diff --git a/diag.c b/diag.c
index e1e0a39..9e5df08 100644
--- a/diag.c
+++ b/diag.c
@@ -92,11 +92,11 @@ int diag_data_recv(int fd, void *data)
 	struct diag_client *client;
 	struct list_head *item;
 	uint8_t buf[4096];
-	uint8_t *ptr;
-	uint8_t *msg;
 	size_t msglen;
 	size_t len;
 	ssize_t n;
+	void *msg;
+	void *ptr;
 
 	for (;;) {
 		n = read(fd, buf, sizeof(buf));
@@ -228,11 +228,11 @@ static int diag_sock_recv(int fd, void *data)
 {
 	struct diag_client *client = data;
 	uint8_t buf[4096];
-	uint8_t *ptr;
-	uint8_t *msg;
 	size_t msglen;
 	size_t len;
 	ssize_t n;
+	void *msg;
+	void *ptr;
 	int ret;
 
 	n = read(fd, buf, sizeof(buf));
diff --git a/hdlc.c b/hdlc.c
index 2df486c..0f9348e 100644
--- a/hdlc.c
+++ b/hdlc.c
@@ -72,17 +72,18 @@ static uint16_t crc_table[256] = {
 	0x3de3, 0x2c6a, 0x1ef1, 0x0f78
 };
 
-uint16_t hdlc_crc_byte(uint16_t crc, uint8_t ch)
+static uint16_t hdlc_crc_byte(uint16_t crc, uint8_t ch)
 {
 	return (crc >> 8) ^ crc_table[(crc ^ ch) & 0xff];
 }
 
-uint8_t *hdlc_encode(uint8_t *src, size_t slen, size_t *dlen)
+void *hdlc_encode(const void *src, size_t slen, size_t *dlen)
 {
+	const uint8_t *end = src + slen;
+	const uint8_t *s = src;
 	uint16_t crc = 0xffff;
 	uint8_t tmp[2];
 	uint8_t *dst;
-	uint8_t *s = src;
 	uint8_t *d;
 	int i;
 
@@ -91,7 +92,7 @@ uint8_t *hdlc_encode(uint8_t *src, size_t slen, size_t *dlen)
 		return NULL;
 
 	d = dst;
-	while (s < src + slen) {
+	while (s < end) {
 		crc = hdlc_crc_byte(crc, *s);
 
 		if (*s == 0x7d || *s == 0x7e) {
@@ -121,8 +122,9 @@ uint8_t *hdlc_encode(uint8_t *src, size_t slen, size_t *dlen)
 	return dst;
 }
 
-uint8_t *hdlc_decode_one(uint8_t **buf, size_t *len, size_t *msglen)
+void *hdlc_decode_one(void **buf, size_t *len, size_t *msglen)
 {
+	uint8_t *end = *buf + *len;
 	uint8_t *dst = *buf;
 	uint8_t *src = *buf;
 	uint8_t *msg = *buf;
@@ -130,7 +132,7 @@ uint8_t *hdlc_decode_one(uint8_t **buf, size_t *len, size_t *msglen)
 	uint8_t ch;
 
 	for (;;) {
-		if (src >= *buf + *len)
+		if (src >= end)
 			return NULL;
 
 		ch = *src++;
diff --git a/hdlc.h b/hdlc.h
index b704409..cd1be03 100644
--- a/hdlc.h
+++ b/hdlc.h
@@ -34,9 +34,7 @@
 
 #include <stdint.h>
 
-uint16_t hdlc_crc_byte(uint16_t crc, uint8_t ch);
+void *hdlc_encode(const void *src, size_t slen, size_t *dlen);
 
-uint8_t *hdlc_encode(uint8_t *src, size_t slen, size_t *dlen);
-
-uint8_t *hdlc_decode_one(uint8_t **buf, size_t *len, size_t *msglen);
+void *hdlc_decode_one(void **buf, size_t *len, size_t *msglen);
 #endif