kbuild: change kbuild to not rely on incorrect GNU make behavior

The kbuild system takes advantage of an incorrect behavior in GNU make.
Once this behavior is fixed, all files in the kernel rebuild every time,
even if nothing has changed.  This patch ensures kbuild works with both
the incorrect and correct behaviors of GNU make.

For more details on the incorrect behavior, see:

http://lists.gnu.org/archive/html/bug-make/2006-03/msg00003.html

Changes in this patch:
  - Keep all targets that are to be marked .PHONY in a variable, PHONY.
  - Add .PHONY: $(PHONY) to mark them properly.
  - Remove any $(PHONY) files from the $? list when determining whether
    targets are up-to-date or not.

Signed-off-by: Paul Smith <psmith@gnu.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

1 files changed, 35 insertions, 29 deletions

diff --git a/Makefile b/Makefile
index 12c8d71..a59c1e2 100644
--- a/Makefile
+++ b/Makefile
@@ -95,7 +95,7 @@ ifdef O
 endif
 
 # That's our default target when none is given on the command line
-.PHONY: _all
+PHONY := _all
 _all:
 
 ifneq ($(KBUILD_OUTPUT),)
@@ -106,7 +106,7 @@ KBUILD_OUTPUT := $(shell cd $(KBUILD_OUTPUT) && /bin/pwd)
 $(if $(KBUILD_OUTPUT),, \
      $(error output directory "$(saved-output)" does not exist))
 
-.PHONY: $(MAKECMDGOALS)
+PHONY += $(MAKECMDGOALS)
 
 $(filter-out _all,$(MAKECMDGOALS)) _all:
 	$(if $(KBUILD_VERBOSE:1=),@)$(MAKE) -C $(KBUILD_OUTPUT) \
@@ -123,7 +123,7 @@ ifeq ($(skip-makefile),)
 
 # If building an external module we do not care about the all: rule
 # but instead _all depend on modules
-.PHONY: all
+PHONY += all
 ifeq ($(KBUILD_EXTMOD),)
 _all: all
 else
@@ -337,14 +337,14 @@ export RCS_TAR_IGNORE := --exclude SCCS --exclude BitKeeper --exclude .svn --exc
 # Rules shared between *config targets and build targets
 
 # Basic helpers built in scripts/
-.PHONY: scripts_basic
+PHONY += scripts_basic
 scripts_basic:
 	$(Q)$(MAKE) $(build)=scripts/basic
 
 # To avoid any implicit rule to kick in, define an empty command.
 scripts/basic/%: scripts_basic ;
 
-.PHONY: outputmakefile
+PHONY += outputmakefile
 # outputmakefile generate a Makefile to be placed in output directory, if
 # using a seperate output directory. This allows convinient use
 # of make in output directory
@@ -420,7 +420,7 @@ ifeq ($(KBUILD_EXTMOD),)
 # Additional helpers built in scripts/
 # Carefully list dependencies so we do not try to build scripts twice
 # in parrallel
-.PHONY: scripts
+PHONY += scripts
 scripts: scripts_basic include/config/MARKER
 	$(Q)$(MAKE) $(build)=$(@)
 
@@ -720,7 +720,7 @@ $(sort $(vmlinux-init) $(vmlinux-main)) $(vmlinux-lds): $(vmlinux-dirs) ;
 # make menuconfig etc.
 # Error messages still appears in the original language
 
-.PHONY: $(vmlinux-dirs)
+PHONY += $(vmlinux-dirs)
 $(vmlinux-dirs): prepare scripts
 	$(Q)$(MAKE) $(build)=$@
 
@@ -773,10 +773,10 @@ kernelrelease = $(KERNELVERSION)$(localver-full)
 # version.h and scripts_basic is processed / created.
 
 # Listed in dependency order
-.PHONY: prepare archprepare prepare0 prepare1 prepare2 prepare3
+PHONY += prepare archprepare prepare0 prepare1 prepare2 prepare3
 
 # prepare-all is deprecated, use prepare as valid replacement
-.PHONY: prepare-all
+PHONY += prepare-all
 
 # prepare3 is used to check if we are building in a separate output directory,
 # and if so do:
@@ -857,7 +857,7 @@ include/linux/version.h: $(srctree)/Makefile .config .kernelrelease FORCE
 
 # ---------------------------------------------------------------------------
 
-.PHONY: depend dep
+PHONY += depend dep
 depend dep:
 	@echo '*** Warning: make $@ is unnecessary now.'
 
@@ -872,21 +872,21 @@ all: modules
 
 #	Build modules
 
-.PHONY: modules
+PHONY += modules
 modules: $(vmlinux-dirs) $(if $(KBUILD_BUILTIN),vmlinux)
 	@echo '  Building modules, stage 2.';
 	$(Q)$(MAKE) -rR -f $(srctree)/scripts/Makefile.modpost
 
 
 # Target to prepare building external modules
-.PHONY: modules_prepare
+PHONY += modules_prepare
 modules_prepare: prepare scripts
 
 # Target to install modules
-.PHONY: modules_install
+PHONY += modules_install
 modules_install: _modinst_ _modinst_post
 
-.PHONY: _modinst_
+PHONY += _modinst_
 _modinst_:
 	@if [ -z "`$(DEPMOD) -V 2>/dev/null | grep module-init-tools`" ]; then \
 		echo "Warning: you may need to install module-init-tools"; \
@@ -913,7 +913,7 @@ depmod_opts	:=
 else
 depmod_opts	:= -b $(INSTALL_MOD_PATH) -r
 endif
-.PHONY: _modinst_post
+PHONY += _modinst_post
 _modinst_post: _modinst_
 	if [ -r System.map -a -x $(DEPMOD) ]; then $(DEPMOD) -ae -F System.map $(depmod_opts) $(KERNELRELEASE); fi
 
@@ -956,7 +956,7 @@ clean: rm-dirs  := $(CLEAN_DIRS)
 clean: rm-files := $(CLEAN_FILES)
 clean-dirs      := $(addprefix _clean_,$(srctree) $(vmlinux-alldirs))
 
-.PHONY: $(clean-dirs) clean archclean
+PHONY += $(clean-dirs) clean archclean
 $(clean-dirs):
 	$(Q)$(MAKE) $(clean)=$(patsubst _clean_%,%,$@)
 
@@ -974,7 +974,7 @@ mrproper: rm-dirs  := $(wildcard $(MRPROPER_DIRS))
 mrproper: rm-files := $(wildcard $(MRPROPER_FILES))
 mrproper-dirs      := $(addprefix _mrproper_,Documentation/DocBook scripts)
 
-.PHONY: $(mrproper-dirs) mrproper archmrproper
+PHONY += $(mrproper-dirs) mrproper archmrproper
 $(mrproper-dirs):
 	$(Q)$(MAKE) $(clean)=$(patsubst _mrproper_%,%,$@)
 
@@ -984,7 +984,7 @@ mrproper: clean archmrproper $(mrproper-dirs)
 
 # distclean
 #
-.PHONY: distclean
+PHONY += distclean
 
 distclean: mrproper
 	@find $(srctree) $(RCS_FIND_IGNORE) \
@@ -1000,7 +1000,7 @@ distclean: mrproper
 # rpm target kept for backward compatibility
 package-dir	:= $(srctree)/scripts/package
 
-.PHONY: %-pkg rpm
+PHONY += %-pkg rpm
 
 %pkg: FORCE
 	$(Q)$(MAKE) -f $(package-dir)/Makefile $@
@@ -1092,12 +1092,12 @@ else # KBUILD_EXTMOD
 
 # We are always building modules
 KBUILD_MODULES := 1
-.PHONY: crmodverdir
+PHONY += crmodverdir
 crmodverdir:
 	$(Q)rm -rf $(MODVERDIR)
 	$(Q)mkdir -p $(MODVERDIR)
 
-.PHONY: $(objtree)/Module.symvers
+PHONY += $(objtree)/Module.symvers
 $(objtree)/Module.symvers:
 	@test -e $(objtree)/Module.symvers || ( \
 	echo; \
@@ -1106,7 +1106,7 @@ $(objtree)/Module.symvers:
 	echo )
 
 module-dirs := $(addprefix _module_,$(KBUILD_EXTMOD))
-.PHONY: $(module-dirs) modules
+PHONY += $(module-dirs) modules
 $(module-dirs): crmodverdir $(objtree)/Module.symvers
 	$(Q)$(MAKE) $(build)=$(patsubst _module_%,%,$@)
 
@@ -1114,11 +1114,11 @@ modules: $(module-dirs)
 	@echo '  Building modules, stage 2.';
 	$(Q)$(MAKE) -rR -f $(srctree)/scripts/Makefile.modpost
 
-.PHONY: modules_install
+PHONY += modules_install
 modules_install: _emodinst_ _emodinst_post
 
-install-dir := $(if $(INSTALL_MOD_DIR),$(INSTALL_MOD_DIR),extra)	
-.PHONY: _emodinst_
+install-dir := $(if $(INSTALL_MOD_DIR),$(INSTALL_MOD_DIR),extra)
+PHONY += _emodinst_
 _emodinst_:
 	$(Q)rm -rf $(MODLIB)/$(install-dir)
 	$(Q)mkdir -p $(MODLIB)/$(install-dir)
@@ -1133,13 +1133,13 @@ quiet_cmd_depmod = DEPMOD  $(KERNELRELEASE)
 		      $(KERNELRELEASE);                       \
                    fi
 
-.PHONY: _emodinst_post
+PHONY += _emodinst_post
 _emodinst_post: _emodinst_
 	$(call cmd,depmod)
 
 clean-dirs := $(addprefix _clean_,$(KBUILD_EXTMOD))
 
-.PHONY: $(clean-dirs) clean
+PHONY += $(clean-dirs) clean
 $(clean-dirs):
 	$(Q)$(MAKE) $(clean)=$(patsubst _clean_%,%,$@)
 
@@ -1161,7 +1161,7 @@ help:
 	@echo  ''
 
 # Dummies...
-.PHONY: prepare scripts
+PHONY += prepare scripts
 prepare: ;
 scripts: ;
 endif # KBUILD_EXTMOD
@@ -1274,7 +1274,7 @@ namespacecheck:
 endif #ifeq ($(config-targets),1)
 endif #ifeq ($(mixed-targets),1)
 
-.PHONY: checkstack
+PHONY += checkstack
 checkstack:
 	$(OBJDUMP) -d vmlinux $$(find . -name '*.ko') | \
 	$(PERL) $(src)/scripts/checkstack.pl $(ARCH)
@@ -1357,4 +1357,10 @@ clean := -f $(if $(KBUILD_SRC),$(srctree)/)scripts/Makefile.clean obj
 
 endif	# skip-makefile
 
+PHONY += FORCE
 FORCE:
+
+
+# Declare the contents of the .PHONY variable as phony.  We keep that
+# information in a variable se we can use it in if_changed and friends.
+.PHONY: $(PHONY)