[PATCH] uml kbuild: avoid useless rebuilds

- Fix some problems with usage of $(targets) (sometimes missing, sometimes
  used badly) that trigger partial rebuilds when doing a rebuild.

- At that purpose, also factor out some common code for symlinks creation.

- Fix a x86-64 build warning, caused by -L/usr/lib, which is anyway useless,
  and invalid in the x86-64 case.

Tested on x86_64 and x86.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/um/Makefile

@@ -126,7 +126,7 @@ define cmd_vmlinux__
 	$(CC) $(CFLAGS_vmlinux) -o $@ \
 	-Wl,-T,$(vmlinux-lds) $(vmlinux-init) \
 	-Wl,--start-group $(vmlinux-main) -Wl,--end-group \
-	-L/usr/lib -lutil \
+	-lutil \
 	$(filter-out $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) \
 	FORCE ,$^) ; rm -f linux
 endef

arch/um/kernel/Makefile

@@ -4,7 +4,7 @@
 #
 
 extra-y := vmlinux.lds
-clean-files := vmlinux.lds.S config.tmp
+clean-files := vmlinux.lds.S
 
 obj-y = checksum.o config.o exec_kern.o exitcode.o \
 	helper.o init_task.o irq.o irq_user.o ksyms.o main.o mem.o mem_user.o \
@@ -34,7 +34,7 @@ USER_OBJS := $(user-objs-y) config.o helper.o main.o process.o tempfile.o \
 
 include arch/um/scripts/Makefile.rules
 
-targets += config.c
+targets := config.c config.tmp
 
 # Be careful with the below Sed code - sed is pitfall-rich!
 # We use sed to lower build requirements, for "embedded" builders for instance.

arch/um/kernel/tt/Makefile

@@ -4,6 +4,7 @@
 #
 
 extra-y := unmap_fin.o
+targets := unmap.o
 clean-files := unmap_tmp.o
 
 obj-y = exec_kern.o exec_user.o gdb.o ksyms.o mem.o mem_user.o process_kern.o \

arch/um/scripts/Makefile.rules

@@ -10,4 +10,18 @@ USER_OBJS := $(foreach file,$(USER_OBJS),$(obj)/$(file))
 $(USER_OBJS): c_flags = -Wp,-MD,$(depfile) $(USER_CFLAGS) $(CFLAGS_$(notdir $@))
 
 quiet_cmd_make_link = SYMLINK $@
-cmd_make_link       = rm -f $@; ln -sf $(srctree)/arch/$(SUBARCH)/$($(notdir $@)-dir)/$(notdir $@) $@
+cmd_make_link       = ln -sf $(srctree)/arch/$(SUBARCH)/$($(notdir $@)-dir)/$(notdir $@) $@
+
+# this needs to be before the foreach, because targets does not accept
+# complete paths like $(obj)/$(f). To make sure this works, use a := assignment,
+# or we will get $(obj)/$(f) in the "targets" value.
+# Also, this forces you to use the := syntax when assigning to targets.
+# Otherwise the line below will cause an infinite loop (if you don't know why,
+# just do it).
+
+targets := $(targets) $(SYMLINKS)
+
+SYMLINKS := $(foreach f,$(SYMLINKS),$(obj)/$(f))
+
+$(SYMLINKS): FORCE
+	$(call if_changed,make_link)

arch/um/sys-i386/Makefile

@@ -7,24 +7,13 @@ obj-$(CONFIG_MODULES) += module.o
 
 USER_OBJS := bugs.o ptrace_user.o sigcontext.o fault.o
 
-include arch/um/scripts/Makefile.rules
-
 SYMLINKS = bitops.c semaphore.c highmem.c module.c
 
-# this needs to be before the foreach, because clean-files does not accept
-# complete paths like $(src)/$f.
-clean-files := $(SYMLINKS)
-
-targets += $(SYMLINKS)
-
-SYMLINKS := $(foreach f,$(SYMLINKS),$(obj)/$f)
-
 bitops.c-dir = lib
 semaphore.c-dir = kernel
 highmem.c-dir = mm
 module.c-dir = kernel
 
-$(SYMLINKS): FORCE
-	$(call if_changed,make_link)
-
 subdir- := util
+
+include arch/um/scripts/Makefile.rules

arch/um/sys-x86_64/Makefile

@@ -19,14 +19,6 @@ include arch/um/scripts/Makefile.rules
 SYMLINKS = bitops.c csum-copy.S csum-partial.c csum-wrappers.c memcpy.S \
 	semaphore.c thunk.S module.c
 
-# this needs to be before the foreach, because clean-files does not accept
-# complete paths like $(src)/$f.
-clean-files := $(SYMLINKS)
-
-targets += $(SYMLINKS)
-
-SYMLINKS := $(foreach f,$(SYMLINKS),$(obj)/$f)
-
 bitops.c-dir = lib
 csum-copy.S-dir = lib
 csum-partial.c-dir = lib
@@ -36,7 +28,4 @@ semaphore.c-dir = kernel
 thunk.S-dir = lib
 module.c-dir = kernel
 
-$(SYMLINKS): FORCE
-	$(call if_changed,make_link)
-
 CFLAGS_csum-partial.o := -Dcsum_partial=arch_csum_partial