In another scenario, we will create a library with functions performing the simple calculations on integers and floating-point numbers. We will write functions for adding six integers and six floating-point values. This example will present argument passing through the registers and also through the stack, showing the order and addresses of stack-allocated arguments. The simplest version of a function adds six integers without advanced stack manipulation. Let's present the code of a function first. It takes the first four arguments from registers, and the latter two from the stack. Please note that for each argument, there is an 8-byte space reserved on the stack.

.code
; ---------------------------------
; sum of six integer arguments
; this is a leaf function
; does not need to reserve shadow space
; arguments as passed by MSVC
    ; a = RCX
    ; b = RDX
    ; c = R8
    ; d = R9
    ; e = [RSP + 28h]
    ; f = [RSP + 30h]
; ---------------------------------
sum_6_int proc
 
    mov rax, rcx
    add rax, rdx   ; a + b
 
    mov rcx, r8 
    add rax, rcx   ; + c
 
    mov rcx, r9
    add rax, rcx   ; + d
 
    mov rcx, QWORD PTR [rsp + 28h]
    add rax, rcx   ; + e
 
    mov rcx, QWORD PTR [rsp + 30h]
    add rax, rcx   ; + f
    ret
sum_6_int endp

The stack from a function perspective looks like in a fig.

The caller passes arguments according to the Windows x64 ABI. The responsibility of the caller is also to reserve the shadow space for all arguments before the call.