lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Mon, 02 Dec 2019 22:15:35 +0100
From:   Toke Høiland-Jørgensen <>
To:     Andrii Nakryiko <>,
        Jiri Olsa <>
Cc:     Arnaldo Carvalho de Melo <>,
        lkml <>,
        Networking <>, bpf <>,
        Ingo Molnar <>,
        Namhyung Kim <>,
        Alexander Shishkin <>,
        Peter Zijlstra <>,
        Michael Petlan <>,
        Jesper Dangaard Brouer <>,
        Daniel Borkmann <>,
        Alexei Starovoitov <>,
        Martin KaFai Lau <>,
        Song Liu <>, Yonghong Song <>,
        Andrii Nakryiko <>,
        Quentin Monnet <>
Subject: Re: [PATCHv4 0/6] perf/bpftool: Allow to link libbpf dynamically

Andrii Nakryiko <> writes:

> On Mon, Dec 2, 2019 at 5:19 AM Jiri Olsa <> wrote:
>> hi,
>> adding support to link bpftool with libbpf dynamically,
>> and config change for perf.
>> It's now possible to use:
>>   $ make -C tools/bpf/bpftool/ LIBBPF_DYNAMIC=1
>> which will detect libbpf devel package and if found, link it with bpftool.
>> It's possible to use arbitrary installed libbpf:
>>   $ make -C tools/bpf/bpftool/ LIBBPF_DYNAMIC=1 LIBBPF_DIR=/tmp/libbpf/
>> I based this change on top of Arnaldo's perf/core, because
>> it contains libbpf feature detection code as dependency.
>> Also available in:
>>   git://
>>   libbpf/dyn
>> v4 changes:
>>   - based on Toke's v3 post, there's no need for additional API exports:
>>     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.
> Whoever understands how this is supposed to work, can you please
> explain? From reading this, I think what we **want** is:
> - all LIBBPF_API-exposed APIs should be dynamically linked against;
> - everything else used from libbpf (e.g., netlink APIs), should come
> from libbpf.a.
> Am I getting the idea right?
> If yes, are we sure it actually works like that in practice? I've
> compiled with LIBBPF_DYNAMIC=1, and what I see is that libelf, libc,
> zlib, etc functions do have relocations against them in ".rela.plt"
> section. None of libbpf exposed APIs, though, have any of such
> relocations. Which to me suggests that they are just statically linked
> against libbpf.a and is just recorded in ELF as a dynamic
> library dependency because of this extra -lbpf flag. Which kind of
> defeats the purpose of this whole endeavor, no?
> I'm no linker expert, though, so I apologize if I got it completely
> wrong, would really appreciate someone to detail this a bit more.
> Thanks!

Ah, that is my mistake: I was getting dynamic libbpf symbols with this
approach, but that was because I had the version of in my
$LIBDIR that had the patch to expose the netlink APIs as versioned
symbols; so it was just pulling in everything from the shared library.

So what I was going for was exactly what you described above; but it
seems that doesn't actually work. Too bad, and sorry for wasting your
time on this :/


Powered by blists - more mailing lists