# 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.

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;
	   uintmax_t 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([jm_AC_TYPE_UINTMAX_T])
   AC_REQUIRE([AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC])

   # for STACK_DIRECTION
   AC_REQUIRE([AC_FUNC_ALLOCA])

   AC_CHECK_HEADERS(unistd.h)

   AC_CHECK_TYPES([siginfo_t, stack_t], , , [#include <signal.h>])])