Error loading module undefined symbol: luaL_setfuncs

Question

I am trying to create a C module to be called from a lua script. I am working on debian linux. I am using mysql-proxy and lua 5.2. I have created (copied from a tutorial) some example functions to be called.

The loader is defined like this:

int luaopen_luacall(lua_State* l)
{

    luaL_newlibtable(l, luacall);
    luaL_setfuncs(l, luacall, 0);
    return 1;
}

To call this from lua I use this code:

luacall = require("luacall")
local f = luacall.fun1()

I have compiled it with this command:

g++ -shared -Wl,-E,-soname,libluacall.so -o luacall.so luacall.c  -fPIC -llua -ldl

When I try to run the script I get the following error on the require command:

 error loading module 'luacall' from file '/usr/lib/mysql-proxy/lua/luacall.so':
        /usr/lib/mysql-proxy/lua/luacall.so: undefined symbol: luaL_setfuncs

I am really lost on what I am doing wrong.

Answer 1

I think I found the problem (not yet the solution): Mysql-proxy runs internally an embended lua library.

mysql-proxy -V

gives as result

mysql-proxy 0.8.1
  chassis: mysql-proxy 0.8.1
  glib2: 2.30.2
  libevent: 2.0.19-stable
  LUA: Lua 5.1.4
    package.path: /usr/lib/mysql-proxy/lua/?.lua
    package.cpath: /usr/lib/mysql-proxy/lua/?.so
-- modules
  admin: 0.8.1
  proxy: 0.8.1

So I am running the wrong lua version. I think that this explains the luaL_setfuncs error. I have seen that even the 0.8.4 version includes this version of lua, so I will have to rewrite the C library.

the final code of the module ends like this (and runs!!!):

static const struct luaL_Reg my_luacall[] = {
    {"trasnquery", trasnquery},
    {"fun2", function_2},
    {NULL, NULL}
};

int luaopen_luacall(lua_State* l)
{
    luaL_register(l, "luacall", my_luacall);
    return 1;
}