Re: [RFC bpf-next 12/15] kbuild, module, bpf: Support CONFIG_DEBUG_INFO_BTF_EXTRA=m

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2025-10-08 at 18:35 +0100, Alan Maguire wrote:

[...]

> diff --git a/include/linux/module.h b/include/linux/module.h
> index e135cc79acee..c2fceaf392c5 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h

[...]

> @@ -8342,12 +8372,12 @@ static int btf_module_notify(struct notifier_block *nb, unsigned long op,
>  {
>  	struct btf_module *btf_mod, *tmp;
>  	struct module *mod = module;
> -	struct btf *btf;
> +	struct bin_attribute *attr;
> +	struct btf *btf = NULL;
>  	int err = 0;
>  
> -	if (mod->btf_data_size == 0 ||
> -	    (op != MODULE_STATE_COMING && op != MODULE_STATE_LIVE &&
> -	     op != MODULE_STATE_GOING))
> +	if (op != MODULE_STATE_COMING && op != MODULE_STATE_LIVE &&
> +	     op != MODULE_STATE_GOING)
>  		goto out;

Removing this check leads to:

  case MODULE_STATE_COMING:
    ...
    btf_mod->btf = btf;
    list_add(new: &btf_mod->list, head: &btf_modules);

Even when `btf` is NULL. Why is it necessary?

>  
>  	switch (op) {
> @@ -8357,8 +8387,10 @@ static int btf_module_notify(struct notifier_block *nb, unsigned long op,
>  			err = -ENOMEM;
>  			goto out;
>  		}
> -		btf = btf_parse_module(mod->name, mod->btf_data, mod->btf_data_size,
> -				       mod->btf_base_data, mod->btf_base_data_size);
> +		if (mod->btf_data_size > 0) {
> +			btf = btf_parse_module(mod->name, mod->btf_data, mod->btf_data_size,
> +					       mod->btf_base_data, mod->btf_base_data_size);
> +		}
>  		if (IS_ERR(btf)) {
>  			kfree(btf_mod);
>  			if (!IS_ENABLED(CONFIG_MODULE_ALLOW_BTF_MISMATCH)) {
> @@ -8370,7 +8402,8 @@ static int btf_module_notify(struct notifier_block *nb, unsigned long op,
>  			}
>  			goto out;
>  		}
> -		err = btf_alloc_id(btf);
> +		if (btf)
> +			err = btf_alloc_id(btf);
>  		if (err) {
>  			btf_free(btf);
>  			kfree(btf_mod);
> @@ -8384,32 +8417,45 @@ static int btf_module_notify(struct notifier_block *nb, unsigned long op,
>  		list_add(&btf_mod->list, &btf_modules);
>  		mutex_unlock(&btf_module_mutex);
>  

[...]

Apologies for delayed response, will read through the rest of the
series and pahole changes tomorrow.