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

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Message-ID: <67fdbee5-14ba-360b-269f-d7030bd7062a@fb.com>
Date:   Sun, 8 Nov 2020 22:13:52 -0800
From:   Yonghong Song <yhs@...com>
To:     Andrii Nakryiko <andrii@...nel.org>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>, <ast@...com>, <daniel@...earbox.net>
CC:     <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



On 11/6/20 4:02 PM, 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: Yonghong Song <yhs@...com>