NASM mov从寄存器到内存

Question

I know there are lots of references out there talking about NASM and mov but either I'm missing something fundamental or people need to write better help guides!

SECTION .data
    fmtStart:       db "Enter two numbers in format '# #'", 10, 0
    fmtTest:        db "sum: %d", 10, 0
    input:          db "%d %d", 0
SECTION .bss                ; BSS, uninitialized variables
    int1:       resd 1
    int2:       resd 1
    sum:        resd 1
SECTION .text               ; Code section.
    global main             ; the standard gcc entry point
    main:                   ; the program label for the entry point
    push ebp            ; set up stack frame
    mov ebp,esp

    ;; Get the data
    push dword fmtStart
    call printf
    add esp, 4

    push dword int2
    push dword int1
    push dword input
    call scanf
    add esp, 12

        ;; Do calculations
        ;; Add
            xor eax, eax
            mov eax, [int1]
            add eax, [int2]
            mov [sum], eax
        push dword sum
        push dword fmtTest
        call printf
        add esp, 24

    mov esp, ebp    ; take down stack frame
    pop ebp         ; same as "leave" op

    mov eax,0       ; normal, no error, return value
    ret                 ; return

I get:

Enter two numbers in format '# #'

2 3

sum: 4247592

which isn't what I get when I add 2 and 3 with my calculator, maybe that's just me though.

my understanding of the code is as follows: the data section declares variables that are initialized to stuff, in this case my formatted strings; the bss section is for uninitialized variables, in this case my input vars and the sum var; the text section is where the code goes; I declare main as the entry point for gcc; I prompt the user for two numbers; I zero out eax with the xor; move the value of int1 to eax; add the value of int2 to eax; move what's in eax to be the value of sum; push it onto the stack with the formatted string; call printf to display stuff; end the program.

--EDIT--

To be clear, either add isn't working or mov isn't working. It seems like add should be working so I'm assuming it's mov. I don't understand what about mov [var], register would be wrong but obviously something isn't right!

Answer 1

Here's the problem:

    push dword sum
    push dword fmtTest
    call printf

printf , unlike scanf , takes its arguments (after the format) by value, while in your code sum is the address of the memory location. Just do:

    push [sum]
    push fmtTest
    call printf

(incidentally, the xor eax,eax before the mov eax,[int1] is useless, since you are immediately rewriting the content of the register)