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

[Quentin Monnet <qmo@kernel.org>]

On 01/04/2024 18:59, Kui-Feng Lee wrote:
> 
> 
> 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!
> 

Acked-by: Quentin Monnet <qmo@kernel.org>