netdev - Re: [PATCH bpf-next v4 1/3] bpf: support writable context for bare tracepoint

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Date:   Fri, 1 Oct 2021 15:21:49 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Hou Tao <houtao1@...wei.com>
Cc:     Alexei Starovoitov <ast@...nel.org>, Yonghong Song <yhs@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next v4 1/3] bpf: support writable context for bare tracepoint

On Thu, Sep 30, 2021 at 2:00 AM Hou Tao <houtao1@...wei.com> wrote:
>
> Commit 9df1c28bb752 ("bpf: add writable context for raw tracepoints")
> supports writable context for tracepoint, but it misses the support
> for bare tracepoint which has no associated trace event.
>
> Bare tracepoint is defined by DECLARE_TRACE(), so adding a corresponding
> DECLARE_TRACE_WRITABLE() macro to generate a definition in __bpf_raw_tp_map
> section for bare tracepoint in a similar way to DEFINE_TRACE_WRITABLE().
>
> Signed-off-by: Hou Tao <houtao1@...wei.com>
> ---

LGTM.

Acked-by: Andrii Nakryiko <andrii@...nel.org>

>  include/trace/bpf_probe.h | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/include/trace/bpf_probe.h b/include/trace/bpf_probe.h
> index a23be89119aa..a8e97f84b652 100644
> --- a/include/trace/bpf_probe.h
> +++ b/include/trace/bpf_probe.h
> @@ -93,8 +93,7 @@ __section("__bpf_raw_tp_map") = {                                     \
>
>  #define FIRST(x, ...) x
>
> -#undef DEFINE_EVENT_WRITABLE
> -#define DEFINE_EVENT_WRITABLE(template, call, proto, args, size)       \
> +#define __CHECK_WRITABLE_BUF_SIZE(call, proto, args, size)             \
>  static inline void bpf_test_buffer_##call(void)                                \
>  {                                                                      \
>         /* BUILD_BUG_ON() is ignored if the code is completely eliminated, but \
> @@ -103,8 +102,12 @@ static inline void bpf_test_buffer_##call(void)                            \
>          */                                                             \
>         FIRST(proto);                                                   \
>         (void)BUILD_BUG_ON_ZERO(size != sizeof(*FIRST(args)));          \
> -}                                                                      \
> -__DEFINE_EVENT(template, call, PARAMS(proto), PARAMS(args), size)
> +}
> +
> +#undef DEFINE_EVENT_WRITABLE
> +#define DEFINE_EVENT_WRITABLE(template, call, proto, args, size) \
> +       __CHECK_WRITABLE_BUF_SIZE(call, PARAMS(proto), PARAMS(args), size) \
> +       __DEFINE_EVENT(template, call, PARAMS(proto), PARAMS(args), size)
>
>  #undef DEFINE_EVENT
>  #define DEFINE_EVENT(template, call, proto, args)                      \
> @@ -119,9 +122,17 @@ __DEFINE_EVENT(template, call, PARAMS(proto), PARAMS(args), size)
>         __BPF_DECLARE_TRACE(call, PARAMS(proto), PARAMS(args))          \
>         __DEFINE_EVENT(call, call, PARAMS(proto), PARAMS(args), 0)
>
> +#undef DECLARE_TRACE_WRITABLE
> +#define DECLARE_TRACE_WRITABLE(call, proto, args, size) \
> +       __CHECK_WRITABLE_BUF_SIZE(call, PARAMS(proto), PARAMS(args), size) \
> +       __BPF_DECLARE_TRACE(call, PARAMS(proto), PARAMS(args)) \
> +       __DEFINE_EVENT(call, call, PARAMS(proto), PARAMS(args), size)
> +
>  #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
>
> +#undef DECLARE_TRACE_WRITABLE
>  #undef DEFINE_EVENT_WRITABLE
> +#undef __CHECK_WRITABLE_BUF_SIZE
>  #undef __DEFINE_EVENT
>  #undef FIRST
>
> --
> 2.29.2
>