3 ms·

Tried it out now with different instructions. There's a pattern, though it's not quite a steganographic message, just a different encoding chosen depending on t

Tried it out now with different instructions. There's a pattern, though it's not quite a steganographic message, just a different encoding chosen depending on the second register operand. 02 C0 ADD AL,AL 02 C1 ADD AL,CL 00 D0 ADD AL,DL 00 D8 ADD AL,BL 02 C4 ADD AL,AH 02 C5 ADD AL,CH 00 F0 ADD AL,DH 00 F8 ADD AL,BH Don't know if this would hold up in court for proving that some code was assembled with A86... edit: other ALU ops are the same; for MOV the "direction bit" is inverted.

a1369209993 4y ago
That's not a a86 thing; it's to avoid generating a modrm byte that can be decoded as a return instruction[0] for ROP gadgets. $ zasm -Mx86 -='add al al;add al dl;add dl al' 000000 - 02 C0 00 D0 02 D0 |...... | $ hex C3 | ndisasm -au - 00000000 C3 ret 0: C2, C3, CA, or CB, so modrm (ax/cx) (dx/bx)
- rep_lodsb 4y ago
  ROP wasn't a concept back then. From the manual of the latest version of A86: A86 assembler package V4.05 January 14, 2000 The entire package is Copyright 2000 Eric Isaacson. All rights reserved.