"udf 0xfe" disassembled incorrectly for ARM Thumb

[lwerdna]

0xDEFE should be udf #0xfe since document DDI0406C.a which declares that it's the first to define an assembler mnemonic for this encoding. Capstone currently emits trap.

Minimal code to reproduce:

#!/usr/bin/env python
from capstone import *
md = Cs(CS_ARCH_ARM, CS_MODE_BIG_ENDIAN|CS_MODE_THUMB)
for i in md.disasm("\xDE\xFE", 0):
	print("0x%x:\t%s\t%s" %(i.address, i.mnemonic, i.op_str))

Bit fields are:

+----+----+--------+
|1101|1110|  imm8.8|
+----+----+--------+
|1101|1110|11111110|
+----+----+--------+

Online disassembler supports this claim.

[Rot127]

llvm-objdump gives:

000003fc <_start>:
     3fc: defe         	trap

Which matches Capstone:

./cstool -d thumb 0xFEDE
 0  fe de  trap	
	ID: 460 (teq)
	Groups: IsThumb