SystemTap可以为target variable生成一系列可打印的字符串：
$$vars
Expands to a character string that is equivalent to sprintf(“parm1=%x … parmN=%x var1=%x … varN=%x”, parm1, …, parmN, var1, …, varN) for each variable in scope at the probe point. Some values may be printed as “=?” if their run-time location cannot be found.
$$locals
Expands to a subset of $$vars containing only the local variables.
$$parms
Expands to a subset of $$vars containing only the function parameters.
$$return
Is available in return probes only. It expands to a string that is equivalent to sprintf(“return=%x”, $return) if the probed function has a return value, or else an empty string.
参考下面例子：
# stap -e 'probe kernel.function("do_dentry_open") {printf("%s\n", $$vars); exit(); }'
f=0xffff880022ec6080 open=0x0 cred=0xffff880030d483c0 empty_fops={...} inode=? error=?
# stap -e 'probe kernel.function("do_dentry_open") {printf("%s\n", $$parms); exit(); }'
f=0xffff880030d453c0 open=0x0 cred=0xffff880030d483c0
# stap -e 'probe kernel.function("do_dentry_open") {printf("%s\n", $$locals); exit(); }'
empty_fops={...} inode=? error=?
在上述变量后加上$或$$可以打印更详细的结构体信息。参考下例：
# stap -e 'probe kernel.function("do_dentry_open") {printf("%s\n", $$parms$); exit(); }'
f={.f_u={...}, .f_path={...}, .f_inode=0x0, .f_op=0x0, .f_lock={...}, .f_count={...}, .f_flags=32768, .f_mode=0, .f_pos=0, .f_owner={...}, .f_cred=0xffff880030d483c0, .f_ra={...}, .f_version=0, .f_security=0xffff880012982b80, .private_data=0x0, .f_ep_links={...}, .f_tfile_llink={...}, .f_mapping=0x0} open=<function>:0x0 cred={.usage={...}, .uid={...}, .gid={...}, .suid={...}, .sgid={...}, .euid={...}, .egid={...}, .fsuid={...}, .fsgid={...}, .securebits=0, .cap_inheritable={...}, .cap_permitted={...}, .cap
# stap -e 'probe kernel.function("do_dentry_open") {printf("%s\n", $$parms$$); exit(); }'
f={.f_u={.fu_llist={.next=0x0}, .fu_rcuhead={.next=0x0, .func=0x0}}, .f_path={.mnt=0xffff8800337510e0, .dentry=0xffff8800318b82d8}, .f_inode=0x0, .f_op=0x0, .f_lock={<union>={.rlock={.raw_lock={.head_tail=0, <class>={.tickets={.head=0, .tail=0}, .owner=0}}}}}, .f_count={.counter=1}, .f_flags=32768, .f_mode=0, .f_pos=0, .f_owner={.lock={.raw_lock={.lock=1048576, .write=1048576}}, .pid=0x0, .pid_type=0, .uid={.val=0}, .euid={.val=0}, .signum=0}, .f_cred=0xffff880030d89300, .f_ra={.start=0, .size=0, .async_si