[RFC v2] xen/arm: build: add missed dependency for head.S

[Wei Chen <wei.chen@linaro.org>]

In current Xen build rules, the build system will only check the
dependencies in current folder and obj-y generated dependencies
in other folder.

But Makefile may add some objects to ALL_OBJS. These objects may
be not in the same folder as Makefile. Use arch/arm/Makefile as
an example:
    ALL_OBJS := $(TARGET_SUBARCH)/head.o

The head.o is not in the same folder as Makefile and is not listed
in obj-y. So, when we update the header files that had been included
in head.S. The build system would not check the dependency of head.S.
The head.S would not be re-compiled.

In this patch, we will get objects added by Makefile and add their
dependencies to check list.

Signed-off-by: Wei Chen <Wei.Chen@linaro.org>
---
v1 -> v2:
- Use a generic method instead of changing Makefiles
---
 xen/Rules.mk | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/xen/Rules.mk b/xen/Rules.mk
index 961d533..fb3087c 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -95,12 +95,21 @@ include $(BASEDIR)/arch/$(TARGET_ARCH)/Rules.mk
 include Makefile
 
 DEPS = .*.d
+
+# In obj-y and ALL_OBJS, there may have some objects are not in the
+# same folder as Makefile, so we have to use gendep to generate
+# dependencies for them.
+DEP_OBJS = $(obj-y)
+
+# Extract objects from ALL_OBJS added by Makefile.
+DEP_OBJS += $(filter-out %built_in.o,$(ALL_OBJS))
+
 define gendep
     ifneq ($(1),$(subst /,:,$(1)))
         DEPS += $(dir $(1)).$(notdir $(1)).d
     endif
 endef
-$(foreach o,$(filter-out %/,$(obj-y)),$(eval $(call gendep,$(o))))
+$(foreach o,$(filter-out %/,$(DEP_OBJS)),$(eval $(call gendep,$(o))))
 
 # Ensure each subdirectory has exactly one trailing slash.
 subdir-n := $(patsubst %,%/,$(patsubst %/,%,$(subdir-n) $(subdir-)))
-- 
2.7.4


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