[RFC PATCH bpf-next 3/8] selftests/bpf: add __ksym extern selftest

[Andrii Nakryiko <andriin@fb.com>]

Validate libbpf is able to handle weak and strong kernel symbol externs in BPF
code correctly.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 .../testing/selftests/bpf/prog_tests/ksyms.c  | 71 +++++++++++++++++++
 .../testing/selftests/bpf/progs/test_ksyms.c  | 32 +++++++++
 2 files changed, 103 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/ksyms.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_ksyms.c

diff --git a/tools/testing/selftests/bpf/prog_tests/ksyms.c b/tools/testing/selftests/bpf/prog_tests/ksyms.c
new file mode 100644
index 000000000000..8f041c9059ed
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/ksyms.c
@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2019 Facebook */
+
+#include <test_progs.h>
+#include "test_ksyms.skel.h"
+#include <sys/stat.h>
+
+static int duration;
+
+static __u64 kallsyms_find(const char *sym)
+{
+	char type, name[256];
+	unsigned long 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, "%lx %c %s%*[^\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 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;
+	struct stat st;
+	__u64 btf_size;
+	int err;
+
+	if (CHECK(stat(btf_path, &st), "stat_btf", "err %d\n", errno))
+		return;
+	btf_size = st.st_size;
+
+	skel = test_ksyms__open_and_load();
+	if (CHECK(!skel, "skel_open", "failed to open and load skeleton\n"))
+		return;
+
+	err = test_ksyms__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__bpf_link_fops != link_fops_addr, "bpf_link_fops",
+	      "got 0x%llx, exp 0x%llx\n",
+	      data->out__bpf_link_fops, link_fops_addr);
+	CHECK(data->out__bpf_link_fops1 != 0, "bpf_link_fops1",
+	      "got %llu, exp %llu\n", data->out__bpf_link_fops1, (__u64)0);
+	CHECK(data->out__btf_size != btf_size, "btf_size",
+	      "got %llu, exp %llu\n", data->out__btf_size, btf_size);
+	CHECK(data->out__fixed_percpu_data != 0, "fixed_percpu_data",
+	      "got %llu, exp %llu\n", data->out__fixed_percpu_data, (__u64)0);
+
+cleanup:
+	test_ksyms__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_ksyms.c b/tools/testing/selftests/bpf/progs/test_ksyms.c
new file mode 100644
index 000000000000..598d6749b691
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_ksyms.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2019 Facebook */
+
+#include <stdbool.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+__u64 out__bpf_link_fops = -1;
+__u64 out__bpf_link_fops1 = -1;
+__u64 out__btf_size = -1;
+__u64 out__fixed_percpu_data = -1;
+
+extern const void bpf_link_fops __ksym;
+/* non-existing symbol, weak, default to zero */
+extern const void bpf_link_fops1 __ksym __weak;
+extern const void __start_BTF __ksym;
+extern const void __stop_BTF __ksym;
+/* fixed_percpu_data is always at zero offset */
+extern const void fixed_percpu_data __ksym;
+
+SEC("raw_tp/sys_enter")
+int handler(const void *ctx)
+{
+	out__bpf_link_fops = (__u64)&bpf_link_fops;
+	out__bpf_link_fops1 = (__u64)&bpf_link_fops1;
+	out__btf_size = (__u64)(&__stop_BTF - &__start_BTF);
+	out__fixed_percpu_data = (__u64)&fixed_percpu_data;
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.24.1