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

# Copyright (C) 2002-2004, 2008-2017 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 15

AC_DEFUN([AC_SYS_XSI_STACK_OVERFLOW_HEURISTIC],

  [

   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* | mirbsd* | netbsd* | kfreebsd* | knetbsd*) # BSD systems

       FAULT_YIELDS_SIGBUS=1 ;;

     hpux*) # HP-UX

       FAULT_YIELDS_SIGBUS=1 ;;

     macos* | darwin*) # Mac OS 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_RUN_IFELSE([AC_LANG_SOURCE(

           [[

            #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 1;

              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 2;

              #endif

              if (sigaction (SIGSEGV, &act, 0) < 0)

                return 3;

              return 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 ()

            {

              int result;

              #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

              result = c_stack_action ();

              if (result != 0)

                return result;

              return 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 (4);

}]])],

      [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_RUN_IFELSE([AC_LANG_SOURCE(

           [[

            #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 (4);

                }

              _exit (5);

            }

            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 1;

              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 2;

              #endif

              if (sigaction (SIGSEGV, &act, 0) < 0)

                return 3;

              return 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 ()

            {

              int result;

              #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

              result = c_stack_action ();

              if (result != 0)

                return result;

              return 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

])