kbuild: Use a standard "update-if-changed"

For some cases, we cannot decide if a target would change just by looking
at its prequisites, i.e. it's quite likely that it remains the same
even though a prequisite changed. The updated timestamp would cause
a lot of unnecessary recompiles. In this case, we actually generate
a temporary file, compare it to the old file and only the contents
are different do overwrite the old file.

The "update-if-changed" snippet remains always the same, so let's
put it into a macro instead of duplicating it. After that change,
scripts/mkversion_h is so small that we rather put the three remaining
lines directly into the Makefile.

Makefile

@@ -301,7 +301,12 @@ include/linux/autoconf.h: .config
 #	this Makefile
 
 include/linux/version.h: Makefile
-	@scripts/mkversion_h $@ $(KERNELRELEASE) $(VERSION) $(PATCHLEVEL) $(SUBLEVEL)
+	@echo -n 'Generating $@'
+	@(echo \#define UTS_RELEASE \"$(KERNELRELEASE)\"; \
+	  echo \#define LINUX_VERSION_CODE `expr $(VERSION) \\* 65536 + $(PATCHLEVEL) \\* 256 + $(SUBLEVEL)`; \
+	 echo '#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))'; \
+	) > $@.tmp
+	@$(update-if-changed)
 
 # Helpers built in scripts/
 # ---------------------------------------------------------------------------
@@ -339,6 +344,7 @@ ifdef CONFIG_MODVERSIONS
 include/linux/modversions.h: scripts/fixdep prepare FORCE
 	@rm -rf .tmp_export-objs
 	@$(MAKE) $(patsubst %,_sfdep_%,$(SUBDIRS))
+	@echo -n 'Generating $@'
 	@( echo "#ifndef _LINUX_MODVERSIONS_H";\
 	   echo "#define _LINUX_MODVERSIONS_H"; \
 	   echo "#include <linux/modsetver.h>"; \
@@ -346,15 +352,8 @@ include/linux/modversions.h: scripts/fixdep prepare FORCE
 	     echo "#include <linux/$${f}>"; \
 	   done; \
 	   echo "#endif"; \
-	) > $@.tmp
-	@rm -rf .tmp_export-objs
-	@if [ -r $@ ] && cmp -s $@ $@.tmp; then \
-		echo $@ was not updated; \
-		rm -f $@.tmp; \
-	else \
-		echo $@ was updated; \
-		mv -f $@.tmp $@; \
-	fi
+	) > $@.tmp; \
+	$(update-if-changed)
 
 $(patsubst %,_sfdep_%,$(SUBDIRS)): FORCE
 	@$(MAKE) -C $(patsubst _sfdep_%, %, $@) fastdep
@@ -660,5 +659,15 @@ if_changed_rule = $(if $(strip $? \
 
 cmd = @$(if $($(quiet)$(1)),echo '  $($(quiet)$(1))' &&) $($(1))
 
+define update-if-changed
+	if [ -r $@ ] && cmp -s $@ $@.tmp; then \
+		echo ' (unchanged)'; \
+		rm -f $@.tmp; \
+	else \
+		echo ' (updated)'; \
+		mv -f $@.tmp $@; \
+	fi
+endef
+
 
 FORCE:

scripts/Makefile

@@ -5,7 +5,7 @@
 # The following temporary rule will make sure that people's
 # trees get updated to the right permissions, since patch(1)
 # can't do it
-CHMOD_FILES := docgen gen-all-syms kernel-doc mkcompile_h mkversion_h makelst
+CHMOD_FILES := docgen gen-all-syms kernel-doc mkcompile_h makelst
 
 all: fixdep split-include $(CHMOD_FILES)
 

scripts/mkversion_h

-TARGET=$1
-KERNELRELEASE=$2
-VERSION=$3
-PATCHLEVEL=$4
-SUBLEVEL=$5
-
-# Generate a temporary version.h
-
-( echo \#define UTS_RELEASE \"$KERNELRELEASE\"
-  echo \#define LINUX_VERSION_CODE `expr $VERSION \\* 65536 + $PATCHLEVEL \\* 256 + $SUBLEVEL`
-  echo '#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))'
-) > .tmpversion
-
-# Only replace the real version.h if the new one is different
-# in order to preserve the timestamp and avoid unnecessary
-# recompilations.
-
-if [ -r $TARGET ] && \
-      cmp -s $TARGET .tmpversion; then
-   echo $TARGET was not updated;
-   rm -f .tmpversion
-else
-   echo $TARGET was updated;
-   mv -f .tmpversion $TARGET
-fi