selftests/bpf: Add load_kallsyms_refresh function

Adding load_kallsyms_refresh function to re-read symbols from
/proc/kallsyms file.

This will be needed to get proper functions addresses from
bpf_testmod.ko module, which is loaded/unloaded several times
during the tests run, so symbols might be already old when
we need to use them.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20221025134148.3300700-6-jolsa@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/trace_helpers.c

@@ -23,7 +23,7 @@ static int ksym_cmp(const void *p1, const void *p2)
 	return ((struct ksym *)p1)->addr - ((struct ksym *)p2)->addr;
 }
 
-int load_kallsyms(void)
+int load_kallsyms_refresh(void)
 {
 	FILE *f;
 	char func[256], buf[256];
@@ -31,12 +31,7 @@ int load_kallsyms(void)
 	void *addr;
 	int i = 0;
 
-	/*
-	 * This is called/used from multiplace places,
-	 * load symbols just once.
-	 */
-	if (sym_cnt)
-		return 0;
+	sym_cnt = 0;
 
 	f = fopen("/proc/kallsyms", "r");
 	if (!f)
@@ -57,6 +52,17 @@ int load_kallsyms(void)
 	return 0;
 }
 
+int load_kallsyms(void)
+{
+	/*
+	 * This is called/used from multiplace places,
+	 * load symbols just once.
+	 */
+	if (sym_cnt)
+		return 0;
+	return load_kallsyms_refresh();
+}
+
 struct ksym *ksym_search(long key)
 {
 	int start = 0, end = sym_cnt;

tools/testing/selftests/bpf/trace_helpers.h

@@ -10,6 +10,8 @@ struct ksym {
 };
 
 int load_kallsyms(void);
+int load_kallsyms_refresh(void);
+
 struct ksym *ksym_search(long key);
 long ksym_get_addr(const char *name);