[genode] Label in l4_ipc_wait

Hello Genode, I have a question regarding Genode Label in Fiasco.OC kernel.

I noticed that Msgbuf_base::label() is the same as the return value of l4_ipc_wait (which is basically genode label):

L4_INLINE l4_msgtag_t l4_ipc_wait(l4_utcb_t *utcb, l4_umword_t *label, l4_timeout_t timeout) L4_NOTHROW;

label is described as following:

* \retval label Label assigned to the source object (IPC gate or IRQ).

But, I can not see any corresponding label in ipc call as we can see below:

L4_INLINE l4_msgtag_t l4_ipc_call(l4_cap_idx_t object, l4_utcb_t *utcb, l4_msgtag_t tag, l4_timeout_t timeout) L4_NOTHROW;

So, here goes the question: Since genode label is passed to the first data of Msgbuf_base::buf, does Fiasco.OC pickup this value and return when l4_ipc_wait function called?

Best regards, Jaeyong