Re: [PATCH bpf-next v3 03/13] bpf: Verifier support for KF_IMPLICIT_ARGS

[Alexei Starovoitov]

On Tue, Jan 20, 2026 at 2:27 PM Ihor Solodrai <ihor.solodrai@xxxxxxxxx> wrote:
>
> Introduction of KF_IMPLICIT_ARGS revealed an issue with zero-extension
> tracking, because an explicit rX = 0 in place of the verifier-supplied
> argument is now absent if the arg is implicit (the BPF prog doesn't
> pass a dummy NULL anymore). To mitigate this, reset the subreg_def of
> all caller saved registers in check_kfunc_call() [1].
>
> [1] https://lore.kernel.org/bpf/b4a760ef828d40dac7ea6074d39452bb0dc82caa.camel@xxxxxxxxx/

...

> -       for (i = 0; i < CALLER_SAVED_REGS; i++)
> -               mark_reg_not_init(env, regs, caller_saved[i]);
> +       for (i = 0; i < CALLER_SAVED_REGS; i++) {
> +               u32 regno = caller_saved[i];
> +
> +               mark_reg_not_init(env, regs, regno);
> +               regs[regno].subreg_def = DEF_NOT_SUBREG;
> +       }

I'm reading that no follow up is necessary anymore and
the new selftests cover this part automatically.