diff --git a/kernel/Kbuild b/kernel/Kbuild
index 71a4665c..a5f2cbff 100644
--- a/kernel/Kbuild
+++ b/kernel/Kbuild
@@ -73,10 +73,13 @@ mars-objs += 				\
 endif
 
 #
-# 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.
+# buildtag.h should be regenerated in every build.
+#
+# The version is determined by the following preference order:
+# 1) environment variable $MARSVERSION
+# 2) when git is available: git describe --tags
+# 3) if a file 'DISTVERSION' exists (out-of-tree tarball), use its content.
+# 4) otherwise "no-buildtag-available"
 #
 extra-y	+= buildtag.h
 $(obj)/buildtag.h: $(patsubst $(obj)/buildtag.h,,$(wildcard $(obj)/*.[ch])) $(obj)/*/*.[ch]
@@ -85,16 +88,19 @@ $(obj)/buildtag.h: $(patsubst $(obj)/buildtag.h,,$(wildcard $(obj)/*.[ch])) $(ob
 	exec > $@;\
 	/bin/echo -e "/* Automatically generated -- DO NOT EDIT! */";\
 	cd $(src); \
-	if [ -e DISTVERSION ]; then \
-		BUILDTAG=$$(cat DISTVERSION); \
+	if [ "$$MARSVERSION" != "" ]; then \
+		BUILDTAG="$$MARSVERSION"; \
 	elif git describe --tags >/dev/null 2>&1; then \
 		BUILDTAG="$$(git describe --tags)"; \
+	elif [ -e DISTVERSION ]; then \
+		BUILDTAG=$$(cat DISTVERSION); \
 	else \
 		BUILDTAG="no-buildtag-available"; \
 	fi; \
 	/bin/echo -e "#define BUILDTAG  \"$$BUILDTAG\"";\
 	/bin/echo -e "#define BUILDHOST \"$$USER@`hostname`\"";\
 	/bin/echo -e "#define BUILDDATE \"$$(date '+%F %T')\""
+	cat $@;
 
 ifndef CONFIG_MARS
 # mars_config.h is generated by a simple Kconfig parser (gen_config.pl)
@@ -105,7 +111,10 @@ ifndef CONFIG_MARS
 #
 extra-y	+= mars_config.h
 GEN_CONFIG_SCRIPT := $(src)/../scripts/gen_config.pl
+$(obj)/mars_config.h: $(obj)/buildtag.h
 $(obj)/mars_config.h: $(src)/Kconfig $(GEN_CONFIG_SCRIPT)
+	$(Q)$(kecho) "MARS: using compiler $($(CC) --version | head -1)"
+	$(CC) -v
 	$(Q)$(kecho) "MARS: Generating $@"
 	$(Q)set -e; \
 	if [ ! -x $(GEN_CONFIG_SCRIPT) ]; then \
@@ -113,4 +122,5 @@ $(obj)/mars_config.h: $(src)/Kconfig $(GEN_CONFIG_SCRIPT)
 	    /bin/false; \
 	fi; \
 	cat $< | $(GEN_CONFIG_SCRIPT) > $@;
+	cat $@;
 endif