--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2008-09-23  Eric Blake  <ebb9@byu.net>
 
+	c-stack: avoid compiler optimizations when provoking overflow
+	* m4/c-stack.m4 (AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC): Make
+	recursion harder to optimize, to ensure a stack overflow occurs.
+	* tests/test-c-stack.c (recurse): Likewise.
+	Borrowed from libsigsegv.
+
 	c-stack: work around Irix sigaltstack bug
 	* m4/c-stack.m4 (AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC): Check
 	whether sigaltstack uses wrong end of stack_t (copied in part from

--- a/m4/c-stack.m4
+++ b/m4/c-stack.m4
@@ -64,15 +64,19 @@
 	   act.sa_handler = segv_handler;
 	   return sigaction (SIGSEGV, &act, 0);
 	 }
-
-	 static int
-	 recurse (char *p)
+	 static volatile int *
+	 recurse_1 (volatile int n, volatile int *p)
 	 {
-	   char array[500];
-	   array[0] = 1;
-	   return *p + recurse (array);
+	   if (n >= 0)
+	     *recurse_1 (n + 1, p) += n;
+	   return p;
 	 }
-
+	 static int
+	 recurse (volatile int n)
+	 {
+	   int sum = 0;
+	   return *recurse_1 (n, &sum);
+	 }
 	 int
 	 main ()
 	 {
@@ -86,7 +90,7 @@
 	   setrlimit (RLIMIT_STACK, &rl);
 	   #endif
 
-	   return c_stack_action () || recurse ("\1");
+	   return c_stack_action () || recurse (0);
 	 }
 	],
 	[ac_cv_sys_stack_overflow_works=yes],
@@ -242,15 +246,19 @@
 	   act.sa_sigaction = segv_handler;
 	   return sigaction (SIGSEGV, &act, 0);
 	 }
-
-	 static int
-	 recurse (char *p)
+	 static volatile int *
+	 recurse_1 (volatile int n, volatile int *p)
 	 {
-	   char array[500];
-	   array[0] = 1;
-	   return *p + recurse (array);
+	   if (n >= 0)
+	     *recurse_1 (n + 1, p) += n;
+	   return p;
 	 }
-
+	 static int
+	 recurse (volatile int n)
+	 {
+	   int sum = 0;
+	   return *recurse_1 (n, &sum);
+	 }
 	 int
 	 main ()
 	 {
@@ -264,7 +272,7 @@
 	   setrlimit (RLIMIT_STACK, &rl);
 	   #endif
 
-	   return c_stack_action () || recurse ("\1");
+	   return c_stack_action () || recurse (0);
 	 }
 	],
 	[ac_cv_sys_xsi_stack_overflow_heuristic=yes],

--- a/tests/test-c-stack.c
+++ b/tests/test-c-stack.c
@@ -41,15 +41,22 @@
     }									     \
   while (0)
 
-static long
-recurse (char *p)
+char *program_name;
+
+static volatile int *
+recurse_1 (volatile int n, volatile int *p)
 {
-  char array[500];
-  array[0] = 1;
-  return *p + recurse (array);
+  if (n >= 0)
+    *recurse_1 (n + 1, p) += n;
+  return p;
 }
 
-char *program_name;
+static int
+recurse (volatile int n)
+{
+  int sum = 0;
+  return *recurse_1 (n, &sum);
+}
 
 int
 main (int argc, char **argv)
@@ -72,8 +79,9 @@
 	  exit_failure = 77;
 	  ++*argv[argc]; /* Intentionally dereference NULL.  */
 	}
-      return recurse ("\1");
+      return recurse (0);
     }
+  fputs ("skipping test: ", stderr);
   perror ("c_stack_action");
   return 77;
 }