[exercises lesson06] after switch to user_process , it cannot response svc call

@xdfm1 Hi xdfm1, i haved seed your exercises about lesson06, it's work , you are so clever. but according to your code, i have modified little , after run user_process , it can't response svc ，

(gdb) 
#0  0x0000000000085200 in ?? ()
#1  0x000000000000003c in user_process () at src/user.c:17
#2  0xffff0000000865f8 in ?? ()

can you help me to look it ? the code link is here