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Date:   Tue, 19 May 2020 08:50:21 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Alan Maguire <alan.maguire@...cle.com>
Cc:     shuah@...nel.org, ast@...nel.org, daniel@...earbox.net,
        andriin@...com, bpf@...r.kernel.org, kafai@...com,
        songliubraving@...com, yhs@...com, john.fastabend@...il.com,
        kpsingh@...omium.org, linux-kselftest@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next] selftests/bpf: add general instructions for
 test execution

On Mon, May 18, 2020 at 12:23:10PM +0100, Alan Maguire wrote:
> Getting a clean BPF selftests run involves ensuring latest trunk LLVM/clang
> are used, pahole is recent (>=1.16) and config matches the specified
> config file as closely as possible.  Document all of this in the general
> README.rst file.  Also note how to work around timeout failures.
> 
> Signed-off-by: Alan Maguire <alan.maguire@...cle.com>
> ---
>  tools/testing/selftests/bpf/README.rst | 46 ++++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/README.rst b/tools/testing/selftests/bpf/README.rst
> index 0f67f1b..b00eebb 100644
> --- a/tools/testing/selftests/bpf/README.rst
> +++ b/tools/testing/selftests/bpf/README.rst
> @@ -1,6 +1,52 @@
>  ==================
>  BPF Selftest Notes
>  ==================
> +First verify the built kernel config options match the config options
> +specified in the config file in this directory.  Test failures for
> +unknown helpers, inability to find BTF etc will be observed otherwise.
> +
> +To ensure the maximum number of tests pass, it is best to use the latest
> +trunk LLVM/clang, i.e.
> +
> +git clone https://github.com/llvm/llvm-project
> +
> +Build/install trunk LLVM:
> +
> +.. code-block:: bash
> +  git clone https://github.com/llvm/llvm-project
> +  cd llvm-project
> +  mkdir build/llvm
> +  cd build/llvm
> +  cmake ../../llvm/
> +  make
> +  sudo make install
> +  cd ../../
> +
> +Build/install trunk clang:
> +
> +.. code-block:: bash
> +  mkdir -p build/clang
> +  cd build/clang
> +  cmake ../../clang
> +  make
> +  sudo make install
> +

these instructions are obsolete and partially incorrect.
May be refer to Documentation/bpf/bpf_devel_QA.rst instead?

> +When building the kernel with CONFIG_DEBUG_INFO_BTF, pahole
> +version 16 or later is also required for BTF function
> +support. pahole can be built from the source at
> +
> +https://github.com/acmel/dwarves
> +
> +It is often available in "dwarves/libdwarves" packages also,
> +but be aware that versions prior to 1.16 will fail with
> +errors that functions cannot be found in BTF.
> +
> +When running selftests, the default timeout of 45 seconds
> +can be exceeded by some tests.  We can override the default
> +timeout via a "settings" file; for example:
> +
> +.. code-block:: bash
> +  echo "timeout=120" > tools/testing/selftests/bpf/settings

Is it really the case?
I've never seen anything like this.

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