selftests/bpf: Fix test_ksyms on non-SMP kernels

On non-SMP kernels __per_cpu_start is not 0, so look it up in kallsyms. Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Andrii Nakryiko <andriin@fb.com> Link: https://lore.kernel.org/bpf/20200910171336.3161995-1-iii@linux.ibm.com

Author: iii-i

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

@@ -32,6 +32,7 @@ static __u64 kallsyms_find(const char *sym)
 
 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;
@@ -63,8 +64,9 @@ void test_ksyms(void)
  "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__per_cpu_start != 0, "__per_cpu_start",
- "got %llu, exp %llu\n", data->out__per_cpu_start, (__u64)0);
+CHECK(data->out__per_cpu_start != per_cpu_start_addr, "__per_cpu_start",
+ "got %llu, exp %llu\n", data->out__per_cpu_start,
+ per_cpu_start_addr);
 
 cleanup:
 test_ksyms__destroy(skel);