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Date: Wed, 29 Nov 2017 18:15:43 -0300
From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Martin KaFai Lau <kafai@fb.com>
Cc: Matthias Kaehlcke <mka@chromium.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>, Yonghong Song <yhs@fb.com>,
        Alexei Starovoitov <ast@fb.com>,
        "David S. Miller" <davem@davemloft.net>,
        Daniel Borkmann <daniel@iogearbox.net>, Wang Nan <wangnan0@huawei.com>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        David Ahern <dsahern@gmail.com>, Jiri Olsa <jolsa@kernel.org>,
        Ingo Molnar <mingo@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>
Subject: Re: 'perf test BPF' failing, libbpf regression wrt "basic API for
 BPF obj name"
Message-ID: <20171129211543.GC31403@kernel.org>
References: <20171128190519.GM3298@kernel.org>
 <20171129210734.lqs23q65ac6avlwr@kafai-mbp>
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Em Wed, Nov 29, 2017 at 01:07:34PM -0800, Martin KaFai Lau escreveu:
> On Tue, Nov 28, 2017 at 04:05:19PM -0300, Arnaldo Carvalho de Melo wrote:
> > 
> > [root@jouet ~]# perf test -v bpf
> > 39: BPF filter                                            :
> > 39.1: Basic BPF filtering                                 :
> > --- start ---
> > test child forked, pid 12198
> > Kernel build dir is set to /lib/modules/4.14.0+/build
> > set env: KBUILD_DIR=/lib/modules/4.14.0+/build
> [ ... ]
> > libbpf: failed to create map (name: 'flip_table'): Invalid argument
> > libbpf: failed to load object '[basic_bpf_test]'
> > bpf: load objects failed
> 88cda1c9da02 ("bpf: libbpf: Provide basic API support to specify BPF obj name")
> is introduced in 4.15.
 
> I think the perf@kernel-4.15 broke on older kernels like 4.14 because
> the new bpf prog/map name is only introduced since 4.15.
 
> The newer perf needs to be compatible with an older kernel?

Sure :-)

If some ABI breaks it should detect that and adapt, and older perf
tools should also gracefully fail in such a case, which I'm not sure
will be the case here, haven't checked perf's BPF integration to see how
it behaves in such a case, but I will.

- Arnaldo