selftests/bpf: Ksyms_btf to test typed ksyms

Selftests for typed ksyms. Tests two types of ksyms: one is a struct,
the other is a plain int. This tests two paths in the kernel. Struct
ksyms will be converted into PTR_TO_BTF_ID by the verifier while int
typed ksyms will be converted into PTR_TO_MEM.

Signed-off-by: Hao Luo <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Acked-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

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

···
 
 static int duration;
 
-static __u64 kallsyms_find(const char *sym)
-{
-	char type, name[500];
-	__u64 addr, res = 0;
-	FILE *f;
-
-	f = fopen("/proc/kallsyms", "r");
-	if (CHECK(!f, "kallsyms_fopen", "failed to open: %d\n", errno))
-		return 0;
-
-	while (fscanf(f, "%llx %c %499s%*[^\n]\n", &addr, &type, name) > 0) {
-		if (strcmp(name, sym) == 0) {
-			res = addr;
-			goto out;
-		}
-	}
-
-	CHECK(false, "not_found", "symbol %s not found\n", sym);
-out:
-	fclose(f);
-	return res;
-}
-
 void test_ksyms(void)
 {
-	__u64 per_cpu_start_addr = kallsyms_find("__per_cpu_start");
-	__u64 link_fops_addr = kallsyms_find("bpf_link_fops");
 	const char *btf_path = "/sys/kernel/btf/vmlinux";
 	struct test_ksyms *skel;
 	struct test_ksyms__data *data;
+	__u64 link_fops_addr, per_cpu_start_addr;
 	struct stat st;
 	__u64 btf_size;
 	int err;
+
+	err = kallsyms_find("bpf_link_fops", &link_fops_addr);
+	if (CHECK(err == -EINVAL, "kallsyms_fopen", "failed to open: %d\n", errno))
+		return;
+	if (CHECK(err == -ENOENT, "ksym_find", "symbol 'bpf_link_fops' not found\n"))
+		return;
+
+	err = kallsyms_find("__per_cpu_start", &per_cpu_start_addr);
+	if (CHECK(err == -EINVAL, "kallsyms_fopen", "failed to open: %d\n", errno))
+		return;
+	if (CHECK(err == -ENOENT, "ksym_find", "symbol 'per_cpu_start' not found\n"))
+		return;
 
 	if (CHECK(stat(btf_path, &st), "stat_btf", "err %d\n", errno))
 		return;

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

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Google */
+
+#include <test_progs.h>
+#include <bpf/libbpf.h>
+#include <bpf/btf.h>
+#include "test_ksyms_btf.skel.h"
+
+static int duration;
+
+void test_ksyms_btf(void)
+{
+	__u64 runqueues_addr, bpf_prog_active_addr;
+	struct test_ksyms_btf *skel = NULL;
+	struct test_ksyms_btf__data *data;
+	struct btf *btf;
+	int percpu_datasec;
+	int err;
+
+	err = kallsyms_find("runqueues", &runqueues_addr);
+	if (CHECK(err == -EINVAL, "kallsyms_fopen", "failed to open: %d\n", errno))
+		return;
+	if (CHECK(err == -ENOENT, "ksym_find", "symbol 'runqueues' not found\n"))
+		return;
+
+	err = kallsyms_find("bpf_prog_active", &bpf_prog_active_addr);
+	if (CHECK(err == -EINVAL, "kallsyms_fopen", "failed to open: %d\n", errno))
+		return;
+	if (CHECK(err == -ENOENT, "ksym_find", "symbol 'bpf_prog_active' not found\n"))
+		return;
+
+	btf = libbpf_find_kernel_btf();
+	if (CHECK(IS_ERR(btf), "btf_exists", "failed to load kernel BTF: %ld\n",
+		  PTR_ERR(btf)))
+		return;
+
+	percpu_datasec = btf__find_by_name_kind(btf, ".data..percpu",
+						BTF_KIND_DATASEC);
+	if (percpu_datasec < 0) {
+		printf("%s:SKIP:no PERCPU DATASEC in kernel btf\n",
+		       __func__);
+		test__skip();
+		goto cleanup;
+	}
+
+	skel = test_ksyms_btf__open_and_load();
+	if (CHECK(!skel, "skel_open", "failed to open and load skeleton\n"))
+		goto cleanup;
+
+	err = test_ksyms_btf__attach(skel);
+	if (CHECK(err, "skel_attach", "skeleton attach failed: %d\n", err))
+		goto cleanup;
+
+	/* trigger tracepoint */
+	usleep(1);
+
+	data = skel->data;
+	CHECK(data->out__runqueues_addr != runqueues_addr, "runqueues_addr",
+	      "got %llu, exp %llu\n",
+	      (unsigned long long)data->out__runqueues_addr,
+	      (unsigned long long)runqueues_addr);
+	CHECK(data->out__bpf_prog_active_addr != bpf_prog_active_addr, "bpf_prog_active_addr",
+	      "got %llu, exp %llu\n",
+	      (unsigned long long)data->out__bpf_prog_active_addr,
+	      (unsigned long long)bpf_prog_active_addr);
+
+cleanup:
+	btf__free(btf);
+	test_ksyms_btf__destroy(skel);
+}

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

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Google */
+
+#include "vmlinux.h"
+
+#include <bpf/bpf_helpers.h>
+
+__u64 out__runqueues_addr = -1;
+__u64 out__bpf_prog_active_addr = -1;
+
+extern const struct rq runqueues __ksym; /* struct type global var. */
+extern const int bpf_prog_active __ksym; /* int type global var. */
+
+SEC("raw_tp/sys_enter")
+int handler(const void *ctx)
+{
+	out__runqueues_addr = (__u64)&runqueues;
+	out__bpf_prog_active_addr = (__u64)&bpf_prog_active;
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";

tools/testing/selftests/bpf/trace_helpers.c

···
 	return 0;
 }
 
+/* open kallsyms and read symbol addresses on the fly. Without caching all symbols,
+ * this is faster than load + find.
+ */
+int kallsyms_find(const char *sym, unsigned long long *addr)
+{
+	char type, name[500];
+	unsigned long long value;
+	int err = 0;
+	FILE *f;
+
+	f = fopen("/proc/kallsyms", "r");
+	if (!f)
+		return -EINVAL;
+
+	while (fscanf(f, "%llx %c %499s%*[^\n]\n", &value, &type, name) > 0) {
+		if (strcmp(name, sym) == 0) {
+			*addr = value;
+			goto out;
+		}
+	}
+	err = -ENOENT;
+
+out:
+	fclose(f);
+	return err;
+}
+
 void read_trace_pipe(void)
 {
 	int trace_fd;

tools/testing/selftests/bpf/trace_helpers.h

···
 int load_kallsyms(void);
 struct ksym *ksym_search(long key);
 long ksym_get_addr(const char *name);
+
+/* open kallsyms and find addresses on the fly, faster than load + search. */
+int kallsyms_find(const char *sym, unsigned long long *addr);
+
 void read_trace_pipe(void);
 
 #endif