[PATCH bpf-next] selftests/bpf: fix probe_user test failure with clang build kernel

[Yonghong Song <yhs@xxxxxx>]

clang build kernel failed the selftest probe_user.
  $ ./test_progs -t probe_user
  $ ...
  $ test_probe_user:PASS:get_kprobe_res 0 nsec
  $ test_probe_user:FAIL:check_kprobe_res wrong kprobe res from probe read: 0.0.0.0:0
  $ #94 probe_user:FAIL

The test attached to kernel function __sys_connect(). In net/socket.c, we have
  int __sys_connect(int fd, struct sockaddr __user *uservaddr, int addrlen)
  {
        ......
  }
  ...
  SYSCALL_DEFINE3(connect, int, fd, struct sockaddr __user *, uservaddr,
                  int, addrlen)
  {
        return __sys_connect(fd, uservaddr, addrlen);
  }

The gcc compiler (8.5.0) does not inline __sys_connect() in syscall entry
function. But latest clang trunk did the inlining. So the bpf program
is not triggered.

To make the test more reliable, let us kprobe the syscall entry function
instead. But x86_64, arm64 and s390 has syscall wrapper and they have
to be handled specially. I also changed the test to use vmlinux.h and CORE
to accommodate relocatable pt_regs structure, similar to
samples/bpf/test_probe_write_user_kern.c.

Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
 .../selftests/bpf/prog_tests/probe_user.c     |  4 +--
 .../selftests/bpf/progs/test_probe_user.c     | 30 +++++++++++++++----
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/probe_user.c b/tools/testing/selftests/bpf/prog_tests/probe_user.c
index 95bd12097358..52fe157e2a90 100644
--- a/tools/testing/selftests/bpf/prog_tests/probe_user.c
+++ b/tools/testing/selftests/bpf/prog_tests/probe_user.c
@@ -3,7 +3,7 @@
 
 void test_probe_user(void)
 {
-	const char *prog_name = "kprobe/__sys_connect";
+	const char *prog_name = "handle_sys_connect";
 	const char *obj_file = "./test_probe_user.o";
 	DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts, );
 	int err, results_map_fd, sock_fd, duration = 0;
@@ -18,7 +18,7 @@ void test_probe_user(void)
 	if (!ASSERT_OK_PTR(obj, "obj_open_file"))
 		return;
 
-	kprobe_prog = bpf_object__find_program_by_title(obj, prog_name);
+	kprobe_prog = bpf_object__find_program_by_name(obj, prog_name);
 	if (CHECK(!kprobe_prog, "find_probe",
 		  "prog '%s' not found\n", prog_name))
 		goto cleanup;
diff --git a/tools/testing/selftests/bpf/progs/test_probe_user.c b/tools/testing/selftests/bpf/progs/test_probe_user.c
index 89b3532ccc75..9b3ddbf6289d 100644
--- a/tools/testing/selftests/bpf/progs/test_probe_user.c
+++ b/tools/testing/selftests/bpf/progs/test_probe_user.c
@@ -1,21 +1,39 @@
 // SPDX-License-Identifier: GPL-2.0
 
-#include <linux/ptrace.h>
-#include <linux/bpf.h>
-
-#include <netinet/in.h>
+#include "vmlinux.h"
 
 #include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
 #include <bpf/bpf_tracing.h>
 
+#if defined(__TARGET_ARCH_x86)
+volatile const int syscall_wrapper = 1;
+#define SYS_PREFIX "__x64_"
+#elif defined(__TARGET_ARCH_s390)
+volatile const int syscall_wrapper = 1;
+#define SYS_PREFIX "__s390x_"
+#elif defined(__TARGET_ARCH_arm64)
+volatile const int syscall_wrapper = 1;
+#define SYS_PREFIX "__arm64_"
+#else
+volatile const int syscall_wrapper = 0;
+#endif
+
 static struct sockaddr_in old;
 
-SEC("kprobe/__sys_connect")
+SEC("kprobe/" SYS_PREFIX "sys_connect")
 int BPF_KPROBE(handle_sys_connect)
 {
-	void *ptr = (void *)PT_REGS_PARM2(ctx);
+	void *ptr;
 	struct sockaddr_in new;
 
+	if (syscall_wrapper == 0) {
+		ptr = (void *)PT_REGS_PARM2_CORE(ctx);
+	} else {
+		struct pt_regs *real_regs = (struct pt_regs *)PT_REGS_PARM1_CORE(ctx);
+		ptr = (void *)PT_REGS_PARM2_CORE(real_regs);
+	}
+
 	bpf_probe_read_user(&old, sizeof(old), ptr);
 	__builtin_memset(&new, 0xab, sizeof(new));
 	bpf_probe_write_user(ptr, &new, sizeof(new));
-- 
2.30.2