From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Andrii Nakryiko <andriin@fb.com>,
bpf@vger.kernel.org, netdev@vger.kernel.org, ast@fb.com,
daniel@iogearbox.net
Cc: andrii.nakryiko@gmail.com, kernel-team@fb.com,
Andrii Nakryiko <andriin@fb.com>
Subject: Re: [PATCH v2 bpf-next] libbpf: make DECLARE_LIBBPF_OPTS macro strictly a variable declaration
Date: Tue, 22 Oct 2019 19:42:01 +0200 [thread overview]
Message-ID: <87imogoexi.fsf@toke.dk> (raw)
In-Reply-To: <20191022172100.3281465-1-andriin@fb.com>
Andrii Nakryiko <andriin@fb.com> writes:
> LIBBPF_OPTS is implemented as a mix of field declaration and memset
> + assignment. This makes it neither variable declaration nor purely
> statements, which is a problem, because you can't mix it with either
> other variable declarations nor other function statements, because C90
> compiler mode emits warning on mixing all that together.
>
> This patch changes LIBBPF_OPTS into a strictly declaration of variable
> and solves this problem, as can be seen in case of bpftool, which
> previously would emit compiler warning, if done this way (LIBBPF_OPTS as
> part of function variables declaration block).
>
> This patch also renames LIBBPF_OPTS into DECLARE_LIBBPF_OPTS to follow
> kernel convention for similar macros more closely.
>
> v1->v2:
> - rename LIBBPF_OPTS into DECLARE_LIBBPF_OPTS (Jakub Sitnicki).
>
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
> +#define DECLARE_LIBBPF_OPTS(TYPE, NAME, ...) \
> + struct TYPE NAME = ({ \
> + memset(&NAME, 0, sizeof(struct TYPE)); \
> + (struct TYPE) { \
> + .sz = sizeof(struct TYPE), \
> + __VA_ARGS__ \
> + }; \
> + })
Found a reference with an explanation of why this works, BTW; turns out
it's a GCC extension:
http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement-Exprs
-Toke
next prev parent reply other threads:[~2019-10-22 17:42 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-22 17:21 [PATCH v2 bpf-next] libbpf: make DECLARE_LIBBPF_OPTS macro strictly a variable declaration Andrii Nakryiko
2019-10-22 17:42 ` Toke Høiland-Jørgensen [this message]
2019-10-22 19:38 ` Daniel Borkmann
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