[PATCH] kbuild: do not create orphan built-in.a or obj-y objects

From: Masahiro Yamada
Date: Wed Dec 18 2019 - 11:04:47 EST


Both 'obj-y += foo/' and 'obj-m += foo/' request Kbuild to visit the
sub-directory foo/, but the difference is that only the former combines
foo/built-in.a into the built-in.a of the current directory because
everything in sub-directories visited by obj-m is supposed to be modular.

So, it makes sense to create built-in.a only if that sub-directory is
reachable by the chain of obj-y. Otherwise, built-in.a will not be
linked into vmlinux anyway. For the same reason, it is pointless to
compile obj-y objects in the directory visited by obj-m.

Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
---

scripts/Makefile.build | 2 +-
scripts/Makefile.lib | 4 ++++
2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index b734ac8a654e..e46b4ee9a120 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -66,7 +66,7 @@ lib-target := $(obj)/lib.a
real-obj-y += $(obj)/lib-ksyms.o
endif

-ifneq ($(strip $(real-obj-y) $(need-builtin)),)
+ifdef need-builtin
builtin-target := $(obj)/built-in.a
endif

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index b51144f271f2..ee930e09d198 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -35,7 +35,11 @@ __subdir-y := $(patsubst %/,%,$(filter %/, $(obj-y)))
subdir-y += $(__subdir-y)
__subdir-m := $(patsubst %/,%,$(filter %/, $(obj-m)))
subdir-m += $(__subdir-m)
+ifdef need-builtin
obj-y := $(patsubst %/, %/built-in.a, $(obj-y))
+else
+obj-y := $(filter-out %/, $(obj-y))
+endif
obj-m := $(filter-out %/, $(obj-m))

# Subdirectories we need to descend into
--
2.17.1