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Common Syntax Errors A-13
Common Syntax
Errors
When a packet filter definition is loaded, the definition is checked for syntax
errors. The syntax errors and their causes are listed in Table A-1.
Table A-1 Possible Syntax Errors When Loading Packet Filters
Syntax Error Description
Opcode not found
An opcode was expected on the line and was not found.
The opcode must be one of those described in “Opcodes” on
page A-1 and must include the size, if any. The opcode and
size must be separated by a single “.” with no intervening
spaces. Any mix of uppercase and lowercase characters is
permitted.
Unknown opcode
An opcode was expected on the line and was not found.
The opcode must be one of those described in “Opcodes” on
page A-1 and must include the size, if any. The opcode and
size must be separated by a single “.” with no intervening
spaces. Any mix of upper and lower case characters is
permitted.
Operands are not
the same size
The opcode requires two operands of the same size. The top
two operands currently on the stack are of different sizes.
Stack underflow
The opcode requires one or more operands. An insufficient
number of operands are currently on the stack.
Stack overflow
The opcode pushes an operand on the stack. The stack does
not have sufficient room for the operand.
No result found
on top of stack
The program must end with a byte operand on the top of
the stack. After the last instruction in the program is
executed, the stack is either empty or contains an operand
other than a byte.
Extra characters
on line
The source line contains extraneous characters that are not
part of the instruction and are not preceded by a comment
character (#).
Expected a byte
operand
The opcode requires a byte operand as one of its parameters.
The operand is of a size other than a byte.
Offset not found
The opcode requires an offset to be specified. None was
found on the line.
Literal not found
The opcode requires a literal value to be specified. None was
found on the line.
String not found
The opcode requires a quoted string to be specified. None
was found on the line.
(continued)