option casemap:none

strdup  proto :qword
printf  proto :qword, :vararg
exit    proto :dword

.data
bstr    db "String 1",0

.data?
buff    dq ?

.code
main proc
  invoke printf, CSTR("Copying %s to buff with strdup using invoke....",10), addr bstr
  invoke strdup, addr bstr
  mov buff, rax
  invoke printf, CSTR("buff now = %s",10), buff
  invoke exit, 0
  ret
main endp
end
;Now, we could target a specific ABI by assigning the call values to the registers like
;.code
;main proc
;  lea rdi, bstr
;  call strdup
;  mov buff, rax
;main endp
;end