dtrace_dtrace4

dtrace:::BEGIN

The dtrace:::BEGIN probe fires at the beginning of a dtrace(1), program before tracing has begun. It provides a convenient place for initializing variables and printing column headers.

Variables such as stack or execname cannot be relied upon in the execution context of the dtrace:::BEGIN probe.

dtrace:::END

The dtrace:::END probe fires at the end of a dtrace(1) program, when all tracing has stopped.

dtrace:::ERROR

The dtrace:::ERROR probe fires when an unexpected runtime error occurs in another probe.

The following table describes the arguments to dtrace:::ERROR.

The fault types are:

DTRACEFLT_UNKNOWN

Unknown fault

DTRACEFLT_BADADDR

Bad address

DTRACEFLT_BADALIGN

Bad alignment

DTRACEFLT_ILLOP

Illegal operation

DTRACEFLT_DIVZERO

Divide-by-zero

DTRACEFLT_NOSCRATCH

Out of scratch space

DTRACEFLT_KPRIV

Illegal kernel access

DTRACEFLT_UPRIV

Illegal user access

DTRACEFLT_TUPOFLOW

Tuple stack overflow

DTRACEFLT_BADSTACK

Bad stack

Example 1 : Custom Column Headers

The following script uses the dtrace:::BEGIN probe to print column headers. Note the pragma line setting the ‘quiet’ option to disable the default column headers.

#pragma D option quiet
dtrace:::BEGIN
{
    printf("   %12s %-20s    %-20s %s\n",
        "DELTA(us)", "OLD", "NEW", "TIMESTAMP");
}

Example 2 : Handling Runtime Errors with dtrace:::ERROR

The following script causes a runtime error by dereferencing a pointer on address 19930908 in the BEGIN probe. As a result, the ERROR probe fires and prints out “Oops” along with the probe arguments. At that point, the program ends and fires the END probe.

ERROR
{
    printf("Oops\n");
    printf("EPID (arg1): %d\n", arg1);
    printf("Action index (arg2): %d\n", arg2);
    printf("DIF offset (arg3): %d\n", arg3);
    printf("Fault type (arg4): %d\n", arg4);
    printf("Accessed address (arg5): %X\n", arg5);
    exit(1);
}
BEGIN
{
    *(int *)0x19931101;
}
END {
    printf("Bye");
}

This script will result in the following output:

CPU     ID                    FUNCTION:NAME
  2      3                           :ERROR Oops
EPID (arg1): 2
Action index (arg2): 1
DIF offset (arg3): 16
Fault type: 1
arg5: 19931101
dtrace: error on enabled probe ID 2 (ID 1: dtrace:::BEGIN): invalid address (0x19931101) in action #1 at DIF offset 16
  2      2                             :END Bye