kbuild: full dependency check on asm-offsets.h

Building asm-offsets.h has been moved to a seperate Kbuild file
located in the top-level directory. This allow us to share the
functionality across the architectures.

The old rules in architecture specific Makefiles will die
in subsequent patches.

Furhtermore the usual kbuild dependency tracking is now used
when deciding to rebuild asm-offsets.s. So we no longer risk
to fail a rebuild caused by asm-offsets.c dependencies being touched.

With this common rule-set we now force the same name across
all architectures. Following patches will fix the rest.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Kbuild

@@ -0,0 +1,41 @@
+#
+# Kbuild for top-level directory of the kernel
+# This file takes care of the following:
+# 1) Generate asm-offsets.h
+
+#####
+# 1) Generate asm-offsets.h 
+#
+
+offsets-file := include/asm-$(ARCH)/asm-offsets.h
+
+always  := $(offsets-file)
+targets := $(offsets-file)
+targets += arch/$(ARCH)/kernel/asm-offsets.s
+
+quiet_cmd_offsets = GEN     $@
+define cmd_offsets
+	cat $< | \
+	(set -e; \
+	 echo "#ifndef __ASM_OFFSETS_H__"; \
+	 echo "#define __ASM_OFFSETS_H__"; \
+	 echo "/*"; \
+	 echo " * DO NOT MODIFY."; \
+	 echo " *"; \
+	 echo " * This file was generated by $(srctree)/Kbuild"; \
+	 echo " *"; \
+	 echo " */"; \
+	 echo ""; \
+	 sed -ne "/^->/{s:^->\([^ ]*\) [\$$#]*\([^ ]*\) \(.*\):#define \1 \2 /* \3 */:; s:->::; p;}"; \
+	 echo ""; \
+	 echo "#endif" ) > $@
+endef
+
+# We use internal kbuild rules to avoid the "is up to date" message from make
+arch/$(ARCH)/kernel/asm-offsets.s: arch/$(ARCH)/kernel/asm-offsets.c FORCE
+	$(Q)mkdir -p $(dir $@)
+	$(call if_changed_dep,cc_s_c)
+
+$(srctree)/$(offsets-file): arch/$(ARCH)/kernel/asm-offsets.s Kbuild
+	$(call cmd,offsets)
+