[3/3] kbuild: show hint if subdir-y/m is used to visit module Makefile

Message ID 20190806100323.22919-3-yamada.masahiro@socionext.com
State New
Headers show
Series
  • [1/3] kbuild: fix false-positive need-builtin
Related show

Commit Message

Masahiro Yamada Aug. 6, 2019, 10:03 a.m.
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@siemens.com>
Cc: Tom Stonecypher <thomas.edwardx.stonecypher@intel.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

---

 scripts/Makefile.build | 7 +++++++
 1 file changed, 7 insertions(+)

-- 
2.17.1

Comments

Masahiro Yamada Aug. 8, 2019, 6:29 a.m. | #1
On Tue, Aug 6, 2019 at 7:03 PM Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
>

> 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@siemens.com>

> Cc: Tom Stonecypher <thomas.edwardx.stonecypher@intel.com>

> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

> ---


This produces false-positive warnings for single-targets.
I will fix up as follows:


diff --git a/Makefile b/Makefile
index 0e37ad2f77bf..fac25e279da6 100644
--- a/Makefile
+++ b/Makefile
@@ -1783,7 +1783,7 @@ 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
 # ===========================================================================



>

>  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

>



-- 
Best Regards
Masahiro Yamada

Patch

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-)),)