STAPEX(3stap)

NAME
stapex - systemtap examples

LANGUAGE BASICS
These examples give a feel for basic systemtap syntax and control structures.

    global odds, evens

    probe begin {
      # "no" and "ne" are local integers
      for (i=0; i<10; i++) {
        if (i % 2) odds [no++] = i
        else evens [ne++] = i
      }
      delete odds[2]
      delete evens[3]
      exit ()
    }

    probe end {
      foreach (x+ in odds) {
        printf ("odds[%d] = %d, x, odds[x])
      }
      foreach (x in evens-) {
        printf ("evens[%d] = %d, x, evens[x])
      }
    }
This prints:
    odds[1] = 1
    odds[3] = 5
    odds[4] = 7
    odds[5] = 9
    evens[5] = 8
    evens[4] = 6
    evens[2] = 2
    evens[1] = 0
Note that all variables types are inferred, and that all locals and globals are automatically initialized.

This script prints the primes between 0 and 49.
    function isprime (x) {
      if (x < 2) return 0
      for (i=2; i<x; i++) {
        if (x % i == 0) return 0
        if (i * i > x) break
      }
      return 1
    }
    probe begin {
      for (i=0; i<50; i++)
        if (isprime (i)) printf("%d, i)
      exit()
    }

This script demonstrates recursive functions.
    function fibonacci(i) {
      if (i < 1) error ("bad number")
      if (i == 1) return 1
      if (i == 2) return 2
      return fibonacci (i-1) + fibonacci (i-2)
    }
    probe begin {
      printf ("11th fibonacci number: %d, fibonacci (11))
      exit ()
    }
Any larger number may exceed the MAXACTION or MAXNESTING limits, and result in an error.

PROBING

To trace entry and exit from a function, use a pair of probes:
    probe kernel.function("sys_mkdir") { println ("enter") }
    probe kernel.function("sys_mkdir").return { println ("exit") }

To list the probeable functions in the kernel, use the listings mode.
    % stap -l 'kernel.function("*")'

To list the probeable functions and local variables in the kernel, use another listings mode.
    % stap -L 'kernel.function("*")'

MORE EXAMPLES

The directory to find more examples can be found in the stappaths (7) manual page, and online at http://sourceware.org/systemtap/examples/

SEE ALSO
stap(1) stapprobes(3stap) stappaths(7)