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UDF

Permanently Undefined.

Syntax

UDF{c}{q} {#}imm ; A1 general registers (A32)

UDF{c}{q} {#}imm ; T1 general registers (T32)

UDF{c}.W {#}imm ; T2 general registers (T32)

Where:

imm

Depends on the instruction variant:

general registers
Is a 16-bit unsigned immediate, in the range 0 to 65535. The PE ignores the value of this constant.
T1 general registers
Is a 8-bit unsigned immediate, in the range 0 to 255. The PE ignores the value of this constant.
T2 general registers
Is a 16-bit unsigned immediate, in the range 0 to 65535. The PE ignores the value of this constant.
c
For T32, see Standard assembler syntax fields in the ARMv8-A Architecture Reference Manual. ARM deprecates using any c value other than AL.
q
See Standard assembler syntax fields in the ARMv8-A Architecture Reference Manual.

Usage

Permanently Undefined generates an Undefined Instruction exception.

The encodings for UDF used in this section are defined as permanently undefined in the ARMv8-A architecture. However:

  • With the T32 instruction set, ARM deprecates using the UDF instruction in an IT block.
  • In the A32 instruction set, UDF is not conditional.