root/user/lib/libc/stdlib/exit.c

DEFINITIONS

1. exit
2. __exit_hack

   1 /*
   2  * Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
   3  *      The President and Fellows of Harvard College.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  */
  30 #include <stdlib.h>
  31 #include <unistd.h>
  33 /*
  34  * C standard function: exit process.
  35  */
  37 void
exit(int code)
  39 {
  40         /*
  41          * In a more complicated libc, this would call functions registered
  42          * with atexit() before calling the syscall to actually exit.
  43          */
_exit(code);
  46 }
  48 /*
  49  * The mips gcc we were using in 2001, and probably other versions as
  50  * well, knows more than is healthy: it knows without being told that
  51  * exit and _exit don't return.
  52  * 
  53  * This causes it to make foolish optimizations that cause broken
  54  * things to happen if _exit *does* return, as it does in the base
  55  * system (because it's unimplemented) and may also do if someone has
  56  * a bug.
  57  *
  58  * The way it works is that if _exit returns, execution falls into
  59  * whatever happens to come after exit(), with the registers set up in
  60  * such a way that when *that* function returns it actually ends up
  61  * calling itself again. This causes weird things to happen.
  62  *
  63  * This function has no purpose except to trap that
  64  * circumstance. Looping doing nothing is not entirely optimal, but
  65  * there's not much we *can* do, and it's better than jumping around
  66  * wildly as would happen if this function were removed.
  67  *
  68  * If you change this to loop calling _exit(), gcc "helpfully"
  69  * optimizes the loop away and the behavior reverts to that previously
  70  * described.
  71  */
  73 void __exit_hack(void);  /* avoid gcc warning */
  75 void
__exit_hack(void)
  77 {
  78         volatile int blah = 1;
  79         while (blah) {}
  80 }