On Thu, Dec 19, 2019 at 05:55:54PM +0900, Masahiro Yamada wrote: > On Thu, Dec 19, 2019 at 5:18 PM Johan Hovold <johan@xxxxxxxxxx> wrote: > > > > On Thu, Dec 19, 2019 at 11:00:15AM +0900, Masahiro Yamada wrote: > > > Hi. > > > > > > On Thu, Dec 19, 2019 at 2:23 AM Johan Hovold <johan@xxxxxxxxxx> wrote: > > > > > > The offending patch is broken since it effectively makes > > > > CONFIG_SERIAL_DEV_BUS bool (built-in or disabled), but for some reason > > > > those symbols do not end up in vmlinux (despite being compiled) when you > > > > add a built-in object goal under a directory that was entered using > > > > obj-m. > > > > > > > > That seems like a bug to me and contradicts the kbuild documentation > > > > (3.6): > > > > > > > > Example: > > > > > > > > #fs/Makefile > > > > obj-$(CONFIG_EXT2_FS) += ext2/ > > > > > > > > If CONFIG_EXT2_FS is set to either ‘y’ (built-in) or ‘m’ > > > > (modular) the corresponding obj- variable will be set, and > > > > kbuild will descend down in the ext2 directory. Kbuild only uses > > > > this information to decide that it needs to visit the directory, > > > > it is the Makefile in the subdirectory that specifies what is > > > > modular and what is built-in. > > > > > > > > I tried adding other targets to obj-y directly and they are also are not > > > > included, seemingly since the directory was entered using obj-m. > > > > > > > > Masahiro or Michal, can you shed some light? > > > > > I saw similar questions in ML in the past. > > > Yes, this is how Kbuild works; > > > Kbuild only links objects in Makefiles visited by obj-y. > > > > > > If you use > > > obj-m += serdev/ > > > all objects in serdev/ are considered as modular. > > > > Well, any objects in serdev/ specified in obj-y would currently be built > > but never included in either built-in.a or any module. > > Right. > > > > I think it is better to make the document > > > clarify this. > > > > Yeah, I don't have a use case for this, but the documentation would need > > to be updated to not have more people look into this. > > > > And at least this behaviour allowed us to catch this bug, but only > > because we had dependent modules that failed to build. I see now that > > you posted a patch adding a general warning about obj-y under obj-m last > > fall, but that was apparently never merged. > > This one? > > https://lore.kernel.org/patchwork/patch/1126959/ Yep, that's the one I meant. > This patch detected several Makefile/Kconfig bugs, > and it is good. > > But, it also turned out to cause false positive warnings > on some architectures. > I thought it was not so easy to fix it. > So, I decided to postpone it. Ok. > > But when was this behaviour changed? And was that done on purpose? > > No. Not changed at all. > > In my understanding, the current behavior has been kept > from the beginning. Ok, thanks for confirming. The contradicting documentation I refer to above has been there since before git at least however. Here's a random example of someone being bit by this five years ago: https://www.spinics.net/lists/linux-kbuild/msg10887.html Would you mind taking a stab at updating the docs? Johan
