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
`v0`	355, the syscall number
`a0`	const sigset_t *uthese
`a1`	siginfo_t *uinfo
`a2`	const struct __kernel_timespec *uts
`a3`	size_t sigsetsize
`v0`	the return value

Then run callsys to enter the kernel.

Same syscall on other architectures