The x64 calling convention (for long mode on x86-64) takes advantage of additional register space in the AMD64/Intel 64 platform. The registers RCX, RDX, R8, R9 are used for integer and pointer arguments, and XMM0, XMM1, XMM2, XMM3 are used for floating point arguments.
stack frame layout on x64
The stack frame layout for functions on x64 is very similar to x86, but with a few key differences. Just like x86, the stack frame on x64 is divided into three parts: parameters, return address, and locals. One of the important principals to understand when it comes to x64 stack frames is that the stack does not fluctuate throughout the course of a given function. In fact, the stack pointer is only permitted to change in the context of a function prologue. Parameters are not pushed and popped from the stack. Instead, stack space is pre-allocated for all of the arguments that would be passed to child functions. This is done, in part, for making it easier to unwind call stacks in the event of an exception.