hw/net/net_tx_pkt: Align l3_hdr

Align the l3_hdr member of NetTxPkt by defining it as a union of
ip_header, ip6_header, and an array of octets.

Fixes: e263cd4 ("Packet abstraction for VMWARE network devices")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1544
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

hw/net/net_tx_pkt.c

@@ -43,7 +43,11 @@ struct NetTxPkt {
     struct iovec *vec;
 
     uint8_t l2_hdr[ETH_MAX_L2_HDR_LEN];
-    uint8_t l3_hdr[ETH_MAX_IP_DGRAM_LEN];
+    union {
+        struct ip_header ip;
+        struct ip6_header ip6;
+        uint8_t octets[ETH_MAX_IP_DGRAM_LEN];
+    } l3_hdr;
 
     uint32_t payload_len;
 
@@ -89,16 +93,14 @@ void net_tx_pkt_update_ip_hdr_checksum(struct NetTxPkt *pkt)
 {
     uint16_t csum;
     assert(pkt);
-    struct ip_header *ip_hdr;
-    ip_hdr = pkt->vec[NET_TX_PKT_L3HDR_FRAG].iov_base;
 
-    ip_hdr->ip_len = cpu_to_be16(pkt->payload_len +
+    pkt->l3_hdr.ip.ip_len = cpu_to_be16(pkt->payload_len +
         pkt->vec[NET_TX_PKT_L3HDR_FRAG].iov_len);
 
-    ip_hdr->ip_sum = 0;
-    csum = net_raw_checksum((uint8_t *)ip_hdr,
+    pkt->l3_hdr.ip.ip_sum = 0;
+    csum = net_raw_checksum(pkt->l3_hdr.octets,
         pkt->vec[NET_TX_PKT_L3HDR_FRAG].iov_len);
-    ip_hdr->ip_sum = cpu_to_be16(csum);
+    pkt->l3_hdr.ip.ip_sum = cpu_to_be16(csum);
 }
 
 void net_tx_pkt_update_ip_checksums(struct NetTxPkt *pkt)
@@ -832,15 +834,14 @@ void net_tx_pkt_fix_ip6_payload_len(struct NetTxPkt *pkt)
 {
     struct iovec *l2 = &pkt->vec[NET_TX_PKT_L2HDR_FRAG];
     if (eth_get_l3_proto(l2, 1, l2->iov_len) == ETH_P_IPV6) {
-        struct ip6_header *ip6 = (struct ip6_header *) pkt->l3_hdr;
         /*
          * TODO: if qemu would support >64K packets - add jumbo option check
          * something like that:
          * 'if (ip6->ip6_plen == 0 && !has_jumbo_option(ip6)) {'
          */
-        if (ip6->ip6_plen == 0) {
+        if (pkt->l3_hdr.ip6.ip6_plen == 0) {
             if (pkt->payload_len <= ETH_MAX_IP_DGRAM_LEN) {
-                ip6->ip6_plen = htons(pkt->payload_len);
+                pkt->l3_hdr.ip6.ip6_plen = htons(pkt->payload_len);
             }
             /*
              * TODO: if qemu would support >64K packets