linux-kernel - Re: [PATCH bpf-next 2/2] selftests: bpf: Add a new test for bare tracepoints

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Date:   Thu, 14 Jan 2021 12:58:22 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next 2/2] selftests: bpf: Add a new test for bare
 tracepoints

On 01/13/21 17:40, Jean-Philippe Brucker wrote:
> On Wed, Jan 13, 2021 at 10:21:31AM +0000, Qais Yousef wrote:
> > On 01/12/21 12:07, Andrii Nakryiko wrote:
> > > > > >         $ sudo ./test_progs -v -t module_attach
> > > > >
> > > > > use -vv when debugging stuff like that with test_progs, it will output
> > > > > libbpf detailed logs, that often are very helpful
> > > >
> > > > I tried that but it didn't help me. Full output is here
> > > >
> > > >         https://paste.debian.net/1180846
> > > >
> > > 
> > > It did help a bit for me to make sure that you have bpf_testmod
> > > properly loaded and its BTF was found, so the problem is somewhere
> > > else. Also, given load succeeded and attach failed with OPNOTSUPP, I
> > > suspect you are missing some of FTRACE configs, which seems to be
> > > missing from selftests's config as well. Check that you have
> > > CONFIG_FTRACE=y and CONFIG_DYNAMIC_FTRACE=y, and you might need some
> > > more. See [0] for a real config we are using to run all tests in
> > > libbpf CI. If you figure out what you were missing, please also
> > > contribute a patch to selftests' config.
> > > 
> > >   [0] https://github.com/libbpf/libbpf/blob/master/travis-ci/vmtest/configs/latest.config
> > 
> > Yeah that occurred to me too. I do have all necessary FTRACE options enabled,
> > including DYNAMIC_FTRACE. I think I did try enabling fault injection too just
> > in case. I have CONFIG_FAULT_INJECTION=y and CONFIG_FUNCTION_ERROR_INJECTION=y.
> 
> Could it come from lack of fentry support on arm64 (or are you testing on
> x86?) Since the arm64 JIT doesn't have trampoline support at the moment, a
> lot of bpf selftests fail with ENOTSUPP.

I am on arm64. I honestly have no clue about this. I'll try to dig out.

Thanks

--
Qais Yousef