ldso: update link map during respawn

move binary to front of link map after respawn. This is required by GDB
in order to load symbol files correctly.

issue #3481

repos/base/src/lib/ldso/include/debug.h

@@ -134,6 +134,20 @@ struct Linker::Link_map
 				first = map->next;
 	}
 
+	static void make_first(Link_map *map)
+	{
+		remove(map);
+
+		if (first) {
+			first->prev = map;
+		}
+
+		map->prev       = nullptr;
+		map->next       = first;
+		first           = map;
+		Debug::d()->map = map;
+	}
+
 	static void dump()
 	{
 		if (!verbose_link_map)

repos/base/src/lib/ldso/main.cc

@@ -193,6 +193,11 @@ class Linker::Elf_object : public Object, private Fifo<Elf_object>::Element
 			Link_map::add(&_map);
 		};
 
+		void link_map_make_first()
+		{
+			Link_map::make_first(&_map);
+		}
+
 		void force_keep() { _keep = KEEP; }
 
 		Link_map const &link_map() const override { return _map; }
@@ -731,6 +736,9 @@ void *Dynamic_linker::_respawn(Env &env, char const *binary, char const *entry_n
 	/* load new binary */
 	construct_at<Binary>(binary_ptr, env, *heap(), config, name.string());
 
+	/* move to front of link map */
+	binary_ptr->link_map_make_first();
+
 	try {
 		return (void *)binary_ptr->lookup_symbol(entry_name);
 	}