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authorMasahiro Yamada <masahiroy@kernel.org>2019-12-19 20:51:00 +0900
committerMasahiro Yamada <masahiroy@kernel.org>2019-12-22 00:25:35 +0900
commit28f94a44298c99c0db85539874b62f21d94fcaa7 (patch)
treecd6fbf7499a88942672ffdcc558138f2da223510 /Makefile
parent8f268881d7d278047b00eed54bbb9288dbd6ab23 (diff)
kbuild: clarify the difference between obj-y and obj-m w.r.t. descending
Kbuild descends into a directory by either 'y' or 'm', but there is an important difference. Kbuild combines the built-in objects into built-in.a in each directory. The built-in.a in the directory visited by obj-y is merged into the built-in.a in the parent directory. This merge happens recursively when Kbuild is ascending back towards the top directory, then built-in objects are linked into vmlinux eventually. This works properly only when the Makefile specifying obj-y is reachable by the chain of obj-y. On the other hand, Kbuild does not take built-in.a from the directory visited by obj-m. This it, all the objects in that directory are supposed to be modular. If Kbuild descends into a directory by obj-m, but the Makefile in the sub-directory specifies obj-y, those objects are just left orphan. The current statement "Kbuild only uses this information to decide that it needs to visit the directory" is misleading. Clarify the difference. Reported-by: Johan Hovold <johan@kernel.org> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Reviewed-by: Johan Hovold <johan@kernel.org>
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