Re: [PATCH bpf-next v15 2/2] selftests/bpf: Enrich subtest_basic_usdt case in selftests to cover SIB handling logic

On Sat, Aug 23, 2025 at 12:19 AM Jiawei Zhao phoenix500526@163.com wrote:

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 | 62 ++++++++++++++++++- tools/testing/selftests/bpf/progs/test_usdt.c | 32 ++++++++++ 2 files changed, 92 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..4b264f7d3324 100644 --- a/tools/testing/selftests/bpf/prog_tests/usdt.c +++ b/tools/testing/selftests/bpf/prog_tests/usdt.c @@ -10,6 +10,26 @@

int lets_test_this(int);

+#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)"
    

• */

+static volatile short array[] = {-1, -2, -3, -4}; +#define USDT_SIB_ARG_SPEC -2@(%%rdx,%%rax,2)

can you locate this before trigger_sib_spec, inside the same #if/#endif area?

+#endif

static volatile int idx = 2; static volatile __u64 bla = 0xFEDCBA9876543210ULL; static volatile short nums[] = {-1, -2, -3, -4}; @@ -25,6 +45,10 @@ 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");

same as above, group all this close to the triggering function inside single #if/#endif block

+#endif

static void __always_inline trigger_func(int x) { long y = 42;

@@ -40,12 +64,27 @@ static void __always_inline trigger_func(int x) { } }

+#if defined(__x86_64__) || defined(__i386__) +static void trigger_sib_spec(void) +{

•   /* Base address + offset + (index * scale) */
  

•   /* Force SIB addressing with inline assembly */
  

•   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 +98,29 @@ 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 +204,16 @@ 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); } diff --git a/tools/testing/selftests/bpf/progs/test_usdt.c b/tools/testing/selftests/bpf/progs/test_usdt.c index 096488f47fbc..63db72253316 100644 --- a/tools/testing/selftests/bpf/progs/test_usdt.c +++ b/tools/testing/selftests/bpf/progs/test_usdt.c @@ -107,4 +107,36 @@ int BPF_USDT(usdt12, int a1, int a2, long a3, long a4, unsigned a5, return 0; }

nit: extra empty line for no good reason

+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;

+/*

• • 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