1 files changed, 105 insertions, 0 deletions
diff --git a/src/basic/static-destruct.h b/src/basic/static-destruct.h
new file mode 100644
index 0000000..2ffc651
--- /dev/null
+++ b/src/basic/static-destruct.h
@@ -0,0 +1,105 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#pragma once
+
+#include "alloc-util.h"
+#include "macro.h"
+#include "memory-util.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. */
+
+#define _common_static_destruct_attrs_                                  \
+        /* 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_
+
+typedef enum StaticDestructorType {
+        STATIC_DESTRUCTOR_SIMPLE,
+        STATIC_DESTRUCTOR_ARRAY,
+        _STATIC_DESTRUCTOR_TYPE_MAX,
+        _STATIC_DESTRUCTOR_INVALID = -EINVAL,
+} StaticDestructorType;
+
+typedef struct SimpleCleanup {
+        void *data;
+        free_func_t destroy;
+} SimpleCleanup;
+
+typedef struct StaticDestructor {
+        StaticDestructorType type;
+        union {
+                SimpleCleanup simple;
+                ArrayCleanup array;
+        };
+} 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);                                                \
+        }                                                               \
+        _common_static_destruct_attrs_                                  \
+        static const StaticDestructor UNIQ_T(static_destructor_entry, uq) = { \
+                .type = STATIC_DESTRUCTOR_SIMPLE,                       \
+                .simple.data = &(variable),                             \
+                .simple.destroy = UNIQ_T(static_destructor_wrapper, uq), \
+        }
+
+#define STATIC_ARRAY_DESTRUCTOR_REGISTER(a, n, func)            \
+        _STATIC_ARRAY_DESTRUCTOR_REGISTER(UNIQ, a, n, func)
+
+#define _STATIC_ARRAY_DESTRUCTOR_REGISTER(uq, a, n, func)               \
+        /* Type-safety check */                                         \
+        _unused_ static void (* UNIQ_T(static_destructor_wrapper, uq))(typeof(a[0]) *x, size_t y) = (func); \
+        _common_static_destruct_attrs_                                  \
+        static const StaticDestructor UNIQ_T(static_destructor_entry, uq) = { \
+                .type = STATIC_DESTRUCTOR_ARRAY,                        \
+                .array.parray = (void**) &(a),                          \
+                .array.pn = &(n),                                       \
+                .array.pfunc = (free_array_func_t) (func),              \
+        };
+
+/* 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 StaticDestructor _weak_ __start_SYSTEMD_STATIC_DESTRUCT[];
+extern const 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) {
+        if (!__start_SYSTEMD_STATIC_DESTRUCT)
+                return;
+
+        for (const StaticDestructor *d = ALIGN_PTR(__start_SYSTEMD_STATIC_DESTRUCT);
+             d < __stop_SYSTEMD_STATIC_DESTRUCT;
+             d = ALIGN_PTR(d + 1))
+                switch (d->type) {
+                case STATIC_DESTRUCTOR_SIMPLE:
+                        d->simple.destroy(d->simple.data);
+                        break;
+
+                case STATIC_DESTRUCTOR_ARRAY:
+                        array_cleanup(&d->array);
+                        break;
+
+                default:
+                        assert_not_reached();
+                }
+}