String Reverse (Not actually NASM)

; Reverse a null-terminated string in-place
; using the stack.

.text 0
    mov si, 32      ; Move our si to start of string
    push 0          ; Push 0 as a marker for stack rewind
read:
    mov acc, [si]   ; Get a letter into acc
    jnz collect     ; Check if we hit '\0'
    jmp rewind
collect:
    push acc        ; Push current char onto the stack
    add si, 1       ; Advance our si pointer
    jmp read

rewind:
    mov si, 32      ; Reload si to start of string
write:
    pop acc         ; Pop off last letter
    mov [si], acc   ; Write it into the string
    add si, 1       ; Advance si
    jnz write       ; Repeat if acc isn't zero
    jmp exit        ;
exit:
                    ; We're done

.data 32
"Hello world."