applet: rework APK_DEFINE_APPLET to use constructor attribute

this allows the applet registration to work in a portable way, without having to
weird things with the linker.

ref #10794

src/apk.c

@@ -409,7 +409,6 @@ int main(int argc, char **argv)
 #ifdef TEST_MODE
 	apk_string_array_init(&test_repos);
 #endif
-	apk_applet_register_builtin();
 
 	apk_argv = malloc(sizeof(char*[argc+2]));
 	memcpy(apk_argv, argv, sizeof(char*[argc]));

src/apk_applet.h

@@ -56,14 +56,10 @@ struct apk_applet {
 extern const struct apk_option_group optgroup_global, optgroup_commit, optgroup_signing;
 
 void apk_applet_register(struct apk_applet *);
-void apk_applet_register_builtin(void);
 struct apk_applet *apk_applet_find(const char *name);
 void apk_applet_help(struct apk_applet *applet, struct apk_out *out);
-typedef void (*apk_init_func_t)(void);
-
 
 #define APK_DEFINE_APPLET(x) \
-static void __register_##x(void) { apk_applet_register(&x); } \
-static apk_init_func_t __regfunc_##x __attribute__((__section__("initapplets"))) __attribute((used)) = __register_##x;
+__attribute__((constructor)) static void __register_##x(void) { apk_applet_register(&x); }
 
 #endif

src/apk_defines.h

@@ -223,6 +223,7 @@ APK_ARRAY(apk_string_array, char *);
 #define foreach_array_item(iter, array) \
 	for (iter = &(array)->item[0]; iter < &(array)->item[(array)->num]; iter++)
 
+#define LIST_HEAD(name) struct list_head name = { &name, &name }
 #define LIST_END (void *) 0xe01
 #define LIST_POISON1 (void *) 0xdeadbeef
 #define LIST_POISON2 (void *) 0xabbaabba

src/applet.c

@@ -10,7 +10,7 @@
 #include "apk_applet.h"
 #include "apk_print.h"
 
-static struct list_head apk_applet_list;
+static LIST_HEAD(apk_applet_list);
 
 #define apk_applet_foreach(iter) list_for_each_entry(iter, &apk_applet_list, node)
 
@@ -20,16 +20,6 @@ void apk_applet_register(struct apk_applet *applet)
 	list_add_tail(&applet->node, &apk_applet_list);
 }
 
-void apk_applet_register_builtin(void)
-{
-	extern apk_init_func_t __start_initapplets[], __stop_initapplets[];
-	apk_init_func_t *p;
-
-	list_init(&apk_applet_list);
-	for (p = __start_initapplets; p < __stop_initapplets; p++)
-		(*p)();
-}
-
 struct apk_applet *apk_applet_find(const char *name)
 {
 	struct apk_applet *a;