[PATCH bpf-next 0/6] Improve libbpf support of old kernels

[PATCH bpf-next 0/6] Improve libbpf support of old kernels

[Andrii Nakryiko]

This patch set improves libbpf's support of old kernels, missing features like
BTF support, global variables support, etc.

Most critical one is a silent drop of CO-RE relocations if libbpf fails to
load BTF (despite sanitization efforts). This is frequently the case for
kernels that have no BTF support whatsoever. There are still useful BPF
applications that could work on such kernels and do rely on CO-RE. To that
end, this series revamps the way BTF is handled in libbpf. Failure to load BTF
into kernel doesn't prevent libbpf from using BTF in its full capability
(e.g., for CO-RE relocations) internally.

Another issue that was identified was reliance of perf_buffer__new() on
BPF_OBJ_GET_INFO_BY_FD command, which is more recent that perf_buffer support
itself. Furthermore, BPF_OBJ_GET_INFO_BY_FD is needed just for some sanity
checks to provide better user errors, so could be safely omitted if kernel
doesn't provide it.

Perf_buffer selftest was adjusted to use skeleton, instead of bpf_prog_load().
The latter uses BPF_F_TEST_RND_HI32 flag, which is a relatively recent
addition and unnecessary fails selftest in libbpf's Travis CI tests. By using
skeleton we both get a shorter selftest and it work on pretty ancient kernels,
giving better libbpf test coverage.

One new selftest was added that relies on basic CO-RE features, but otherwise
doesn't expect any recent features (like global variables) from kernel. Again,
it's good to have better coverage of old kernels in libbpf testing.

Cc: Matthew Lim <matthewlim@fb.com>

Andrii Nakryiko (6):
  libbpf: make BTF finalization strict
  libbpf: add btf__set_fd() for more control over loaded BTF FD
  libbpf: improve BTF sanitization handling
  selftests/bpf: add test relying only on CO-RE and no recent kernel
    features
  libbpf: handle missing BPF_OBJ_GET_INFO_BY_FD gracefully in
    perf_buffer
  selftests/bpf: switch perf_buffer test to tracepoint and skeleton

 tools/lib/bpf/btf.c                           |   7 +-
 tools/lib/bpf/btf.h                           |   1 +
 tools/lib/bpf/libbpf.c                        | 150 ++++++++++--------
 tools/lib/bpf/libbpf.map                      |   1 +
 .../selftests/bpf/prog_tests/core_retro.c     |  33 ++++
 .../selftests/bpf/prog_tests/perf_buffer.c    |  42 ++---
 .../selftests/bpf/progs/test_core_retro.c     |  30 ++++
 .../selftests/bpf/progs/test_perf_buffer.c    |   4 +-
 8 files changed, 167 insertions(+), 101 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/core_retro.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_core_retro.c

-- 
2.24.1

[PATCH bpf-next 1/6] libbpf: make BTF finalization strict

[Andrii Nakryiko]

With valid ELF and valid BTF, there is no reason (apart from bugs) why BTF
finalization should fail. So make it strict and return error if it fails. This
makes CO-RE relocation more reliable, as they are not going to be just
silently skipped, if BTF finalization failed.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 tools/lib/bpf/libbpf.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 4ea7f4f1a691..f4a1cf7f4873 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2473,19 +2473,11 @@ static int bpf_object__finalize_btf(struct bpf_object *obj)
 		return 0;
 
 	err = btf__finalize_data(obj, obj->btf);
-	if (!err)
-		return 0;
-
-	pr_warn("Error finalizing %s: %d.\n", BTF_ELF_SEC, err);
-	btf__free(obj->btf);
-	obj->btf = NULL;
-	btf_ext__free(obj->btf_ext);
-	obj->btf_ext = NULL;
-
-	if (libbpf_needs_btf(obj)) {
-		pr_warn("BTF is required, but is missing or corrupted.\n");
-		return -ENOENT;
+	if (err) {
+		pr_warn("Error finalizing %s: %d.\n", BTF_ELF_SEC, err);
+		return err;
 	}
+
 	return 0;
 }
 
-- 
2.24.1

[PATCH bpf-next 2/6] libbpf: add btf__set_fd() for more control over loaded BTF FD

[Andrii Nakryiko]

Add setter for BTF FD to allow application more fine-grained control in more
advanced scenarios. Storing BTF FD inside `struct btf` provides little benefit
and probably would be better done differently (e.g., btf__load() could just
return FD on success), but we are stuck with this due to backwards
compatibility. The main problem is that it's impossible to load BTF and than
free user-space memory, but keep FD intact, because `struct btf` assumes
ownership of that FD upon successful load and will attempt to close it during
btf__free(). To allow callers (e.g., libbpf itself for BTF sanitization) to
have more control over this, add btf__set_fd() to allow to reset FD
arbitrarily, if necessary.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 tools/lib/bpf/btf.c      | 7 ++++++-
 tools/lib/bpf/btf.h      | 1 +
 tools/lib/bpf/libbpf.map | 1 +
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index bfef3d606b54..c8861c9e3635 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -389,7 +389,7 @@ void btf__free(struct btf *btf)
 	if (!btf)
 		return;
 
-	if (btf->fd != -1)
+	if (btf->fd >= 0)
 		close(btf->fd);
 
 	free(btf->data);
@@ -700,6 +700,11 @@ int btf__fd(const struct btf *btf)
 	return btf->fd;
 }
 
+void btf__set_fd(struct btf *btf, int fd)
+{
+	btf->fd = fd;
+}
+
 const void *btf__get_raw_data(const struct btf *btf, __u32 *size)
 {
 	*size = btf->data_size;
diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index 06cd1731c154..173eff23c472 100644
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -79,6 +79,7 @@ LIBBPF_API __s64 btf__resolve_size(const struct btf *btf, __u32 type_id);
 LIBBPF_API int btf__resolve_type(const struct btf *btf, __u32 type_id);
 LIBBPF_API int btf__align_of(const struct btf *btf, __u32 id);
 LIBBPF_API int btf__fd(const struct btf *btf);
+LIBBPF_API void btf__set_fd(struct btf *btf, int fd);
 LIBBPF_API const void *btf__get_raw_data(const struct btf *btf, __u32 *size);
 LIBBPF_API const char *btf__name_by_offset(const struct btf *btf, __u32 offset);
 LIBBPF_API int btf__get_from_id(__u32 id, struct btf **btf);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 6544d2cd1ed6..c5d5c7664c3b 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -288,4 +288,5 @@ LIBBPF_0.1.0 {
 		bpf_map__value_size;
 		bpf_program__autoload;
 		bpf_program__set_autoload;
+		btf__set_fd;
 } LIBBPF_0.0.9;
-- 
2.24.1

[PATCH bpf-next 3/6] libbpf: improve BTF sanitization handling

[Andrii Nakryiko]

Change sanitization process to preserve original BTF, which might be used by
libbpf itself for Kconfig externs, CO-RE relocs, etc, even if kernel is old
and doesn't support BTF. To achieve that, if libbpf detects the need for BTF
sanitization, it would clone original BTF, sanitize it in-place, attempt to
load it into kernel, and if successful, will preserve loaded BTF FD in
original `struct btf`, while freeing sanitized local copy.

If kernel doesn't support any BTF, original btf and btf_ext will still be
preserved to be used later for CO-RE relocation and other BTF-dependent libbpf
features, which don't dependon kernel BTF support.

Patch takes care to not specify BTF and BTF.ext features when loading BPF
programs and/or maps, if it was detected that kernel doesn't support BTF
features.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 tools/lib/bpf/libbpf.c | 103 +++++++++++++++++++++++------------------
 1 file changed, 58 insertions(+), 45 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index f4a1cf7f4873..b4f50d12f51f 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2338,18 +2338,23 @@ static bool section_have_execinstr(struct bpf_object *obj, int idx)
 	return false;
 }
 
-static void bpf_object__sanitize_btf(struct bpf_object *obj)
+static bool btf_needs_sanitization(struct bpf_object *obj)
+{
+	bool has_func_global = obj->caps.btf_func_global;
+	bool has_datasec = obj->caps.btf_datasec;
+	bool has_func = obj->caps.btf_func;
+
+	return !has_func || !has_datasec || !has_func_global;
+}
+
+static void bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
 {
 	bool has_func_global = obj->caps.btf_func_global;
 	bool has_datasec = obj->caps.btf_datasec;
 	bool has_func = obj->caps.btf_func;
-	struct btf *btf = obj->btf;
 	struct btf_type *t;
 	int i, j, vlen;
 
-	if (!obj->btf || (has_func && has_datasec && has_func_global))
-		return;
-
 	for (i = 1; i <= btf__get_nr_types(btf); i++) {
 		t = (struct btf_type *)btf__type_by_id(btf, i);
 
@@ -2402,17 +2407,6 @@ static void bpf_object__sanitize_btf(struct bpf_object *obj)
 	}
 }
 
-static void bpf_object__sanitize_btf_ext(struct bpf_object *obj)
-{
-	if (!obj->btf_ext)
-		return;
-
-	if (!obj->caps.btf_func) {
-		btf_ext__free(obj->btf_ext);
-		obj->btf_ext = NULL;
-	}
-}
-
 static bool libbpf_needs_btf(const struct bpf_object *obj)
 {
 	return obj->efile.btf_maps_shndx >= 0 ||
@@ -2530,30 +2524,50 @@ static int bpf_object__load_vmlinux_btf(struct bpf_object *obj)
 
 static int bpf_object__sanitize_and_load_btf(struct bpf_object *obj)
 {
+	struct btf *kern_btf = obj->btf;
+	bool btf_mandatory, sanitize;
 	int err = 0;
 
 	if (!obj->btf)
 		return 0;
 
-	bpf_object__sanitize_btf(obj);
-	bpf_object__sanitize_btf_ext(obj);
+	sanitize = btf_needs_sanitization(obj);
+	if (sanitize) {
+		const void *orig_data;
+		void *san_data;
+		__u32 sz;
 
-	err = btf__load(obj->btf);
-	if (err) {
-		pr_warn("Error loading %s into kernel: %d.\n",
-			BTF_ELF_SEC, err);
-		btf__free(obj->btf);
-		obj->btf = NULL;
-		/* btf_ext can't exist without btf, so free it as well */
-		if (obj->btf_ext) {
-			btf_ext__free(obj->btf_ext);
-			obj->btf_ext = NULL;
-		}
+		/* clone BTF to sanitize a copy and leave the original intact */
+		orig_data = btf__get_raw_data(obj->btf, &sz);
+		san_data = malloc(sz);
+		if (!san_data)
+			return -ENOMEM;
+		memcpy(san_data, orig_data, sz);
+		kern_btf = btf__new(san_data, sz);
+		if (IS_ERR(kern_btf))
+			return PTR_ERR(kern_btf);
 
-		if (kernel_needs_btf(obj))
-			return err;
+		bpf_object__sanitize_btf(obj, kern_btf);
 	}
-	return 0;
+
+	err = btf__load(kern_btf);
+	if (sanitize) {
+		if (!err) {
+			/* move fd to libbpf's BTF */
+			btf__set_fd(obj->btf, btf__fd(kern_btf));
+			btf__set_fd(kern_btf, -1);
+		}
+		btf__free(kern_btf);
+	}
+	if (err) {
+		btf_mandatory = kernel_needs_btf(obj);
+		pr_warn("Error loading .BTF into kernel: %d. %s\n", err,
+			btf_mandatory ? "BTF is mandatory, can't proceed."
+				      : "BTF is optional, ignoring.");
+		if (!btf_mandatory)
+			err = 0;
+	}
+	return err;
 }
 
 static int bpf_object__elf_collect(struct bpf_object *obj)
@@ -3777,7 +3791,7 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map)
 	create_attr.btf_fd = 0;
 	create_attr.btf_key_type_id = 0;
 	create_attr.btf_value_type_id = 0;
-	if (obj->btf && !bpf_map_find_btf_info(obj, map)) {
+	if (obj->btf && btf__fd(obj->btf) >= 0 && !bpf_map_find_btf_info(obj, map)) {
 		create_attr.btf_fd = btf__fd(obj->btf);
 		create_attr.btf_key_type_id = map->btf_key_type_id;
 		create_attr.btf_value_type_id = map->btf_value_type_id;
@@ -5361,18 +5375,17 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
 		load_attr.kern_version = kern_version;
 		load_attr.prog_ifindex = prog->prog_ifindex;
 	}
-	/* if .BTF.ext was loaded, kernel supports associated BTF for prog */
-	if (prog->obj->btf_ext)
-		btf_fd = bpf_object__btf_fd(prog->obj);
-	else
-		btf_fd = -1;
-	load_attr.prog_btf_fd = btf_fd >= 0 ? btf_fd : 0;
-	load_attr.func_info = prog->func_info;
-	load_attr.func_info_rec_size = prog->func_info_rec_size;
-	load_attr.func_info_cnt = prog->func_info_cnt;
-	load_attr.line_info = prog->line_info;
-	load_attr.line_info_rec_size = prog->line_info_rec_size;
-	load_attr.line_info_cnt = prog->line_info_cnt;
+	/* specify func_info/line_info only if kernel supports them */
+	btf_fd = bpf_object__btf_fd(prog->obj);
+	if (btf_fd >= 0 && prog->obj->caps.btf_func) {
+		load_attr.prog_btf_fd = btf_fd;
+		load_attr.func_info = prog->func_info;
+		load_attr.func_info_rec_size = prog->func_info_rec_size;
+		load_attr.func_info_cnt = prog->func_info_cnt;
+		load_attr.line_info = prog->line_info;
+		load_attr.line_info_rec_size = prog->line_info_rec_size;
+		load_attr.line_info_cnt = prog->line_info_cnt;
+	}
 	load_attr.log_level = prog->log_level;
 	load_attr.prog_flags = prog->prog_flags;
 
-- 
2.24.1

[PATCH bpf-next 4/6] selftests/bpf: add test relying only on CO-RE and no recent kernel features

[Andrii Nakryiko]

Add a test that relies on CO-RE, but doesn't expect any of the recent
features, not available on old kernels. This is useful for Travis CI tests
running against very old kernels (e.g., libbpf has 4.9 kernel testing now), to
verify that CO-RE still works, even if kernel itself doesn't support BTF yet,
as long as there is .BTF embedded into vmlinux image by pahole. Given most of
CO-RE doesn't require any kernel awareness of BTF, it is a useful test to
validate that libbpf's BTF sanitization is working well even with ancient
kernels.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 .../selftests/bpf/prog_tests/core_retro.c     | 33 +++++++++++++++++++
 .../selftests/bpf/progs/test_core_retro.c     | 30 +++++++++++++++++
 2 files changed, 63 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/core_retro.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_core_retro.c

diff --git a/tools/testing/selftests/bpf/prog_tests/core_retro.c b/tools/testing/selftests/bpf/prog_tests/core_retro.c
new file mode 100644
index 000000000000..78e30d3a23d5
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/core_retro.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2020 Facebook
+#define _GNU_SOURCE
+#include <test_progs.h>
+#include "test_core_retro.skel.h"
+
+void test_core_retro(void)
+{
+	int err, zero = 0, res, duration = 0;
+	struct test_core_retro *skel;
+
+	/* load program */
+	skel = test_core_retro__open_and_load();
+	if (CHECK(!skel, "skel_load", "skeleton open/load failed\n"))
+		goto out_close;
+
+	/* attach probe */
+	err = test_core_retro__attach(skel);
+	if (CHECK(err, "attach_kprobe", "err %d\n", err))
+		goto out_close;
+
+	/* trigger */
+	usleep(1);
+
+	err = bpf_map_lookup_elem(bpf_map__fd(skel->maps.results), &zero, &res);
+	if (CHECK(err, "map_lookup", "failed to lookup result: %d\n", errno))
+		goto out_close;
+
+	CHECK(res != getpid(), "pid_check", "got %d != exp %d\n", res, getpid());
+
+out_close:
+	test_core_retro__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_core_retro.c b/tools/testing/selftests/bpf/progs/test_core_retro.c
new file mode 100644
index 000000000000..75c60c3c29cf
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_core_retro.c
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2020 Facebook
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
+
+struct task_struct {
+	int tgid;
+} __attribute__((preserve_access_index));
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, int);
+} results SEC(".maps");
+
+SEC("tp/raw_syscalls/sys_enter")
+int handle_sys_enter(void *ctx)
+{
+	struct task_struct *task = (void *)bpf_get_current_task();
+	int tgid = BPF_CORE_READ(task, tgid);
+	int zero = 0;
+
+	bpf_map_update_elem(&results, &zero, &tgid, 0);
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.24.1

[PATCH bpf-next 5/6] libbpf: handle missing BPF_OBJ_GET_INFO_BY_FD gracefully in perf_buffer

[Andrii Nakryiko]

perf_buffer__new() is relying on BPF_OBJ_GET_INFO_BY_FD availability for few
sanity checks. OBJ_GET_INFO for maps is actually much more recent feature than
perf_buffer support itself, so this causes unnecessary problems on old kernels
before BPF_OBJ_GET_INFO_BY_FD was added.

This patch makes those sanity checks optional and just assumes best if command
is not supported. If user specified something incorrectly (e.g., wrong map
type), kernel will reject it later anyway, except user won't get a nice
explanation as to why it failed. This seems like a good trade off for
supporting perf_buffer on old kernels.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 tools/lib/bpf/libbpf.c | 31 ++++++++++++++++++++-----------
 1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b4f50d12f51f..6f86b57a7e24 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8587,7 +8587,7 @@ static struct perf_buffer *__perf_buffer__new(int map_fd, size_t page_cnt,
 					      struct perf_buffer_params *p)
 {
 	const char *online_cpus_file = "/sys/devices/system/cpu/online";
-	struct bpf_map_info map = {};
+	struct bpf_map_info map;
 	char msg[STRERR_BUFSIZE];
 	struct perf_buffer *pb;
 	bool *online = NULL;
@@ -8600,19 +8600,28 @@ static struct perf_buffer *__perf_buffer__new(int map_fd, size_t page_cnt,
 		return ERR_PTR(-EINVAL);
 	}
 
+	/* best-effort sanity checks */
+	memset(&map, 0, sizeof(map));
 	map_info_len = sizeof(map);
 	err = bpf_obj_get_info_by_fd(map_fd, &map, &map_info_len);
 	if (err) {
 		err = -errno;
-		pr_warn("failed to get map info for map FD %d: %s\n",
-			map_fd, libbpf_strerror_r(err, msg, sizeof(msg)));
-		return ERR_PTR(err);
-	}
-
-	if (map.type != BPF_MAP_TYPE_PERF_EVENT_ARRAY) {
-		pr_warn("map '%s' should be BPF_MAP_TYPE_PERF_EVENT_ARRAY\n",
-			map.name);
-		return ERR_PTR(-EINVAL);
+		/* if BPF_OBJ_GET_INFO_BY_FD is supported, will return
+		 * -EBADFD, -EFAULT, or -E2BIG on real error
+		 */
+		if (err != -EINVAL) {
+			pr_warn("failed to get map info for map FD %d: %s\n",
+				map_fd, libbpf_strerror_r(err, msg, sizeof(msg)));
+			return ERR_PTR(err);
+		}
+		pr_debug("failed to get map info for FD %d; API not supported? Ignoring...\n",
+			 map_fd);
+	} else {
+		if (map.type != BPF_MAP_TYPE_PERF_EVENT_ARRAY) {
+			pr_warn("map '%s' should be BPF_MAP_TYPE_PERF_EVENT_ARRAY\n",
+				map.name);
+			return ERR_PTR(-EINVAL);
+		}
 	}
 
 	pb = calloc(1, sizeof(*pb));
@@ -8644,7 +8653,7 @@ static struct perf_buffer *__perf_buffer__new(int map_fd, size_t page_cnt,
 			err = pb->cpu_cnt;
 			goto error;
 		}
-		if (map.max_entries < pb->cpu_cnt)
+		if (map.max_entries && map.max_entries < pb->cpu_cnt)
 			pb->cpu_cnt = map.max_entries;
 	}
 
-- 
2.24.1

[PATCH bpf-next 6/6] selftests/bpf: switch perf_buffer test to tracepoint and skeleton

[Andrii Nakryiko]

Switch perf_buffer test to use skeleton to avoid use of bpf_prog_load() and
make test a bit more succinct. Also switch BPF program to use tracepoint
instead of kprobe, as that allows to support older kernels, which had
tracepoint support before kprobe support in the form that libbpf expects
(i.e., libbpf expects /sys/bus/event_source/devices/kprobe/type, which doesn't
always exist on old kernels).

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 .../selftests/bpf/prog_tests/perf_buffer.c    | 42 ++++++-------------
 .../selftests/bpf/progs/test_perf_buffer.c    |  4 +-
 2 files changed, 14 insertions(+), 32 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/perf_buffer.c b/tools/testing/selftests/bpf/prog_tests/perf_buffer.c
index a122ce3b360e..c33ec180b3f2 100644
--- a/tools/testing/selftests/bpf/prog_tests/perf_buffer.c
+++ b/tools/testing/selftests/bpf/prog_tests/perf_buffer.c
@@ -4,6 +4,7 @@
 #include <sched.h>
 #include <sys/socket.h>
 #include <test_progs.h>
+#include "test_perf_buffer.skel.h"
 #include "bpf/libbpf_internal.h"
 
 /* AddressSanitizer sometimes crashes due to data dereference below, due to
@@ -25,16 +26,11 @@ static void on_sample(void *ctx, int cpu, void *data, __u32 size)
 
 void test_perf_buffer(void)
 {
-	int err, prog_fd, on_len, nr_on_cpus = 0,  nr_cpus, i, duration = 0;
-	const char *prog_name = "kprobe/sys_nanosleep";
-	const char *file = "./test_perf_buffer.o";
+	int err, on_len, nr_on_cpus = 0,  nr_cpus, i, duration = 0;
 	struct perf_buffer_opts pb_opts = {};
-	struct bpf_map *perf_buf_map;
+	struct test_perf_buffer *skel;
 	cpu_set_t cpu_set, cpu_seen;
-	struct bpf_program *prog;
-	struct bpf_object *obj;
 	struct perf_buffer *pb;
-	struct bpf_link *link;
 	bool *online;
 
 	nr_cpus = libbpf_num_possible_cpus();
@@ -51,33 +47,21 @@ void test_perf_buffer(void)
 			nr_on_cpus++;
 
 	/* load program */
-	err = bpf_prog_load(file, BPF_PROG_TYPE_KPROBE, &obj, &prog_fd);
-	if (CHECK(err, "obj_load", "err %d errno %d\n", err, errno)) {
-		obj = NULL;
-		goto out_close;
-	}
-
-	prog = bpf_object__find_program_by_title(obj, prog_name);
-	if (CHECK(!prog, "find_probe", "prog '%s' not found\n", prog_name))
+	skel = test_perf_buffer__open_and_load();
+	if (CHECK(!skel, "skel_load", "skeleton open/load failed\n"))
 		goto out_close;
 
-	/* load map */
-	perf_buf_map = bpf_object__find_map_by_name(obj, "perf_buf_map");
-	if (CHECK(!perf_buf_map, "find_perf_buf_map", "not found\n"))
-		goto out_close;
-
-	/* attach kprobe */
-	link = bpf_program__attach_kprobe(prog, false /* retprobe */,
-					  SYS_NANOSLEEP_KPROBE_NAME);
-	if (CHECK(IS_ERR(link), "attach_kprobe", "err %ld\n", PTR_ERR(link)))
+	/* attach probe */
+	err = test_perf_buffer__attach(skel);
+	if (CHECK(err, "attach_kprobe", "err %d\n", err))
 		goto out_close;
 
 	/* set up perf buffer */
 	pb_opts.sample_cb = on_sample;
 	pb_opts.ctx = &cpu_seen;
-	pb = perf_buffer__new(bpf_map__fd(perf_buf_map), 1, &pb_opts);
+	pb = perf_buffer__new(bpf_map__fd(skel->maps.perf_buf_map), 1, &pb_opts);
 	if (CHECK(IS_ERR(pb), "perf_buf__new", "err %ld\n", PTR_ERR(pb)))
-		goto out_detach;
+		goto out_close;
 
 	/* trigger kprobe on every CPU */
 	CPU_ZERO(&cpu_seen);
@@ -94,7 +78,7 @@ void test_perf_buffer(void)
 					     &cpu_set);
 		if (err && CHECK(err, "set_affinity", "cpu #%d, err %d\n",
 				 i, err))
-			goto out_detach;
+			goto out_close;
 
 		usleep(1);
 	}
@@ -110,9 +94,7 @@ void test_perf_buffer(void)
 
 out_free_pb:
 	perf_buffer__free(pb);
-out_detach:
-	bpf_link__destroy(link);
 out_close:
-	bpf_object__close(obj);
+	test_perf_buffer__destroy(skel);
 	free(online);
 }
diff --git a/tools/testing/selftests/bpf/progs/test_perf_buffer.c b/tools/testing/selftests/bpf/progs/test_perf_buffer.c
index ad59c4c9aba8..8207a2dc2f9d 100644
--- a/tools/testing/selftests/bpf/progs/test_perf_buffer.c
+++ b/tools/testing/selftests/bpf/progs/test_perf_buffer.c
@@ -12,8 +12,8 @@ struct {
 	__uint(value_size, sizeof(int));
 } perf_buf_map SEC(".maps");
 
-SEC("kprobe/sys_nanosleep")
-int BPF_KPROBE(handle_sys_nanosleep_entry)
+SEC("tp/raw_syscalls/sys_enter")
+int handle_sys_enter(void *ctx)
 {
 	int cpu = bpf_get_smp_processor_id();
 
-- 
2.24.1

Re: [PATCH bpf-next 0/6] Improve libbpf support of old kernels

[Daniel Borkmann]

On 7/8/20 3:53 AM, Andrii Nakryiko wrote:
> This patch set improves libbpf's support of old kernels, missing features like
> BTF support, global variables support, etc.
> 
> Most critical one is a silent drop of CO-RE relocations if libbpf fails to
> load BTF (despite sanitization efforts). This is frequently the case for
> kernels that have no BTF support whatsoever. There are still useful BPF
> applications that could work on such kernels and do rely on CO-RE. To that
> end, this series revamps the way BTF is handled in libbpf. Failure to load BTF
> into kernel doesn't prevent libbpf from using BTF in its full capability
> (e.g., for CO-RE relocations) internally.
> 
> Another issue that was identified was reliance of perf_buffer__new() on
> BPF_OBJ_GET_INFO_BY_FD command, which is more recent that perf_buffer support
> itself. Furthermore, BPF_OBJ_GET_INFO_BY_FD is needed just for some sanity
> checks to provide better user errors, so could be safely omitted if kernel
> doesn't provide it.
> 
> Perf_buffer selftest was adjusted to use skeleton, instead of bpf_prog_load().
> The latter uses BPF_F_TEST_RND_HI32 flag, which is a relatively recent
> addition and unnecessary fails selftest in libbpf's Travis CI tests. By using
> skeleton we both get a shorter selftest and it work on pretty ancient kernels,
> giving better libbpf test coverage.
> 
> One new selftest was added that relies on basic CO-RE features, but otherwise
> doesn't expect any recent features (like global variables) from kernel. Again,
> it's good to have better coverage of old kernels in libbpf testing.
> 
> Cc: Matthew Lim <matthewlim@fb.com>
> 
> Andrii Nakryiko (6):
>    libbpf: make BTF finalization strict
>    libbpf: add btf__set_fd() for more control over loaded BTF FD
>    libbpf: improve BTF sanitization handling
>    selftests/bpf: add test relying only on CO-RE and no recent kernel
>      features
>    libbpf: handle missing BPF_OBJ_GET_INFO_BY_FD gracefully in
>      perf_buffer
>    selftests/bpf: switch perf_buffer test to tracepoint and skeleton
> 
>   tools/lib/bpf/btf.c                           |   7 +-
>   tools/lib/bpf/btf.h                           |   1 +
>   tools/lib/bpf/libbpf.c                        | 150 ++++++++++--------
>   tools/lib/bpf/libbpf.map                      |   1 +
>   .../selftests/bpf/prog_tests/core_retro.c     |  33 ++++
>   .../selftests/bpf/prog_tests/perf_buffer.c    |  42 ++---
>   .../selftests/bpf/progs/test_core_retro.c     |  30 ++++
>   .../selftests/bpf/progs/test_perf_buffer.c    |   4 +-
>   8 files changed, 167 insertions(+), 101 deletions(-)
>   create mode 100644 tools/testing/selftests/bpf/prog_tests/core_retro.c
>   create mode 100644 tools/testing/selftests/bpf/progs/test_core_retro.c
> 

Applied, thanks!