netdev - Re: [PATCH bpf-next] selftests/bpf: guess function end for test_get_branch

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Message-ID: <CAEf4BzYdfgZDh4pLkeFr_BbzhOgg26PX1fgUZgi04w-n4p11bw@mail.gmail.com>
Date:   Mon, 25 Oct 2021 21:46:48 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next] selftests/bpf: guess function end for test_get_branch_snapshot

On Fri, Oct 22, 2021 at 4:48 PM Song Liu <songliubraving@...com> wrote:
>
> Function in modules could appear in /proc/kallsyms in random order.
>
> ffffffffa02608a0 t bpf_testmod_loop_test
> ffffffffa02600c0 t __traceiter_bpf_testmod_test_writable_bare
> ffffffffa0263b60 d __tracepoint_bpf_testmod_test_write_bare
> ffffffffa02608c0 T bpf_testmod_test_read
> ffffffffa0260d08 t __SCT__tp_func_bpf_testmod_test_writable_bare
> ffffffffa0263300 d __SCK__tp_func_bpf_testmod_test_read
> ffffffffa0260680 T bpf_testmod_test_write
> ffffffffa0260860 t bpf_testmod_test_mod_kfunc
>
> Therefore, we cannot reliably use kallsyms_find_next() to find the end of
> a function. Replace it with a simple guess (start + 128). This is good
> enough for this test.

It's so annoying that sizes of all those symbols are known and
available in ELF, yet kallsyms don't expose them :( I've applied this
"fix", but it makes me very sad.

>
> Signed-off-by: Song Liu <songliubraving@...com>
> ---
>  .../bpf/prog_tests/get_branch_snapshot.c      |  7 ++--
>  tools/testing/selftests/bpf/trace_helpers.c   | 36 -------------------
>  tools/testing/selftests/bpf/trace_helpers.h   |  5 ---
>  3 files changed, 4 insertions(+), 44 deletions(-)
>

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