selftests/bpf: 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 <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Acked-by: Yonghong Song <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

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

···
+// 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 stackid_hmap_fd, stackmap_fd, stack_amap_fd;
+	int err, stack_trace_len;
+
+	skel = stacktrace_map_skip__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
+		return;
+
+	/* find map fds */
+	stackid_hmap_fd = bpf_map__fd(skel->maps.stackid_hmap);
+	if (!ASSERT_GE(stackid_hmap_fd, 0, "stackid_hmap fd"))
+		goto out;
+
+	stackmap_fd = bpf_map__fd(skel->maps.stackmap);
+	if (!ASSERT_GE(stackmap_fd, 0, "stackmap fd"))
+		goto out;
+
+	stack_amap_fd = bpf_map__fd(skel->maps.stack_amap);
+	if (!ASSERT_GE(stack_amap_fd, 0, "stack_amap fd"))
+		goto out;
+
+	skel->bss->pid = getpid();
+
+	err = stacktrace_map_skip__attach(skel);
+	if (!ASSERT_OK(err, "skel_attach"))
+		goto out;
+
+	/* give some time for bpf program run */
+	sleep(1);
+
+	/* disable stack trace collection */
+	skel->bss->control = 1;
+
+	/* 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 (!ASSERT_OK(err, "compare_map_keys stackid_hmap vs. stackmap"))
+		goto out;
+
+	err = compare_map_keys(stackmap_fd, stackid_hmap_fd);
+	if (!ASSERT_OK(err, "compare_map_keys stackmap vs. stackid_hmap"))
+		goto out;
+
+	stack_trace_len = TEST_STACK_DEPTH * sizeof(__u64);
+	err = compare_stack_ips(stackmap_fd, stack_amap_fd, stack_trace_len);
+	if (!ASSERT_OK(err, "compare_stack_ips stackmap vs. stack_amap"))
+		goto out;
+
+	if (!ASSERT_EQ(skel->bss->failed, 0, "skip_failed"))
+		goto out;
+
+out:
+	stacktrace_map_skip__destroy(skel);
+}

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

···
+// SPDX-License-Identifier: GPL-2.0
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+
+#define TEST_STACK_DEPTH	2
+#define TEST_MAX_ENTRIES	16384
+
+typedef __u64 stack_trace_t[TEST_STACK_DEPTH];
+
+struct {
+	__uint(type, BPF_MAP_TYPE_STACK_TRACE);
+	__uint(max_entries, TEST_MAX_ENTRIES);
+	__type(key, __u32);
+	__type(value, stack_trace_t);
+} stackmap SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, TEST_MAX_ENTRIES);
+	__type(key, __u32);
+	__type(value, __u32);
+} stackid_hmap SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, TEST_MAX_ENTRIES);
+	__type(key, __u32);
+	__type(value, stack_trace_t);
+} stack_amap SEC(".maps");
+
+int pid = 0;
+int control = 0;
+int failed = 0;
+
+SEC("tracepoint/sched/sched_switch")
+int oncpu(struct trace_event_raw_sched_switch *ctx)
+{
+	__u32 max_len = TEST_STACK_DEPTH * sizeof(__u64);
+	__u32 key = 0, val = 0;
+	__u64 *stack_p;
+
+	if (pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	if (control)
+		return 0;
+
+	/* 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 {
+		/* old kernel doesn't support skipping that many entries */
+		failed = 2;
+	}
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";