No, I don't think Lua (or the author) is inlining the external function. What's being JIT'd is the Lua code into machine code, and where Lua would need to call

No, I don't think Lua (or the author) is inlining the external function. What's being JIT'd is the Lua code into machine code, and where Lua would need to call a C function, it (apparently) is just emitting a `call the_external_fn` into the JIT's resulting assembly. That's a direct function call, so it's about as fast as you're going to get, but somewhat counter-intuitively, it'll be faster than C, as we don't do anything with the PLT or indirection. Just call the function.