#+title: Oreo's Virtual Machine (OVM)
#+author: Aryadev Chavali
#+date: 2023-10-15

A stack based virtual machine in C11, with a dynamic register setup
which acts as variable space.  Deals primarily in bytes, doesn't make
assertions about typing and is very simple to target.
* How to build
Requires =GNU make= and a compliant C11 compiler.  Code base has been
tested against =gcc= and =clang=, but given how the project has been
written without use of GNU'isms (that I'm aware of) it shouldn't be an
issue to compile using something like =tcc= or another compiler (look
at [[file:Makefile::CC=gcc][here]] to change the compiler).

To build everything simply run ~make~.  This will build:
+ [[file:lib/inst.c][instruction bytecode system]] which provides
  object files to target the VM
+ [[file:vm/main.c][VM executable]] which executes bytecode
+ [[file:asm/main.c][Assembler executable]] which assembles compliant
  assembly code to VM bytecode
+ [[file:examples/][Assembly examples]] which provide some source code
  examples on common programs one may write.  Use this to figure out
  how to write compliant assembly.  Also a good test of both the VM
  and assembler.

You may also build each component individually through the
corresponding recipe:
+ ~make lib~
+ ~make vm~
+ ~make asm~
+ ~make examples~
* Instructions to target the virtual machine
You need to link with the object files for
[[file:lib/base.c][base.c]], [[file:lib/darr.c][darr.c]] and
[[file:lib/inst.c][inst.c]] to be able to properly target the OVM.
The basic idea is to create some instructions via ~inst_t~,
instantiating a ~prog_t~ structure which wraps those instructions
(includes a header and other useful things for the runtime), then
using ~prog_write_file~ to serialise and write bytecode to a file
pointer.

To execute directly compiled bytecode use the ~ovm.out~ executable on
the bytecode file.

For clarity, one may build ~lib~ (~make lib~) then use the resulting
object files to link and create bytecode for the virtual machine.
** In memory virtual machine
Instead of serialising and writing bytecode to a file, one may instead
serialise bytecode in memory using ~prog_write_bytecode~ which writes
bytecode to a dynamic byte buffer, so called *in memory compilation*.
To execute this bytecode, deserialise the bytecode into a program then
load it into a complete ~vm_t~ structure (linking with
[[file:vm/runtime.c][runtime.c]]).

In fact, you may skip the process of serialising entirely.  You can
emit a ~prog_t~ structure corresponding to source code, load it
directly into the ~vm_t~ structure, then execute.  To do so is a bit
involved, so I recommend looking at [[file:vm/main.c]].  In rough
steps:
+ Create a virtual machine "from scratch" (load the necessary
  components (the stack, heap and call stack) by hand)
+ Load program into VM (~vm_load_program~)
+ Run ~vm_execute_all~

This is recommended if writing an interpreted language such as a Lisp,
where on demand execution of code is more suitable.
* Lines of code
#+begin_src sh :results table :exports results
find -name '*.[ch]' -exec wc -l '{}' ';'
#+end_src

#+RESULTS:
|  301 | ./vm/runtime.h |
|   92 | ./vm/main.c    |
| 1059 | ./vm/runtime.c |
|  500 | ./lib/inst.c   |
|   39 | ./lib/darr.h   |
|  265 | ./lib/inst.h   |
|   42 | ./lib/heap.h   |
|   90 | ./lib/base.h   |
|  101 | ./lib/heap.c   |
|   39 | ./lib/base.c   |
|   77 | ./lib/darr.c   |
|  654 | ./asm/parser.c |
|  142 | ./asm/main.c   |
|   83 | ./asm/lexer.h  |
|   65 | ./asm/parser.h |
|  549 | ./asm/lexer.c  |