plugin-constructors: Add script to generate constructor registration

Using a Python script so this works in cross-compilation situations.

src/libstrongswan/Makefile.am

@@ -195,6 +195,7 @@ endif
 EXTRA_DIST = \
 asn1/oid.txt asn1/oid.pl \
 crypto/proposal/proposal_keywords_static.txt \
+plugins/plugin_constructors.py \
 Android.mk
 
 BUILT_SOURCES = \

src/libstrongswan/plugins/plugin_constructors.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2017 Tobias Brunner
+# HSR Hochschule fuer Technik Rapperswil
+#
+# This program is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by the
+# Free Software Foundation; either version 2 of the License, or (at your
+# option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+# or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+# for more details.
+
+import sys
+from argparse import ArgumentParser
+
+def generate_output(plugins):
+	"""Generate a source file containing plugin constructor registrations"""
+	print("/**")
+	print(" * Register plugin constructors for static libraries")
+	print(" * Created by {0}".format(__file__))
+	print(" */")
+	print("")
+	print("#include <plugins/plugin.h>")
+	print("#include <plugins/plugin_loader.h>")
+	print("")
+
+	for plugin in plugins:
+		print("plugin_t *{0}_plugin_create();".format(plugin.replace('-', '_')))
+
+	print("")
+	print("static void register_plugins() __attribute__ ((constructor));")
+	print("static void register_plugins()")
+	print("{")
+
+	for plugin in plugins:
+		print('	plugin_constructor_register("{0}", {1}_plugin_create);'.format(plugin, plugin.replace('-', '_')))
+
+	print("}")
+
+	print("")
+	print("static void unregister_plugins() __attribute__ ((destructor));")
+	print("static void unregister_plugins()")
+	print("{")
+
+	for plugin in plugins:
+		print('	plugin_constructor_register("{0}", NULL);'.format(plugin))
+
+	print("}")
+	print("")
+
+parser = ArgumentParser(description = "Generate constructor registration for a list of plugins")
+parser.add_argument('plugins', metavar="plugin", nargs="*",
+					help = "name of a plugin for which to generate constructor registration")
+
+
+args = parser.parse_args()
+generate_output(args.plugins);