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kbuild: add more hints about SUBDIRS replacement

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Commit 0126be38d9 ("kbuild: announce removal of SUBDIRS if used")
added a hint about the 'SUBDIRS' replacement, but it was not clear
enough.

Multiple people sent me similar questions, patches. For instance,

  https://lkml.org/lkml/2019/1/17/456

I did not mean to use M= for building a subdirectory in the kernel tree.

From commit 669efc76b3 ("net: hns3: fix compile error"), people
already (ab)use M=... to do that because it seems to work to some extent.

Documentation/kbuild/kbuild.txt says M= and KBUILD_EXTMOD are used for
building external modules.

In fact, Kbuild supports the single target '%/' for this purpose, but
this may not be noticed much.

Kindly add more hints.

Makefile:213: ================= WARNING ================
Makefile:214: 'SUBDIRS' will be removed after Linux 5.3
Makefile:215:
Makefile:216: If you are building an individual subdirectory
Makefile:217: in the kernel tree, you can do like this:
Makefile:218: $ make path/to/dir/you/want/to/build/
Makefile:219: (Do not forget the trailing slash)
Makefile:220:
Makefile:221: If you are building an external module,
Makefile:222: Please use 'M=' or 'KBUILD_EXTMOD' instead
Makefile:223: ==========================================

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
This commit is contained in:
Masahiro Yamada 2019-06-25 17:51:27 +09:00
parent 0c4ab18fc3
commit 4e8fc3f55a
1 changed files with 7 additions and 0 deletions
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Makefile
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@ -212,6 +212,13 @@ endif
ifdef SUBDIRS
$(warning ================= WARNING ================)
$(warning 'SUBDIRS' will be removed after Linux 5.3)
$(warning )
$(warning If you are building an individual subdirectory)
$(warning in the kernel tree, you can do like this:)
$(warning $$ make path/to/dir/you/want/to/build/)
$(warning (Do not forget the trailing slash))
$(warning )
$(warning If you are building an external module,)
$(warning Please use 'M=' or 'KBUILD_EXTMOD' instead)
$(warning ==========================================)
KBUILD_EXTMOD ?= $(SUBDIRS)