diff --git a/Makefile.in b/Makefile.in
index 9d158f8..fc7a20e 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -166,8 +166,8 @@ am__DIST_COMMON = $(srcdir)/Makefile.in $(top_srcdir)/ac/ar-lib \
 	$(top_srcdir)/ac/compile $(top_srcdir)/ac/config.guess \
 	$(top_srcdir)/ac/config.sub $(top_srcdir)/ac/install-sh \
 	$(top_srcdir)/ac/ltmain.sh $(top_srcdir)/ac/missing ac/ar-lib \
-	ac/compile ac/config.guess ac/config.sub ac/install-sh \
-	ac/ltmain.sh ac/missing
+	ac/compile ac/config.guess ac/config.sub ac/depcomp \
+	ac/install-sh ac/ltmain.sh ac/missing
 DISTFILES = $(DIST_COMMON) $(DIST_SOURCES) $(TEXINFOS) $(EXTRA_DIST)
 distdir = $(PACKAGE)-$(VERSION)
 top_distdir = $(distdir)
@@ -306,6 +306,7 @@ SET_MAKE = @SET_MAKE@
 SHELL = @SHELL@
 STRIP = @STRIP@
 UNICOWS_LIBS = @UNICOWS_LIBS@
+UNWIND_LIBS = @UNWIND_LIBS@
 VERSION = @VERSION@
 abs_builddir = @abs_builddir@
 abs_srcdir = @abs_srcdir@
@@ -353,7 +354,6 @@ pdfdir = @pdfdir@
 prefix = @prefix@
 program_transform_name = @program_transform_name@
 psdir = @psdir@
-runstatedir = @runstatedir@
 sbindir = @sbindir@
 sharedstatedir = @sharedstatedir@
 srcdir = @srcdir@
@@ -584,7 +584,7 @@ distdir: $(DISTFILES)
 	  ! -type d ! -perm -444 -exec $(install_sh) -c -m a+r {} {} \; \
 	|| chmod -R a+r "$(distdir)"
 dist-gzip: distdir
-	tardir=$(distdir) && $(am__tar) | GZIP=$(GZIP_ENV) gzip -c >$(distdir).tar.gz
+	tardir=$(distdir) && $(am__tar) | eval GZIP= gzip $(GZIP_ENV) -c >$(distdir).tar.gz
 	$(am__post_remove_distdir)
 
 dist-bzip2: distdir
@@ -610,7 +610,7 @@ dist-shar: distdir
 	@echo WARNING: "Support for shar distribution archives is" \
 	               "deprecated." >&2
 	@echo WARNING: "It will be removed altogether in Automake 2.0" >&2
-	shar $(distdir) | GZIP=$(GZIP_ENV) gzip -c >$(distdir).shar.gz
+	shar $(distdir) | eval GZIP= gzip $(GZIP_ENV) -c >$(distdir).shar.gz
 	$(am__post_remove_distdir)
 
 dist-zip: distdir
@@ -628,7 +628,7 @@ dist dist-all:
 distcheck: dist
 	case '$(DIST_ARCHIVES)' in \
 	*.tar.gz*) \
-	  GZIP=$(GZIP_ENV) gzip -dc $(distdir).tar.gz | $(am__untar) ;;\
+	  eval GZIP= gzip $(GZIP_ENV) -dc $(distdir).tar.gz | $(am__untar) ;;\
 	*.tar.bz2*) \
 	  bzip2 -dc $(distdir).tar.bz2 | $(am__untar) ;;\
 	*.tar.lz*) \
@@ -638,7 +638,7 @@ distcheck: dist
 	*.tar.Z*) \
 	  uncompress -c $(distdir).tar.Z | $(am__untar) ;;\
 	*.shar.gz*) \
-	  GZIP=$(GZIP_ENV) gzip -dc $(distdir).shar.gz | unshar ;;\
+	  eval GZIP= gzip $(GZIP_ENV) -dc $(distdir).shar.gz | unshar ;;\
 	*.zip*) \
 	  unzip $(distdir).zip ;;\
 	esac
diff --git a/configure b/configure
index 04774ec..a759bd2 100755
--- a/configure
+++ b/configure
@@ -653,6 +653,8 @@ HCL_SIZEOF_CHAR16_T
 HCL_SIZEOF_WCHAR_T
 ENABLE_HCLEX_FALSE
 ENABLE_HCLEX_TRUE
+ENABLE_LIBUNWIND_FALSE
+ENABLE_LIBUNWIND_TRUE
 ENABLE_LIBLTDL_FALSE
 ENABLE_LIBLTDL_TRUE
 ENABLE_STATIC_MODULE_FALSE
@@ -667,6 +669,7 @@ PACKAGE_VERSION_MINOR
 PACKAGE_VERSION_MAJOR
 QUADMATH_LIBS
 UNICOWS_LIBS
+UNWIND_LIBS
 LTDL_LIBS
 DL_LIBS
 PTHREAD_CFLAGS
@@ -779,7 +782,6 @@ infodir
 docdir
 oldincludedir
 includedir
-runstatedir
 localstatedir
 sharedstatedir
 sysconfdir
@@ -818,6 +820,7 @@ enable_cxx
 enable_dynamic_module
 enable_static_module
 enable_libltdl
+enable_libunwind
 enable_hclex
 '
       ac_precious_vars='build_alias
@@ -872,7 +875,6 @@ datadir='${datarootdir}'
 sysconfdir='${prefix}/etc'
 sharedstatedir='${prefix}/com'
 localstatedir='${prefix}/var'
-runstatedir='${localstatedir}/run'
 includedir='${prefix}/include'
 oldincludedir='/usr/include'
 docdir='${datarootdir}/doc/${PACKAGE_TARNAME}'
@@ -1125,15 +1127,6 @@ do
   | -silent | --silent | --silen | --sile | --sil)
     silent=yes ;;
 
-  -runstatedir | --runstatedir | --runstatedi | --runstated \
-  | --runstate | --runstat | --runsta | --runst | --runs \
-  | --run | --ru | --r)
-    ac_prev=runstatedir ;;
-  -runstatedir=* | --runstatedir=* | --runstatedi=* | --runstated=* \
-  | --runstate=* | --runstat=* | --runsta=* | --runst=* | --runs=* \
-  | --run=* | --ru=* | --r=*)
-    runstatedir=$ac_optarg ;;
-
   -sbindir | --sbindir | --sbindi | --sbind | --sbin | --sbi | --sb)
     ac_prev=sbindir ;;
   -sbindir=* | --sbindir=* | --sbindi=* | --sbind=* | --sbin=* \
@@ -1271,7 +1264,7 @@ fi
 for ac_var in	exec_prefix prefix bindir sbindir libexecdir datarootdir \
 		datadir sysconfdir sharedstatedir localstatedir includedir \
 		oldincludedir docdir infodir htmldir dvidir pdfdir psdir \
-		libdir localedir mandir runstatedir
+		libdir localedir mandir
 do
   eval ac_val=\$$ac_var
   # Remove trailing slashes.
@@ -1424,7 +1417,6 @@ Fine tuning of the installation directories:
   --sysconfdir=DIR        read-only single-machine data [PREFIX/etc]
   --sharedstatedir=DIR    modifiable architecture-independent data [PREFIX/com]
   --localstatedir=DIR     modifiable single-machine data [PREFIX/var]
-  --runstatedir=DIR       modifiable per-process data [LOCALSTATEDIR/run]
   --libdir=DIR            object code libraries [EPREFIX/lib]
   --includedir=DIR        C header files [PREFIX/include]
   --oldincludedir=DIR     C header files for non-gcc [/usr/include]
@@ -1484,6 +1476,7 @@ Optional Features:
   --enable-static-module  build modules statically into the main
                           library(default. no)
   --enable-libltdl        use libltdl(default. no)
+  --enable-libunwind      use libunwind(default. no)
   --enable-hclex          build libhclex(default. no)
 
 Optional Packages:
@@ -18246,6 +18239,18 @@ fi
 
 done
 
+for ac_header in libunwind.h
+do :
+  ac_fn_c_check_header_mongrel "$LINENO" "libunwind.h" "ac_cv_header_libunwind_h" "$ac_includes_default"
+if test "x$ac_cv_header_libunwind_h" = xyes; then :
+  cat >>confdefs.h <<_ACEOF
+#define HAVE_LIBUNWIND_H 1
+_ACEOF
+
+fi
+
+done
+
 
 
 
@@ -18454,6 +18459,57 @@ fi
 LIBS="$save_LIBS"
 
 
+if test "x${ac_cv_header_libunwind_h}" = "xyes"
+then
+	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for unw_backtrace in -lunwind" >&5
+$as_echo_n "checking for unw_backtrace in -lunwind... " >&6; }
+if ${ac_cv_lib_unwind_unw_backtrace+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  ac_check_lib_save_LIBS=$LIBS
+LIBS="-lunwind  $LIBS"
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+/* Override any GCC internal prototype to avoid an error.
+   Use char because int might match the return type of a GCC
+   builtin and then its argument prototype would still apply.  */
+#ifdef __cplusplus
+extern "C"
+#endif
+char unw_backtrace ();
+int
+main ()
+{
+return unw_backtrace ();
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  ac_cv_lib_unwind_unw_backtrace=yes
+else
+  ac_cv_lib_unwind_unw_backtrace=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+LIBS=$ac_check_lib_save_LIBS
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_lib_unwind_unw_backtrace" >&5
+$as_echo "$ac_cv_lib_unwind_unw_backtrace" >&6; }
+if test "x$ac_cv_lib_unwind_unw_backtrace" = xyes; then :
+
+			UNWIND_LIBS="-lunwind"
+
+$as_echo "#define HAVE_UNWIND_LIB 1" >>confdefs.h
+
+
+
+fi
+
+
+fi
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for main in -lunicows" >&5
 $as_echo_n "checking for main in -lunicows... " >&6; }
 if ${ac_cv_lib_unicows_main+:} false; then :
@@ -21148,6 +21204,34 @@ else
 fi
 
 
+# Check whether --enable-libunwind was given.
+if test "${enable_libunwind+set}" = set; then :
+  enableval=$enable_libunwind; enable_libunwind_is=$enableval
+else
+  enable_libunwind_is=no
+
+fi
+
+if test "x${enable_libunwind_is}" = "xyes"
+then
+	if test "x${ac_cv_header_unwind_h}" = "xyes"  -a "${UNWIND_LIBS}" != ""
+	then
+
+$as_echo "#define HCL_ENABLE_LIBUNWIND /**/" >>confdefs.h
+
+	else
+		enable_libunwind_is="no"
+	fi
+fi
+ if test "x${enable_libunwind_is}" = "xyes"; then
+  ENABLE_LIBUNWIND_TRUE=
+  ENABLE_LIBUNWIND_FALSE='#'
+else
+  ENABLE_LIBUNWIND_TRUE='#'
+  ENABLE_LIBUNWIND_FALSE=
+fi
+
+
 # Check whether --enable-hclex was given.
 if test "${enable_hclex+set}" = set; then :
   enableval=$enable_hclex; enable_hclex_is=$enableval
@@ -21363,6 +21447,10 @@ if test -z "${ENABLE_LIBLTDL_TRUE}" && test -z "${ENABLE_LIBLTDL_FALSE}"; then
   as_fn_error $? "conditional \"ENABLE_LIBLTDL\" was never defined.
 Usually this means the macro was only invoked conditionally." "$LINENO" 5
 fi
+if test -z "${ENABLE_LIBUNWIND_TRUE}" && test -z "${ENABLE_LIBUNWIND_FALSE}"; then
+  as_fn_error $? "conditional \"ENABLE_LIBUNWIND\" was never defined.
+Usually this means the macro was only invoked conditionally." "$LINENO" 5
+fi
 if test -z "${ENABLE_HCLEX_TRUE}" && test -z "${ENABLE_HCLEX_FALSE}"; then
   as_fn_error $? "conditional \"ENABLE_HCLEX\" was never defined.
 Usually this means the macro was only invoked conditionally." "$LINENO" 5
diff --git a/configure.ac b/configure.ac
index 085c819..22f89f8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -122,6 +122,7 @@ AC_CHECK_HEADERS([stddef.h wchar.h wctype.h errno.h signal.h fcntl.h dirent.h])
 AC_CHECK_HEADERS([time.h sys/time.h utime.h spawn.h execinfo.h ucontext.h])
 AC_CHECK_HEADERS([dlfcn.h ltdl.h sys/mman.h sys/uio.h])
 AC_CHECK_HEADERS([sys/devpoll.h sys/epoll.h poll.h])
+AC_CHECK_HEADERS([libunwind.h])
 
 dnl check data types
 dnl AC_CHECK_TYPE([wchar_t], 
@@ -161,6 +162,17 @@ AC_SEARCH_LIBS([lt_dlopen], [ltdl], [
 LIBS="$save_LIBS"
 AC_SUBST(LTDL_LIBS)
 
+if test "x${ac_cv_header_libunwind_h}" = "xyes" 
+then
+	AC_CHECK_LIB([unwind], [unw_backtrace], 
+		[
+			UNWIND_LIBS="-lunwind"
+			AC_DEFINE([HAVE_UNWIND_LIB], [1], [libunwind is available])
+		]
+	)
+	AC_SUBST(UNWIND_LIBS)
+fi
+
 dnl check is the import library for unicows.dll exists
 dnl this check doesn't look for a particular symbol
 dnl but for the symbol 'main' since i want to check 
@@ -643,6 +655,23 @@ then
 fi
 AM_CONDITIONAL(ENABLE_LIBLTDL, test "x${enable_libltdl_is}" = "xyes")
 
+dnl ===== enable-libunwind =====
+AC_ARG_ENABLE([libunwind],
+	[AS_HELP_STRING([--enable-libunwind],[use libunwind(default. no)])],
+	enable_libunwind_is=$enableval,
+	enable_libunwind_is=no
+)
+if test "x${enable_libunwind_is}" = "xyes"
+then
+	if test "x${ac_cv_header_unwind_h}" = "xyes"  -a "${UNWIND_LIBS}" != ""
+	then
+		AC_DEFINE([HCL_ENABLE_LIBUNWIND],[],[use libunwind for backtracing stack frames])
+	else
+		enable_libunwind_is="no"
+	fi
+fi
+AM_CONDITIONAL(ENABLE_LIBUNWIND, test "x${enable_libunwind_is}" = "xyes")
+
 dnl ===== enable-hclex =====
 AC_ARG_ENABLE([hclex],
 	[AS_HELP_STRING([--enable-hclex],[build libhclex(default. no)])],
diff --git a/lib/Makefile.am b/lib/Makefile.am
index b2a151d..fa94b22 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -28,6 +28,9 @@ else
 LIBADD_LIB_COMMON += $(DL_LIBS)
 endif
 
+if ENABLE_LIBUNWIND
+LIBADD_LIB_COMMON += $(UNWIND_LIBS)
+endif
 
 pkgincludedir = $(includedir)
 pkglibdir = $(libdir)
diff --git a/lib/Makefile.in b/lib/Makefile.in
index 63aa4bf..9d9f4ff 100644
--- a/lib/Makefile.in
+++ b/lib/Makefile.in
@@ -90,15 +90,16 @@ build_triplet = @build@
 host_triplet = @host@
 @ENABLE_LIBLTDL_TRUE@am__append_1 = $(LTDL_LIBS)
 @ENABLE_LIBLTDL_FALSE@am__append_2 = $(DL_LIBS)
-@ENABLE_STATIC_MODULE_TRUE@am__append_3 = -lhcl-arr -lhcl-dic \
+@ENABLE_LIBUNWIND_TRUE@am__append_3 = $(UNWIND_LIBS)
+@ENABLE_STATIC_MODULE_TRUE@am__append_4 = -lhcl-arr -lhcl-dic \
 @ENABLE_STATIC_MODULE_TRUE@	-lhcl-str
-@ENABLE_STATIC_MODULE_TRUE@am__append_4 = $(abs_builddir)/../mod/libhcl-arr.la \
+@ENABLE_STATIC_MODULE_TRUE@am__append_5 = $(abs_builddir)/../mod/libhcl-arr.la \
 @ENABLE_STATIC_MODULE_TRUE@	$(abs_builddir)/../mod/libhcl-dic.la \
 @ENABLE_STATIC_MODULE_TRUE@	$(abs_builddir)/../mod/libhcl-str.la
 bin_PROGRAMS = hcl$(EXEEXT) $(am__EXEEXT_1)
-@ENABLE_HCLEX_TRUE@am__append_5 = libhclex.la
-@ENABLE_HCLEX_TRUE@am__append_6 = hcl-c.h hcl-s.h hcl-tmr.h hcl-xutl.h hcl-json.h
-@ENABLE_HCLEX_TRUE@am__append_7 = hcls hclc hclj
+@ENABLE_HCLEX_TRUE@am__append_6 = libhclex.la
+@ENABLE_HCLEX_TRUE@am__append_7 = hcl-c.h hcl-s.h hcl-tmr.h hcl-xutl.h hcl-json.h
+@ENABLE_HCLEX_TRUE@am__append_8 = hcls hclc hclj
 subdir = lib
 ACLOCAL_M4 = $(top_srcdir)/aclocal.m4
 am__aclocal_m4_deps = $(top_srcdir)/m4/ax_check_sign.m4 \
@@ -148,8 +149,9 @@ LTLIBRARIES = $(pkglib_LTLIBRARIES)
 am__DEPENDENCIES_1 =
 @ENABLE_LIBLTDL_TRUE@am__DEPENDENCIES_2 = $(am__DEPENDENCIES_1)
 @ENABLE_LIBLTDL_FALSE@am__DEPENDENCIES_3 = $(am__DEPENDENCIES_1)
-am__DEPENDENCIES_4 = $(am__DEPENDENCIES_1) $(am__DEPENDENCIES_2) \
-	$(am__DEPENDENCIES_3)
+@ENABLE_LIBUNWIND_TRUE@am__DEPENDENCIES_4 = $(am__DEPENDENCIES_1)
+am__DEPENDENCIES_5 = $(am__DEPENDENCIES_1) $(am__DEPENDENCIES_2) \
+	$(am__DEPENDENCIES_3) $(am__DEPENDENCIES_4)
 am_libhcl_la_OBJECTS = libhcl_la-bigint.lo libhcl_la-comp.lo \
 	libhcl_la-debug.lo libhcl_la-decode.lo libhcl_la-dic.lo \
 	libhcl_la-err.lo libhcl_la-exec.lo libhcl_la-gc.lo \
@@ -370,6 +372,7 @@ SET_MAKE = @SET_MAKE@
 SHELL = @SHELL@
 STRIP = @STRIP@
 UNICOWS_LIBS = @UNICOWS_LIBS@
+UNWIND_LIBS = @UNWIND_LIBS@
 VERSION = @VERSION@
 abs_builddir = @abs_builddir@
 abs_srcdir = @abs_srcdir@
@@ -417,7 +420,6 @@ pdfdir = @pdfdir@
 prefix = @prefix@
 program_transform_name = @program_transform_name@
 psdir = @psdir@
-runstatedir = @runstatedir@
 sbindir = @sbindir@
 sharedstatedir = @sharedstatedir@
 srcdir = @srcdir@
@@ -441,10 +443,11 @@ CPPFLAGS_ALL_COMMON = \
 ##################################################
 CPPFLAGS_LIB_COMMON = $(CPPFLAGS_ALL_COMMON)
 LDFLAGS_LIB_COMMON = $(LDFLAGS_ALL_COMMON) -version-info 1:0:0 -no-undefined
-LIBADD_LIB_COMMON = $(LIBM) $(am__append_1) $(am__append_2)
+LIBADD_LIB_COMMON = $(LIBM) $(am__append_1) $(am__append_2) \
+	$(am__append_3)
 pkginclude_HEADERS = hcl.h hcl-cmn.h hcl-opt.h hcl-rbt.h hcl-utl.h \
-	$(am__append_6)
-pkglib_LTLIBRARIES = libhcl.la $(am__append_5)
+	$(am__append_7)
+pkglib_LTLIBRARIES = libhcl.la $(am__append_6)
 libhcl_la_SOURCES = \
 	hcl.h \
 	hcl-cmn.h \
@@ -478,8 +481,8 @@ libhcl_la_SOURCES = \
 
 libhcl_la_CPPFLAGS = $(CPPFLAGS_LIB_COMMON)
 libhcl_la_LDFLAGS = $(LDFLAGS_LIB_COMMON)
-libhcl_la_LIBADD = $(LIBADD_LIB_COMMON) $(am__append_3)
-libhcl_la_DEPENDENCIES = $(am__append_4)
+libhcl_la_LIBADD = $(LIBADD_LIB_COMMON) $(am__append_4)
+libhcl_la_DEPENDENCIES = $(am__append_5)
 hcl_SOURCES = main.c 
 hcl_CPPFLAGS = $(CPPFLAGS_LIB_COMMON)
 hcl_LDFLAGS = $(LDFLAGS_LIB_COMMON)
diff --git a/lib/err.c b/lib/err.c
index 41f253c..3c71df1 100644
--- a/lib/err.c
+++ b/lib/err.c
@@ -26,6 +26,10 @@
 
 #include "hcl-prv.h"
 
+#if defined(HCL_ENABLE_LIBUNWIND)
+#	include <libunwind.h>
+#endif
+
 static hcl_ooch_t errstr_0[] = {'n','o',' ','e','r','r','o','r','\0'};
 static hcl_ooch_t errstr_1[] = {'g','e','n','e','r','i','c',' ','e','r','r','o','r','\0'};
 static hcl_ooch_t errstr_2[] = {'n','o','t',' ','i','m','p','l','e','m','e','n','t','e','d','\0'};
@@ -472,22 +476,45 @@ void hcl_setsynerrufmt (hcl_t* hcl, hcl_synerrnum_t num, const hcl_ioloc_t* loc,
 	}
 }
 
-
 /* -------------------------------------------------------------------------- 
- * ASSERTION FAILURE HANDLERsemaphore heap full
+ * STACK FRAME BACKTRACE
  * -------------------------------------------------------------------------- */
-
-void hcl_assertfailed (hcl_t* hcl, const hcl_bch_t* expr, const hcl_bch_t* file, hcl_oow_t line)
+#if defined(HCL_ENABLE_LIBUNWIND)
+static void backtrace_stack_frames (hcl_t* hcl)
+{
+	unw_cursor_t cursor;
+	unw_context_t context;
+
+	unw_getcontext(&context);
+	unw_init_local(&cursor, &context);
+
+	int n=0;
+	while (unw_step(&cursor)) 
+	{
+		unw_word_t ip, sp, off;
+
+		unw_get_reg (&cursor, UNW_REG_IP, &ip);
+		unw_get_reg (&cursor, UNW_REG_SP, &sp);
+
+		char symbol[256];
+
+		if (!unw_get_proc_name(&cursor, symbol, HCL_COUNTOF(symbol), &off)) 
+		{
+			hcl_copy_bcstr (symbol, "<unknown>");
+		}
+
+		hcl_logbfmt (hcl, HCL_LOG_UNTYPED | HCL_LOG_DEBUG, 
+			"#%-2d 0x%016p p=0x%016p %s + 0x%zu\n", 
+			++n, (void*)ip, (void*)sp, symbol, (hcl_oow_t)off);
+	}
+}
+#elif defined(HAVE_BACKTRACE)
+static void backtrace_stack_frames (hcl_t* hcl)
 {
-#if defined(HAVE_BACKTRACE)
 	void* btarray[128];
 	hcl_oow_t btsize;
 	char** btsyms;
-#endif
 
-	hcl_logbfmt (hcl, HCL_LOG_UNTYPED | HCL_LOG_FATAL, "ASSERTION FAILURE: %s at %s:%zu\n", expr, file, line);
-
-#if defined(HAVE_BACKTRACE)
 	btsize = backtrace (btarray, HCL_COUNTOF(btarray));
 	btsyms = backtrace_symbols (btarray, btsize);
 	if (btsyms)
@@ -501,8 +528,22 @@ void hcl_assertfailed (hcl_t* hcl, const hcl_bch_t* expr, const hcl_bch_t* file,
 		}
 		free (btsyms);
 	}
+}
+#else
+static void backtrace_stack_frames (hcl_t* hcl)
+{
+	/* do nothing. not supported */
+}
 #endif
 
+/* -------------------------------------------------------------------------- 
+ * ASSERTION FAILURE HANDLERsemaphore heap full
+ * -------------------------------------------------------------------------- */
+
+void hcl_assertfailed (hcl_t* hcl, const hcl_bch_t* expr, const hcl_bch_t* file, hcl_oow_t line)
+{
+	hcl_logbfmt (hcl, HCL_LOG_UNTYPED | HCL_LOG_FATAL, "ASSERTION FAILURE: %s at %s:%zu\n", expr, file, line);
+	backtrace_stack_frames (hcl);
 
 #if defined(_WIN32)
 	ExitProcess (249);
diff --git a/lib/hcl-cfg.h.in b/lib/hcl-cfg.h.in
index fe7850d..7cbac63 100644
--- a/lib/hcl-cfg.h.in
+++ b/lib/hcl-cfg.h.in
@@ -81,6 +81,9 @@
 /* Define to 1 if you have the `isatty' function. */
 #undef HAVE_ISATTY
 
+/* Define to 1 if you have the <libunwind.h> header file. */
+#undef HAVE_LIBUNWIND_H
+
 /* Define to 1 if you have the `log10q' function. */
 #undef HAVE_LOG10Q
 
@@ -213,6 +216,9 @@
 /* Define to 1 if you have the <unistd.h> header file. */
 #undef HAVE_UNISTD_H
 
+/* libunwind is available */
+#undef HAVE_UNWIND_LIB
+
 /* Define to 1 if you have the `usleep' function. */
 #undef HAVE_USLEEP
 
@@ -264,6 +270,9 @@
 /* use libltdl when loading a dynamic module */
 #undef HCL_ENABLE_LIBLTDL
 
+/* use libunwind for backtracing stack frames */
+#undef HCL_ENABLE_LIBUNWIND
+
 /* link modules statically into the main library */
 #undef HCL_ENABLE_STATIC_MODULE
 
diff --git a/mod/Makefile.in b/mod/Makefile.in
index 40b1ca0..10bc392 100644
--- a/mod/Makefile.in
+++ b/mod/Makefile.in
@@ -329,6 +329,7 @@ SET_MAKE = @SET_MAKE@
 SHELL = @SHELL@
 STRIP = @STRIP@
 UNICOWS_LIBS = @UNICOWS_LIBS@
+UNWIND_LIBS = @UNWIND_LIBS@
 VERSION = @VERSION@
 abs_builddir = @abs_builddir@
 abs_srcdir = @abs_srcdir@
@@ -376,7 +377,6 @@ pdfdir = @pdfdir@
 prefix = @prefix@
 program_transform_name = @program_transform_name@
 psdir = @psdir@
-runstatedir = @runstatedir@
 sbindir = @sbindir@
 sharedstatedir = @sharedstatedir@
 srcdir = @srcdir@