I created a program that count a factorial. Everything should be ok, except a multiplication. I have no idea what kind of mistake I made. Below I'll show you a debugger statement:
error: invalid combination of opcode and operands
part of program include multiplication (imul):
_middle:
cmp dil,1 ;; dil is the counter, sil contain the final result
jl _end
imul sil,dil ;; here is the problem
dec dil
jmp _middle
If necessary, I can post the rest of program.
The Intel manual lists the following variants of IMUL:
F6 /5 IMUL r/m8* M Valid Valid AX? AL * r/m byte.
F7 /5 IMUL r/m16 M Valid Valid DX:AX ? AX * r/m word.
F7 /5 IMUL r/m32 M Valid Valid EDX:EAX ? EAX * r/m32.
REX.W + F7 /5 IMUL r/m64 M Valid N.E. RDX:RAX ? RAX * r/m64.
0F AF /r IMUL r16, r/m16 RM Valid Valid word register ? word register * r/m16.
0F AF /r IMUL r32, r/m32 RM Valid Valid doubleword register ? doubleword register *
r/m32.
REX.W + 0F AF /r IMUL r64, r/m64 RM Valid N.E. Quadword register ? Quadword register *
r/m64.
6B /r ib IMUL r16, r/m16, imm8 RMI Valid Valid word register ? r/m16 * sign-extended
immediate byte.
6B /r ib IMUL r32, r/m32, imm8 RMI Valid Valid doubleword register ? r/m32 * signextended
immediate byte.
REX.W + 6B /r ib IMUL r64, r/m64, imm8 RMI Valid N.E. Quadword register ? r/m64 * sign-extended
immediate byte.
69 /r iw IMUL r16, r/m16, imm16 RMI Valid Valid word register ? r/m16 * immediate word.
69 /r id IMUL r32, r/m32, imm32 RMI Valid Valid doubleword register ? r/m32 * immediate
doubleword.
REX.W + 69 /r id IMUL r64, r/m64, imm32 RMI Valid N.E. Quadword reg
You're supplying two 8-bit registers as operands, but as you can see in the above table there's no such variant of IMUL.
You could do something like:
mov al,dil
imul sil
; The result will be in AX
