rt_sigtimedwait

synchronously wait for queued signals

sys_rt_sigtimedwait(const sigset_t *uthese, siginfo_t *uinfo, const struct __kernel_timespec *uts, size_t sigsetsize)

register	value
`r1`	177, the syscall number
`r2`	const sigset_t *uthese
`r3`	siginfo_t *uinfo
`r4`	const struct __kernel_timespec *uts
`r5`	size_t sigsetsize
`r2`	the return value

Then run svc 0 to enter the kernel.

Same syscall on other architectures