[PATCH bpf-next v12 2/2] selftests/bpf: Enrich subtest_basic_usdt case in selftests to cover SIB handling logic

[Jiawei Zhao <phoenix500526@163.com>]

When using GCC on x86-64 to compile an usdt prog with -O1 or higher
optimization, the compiler will generate SIB addressing mode for global
array and PC-relative addressing mode for global variable,
e.g. "1@-96(%rbp,%rax,8)" and "-1@4+t1(%rip)".

In this patch:
- enrich subtest_basic_usdt test case to cover SIB addressing usdt argument spec
  handling logic

Signed-off-by: Jiawei Zhao <phoenix500526@163.com>
---
 tools/testing/selftests/bpf/prog_tests/usdt.c | 44 ++++++++++++++++++-
 tools/testing/selftests/bpf/progs/test_usdt.c | 30 +++++++++++++
 2 files changed, 72 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/usdt.c b/tools/testing/selftests/bpf/prog_tests/usdt.c
index 9057e983cc54..c04b416aa4a8 100644
--- a/tools/testing/selftests/bpf/prog_tests/usdt.c
+++ b/tools/testing/selftests/bpf/prog_tests/usdt.c
@@ -25,6 +25,10 @@ unsigned short test_usdt0_semaphore SEC(".probes");
 unsigned short test_usdt3_semaphore SEC(".probes");
 unsigned short test_usdt12_semaphore SEC(".probes");
 
+#if ((defined(__x86_64__) || defined(__i386__)) && defined(__GNUC__) && !defined(__clang__))
+unsigned short test_usdt_sib_semaphore SEC(".probes");
+#endif
+
 static void __always_inline trigger_func(int x) {
 	long y = 42;
 
@@ -40,12 +44,29 @@ static void __always_inline trigger_func(int x) {
 	}
 }
 
+#if ((defined(__x86_64__) || defined(__i386__)) && defined(__GNUC__) && !defined(__clang__))
+static __attribute__((optimize("O1"))) void trigger_sib_spec(void)
+{
+	/* Base address + offset + (index * scale) */
+	/* Force SIB addressing with inline assembly */
+	asm volatile(
+		"# probe point with memory access\n"
+		STAP_PROBE_ASM(test, usdt_sib, -2@(%%rdx,%%rax,2))
+		"# end probe point"
+		:
+		: "d"(nums), "a"(0)
+		: "memory"
+	);
+}
+#endif
+
 static void subtest_basic_usdt(void)
 {
 	LIBBPF_OPTS(bpf_usdt_opts, opts);
 	struct test_usdt *skel;
 	struct test_usdt__bss *bss;
 	int err, i;
+	const __u64 expected_cookie = 0xcafedeadbeeffeed;
 
 	skel = test_usdt__open_and_load();
 	if (!ASSERT_OK_PTR(skel, "skel_open"))
@@ -59,20 +80,29 @@ static void subtest_basic_usdt(void)
 		goto cleanup;
 
 	/* usdt0 won't be auto-attached */
-	opts.usdt_cookie = 0xcafedeadbeeffeed;
+	opts.usdt_cookie = expected_cookie;
 	skel->links.usdt0 = bpf_program__attach_usdt(skel->progs.usdt0,
 						     0 /*self*/, "/proc/self/exe",
 						     "test", "usdt0", &opts);
 	if (!ASSERT_OK_PTR(skel->links.usdt0, "usdt0_link"))
 		goto cleanup;
 
+#if ((defined(__x86_64__) || defined(__i386__)) && defined(__GNUC__) && !defined(__clang__))
+	opts.usdt_cookie = expected_cookie;
+	skel->links.usdt_sib = bpf_program__attach_usdt(skel->progs.usdt_sib,
+								0 /*self*/, "/proc/self/exe",
+								"test", "usdt_sib", &opts);
+	if (!ASSERT_OK_PTR(skel->links.usdt_sib, "usdt_sib_link"))
+		goto cleanup;
+#endif
+
 	trigger_func(1);
 
 	ASSERT_EQ(bss->usdt0_called, 1, "usdt0_called");
 	ASSERT_EQ(bss->usdt3_called, 1, "usdt3_called");
 	ASSERT_EQ(bss->usdt12_called, 1, "usdt12_called");
 
-	ASSERT_EQ(bss->usdt0_cookie, 0xcafedeadbeeffeed, "usdt0_cookie");
+	ASSERT_EQ(bss->usdt0_cookie, expected_cookie, "usdt0_cookie");
 	ASSERT_EQ(bss->usdt0_arg_cnt, 0, "usdt0_arg_cnt");
 	ASSERT_EQ(bss->usdt0_arg_ret, -ENOENT, "usdt0_arg_ret");
 	ASSERT_EQ(bss->usdt0_arg_size, -ENOENT, "usdt0_arg_size");
@@ -156,6 +186,16 @@ static void subtest_basic_usdt(void)
 	ASSERT_EQ(bss->usdt3_args[1], 42, "usdt3_arg2");
 	ASSERT_EQ(bss->usdt3_args[2], (uintptr_t)&bla, "usdt3_arg3");
 
+#if ((defined(__x86_64__) || defined(__i386__)) && defined(__GNUC__) && !defined(__clang__))
+	trigger_sib_spec();
+	ASSERT_EQ(bss->usdt_sib_called, 1, "usdt_sib_called");
+	ASSERT_EQ(bss->usdt_sib_cookie, expected_cookie, "usdt_sib_cookie");
+	ASSERT_EQ(bss->usdt_sib_arg_cnt, 1, "usdt_sib_arg_cnt");
+	ASSERT_EQ(bss->usdt_sib_arg, nums[0], "usdt_sib_arg");
+	ASSERT_EQ(bss->usdt_sib_arg_ret, 0, "usdt_sib_arg_ret");
+	ASSERT_EQ(bss->usdt_sib_arg_size, sizeof(nums[0]), "usdt_sib_arg_size");
+#endif
+
 cleanup:
 	test_usdt__destroy(skel);
 }
diff --git a/tools/testing/selftests/bpf/progs/test_usdt.c b/tools/testing/selftests/bpf/progs/test_usdt.c
index 096488f47fbc..b5f883bca66b 100644
--- a/tools/testing/selftests/bpf/progs/test_usdt.c
+++ b/tools/testing/selftests/bpf/progs/test_usdt.c
@@ -107,4 +107,34 @@ int BPF_USDT(usdt12, int a1, int a2, long a3, long a4, unsigned a5,
 	return 0;
 }
 
+
+int usdt_sib_called;
+u64 usdt_sib_cookie;
+int usdt_sib_arg_cnt;
+int usdt_sib_arg_ret;
+u64 usdt_sib_arg;
+int usdt_sib_arg_size;
+
+// Note: usdt_sib is only tested on x86-related architectures, so it requires
+// manual attach since auto-attach will panic tests under other architectures
+SEC("usdt")
+int usdt_sib(struct pt_regs *ctx)
+{
+	long tmp;
+
+	if (my_pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	__sync_fetch_and_add(&usdt_sib_called, 1);
+
+	usdt_sib_cookie = bpf_usdt_cookie(ctx);
+	usdt_sib_arg_cnt = bpf_usdt_arg_cnt(ctx);
+
+	usdt_sib_arg_ret = bpf_usdt_arg(ctx, 0, &tmp);
+	usdt_sib_arg = (short)tmp;
+	usdt_sib_arg_size = bpf_usdt_arg_size(ctx, 0);
+
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.43.0