General differences in 64 bit:	
	Default size is 64 bits
		If you wanted 32, use movl, addl, etc.
	push and pop operate with 64 bits now
	64-bit registers start with r
		rax, rdi, rbp, etc.
		Use 64-bit version when dealing with memory addresses
		If dealing with a C int, still use e (eax, etc)
			 Unless you need to clear the whole register...

System Calls:
	syscall replaces int 0x80
		It's an instruction in x86_64
		Fundamentally, it does the same thing
	Parameter order:
		rax:  System Call Number
		After that:  rdi, rsi, rdx, r10, r8, r9
		An explanation:
			/usr/src/linux-source-6.1/arch/x86/entry/entry_64.S
	System call numbers are different
		Table at:  /usr/src/linux-source-6.1/arch/x86/entry/syscalls/syscall_64.tbl
	Other than all that, they're pretty similar

Exampls:
	Hello world with write:  hw_64.s
	Demo with printf/scanf:  functions_64.s
	
Function Calls:
	Different calling convention (see Wikipedia)
		Now a lot of parameters go into registers
	Other than that, it's basically the same
	You need to have the stack aligned on a 16-byte boundary!
		As in, the last hex digit should be 0
		Otherwise it'll mysteriously segfault