Re: [PATCH bpf-next v3 05/11] bpf: Support stack arguments for kfunc calls

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

On 4/8/26 8:05 AM, Alexei Starovoitov wrote:
> On Tue, Apr 7, 2026 at 9:53 PM Yonghong Song <yonghong.song@linux.dev> wrote:
>>
>> In the next revision, I will discard this patch and implement it properly.
>> In most cases, for related functions w.r.t. stack argument validation,
>> I will ensure functions has parameters like (reg_state, regno, argno).
>> If the argument is a stack argument, regno will be -1 (not a register).
>> In cases where argno is not really available, argno will be -1. But in
>> any case, at least one of them is positive. The verification log will
>> print out message properly. If regno is non-negative, log 'regno' is needed.
>> Otherwise, log 'argno'.
> that also sounds quite hacky.
> Just pass two reg_states for reg and for next reg,
> and argno of the first reg. That's it.
> argno is always valid for printing and argno+1 is also correct number.
> Both reg and next_reg are also always valid pointers
> that get_kfunc_arg_reg() returned.

I will give a try. In most cases, only one reg_state is needed. But
there are a few cases (e.g. KF_ARG_PTR_TO_MEM_SIZE), two reg_states
are needed.