| Message ID | 20230228031317.3415484-1-davidgow@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Documentation: kbuild: Add note about using (subst m,y) | expand |
On Tue, Feb 28, 2023 at 12:13 PM David Gow <davidgow@google.com> wrote: > > THe kbuild documentation already notes that, where there's an obj-y > target in a subdirectory, it will be orphaned if the subdirectory uses > obj-m. Suggest a way of forcing the directory to obj-y when it's based > on a config option which could be 'm'. > > Linus made several suggestions as to how this is usually done here: > https://lore.kernel.org/linux-kselftest/CAHk-=wgK07PQ_DBBbAbSJ41t__6de1xZ6q7RRu-JS=2SU0wqLQ@mail.gmail.com/ > > This only documents the first one, which seems most common. > > Signed-off-by: David Gow <davidgow@google.com> > --- > Documentation/kbuild/makefiles.rst | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst > index e67eb261c9b0..d9eb24799f52 100644 > --- a/Documentation/kbuild/makefiles.rst > +++ b/Documentation/kbuild/makefiles.rst > @@ -254,6 +254,17 @@ 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. > > +This means that, if a directory contains both obj-y and obj-m targets, > +it should be added with obj-y. If this directory nevertheless should > +only be built when a config option is enabled (typically to support > +a module which requires one or two files to nevertheless be built-in), > +'subst m,y' can be used to ensure obj-y is used. > + > +Example:: > + > + #drivers/Makefile > + obj-$(subst m,y,$(CONFIG_HYPERV)) += hv/ > + I think many subsystems simply do obj-y += hv/ I do not think we need to advertise hyperv's way since it does not look very pretty. Mostly, it looks like this: obj-y += kunit/ and obj-$(CONFIG_KUNIT_HOOK) += hook.o Bikeshed: I think Linus' suggestion is OK, but the BSD style seems less ugly, of course, that is just a matter of style. obj-$(CONFIG_HYPERV:m=y) += kunit/ > Kbuild also supports dedicated syntax, subdir-y and subdir-m, for > descending into subdirectories. It is a good fit when you know they > do not contain kernel-space objects at all. A typical usage is to let > -- > 2.39.2.722.g9855ee24e9-goog > -- Best Regards Masahiro Yamada
From: Masahiro Yamada <masahiroy@kernel.org> Date: Tue, 28 Feb 2023 17:30:09 +0900 > On Tue, Feb 28, 2023 at 12:13 PM David Gow <davidgow@google.com> wrote: [...] >> +Example:: >> + >> + #drivers/Makefile >> + obj-$(subst m,y,$(CONFIG_HYPERV)) += hv/ >> + > > > I think many subsystems simply do > > obj-y += hv/ This creates a ton of empty built-in.a, each of them is listed in the Kbuild output. Someone may think that if a directory contains built-in.a, then something was built there. Sure it's their problems, but I'd prefer to not pollute the log and built-in.a contents when possible (empty files are still listed there IIRC). > > > I do not think we need to advertise hyperv's way > since it does not look very pretty. > > > > > > > > Mostly, it looks like this: > > > obj-y += kunit/ > > and > > obj-$(CONFIG_KUNIT_HOOK) += hook.o > > > > > > > > Bikeshed: > > I think Linus' suggestion is OK, but > the BSD style seems less ugly, > of course, that is just a matter of style. > > > obj-$(CONFIG_HYPERV:m=y) += kunit/ I'd vote for this one, it's compact and readable. > > > > >> Kbuild also supports dedicated syntax, subdir-y and subdir-m, for >> descending into subdirectories. It is a good fit when you know they >> do not contain kernel-space objects at all. A typical usage is to let >> -- >> 2.39.2.722.g9855ee24e9-goog >> > > > -- > Best Regards > Masahiro Yamada > Thanks, Olek
On Wed, Mar 1, 2023 at 12:16 AM Alexander Lobakin <aleksander.lobakin@intel.com> wrote: > > From: Masahiro Yamada <masahiroy@kernel.org> > Date: Tue, 28 Feb 2023 17:30:09 +0900 > > > On Tue, Feb 28, 2023 at 12:13 PM David Gow <davidgow@google.com> wrote: > > [...] > > >> +Example:: > >> + > >> + #drivers/Makefile > >> + obj-$(subst m,y,$(CONFIG_HYPERV)) += hv/ > >> + > > > > > > I think many subsystems simply do > > > > obj-y += hv/ > > This creates a ton of empty built-in.a, each of them is listed in the > Kbuild output. Someone may think that if a directory contains > built-in.a, then something was built there. Sure it's their problems, > but I'd prefer to not pollute the log and built-in.a contents when > possible (empty files are still listed there IIRC). You can choose whichever you like. Up to each subsystem maintainer.
diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst index e67eb261c9b0..d9eb24799f52 100644 --- a/Documentation/kbuild/makefiles.rst +++ b/Documentation/kbuild/makefiles.rst @@ -254,6 +254,17 @@ 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. +This means that, if a directory contains both obj-y and obj-m targets, +it should be added with obj-y. If this directory nevertheless should +only be built when a config option is enabled (typically to support +a module which requires one or two files to nevertheless be built-in), +'subst m,y' can be used to ensure obj-y is used. + +Example:: + + #drivers/Makefile + obj-$(subst m,y,$(CONFIG_HYPERV)) += hv/ + Kbuild also supports dedicated syntax, subdir-y and subdir-m, for descending into subdirectories. It is a good fit when you know they do not contain kernel-space objects at all. A typical usage is to let
THe kbuild documentation already notes that, where there's an obj-y target in a subdirectory, it will be orphaned if the subdirectory uses obj-m. Suggest a way of forcing the directory to obj-y when it's based on a config option which could be 'm'. Linus made several suggestions as to how this is usually done here: https://lore.kernel.org/linux-kselftest/CAHk-=wgK07PQ_DBBbAbSJ41t__6de1xZ6q7RRu-JS=2SU0wqLQ@mail.gmail.com/ This only documents the first one, which seems most common. Signed-off-by: David Gow <davidgow@google.com> --- Documentation/kbuild/makefiles.rst | 11 +++++++++++ 1 file changed, 11 insertions(+)