extract arp into its own static library; add empty arp::init() called from dispatch_init to anchor the .o so the self-registration constructor links in

CMakeLists.txt

@@ -6,9 +6,9 @@ add_subdirectory(debug_log)
 add_subdirectory(msgpack)
 add_subdirectory(eth)
 add_subdirectory(ipv4)
+add_subdirectory(arp)
 
 add_library(limen STATIC
-    src/arp.cpp
     src/dispatch.cpp
     src/flash.cpp
     src/handlers.cpp
@@ -31,6 +31,7 @@ target_link_libraries(limen PUBLIC
     msgpack
     eth
     ipv4
+    arp
     pico_stdlib
     pico_sha256
 )

arp/CMakeLists.txt

@@ -0,0 +1,11 @@
+add_library(arp STATIC arp.cpp)
+
+target_include_directories(arp PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+
+target_compile_options(arp PRIVATE -Wall -Wextra -Wno-unused-parameter)
+
+target_link_libraries(arp PUBLIC
+    util
+    eth
+    ipv4
+)

arp/arp.cpp

@@ -41,6 +41,8 @@ void handle(std::span<const uint8_t> frame, span_writer& tx) {
     eth::send_raw(buf.span());
 }
 
+void init() {}
+
 __attribute__((constructor))
 static void register_ethertype() {
     eth::register_ethertype(eth::ETH_ARP, handle);

arp/arp.h

@@ -19,6 +19,7 @@ struct __attribute__((packed)) header {
 };
 static_assert(sizeof(header) == 28);
 
+void init();
 void handle(std::span<const uint8_t> frame, span_writer& tx);
 
 } // namespace arp

src/dispatch.cpp

@@ -5,6 +5,7 @@
 #include "timer_queue.h"
 #include "eth.h"
 #include "ipv4.h"
+#include "arp.h"
 #include "igmp.h"
 #include "udp.h"
 #include "debug_log.h"
@@ -37,6 +38,7 @@ void dispatch_init(uint16_t port_be) {
     udp::register_port(port_be, on_udp_message);
     eth::init();
     ipv4::init();
+    arp::init();
     dispatch_schedule_ms(60000, igmp_reannounce);
     dlog("dispatch_init complete");
 }