Re: Kbuilds and Makefiles in building the kernel

Nagy =C3=81brah=C3=A1m Zsombor <[email protected]> =E6=96=BC 2025=E5=B9=
=B411=E6=9C=8829=E6=97=A5=E9=80=B1=E5=85=AD =E4=B8=8B=E5=8D=889:22=E5=AF=AB=
=E9=81=93=EF=BC=9A
>
> On Sat, 2025-11-29 at 12:09 +0800, Nick Huang wrote:
> > Nagy =C3=81brah=C3=A1m Zsombor <[email protected]> =E6=96=BC 2025=E5=
=B9=B411=E6=9C=8828=E6=97=A5=E9=80=B1=E4=BA=94 =E4=B8=8B=E5=8D=884:18=E5=AF=
=AB=E9=81=93=EF=BC=9A
> > >
> > > On Fri, 2025-11-28 at 08:12 +0800, Nick Huang wrote:
> > > > Nagy =C3=81brah=C3=A1m Zsombor <[email protected]> =E6=96=BC 2025=
=E5=B9=B411=E6=9C=8828=E6=97=A5 =E9=80=B1=E4=BA=94
> > > > =E4=B8=8A=E5=8D=881:37=E5=AF=AB=E9=81=93=EF=BC=9A
> > > > >
> > > > > On Thu, 2025-11-27 at 19:26 +0800, Nick Huang wrote:
> > > > > > Abraham Zsombor Nagy <[email protected]> =E6=96=BC 2025=E5=B9=
=B411=E6=9C=8827=E6=97=A5=E9=80=B1=E5=9B=9B
> > > > > > =E4=B8=8B=E5=8D=886:43=E5=AF=AB=E9=81=93=EF=BC=9A
> > > > > > >
> > > > > > > Hello,
> > > > > > >
> > > > > > > https://docs.kernel.org/kbuild/makefiles.html#the-kbuild-file=
s
> > > > > > > stat
> > > > > > > es
> > > > > > > that when a directory contains a Kbuild file, the Makefile
> > > > > > > is
> > > > > > > skipped in
> > > > > > > that directory.
> > > > > > >
> > > > > > > It feels to me that both files are in use e.g. under
> > > > > > > arch/x86/
> > > > > > > directory.
> > > > > > >
> > > > > > > I'm trying to see what files are the core of the kernel and
> > > > > > > what
> > > > > > > files
> > > > > > > can be configured for x86 by partially parsing the
> > > > > > > Makefiles
> > > > > > > and
> > > > > > > the
> > > > > > > Kbuild files. Would it be sufficient to parse them as:
> > > > > > >
> > > > > > > if file =3D=3D "Makefile" or file =3D=3D "Kbuild":
> > > > > > >
> > > > > > >  > parse(file)
> > > > > > >
> > > > > > > or it should prefer the Kbuild file when present, or it is
> > > > > > > using
> > > > > > > some
> > > > > > > other logic?
> > > > > > >
> > > > > > > Sincerely,
> > > > > > >
> > > > > > > Abraham Nagy
> > > > > > >
> > > > > > >
> > > > > >
> > > > > > Hi  Abraham Zsombor Nagy
> > > > > > What functionality are you trying to add that would require
> > > > > > modifying
> > > > > > the Makefile or Kbuild?
> > > > > >
> > > > > > Sincerely,
> > > > > > Nick Huang
> > > > >
> > > > > Hi Nick,
> > > > >
> > > > > I'm not modifying the build files, only writing a script that
> > > > > walks
> > > > > through the source tree and parses Makefiles and Kbuild files
> > > > > to
> > > > > list
> > > > > what source files are linked to the kernel by default and by
> > > > > CONFIG_*
> > > > > options. This is to see what to read through to get a basic
> > > > > understanding of the kernel at a given config.
> > > > >
> > > > > As I understand the documentation linked above, I should skip
> > > > > Makefiles
> > > > > when Kbuild files are present in a directory, but Makefiles
> > > > > feels
> > > > > to
> > > > > have important lines too.
> > > > >
> > > > > The approach is something like to extract object files and
> > > > > subdirectories from lines that start with python regex "^\S+-y"
> > > > > or
> > > > > "^\S+-\$\(CONFIG.*\)".
> > > > >
> > > > > Sincerely,
> > > > > Abraham
> > > > >
> > > > >
> > > >
> > > > Hi Abraham
> > > > You can use git grep -n "CONFIG_**" to find the files you need.
> > > >
> > > > Sincerely,
> > > > Nick
> > >
> > > Hello Nick,
> > >
> > > Thank you, I've just tried git grep, it seems convenient, however I
> > > still need to further script and fine-tune the output, in which
> > > case I
> > > think having a customizable walk algorithm is the way to start
> > > with.
> > >
> > > find/git & grep walks through the directory tree that could include
> > > build files and sources that are from an incompatible set of config
> > > options. Also, there are some Makefiles that end the line with a
> > > backslash '\' saying to process the next line too, but which won't
> > > have
> > > regex match.
> > >
> > > A custom algorithm can start from a Makefile (and Kbuild file?)_and
> > > walk directories only that are visible from there. This way I can
> > > enforce a horizon of config options that are meaningfully able to
> > > extend the kernel. E.g. starting with minimal config, seeing the
> > > available additional configs, then in subsequent calls adding
> > > configs
> > > one by one until I have a whole kernel (but without extra parts).
> > >
> > > Make menuconfig combined with git grep and a text editor could
> > > help,
> > > but it would require more manual handling to achieve the same.
> > >
> > > Sincerely,
> > > Abraham
> >
> > Hi Abraham
> >
> > Are you trying to find out which configs can be enabled? If so, I
> > suggest you check the description of each Kconfig to see if it=E2=80=99=
s what
> > you need, or if you have a clear idea of the functionality you want
> > to
> > implement.
> >
> > Is your main goal to build a Linux kernel?
> >
> > Sincerely,
> > Nick
>
> Hi Nick,
>
> Yes, my main goal is to build a Linux kernel that is configured
> specifically for my laptop and usage. Slowly, I would like to learn the
> build process too and to get familiar with the source roughly.
>
> I see that Kconfig has the config dependencies and feature description,
> but yet I would need a script to find the corresponding sources that
> parses Kconfig files. If I understand well, it is for composing a
> meaningful .config file that then passed to the kernel build system.
>
> My approach would start with the build files, list the included object
> files and visible config options that include additional object files.
> I would continue this listing with build files in mentioned
> subdirectories, then grep the corresponding source files for the rest
> of the configs. Then, I would browse the source based on this overview.
>
> To see how Makefiles and Kbuild files are used, I would need to check
> the build system, but I'm hoping I can get some guidance.
>
> Sincerely,
> Abraham
Hi Abraham

Do I only need to build the kernel without modifying any code?

Sincerely,
Nick