ABI documentation

[Dom Disc]

I have looked into the Application Binary Interface document and 
found the following:

> 39.12 Function Calling Conventions
> 
> [...]
> 
> 39.12.2 Return Value
> 
>     long and ulong are returned in EDX,EAX, where EDX gets the 
> most significant half.

Is this really true? Or is this only for 32bit systems?
Because, I see the return value of ulong in RAX. I'm also not 
sure if the convention for the input parameters has changed. For 
a function with three ulong parameters I get the parameters in 
RDI, RSI and RDX respectively.

Where can I find the correct and current documentation for 64bit 
systems?