How to use the stap -L option?

Question

I am following the SystemTap tutorial and I am trying to do exercise 1 from section 2.3 - "Tracing. Exercises". The -L option seems to never work. I got this script:

probe kernel.function("*nit*"){}

I type in a terminal:

$ stap -L PROBE t.stp

and nothing happens.

Answer 1

$ stap -L 'kernel.function("blahblah")'

Systemtap is great, but poor documentation.

Answer 2

From man stap (with systemtap*-1.7-2.fc15.x86_64 RPMs installed)

   stap [ OPTIONS ] -l PROBE [ ARGUMENTS ]
   stap [ OPTIONS ] -L PROBE [ ARGUMENTS ]

   -l PROBE
          Instead of running a probe script, just list all available probe
          points  matching  the given single probe point.  The pattern may
          include wildcards and aliases, but not comma-separated  multiple
          probe  points.  The process result code will indicate failure if
          there are no matches.

   -L PROBE
          Similar to "-l", but list probe points  and  script-level  local
          variables.

"probe points" refer to 'kernel.function("blahblah")', etc. There is no keyword "probe" before and no probe handler afterwards.

Answer 3

You can try the following examples.

To get a list of all Kernel functions.

$ stap -l 'kernel.function("*")' | sort

kernel.function("vfs_read@/build/linux-lts-xenial-Hu9lgy/linux-lts-xenial-4.4.0/fs/read_write.c:440") [....]

To get a Kernel function & arguments (local variables)

$ stap -L 'kernel.function("*")' | grep vfs_read

kernel.function("vfs_read@/build/linux-lts-xenial-Hu9lgy/linux-lts-xenial-4.4.0/fs/read_write.c:440") $file:struct file* $buf:char* $count:size_t $pos:loff_t*

[....]

Answer 4

stap -L kernel.function("*nit*") | sort

Answer 5

Just to add on to what more learned people than me have said:

stap -L 'module("module-name-here").function("*")'

For regular kernel probes:

stap -L 'kernel.function("*")'

Hope this helps someone else in the future!