本文内容基于版本：Lua 5.3.0

global_State与lua_State结构的关联

// luaconf.h
/*
@@ LUA_EXTRASPACE defines the size of a raw memory area associated with
** a Lua state with very fast access.
** CHANGE it if you need a different size.
*/
#define LUA_EXTRASPACE        (sizeof(void *))

// lstate.c
/*
** thread state + extra space
*/
typedef struct LX {
  lu_byte extra_[LUA_EXTRASPACE];
  lua_State l;
} LX;

/*
** Main thread combines a thread state and the global state
*/
typedef struct LG {
  LX l;
  global_State g;
} LG;