Replace stackovf with gnulib c-stack.

* m4/gnulib.cache.m4: Import c-stack module.
* configure.ac (AC_CHECK_HEADERS_ONCE): Remove check for
siginfo.h, sys/wait.h.
(AC_CHECK_TYPES): Likewise for siginfo_t.
(AC_CHECK_MEMBERS): Likewise for sa_sigaction, ss_sp.
(AC_CHECK_FUNCS_ONCE): Likewise for sigaction, sigaltstack,
sigstack, sigvec, strerror.
(M4_cv_use_stackovf): Likewise for stack overflow detection.
* src/Makefile.am (m4_SOURCES): Don't build stackovf.c.
* src/stackovf.c: Delete.
* src/m4.h (setup_stackovf_trap): Delete.
* src/m4.c (stackovf_handler): Delete.
(main): Use c_stack_action instead of setup_stackovf_trap.  If
stack overflow is detectable, don't limit -L artificially.
(usage): Document unlimited default on supported systems.
* doc/m4.texinfo (Limits control): Document new default nesting
limit.
* NEWS: Document this change.

Signed-off-by: Eric Blake <ebb9@byu.net>

9 files changed, 43 insertions, 518 deletions

diff --git a/ChangeLog b/ChangeLog
index 4e196af0..8ce45459 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,25 @@
+2008-06-06  Eric Blake  <ebb9@byu.net>
+
+	Replace stackovf with gnulib c-stack.
+	* m4/gnulib.cache.m4: Import c-stack module.
+	* configure.ac (AC_CHECK_HEADERS_ONCE): Remove check for
+	siginfo.h, sys/wait.h.
+	(AC_CHECK_TYPES): Likewise for siginfo_t.
+	(AC_CHECK_MEMBERS): Likewise for sa_sigaction, ss_sp.
+	(AC_CHECK_FUNCS_ONCE): Likewise for sigaction, sigaltstack,
+	sigstack, sigvec, strerror.
+	(M4_cv_use_stackovf): Likewise for stack overflow detection.
+	* src/Makefile.am (m4_SOURCES): Don't build stackovf.c.
+	* src/stackovf.c: Delete.
+	* src/m4.h (setup_stackovf_trap): Delete.
+	* src/m4.c (stackovf_handler): Delete.
+	(main): Use c_stack_action instead of setup_stackovf_trap.  If
+	stack overflow is detectable, don't limit -L artificially.
+	(usage): Document unlimited default on supported systems.
+	* doc/m4.texinfo (Limits control): Document new default nesting
+	limit.
+	* NEWS: Document this change.
+
 2008-06-03  Eric Blake  <ebb9@byu.net>
 
 	Use progname module rather than rolling our own program_name.
diff --git a/NEWS b/NEWS
index 2a4ba93e..1014a917 100644
--- a/NEWS
+++ b/NEWS
@@ -9,6 +9,9 @@ Foundation, Inc.
    a macro.  This was most noticeable with `traceon(`traceon')', but
    would also happen in cases such as `foo(traceon(`foo'))'.
 
+** The `-L'/`--nesting-limit' command-line option now defaults to 0 for
+   unlimited on platforms that can detect and deal with stack overflow.
+
 ** A number of portability improvements inherited from gnulib.
 
 * Noteworthy changes in Version 1.4.11 (2008-04-02) [stable]
diff --git a/configure.ac b/configure.ac
index ea4e130c..3fb059b6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -32,27 +32,8 @@ AC_CONFIG_HEADERS([lib/config.h:lib/config.hin])
 AC_PROG_CC
 M4_EARLY
 
-AC_CHECK_HEADERS_ONCE([siginfo.h sys/wait.h])
-AC_CHECK_TYPES([siginfo_t], [], [],
-[[#include <signal.h>
-#if HAVE_SIGINFO_H
-# include <siginfo.h>
-#endif
-]])
-AC_CHECK_MEMBERS([struct sigaction.sa_sigaction], [], [],
-[[#include <signal.h>
-]])
-AC_CHECK_MEMBERS([stack_t.ss_sp], [], [],
-[[#include <signal.h>
-#if HAVE_SIGINFO_H
-# include <siginfo.h>
-#endif
-]])
-
 AC_TYPE_SIGNAL
 
-AC_CHECK_FUNCS_ONCE([sigaction sigaltstack sigstack sigvec strerror])
-
 # Tandem/NSK is broken - it has 'long long int' but not
 # 'unsigned long long int', which confuses assumptions made by gnulib.
 # Simply pretend that neither type exists if both do not work.
@@ -67,45 +48,6 @@ fi
 
 M4_INIT
 
-# Code from Jim Avera <jima@netcom.com>.
-# stackovf.c requires:
-#  1. Either sigaction with SA_ONSTACK, or sigvec with SV_ONSTACK
-#  2. Either sigaltstack or sigstack
-#  3. getrlimit, including support for RLIMIT_STACK
-AC_CACHE_CHECK([if stack overflow is detectable], [M4_cv_use_stackovf],
-[M4_cv_use_stackovf=no
-if test "$ac_cv_func_sigaction" = yes || test "$ac_cv_func_sigvec" = yes; then
-  if test "$ac_cv_func_sigaltstack" = yes || test "$ac_cv_func_sigstack" = yes; then
-    AC_LINK_IFELSE([AC_LANG_PROGRAM([[
-#include <sys/time.h>
-#include <sys/resource.h>
-#include <signal.h>
-]], [[struct rlimit r; getrlimit (RLIMIT_STACK, &r);
-#if (!defined(HAVE_SIGACTION) || !defined(SA_ONSTACK)) \
-    && (!defined(HAVE_SIGVEC) || !defined(SV_ONSTACK))
-choke me		/* SA_ONSTACK and/or SV_ONSTACK are not defined */
-#endif
-]])], [M4_cv_use_stackovf=yes])
-  fi
-fi])
-AM_CONDITIONAL([STACKOVF], [test "$M4_cv_use_stackovf" = yes])
-if test "$M4_cv_use_stackovf" = yes; then
-  AC_DEFINE([USE_STACKOVF], [1],
-    [Define to 1 if using stack overflow detection])
-  AC_CHECK_TYPES([rlim_t], [],
-    [AC_DEFINE([rlim_t], [int],
-      [Define to int if rlim_t is not defined in sys/resource.h])],
-    [[#include <sys/resource.h>
-  ]])
-  AC_CHECK_TYPES([stack_t], [],
-    [AC_DEFINE([stack_t], [struct sigaltstack],
-      [Define to struct sigaltstack if stack_t is not in signal.h])],
-    [[#include <signal.h>
-  ]])
-  AC_CHECK_TYPES([sigcontext], [], [], [[#include <signal.h>
-  ]])
-fi
-
 AC_CACHE_CHECK([if system() agrees with pclose()],
   [M4_cv_func_system_consistent],
   [AC_RUN_IFELSE([AC_LANG_PROGRAM([
diff --git a/doc/m4.texinfo b/doc/m4.texinfo
index 00b9024d..f5b49d82 100644
--- a/doc/m4.texinfo
+++ b/doc/m4.texinfo
@@ -757,15 +757,16 @@ increase this value, unless you define an excessive number of macros.
 @cindex limit, nesting
 Artificially limit the nesting of macro calls to @var{NUM} levels,
 stopping program execution if this limit is ever exceeded.  When not
-specified, nesting is limited to 1024 levels.  A value of zero means
+specified, nesting defaults to unlimited on platforms that can detect
+stack overflow, and to 1024 levels otherwise.  A value of zero means
 unlimited; but then heavily nested code could potentially cause a stack
 overflow.
 
-The precise effect of this option might be more correctly associated
+The precise effect of this option is more correctly associated
 with textual nesting than dynamic recursion.  It has been useful
-when some complex @code{m4} input was generated by mechanical means.
-Most users would never need this option.  If shown to be obtrusive,
-this option (which is still experimental) might well disappear.
+when some complex @code{m4} input was generated by mechanical means, and
+also in diagnosing recursive algorithms that do not scale well.
+Most users never need to change this option from its default.
 
 @cindex rescanning
 This option does @emph{not} have the ability to break endless
diff --git a/m4/gnulib-cache.m4 b/m4/gnulib-cache.m4
index 352b70d1..c653c93d 100644
--- a/m4/gnulib-cache.m4
+++ b/m4/gnulib-cache.m4
@@ -15,7 +15,7 @@
 
 
 # Specification in the form of a command-line invocation:
-#   gnulib-tool --import --dir=. --local-dir=local --lib=libm4 --source-base=lib --m4-base=m4 --doc-base=doc --aux-dir=build-aux --with-tests --no-libtool --macro-prefix=M4 announce-gen assert autobuild avltree-oset binary-io clean-temp cloexec close-stream closein config-h error fdl fflush fopen-safer fseeko gendocs getopt git-version-gen gnumakefile gnupload gpl-3.0 intprops mkstemp obstack progname regex stdbool stdint stdlib-safer strstr strtod strtol unlocked-io verror version-etc version-etc-fsf xalloc xprintf xvasprintf-posix
+#   gnulib-tool --import --dir=. --local-dir=local --lib=libm4 --source-base=lib --m4-base=m4 --doc-base=doc --aux-dir=build-aux --with-tests --no-libtool --macro-prefix=M4 announce-gen assert autobuild avltree-oset binary-io c-stack clean-temp cloexec close-stream closein config-h error fdl fflush fopen-safer fseeko gendocs getopt git-version-gen gnumakefile gnupload gpl-3.0 intprops mkstemp obstack progname regex stdbool stdint stdlib-safer strstr strtod strtol unlocked-io verror version-etc version-etc-fsf xalloc xprintf xvasprintf-posix
 
 # Specification in the form of a few gnulib-tool.m4 macro invocations:
 gl_LOCAL_DIR([local])
@@ -25,6 +25,7 @@ gl_MODULES([
   autobuild
   avltree-oset
   binary-io
+  c-stack
   clean-temp
   cloexec
   close-stream
diff --git a/src/Makefile.am b/src/Makefile.am
index f2c15244..900f8ea6 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -24,7 +24,4 @@ AM_CPPFLAGS = -I$(top_srcdir)/lib -I../lib
 bin_PROGRAMS = m4
 m4_SOURCES = m4.h m4.c builtin.c debug.c eval.c format.c freeze.c input.c \
 macro.c output.c path.c symtab.c
-if STACKOVF
-m4_SOURCES += stackovf.c
-endif
 m4_LDADD = ../lib/libm4.a $(LIBM4_LIBDEPS) $(POW_LIB)
diff --git a/src/m4.c b/src/m4.c
index ca341cc8..880f13df 100644
--- a/src/m4.c
+++ b/src/m4.c
@@ -1,7 +1,7 @@
 /* GNU m4 -- A simple macro processor
 
-   Copyright (C) 1989, 1990, 1991, 1992, 1993, 1994, 2004, 2005, 2006, 2007
-   Free Software Foundation, Inc.
+   Copyright (C) 1989, 1990, 1991, 1992, 1993, 1994, 2004, 2005, 2006,
+   2007, 2008 Free Software Foundation, Inc.
 
    This file is part of GNU M4.
 
@@ -25,6 +25,7 @@
 #include <limits.h>
 #include <signal.h>
 
+#include "c-stack.h"
 #include "progname.h"
 #include "version-etc.h"
 
@@ -110,21 +111,6 @@ m4_error_at_line (int status, int errnum, const char *file, int line,
   if (fatal_warnings && ! retcode)
     retcode = EXIT_FAILURE;
 }
-
-#ifdef USE_STACKOVF
-
-/*---------------------------------------.
-| Tell user stack overflowed and abort.	 |
-`---------------------------------------*/
-
-static void
-stackovf_handler (void)
-{
-  M4ERROR ((EXIT_FAILURE, 0,
-	    "ERROR: stack overflow.  (Infinite define recursion?)"));
-}
-
-#endif /* USE_STACKOV */
 
 
 /*---------------------------------------------.
@@ -175,15 +161,15 @@ Preprocessor features:\n\
   -s, --synclines              generate `#line NUM \"FILE\"' lines\n\
   -U, --undefine=NAME          undefine NAME\n\
 ", stdout);
-      fputs ("\
-\n\
+      puts ("");
+      xprintf (_("\
 Limits control:\n\
   -G, --traditional            suppress all GNU extensions\n\
   -H, --hashsize=PRIME         set symbol lookup hash table size [509]\n\
-  -L, --nesting-limit=NUMBER   change artificial nesting limit [1024]\n\
-", stdout);
+  -L, --nesting-limit=NUMBER   change nesting limit, 0 for unlimited [%d]\n\
+"), nesting_limit);
+      puts ("");
       fputs ("\
-\n\
 Frozen state files:\n\
   -F, --freeze-state=FILE      produce a frozen state on FILE at end\n\
   -R, --reload-state=FILE      reload a frozen state from FILE at start\n\
@@ -338,9 +324,8 @@ main (int argc, char *const *argv, char *const *envp)
 
   include_init ();
   debug_init ();
-#ifdef USE_STACKOVF
-  setup_stackovf_trap (argv, envp, stackovf_handler);
-#endif
+  if (c_stack_action (NULL) == 0)
+    nesting_limit = 0;
 
   /* First, we decode the arguments, to size up tables and stuff.  */
 
diff --git a/src/m4.h b/src/m4.h
index af3fd15d..929fd418 100644
--- a/src/m4.h
+++ b/src/m4.h
@@ -139,10 +139,6 @@ void m4_error_at_line (int, int, const char *, int,
 #define M4ERROR(Arglist) (m4_error Arglist)
 #define M4ERROR_AT_LINE(Arglist) (m4_error_at_line Arglist)
 
-#ifdef USE_STACKOVF
-void setup_stackovf_trap (char *const *, char *const *,
-			  void (*handler) (void));
-#endif
 
 /* File: debug.c  --- debugging and tracing function.  */
 
diff --git a/src/stackovf.c b/src/stackovf.c
deleted file mode 100644
index 3877cd9d..00000000
--- a/src/stackovf.c
+++ /dev/null
@@ -1,422 +0,0 @@
-/* Detect stack overflow (when getrlimit and sigaction or sigvec are available)
-
-   Copyright (C) 1993, 1994, 2006, 2007 Free Software Foundation, Inc.
-   Jim Avera <jima@netcom.com>, October 1993.
-
-   This file is part of GNU M4.
-
-   GNU M4 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 3 of the License, or
-   (at your option) any later version.
-
-   GNU M4 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, see <http://www.gnu.org/licenses/>.
- */
-
-/* Compiled only when USE_STACKOVF is defined, which itself requires
-   getrlimit with the RLIMIT_STACK option, and support for alternate
-   signal stacks using either SVR4 or BSD interfaces.
-
-   This should compile on ANY system which supports either sigaltstack()
-   or sigstack(), with or without <siginfo.h> or another way to determine
-   the fault address.
-
-   There is no completely portable way to determine if a SIGSEGV signal
-   indicates a stack overflow.  The fault address can be used to infer
-   this.  However, the fault address is passed to the signal handler in
-   different ways on various systems.  One of three methods are used to
-   determine the fault address:
-
-      1. The siginfo parameter (with siginfo.h, i.e., SVR4).
-
-      2. 4th "addr" parameter (assumed if struct sigcontext is defined,
-	 i.e., SunOS 4.x/BSD).
-
-      3. None (if no method is available).  This case just prints a
-      message before aborting with a core dump.  That way the user at
-      least knows that it *might* be a recursion problem.
-
-   Jim Avera <jima@netcom.com> writes, on Tue, 5 Oct 93 19:27 PDT:
-
-      "I got interested finding out how a program could catch and
-      diagnose its own stack overflow, and ended up modifying m4 to do
-      this.  Now it prints a nice error message and exits.
-
-      How it works: SIGSEGV is caught using a separate signal stack.  The
-      signal handler declares a stack overflow if the fault address is
-      near the end of the stack region, or if the maximum VM address
-      space limit has been reached.  Otherwise, it returns to re-execute
-      the instruction with SIG_DFL set, so that any real bugs cause a
-      core dump as usual."
-
-   Jim Avera <jima@netcom.com> writes, on Fri, 24 Jun 94 12:14 PDT:
-
-      "The stack-overflow detection code would still be needed to avoid a
-      SIGSEGV abort if swap space was exhausted at the moment the stack
-      tried to grow.  This is probably unlikely to occur with the
-      explicit nesting limit option of GNU m4."
-
-   Jim Avera <jima@netcom.com> writes, on Wed, 6 Jul 1994 14:41 PDT:
-
-      "When a stack overflow occurs, a SIGSEGV signal is sent, which by
-      default aborts the process with a core dump.
-
-      The code in stackovf.c catches SIGSEGV using a separate signal
-      stack.  The signal handler determines whether or not the SIGSEGV
-      arose from a stack overflow.  If it is a stack overflow, an
-      external function is called (which, in m4, prints a message an
-      exits).  Otherwise the SIGSEGV represents an m4 bug, and the signal
-      is re-raised with SIG_DFL set, which results in an abort and core
-      dump in the usual way.  It seems important (to me) that internal m4
-      bugs not be reported as user recursion errors, or vice-versa."  */
-
-#include "m4.h"			/* stdlib.h, xmalloc() */
-
-#include <assert.h>
-#include <sys/time.h>
-#include <sys/resource.h>
-#include <signal.h>
-
-#if HAVE_SIGINFO_H
-# include <siginfo.h>
-#endif
-
-#ifndef SA_RESETHAND
-# define SA_RESETHAND 0
-#endif
-#ifndef SA_SIGINFO
-# define SA_SIGINFO 0
-#endif
-
-#ifndef SIGSTKSZ
-# define SIGSTKSZ 8192
-#endif
-
-/* If the trap address is within STACKOVF_DETECT bytes of the calculated
-   stack limit, we diagnose a stack overflow.  This must be large enough
-   to cover errors in our estimatation of the limit address, and to
-   account for the maximum size of local variables (the amount the
-   trapping reference might exceed the stack limit).  Also, some machines
-   may report an arbitrary address within the same page frame.
-   If the value is too large, we might call some other SIGSEGV a stack
-   overflow, masking a bug.  */
-
-#ifndef STACKOVF_DETECT
-# define STACKOVF_DETECT 16384
-#endif
-
-typedef void (*handler_t) (void);
-
-static const char *stackbot;
-static const char *stackend;
-static const char *arg0;
-static handler_t stackovf_handler;
-
-/* The following OS-independent procedure is called from the SIGSEGV
-   signal handler.  The signal handler obtains information about the trap
-   in an OS-dependent manner, and passes a parameter with the meanings as
-   explained below.
-
-   If the OS explicitly identifies a stack overflow trap, either pass
-   PARAM_STACKOVF if a stack overflow, or pass PARAM_NOSTACKOVF if not
-   (id est, it is a random bounds violation).  Otherwise, if the fault
-   address is available, pass the fault address.  Otherwise (if no
-   information is available), pass NULL.
-
-   Not given an explicit indication, we compare the fault address with
-   the estimated stack limit, and test to see if overall VM space is
-   exhausted.
-
-   If a stack overflow is identified, then the external *stackovf_handler
-   function is called, which should print an error message and exit.  If
-   it is NOT a stack overflow, then we silently abort with a core dump by
-   returning to re-raise the SIGSEGV with SIG_DFL set.  If indeterminate,
-   then we do not call *stackovf_handler, but instead print an ambiguous
-   message and abort with a core dump.  This only occurs on systems which
-   provide no information, but is better than nothing.  */
-
-#define PARAM_STACKOVF ((const char *) (1 + STACKOVF_DETECT))
-#define PARAM_NOSTACKOVF ((const char *) (2 + STACKOVF_DETECT))
-
-static void
-process_sigsegv (int signo, const char *p)
-{
-  long diff;
-  diff = (p - stackend);
-
-#ifdef DEBUG_STKOVF
-  {
-    char buf[140];
-
-    snprintf (buf, sizeof buf,
-              "process_sigsegv: p=%#lx stackend=%#lx diff=%ld bot=%#lx\n",
-              (long) p, (long) stackend, (long) diff, (long) stackbot);
-    write (2, buf, strlen (buf));
-  }
-#endif
-
-  if (p != PARAM_NOSTACKOVF)
-    {
-      if ((long) sbrk (8192) == (long) -1)
-	{
-
-	  /* sbrk failed.  Assume the RLIMIT_VMEM prevents expansion even
-	     if the stack limit has not been reached.  */
-
-	  write (2, "VMEM limit exceeded?\n", 21);
-	  p = PARAM_STACKOVF;
-	}
-      if (diff >= -STACKOVF_DETECT && diff <= STACKOVF_DETECT)
-	{
-
-	  /* The fault address is "sufficiently close" to the stack lim.  */
-
-	  p = PARAM_STACKOVF;
-	}
-      if (p == PARAM_STACKOVF)
-	{
-
-	  /* We have determined that this is indeed a stack overflow.  */
-
-	  (*stackovf_handler) ();	/* should call exit() */
-	}
-    }
-  if (p == NULL)
-    {
-      const char *cp;
-
-      cp = "\
-Memory bounds violation detected (SIGSEGV).  Either a stack overflow\n\
-occurred, or there is a bug in ";
-      write (2, cp, strlen (cp));
-      write (2, arg0, strlen (arg0));
-      cp = ".  Check for possible infinite recursion.\n";
-      write (2, cp, strlen (cp));
-    }
-
-  /* Return to re-execute the instruction which caused the trap with
-     SIGSEGV set to SIG_DFL.  An abort with core dump should occur.  */
-
-  signal (signo, SIG_DFL);
-}
-
-#if HAVE_STRUCT_SIGACTION_SA_SIGACTION
-
-/* POSIX.  */
-
-static void
-sigsegv_handler (int signo, siginfo_t *ip, void *context)
-{
-  process_sigsegv
-    (signo, (ip != NULL
-	     && ip->si_signo == SIGSEGV ? (char *) ip->si_addr : NULL));
-}
-
-#elif HAVE_SIGINFO_T
-
-/* SVR4.  */
-
-static void
-sigsegv_handler (int signo, siginfo_t *ip)
-{
-  process_sigsegv
-    (signo, (ip != NULL
-	     && ip->si_signo == SIGSEGV ? (char *) ip->si_addr : NULL));
-}
-
-#elif HAVE_SIGCONTEXT
-
-/* SunOS 4.x (and BSD?).  (not tested) */
-
-static void
-sigsegv_handler (int signo, int code, struct sigcontext *scp, char *addr)
-{
-  process_sigsegv (signo, addr);
-}
-
-#else /* not HAVE_SIGCONTEXT */
-
-/* OS provides no information.  */
-
-static void
-sigsegv_handler (int signo)
-{
-  process_sigsegv (signo, NULL);
-}
-
-#endif /* not HAVE_SIGCONTEXT */
-
-/* Arrange to trap a stack-overflow and call a specified handler.  The
-   call is on a dedicated signal stack.
-
-   argv and envp are as passed to main().
-
-   If a stack overflow is not detected, then the SIGSEGV is re-raised
-   with action set to SIG_DFL, causing an abort and coredump in the usual
-   way.
-
-   Detection of a stack overflow depends on the trap address being near
-   the stack limit address.  The stack limit can not be directly
-   determined in a portable way, but we make an estimate based on the
-   address of the argv and environment vectors, their contents, and the
-   maximum stack size obtained using getrlimit.  */
-
-void
-setup_stackovf_trap (char *const *argv, char *const *envp, handler_t handler)
-{
-  struct rlimit rl;
-  rlim_t stack_len;
-  int grows_upward;
-  register char *const *v;
-  register char *p;
-#if HAVE_SIGACTION && defined SA_ONSTACK
-  struct sigaction act;
-#elif HAVE_SIGVEC && defined SV_ONSTACK
-  struct sigvec vec;
-#else
-
-Error - Do not know how to set up stack-ovf trap handler...
-
-#endif
-
-  arg0 = argv[0];
-  stackovf_handler = handler;
-
-  /* Calculate the approximate expected addr for a stack-ovf trap.  */
-
-  if (getrlimit (RLIMIT_STACK, &rl) < 0)
-    error (EXIT_FAILURE, errno, "getrlimit");
-  stack_len = (rl.rlim_cur < rl.rlim_max ? rl.rlim_cur : rl.rlim_max);
-  stackbot = (char *) argv;
-  grows_upward = ((char *) &stack_len > stackbot);
-  if (grows_upward)
-    {
-
-      /* Grows toward increasing addresses.  */
-
-      for (v = argv; (p = (char *) *v) != NULL; v++)
-	{
-	  if (p < stackbot)
-	    stackbot = p;
-	}
-      if ((char *) envp < stackbot)
-	stackbot = (char *) envp;
-      for (v = envp; (p = (char *) *v) != NULL; v++)
-	{
-	  if (p < stackbot)
-	    stackbot = p;
-	}
-      stackend = stackbot + stack_len;
-    }
-  else
-    {
-
-      /* The stack grows "downward" (toward decreasing addresses).  */
-
-      for (v = argv; (p = (char *) *v) != NULL; v++)
-	{
-	  if (p > stackbot)
-	    stackbot = p;
-	}
-      if ((char *) envp > stackbot)
-	stackbot = (char *) envp;
-      for (v = envp; (p = (char *) *v) != NULL; v++)
-	{
-	  if (p > stackbot)
-	    stackbot = p;
-	}
-      stackend = stackbot - stack_len;
-    }
-
-  /* Allocate a separate signal-handler stack.  */
-
-#if HAVE_SIGALTSTACK && (HAVE_SIGINFO_T || ! HAVE_SIGSTACK)
-
-  /* Use sigaltstack only if siginfo_t is available, unless there is no
-     choice.  */
-
-  {
-    stack_t ss;
-# ifndef HAVE_STACK_T_SS_SP
-    /* This workaround is for BSD/OS 4.0.1:
-       http://lists.gnu.org/archive/html/bug-m4/2006-12/msg00004.html  */
-#  define ss_sp ss_base
-# endif
-
-    ss.ss_size = SIGSTKSZ;
-    ss.ss_sp = xmalloc ((unsigned) ss.ss_size);
-    ss.ss_flags = 0;
-    if (sigaltstack (&ss, NULL) < 0)
-      {
-	/* Oops - sigaltstack exists but doesn't work.  We can't
-	   install the overflow detector, but should gracefully treat
-	   it as though sigaltstack doesn't exist.  For example, this
-	   happens when compiled with Linux 2.1 headers but run
-	   against Linux 2.0 kernel.  */
-	free (ss.ss_sp);
-	if (errno == ENOSYS)
-	  return;
-	error (EXIT_FAILURE, errno, "sigaltstack");
-      }
-  }
-
-#elif HAVE_SIGSTACK
-
-  {
-    struct sigstack ss;
-    char *stackbuf = xmalloc (2 * SIGSTKSZ);
-
-    ss.ss_sp = stackbuf + SIGSTKSZ;
-    ss.ss_onstack = 0;
-    if (sigstack (&ss, NULL) < 0)
-      {
-	/* Oops - sigstack exists but doesn't work.  We can't install
-	   the overflow detector, but should gracefully treat it as
-	   though sigstack doesn't exist.  For example, this happens
-	   when compiled with Linux 2.1 headers but run against Linux
-	   2.0 kernel.  */
-	free (stackbuf);
-	if (errno == ENOSYS)
-	  return;
-	error (EXIT_FAILURE, errno, "sigstack");
-      }
-  }
-
-#else /* not HAVE_SIGSTACK */
-
-Error - Do not know how to set up stack-ovf trap handler...
-
-#endif /* not HAVE_SIGSTACK */
-
-  /* Arm the SIGSEGV signal handler.  */
-
-#if HAVE_SIGACTION && defined SA_ONSTACK
-
-  sigaction (SIGSEGV, NULL, &act);
-# if HAVE_STRUCT_SIGACTION_SA_SIGACTION
-  act.sa_sigaction = sigsegv_handler;
-# else /* ! HAVE_STRUCT_SIGACTION_SA_SIGACTION */
-  act.sa_handler = (RETSIGTYPE (*) (int)) sigsegv_handler;
-# endif /* ! HAVE_STRUCT_SIGACTION_SA_SIGACTION */
-  sigemptyset (&act.sa_mask);
-  act.sa_flags = (SA_ONSTACK | SA_RESETHAND | SA_SIGINFO);
-  if (sigaction (SIGSEGV, &act, NULL) < 0)
-    error (EXIT_FAILURE, errno, "sigaction");
-
-#else /* ! HAVE_SIGACTION */
-
-  vec.sv_handler = (RETSIGTYPE (*) (int)) sigsegv_handler;
-  vec.sv_mask = 0;
-  vec.sv_flags = (SV_ONSTACK | SV_RESETHAND);
-  if (sigvec (SIGSEGV, &vec, NULL) < 0)
-    error (EXIT_FAILURE, errno, "sigvec");
-
-#endif /* ! HAVE_SIGACTION */
-
-}