Commit 69424097 authored by Jiawei Zhao's avatar Jiawei Zhao Committed by Andrii Nakryiko
Browse files

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, e.g. "1@-96(%rbp,%rax,8)".

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

Signed-off-by: default avatarJiawei Zhao <phoenix500526@163.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250827053128.1301287-3-phoenix500526@163.com
parent 758acb9c

tools/testing/selftests/bpf/prog_tests/usdt.c

+81 −2
Original line number Diff line number Diff line
@@ -40,12 +40,72 @@ static void __always_inline trigger_func(int x) { 
	}

}



#if defined(__x86_64__) || defined(__i386__)

/*

 * SIB (Scale-Index-Base) addressing format: "size@(base_reg, index_reg, scale)"

 * - 'size' is the size in bytes of the array element, and its sign indicates

 *   whether the type is signed (negative) or unsigned (positive).

 * - 'base_reg' is the register holding the base address, normally rdx or edx

 * - 'index_reg' is the register holding the index, normally rax or eax

 * - 'scale' is the scaling factor (typically 1, 2, 4, or 8), which matches the

 *    size of the element type.

 *

 * For example, for an array of 'short' (signed 2-byte elements), the SIB spec would be:

 * - size: -2 (negative because 'short' is signed)

 * - scale: 2 (since sizeof(short) == 2)

 *

 * The resulting SIB format: "-2@(%%rdx,%%rax,2)" for x86_64, "-2@(%%edx,%%eax,2)" for i386

 */

static volatile short array[] = {-1, -2, -3, -4};



#if defined(__x86_64__)

#define USDT_SIB_ARG_SPEC -2@(%%rdx,%%rax,2)

#else

#define USDT_SIB_ARG_SPEC -2@(%%edx,%%eax,2)

#endif



unsigned short test_usdt_sib_semaphore SEC(".probes");



static void trigger_sib_spec(void)

{

	/*

	 * Force SIB addressing with inline assembly.

	 *

	 * You must compile with -std=gnu99 or -std=c99 to use the

	 * STAP_PROBE_ASM macro.

	 *

	 * The STAP_PROBE_ASM macro generates a quoted string that gets

	 * inserted between the surrounding assembly instructions. In this

	 * case, USDT_SIB_ARG_SPEC is embedded directly into the instruction

	 * stream, creating a probe point between the asm statement boundaries.

	 * It works fine with gcc/clang.

	 *

	 * Register constraints:

	 * - "d"(array): Binds the 'array' variable to %rdx or %edx register

	 * - "a"(0): Binds the constant 0 to %rax or %eax register

	 * These ensure that when USDT_SIB_ARG_SPEC references %%rdx(%edx) and

	 * %%rax(%eax), they contain the expected values for SIB addressing.

	 *

	 * The "memory" clobber prevents the compiler from reordering memory

	 * accesses around the probe point, ensuring that the probe behavior

	 * is predictable and consistent.

	 */

	asm volatile(

		STAP_PROBE_ASM(test, usdt_sib, USDT_SIB_ARG_SPEC)

		:

		: "d"(array), "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 +119,29 @@ 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__)

	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 +225,16 @@ 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, 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);

}

tools/testing/selftests/bpf/progs/test_usdt.c

+31 −0
Original line number Diff line number Diff line
@@ -107,4 +107,35 @@ 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;

short usdt_sib_arg;

int usdt_sib_arg_size;



/*

 * 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";