pkg/lwip: Fix dualstack build when only using 6lowpan

[yarrick]

Contribution description

• Disable ARP if Ethernet is not used
• Use macro converting netif v6 address to ip6_addr_t (which is noop in v6-only setup)

Testing procedure

BOARD=iotlab-m3 LWIP_IPV4=1 LWIP_IPV6=1 make -C tests/lwip -j now works

BOARD=iotlab-m3 LWIP_IPV4=1 make -C tests/lwip -j is still broken (since it disables IPv6): linking fails with undefined reference to 'ipv6_addr_link_local_prefix'

Issues/PRs references

Part of #17162

[miri64]

Part of #17162

Why only "Part of" and not "Fixes"?

[miri64]

BOARD=iotlab-m3 LWIP_IPV4=1 make -C tests/lwip -j is still broken (since it disables IPv6): linking fails with undefined reference to 'ipv6_addr_link_local_prefix'

This can be fixed when applying

diff --git a/pkg/lwip/contrib/netdev/lwip_netdev.c b/pkg/lwip/contrib/netdev/lwip_netdev.c
index e70e4eacee..34398470db 100644
--- a/pkg/lwip/contrib/netdev/lwip_netdev.c
+++ b/pkg/lwip/contrib/netdev/lwip_netdev.c
@@ -159,17 +159,19 @@ err_t lwip_netdev_init(struct netif *netif)
             if (netdev->driver->set(netdev, NETOPT_SRC_LEN, &val, sizeof(val)) < 0) {
                 return ERR_IF;
             }
-            /* netif_create_ip6_linklocal_address() does weird byte-swapping
-             * with full IIDs, so let's do it ourselves */
-            addr = ip_2_ip6(&(netif->ip6_addr[0]));
-            /* addr->addr is a uint32_t array */
-            if (l2util_ipv6_iid_from_addr(dev_type,
-                                          netif->hwaddr, netif->hwaddr_len,
-                                          (eui64_t *)&addr->addr[2]) < 0) {
-                return ERR_IF;
+            if (IS_USED(MODULE_IPV6_ADDR)) {
+                /* netif_create_ip6_linklocal_address() does weird byte-swapping
+                 * with full IIDs, so let's do it ourselves */
+                addr = ip_2_ip6(&(netif->ip6_addr[0]));
+                /* addr->addr is a uint32_t array */
+                if (l2util_ipv6_iid_from_addr(dev_type,
+                                              netif->hwaddr, netif->hwaddr_len,
+                                              (eui64_t *)&addr->addr[2]) < 0) {
+                    return ERR_IF;
+                }
+                ipv6_addr_set_link_local_prefix((ipv6_addr_t *)&addr->addr[0]);
+                ip6_addr_assign_zone(addr, IP6_UNICAST, netif);
             }
-            ipv6_addr_set_link_local_prefix((ipv6_addr_t *)&addr->addr[0]);
-            ip6_addr_assign_zone(addr, IP6_UNICAST, netif);
             /* Set address state. */
 #if LWIP_IPV6_DUP_DETECT_ATTEMPTS
             /* Will perform duplicate address detection (DAD). */

However, then another error is revealed:

tests/lwip/bin/iotlab-m3/application_tests_lwip/ip.o:tests/lwip/ip.c:70: undefined reference to `ipv6_addr_to_str'

Which is weird, as this part of the code is #if IS_USED(MODULE_LWIP_IPV6)'d... make info-modules reveals that the module is indeed selected. However, LWIP_IPV6 is 0 as can be shown with. Will have a look where this is coming from...

diff --git a/tests/lwip/Makefile b/tests/lwip/Makefile
index c7b2472561..42dde78c7c 100644
--- a/tests/lwip/Makefile
+++ b/tests/lwip/Makefile
@@ -16,0 +17,2 @@ endif
+$(warning $(LWIP_IPV6))
+

[miri64]

Ah...

RIOT/sys/Makefile.dep

Lines 175 to 179 in ff8983c

	ifneq (,$(filter ieee802154 nrfmin esp_now cc110x,$(USEMODULE)))
	ifneq (,$(filter lwip%, $(USEMODULE)))
	USEMODULE += lwip_sixlowpan
	endif
	endif

selects lwip_sixlowpan (weird that this is in sys/Makefile.dep, this should be in pkg/lwip/Makefile.dep IMHO). That leads to

RIOT/pkg/lwip/Makefile.dep

Lines 59 to 62 in ff8983c

	ifneq (,$(filter lwip_sixlowpan,$(USEMODULE)))
	USEMODULE += lwip_ipv6_autoconfig
	USEMODULE += l2util
	endif

which leads to

RIOT/pkg/lwip/Makefile.dep

Lines 26 to 28 in ff8983c

	ifneq (,$(filter lwip_ipv6_autoconfig lwip_ipv6_mld,$(USEMODULE)))
	USEMODULE += lwip_ipv6
	endif

IMHO the very first dependency listed should depend on lwip_ipv6% rather than lwip.

[yarrick]

Only part of because it only fixes the dualstack issue, and not when IPv6 is totally missing.

I don't think we should guard on ipv6_addr, it could be useful to still format such addresses without having protocol support for them. The issue might be that lwip_sixlowpan is enabled from sys/, but that does not depend on actual ipv6 support inside lwIP. I think this could be a separate PR however (either skip those interfaces, include ipv6 anyway, or fail to even try to compile anything)

[miri64]

I don't think we should guard on ipv6_addr, it could be useful to still format such addresses without having protocol support for them.

Then ipv6_addr and ipv4_addr should be included in tests/lwip/Makefile in all cases.

[miri64]

But yes, this can be done as a follow-up. Likewise the dependency fix.

[miri64]

Fixes the issue described in #17162.

[miri64]

🎉 Congrats on your first merge commit!