[RFC 2/2] Kbuild: Support nested composite objects

[Elliot Berman <eberman@codeaurora.org>]

Kbuild composite objects only supports one level of composite objects.
That is, a composite object may only be composed of real compilable
source files.

As a simple example, the following Kbuild description is now supported:

bar-a-y := a/bar0.o a/bar1.o
bar-b-y := b/bar2.o b/bar3.o

foo-objs := bar-a.o bar-b.o

obj-m += foo.o

Add such support by recursively searching for composite objects and
listing them in $(multi-used-*) and $(real-obj-*).

Signed-off-by: Elliot Berman <eberman@codeaurora.org>
---
 scripts/Makefile.lib | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 93e4f10..5118204 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -59,14 +59,22 @@ endif
 # Expand $(foo-objs) $(foo-y) by calling $(call suffix-search,foo.o,-objs -y)
 suffix-search = $(foreach s,$(2),$($(1:.o=$s)))
 # If $(foo-objs), $(foo-y), $(foo-m), or $(foo-) exists, foo.o is a composite object
-multi-search = $(sort $(foreach m,$(1), $(if $(strip $(call suffix-search,$(m),$(2) -)), $(m))))
+# Do this recursively to find nested composite objects. For backwards compatibility,
+# foo-y may contain foo.o bar.o . We shouldn't recurse further in this case.
+multi-search = $(sort $(foreach m,$(1),$(if $(strip $(call suffix-search,$(m),$(2) -)),\
+	$(m) $(call multi-search,$(filter-out $(m),$(call suffix-search,$(m),$(2))),$(2)))))
 multi-used-y := $(call multi-search,$(obj-y),-objs -y)
 multi-used-m := $(call multi-search,$(obj-m),-objs -y -m)
 multi-used   := $(multi-used-y) $(multi-used-m)
 
 # Replace multi-part objects by their individual parts,
 # including built-in.a from subdirectories
-real-search = $(foreach m,$(1), $(if $(strip $(call suffix-search,$(m),$(2) -)),$(call suffix-search,$(m),$(2)),$(m)))
+# Recursively search for real files. For backwards compatibility,
+# foo-y may contain foo.o bar.o . foo.o in this context is a real object, and
+# shouldn't be recursed into.
+real-search = $(foreach m,$(1), $(if $(strip $(call suffix-search,$(m),$(2) -)), \
+	$(filter $(m),$(call suffix-search,$(m),$(2))) $(call real-search,$(filter-out $(m),$(call suffix-search,$(m),$(2))),$(2)),\
+	$(m)))
 real-obj-y := $(call real-search, $(obj-y),-objs -y)
 real-obj-m := $(call real-search, $(obj-m),-objs -y -m)
 
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