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, 8 insertions, 5 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)))