Re: [PATCH dwarves v4 0/6] btf_encoder: emit type tags for bpf_arena pointers

["Ihor Solodrai" <ihor.solodrai@linux.dev>]

On 3/24/25 11:07 AM, Ihor Solodrai wrote:
> On 3/23/25 4:11 AM, Alan Maguire wrote:
>> [...]
>>
>> hi Ihor, I took a look at the series and merged it with latest next
>> branch; results are in
>>
>> https://web.git.kernel.org/pub/scm/devel/pahole/pahole.git/log/?h=next.attributes-v4
>>
>> ...if you want to take a look.
>>
>> There are a few small things I think that it would be good to resolve
>> before landing this.
>>
>> First, when testing this with -DLIBBPF_EMBEDDED=OFF and a packaged
>> libbpf 1.5 - which means we wouldn't have the latest attributes-related
>> libbpf function; I saw:
>>
>>   BTF     .tmp_vmlinux1.btf.o
>> btf__add_type_attr is not available, is libbpf < 1.6?
>> error: failed to encode function 'bbr_cwnd_event': invalid proto
>> Failed to encode BTF
>>   NM      .tmp_vmlinux1.syms
>
> Hi Alan. Thanks for testing. This is my mistake, I should've checked
> for attributes feature here:
>
> @@ -731,6 +812,10 @@ static int32_t btf_encoder__add_func_proto(struct btf_encoder *encoder, struct f
>  
>  	assert(ftype != NULL || state != NULL);
>  
> +	if (is_kfunc_state(state) && encoder->tag_kfuncs)
> +		if (btf__add_bpf_arena_type_tags(encoder->btf, state) < 0)
> +			return -1;

Actually, I added this check in a different patch so the failure must
have happened in a different place.

In any case, the point remains that it's better to check for feature
availability (hence for API availability) in one place. Your
suggestion to add a feature check makes sense to me. Thank you.

> [...]