kbuild: add GNU GLOBAL tags generation

GNU GLOBAL (http://www.gnu.org/software/global/) is a source code tagging system
It is really cheap to support it in kbuild system.
Signed-off-by: Jianbin Kang <kjbmail@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

Makefile

@@ -420,7 +420,7 @@ endif
 # of make so .config is not included in this case either (for *config).
 
 no-dot-config-targets := clean mrproper distclean \
-			 cscope TAGS tags help %docs check% coccicheck \
+			 cscope gtags TAGS tags help %docs check% coccicheck \
 			 include/linux/version.h headers_% \
 			 kernelversion %src-pkg
 
@@ -1134,7 +1134,7 @@ CLEAN_FILES +=	vmlinux System.map \
 MRPROPER_DIRS  += include/config usr/include include/generated
 MRPROPER_FILES += .config .config.old .version .old_version             \
                   include/linux/version.h                               \
-		  Module.symvers tags TAGS cscope*
+		  Module.symvers tags TAGS cscope* GPATH GTAGS GRTAGS GSYMS
 
 # clean - Delete most, but leave enough to build external modules
 #
@@ -1221,6 +1221,7 @@ help:
 	@echo  '  modules_prepare - Set up for building external modules'
 	@echo  '  tags/TAGS	  - Generate tags file for editors'
 	@echo  '  cscope	  - Generate cscope index'
+	@echo  '  gtags           - Generate GNU GLOBAL index'
 	@echo  '  kernelrelease	  - Output the release version string'
 	@echo  '  kernelversion	  - Output the version stored in Makefile'
 	@echo  '  headers_install - Install sanitised kernel headers to INSTALL_HDR_PATH'; \
@@ -1379,7 +1380,7 @@ clean: $(clean-dirs)
 quiet_cmd_tags = GEN     $@
       cmd_tags = $(CONFIG_SHELL) $(srctree)/scripts/tags.sh $@
 
-tags TAGS cscope: FORCE
+tags TAGS cscope gtags: FORCE
 	$(call cmd,tags)
 
 # Scripts to check various things for consistency

scripts/tags.sh

@@ -114,6 +114,11 @@ docscope()
 	cscope -b -f cscope.out
 }
 
+dogtags()
+{
+	all_sources | gtags -f -
+}
+
 exuberant()
 {
 	all_sources | xargs $1 -a                               \
@@ -185,6 +190,10 @@ case "$1" in
 		docscope
 		;;
 
+	"gtags")
+		dogtags
+		;;
+
 	"tags")
 		rm -f tags
 		xtags ctags