diplodocus.org Git - nmh/blob - sbr/done.c

   1 /* done.c -- terminate the program
   2  *
   3  * This code is Copyright (c) 2002, by the authors of nmh.  See the
   4  * COPYRIGHT file in the root directory of the nmh distribution for
   5  * complete copyright information.
   6  */
   7
   8 #include <h/mh.h>
   9
  10 /* It's undefined behaviour in C99 to convert from a function pointer to
  11  * a data-object pointer, e.g. void pointer.  gcc's -pedantic warns of
  12  * this and can stop compilation.  POSIX requires the operation however,
  13  * e.g. for dlsym(3), and so we know it's safe on POSIX platforms, e.g.
  14  * the pointers are of the same size.  Thus use a union to subvert gcc's
  15  * check.  The function-pointer equivalent of a void pointer is any
  16  * function-pointer type as all function pointers are defined to be
  17  * convertible from one another;  use the simplest available. */
  18 typedef union {
  19     void *v;
  20     void (*f)(void);
  21 } generic_pointer;
  22
  23 static void (*altexit)(int) NORETURN = exit;
  24
  25 /* set_done changes the path of done() from exit(3), or back to exit(3).
  26  * Anything else will work, but a standard-error warning will report the
  27  * old non-exit() value has been trampled. */
  28 void
  29 set_done(void (*new)(int) NORETURN)
  30 {
  31     generic_pointer gpo, gpn;
  32
  33     if (altexit != exit && new != exit) {
  34         gpo.f = (void (*)(void))altexit;
  35         gpn.f = (void (*)(void))new;
  36         inform("altexit trampled: %p %p", gpo.v, gpn.v);
  37     }
  38     altexit = new;
  39 }
  40
  41 void NORETURN
  42 done(int status)
  43 {
  44     (*altexit)(status);
  45 }