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])
}
}
odds[1] = 1 odds[3] = 5 odds[4] = 7 odds[5] = 9 evens[5] = 8 evens[4] = 6 evens[2] = 2 evens[1] = 0
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 ()
}
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 [aq]kernel.function("*")[aq]
To list the probeable functions and local variables in the kernel, use another listings mode.
% stap -L [aq]kernel.function("*")[aq]
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.