ud2
Undefined Instruction
UD2
Generates an invalid opcode exception.
Details
Generates an invalid opcode exception (#UD) unconditionally, causing the processor to raise a fault. This instruction has no operands and performs no other operation. It is commonly used for intentional traps, unreachable code markers, and testing exception handling.
Pseudocode Operation
raise InvalidOpcodeException()Example
UD2
Encoding
Binary Layout
0F
+0
0B
+1
Operands
Reference (Intel® SDM)
Instruction Forms
| Opcode | Instruction | Op/En | 64/32-bit Mode | CPUID | Description |
|---|---|---|---|---|---|
| 0F FF /r | UD01 r32, r/m32 | RM | Valid Valid | Raise invalid opcode exception. | |
| 0F B9 /r | UD1 r32, r/m32 | RM | Valid Valid | Raise invalid opcode exception. | |
| 0F 0B | UD2 | ZO | Valid Valid | Raise invalid opcode exception. | |
| D6 | UDB | Valid N.E. | Z0 | Raise invalid opcode exception. |
Description
Generates an invalid opcode exception. This instruction is provided for software testing to explicitly generate an invalid opcode exception. The opcodes for this instruction are reserved for this purpose.
Other than raising the invalid opcode exception, this instruction has no effect on processor state or memory.
Even though it is the execution of the UD instruction that causes the invalid opcode exception, the instruction pointer saved by delivery of the exception references the UD instruction (and not the following instruction).
This instruction’s operation is the same in non-64-bit modes and 64-bit mode.
Operation
#UD (* Generates invalid opcode exception *);
Flags Affected
None. Exceptions (All Operating Modes) #UD Raises an invalid opcode exception in all operating modes. (UDB does so only in 64-bit mode.) UD—Undefined Instruction Vol. 2B 4-736