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stapex

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

Larger examples, demos and samples can be found in /usr/doc/systemtap*/examples, each example comes with either a .txt or .meta file explaining what the example, sample or demo does and how it is ordinarily run.

SEE ALSO

/usr/share/doc/systemtap-doc/examples stap(1) stapprobes(5) stapfuncs(5)