macro: add helper for module origin id

These need to be redefined in every module that we need to guard, so add
a macro

diff --git a/src/basic/origin-id.h b/src/basic/origin-id.h
new file mode 100644 (file)
index 0000000..c55b0a3
--- /dev/null
+++ b/src/basic/origin-id.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include <pthread.h>
+
+#include "random-util.h"
+
+/* This pattern needs to be repeated exactly in multiple modules, so macro it.
+ * To ensure an object is not passed into a different module (e.g.: when two shared objects statically
+ * linked to libsystemd get loaded in the same process, and the object created by one is passed to the
+ * other, see https://github.com/systemd/systemd/issues/27216), create a random static global random
+ * (mixed with PID, so that we can also check for reuse after fork) that is stored in the object and
+ * checked by public API on use. */
+#define _DEFINE_ORIGIN_ID_HELPERS(type, name, scope)                  \
+static uint64_t origin_id;                                            \
+                                                                      \
+static void origin_id_initialize(void) {                              \
+        origin_id = random_u64();                                     \
+}                                                                     \
+                                                                      \
+static uint64_t origin_id_query(void) {                               \
+        static pthread_once_t once = PTHREAD_ONCE_INIT;               \
+        assert_se(pthread_once(&once, origin_id_initialize) == 0);    \
+        return origin_id ^ getpid_cached();                           \
+}                                                                     \
+                                                                      \
+scope bool name##_origin_changed(type *p) {                           \
+        assert(p);                                                    \
+        return p->origin_id != origin_id_query();                     \
+}
+
+#define DEFINE_ORIGIN_ID_HELPERS(type, name)                          \
+        _DEFINE_ORIGIN_ID_HELPERS(type, name,);
+
+#define DEFINE_PRIVATE_ORIGIN_ID_HELPERS(type, name)                  \
+        _DEFINE_ORIGIN_ID_HELPERS(type, name, static);