diff --git a/lib/aos/coreboot.c b/lib/aos/coreboot.c
index f493232..adbfd2d 100644
--- a/lib/aos/coreboot.c
+++ b/lib/aos/coreboot.c
@@ -290,6 +290,7 @@ errval_t coreboot(coreid_t mpid,
     };
 
     struct Elf64_Sym * boot_entry_psci_sym = elf64_find_symbol_by_name((genvaddr_t) bootdriver_elf_addr, bootdriver_elf_frame_id.bytes, "boot_entry_psci", false, STT_FUNC, 0);
+    assert(boot_entry_psci_sym != NULL);
 
     genvaddr_t reloc_bootdriver_entry;
     err = load_elf_binary((genvaddr_t) bootdriver_elf_addr, &bootdriver_mem_info, boot_entry_psci_sym->st_value, &reloc_bootdriver_entry);
@@ -304,6 +305,7 @@ errval_t coreboot(coreid_t mpid,
     };
 
     struct Elf64_Sym * arch_init_sym = elf64_find_symbol_by_name((genvaddr_t) cpudriver_elf_addr, cpudriver_elf_frame_id.bytes, "arch_init", false, STT_FUNC, 0);
+    assert(arch_init_sym != NULL);
 
     genvaddr_t reloc_cpudriver_entry;
     err = load_elf_binary((genvaddr_t) cpudriver_elf_addr, &cpudriver_mem_info, arch_init_sym->st_value, &reloc_cpudriver_entry);
diff --git a/lib/aos/paging.c b/lib/aos/paging.c
index 316e62e..ebc0ac7 100644
--- a/lib/aos/paging.c
+++ b/lib/aos/paging.c
@@ -287,6 +287,7 @@ static errval_t pt_ensure_slabs(struct paging_state *st) {
         // debug_printf("DEBUG rueegges: pt_ensure_slabs - refilling pt_slab DONE\n");
 
         if(err_is_fail(err)) {
+            DEBUG_PRINTF("pt_slabs refill failed\n");
             return err_push(err, LIB_ERR_SLAB_REFILL);
         }
     }
@@ -303,6 +304,7 @@ static errval_t pt_ensure_slabs(struct paging_state *st) {
         // debug_printf("DEBUG rueegges: pt_ensure_slabs - refilling pt_children_slabs DONE\n");
 
         if(err_is_fail(err)) {
+            DEBUG_PRINTF("pt_children_slabs refill failed\n");
             return err_push(err, LIB_ERR_SLAB_REFILL);
         }
     }
diff --git a/usr/init/main.c b/usr/init/main.c
index 8903453..d84bb8b 100644
--- a/usr/init/main.c
+++ b/usr/init/main.c
@@ -69,6 +69,7 @@ bsp_main(int argc, char *argv[]) {
     struct frame_identity urpc_frame_id;
     err = frame_identify(urpc_frame, &urpc_frame_id);
     if(err_is_fail(err)) return err_push(err, LIB_ERR_CAP_IDENTIFY);
+
     // boot second core
     char *cpu_driver_name;
     switch (platform_info.platform) {
@@ -108,12 +109,43 @@ bsp_main(int argc, char *argv[]) {
 
 static int
 app_main(int argc, char *argv[]) {
+    errval_t err;
+
+    debug_printf("[app_main]\n");
+
     // Implement me in Milestone 5
     // Remember to call
     // - grading_setup_app_init(..);
     // - grading_test_early();
     // - grading_test_late();
-    return LIB_ERR_NOT_IMPLEMENTED;
+
+    // TODO: get the bootinfo
+    bi = NULL;
+
+    // Grading
+    grading_setup_app_init(bi);
+
+    // TODO: initialize mem allocator, vspace management here
+
+    // Grading
+    grading_test_early();
+
+    // TODO: Spawn system processes etc. here
+    // Grading
+    grading_test_late();
+
+    debug_printf("Message handler loop\n");
+    // Hang around
+    struct waitset *default_ws = get_default_waitset();
+    while (true) {
+        err = event_dispatch(default_ws);
+        if (err_is_fail(err)) {
+            DEBUG_ERR(err, "in event_dispatch");
+            abort();
+        }
+    }
+
+    return EXIT_SUCCESS;
 }
 
 int main(int argc, char *argv[])