libbpf-rs: Add test for kernel tracepoint usage

Currently there exist no test for attaching of a BPF program to a kernel
tracepoint. Add one.

Signed-off-by: Daniel Müller <deso@posteo.net>

Author: d-e-s-o

libbpf-rs/tests/bin/src/tracepoint.bpf.c

@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/usdt.bpf.h>
+
+struct {
+    __uint(type, BPF_MAP_TYPE_RINGBUF);
+    __uint(max_entries, 4096 /* one page */);
+} ringbuf SEC(".maps");
+
+SEC("tracepoint/syscalls/sys_enter_getpid")
+int handle__tracepoint(void *ctx)
+{
+    int *value;
+
+    value = bpf_ringbuf_reserve(&ringbuf, sizeof(int), 0);
+    if (value) {
+        *value = 1;
+        bpf_ringbuf_submit(value, 0);
+    }
+
+    return 0;
+}
+
+char LICENSE[] SEC("license") = "GPL";

libbpf-rs/tests/bin/tracepoint.bpf.o

@@ -898,3 +898,41 @@ fn test_object_program_insns() {
     let insns = prog.insns();
     assert!(!insns.is_empty());
 }
+
+/// Check that we can attach a BPF program to a kernel tracepoint.
+#[test]
+fn test_object_tracepoint() {
+    bump_rlimit_mlock();
+
+    let mut obj = get_test_object("tracepoint.bpf.o");
+    let prog = obj
+        .prog_mut("handle__tracepoint")
+        .expect("Failed to find program");
+
+    let _link = prog
+        .attach_tracepoint("syscalls", "sys_enter_getpid")
+        .expect("Failed to attach prog");
+
+    let mut builder = libbpf_rs::RingBufferBuilder::new();
+    let map = obj.map("ringbuf").expect("Failed to get ringbuf map");
+
+    static mut V: i32 = 0;
+    fn callback(data: &[u8]) -> i32 {
+        let mut value: i32 = 0;
+        plain::copy_from_bytes(&mut value, data).expect("Wrong size");
+
+        unsafe {
+            V = value;
+        }
+
+        0
+    }
+
+    builder.add(map, callback).expect("Failed to add ringbuf");
+    let mgr = builder.build().expect("Failed to build");
+
+    let _pid = unsafe { libc::getpid() };
+    mgr.consume().expect("Failed to consume ringbuf");
+
+    unsafe { assert_eq!(V, 1) };
+}