IDIV can accept 1, 2, or 3 operands. Specifying the data size of a variable in NASM is only necessary when the variable is a source operand. A value stored in the ebx register can be sign extended into edx: ebx with the CDQ instruction. The ALIGNB directive can only be used in the.bss section of NASM code. When using an extension instruction in GAS, you must append two characters to indicate the sizes of the source and destination operands