python: Enable -m switch on gem5 binary (#453)

With -m, you can now run a module from the command line that is embedded
in the gem5 binary.
This will allow us to put some common "scripts" in the stdlib instead of
in the "configs" directory.

src/python/importer.py

@@ -38,6 +38,9 @@ class ByteCodeLoader(importlib.abc.Loader):
     def exec_module(self, module):
         exec(self.code, module.__dict__)
 
+    def get_code(self, _):
+        return self.code
+
 
 # Simple importer that allows python to import data from a dict of
 # code objects.  The keys are the module path, and the items are the

src/python/m5/main.py

@@ -39,6 +39,7 @@
 import code
 import datetime
 import os
+import runpy
 import socket
 import sys
 
@@ -183,6 +184,16 @@ def parse_options():
         del parser.rargs[:]
         setattr(parser.values, option.dest, (value, extra_args))
 
+    option(
+        "-m",
+        type=str,
+        help="run library module as a script (terminates option list)",
+        default="",
+        metavar="mod",
+        action="callback",
+        callback=collect_args,
+    )
+
     option(
         "-c",
         type=str,
@@ -525,7 +536,9 @@ def main():
         print()
 
     # check to make sure we can find the listed script
-    if not options.c and (not arguments or not os.path.isfile(arguments[0])):
+    if not (options.c or options.m) and (
+        not arguments or not os.path.isfile(arguments[0])
+    ):
         if arguments and not os.path.isfile(arguments[0]):
             print(f"Script {arguments[0]} not found")
 
@@ -603,43 +616,49 @@ def main():
 
     sys.argv = arguments
 
-    if options.c:
-        filedata = options.c[0]
-        filecode = compile(filedata, "<string>", "exec")
-        sys.argv = ["-c"] + options.c[1]
-        scope = {"__name__": "__m5_main__"}
+    if options.m:
+        sys.argv = [options.m[0]] + options.m[1]
+        runpy.run_module(options.m[0], run_name="__m5_main__")
     else:
-        # If `-P` was used (`options.P == true`), don't prepend the script
-        # directory to the `sys.path`. This mimics Python 3's `-P` option
-        # (https://docs.python.org/3/using/cmdline.html#cmdoption-P).
-        if not options.P:
-            sys.path = [os.path.dirname(sys.argv[0])] + sys.path
-        filename = sys.argv[0]
-        filedata = open(filename).read()
-        filecode = compile(filedata, filename, "exec")
-        scope = {"__file__": filename, "__name__": "__m5_main__"}
+        if options.c:
+            filedata = options.c[0]
+            filecode = compile(filedata, "<string>", "exec")
+            sys.argv = ["-c"] + options.c[1]
+            scope = {"__name__": "__m5_main__"}
+        else:
+            # If `-P` was used (`options.P == true`), don't prepend the script
+            # directory to the `sys.path`. This mimics Python 3's `-P` option
+            # (https://docs.python.org/3/using/cmdline.html#cmdoption-P).
+            if not options.P:
+                sys.path = [os.path.dirname(sys.argv[0])] + sys.path
+            filename = sys.argv[0]
+            filedata = open(filename).read()
+            filecode = compile(filedata, filename, "exec")
+            scope = {"__file__": filename, "__name__": "__m5_main__"}
 
-    # if pdb was requested, execfile the thing under pdb, otherwise,
-    # just do the execfile normally
-    if options.pdb:
-        import pdb
-        import traceback
+        # if pdb was requested, execfile the thing under pdb, otherwise,
+        # just do the execfile normally
+        if options.pdb:
+            import pdb
+            import traceback
 
-        pdb = pdb.Pdb()
-        try:
-            pdb.run(filecode, scope)
-        except SystemExit:
-            print("The program exited via sys.exit(). Exit status: ", end=" ")
-            print(sys.exc_info()[1])
-        except:
-            traceback.print_exc()
-            print("Uncaught exception. Entering post mortem debugging")
-            t = sys.exc_info()[2]
-            while t.tb_next is not None:
-                t = t.tb_next
-                pdb.interaction(t.tb_frame, t)
-    else:
-        exec(filecode, scope)
+            pdb = pdb.Pdb()
+            try:
+                pdb.run(filecode, scope)
+            except SystemExit:
+                print(
+                    "The program exited via sys.exit(). Exit status: ", end=" "
+                )
+                print(sys.exc_info()[1])
+            except:
+                traceback.print_exc()
+                print("Uncaught exception. Entering post mortem debugging")
+                t = sys.exc_info()[2]
+                while t.tb_next is not None:
+                    t = t.tb_next
+                    pdb.interaction(t.tb_frame, t)
+        else:
+            exec(filecode, scope)
 
     # once the script is done
     if options.interactive: