Andrii Nakryiko <andriin@xxxxxx> 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@xxxxxx>
Acked-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
> +#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
