Attempting to decode: f3 aa 
iclass REP_STOSB	category STRINGOP	ISA-extension BASE	ISA-set I86
instruction-length 2
operand-width 8
effective-operand-width 32
effective-address-width 32
stack-address-width 32
iform-enum-name REP_STOSB
iform-enum-name-dispatch (zero based) 0
iclass-max-iform-dispatch 1
Nominal opcode position 1
Nominal opcode 0xaa
Operands
#   TYPE               DETAILS        VIS  RW       OC2 BITS BYTES NELEM ELEMSZ   ELEMTYPE   REGCLASS
#   ====               =======        ===  ==       === ==== ===== ===== ======   ========   ========
0   MEM0           (see below) SUPPRESSED  CW         B    8     1     1      8       UINT    INVALID
1  BASE0             BASE0=EDI SUPPRESSED RCW       ASZ   32     4     1     32        INT        GPR
2   REG0               REG0=AL SUPPRESSED   R         B    8     1     1      8        INT        GPR
3   REG1              REG1=ECX SUPPRESSED RCW       ASZ   32     4     1     32        INT        GPR
4   REG2           REG2=EFLAGS SUPPRESSED   R         Y   32     4     1     32        INT      FLAGS
Memory Operands
  0 written SEG= ES BASE= EDI/GPR  ASZ0=32
  MemopBytes = 1
FLAGS:
   reads-rflags df-tst 
       read:                            df  mask=0x400
    written:                                mask=0x0
  undefined:                                mask=0x0
ATTRIBUTES: BYTEOP FIXED_BASE0 REP 
REAL REP 	corresponding no-rep iclass: STOSB
F3 PREFIX
Number of legacy prefixes: 1 
ISA SET: [I86]