netdev - Re: static and dynamic linking. Was: [PATCH bpf-next v3 1/5] bpf: Support chain calling multiple BPF

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Date:   Tue, 12 Nov 2019 16:32:27 +0000
From:   Edward Cree <ecree@...arflare.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>
CC:     John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Marek Majkowski <marek@...udflare.com>,
        Lorenz Bauer <lmb@...udflare.com>,
        Alan Maguire <alan.maguire@...cle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        David Miller <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>
Subject: Re: static and dynamic linking. Was: [PATCH bpf-next v3 1/5] bpf:
 Support chain calling multiple BPF

On 12/11/2019 02:51, Alexei Starovoitov wrote:
> There
> could be a 'root' bpf program (let's call it rootlet.o) that looks like:
This looks a lot like what I had in mind...
> We can introduce dynamic linking. The second part of 'BPF trampoline' patches
> allows tracing programs to attach to other BPF programs. The idea of dynamic
> linking is to replace a program or subprogram instead of attaching to it.
... as does this, particularly the "partial verification" / verify a subprog
 as a separate unit with its own contract.
> The rootlet.o calls into firewall1.o directly. So no retpoline to worry about
> and firewall1.o can use bpf_tail_call() if it wants so. That tail_call will
> still return back to rootlet.o
Yep, that's a really nice gain that comes out of partial verification.

+1 to this whole proposal.

-Ed