trace: extract stap_escape() function for reuse

SystemTap reserved words sometimes conflict with QEMU variable names.
We escape them to prevent conflicts.

Move escaping into its own function so the next patch can reuse it.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

scripts/tracetool/format/stap.py

@@ -27,6 +27,13 @@
     )
 
 
+def stap_escape(identifier):
+    # Append underscore to reserved keywords
+    if identifier in RESERVED_WORDS:
+        return identifier + '_'
+    return identifier
+
+
 def generate(events, backend):
     events = [e for e in events
               if "disable" not in e.properties]
@@ -45,9 +52,7 @@ def generate(events, backend):
         i = 1
         if len(e.args) > 0:
             for name in e.args.names():
-                # Append underscore to reserved keywords
-                if name in RESERVED_WORDS:
-                    name += '_'
+                name = stap_escape(name)
                 out('  %s = $arg%d;' % (name, i))
                 i += 1