netdev - Re: [PATCH bpf-next 2/2] selftests/bpf: Add test for bpf_kfunc

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Date:   Thu, 16 Mar 2023 16:23:49 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...nel.org>,
        David Vernet <void@...ifault.com>,
        Dave Marchevsky <davemarchevsky@...a.com>,
        Tejun Heo <tj@...nel.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 2/2] selftests/bpf: Add test for bpf_kfunc_exists().

On Thu, Mar 16, 2023 at 3:35 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Thu, Mar 16, 2023 at 1:34 PM Andrii Nakryiko
> <andrii.nakryiko@...il.com> wrote:
> >
> > On Wed, Mar 15, 2023 at 3:36 PM Alexei Starovoitov
> > <alexei.starovoitov@...il.com> wrote:
> > >
> > > From: Alexei Starovoitov <ast@...nel.org>
> > >
> > > Add load and run time test for bpf_kfunc_exists() and check that the verifier
> > > performs dead code elimination for non-existing kfunc.
> > >
> > > Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> > > ---
> >
> > we have prog_tests/ksyms_btf.c and progs/test_ksyms_weak.c which do
> > these kind of tests for variable ksyms, let's just add kfunc ksyms
> > there (user-space part has also checking that captured pointer value
> > is correct and stuff like that, we probably want that for kfuncs as
> > well)
>
> That's where initially I tried to place the test, but test_ksyms_weak.c
> is used in light skeleton as well which is pickier about
> resolving ksyms.
> libbpf was lucky in that sense.
> It does:
>       if (btf_is_var(t))
>           err = bpf_object__resolve_ksym_var_btf_id(obj, ext);
>       else
>           err = bpf_object__resolve_ksym_func_btf_id(obj, ext);
> while gen_loader for lksel assumes bpf_call insn as the only option for kfunc.
> I figured I'll add basic support for kfunc detection first and
> address lksel later when I have more time.
> Hence the reason to pick:
>  .../selftests/bpf/progs/task_kfunc_success.c       | 14 +++++++++++++-
> as a location for the test.

ok, sounds good, maybe mention this limitation in the commit message?