fastcall myFunction, "a message"

; (normally in masm and jwasm I would use:

invoke myFunction, CStr("a message")
    

; I'm used to

myFunction proc frame uses rsi arguments:VARARG
ret
endp

; and then rcx = count and arguments are on the stack 

    

How would I go about using 64bit fastcall macro and support some form of string literals and vararg ?

include 'win64ax.inc'

.code

proc start
        fastcall func,'string1','string2'
        fastcall ExitProcess,0
endp

proc func arg1,arg2,arg3,arg4,more_args
        mov     [arg1],rcx
        mov     [arg2],rdx
        mov     [arg3],r8
        mov     [arg4],r9
        ;...
        ret
endp

.end start    

... and then rcx = count and arguments are on the stack