stdlib/cxa_atexit.c

   1 /* Copyright (C) 1999-2022 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 <sysdep.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 #ifdef PTR_MANGLE
  53   PTR_MANGLE (func);
  54 #endif
  55   new->func.cxa.fn = (void (*) (void *, int)) func;
  56   new->func.cxa.arg = arg;
  57   new->func.cxa.dso_handle = d;
  58   new->flavor = ef_cxa;
  59   __libc_lock_unlock (__exit_funcs_lock);
  60   return 0;
  61 }
  62
  63
  64 /* Register a function to be called by exit or when a shared library
  65    is unloaded.  This function is only called from code generated by
  66    the C++ compiler.  */
  67 int
  68 __cxa_atexit (void (*func) (void *), void *arg, void *d)
  69 {
  70   return __internal_atexit (func, arg, d, &__exit_funcs);
  71 }
  72 libc_hidden_def (__cxa_atexit)
  73
  74
  75 static struct exit_function_list initial;
  76 struct exit_function_list *__exit_funcs = &initial;
  77 uint64_t __new_exitfn_called;
  78
  79 /* Must be called with __exit_funcs_lock held.  */
  80 struct exit_function *
  81 __new_exitfn (struct exit_function_list **listp)
  82 {
  83   struct exit_function_list *p = NULL;
  84   struct exit_function_list *l;
  85   struct exit_function *r = NULL;
  86   size_t i = 0;
  87
  88   if (__exit_funcs_done)
  89     /* Exit code is finished processing all registered exit functions,
  90        therefore we fail this registration.  */
  91     return NULL;
  92
  93   for (l = *listp; l != NULL; p = l, l = l->next)
  94     {
  95       for (i = l->idx; i > 0; --i)
  96         if (l->fns[i - 1].flavor != ef_free)
  97           break;
  98
  99       if (i > 0)
 100         break;
 101
 102       /* This block is completely unused.  */
 103       l->idx = 0;
 104     }
 105
 106   if (l == NULL || i == sizeof (l->fns) / sizeof (l->fns[0]))
 107     {
 108       /* The last entry in a block is used.  Use the first entry in
 109          the previous block if it exists.  Otherwise create a new one.  */
 110       if (p == NULL)
 111         {
 112           assert (l != NULL);
 113           p = (struct exit_function_list *)
 114             calloc (1, sizeof (struct exit_function_list));
 115           if (p != NULL)
 116             {
 117               p->next = *listp;
 118               *listp = p;
 119             }
 120         }
 121
 122       if (p != NULL)
 123         {
 124           r = &p->fns[0];
 125           p->idx = 1;
 126         }
 127     }
 128   else
 129     {
 130       /* There is more room in the block.  */
 131       r = &l->fns[i];
 132       l->idx = i + 1;
 133     }
 134
 135   /* Mark entry as used, but we don't know the flavor now.  */
 136   if (r != NULL)
 137     {
 138       r->flavor = ef_us;
 139       ++__new_exitfn_called;
 140     }
 141
 142   return r;
 143 }