gistfile1.txt

diff --git a/core/msg.c b/core/msg.c
index a46875f16e..1c9886d718 100644
--- a/core/msg.c
+++ b/core/msg.c
@@ -33,7 +33,7 @@
 #include "irq.h"
 #include "cib.h"
 
-#define ENABLE_DEBUG    (0)
+#define ENABLE_DEBUG    (1)
 #include "debug.h"
 
 static int _msg_receive(msg_t *m, int block);
@@ -162,6 +162,7 @@ static int _msg_send(msg_t *m, kernel_pid_t target_pid, bool block, unsigned sta
         /* copy msg to target */
         msg_t *target_message = (msg_t*) target->wait_data;
         *target_message = *m;
+
         sched_set_status(target, STATUS_PENDING);
 
         irq_restore(state);
@@ -212,7 +213,7 @@ int msg_send_int(msg_t *m, kernel_pid_t target_pid)
         return 1;
     }
     else {
-        DEBUG("msg_send_int: Receiver not waiting.\n");
+        DEBUG("msg_send_int: Receiver pid=%" PRIkernel_pid " not waiting.\n", target_pid);
         return (queue_msg(target, m));
     }
 }
@@ -289,6 +290,8 @@ int msg_receive(msg_t *m)
 static int _msg_receive(msg_t *m, int block)
 {
     unsigned state = irq_disable();
+    volatile msg_t *_m = (volatile msg_t *)m;
+    _m->content.value = 0x87654321;
     DEBUG("_msg_receive: %" PRIkernel_pid ": _msg_receive.\n",
           sched_active_thread->pid);
 
@@ -329,13 +332,17 @@ static int _msg_receive(msg_t *m, int block)
             irq_restore(state);
             thread_yield_higher();
 
+            if (_m->content.value == 0x87654321) {
+                DEBUG("_msg_receive(): %" PRIkernel_pid ": BUG\n", sched_active_thread->pid);
+                assert(false);
+            }
             /* sender copied message */
+            return 1;
         }
         else {
             irq_restore(state);
+            return 2;
         }
-
-        return 1;
     }
     else {
         DEBUG("_msg_receive: %" PRIkernel_pid ": _msg_receive(): Waking up waiting thread.\n",
@@ -366,7 +373,7 @@ static int _msg_receive(msg_t *m, int block)
         if (sender_prio < THREAD_PRIORITY_IDLE) {
             sched_switch(sender_prio);
         }
-        return 1;
+        return 3;
     }
 
     DEBUG("This should have never been reached!\n");
diff --git a/sys/net/gnrc/network_layer/ipv6/gnrc_ipv6.c b/sys/net/gnrc/network_layer/ipv6/gnrc_ipv6.c
index feb2e8f10f..a62887c250 100644
--- a/sys/net/gnrc/network_layer/ipv6/gnrc_ipv6.c
+++ b/sys/net/gnrc/network_layer/ipv6/gnrc_ipv6.c
@@ -180,7 +180,8 @@ static void *_event_loop(void *args)
     /* start event loop */
     while (1) {
         DEBUG("ipv6: waiting for incoming message.\n");
-        msg_receive(&msg);
+        memset(&msg, 0, sizeof(msg));
+        int res = msg_receive(&msg);
 
         switch (msg.type) {
             case GNRC_NETAPI_MSG_TYPE_RCV:
@@ -220,6 +221,7 @@ static void *_event_loop(void *args)
                 gnrc_ipv6_nib_handle_timer_event(msg.content.ptr, msg.type);
                 break;
             default:
+                printf("ipv6: unknown message type 0x%04x, res=%i\n", msg.type, res);
                 break;
         }
     }