Adjust to c-stack changes in gnulib.

* src/Makefile.am (m4_LDADD): Use libsigsegv when available and
necessary, via LIBCSTACK.
* src/m4.c (main) [DEBUG_STACKOVF]: Make it easier to test fault
handlers.
* checks/stackovf.test: New file.
* checks/Makefile.in (CHECKS): Add stackovf.test, and factor...
(DOC_CHECKS): ...generated documentation tests into new macro.
(DISTFILES): Distribute stackovf.test.
* checks/check-them: Special-case stackovf.test.
* NEWS: Enhance the NEWS item for -L improvements.
* README: Mention the optional dependency.
* HACKING: Mention maintenance burden added by libsigsegv.

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

9 files changed, 173 insertions, 7 deletions

diff --git a/ChangeLog b/ChangeLog
index c51d171a..e182a2b9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,19 @@
+2008-07-17  Eric Blake  <ebb9@byu.net>
+
+	Adjust to c-stack changes in gnulib.
+	* src/Makefile.am (m4_LDADD): Use libsigsegv when available and
+	necessary, via LIBCSTACK.
+	* src/m4.c (main) [DEBUG_STACKOVF]: Make it easier to test fault
+	handlers.
+	* checks/stackovf.test: New file.
+	* checks/Makefile.in (CHECKS): Add stackovf.test, and factor...
+	(DOC_CHECKS): ...generated documentation tests into new macro.
+	(DISTFILES): Distribute stackovf.test.
+	* checks/check-them: Special-case stackovf.test.
+	* NEWS: Enhance the NEWS item for -L improvements.
+	* README: Mention the optional dependency.
+	* HACKING: Mention maintenance burden added by libsigsegv.
+
 2008-06-23  Eric Blake  <ebb9@byu.net>
 
 	Adjust to new gnulib-tool layout.
diff --git a/HACKING b/HACKING
index fd8cd1ed..e127494b 100644
--- a/HACKING
+++ b/HACKING
@@ -62,6 +62,13 @@ and is not part of a release distribution.
   Note that none of these bootstrapping dependencies should be required
   by a distributed release.
 
+* M4 has an optional build dependency.  In order to ensure that the
+  dependency remains optional, you can avoid the library by using
+  `./configure --without-libsigsegv-prefix'.  In order to ensure that
+  the dependency is still viable with the current code base, you should
+  install:
+  - Libsigsegv 2.5 or later
+
 * Either add the gnulib directory to your PATH, or run
     GNULIB_TOOL=path/to/gnulib/gnulib-tool ./bootstrap
 
diff --git a/NEWS b/NEWS
index 5aae8561..bfda4d41 100644
--- a/NEWS
+++ b/NEWS
@@ -38,7 +38,12 @@ Foundation, Inc.
      http://git.sv.gnu.org/gitweb/?p=autoconf.git;a=commitdiff;h=56d42fa71
 
 ** The `-L'/`--nesting-limit' command-line option now defaults to 0 for
-   unlimited on platforms that can detect and deal with stack overflow.
+   unlimited on platforms that can detect and deal with stack overflow.  On
+   systems that lack alternate stack support, such as Cygwin, and on
+   systems that do not obey the POSIX semantics for distinguishing stack
+   overflow from other exceptions, such as Linux, you can optionally
+   install the libsigsegv library to enhance m4's ability to accurately
+   report stack overflow: http://www.gnu.org/software/libsigsegv/
 
 ** The `defn' builtin now warns when operating on an undefined macro name.
    To simulate 1.4.x behavior, use:
diff --git a/README b/README
index 548ffb9d..ea5061fe 100644
--- a/README
+++ b/README
@@ -19,6 +19,15 @@ ahead and start with `./configure'.  If you are trying to build `m4'
 from git or CVS, more information can be found in the file HACKING,
 only found in a version control checkout.
 
+M4 has an optional dependency on the libsigsegv library:
+  http://www.gnu.org/software/libsigsegv/
+If the library has not been installed in the standard location, you
+can use `./configure --with-libsigsegv-prefix=/path/to/dir', to make
+the build of `m4' use /path/to/dir/include/sigsegv.h as appropriate.
+The use of this library is optional; the only difference in having it
+available is that it increases the number of platforms where `m4' can
+correctly distinguish stack overflow from an internal bug.
+
 In the subdirectory `examples' you will find various m4 files, ranging
 from trivial test files to rather advanced macros.  If you intend to
 use m4 seriously, you might find useful material down there.
diff --git a/checks/Makefile.in b/checks/Makefile.in
index 0e1091e5..c43c2ccd 100644
--- a/checks/Makefile.in
+++ b/checks/Makefile.in
@@ -36,14 +36,16 @@ program_transform_name = @program_transform_name@
 AWK = @AWK@
 
 # Vern says that the first star is required around an Alpha make bug.
-CHECKS = $(srcdir)/*[0-9][0-9][0-9].*
+DOC_CHECKS = $(srcdir)/*[0-9][0-9][0-9].*
+CHECKS = $(DOC_CHECKS) $(srcdir)/stackovf.test
 # Makefile.in is automatically distributed by automake.
-DISTFILES = $(srcdir)/get-them $(srcdir)/check-them $(srcdir)/stamp-checks
+DISTFILES = $(srcdir)/get-them $(srcdir)/check-them $(srcdir)/stamp-checks \
+	$(srcdir)/stackovf.test
 
 all: $(srcdir)/stamp-checks
 
 $(srcdir)/stamp-checks: $(srcdir)/get-them $(srcdir)/../doc/m4.texinfo
-	rm -f $(CHECKS)
+	rm -f $(DOC_CHECKS)
 	cd $(srcdir) && AWK=$(AWK) ./get-them ../doc/m4.texinfo
 	touch $(srcdir)/stamp-checks
 
@@ -73,13 +75,13 @@ distclean: clean
 	rm -f Makefile
 
 maintainer-clean realclean: distclean
-	rm -f $(CHECKS) $(srcdir)/stamp-checks
+	rm -f $(DOC_CHECKS) $(srcdir)/stamp-checks
 
 distdir: dist
 
 dist: $(DISTFILES)
 	@echo "Copying distribution files"
-	@for file in $(DISTFILES) $(CHECKS); do \
+	@for file in $(DISTFILES) $(DOC_CHECKS); do \
 	  ln $$file ../$(PACKAGE)-$(VERSION)/checks 2> /dev/null \
 	    || cp -p $$file ../$(PACKAGE)-$(VERSION)/checks; \
 	done
diff --git a/checks/check-them b/checks/check-them
index 7fba1d6f..f66322b9 100755
--- a/checks/check-them
+++ b/checks/check-them
@@ -70,6 +70,18 @@ do
     continue
   }
   echo "Checking $file"
+
+  case $file in
+    *stackovf.test)
+      "$file" "$m4"
+      case $? in
+	77) skipped="$skipped $file";;
+	0) ;;
+	*) failed="$failed $file"
+      esac
+      continue ;;
+  esac
+
   options=`sed -ne '3s/^dnl @ extra options: //p;3q' "$file"`
   sed -e '/^dnl @/d' -e '/^\^D$/q' "$file" \
     | LC_MESSAGES=C M4PATH=$examples "$m4" -d $options - >$out 2>$err
diff --git a/checks/stackovf.test b/checks/stackovf.test
new file mode 100755
index 00000000..4b938e75
--- /dev/null
+++ b/checks/stackovf.test
@@ -0,0 +1,99 @@
+#!/bin/sh
+# This file is part of the GNU m4 testsuite
+# Copyright (C) 2000, 2003, 2007, 2008 Free Software Foundation, Inc.
+#
+# 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/>.
+
+# Script to verify that stack overflow is diagnosed properly when
+# there is infinite macro call nesting, provided the OS supports it.
+
+m4="$1"
+
+# Skip this test if -L defaults to 1024 instead of 0, as that is our
+# indicator that the OS does not support stack overflow detection.
+("$m4" --help | grep 'nesting.*\[0\]') >/dev/null 2>&1 \
+  || {
+       echo "$0: skipping test, no stack overflow support detected in $m4"
+       exit 77
+     }
+
+# On some systems the ulimit command is available in ksh or bash but not sh
+(exec 2>/dev/null; ulimit -Ss 300) || {
+  for altshell in bash bsh ksh zsh ; do
+    if (exec >/dev/null 2>&1; $altshell -c 'ulimit -Ss 300') && test -z "$2"
+    then
+      echo "Using $altshell because it supports ulimit"
+      exec $altshell "$0" "$@" running-with-$altshell
+      exit 1
+    fi
+  done
+}
+
+tmpdir=
+trap 'st=$?; rm -rf "$tmpdir" && exit $st' 0
+trap '(exit $?); exit $?' 1 2 3 15
+
+# Create a temporary subdirectory $tmpdir in $TMPDIR (default /tmp).
+# Use mktemp if possible; otherwise fall back on mkdir,
+# with $RANDOM to make collisions less likely.
+: ${TMPDIR=/tmp}
+{
+  tmpdir=`
+    (umask 077 && mktemp -d "$TMPDIR/m4stk-XXXXXX") 2>/dev/null
+  ` &&
+  test -n "$tmpdir" && test -d "$tmpdir"
+} || {
+  tmpdir=$TMPDIR/m4stk-$$-$RANDOM
+  (umask 077 && mkdir "$tmpdir")
+} || exit $?
+tmpfile="$tmpdir"/m4.out
+
+# Limit the stack size if the shell we are running permits it
+if (exec 2>/dev/null; ulimit -Ss 50)
+then
+  ulimit -Ss 50
+  echo "Stack soft limit set to `ulimit -s`K";
+else
+  echo "Can't reset stack limit - this may take a while..."
+fi
+
+# Induce stack overflow.
+echo 'define(a,a(a))a' | "$m4" > "$tmpfile" 2>&1
+result=$?
+
+exitcode=1
+if test $result -eq 0 ; then
+  echo "Failure - $m4 did not abort"
+else
+  # See if stack overflow was diagnosed.
+  case `cat "$tmpfile"` in
+    *stack\ overflow*)
+      case `echo "$tmpdir"/*` in
+	$tmpfile)
+	   echo "Pass"
+	   exitcode=0 ;;
+	*) echo "Failure - $m4 created unexpected core dump"
+	   ls -l "$tmpdir" ;;
+      esac ;;
+    *)	echo "Failure - $m4 aborted unexpectedly";
+	;;
+    esac
+fi
+
+test $exitcode = 0 ||
+    { echo "Output from $m4:"; cat $tmpfile; }
+
+exit $exitcode
diff --git a/src/Makefile.am b/src/Makefile.am
index 900f8ea6..80b9acf8 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -24,4 +24,4 @@ AM_CPPFLAGS = -I$(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
-m4_LDADD = ../lib/libm4.a $(LIBM4_LIBDEPS) $(POW_LIB)
+m4_LDADD = ../lib/libm4.a $(LIBM4_LIBDEPS) $(POW_LIB) $(LIBCSTACK)
diff --git a/src/m4.c b/src/m4.c
index 970aa8b6..a24f82dd 100644
--- a/src/m4.c
+++ b/src/m4.c
@@ -488,6 +488,22 @@ main (int argc, char *const *argv, char *const *envp)
   sigaction (SIGFPE, &act, NULL);
   sigaction (SIGBUS, &act, NULL);
 
+#ifdef DEBUG_STKOVF
+  /* Make it easier to test our fault handlers.  Exporting M4_CRASH=0
+     attempts a SIGSEGV, exporting it as 1 attempts an assertion
+     failure with a fallback to abort.  */
+  {
+    char *crash = getenv ("M4_CRASH");
+    if (crash)
+      {
+        if (!atoi (crash))
+          ++*(int *) 8;
+        assert (false);
+        abort ();
+      }
+  }
+#endif /* DEBUG_STKOVF */
+
   /* First, we decode the arguments, to size up tables and stuff.  */
   head = tail = NULL;