new file mode 100644
--- /dev/null
+++ b/m4/c-stack.m4
@@ -0,0 +1,136 @@
+# Check prerequisites for compiling lib/c-stack.c.
+
+# Copyright (C) 2002 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+# 02111-1307, USA.
+
+# Written by Paul Eggert.
+
+AC_DEFUN([AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC],
+  [# for STACK_DIRECTION
+   AC_REQUIRE([AC_FUNC_ALLOCA])
+
+   AC_CACHE_CHECK([for working C stack overflow detection],
+     ac_cv_sys_xsi_stack_overflow_heuristic,
+     [AC_TRY_RUN(
+	[
+	 #include <signal.h>
+	 #include <ucontext.h>
+
+	 static union
+	 {
+	   char buffer[SIGSTKSZ];
+	   long double ld;
+	   long u;
+	   void *p;
+	 } alternate_signal_stack;
+
+	 #if STACK_DIRECTION
+	 # define find_stack_direction(ptr) STACK_DIRECTION
+	 #else
+	 static int
+	 find_stack_direction (char const *addr)
+	 {
+	   char dummy;
+	   return (! addr ? find_stack_direction (&dummy)
+		   : addr < &dummy ? 1 : -1);
+	 }
+	 #endif
+
+	 static void
+	 segv_handler (int signo, siginfo_t *info, void *context)
+	 {
+	   if (0 < info->si_code)
+	     {
+	       ucontext_t const *user_context = context;
+	       char const *stack_min = user_context->uc_stack.ss_sp;
+	       size_t stack_size = user_context->uc_stack.ss_size;
+	       char const *faulting_address = info->si_addr;
+	       size_t s = faulting_address - stack_min;
+	       size_t page_size = sysconf (_SC_PAGESIZE);
+	       if (find_stack_direction (0) < 0)
+		 s += page_size;
+	       if (s < stack_size + page_size)
+		 _exit (0);
+	     }
+
+	   _exit (1);
+	 }
+
+	 static int
+	 c_stack_action (void)
+	 {
+	   stack_t st;
+	   struct sigaction act;
+	   int r;
+
+	   st.ss_flags = 0;
+	   st.ss_sp = alternate_signal_stack.buffer;
+	   st.ss_size = sizeof alternate_signal_stack.buffer;
+	   r = sigaltstack (&st, 0);
+	   if (r != 0)
+	     return r;
+
+	   sigemptyset (&act.sa_mask);
+	   act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND | SA_SIGINFO;
+	   act.sa_sigaction = segv_handler;
+	   return sigaction (SIGSEGV, &act, 0);
+	 }
+
+	 static int
+	 recurse (char *p)
+	 {
+	   char array[500];
+	   array[0] = 1;
+	   return *p + recurse (array);
+	 }
+
+	 int
+	 main (void)
+	 {
+	   c_stack_action ();
+	   return recurse ("\1");
+	 }
+	],
+	[ac_cv_sys_xsi_stack_overflow_heuristic=yes],
+	[ac_cv_sys_xsi_stack_overflow_heuristic=no],
+	[ac_cv_sys_xsi_stack_overflow_heuristic=cross-compiling])])
+
+   if test $ac_cv_sys_xsi_stack_overflow_heuristic = yes; then
+     AC_DEFINE(HAVE_XSI_STACK_OVERFLOW_HEURISTIC, 1,
+       [Define to 1 if extending the stack slightly past the limit causes
+	a SIGSEGV, and an alternate stack can be established with sigaltstack,
+	and the signal handler is passed a context that specifies the
+	run time stack.  This behavior is defined by POSIX 1003.1-2001
+        with the X/Open System Interface (XSI) option
+	and is a standardized way to implement a SEGV-based stack
+        overflow detection heuristic.])
+   fi])
+
+
+AC_DEFUN([jm_PREREQ_C_STACK],
+  [AC_REQUIRE([AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC])
+
+   # for STACK_DIRECTION
+   AC_REQUIRE([AC_FUNC_ALLOCA])
+
+   AC_CHECK_FUNCS(getcontext sigaltstack)
+   AC_CHECK_DECLS([getcontext], , , [#include <ucontext.h>])
+   AC_CHECK_DECLS([sigaltstack], , , [#include <signal.h>])
+
+   AC_CHECK_HEADERS(sys/resource.h ucontext.h unistd.h)
+
+   AC_CHECK_TYPES([stack_t], , , [#include <signal.h>])])