Supply Pallene Tracer Error Handler Function

[singul4ri7y]

Changelog:

• Supply the error handler function to be used against xpcall.

[hugomg]

I wonder if assigning to a global variable might cause trouble with Lua environments that don't allow assigning to globals. For example, the strict.lua that sets the __newindex global metatable...

[singul4ri7y]

I think, here setting the global variable won't cause us any issue. Because even if the script manages to override the __newindex metamethod, we will be setting the global variable prior to calling the main chunk. Hence, setting global before the metamethod override.

[hugomg]

I suppose that would depend on the order that the modules are required. If they require strict.lua before they run the tracer initializer, then it could cause the trouble?

[singul4ri7y]

Actually the function is not supplied with tracer initializer. It is being supplied by setting Lua global prior calling the MAIN chunk, before any of the module is initialized, in the main function of pt-lua. So, we are bulletproof here.

int main (int argc, char **argv) {
  int status, result;
  lua_State *L = luaL_newstate();  /* create state */
  if (L == NULL) {
    l_message(argv[0], "cannot create state: not enough memory");
    return EXIT_FAILURE;
  }
  lua_gc(L, LUA_GCSTOP);  /* stop GC while building state */

  /* -------- PALLENE TRACER CODE -------- */
  (void) pallene_tracer_init(L);  /* initialize pallene tracer */
  lua_pop(L, 1);  /* We do not need the finalizer object here */

  /* supply the message handler function with custom tracebacks. */
  lua_pushcfunction(L, msghandler);
  lua_setglobal(L, "pallene_tracer_errhandler");
  /* -------- PALLENE TRACER CODE END -------- */

  lua_pushcfunction(L, &pmain);  /* to call 'pmain' in protected mode */
  lua_pushinteger(L, argc);  /* 1st argument */
  lua_pushlightuserdata(L, argv); /* 2nd argument */
  status = lua_pcall(L, 2, 1, 0);  /* do the call */
  result = lua_toboolean(L, -1);  /* get result */
  report(L, status);
  lua_close(L);
  return (result && status == LUA_OK) ? EXIT_SUCCESS : EXIT_FAILURE;
}

[hugomg]

Oh, that makes sense.

Does pt-lua accept "-l" command line flags and, if so, do those requires run before or after our "main"?

Can you also please add a comment explaining why this global is safe?

[singul4ri7y]

pt-lua is exact copy of lua.c. So, whatever Lua frontend can do, pt-lua can do as well. To answer your question, yes pt-lua do accept -l and the require happens after we are done setting the global as the code suggest. The pmain function is responsible for parsing the flags and we are setting the global just before calling pmain with a protected call.

Comment where? Here, or in the code explaining?

[hugomg]

Comment in the code, next to where you set the global.

[singul4ri7y]

Can you please clarify to comment about what exactly? Safe/unsafe in what way?

[hugomg]

Just say that it's ok to set a global variable, because no other code has run yet. No one could have messed with the global meta table.

[singul4ri7y]

Done, we can merge the PR now.

[hugomg]

Since there are many PRs at the same time, please rebase them before merging. Cheers!