Passing parameters to assembler functions in 'C' 64 style.

Hi. 
I started to write assembler functions for C on 64-bit arch. On 32-bit arch. every parameters ware put on stack, now is different, what can be easyly seen reading source program. For example if im passing one  
(int *) parameter, adress (&int) is kept in %rdi register, and so one if u are passing more parameters. Ofcurse is not dificult to use it if u know but is there any key according to which parameters are stored?. I've made some "experiments" with different numbers and kind parameters, but the "key" must be described somewhere.

Luke