Demo: The System Call Interface

Two demos for part 02, on how a program crosses into the kernel and what that crossing costs.

Demo	What it shows
syscalls/	A program that talks to the kernel directly, in assembly, through nothing but the syscall instruction.
syscall-overhead/	The same trivial operation as a real system call and as a plain function call: the system call is roughly seventy times slower.

The first makes the interface concrete; the second puts a price on using it. Together they set up part 04, which is entirely about avoiding that price.