Check for support

zcat /proc/config.gz | grep -i binfmt_misc

Expected output:

CONFIG_BINFMT_MISC=y

You can locate the mount point using the `findmnt` tool: ```

# Locate the control interface
findmnt binfmt_misc

# Example output:
TARGET                   SOURCE      FSTYPE      OPTIONS
/proc/sys/fs/binfmt_misc binfmt_misc binfmt_misc rw,relatime

According to the LuaJIT source, the bytecode magic bytes are 0x1b, 0x4c, and 0x4a, with the fourth byte indicating the LuaJIT version. The header begins at offset 0, and the runtime handles version checks automatically. ```

/* Bytecode dump header definitions */ #define BCDUMP_HEAD1 0x1b #define BCDUMP_HEAD2 0x4c #define BCDUMP_HEAD3 0x4a

To register LuaJIT bytecode as an executable format: ```

# As root, write the following string to the control file
echo ":luajit:M::\x1b\x4c\x4a::/usr/bin/luajit:" > /proc/sys/fs/binfmt_misc/register

# Verify registration was successful
ls -al /proc/sys/fs/binfmt_misc

With this setup, you can execute bytecode files directly: ```

Create some bytecode

luajit -be "print('hello world via binfmt_misc')" binfmt_test

Mark the file as executable

chmod +x binfmt_test

Run the test

./binfmt_test

Output:

hello world via binfmt_misc

This Linux feature enables treating LuaJIT bytecode as a first-class executable format, offering numerous potential applications. For example, precompiling frequently used scripts into bytecode can improve loading times, which is beneficial in environments like live CDs or embedded systems. ### Use Cases for LuaJIT

#### Embedding LuaJIT

- GSL Shell: A library binding to the GNU Scientific Library (GSL) with a Lua shell interface.
- Redis fork: A version of Redis that embeds LuaJIT instead of PUC-Lua.
- Tarantool: A replicated, persistent in-memory database and LuaJIT application server.
- Csound: An open-source sound synthesis system embedding LuaJIT for algorithmic composition.
- Knot-resolver: A validating DNS resolver using LuaJIT for configuration and extensibility.

#### Supporting LuaJIT

- ZeroBrane Studio: A lightweight Lua IDE supporting debugging under LuaJIT.
- ULua: A portable LuaJIT-based distribution for Windows, OSX, and Linux.
- Luapower: A free and open-source LuaJIT module distribution system.

#### Implemented with LuaJIT

- Snabb Switch: An open-source virtualized Ethernet switch for cloud networks.
- YEng: An open-source game engine.
- Goluwa: An experimental game engine written in LuaJIT.
- KOReader: An open-source e-book reader supporting multiple formats, running on LuaJIT.

### Architectural Support

LuaJIT supports various number modes and floating-point units across architectures: | Architecture | Number Modes | FPU | ABI |
|---|---|---|---|
| x86 | single\|(dual) | x87\|SSE2 | hardfp |
| x64 | single\|(dual) | SSE2 | hardfp |
| ARM | dual | soft\|VFP | softfp\|hardfp |
| PPC | dual\|single | FPU-dbl | hardfp |
| e500 | single | SPE | softfp |
| MIPS | single | FPU-dbl | hardfp |

</div>