systemtap get var of the tracepoing

kernel.trace("sched_switch")

func:
func:perf_trace_sched_stat_template
 get the function in

probe begin {
    printf("Begin")
}

probe kernel.function("tracepoint_probe_register") {
//    printf("pre_comm:%s\n", kernel_string($prev->comm))
    printf("func:%s\n", symname($probe))

}

probe end {
    printf("End")
}

defined in include/trace/trace_events.h