netdev - Re: [PATCH bpf-next 01/10] bpf: add typecast to raw

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Date:   Sat, 5 Oct 2019 11:40:04 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>, x86@...nel.org,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 01/10] bpf: add typecast to raw_tracepoints to
 help BTF generation

On Fri, Oct 4, 2019 at 10:05 PM Alexei Starovoitov <ast@...nel.org> wrote:
>
> When pahole converts dwarf to btf it emits only used types.
> Wrap existing __bpf_trace_##template() function into
> btf_trace_##template typedef and use it in type cast to
> make gcc emits this type into dwarf. Then pahole will convert it to btf.
> The "btf_trace_" prefix will be used to identify BTF enabled raw tracepoints.
>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---

Acked-by: Andrii Nakryiko <andriin@...com>

>  include/trace/bpf_probe.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/trace/bpf_probe.h b/include/trace/bpf_probe.h
> index d6e556c0a085..ff1a879773df 100644
> --- a/include/trace/bpf_probe.h
> +++ b/include/trace/bpf_probe.h
> @@ -74,11 +74,12 @@ static inline void bpf_test_probe_##call(void)                              \
>  {                                                                      \
>         check_trace_callback_type_##call(__bpf_trace_##template);       \
>  }                                                                      \
> +typedef void (*btf_trace_##template)(void *__data, proto);             \
>  static struct bpf_raw_event_map        __used                                  \
>         __attribute__((section("__bpf_raw_tp_map")))                    \
>  __bpf_trace_tp_map_##call = {                                          \
>         .tp             = &__tracepoint_##call,                         \
> -       .bpf_func       = (void *)__bpf_trace_##template,               \
> +       .bpf_func       = (void *)(btf_trace_##template)__bpf_trace_##template, \
>         .num_args       = COUNT_ARGS(args),                             \
>         .writable_size  = size,                                         \
>  };
> --
> 2.20.0
>