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From:   Martin Lau <kafai@fb.com>
To:     Arnd Bergmann <arnd@arndb.de>
CC:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Randy Dunlap <rdunlap@infradead.org>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andriin@fb.com>,
        Quentin Monnet <quentin.monnet@netronome.com>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] bpf: Fix build in minimal configurations, again
Thread-Topic: [PATCH] bpf: Fix build in minimal configurations, again
Thread-Index: AQHVr5luvUr1OsnMX0ud4dyRR00tDqe0BX+A
Date:   Tue, 10 Dec 2019 23:34:24 +0000
Message-ID: <20191210233421.vnybkzc6noskmsjt@kafai-mbp>
References: <20191210203553.2941035-1-arnd@arndb.de>
In-Reply-To: <20191210203553.2941035-1-arnd@arndb.de>
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On Tue, Dec 10, 2019 at 09:35:46PM +0100, Arnd Bergmann wrote:
> Building with -Werror showed another failure:
>=20
> kernel/bpf/btf.c: In function 'btf_get_prog_ctx_type.isra.31':
> kernel/bpf/btf.c:3508:63: error: array subscript 0 is above array bounds =
of 'u8[0]' {aka 'unsigned char[0]'} [-Werror=3Darray-bounds]
>   ctx_type =3D btf_type_member(conv_struct) + bpf_ctx_convert_map[prog_ty=
pe] * 2;
>=20
> I don't actually understand why the array is empty, but a similar
> fix has addressed a related problem, so I suppose we can do the
> same thing here.
>=20
> Fixes: ce27709b8162 ("bpf: Fix build in minimal configurations")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  kernel/bpf/btf.c | 1 +
>  1 file changed, 1 insertion(+)
>=20
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 7d40da240891..ed2075884724 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -3470,6 +3470,7 @@ static u8 bpf_ctx_convert_map[] =3D {
>  	[_id] =3D __ctx_convert##_id,
>  #include <linux/bpf_types.h>
>  #undef BPF_PROG_TYPE
> +	0, /* avoid empty array */
If bpf_types.h is empty, the prog should have already failed
earlier in find_prog_type() in syscall.c, so 0 here should
be fine.

Acked-by: Martin KaFai Lau <kafai@fb.com>