LuaJIT

# Status

LuaJIT 2.0 is the current stable branch. This branch is in feature-freeze — new features will only be added to LuaJIT 2.1.

## Current Status

LuaJIT ought to run all Lua 5.1-compatible source code just fine. It's considered a serious bug if the VM crashes or produces unexpected results — please report this.

Known incompatibilities and issues in LuaJIT 2.0:

- There are some differences in implementation-defined behavior. These either have a good reason, are arbitrary design choices or are due to quirks in the VM. The latter cases may get fixed if a demonstrable need is shown.
- The Lua debug API is missing a couple of features (return hooks for non-Lua functions) and shows slightly different behavior in LuaJIT (no per-coroutine hooks, no tail call counting).
- Currently some out-of-memory errors from on-trace code are not handled correctly. The error may fall through an on-trace `pcall` or it may be passed on to the function set with `lua_atpanic` on x64. This issue will be fixed with the new garbage collector.
- LuaJIT on 64 bit systems provides a limited range of 47 bits for the legacy `lightuserdata` data type. This is only relevant on x64 systems which use the negative part of the virtual address space in user mode, e.g. Solaris/x64, and on ARM64 systems configured with a 48 bit or 52 bit VA. Avoid using `lightuserdata` to hold pointers that may point outside of that range, e.g. variables on the stack. In general, avoid this data type for new code and replace it with (much more performant) FFI bindings. FFI cdata pointers can address the full 64 bit range.

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