brixen / govm

Experimental Go virtual machine illustrating the new Rubinius instruction set and interpreter

Go VM

An experimental proof-of-concept that illustrates the new instruction set and interpreter architecture in Rubinius.

A few notes:

1. Everything is starting in a single file until I learn how to properly modularize things in Go.
2. One of the more interesting aspects of this is the difference in memory management in C/C++ and Go. For example, in Rubinius, we can cast a pointer to a function as an intptr_t to store in the opcode sequence. This is strictly forbidden in Go.
3. One of the challenges writing a just-in-time (JIT) compiler is the potential mismatch between a program's semantics as interpreted versus as JIT compiled. It would be easy to cast this a checking whether the JIT is "correct", but it's not that simple. A better way to think about it is whether the JIT is the "same as" the interpreter because bugs can become features. The best way to ensure the JIT is the same is to use the same code that the interpreter uses.
4. The point above has informed the design of the instruction set and interpreter, specifically the separate of the interpreter from the instruction set functions. The instruction mutates program state, while the interpreter mutates the PC/IP (program counter / instruction pointer). The (naive) JIT serializes (calls one after the other) the instructions in the opcode sequence.