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
		There are some extra registers:  r8, r9, r10, r11, r12, r13, r14, r15
			These can have d, w, or b suffix for 32, 16, or 8 bites
		If dealing with a C int, still use 32-bit (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

Examples:
	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

Now that we're 64-bit:
	Let's interact with a C program!

A minor compatibility issue:  Executable stacks
	We don't actually need one
	Could set as a linker option with -z
	Could also put a .section .note.GNU-stack in the assembly

C libary used from Assembly:
	Write the library in a c file
	Compile it with gcc -c -o library_name.o source_code.c
	Assemble your program as usual
	Link it all together!  Probably something like this:
	ld asm_object.o library_name.o -lc -z execstack --dynamic-linker /lib64/ld-linux-x86-64.so.2
	Run the binary that comes out of all this

Assembly library used from C:
	Write the library, build with as as usual
	Write the C program and use the function
	Make a C prototype for the function, either in the main file or a header
	Build the program with gcc or clang:
	gcc c_source.c asm_library.o -z execstack
		
Could we make a build script for this?
	Of course!