RDTSCP from dlang

[kookman via Digitalmars-d-learn]

On Wednesday, 31 August 2016 at 07:36:16 UTC, rikki cattermole 
wrote:

> http://dlang.org/spec/abi.html#register_conventions

That link talks about for functions defined extern(C) and 
extern(D), and gives specific info for win32.

I'm using linux x86_64, does that mean I can assume standard 
x86_64 ABI? ie even if the function is not extern?