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
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/doc/systemtap*/examples stap(1) stapprobes(3stap) stapfuncs(3stap)