How is Lua ran on the VM?

CoderHusk · January 21, 2021, 5:42am

I have a general idea, that being the tokens are fed to the VM which are then translated to assembly instructions. From there, being converted to cpu instructions (machine code). However I am not sure if I am correct, so what is the exact process on how lua is built?

luya_yobanka · January 21, 2021, 6:08am

Roughly speaking, that’s what’s going on internally. Unfortunately the implementation of Lua Roblox is closed and the exact details are not known, except for some publications.

Since Lua Roblox (now Luau) is an implementation of Lua 5.1, all documentation on the Lua 5.1 MV should be applied to Lua Roblox.

Here are some interesting links:

gist.github.com

https://gist.github.com/zeux/bb646a63c02ff2828117092036d2d174

luau_features.pdf

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roblox-lua-vm.md

We're working on a new Lua VM for Roblox and also introducing optional type checking to Lua (based on a combination of type inference
and type annotations - the latter require extensions to the syntax). This page summarizes the questions often asked.

# Why not just use LuaJIT?

We obviously know about LuaJIT; it's a fantastic project, and really what inspired us to go down this route - it provided an existence
proof that Lua can be much faster. Our primary performance target is a wide set of platforms, many of which (iOS, Xbox) don't allow JIT
per se - but LuaJIT has a very fast interpreter. So - use it, we're done? Well...

LuaJIT is a large, almost complete rewrite of Lua VM. Over the years we had a set of changes aimed at improving sandboxing in the VM -

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https://thesephist.com/posts/lua/