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

delete evens

exit ()
}
probe end {

foreach (x+ in odds) {

printf ("odds[%d] = %d\n", x, odds[x])

}

foreach (x in evens-) {

printf ("evens[%d] = %d\n", x, evens[x])

}
}```

This prints:

```odds = 1
odds = 5
odds = 7
odds = 9
evens = 8
evens = 6
evens = 2
evens = 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\n", 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\n", 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, and online at http://sourceware.org/systemtap/examples/

```stap(1)