Re: [PATCH bpf-next v2 04/10] bpf: Let the by-value struct walk take the kinds of member it accepts

[Yonghong Song <yonghong.song@linux.dev>]

On 8/25/26 2:59 PM, bot+bpf-ci@kernel.org wrote:
>> bpf: Let the by-value struct walk take the kinds of member it accepts
>>
>>      Use btf_struct_is_composed_of() instead of btf_type_is_scalar_struct() in
>>      btf.c so in the future, non scalar member (e.g. arena pointer) can be
>>      supported as well. There is no functional change.
>>
>>      Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
> This isn't a bug, but the changelog only describes the one-line call swap
> in btf.c, while two other parts of the diff are what the "no functional
> change" claim rests on.
>
> The first is a new enumeration in a global header:
>
>> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
>> +/* Kinds of member a by-value struct or union may be composed of. */
>> +enum btf_member_kind {
>> +	BTF_MEMBER_SCALAR	= BIT(0), /* an int or an enum, or an array of them */
>> +	BTF_MEMBER_ARENA_PTR	= BIT(1), /* a pointer carrying the "arena" type tag */
>> +};
> The second is the array-member branch of the walk losing its trailing
> continue and falling through into the shared kind check:
>
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>>   			member_type = btf_type_skip_modifiers(btf, array->type, NULL);
>> -			if (!btf_type_is_scalar(member_type))
>> -				return false;
>> -			continue;
>>   		}
>> -		if (!btf_type_is_scalar(member_type))
>> +		if (!btf_member_kind_allowed(btf, member_type, member_kinds))
>>   			return false;
> Equivalence here holds because btf_member_kind_allowed() collapses to
> btf_type_is_scalar() when the mask is BTF_MEMBER_SCALAR alone, and because
> the shared check is the last statement of the for_each_member() body, so no
> member is skipped or checked twice.
>
> Would it help to mention the new enum btf_member_kind in bpf_verifier.h and
> this array-branch fall-through in the changelog, since those are what the
> "no functional change" claim rests on?

New enum btf_member_kind is self explanable in the code.
In the commit message, I will explain array-branch fall-through thing.

>
>
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
>
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/32899532405