futex_waitv

wait for FUTEX_WAKE operation on a vector of futexes

sys_futex_waitv(struct futex_waitv *waiters, unsigned int nr_futexes, unsigned int flags, struct __kernel_timespec *timeout, clockid_t clockid)

register	value
`a7`	449, the syscall number
`a0`	struct futex_waitv *waiters
`a1`	unsigned int nr_futexes
`a2`	unsigned int flags
`a3`	struct __kernel_timespec *timeout
`a4`	clockid_t clockid
`a0`	the return value

Then run ecall to enter the kernel.

Same syscall on other architectures