netdev - RE: [PATCH bpf] libbpf: don't attempt to load unused subprog as an entry-point BPF program

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Date:   Mon, 09 Nov 2020 13:19:00 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, ast@...com, daniel@...earbox.net
Cc:     andrii@...nel.org, kernel-team@...com,
        Dmitrii Banshchikov <dbanschikov@...com>
Subject: RE: [PATCH bpf] libbpf: don't attempt to load unused subprog as an
 entry-point BPF program

Andrii Nakryiko wrote:
> If BPF code contains unused BPF subprogram and there are no other subprogram
> calls (which can realistically happen in real-world applications given
> sufficiently smart Clang code optimizations), libbpf will erroneously assume
> that subprograms are entry-point programs and will attempt to load them with
> UNSPEC program type.
> 
> Fix by not relying on subcall instructions and rather detect it based on the
> structure of BPF object's sections.
> 
> Reported-by: Dmitrii Banshchikov <dbanschikov@...com>
> Fixes: 9a94f277c4fb ("tools: libbpf: restore the ability to load programs from .text section")
> Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
> ---

Acked-by: John Fastabend <john.fastabend@...il.com>