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Date:   Mon, 2 Dec 2019 09:59:30 +0100
From:   Jiri Olsa <jolsa@redhat.com>
To:     Daniel Borkmann <daniel@iogearbox.net>
Cc:     Toke =?iso-8859-1?Q?H=F8iland-J=F8rgensen?= <toke@redhat.com>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Jiri Olsa <jolsa@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>, netdev@vger.kernel.org,
        bpf@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Michael Petlan <mpetlan@redhat.com>,
        Jesper Dangaard Brouer <brouer@redhat.com>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andriin@fb.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>, kubakici@wp.pl
Subject: Re: [PATCH bpf v3] bpftool: Allow to link libbpf dynamically
Message-ID: <20191202085930.GB5849@krava>
References: <20191128160712.1048793-1-toke@redhat.com>
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 <87a78evl2v.fsf@toke.dk>
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On Sat, Nov 30, 2019 at 12:56:49AM +0100, Daniel Borkmann wrote:
> On 11/29/19 3:00 PM, Toke H=F8iland-J=F8rgensen wrote:
> > Daniel Borkmann <daniel@iogearbox.net> writes:
> > > On 11/28/19 5:07 PM, Toke H=F8iland-J=F8rgensen wrote:
> > > > From: Jiri Olsa <jolsa@kernel.org>
> [...]
> > > >    ifeq ($(srctree),)
> > > >    srctree :=3D $(patsubst %/,%,$(dir $(CURDIR)))
> > > > @@ -63,6 +72,19 @@ RM ?=3D rm -f
> > > >    FEATURE_USER =3D .bpftool
> > > >    FEATURE_TESTS =3D libbfd disassembler-four-args reallocarray zli=
b
> > > >    FEATURE_DISPLAY =3D libbfd disassembler-four-args zlib
> > > > +ifdef LIBBPF_DYNAMIC
> > > > +  FEATURE_TESTS   +=3D libbpf
> > > > +  FEATURE_DISPLAY +=3D libbpf
> > > > +
> > > > +  # for linking with debug library run:
> > > > +  # make LIBBPF_DYNAMIC=3D1 LIBBPF_DIR=3D/opt/libbpf
> > >=20
> > > The Makefile already has BPF_DIR which points right now to
> > > '$(srctree)/tools/lib/bpf/' and LIBBPF_PATH for the final one and
> > > where $(LIBBPF_PATH)libbpf.a is expected to reside. Can't we improve
> > > the Makefile to reuse and work with these instead of adding yet
> > > another LIBBPF_DIR var which makes future changes in this area more
> > > confusing? The libbpf build spills out libbpf.{a,so*} by default
> > > anyway.
> >=20
> > I see what you mean; however, LIBBPF_DIR is meant to be specifically an
> > override for the dynamic library, not just the path to libbpf.
> >=20
> > Would it be less confusing to overload the LIBBPF_DYNAMIC variable
> > instead? I.e.,
> >=20
> > make LIBBPF_DYNAMIC=3D1
> >=20
> > would dynamically link against the libbpf installed in the system, but
> >=20
> > make LIBBPF_DYNAMIC=3D/opt/libbpf
> >=20
> > would override that and link against whatever is in /opt/libbpf instead=
?
> > WDYT?
>=20
> Hm, given perf tool has similar LIB*_DIR vars in place for its libs, it p=
robably
> makes sense to stick with this convention as well then. Perhaps better in=
 this
> case to just rename s/BPF_DIR/BPF_SRC_DIR/, s/LIBBPF_OUTPUT/LIBBPF_BUILD_=
OUTPUT/,
> and s/LIBBPF_PATH/LIBBPF_BUILD_PATH/ to make their purpose more clear.

ok, will have separate patch for this

>=20
> One thing that would be good to do as well for this patch is to:
>=20
>  i) Document both LIBBPF_DYNAMIC and LIBBPF_DIR in the Makefile comment y=
ou
>     added at the top along with a simple usage example.

ok

>=20
> ii) Extend tools/testing/selftests/bpf/test_bpftool_build.sh with a dynam=
ic
>     linking test case, e.g. building libbpf into a temp dir and pointing
>     LIBBPF_DIR to it for bpftool LIBBPF_DYNAMIC=3D1 build.

ok, will send new version soon

thanks,
jirka

>=20
> Thanks,
> Daniel
>=20