From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Daniel Borkmann <daniel@iogearbox.net>,
Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: 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
Date: Fri, 29 Nov 2019 15:00:40 +0100 [thread overview]
Message-ID: <87a78evl2v.fsf@toke.dk> (raw)
In-Reply-To: <f6e8f6d2-6155-3b20-9975-81e29e460915@iogearbox.net>
Daniel Borkmann <daniel@iogearbox.net> writes:
> On 11/28/19 5:07 PM, Toke Høiland-Jørgensen wrote:
>> From: Jiri Olsa <jolsa@kernel.org>
>>
>> Currently we support only static linking with kernel's libbpf
>> (tools/lib/bpf). This patch adds LIBBPF_DYNAMIC compile variable
>> that triggers libbpf detection and bpf dynamic linking:
>>
>> $ make -C tools/bpf/bpftool make LIBBPF_DYNAMIC=1
>>
>> If libbpf is not installed, build (with LIBBPF_DYNAMIC=1) stops with:
>>
>> $ make -C tools/bpf/bpftool LIBBPF_DYNAMIC=1
>> Auto-detecting system features:
>> ... libbfd: [ on ]
>> ... disassembler-four-args: [ on ]
>> ... zlib: [ on ]
>> ... libbpf: [ OFF ]
>>
>> Makefile:102: *** Error: No libbpf devel library found, please install libbpf-devel or libbpf-dev.
>>
>> Adding LIBBPF_DIR compile variable to allow linking with
>> libbpf installed into specific directory:
>>
>> $ make -C tools/lib/bpf/ prefix=/tmp/libbpf/ install_lib install_headers
>> $ make -C tools/bpf/bpftool/ LIBBPF_DYNAMIC=1 LIBBPF_DIR=/tmp/libbpf/
>>
>> It might be needed to clean build tree first because features
>> framework does not detect the change properly:
>>
>> $ make -C tools/build/feature clean
>> $ make -C tools/bpf/bpftool/ clean
>>
>> Since bpftool uses bits of libbpf that are not exported as public API in
>> the .so version, we also pass in libbpf.a to the linker, which allows it to
>> pick up the private functions from the static library without having to
>> expose them as ABI.
>>
>> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
>> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
>> ---
>> v3:
>> - Keep $(LIBBPF) in $LIBS, and just add -lbpf on top
>> - Fix typo in error message
>> v2:
>> - Pass .a file to linker when dynamically linking, so bpftool can use
>> private functions from libbpf without exposing them as API.
>>
>> tools/bpf/bpftool/Makefile | 34 ++++++++++++++++++++++++++++++++++
>> 1 file changed, 34 insertions(+)
>>
>> diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
>> index 39bc6f0f4f0b..15052dcaa39b 100644
>> --- a/tools/bpf/bpftool/Makefile
>> +++ b/tools/bpf/bpftool/Makefile
>> @@ -1,6 +1,15 @@
>> # SPDX-License-Identifier: GPL-2.0-only
>> +# LIBBPF_DYNAMIC to enable libbpf dynamic linking.
>> +
>> include ../../scripts/Makefile.include
>> include ../../scripts/utilities.mak
>> +include ../../scripts/Makefile.arch
>> +
>> +ifeq ($(LP64), 1)
>> + libdir_relative = lib64
>> +else
>> + libdir_relative = lib
>> +endif
>>
>> ifeq ($(srctree),)
>> srctree := $(patsubst %/,%,$(dir $(CURDIR)))
>> @@ -63,6 +72,19 @@ RM ?= rm -f
>> FEATURE_USER = .bpftool
>> FEATURE_TESTS = libbfd disassembler-four-args reallocarray zlib
>> FEATURE_DISPLAY = libbfd disassembler-four-args zlib
>> +ifdef LIBBPF_DYNAMIC
>> + FEATURE_TESTS += libbpf
>> + FEATURE_DISPLAY += libbpf
>> +
>> + # for linking with debug library run:
>> + # make LIBBPF_DYNAMIC=1 LIBBPF_DIR=/opt/libbpf
>
> The Makefile already has BPF_DIR which points right now to
> '$(srctree)/tools/lib/bpf/' and LIBBPF_PATH for the final one and
> where $(LIBBPF_PATH)libbpf.a is expected to reside. Can't we improve
> the Makefile to reuse and work with these instead of adding yet
> another LIBBPF_DIR var which makes future changes in this area more
> confusing? The libbpf build spills out libbpf.{a,so*} by default
> anyway.
I see what you mean; however, LIBBPF_DIR is meant to be specifically an
override for the dynamic library, not just the path to libbpf.
Would it be less confusing to overload the LIBBPF_DYNAMIC variable
instead? I.e.,
make LIBBPF_DYNAMIC=1
would dynamically link against the libbpf installed in the system, but
make LIBBPF_DYNAMIC=/opt/libbpf
would override that and link against whatever is in /opt/libbpf instead?
WDYT?
> Was wondering whether we could drop LIBBPF_DYNAMIC altogether and have
> some sort of auto detection, but given for perf the `make
> LIBBPF_DYNAMIC=1` option was just applied to perf tree it's probably
> better to stay consistent plus static linking would stay as-is for
> preferred method for bpftool, so that part seems fine.
When adding LIBBPF_DYNAMIC in a packaging script, we *want* the build to
fail if it doesn't work, instead of just silently falling back to a
statically linked version. Also, for something in the kernel tree like
bpftool, I think it makes more sense to default to the in-tree version
and make dynamic linking explicitly opt-in.
>> + ifdef LIBBPF_DIR
>> + LIBBPF_CFLAGS := -I$(LIBBPF_DIR)/include
>> + LIBBPF_LDFLAGS := -L$(LIBBPF_DIR)/$(libdir_relative)
>> + FEATURE_CHECK_CFLAGS-libbpf := $(LIBBPF_CFLAGS)
>> + FEATURE_CHECK_LDFLAGS-libbpf := $(LIBBPF_LDFLAGS)
>> + endif
>> +endif
>>
>> check_feat := 1
>> NON_CHECK_FEAT_TARGETS := clean uninstall doc doc-clean doc-install doc-uninstall
>> @@ -88,6 +110,18 @@ ifeq ($(feature-reallocarray), 0)
>> CFLAGS += -DCOMPAT_NEED_REALLOCARRAY
>> endif
>>
>> +ifdef LIBBPF_DYNAMIC
>> + ifeq ($(feature-libbpf), 1)
>> + # bpftool uses non-exported functions from libbpf, so just add the dynamic
>> + # version of libbpf and let the linker figure it out
>> + LIBS := -lbpf $(LIBS)
>
> Seems okay as a workaround for bpftool and avoids getting into the
> realm of declaring libbpf as another half-baked netlink library if
> we'd have exposed these. Ideally the netlink symbols shouldn't be
> needed at all from libbpf, but I presume the rationale back then was
> that given it's used internally in libbpf for some of the APIs and was
> needed in bpftool's net subcommand as well later on, it avoided
> duplicating the code given statically linked and both are in-tree
> anyway.
Yeah, I do think it's a little odd that bpftool is using "private" parts
of libbpf, but since we can solve it like this I think that is OK.
-Toke
next prev parent reply other threads:[~2019-11-29 14:00 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-27 9:48 [PATCH 0/3] perf/bpftool: Allow to link libbpf dynamically Jiri Olsa
2019-11-27 9:48 ` [PATCH 1/3] perf tools: Allow to specify libbpf install directory Jiri Olsa
2019-11-27 9:48 ` [PATCH 2/3] libbpf: Export netlink functions used by bpftool Jiri Olsa
2019-11-27 9:48 ` [PATCH 3/3] bpftool: Allow to link libbpf dynamically Jiri Olsa
2019-11-27 13:38 ` Quentin Monnet
2019-11-27 14:15 ` Jiri Olsa
2019-11-27 14:24 ` Arnaldo Carvalho de Melo
2019-11-27 14:31 ` Quentin Monnet
2019-11-27 15:48 ` Arnaldo Carvalho de Melo
2019-11-27 15:52 ` Quentin Monnet
2019-11-27 15:59 ` Arnaldo Carvalho de Melo
2019-11-27 14:29 ` Quentin Monnet
2019-11-27 16:41 ` Alexei Starovoitov
2019-11-27 16:37 ` [PATCH 0/3] perf/bpftool: " Alexei Starovoitov
2019-11-27 18:44 ` Arnaldo Carvalho de Melo
2019-11-27 20:24 ` Andrii Nakryiko
2019-11-27 21:22 ` Daniel Borkmann
2019-11-27 22:47 ` Jiri Olsa
2019-11-28 9:06 ` Toke Høiland-Jørgensen
2019-11-28 14:53 ` [PATCH bpf v2] bpftool: " Toke Høiland-Jørgensen
2019-11-28 15:32 ` Quentin Monnet
2019-11-28 15:52 ` Toke Høiland-Jørgensen
2019-11-28 16:07 ` [PATCH bpf v3] " Toke Høiland-Jørgensen
2019-11-28 17:30 ` Quentin Monnet
2019-11-29 8:12 ` Jiri Olsa
2019-11-29 8:24 ` Toke Høiland-Jørgensen
2019-11-29 10:24 ` Daniel Borkmann
2019-11-29 14:00 ` Toke Høiland-Jørgensen [this message]
2019-11-29 23:56 ` Daniel Borkmann
2019-12-02 8:59 ` Jiri Olsa
2019-12-02 17:09 ` [PATCH 0/3] perf/bpftool: " Andrii Nakryiko
2019-12-02 18:08 ` Toke Høiland-Jørgensen
2019-12-02 18:42 ` Andrii Nakryiko
2019-12-02 18:54 ` Arnaldo Carvalho de Melo
2019-12-02 19:21 ` Jiri Olsa
2019-12-02 19:54 ` Andrii Nakryiko
2019-12-02 20:02 ` Jiri Olsa
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87a78evl2v.fsf@toke.dk \
--to=toke@redhat.com \
--cc=a.p.zijlstra@chello.nl \
--cc=acme@kernel.org \
--cc=alexander.shishkin@linux.intel.com \
--cc=alexei.starovoitov@gmail.com \
--cc=andriin@fb.com \
--cc=bpf@vger.kernel.org \
--cc=brouer@redhat.com \
--cc=daniel@iogearbox.net \
--cc=jolsa@kernel.org \
--cc=kafai@fb.com \
--cc=kubakici@wp.pl \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=mpetlan@redhat.com \
--cc=namhyung@kernel.org \
--cc=netdev@vger.kernel.org \
--cc=songliubraving@fb.com \
--cc=yhs@fb.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).