STAPEX(3stap)                                                                                                                        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] = %d0, x, odds[x])
                }
                foreach (x in evens-) {
                  printf ("evens[%d] = %d0, 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("%d0, 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: %d0, 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.

SEE ALSO

       stap(1) stapprobes(3stap) stapfuncs(3stap) stappaths(7)

                                                                                                                                     STAPEX(3stap)