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chibi vm

a fork of chibicc which targets a virtual machine.

motivation

the virtual machine is planned for use in fluent and probably other smaller language projects. the idea is that using an already well-tested parser for a well-defined language operating at a similar level of hardware abstraction should give me plenty of space to test ideas and figure out edge cases. in pursuit of these goals, I chose chibicc for the small size, readability, extensive documentation with the attached book, and requiring basically zero build system.

goals

the primary goal is to create a vm that is general enough to do basically any computational task, simple enough to read and understand in a day or two, and with an interface that is pleasant to hack on.

  • math with unsigned + signed integers and IEEE-754 floating point
  • boolean logic and comparisons
  • arbitrary datatypes (pointers, arrays, structs, unions are all supported)
  • generic control flow
  • functions
  • well-defined call convention and stack mechanics
  • elf-like segmented process memory mapping
  • very good test coverage
  • native function bindings
  • linking multiple translation units, allowing for parallelism

non-goals

  • implementing all features of C
    • this is a proof of concept project. if I'm satisfied that the design is robust and will require minimal (if any) future changes, there's no point going further
    • supporting parts of C that I don't like and don't plan to include in my own language projects (goto, bitfields, explicit inline...) is a waste of time for my goals

getting started

chibi-vm is built with zig 0.11.0. just zig build for a debug build or zig build -Doptimize=ReleaseFast for a release build.

usage

you can run chibi-vm to see a (hopefully helpful) list of subcommands to use. chibi-vm run will let you interpret a C program.

compiler tests

once the executable is built, you can run end-to-end tests with ./runtests.py. it is written in relatively generic python 3, and uses the wonderful c-testsuite. you can use the results of the script to see how well this project stacks up against the big boys :)

vm tests

there is also extensive testing of the bytecode vm internals. these tests can be run with zig build test, and can be found in the source code itself.

project structure

cc contains the c frontend, which is a thin wrapper over chibi that then traverses the AST to generate vm code. since it's not the main product of this project, this code is untested and not particularly well-vetted.

cc/chibi contains the chibicc source which I have left untouched. only the parser and source file mechanics are relevant to this project.

tests contains the c test suite. runtests.py will run a manually filtered subset of this suite.

vm contains the virtual machine, and definitions for opcodes, translation units, etc. this code is well tested and commented.