1 files changed, 90 insertions, 0 deletions
diff --git a/make/subdir.mk b/make/subdir.mk
new file mode 100644
index 000000000000..900f7e6ab7bd
--- /dev/null
+++ b/make/subdir.mk
@@ -0,0 +1,90 @@
+# This file is intended to be included from each subdirectory makefile.
+#
+# Subdirectory makefiles must define:
+#   SubDirs - The subdirectories to traverse.
+#   ObjNames - The objects available in that directory.
+#   Implementation - The library configuration the objects should go in (Generic or
+#                    Optimized)
+#   Dependencies - Any dependences for the object files.
+#
+# Subdirectory makefiles may define:
+#   OnlyArchs - Only build the objects for the listed archs.
+#   OnlyConfigs - Only build the objects for the listed configurations.
+
+ifeq ($(Dir),)
+  $(error "No Dir variable defined.")
+endif
+
+###
+# Include child makefile fragments
+
+# The list of variables which are intended to be overridden in a subdirectory
+# makefile.
+RequiredSubdirVariables := SubDirs ObjNames Implementation Dependencies
+OptionalSubdirVariables := OnlyArchs OnlyConfigs
+
+# Template: subdir_traverse_template subdir
+define subdir_traverse_template
+$(call Set,Dir,$(1))
+ifneq ($(DEBUGMAKE),)
+  $$(info MAKE: $(Dir): Processing subdirectory)
+endif
+
+# Construct the variable key for this directory.
+$(call Set,DirKey,SubDir.$(subst .,,$(subst /,__,$(1))))
+$(call Append,SubDirKeys,$(DirKey))
+$(call Set,$(DirKey).Dir,$(Dir))
+
+# Reset subdirectory specific variables to sentinel value.
+$$(foreach var,$$(RequiredSubdirVariables) $$(OptionalSubdirVariables),\
+  $$(call Set,$$(var),UNDEFINED))
+
+# Get the subdirectory variables.
+include $(1)/Makefile.mk
+
+ifeq ($(DEBUGMAKE),2)
+$$(foreach var,$(RequiredSubdirVariables) $(OptionalSubdirVariables),\
+  $$(if $$(call strneq,UNDEFINED,$$($$(var))), \
+	$$(info MAKE: $(Dir): $$(var) is defined), \
+	$$(info MAKE: $(Dir): $$(var) is undefined)))
+endif
+
+# Check for undefined required variables, and unset sentinel value from optional
+# variables.
+$$(foreach var,$(RequiredSubdirVariables),\
+  $$(if $$(call strneq,UNDEFINED,$$($$(var))),, \
+	$$(error $(Dir): variable '$$(var)' was not undefined)))
+$$(foreach var,$(OptionalSubdirVariables),\
+  $$(if $$(call strneq,UNDEFINED,$$($$(var))),, \
+	$$(call Set,$$(var),)))
+
+# Collect all subdirectory variables for subsequent use.
+$$(foreach var,$(RequiredSubdirVariables) $(OptionalSubdirVariables),\
+  $$(call Set,$(DirKey).$$(var),$$($$(var))))
+
+# Recurse.
+include make/subdir.mk
+
+# Restore directory variable, for cleanliness.
+$$(call Set,Dir,$(1))
+
+ifneq ($(DEBUGMAKE),)
+  $$(info MAKE: $$(Dir): Done processing subdirectory)
+endif
+endef
+
+# Evaluate this now so we do not have to worry about order of evaluation.
+
+SubDirsList := $(strip \
+  $(if $(call streq,.,$(Dir)),\
+       $(SubDirs),\
+       $(SubDirs:%=$(Dir)/%)))
+ifeq ($(SubDirsList),)
+else
+  ifneq ($(DEBUGMAKE),)
+    $(info MAKE: Descending into subdirs: $(SubDirsList))
+  endif
+
+  $(foreach subdir,$(SubDirsList),\
+	$(eval $(call subdir_traverse_template,$(subdir))))
+endif