Re: [PATCH bpf-next v1 1/3] bpf: Show more useful info in stack depth stats

On Sun, 2026-08-02 at 01:03 +0200, Kumar Kartikeya Dwivedi wrote:
> Currently, the output of stack depth statistics is two crude, with a
> list of captured stack depths ordered by the subprog numbers. The actual
> subprog numbers are determined by libbpf, hence it is hard to associate
> the stack depth statistic back to the subprog by name.
> 
> Change the format to:
> stack depth <subprog>=<depth> ... max=<depth>
> 
> In case the subprog name is not specified, use subprog[N] as the string.
> 
> Suggested-by: Andrii Nakryiko <[email protected]>
> Signed-off-by: Kumar Kartikeya Dwivedi <[email protected]>
> ---
>  kernel/bpf/verifier.c                         | 16 ++++++++++++----
>  .../bpf/progs/verifier_basic_stack.c          |  4 ++--
>  .../bpf/progs/verifier_bpf_fastcall.c         | 19 +++++++++++--------
>  .../bpf/progs/verifier_private_stack.c        |  9 ++++++---
>  .../selftests/bpf/progs/verifier_var_off.c    |  4 ++--
>  5 files changed, 33 insertions(+), 19 deletions(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 8d0635ee48c7..51ac0a9ae339 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -18703,10 +18703,18 @@ static void print_verification_stats(struct bpf_verifier_env *env)
>  	if (env->log.level & BPF_LOG_STATS) {
>  		verbose(env, "verification time %lld usec\n",
>  			div_u64(env->verification_time, 1000));
> -		verbose(env, "stack depth %d", env->subprog_info[0].stack_depth);
> -		for (i = 1; i < subprog_cnt; i++)
> -			verbose(env, "+%d", env->subprog_info[i].stack_depth);
> -		verbose(env, " max %d\n", env->max_stack_depth);
> +		verbose(env, "stack depth");
> +		for (i = 0; i < subprog_cnt; i++) {
> +			const char *name = env->subprog_info[i].name;
> +
> +			if (name && name[0])
> +				verbose(env, " %s=%d", name,
> +					env->subprog_info[i].stack_depth);
> +			else
> +				verbose(env, " subprog[%d]=%d", i,
> +					env->subprog_info[i].stack_depth);

That would be not very convenient to parse by veristat,
but I'd print every subprogram on it's own line.

> +		}
> +		verbose(env, " max=%d\n", env->max_stack_depth);

I think check_max_stack_depth_subprog() needs a similar update,
at the moment it reports a not very helpful error like this:

  combined stack size of 34 calls is 528. Too large

Printing the offending spine would be helpful.

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