TerrorVM

A register-based, garbage-collected, stackless, lightweight Virtual Machine for object-oriented programming languages.

Ships with a naive implementation of a reference-counting Garbage Collector, although it will implement a more advanced GC algorithm, probably Baker's treadmill.

Eventually the VM will be optimized to be fast on ARM processors, but for now it compiles to both ARM (tested on Android) and x86 architectures. It will also use LLVM for JIT-compiling code to native at runtime.

Anyway, it's a work in progress! :)

Building the VM

$ git clone git://github.com/txus/terrorvm.git
$ cd terrorvm
$ make

To run the tests:

$ make dev

And to clean the mess:

$ make clean

Running programs

TerrorVM runs .tvm bytecode files such as the hello_world.tvm under the examples directory.

$ ./bin/vm examples/hello_world.tvm

It ships with a simple compiler written in Ruby (Rubinius) that compiles a tiny subset of Ruby to .tvm files. Check out the compiler directory, which has its own Readme, and the compiler/examples where we have the hello_world.rb file used to produce the hello_world.tvm.

TerrorVM doesn't need Ruby to run; even the example compiler is a proof of concept and could be written in any language (even in C obviously).

Implementing your own dynamic language running on TerrorVM

TerrorVM is designed to run dynamic languages. You can easily implement a compiler of your own that compiles your favorite dynamic language down to TVM bytecode.

I've written a demo compiler in Ruby under the compiler/ folder, just to show how easy it is to write your own. This demo compiler compiles a subset of Ruby down to TerrorVM bytecode, so you can easily peek at the source code or just copy and modify it.

You can write your compiler in whatever language you prefer, of course.

Bytecode format

TerrorVM files are encoded with a header containing _main (the method that will be the entry point), some info about number of registers, local variables, literals and instructions used by the method, followed by all the literals, and then all the instructions. It starts like this:

_main

Then info encoded in the format :num_registers:num_locals:num_literals:num_instructions:

:10:2:4:17

Then all the literals, each one in a line (the ones starting with " are string literals):

123
"print
"Goodbye world!
"Hello world!

And then all the instructions:

0x2000000
0x51000000
0x9010000
0x51010100
...

Instructions have a compact 3-operand representation, 8-bit each, for a total of 32-bit per instruction.

VM primitive functions

TerrorVM exposes a VM object that responds to primitive, which returns a hash with some VM primitive functions exposed as Terror Function objects. A simple example of those are arithmetic functions (+, -, *, /) used by Integer objects, for example. To use this in your functions, do it like this:

VM.primitive[:+].apply(3, 4) # this is the same as 3 + 4 or 3.+(4)

Examples

• Hello world (Ruby code, TVM bytecode)
• Numbers (Ruby code, TVM code)
• Objects with prototypal inheritance (Ruby code, TVM bytecode)
• Exposed VM primitives (Ruby code, TVM bytecode)

Instruction set

• NOOP: no operation -- does nothing.

Loading values

• MOVE A, B: copies the contents in register B to register A.
• LOADI A, B: loads the integer (from the literal pool) at index B into register A.
• LOADS A, B: loads the string (from the literal pool) at index B into register A.
• LOADNIL A: loads the special value nil into register A.
• LOADBOOL A, B: loads a boolean into register A, being true if B is the number 1 or false if B is 0.
• LOADSELF A: loads the current self into register A.

Branching

• JMP A: unconditionally jumps A instructions.
• JIF A, B: jumps A instructions if the contents of the register B are either false or nil.
• JIT A, B: jumps A instructions if the contents of the register B are neither false nor nil.

Local variables

• LOADLOCAL A, B: loads the value in the locals table at index B into the register A.
• SETLOCAL A, B: stores the contents of the register A in the locals table at index B.

Slots

• LOADSLOT A, B, C: loads the slot named C from the object B to the register A.
• SETSLOT A, B, C: sets the slot named B from the object A to the value in the register C.

Arrays

• MAKEARRAY A, B, C: Takes C registers starting from register B, creates an array with them and stores it in register A.

Message sending and call frames

• SEND A, B, C: send a message specified by the string in the literals table at index B to the receiver A, with N arguments depending on the arity of the method, the first argument being in the register C.
• RET A: return from the current call frame to the caller with the value in the register A.

Debugging

• DUMP: Print the contents of all the registers to the standard output.

Who's this

This was made by Josep M. Bach (Txus) under the MIT license. I'm @txustice on twitter (where you should probably follow me!).