Re: [PATCH bpf-next 08/12] bpf: Record a 16-byte argument alignment in the function model

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

On 9/3/26 11:09 PM, bot+bpf-ci@kernel.org wrote:
>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>> index 3a7eb2185c35..5b93aa97f1bc 100644
>> --- a/include/linux/bpf.h
>> +++ b/include/linux/bpf.h
>> @@ -1193,6 +1193,9 @@ struct bpf_prog_offload {
>>   	u32			jited_len;
>>   };
>>
>> +/* Argument aligned to 16 bytes. */
>> +#define BTF_FMODEL_ALIGN16_ARG		BIT(0)
>> +
>>   /* The argument is signed. */
>>   #define BTF_FMODEL_SIGNED_ARG		BIT(1)
> [ ... ]
>
>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
>> index 6c391449e298..f933a675b0a8 100644
>> --- a/kernel/bpf/btf.c
>> +++ b/kernel/bpf/btf.c
>> @@ -7633,6 +7633,15 @@ int btf_distill_func_proto(struct bpf_verifier_log *log,
>>   		}
>>   		m->arg_size[i] = ret;
>>   		m->arg_flags[i] = __get_arg_fmodel_flags(btf, &args[i], t);
>> +
>> +		align16 = btf_type_align16(btf, t, 0);
>> +		if (align16 < 0) {
>> +			bpf_log(log, "The function %s arg%d type %s has unknown alignment.\n",
>> +				tname, i, btf_type_str(t));
>> +			return -EINVAL;
>> +		} else if (align16) {
>> +			m->arg_flags[i] |= BTF_FMODEL_ALIGN16_ARG;
>> +		}
>>   	}
>>   	m->nr_args = nargs;
>>   	return 0;
> [ ... ]
>
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index 030fb37c22ef..461883158ffa 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -11748,6 +11748,31 @@ bool btf_struct_is_composed_of(struct bpf_verifier_env *env,
>>   	return btf_struct_member_walk(env, btf, t, member_kinds, 0, NULL);
>>   }
>>
>> +int btf_type_align16(const struct btf *btf, const struct btf_type *t, int rec)
>> +{
>> +	const struct btf_member *member;
>> +	int ret;
>> +	u32 i;
>> +
>> +	while (btf_type_is_array(t))
>> +		t = btf_type_skip_modifiers(btf, btf_array(t)->type, NULL);
>> +
>> +	if (btf_type_is_int(t))
>> +		return t->size > 8;
>> +	if (!btf_type_is_struct(t))
>> +		return 0;
>> +	if (rec >= BTF_MEMBER_MAX_DEPTH)
>> +		return -E2BIG;
>> +
>> +	for_each_member(i, t, member) {
>> +		ret = btf_type_align16(btf, btf_type_skip_modifiers(btf, member->type, NULL),
>> +				       rec + 1);
>> +		if (ret)
>> +			return ret;
>> +	}
>> +	return 0;
>> +}
> This isn't a bug, but btf_type_align16() looks structurally similar to
> kfunc_arg_align() further down in the same file. Both walk types with the
> same pattern: strip arrays with `while (btf_type_is_array(t))`, test for
> `btf_type_is_int(t)` with `t->size > 8`, bail on `!btf_type_is_struct(t)`,
> check `rec >= BTF_MEMBER_MAX_DEPTH`, and recurse through members via
> `btf_type_skip_modifiers(btf, member->type, NULL)`. Could the two share one
> walk, and would hiding the `rec` argument behind a wrapper keep the exported
> signature simpler, the way btf_struct_is_composed_of() wraps
> btf_struct_member_walk()?

This is for arm64 jit. I will simplify it and this patch is not necessary any more.

>
>
> ---
> 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/33840714551