Invalid combination of opcode and operands? (x86 D

问题:

This question already has answers here:

Why cannot do mov [eax], [ebx] [duplicate] (3 answers)

Closed last year.

org 100h

mov ah, 9
mov dx, str1
mov byte [str1+2], [char]
int 21h

mov ah, 4Ch
int 21h

str1 db 'String$'
char db "o"

Why does NASM give me this error message:

Error on line 5: Invalid combination of opcode and operands

mov byte [str1+2], [char] 

in this line I'm trying to move the byte stored on *char to the address *str1+2.

回答1:

Intel architecture processors generally can't transfer data from memory to memory in one instruction. You need to write something like:

mov byte al, [char]
mov byte [str1+2], al