bpf/selftests: Test skipping stacktrace

Add a test case for stacktrace with skip > 0 using a small sized
buffer.  It didn't support skipping entries greater than or equal to
the size of buffer and filled the skipped part with 0.

Signed-off-by: Namhyung Kim <[email protected]>

Author: namhyung

tools/testing/selftests/bpf/prog_tests/stacktrace_map_skip.c

@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include "stacktrace_map_skip.skel.h"
+
+#define TEST_STACK_DEPTH  2
+
+void test_stacktrace_map_skip(void)
+{
+	struct stacktrace_map_skip *skel;
+	int control_map_fd, stackid_hmap_fd, stackmap_fd, stack_amap_fd;
+	int err, stack_trace_len;
+	__u32 key, val, duration = 0;
+
+	skel = stacktrace_map_skip__open_and_load();
+	if (CHECK(!skel, "skel_open_and_load", "skeleton open failed\n"))
+		return;
+
+	/* find map fds */
+	control_map_fd = bpf_map__fd(skel->maps.control_map);
+	if (CHECK_FAIL(control_map_fd < 0))
+		goto out;
+
+	stackid_hmap_fd = bpf_map__fd(skel->maps.stackid_hmap);
+	if (CHECK_FAIL(stackid_hmap_fd < 0))
+		goto out;
+
+	stackmap_fd = bpf_map__fd(skel->maps.stackmap);
+	if (CHECK_FAIL(stackmap_fd < 0))
+		goto out;
+
+	stack_amap_fd = bpf_map__fd(skel->maps.stack_amap);
+	if (CHECK_FAIL(stack_amap_fd < 0))
+		goto out;
+
+	err = stacktrace_map_skip__attach(skel);
+	if (CHECK(err, "skel_attach", "skeleton attach failed\n"))
+		goto out;
+
+	/* give some time for bpf program run */
+	sleep(1);
+
+	/* disable stack trace collection */
+	key = 0;
+	val = 1;
+	bpf_map_update_elem(control_map_fd, &key, &val, 0);
+
+	/* for every element in stackid_hmap, we can find a corresponding one
+	 * in stackmap, and vise versa.
+	 */
+	err = compare_map_keys(stackid_hmap_fd, stackmap_fd);
+	if (CHECK(err, "compare_map_keys stackid_hmap vs. stackmap",
+		  "err %d errno %d\n", err, errno))
+		goto out;
+
+	err = compare_map_keys(stackmap_fd, stackid_hmap_fd);
+	if (CHECK(err, "compare_map_keys stackmap vs. stackid_hmap",
+		  "err %d errno %d\n", err, errno))
+		goto out;
+
+	stack_trace_len = TEST_STACK_DEPTH * sizeof(__u64);
+	err = compare_stack_ips(stackmap_fd, stack_amap_fd, stack_trace_len);
+	if (CHECK(err, "compare_stack_ips stackmap vs. stack_amap",
+		  "err %d errno %d\n", err, errno))
+		goto out;
+
+	if (CHECK(skel->bss->failed, "check skip",
+		  "failed to skip some depth: %d", skel->bss->failed))
+		goto out;
+
+out:
+	stacktrace_map_skip__destroy(skel);
+}

tools/testing/selftests/bpf/progs/stacktrace_map_skip.c

@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+
+#define TEST_STACK_DEPTH         2
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u32);
+} control_map SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 16384);
+	__type(key, __u32);
+	__type(value, __u32);
+} stackid_hmap SEC(".maps");
+
+typedef __u64 stack_trace_t[TEST_STACK_DEPTH];
+
+struct {
+	__uint(type, BPF_MAP_TYPE_STACK_TRACE);
+	__uint(max_entries, 16384);
+	__type(key, __u32);
+	__type(value, stack_trace_t);
+} stackmap SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 16384);
+	__type(key, __u32);
+	__type(value, stack_trace_t);
+} stack_amap SEC(".maps");
+
+/* taken from /sys/kernel/debug/tracing/events/sched/sched_switch/format */
+struct sched_switch_args {
+	unsigned long long pad;
+	char prev_comm[TASK_COMM_LEN];
+	int prev_pid;
+	int prev_prio;
+	long long prev_state;
+	char next_comm[TASK_COMM_LEN];
+	int next_pid;
+	int next_prio;
+};
+
+int failed = 0;
+
+SEC("tracepoint/sched/sched_switch")
+int oncpu(struct sched_switch_args *ctx)
+{
+	__u32 max_len = TEST_STACK_DEPTH * sizeof(__u64);
+	__u32 key = 0, val = 0, *value_p;
+	__u64 *stack_p;
+
+	value_p = bpf_map_lookup_elem(&control_map, &key);
+	if (value_p && *value_p)
+		return 0; /* skip if non-zero *value_p */
+
+	/* it should allow skipping whole buffer size entries */
+	key = bpf_get_stackid(ctx, &stackmap, TEST_STACK_DEPTH);
+	if ((int)key >= 0) {
+		/* The size of stackmap and stack_amap should be the same */
+		bpf_map_update_elem(&stackid_hmap, &key, &val, 0);
+		stack_p = bpf_map_lookup_elem(&stack_amap, &key);
+		if (stack_p) {
+			bpf_get_stack(ctx, stack_p, max_len, TEST_STACK_DEPTH);
+			/* it wrongly skipped all the entries and filled zero */
+			if (stack_p[0] == 0)
+				failed = 1;
+		}
+	} else if ((int)key == -14/*EFAULT*/) {
+		/* old kernel doesn't support skipping that many entries */
+		failed = 2;
+	}
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";