On 23/1/26 08:53, Andrii Nakryiko wrote:

On Tue, Jan 20, 2026 at 7:26 AM Leon Hwang [off-list ref] wrote:

quoted

To support the extended BPF syscall introduced in the previous commit,
introduce the following internal APIs:

* 'sys_bpf_ext()'
* 'sys_bpf_ext_fd()'
  They wrap the raw 'syscall()' interface to support passing extended
  attributes.
* 'probe_sys_bpf_ext()'
  Check whether current kernel supports the BPF syscall common attributes.

Signed-off-by: Leon Hwang <redacted>
---
 tools/lib/bpf/bpf.c             | 32 ++++++++++++++++++++++++++++++++
 tools/lib/bpf/features.c        |  8 ++++++++
 tools/lib/bpf/libbpf_internal.h |  3 +++
 3 files changed, 43 insertions(+)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 21b57a629916..ed9c6eaeb656 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c

@@ -69,6 +69,38 @@ static inline __u64 ptr_to_u64(const void *ptr)
        return (__u64) (unsigned long) ptr;
 }

+static inline int sys_bpf_ext(enum bpf_cmd cmd, union bpf_attr *attr,
+                             unsigned int size,
+                             struct bpf_common_attr *attr_common,
+                             unsigned int size_common)
+{
+       cmd = attr_common ? (cmd | BPF_COMMON_ATTRS) : (cmd & ~BPF_COMMON_ATTRS);
+       return syscall(__NR_bpf, cmd, attr, size, attr_common, size_common);
+}
+
+static inline int sys_bpf_ext_fd(enum bpf_cmd cmd, union bpf_attr *attr,
+                                unsigned int size,
+                                struct bpf_common_attr *attr_common,
+                                unsigned int size_common)
+{
+       int fd;
+
+       fd = sys_bpf_ext(cmd, attr, size, attr_common, size_common);
+       return ensure_good_fd(fd);
+}
+
+int probe_sys_bpf_ext(void)
+{
+       const size_t attr_sz = offsetofend(union bpf_attr, prog_token_fd);
+       union bpf_attr attr;
+
+       memset(&attr, 0, attr_sz);
+       /* This syscall() will return error always. */

I'll cite myself from the last review:

quoted

But fd should really not be >= 0, and if it is -- it's some problem,
so I'd return an error in that case to keep us aware, which is why I'm
saying I'd just return inside if (fd >= 0) { }

I didn't say let's just ignore syscall return with (void) cast and
happily check errno no matter what, did I? Drop the comment, and
handle fd >= 0 case explicitly, please.

My mistake — sorry for the misunderstanding.

You’re right; the return value should not be ignored. In the next
revision, I’ll handle the fd >= 0 case explicitly and drop the comment.
The logic will be updated along the lines of:

fd = syscall(__NR_bpf, BPF_PROG_LOAD | BPF_COMMON_ATTRS,
             &attr, attr_sz, NULL, sizeof(struct bpf_common_attr));
if (fd >= 0) {
        close(fd);
        return 0;
}
return errno == EFAULT;

Thanks,
Leon