module loading in C

[Hans van der Meer <H.vanderMeer@...>]

I am wrestling with keeping modules from crashing(disappearing?).

I have module A loaded from a lua program wth require, while  
submodules A1, A2, .. are loaded by A on demand. The code for the  
submodule loading:

lua_getglobal(L, subsystem); /* char *subsystem */
if (lua_isnil(L, -1)) {
    lua_pop(L, 1); /* pop the nil */
    lua_getglobal(L, "require");  /* setup call to require */
    lua_pushstring(L, subsystem); /* argument is name of module to  
load */
    if (lua_pcall(L, 1, 1, 0)) luaL_error(L, "require failed");
}

If I have in the Lua program a statement:
subsys = require "A1"
before the programmatic loading will occur all is well, leave it out  
and the program may crash when trying to enter a function in the  
submodule A1. This occurs in the endgame of the program execution.  
This follows from the fact that putting an offending operation within  
a local do-end block has the garbage collector kick in at an earlier  
moment.

I tried to fixate the module by putting the table returned by the  
pcall to require in either LUA_ENVIRONINDEX or LUA_GLOBALSINDEX but  
neither does work.
Clearly I am missing an essential point. But what?
I hope someone can point me in the right direction.

Hans van der Meer