uVM - Micro Virtual Machine

uVM is simply an experiment in developing a working virtual machine with it's own bytecode.

Requirements

• CMake version 3.8 or higher
• Clang and Clang++

Building

1. git clone the repository
2. cmake .
3. make

Usage

uvm [-v] [-h] [-d <stack_depth>] -f <your_file_of_bytecode>.uc

• -v: Enable verbose logging mode
• -h: Show usage
• -f <file_name>.uc: Load the uvm bytecode file for processing
• -d <stack_depth>: The maximum stack depth in words

Testing

CMake tests are used to confirm a handful of sample programs will run successfully in the VM

1. cmake .
2. make test

Architecture

uVM is a stack machine. That is, it gets all of it's arguments from the stack, and returns the result of the computation back to the stack when it's done.

There are some exceptions to this. In particular the current version of uvm supports a single variable, called 0, that can be written to using xpop0 where x is the datatype of the thing getting taken off the stack.

Additionally 0 can be placed on the top of the stack using xpush0.

uVM Instruction Set

uVM possesses the standard issue instruction set you might expect in a simple VM:

Instruction	Opcode	Action
ipush X	0	Pushes integer X onto the stack
ipush0	1	Pushes the integer in 0 onto the stack
ipop0	2	Pops the top integer of the stack off and into variable 0
icmp	3	Compares the top two items on the stack together and returns a boolean result
iadd	4	Adds the top two integer arguments of the stack together
isub	5	Subtracts the top two integer arguments of the stack from each other
jmp LABEL	6	Unconditional jump to label
jc LABEL	7	Jump if the top of the stack is a 1
halt	8	Halts the VM

As I learn more about VM development this instruction set will likely become much more robust.

TODO

• [] Tests for good paths for all instructions
• [] Tests for uncompilable code
• [] Tests for maximum stack size reached
• [] Tests to make sure the maximum stack depth is always greater than 0
• [] Logging out current stack position, etc when verbose mode is enabled
• [] If verbose mode isn't enabled it shows the ascii loading while processing
• [] Come up with a way to allow the user to echo to the screen
• [] It would be cool to eventually write a high level language compiler that compiles down to the uvm