stdlib: Add 'common.Options' as a banned stdlib module

This commit adds the concept of a "banned module" to the stdlib. This
blocks the user from importing modules from elsewhere in the project
with known incompatibility to the stdlib.

'common.Options' has been added to this as 'common.Options' will import
options to an stdlib run which are not supported.

Issue-on: https://gem5.atlassian.net/browse/GEM5-1282
Change-Id: I8f2b1e24d03fab2872c735342dc8a1ff6528fb5d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/63071
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>

src/python/gem5/simulate/simulator.py

@@ -32,6 +32,7 @@ from m5.objects import Root
 from m5.util import warn
 
 import os
+import sys
 from pathlib import Path
 from typing import Optional, List, Tuple, Dict, Generator, Union
 
@@ -70,6 +71,16 @@ class Simulator:
     This will run a simulation and execute default behavior for exit events.
     """
 
+    # Here we declare the modules which should not be imported into any gem5
+    # standard library run. The key is the module (e.g,
+    # "import common.Options") and the value is the reason, which will be
+    # output in the case this module is imported.
+    # This is checked with the `run` function is executed.
+    _banned_modules = {
+        "common.Options": "The options provided by 'Options' are not "
+        "compatible with the gem5 standard library.",
+    }
+
     def __init__(
         self,
         board: AbstractBoard,
@@ -344,6 +355,15 @@ class Simulator:
         reset. This is the **maximum number of ticks per simululation run**.
         """
 
+        # Check to ensure no banned module has been imported.
+        for banned_module in self._banned_modules.keys():
+            if banned_module in sys.modules:
+                raise Exception(
+                    f"The banned module '{banned_module}' has been included. "
+                    "Please do not use this in your simulations. "
+                    f"Reason: {self._banned_modules[banned_module]}"
+                )
+
         # We instantiate the board if it has not already been instantiated.
         self._instantiate()