1 files changed, 63 insertions, 0 deletions
diff --git a/src/basic/static-destruct.h b/src/basic/static-destruct.h
new file mode 100644
index 0000000..97baac7
--- /dev/null
+++ b/src/basic/static-destruct.h
@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#pragma once
+
+#include "alloc-util.h"
+#include "macro.h"
+
+/* A framework for registering static variables that shall be freed on shutdown of a process. It's a bit like gcc's
+ * destructor attribute, but allows us to precisely schedule when we want to free the variables. This is supposed to
+ * feel a bit like the gcc cleanup attribute, but for static variables. Note that this does not work for static
+ * variables declared in .so's, as the list is private to the same linking unit. But maybe that's a good thing. */
+
+typedef struct StaticDestructor {
+        void *data;
+        free_func_t destroy;
+} StaticDestructor;
+
+#define STATIC_DESTRUCTOR_REGISTER(variable, func) \
+        _STATIC_DESTRUCTOR_REGISTER(UNIQ, variable, func)
+
+#define _STATIC_DESTRUCTOR_REGISTER(uq, variable, func)                 \
+        /* Type-safe destructor */                                      \
+        static void UNIQ_T(static_destructor_wrapper, uq)(void *p) {    \
+                typeof(variable) *q = p;                                \
+                func(q);                                                \
+        }                                                               \
+        /* Older compilers don't know "retain" attribute. */            \
+        _Pragma("GCC diagnostic ignored \"-Wattributes\"")              \
+        /* The actual destructor structure we place in a special section to find it. */ \
+        _section_("SYSTEMD_STATIC_DESTRUCT")                            \
+        /* Use pointer alignment, since that is apparently what gcc does for static variables. */ \
+        _alignptr_                                                      \
+        /* Make sure this is not dropped from the image despite not being explicitly referenced. */ \
+        _used_                                                          \
+        /* Prevent garbage collection by the linker. */                 \
+        _retain_                                                        \
+        /* Make sure that AddressSanitizer doesn't pad this variable: we want everything in this section
+         * packed next to each other so that we can enumerate it. */     \
+        _variable_no_sanitize_address_                                  \
+        static const StaticDestructor UNIQ_T(static_destructor_entry, uq) = { \
+                .data = &(variable),                                    \
+                .destroy = UNIQ_T(static_destructor_wrapper, uq),       \
+        }
+
+/* Beginning and end of our section listing the destructors. We define these as weak as we want this to work
+ * even if no destructors are defined and the section is missing. */
+extern const struct StaticDestructor _weak_ __start_SYSTEMD_STATIC_DESTRUCT[];
+extern const struct StaticDestructor _weak_ __stop_SYSTEMD_STATIC_DESTRUCT[];
+
+/* The function to destroy everything. (Note that this must be static inline, as it's key that it remains in
+ * the same linking unit as the variables we want to destroy.) */
+static inline void static_destruct(void) {
+        const StaticDestructor *d;
+
+        if (!__start_SYSTEMD_STATIC_DESTRUCT)
+                return;
+
+        d = ALIGN_PTR(__start_SYSTEMD_STATIC_DESTRUCT);
+        while (d < __stop_SYSTEMD_STATIC_DESTRUCT) {
+                d->destroy(d->data);
+                d = ALIGN_PTR(d + 1);
+        }
+}