[PATCH] bpf: selftests: fix missing declaration for bpf_copy_from_user_task_str

[PATCH] bpf: selftests: fix missing declaration for bpf_copy_from_user_task_str

[Sun Jian]

Clang BPF compilation fails in bpf_iter_tasks.c due to an implicit
declaration of bpf_copy_from_user_task_str(), which is a BPF kfunc
exported by the kernel.

Add an explicit prototype in the test program to make the kfunc visible
to the BPF compiler and fix the build error.

No functional change intended.

Signed-off-by: Sun Jian <sun.jian.kdev@gmail.com>
---
 tools/testing/selftests/bpf/progs/bpf_iter_tasks.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_tasks.c b/tools/testing/selftests/bpf/progs/bpf_iter_tasks.c
index 966ee5a7b066..f5f396b5aa27 100644
--- a/tools/testing/selftests/bpf/progs/bpf_iter_tasks.c
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_tasks.c
@@ -4,6 +4,11 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 
+extern int bpf_copy_from_user_task_str(void *dst, u32 dst__sz,
+				       const void *unsafe_ptr,
+				       struct task_struct *task,
+				       u64 flags);
+
 char _license[] SEC("license") = "GPL";
 
 uint32_t tid = 0;
-- 
2.43.0

Re: [PATCH] bpf: selftests: fix missing declaration for bpf_copy_from_user_task_str

[Alexei Starovoitov]

On Wed, Dec 31, 2025 at 8:33 AM Sun Jian <sun.jian.kdev@gmail.com> wrote:
>
> Clang BPF compilation fails in bpf_iter_tasks.c due to an implicit
> declaration of bpf_copy_from_user_task_str(), which is a BPF kfunc
> exported by the kernel.

nope. It's there in vmlinux.h
Fix your build setup instead.

pw-bot: cr

> Add an explicit prototype in the test program to make the kfunc visible
> to the BPF compiler and fix the build error.
>
> No functional change intended.
>
> Signed-off-by: Sun Jian <sun.jian.kdev@gmail.com>
> ---
>  tools/testing/selftests/bpf/progs/bpf_iter_tasks.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_tasks.c b/tools/testing/selftests/bpf/progs/bpf_iter_tasks.c
> index 966ee5a7b066..f5f396b5aa27 100644
> --- a/tools/testing/selftests/bpf/progs/bpf_iter_tasks.c
> +++ b/tools/testing/selftests/bpf/progs/bpf_iter_tasks.c
> @@ -4,6 +4,11 @@
>  #include <bpf/bpf_helpers.h>
>  #include <bpf/bpf_tracing.h>
>
> +extern int bpf_copy_from_user_task_str(void *dst, u32 dst__sz,
> +                                      const void *unsafe_ptr,
> +                                      struct task_struct *task,
> +                                      u64 flags);
> +
>  char _license[] SEC("license") = "GPL";
>
>  uint32_t tid = 0;
> --
> 2.43.0
>