From: "Toke Høiland-Jørgensen" <toke@toke.dk>
To: Andrii Nakryiko <andrii@kernel.org>,
bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net
Cc: andrii@kernel.org, kernel-team@fb.com
Subject: Re: [PATCH bpf-next 1/2] libbpf: don't require full struct enum64 in UAPI headers
Date: Tue, 27 Sep 2022 13:43:45 +0200 [thread overview]
Message-ID: <87zgelrqj2.fsf@toke.dk> (raw)
In-Reply-To: <20220927042940.147185-1-andrii@kernel.org>
Andrii Nakryiko <andrii@kernel.org> writes:
> Drop the requirement for system-wide kernel UAPI headers to provide full
> struct btf_enum64 definition. This is an unexpected requirement that
> slipped in libbpf 1.0 and put unnecessary pressure ([0]) on users to have
> a bleeding-edge kernel UAPI header from unreleased Linux 6.0.
>
> To achieve this, we forward declare struct btf_enum64. But that's not
> enough as there is btf_enum64_value() helper that expects to know the
> layout of struct btf_enum64. So we get a bit creative with
> reinterpreting memory layout as array of __u32 and accesing lo32/hi32
> fields as array elements. Alternative way would be to have a local
> pointer variable for anonymous struct with exactly the same layout as
> struct btf_enum64, but that gets us into C++ compiler errors complaining
> about invalid type casts. So play it safe, if ugly.
>
> [0] Closes: https://github.com/libbpf/libbpf/issues/562
>
> Reported-by: Toke Høiland-Jørgensen <toke@toke.dk>
> Fixes: d90ec262b35b ("libbpf: Add enum64 support for btf_dump")
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
This seems like a reasonable (and only a bit ugly) workaround; thanks!
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
prev parent reply other threads:[~2022-09-27 11:53 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-27 4:29 [PATCH bpf-next 1/2] libbpf: don't require full struct enum64 in UAPI headers Andrii Nakryiko
2022-09-27 4:29 ` [PATCH bpf-next 2/2] selftests/bpf: enforce C++11 mode for test_cpp test Andrii Nakryiko
2022-09-27 13:28 ` Daniel Borkmann
2022-09-27 11:43 ` Toke Høiland-Jørgensen [this message]
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