1/* Copyright (C) 1999-2024 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <https://www.gnu.org/licenses/>. */
17
18#include <assert.h>
19#include <stdlib.h>
20#include <stdint.h>
21
22#include <libc-lock.h>
23#include "exit.h"
24#include <pointer_guard.h>
25
26#undef __cxa_atexit
27
28/* See concurrency notes in stdlib/exit.h where this lock is declared. */
29__libc_lock_define_initialized (, __exit_funcs_lock)
30
31
32int
33attribute_hidden
34__internal_atexit (void (*func) (void *), void *arg, void *d,
35 struct exit_function_list **listp)
36{
37 struct exit_function *new;
38
39 /* As a QoI issue we detect NULL early with an assertion instead
40 of a SIGSEGV at program exit when the handler is run (bug 20544). */
41 assert (func != NULL);
42
43 __libc_lock_lock (__exit_funcs_lock);
44 new = __new_exitfn (listp);
45
46 if (new == NULL)
47 {
48 __libc_lock_unlock (__exit_funcs_lock);
49 return -1;
50 }
51
52 PTR_MANGLE (func);
53 new->func.cxa.fn = (void (*) (void *, int)) func;
54 new->func.cxa.arg = arg;
55 new->func.cxa.dso_handle = d;
56 new->flavor = ef_cxa;
57 __libc_lock_unlock (__exit_funcs_lock);
58 return 0;
59}
60
61
62/* Register a function to be called by exit or when a shared library
63 is unloaded. This function is only called from code generated by
64 the C++ compiler. */
65int
66__cxa_atexit (void (*func) (void *), void *arg, void *d)
67{
68 return __internal_atexit (func, arg, d, listp: &__exit_funcs);
69}
70libc_hidden_def (__cxa_atexit)
71
72
73static struct exit_function_list initial;
74struct exit_function_list *__exit_funcs = &initial;
75uint64_t __new_exitfn_called;
76
77/* Must be called with __exit_funcs_lock held. */
78struct exit_function *
79__new_exitfn (struct exit_function_list **listp)
80{
81 struct exit_function_list *p = NULL;
82 struct exit_function_list *l;
83 struct exit_function *r = NULL;
84 size_t i = 0;
85
86 if (__exit_funcs_done)
87 /* Exit code is finished processing all registered exit functions,
88 therefore we fail this registration. */
89 return NULL;
90
91 for (l = *listp; l != NULL; p = l, l = l->next)
92 {
93 for (i = l->idx; i > 0; --i)
94 if (l->fns[i - 1].flavor != ef_free)
95 break;
96
97 if (i > 0)
98 break;
99
100 /* This block is completely unused. */
101 l->idx = 0;
102 }
103
104 if (l == NULL || i == sizeof (l->fns) / sizeof (l->fns[0]))
105 {
106 /* The last entry in a block is used. Use the first entry in
107 the previous block if it exists. Otherwise create a new one. */
108 if (p == NULL)
109 {
110 assert (l != NULL);
111 p = (struct exit_function_list *)
112 calloc (nmemb: 1, size: sizeof (struct exit_function_list));
113 if (p != NULL)
114 {
115 p->next = *listp;
116 *listp = p;
117 }
118 }
119
120 if (p != NULL)
121 {
122 r = &p->fns[0];
123 p->idx = 1;
124 }
125 }
126 else
127 {
128 /* There is more room in the block. */
129 r = &l->fns[i];
130 l->idx = i + 1;
131 }
132
133 /* Mark entry as used, but we don't know the flavor now. */
134 if (r != NULL)
135 {
136 r->flavor = ef_us;
137 ++__new_exitfn_called;
138 }
139
140 return r;
141}
142

source code of glibc/stdlib/cxa_atexit.c