unit-tests: Support testable functions on Windows, avoid weak GCC symbols

Instead of using weak symbols, we use dlsym() on Windows to find an arbitrary
symbol in libtest to detect its linkage. Instead of creating the associated
hashtable in the test runner, we maintain it in libstrongswan, making it
significantly simpler.

src/libstrongswan/utils/test.c

@@ -20,13 +20,23 @@
 /**
  * A collection of testable functions
  */
-hashtable_t *testable_functions;
+static hashtable_t *functions = NULL;
+
+#ifndef WIN32
+bool test_runner_available __attribute__((weak));
+#endif
 
 /**
- * The function that actually initializes the hash table above.  Provided
- * by the test runner.
+ * Check if we have libtest linkage and need testable functions
  */
-void testable_functions_create() __attribute__((weak));
+static bool has_libtest_linkage()
+{
+#ifdef WIN32
+	return dlsym(RTLD_DEFAULT, "test_runner_available");
+#else
+	return test_runner_available;
+#endif
+}
 
 /*
  * Described in header.
@@ -35,33 +45,48 @@ void testable_function_register(char *name, void *fn)
 {
 	bool old = FALSE;
 
-	if (!testable_functions_create)
-	{	/* not linked to the test runner */
-		return;
-	}
-	else if (!fn && !testable_functions)
-	{	/* ignore as testable_functions has already been destroyed */
-		return;
-	}
-
 	if (lib && lib->leak_detective)
 	{
 		old = lib->leak_detective->set_state(lib->leak_detective, FALSE);
 	}
-	if (!testable_functions)
+
+	if (has_libtest_linkage())
 	{
-		testable_functions_create();
-	}
-	if (fn)
-	{
-		testable_functions->put(testable_functions, name, fn);
-	}
-	else
-	{
-		testable_functions->remove(testable_functions, name);
+		if (!functions)
+		{
+			chunk_hash_seed();
+			functions = hashtable_create(hashtable_hash_str,
+										 hashtable_equals_str, 8);
+		}
+		if (fn)
+		{
+			functions->put(functions, name, fn);
+		}
+		else
+		{
+			functions->remove(functions, name);
+			if (functions->get_count(functions) == 0)
+			{
+				functions->destroy(functions);
+				functions = NULL;
+			}
+		}
 	}
+
 	if (lib && lib->leak_detective)
 	{
 		lib->leak_detective->set_state(lib->leak_detective, old);
 	}
 }
+
+/*
+ * Described in header.
+ */
+void* testable_function_get(char *name)
+{
+	if (functions)
+	{
+		return functions->get(functions, name);
+	}
+	return NULL;
+}