diff --git a/mio/Makefile.in b/mio/Makefile.in
index c3bfc6b..2fe5d77 100644
--- a/mio/Makefile.in
+++ b/mio/Makefile.in
@@ -300,6 +300,7 @@ SOCKET_LIBS = @SOCKET_LIBS@
 SSL_LIBS = @SSL_LIBS@
 STRIP = @STRIP@
 UNICOWS_LIBS = @UNICOWS_LIBS@
+UNWIND_LIBS = @UNWIND_LIBS@
 VERSION = @VERSION@
 abs_builddir = @abs_builddir@
 abs_srcdir = @abs_srcdir@
@@ -346,6 +347,7 @@ pdfdir = @pdfdir@
 prefix = @prefix@
 program_transform_name = @program_transform_name@
 psdir = @psdir@
+runstatedir = @runstatedir@
 sbindir = @sbindir@
 sharedstatedir = @sharedstatedir@
 srcdir = @srcdir@
@@ -576,7 +578,7 @@ 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) | eval GZIP= gzip $(GZIP_ENV) -c >$(distdir).tar.gz
+	tardir=$(distdir) && $(am__tar) | GZIP=$(GZIP_ENV) gzip -c >$(distdir).tar.gz
 	$(am__post_remove_distdir)
 
 dist-bzip2: distdir
@@ -602,7 +604,7 @@ 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) | eval GZIP= gzip $(GZIP_ENV) -c >$(distdir).shar.gz
+	shar $(distdir) | GZIP=$(GZIP_ENV) gzip -c >$(distdir).shar.gz
 	$(am__post_remove_distdir)
 
 dist-zip: distdir
@@ -620,7 +622,7 @@ dist dist-all:
 distcheck: dist
 	case '$(DIST_ARCHIVES)' in \
 	*.tar.gz*) \
-	  eval GZIP= gzip $(GZIP_ENV) -dc $(distdir).tar.gz | $(am__untar) ;;\
+	  GZIP=$(GZIP_ENV) gzip -dc $(distdir).tar.gz | $(am__untar) ;;\
 	*.tar.bz2*) \
 	  bzip2 -dc $(distdir).tar.bz2 | $(am__untar) ;;\
 	*.tar.lz*) \
@@ -630,7 +632,7 @@ distcheck: dist
 	*.tar.Z*) \
 	  uncompress -c $(distdir).tar.Z | $(am__untar) ;;\
 	*.shar.gz*) \
-	  eval GZIP= gzip $(GZIP_ENV) -dc $(distdir).shar.gz | unshar ;;\
+	  GZIP=$(GZIP_ENV) gzip -dc $(distdir).shar.gz | unshar ;;\
 	*.zip*) \
 	  unzip $(distdir).zip ;;\
 	esac
diff --git a/mio/configure b/mio/configure
index 8934747..0f780d6 100755
--- a/mio/configure
+++ b/mio/configure
@@ -649,6 +649,8 @@ MIO_SIZEOF_INT
 MIO_SIZEOF_LONG
 MIO_SIZEOF_LONG_LONG
 MIO_SIZEOF_WCHAR_T
+ENABLE_LIBUNWIND_FALSE
+ENABLE_LIBUNWIND_TRUE
 ENABLE_CXX_FALSE
 ENABLE_CXX_TRUE
 BUILD_MODE
@@ -656,6 +658,7 @@ PACKAGE_VERSION_PATCH
 PACKAGE_VERSION_MINOR
 PACKAGE_VERSION_MAJOR
 QUADMATH_LIBS
+UNWIND_LIBS
 SSL_LIBS
 UNICOWS_LIBS
 SENDFILE_LIBS
@@ -768,6 +771,7 @@ infodir
 docdir
 oldincludedir
 includedir
+runstatedir
 localstatedir
 sharedstatedir
 sysconfdir
@@ -804,6 +808,7 @@ enable_ssl
 enable_debug
 enable_unicode
 enable_cxx
+enable_libunwind
 '
       ac_precious_vars='build_alias
 host_alias
@@ -857,6 +862,7 @@ datadir='${datarootdir}'
 sysconfdir='${prefix}/etc'
 sharedstatedir='${prefix}/com'
 localstatedir='${prefix}/var'
+runstatedir='${localstatedir}/run'
 includedir='${prefix}/include'
 oldincludedir='/usr/include'
 docdir='${datarootdir}/doc/${PACKAGE_TARNAME}'
@@ -1109,6 +1115,15 @@ 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=$ac_optarg ;;
+
   -sbindir | --sbindir | --sbindi | --sbind | --sbin | --sbi | --sb)
     ac_prev=sbindir ;;
   -sbindir=* | --sbindir=* | --sbindi=* | --sbind=* | --sbin=* \
@@ -1246,7 +1261,7 @@ fi
 for ac_var in	exec_prefix prefix bindir sbindir libexecdir datarootdir \
 		datadir sysconfdir sharedstatedir localstatedir includedir \
 		oldincludedir docdir infodir htmldir dvidir pdfdir psdir \
-		libdir localedir mandir
+		libdir localedir mandir runstatedir
 do
   eval ac_val=\$$ac_var
   # Remove trailing slashes.
@@ -1399,6 +1414,7 @@ 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]
@@ -1455,6 +1471,7 @@ Optional Features:
                           no:4 (default. yes)
   --enable-cxx            build the library for C++ if a C++ compiler is
                           available (default. yes)
+  --enable-libunwind      use libunwind(default. no)
 
 Optional Packages:
   --with-PACKAGE[=ARG]    use PACKAGE [ARG=yes]
@@ -18646,6 +18663,57 @@ done
 fi
 
 
+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"
+
+$as_echo "#define HAVE_UNWIND_LIB 1" >>confdefs.h
+
+
+
+fi
+
+
+fi
+
 ac_header_dirent=no
 for ac_hdr in dirent.h sys/ndir.h sys/dir.h ndir.h; do
   as_ac_Header=`$as_echo "ac_cv_header_dirent_$ac_hdr" | $as_tr_sh`
@@ -21581,10 +21649,8 @@ else
 
 fi
 
-
 test "${HAVE_CXX}" = "yes" || enable_cxx_is="no"
 test "${ax_cv_cxx_have_std_namespace}" = "yes" || enable_cxx_is="no"
-
  if test "${enable_cxx_is}" = "yes" ; then
   ENABLE_CXX_TRUE=
   ENABLE_CXX_FALSE='#'
@@ -21594,6 +21660,35 @@ 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${ac_cv_header_libunwind_h}" = "xyes"  -a "${UNWIND_LIBS}" != ""
+        then
+
+$as_echo "#define MIO_ENABLE_LIBUNWIND /**/" >>confdefs.h
+
+        else
+                enable_libunwind_is="no"
+        fi
+fi
+ if test "x${enable_libunwind_is}" = "xyes"; then
+  ENABLE_LIBUNWIND_TRUE=
+  ENABLE_LIBUNWIND_FALSE='#'
+else
+  ENABLE_LIBUNWIND_TRUE='#'
+  ENABLE_LIBUNWIND_FALSE=
+fi
+
+
 MIO_SIZEOF_WCHAR_T=$ac_cv_sizeof_wchar_t
 
 MIO_SIZEOF_LONG_LONG=$ac_cv_sizeof_long_long
@@ -21780,6 +21875,10 @@ if test -z "${ENABLE_CXX_TRUE}" && test -z "${ENABLE_CXX_FALSE}"; then
   as_fn_error $? "conditional \"ENABLE_CXX\" was never defined.
 Usually this means the macro was only invoked conditionally." "$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
 
 : "${CONFIG_STATUS=./config.status}"
 ac_write_fail=0
diff --git a/mio/configure.ac b/mio/configure.ac
index b821c07..c083e5d 100644
--- a/mio/configure.ac
+++ b/mio/configure.ac
@@ -303,6 +303,17 @@ then
 fi
 AC_SUBST(SSL_LIBS)
 
+if test "x${ac_cv_header_libunwind_h}" = "xyes"
+then
+	AC_CHECK_LIB([unwind], [unw_backtrace],
+		[
+			UNWIND_LIBS="-lunwind"
+			AC_DEFINE([HAVE_UNWIND_LIB], [1], [libunwind is available])
+		]
+	)
+	AC_SUBST(UNWIND_LIBS)
+fi
+
 AC_STRUCT_DIRENT_D_TYPE
 AC_CHECK_MEMBERS([DIR.d_fd, DIR.dd_fd],,,[[#include <dirent.h>]])
 AC_CHECK_MEMBERS([struct stat.st_birthtime])
@@ -833,14 +844,29 @@ AC_ARG_ENABLE([cxx],
 	enable_cxx_is=$enableval,
 	enable_cxx_is=yes
 )
-
 dnl disable c++ if no c++ compiler was found
 test "${HAVE_CXX}" = "yes" || enable_cxx_is="no"
 dnl disable c++ if the compiler is too old.
 test "${ax_cv_cxx_have_std_namespace}" = "yes" || enable_cxx_is="no"
-
 AM_CONDITIONAL(ENABLE_CXX, test "${enable_cxx_is}" = "yes" )
 
+
+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${ac_cv_header_libunwind_h}" = "xyes"  -a "${UNWIND_LIBS}" != ""
+        then
+                AC_DEFINE([MIO_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")
+
 AC_SUBST(MIO_SIZEOF_WCHAR_T, $ac_cv_sizeof_wchar_t)
 AC_SUBST(MIO_SIZEOF_LONG_LONG, $ac_cv_sizeof_long_long)
 AC_SUBST(MIO_SIZEOF_LONG, $ac_cv_sizeof_long)
diff --git a/mio/lib/Makefile.am b/mio/lib/Makefile.am
index 8feddf8..5d5aa4f 100644
--- a/mio/lib/Makefile.am
+++ b/mio/lib/Makefile.am
@@ -40,6 +40,9 @@ libmio_la_SOURCES = \
 	mio-tmr.c \
 	sck-addr.c \
 	sck-addr.h \
+	sys-ass.c \
+	sys-err.c \
+	sys-log.c \
 	utf8.c \
 	utl.c
 libmio_la_CPPFLAGS = $(CPPFLAGS_LIB_COMMON)
diff --git a/mio/lib/Makefile.in b/mio/lib/Makefile.in
index 42e2053..9087fbd 100644
--- a/mio/lib/Makefile.in
+++ b/mio/lib/Makefile.in
@@ -143,7 +143,9 @@ libmio_la_DEPENDENCIES = $(am__DEPENDENCIES_2) $(am__DEPENDENCIES_1)
 am_libmio_la_OBJECTS = libmio_la-err.lo libmio_la-logfmt.lo \
 	libmio_la-mio.lo libmio_la-mio-pro.lo libmio_la-mio-sck.lo \
 	libmio_la-mio-tim.lo libmio_la-mio-tmr.lo \
-	libmio_la-sck-addr.lo libmio_la-utf8.lo libmio_la-utl.lo
+	libmio_la-sck-addr.lo libmio_la-sys-ass.lo \
+	libmio_la-sys-err.lo libmio_la-sys-log.lo libmio_la-utf8.lo \
+	libmio_la-utl.lo
 libmio_la_OBJECTS = $(am_libmio_la_OBJECTS)
 AM_V_lt = $(am__v_lt_@AM_V@)
 am__v_lt_ = $(am__v_lt_@AM_DEFAULT_V@)
@@ -316,6 +318,7 @@ SOCKET_LIBS = @SOCKET_LIBS@
 SSL_LIBS = @SSL_LIBS@
 STRIP = @STRIP@
 UNICOWS_LIBS = @UNICOWS_LIBS@
+UNWIND_LIBS = @UNWIND_LIBS@
 VERSION = @VERSION@
 abs_builddir = @abs_builddir@
 abs_srcdir = @abs_srcdir@
@@ -362,6 +365,7 @@ pdfdir = @pdfdir@
 prefix = @prefix@
 program_transform_name = @program_transform_name@
 psdir = @psdir@
+runstatedir = @runstatedir@
 sbindir = @sbindir@
 sharedstatedir = @sharedstatedir@
 srcdir = @srcdir@
@@ -409,6 +413,9 @@ libmio_la_SOURCES = \
 	mio-tmr.c \
 	sck-addr.c \
 	sck-addr.h \
+	sys-ass.c \
+	sys-err.c \
+	sys-log.c \
 	utf8.c \
 	utl.c
 
@@ -574,6 +581,9 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libmio_la-mio-tmr.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libmio_la-mio.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libmio_la-sck-addr.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libmio_la-sys-ass.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libmio_la-sys-err.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libmio_la-sys-log.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libmio_la-utf8.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libmio_la-utl.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/mio-main.Po@am__quote@
@@ -658,6 +668,27 @@ libmio_la-sck-addr.lo: sck-addr.c
 @AMDEP_TRUE@@am__fastdepCC_FALSE@	DEPDIR=$(DEPDIR) $(CCDEPMODE) $(depcomp) @AMDEPBACKSLASH@
 @am__fastdepCC_FALSE@	$(AM_V_CC@am__nodep@)$(LIBTOOL) $(AM_V_lt) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) --mode=compile $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libmio_la_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -c -o libmio_la-sck-addr.lo `test -f 'sck-addr.c' || echo '$(srcdir)/'`sck-addr.c
 
+libmio_la-sys-ass.lo: sys-ass.c
+@am__fastdepCC_TRUE@	$(AM_V_CC)$(LIBTOOL) $(AM_V_lt) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) --mode=compile $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libmio_la_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -MT libmio_la-sys-ass.lo -MD -MP -MF $(DEPDIR)/libmio_la-sys-ass.Tpo -c -o libmio_la-sys-ass.lo `test -f 'sys-ass.c' || echo '$(srcdir)/'`sys-ass.c
+@am__fastdepCC_TRUE@	$(AM_V_at)$(am__mv) $(DEPDIR)/libmio_la-sys-ass.Tpo $(DEPDIR)/libmio_la-sys-ass.Plo
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	$(AM_V_CC)source='sys-ass.c' object='libmio_la-sys-ass.lo' libtool=yes @AMDEPBACKSLASH@
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	DEPDIR=$(DEPDIR) $(CCDEPMODE) $(depcomp) @AMDEPBACKSLASH@
+@am__fastdepCC_FALSE@	$(AM_V_CC@am__nodep@)$(LIBTOOL) $(AM_V_lt) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) --mode=compile $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libmio_la_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -c -o libmio_la-sys-ass.lo `test -f 'sys-ass.c' || echo '$(srcdir)/'`sys-ass.c
+
+libmio_la-sys-err.lo: sys-err.c
+@am__fastdepCC_TRUE@	$(AM_V_CC)$(LIBTOOL) $(AM_V_lt) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) --mode=compile $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libmio_la_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -MT libmio_la-sys-err.lo -MD -MP -MF $(DEPDIR)/libmio_la-sys-err.Tpo -c -o libmio_la-sys-err.lo `test -f 'sys-err.c' || echo '$(srcdir)/'`sys-err.c
+@am__fastdepCC_TRUE@	$(AM_V_at)$(am__mv) $(DEPDIR)/libmio_la-sys-err.Tpo $(DEPDIR)/libmio_la-sys-err.Plo
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	$(AM_V_CC)source='sys-err.c' object='libmio_la-sys-err.lo' libtool=yes @AMDEPBACKSLASH@
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	DEPDIR=$(DEPDIR) $(CCDEPMODE) $(depcomp) @AMDEPBACKSLASH@
+@am__fastdepCC_FALSE@	$(AM_V_CC@am__nodep@)$(LIBTOOL) $(AM_V_lt) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) --mode=compile $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libmio_la_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -c -o libmio_la-sys-err.lo `test -f 'sys-err.c' || echo '$(srcdir)/'`sys-err.c
+
+libmio_la-sys-log.lo: sys-log.c
+@am__fastdepCC_TRUE@	$(AM_V_CC)$(LIBTOOL) $(AM_V_lt) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) --mode=compile $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libmio_la_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -MT libmio_la-sys-log.lo -MD -MP -MF $(DEPDIR)/libmio_la-sys-log.Tpo -c -o libmio_la-sys-log.lo `test -f 'sys-log.c' || echo '$(srcdir)/'`sys-log.c
+@am__fastdepCC_TRUE@	$(AM_V_at)$(am__mv) $(DEPDIR)/libmio_la-sys-log.Tpo $(DEPDIR)/libmio_la-sys-log.Plo
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	$(AM_V_CC)source='sys-log.c' object='libmio_la-sys-log.lo' libtool=yes @AMDEPBACKSLASH@
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	DEPDIR=$(DEPDIR) $(CCDEPMODE) $(depcomp) @AMDEPBACKSLASH@
+@am__fastdepCC_FALSE@	$(AM_V_CC@am__nodep@)$(LIBTOOL) $(AM_V_lt) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) --mode=compile $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libmio_la_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -c -o libmio_la-sys-log.lo `test -f 'sys-log.c' || echo '$(srcdir)/'`sys-log.c
+
 libmio_la-utf8.lo: utf8.c
 @am__fastdepCC_TRUE@	$(AM_V_CC)$(LIBTOOL) $(AM_V_lt) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) --mode=compile $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libmio_la_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -MT libmio_la-utf8.lo -MD -MP -MF $(DEPDIR)/libmio_la-utf8.Tpo -c -o libmio_la-utf8.lo `test -f 'utf8.c' || echo '$(srcdir)/'`utf8.c
 @am__fastdepCC_TRUE@	$(AM_V_at)$(am__mv) $(DEPDIR)/libmio_la-utf8.Tpo $(DEPDIR)/libmio_la-utf8.Plo
diff --git a/mio/lib/err.c b/mio/lib/err.c
index d1c7e35..9207add 100644
--- a/mio/lib/err.c
+++ b/mio/lib/err.c
@@ -78,208 +78,6 @@ const mio_ooch_t* mio_errnum_to_errstr (mio_errnum_t errnum)
 	return (errnum >= 0 && errnum < MIO_COUNTOF(errstr))? errstr[errnum]: e_unknown;
 }
 
-/* -------------------------------------------------------------------------- 
- * ERROR MESSAGE CONVERSION
- * -------------------------------------------------------------------------- */
-#include <errno.h>
-
-static mio_errnum_t errno_to_errnum (int errcode)
-{
-	switch (errcode)
-	{
-		case ENOMEM: return MIO_ESYSMEM;
-		case EINVAL: return MIO_EINVAL;
-
-	#if defined(EBUSY)
-		case EBUSY: return MIO_EBUSY;
-	#endif
-		case EACCES: return MIO_EACCES;
-	#if defined(EPERM)
-		case EPERM: return MIO_EPERM;
-	#endif
-	#if defined(ENOTDIR)
-		case ENOTDIR: return MIO_ENOTDIR;
-	#endif
-		case ENOENT: return MIO_ENOENT;
-	#if defined(EEXIST)
-		case EEXIST: return MIO_EEXIST;
-	#endif
-	#if defined(EINTR)
-		case EINTR:  return MIO_EINTR;
-	#endif
-
-	#if defined(EPIPE)
-		case EPIPE:  return MIO_EPIPE;
-	#endif
-
-	#if defined(EAGAIN) && defined(EWOULDBLOCK) && (EAGAIN != EWOULDBLOCK)
-		case EAGAIN: 
-		case EWOULDBLOCK: return MIO_EAGAIN;
-	#elif defined(EAGAIN)
-		case EAGAIN: return MIO_EAGAIN;
-	#elif defined(EWOULDBLOCK)
-		case EWOULDBLOCK: return MIO_EAGAIN;
-	#endif
-
-	#if defined(EBADF)
-		case EBADF: return MIO_EBADHND;
-	#endif
-
-	#if defined(EIO)
-		case EIO: return MIO_EIOERR;
-	#endif
-
-		default: return MIO_ESYSERR;
-	}
-}
-
-#if defined(_WIN32)
-static mio_errnum_t winerr_to_errnum (DWORD errcode)
-{
-	switch (errcode)
-	{
-		case ERROR_NOT_ENOUGH_MEMORY:
-		case ERROR_OUTOFMEMORY:
-			return MIO_ESYSMEM;
-
-		case ERROR_INVALID_PARAMETER:
-		case ERROR_INVALID_NAME:
-			return MIO_EINVAL;
-
-		case ERROR_INVALID_HANDLE:
-			return MIO_EBADHND;
-
-		case ERROR_ACCESS_DENIED:
-		case ERROR_SHARING_VIOLATION:
-			return MIO_EACCES;
-
-	#if defined(ERROR_IO_PRIVILEGE_FAILED)
-		case ERROR_IO_PRIVILEGE_FAILED:
-	#endif
-		case ERROR_PRIVILEGE_NOT_HELD:
-			return MIO_EPERM;
-
-		case ERROR_FILE_NOT_FOUND:
-		case ERROR_PATH_NOT_FOUND:
-			return MIO_ENOENT;
-
-		case ERROR_ALREADY_EXISTS:
-		case ERROR_FILE_EXISTS:
-			return MIO_EEXIST;
-
-		case ERROR_BROKEN_PIPE:
-			return MIO_EPIPE;
-
-		default:
-			return MIO_ESYSERR;
-	}
-}
-#endif
-
-#if defined(__OS2__)
-static mio_errnum_t os2err_to_errnum (APIRET errcode)
-{
-	/* APIRET e */
-	switch (errcode)
-	{
-		case ERROR_NOT_ENOUGH_MEMORY:
-			return MIO_ESYSMEM;
-
-		case ERROR_INVALID_PARAMETER: 
-		case ERROR_INVALID_NAME:
-			return MIO_EINVAL;
-
-		case ERROR_INVALID_HANDLE: 
-			return MIO_EBADHND;
-
-		case ERROR_ACCESS_DENIED: 
-		case ERROR_SHARING_VIOLATION:
-			return MIO_EACCES;
-
-		case ERROR_FILE_NOT_FOUND:
-		case ERROR_PATH_NOT_FOUND:
-			return MIO_ENOENT;
-
-		case ERROR_ALREADY_EXISTS:
-			return MIO_EEXIST;
-
-		/*TODO: add more mappings */
-		default:
-			return MIO_ESYSERR;
-	}
-}
-#endif
-
-#if defined(macintosh)
-static mio_errnum_t macerr_to_errnum (int errcode)
-{
-	switch (e)
-	{
-		case notEnoughMemoryErr:
-			return MIO_ESYSMEM;
-		case paramErr:
-			return MIO_EINVAL;
-
-		case qErr: /* queue element not found during deletion */
-		case fnfErr: /* file not found */
-		case dirNFErr: /* direcotry not found */
-		case resNotFound: /* resource not found */
-		case resFNotFound: /* resource file not found */
-		case nbpNotFound: /* name not found on remove */
-			return MIO_ENOENT;
-
-		/*TODO: add more mappings */
-		default: 
-			return MIO_ESYSERR;
-	}
-}
-#endif
-
-static mio_errnum_t syserrstrb (mio_t* mio, int syserr_type, int syserr_code, mio_bch_t* buf, mio_oow_t len)
-{
-	switch (syserr_type)
-	{
-		case 1: 
-		#if defined(_WIN32)
-			if (buf)
-			{
-				DWORD rc;
-				rc = FormatMessageA (
-					FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
-					NULL, syserr_code, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), 
-					buf, len, MIO_NULL
-				);
-				while (rc > 0 && buf[rc - 1] == '\r' || buf[rc - 1] == '\n') buf[--rc] = '\0';
-			}
-			return winerr_to_errnum(syserr_code);
-		#elif defined(__OS2__)
-			/* TODO: convert code to string */
-			if (buf) mio_copy_bcstr (buf, len, "system error");
-			return os2err_to_errnum(syserr_code);
-		#elif defined(macintosh)
-			/* TODO: convert code to string */
-			if (buf) mio_copy_bcstr (buf, len, "system error");
-			return os2err_to_errnum(syserr_code);
-		#else
-			/* in other systems, errno is still the native system error code.
-			 * fall thru */
-		#endif
-
-		case 0:
-		#if defined(HAVE_STRERROR_R)
-			if (buf) strerror_r (syserr_code, buf, len);
-		#else
-			/* this is not thread safe */
-			if (buf) mio_copy_bcstr (buf, len, strerror(syserr_code));
-		#endif
-			return errno_to_errnum(syserr_code);
-	}
-
-	if (buf) mio_copy_bcstr (buf, len, "system error");
-	return MIO_ESYSERR;
-}
-
-
 /* -------------------------------------------------------------------------- 
  * ERROR NUMBER/MESSAGE HANDLING
  * -------------------------------------------------------------------------- */
@@ -321,7 +119,7 @@ void mio_seterrwithsyserr (mio_t* mio, int syserr_type, int syserr_code)
 
 	/*if (mio->vmprim.syserrstrb)
 	{*/
-		errnum = /*mio->vmprim.*/syserrstrb(mio, syserr_type, syserr_code, mio->errmsg.tmpbuf.bch, MIO_COUNTOF(mio->errmsg.tmpbuf.bch));
+		errnum = /*mio->vmprim.*/mio_sys_syserrstrb(mio, syserr_type, syserr_code, mio->errmsg.tmpbuf.bch, MIO_COUNTOF(mio->errmsg.tmpbuf.bch));
 		mio_seterrbfmt (mio, errnum, "%hs", mio->errmsg.tmpbuf.bch);
 	/*
 	}
@@ -344,7 +142,7 @@ void mio_seterrbfmtwithsyserr (mio_t* mio, int syserr_type, int syserr_code, con
 	/*
 	if (mio->vmprim.syserrstrb)
 	{*/
-		errnum = /*mio->vmprim.*/syserrstrb(mio, syserr_type, syserr_code, mio->errmsg.tmpbuf.bch, MIO_COUNTOF(mio->errmsg.tmpbuf.bch));
+		errnum = mio_sys_syserrstrb(mio, syserr_type, syserr_code, mio->errmsg.tmpbuf.bch, MIO_COUNTOF(mio->errmsg.tmpbuf.bch));
 		
 		va_start (ap, fmt);
 		mio_seterrbfmtv (mio, errnum, fmt, ap);
@@ -368,7 +166,7 @@ void mio_seterrbfmtwithsyserr (mio_t* mio, int syserr_type, int syserr_code, con
 	else
 	{
 		MIO_ASSERT (mio, mio->vmprim.syserrstru != MIO_NULL);
-		errnum = mio->vmprim.syserrstru(mio, syserr_type, syserr_code, mio->errmsg.tmpbuf.uch, MIO_COUNTOF(mio->errmsg.tmpbuf.uch));
+		errnum = mio_sys_syserrstru(mio, syserr_type, syserr_code, mio->errmsg.tmpbuf.uch, MIO_COUNTOF(mio->errmsg.tmpbuf.uch));
 
 		va_start (ap, fmt);
 		mio_seterrbfmtv (mio, errnum, fmt, ap);
@@ -401,7 +199,7 @@ void mio_seterrufmtwithsyserr (mio_t* mio, int syserr_type, int syserr_code, con
 	
 	/*if (mio->vmprim.syserrstrb)
 	{*/
-		errnum = /*mio->vmprim.*/syserrstrb(mio, syserr_type, syserr_code, mio->errmsg.tmpbuf.bch, MIO_COUNTOF(mio->errmsg.tmpbuf.bch));
+		errnum = mio_sys_syserrstrb(mio, syserr_type, syserr_code, mio->errmsg.tmpbuf.bch, MIO_COUNTOF(mio->errmsg.tmpbuf.bch));
 
 		va_start (ap, fmt);
 		mio_seterrufmtv (mio, errnum, fmt, ap);
@@ -425,7 +223,7 @@ void mio_seterrufmtwithsyserr (mio_t* mio, int syserr_type, int syserr_code, con
 	else
 	{
 		MIO_ASSERT (mio, mio->vmprim.syserrstru != MIO_NULL);
-		errnum = mio->vmprim.syserrstru(mio, syserr_type, syserr_code, mio->errmsg.tmpbuf.uch, MIO_COUNTOF(mio->errmsg.tmpbuf.uch));
+		errnum = mio_sys_syserrstru(mio, syserr_type, syserr_code, mio->errmsg.tmpbuf.uch, MIO_COUNTOF(mio->errmsg.tmpbuf.uch));
 
 		va_start (ap, fmt);
 		mio_seterrufmtv (mio, errnum, fmt, ap);
diff --git a/mio/lib/logfmt.c b/mio/lib/logfmt.c
index d572ecf..f30e30b 100644
--- a/mio/lib/logfmt.c
+++ b/mio/lib/logfmt.c
@@ -202,7 +202,7 @@ static int put_ooch (mio_t* mio, mio_bitmask_t mask, mio_ooch_t ch, mio_oow_t le
 			/* no line ending - append a line terminator */
 			mio->log.ptr[mio->log.len++] = '\n';
 		}
-		vmprim_log_write (mio, mio->log.last_mask, mio->log.ptr, mio->log.len);
+		prim_write_log (mio, mio->log.last_mask, mio->log.ptr, mio->log.len);
 		mio->log.len = 0;
 	}
 
@@ -246,7 +246,7 @@ redo:
 					/* no line ending - append a line terminator */
 					mio->log.ptr[mio->log.len++] = '\n';
 				}
-				vmprim_log_write (mio, mio->log.last_mask, mio->log.ptr, mio->log.len);
+				prim_write_log (mio, mio->log.last_mask, mio->log.ptr, mio->log.len);
 				mio->log.len = 0;
 			}
 
@@ -297,7 +297,7 @@ static int put_oocs (mio_t* mio, mio_bitmask_t mask, const mio_ooch_t* ptr, mio_
 			mio->log.ptr[mio->log.len++] = '\n';
 		}
 
-		vmprim_log_write (mio, mio->log.last_mask, mio->log.ptr, mio->log.len);
+		prim_write_log (mio, mio->log.last_mask, mio->log.ptr, mio->log.len);
 		mio->log.len = 0;
 	}
 
@@ -341,7 +341,7 @@ redo:
 					/* no line ending - append a line terminator */
 					mio->log.ptr[mio->log.len++] = '\n';
 				}
-				vmprim_log_write (mio, mio->log.last_mask, mio->log.ptr, mio->log.len);
+				prim_write_log (mio, mio->log.last_mask, mio->log.ptr, mio->log.len);
 				mio->log.len = 0;
 			}
 
@@ -441,7 +441,7 @@ mio_ooi_t mio_logbfmt (mio_t* mio, mio_bitmask_t mask, const mio_bch_t* fmt, ...
 
 	if (mio->log.len > 0 && mio->log.ptr[mio->log.len - 1] == '\n')
 	{
-		vmprim_log_write (mio, mio->log.last_mask, mio->log.ptr, mio->log.len);
+		prim_write_log (mio, mio->log.last_mask, mio->log.ptr, mio->log.len);
 		mio->log.len = 0;
 	}
 	return (x <= -1)? -1: fo.count;
@@ -469,7 +469,7 @@ mio_ooi_t mio_logufmt (mio_t* mio, mio_bitmask_t mask, const mio_uch_t* fmt, ...
 
 	if (mio->log.len > 0 && mio->log.ptr[mio->log.len - 1] == '\n')
 	{
-		vmprim_log_write (mio, mio->log.last_mask, mio->log.ptr, mio->log.len);
+		prim_write_log (mio, mio->log.last_mask, mio->log.ptr, mio->log.len);
 		mio->log.len = 0;
 	}
 
diff --git a/mio/lib/mio-cfg.h.in b/mio/lib/mio-cfg.h.in
index 7e189e6..dbd15b9 100644
--- a/mio/lib/mio-cfg.h.in
+++ b/mio/lib/mio-cfg.h.in
@@ -663,6 +663,9 @@
 /* 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 `uselocale' function. */
 #undef HAVE_USELOCALE
 
@@ -729,6 +732,9 @@
 /* Define to the sub-directory where libtool stores uninstalled libraries. */
 #undef LT_OBJDIR
 
+/* use libunwind for backtracing stack frames */
+#undef MIO_ENABLE_LIBUNWIND
+
 /* Use the unicode character type as the default character type */
 #undef MIO_ENABLE_UNICODE
 
diff --git a/mio/lib/mio-prv.h b/mio/lib/mio-prv.h
index e38da16..9d8b9c7 100644
--- a/mio/lib/mio-prv.h
+++ b/mio/lib/mio-prv.h
@@ -33,7 +33,6 @@
 
 
 /*TODO: redefine and remove these */
-#include <assert.h>
 #include <string.h>
 #include <stdio.h>
 /*TODO: redefine these */
@@ -41,7 +40,15 @@
 #define MIO_MEMCPY(dst,src,count) memcpy(dst,src,count)
 #define MIO_MEMMOVE(dst,src,count) memmove(dst,src,count)
 #define MIO_MEMCMP(dst,src,count) memcmp(dst,src,count)
-#define MIO_ASSERT assert
+
+/* =========================================================================
+ * MIO ASSERTION
+ * ========================================================================= */
+#if defined(MIO_BUILD_RELEASE)
+#	define MIO_ASSERT(mio,expr) ((void)0)
+#else
+#	define MIO_ASSERT(mio,expr) ((void)((expr) || mio_sys_assertfail(mio, #expr, __FILE__, __LINE__), 0)))
+#endif
 
 
 #define MIO_EPOCH_YEAR  (1970)
@@ -63,6 +70,15 @@
 #define MIO_SECS_PER_HOUR  (MIO_SECS_PER_MIN*MIO_MINS_PER_HOUR)
 #define MIO_SECS_PER_DAY   (MIO_SECS_PER_MIN*MIO_MINS_PER_DAY)
 
+/* i don't want an error raised inside the callback to override 
+ * the existing error number and message. */
+#define prim_write_log(mio,mask,ptr,len) do { \
+		int shuterr = (mio)->shuterr; \
+		(mio)->shuterr = 1; \
+		mio_sys_writelog (mio, mask, ptr, len); \
+		(mio)->shuterr = shuterr; \
+	} while(0)
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -121,6 +137,29 @@ int mio_gettmrtmout (
 	mio_ntime_t*       tmout
 );
 
+/* ========================================================================== */
+void mio_sys_assertfail (
+	mio_t*           mio, 
+	const mio_bch_t* expr,
+	const mio_bch_t* file,
+	mio_oow_t        line
+);
+
+mio_errnum_t mio_sys_syserrstrb (
+	mio_t*            mio,
+	int               syserr_type,
+	int               syserr_code,
+	mio_bch_t*        buf,
+	mio_oow_t         len
+);
+
+void mio_sys_writelog (
+	mio_t*            mio,
+	mio_bitmask_t     mask,
+	const mio_ooch_t* msg,
+	mio_oow_t         len
+);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/mio/lib/mio.h b/mio/lib/mio.h
index 427cd6e..37af758 100644
--- a/mio/lib/mio.h
+++ b/mio/lib/mio.h
@@ -368,13 +368,13 @@ enum mio_dev_event_t
 };
 typedef enum mio_dev_event_t mio_dev_event_t;
 
-
-
-
-
 #define MIO_CWQFL_SIZE 16
 #define MIO_CWQFL_ALIGN 16
 
+/* ========================================================================= */
+
+/* ========================================================================= */
+
 typedef struct mio_mux_t mio_mux_t;
 
 struct mio_t
diff --git a/mio/lib/sys-ass.c b/mio/lib/sys-ass.c
new file mode 100644
index 0000000..94316fe
--- /dev/null
+++ b/mio/lib/sys-ass.c
@@ -0,0 +1,174 @@
+/*
+ * $Id$
+ *
+    Copyright (c) 2015-2016 Chung, Hyung-Hwan. All rights reserved.
+
+    Redistribution and use in source and binary forms, with or without
+    modification, are permitted provided that the following conditions
+    are met:
+    1. Redistributions of source code must retain the above copyright
+       notice, this list of conditions and the following disclaimer.
+    2. Redistributions in binary form must reproduce the above copyright
+       notice, this list of conditions and the following disclaimer in the
+       documentation and/or other materials provided with the distribution.
+
+    THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR
+    IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WAfRRANTIES
+    OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+    IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+    NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+    THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#if defined(_WIN32)
+#	include <windows.h>
+#	include <errno.h>
+
+#elif defined(__OS2__)
+#	define INCL_DOSERRORS
+#	include <os2.h>
+#	include <errno.h>
+
+#elif defined(__DOS__)
+#	include <dos.h>
+#	include <errno.h>
+
+#	if defined(_INTELC32_)
+#		define DOS_EXIT 0x4C
+#		include <i32.h>
+#		include <stk.h>
+#	else
+#		include <dosfunc.h>
+#	endif
+
+#elif defined(macintosh)
+#	include <Types.h>
+#	include <OSUtils.h>
+#	include <Timer.h>
+
+#	include <MacErrors.h>
+#	include <Process.h>
+#	include <Dialogs.h>
+#	include <TextUtils.h>
+
+	/* TODO: a lot to do */
+
+#elif defined(vms) || defined(__vms)
+#	define __NEW_STARLET 1
+#	include <starlet.h> /* (SYS$...) */
+#	include <ssdef.h> /* (SS$...) */
+#	include <lib$routines.h> /* (lib$...) */
+
+	/* TODO: a lot to do */
+
+#else
+#	include <sys/types.h>
+#	include <unistd.h>
+#	include <errno.h>
+#endif
+
+#if defined(MIO_BUILD_RELEASE)
+
+void mio_sys_assertfail (mio_t* mio, const mio_bch_t* expr, const mio_bch_t* file, mio_oow_t line)
+{
+	/* do nothing */
+}
+
+#else /* defined(MIO_BUILD_RELEASE) */
+
+#if defined(MIO_ENABLE_LIBUNWIND)
+#include <libunwind.h>
+static void backtrace_stack_frames (mio_t* mio)
+{
+	unw_cursor_t cursor;
+	unw_context_t context;
+	int n;
+
+	unw_getcontext(&context);
+	unw_init_local(&cursor, &context);
+
+	mio_logbfmt (mio, MIO_LOG_UNTYPED | MIO_LOG_DEBUG, "[BACKTRACE]\n");
+	for (n = 0; unw_step(&cursor) > 0; n++) 
+	{
+		unw_word_t ip, sp, off;
+		char symbol[256];
+
+		unw_get_reg (&cursor, UNW_REG_IP, &ip);
+		unw_get_reg (&cursor, UNW_REG_SP, &sp);
+
+		if (unw_get_proc_name(&cursor, symbol, MIO_COUNTOF(symbol), &off)) 
+		{
+			mio_copy_bcstr (symbol, MIO_COUNTOF(symbol), "<unknown>");
+		}
+
+		mio_logbfmt (mio, MIO_LOG_UNTYPED | MIO_LOG_DEBUG, 
+			"#%02d ip=0x%*p sp=0x%*p %s+0x%zu\n", 
+			n, MIO_SIZEOF(void*) * 2, (void*)ip, MIO_SIZEOF(void*) * 2, (void*)sp, symbol, (mio_oow_t)off);
+	}
+}
+#elif defined(HAVE_BACKTRACE)
+#include <execinfo.h>
+static void backtrace_stack_frames (mio_t* mio)
+{
+	void* btarray[128];
+	mio_oow_t btsize;
+	char** btsyms;
+
+	btsize = backtrace (btarray, MIO_COUNTOF(btarray));
+	btsyms = backtrace_symbols (btarray, btsize);
+	if (btsyms)
+	{
+		mio_oow_t i;
+		mio_logbfmt (mio, MIO_LOG_UNTYPED | MIO_LOG_DEBUG, "[BACKTRACE]\n");
+
+		for (i = 0; i < btsize; i++)
+		{
+			mio_logbfmt(mio, MIO_LOG_UNTYPED | MIO_LOG_DEBUG, "  %s\n", btsyms[i]);
+		}
+		free (btsyms);
+	}
+}
+#else
+static void backtrace_stack_frames (mio_t* mio)
+{
+	/* do nothing. not supported */
+}
+#endif /* defined(MIO_ENABLE_LIBUNWIND) */
+
+void mio_sys_assertfail (mio_t* mio, const mio_bch_t* expr, const mio_bch_t* file, mio_oow_t line)
+{
+	mio_logbfmt (mio, MIO_LOG_UNTYPED | MIO_LOG_FATAL, "ASSERTION FAILURE: %s at %s:%zu\n", expr, file, line);
+	backtrace_stack_frames (mio);
+
+#if defined(_WIN32)
+	ExitProcess (249);
+#elif defined(__OS2__)
+	DosExit (EXIT_PROCESS, 249);
+#elif defined(__DOS__)
+	{
+		union REGS regs;
+		regs.h.ah = DOS_EXIT;
+		regs.h.al = 249;
+		intdos (&regs, &regs);
+	}
+#elif defined(vms) || defined(__vms)
+	lib$stop (SS$_ABORT); /* use SS$_OPCCUS instead? */
+	/* this won't be reached since lib$stop() terminates the process */
+	sys$exit (SS$_ABORT); /* this condition code can be shown with
+	                       * 'show symbol $status' from the command-line. */
+#elif defined(macintosh)
+
+	ExitToShell ();
+
+#else
+
+	kill (getpid(), SIGABRT);
+	_exit (1);
+#endif
+}
+
+#endif /* defined(MIO_BUILD_RELEASE) */
diff --git a/mio/lib/sys-err.c b/mio/lib/sys-err.c
new file mode 100644
index 0000000..600d8a9
--- /dev/null
+++ b/mio/lib/sys-err.c
@@ -0,0 +1,226 @@
+/*
+ * $Id$
+ *
+    Copyright (c) 2015-2016 Chung, Hyung-Hwan. All rights reserved.
+
+    Redistribution and use in source and binary forms, with or without
+    modification, are permitted provided that the following conditions
+    are met:
+    1. Redistributions of source code must retain the above copyright
+       notice, this list of conditions and the following disclaimer.
+    2. Redistributions in binary form must reproduce the above copyright
+       notice, this list of conditions and the following disclaimer in the
+       documentation and/or other materials provided with the distribution.
+
+    THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR
+    IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WAfRRANTIES
+    OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+    IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+    NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+    THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "mio-prv.h"
+
+#include <errno.h>
+
+static mio_errnum_t errno_to_errnum (int errcode)
+{
+	switch (errcode)
+	{
+		case ENOMEM: return MIO_ESYSMEM;
+		case EINVAL: return MIO_EINVAL;
+
+	#if defined(EBUSY)
+		case EBUSY: return MIO_EBUSY;
+	#endif
+		case EACCES: return MIO_EACCES;
+	#if defined(EPERM)
+		case EPERM: return MIO_EPERM;
+	#endif
+	#if defined(ENOTDIR)
+		case ENOTDIR: return MIO_ENOTDIR;
+	#endif
+		case ENOENT: return MIO_ENOENT;
+	#if defined(EEXIST)
+		case EEXIST: return MIO_EEXIST;
+	#endif
+	#if defined(EINTR)
+		case EINTR:  return MIO_EINTR;
+	#endif
+
+	#if defined(EPIPE)
+		case EPIPE:  return MIO_EPIPE;
+	#endif
+
+	#if defined(EAGAIN) && defined(EWOULDBLOCK) && (EAGAIN != EWOULDBLOCK)
+		case EAGAIN: 
+		case EWOULDBLOCK: return MIO_EAGAIN;
+	#elif defined(EAGAIN)
+		case EAGAIN: return MIO_EAGAIN;
+	#elif defined(EWOULDBLOCK)
+		case EWOULDBLOCK: return MIO_EAGAIN;
+	#endif
+
+	#if defined(EBADF)
+		case EBADF: return MIO_EBADHND;
+	#endif
+
+	#if defined(EIO)
+		case EIO: return MIO_EIOERR;
+	#endif
+
+		default: return MIO_ESYSERR;
+	}
+}
+
+#if defined(_WIN32)
+static mio_errnum_t winerr_to_errnum (DWORD errcode)
+{
+	switch (errcode)
+	{
+		case ERROR_NOT_ENOUGH_MEMORY:
+		case ERROR_OUTOFMEMORY:
+			return MIO_ESYSMEM;
+
+		case ERROR_INVALID_PARAMETER:
+		case ERROR_INVALID_NAME:
+			return MIO_EINVAL;
+
+		case ERROR_INVALID_HANDLE:
+			return MIO_EBADHND;
+
+		case ERROR_ACCESS_DENIED:
+		case ERROR_SHARING_VIOLATION:
+			return MIO_EACCES;
+
+	#if defined(ERROR_IO_PRIVILEGE_FAILED)
+		case ERROR_IO_PRIVILEGE_FAILED:
+	#endif
+		case ERROR_PRIVILEGE_NOT_HELD:
+			return MIO_EPERM;
+
+		case ERROR_FILE_NOT_FOUND:
+		case ERROR_PATH_NOT_FOUND:
+			return MIO_ENOENT;
+
+		case ERROR_ALREADY_EXISTS:
+		case ERROR_FILE_EXISTS:
+			return MIO_EEXIST;
+
+		case ERROR_BROKEN_PIPE:
+			return MIO_EPIPE;
+
+		default:
+			return MIO_ESYSERR;
+	}
+}
+#endif
+
+#if defined(__OS2__)
+static mio_errnum_t os2err_to_errnum (APIRET errcode)
+{
+	/* APIRET e */
+	switch (errcode)
+	{
+		case ERROR_NOT_ENOUGH_MEMORY:
+			return MIO_ESYSMEM;
+
+		case ERROR_INVALID_PARAMETER: 
+		case ERROR_INVALID_NAME:
+			return MIO_EINVAL;
+
+		case ERROR_INVALID_HANDLE: 
+			return MIO_EBADHND;
+
+		case ERROR_ACCESS_DENIED: 
+		case ERROR_SHARING_VIOLATION:
+			return MIO_EACCES;
+
+		case ERROR_FILE_NOT_FOUND:
+		case ERROR_PATH_NOT_FOUND:
+			return MIO_ENOENT;
+
+		case ERROR_ALREADY_EXISTS:
+			return MIO_EEXIST;
+
+		/*TODO: add more mappings */
+		default:
+			return MIO_ESYSERR;
+	}
+}
+#endif
+
+#if defined(macintosh)
+static mio_errnum_t macerr_to_errnum (int errcode)
+{
+	switch (e)
+	{
+		case notEnoughMemoryErr:
+			return MIO_ESYSMEM;
+		case paramErr:
+			return MIO_EINVAL;
+
+		case qErr: /* queue element not found during deletion */
+		case fnfErr: /* file not found */
+		case dirNFErr: /* direcotry not found */
+		case resNotFound: /* resource not found */
+		case resFNotFound: /* resource file not found */
+		case nbpNotFound: /* name not found on remove */
+			return MIO_ENOENT;
+
+		/*TODO: add more mappings */
+		default: 
+			return MIO_ESYSERR;
+	}
+}
+#endif
+
+mio_errnum_t mio_sys_syserrstrb (mio_t* mio, int syserr_type, int syserr_code, mio_bch_t* buf, mio_oow_t len)
+{
+	switch (syserr_type)
+	{
+		case 1: 
+		#if defined(_WIN32)
+			if (buf)
+			{
+				DWORD rc;
+				rc = FormatMessageA (
+					FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
+					NULL, syserr_code, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), 
+					buf, len, MIO_NULL
+				);
+				while (rc > 0 && buf[rc - 1] == '\r' || buf[rc - 1] == '\n') buf[--rc] = '\0';
+			}
+			return winerr_to_errnum(syserr_code);
+		#elif defined(__OS2__)
+			/* TODO: convert code to string */
+			if (buf) mio_copy_bcstr (buf, len, "system error");
+			return os2err_to_errnum(syserr_code);
+		#elif defined(macintosh)
+			/* TODO: convert code to string */
+			if (buf) mio_copy_bcstr (buf, len, "system error");
+			return os2err_to_errnum(syserr_code);
+		#else
+			/* in other systems, errno is still the native system error code.
+			 * fall thru */
+		#endif
+
+		case 0:
+		#if defined(HAVE_STRERROR_R)
+			if (buf) strerror_r (syserr_code, buf, len);
+		#else
+			/* this is not thread safe */
+			if (buf) mio_copy_bcstr (buf, len, strerror(syserr_code));
+		#endif
+			return errno_to_errnum(syserr_code);
+	}
+
+	if (buf) mio_copy_bcstr (buf, len, "system error");
+	return MIO_ESYSERR;
+}
+
diff --git a/mio/lib/sys-log.c b/mio/lib/sys-log.c
new file mode 100644
index 0000000..af0bd47
--- /dev/null
+++ b/mio/lib/sys-log.c
@@ -0,0 +1,261 @@
+/*
+ * $Id$
+ *
+    Copyright (c) 2015-2016 Chung, Hyung-Hwan. All rights reserved.
+
+    Redistribution and use in source and binary forms, with or without
+    modification, are permitted provided that the following conditions
+    are met:
+    1. Redistributions of source code must retain the above copyright
+       notice, this list of conditions and the following disclaimer.
+    2. Redistributions in binary form must reproduce the above copyright
+       notice, this list of conditions and the following disclaimer in the
+       documentation and/or other materials provided with the distribution.
+
+    THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR
+    IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WAfRRANTIES
+    OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+    IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+    NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+    THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "mio-prv.h"
+
+static int write_all (int fd, const mio_bch_t* ptr, mio_oow_t len)
+{
+	while (len > 0)
+	{
+		mio_ooi_t wr;
+
+		wr = write(fd, ptr, len);
+
+		if (wr <= -1)
+		{
+		#if defined(EAGAIN) && defined(EWOULDBLOCK) && (EAGAIN == EWOULDBLOCK)
+			if (errno == EAGAIN) continue;
+		#else
+			#if defined(EAGAIN)
+			if (errno == EAGAIN) continue;
+			#elif defined(EWOULDBLOCK)
+			if (errno == EWOULDBLOCK) continue;
+			#endif
+		#endif
+
+		#if defined(EINTR)
+			/* TODO: would this interfere with non-blocking nature of this VM? */
+			if (errno == EINTR) continue;
+		#endif
+			return -1;
+		}
+
+		ptr += wr;
+		len -= wr;
+	}
+
+	return 0;
+}
+
+static int write_log (mio_t* mio, int fd, const mio_bch_t* ptr, mio_oow_t len)
+{
+	xtn_t* xtn = GET_XTN(mio);
+
+	while (len > 0)
+	{
+		if (xtn->log.out.len > 0)
+		{
+			mio_oow_t rcapa, cplen;
+
+			rcapa = MIO_COUNTOF(xtn->log.out.buf) - xtn->log.out.len;
+			cplen = (len >= rcapa)? rcapa: len;
+
+			MIO_MEMCPY (&xtn->log.out.buf[xtn->log.out.len], ptr, cplen);
+			xtn->log.out.len += cplen;
+			ptr += cplen;
+			len -= cplen;
+
+			if (xtn->log.out.len >= MIO_COUNTOF(xtn->log.out.buf))
+			{
+				int n;
+				n = write_all(fd, xtn->log.out.buf, xtn->log.out.len);
+				xtn->log.out.len = 0;
+				if (n <= -1) return -1;
+			}
+		}
+		else
+		{
+			mio_oow_t rcapa;
+
+			rcapa = MIO_COUNTOF(xtn->log.out.buf);
+			if (len >= rcapa)
+			{
+				if (write_all(fd, ptr, rcapa) <= -1) return -1;
+				ptr += rcapa;
+				len -= rcapa;
+			}
+			else
+			{
+				MIO_MEMCPY (xtn->log.out.buf, ptr, len);
+				xtn->log.out.len += len;
+				ptr += len;
+				len -= len;
+				
+			}
+		}
+	}
+
+	return 0;
+}
+
+static void flush_log (mio_t* mio, int fd)
+{
+	xtn_t* xtn = GET_XTN(mio);
+	if (xtn->log.out.len > 0)
+	{
+		write_all (fd, xtn->log.out.buf, xtn->log.out.len);
+		xtn->log.out.len = 0;
+	}
+}
+
+void mio_sys_writelog (mio_t* mio, mio_bitmask_t mask, const mio_ooch_t* msg, mio_oow_t len)
+{
+	xtn_t* xtn = GET_XTN(mio);
+	mio_bch_t buf[256];
+	mio_oow_t ucslen, bcslen, msgidx;
+	int n, logfd;
+
+	if (mask & MIO_LOG_STDERR)
+	{
+		/* the messages that go to STDERR don't get masked out */
+		logfd = 2;
+	}
+	else
+	{
+#if 0
+		if (!(xtn->log.mask & mask & ~MIO_LOG_ALL_LEVELS)) return;  /* check log types */
+		if (!(xtn->log.mask & mask & ~MIO_LOG_ALL_TYPES)) return;  /* check log levels */
+#endif
+
+		if (mask & MIO_LOG_STDOUT) logfd = 1;
+		else
+		{
+			logfd = xtn->log.fd;
+			if (logfd <= -1) return;
+		}
+	}
+
+/* TODO: beautify the log message.
+ *       do classification based on mask. */
+	if (!(mask & (MIO_LOG_STDOUT | MIO_LOG_STDERR)))
+	{
+		time_t now;
+		char ts[32];
+		size_t tslen;
+		struct tm tm, *tmp;
+
+		now = time(MIO_NULL);
+	#if defined(_WIN32)
+		tmp = localtime(&now);
+		tslen = strftime(ts, sizeof(ts), "%Y-%m-%d %H:%M:%S %z ", tmp);
+		if (tslen == 0) 
+		{
+			tslen = sprintf(ts, "%04d-%02d-%02d %02d:%02d:%02d ", tmp->tm_year + 1900, tmp->tm_mon + 1, tmp->tm_mday, tmp->tm_hour, tmp->tm_min, tmp->tm_sec);
+		}
+	#elif defined(__OS2__)
+		#if defined(__WATCOMC__)
+		tmp = _localtime(&now, &tm);
+		#else
+		tmp = localtime(&now);
+		#endif
+
+		#if defined(__BORLANDC__)
+		/* the borland compiler doesn't handle %z properly - it showed 00 all the time */
+		tslen = strftime(ts, sizeof(ts), "%Y-%m-%d %H:%M:%S %Z ", tmp);
+		#else
+		tslen = strftime(ts, sizeof(ts), "%Y-%m-%d %H:%M:%S %z ", tmp);
+		#endif
+		if (tslen == 0) 
+		{
+			tslen = sprintf(ts, "%04d-%02d-%02d %02d:%02d:%02d ", tmp->tm_year + 1900, tmp->tm_mon + 1, tmp->tm_mday, tmp->tm_hour, tmp->tm_min, tmp->tm_sec);
+		}
+
+	#elif defined(__DOS__)
+		tmp = localtime(&now);
+		/* since i know that %z/%Z is not available in strftime, i switch to sprintf immediately */
+		tslen = sprintf(ts, "%04d-%02d-%02d %02d:%02d:%02d ", tmp->tm_year + 1900, tmp->tm_mon + 1, tmp->tm_mday, tmp->tm_hour, tmp->tm_min, tmp->tm_sec);
+	#else
+		#if defined(HAVE_LOCALTIME_R)
+		tmp = localtime_r(&now, &tm);
+		#else
+		tmp = localtime(&now);
+		#endif
+
+		#if defined(HAVE_STRFTIME_SMALL_Z)
+		tslen = strftime(ts, sizeof(ts), "%Y-%m-%d %H:%M:%S %z ", tmp);
+		#else
+		tslen = strftime(ts, sizeof(ts), "%Y-%m-%d %H:%M:%S %Z ", tmp); 
+		#endif
+		if (tslen == 0) 
+		{
+			tslen = sprintf(ts, "%04d-%02d-%02d %02d:%02d:%02d ", tmp->tm_year + 1900, tmp->tm_mon + 1, tmp->tm_mday, tmp->tm_hour, tmp->tm_min, tmp->tm_sec);
+		}
+	#endif
+		write_log (mio, logfd, ts, tslen);
+	}
+
+	if (logfd == xtn->log.fd && (xtn->log.fd_flag & LOGFD_TTY))
+	{
+		if (mask & MIO_LOG_FATAL) write_log (mio, logfd, "\x1B[1;31m", 7);
+		else if (mask & MIO_LOG_ERROR) write_log (mio, logfd, "\x1B[1;32m", 7);
+		else if (mask & MIO_LOG_WARN) write_log (mio, logfd, "\x1B[1;33m", 7);
+	}
+
+#if defined(MIO_OOCH_IS_UCH)
+	msgidx = 0;
+	while (len > 0)
+	{
+		ucslen = len;
+		bcslen = MIO_COUNTOF(buf);
+
+		n = mio_convootobchars(mio, &msg[msgidx], &ucslen, buf, &bcslen);
+		if (n == 0 || n == -2)
+		{
+			/* n = 0: 
+			 *   converted all successfully 
+			 * n == -2: 
+			 *    buffer not sufficient. not all got converted yet.
+			 *    write what have been converted this round. */
+
+			MIO_ASSERT (mio, ucslen > 0); /* if this fails, the buffer size must be increased */
+
+			/* attempt to write all converted characters */
+			if (write_log(mio, logfd, buf, bcslen) <= -1) break;
+
+			if (n == 0) break;
+			else
+			{
+				msgidx += ucslen;
+				len -= ucslen;
+			}
+		}
+		else if (n <= -1)
+		{
+			/* conversion error */
+			break;
+		}
+	}
+#else
+	write_log (mio, logfd, msg, len);
+#endif
+
+	if (logfd == xtn->log.fd && (xtn->log.fd_flag & LOGFD_TTY))
+	{
+		if (mask & (MIO_LOG_FATAL | MIO_LOG_ERROR | MIO_LOG_WARN)) write_log (mio, logfd, "\x1B[0m", 4);
+	}
+
+	flush_log (mio, logfd);
+}