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Solaris Dynamic Tracing Guide

ERROR Probe

The ERROR probe fires when a run-time error occurs in executing a clause for a DTrace probe. For example, if a clause attempts to dereference a NULL pointer, the ERROR probe will fire, as shown in the following example.

Example 17–1 error.d: Record Errors

BEGIN
{
	*(char *)NULL;
}

ERROR
{
	printf("Hit an error!");
}

When you run this program, you will see output like the following example:


# dtrace -s ./error.d
dtrace: script './error.d' matched 2 probes
CPU     ID                    FUNCTION:NAME
  2      3                           :ERROR Hit an error!
dtrace: error on enabled probe ID 1 (ID 1: dtrace:::BEGIN): invalid address
(0x0) in action #1 at DIF offset 12
dtrace: 1 error on CPU 2

The output shows that the ERROR probe fired, and also illustrates dtrace(1M) reporting the error. dtrace has its own enabling of the ERROR probe to allow it to report errors. Using the ERROR probe, you can create your own custom error handling.

The arguments to the ERROR probe are as follows:

arg1

The enabled probe identifier (EPID) of the probe that caused the error

arg2

The index of the action that caused the fault 

arg3

The DIF offset into that action or -1 if not applicable

arg4

The fault type 

arg5

Value particular to the fault type 

The table below describes the various fault types and the value that arg5 will have for each:

arg4 Value

Description 

arg5 Meaning

DTRACEFLT_UNKNOWN

Unknown fault type 

None 

DTRACEFLT_BADADDR

Access to unmapped or invalid address 

Address accessed 

DTRACEFLT_BADALIGN

Unaligned memory access 

Address accessed 

DTRACEFLT_ILLOP

Illegal or invalid operation 

None 

DTRACEFLT_DIVZERO

Integer divide by zero 

None 

DTRACEFLT_NOSCRATCH

Insufficient scratch space to satisfy scratch allocation 

None 

DTRACEFLT_KPRIV

Attempt to access a kernel address or property without sufficient privileges 

Address accessed or 0 if not applicable

DTRACEFLT_UPRIV

Attempt to access a user address or property without sufficient privileges 

Address accessed or 0 if not applicable

DTRACEFLT_TUPOFLOW

DTrace internal parameter stack overflow 

None 

If the actions taken in the ERROR probe itself cause an error, that error is silently dropped — the ERROR probe will not be recursively invoked.