netdev - Re: [PATCH bpf] samples/bpf: kbuild: add CONFIG_SAMPLE

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Date:   Thu, 3 Oct 2019 19:37:51 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf] samples/bpf: kbuild: add CONFIG_SAMPLE_BPF Kconfig

On Thu, 3 Oct 2019 at 19:16, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
>
> On Thu, Oct 3, 2019 at 3:52 AM Björn Töpel <bjorn.topel@...il.com> wrote:
> >
> > On Thu, 3 Oct 2019 at 12:37, Masahiro Yamada
> > <yamada.masahiro@...ionext.com> wrote:
> > >
> > > On Thu, Oct 3, 2019 at 3:28 PM Björn Töpel <bjorn.topel@...il.com> wrote:
> > > >
> > > > On Thu, 3 Oct 2019 at 01:14, Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org> wrote:
> > > > >
> > > > > On Wed, Oct 02, 2019 at 09:41:15AM +0200, Björn Töpel wrote:
> > > > > >On Wed, 2 Oct 2019 at 03:49, Masahiro Yamada
> > > > > ><yamada.masahiro@...ionext.com> wrote:
> > > > > >>
> > > > > >[...]
> > > > > >> > Yes, the BPF samples require clang/LLVM with BPF support to build. Any
> > > > > >> > suggestion on a good way to address this (missing tools), better than
> > > > > >> > the warning above? After the commit 394053f4a4b3 ("kbuild: make single
> > > > > >> > targets work more correctly"), it's no longer possible to build
> > > > > >> > samples/bpf without support in the samples/Makefile.
> > > > > >>
> > > > > >>
> > > > > >> You can with
> > > > > >>
> > > > > >> "make M=samples/bpf"
> > > > > >>
> > > > > >
> > > > > >Oh, I didn't know that. Does M= support "output" builds (O=)?
> > >
> > > No.
> > > O= points to the output directory of vmlinux,
> > > not of the external module.
> > >
> > > You cannot put the build artifacts from samples/bpf/
> > > in a separate directory.
> > >
> >
> > Hmm, I can't even get "make M=samples/bpf/" to build. Am I missing
> > something obvious?
>
> There were 3 or 4 separate fixes submitted for samples/bpf yesterday,
> maybe you are hitting some of those issues. Try to pull latest (not
> sure if bpf or bpf-next tree). I tried make M=samples/bpf and it
> worked for me.
>

Yeah, it was PEBKAC. "make M=samples/bpf" works if you have a proper
.config + "make prepare" ;-)

I guess I need to change my workflow. I build all my kernels "O=", and
did so with samples/bpf as well. Everything ended up in the same
output directory. Now I need to have all this build output in source
tree, and need to manage the .config files in where the source is at.
Oh well... I'll stop complaining now. :-)

Thanks,
Björn

> >
> > Prior 394053f4a4b3 "make samples/bpf/" and "make O=/foo/bar
> > samples/bpf/" worked, but I guess I can live with that...
> >
> >
> > Thanks!
> > Björn
> >
> >
> > >
> > >
> > > > > >I usually just build samples/bpf/ with:
> > > > > >
> > > > > >  $ make V=1 O=/home/foo/build/bleh samples/bpf/
> > > > > >
> > > > > >
> > > > > >Björn
> > > > >
> > > > > Shouldn't README be updated?
> > > > >
> > > >
> > > > Hmm, the M= variant doesn't work at all for me. The build is still
> > > > broken for me. Maybe I'm missing anything obvious...
> > > >
> > > >
> > > > > --
> > > > > Regards,
> > > > > Ivan Khoronzhuk
> > >
> > >
> > >
> > > --
> > > Best Regards
> > > Masahiro Yamada