# stapex

Langue: en

Autres versions - même langue

Version: 2007-03-26 (fedora - 16/08/07)

Section: 5 (Format de fichier)

# Sommaire

## 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") { log ("enter") }
probe kernel.function("sys_mkdir").return { log ("exit") }
```

To list the probeable functions in the kernel, use the last-pass option to the translator. That output needs to be filtered because each inlined function instance is listed separately.

```% stap -p2 -e [aq]probe kernel.function("*") {}[aq] | sort | uniq
```