netdev - Re: [PATCH bpf-next v5 9/9] selftest/bpf: Implement tests for bpftool gen min_core

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Date:   Fri, 28 Jan 2022 18:23:19 -0500
From:   Mauricio Vásquez Bernal <mauricio@...volk.io>
To:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Quentin Monnet <quentin@...valent.com>,
        Rafael David Tinoco <rafaeldtinoco@...il.com>,
        Lorenzo Fontana <lorenzo.fontana@...stic.co>,
        Leonardo Di Donato <leonardo.didonato@...stic.co>
Subject: Re: [PATCH bpf-next v5 9/9] selftest/bpf: Implement tests for bpftool
 gen min_core_btf

On Fri, Jan 28, 2022 at 5:33 PM Mauricio Vásquez <mauricio@...volk.io> wrote:
>
> This commit implements some integration tests for "BTFGen". The goal
> of such tests is to verify that the generated BTF file contains the
> expected types.
>

This is not an exhaustive list of test cases. I'm not sure if this is
the approach we should follow to implement such tests, it seems to me
that checking each generated BTF file by hand is a lot of work but I
don't have other ideas to simplify it.

I considered different options to write these tests:
1. Use core_reloc_types.h to create a "source" BTF file with a lot of
types, then run BTFGen for all test_core_reloc_*.o files and use the
generated BTF file as btf_src_file in core_reloc.c. In other words,
re-run all test_core_reloc tests using a generated BTF file as source
instead of the "btf__core_reloc_" #name ".o" one. I think this test is
great because it tests the full functionality and actually checks that
the programs are able to run using the generated file. The problem is
how do we test that the BTFGen is creating an optimized file? Just
copying the source file without any modification will make all those
tests pass. We could check that the generated file is small (by
checking the size or the number of types) but it doesn't seem a very
reliable approach to me.
2. We could write some .c files with the types we expect to have on
the generated file and compare it with the generated file. The issue
here is that comparing those BTF files doesn't seem to be too
trivial...

Do you have any suggestions about it? Thanks!