[PATCH] selftests/bpf: test accounting of tail calls when prog is NULL

[Hari Bathini <hbathini@linux.ibm.com>]

Test whether tail call count is incorrectly accounted for, when the
tail call fails due to a missing BPF program.

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
---

- powerpc64 BPF JIT has been incorrectly accounting for tailcall count
  even when BPF program to tailcall into is missing. A simple change
  to one of the tailcall selftests could have flagged it earlier.

    https://lore.kernel.org/all/20260216065639.1750181-2-hbathini@linux.ibm.com/

 tools/testing/selftests/bpf/progs/tailcall3.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/progs/tailcall3.c b/tools/testing/selftests/bpf/progs/tailcall3.c
index f60bcd7b8d4b..204f19c30a3e 100644
--- a/tools/testing/selftests/bpf/progs/tailcall3.c
+++ b/tools/testing/selftests/bpf/progs/tailcall3.c
@@ -5,7 +5,7 @@
 
 struct {
 	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
-	__uint(max_entries, 1);
+	__uint(max_entries, 2);
 	__uint(key_size, sizeof(__u32));
 	__uint(value_size, sizeof(__u32));
 } jmp_table SEC(".maps");
@@ -23,6 +23,9 @@ int classifier_0(struct __sk_buff *skb)
 SEC("tc")
 int entry(struct __sk_buff *skb)
 {
+	/* prog == NULL case */
+	bpf_tail_call_static(skb, &jmp_table, 1);
+
 	bpf_tail_call_static(skb, &jmp_table, 0);
 	return 0;
 }
-- 
2.53.0