Re: [PATCH bpf 2/2] bpf: selftest to verify mixing bpf2bpf calls and tailcalls with insn patch

Maciej Fijalkowski wrote:

On Tue, Jun 08, 2021 at 12:30:33PM -0700, John Fastabend wrote:

quoted

This adds some extra noise to the tailcall_bpf2bpf4 tests that will cause
verifier to patch insns. This then moves around subprog start/end insn
index and poke descriptor insn index to ensure that verify and JIT will
continue to track these correctly.

This test is the most complicated one where I tried to document the scope
of it on the side of prog_tests/tailcalls.c. I feel that it would make it
more difficult to debug it if under any circumstances something would have
been broken with that logic.

Maybe a separate test scenario? Or is this an overkill? If so, I would
vote for moving it to tailcall_bpf2bpf1.c and have a little comment that
testing other bpf helpers mixed in is in scope of that test.

I like pushing it into the complex test to get the most instruction
patching combinations possible.

quoted

Reviewed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
 .../selftests/bpf/progs/tailcall_bpf2bpf4.c        |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf4.c b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf4.c
index 9a1b166b7fbe..0d70de5f97e2 100644
--- a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf4.c
+++ b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf4.c

@@ -2,6 +2,13 @@
 #include <linux/bpf.h>
 #include <bpf/bpf_helpers.h>
 
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__uint(key_size, sizeof(__u32));
+	__uint(value_size, sizeof(__u32));
+} nop_table SEC(".maps");
+
 struct {
 	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
 	__uint(max_entries, 3);

@@ -11,9 +18,19 @@ struct {
 
 static volatile int count;
 
+__noinline
+int subprog_noise(struct __sk_buff *skb)
+{
+	__u32 key = 0;
+
+	bpf_map_lookup_elem(&nop_table, &key);
+	return 0;
+}
+
 __noinline
 int subprog_tail_2(struct __sk_buff *skb)
 {
+	subprog_noise(skb);
 	bpf_tail_call_static(skb, &jmp_table, 2);
 	return skb->len * 3;
 }