diff --git a/.gitignore b/.gitignore
index fdcc1e0a..b30acf10 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,7 +7,8 @@ modules.*
 *.ko
 \#*
 .#*
-buildtag.h
+kernel/buildtag.h
+kernel/mars_config.h
 *.orig
 *.rej
 
diff --git a/gen_config.pl b/gen_config.pl
new file mode 100755
index 00000000..c2fc61e8
--- /dev/null
+++ b/gen_config.pl
@@ -0,0 +1,124 @@
+#!/usr/bin/perl
+
+use strict;
+use warnings;
+
+use 5.010;
+
+use Data::Dumper;
+
+my $DEBUG = 0;
+
+##
+## Parse Kconfig from STDIN
+##
+
+my $option;
+my $type;
+my @default;
+
+while (my $line = <STDIN>) {
+    if ($line =~ /^config\s+(\w+)\W*$/) {
+        $option = $1;
+        printf STDERR "OPTION: %s\n", $option if $DEBUG;
+    }
+    elsif ($line =~ /^\s+(tristate|bool|int|string)\s+.*$/) {
+        $type = $1;
+        printf STDERR "TYPE: %s\n", $type if $DEBUG;
+    }
+    elsif ($line =~ /^\s+default\s+(.*)$/) {
+        printf STDERR "DEFAULT: %s\n", $1 if $DEBUG;
+        push @default, {
+            option => $option,
+            type => $type,
+            value => $1,
+        } if $option;
+    }
+    elsif ($line =~ /^\s+---help---\s+$/) {
+        # ignore lines after this by unsetting $option
+        undef $option;
+        # Kconfig syntax allows to have directives after the help section,
+        # but we do not use this freedom here, for simplicity.
+    }
+}
+
+print STDERR Dumper(\@default) if $DEBUG;
+
+
+##
+## Print the header
+##
+
+print qq%
+#ifndef MARS_CONFIG_H
+#define MARS_CONFIG_H
+
+/*
+ * Module default settings from Kconfig
+ *
+ * If the module is built as an external module, this file provides
+ * reasonable default settings for configuration variables CONFIG_*.
+ * The defaults are extracted from Kconfig. If you want to change a
+ * setting, please edit Kconfig directly and regenerate this file.
+ * 
+ * This file was auto-generated with $0
+ * -- DO NOT EDIT MANUALLY --
+ */
+
+#ifndef CONFIG_MARS_HAVE_BIGMODULE
+#define CONFIG_MARS_HAVE_BIGMODULE
+#endif
+%;
+
+##
+## Print option defaults
+##
+
+foreach my $opt (@default) {
+
+    my $optname = $opt->{option};
+    my $optval = $opt->{value};
+
+    if (!defined($optname) || !defined($optval)) {
+        printf(STDERR "SKIPPED option due to missing parameters: optname=%s optval=%s\n",
+               $optname||'', $optval||'');
+        next;
+    }
+
+    given ($opt->{type}) {
+
+        when ('tristate') {
+            # ignore tristate
+        }
+
+        when ('bool') {
+            if ($optval eq 'n') {
+                print qq%
+/* CONFIG_$optname is unset */
+%;
+            }
+            else {
+                print qq%
+#ifndef CONFIG_$optname
+#define CONFIG_$optname 1
+#endif
+%;
+            }
+        }
+
+        when (['int', 'string']) {
+            print qq%
+#ifndef CONFIG_$optname
+#define CONFIG_$optname $optval
+#endif
+%;
+        }
+
+    }
+
+}
+
+print qq%
+
+#endif  /* MARS_CONFIG_H */
+%;
diff --git a/kernel/Makefile b/kernel/Makefile
index cea083eb..5f1f1e07 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -2,6 +2,10 @@
 # Makefile for MARS
 #
 
+ifneq ($(KBUILD_EXTMOD),)
+  CONFIG_MARS_BIGMODULE := m
+endif
+
 mars-objs :=				\
 	brick_say.o			\
 	brick_mem.o			\
@@ -65,11 +69,42 @@ mars-objs += 				\
 
 endif
 
-.PHONY FORCE: block/mars/kernel/buildtag.h
-block/mars/kernel/buildtag.h:
-	set -e; exec > $@;\
-	cd block/mars;\
+#
+# buildtag.h should be regenerated in every build. If a file
+# 'DISTVERSION' exists (out-of-tree tarball), its content is
+# used as the BUILDTAG. Otherwise, if git is available, the
+# git HEAD revision is used instead.
+#
+extra-y	+= buildtag.h
+$(obj)/buildtag.h: $(patsubst $(obj)/buildtag.h,,$(wildcard $(obj)/*.[ch])) $(obj)/*/*.[ch]
+	$(Q)$(kecho) "MARS: Generating $@"
+	$(Q)set -e; \
+	exec > $@;\
 	/bin/echo -e "/* Automatically generated -- DO NOT EDIT! */";\
-	/bin/echo -e "#define BUILDTAG  \"$$(git log -1 --pretty='format:%H')\"";\
+	cd $(src); \
+	if [ -e DISTVERSION ]; then \
+		BUILDTAG=$$(cat DISTVERSION); \
+	elif git rev-parse --git-dir >/dev/null 2>&1; then \
+		BUILDTAG="$$(git rev-parse HEAD)"; \
+	else \
+		BUILDTAG="no-buildtag-available"; \
+	fi; \
+	/bin/echo -e "#define BUILDTAG  \"$$BUILDTAG\"";\
 	/bin/echo -e "#define BUILDHOST \"$$USER@$$HOSTNAME\"";\
 	/bin/echo -e "#define BUILDDATE \"$$(date '+%F %T')\""
+
+#
+# mars_config.h is generated by a simple Kconfig parser (gen_config.pl)
+# at build time.
+# It is used for out-of-tree builds.
+# In-tree builds should not be disturbed due to #ifndef safeguarding.
+#
+extra-y	+= mars_config.h
+$(obj)/mars_config.h: $(src)/Kconfig $(src)/../gen_config.pl
+	$(Q)$(kecho) "MARS: Generating $@"
+	$(Q)set -e; \
+	if [ ! -x $(src)/../gen_config.pl ]; then \
+	    $(kecho) "MARS: cannot execute script $(src)/../gen_config.pl"; \
+	    /bin/false; \
+	fi; \
+	cat $< | $(src)/../gen_config.pl > $@;
diff --git a/kernel/brick.h b/kernel/brick.h
index 3a542422..1d178fd4 100644
--- a/kernel/brick.h
+++ b/kernel/brick.h
@@ -9,6 +9,9 @@
 
 #include <asm/atomic.h>
 
+// include default config
+#include "mars_config.h"
+
 #include "brick_locks.h"
 #include "meta.h"
 
diff --git a/kernel/brick_say.h b/kernel/brick_say.h
index 2960e054..f5acfbfa 100644
--- a/kernel/brick_say.h
+++ b/kernel/brick_say.h
@@ -2,6 +2,9 @@
 #ifndef BRICK_SAY_H
 #define BRICK_SAY_H
 
+// include default config
+#include "mars_config.h"
+
 /////////////////////////////////////////////////////////////////////////
 
 extern int brick_say_logging;
diff --git a/kernel/mars.h b/kernel/mars.h
index cf4926eb..0e73c73e 100644
--- a/kernel/mars.h
+++ b/kernel/mars.h
@@ -7,6 +7,9 @@
 
 //#define MARS_TRACING // write runtime trace data to /mars/trace.csv
 
+// include default config
+#include "mars_config.h"
+
 /////////////////////////////////////////////////////////////////////////
 
 // include the generic brick infrastructure