netdev - Re: [PATCH bpf-next 09/29] bpf: Add support to load multi func tracing program

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Message-ID: <20211119041159.7rebb5lz2ybnygqr@ast-mbp.dhcp.thefacebook.com>
Date:   Thu, 18 Nov 2021 20:11:59 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCH bpf-next 09/29] bpf: Add support to load multi func
 tracing program

On Thu, Nov 18, 2021 at 12:24:35PM +0100, Jiri Olsa wrote:
> +
> +DEFINE_BPF_MULTI_FUNC(unsigned long a1, unsigned long a2,
> +		      unsigned long a3, unsigned long a4,
> +		      unsigned long a5, unsigned long a6)

This is probably a bit too x86 specific. May be make add all 12 args?
Or other places would need to be tweaked?

> +BTF_ID_LIST_SINGLE(bpf_multi_func_btf_id, func, bpf_multi_func)
...
> -	prog->aux->attach_btf_id = attr->attach_btf_id;
> +	prog->aux->attach_btf_id = multi_func ? bpf_multi_func_btf_id[0] : attr->attach_btf_id;

Just ignoring that was passed in uattr?
Maybe instead of ignoring dopr BPF_F_MULTI_FUNC and make libbpf
point to that btf_id instead?
Then multi or not can be checked with if (attr->attach_btf_id == bpf_multi_func_btf_id[0]).