udf

Undefined Instruction

UDF #<imm>

Permanently undefined instruction (generates Undefined Instruction exception).

Pseudocode Operation

UndefinedInstructionException(imm12 ∘ imm4)

Example

UDF #16

Encoding

Binary Layout

1110

31:28

01111111

27:20

imm12

19:8

1111

7:4

imm4

3:0

Format System

Opcode 0xE7F000F0

Extension A32 (Base)

Operands

imm
ID

Other forms of udf

udf Undefined Instruction (Thumb)

Reference

View in Arm A64 ISA Reference ↗ Arm AArch32 ISA

Instruction Forms

Encoding	Instruction	ISA	Bit pattern
0xE7F000F0	UDF{<c>}{<q>} {#}<imm>	A32	1110 \| 01111111 \| imm12 \| 1111 \| imm4
0xDE00	UDF{<c>}{<q>} {#}<imm>	T32	1101111 \| 0 \| imm8
0xF7F0A000	UDF{<c>}.W {#}<imm>	T32	11110111111 \| 1 \| imm4 \| 10 \| 1 \| 0 \| imm12

Description

Permanently Undefined generates an Undefined Instruction exception. The encodings for UDF used in this section are defined as permanently undefined. However:

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    UNDEFINED;

udf