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

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Message-ID: <20250821140623.971621-3-phoenix500526@163.com>
Date: Thu, 21 Aug 2025 14:06:23 +0000
From: Jiawei Zhao <phoenix500526@....com>
To: ast@...nel.org
Cc: daniel@...earbox.net,
	andrii@...nel.org,
	yonghong.song@...ux.dev,
	bpf@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next v12 2/2] selftests/bpf: Enrich subtest_basic_usdt case in selftests to cover SIB handling logic

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@...1(%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@....com>
---
 tools/testing/selftests/bpf/prog_tests/usdt.c | 30 +++++++++++++++++++
 tools/testing/selftests/bpf/progs/test_usdt.c | 28 +++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/usdt.c b/tools/testing/selftests/bpf/prog_tests/usdt.c
index 9057e983cc54..56990d4b5861 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__)
+unsigned short test_usdt_sib_semaphore SEC(".probes");
+#endif
+
 static void __always_inline trigger_func(int x) {
 	long y = 42;
 
@@ -40,6 +44,22 @@ static void __always_inline trigger_func(int x) {
 	}
 }
 
+#if defined(__x86_64__) || defined(__i386__)
+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);
@@ -156,6 +176,16 @@ 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__)
+	trigger_sib_spec();
+	ASSERT_EQ(bss->usdt_sib_called, 1, "usdt_sib_called");
+	ASSERT_EQ(bss->usdt_sib_cookie, 0, "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..8b499732e6a8 100644
--- a/tools/testing/selftests/bpf/progs/test_usdt.c
+++ b/tools/testing/selftests/bpf/progs/test_usdt.c
@@ -107,4 +107,32 @@ 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;
+
+SEC("usdt//proc/self/exe:test:usdt_sib")
+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