[PATCH v4] btf: reject to register duplicated kfunc

[PATCH v4] btf: reject to register duplicated kfunc

[Song Chen]

I had an ebpf program which calls a kfunc defined and
implemented in one of my kernel modules, it was working
fine in 6.16, but was rejected to run by libbpf in 6.19,
the error message was:

libbpf: extern (func ksym) 'bpf_strstr': func_proto [5]
incompatible with vmlinux [94389]

The reason is there is a new added kfunc in kernel 6.19
which happens to be the same name with my kfunc. However the
error message is not obvious enough to address problem
immediately.

Therefore, this patches searches duplicated kfunc in
both btf_vmlinux and btf_modules list before a kernel module
attempts to register kfuncs through register_btf_kfunc_id_set,
it prints clear error message and returns error code if same name
kfunc has already implemented and registered, then developer
knows at the first place.

Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Suggested-by: Kaitao Cheng <kaitao.cheng@linux.dev>
Reviewed-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Song Chen <chensong_2000@126.com>

---
changelog:
v1 --- v2:
libbpf has already specified which module this kfunc belongs to as
ebpf code onwer's expectation, then verifier uses
find_kallsyms_symbol_value to search kfunc's addr.

v2 --- v3:
After v2, I tried a new idea of introducing a namespace in libbpf
to specify kfunc owner in an ebpf program suggested by Kaitao Cheng,
please see [1]. Alex suggested to go back to report an error during
kmod load on conflicting kfunc name for now. What's more, v2 only
searched bpf_vmlinux, v3 also traverses btf_modules list.

v3 --- v4
Fixed some coding style problems suggested from Kaitao Cheng.
---
 kernel/bpf/btf.c | 38 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 4872d2a6c42d..fe1612677a4a 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -8618,6 +8618,41 @@ static int btf_check_iter_kfuncs(struct btf *btf, const char *func_name,
 	return 0;
 }
 
+static int btf_check_kfunc_name(struct btf *btf, const char *func_name, u32 kind)
+{
+#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+	struct btf_module *btf_mod, *tmp;
+#endif
+	s32 id;
+
+	if (!btf_is_module(btf))
+		return 0;
+
+	id = btf_find_by_name_kind(bpf_get_btf_vmlinux(), func_name, kind);
+	if (id >= 0) {
+		pr_err("kfunc %s (id: %d) is already present in vmlinux.\n",
+				func_name, id);
+		return -EINVAL;
+	}
+
+#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+	mutex_lock(&btf_module_mutex);
+	list_for_each_entry_safe(btf_mod, tmp, &btf_modules, list) {
+		if (btf_mod->btf == btf)
+			continue;
+		id = btf_find_by_name_kind(btf_mod->btf, func_name, kind);
+		if (id >= 0) {
+			pr_err("kfunc %s (id: %d) is already present in module %s.\n",
+					func_name, id, btf_mod->module->name);
+			mutex_unlock(&btf_module_mutex);
+			return -EINVAL;
+		}
+	}
+	mutex_unlock(&btf_module_mutex);
+#endif
+	return 0;
+}
+
 static int btf_check_kfunc_protos(struct btf *btf, u32 func_id, u32 func_flags)
 {
 	const struct btf_type *func;
@@ -8631,7 +8666,8 @@ static int btf_check_kfunc_protos(struct btf *btf, u32 func_id, u32 func_flags)
 
 	/* sanity check kfunc name */
 	func_name = btf_name_by_offset(btf, func->name_off);
-	if (!func_name || !func_name[0])
+	if (!func_name || !func_name[0] ||
+		btf_check_kfunc_name(btf, func_name, BTF_INFO_KIND(func->info)))
 		return -EINVAL;
 
 	func = btf_type_by_id(btf, func->type);
-- 
2.43.0

Re: [PATCH v4] btf: reject to register duplicated kfunc

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Kfunc registration incorrectly fails if the kfunc name matches ANY internal or static function in vmlinux or loaded modules, introducing load-order dependencies.
--

commit 8a8189baf0633350e5ca2b793c2340e48f4787df
Author: Song Chen <chensong_2000@126.com>

btf: reject to register duplicated kfunc

This commit attempts to prevent duplicate BPF kfunc registrations by searching
for existing kfunc names in vmlinux and other modules' BTF data during kfunc
registration.

> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index a62d785812076..ad6b925125dee 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -8684,6 +8684,41 @@ static int btf_check_iter_kfuncs(struct btf *btf, const char *func_name,
>  	return 0;
>  }
>  
> +static int btf_check_kfunc_name(struct btf *btf, const char *func_name, u32 kind)
> +{
> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +	struct btf_module *btf_mod, *tmp;
> +#endif
> +	s32 id;
> +
> +	if (!btf_is_module(btf))
> +		return 0;

[Severity: High]
Does this bypass collision checks for built-in vmlinux kfuncs? It looks like
this might fail to catch intra-kernel name collisions.

> +
> +	id = btf_find_by_name_kind(bpf_get_btf_vmlinux(), func_name, kind);

[Severity: High]
Since modern kernels generate BTF for all global and static functions, does
btf_find_by_name_kind() with BTF_KIND_FUNC search the entire BTF data rather
than just registered kfuncs?

Will this incorrectly reject a valid kfunc registration if its name happens
to match any unrelated static or internal function anywhere in vmlinux?

> +	if (id >= 0) {
> +		pr_err("kfunc %s (id: %d) is already present in vmlinux.\n",
> +				func_name, id);
> +		return -EINVAL;
> +	}
> +
> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +	mutex_lock(&btf_module_mutex);
> +	list_for_each_entry_safe(btf_mod, tmp, &btf_modules, list) {
> +		if (btf_mod->btf == btf)
> +			continue;

[Severity: High]
Are we skipping collision detection within the module's own BTF here?

> +		id = btf_find_by_name_kind(btf_mod->btf, func_name, kind);

[Severity: High]
Can this create unpredictable load-order dependencies between unrelated
modules?

If module A has a static function named "foo", and module B registers a
kfunc named "foo", it appears B will fail to load if A is already loaded,
but will succeed if B is loaded first. Should this code check against actually
registered kfunc sets rather than all functions in every module's BTF?

> +		if (id >= 0) {
> +			pr_err("kfunc %s (id: %d) is already present in module %s.\n",
> +					func_name, id, btf_mod->module->name);
> +			mutex_unlock(&btf_module_mutex);
> +			return -EINVAL;
> +		}
> +	}
> +	mutex_unlock(&btf_module_mutex);
> +#endif
> +	return 0;
> +}
> +

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260602110710.19642-1-chensong_2000@126.com?part=1

Re: [PATCH v4] btf: reject to register duplicated kfunc

[Kaitao Cheng]

在 2026/6/2 19:07, Song Chen 写道:
> I had an ebpf program which calls a kfunc defined and
> implemented in one of my kernel modules, it was working
> fine in 6.16, but was rejected to run by libbpf in 6.19,
> the error message was:
> 
> libbpf: extern (func ksym) 'bpf_strstr': func_proto [5]
> incompatible with vmlinux [94389]
> 
> The reason is there is a new added kfunc in kernel 6.19
> which happens to be the same name with my kfunc. However the
> error message is not obvious enough to address problem
> immediately.
> 
> Therefore, this patches searches duplicated kfunc in
> both btf_vmlinux and btf_modules list before a kernel module
> attempts to register kfuncs through register_btf_kfunc_id_set,
> it prints clear error message and returns error code if same name
> kfunc has already implemented and registered, then developer
> knows at the first place.
> 
> Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
> Suggested-by: Kaitao Cheng <kaitao.cheng@linux.dev>
> Reviewed-by: Yonghong Song <yonghong.song@linux.dev>
> Signed-off-by: Song Chen <chensong_2000@126.com>
> 
> ---
> changelog:
> v1 --- v2:
> libbpf has already specified which module this kfunc belongs to as
> ebpf code onwer's expectation, then verifier uses
> find_kallsyms_symbol_value to search kfunc's addr.
> 
> v2 --- v3:
> After v2, I tried a new idea of introducing a namespace in libbpf
> to specify kfunc owner in an ebpf program suggested by Kaitao Cheng,
> please see [1]. Alex suggested to go back to report an error during
> kmod load on conflicting kfunc name for now. What's more, v2 only
> searched bpf_vmlinux, v3 also traverses btf_modules list.
> 
> v3 --- v4
> Fixed some coding style problems suggested from Kaitao Cheng.
> ---
>  kernel/bpf/btf.c | 38 +++++++++++++++++++++++++++++++++++++-
>  1 file changed, 37 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 4872d2a6c42d..fe1612677a4a 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -8618,6 +8618,41 @@ static int btf_check_iter_kfuncs(struct btf *btf, const char *func_name,
>  	return 0;
>  }
>  
> +static int btf_check_kfunc_name(struct btf *btf, const char *func_name, u32 kind)
> +{
> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +	struct btf_module *btf_mod, *tmp;
> +#endif
> +	s32 id;
> +
> +	if (!btf_is_module(btf))
> +		return 0;
> +
> +	id = btf_find_by_name_kind(bpf_get_btf_vmlinux(), func_name, kind);
> +	if (id >= 0) {
> +		pr_err("kfunc %s (id: %d) is already present in vmlinux.\n",
> +				func_name, id);
> +		return -EINVAL;
> +	}
> +
> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +	mutex_lock(&btf_module_mutex);
> +	list_for_each_entry_safe(btf_mod, tmp, &btf_modules, list) {
> +		if (btf_mod->btf == btf)
> +			continue;
> +		id = btf_find_by_name_kind(btf_mod->btf, func_name, kind);
> +		if (id >= 0) {
> +			pr_err("kfunc %s (id: %d) is already present in module %s.\n",
> +					func_name, id, btf_mod->module->name);
> +			mutex_unlock(&btf_module_mutex);
> +			return -EINVAL;
> +		}
> +	}
> +	mutex_unlock(&btf_module_mutex);
> +#endif
> +	return 0;
> +}
> +
>  static int btf_check_kfunc_protos(struct btf *btf, u32 func_id, u32 func_flags)
>  {
>  	const struct btf_type *func;
> @@ -8631,7 +8666,8 @@ static int btf_check_kfunc_protos(struct btf *btf, u32 func_id, u32 func_flags)
>  
>  	/* sanity check kfunc name */
>  	func_name = btf_name_by_offset(btf, func->name_off);
> -	if (!func_name || !func_name[0])
> +	if (!func_name || !func_name[0] ||
> +		btf_check_kfunc_name(btf, func_name, BTF_INFO_KIND(func->info)))
>  		return -EINVAL;
>  
>  	func = btf_type_by_id(btf, func->type);

Reviewed-by: Kaitao Cheng <chengkaitao@kylinos.cn>

-- 
Thanks
Kaitao Cheng

Re: [PATCH v4] btf: reject to register duplicated kfunc

[Yonghong Song]

On 6/2/26 4:07 AM, Song Chen wrote:
> I had an ebpf program which calls a kfunc defined and
> implemented in one of my kernel modules, it was working
> fine in 6.16, but was rejected to run by libbpf in 6.19,
> the error message was:
>
> libbpf: extern (func ksym) 'bpf_strstr': func_proto [5]
> incompatible with vmlinux [94389]
>
> The reason is there is a new added kfunc in kernel 6.19
> which happens to be the same name with my kfunc. However the
> error message is not obvious enough to address problem
> immediately.
>
> Therefore, this patches searches duplicated kfunc in
> both btf_vmlinux and btf_modules list before a kernel module
> attempts to register kfuncs through register_btf_kfunc_id_set,
> it prints clear error message and returns error code if same name
> kfunc has already implemented and registered, then developer
> knows at the first place.
>
> Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
> Suggested-by: Kaitao Cheng <kaitao.cheng@linux.dev>
> Reviewed-by: Yonghong Song <yonghong.song@linux.dev>
> Signed-off-by: Song Chen <chensong_2000@126.com>

The subject can be [PATCH bpf v4] bpf: Reject to register duplicated kfunc

>
> ---
> changelog:
> v1 --- v2:
> libbpf has already specified which module this kfunc belongs to as
> ebpf code onwer's expectation, then verifier uses
> find_kallsyms_symbol_value to search kfunc's addr.
>
> v2 --- v3:
> After v2, I tried a new idea of introducing a namespace in libbpf
> to specify kfunc owner in an ebpf program suggested by Kaitao Cheng,
> please see [1]. Alex suggested to go back to report an error during
> kmod load on conflicting kfunc name for now. What's more, v2 only
> searched bpf_vmlinux, v3 also traverses btf_modules list.
>
> v3 --- v4
> Fixed some coding style problems suggested from Kaitao Cheng.
> ---
>   kernel/bpf/btf.c | 38 +++++++++++++++++++++++++++++++++++++-
>   1 file changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 4872d2a6c42d..fe1612677a4a 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -8618,6 +8618,41 @@ static int btf_check_iter_kfuncs(struct btf *btf, const char *func_name,
>   	return 0;
>   }
>   
> +static int btf_check_kfunc_name(struct btf *btf, const char *func_name, u32 kind)
> +{
> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +	struct btf_module *btf_mod, *tmp;
> +#endif
> +	s32 id;

	s32 err = 0, id;

> +
> +	if (!btf_is_module(btf))
> +		return 0;
> +
> +	id = btf_find_by_name_kind(bpf_get_btf_vmlinux(), func_name, kind);
> +	if (id >= 0) {
> +		pr_err("kfunc %s (id: %d) is already present in vmlinux.\n",
> +				func_name, id);
> +		return -EINVAL;
> +	}
> +
> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +	mutex_lock(&btf_module_mutex);
> +	list_for_each_entry_safe(btf_mod, tmp, &btf_modules, list) {
> +		if (btf_mod->btf == btf)
> +			continue;
> +		id = btf_find_by_name_kind(btf_mod->btf, func_name, kind);
> +		if (id >= 0) {
> +			pr_err("kfunc %s (id: %d) is already present in module %s.\n",
> +					func_name, id, btf_mod->module->name);
> +			mutex_unlock(&btf_module_mutex);
> +			return -EINVAL;

Let us avoid the above mutex_unlock and 'return -EINVAL', just do
	err = -EINVAL;
	break;

> +		}
> +	}
> +	mutex_unlock(&btf_module_mutex);
> +#endif
> +	return 0;

	return err;

> +}
> +
>   static int btf_check_kfunc_protos(struct btf *btf, u32 func_id, u32 func_flags)
>   {
>   	const struct btf_type *func;
> @@ -8631,7 +8666,8 @@ static int btf_check_kfunc_protos(struct btf *btf, u32 func_id, u32 func_flags)
>   
>   	/* sanity check kfunc name */
>   	func_name = btf_name_by_offset(btf, func->name_off);
> -	if (!func_name || !func_name[0])
> +	if (!func_name || !func_name[0] ||
> +		btf_check_kfunc_name(btf, func_name, BTF_INFO_KIND(func->info)))

format issue:
	if (!func_name || !func_name[0] ||
	    btf_check_kfunc_name(btf, func_name, BTF_INFO_KIND(func->info)))
	...	

>   		return -EINVAL;
>   
>   	func = btf_type_by_id(btf, func->type);

Re: [PATCH v4] btf: reject to register duplicated kfunc

[Leon Hwang]

On 3/6/26 01:13, Yonghong Song wrote:
> 
> 
> On 6/2/26 4:07 AM, Song Chen wrote:
[...]
>> +
>> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
>> +    mutex_lock(&btf_module_mutex);
>> +    list_for_each_entry_safe(btf_mod, tmp, &btf_modules, list) {
>> +        if (btf_mod->btf == btf)
>> +            continue;
>> +        id = btf_find_by_name_kind(btf_mod->btf, func_name, kind);
>> +        if (id >= 0) {
>> +            pr_err("kfunc %s (id: %d) is already present in module
>> %s.\n",
>> +                    func_name, id, btf_mod->module->name);
>> +            mutex_unlock(&btf_module_mutex);
>> +            return -EINVAL;
> 
> Let us avoid the above mutex_unlock and 'return -EINVAL', just do
>     err = -EINVAL;
>     break;
> 

Better to use guard(mutex)(&btf_module_mutex)?

Thanks,
Leon

>> [...]

Re: [PATCH v4] btf: reject to register duplicated kfunc

[Song Chen]

Hi,

在 2026/6/3 10:18, Leon Hwang 写道:
> On 3/6/26 01:13, Yonghong Song wrote:
>>
>>
>> On 6/2/26 4:07 AM, Song Chen wrote:
> [...]
>>> +
>>> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
>>> +    mutex_lock(&btf_module_mutex);
>>> +    list_for_each_entry_safe(btf_mod, tmp, &btf_modules, list) {
>>> +        if (btf_mod->btf == btf)
>>> +            continue;
>>> +        id = btf_find_by_name_kind(btf_mod->btf, func_name, kind);
>>> +        if (id >= 0) {
>>> +            pr_err("kfunc %s (id: %d) is already present in module
>>> %s.\n",
>>> +                    func_name, id, btf_mod->module->name);
>>> +            mutex_unlock(&btf_module_mutex);
>>> +            return -EINVAL;
>>
>> Let us avoid the above mutex_unlock and 'return -EINVAL', just do
>>      err = -EINVAL;
>>      break;
>>
> 
> Better to use guard(mutex)(&btf_module_mutex)?
> 

This is the first time i used guard and it's awesome. I have tested in 
my code and will send a new patch later, many thanks.


> Thanks,
> Leon
> 
>>> [...]


Song

Re: [PATCH v4] btf: reject to register duplicated kfunc

[Song Chen]

Hi,

在 2026/6/3 01:13, Yonghong Song 写道:
> 
> 
> On 6/2/26 4:07 AM, Song Chen wrote:
>> I had an ebpf program which calls a kfunc defined and
>> implemented in one of my kernel modules, it was working
>> fine in 6.16, but was rejected to run by libbpf in 6.19,
>> the error message was:
>>
>> libbpf: extern (func ksym) 'bpf_strstr': func_proto [5]
>> incompatible with vmlinux [94389]
>>
>> The reason is there is a new added kfunc in kernel 6.19
>> which happens to be the same name with my kfunc. However the
>> error message is not obvious enough to address problem
>> immediately.
>>
>> Therefore, this patches searches duplicated kfunc in
>> both btf_vmlinux and btf_modules list before a kernel module
>> attempts to register kfuncs through register_btf_kfunc_id_set,
>> it prints clear error message and returns error code if same name
>> kfunc has already implemented and registered, then developer
>> knows at the first place.
>>
>> Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
>> Suggested-by: Kaitao Cheng <kaitao.cheng@linux.dev>
>> Reviewed-by: Yonghong Song <yonghong.song@linux.dev>
>> Signed-off-by: Song Chen <chensong_2000@126.com>
> 
> The subject can be [PATCH bpf v4] bpf: Reject to register duplicated kfunc
> 
>>
>> ---
>> changelog:
>> v1 --- v2:
>> libbpf has already specified which module this kfunc belongs to as
>> ebpf code onwer's expectation, then verifier uses
>> find_kallsyms_symbol_value to search kfunc's addr.
>>
>> v2 --- v3:
>> After v2, I tried a new idea of introducing a namespace in libbpf
>> to specify kfunc owner in an ebpf program suggested by Kaitao Cheng,
>> please see [1]. Alex suggested to go back to report an error during
>> kmod load on conflicting kfunc name for now. What's more, v2 only
>> searched bpf_vmlinux, v3 also traverses btf_modules list.
>>
>> v3 --- v4
>> Fixed some coding style problems suggested from Kaitao Cheng.
>> ---
>>   kernel/bpf/btf.c | 38 +++++++++++++++++++++++++++++++++++++-
>>   1 file changed, 37 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
>> index 4872d2a6c42d..fe1612677a4a 100644
>> --- a/kernel/bpf/btf.c
>> +++ b/kernel/bpf/btf.c
>> @@ -8618,6 +8618,41 @@ static int btf_check_iter_kfuncs(struct btf 
>> *btf, const char *func_name,
>>       return 0;
>>   }
>> +static int btf_check_kfunc_name(struct btf *btf, const char 
>> *func_name, u32 kind)
>> +{
>> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
>> +    struct btf_module *btf_mod, *tmp;
>> +#endif
>> +    s32 id;
> 
>      s32 err = 0, id;
> 
>> +
>> +    if (!btf_is_module(btf))
>> +        return 0;
>> +
>> +    id = btf_find_by_name_kind(bpf_get_btf_vmlinux(), func_name, kind);
>> +    if (id >= 0) {
>> +        pr_err("kfunc %s (id: %d) is already present in vmlinux.\n",
>> +                func_name, id);
>> +        return -EINVAL;
>> +    }
>> +
>> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
>> +    mutex_lock(&btf_module_mutex);
>> +    list_for_each_entry_safe(btf_mod, tmp, &btf_modules, list) {
>> +        if (btf_mod->btf == btf)
>> +            continue;
>> +        id = btf_find_by_name_kind(btf_mod->btf, func_name, kind);
>> +        if (id >= 0) {
>> +            pr_err("kfunc %s (id: %d) is already present in module 
>> %s.\n",
>> +                    func_name, id, btf_mod->module->name);
>> +            mutex_unlock(&btf_module_mutex);
>> +            return -EINVAL;
> 
> Let us avoid the above mutex_unlock and 'return -EINVAL', just do
>      err = -EINVAL;
>      break;
> 
>> +        }
>> +    }
>> +    mutex_unlock(&btf_module_mutex);
>> +#endif
>> +    return 0;
> 
>      return err;
> 

I will go with guard(mutex), please review my next submit and let me 
know if you're ok with it or not. Thanks.

>> +}
>> +
>>   static int btf_check_kfunc_protos(struct btf *btf, u32 func_id, u32 
>> func_flags)
>>   {
>>       const struct btf_type *func;
>> @@ -8631,7 +8666,8 @@ static int btf_check_kfunc_protos(struct btf 
>> *btf, u32 func_id, u32 func_flags)
>>       /* sanity check kfunc name */
>>       func_name = btf_name_by_offset(btf, func->name_off);
>> -    if (!func_name || !func_name[0])
>> +    if (!func_name || !func_name[0] ||
>> +        btf_check_kfunc_name(btf, func_name, BTF_INFO_KIND(func->info)))
> 
> format issue:
>      if (!func_name || !func_name[0] ||
>          btf_check_kfunc_name(btf, func_name, BTF_INFO_KIND(func->info)))
>      ...
> 

I will fix it with indentation plus space.

>>           return -EINVAL;
>>       func = btf_type_by_id(btf, func->type);
> 


many thanks.

Song