udf

Undefined Instruction (Thumb)

UDF #<imm>

Permanently undefined instruction (Thumb).

Details

Undefined Instruction (Thumb encoding). This T32 instruction is permanently undefined and raises an Undefined Instruction exception when executed. The 8-bit immediate value is available to the exception handler. No condition flags are affected.

Pseudocode Operation

UndefinedInstructionException(imm8)

Example

UDF #16

Encoding

Binary Layout
1101111
0
imm8
 
Format Thumb System
Opcode 0xDE00
Extension T32 (Thumb)

Operands

  • imm
    ID

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;