ext: In sst, set sys.argv up even when not initializing python.

pybind11 gives us a simple way to set up sys.argv when initializing the
python interpreter, but we need to set that up even if the python
interpreter is already running. We need to do that manually, which we do
like gem5's main() used to.

Change-Id: If9b79a80e05158226d13f68bf06a2a98a36c2602
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/54310
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

ext/sst/gem5.cc

@@ -382,8 +382,27 @@ gem5Component::initPython(int argc, char *_argv[])
     // Initialize gem5 special signal handling.
     gem5::initSignals();
 
-    if (!Py_IsInitialized())
+    if (!Py_IsInitialized()) {
-        py::initialize_interpreter(false, argc, _argv);
+        py::initialize_interpreter(true, argc, _argv);
+    } else {
+        // pybind doesn't provide a way to set sys.argv if not initializing the
+        // interpreter, so we have to do that manually if it's already running.
+        py::list py_argv;
+        auto sys = py::module::import("sys");
+        if (py::hasattr(sys, "argv")) {
+            // sys.argv already exists, so grab that.
+            py_argv = sys.attr("argv");
+        } else {
+            // sys.argv doesn't exist, so create it.
+            sys.add_object("argv", py_argv);
+        }
+        // Clear out argv just in case it has something in it.
+        py_argv.attr("clear")();
+
+        // Fill it with our argvs.
+        for (int i = 0; i < argc; i++)
+            py_argv.append(_argv[i]);
+    }
 
     auto importer = py::module_::import("importer");
     importer.attr("install")();