Since commit ff9b45c55b26 ("kbuild: modpost: read modules.order instead
of $(MODVERDIR)/*.mod"), a module is no longer built in the following
pattern:
[Makefile]
subdir-y := some-module
[some-module/Makefile]
obj-m := some-module.o
You cannot write Makefile this way in upstream because modules.order is
not correctly generated. subdir-y is used to descend to a sub-directory
that builds tools, device trees, etc.
For external modules, the modules order does not matter. So, the
Makefile above was known to work.
I believe the Makefile should be re-written as follows:
[Makefile]
obj-m := some-module/
[some-module/Makefile]
obj-m := some-module.o
However, people will have no idea if their Makefile suddenly stops
working. In fact, I received questions from multiple people.
Show a warning if obj-m is specified in a Makefile visited by subdir-y
or subdir-m.
Cc: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Cc: Tom Stonecypher <thomas.edwardx.stonecypher@xxxxxxxxx>
Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
---
scripts/Makefile.build | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 37a1d2cd49d4..4a26c7ed9198 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -52,6 +52,13 @@ ifndef obj
$(warning kbuild: Makefile.build is included improperly)
endif
+ifeq ($(need-modorder),)
+ifneq ($(obj-m),)
+$(warning $(patsubst %.o,'%.ko',$(obj-m)) will not be built even though obj-m is specified.)
+$(warning You cannot use subdir-y/m to visit a module Makefile. Use obj-y/m instead.)
+endif
+endif
+
# ===========================================================================
ifneq ($(strip $(lib-y) $(lib-m) $(lib-)),)
--
2.17.1
