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
`r2`	449, the syscall number
`r4`	struct futex_waitv *waiters
`r5`	unsigned int nr_futexes
`r6`	unsigned int flags
`r7`	struct __kernel_timespec *timeout
`r8`	clockid_t clockid
`r2`	the return value

Then run trap to enter the kernel.

Same syscall on other architectures