Re: [PATCH bpf-next 03/11] tools, bpf: fix bpftool build with !CONFIG_BPF_EVENTS

[Song Liu]

On Thu, Apr 14, 2022 at 3:45 PM Alexander Lobakin <alobakin@xxxxx> wrote:
>
> Fix the following error when building bpftool:
>
>   CLANG   profiler.bpf.o
>   CLANG   pid_iter.bpf.o
> skeleton/profiler.bpf.c:18:21: error: invalid application of 'sizeof' to an incomplete type 'struct bpf_perf_event_value'
>         __uint(value_size, sizeof(struct bpf_perf_event_value));
>                            ^     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_helpers.h:13:39: note: expanded from macro '__uint'
>                                       ^~~
> tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_helper_defs.h:7:8: note: forward declaration of 'struct bpf_perf_event_value'
> struct bpf_perf_event_value;
>        ^
>
> struct bpf_perf_event_value is being used in the kernel only when
> CONFIG_BPF_EVENTS is enabled, so it misses a BTF entry then.
> Emit the type unconditionally to fix the problem.
>
> Fixes: 47c09d6a9f67 ("bpftool: Introduce "prog profile" command")
> Signed-off-by: Alexander Lobakin <alobakin@xxxxx>

Acked-by: Song Liu <songliubraving@xxxxxx>

> ---
>  kernel/bpf/syscall.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 34fdf27d14cf..dd8284a60a8e 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -4286,6 +4286,7 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
>                 goto out;
>         case BPF_PROG_TYPE_PERF_EVENT:
>         case BPF_PROG_TYPE_TRACEPOINT:
> +               BTF_TYPE_EMIT(struct bpf_perf_event_value);
>                 if (attr->link_create.attach_type != BPF_PERF_EVENT) {
>                         ret = -EINVAL;
>                         goto out;
> --
> 2.35.2
>
>