netdev - Re: [PATCH bpf-next 1/2] bpf: Use --no-fail option if CONFIG

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Date:   Tue, 22 Sep 2020 20:47:55 +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>,
        Andrii Nakryiko <andriin@...com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Seth Forshee <seth.forshee@...onical.com>
Subject: Re: [PATCH bpf-next 1/2] bpf: Use --no-fail option if CONFIG_BPF is
 not enabled

On Mon, Sep 21, 2020 at 02:55:27PM -0700, Andrii Nakryiko wrote:
> On Fri, Sep 18, 2020 at 5:30 AM Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > Currently all the resolve_btfids 'users' are under CONFIG_BPF
> > code, so if we have CONFIG_BPF disabled, resolve_btfids will
> > fail, because there's no data to resolve.
> >
> > In case CONFIG_BPF is disabled, using resolve_btfids --no-fail
> > option, that makes resolve_btfids leave quietly if there's no
> > data to resolve.
> >
> > Fixes: c9a0f3b85e09 ("bpf: Resolve BTF IDs in vmlinux image")
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> 
> If no CONFIG_BTF is specified, there is no need to even run
> resolve_btfids. So why not do just that -- run resolve_btfids only
> if both CONFIG_BPF and CONFIG_DEBUG_INFO_BTF are specified?

we can have CONFIG_DEBUG_INFO_BTF without CONFIG_BPF being enabled,
so we could in theory have in future some BTF ID user outside bpf code,
but I guess we can enable that, when it actually happens

jirka

> 
> 
> >  scripts/link-vmlinux.sh | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> > index e6e2d9e5ff48..3173b8cf08cb 100755
> > --- a/scripts/link-vmlinux.sh
> > +++ b/scripts/link-vmlinux.sh
> > @@ -342,8 +342,13 @@ vmlinux_link vmlinux "${kallsymso}" ${btf_vmlinux_bin_o}
> >
> >  # fill in BTF IDs
> >  if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then
> > -info BTFIDS vmlinux
> > -${RESOLVE_BTFIDS} vmlinux
> > +       info BTFIDS vmlinux
> > +       # Let's be more permissive if CONFIG_BPF is disabled
> > +       # and do not fail if there's no data to resolve.
> > +       if [ -z "${CONFIG_BPF}" ]; then
> > +         no_fail=--no-fail
> > +       fi
> > +       ${RESOLVE_BTFIDS} $no_fail vmlinux
> >  fi
> >
> >  if [ -n "${CONFIG_BUILDTIME_TABLE_SORT}" ]; then
> > --
> > 2.26.2
> >
>