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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Wed, 1 Dec 2021 12:36:29 -0800
Message-ID: <CAADnVQKjOGr+v-xA6JP2wriha6BFFA0cs8cdUY-74ft2YYzXkg@mail.gmail.com>
Subject: Re: [PATCH bpf-next 06/29] bpf: Add bpf_arg/bpf_ret_value helpers for
 tracing programs
To:     Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc:     Jiri Olsa <jolsa@redhat.com>, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@chromium.org>
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On Wed, Dec 1, 2021 at 10:00 AM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> But you emphasized an important point, that it's probably good to
> allow users to distinguish errors from reading actual value 0. There
> are and will be situations where argument isn't available or some
> combination of conditions are not supported. So I think, while it's a
> bit more verbose, these forms are generally better:
>
> int bpf_get_func_arg(int n, u64 *value);
> int bpf_get_func_ret(u64 *value);
>
> WDYT?

Makes sense to me.
The verifier will be able to inline it just fine.
Two extra insns only compared to direct return.