Kunit to check the longest symbol length

lib/Kconfig.debug

@@ -2621,6 +2621,18 @@ config FORTIFY_KUNIT_TEST
 	  by the str*() and mem*() family of functions. For testing runtime
 	  traps of FORTIFY_SOURCE, see LKDTM's "FORTIFY_*" tests.
 
+config LONGEST_SYMBOL
+	bool "longest symbol basic test"
+
+config LONGEST_SYM_KUNIT_TEST
+	tristate "Test the longest symbol possible" if !KUNIT_ALL_TESTS
+	depends on LONGEST_SYMBOL && KUNIT && KPROBES
+	default KUNIT_ALL_TESTS
+	help
+	  Tests the longest symbol possible
+
+	  If unsure, say N.
+
 config HW_BREAKPOINT_KUNIT_TEST
 	bool "Test hw_breakpoint constraints accounting" if !KUNIT_ALL_TESTS
 	depends on HAVE_HW_BREAKPOINT

lib/Makefile

@@ -391,6 +391,8 @@ CFLAGS_fortify_kunit.o += $(DISABLE_STRUCTLEAK_PLUGIN)
 obj-$(CONFIG_FORTIFY_KUNIT_TEST) += fortify_kunit.o
 obj-$(CONFIG_STRSCPY_KUNIT_TEST) += strscpy_kunit.o
 obj-$(CONFIG_SIPHASH_KUNIT_TEST) += siphash_kunit.o
+obj-$(CONFIG_LONGEST_SYMBOL) += longest_symbol.o
+obj-$(CONFIG_LONGEST_SYM_KUNIT_TEST) += longest_symbol_kunit.o
 
 obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
 

lib/longest_symbol.c

@@ -0,0 +1,18 @@
+#include "longest_symbol.h"
+#include <linux/kallsyms.h>
+
+int noinline LONGEST_SYM_NAME(void)
+{
+	return 424242;
+}
+
+int noinline LONGEST_SYM_NAME_PLUS1(void)
+{
+	return 434343;
+}
+
+_Static_assert(sizeof(__stringify(LONGEST_SYM_NAME)) == KSYM_NAME_LEN, \
+"Incorrect symbol length found. Expected KSYM_NAME_LEN: " \
+__stringify(KSYM_NAME) ", but found: " \
+__stringify(sizeof(LONGEST_SYM_NAME)));
+

lib/longest_symbol.h

@@ -0,0 +1,22 @@
+#ifndef _LONGEST_SYMBOL_H
+#define _LONGEST_SYMBOL_H
+
+#define DI(name) s##name##name
+#define DDI(name) DI(n##name##name)
+#define DDDI(name) DDI(n##name##name)
+#define DDDDI(name) DDDI(n##name##name)
+#define DDDDDI(name) DDDDI(n##name##name)
+
+#define PLUS1(name) name##e
+
+/*Generate a symbol whose name length is 511 */
+#define LONGEST_SYM_NAME  DDDDDI(g1h2i3j4k5l6m7n)
+
+/*Generate a symbol whose name length is 512 */
+#define LONGEST_SYM_PLUS1 PLUS1(LONGEST_SYM_NAME)
+
+int noinline LONGEST_SYM_NAME(void);
+
+int noinline LONGEST_SYM_NAME_PLUS1(void);
+
+#endif

lib/longest_symbol_kunit.c

@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test the longest symbol length
+ * execute with:
+ * ./tools/testing/kunit/kunit.py run longest-symbol --arch=x86_64 --kconfig_add CONFIG_LONGEST_SYMBOL=y --kconfig_add CONFIG_KPROBES=y --kconfig_add CONFIG_MODULES=y
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include "longest_symbol.h"
+#include <kunit/test.h>
+#include <linux/stringify.h>
+#include <linux/kprobes.h>
+
+static void test_longest_symbol(struct kunit *test)
+{
+	KUNIT_EXPECT_EQ(test, 424242, LONGEST_SYM_NAME());
+};
+
+static void test_longest_symbol_kallsyms(struct kunit *test)
+{
+	unsigned long (*kallsyms_lookup_name)(const char *name);
+	static int (*longest_sym)(void);
+
+	struct kprobe kp = {
+		.symbol_name = "kallsyms_lookup_name",
+	};
+
+	if (register_kprobe(&kp) < 0) {
+		pr_info("test_longest_symbol_kallsyms: kprobe not registered\n");
+		kunit_warn(test, "test_longest_symbol kallsyms: kprobe not registered\n");
+		KUNIT_ASSERT_TRUE(test, register_kprobe(&kp) < 0);
+		KUNIT_FAIL(test, "test_longest_symbol kallsysms: kprobe not registered\n");
+		return;
+	}
+
+	kunit_warn(test, "test_longest_symbol kallsyms: kprobe registered\n");
+	kallsyms_lookup_name = (unsigned long (*)(const char *name))kp.addr;
+	unregister_kprobe(&kp);
+
+	longest_sym = \
+	    (void*) kallsyms_lookup_name(__stringify(LONGEST_SYM_NAME));
+	KUNIT_EXPECT_EQ(test, 424242, longest_sym());
+};
+
+static void test_longest_symbol_plus1(struct kunit *test)
+{
+	KUNIT_EXPECT_EQ(test, 434343, LONGEST_SYM_NAME_PLUS1());
+};
+
+static void test_longest_symbol_plus1_kallsyms(struct kunit *test)
+{
+	unsigned long (*kallsyms_lookup_name)(const char *name);
+	static int (*longest_sym_plus1)(void);
+
+	struct kprobe kp = {
+		.symbol_name = "kallsyms_lookup_name",
+	};
+
+	if (register_kprobe(&kp) < 0) {
+		pr_info("test_longest_symbol_plus1_kallsyms: "
+				"kprobe not registered\n");
+		KUNIT_ASSERT_TRUE(test, register_kprobe(&kp) < 0);
+		KUNIT_FAIL(test, "test_longest_symbol kallsysms: kprobe not registered\n");
+		return;
+	}
+
+	kallsyms_lookup_name = (unsigned long (*)(const char *name))kp.addr;
+	unregister_kprobe(&kp);
+
+	longest_sym_plus1 = \
+	    (void*) kallsyms_lookup_name(__stringify(LONGEST_SYM_NAME_PLUS1));
+	KUNIT_EXPECT_EQ(test, 434343, longest_sym_plus1());
+};
+
+static struct kunit_case longest_symbol_test_cases[] = {
+	KUNIT_CASE(test_longest_symbol),
+	KUNIT_CASE(test_longest_symbol_kallsyms),
+	KUNIT_CASE(test_longest_symbol_plus1),
+	KUNIT_CASE(test_longest_symbol_plus1_kallsyms),
+	{}
+};
+
+static struct kunit_suite longest_symbol_test_suite = {
+	.name = "longest-symbol",
+	.test_cases = longest_symbol_test_cases,
+};
+kunit_test_suite(longest_symbol_test_suite);
+
+MODULE_LICENSE("GPL");