Re: [PATCH bpf-next] bpftool: use __typeof__() instead of typeof() in BPF skeleton

[Kui-Feng Lee <sinquersw@gmail.com>]

On 4/1/24 10:07, Andrii Nakryiko wrote:
> When generated BPF skeleton header is included in C++ code base, some
> compiler setups will emit warning about using language extensions due to
> typeof() usage, resulting in something like:
> 
>    error: extension used [-Werror,-Wlanguage-extension-token]
>    obj->struct_ops.empty_tcp_ca = (typeof(obj->struct_ops.empty_tcp_ca))
>                                    ^
> 
> It looks like __typeof__() is a preferred way to do typeof() with better
> C++ compatibility behavior, so switch to that. With __typeof__() we get
> no such warning.
> 
> Fixes: c2a0257c1edf ("bpftool: Cast pointers for shadow types explicitly.")
> Fixes: 00389c58ffe9 ("bpftool: Add support for subskeletons")
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
>   tools/bpf/bpftool/gen.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index 786268f1a483..b3979ddc0189 100644
> --- a/tools/bpf/bpftool/gen.c
> +++ b/tools/bpf/bpftool/gen.c
> @@ -386,7 +386,7 @@ static int codegen_subskel_datasecs(struct bpf_object *obj, const char *obj_name
>   			 */
>   			needs_typeof = btf_is_array(var) || btf_is_ptr_to_func_proto(btf, var);
>   			if (needs_typeof)
> -				printf("typeof(");
> +				printf("__typeof__(");
>   
>   			err = btf_dump__emit_type_decl(d, var_type_id, &opts);
>   			if (err)
> @@ -1131,7 +1131,7 @@ static void gen_st_ops_shadow_init(struct btf *btf, struct bpf_object *obj)
>   			continue;
>   		codegen("\
>   			\n\
> -				obj->struct_ops.%1$s = (typeof(obj->struct_ops.%1$s))\n\
> +				obj->struct_ops.%1$s = (__typeof__(obj->struct_ops.%1$s))\n\
>   					bpf_map__initial_value(obj->maps.%1$s, NULL);\n\
>   			\n\
>   			", ident);


LGTM!

Acked-by: Kui-Feng Lee <thinker.li@gmail.com>

Thanks!