[PATCH bpf-next v2 2/2] selftests/bpf: check whether s32 is sufficient for kfunc offset

[Hou Tao <houtao1@xxxxxxxxxx>]

In add_kfunc_call(), bpf_kfunc_desc->imm with type s32 is used to
represent the offset of called kfunc from __bpf_call_base, so
add a test to ensure that the offset will not be overflowed.

Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
---
 .../selftests/bpf/prog_tests/ksyms_module.c   | 72 +++++++++++++++++++
 1 file changed, 72 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/ksyms_module.c b/tools/testing/selftests/bpf/prog_tests/ksyms_module.c
index d490ad80eccb..ce0cd3446931 100644
--- a/tools/testing/selftests/bpf/prog_tests/ksyms_module.c
+++ b/tools/testing/selftests/bpf/prog_tests/ksyms_module.c
@@ -6,6 +6,76 @@
 #include "test_ksyms_module.lskel.h"
 #include "test_ksyms_module.skel.h"
 
+/* Most logic comes from bpf_object__read_kallsyms_file() */
+static int test_find_func_in_kallsyms(const char *func, unsigned long *addr)
+{
+	/* Same as KSYM_NAME_LEN */
+	char sym_name[128];
+	char sym_type;
+	unsigned long sym_addr;
+	int ret, err;
+	FILE *f;
+
+	f = fopen("/proc/kallsyms", "r");
+	if (!f)
+		return -errno;
+
+	err = -ENOENT;
+	while (true) {
+		ret = fscanf(f, "%lx %c %127s%*[^\n]\n",
+			     &sym_addr, &sym_type, sym_name);
+		if (ret == EOF && feof(f))
+			break;
+
+		if (ret != 3) {
+			err = -EINVAL;
+			break;
+		}
+
+		if ((sym_type == 't' || sym_type == 'T') &&
+		    !strcmp(sym_name, func)) {
+			*addr = sym_addr;
+			err = 0;
+			break;
+		}
+	}
+
+	fclose(f);
+	return err;
+}
+
+/*
+ * Check whether or not s32 in bpf_kfunc_desc is sufficient
+ * to represent the offset between bpf_testmod_test_mod_kfunc
+ * and __bpf_call_base.
+ */
+void test_ksyms_module_valid_offset(void)
+{
+	unsigned long kfunc_addr;
+	unsigned long base_addr;
+	int used_offset;
+	long actual_offset;
+	int err;
+
+	if (!env.has_testmod) {
+		test__skip();
+		return;
+	}
+
+	err = test_find_func_in_kallsyms("bpf_testmod_test_mod_kfunc",
+					 &kfunc_addr);
+	if (!ASSERT_OK(err, "find kfunc addr"))
+		return;
+
+	err = test_find_func_in_kallsyms("__bpf_call_base", &base_addr);
+	if (!ASSERT_OK(err, "find base addr"))
+		return;
+
+	used_offset = kfunc_addr - base_addr;
+	actual_offset = kfunc_addr - base_addr;
+	ASSERT_EQ((long)used_offset, actual_offset, "kfunc offset overflowed");
+}
+
 void test_ksyms_module_lskel(void)
 {
 	struct test_ksyms_module_lskel *skel;
@@ -55,6 +125,8 @@ void test_ksyms_module_libbpf(void)
 
 void test_ksyms_module(void)
 {
+	if (test__start_subtest("valid_offset"))
+		test_ksyms_module_valid_offset();
 	if (test__start_subtest("lskel"))
 		test_ksyms_module_lskel();
 	if (test__start_subtest("libbpf"))
-- 
2.27.0