[lwip-devel] byte order, packing, optimizations

[Stéphane Lesage]

This is a follow-up from http://savannah.nongnu.org/bugs/?27352

>Oh, and when the structs are packed, I don't think we can copy
>u16_t because the port may be free to use unaligned pbuf
>payloads when setting MEM_ALIGN to 1!

Any port which cannot do misaligned access will set MEM_ALIGN to 2 or 4. 
Even x86 needs MEM_ALIGN=4 for better performance.

SMEMCPY(&hdr->sipaddr, ipsrc_addr, sizeof(ip_addr_t));

why take the risk of several calls to memcpy inside a function that is 
called for every packet ?
hdr->sipaddr is ip_addr2, why not copy 2 u16_t directly or use a 
well-defined macro ?

>>BTW, ip_addr_set should be use only for safe copy, the latest
>> modifications use it everywhere, even if we don't have to check
>> the pointer.
>I might have to check that again, but I think the only places where I 
used that unchecked is the SNMP code.
>If there are other places where it is used unchecked, please tell me.

In most of the following places, the pointer is a field of a structure, 
so it will never be null:

core\dhcp.c(249):    ip_addr_set(&dhcp->offered_ip_addr, 
&dhcp->msg_in->yiaddr);
core\dhcp.c(536):  ip_addr_set(&dhcp->offered_ip_addr, 
&dhcp->msg_in->yiaddr);
core\dhcp.c(541):  ip_addr_set(&dhcp->offered_si_addr, 
&dhcp->msg_in->siaddr);
core\dhcp.c(928):    ip_addr_set(&sn_mask, &dhcp->offered_sn_mask);
core\dhcp.c(941):  ip_addr_set(&gw_addr, &dhcp->offered_gw_addr);
core\dhcp.c(1650):    ip_addr_set(&dhcp->msg_out->ciaddr, &netif->ip_addr);
core\tcp.c(235):    ip_addr_set(&local_ip, &(pcb->local_ip));
core\tcp.c(236):    ip_addr_set(&remote_ip, &(pcb->remote_ip));
core\tcp.c(390):  ip_addr_set(&lpcb->local_ip, &pcb->local_ip);
core\tcp_in.c(436):    ip_addr_set(&(npcb->local_ip), &(iphdr->dest));
core\tcp_in.c(438):    ip_addr_set(&(npcb->remote_ip), &(iphdr->src));
core\tcp_out.c(706):    ip_addr_set(&(pcb->local_ip), &(netif->ip_addr));
core\ipv4\icmp.c(187):    ip_addr_set(&tmpaddr, &iphdr->src);
core\ipv4\icmp.c(188):    ip_addr_set(&iphdr->src, &iphdr->dest);
core\ipv4\icmp.c(189):    ip_addr_set(&iphdr->dest, &tmpaddr);
core\ipv4\igmp.c(285):    ip_addr_set(&(group->group_address), addr);
core\ipv4\igmp.c(735):    ip_addr_set(&src, &((group->netif)->ip_addr));
core\ipv4\igmp.c(739):      ip_addr_set(&(igmp->igmp_group_address), 
&(group->group_address));
core\ipv4\igmp.c(744):        ip_addr_set(&(igmp->igmp_group_address), 
&(group->group_address));
core\ipv4\ip.c(569):      ip_addr_set(&(iphdr->src), &(netif->ip_addr));
core\ipv6\icmp6.c(79):    ip_addr_set(&tmpaddr, &(iphdr->src));
core\ipv6\icmp6.c(80):    ip_addr_set(&(iphdr->src), &(iphdr->dest));
core\ipv6\icmp6.c(81):    ip_addr_set(&(iphdr->dest), &tmpaddr);
core\ipv6\ip6.c(290):      ip_addr_set(&(iphdr->src), &(netif->ip_addr));
core\snmp\msg_out.c(233):      ip_addr_set(&trap_msg.dip, &td->dip);
core\snmp\msg_out.c(236):      ip_addr_set(&dst_ip, &dst_if->ip_addr);


should be changed to:
#define ip_addr_set_any(ipaddr) (ipaddr)->addr = IPADDR_ANY

core\dhcp.c(837):  ip_addr_set(&dhcp->offered_ip_addr, IP_ADDR_ANY);
core\udp.c(742):  ip_addr_set(&pcb->remote_ip, IP_ADDR_ANY);
core\snmp\mib2.c(1445):    ip_addr_set(&dst, &ip_addr_any);
core\snmp\mib2.c(1522):    ip_addr_set(&dst, &ip_addr_any);