Question

I am currently writing a compiler which produces x86-32 code.

However, I have a problem when trying to implement division.

idivl %ecx, %ebx

This code gives me the following error:

Error: operand type mismatch for `idiv'

Does anyone know why? The above lines are the only time idiv appears in my code.

Answer 1

According to my reference, IDIV divides the 64-bit integer EDX:EAX by the provided register’s value.

idiv — Integer Division

The idiv instruction divides the contents of the 64 bit integer EDX:EAX (constructed by viewing EDX as the most significant four bytes
and EAX as the least significant four bytes) by the specified operand
value. The quotient result of the division is stored into EAX, while
the remainder is placed in EDX.

Syntax

idiv <reg32>
idiv <mem>

Examples

idiv ebx ; divide the contents of EDX:EAX by the contents of EBX. Place the quotient in EAX and the remainder in EDX.
idiv DWORD PTR [var] ; divide the contents of EDX:EAS by the 32-bit value stored at memory location var. Place the quotient in EAX

and the remainder in EDX.

The idivl instruction behaves exactly like idiv, except idivl is a signed division.

See http://www.cs.virginia.edu/~evans/cs216/guides/x86.html

Another great ref: http://ref.x86asm.net/