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>

8 files changed, 52 insertions, 25 deletions

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index c3d2e4e068c4..59620b1554e0 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -116,16 +116,18 @@ make-cmd = $(subst \#,\\\#,$(subst $$,$$$$,$(call escsq,$(cmd_$(1)))))
 # function to only execute the passed command if necessary
 # >'< substitution is for echo to work, >$< substitution to preserve $ when reloading .cmd file
 # note: when using inline perl scripts [perl -e '...$$t=1;...'] in $(cmd_xxx) double $$ your perl vars
-# 
-if_changed = $(if $(strip $? $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ), \
+#
+if_changed = $(if $(strip $(filter-out $(PHONY),$?)          \
+                $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ), \
         @set -e; \
         $(echo-cmd) $(cmd_$(1)); \
         echo 'cmd_$@ := $(make-cmd)' > $(@D)/.$(@F).cmd)
 
 # execute the command and also postprocess generated .d dependencies
 # file
-if_changed_dep = $(if $(strip $? $(filter-out FORCE $(wildcard $^),$^)\
-        $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ),                  \
+if_changed_dep = $(if $(strip $(filter-out $(PHONY),$?)  \
+                $(filter-out FORCE $(wildcard $^),$^)    \
+        $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ),     \
         @set -e; \
         $(echo-cmd) $(cmd_$(1)); \
         scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(@D)/.$(@F).tmp; \
@@ -135,6 +137,7 @@ if_changed_dep = $(if $(strip $? $(filter-out FORCE $(wildcard $^),$^)\
 # Usage: $(call if_changed_rule,foo)
 # will check if $(cmd_foo) changed, or any of the prequisites changed,
 # and if so will execute $(rule_foo)
-if_changed_rule = $(if $(strip $? $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ),\
+if_changed_rule = $(if $(strip $(filter-out $(PHONY),$?)            \
+                        $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ),\
                         @set -e; \
                         $(rule_$(1)))
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 6ac96ea92bfc..7afe3e76cb5a 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -4,7 +4,7 @@
 
 src := $(obj)
 
-.PHONY: __build
+PHONY := __build
 __build:
 
 # Read .config if it exist, otherwise ignore
@@ -308,14 +308,14 @@ targets += $(multi-used-y) $(multi-used-m)
 # Descending
 # ---------------------------------------------------------------------------
 
-.PHONY: $(subdir-ym)
+PHONY += $(subdir-ym)
 $(subdir-ym):
         $(Q)$(MAKE) $(build)=$@
 
 # Add FORCE to the prequisites of a target to force it to be always rebuilt.
 # ---------------------------------------------------------------------------
 
-.PHONY: FORCE
+PHONY += FORCE
 
 FORCE:
 
@@ -330,3 +330,9 @@ cmd_files := $(wildcard $(foreach f,$(targets),$(dir $(f)).$(notdir $(f)).cmd))
 ifneq ($(cmd_files),)
   include $(cmd_files)
 endif
+
+
+# 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)
diff --git a/scripts/Makefile.clean b/scripts/Makefile.clean
index 8974ea5fc878..cff33498fa16 100644
--- a/scripts/Makefile.clean
+++ b/scripts/Makefile.clean
@@ -4,7 +4,7 @@
 
 src := $(obj)
 
-.PHONY: __clean
+PHONY := __clean
 __clean:
 
 # Shorthand for $(Q)$(MAKE) scripts/Makefile.clean obj=dir
@@ -87,10 +87,16 @@ endif
 # Descending
 # ---------------------------------------------------------------------------
 
-.PHONY: $(subdir-ymn)
+PHONY += $(subdir-ymn)
 $(subdir-ymn):
         $(Q)$(MAKE) $(clean)=$@
 
 # If quiet is set, only print short version of command
 
 cmd = @$(if $($(quiet)cmd_$(1)),echo '  $($(quiet)cmd_$(1))' &&) $(cmd_$(1))
+
+
+# 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)
diff --git a/scripts/Makefile.modinst b/scripts/Makefile.modinst
index 23fd1bdc25ce..2686dd5dce8c 100644
--- a/scripts/Makefile.modinst
+++ b/scripts/Makefile.modinst
@@ -2,7 +2,7 @@
 # Installing modules
 # ==========================================================================
 
-.PHONY: __modinst
+PHONY := __modinst
 __modinst:
 
 include scripts/Kbuild.include
@@ -12,7 +12,7 @@ include scripts/Kbuild.include
 __modules := $(sort $(shell grep -h '\.ko' /dev/null $(wildcard $(MODVERDIR)/*.mod)))
 modules := $(patsubst %.o,%.ko,$(wildcard $(__modules:.ko=.o)))
 
-.PHONY: $(modules)
+PHONY += $(modules)
 __modinst: $(modules)
         @:
 
@@ -27,3 +27,9 @@ modinst_dir = $(if $(KBUILD_EXTMOD),$(ext-mod-dir),kernel/$(@D))
 
 $(modules):
         $(call cmd,modules_install,$(MODLIB)/$(modinst_dir))
+
+
+# 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)
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 563e3c5bd8dd..0cfbe1cf2433 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -32,7 +32,7 @@
 # Step 4 is solely used to allow module versioning in external modules,
 # where the CRC of each module is retrieved from the Module.symers file.
 
-.PHONY: _modpost
+PHONY := _modpost
 _modpost: __modpost
 
 include .config
@@ -60,7 +60,7 @@ quiet_cmd_modpost = MODPOST
         $(if $(KBUILD_EXTMOD),-o $(modulesymfile)) \
         $(filter-out FORCE,$^)
 
-.PHONY: __modpost
+PHONY += __modpost
 __modpost: $(wildcard vmlinux) $(modules:.ko=.o) FORCE
         $(call cmd,modpost)
 
@@ -97,7 +97,7 @@ targets += $(modules)
 # Add FORCE to the prequisites of a target to force it to be always rebuilt.
 # ---------------------------------------------------------------------------