Re: [PATCH bpf-next v5 08/14] bpf: Report Register Type Safety errors

On Sat, 2026-08-15 at 07:34 +0000, [email protected] wrote:
> > diff --git a/kernel/bpf/diagnostics.c b/kernel/bpf/diagnostics.c
> 
> [ ... ]
> 
> > +static int diag_stack_argno(u8 slot)
> > +{
> > +	return MAX_BPF_FUNC_REG_ARGS + slot + 1;
> > +}
> > +
> > +static void diag_format_stack_arg(char *buf, size_t size, u8 slot, const char *arg_name)
> > +{
> > +	int argno = diag_stack_argno(slot);
> > +	const char *ordinal = diag_arg_ordinal(argno);
> > +
> > +	if (ordinal && arg_name)
> > +		scnprintf(buf, size, "outgoing stack argument %u (%s argument, %s)", slot + 1,
> > +			  ordinal, arg_name);
> 
> [ ... ]
> 
> > +static const char *diag_mod_target_desc(struct bpf_verifier_env *env,
> > +					const struct bpf_diag_mod_target *target)
> > +{
> > +	switch (target->kind) {
> > +	case BPF_DIAG_MOD_TARGET_REG:
> > +		return bpf_diag_fmt(env, "R%u", target->regno);
> > +	case BPF_DIAG_MOD_TARGET_STACK_ARG:
> > +		return bpf_diag_fmt(env, "stack arg%d", diag_stack_argno(target->stack_arg));
>                                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> Does this numbering match the rest of the diagnostic output?
> 
> diag_stack_argno() returns MAX_BPF_FUNC_REG_ARGS + slot + 1, which for
> slot 0 gives 6 (the absolute argument ordinal). But diag_format_stack_arg()
> uses slot + 1 to label the same slot, and the pre-existing verbose() message
> in check_outgoing_stack_args() also uses spi + 1.

This is legit, I think we need to use verifier.c:reg_arg_name() here.

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