X-Git-Url: https://diplodocus.org/git/nmh/blobdiff_plain/38615191e71744b066425e0c44412b62dbe49cc2..f5bfa5864d2feef66948fde764c376b7a9f8b839:/sbr/done.c

diff --git a/sbr/done.c b/sbr/done.c
index 938fdb2d..cd76fac5 100644
--- a/sbr/done.c
+++ b/sbr/done.c
@@ -1,8 +1,4 @@
-
-/*
- * done.c -- terminate the program
- *
- * $Id$
+/* done.c -- terminate the program
  *
  * This code is Copyright (c) 2002, by the authors of nmh.  See the
  * COPYRIGHT file in the root directory of the nmh distribution for
@@ -11,4 +7,39 @@
 
 #include <h/mh.h>
 
-void (*done) (int) = exit;
+/* It's undefined behaviour in C99 to convert from a function pointer to
+ * a data-object pointer, e.g. void pointer.  gcc's -pedantic warns of
+ * this and can stop compilation.  POSIX requires the operation however,
+ * e.g. for dlsym(3), and so we know it's safe on POSIX platforms, e.g.
+ * the pointers are of the same size.  Thus use a union to subvert gcc's
+ * check.  The function-pointer equivalent of a void pointer is any
+ * function-pointer type as all function pointers are defined to be
+ * convertible from one another;  use the simplest available. */
+typedef union {
+    void *v;
+    void (*f)(void);
+} generic_pointer;
+
+static void (*altexit)(int) NORETURN = exit;
+
+/* set_done changes the path of done() from exit(3), or back to exit(3).
+ * Anything else will work, but a standard-error warning will report the
+ * old non-exit() value has been trampled. */
+void
+set_done(void (*new)(int) NORETURN)
+{
+    generic_pointer gpo, gpn;
+
+    if (altexit != exit && new != exit) {
+        gpo.f = (void (*)(void))altexit;
+        gpn.f = (void (*)(void))new;
+        inform("altexit trampled: %p %p", gpo.v, gpn.v);
+    }
+    altexit = new;
+}
+
+void NORETURN
+done(int status)
+{
+    (*altexit)(status);
+}