linux-kernel - Re: [PATCH bpf-next 0/2] Add PROG_TEST_RUN support to BPF_PROG_TYPE

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Date:   Sun, 29 May 2022 23:00:48 -0700
From:   Song Liu <song@...nel.org>
To:     Daniel Xu <dxu@...uu.xyz>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next 0/2] Add PROG_TEST_RUN support to BPF_PROG_TYPE_KPROBE

On Sun, May 29, 2022 at 3:06 PM Daniel Xu <dxu@...uu.xyz> wrote:
>
> This patchset adds PROG_TEST_RUN support to BPF_PROG_TYPE_KPROBE progs.
> On top of being generally useful for unit testing kprobe progs, this
> feature more specifically helps solve a relability problem with bpftrace
> BEGIN and END probes.
>
> BEGIN and END probes are run exactly once at the beginning and end of a
> bpftrace tracing session, respectively. bpftrace currently implements
> the probes by creating two dummy functions and attaching the BEGIN and
> END progs, if defined, to those functions and calling the dummy
> functions as appropriate. This works pretty well most of the time except
> for when distros strip symbols from bpftrace. Every now and then this
> happens and users get confused. Having PROG_TEST_RUN support will help
> solve this issue by allowing us to directly trigger uprobes from
> userspace.
>
> Admittedly, this is a pretty specific problem and could probably be
> solved other ways. However, PROG_TEST_RUN also makes unit testing more
> convenient, especially as users start building more complex tracing
> applications. So I see this as killing two birds with one stone.

We have BPF_PROG_RUN which is an alias of BPF_PROG_TEST_RUN. I guess
that's a better name for the BEGIN/END use case.

Have you checked out bpf_prog_test_run_raw_tp()? AFAICT, it works as good as
kprobe for this use case.

Thanks,
Song