Division in x86-64 assembly [duplicate]

Question

I am traying to make a simple division in x86-64 and when I give input like 4 and 2 the result should look like 4 / 2 = 2 but I am getting 4 / 0 = 0 any ideas ?

4 / 2 = 2 instead I got 4 / 0 = 0

 sub $8, %rsp

        mov $input_format, %rdi
        mov $a, %rax
        mov $b, %rsi
        mov $0, %al
        call scanf

        xor %rdx, %rdx
        mov a, %rax
        mov b, %rsi
        idiv %rsi

        mov $output_format, %rdi
        mov $0, %al
        call printf

        add $8, %rsp