selftests/bpf: Test gen_prologue and gen_epilogue

This test adds a new struct_ops "bpf_testmod_st_ops" in bpf_testmod.
The ops of the bpf_testmod_st_ops is triggered by new kfunc calls
"bpf_kfunc_st_ops_test_*logue". These new kfunc calls are
primarily used by the SEC("syscall") program. The test triggering
sequence is like:
    SEC("syscall")
    syscall_prologue(struct st_ops_args *args)
        bpf_kfunc_st_op_test_prologue(args)
	    st_ops->test_prologue(args)

.gen_prologue adds 1000 to args->a
.gen_epilogue adds 10000 to args->a
.gen_epilogue will also set the r0 to 2 * args->a.

The .gen_prologue and .gen_epilogue of the bpf_testmod_st_ops
will test the prog->aux->attach_func_name to decide if
it needs to generate codes.

The main programs of the pro_epilogue.c will call a
new kfunc bpf_kfunc_st_ops_inc10 which does "args->a += 10".
It will also call a subprog() which does "args->a += 1".

This patch uses the test_loader infra to check the __xlated
instructions patched after gen_prologue and/or gen_epilogue.
The __xlated check is based on Eduard's example (Thanks!) in v1.

args->a is returned by the struct_ops prog (either the main prog
or the epilogue). Thus, the __retval of the SEC("syscall") prog
is checked. For example, when triggering the ops in the
'SEC("struct_ops/test_epilogue") int test_epilogue'
The expected args->a is +1 (subprog call) + 10 (kfunc call)
    	     	     	+ 10000 (.gen_epilogue) = 10011.
The expected return value is 2 * 10011 (.gen_epilogue).

Suggested-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20240829210833.388152-7-martin.lau@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h
index c6c314965bb1..7e76532be5fa 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h
@@ -148,4 +148,10 @@ struct sk_buff *bpf_kfunc_nested_acquire_nonzero_offset_test(struct sk_buff_head
 struct sk_buff *bpf_kfunc_nested_acquire_zero_offset_test(struct sock_common *ptr) __ksym;
 void bpf_kfunc_nested_release_test(struct sk_buff *ptr) __ksym;
 
+struct st_ops_args;
+int bpf_kfunc_st_ops_test_prologue(struct st_ops_args *args) __ksym;
+int bpf_kfunc_st_ops_test_epilogue(struct st_ops_args *args) __ksym;
+int bpf_kfunc_st_ops_test_pro_epilogue(struct st_ops_args *args) __ksym;
+int bpf_kfunc_st_ops_inc10(struct st_ops_args *args) __ksym;
+
 #endif /* _BPF_TESTMOD_KFUNC_H */