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selftests/bpf: Enrich subtest_basic_usdt case in selftests to cover SIB handling logic

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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: Jiawei Zhao <phoenix500526@163.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250827053128.1301287-3-phoenix500526@163.com
This commit is contained in:
Jiawei Zhao 2025-08-27 05:31:28 +00:00 committed by Andrii Nakryiko
parent 758acb9ccf
commit 69424097ee
2 changed files with 112 additions and 2 deletions
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83
tools/testing/selftests/bpf/prog_tests/usdt.c
View File

@ -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);
}

31
tools/testing/selftests/bpf/progs/test_usdt.c
View File

@ -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";