On Fri, Dec 20, 2019 at 4:53 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Thu, Dec 19, 2019 at 08:51:00PM +0900, Masahiro Yamada wrote: > > 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, so built-in objects > > are linked into vmlinux eventually. This works properly only when the > > Makefile that specifies 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. > > > + Kbuild uses this information not only to decide that it needs to visit > > + the directory, but also to decide whether or not to link objects from > > + the directory into vmlinux. > > + > > + When Kbuild descends into the directory with 'y', all built-in objects > > + from that directory are combined into the built-in.a, which will be > > + eventually linked into vmlinux. > > + > > + When Kbuild descends into the directory with 'm', in contrast, nothing > > + from that directory will be linked into vmlinux. If the Makefile in > > + that directory specifies obj-y, those objects will be left orphan. > > + It is very likely a bug of the Makefile or of dependencies in Kconfig. > > Perhaps the implementation should be changed to match the documentation? > This seems like a very subtle point for people to know. I also considered this, but I do not think the current behavior is too odd. So, I am not changing it. -- Best Regards Masahiro Yamada
