Re: [PATCH bpf-next v2 2/5] verifier: parse BTF type tags for function arguments

["Emil Tsalapatis" <emil@etsalapatis.com>]

On Mon Jun 1, 2026 at 2:37 PM EDT, Eduard Zingerman wrote:
> On Fri, 2026-05-29 at 20:22 -0400, Emil Tsalapatis wrote:
>> The BTF parsing logic for function arguments goes through
>> the arguments' decl tags, but does not go into their type
>> tags. Add type tag parsing for function arguments.
>> 
>> Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
>> ---
>
> Acked-by: Eduard Zingerman <eddyz87@gmail.com>
>
> [...]
>
>> +static int btf_scan_type_tags(struct bpf_verifier_env *env,
>> +			      const struct btf *btf, u32 type_id,
>> +			      u32 *tags)
>> +{
>> +	const struct btf_type *t;
>> +
>> +	/* Find the first pointer type in the chain. */
>> +	t = btf_type_skip_modifiers(btf, type_id, NULL);
>> +	if (!t || !btf_type_is_ptr(t))
>> +		return 0;
>
> Nit: do we want to report -EOPNOTSUPP if type tag is attached to a non-pointer type?
>

Let's do that. Since compilers can't really produce that yet that would
only be the case for handcrafted BTF, right?

>> +
>> +	/* We got a pointer, get all associated type tags. */
>> +	t = btf_type_by_id(btf, t->type);
>> +	while (t && btf_type_is_type_tag(t)) {
>> +		const char *tag = __btf_name_by_offset(btf, t->name_off);
>> +
>> +		if (strcmp(tag, "arena") == 0) {
>> +			*tags |= ARG_TAG_ARENA;
>> +		} else {
>> +			bpf_log(&env->log, "function signature member has unsupported type tag '%s'\n",
>> +				tag);
>> +			return -EOPNOTSUPP;
>> +		}
>> +
>> +		t = btf_type_by_id(btf, t->type);
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>
> [...]