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>

3 files changed, 12 insertions, 3 deletions

diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index fbfc14a56b96..585d334234f4 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -1,6 +1,9 @@
 #
 # arch/arm/Makefile
 #
+# This file is included by the global makefile so that you can add your own
+# architecture-specific flags and dependencies.
+#
 # This file is subject to the terms and conditions of the GNU General Public
 # License.  See the file "COPYING" in the main directory of this archive
 # for more details.
@@ -176,7 +179,7 @@ endif
 
 archprepare: maketools
 
-.PHONY: maketools FORCE
+PHONY += maketools FORCE
 maketools: include/linux/version.h include/asm-arm/.arch FORCE
         $(Q)$(MAKE) $(build)=arch/arm/tools include/asm-arm/mach-types.h
 
diff --git a/arch/arm/boot/Makefile b/arch/arm/boot/Makefile
index a174d63395ea..ec9c400c7f82 100644
--- a/arch/arm/boot/Makefile
+++ b/arch/arm/boot/Makefile
@@ -1,6 +1,9 @@
 #
 # arch/arm/boot/Makefile
 #
+# This file is included by the global makefile so that you can add your own
+# architecture-specific flags and dependencies.
+#
 # This file is subject to the terms and conditions of the GNU General Public
 # License.  See the file "COPYING" in the main directory of this archive
 # for more details.
@@ -73,7 +76,7 @@ $(obj)/bootpImage: $(obj)/bootp/bootp FORCE
         $(call if_changed,objcopy)
         @echo '  Kernel: $@ is ready'
 
-.PHONY: initrd FORCE
+PHONY += initrd FORCE
 initrd:
         @test "$(INITRD_PHYS)" != "" || \
         (echo This machine does not support INITRD; exit -1)
diff --git a/arch/arm/boot/bootp/Makefile b/arch/arm/boot/bootp/Makefile
index 8e8879b6b3d7..c394e305447c 100644
--- a/arch/arm/boot/bootp/Makefile
+++ b/arch/arm/boot/bootp/Makefile
@@ -1,6 +1,9 @@
 #
 # linux/arch/arm/boot/bootp/Makefile
 #
+# This file is included by the global makefile so that you can add your own
+# architecture-specific flags and dependencies.
+#
 
 LDFLAGS_bootp   :=-p --no-undefined -X \
                  --defsym initrd_phys=$(INITRD_PHYS) \
@@ -21,4 +24,4 @@ $(obj)/kernel.o: arch/arm/boot/zImage FORCE
 
 $(obj)/initrd.o: $(INITRD) FORCE
 
-.PHONY: $(INITRD) FORCE
+PHONY += $(INITRD) FORCE