netdev - Re: [PATCH 6/9] bpf: Compile bpfwl tool at kernel compilation start

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Date:   Fri, 15 May 2020 16:57:52 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Yonghong Song <yhs@...com>, Martin KaFai Lau <kafai@...com>,
        David Miller <davem@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Wenbo Zhang <ethercflow@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Andrii Nakryiko <andriin@...com>,
        Brendan Gregg <bgregg@...flix.com>,
        Florent Revest <revest@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 6/9] bpf: Compile bpfwl tool at kernel compilation start

On Thu, May 14, 2020 at 03:38:57PM -0700, Andrii Nakryiko wrote:
> On Wed, May 6, 2020 at 6:31 AM Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > The bpfwl tool will be used during the vmlinux linking,
> > so it's necessary it's ready.
> >
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  Makefile           | 21 +++++++++++++++++----
> >  tools/Makefile     |  3 +++
> >  tools/bpf/Makefile |  5 ++++-
> >  3 files changed, 24 insertions(+), 5 deletions(-)
> >
> 
> [...]
> 
> >
> > +prepare-bpfwl: $(bpfwl_target)
> > +ifeq ($(SKIP_BTF_WHITELIST_GENERATION),1)
> > +       @echo "warning: Cannot use BTF whitelist checks, please install libelf-dev, libelf-devel or elfutils-libelf-devel" >&2
> > +endif
> 
> When we added BTF dedup and generation first time, we also made pahole
> unavailability or any error during deduplication process an error. It
> actually was very confusing to users and they often missed that BTF
> generation didn't happen, but they would notice it only at runtime
> (after a confusing debugging session).
> 
> So I wonder if it's better to make this an error instead? Just guard
> whitelist generation on whether CONFIG_DEBUG_INFO_BTF is enabled or
> not?

ok, makes sense.. I'll let it fail if there's CONFIG_DEBUG_INFO_BTF
enabled and we'are missing libelf

> 
> >  # Generate some files
> >  # ---------------------------------------------------------------------------
> >
> > diff --git a/tools/Makefile b/tools/Makefile
> > index bd778812e915..85af6ebbce91 100644
> > --- a/tools/Makefile
> > +++ b/tools/Makefile
> > @@ -67,6 +67,9 @@ cpupower: FORCE
> >  cgroup firewire hv guest bootconfig spi usb virtio vm bpf iio gpio objtool leds wmi pci firmware debugging: FORCE
> >         $(call descend,$@)
> >
> > +bpf/%: FORCE
> > +       $(call descend,$@)
> > +
> >  liblockdep: FORCE
> >         $(call descend,lib/lockdep)
> >
> > diff --git a/tools/bpf/Makefile b/tools/bpf/Makefile
> > index f897eeeb0b4f..d4ea2b5a2e58 100644
> > --- a/tools/bpf/Makefile
> > +++ b/tools/bpf/Makefile
> > @@ -124,5 +124,8 @@ runqslower_install:
> >  runqslower_clean:
> >         $(call descend,runqslower,clean)
> >
> > +bpfwl:
> > +       $(call descend,bpfwl)
> > +
> >  .PHONY: all install clean bpftool bpftool_install bpftool_clean \
> > -       runqslower runqslower_install runqslower_clean
> > +       runqslower runqslower_install runqslower_clean bpfwl
> 
> what about install/clean subcommands? At least clean seems like a good idea?

not sure about install, does not seem necessary for this tool,
but I'll add propagation of clean (it's defined in bpfwl already)

thanks,
jirka