stdlib/cxa_atexit.c

   1 /* Copyright (C) 1999-2023 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
  32 int
  33 attribute_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.  */
  65 int
  66 __cxa_atexit (void (*func) (void *), void *arg, void *d)
  67 {
  68   return __internal_atexit (func, arg, d, &__exit_funcs);
  69 }
  70 libc_hidden_def (__cxa_atexit)
  71
  72
  73 static struct exit_function_list initial;
  74 struct exit_function_list *__exit_funcs = &initial;
  75 uint64_t __new_exitfn_called;
  76
  77 /* Must be called with __exit_funcs_lock held.  */
  78 struct 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 (1, 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 }