[PATCH bpf-next v2 5/6] selftests/bpf: Test typeless module ksym resolution

[Samuel Wu <wusamuel@google.com>]

Typeless module ksyms are resolved through kallsyms, but the existing
module ksym tests (ksyms_module, ksym_race) only use typed ksyms, which
are resolved through BTF. With KALLSYMS_QUERY, libbpf resolves module
symbols through the module lookup path of the ioctl.

Add a weak typeless extern for bpf_testmod_ksym_percpu to the ksyms test
and check that its address matches /proc/kallsyms when bpf_testmod is
loaded.

Signed-off-by: Samuel Wu <wusamuel@google.com>
---
 tools/testing/selftests/bpf/prog_tests/ksyms.c | 7 +++++++
 tools/testing/selftests/bpf/progs/test_ksyms.c | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/ksyms.c b/tools/testing/selftests/bpf/prog_tests/ksyms.c
index dc7aab532fb1..62760284f746 100644
--- a/tools/testing/selftests/bpf/prog_tests/ksyms.c
+++ b/tools/testing/selftests/bpf/prog_tests/ksyms.c
@@ -11,6 +11,7 @@ void test_ksyms(void)
 	struct test_ksyms *skel;
 	struct test_ksyms__data *data;
 	__u64 link_fops_addr, per_cpu_start_addr;
+	__u64 testmod_ksym_addr;
 	struct stat st;
 	__u64 btf_size;
 	int err;
@@ -48,6 +49,12 @@ void test_ksyms(void)
 	ASSERT_EQ(data->out__btf_size, btf_size, "btf_size");
 	ASSERT_EQ(data->out__per_cpu_start, per_cpu_start_addr, "__per_cpu_start");
 
+	if (env.has_testmod &&
+	    ASSERT_OK(kallsyms_find("bpf_testmod_ksym_percpu", &testmod_ksym_addr),
+		      "bpf_testmod_ksym_percpu: kallsyms_find"))
+		ASSERT_EQ(data->out__bpf_testmod_ksym, testmod_ksym_addr,
+			  "bpf_testmod_ksym_percpu");
+
 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
index 6c9cbb5a3bdf..69309f2a2d0a 100644
--- a/tools/testing/selftests/bpf/progs/test_ksyms.c
+++ b/tools/testing/selftests/bpf/progs/test_ksyms.c
@@ -9,6 +9,7 @@ __u64 out__bpf_link_fops = -1;
 __u64 out__bpf_link_fops1 = -1;
 __u64 out__btf_size = -1;
 __u64 out__per_cpu_start = -1;
+__u64 out__bpf_testmod_ksym = -1;
 
 extern const void bpf_link_fops __ksym;
 extern const void __start_BTF __ksym;
@@ -16,6 +17,7 @@ extern const void __stop_BTF __ksym;
 extern const void __per_cpu_start __ksym;
 /* non-existing symbol, weak, default to zero */
 extern const void bpf_link_fops1 __ksym __weak;
+extern const void bpf_testmod_ksym_percpu __ksym __weak;
 
 SEC("raw_tp/sys_enter")
 int handler(const void *ctx)
@@ -25,6 +27,7 @@ int handler(const void *ctx)
 	out__per_cpu_start = (__u64)&__per_cpu_start;
 
 	out__bpf_link_fops1 = (__u64)&bpf_link_fops1;
+	out__bpf_testmod_ksym = (__u64)&bpf_testmod_ksym_percpu;
 
 	return 0;
 }
-- 
2.56.0.257.gf7497c7d27-goog