Provided by: systemtap-doc_2.3-1ubuntu1.4_all 

NAME
function::fastcall - Mark function as declared fastcall
SYNOPSIS
fastcall()
ARGUMENTS
None
DESCRIPTION
Call this function before accessing arguments using the *_arg functions if the probed kernel function was
declared fastcall in the source.
SystemTap Tapset Reference March 2016 FUNCTION::FASTCALL(3stap)