tiny-vm

tiny-vm is an attempt to create a virtual machine similar to the Java Virtual Machine (JVM). Like the JVM, it doesn't run machine code but a very minimalist assembly language.

Operations

The language supports the following operations:

INSTR	Description
HALT	Halts the machine
NOOP	Does nothing
LOAD $1 $2	Loads $2 into register $1
ADD $1 $2 $3	Loads the result of registers $1 + $2 into register $3
PRINTREG $1	Prints register $1
PRINT $1 $2	Prints a string with length $1 and UTF-8 encoded contents $2

Frontend

The Main class accepts a file as the first argument which it will attempt to read the above instructions from. It will then compile these to the above binary format. The following would be a valid program:

# just a simple program
PRINT hello world!
NOOP
LOAD 0 128
PRINTREG 0
LOAD 1 2
PRINTREG 1
ADD 0 1 2
PRINTREG 2
HALT

Intermediate Code

During intermediate code generation, the code is written in a file with the .tiny extension. The instructions are encoded as follows:

INSTR	FORMAT	Description
HALT	byte 0	Halts the machine
LOAD	byte 1, byte $1, int $2	Loads $2 into register $1
ADD	byte 2, byte $1, byte $2, byte $3	Loads the result of $1 + $2 into $3
NOOP	byte 9	Does nothing
PRINTREG	byte 42, byte $1	Prints register $1
PRINT	int $1, byte[] $2	Prints a string with length $1 and UTF-8 encoded contents $2

Execution

Afterwards it is run. Instructions from the intermediate code are executed one by one.

The output of the above program will be:

0 Executing Print
  "hello world!"
1 Executing Noop
2 Executing Load
3 Executing PrintRegister
  Register 0: 128
4 Executing Load
5 Executing PrintRegister
  Register 1: 2
6 Executing Add
7 Executing PrintRegister
  Register 2: 130
8 Executing Halt

Building

To build and run tests, execute gradle build or create a jar with gradle jar.

Running an example

1. Run gradle jar

2. Go to the directory build/libs which contains the tiny-vm.jar file.

3. Write a program or copy the program in the Frontend section above. Hint: Don't forget to use HALT as the last statement.

4. Run the program via java -jar tiny-vm.jar test.txt.

5. Enjoy :)