease)
 {
 	size_t		 fn_len = 0, sn_len = 0, pr_len = 0;
 	struct imsg_hdr	 hdr;
@@ -2460,8 +2459,8 @@
 int
 check_option(struct client_lease *l, int option)
 {
-	char *opbuf;
-	char *sbuf;
+	const char *opbuf;
+	const char *sbuf;
 
 	/* we use this, since this is what gets passed to dhclient-script */
 
@@ -2721,7 +2720,7 @@
  * otherwise, return 0
  */
 int
-ipv4addrs(char * buf)
+ipv4addrs(const char * buf)
 {
 	struct in_addr jnk;
 	int count = 0;
@@ -2739,7 +2738,7 @@
 }
 
 
-char *
+const char *
 option_as_string(unsigned int code, unsigned char *data, int len)
 {
 	static char optbuf[32768]; /* XXX */
Index: head/sbin/dhclient/dhcpd.h
===================================================================
--- head/sbin/dhclient/dhcpd.h
+++ head/sbin/dhclient/dhcpd.h
@@ -235,7 +235,7 @@
 
 struct hash_bucket {
 	struct hash_bucket *next;
-	unsigned char *name;
+	const unsigned char *name;
 	int len;
 	unsigned char *value;
 };
@@ -258,26 +258,27 @@
 /* options.c */
 int cons_options(struct packet *, struct dhcp_packet *, int,
     struct tree_cache **, int, int, int, u_int8_t *, int);
-char *pretty_print_option(unsigned int,
+const char *pretty_print_option(unsigned int,
     unsigned char *, int, int, int);
 void do_packet(struct interface_info *, struct dhcp_packet *,
     int, unsigned int, struct iaddr, struct hardware *);
 
 /* errwarn.c */
 extern int warnings_occurred;
-void error(char *, ...) __attribute__ ((__format__ (__printf__, 1, 2)));
-int warning(char *, ...) __attribute__ ((__format__ (__printf__, 1, 2)));
-int note(char *, ...) __attribute__ ((__format__ (__printf__, 1, 2)));
-int debug(char *, ...) __attribute__ ((__format__ (__printf__, 1, 2)));
-int parse_warn(char *, ...) __attribute__ ((__format__ (__printf__, 1, 2)));
+void error(const char *, ...) __attribute__ ((__format__ (__printf__, 1, 2)));
+int warning(const char *, ...) __attribute__ ((__format__ (__printf__, 1, 2)));
+int note(const char *, ...) __attribute__ ((__format__ (__printf__, 1, 2)));
+int debug(const char *, ...) __attribute__ ((__format__ (__printf__, 1, 2)));
+int parse_warn(const char *, ...) __attribute__ ((__format__ (__printf__, 1, 2)));
 
 /* conflex.c */
 extern int lexline, lexchar;
-extern char *token_line, *tlname;
+extern char *token_line;
+extern const char *tlname;
 extern char comments[4096];
 extern int comment_index;
 extern int eol_token;
-void new_parse(char *);
+void new_parse(const char *);
 int next_token(char **, FILE *);
 int peek_token(char **, FILE *);
 
@@ -321,7 +322,7 @@
 void got_one(struct protocol *);
 void add_timeout(time_t, void (*)(void *), void *);
 void cancel_timeout(void (*)(void *), void *);
-void add_protocol(char *, int, void (*)(struct protocol *), void *);
+void add_protocol(const char *, int, void (*)(struct protocol *), void *);
 void remove_protocol(struct protocol *);
 int interface_link_status(char *);
 void interface_set_mtu_unpriv(int, u_int16_t);
@@ -329,8 +330,8 @@
 
 /* hash.c */
 struct hash_table *new_hash(void);
-void add_hash(struct hash_table *, unsigned char *, int, unsigned char *);
-unsigned char *hash_lookup(struct hash_table *, unsigned char *, int);
+void add_hash(struct hash_table *, const unsigned char *, int, unsigned char *);
+void *hash_lookup(struct hash_table *, unsigned char *, int);
 
 /* tables.c */
 extern struct option dhcp_options[256];
@@ -358,7 +359,7 @@
 
 /* dhclient.c */
 extern cap_channel_t *capsyslog;
-extern char *path_dhclient_conf;
+extern const char *path_dhclient_conf;
 extern char *path_dhclient_db;
 extern time_t cur_time;
 extern int log_priority;
@@ -393,12 +394,12 @@
 void rewrite_client_leases(void);
 void write_client_lease(struct interface_info *, struct client_lease *, int);
 
-void	 priv_script_init(char *, char *);
-void	 priv_script_write_params(char *, struct client_lease *);
+void	 priv_script_init(const char *, char *);
+void	 priv_script_write_params(const char *, struct client_lease *);
 int	 priv_script_go(void);
 
-void script_init(char *, struct string_list *);
-void script_write_params(char *, struct client_lease *);
+void script_init(const char *, struct string_list *);
+void script_write_params(const char *, struct client_lease *);
 int script_go(void);
 void client_envadd(struct client_state *,
     const char *, const char *, const char *, ...);
@@ -442,7 +443,7 @@
 
 /* privsep.c */
 struct buf	*buf_open(size_t);
-int		 buf_add(struct buf *, void *, size_t);
+int		 buf_add(struct buf *, const void *, size_t);
 int		 buf_close(int, struct buf *);
 ssize_t		 buf_read(int, void *, size_t);
 void		 dispatch_imsg(struct interface_info *, int);
Index: head/sbin/dhclient/dispatch.c
===================================================================
--- head/sbin/dhclient/dispatch.c
+++ head/sbin/dhclient/dispatch.c
@@ -49,10 +49,14 @@
 
 #include <sys/ioctl.h>
 
+#include <assert.h>
 #include <net/if_media.h>
 #include <ifaddrs.h>
 #include <poll.h>
 
+/* Assert that pointer p is aligned to at least align bytes */
+#define assert_aligned(p, align) assert((((uintptr_t)p) & ((align) - 1)) == 0)
+
 struct protocol *protocols;
 struct timeout *timeouts;
 static struct timeout *free_timeouts;
@@ -73,7 +77,6 @@
 discover_interfaces(struct interface_info *iface)
 {
 	struct ifaddrs *ifap, *ifa;
-	struct sockaddr_in foo;
 	struct ifreq *tif;
 
 	if (getifaddrs(&ifap) != 0)
@@ -93,15 +96,30 @@
 		 * and record it in a linked list.
 		 */
 		if (ifa->ifa_addr->sa_family == AF_LINK) {
-			struct sockaddr_dl *foo =
-			    (struct sockaddr_dl *)ifa->ifa_addr;
+			struct sockaddr_dl *foo;
 
+			/* 
+			 * The implementation of getifaddrs should guarantee
+			 * this alignment
+			 */
+			assert_aligned(ifa->ifa_addr,
+				       _Alignof(struct sockaddr_dl));
+#ifdef __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wcast-align"
+#endif
+			foo = (struct sockaddr_dl *)ifa->ifa_addr;
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
+
 			iface->index = foo->sdl_index;
 			iface->hw_address.hlen = foo->sdl_alen;
 			iface->hw_address.htype = HTYPE_ETHER; /* XXX */
 			memcpy(iface->hw_address.haddr,
 			    LLADDR(foo), foo->sdl_alen);
 		} else if (ifa->ifa_addr->sa_family == AF_INET) {
+			struct sockaddr_in foo;
 			struct iaddr addr;
 
 			memcpy(&foo, ifa->ifa_addr, sizeof(foo));
@@ -437,7 +455,7 @@
 
 /* Add a protocol to the list of protocols... */
 void
-add_protocol(char *name, int fd, void (*handler)(struct protocol *),
+add_protocol(const char *name, int fd, void (*handler)(struct protocol *),
     void *local)
 {
 	struct protocol *p;
Index: head/sbin/dhclient/errwarn.c
===================================================================
--- head/sbin/dhclient/errwarn.c
+++ head/sbin/dhclient/errwarn.c
@@ -49,7 +49,7 @@
 
 #include "dhcpd.h"
 
-static void do_percentm(char *obuf, size_t size, char *ibuf);
+static void do_percentm(char *obuf, size_t size, const char *ibuf);
 
 static char mbuf[1024];
 static char fbuf[1024];
@@ -60,7 +60,7 @@
  * Log an error message, then exit.
  */
 void
-error(char *fmt, ...)
+error(const char *fmt, ...)
 {
 	va_list list;
 
@@ -94,7 +94,7 @@
  * Log a warning message...
  */
 int
-warning(char *fmt, ...)
+warning(const char *fmt, ...)
 {
 	va_list list;
 
@@ -120,7 +120,7 @@
  * Log a note...
  */
 int
-note(char *fmt, ...)
+note(const char *fmt, ...)
 {
 	va_list list;
 
@@ -146,7 +146,7 @@
  * Log a debug message...
  */
 int
-debug(char *fmt, ...)
+debug(const char *fmt, ...)
 {
 	va_list list;
 
@@ -172,10 +172,10 @@
  * Find %m in the input string and substitute an error message string.
  */
 static void
-do_percentm(char *obuf, size_t size, char *ibuf)
+do_percentm(char *obuf, size_t size, const char *ibuf)
 {
 	char ch;
-	char *s = ibuf;
+	const char *s = ibuf;
 	char *t = obuf;
 	size_t prlen;
 	size_t fmt_left;
@@ -205,7 +205,7 @@
 }
 
 int
-parse_warn(char *fmt, ...)
+parse_warn(const char *fmt, ...)
 {
 	va_list list;
 	static char spaces[] =
Index: head/sbin/dhclient/hash.c
===================================================================
--- head/sbin/dhclient/hash.c
+++ head/sbin/dhclient/hash.c
@@ -47,7 +47,7 @@
 
 #include "dhcpd.h"
 
-static int do_hash(unsigned char *, int, int);
+static int do_hash(const unsigned char *, int, int);
 
 struct hash_table *
 new_hash(void)
@@ -62,9 +62,9 @@
 }
 
 static int
-do_hash(unsigned char *name, int len, int size)
+do_hash(const unsigned char *name, int len, int size)
 {
-	unsigned char *s = name;
+	const unsigned char *s = name;
 	int accum = 0, i = len;
 
 	while (i--) {
@@ -77,7 +77,7 @@
 	return (accum % size);
 }
 
-void add_hash(struct hash_table *table, unsigned char *name, int len,
+void add_hash(struct hash_table *table, const unsigned char *name, int len,
     unsigned char *pointer)
 {
 	struct hash_bucket *bp;
@@ -86,7 +86,7 @@
 	if (!table)
 		return;
 	if (!len)
-		len = strlen((char *)name);
+		len = strlen((const char *)name);
 
 	hashno = do_hash(name, len, table->hash_count);
 	bp = new_hash_bucket();
@@ -102,7 +102,7 @@
 	table->buckets[hashno] = bp;
 }
 
-unsigned char *
+void *
 hash_lookup(struct hash_table *table, unsigned char *name, int len)
 {
 	struct hash_bucket *bp;
Index: head/sbin/dhclient/options.c
===================================================================
--- head/sbin/dhclient/options.c
+++ head/sbin/dhclient/options.c
@@ -628,7 +628,7 @@
 /*
  * Format the specified option so that a human can easily read it.
  */
-char *
+const char *
 pretty_print_option(unsigned int code, unsigned char *data, int len,
     int emit_commas, int emit_quotes)
 {
Index: head/sbin/dhclient/privsep.h
===================================================================
--- head/sbin/dhclient/privsep.h
+++ head/sbin/dhclient/privsep.h
@@ -46,6 +46,6 @@
 };
 
 struct buf	*buf_open(size_t);
-int		 buf_add(struct buf *, void *, size_t);
+int		 buf_add(struct buf *, const void *, size_t);
 int		 buf_close(int, struct buf *);
 ssize_t		 buf_read(int sock, void *, size_t);
Index: head/sbin/dhclient/privsep.c
===================================================================
--- head/sbin/dhclient/privsep.c
+++ head/sbin/dhclient/privsep.c
@@ -39,7 +39,7 @@
 }
 
 int
-buf_add(struct buf *buf, void *data, size_t len)
+buf_add(struct buf *buf, const void *data, size_t len)
 {
 	if (buf->wpos + len > buf->size)
 		return (-1);
Index: head/sbin/dhclient/tables.c
===================================================================
--- head/sbin/dhclient/tables.c
+++ head/sbin/dhclient/tables.c
@@ -440,11 +440,11 @@
 	for (i = 0; i < 256; i++) {
 		dhcp_universe.options[i] = &dhcp_options[i];
 		add_hash(dhcp_universe.hash,
-		    (unsigned char *)dhcp_options[i].name, 0,
+		    (const unsigned char *)dhcp_options[i].name, 0,
 		    (unsigned char *)&dhcp_options[i]);
 	}
 	universe_hash.hash_count = DEFAULT_HASH_SIZE;
 	add_hash(&universe_hash,
-	    (unsigned char *)dhcp_universe.name, 0,
+	    (const unsigned char *)dhcp_universe.name, 0,
 	    (unsigned char *)&dhcp_universe);
 }
Index: head/sbin/dhclient/tests/fake.c
===================================================================
--- head/sbin/dhclient/tests/fake.c
+++ head/sbin/dhclient/tests/fake.c
@@ -9,7 +9,7 @@
 extern jmp_buf env;
 
 void
-error(char *fmt, ...)
+error(const char *fmt, ...)
 {
 	va_list ap;
 
@@ -22,7 +22,7 @@
 }
 
 int
-warning(char *fmt, ...)
+warning(const char *fmt, ...)
 {
 	va_list ap;
 
@@ -39,7 +39,7 @@
 }
 
 int
-note(char *fmt, ...)
+note(const char *fmt, ...)
 {
 	int ret;
 	va_list ap;
Index: head/sbin/dhclient/tree.h
===================================================================
--- head/sbin/dhclient/tree.h
+++ head/sbin/dhclient/tree.h
@@ -57,14 +57,14 @@
 };
 
 struct universe {
-	char *name;
+	const char *name;
 	struct hash_table *hash;
 	struct option *options[256];
 };
 
 struct option {
-	char *name;
-	char *format;
+	const char *name;
+	const char *format;
 	struct universe *universe;
 	unsigned char code;
 };