Re: PATCH: How to handle CallInfo func field safely?

[Hugo Musso Gualandi <hgualandi@...>]

> I analyzed the use of CallInfo func field,
> then I figured out that the field is used as either CClosure or 
> LClosure.

There are actually 3 kinds of functions:
- Lua closures
- C closures
- Light C functions

The Lua calling convention is to push the function object to the Lua 
stack, followed by the function arguments. The `func` field refers to 
this function object, which can be any of the 3 function types.

> First, at the entry of the VM dispatch loop (Lua 5.4.3),
> the CallInfo func field is cast as LClosure as follows:

The VM dispatch loop only makes sense for Lua closures. It's only 
called in situations where it's known that it's a Lua closure.

That said, now that you mention it really is a bit strange that it does 
a straight cast with clLvalue, without any checking. I wonder if it 
would make sense to have the `cl` be one of the parameters to 
luaV_execute. The places that call luaV_execute are all places that 
have checked the type tag of the function object and have the `cl` at 
hand.

> Furthermore, the function index2value (./src/lapi.c) assumes that
> ci->func is type of either CClosure or LClosure implicitly as follows:

I think you might mean "light C function" instead of "Lua closure". The 
C API stuff is only accessible to C functions.

-- Hugo