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kbuild: show hint if subdir-y/m is used to visit module Makefile

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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 for a while if obj-m is specified in a Makefile visited
by subdir-y or subdir-m.

I touched the %/ rule to avoid false-positive warnings for the single
target.

Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Tom Stonecypher <thomas.edwardx.stonecypher@intel.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Tested-by: Jan Kiszka <jan.kiszka@siemens.com>
This commit is contained in:
Masahiro Yamada 2019-08-08 20:21:11 +09:00
parent 4f2c8f3089
commit c07d8d47bc
2 changed files with 8 additions and 1 deletions
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2
Makefile
View File

@ -1788,7 +1788,7 @@ PHONY += /
/: ./
%/: prepare FORCE
$(Q)$(MAKE) KBUILD_MODULES=1 $(build)=$(build-dir)
$(Q)$(MAKE) KBUILD_MODULES=1 $(build)=$(build-dir) need-modorder=1
# FIXME Should go into a make.lib or something
# ===========================================================================

7
scripts/Makefile.build
View File

@ -52,6 +52,13 @@ ifndef obj
$(warning kbuild: Makefile.build is included improperly)
endif
ifeq ($(MAKECMDGOALS)$(need-modorder),)
ifneq ($(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-)),)