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  3. [PATCH bpf-next v11 0/3] libbpf: fix USDT SIB argument handling causing unrecognized register error
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[PATCH bpf-next v11 2/3] selftests/bpf: Add an usdt_o1 test case in selftests to cover SIB handling logic

Jiawei Zhao posted 3 patches 4 months ago
There is a newer version of this series
[PATCH bpf-next v11 2/3] selftests/bpf: Add an usdt_o1 test case in selftests to cover SIB handling logic
Posted by Jiawei Zhao 4 months ago 
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_o1 test case to cover SIB addressing usdt argument spec
  handling logic

Signed-off-by: Jiawei Zhao <phoenix500526@163.com>
---
 .../selftests/bpf/prog_tests/usdt_o1.c        | 70 +++++++++++++++++++
 .../selftests/bpf/progs/test_usdt_o1.c        | 37 ++++++++++
 2 files changed, 107 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/usdt_o1.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_usdt_o1.c

diff --git a/tools/testing/selftests/bpf/prog_tests/usdt_o1.c b/tools/testing/selftests/bpf/prog_tests/usdt_o1.c
new file mode 100644
index 000000000000..706168e804cb
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/usdt_o1.c
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Jiawei Zhao <phoenix500526@163.com>. */
+#include <test_progs.h>
+
+#include "../sdt.h"
+#include "test_usdt_o1.skel.h"
+
+#if (defined(__GNUC__) && !defined(__clang__))
+#pragma GCC optimize("O1")
+#else
+#pragma message("non-gcc compiler: the correct probes might not be installed")
+#endif
+
+
+#define test_value 0xFEDCBA9876543210ULL
+#define SEC(name) __attribute__((section(name), used))
+
+int lets_test_this(int);
+static volatile __u64 array[1] = {test_value};
+
+static __always_inline void trigger_func(void)
+{
+	/* Base address + offset + (index * scale) */
+	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_o1 *skel;
+	struct test_usdt_o1__bss *bss;
+	int err;
+
+	skel = test_usdt_o1__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	bss = skel->bss;
+	bss->my_pid = getpid();
+
+	err = test_usdt_o1__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_o1__destroy(skel);
+}
+
+void test_usdt_o1(void)
+{
+	basic_sib_usdt();
+}
diff --git a/tools/testing/selftests/bpf/progs/test_usdt_o1.c b/tools/testing/selftests/bpf/progs/test_usdt_o1.c
new file mode 100644
index 000000000000..14602aa54578
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_usdt_o1.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";
-- 
2.43.0
Re: [PATCH bpf-next v11 2/3] selftests/bpf: Add an usdt_o1 test case in selftests to cover SIB handling logic
Posted by Andrii Nakryiko 3 months, 4 weeks ago 
On Mon, Aug 18, 2025 at 12:46 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:
> - add usdt_o1 test case to cover SIB addressing usdt argument spec
>   handling logic
>
> Signed-off-by: Jiawei Zhao <phoenix500526@163.com>
> ---
>  .../selftests/bpf/prog_tests/usdt_o1.c        | 70 +++++++++++++++++++
>  .../selftests/bpf/progs/test_usdt_o1.c        | 37 ++++++++++
>  2 files changed, 107 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/usdt_o1.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_usdt_o1.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/usdt_o1.c b/tools/testing/selftests/bpf/prog_tests/usdt_o1.c
> new file mode 100644
> index 000000000000..706168e804cb
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/usdt_o1.c
> @@ -0,0 +1,70 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2025 Jiawei Zhao <phoenix500526@163.com>. */
> +#include <test_progs.h>
> +
> +#include "../sdt.h"
> +#include "test_usdt_o1.skel.h"
> +
> +#if (defined(__GNUC__) && !defined(__clang__))
> +#pragma GCC optimize("O1")

that optimize attribute is a function attribute, while your earlier
version just randomly put it here. Have you tried using that optimize
attribute on a function properly?

One of the points of that attribute suggestion was to avoid the need
to add another file in prog_tests and keeping various USDT test cases
in one test, so can you give that attribute another try and see if it
works?

> +#else
> +#pragma message("non-gcc compiler: the correct probes might not be installed")

hm... non-gcc is expected, so I don't think we should pollute compiler
output with extra messages

> +#endif
> +
> +
> +#define test_value 0xFEDCBA9876543210ULL
> +#define SEC(name) __attribute__((section(name), used))
> +
> +int lets_test_this(int);
> +static volatile __u64 array[1] = {test_value};
> +
> +static __always_inline void trigger_func(void)
> +{
> +       /* Base address + offset + (index * scale) */
> +       for (volatile int i = 0; i <= 0; i++)
> +               STAP_PROBE1(test, usdt1, array[i]);

I think I saw a bunch of mentions that getting desired SIB form for
USDT arg was a challenge, right? Have you checked STAP_PROBE_ASM from
sdt.h? That will allow to define USDT from inside assembly block,
which should give you a lot of control over the shape of the argument.


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