one question about l4_thread_ex_regs flags

[Adam Lackorzynski]

Hi,

On Sun Aug 23, 2009 at 01:24:24 +0800, Guanghui, Cheng wrote:
> 	About the l4_thread_ex_regs system call there are 2 flags related with 
> exception ipc.  I only know the thread with these flags could generate the 
> exception ipc but i don't know what is the difference between these flags: 
> L4_THREAD_EX_REGS_RAISE_EXCEPTION , L4_THREAD_EX_REGS_ALIEN and 
> L4_THREAD_EX_REGS_ALIEN | L4_THREAD_EX_REGS_ALIEN.
> 
> 	So, i write a following program to test the behaviour with different flags :
> 
> void idle(void *data)
> {
> 	l4_sleep(1000);
> 	l4_sleep(1000);
> 	l4_sleep(1000);
> 	l4_sleep(1000);
> 	l4_sleep(1000);
> }
> int main()
> {
> 	...
> 	l4_threadid_t me = l4_myself();
> 	l4thread_create(idle, NULL, L4THREAD_CREATE_ASYNC);
> 	...
> 	l4_thread_ex_regs_flags(idle_thread,  ~0UL, ~0UL,
> 		&_preempter, &me,
>  		&o, &o, &o,
> 		L4_THREAD_EX_REGS_RAISE_EXCEPTION
> 		| L4_THREAD_EX_REGS_ALIEN);
> 	while(1)
> 	{
> 		l4_ipc_wait(&src, ...);
> 		printf("thread :%d:%d\n", src.id.task, src.id.lthread);
> 	}
> }
> 
> 	I tried 3 combination about these 2 flags but the output is the same as this:
> 
> exceptio| thread :8:3
> 
> 	i don't know why there is only one exception ipc. But the idle function 
> includes 5 system calls.  Additionally, it seems the ALIEN state is 
> TEMPORARILY. I set once there is one exception ipc, twice two exception ipc. 
> Can you explain me?

The output will always come from the same thread so the output should
always be the same?!
L4_THREAD_EX_REGS_RAISE_EXCEPTION is in effect once,
L4_THREAD_EX_REGS_ALIEN is a permanent state of the thread. If you do
not set it in a following exregs call it's cleared again. If you do a
trigger-exception, you get an exception IPC, if you do it again, you get
the next. But exception IPC is also about sending a reply, so you need
to reply to the receiving IPC to allow the thread to continue.



Adam
-- 
Adam                 adam at os.inf.tu-dresden.de
  Lackorzynski         http://os.inf.tu-dresden.de/~adam/