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Date:   Wed, 29 Nov 2017 18:15:43 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Martin KaFai Lau <kafai@...com>
Cc:     Matthias Kaehlcke <mka@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Yonghong Song <yhs@...com>, Alexei Starovoitov <ast@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Wang Nan <wangnan0@...wei.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>
Subject: Re: 'perf test BPF' failing, libbpf regression wrt "basic API for
 BPF obj name"

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@...et ~]# 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@...nel-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

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