livepatch/selftests: add __asm__ symbol renaming examples

GCC can rename symbols like static data and optimized functions, adding
a suffix that includes illegal C characters.  Extend the klp-convert
examples to demonstrate how to use __asm__ renaming from C code to
create klp-relocations to such renamed symbols.

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>

lib/livepatch/test_klp_convert.h

@@ -10,5 +10,7 @@ extern char driver_name[];
 extern char homonym_string[];
 extern const char *get_homonym_string(void);
 extern const char *test_klp_get_driver_name(void);
+extern char klp_string_a[] __asm__("klp_string.12345");
+extern char klp_string_b[] __asm__("klp_string.67890");
 
 #endif

lib/livepatch/test_klp_convert1.c

@@ -25,13 +25,20 @@ void print_homonym_string(void)
 	pr_info("get_homonym_string(), 1: %s\n", get_homonym_string());
 }
 
+void print_static_strings(void)
+{
+	pr_info("klp_string.12345 = %s\n", klp_string_a);
+	pr_info("klp_string.67890 = %s\n", klp_string_b);
+}
+
 /* provide a sysfs handle to invoke debug functions */
 static int print_debug;
 static int print_debug_set(const char *val, const struct kernel_param *kp)
 {
 	print_saved_command_line();
 	print_driver_name();
 	print_homonym_string();
+	print_static_strings();
 
 	return 0;
 }
@@ -67,6 +74,7 @@ KLP_MODULE_RELOC(test_klp_convert_mod) test_klp_convert_mod_relocs_a[] = {
 	KLP_SYMPOS(homonym_string, 1),
 	KLP_SYMPOS(get_homonym_string, 1),
 	KLP_SYMPOS(test_klp_get_driver_name, 0),
+	KLP_SYMPOS(klp_string_b, 1),
 };
 
 static struct klp_func funcs[] = {

lib/livepatch/test_klp_convert_mod_a.c

@@ -20,6 +20,12 @@ __used static const char *get_homonym_string(void)
 	return homonym_string;
 }
 
+__used static void static_string_function(void)
+{
+	__used static char klp_string[] __asm__("klp_string.12345") =
+		__FILE__ " static string";
+}
+
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Joe Lawrence <joe.lawrence@redhat.com>");
 MODULE_DESCRIPTION("Livepatch test: klp-convert module");

lib/livepatch/test_klp_convert_mod_b.c

@@ -11,3 +11,9 @@ __used static const char *get_homonym_string(void)
 {
 	return homonym_string;
 }
+
+__used static void static_string_function(void)
+{
+	__used static char klp_string[] __asm__("klp_string.67890") =
+		__FILE__ " static string";
+}

tools/testing/selftests/livepatch/test-livepatch.sh

@@ -200,6 +200,8 @@ $MOD_KLP_CONVERT1: driver_name, 0: $MOD_KLP_CONVERT_MOD
 $MOD_KLP_CONVERT1: test_klp_get_driver_name(), 0: $MOD_KLP_CONVERT_MOD
 $MOD_KLP_CONVERT1: homonym_string, 1: homonym string A
 $MOD_KLP_CONVERT1: get_homonym_string(), 1: homonym string A
+test_klp_convert1: klp_string.12345 = lib/livepatch/test_klp_convert_mod_a.c static string
+test_klp_convert1: klp_string.67890 = lib/livepatch/test_klp_convert_mod_b.c static string
 % echo 0 > /sys/kernel/livepatch/$MOD_KLP_CONVERT1/enabled
 livepatch: '$MOD_KLP_CONVERT1': initializing unpatching transition
 livepatch: '$MOD_KLP_CONVERT1': starting unpatching transition
@@ -265,6 +267,8 @@ $MOD_KLP_CONVERT1: driver_name, 0: $MOD_KLP_CONVERT_MOD
 $MOD_KLP_CONVERT1: test_klp_get_driver_name(), 0: $MOD_KLP_CONVERT_MOD
 $MOD_KLP_CONVERT1: homonym_string, 1: homonym string A
 $MOD_KLP_CONVERT1: get_homonym_string(), 1: homonym string A
+test_klp_convert1: klp_string.12345 = lib/livepatch/test_klp_convert_mod_a.c static string
+test_klp_convert1: klp_string.67890 = lib/livepatch/test_klp_convert_mod_b.c static string
 % echo 0 > /sys/kernel/livepatch/$MOD_KLP_CONVERT1/enabled
 livepatch: '$MOD_KLP_CONVERT1': initializing unpatching transition
 livepatch: '$MOD_KLP_CONVERT1': starting unpatching transition