Alexei Starovoitov wrote:

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>
---
 .../selftests/bpf/prog_tests/fexit_bpf2bpf.c  | 20 ++++++-
 .../selftests/bpf/progs/fexit_bpf2bpf.c       | 57 +++++++++++++++++++
 .../selftests/bpf/progs/test_pkt_access.c     |  8 ++-
 3 files changed, 83 insertions(+), 2 deletions(-)

Acked-by: John Fastabend <john.fastabend@gmail.com>