ubpf VS LjTools

eBPF doesn't run in user space in the context of eBPF in the linux kernel. It's verified so that the kernel can be sure it won't loop forever and then gets JIT'ed and run in kernel space.

There are some user space BPF vms like https://github.com/iovisor/ubpf and Solana.

ubpf: https://github.com/iovisor/ubpf

The usual recommendation have been given. Now for more touristic approach what I would like to use if given excuse and time. All those options are mostly written in C:

- QBE [1] - small compiler backend with nice IL

- DynASM [2] - IIUC the laujit's backend, that can and is used by other languages

- uBPF - Userspace eBPF VM. Depending on your DSL the eBPF toolchain could fit your use-case, but this would probably be the biggest excursion.

[1] https://c9x.me/compile/

[2] https://luajit.org/dynasm.html

[3] https://github.com/iovisor/ubpf

There are eBPF-specific userspace implementations you can consider looking into but right now the best support for bpf would be the linux kernel so if the goal is learning you'll most likely want to run linux in a proper virtual machine (e.g. Qemu, VirtualBox, Parallels, etc.)

This may be entirely irrelevant to what you are looking for, but a good widely used finite register-based VM is the eBPF VM in the Linux Kernel. The IOVisor uBPF project (https://github.com/iovisor/ubpf) is a version of the VM in user space.

I dug a little more and came across this tool which does seem to have the capability to view all LuaJIT Bytecode. https://github.com/rochus-keller/LjTools

> a large lua game code base, over 4000 files, 1.5 million lines of code

Interesting; how do you manage to keep consistency? Do you have special tools to e.g. detect inadvertent global variables? I once wrote a Smalltalk VM in Lua (https://github.com/rochus-keller/Smalltalk/blob/master/Inter...) which is a much smaller code base but even with this size I quickly would have lost track of e.g. scopes and names without tools I had to write myself (https://github.com/rochus-keller/LJTools).

Most of my languages have VM backends; see e.g. https://github.com/rochus-keller/Oberon; I implemented different backends generating LuaJIT bytecode; a year ago I switched to Mono which is based on ECMA-335; here is a discussion why I switched: https://github.com/rochus-keller/Oberon/releases/tag/IDEv0.9.0; I implemented utility libraries for both LuaJIT and CIL bytecode; see https://github.com/rochus-keller/LjTools/, https://github.com/rochus-keller/Pelib/ and https://github.com/rochus-keller/MonoTools/. I evaluated many VMs and think the mentioned ones are best suited. There were a lot of challenges with both technologies, what is to be expected, and too much to describe here.

LuaJIT is well suited as a backend/runtime environment for custom languages; I did it several times (see e.g. https://github.com/rochus-keller/Smalltalk, https://github.com/rochus-keller/Som/, https://github.com/rochus-keller/Oberon/). I also implemented a bit of infrastructure to ease the reuse: https://github.com/rochus-keller/LjTools. LuaJIT has some limitations though; if you require closures you have to know that the corresponding LuaJIT FNEW bytecode is not yet supported by the JIT, i.e. switches to the interpreter; as a work-around I implemented my own closures; LuaJIT also doesn't support multi-threading, but co-routines; and there is no debugger, and the infrastructure to implement one has limitations (i.e. performance is low when running to breakpoints). For most of my projects this was no issue. Recently I switched to CIL/Mono for my Oberon+ implementation which was a good move. But still I consider LuaJIT a good choice if you can cope with the mentioned limitations. The major advantage of LuaJIT is the small footprint and impressive performance for dynamic languages.

Implementing a VM is certainly interesting, but if you just need a fast backend you could generate LuaJIT bytecode (see e.g. https://github.com/rochus-keller/ljtools/ LuaJitComposer.h/cpp).

If you want to re-use LuaJIT as a backend, have e.g. a look at https://github.com/rochus-keller/ljtools

Recently I mostly use https://github.com/rochus-keller/LjTools#lua-parser-and-ide-features