selftests/bpf: Add tests for program extensions

Add program extension tests that build on top of fexit_bpf2bpf tests.
Replace three global functions in previously loaded test_pkt_access.c program
with three new implementations:
int get_skb_len(struct __sk_buff *skb);
int get_constant(long val);
int get_skb_ifindex(int val, struct __sk_buff *skb, int var);
New function return the same results as original only if arguments match.

new_get_skb_ifindex() demonstrates that 'skb' argument doesn't have to be first
and only argument of BPF program. All normal skb based accesses are available.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20200121005348.2769920-4-ast@kernel.org

1 files changed, 7 insertions, 1 deletions

diff --git a/tools/testing/selftests/bpf/progs/test_pkt_access.c b/tools/testing/selftests/bpf/progs/test_pkt_access.c
index 7c9fcfd2b463..e72eba4a93d2 100644
--- a/tools/testing/selftests/bpf/progs/test_pkt_access.c
+++ b/tools/testing/selftests/bpf/progs/test_pkt_access.c
@@ -57,12 +57,18 @@ int get_skb_len(struct __sk_buff *skb)
 	return skb->len;
 }
 
+__attribute__ ((noinline))
+int get_constant(long val)
+{
+	return val - 122;
+}
+
 int get_skb_ifindex(int, struct __sk_buff *skb, int);
 
 __attribute__ ((noinline))
 int test_pkt_access_subprog3(int val, struct __sk_buff *skb)
 {
-	return get_skb_len(skb) * get_skb_ifindex(val, skb, 1);
+	return get_skb_len(skb) * get_skb_ifindex(val, skb, get_constant(123));
 }
 
 __attribute__ ((noinline))