Re: [PATCH bpf-next v1 10/14] bpf: Correct Program Structure diagnostic context

[Eduard Zingerman <eddyz87@gmail.com>]

On Sun, 2026-08-16 at 03:57 +0200, Kumar Kartikeya Dwivedi wrote:

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 3de9e4f617b6..d2f08c6612c6 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2995,15 +2995,13 @@ static int add_kfuncs(struct bpf_verifier_env *env)
>  	return 0;
>  }
>  
> -static int check_subprogs(struct bpf_verifier_env *env)
> +static void find_subprog_properties(struct bpf_verifier_env *env)
>  {
> -	int i, subprog_start, subprog_end, off, cur_subprog = 0;
> +	int i, subprog_end, cur_subprog = 0;
>  	struct bpf_subprog_info *subprog = env->subprog_info;
>  	struct bpf_insn *insn = env->prog->insnsi;
>  	int insn_cnt = env->prog->len;
>  
> -	/* now check that all jumps are within the same subprog */
> -	subprog_start = subprog[cur_subprog].start;
>  	subprog_end = subprog[cur_subprog + 1].start;
>  	for (i = 0; i < insn_cnt; i++) {
>  		u8 code = insn[i].code;
> @@ -3017,6 +3015,27 @@ static int check_subprogs(struct bpf_verifier_env *env)
>  		if (BPF_CLASS(code) == BPF_LD &&
>  		    (BPF_MODE(code) == BPF_ABS || BPF_MODE(code) == BPF_IND))
>  			subprog[cur_subprog].has_ld_abs = true;
> +		if (i == subprog_end - 1) {
> +			cur_subprog++;
> +			if (cur_subprog < env->subprog_cnt)
> +				subprog_end = subprog[cur_subprog + 1].start;
> +		}

Nit: in situations like this doing two nested loops reads much better:
     for each subprog:
       for insn from star to end:
         ...

> +	}
> +}

...

> @@ -3126,8 +3146,9 @@ static int sort_subprogs_topo(struct bpf_verifier_env *env)
>  					bpf_diag_program_structure(
>  						env, idx, "recursive subprogram call",
>  						"Rewrite the recursion as an explicit bounded loop, or split the logic so subprogram calls do not form a cycle.",
> -						"This bpf2bpf call would make the subprogram call graph recursive. "
> -						"The verifier requires a finite, acyclic call graph so it can bound stack depth and analysis.");
> +						"The call from %s() to %s() would make the subprogram call graph recursive. "
> +						"The verifier requires a finite, acyclic call graph so it can bound stack depth and analysis.",
> +						bpf_subprog_name(env, cur), bpf_subprog_name(env, callee));

Nit: I'd drop this hunk, I think that initial suggestion from the bot
     was bogus. What would be really helpful is to draw the whole
     cycle, but we don't have such info here.

>  					ret = -EINVAL;
>  					goto out;
>  				}