Hi Yonghong,
I noticed that the USDT argument specification generated by GCC 14 is '8@array(,%rax,8)'. This pattern is currently not handled correctly. I'm exploring whether I can use DWARF information to calculate the address of this variable. This approach seems to work. However, since I can't reproduce the same issue on my machine, I plan to implement this approach for the PC-relative issue in a separate patch. Would that affect the merging of this patch?
At 2025-08-07 02:17:34, "Yonghong Song" yonghong.song@linux.dev wrote:
On 8/6/25 2:24 AM, Jiawei Zhao 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:
- add usdt_o2 test case to cover SIB addressing usdt argument spec handling logic
Signed-off-by: Jiawei Zhao phoenix500526@163.com
tools/testing/selftests/bpf/Makefile | 8 +++ .../selftests/bpf/prog_tests/usdt_o2.c | 71 +++++++++++++++++++ .../selftests/bpf/progs/test_usdt_o2.c | 37 ++++++++++ 3 files changed, 116 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/usdt_o2.c create mode 100644 tools/testing/selftests/bpf/progs/test_usdt_o2.c
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index 910d8d6402ef..68cf6a9cf05f 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -759,6 +759,14 @@ TRUNNER_BPF_BUILD_RULE := $$(error no BPF objects should be built) TRUNNER_BPF_CFLAGS := $(eval $(call DEFINE_TEST_RUNNER,test_maps)) +# Use -O2 optimization to generate SIB addressing usdt argument spec +# Only apply on x86 architecture where SIB addressing is relevant +ifeq ($(ARCH), x86) +$(OUTPUT)/usdt_o2.test.o: CFLAGS:=$(subst O0,O2,$(CFLAGS)) +$(OUTPUT)/cpuv4/usdt_o2.test.o: CFLAGS:=$(subst O0,O2,$(CFLAGS)) +$(OUTPUT)/no_alu32/usdt_o2.test.o: CFLAGS:=$(subst O0,O2,$(CFLAGS)) +endif
I tried your selftest with gcc14 and llvm20 in my environment. See below:
llvm20: Displaying notes found in: .note.stapsdt Owner Data size Description stapsdt 0x0000002f NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt1 Location: 0x00000000000003ac, Base: 0x0000000000000000, Semaphore: 0x0000000000000000 Arguments: 8@-64(%rbp)
gcc14: Displaying notes found in: .note.stapsdt Owner Data size Description stapsdt 0x00000034 NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt1 Location: 0x0000000000000334, Base: 0x0000000000000000, Semaphore: 0x0000000000000000 Arguments: 8@array(,%rax,8)
llvm20 and gcc14 generate different usdt patterns. '8@-64(%rbp)' already supports so with SIB support, the test should pass CI, I think.
- # Define test_verifier test runner. # It is much simpler than test_maps/test_progs and sufficiently different from # them (e.g., test.h is using completely pattern), that it's worth just
diff --git a/tools/testing/selftests/bpf/prog_tests/usdt_o2.c b/tools/testing/selftests/bpf/prog_tests/usdt_o2.c new file mode 100644 index 000000000000..f04b756b3640 --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/usdt_o2.c @@ -0,0 +1,71 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2025 Jiawei Zhao phoenix500526@163.com. */ +#include <test_progs.h>
+#define _SDT_HAS_SEMAPHORES 1 +#include "../sdt.h" +#include "test_usdt_o2.skel.h"
+int lets_test_this(int);
+#define test_value 0xFEDCBA9876543210ULL +#define SEC(name) __attribute__((section(name), used))
+static volatile __u64 array[1] = {test_value}; +unsigned short test_usdt1_semaphore SEC(".probes");
+static __always_inline void trigger_func(void) +{
- /* Base address + offset + (index * scale) */
- if (test_usdt1_semaphore) {
for (volatile int i = 0; i <= 0; i++)STAP_PROBE1(test, usdt1, array[i]);- }
+}
+static void basic_sib_usdt(void) +{
- LIBBPF_OPTS(bpf_usdt_opts, opts);
- struct test_usdt_o2 *skel;
- struct test_usdt_o2__bss *bss;
- int err;
- skel = test_usdt_o2__open_and_load();
- if (!ASSERT_OK_PTR(skel, "skel_open"))
return;- bss = skel->bss;
- bss->my_pid = getpid();
- err = test_usdt_o2__attach(skel);
- if (!ASSERT_OK(err, "skel_attach"))
goto cleanup;- /* usdt1 won't be auto-attached */
- opts.usdt_cookie = 0xcafedeadbeeffeed;
- skel->links.usdt1 = bpf_program__attach_usdt(skel->progs.usdt1,
0 /*self*/, "/proc/self/exe","test", "usdt1", &opts);- if (!ASSERT_OK_PTR(skel->links.usdt1, "usdt1_link"))
goto cleanup;- trigger_func();
- ASSERT_EQ(bss->usdt1_called, 1, "usdt1_called");
- ASSERT_EQ(bss->usdt1_cookie, 0xcafedeadbeeffeed, "usdt1_cookie");
- ASSERT_EQ(bss->usdt1_arg_cnt, 1, "usdt1_arg_cnt");
- ASSERT_EQ(bss->usdt1_arg, test_value, "usdt1_arg");
- ASSERT_EQ(bss->usdt1_arg_ret, 0, "usdt1_arg_ret");
- ASSERT_EQ(bss->usdt1_arg_size, sizeof(array[0]), "usdt1_arg_size");
+cleanup:
- test_usdt_o2__destroy(skel);
+}
+void test_usdt_o2(void) +{
- basic_sib_usdt();
+} diff --git a/tools/testing/selftests/bpf/progs/test_usdt_o2.c b/tools/testing/selftests/bpf/progs/test_usdt_o2.c new file mode 100644 index 000000000000..14602aa54578 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/test_usdt_o2.c @@ -0,0 +1,37 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
+#include "vmlinux.h" +#include <bpf/bpf_helpers.h> +#include <bpf/usdt.bpf.h>
+int my_pid;
+int usdt1_called; +u64 usdt1_cookie; +int usdt1_arg_cnt; +int usdt1_arg_ret; +u64 usdt1_arg; +int usdt1_arg_size;
+SEC("usdt") +int usdt1(struct pt_regs *ctx) +{
- long tmp;
- if (my_pid != (bpf_get_current_pid_tgid() >> 32))
return 0;- __sync_fetch_and_add(&usdt1_called, 1);
- usdt1_cookie = bpf_usdt_cookie(ctx);
- usdt1_arg_cnt = bpf_usdt_arg_cnt(ctx);
- usdt1_arg_ret = bpf_usdt_arg(ctx, 0, &tmp);
- usdt1_arg = (u64)tmp;
- usdt1_arg_size = bpf_usdt_arg_size(ctx, 0);
- return 0;
+}
+char _license[] SEC("license") = "GPL";