path: root/m4/c-stack.m4

# Check prerequisites for compiling lib/c-stack.c.

# Copyright (C) 2002, 2003, 2004, 2008, 2009 Free Software Foundation, Inc.
# This file is free software; the Free Software Foundation
# gives unlimited permission to copy and/or distribute it,
# with or without modifications, as long as this notice is preserved.

# Written by Paul Eggert.

# serial 9

AC_DEFUN([AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC],
  [# for STACK_DIRECTION
   AC_REQUIRE([AC_FUNC_ALLOCA])
   AC_REQUIRE([AC_CANONICAL_HOST])
   AC_CHECK_FUNCS_ONCE([setrlimit])
   AC_CHECK_HEADERS_ONCE([ucontext.h])

   dnl List of signals that are sent when an invalid virtual memory address
   dnl is accessed, or when the stack overflows.
   dnl Either { SIGSEGV } or { SIGSEGV, SIGBUS }.
   case "$host_os" in
     sunos4* | freebsd* | dragonfly* | openbsd* | netbsd* | kfreebsd* | knetbsd*) # BSD systems
       FAULT_YIELDS_SIGBUS=1 ;;
     hpux*) # HP-UX
       FAULT_YIELDS_SIGBUS=1 ;;
     macos* | darwin*) # MacOS X
       FAULT_YIELDS_SIGBUS=1 ;;
     gnu*) # Hurd
       FAULT_YIELDS_SIGBUS=1 ;;
     *)
       FAULT_YIELDS_SIGBUS=0 ;;
   esac
   AC_DEFINE_UNQUOTED([FAULT_YIELDS_SIGBUS], [$FAULT_YIELDS_SIGBUS],
     [Define to 1 if an invalid memory address access may yield a SIGBUS.])

   AC_CACHE_CHECK([for working C stack overflow detection],
     [ac_cv_sys_stack_overflow_works],
     [AC_TRY_RUN(
	[
	 #include <unistd.h>
	 #include <signal.h>
	 #if HAVE_SETRLIMIT
	 # include <sys/types.h>
	 # include <sys/time.h>
	 # include <sys/resource.h>
	 #endif
	 #ifndef SIGSTKSZ
	 # define SIGSTKSZ 16384
	 #endif

	 static union
	 {
	   char buffer[2 * SIGSTKSZ];
	   long double ld;
	   long u;
	   void *p;
	 } alternate_signal_stack;

	 static void
	 segv_handler (int signo)
	 {
	   _exit (0);
	 }

	 static int
	 c_stack_action ()
	 {
	   stack_t st;
	   struct sigaction act;
	   int r;

	   st.ss_flags = 0;
	   /* Use the midpoint to avoid Irix sigaltstack bug.  */
	   st.ss_sp = alternate_signal_stack.buffer + SIGSTKSZ;
	   st.ss_size = SIGSTKSZ;
	   r = sigaltstack (&st, 0);
	   if (r != 0)
	     return r;

	   sigemptyset (&act.sa_mask);
	   act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND;
	   act.sa_handler = segv_handler;
	   #if FAULT_YIELDS_SIGBUS
	   if (sigaction (SIGBUS, &act, 0) < 0)
	     return -1;
	   #endif
	   return sigaction (SIGSEGV, &act, 0);
	 }
	 static volatile int *
	 recurse_1 (volatile int n, volatile int *p)
	 {
	   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 ()
	 {
	   #if HAVE_SETRLIMIT && defined RLIMIT_STACK
	   /* Before starting the endless recursion, try to be friendly
	      to the user's machine.  On some Linux 2.2.x systems, there
	      is no stack limit for user processes at all.  We don't want
	      to kill such systems.  */
	   struct rlimit rl;
	   rl.rlim_cur = rl.rlim_max = 0x100000; /* 1 MB */
	   setrlimit (RLIMIT_STACK, &rl);
	   #endif

	   return c_stack_action () || recurse (0);
	 }
	],
	[ac_cv_sys_stack_overflow_works=yes],
	[ac_cv_sys_stack_overflow_works=no],
	[ac_cv_sys_stack_overflow_works=cross-compiling])])

  if test $ac_cv_sys_stack_overflow_works = yes; then
   AC_DEFINE([HAVE_STACK_OVERFLOW_HANDLING], [1],
     [Define to 1 if extending the stack slightly past the limit causes
      a SIGSEGV which can be handled on an alternate stack established
      with sigaltstack.])

    dnl The ss_sp field of a stack_t is, according to POSIX, the lowest address
    dnl of the memory block designated as an alternate stack. But IRIX 5.3
    dnl interprets it as the highest address!
    AC_CACHE_CHECK([for correct stack_t interpretation],
      [gl_cv_sigaltstack_low_base], [
      AC_RUN_IFELSE([
	AC_LANG_SOURCE([[
#include <stdlib.h>
#include <signal.h>
#if HAVE_SYS_SIGNAL_H
# include <sys/signal.h>
#endif
#ifndef SIGSTKSZ
# define SIGSTKSZ 16384
#endif
volatile char *stack_lower_bound;
volatile char *stack_upper_bound;
static void check_stack_location (volatile char *addr)
{
  if (addr >= stack_lower_bound && addr <= stack_upper_bound)
    exit (0);
  else
    exit (1);
}
static void stackoverflow_handler (int sig)
{
  char dummy;
  check_stack_location (&dummy);
}
int main ()
{
  char mystack[2 * SIGSTKSZ];
  stack_t altstack;
  struct sigaction action;
  /* Install the alternate stack.  */
  altstack.ss_sp = mystack + SIGSTKSZ;
  altstack.ss_size = SIGSTKSZ;
  stack_lower_bound = (char *) altstack.ss_sp;
  stack_upper_bound = (char *) altstack.ss_sp + altstack.ss_size - 1;
  altstack.ss_flags = 0; /* no SS_DISABLE */
  if (sigaltstack (&altstack, NULL) < 0)
    exit (2);
  /* Install the SIGSEGV handler.  */
  sigemptyset (&action.sa_mask);
  action.sa_handler = &stackoverflow_handler;
  action.sa_flags = SA_ONSTACK;
  if (sigaction (SIGSEGV, &action, (struct sigaction *) NULL) < 0)
    exit(3);
  /* Provoke a SIGSEGV.  */
  raise (SIGSEGV);
  exit (3);
}]])],
      [gl_cv_sigaltstack_low_base=yes],
      [gl_cv_sigaltstack_low_base=no],
      [gl_cv_sigaltstack_low_base=cross-compiling])])
   if test "$gl_cv_sigaltstack_low_base" = no; then
      AC_DEFINE([SIGALTSTACK_SS_REVERSED], [1],
	[Define if sigaltstack() interprets the stack_t.ss_sp field
	 incorrectly, as the highest address of the alternate stack range
	 rather than as the lowest address.])
    fi

   AC_CACHE_CHECK([for precise C stack overflow detection],
     ac_cv_sys_xsi_stack_overflow_heuristic,
     [AC_TRY_RUN(
	[
	 #include <unistd.h>
	 #include <signal.h>
	 #if HAVE_UCONTEXT_H
	 # include <ucontext.h>
	 #endif
	 #if HAVE_SETRLIMIT
	 # include <sys/types.h>
	 # include <sys/time.h>
	 # include <sys/resource.h>
	 #endif
	 #ifndef SIGSTKSZ
	 # define SIGSTKSZ 16384
	 #endif

	 static union
	 {
	   char buffer[2 * 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)
	     {
	       /* For XSI heuristics to work, we need uc_stack to describe
		  the interrupted stack (as on Solaris), and not the
		  currently executing stack (as on Linux).  */
	       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 ()
	 {
	   stack_t st;
	   struct sigaction act;
	   int r;

	   st.ss_flags = 0;
	   /* Use the midpoint to avoid Irix sigaltstack bug.  */
	   st.ss_sp = alternate_signal_stack.buffer + SIGSTKSZ;
	   st.ss_size = SIGSTKSZ;
	   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;
	   #if FAULT_YIELDS_SIGBUS
	   if (sigaction (SIGBUS, &act, 0) < 0)
	     return -1;
	   #endif
	   return sigaction (SIGSEGV, &act, 0);
	 }
	 static volatile int *
	 recurse_1 (volatile int n, volatile int *p)
	 {
	   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 ()
	 {
	   #if HAVE_SETRLIMIT && defined RLIMIT_STACK
	   /* Before starting the endless recursion, try to be friendly
	      to the user's machine.  On some Linux 2.2.x systems, there
	      is no stack limit for user processes at all.  We don't want
	      to kill such systems.  */
	   struct rlimit rl;
	   rl.rlim_cur = rl.rlim_max = 0x100000; /* 1 MB */
	   setrlimit (RLIMIT_STACK, &rl);
	   #endif

	   return c_stack_action () || recurse (0);
	 }
	],
	[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
  fi])


AC_DEFUN([gl_PREREQ_C_STACK],
  [AC_REQUIRE([AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC])
   AC_REQUIRE([gl_LIBSIGSEGV])

   # for STACK_DIRECTION
   AC_REQUIRE([AC_FUNC_ALLOCA])

   AC_CHECK_FUNCS_ONCE([sigaltstack])
   AC_CHECK_DECLS([sigaltstack], , , [#include <signal.h>])

   AC_CHECK_HEADERS_ONCE([unistd.h ucontext.h])

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

   dnl c-stack does not need -lsigsegv if the system has XSI heuristics.
   if test "$gl_cv_lib_sigsegv" = yes \
       && test $"ac_cv_sys_xsi_stack_overflow_heuristic" != yes ; then
     AC_SUBST([LIBCSTACK], [$LIBSIGSEGV])
     AC_SUBST([LTLIBCSTACK], [$LTLIBSIGSEGV])
   fi
])

AC_DEFUN([gl_C_STACK],
[
  dnl Prerequisites of lib/c-stack.c.
  gl_PREREQ_C_STACK
])