Utcb in syscall

hi ,in sys_ipc_wrapper, the code first get the current thread's syscall entry frame: .... Thread *curr=current_thread(); Syscall_frame *f = curr-regs(); ... according to the Syscall_frame's implemention, it can get the Utcb by Syscall_frame::utcb(). but the following code get the Utcb in another way: Utcb *utcb = curr->utcb().access(true); what's the difference between those two Utcb?