[RFC] bpf: Issue with bpf_fentry_test7 call

[Jiri Olsa <olsajiri@xxxxxxxxx>]

hi,   
The bpf CI is broken due to clang emitting 2 functions for
bpf_fentry_test7:

  # cat available_filter_functions | grep bpf_fentry_test7
  bpf_fentry_test7
  bpf_fentry_test7.specialized.1

The tests attach to 'bpf_fentry_test7' while the function with
'.specialized.1' suffix is executed in bpf_prog_test_run_tracing.

It looks like clang optimalization that comes from passing 0
as argument and returning it directly in bpf_fentry_test7.

I'm not sure there's a way to disable this, so far I came
up with solution below that passes real pointer, but I think
that was not the original intention for the test.

We had issue with this function back in august:
  32337c0a2824 bpf: Prevent inlining of bpf_fentry_test7()

I'm not sure why it started to show now? was clang updated for CI?

I'll try to find out more, but any clang ideas are welcome ;-)

thanks,
jirka


---
diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index c9fdcc5cdce1..33208eec9361 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -543,7 +543,7 @@ struct bpf_fentry_test_t {
 int noinline bpf_fentry_test7(struct bpf_fentry_test_t *arg)
 {
 	asm volatile ("");
-	return (long)arg;
+	return 0;
 }
 
 int noinline bpf_fentry_test8(struct bpf_fentry_test_t *arg)
@@ -668,7 +668,7 @@ int bpf_prog_test_run_tracing(struct bpf_prog *prog,
 		    bpf_fentry_test4((void *)7, 8, 9, 10) != 34 ||
 		    bpf_fentry_test5(11, (void *)12, 13, 14, 15) != 65 ||
 		    bpf_fentry_test6(16, (void *)17, 18, 19, (void *)20, 21) != 111 ||
-		    bpf_fentry_test7((struct bpf_fentry_test_t *)0) != 0 ||
+		    bpf_fentry_test7(&arg) != 0 ||
 		    bpf_fentry_test8(&arg) != 0 ||
 		    bpf_fentry_test9(&retval) != 0)
 			goto out;
diff --git a/tools/testing/selftests/bpf/progs/fentry_test.c b/tools/testing/selftests/bpf/progs/fentry_test.c
index 52a550d281d9..95c5c34ccaa8 100644
--- a/tools/testing/selftests/bpf/progs/fentry_test.c
+++ b/tools/testing/selftests/bpf/progs/fentry_test.c
@@ -64,7 +64,7 @@ __u64 test7_result = 0;
 SEC("fentry/bpf_fentry_test7")
 int BPF_PROG(test7, struct bpf_fentry_test_t *arg)
 {
-	if (!arg)
+	if (arg)
 		test7_result = 1;
 	return 0;
 }
diff --git a/tools/testing/selftests/bpf/progs/fexit_test.c b/tools/testing/selftests/bpf/progs/fexit_test.c
index 8f1ccb7302e1..ffb30236ca02 100644
--- a/tools/testing/selftests/bpf/progs/fexit_test.c
+++ b/tools/testing/selftests/bpf/progs/fexit_test.c
@@ -65,7 +65,7 @@ __u64 test7_result = 0;
 SEC("fexit/bpf_fentry_test7")
 int BPF_PROG(test7, struct bpf_fentry_test_t *arg)
 {
-	if (!arg)
+	if (arg)
 		test7_result = 1;
 	return 0;
 }