watch a var in linux kernel

varwatch2.stp

#! /usr/bin/env stap

probe kernel.statement("do_generic_file_read@mm/filemap.c:1772") {
   printf("%s[%d] %s %ld:\n", execname(), tid(), pp(), $index);
}

probe kernel.function("submit_bio@block/blk-core.c") {
    printf("%s[%d] %s i_sector:%lu, size:%u\n", execname(), tid(), pp(), $bio->bi_sector, $bio->bi_size);
}


>> stap -L 'kernel.function("finish_task_switch")'
<< kernel.function("finish_task_switch@kernel/sched/core.c:2376") $rq:struct rq* $prev:struct task_struct*