Question

I’m fed up with this. I’ve been trying to just get a grip on assembly for awhile, but I feel like I’m coding towards my compiler rather than a language.

I’ve been using this tutorial, and so far it’s giving me hell. I’m using NASM, which may be the problem, but I figured it was the most popular one. I’m simply trying to learn the most general form of assembly, so I decided to learn x86. I keep running into stupid errors, like not being able to increment a variable. Here’s the latest one: not being able to use div.

mov bx, 0;
mov cx, 0;
jmp start;
 start:
 inc cx;
 mov ax, cx;
 div 3; <-- invalid combination of opcode and operand
 cmp ah,0;
 jz totalvalue;
 mov ax, cx;
 div 5; <-- invalid combination of opcode and operand
 cmp ah, 0;
 jz totalvalue;
 cmp cx, 1000;
 jz end;

 totalvalue:
 add bx,cx;
 jmp start;

jmp end;
 end:
   mov ah,4ch;
   mov al,00;
   int 21h;

Should I change compilers? It seems like division should be standard. Do I need to read two tutorials (one on NASM, and one on x86?). Any specific help on this problem?

Answer 1

One of the things about assembly, like any other language, is that it is, in part, defined by the assembler. That “div 5” seems awfully strange to me – but I learned assembly using MASM, which has a different syntax. Based on the comments in the tutorial, it looks like the assembler used for that tutorial has some “implied” operands for the instruction, whereas NASM does not, and expects the Intel syntax for the div instruction.

IMHO, you’ll be best served by using NASM, but getting a tutorial that’s either NASM-specific, or geared to the ‘pure’ Intel syntax. The Art of Assembly book is a good resource for the Intel syntax.

(edit: if the link above fails, try this, which is where the link above forwards)