libdhcp: Reduce stack use

1 files changed, 65 insertions, 64 deletions

diff --git a/libdhcp/dhcp_client.c b/libdhcp/dhcp_client.c
index bb21564..3728e19 100644
--- a/libdhcp/dhcp_client.c
+++ b/libdhcp/dhcp_client.c
@@ -248,7 +248,7 @@ static inline enum requirement dhcp_table5(typeof((struct dhcp_client){}.state)
  * @return client->last_sent_msgtyp
  * @return whether there was an error
  */
-static bool dhcp_client_send(struct dhcp_client *client, uint8_t msgtyp, const char *errstr) {
+static bool dhcp_client_send(struct dhcp_client *client, uint8_t msgtyp, const char *errstr, struct dhcp_msg *scratch_msg) {
 	/**********************************************************************\
 	 * Preconditions                                                      *
 	\**********************************************************************/
@@ -290,17 +290,17 @@ static bool dhcp_client_send(struct dhcp_client *client, uint8_t msgtyp, const c
 	 * Build the message                                                  *
 	\**********************************************************************/
 
-	struct dhcp_msg msg = {0};
+	*scratch_msg = (struct dhcp_msg){0};
 	size_t optlen = 0;
 
 	/* Base structure.
 	 * https://datatracker.ietf.org/doc/html/rfc2131#page-37 */
-	msg.op     = DHCP_OP_BOOTREQUEST;
-	msg.htype  = DHCP_HTYPE_ETHERNET;
-	msg.hlen   = sizeof(client->self_eth_addr);
-	msg.hops   = 0; /* relays increment this when they forward it along */
-	msg.xid    = uint32be_marshal(client->xid);
-	msg.secs   = uint16be_marshal( ({
+	scratch_msg->op     = DHCP_OP_BOOTREQUEST;
+	scratch_msg->htype  = DHCP_HTYPE_ETHERNET;
+	scratch_msg->hlen   = sizeof(client->self_eth_addr);
+	scratch_msg->hops   = 0; /* relays increment this when they forward it along */
+	scratch_msg->xid    = uint32be_marshal(client->xid);
+	scratch_msg->secs   = uint16be_marshal( ({
 		uint16_t secs;
 		switch (msgtyp) {
 		case DHCP_MSGTYP_DISCOVER: case DHCP_MSGTYP_INFORM:
@@ -335,42 +335,42 @@ static bool dhcp_client_send(struct dhcp_client *client, uint8_t msgtyp, const c
 	}) );
 	switch (msgtyp) {
 	case DHCP_MSGTYP_DISCOVER: case DHCP_MSGTYP_INFORM: case DHCP_MSGTYP_REQUEST:
-		msg.flags = uint16be_marshal(server_broadcasts ? DHCP_FLAG_BROADCAST : 0);
+		scratch_msg->flags = uint16be_marshal(server_broadcasts ? DHCP_FLAG_BROADCAST : 0);
 		break;
 	case DHCP_MSGTYP_DECLINE: case DHCP_MSGTYP_RELEASE:
-		msg.flags = uint16be_marshal(0);
+		scratch_msg->flags = uint16be_marshal(0);
 		break;
 	}
 	switch (msgtyp) {
-	case DHCP_MSGTYP_DISCOVER: msg.ciaddr = net_ip4_addr_zero;         break;
-	case DHCP_MSGTYP_INFORM:   msg.ciaddr = client->lease_client_addr; break;
+	case DHCP_MSGTYP_DISCOVER: scratch_msg->ciaddr = net_ip4_addr_zero;         break;
+	case DHCP_MSGTYP_INFORM:   scratch_msg->ciaddr = client->lease_client_addr; break;
 	case DHCP_MSGTYP_REQUEST: switch (client->state) {
 		case STATE_SELECTING: case STATE_INIT_REBOOT:
-		                   msg.ciaddr = net_ip4_addr_zero;         break;
+		                   scratch_msg->ciaddr = net_ip4_addr_zero;         break;
 		case STATE_BOUND: case STATE_RENEWING: /* case STATE_REBINDING: */
 			/* RFC 2131 includes "REBINDING" here, but a
 			 * DHCPREQUEST is never sent in the REBINDING
 			 * state.  */
-		                   msg.ciaddr = client->lease_client_addr; break;
+		                   scratch_msg->ciaddr = client->lease_client_addr; break;
 		case IMPOSSIBLE_REQUEST_STATES:
 			assert_notreached("invalid client state for sending DHCPREQUEST");
-		}                                                          break;
-	case DHCP_MSGTYP_DECLINE:  msg.ciaddr = net_ip4_addr_zero;         break;
-	case DHCP_MSGTYP_RELEASE:  msg.ciaddr = client->lease_client_addr; break;
+		}                                                                   break;
+	case DHCP_MSGTYP_DECLINE:  scratch_msg->ciaddr = net_ip4_addr_zero;         break;
+	case DHCP_MSGTYP_RELEASE:  scratch_msg->ciaddr = client->lease_client_addr; break;
 	}
-	msg.yiaddr = net_ip4_addr_zero; /* only set by servers */
-	msg.siaddr = net_ip4_addr_zero; /* only set by servers */
-	msg.giaddr = net_ip4_addr_zero; /* only set by relays */
-	memcpy(msg.chaddr, client->self_eth_addr.octets, sizeof(client->self_eth_addr));
-	/* msg.sname = "options, if indicated in 'sname/file' option'; otherwise unused"; */
-	/* msg.file  = "options, if indicated in 'sname/file' option'; otherwise unused"; */
+	scratch_msg->yiaddr = net_ip4_addr_zero; /* only set by servers */
+	scratch_msg->siaddr = net_ip4_addr_zero; /* only set by servers */
+	scratch_msg->giaddr = net_ip4_addr_zero; /* only set by relays */
+	memcpy(scratch_msg->chaddr, client->self_eth_addr.octets, sizeof(client->self_eth_addr));
+	/* scratch_msg->sname = "options, if indicated in 'sname/file' option'; otherwise unused"; */
+	/* scratch_msg->file  = "options, if indicated in 'sname/file' option'; otherwise unused"; */
 
 	/* Magic cookie.
 	 * https://datatracker.ietf.org/doc/html/rfc2131#section-4.1 */
-	msg.options[optlen++] = dhcp_magic_cookie[0];
-	msg.options[optlen++] = dhcp_magic_cookie[1];
-	msg.options[optlen++] = dhcp_magic_cookie[2];
-	msg.options[optlen++] = dhcp_magic_cookie[3];
+	scratch_msg->options[optlen++] = dhcp_magic_cookie[0];
+	scratch_msg->options[optlen++] = dhcp_magic_cookie[1];
+	scratch_msg->options[optlen++] = dhcp_magic_cookie[2];
+	scratch_msg->options[optlen++] = dhcp_magic_cookie[3];
 
 	/* Options.  */
 	for (uint8_t opt = 1; opt < 255; opt++) {
@@ -415,7 +415,7 @@ static bool dhcp_client_send(struct dhcp_client *client, uint8_t msgtyp, const c
 				else {
 					_val16 = uint16be_marshal(20 /* IP header */ +
 					                          8  /* UDP header */ +
-					                          sizeof(msg));
+					                          sizeof(*scratch_msg));
 					V_OBJ(_val16);
 				}
 				break;
@@ -437,9 +437,9 @@ static bool dhcp_client_send(struct dhcp_client *client, uint8_t msgtyp, const c
 					uint8_t len = val.len - done > UINT8_MAX
 						? UINT8_MAX
 						: val.len - done;
-					msg.options[optlen++] = opt;
-					msg.options[optlen++] = len;
-					memcpy(&msg.options[optlen], &((char*)val.ptr)[done], len);
+					scratch_msg->options[optlen++] = opt;
+					scratch_msg->options[optlen++] = len;
+					memcpy(&scratch_msg->options[optlen], &((char*)val.ptr)[done], len);
 					optlen += len;
 					done += len;
 				}
@@ -449,13 +449,13 @@ static bool dhcp_client_send(struct dhcp_client *client, uint8_t msgtyp, const c
 			assert_notreached("bad table");
 		}
 	}
-	msg.options[optlen++] = DHCP_OPT_END;
+	scratch_msg->options[optlen++] = DHCP_OPT_END;
 	assert(optlen <= CONFIG_DHCP_OPT_SIZE);
 
 	/**********************************************************************\
 	 * Send                                                               *
 	\**********************************************************************/
-	ssize_t r = VCALL(client->sock, sendto, &msg, DHCP_MSG_BASE_SIZE + optlen,
+	ssize_t r = VCALL(client->sock, sendto, scratch_msg, DHCP_MSG_BASE_SIZE + optlen,
 	                  client_broadcasts ? net_ip4_addr_broadcast : client->lease_server_id, DHCP_PORT_SERVER);
 	if (r < 0) {
 		debugf("error: sendto: %zd", r);
@@ -741,16 +741,15 @@ static void dhcp_client_take_lease(struct dhcp_client *client, struct dhcp_recv_
 
 static void dhcp_client_setstate(struct dhcp_client *client,
                                  typeof((struct dhcp_client){}.state) newstate,
-                                 uint8_t send_msgtyp, const char *errstr) {
+                                 uint8_t send_msgtyp, const char *errstr, struct dhcp_recv_msg *scratch_msg) {
 	if (send_msgtyp)
-		(void)dhcp_client_send(client, send_msgtyp, errstr);
+		(void)dhcp_client_send(client, send_msgtyp, errstr, &scratch_msg->raw);
 	client->state = newstate;
 }
 
-static __attribute__((noreturn)) void dhcp_client_run(struct dhcp_client *client) {
+static __attribute__((noreturn)) void dhcp_client_run(struct dhcp_client *client, struct dhcp_recv_msg *scratch_msg) {
 	assert(client);
 
-	struct dhcp_recv_msg msg;
 	ssize_t r;
 
 	/* State transition diagram: https://datatracker.ietf.org/doc/html/rfc2131#page-35 */
@@ -759,24 +758,24 @@ static __attribute__((noreturn)) void dhcp_client_run(struct dhcp_client *client
 		case STATE_INIT:
 			client->xid = rand_uint63n(UINT32_MAX);
 			client->time_ns_init = VCALL(bootclock, get_time_ns);
-			dhcp_client_setstate(client, STATE_SELECTING, DHCP_MSGTYP_DISCOVER, NULL);
+			dhcp_client_setstate(client, STATE_SELECTING, DHCP_MSGTYP_DISCOVER, NULL, scratch_msg);
 			break;
 		case STATE_SELECTING:
 			VCALL(client->sock, set_read_deadline, client->time_ns_init+CONFIG_DHCP_SELECTING_NS);
-			switch ((r = dhcp_client_recv(client, &msg))) {
+			switch ((r = dhcp_client_recv(client, scratch_msg))) {
 			case 0:
-				switch (msg.options[DHCP_OPT_DHCP_MSG_TYPE].dat[0]) {
+				switch (scratch_msg->options[DHCP_OPT_DHCP_MSG_TYPE].dat[0]) {
 				case DHCP_MSGTYP_OFFER:
 					/* Accept the first offer.  */
-					dhcp_client_take_lease(client, &msg, false);
-					dhcp_client_setstate(client, STATE_REQUESTING, DHCP_MSGTYP_REQUEST, NULL);
+					dhcp_client_take_lease(client, scratch_msg, false);
+					dhcp_client_setstate(client, STATE_REQUESTING, DHCP_MSGTYP_REQUEST, NULL, scratch_msg);
 					break;
 				default:
 					/* ignore */
 				}
 				break;
 			case -NET_ETIMEDOUT:
-				dhcp_client_setstate(client, STATE_INIT, 0, NULL);
+				dhcp_client_setstate(client, STATE_INIT, 0, NULL, scratch_msg);
 				break;
 			default:
 				assert(r < 0);
@@ -785,18 +784,18 @@ static __attribute__((noreturn)) void dhcp_client_run(struct dhcp_client *client
 			break;
 		case STATE_REQUESTING:
 			VCALL(client->sock, set_read_deadline, 0);
-			switch ((r = dhcp_client_recv(client, &msg))) {
+			switch ((r = dhcp_client_recv(client, scratch_msg))) {
 			case 0:
-				switch (msg.options[DHCP_OPT_DHCP_MSG_TYPE].dat[0]) {
+				switch (scratch_msg->options[DHCP_OPT_DHCP_MSG_TYPE].dat[0]) {
 				case DHCP_MSGTYP_NAK:
-					dhcp_client_setstate(client, STATE_INIT, 0, NULL);
+					dhcp_client_setstate(client, STATE_INIT, 0, NULL, scratch_msg);
 					break;
 				case DHCP_MSGTYP_ACK:
 					if (dhcp_check_conflict(client->sock, client->lease_client_addr)) {
-						dhcp_client_setstate(client, STATE_INIT, DHCP_MSGTYP_DECLINE, "IP is already in use");
+						dhcp_client_setstate(client, STATE_INIT, DHCP_MSGTYP_DECLINE, "IP is already in use", scratch_msg);
 					} else {
-						dhcp_client_take_lease(client, &msg, true);
-						dhcp_client_setstate(client, STATE_BOUND, 0, NULL);
+						dhcp_client_take_lease(client, scratch_msg, true);
+						dhcp_client_setstate(client, STATE_BOUND, 0, NULL, scratch_msg);
 					}
 					break;
 				default:
@@ -810,12 +809,12 @@ static __attribute__((noreturn)) void dhcp_client_run(struct dhcp_client *client
 			break;
 		case STATE_BOUND:
 			VCALL(client->sock, set_read_deadline, client->lease_time_ns_t1);
-			switch ((r = dhcp_client_recv(client, &msg))) {
+			switch ((r = dhcp_client_recv(client, scratch_msg))) {
 			case 0:
 				/* discard */
 				break;
 			case -NET_ETIMEDOUT:
-				dhcp_client_setstate(client, STATE_RENEWING, DHCP_MSGTYP_REQUEST, NULL);
+				dhcp_client_setstate(client, STATE_RENEWING, DHCP_MSGTYP_REQUEST, NULL, scratch_msg);
 				break;
 			default:
 				assert(r < 0);
@@ -827,16 +826,16 @@ static __attribute__((noreturn)) void dhcp_client_run(struct dhcp_client *client
 			client->time_ns_init = VCALL(bootclock, get_time_ns);
 
 			VCALL(client->sock, set_read_deadline, client->lease_time_ns_t2);
-			switch ((r = dhcp_client_recv(client, &msg))) {
+			switch ((r = dhcp_client_recv(client, scratch_msg))) {
 			case 0:
-				switch (msg.options[DHCP_OPT_DHCP_MSG_TYPE].dat[0]) {
+				switch (scratch_msg->options[DHCP_OPT_DHCP_MSG_TYPE].dat[0]) {
 				case DHCP_MSGTYP_NAK:
 					VCALL(client->iface, ifdown);
-					dhcp_client_setstate(client, STATE_INIT, 0, NULL);
+					dhcp_client_setstate(client, STATE_INIT, 0, NULL, scratch_msg);
 					break;
 				case DHCP_MSGTYP_ACK:
-					dhcp_client_take_lease(client, &msg, true);
-					dhcp_client_setstate(client, STATE_BOUND, 0, NULL);
+					dhcp_client_take_lease(client, scratch_msg, true);
+					dhcp_client_setstate(client, STATE_BOUND, 0, NULL, scratch_msg);
 					break;
 				default:
 					/* ignore */
@@ -844,7 +843,7 @@ static __attribute__((noreturn)) void dhcp_client_run(struct dhcp_client *client
 				break;
 			case -NET_ETIMEDOUT:
 				client->lease_server_id = net_ip4_addr_zero;
-				dhcp_client_setstate(client, STATE_REBINDING, DHCP_MSGTYP_REQUEST, NULL);
+				dhcp_client_setstate(client, STATE_REBINDING, DHCP_MSGTYP_REQUEST, NULL, scratch_msg);
 				break;
 			default:
 				assert(r < 0);
@@ -853,16 +852,16 @@ static __attribute__((noreturn)) void dhcp_client_run(struct dhcp_client *client
 			break;
 		case STATE_REBINDING:
 			VCALL(client->sock, set_read_deadline, client->lease_time_ns_end);
-			switch ((r = dhcp_client_recv(client, &msg))) {
+			switch ((r = dhcp_client_recv(client, scratch_msg))) {
 			case 0:
-				switch (msg.options[DHCP_OPT_DHCP_MSG_TYPE].dat[0]) {
+				switch (scratch_msg->options[DHCP_OPT_DHCP_MSG_TYPE].dat[0]) {
 				case DHCP_MSGTYP_NAK:
 					VCALL(client->iface, ifdown);
-					dhcp_client_setstate(client, STATE_BOUND, 0, NULL);
+					dhcp_client_setstate(client, STATE_BOUND, 0, NULL, scratch_msg);
 					break;
 				case DHCP_MSGTYP_ACK:
-					dhcp_client_take_lease(client, &msg, true);
-					dhcp_client_setstate(client, STATE_BOUND, 0, NULL);
+					dhcp_client_take_lease(client, scratch_msg, true);
+					dhcp_client_setstate(client, STATE_BOUND, 0, NULL, scratch_msg);
 					break;
 				default:
 					/* ignore */
@@ -870,7 +869,7 @@ static __attribute__((noreturn)) void dhcp_client_run(struct dhcp_client *client
 				break;
 			case -NET_ETIMEDOUT:
 				VCALL(client->iface, ifdown);
-				dhcp_client_setstate(client, STATE_BOUND, 0, NULL);
+				dhcp_client_setstate(client, STATE_BOUND, 0, NULL, scratch_msg);
 				break;
 			default:
 				assert(r < 0);
@@ -915,5 +914,7 @@ __attribute__((noreturn)) void dhcp_client_main(implements_net_iface *iface,
 
 	assert(client.sock);
 
-	dhcp_client_run(&client);
+	struct dhcp_recv_msg scratch;
+
+	dhcp_client_run(&client, &scratch);
 }