1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
2
3 #pragma once
4
5 #include "alloc-util.h"
6 #include "macro.h"
7
8 /* A framework for registering static variables that shall be freed on shutdown of a process. It's a bit like gcc's
9 * destructor attribute, but allows us to precisely schedule when we want to free the variables. This is supposed to
10 * feel a bit like the gcc cleanup attribute, but for static variables. Note that this does not work for static
11 * variables declared in .so's, as the list is private to the same linking unit. But maybe that's a good thing. */
12
13 typedef struct StaticDestructor {
14 void *data;
15 free_func_t destroy;
16 } StaticDestructor;
17
18 #define STATIC_DESTRUCTOR_REGISTER(variable, func) \
19 _STATIC_DESTRUCTOR_REGISTER(UNIQ, variable, func)
20
21 #define _STATIC_DESTRUCTOR_REGISTER(uq, variable, func) \
22 /* Type-safe destructor */ \
23 static void UNIQ_T(static_destructor_wrapper, uq)(void *p) { \
24 typeof(variable) *q = p; \
25 func(q); \
26 } \
27 /* Older compilers don't know "retain" attribute. */ \
28 _Pragma("GCC diagnostic ignored \"-Wattributes\"") \
29 /* The actual destructor structure we place in a special section to find it. */ \
30 _section_("SYSTEMD_STATIC_DESTRUCT") \
31 /* Use pointer alignment, since that is apparently what gcc does for static variables. */ \
32 _alignptr_ \
33 /* Make sure this is not dropped from the image despite not being explicitly referenced. */ \
34 _used_ \
35 /* Prevent garbage collection by the linker. */ \
36 _retain_ \
37 /* Make sure that AddressSanitizer doesn't pad this variable: we want everything in this section
38 * packed next to each other so that we can enumerate it. */ \
39 _variable_no_sanitize_address_ \
40 static const StaticDestructor UNIQ_T(static_destructor_entry, uq) = { \
41 .data = &(variable), \
42 .destroy = UNIQ_T(static_destructor_wrapper, uq), \
43 }
44
45 /* Beginning and end of our section listing the destructors. We define these as weak as we want this to work
46 * even if no destructors are defined and the section is missing. */
47 extern const struct StaticDestructor _weak_ __start_SYSTEMD_STATIC_DESTRUCT[];
48 extern const struct StaticDestructor _weak_ __stop_SYSTEMD_STATIC_DESTRUCT[];
49
50 /* The function to destroy everything. (Note that this must be static inline, as it's key that it remains in
51 * the same linking unit as the variables we want to destroy.) */
static_destruct(void)52 static inline void static_destruct(void) {
53 const StaticDestructor *d;
54
55 if (!__start_SYSTEMD_STATIC_DESTRUCT)
56 return;
57
58 d = ALIGN_TO_PTR(__start_SYSTEMD_STATIC_DESTRUCT, sizeof(void*));
59 while (d < __stop_SYSTEMD_STATIC_DESTRUCT) {
60 d->destroy(d->data);
61 d = ALIGN_TO_PTR(d + 1, sizeof(void*));
62 }
63 }
64