[bpf-next,v4,2/2] selftests/bpf: add BTF.ext line/func info getter tests

Commit Message

Mykyta Yatsenko April 3, 2025, 10:28 p.m. UTC

From: Mykyta Yatsenko <[e-mail]>

Add selftests checking that line and func info retrieved by newly added
libbpf APIs are the same as returned by kernel via bpf_prog_get_info_by_fd.

Signed-off-by: Mykyta Yatsenko <[e-mail]>
---
 .../selftests/bpf/prog_tests/test_btf_ext.c   | 69 +++++++++++++++++++
 .../selftests/bpf/progs/test_btf_ext.c        | 26 +++++++
 2 files changed, 95 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/test_btf_ext.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_btf_ext.c

Comments

Andrii Nakryiko April 4, 2025, 5:19 p.m. UTC | #1

On Thu, Apr 3, 2025 at 3:28 PM Mykyta Yatsenko
<[e-mail]> wrote:
>
> From: Mykyta Yatsenko <[e-mail]>
>
> Add selftests checking that line and func info retrieved by newly added
> libbpf APIs are the same as returned by kernel via bpf_prog_get_info_by_fd.
>
> Signed-off-by: Mykyta Yatsenko <[e-mail]>
> ---
>  .../selftests/bpf/prog_tests/test_btf_ext.c   | 69 +++++++++++++++++++
>  .../selftests/bpf/progs/test_btf_ext.c        | 26 +++++++
>  2 files changed, 95 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/test_btf_ext.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_btf_ext.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/test_btf_ext.c b/tools/testing/selftests/bpf/prog_tests/test_btf_ext.c
> new file mode 100644
> index 000000000000..76d3eb520982
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/test_btf_ext.c
> @@ -0,0 +1,69 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2025 Meta Platforms Inc. */
> +#include <test_progs.h>
> +#include "test_btf_ext.skel.h"
> +#include "btf_helpers.h"
> +
> +static void subtest_line_func_info(void)
> +{
> +       struct test_btf_ext *skel;
> +       struct bpf_prog_info info;
> +       struct bpf_line_info line_info[128], *libbpf_line_info;
> +       struct bpf_func_info func_info[128], *libbpf_func_info;
> +       __u32 info_len = sizeof(info), libbbpf_line_info_cnt, libbbpf_func_info_cnt;
> +       int err, fd;
> +
> +       skel = test_btf_ext__open_and_load();
> +       if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
> +               return;
> +
> +       fd = bpf_program__fd(skel->progs.global_func);
> +
> +       memset(&info, 0, sizeof(info));
> +       info.line_info = ptr_to_u64(&line_info);
> +       info.nr_line_info = sizeof(line_info);
> +       info.line_info_rec_size = sizeof(*line_info);
> +       err = bpf_prog_get_info_by_fd(fd, &info, &info_len);
> +       if (!ASSERT_OK(err, "prog_line_info"))
> +               goto out;
> +
> +       libbpf_line_info = bpf_program__line_info(skel->progs.global_func);
> +       libbbpf_line_info_cnt = bpf_program__line_info_cnt(skel->progs.global_func);
> +
> +       memset(&info, 0, sizeof(info));
> +       info.func_info = ptr_to_u64(&func_info);
> +       info.nr_func_info = sizeof(func_info);
> +       info.func_info_rec_size = sizeof(*func_info);
> +       err = bpf_prog_get_info_by_fd(fd, &info, &info_len);
> +       if (!ASSERT_OK(err, "prog_func_info"))
> +               goto out;
> +
> +       libbpf_func_info = bpf_program__func_info(skel->progs.global_func);
> +       libbbpf_func_info_cnt = bpf_program__func_info_cnt(skel->progs.global_func);
> +
> +       if (!ASSERT_OK_PTR(libbpf_line_info, "bpf_program__line_info"))
> +               goto out;
> +       if (!ASSERT_EQ(libbbpf_line_info_cnt, info.nr_line_info, "line_info_cnt"))
> +               goto out;
> +       if (!ASSERT_OK_PTR(libbpf_func_info, "bpf_program__func_info"))
> +               goto out;
> +       if (!ASSERT_EQ(libbbpf_func_info_cnt, info.nr_func_info, "func_info_cnt"))
> +               goto out;
> +       /* Skip checks on s390x as it seems to be adding some preamble to function entry point
> +        * shifting instruction offsets by 1 byte
> +        */
> +#if !defined(__TARGET_ARCH_s390) && !defined (__s390x__)
> +       ASSERT_MEMEQ(libbpf_line_info, line_info, libbbpf_line_info_cnt * sizeof(*line_info),
> +                    "line_info");
> +       ASSERT_MEMEQ(libbpf_func_info, func_info, libbbpf_func_info_cnt * sizeof(*func_info),
> +                    "func_info");
> +#endif
> +out:
> +       test_btf_ext__destroy(skel);
> +}
> +
> +void test_btf_ext(void)
> +{
> +       if (test__start_subtest("line_func_info"))
> +               subtest_line_func_info();
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_btf_ext.c b/tools/testing/selftests/bpf/progs/test_btf_ext.c
> new file mode 100644
> index 000000000000..e4efcf823f6b
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_btf_ext.c
> @@ -0,0 +1,26 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright (c) 2025 Meta Platforms Inc. */
> +
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include "bpf_misc.h"
> +
> +char _license[] SEC("license") = "GPL";
> +
> +__noinline static void f0(void)
> +{
> +       __u8 a = 1;

ok, so this will generate

       0:       b4 01 00 00 01 00 00 00 w1 = 0x1
       1:       73 1a ff ff 00 00 00 00 *(u8 *)(r10 - 0x1) = w1

And on s390x (and a bunch of other architectures), verifier will
inject extra special zero-extension instruction after `w1 = 0x1`,
which shifts all the instruction indices. You can look at how
bpf_jit_needs_zext() is defined and used in verifier.c, if you are
curious for details.

But given the purpose of the test is to make sure that libbpf gives us
full and correct information, all that zext business is a distraction
and we should just avoid all this.

So, let's just use full __u64 variables here and be done with this
(meaning, no s390x exceptions, just simple BPF code that doesn't get
enhanced or transformed by the verifier).

pw-bot: cr

> +       __u8 b = 2;
> +       __u8 c = 3;
> +
> +       __sink(a);
> +       __sink(b);
> +       __sink(c);
> +}
> +
> +SEC("xdp")
> +int global_func(struct xdp_md *xdp)
> +{
> +       f0();
> +       return XDP_DROP;
> +}
> --
> 2.49.0
>

Patch

diff --git a/tools/testing/selftests/bpf/prog_tests/test_btf_ext.c b/tools/testing/selftests/bpf/prog_tests/test_btf_ext.c
new file mode 100644
index 000000000000..76d3eb520982
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/test_btf_ext.c
@@ -0,0 +1,69 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms Inc. */
+#include <test_progs.h>
+#include "test_btf_ext.skel.h"
+#include "btf_helpers.h"
+
+static void subtest_line_func_info(void)
+{
+	struct test_btf_ext *skel;
+	struct bpf_prog_info info;
+	struct bpf_line_info line_info[128], *libbpf_line_info;
+	struct bpf_func_info func_info[128], *libbpf_func_info;
+	__u32 info_len = sizeof(info), libbbpf_line_info_cnt, libbbpf_func_info_cnt;
+	int err, fd;
+
+	skel = test_btf_ext__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
+		return;
+
+	fd = bpf_program__fd(skel->progs.global_func);
+
+	memset(&info, 0, sizeof(info));
+	info.line_info = ptr_to_u64(&line_info);
+	info.nr_line_info = sizeof(line_info);
+	info.line_info_rec_size = sizeof(*line_info);
+	err = bpf_prog_get_info_by_fd(fd, &info, &info_len);
+	if (!ASSERT_OK(err, "prog_line_info"))
+		goto out;
+
+	libbpf_line_info = bpf_program__line_info(skel->progs.global_func);
+	libbbpf_line_info_cnt = bpf_program__line_info_cnt(skel->progs.global_func);
+
+	memset(&info, 0, sizeof(info));
+	info.func_info = ptr_to_u64(&func_info);
+	info.nr_func_info = sizeof(func_info);
+	info.func_info_rec_size = sizeof(*func_info);
+	err = bpf_prog_get_info_by_fd(fd, &info, &info_len);
+	if (!ASSERT_OK(err, "prog_func_info"))
+		goto out;
+
+	libbpf_func_info = bpf_program__func_info(skel->progs.global_func);
+	libbbpf_func_info_cnt = bpf_program__func_info_cnt(skel->progs.global_func);
+
+	if (!ASSERT_OK_PTR(libbpf_line_info, "bpf_program__line_info"))
+		goto out;
+	if (!ASSERT_EQ(libbbpf_line_info_cnt, info.nr_line_info, "line_info_cnt"))
+		goto out;
+	if (!ASSERT_OK_PTR(libbpf_func_info, "bpf_program__func_info"))
+		goto out;
+	if (!ASSERT_EQ(libbbpf_func_info_cnt, info.nr_func_info, "func_info_cnt"))
+		goto out;
+	/* Skip checks on s390x as it seems to be adding some preamble to function entry point
+	 * shifting instruction offsets by 1 byte
+	 */
+#if !defined(__TARGET_ARCH_s390) && !defined (__s390x__)
+	ASSERT_MEMEQ(libbpf_line_info, line_info, libbbpf_line_info_cnt * sizeof(*line_info),
+		     "line_info");
+	ASSERT_MEMEQ(libbpf_func_info, func_info, libbbpf_func_info_cnt * sizeof(*func_info),
+		     "func_info");
+#endif
+out:
+	test_btf_ext__destroy(skel);
+}
+
+void test_btf_ext(void)
+{
+	if (test__start_subtest("line_func_info"))
+		subtest_line_func_info();
+}
diff --git a/tools/testing/selftests/bpf/progs/test_btf_ext.c b/tools/testing/selftests/bpf/progs/test_btf_ext.c
new file mode 100644
index 000000000000..e4efcf823f6b
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_btf_ext.c
@@ -0,0 +1,26 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2025 Meta Platforms Inc. */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+__noinline static void f0(void)
+{
+	__u8 a = 1;
+	__u8 b = 2;
+	__u8 c = 3;
+
+	__sink(a);
+	__sink(b);
+	__sink(c);
+}
+
+SEC("xdp")
+int global_func(struct xdp_md *xdp)
+{
+	f0();
+	return XDP_DROP;
+}